WO2011138110A1

WO2011138110A1 - Circuit and method for controlling a linear compressor

Info

Publication number: WO2011138110A1
Application number: PCT/EP2011/055266
Authority: WO
Inventors: Hans-Wilhelm Klein; Eberhard Weidner
Original assignee: BSH Bosch und Siemens Hausgeräte GmbH
Priority date: 2010-05-03
Filing date: 2011-04-05
Publication date: 2011-11-10
Also published as: DE102010028506A1

Abstract

The invention relates to a circuit for controlling a linear compressor, comprising a first input connection (130) and a second input connection (131) for providing the linear compressor with an electric supply voltage (Uv), an output connection (132) to which the linear compressor can be connected, a motor switch (110) for electrically connecting the second input connection (131) to the output connection (132), and a free-wheel switch (120), which is electrically connected to the first input connection (130) and to the output connection (132) of the control circuit and is provided to electrically connect the input connection (130) and the output connection (132) when the motor switch (110) is opened.

Description

Circuit and method for driving

a linear compressor

The present invention relates to a circuit for controlling a linear compressor and to a method for controlling a linear compressor.

Typical linear compressors have a bushing in which a piston is movable back and forth. The piston delimits to one side a piston chamber, in which an inlet valve in a valve plate gas can be admitted. At a

Compression stroke of the piston is compressed, the gas introduced into the piston chamber and ejected via an outlet valve in the valve plate. The piston is driven via a piston rod by a linear motor, which converts the electrical energy supplied to it into a linear, oscillating movement. Compared to piston compressors with a rotary drive, e.g. Via a connecting rod driven by a rotary motor, linear compressors have the advantage that the piston stroke can be changed and thus a higher efficiency can be achieved. such

Linear compressors are used in the household sector for refrigerators and freezers and the like.

To drive the linear motor, an electrical drive circuit is necessary. US Patent 5,947,693 discloses a circuit for driving a linear compressor, in which a linear compressor is connected via a triac to a power supply. A position sensor detects the position of the linear compressor piston, and a controller shifts the triac depending on the detected position. The adjustment of the power supply to the current operating state is thus carried out by phase control. The disadvantage of this arrangement is that it requires a linear compressor, which is designed mechanically for operation on the mains voltage with eg 50 Hz and therefore can only be operated rigidly in all operating conditions with this single frequency. Furthermore, since the triac can not be switched off by the control, there is no possibility of stopping the introduction of energy into the bulb in the event of short-term, uncontrollable voltage spikes in the network. Under certain circumstances, the piston may move beyond a maximum allowable stroke and thus damaged in such conditions. US Patent 5,947,693 further discloses a circuit for driving a

Linear compressor with a converter and a DC link. In this arrangement, the power supply and the operating frequency of the linear compressor can be changed and adapted to the operating conditions via a pulse width modulation. An uncontrolled power supply, as in the triac circuit can be prevented in this arrangement, and there is the possibility of the

For a short time electrically braking the linear drive.

EP 1 017 156 discloses a driving circuit for a load with a rectifier bridge and two loop-back paths, which are arranged parallel to the load and are switched on in each case with positive or negative half-waves of a supply voltage.

However, the last-mentioned arrangements have in common that they are relatively expensive, which is associated with higher costs.

It is therefore an object of the present invention to provide a circuit for driving a linear compressor, which is inexpensive and at the same time can prevent or limit overvoltages or overcurrent. The linear compressor is preferably in a refrigerator for the compression of the

Refrigerant used. Under a refrigerator is in particular a

Domestic refrigeration appliance understood, so a refrigeration appliance to the household in

Households or may be used in the catering sector, and

in particular serves to store food and / or drinks in household quantities at certain temperatures, such as a refrigerator, a

Freezer, a fridge freezer, a freezer or a

Wine storage cabinet.

