WO2012090242A1 - Power converter and solar power generation system - Google Patents

Abstract

A solar power generation system has the problem of improving the MPPT efficiency, so various methods other than the hill-climbing method are proposed. The quick scan method that scans the characteristics of a solar cell at that point of time is an excellent method because this method can be obtained with simple control and circuit, but there has been the risk of the occurrence of restriction in the inductance value of a choke coil. A solar power generation system is equipped with a current control means for controlling a switching element so that the current of a solar cell is controlled to be approximately equal to a target current value and a target value varying means for varying the target current value. The system has a detection mode and a steady-state mode. In the detection mode, while gradually increasing the target current value from zero, power is calculated in each increment and the target current value at the point that maximizes the power is obtained. In the steady-state mode, the system operates at the obtained target current value.

Description

Power converter and photovoltaic power generation system

The present invention relates to a system that obtains desired power by converting power generated by a solar cell using a power converter, and in particular, by controlling a converter connected to the solar cell, the maximum point of power of the solar cell is determined. The present invention relates to a maximum power tracking control method for detecting and operating a converter at a detected maximum power point.

FIG. 4 is a graph showing current-voltage characteristics and current-power characteristics of the solar cell.

The characteristics of the output voltage Vpv and the output current Ipv of the solar cell are generally nonlinear characteristics as shown by the solid line in FIG. That is, the voltage-current characteristic is a characteristic in which the short-circuit current Isc is obtained at the voltage Vpv = 0 and the current Ipv = 0 is obtained at the open-circuit voltage Voc. The voltage-power characteristic has a maximum power value Pmax at the voltage Vpmax. At this maximum power point Pmax, Ipv = Ipmax. Since the voltage-current characteristics and voltage-power characteristics vary depending on the sunshine conditions and temperature conditions, in order to efficiently extract power from the solar cell, always search for this maximum power point and convert the power connected to the solar cell. It is necessary to follow-up control the solar cell so that the operating point of the solar cell becomes the maximum power point.

As a method well known as the maximum power tracking control method, there is a hill climbing method. This hill-climbing method minutely changes the input voltage command value of the power converter, and determines whether the generated power of the solar cell increases or decreases according to this. Then, based on this determination result, a change direction for changing the next voltage command value to slightly increase or decrease is determined, and the command value is minutely changed repeatedly.

Alternatively, there is a method disclosed in Japanese Patent No. 4294346. This method has a power conversion circuit having a configuration in which an inductor and a switching element are connected in series to two terminals of a solar cell. When a maximum power point is detected, the switching element is held in an on state to flow through the inductor. By changing the current from zero to short-circuit current, the current-voltage characteristics at this time are scanned to detect the current and voltage at the maximum power point, and the operating point of the solar cell is the current at the maximum power point obtained by scanning, The power conversion circuit is operated so as to be a voltage. Since this method can scan the entire current-voltage characteristics of the solar cell at high speed, it is faster in response than the hill-climbing method. Is possible.

Japanese Patent No. 4294346

The above hill-climbing method has a risk of slow response. In addition, there is a fear that it is not possible to cope with the double peak characteristics that occur when a partial shadow occurs in the solar cell.

Further, the scanning method disclosed in Patent Document 1 described above flows into the choke coil L of the power conversion circuit by keeping the switching element on when scanning the characteristics of the current Ipv-voltage Vpv of the solar cell. The rate of change di / dt of the current Ipv is
di / dt = Vpv / L
Ipv is changed using the fact that Therefore, the current change rate di / dt is inversely proportional to the inductance value (L value) of the choke coil. In order to scan the change of Ipv with high accuracy, it is necessary to suppress the current change rate di / dt to an appropriate value, and the L value has a lower limit value. For this reason, the choke coil needs to have an inductance value equal to or higher than the lower limit value. In the scan method of Patent Document 1, it may be difficult to improve the trade-off between the reduction in the volume of the choke coil and the detection accuracy.

The problems to be solved by the present invention include improvement in responsiveness, response to partial shadows, reduction in volume and weight of the choke coil of the power converter in the photovoltaic power generation system, and cost reduction. By ensuring the detection accuracy of the maximum power point, it is to realize a small, light and low cost photovoltaic power generation system which always has a high MPPT efficiency.

The present invention provides a solar power generation system having a solar cell and a power converter connected to the solar cell, wherein the power converter flows into the power converter from at least one switching element and a solar cell. By detecting the current and obtaining the input current, the current target value, the voltage detecting means for obtaining the input voltage by detecting the voltage input to the power converter, and switching control of the switching element Current control means for controlling the input current to a value substantially equal to the current target value; and target value variable means for changing the current target value; and the target current value is made substantially zero by the target value variable means. The current control means is operated while increasing sequentially from the above, and each time the power at that time is calculated from the input current and the input voltage, and the power There characterized in that it has a steady-state mode for operating said current control means with a detection mode for obtaining the current target value of the point having the maximum the current target value determined by the detection mode. In the detection mode, the mode may transition to the steady mode after a predetermined time has elapsed, or may transition to the steady mode when the input voltage drops below a predetermined value. In addition, the transition from the steady mode to the detection mode is performed at regular intervals, and at that time, the power of the steady mode fluctuates by a predetermined ratio or more with respect to the maximum power detected in the detection mode. In some cases, it is also effective to transition to the detection mode without waiting for the elapse of the predetermined time.

In the detection mode, the target value variable means can change the current target value by increasing the current target value by increasing the current target value after exceeding a current value smaller than the current target value used in the previous steady mode. The rate of increase of the target value variable means is moderate compared to the outside of the predetermined width when it is within a predetermined width based on the current target value in the previous steady mode. May be.

Furthermore, when there are a plurality of the power converters and one of the power converters is in the detection mode, the other power converter is set to the steady mode, or the operation of the steady mode is performed once. Assuming that time is T and n is the number of power converters in parallel, it is also effective means that each power converter transitions from the steady mode to the detection mode with a delay of T / n.

Alternatively, at the time of starting the solar system, the detection mode and the steady mode are repeated, and the current increase rate of the current target value varying means in the detection mode of the plurality of times is higher than that of the previous time in the detection mode. Select the conditions under which the error between the obtained maximum power value and the maximum power value obtained in the steady mode immediately after that is less than the predetermined value and the current increase rate of the current target value variable means is as large as possible. The increase rate may be used as the current increase rate of the current target value varying means in the subsequent detection mode.

The power converter has a function of a step-up / down converter, and in the detection mode, the current target value may be increased to make a transition from the step-down operation to the step-up operation. In the steady mode, the current obtained in the immediately preceding detection mode may be used. Using the target value as an initial value, the current target value is slightly increased or decreased, and as a result, the increase or decrease in power is determined from the input voltage and current changed, and the current target value is decreased in the direction in which the power increases. It may be changed.

A solar power generation system in which a solar cell, a power converter, and a commercial system are connected, wherein the power converter has a detection mode and a steady mode for detecting the maximum power of the solar cell, and the detection mode also includes the detection mode The problem of the present invention can also be solved by having a function of outputting the power of the solar cell from the power converter to the commercial system.

Alternatively, the present invention relates to a current target for controlling the current of the solar cell when detecting the maximum power point of the solar cell in a power converter that performs tracking control so that the solar cell operates at the maximum power point. Once the value is changed to a predetermined current value, the power of the solar cell is sampled and the maximum power point is detected while changing every predetermined current width from the predetermined current value to the short-circuit current. Features.

Alternatively, the present invention relates to a current target for controlling the current of the solar cell when detecting the maximum power point of the solar cell in a power converter that performs tracking control so that the solar cell operates at the maximum power point. Once the value is set to a predetermined current value, the power of the solar cell is sampled and the maximum power point is changed while changing the current target value for each predetermined current width until the voltage of the solar cell reaches a predetermined voltage. Is detected.

Alternatively, in the detection control mode for detecting the maximum power point of the solar cell from the output current and output voltage of the solar cell and the maximum power point tracking control method for the solar cell consisting of a steady control mode, the detection control mode is a current target. A target value setting step for determining a value, a current control step for controlling the output current to a value substantially equal to the current target value, a current / voltage detection step for detecting the output current and the output voltage, and the output current A power / current storage step for storing power obtained by multiplication with the output voltage and an output current at that time, wherein the current target value gradually increases in the target value setting step, and the power / current storage In the step, the power stored in the previous power / current storage step is compared with the current power, and the larger power and the output current at that time are stored. Then, the detection control mode transitions to the steady control mode after a lapse of a predetermined time, and in the steady control mode, the output current and output voltage of the solar cell are calculated according to the maximum power point that is the power stored in the power / current storage step. It is characterized by controlling.

