WO2012103993A1

WO2012103993A1 - Method and apparatus for calibrating at least one current sensor

Info

Publication number: WO2012103993A1
Application number: PCT/EP2011/074147
Authority: WO
Inventors: Julian DOERREICH; Dimitrios Stavrianos; Tankut UZAN
Original assignee: Robert Bosch Gmbh
Priority date: 2011-02-03
Filing date: 2011-12-28
Publication date: 2012-08-09
Also published as: DE102011003566A1

Abstract

The invention relates to a method and to an apparatus for calibrating a current sensor (7-U; 7-V; 7-W), which is used to detect a phase current (l_U; l_V; l_W) of an electrical machine (1) that is controlled by an inverter (2). To this end, a control unit (5) switches the electrical machine (1) into a short-circuit mode, in which at least an actual value of the phase current (l_U; l_V; l_W) is detected by the current sensor (7-U; 7-V; 7-W). An evaluation unit (6) compares the detected actual value or a parameter derived from the at least one detected actual value with a prespecifiable setpoint value and determines, on the basis of a deviation of the actual value or of the parameter derived therefrom from the setpoint value, a deviation of the at least one current sensor (7-U; 7-V; 7-W) from a standard condition.

Description

Description title

Method and device for calibrating at least one current sensor

The invention relates to a method and a device for calibrating at least one current sensor, which serves for detecting a phase current of an electric machine controlled by an inverter.

State of the art

For the drive in hybrid or electric vehicles electrical machines in the form of induction machines are usually used, which in conjunction with inverters - often referred to as inverter - are operated. The electrical machines are operated either in motor or generator mode. During engine operation, the electric machine generates a drive torque, which when used in a hybrid vehicle

Internal combustion engine, for example in an acceleration phase, supported. In generator mode, the electric machine generates electrical energy that is stored in an energy storage such as a battery or a super-cab. Operating mode and power of the electrical machine are set via the inverter.

Known inverters comprise a series of switching elements, with which the individual phases (U, V, W) of the electric machine can be switched against a high supply voltage potential or against a low one

Supply voltage potential can be switched. In each case, two series-connected switching elements form a half-bridge branch, wherein a first switching element with the high supply voltage potential and a second switching element with the low supply voltage potential are connected. Each phase of the electric machine is then one each

Half bridge branch connected. The switching elements of an external

Controlled control unit, which depends on the driver's request

(Acceleration or braking) a target operating point for the electric Machine calculated. The inverter is connected to the control unit and receives from this the corresponding operating data or control commands.

For this purpose, current sensors are provided, which are usually in the

Connecting lines between the inverter and the electric machine are arranged and detect the currents in the individual phases of the electric machine (phase currents).

However, the current sensors can scatter due to manufacturing tolerances and / or drift depending on temperature, current amount and / or aging. However, such variations (offsets) and drifts have a negative effect on the accuracy of a torque control of the electrical machine, so that a calibration of the current sensors is required.

Disclosure of the invention

The invention provides a method for calibrating at least one

A current sensor for detecting a phase current of an inverter-controlled electric machine in which the electric machine is switched to a short-circuit mode in which all switching elements of the inverter connected to a high supply voltage potential are closed and all of them low

Supply voltage potential connected switching elements of the

Inverter are open or all with the high

Supply voltage potential connected switching elements of the

Inverter open and all with the low

Supply voltage potential connected switching elements of the

Inverter are closed. In the short-circuit mode, at least one actual value of the phase current is then detected. Subsequently, the detected actual value or a variable derived from the at least one detected actual value is compared with a predefinable desired value and stored in

Dependent on a deviation of the actual value or the quantity derived therefrom, a deviation of the at least one current sensor from a standard state is determined by the desired value. The invention also provides an apparatus for calibrating at least one current sensor which serves to detect a phase current of an electrical machine controlled by an inverter. The device in this case comprises a control unit, which switches the electric machine into a short-circuit mode, in which all with a high

Supply voltage potential connected switching elements of the

Inverter closed and all with a low

Supply voltage potential connected switching elements of the

Inverter are open or all with the high

Supply voltage potential connected switching elements of the

Inverter open and all with the low

Supply voltage potential connected switching elements of the

Inverter are closed. The at least one current sensor detects at least one actual value of the phase current in the short-circuit mode. The

Device also comprises an evaluation unit, which detects the detected

The actual value or a variable derived from the at least one detected actual value is compared with a predefinable desired value and a deviation of the at least one current sensor from a standard state is determined as a function of a deviation of the actual value or the quantity derived therefrom.