According to one embodiment of the invention, a circuit for driving a linear compressor comprises a first input terminal and a second input terminal for providing an electrical supply voltage for the linear compressor, an output terminal to which the linear compressor is connectable, a motor switch for electrically connecting the second input terminal to the Output terminal, and a freewheel switch, which with the first

Input terminal and the output terminal of the drive circuit is electrically connected and provided to electrically connect the input terminal and the output terminal when opening the motor switch. A corresponding method for driving such a circuit comprises:

Providing an electrical supply voltage to the linear compressor via the first input terminal and the second input terminal;

Close the motor switch to connect the second one electrically

Input terminal to the output terminal; and

Opening the motor switch for electrically disconnecting the second input terminal from the output terminal;

wherein the first input terminal when opening the motor switch by the

Free-wheeling switch is electrically connected to the output terminal. Here, the term "connection" in the electrical sense to understand, so in particular includes fixed, no longer separable wiring.

Such a circuit or such a method can be set up with relatively little effort. For example, the motor switch and the freewheeling switch each have exactly one transistor. Thus, only two transistors are provided in the entire circuit, which is advantageous, in particular if the transistors are designed as comparatively expensive IGBTs or power MOSFETs. In this case, the motor switch and the freewheeling switch can be controlled such that always only either the motor switch or the freewheel switch is closed.

The motor switch and the freewheeling switch may each further comprise four diodes, which are arranged in a bridge circuit such that current always flows in one direction only through the transistor. This ensures that the transistors are always traversed by current in the same direction. The first supply connection can be connected directly to the first connection, or indirectly, for example via a fourth connection provided on the circuit. It can also be provided a control unit, which in case of concern

AC voltage at the first and second terminals during a half cycle of the AC voltage turns on the motor switch for a certain duty cycle, and after this duty cycle turns off the motor switch and turns on the freewheel switch. Thus, the current flowing through the linear compressor motor current can be freely designed, which offers various control engineering advantages.

Further, the control unit may comprise means for detecting the current flowing through the motor switch or by the linear compressor or the supply voltage, and be configured to turn off the motor switch and turn on the freewheel switch in the presence of an overcurrent or an overvoltage. Thus, effective protection against overvoltages or overcurrents can be realized.

Further embodiments will be explained with reference to the accompanying figures. Show it:

Fig. 1 is a block diagram of a circuit 100 according to the invention for driving a linear compressor; and

Fig. 2 is a graph showing the course of the mains voltage Uv and the current flowing through the linear motor of the linear compressor 160 motor current Im.

Unless otherwise indicated, like reference numerals in the figures denote like or functionally identical elements.

1 shows a block diagram of a circuit 100 according to the invention for driving a linear compressor. The circuit 100 comprises a bidirectional disconnectable AC switch unit 102 and a control unit 104. The disconnectable AC switch unit 102 includes a motor switch 110 and a freewheeling switch 120. Further, the turn-off AC switch unit 102 has a first terminal 130, a second terminal 131, a third terminal 132 and a fourth terminal 133.

The first and second terminals 130, 131 are connected to corresponding terminals of an AC power supply 150 via an EMC filter 140, respectively. The AC power supply 150 provides a supply voltage Uv. The Circuit 100 is connected via the third and the fourth connection 132, 133 to the linear motor of a linear compressor 160, wherein the fourth connection 133 is connected to a first supply connection 161 of the linear compressor 160 and the third connection 132 is connected to a second supply connection 162 of the linear compressor 160.

The motor switch 1 10 has a transistor 1 1 1, four diodes 1 12, 1 13, 1 14 and 1 15 and a shunt resistor 1 16, and is disposed between the second terminal 131 and the third terminal 132. The transistor 1 1 1 may be formed for example as IGBT or as a power MOSFET. In the illustrated example, the transistor 1 1 1 is an IGBT. The diodes 1 12, 1 13, 1 14, 1 15 and the transistor 1 1 1 are arranged in an H-bridge such that current can flow through the motor switch 1 10 in the closed state in both directions, but always in one direction through the Transistor 1 1 1 flows. For example, the anode of the diode 1 12 and the cathode of the diode 1 14 with the second terminal 131 and the anode of the diode 1 13 and the cathode of the diode 1 15 are connected to the third terminal 132. The collector of the transistor 1 1 1 is connected to the cathode of the diode 1 12 and the cathode of the diode 1 13 and the emitter of the transistor 1 1 1 is connected via the shunt resistor 1 16 to the anode of the diode 1 14 and the anode of Diode 1 15 connected. The base of the transistor 1 1 1 is connected via a control line 170 to the controller 104, so that the transistor 1 1 1 can be controlled by the control unit 104 via this control line 170.