Alternatively, the present invention provides the detection control mode in which the maximum power point of the solar cell is detected from the output current and the output voltage of the solar cell, and the maximum power point tracking control method of the solar cell that includes the steady control mode. The mode is a target value setting step for determining a current target value, a current control step for controlling the output current to a value substantially equal to the current target value, a current / voltage detection step for detecting the output current and the output voltage, A power / current storage step for storing the power obtained by multiplying the output current and the output voltage and the output current at that time, and in the target value setting step, the current target value gradually increases, In the power / current storage step, the power stored in the previous power / current storage step is compared with the current power, and the larger power and the output power at that time are compared. The detection control mode ends when the voltage detected in the current / voltage detection step reaches a predetermined value and transitions to the steady control mode. In the steady control mode, the power / current is The output current and output voltage of the solar cell are controlled according to the maximum power point that is the power stored in the storing step.

Alternatively, the present invention provides the detection control mode in which the maximum power point of the solar cell is detected from the output current and the output voltage of the solar cell, and the maximum power point tracking control method of the solar cell that includes the steady control mode. The mode is a target value setting step for determining a current target value, a current control step for controlling the output current to a value substantially equal to the current target value, a current / voltage detection step for detecting the output current and the output voltage, A power / current storage step for storing the power obtained by multiplying the output current and the output voltage and the output current at that time, and in the target value setting step, the current target value gradually increases, The detection control mode ends when the voltage detected in the current / voltage detection step reaches a predetermined value, and transitions to the steady control mode. In the control mode of the power stored in said power-current storage step, and controlling the output current and the output voltage of the solar cell in accordance with the maximum power point of maximum power.

Alternatively, the present invention includes a step of detecting an output voltage and an output current of a solar cell, a step of determining a target value of the output current, a step of controlling the output current to a value substantially equal to the target value, and the output A step of storing the power obtained by multiplying the current by the output voltage and the output current at that time, the target value gradually increasing in the step of determining the target value, and the previous power / current storage in the step of storing The power stored in the step is compared with the current power, and the larger power and the output current at that time are stored.

In the present invention, the time change rate of the current does not depend on the inductance value of the choke coil but depends on the increasing rate of the set current target value. For this reason, the inductance value of the choke coil can be freely set while ensuring excellent response to the detection accuracy of the maximum power point and the temperature change, aging, and partial shadow occurrence of the solar cell characteristics of the conventional scanning method. It becomes possible to select.

Therefore, according to the present invention, the inductance value of the choke coil of the power converter in the photovoltaic power generation system takes into consideration the optimum switching frequency determined from the speed of the switching element and diode, switching loss, ripple current on the output side, and the like. Can be selected. For this reason, the inductance value of a choke coil can be reduced more than before by using a high-speed switching element. As a result, the volume of the choke coil can be reduced and the weight of the choke coil can be reduced. When the inductance of the choke coil is reduced, the length of the copper wire that is the material of the choke coil can be shortened, and the core volume made of the ferrite material can be reduced. As a result, the choke coil is small and light, and the cost can be reduced. A low-inductance choke coil can be mounted on a substrate, contributing to a reduction in the number of man-hours when manufacturing power conditioners.

As a result, according to the present invention, it is possible to realize a solar power generation system that always has a high MPPT efficiency and is small, light, and low in cost.

The figure which shows the circuit structure of Example 1 of this invention. The waveform of each part which shows the circuit operation | movement of Example 1 of this invention. An example of the circuit structure of the input filter of FIG. The graph which shows the current-voltage characteristic and current-power characteristic of a solar cell. The figure which shows the circuit structure of Example 2 of this invention. The PAD figure which shows a detection mode among the control algorithms of Example 2 of this invention. The PAD figure which shows a stationary mode among the control algorithms of Example 2 of this invention. The waveform of each part which shows the circuit operation | movement of Example 2 of this invention. The figure which shows the change of the electric current target value of Example 3 of this invention. The figure which shows the change of the electric current target value of Example 4 of this invention. FIG. 9 is a block diagram showing a circuit configuration of a fifth embodiment of the present invention. The figure which shows the mode transition of Example 5 of this invention. The figure which shows the operation | movement at the time of starting of Example 6 of this invention. The figure which shows the circuit structure of Example 7 of this invention. The waveform of each part which shows the circuit operation | movement of Example 7 of this invention. The PAD figure which shows the control algorithm in the steady mode of Example 8 of this invention.

In the present invention, the following configuration is proposed in order to contribute to the realization of a small, lightweight and low-cost solar power generation system.

A first embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG.

FIG. 1 is a diagram showing a circuit configuration of Embodiment 1 of the present invention. First, in FIG. 1, 1 is a solar panel, 2 is a power conditioner, 3 is a commercial system, 4 is an input filter, 7 is a DC-DC converter, 8 is a choke coil, 9 is a power MOSFET, 10 is a boost diode, 11 is a capacitor, 12 is a grid interconnection inverter, 13 is a current sensor, 14 is a control circuit, 15a and 15b are voltage dividing resistors, 16 is a target value variable means, 17 is a mode switch, 18 is a subtractor, and 19 is PI. A control block, 20 is a multiplier, 21a and 21b are AD converters, 22a is a PWM circuit, and 23 is a maximum value determination circuit.

In FIG. 1, the power conditioner 2 includes an input filter 4, a DC-DC converter 7, a grid interconnection inverter 12, and a control circuit 14. Both ends of the solar cell panel 1 are connected to the input side terminals of the input filter 4 inside the power conditioner 2, and the converter side terminal of the input filter 4 is connected to the DC-DC converter 7. Is connected to the grid interconnection inverter 12. The grid interconnection inverter 12 is connected to the commercial system 3 outside the power conditioner 2. The DC-DC converter 7 includes a choke coil 8, voltage dividing resistors 15a and 15b, a power MOSFET 9, a boost diode 10, a capacitor 11, and a current sensor 13, and the choke coil 8 and the drain of the power MOSFET 9 are connected. Yes. The input side of the choke coil 8 is connected to the converter side terminal of the input filter 4. The source of the power MOSFET 9 is connected to the converter side terminal of the input filter 4. Voltage dividing resistors 15 a and 15 b are connected in series at both ends of the converter side terminal of the input filter 4 and inside the DC-DC converter 7. The anode of the boost diode 10 is connected to the drain of the power MOSFET 9. A capacitor 11 is connected between the cathode of the boost diode 10 and the source of the power MOSFET 9. Both ends of the capacitor 11 are connected to the grid interconnection inverter 12 outside the DC-DC converter 7.

On the other hand, in the control circuit 14, AD converters 21a and 21b, target value variable means 16, mode switcher 17, subtractor 18, PI control block 19, multiplier 20, PWM circuit 22a, and maximum value determination circuit 23 are provided. is there.

* Connected to the AD converter 21a from the midpoint of the voltage dividing resistors 15a and 15b. The current sensor 13 is connected to the AD converter 21b. If the current flowing through the choke coil 8 is IL, the output of the AD converter 21b is ILave, which is the average value of IL, and the output of the AD converter 21a is Vin. ILave and Vin are input to the multiplier 20, and the output is input to the maximum value determination circuit 23 as Ppv. ILave is input to the minus terminal of the subtractor 18. The Iref that is the output of the mode switch 17 is connected to the plus side input terminal of the subtractor 18. The output of the subtracter 18 is input to the PI control block 19. Iref is input to the maximum value determination circuit 23. The output of the PI control block 19 is input to the PWM circuit 22a. The output of the PWM circuit 22a is output to the outside of the control circuit 14 as the S1 control signal and is connected to the gate of the power MOSFET 9 inside the DC-DC converter 7. The output of the maximum value determination circuit 23 is connected to the stationary side of the mode switch 17 as IrefM. A target value variable means 16 is connected to the detection side of the mode switch 17. Here, the current target value Iref is output from the mode switch 17 and is a target value of the current IL flowing through the choke coil 8.