Advantages of the invention

In order to be able to calibrate current sensors, one needs at least one reference point to which the current flow through a sensor in the standard state is known. In the short-circuit mode of the electric machine, phase currents set in, the values of which are essentially influenced only by the electrical machine and the temperature and which are consequently known in advance. The invention is based on the basic idea to use these known current values to deviations of a current sensor, which the

Phase current detected to determine from a standard state. The

The method according to the invention and the method according to the invention offer the advantage that the calibration takes place "under load", which makes it possible for a current sensor even with different amounts of current and therefrom

to calibrate the resulting speeds. This in turn is particularly advantageous because the deviations of a current sensor from a Norm state, ie the offsets and drifts over temperature, current amount and aging, not linear. The inventive calibration in

Short-circuit mode also offers the possibility of evaluating a deviation from a standard value not only in terms of absolute value, but also taking into account the sign of the deviation.

In order to increase the accuracy of the calibration method according to the invention, it is provided according to an embodiment of the invention to detect actual values of the phase current over at least one full period, to integrate the detected actual values, to compare the resulting current integral or a quantity derived therefrom with a desired value and depending on a deviation of the current integral or a quantity derived therefrom, the deviation of the at least one current sensor from a standard state can be determined from the desired value.

In a short circuit mode, which is often referred to as an active short circuit, the phase currents oscillate around the zero point. If the detected actual values of a phase current are integrated over one or more full periods, e.g. triggered by a zero crossing of a rising edge, the current integral must be zero. The value "zero" thus represents the desired value. If a value deviating therefrom results for the current sensor to be calibrated, a measured value of the current sensor can be corrected according to the magnitude and sign of this deviation and thus the current sensor can be calibrated.

If, in each case, a current sensor for detecting the respective phase current is provided for each phase of the electrical machine, a summation current of the current sensors can also be used for the calibration. For this purpose, at least one actual value of the respective phase current is detected by each current sensor in the short-circuit mode of the electrical machine. The detected actual values are then summed up and the resulting summation current is compared with a predefinable setpoint value. Depending on one

Deviation of the summation current from the setpoint, the deviation of the current sensors from a standard state is then determined. Since the phase current to be detected by the current sensor in the short-circuit

Mode is dependent on the speed of the electric machine, it is according to According to an embodiment of the invention, in the short-circuit mode, a variable characterizing the rotational speed of the electric machine is detected and the desired value is predetermined as a function of the detected rotational speed.

In addition, the phase current to be detected by the current sensor in the short-circuit mode is also dependent on a temperature in the region of the current sensor. Therefore, it is advantageous to detect a temperature in the region of the at least one current sensor and to specify the desired value as a function of the detected temperature.

A particularly simple realization results when the speed and / or temperature-dependent setpoints are specified in the form of characteristic curves which are stored in an evaluation unit.

To further increase the accuracy of the calibration, the deviation of the current sensors from a standard state can also be determined at at least two different rotational speeds and / or temperatures.

Advantageously, an offset in the de-energized state of the electrical machine can additionally be determined for the at least one current sensor. If a current sensor for detecting the respective phase current is provided for each phase of the electrical machine, this can be done concretely in that at least one actual value of the respective phase current is detected by each current sensor in the de-energized state and the detected actual values are added up. In the de-energized state must in the normal state of

Current sensors give a total current of "zero". In this respect, the resulting summation current can be interpreted as the total offset of the current sensors.

Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying figures.

Brief description of the drawings Show it:

1 is a schematic block diagram of an inverter-controlled electric machine;

2 shows a flow chart of a calibration method according to the invention. Description of the embodiments

Figure 1 shows a schematic representation of a three-phase electric machine 1, which may for example be designed as a synchronous, asynchronous or reluctance machine, with a connected thereto

Inverter in the form of a pulse inverter 2. The pulse inverter 2 includes switching elements 3a-3f in the form of circuit breakers, which are connected to individual phases U, V, W of the electric machine 1 and the phases U, V, W either against a high supply voltage potential T + or switch a low supply voltage potential T-. The connected to the high supply voltage potential T + switching elements 3a-3c are also called "high-side switch" and the low

Supply voltage potential T- connected switch 3d-3f referred to as "low-side switch" and can be embodied for example as Insulated Gate Bipolar Transistor (IGBT) or as Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) The pulse inverter 2 further comprises a plurality of free-wheeling diodes 4a-4f, which are each arranged parallel to one of the switching elements 3a-3f The switching elements 3a and 3d, 3b and 3e and 3c and 3f in each case form a half bridge 10a, 10b or 10f, which in each case one of the phases U, V , W are assigned to the electric machine 1.