Next, FIG. 2 will be described. FIG. 2 shows the circuit operation of the first embodiment, and shows the operation waveform of each part of the circuit of FIG. 1 with the horizontal axis as time. In order from the top, the operation state of the DC-DC converter 7 is distinguished between the steady mode and the detection mode, and as Vpv, the voltage waveforms in the steady mode and the detection mode at both ends of the solar cell panel 1 in FIG. 1, the current target values Iref and S1 control. The gate waveform of the power MOSFET 9 as a signal, the solid line indicates IL, the dotted line indicates ILave, and the DC-DC converter 7 output power indicates the power output from the DC-DC converter 7 to the grid interconnection inverter. Here, the detection mode is a mode for detecting the maximum power point of the solar cell, and the steady mode is a power converter (power conditioner 2) so that the current at the maximum power point obtained in the detection mode is obtained. ).

Next, FIG. 3 is a diagram showing an example of the inside of the input filter 4 in FIG. In FIG. 3, 5a and 5b are common mode chokes, 6a, 6b, 6c, 6d and 6e are filter capacitors, and 27 is a normal mode choke. In FIG. 3, a filter capacitor 6a is connected to both ends of the input side terminal of the input filter 4, and an input side terminal of the common mode choke 5a is connected to both ends of the filter capacitor 6a. The output side terminal of the common mode choke 5a is connected to a series body of filter capacitors 6b and 6c. The midpoint of the filter capacitors 6b and 6c is connected to the frame ground. Both ends of the filter capacitor 6d are connected to both ends of the series body of the filter capacitors 6b and 6c. Both ends of the filter capacitor 6d are connected to the input side terminals of the common mode choke 5b. A normal mode choke 27 is connected to one of output terminals of the common mode choke 5b, and a filter capacitor 6e is connected between the normal mode choke 27 and the other terminal of the common mode choke 5b. Then, both terminals of the filter capacitor 6 e become the converter side terminals and are drawn out of the input filter 4.

Next, FIG. 4 is a graph showing the current-voltage characteristics and current-power characteristics of the solar cell, with the horizontal axis representing the current Ipv of the solar cell panel 1, the vertical axis representing the voltage Vpv (left side), and the power Ppv (right side). As a solid line, the characteristics of the output current Ipv and the voltage Vpv of the solar cell panel 1 are shown. On the other hand, the dotted line indicates the characteristics of the output current Ipv and the power Ppv of the solar cell panel 1.

Next, the operation will be described. In the steady mode, the mode switch 17 in FIG. 1 is connected to the steady mode side. Therefore, the current target value Iref is IrefM that is the output of the maximum value determination circuit 23. In this embodiment, IrefM in the stationary mode period before the detection mode in FIG. 2 is defined as IrefM (n−1), and IrefM in the stationary mode period after the detection mode in FIG. 2 is defined as IrefM (n). Therefore, if the current time is the steady mode before the detection mode in FIG. 2, the current target value is IrefM (n−1). At this time, in the present invention, the DC-DC converter 7 performs a current control operation so that the average value ILave of the current flowing through the choke coil 8 (L) matches IrefM (n−1). In the DC-DC converter 7, the current flowing through the choke coil 8 (L) is detected by the current sensor 13. Since the current IL flowing through the choke coil 8 (L) pulsates by switching of the power MOSFET 9 described later, the current IL detected by the current sensor 13 is taken into the control circuit 14 via the AD converter 21b and recognized as the average value ILave. The As a method for extracting the average value ILave from the pulsating current IL, there is a method of providing a first-order lag filter for attenuating the switching frequency component of the power MOSFET 9 (S1) in the current sensor 13, or a timing at which the AD converter 21a is taken in by a PWM cycle. There is a method of always sampling the central value of the pulsation in synchronization with the pulsation, and any method may be used as long as the average value ILave can be extracted from the pulsating current IL. This ILave is subtracted from the current target value Iref in the subtractor 18. At this time, since Iref = IrefM (n−1), the current error which is the output of the subtractor 18 is IrefM (n−1) −. ILave. This current error is input to the PI control block 19 and is subjected to proportional integration calculation. The output of the PI control block 19 is a duty ratio, and this duty ratio is input to the PWM circuit 22a to generate a PWM pulse. This PWM pulse is an S1 control signal and has a pulse waveform as shown in FIG. The S1 control signal is input to the gate of the power MOSFET 9 (S1) and drives the power MOSFET 9 (S1). The power MOSFET 9 (S1) is repeatedly turned on and off by switching. When the power MOSFET 9 (S1) is turned on, a closed circuit of the solar cell panel 1-input filter 4-choke coil 8 (L) -power MOSFET 9 (S1) -input filter 4-solar cell panel 1 is formed. A current flows from the panel 1 to the choke coil 8 (L). Next, when the power MOSFET 9 (S1) is turned OFF, the solar cell panel 1-input filter 4-choke coil 8 (L) -boost diode 10 (D1) -capacitor 11 (Cpn) -input filter 4-solar cell panel 1 circuit The excitation energy stored in the choke coil 8 (L) is released to the capacitor 11 (Cpn).

When the current error IrefM (n−1) −ILave is positive, the ON width of the S1 control signal increases to increase the excitation energy stored in the choke coil 8 (L), and conversely the current error IrefM (n−1) When -ILave is negative, the ON width of the S1 control signal is reduced to reduce the excitation energy stored in the choke coil 8 (L). By repeating this operation, the current error IrefM (n−1) −ILave is controlled to be zero, in other words, ILave is controlled to be equal to IrefM (n−1). At this time, in the steady mode of FIG. 2, ILave becomes a constant value equal to IrefM (n−1) as shown by a dotted line, and the waveform of IL increases during the period when the power MOSFET 9 (S1) is ON as shown by a solid line. However, the power MOSFET 9 (S1) decreases during the OFF period. The ILave waveform passes through the center of the IL waveform.

When the power MOSFET 9 (S1) is turned on, the excitation energy is stored in the choke coil 8 (L) and IL increases. When the power MOSFET 9 (S1) is turned off, the excitation energy stored in the choke coil 8 (L) is a capacitor. 11 (Cpn) is released and IL decreases.

Here, the current error IrefM (n−1) −ILave is not limited to zero control, but may be controlled to be a value close to zero.

At this time, in the input filter 4 of FIG. 3, the pulsation component of IL due to the switching of the power MOSFET 9 (S1) is cut mainly by the normal mode choke 27 and the filter capacitor 5e, and flows into the DC-DC converter 7 from the solar cell panel 1. The current Ipv to be performed has substantially the same DC value as ILave. On the other hand, regarding the voltage, the voltage Vpv of the solar cell panel 1 input to the input filter 4 and the output voltage Vin of the input filter 4 have substantially the same DC component, and Vin includes a high-frequency component accompanying switching.

As a result, DC power of Ipv and Vpv flows from the solar cell panel 1 to the DC-DC converter 7, and the loss of the DC-DC converter 7 can be subtracted from the DC-DC converter 7 to the grid interconnection inverter 12. Electric power is output. The grid interconnection inverter 12 converts the DC power input from the DC-DC converter 7 into a sine wave current synchronized with the voltage phase of the commercial system 3 and outputs the sine wave current to the commercial system 3.

Next, the detection mode will be described. In the present embodiment, the transition to the detection mode is made after a certain time has elapsed in the steady mode. The detection mode is started by switching the mode switch 17 in FIG. 1 to the detection mode side. At this time, the initial value of the target value varying means 16 is set to zero. For this reason, when the mode switch 17 is switched to the detection mode, Iref becomes zero from IrefM (n−1) in the steady mode so far. The average value ILave of the current flowing through the choke coil 8 (L) is not changed from the normal mode until then, and is subtracted from the current target value Iref in the subtractor 18. However, since Iref = 0 at the beginning of the detection mode, The current error that is the output of the subtractor 18 is −ILave. This current error is input to the PI control block 19 and is subjected to proportional integration calculation. The output of the PI control block 19 is a duty ratio, and this duty ratio is input to the PWM circuit 22a to generate a PWM pulse. This PWM pulse is an S1 control signal and has a pulse waveform as shown in FIG. The S1 control signal is input to the gate of the power MOSFET 9 (S1) and drives the power MOSFET 9 (S1). When the power MOSFET 9 (S1) is turned on, excitation energy is stored in the choke coil 8 (L) and IL increases. When the power MOSFET 9 (S1) is turned off, the excitation energy stored in the choke coil 8 (L) is Released to (Cpn) and IL decreases. As a result, the DC-DC converter 7 is current-controlled so that the current error -ILave becomes zero. As a result, the average value ILave of the current flowing through the choke coil 8 (L) becomes zero, and the current Ipv output from the solar cell panel 1 also becomes zero. At this time, the voltage of the solar cell panel 1 rises to the open circuit voltage Voc when Ipv is zero, as shown in the current-voltage characteristics of FIG. This change is also shown in FIG. 2, where ILave, that is, the average value of IL (dotted line) decreases to zero, and Vpv increases to Voc. At this time, instead of changing Iref to zero, a method of stopping the switching of the power MOSFET 9 for a certain time at the beginning of the detection mode may be used. Next, as shown in FIG. 2, the current target value Iref is gradually increased from zero with a slope di / dt. This operation is achieved by increasing the current target value Iref output from the target value varying means 16 by a minute amount ΔIref every predetermined time tx as shown in FIG. Iref increases with a slope of di / dt = ΔIref / tx. At this time, when the switching of the power MOSFET 9 is stopped at the beginning of the detection mode, the switching is resumed. Accordingly, as shown in FIG. 2, ILave is kept substantially equal to Iref, and therefore IL increases following the increase in Iref. Also at this time, as described above, Ipv is substantially equal to ILave due to the action of the input filter 4, so that Ipv gradually increases from zero in the detection mode. Vpv changes according to the characteristic of the solid line shown in FIG. At this time, ILave and Vin are sampled by the AD converters 21a and 21b each time. The sampling period ts is shorter than the time tx when Iref changes. Since the detected ILave and Vin can be regarded as Ipv and Vpv, respectively, and Ppv is calculated by the multiplier 20 by detecting them, the maximum value determination circuit 23 calculates Ppv and Iref at that time as (Ppv, Iref ). The maximum value determination circuit 23 stores Ppv as the maximum power point PMax and stores Iref at that time as IrefM when Ppv is larger than before in the set of (Ppv, Iref) sequentially input. Since Iref increases with a slope of di / dt = ΔIref / tx, it reaches the short-circuit current value Isc shown in FIG. 4 in the time of tx * Isc / ΔIref. As the current Ipv increases, the voltage Vpv gradually decreases from Voc and becomes Vpv = 0 at the short-circuit current value Isc. Since the maximum power point (Pmax, Ipmax) is passed during this period, (PMax, IrefM) = (Pmax, Ipmax) is stored in the maximum value determination circuit 23 at the time of Iref = Isc. become. In the present embodiment, the detection mode is executed for a period of Ts as shown in FIG.
tx * Isc / ΔIref <Ts
Therefore, the current target value Iref reaches or exceeds Isc by Ts. When Iref is greater than Isc, ILave <Iref and current control for causing IL to follow Iref cannot be performed. At this time, the power MOSFET 9 operates with the maximum on-time width set in advance by the PWM circuit 22a. To do.

As a result, at the end of the detection mode, that is, at the time when the time Ts has elapsed from the start of the detection mode, the maximum value determination circuit 23 stores (Pmax, Ipmax) as (PMax, IrefM).

Therefore, in the next steady mode, the maximum value determination circuit 23 outputs Ipmax as IrefM. In the steady mode, as described above, the mode switch 17 is again connected to the steady side, Iref = IrefM (n) = Ipmax, and current control is performed so that the average value ILave of IL becomes Ipmax. If the time in the steady mode is T, the time is sufficiently longer than the time Ts in the detection mode. For example, the detection mode time Ts is on the order of 1 ms to several tens of ms, and the steady mode time T is on the order of 1 s to several minutes. Further, the inductance value of the choke coil 8 used at this time is a value approximately between 100 μH and 1 mH, and can be mounted on a printed circuit board.

In this embodiment, di / dt in the detection mode does not depend on the inductance value of the choke coil 8, but depends on the increasing rate of the current target value to be set. Therefore, the inductance value of the choke coil can be freely set. This makes it possible to select a solar power generation system that is small, light, and low in cost.

In this way, in this embodiment, the maximum power point of the solar cell panel is detected every predetermined time, and the power conditioner can be operated at the detected maximum power point. In the present invention, as shown in FIG. 2, even in the detection mode, the electric power of the solar cell panel 1 is output from the DC-DC converter 7 and output to the commercial system 3 side via the system interconnection inverter 12. For this reason, even if di / dt is made small in order to improve the detection accuracy, that is, the increase rate of the current change is slowed and the detection mode is extended, the loss of power from the solar cell panel can be minimized. .

In this embodiment, it is also effective to use a gate drive circuit between the PWM circuit 22a and the power MOSFET 9. The power MOSFET 9 may be replaced with another switching element such as IGBT or SiC-MOSFET. It is also effective to apply a SiC device to the boost diode 10. The configuration of the DC-DC converter 7 is preferably the step-up converter shown in FIG. 1, but may be other non-insulated converters or isolated converters. Further, the input filter 4 may have other functions as long as it has a similar function, that is, a circuit configuration that prevents the current of the switching component from flowing to the solar cell panel side and reduces common mode noise. Further, the control circuit may be constituted by an analog circuit having a similar function. Although the PWM circuit 22a is a circuit that performs pulse width modulation control, it can be replaced by pulse frequency modulation control (PFM), pulse density modulation control (PDM), or the like. Further, the PI control block 19 is a block that performs proportional-integral control, but may be configured by an analog circuit such as an operational amplifier as described above, or may be replaced by PID (proportional-integral delay) control or the like.

In the present embodiment, the initial value of the target value varying means 16 is set to zero, but this is not restrictive. The reason why the initial value of the target value varying means 16 is set to zero is that it also means that there is no leakage in sampling when detecting the maximum power point. Therefore, the initial value of the target value varying means 16 is not limited to zero, and may be a value close to zero.

Further, the value of the target value variable means 16 may be changed to zero or a value close to zero by gradually reducing the value of the target value variable means 16 when transitioning from the steady mode to the detection mode. By gradually reducing the value of the target value varying means 16, it is possible to prevent a voltage jump due to the parasitic inductance of the cable between the solar cell panel 1 and the power conditioner 2.

In addition, the timing for gradually increasing the current target value Iref from zero or a value close to zero is when the case where the ILave is zero or a value close to zero is detected, or when a certain time has elapsed. It may be when a certain number of switching times is counted.

In the present embodiment, the maximum value determination circuit 23 sets Ppv as the maximum power point PMax when Ppv is larger than the previous set (Ppv, Iref), and Iref at that time is IrefM. However, this is not the case. Since it is only necessary to know the maximum power point PMax, all of the pairs (Ppv, Iref) sequentially input by the maximum value determination circuit 23 are stored, and the largest stored Ppv may be used as the maximum power point PMax. . In this case, Iref at the maximum power point PMax is set to IrefM, and the subsequent steady mode is as described above for outputting Ipmax as IrefM.

In the present embodiment, the transition from the steady mode to the detection mode is made after a lapse of a fixed time, but this is not restrictive. It is only necessary to provide a timing for transition from the steady mode to the detection mode, and transition may be performed under a predetermined condition such as the number of times of switching.

In this embodiment, the detection mode is changed to the steady mode after a lapse of a certain time, but this is not restrictive. The transition from the detection mode to the steady mode may be performed at the stage where the detection mode is completed or the stage where the maximum power point is detected, and the transition may be performed under a predetermined condition such as the number of times of switching.

In the present embodiment, the target current value is determined by the target value varying means 16, but this is not restrictive. A voltage value may be used instead of a current value.

In the present embodiment, the increase amount ΔIref is set to a minute amount, but this is not restrictive.

Next, a second embodiment of the present invention will be described with reference to FIG. 5, FIG. 6, FIG. 7 and FIG. FIG. 5 is a diagram showing a circuit configuration of the present invention, and the same components as those in FIG. 1 are given the same symbols. In addition, in FIG. 5, 28 is a control block.

FIG. 5 is a diagram showing a circuit configuration of the second embodiment of the present invention.

5 is mostly the same as that described with reference to FIG. 1 in the first embodiment, and therefore only the differences will be described below.