The pulse-controlled inverter 2 determines the power and operating mode of the electric machine 1 and is controlled accordingly by a first control unit 5, which is shown only schematically and which can also be integrated in the inverter 2. The electric machine 1 can be operated either in the engine or generator mode.

Parallel to the pulse inverter 2, a so-called intermediate circuit capacitor 6 is arranged, which also integrates into the pulse inverter 2 may be and which essentially serves to stabilize a voltage of an energy storage, so for example a battery voltage.

In the connecting lines between the pulse inverter 2 and the electric machine 1, a current sensor 7-U or 7-V or 7-W is respectively arranged, which of the detection of the phase currents l_U, l_V and l_W in the phases U and V and W of the electric machine 1 serve. Output signals of the current sensors 7-U, 7-V and 7-W are supplied to the control unit 5 and taken into account in the control of the pulse inverter.

The electric machine 1 is designed in the illustrated embodiment, three-phase, but may also have fewer or more than three phases.

In order to ensure sufficient accuracy in the control of the torque of the electric machine 1 by the control unit 5, the current sensors 7-U, 7-V and 7-W are calibrated. The invention

Calibration method will be explained below with reference to FIG 2.

In a first step S1, the electric machine is active in a

Short circuit mode switched. For this purpose, all connected to the high supply voltage potential T + switching elements 3a-3c of the pulse inverter 2 (high-side switch) are closed by the control unit 5 and all connected to the low supply voltage potential T- switching elements 3d-3f of the pulse inverter 2 (low-side switch ) or all the high-side switches 3a-3c open and all the low-side switches 3d-3f of the

Inverter closed.

In a second step S2, at least one actual value of the respective phase current l_U or, I_V or, I_W is detected by each of the current sensors 7 -U, 7-V and 7-W. In addition, a variable characterizing the rotational speed of the electric machine 1 and a temperature in the region of the current sensors 7-U, 7-V and 7-W are detected.

In a third step S3, the detected actual values are replaced by a

Evaluation unit 8, which may be integrated in the control unit 5 or may be implemented as a separate unit, each with a predetermined Setpoint compared. The setpoints are stored in speed and temperature-dependent form in the evaluation unit 8 in the form of characteristics. Depending on the resulting deviations of the actual values from the respective desired values, the deviations of the individual current sensors 7-U, 7-V and 7-W from a standard state are then determined. The current sensors are thus calibrated and the deviations determined can be taken into account by the control unit 5 during the processing of the output signals of the current sensors 7-U, 7-V and 7-W, respectively.

Alternatively or additionally, actual values of the phase currents I_U, I_V and I_W can also be detected in each case over one or more periods in step S2. In this case, the actual values are first integrated in step S3 for each of the phase currents I_U, I_V and I_W. Subsequently, the resulting current integrals are compared with corresponding (integral) setpoint values and the deviations of the individual current sensors 7-U, 7-V and 7-W from the standard state are determined as a function of the comparison results. Because the

Phase currents l_U, | _V and l_W oscillate around the zero point in the short-circuit mode, the current integral when integrated over one or more full periods, e.g. triggered by a zero crossing of a rising edge, giving zero. The value "zero" thus represents the desired value in this case.

In addition to the individual currents in the phases U, V and W can also be a

Total current of the phases are used for calibration. Thus, as an alternative or in addition to the evaluation methods described in step S3, the actual values of the individual phase currents I_U, I_V and I_W can also be added up and the total current can be compared with a corresponding (sum) desired value.

The setpoint values for evaluating the current integral and the total current can of course also be stored in the evaluation unit in the form of speed-dependent and temperature-dependent characteristic curves.

In order to increase the quality of the calibration, the steps S1 to S3 become advantageous at different operating points, ie different

Speeds and / or temperatures repeated. In addition, an offset of the current sensors 7-U, 7-V and 7-W can also be determined in the de-energized state of the electric machine. For this purpose, the electric machine 1 is first switched to a freewheeling mode, in which all switches 3a-3f of the pulse-controlled inverter are open. In this de-energized state, at least one actual value of the respective phase current I_U or I_V or I_W is detected by each of the current sensors 7-U, 7-V and 7-W. These recorded actual values then become

summed up. If this results in a sum current different from "zero", then this is interpreted as the total offset of the current sensors 7-U, 7-V and 7-W.