Inside the control circuit 14, there are AD converters 21a and 21b, a subtractor 18, a PI control block 19, a PWM circuit 22a, and a control block 28. And it connects to AD converter 21a from the midpoint of voltage dividing resistance 15a, 15b. The current sensor 13 is connected to the AD converter 21b. The output of the AD converter 21b is ILave which is an average value of IL, and the output of one AD converter 21a is Vin. ILave and Vin are input to the control block 28 for information processing. The output of the control block 28 is Iref and is connected to the plus side input terminal of the subtractor 18. ILave is also input to the minus terminal of the subtractor 18. The output of the subtracter 18 is input to the PI control block 19. The output of the PI control block 19 is input to the PWM circuit 22a. The output of the PWM circuit 22a is output to the outside of the control circuit 14 as the S1 control signal and is connected to the gate of the power MOSFET 9 inside the DC-DC converter 7.

FIG. 6 is a PAD diagram showing the detection mode in the control algorithm of the second embodiment of the present invention, and FIG. 7 is a PAD diagram showing the steady mode in the control algorithm of the second embodiment of the present invention.

FIG. 6 is a PAD diagram showing the processing contents inside the control block 28 of FIG. 5, and shows the processing contents of the detection mode.

On the other hand, FIG. 7 is a PAD diagram showing the processing contents of the same control block 28, showing the processing contents of the steady mode.

FIG. 8 is a diagram showing an operation waveform of each part in the present embodiment.

Next, the operation in this embodiment will be described. In FIG. 5, the operation of the DC-DC converter 7 is the same as that of the first embodiment, and therefore, the contents mainly related to the control block 28 will be described in detail.

In FIG. 5, the L current average value ILave and the input voltage Vin are converted into digital signals by the AD converters 21b and 21a, respectively, and input to the control block 28, regardless of the detection mode or the steady mode. Is output. In FIG. 6, when the detection mode is started, first, Iref = 0 is set, and Iref = 0 is output from the control block 28. The control circuit 14 is preferably a microcomputer or a DSP (digital signal processor). In the control circuit 14, ILave AD-converted by the AD converter 21 b is compared with 0 (= Iref), and the time ratio of the power MOSFET 9 (S 1) necessary for making ILave zero in the PI control block 19 is determined. Output. Then, the PWM circuit 22a converts the duty ratio into a pulse width, and performs switching control of the gate of the power MOSFET 9 (S1) as an S1 control signal. By this current feedback control, the average value ILave of the current flowing through the choke coil L is reduced to zero. In the PAD diagram, this ILave is taken in every sampling period. When ILave> 0, ILave is repeatedly read, and when ILave = 0, the operation shifts to reading Vin.

First, PMax = 0 is set.

Here, Vmin is set in advance. Vmin may be a value of 0 V or more. Then, when Vin> Vmin, that is, until the voltage Vpv between terminals of the solar cell is lowered to Vmin, the following operation is performed. The operation is to add the current target value Iref to the current Iref, add ΔIref, read ILave and Vin, calculate the power Ppv by the product of them, and if Ppv is greater than PMax, the maximum power value PMax Is the current Ppv and at the same time IrefM is the current Iref. Repeat the above steps.

Then, when Vin ≦ Vmin, IrefM is output as Iref which is the output of the control block 28. The detection mode is completed by the operations so far, and the mode is changed to the steady mode. As shown in the Ppv waveform of FIG. 8, the detection mode end determination is performed at a point (◯ mark) where Vpv is lower than Vmin, and transitions to the steady mode.

Next, the PAD diagram for the steady mode is as shown in FIG. That is, Iref, which is output from the control block 28, is set to Iref = IrefM, and IrefM obtained in the above-described detection mode is output. The start of the steady mode is set as time t = 0, and the following repetitive operation is started. In the repetitive operation, ILave and Vin are read and Ppv = ILave × Vin is calculated. Then, | PMax−Ppv | is calculated using the maximum power PMax obtained in the previous detection mode. If this result exceeds a predetermined ΔP value, the repetition is interrupted with t = T, and the detection mode is entered. On the other hand, when the calculation result of | PMax−Ppv | is smaller than ΔP, the time obtained by adding Δt to the current t is set to t. The above operation is repeated until t reaches T, which is a predetermined steady mode time. Here, when | PMax−Ppv |> ΔP is established, it indicates that the power generation characteristics of the solar cell panel 1 such as sudden change in sunshine and generation of shadows have suddenly changed from the characteristics measured in the previous detection mode. Sometimes high MPPT efficiency can be maintained by redoing the detection mode to obtain a new maximum power value. In the present embodiment, the transition from the steady mode to the detection mode is made after a lapse of a fixed time, but the present invention is not limited to this. It is only necessary to provide a timing for transition from the steady mode to the detection mode, and transition may be performed under a predetermined condition such as the number of times of switching.

As a major difference between the first embodiment and the present embodiment, in addition to the transition to the detection mode when the power fluctuation is large in the steady mode, the end of the detection mode described above is the input voltage, that is, the voltage of the solar panel 1 is zero or The point that it judges by decreasing to near zero is mentioned. By adopting such an algorithm, in this embodiment, the transition from the detection mode to the steady mode can be made immediately, so that the time loss is reduced and the MPPT efficiency can be further improved.

In the present invention, by setting Vmin, detection can be stopped before the short circuit current of the solar cell panel is reached. If the auxiliary power supply for driving the inverter is taken from Vin, the inverter will stop if Vin is lowered to zero. Therefore, detection is made by setting the minimum voltage at which the auxiliary power supply operates to Vmin. There is no problem that the auxiliary power supply stops in the mode.

In this embodiment, it is also effective to use a gate drive circuit between the PWM circuit 22a and the power MOSFET 9. The power MOSFET 9 may be replaced with another switching element such as IGBT or SiC-MOSFET. It is also effective to apply a SiC device to the boost diode 10. The configuration of the DC-DC converter 7 is preferably the step-up converter shown in FIG. 5, but may be other non-insulated converters or isolated converters. Further, the input filter 4 may have a circuit configuration that serves to prevent the current of the switching component from flowing to the solar cell panel side and reduce common mode noise. Further, the control circuit 14 may be constituted by an analog circuit having a similar function. The control circuit 14 may be a microcomputer or a DSP, and the AD converters 21a and 21b may be installed outside the control circuit 14 to input the digitally converted state quantity to the control circuit 14. Although the PWM circuit 22a is a circuit that performs pulse width modulation control, it can be replaced by pulse frequency modulation control (PFM), pulse density modulation control (PDM), or the like. Further, the PI control block 19 is a block that performs proportional-integral control, but may be configured by an analog circuit such as an operational amplifier, or may be replaced by PID (proportional-integral delay) control or the like.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 9 is a diagram showing the time change of the current target value in the detection mode of the present invention. By applying the current change pattern of the present embodiment to the target value varying means 16 in FIG. 1, the following operation is performed, and a new effect can be obtained.

The upper part of FIG. 9 shows the mode transition, and the lower part shows the change of the current target value according to the mode transition. In FIG. 9, the horizontal axis is time. In FIG. 9, the current target value Iref in the previous steady mode is IrefM (n−1). In the detection mode, Iref once becomes zero, and increases with time at an increase rate a of current change as shown in the figure. When the current value that is smaller by ΔI than the current target value IrefM (n−1) at the previous steady state is reached, the current change becomes an increase rate b. The increase rate b is slower than the previous increase rate a, and the slope (di / dt) of the current target value Iref becomes gentle, so that high detection accuracy can be obtained in the vicinity of IrefM (n−1). On the other hand, in the region where the current is sufficiently smaller than IrefM (n−1), the time of the detection mode can be shortened by setting the time change of the current to the increase rate a. As described above, in this embodiment, it is possible to solve the conflicting problems of the detection mode time reduction and the detection accuracy improvement.

In this embodiment, Iref is once set to zero, but this is not a limitation. The initial value of Iref is once set to zero because it also means that there is no leakage in sampling when detecting the maximum power point. Therefore, the initial value of Iref may be a value close to zero instead of zero.

In this embodiment, the timing at which the increase rate a changes to the increase rate b is when the current value has reached a current value that is smaller by ΔI from the current target value IrefM (n−1) at the previous steady state, but this is not limited. . Since the purpose is to shorten the detection mode time and improve the detection accuracy, a method of changing the increase rate with the passage of a fixed time may be used.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 10 is a diagram showing the time change of the target current value in the detection mode of the present invention. By applying the current change pattern of the present embodiment to the target value varying means 16 in FIG. 1, the following operation is performed, and a new effect can be obtained.

The upper part of FIG. 10 shows the mode transition, and the lower part shows the change of the current target value according to the mode transition. In FIG. 10, the horizontal axis is time. In FIG. 10, the current target value Iref in the previous steady mode is IrefM (n−1). In the detection mode, Iref once becomes zero, and increases with time at an increase rate a of current change as shown in the figure. When the current value that is smaller by ΔI than the current target value IrefM (n−1) at the previous steady state is reached, the current change becomes an increase rate b. The increase rate b is slower than the previous increase rate a, and the slope (di / dt) of the current target value Iref becomes gentle, so that high detection accuracy can be obtained in the vicinity of IrefM (n−1). Further, when the current Iref increases and reaches a current value that is larger than IrefM (n−1) by ΔI, the current change becomes an increase rate c. The increase rate c is steeper than the increase rate b, and the increase rate c may be set to the increase rate a.

As described above, in a region where the current is sufficiently smaller or larger than IrefM (n−1), the time of detection mode can be shortened by setting the time change of the current to increase rate a or increase rate c. it can. In the present embodiment, it is possible to solve the conflicting problems of shortening the detection mode time and improving the detection accuracy.

In this embodiment, Iref is once set to zero, but this is not a limitation. The initial value of Iref is once set to zero because it also means that there is no leakage in sampling when detecting the maximum power point. Therefore, the initial value of Iref may be a value close to zero instead of zero.

In this embodiment, the timing at which the increase rate a changes to the increase rate b is when the current value has reached a current value that is smaller by ΔI from the current target value IrefM (n−1) at the previous steady state, but this is not limited. . Since the purpose is to shorten the detection mode time and improve the detection accuracy, a method of changing the increase rate with the passage of a fixed time may be used. The same applies to the timing at which the increase rate b changes to the increase rate c.

Next, a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 11 is a circuit block diagram showing a circuit configuration in the fifth embodiment of the present invention.

FIG. 12 is a diagram showing the mode transition of the fifth embodiment of the present invention, and is a sequence describing the operation mode of the DC-DC converter of the present embodiment.

In FIG. 11, the same symbols are assigned to the same components as in FIGS. 1 and 5 in the above-described embodiment. In FIG. 11, 1a and 1b are solar cell panels, 4a and 4b are input filters, and 7a and 7b are DC-DC converters.

Next, the configuration of FIG. 11 will be described. Solar cell panels 1a and 1b are connected to input filters 4a and 4b in power conditioner 2, respectively. Input filters 4a and 4b are connected to DC- DC converters 7a and 7b, respectively. The outputs of the DC- DC converters 7a and 7b are connected to the grid interconnection inverter 12. The grid interconnection inverter 12 is connected to the commercial system 3 outside the power conditioner 2. Control circuits 14a and 14b are connected to DC- DC converters 7a and 7b, respectively.

The input filters 4a and 4b preferably have the configuration shown in FIG. 3, but may have other configurations. The DC- DC converters 7a and 7b are preferably the boost converter shown in FIG. 1, but may be other non-insulated converters or isolated converters.

Next, the operation of this embodiment will be described. The control circuits 14a and 14b control the operating states of the DC- DC converters 7a and 7b to which the control circuits 14a and 14b are connected, respectively. At this time, as shown in the mode of FIG. 12, the DC- DC converters 7a and 7b operate at the time Ts in the detection mode and the time T in the steady mode, and at the time T after the DC-DC converter 7a enters the detection mode. / 2 passes, the DC-DC converter 7b shifts to the detection mode. Although not shown, similarly, the DC-DC converter 7a transitions to the detection mode after the time T / 2 has elapsed since the DC-DC converter 7b entered the detection mode. Since T is a sufficiently long time with respect to Ts, the two DC- DC converters 7a and 7b do not simultaneously shift to the detection mode by controlling in this way, and at least one of the DC-DC converters is in the steady mode. Works with.

This example can be applied to a case where N series solar cell panels are connected to N DC-DC converters. In this case, there are DC-DC converters 1 to N, and the DC-DC converter [n] (1 ≦ n ≦ N) is a DC-DC converter [n−1] (however, when n = 1, the converter [N ]) Transitions to the detection mode after the time T / n has elapsed since entering the detection mode.

This operation allows each of the DC-DC converters to transition to the detection mode. In the detection mode, the output is lower than the maximum power, but the output power of the entire DC-DC converter group is averaged, and stable power can be output from the grid interconnection inverter 12 to the commercial system. .

In the present embodiment, the transition from the steady mode to the detection mode is made after a lapse of a fixed time, but this is not restrictive. It is only necessary to provide a timing for transition from the steady mode to the detection mode, and transition may be performed under a predetermined condition such as the number of times of switching.

In this embodiment, the detection mode is changed to the steady mode after a lapse of a certain time, but this is not restrictive. The transition from the detection mode to the steady mode may be performed at the stage where the detection mode is completed or the stage where the maximum power point is detected, and the transition may be performed under a predetermined condition such as the number of times of switching.

Next, the optimum condition extraction method (auto tuning) according to the sixth embodiment of the present invention will be described with reference to FIG. FIG. 13 is a diagram showing the time change of the current target value at the time of start-up of the present invention. By applying the current change pattern of the present embodiment at the time of starting each of the above-described embodiments, a new effect can be obtained.

The upper part of FIG. 13 shows the mode transition, the middle part shows the change of the current target value according to the mode transition, and the lower part shows the change of the power value according to the mode transition. The horizontal axis in FIG. 13 indicates time. In FIG. 13, when the inverter is activated, the first detection mode is started as shown. The detection mode is executed with an increase rate a for the time variation of the first current target value Iref, and the current target value IrefM that takes the maximum power value PMax is obtained. The maximum power value obtained at this time is PMax (a), and the current target value is IrefM (a). Subsequently, the first steady mode is started with IrefM (a) as a current target value. The steady mode is performed for a predetermined time, and the power Ppv obtained at this time is measured. This Ppv is defined as Ppv (a). And
ΔP (a) = | PMmax (a) −Ppv (a) |
ΔP (a) is calculated by the following equation.

Next, the second detection mode is started with the time change of the current target value Iref as an increase rate b larger than the increase rate a. The detection mode is executed, and a current target value IrefM that takes the maximum power value PMax is obtained. The maximum power value obtained at this time is PMax (b), and the current target value is IrefM (b). Subsequently, the second steady mode is started using IrefM (b) as a current target value. The steady mode is performed for a predetermined time, and the power Ppv obtained at this time is measured. This Ppv is defined as Ppv (b). And
ΔP (b) = | PMmax (b) −Ppv (b) |
ΔP (b) is calculated by the following equation.

In this way, the detection mode and the steady mode are executed n times to obtain ΔP (1) to ΔP (n). Then, by comparing with a predetermined ΔP, a condition that is smaller than this ΔP and has the largest increase rate is obtained. Then, the obtained increase rate is set as an increase rate in the subsequent detection mode and operated.

Depending on the response characteristics of the solar cell panel 1 and the inductance and capacitance included in the cable between the solar cell panel 1 and the power conditioner 2, the input filter 4, and the wiring of the substrate, the IV characteristics of the solar cell are sometimes Since it has a constant, in order to ignore the delay of the response characteristic, it is desirable that the increase rate of the current target value in the detection mode is as low as possible. Moreover, since the number of sampling points increases as the increase rate is lower, the detection accuracy of the maximum power point is also improved. On the other hand, however, there is a trade-off characteristic that the time spent in the detection mode increases as the rate of increase in the current target value decreases, and the MPPT efficiency deteriorates because the time for generating power at the operating point deviating from the maximum power point increases. Therefore, in this embodiment, it is possible to obtain an optimum increase rate at the time of startup by performing the above operation. Moreover, in the certification test of a power conditioner, there may be a case where an evaluation test is performed with a solar cell simulation power source having characteristics different from those of an actual solar cell panel. Since the response characteristics of the solar cell simulation power source are different from those of the solar cell panel, it is necessary to set the increase rate of the target current value in the detection mode to be low. Even in this case, the optimum condition extraction method (auto tuning) of this embodiment functions effectively.

Next, a seventh embodiment of the present invention will be described with reference to FIGS. FIG. 14 is a circuit diagram showing the circuit configuration of the seventh embodiment of the present invention. FIG. 15 is a waveform diagram of each part showing the circuit operation of the seventh embodiment of the present invention.