Claims

Method for calibrating at least one current sensor (7-U; 7-V; 7-W), which is used to detect a phase current (l_U; l_V; l_W) of an electric machine (1) controlled by an inverter (2), in which

- The electric machine (1) is switched to a short-circuit mode, in which all of a high supply voltage potential (T +) connected switching elements (3a-3c) of the inverter (2)

closed and all with a low

Supply voltage potential (T) connected switching elements (3d-3f) of the inverter (2) are open or all with the high

Supply voltage potential (T +) connected switching elements (3a- 3c) of the inverter (2) open and all with the low

Supply voltage potential (T) connected switching elements (3d-3f) of the inverter (2) are closed,

- at least one actual value of the phase current (l_U; l_V; l_W) is detected,

the detected actual value or one of the at least one detected

Actual value derived is compared with a predefinable setpoint and

- depending on a deviation of the actual value or the resulting

derived quantity of the target value, a deviation of the at least one current sensor (7-U; 7-V; 7-W) is determined by a standard state.

Method according to one of the preceding claims, wherein

Actual values of the phase current (l_U; l_V; l_W) are recorded over at least one full period,

- the recorded actual values are integrated,

the resulting current integral or a quantity derived therefrom is compared with a desired value and, depending on a deviation of the current integral or a quantity derived therefrom

Desired value of the deviation of the at least one current sensor (7-U; 7-V; 7-W) is determined by a standard state. Method according to one of claims 1 or 2, wherein for each phase (U; V; W) of the electrical machine (1) there is respectively a current sensor (7-U; 7-V; 7-W) for detecting the respective phase current (L_U; l_V; l_W) is provided and where

- of each current sensor (7-U; 7-V; 7-W) in short-circuit mode of

electrical machine (1) at least one actual value of the respective

Phase current (l_U; l_V; l_W) is detected,

- the recorded actual values are added up,

- The resulting total current with a predetermined setpoint

is compared and

as a function of a deviation of the summation current from the

Setpoint the deviation of the current sensors (7-U, 7-V, 7-W) is determined by a standard state.

The method of claim 1, wherein in the short-circuit mode, a speed characterizing the speed of the electric machine (1) is detected and the desired value is specified as a function of the detected rotational speed.

Method according to one of claims 1 or 2, wherein a temperature in the region of the at least one current sensor (7-U; 7-V; 7-W) is detected and the desired value is predetermined as a function of the detected temperature.

Method according to one of claims 2 or 3, wherein speed and / or temperature-dependent setpoints in the form of characteristics in a

Evaluation unit (8) are stored.

Method according to one of claims 4 to 6, wherein the deviation of the

Current sensors (7-U, 7-V, 7-W) of a standard state at least two different speeds and / or temperatures is determined.

Method according to one of the preceding claims, wherein for the at least one current sensor (7-U; 7-V; 7-W) additionally an offset in the de-energized state of the electrical machine (1) is determined.

9. The method according to claim 8, wherein for each phase (U; V; W) of the electrical machine (1) a respective current sensor (7-U; 7-V; 7-W) for detecting the respective phase current (IJJ; l_W) is provided and wherein

from each current sensor (7-U, 7-V, 7-W) in the de-energized state

at least one actual value of the respective phase current (l_U; l_V; l_W) is detected,

- the recorded actual values are added up,

- The resulting summation current is interpreted as the total offset of the current sensors (7-U, 7-V, 7-W).

10. An apparatus for calibrating at least one current sensor (7-U; 7-V; 7-W) which serves to detect a phase current (IJJ; l_V; l_W) of an electrical machine (1) controlled by an inverter (2)

- A control unit (5), which the electric machine (1) in a

Short circuit mode switches, in which all with a high

Supply voltage potential (T +) connected switching elements (s) of the inverter (2) are closed and all connected to a low supply voltage potential (T-) switching elements (3d-3f) of the inverter (2) are open or all with the high

- The at least one current sensor (7-U; 7-V; 7-W), which detects at least one actual value of the phase current (L_U; l_V; l_W), and

an evaluation unit which compares the detected actual value or a variable derived from the at least one detected actual value with a predefinable desired value and in dependence on a

Deviation of the actual value or the quantity derived therefrom from the desired value a deviation of the at least one current sensor (7-U; 7-V; 7-W) from a standard state.