14, the same symbols are assigned to the same components as those in FIGS. 1, 5, and 11. In addition, in FIG. 14, 22b is a PWM circuit, 24 is a power MOSFET, 25 is a diode, and 26 is a signal processing circuit. The connection in the circuit diagram of FIG. 14 is mostly the same as the circuit diagram of FIG. Different parts will be described below. The drain of the power MOSFET 24 (S2) is connected to the positive side of the converter side of the input filter 4, and the cathode of the diode 25 (D2) is connected to the source of the power MOSFET 24 (S2). A choke coil 8 is connected to this connection point. The anode of the diode 25 (D2) is connected to the negative side of the input filter 4 on the converter side. On the other hand, in the control circuit 14, the output of the PI control block 19 is connected to the signal processing circuit 26, and the signal processing circuit 26 is connected to the PWM circuits 22a and 22b. The PWM circuit 22a is connected to the gate of the power MOSFET 9 (S1), and the PWM circuit 22b is connected to the gate of the power MOSFET 24 (S2). As described above, FIG. 14 shows a circuit configuration of a so-called H-bridge type buck-boost converter, and the feature of this embodiment is that the buck-boost operation is performed in the detection mode.

Next, the operation will be described. As shown in FIG. 15, the open circuit voltage Voc of the solar cell panel 1 is higher than the voltage Vpn of the capacitor 11. Therefore, Vpv always rises to Voc higher than Vpn when transitioning from the steady mode to the detection mode. Therefore, the detection mode starts from the boost mode. That is, when Vpv> Vpn, the power MOSFET 24 (S2) is switched, and the power MOSFET 9 (S1) is turned off to operate as a step-down converter. At this time, when the power MOSFET 24 (S2) is turned on, the solar cell panel 1-input filter 4-power MOSFET 24 (S2) -choke coil 8 (L) -boost diode 10 (D1) -capacitor 11 (Cpn) -input filter 4- A closed circuit of the solar cell panel 1 is formed, and a current flows through the choke coil 8. Next, when S2 is turned off, the solar cell panel 1 side and the choke coil 8 (L) are disconnected, and the choke coil 8 (L) —the boost diode 10 (D1) —the capacitor 11 (Cpn) —the diode 25 (D2) — Current circulates in the closed circuit of the choke coil 8 (L). At this time, the current is controlled so that the average value ILave of the current IL flowing through the choke coil 8 (L) becomes the current target value Iref.

Since Vref decreases as Iref increases, Vpv> Vpn changes to Vpv <Vpn during the detection mode. Therefore, when Vpv <Vpn, the power MOSFET 24 (S2) is turned on and the power MOSFET 9 (S1) is switched to operate as a boost converter. At this time, when the power MOSFET 9 (S1) is turned on, the solar cell panel 1-input filter 4-power MOSFET 24 (S2) -choke coil 8 (L) -power MOSFET 9 (S1) -input filter 4-closed circuit of the solar cell panel 1 Is formed, and a current flows through the choke coil 8 to accumulate excitation energy. Next, when the power MOSFET 9 (S1) is turned off, the solar cell panel 1-input filter 4-MOSFET 24 (S2) -choke coil 8 (L) -boost diode 10 (D1) -capacitor 11 (Cpn) -input filter 4-sun A current flows through the closed circuit of the battery panel 1. At this time, similarly to the step-down converter operation, current control is performed so that the average value ILave of the current IL flowing through the choke coil 8 (L) becomes the current target value Iref.

In the current control, in both step-down mode and step-up mode, IL is detected by the current sensor 13, taken in by the AD converter 21 b, the difference from Iref is taken by the subtractor 18, and this difference is calculated by the PI control block 19. The duty ratio of the power MOSFET 24 and the power MOSFET 9 is determined and the power MOSFET is switched. At this time, the signal processing circuit 26 performs the following processing. First, if the lower limit of the signal input from the PI control block is 0 and the upper limit is 2,
Signal processing circuit 26 Input signal: S_in 0 ≦ S_in <2
S_S2 = S_in where S_S2 = 1 when S_in> 1
S_S1 = S_in-1 where S_S1 = 0 when S_in <1
To control. When the signals S_S1 and S_S2 are 0, the duty ratio is zero. When the signals S_S1 and S_S2 are 1, the duty ratio is 100%.

By controlling as described above, current control can be performed in a wide range of the voltage of the solar cell panel in the detection mode from 0 to Voc without switching the operation between the step-up mode and the step-down mode.

Next, an eighth embodiment of the present invention will be described with reference to FIG. FIG. 16 is a PAD diagram in the steady mode of the photovoltaic power generation system according to the present invention. The circuit configuration for realizing the operation of the PAD diagram may be any of FIGS. Further, as the detection mode algorithm in the present embodiment, the algorithm of the PAD diagram shown in FIG. 6 is suitable.

In FIG. 16, when the steady mode is started, IrefM obtained in the previous detection mode is used, and Iref = IrefM, t = 0, t <T, and the following processing is repeated.

In the repeated processing, the current Ib detected the last time is set to Ibb, and the last detected current ILave is set to Ib. Thereafter, ILave and Vin are taken in, ILave × Vin is calculated, and this is defined as Ppv. Then, the absolute value of PMax-Ppv is calculated using PMax, which is the maximum power obtained in the previous detection mode. If | PMax-Ppv | is greater than a predetermined ΔP, the solar radiation abrupt change is set to t = T, The steady mode is terminated and the mode is changed to the detection mode. When | PMax−Ppv | is smaller than a predetermined ΔP, t is set to t + Δt, and the next processing is started.

The following processing is a maximum power tracking control method called a so-called hill-climbing method. That is, if Ppv is larger than the previous calculation value Ppv (z−1), X = 0 and Ix = 0. When Ppv is exactly the same as Ppv (Z-1), X = 1 and Ix = Ibb. If the relationship between Ppv and Ppv (Z-1) is neither of the above, X = −1 and Ix = Ib. Next, if ILave is greater than Ix, dIref = + dI, otherwise dIref = −dI. Next, when Ix = 0, dIref = 0. And the following formula IrefM + dIref * X
And the result of the calculation is IrefM.

Repeat the process so far until t reaches T. When t becomes T, the state shifts to the detection mode shown in FIG.

As described above, in this embodiment, the maximum power point is detected in the detection mode shown in FIG. 6, and in the steady mode, a sudden change in solar radiation is detected and the detection mode is changed, and the hill-climbing method is performed with the maximum power point as an initial value. The maximum power follow-up control is performed. In this embodiment, two different maximum power detection methods are provided in the detection mode and the steady mode, and the following effects are obtained.

Since scanning in the detection mode is performed at regular intervals, it is possible to eliminate the concern of convergence to the maximum value that the hill-climbing method falls when two-climbing characteristics such as partial shadows occur.

Although there is a concern that the MPPT efficiency is lowered by frequently performing the detection mode, the frequency of the detection mode can be lowered by using the hill-climbing method together, and the decrease in the MPPT efficiency can be prevented.

In this embodiment, another maximum power tracking method may be used in addition to the hill climbing method.

Of course, also in the present embodiment, the combined use of the above-described activation method and processing for changing the increase rate is also effective.

The present invention can be applied to a photovoltaic power generation system linked to a commercial system for home use. Further, the present invention can be applied to a large-scale photovoltaic power generation system such as a solar power generation system such as a DC power supply system that is not connected to the grid, a solar cell system for remote islands and mountain huts, a solar cell system for smart grids, and a mega solar system.

1, 1a, 1b Solar panel 2 Power conditioner 3 Commercial system 4, 4a, 4b Input filter 5a, 5b Common mode choke 6a, 6b, 6c, 6d Filter capacitor 7, 7a, 7b DC-DC converter 8 Choke coil 9 , 24 Power MOSFET
DESCRIPTION OF SYMBOLS 10 Boosting diode 11 Capacitor 12 Grid connection inverter 13 Current sensor 14, 14a, 14b Control circuit 15a, 15b Voltage dividing resistor 16 Target value variable means 17 Mode switch 18 Subtractor 19 PI control block 20 Multiplier 21a, 21b AD conversion 22a, 22b PWM circuit 23 Maximum value determination circuit 25 Diode 26 Signal processing circuit 27 Normal mode choke 28 Control block

Claims (22)

1. In a solar power generation system having a solar cell and a power converter connected to the solar cell,
   The power converter includes at least one switching element;
   Current detection means for obtaining an input current by detecting a current flowing from the solar cell to the power converter;
   Current target value,
   Voltage detecting means for detecting an input voltage to the power converter and obtaining an input voltage;
   Current control means for controlling the input current to a value substantially equal to the current target value by switching control of the switching element;
   A target value varying means for varying the current target value;
   The current control means is operated while sequentially increasing the current target value from substantially zero by the target value varying means, and each time the power at that time is calculated from the input current and the input voltage,
   A detection mode for obtaining a current target value at a point where the power becomes maximum;
   A photovoltaic power generation system comprising a steady mode in which the current control means is operated using the current target value obtained in the detection mode.
2. 2. The photovoltaic power generation system according to claim 1, wherein, in the detection mode, transition to the steady mode is made after a lapse of a predetermined time.
3. 2. The photovoltaic power generation system according to claim 1, wherein, in the detection mode, when the input voltage decreases to a predetermined value or less, a transition is made to the steady mode.
4. 4. The photovoltaic power generation system according to claim 1, wherein the transition from the steady mode to the detection mode is performed at regular intervals.
5. 5. The method according to claim 4, wherein when the power in the steady mode fluctuates more than a predetermined ratio with respect to the maximum power detected in the detection mode, transition to the detection mode without waiting for the elapse of the predetermined time. A solar power generation system.
6. 6. The variable method of the target value varying means in the detection mode according to claim 1, wherein the current value is exceeded after a current value that is smaller by a predetermined value than the current target value used in the previous steady mode. A photovoltaic power generation system characterized by making the rate of increase of the target value more gradual than the rate of increase so far.
7. 6. The target value varying means according to claim 1, wherein the target value varying means in the detection mode is within a predetermined width with reference to the current target value in the previous steady mode. The solar power generation system is characterized in that the rate of increase in the power is made moderate compared to the outside of the predetermined width.
8. The power converter according to any one of claims 1 to 7, wherein the power converter includes a plurality of power converters, and when one of the power converters is in a detection mode, the other power converter is in a steady mode. A solar power generation system.
9. 9. The power converter according to claim 8, wherein when the operation time of the steady mode at one time is T and the parallel number of the power converters is n, each power converter shifts from the steady mode to the detection mode with a delay of T / n. A solar power generation system characterized by
10. In any one of Claim 1-9, while starting the said solar system, while repeating multiple detection mode and steady mode, the current increase rate of the electric current target value variable means in the said multiple detection mode is the last time The error between the maximum power value obtained in the detection mode and the maximum power value obtained in the steady mode immediately thereafter is not more than a predetermined value and the current increase rate of the current target value variable means can be as high as possible. A photovoltaic power generation system characterized by selecting a large condition and using the selected current increase rate as the current increase rate of the current target value variable means in the subsequent detection mode.
11. 11. The photovoltaic power generation according to claim 1, wherein the power converter has a function of a step-up / step-down converter and transitions from a step-down operation to a step-up operation as the current target value increases in the detection mode. system.
12. 12. In any one of claims 1 to 11, in the steady mode, the current target value obtained in the immediately preceding detection mode is used as an initial value, the current target value is slightly increased or decreased, and the input voltage and current changed as a result are changed. The photovoltaic power generation system is characterized in that the increase or decrease in power is determined and the current target value is slightly changed in a direction in which the power becomes larger.
13. A solar power generation system in which a solar cell, a power converter, and a commercial system are connected, wherein the power converter has a detection mode and a steady mode for detecting the maximum power of the solar cell, and the detection mode also includes the detection mode A solar power generation system having a function of outputting electric power of a solar cell from the power converter to the commercial system.
14. In a solar power generation system including a solar cell and a power converter connected to the solar cell, the power converter includes at least one switching element, a current target value,
    A current control function for controlling the current flowing from the solar cell to the power converter by switching control of the switching element to a value substantially equal to the current target value; current detection means for detecting the current; and the current target And a means for changing the value,
    It has a detection mode and a steady mode that operate alternately,
    While operating the current control function in the detection mode and the steady mode,
    In the detection mode, the input voltage and the detection value of the current detection means are increased until the input voltage of the power converter decreases to a predetermined value or less while increasing the current target value sequentially from substantially zero by the target value variable means. , Calculate the instantaneous power using the sampled value, store the current target value of the point where the instantaneous power is maximum,
    In the next steady mode, the power converter is operated using the stored current target value.
15. In the power converter that performs tracking control so that the solar cell operates at the maximum power point,
    When detecting the maximum power point of the solar cell, a current target value for controlling the current of the solar cell is once set to a predetermined current value, and then a predetermined current value is reached from the predetermined current value to a short-circuit current. A power converter, wherein the power of the solar cell is sampled and the maximum power point is detected while changing for each current width.
16. In the power converter that performs tracking control so that the solar cell operates at the maximum power point,
    When detecting the maximum power point of the solar cell, the current target value for controlling the current of the solar cell is once set to a predetermined current value, and then the current of the solar cell reaches a predetermined voltage. A power converter characterized by sampling the power of the solar cell and detecting the maximum power point while changing a target value for each predetermined current width.
17. In the detection control mode for detecting the maximum power point of the solar cell from the output current and output voltage of the solar cell, and the maximum power point tracking control method of the solar cell consisting of the steady control mode,
    The detection control mode includes a target value setting step for determining a current target value, a current control step for controlling the output current to a value substantially equal to the current target value, and current / voltage detection for detecting the output current and the output voltage. A power and current storage step for storing a power obtained by multiplying the output current and the output voltage and the output current at that time,
    In the target value setting step, the current target value gradually increases,
    In the power / current storage step, the power stored in the previous power / current storage step is compared with the current power, and the larger power and the output current at that time are stored.
    The detection control mode transitions to the steady control mode after a predetermined time has elapsed,
    A maximum power point tracking control method, wherein in the steady control mode, an output current and an output voltage of a solar cell are controlled according to a maximum power point that is the power stored in the power / current storage step.
18. In the detection control mode for detecting the maximum power point of the solar cell from the output current and output voltage of the solar cell, and the maximum power point tracking control method of the solar cell consisting of the steady control mode,
    The detection control mode includes a target value setting step for determining a current target value, a current control step for controlling the output current to a value substantially equal to the current target value, and current / voltage detection for detecting the output current and the output voltage. A power and current storage step for storing a power obtained by multiplying the output current and the output voltage and the output current at that time,
    In the target value setting step, the current target value gradually increases,
    In the power / current storage step, the power stored in the previous power / current storage step is compared with the current power, and the larger power and the output current at that time are stored.
    The detection control mode ends when the voltage detected in the current / voltage detection step reaches a predetermined value and transitions to the steady control mode,
    A maximum power point tracking control method, wherein in the steady control mode, an output current and an output voltage of a solar cell are controlled according to a maximum power point that is the power stored in the power / current storage step.
19. In the detection control mode for detecting the maximum power point of the solar cell from the output current and output voltage of the solar cell, and the maximum power point tracking control method of the solar cell consisting of the steady control mode,
    The detection control mode includes a target value setting step for determining a current target value, a current control step for controlling the output current to a value substantially equal to the current target value, and current / voltage detection for detecting the output current and the output voltage. A power and current storage step for storing a power obtained by multiplying the output current and the output voltage and the output current at that time,
    In the target value setting step, the current target value gradually increases,
    The detection control mode ends when the voltage detected in the current / voltage detection step reaches a predetermined value and transitions to the steady control mode,
    A maximum power point tracking control method, wherein, in the steady control mode, the output current and output voltage of a solar cell are controlled according to a maximum power point that is maximum power among the power stored in the power / current storage step.
20. Detecting the output voltage and output current of the solar cell;
    Determining a target value of the output current;
    Controlling the output current to a value substantially equal to the target value;
    The power comprising the multiplication of the output current and the output voltage and the step of storing the output current at that time,
    In the step of determining the target value, the target value gradually increases,
    In the storing step, the power stored in the previous power / current storing step is compared with the current power, and the larger power and the output current at that time are stored, and the maximum power point detection control is characterized. Method.
21. A power converter having the control method according to any one of claims 17 to 20.
22. A solar power generation system comprising the power converter according to claim 14, claim 15, or claim 21 and a solar battery.

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