The one-way switch 120 has a transistor 121, four diodes 122, 123, 124, and 125, and is disposed between the first terminal 130 and the third terminal 132. The transistor 121 may be formed, for example, as an IGBT or as a power MOSFET. In the illustrated example, the transistor 121 is an IGBT. The diodes 122, 123, 124, 125 and the transistor 121 are arranged in an H-bridge such that current can flow through the freewheeling switch 120 in both directions in the closed state, but always flows through the transistor 121 in the same direction. The arrangement of the diodes 122-125 and of the transistor 121 may correspond to that in the motor switch 110. The base of the transistor 121 is connected via a control line 171 to the control unit 104, so that the transistor 1 1 1 can be controlled by the control unit 104 via this control line 171. Due to the Potential differences between the transistors 1 1 1 and 121, the transistor 121 is driven potential-free.

The control unit 104 determines the supply voltage Uv via a sensor line 172, which is connected to the first terminal 130. Further, the control unit 104 is connected via a sensor line 173 to the node between the transistor 1 1 1 and the shunt resistor 1 16 and via a sensing line 174 to the node between the shunt resistor 1 16 and the anodes of the diodes 1 14 and 1 15 connected. Via these sensor lines 173 and 174, the control unit 104 determines the current flowing through the transistor 1 1 1 current. By means of a microcontroller, not shown, determines the control unit 104 from the signals of the sensor lines amplitude and zero crossing of the supply voltage Uv and amplitude and phase of the motor current Im.

Finally, the control unit 104 is connected via a sensor line 175 to a sensor provided on the linear compressor 160. This sensor detects the position of the piston in the linear compressor. The sensor signal generated by this sensor is used to control the linear motor of the linear compressor 160.

FIG. 2 shows a graph illustrating the profile of the mains voltage Uv and of the motor current Im flowing through the linear motor of the linear compressor 160.

At a predetermined time T1 during the positive half cycle of the mains voltage Uv, the control unit 104 switches the motor switch 1 10 on via the control line 170 and the freewheeling switch 120 off. A current Im begins to flow through the linear motor, which is an inductive load. During this switch-on phase 200, the current flows from the first terminal 130 via the fourth terminal 133 through the linear motor and from there via the third terminal 132 through the diode 1 13, the transistor 1 1 1, the shunt resistor 1 16, the diode 1 14 to the second terminal 131. At a given time T2, the control unit 104 switches off the motor switch 1 10 and the freewheeling switch 120 by corresponding control of the transistor 121 via the control line 171 a. Due to the inductive load of the linear motor, the motor current Im flows as a freewheeling current in this freewheeling phase 210, driven by the winding inductance of the motor coil. The motor current Im sounds off depending on of the current electromotive force and the time constant L / R, where L represents the inductance of the motor coil and R the winding resistance of the motor coil. This current Im flows from the third terminal via the diode 123, the transistor 121 and the diode 124 to the first terminal 130. At the zero crossing of the mains voltage, the current Im has decayed substantially to zero.

During the negative half cycle of the mains voltage Uv, the control unit 104 switches on again the motor switch 1 10 and the freewheeling switch 120 at the time T3. The current flow during this switch-on phase 220 corresponds to the opposite current path during the switch-on phase, but the current now flows through the diodes 12 and 15. At time T4, the control unit turns off the engine switch 1 10 and the freewheel switch 120 again.

As shown in Fig. 1, the mains voltage Uv is provided via the EMC filter 140, which may be formed for example as an LC filter. The EMC filter 140 smoothes the steep current edge arising in each case when switching off the motor switch 1 10 in the line current profile and thus helps to meet the EMC requirements.

With the circuit 100 shown above, a cost-effective control of the linear compressor 160 can be realized. In particular, this circuit 100 has only two IBGTs and is thus less expensive than circuits in which four relatively expensive IGBTs are provided for driving the linear motor in an H full bridge.

Furthermore, it is possible with the circuit 100 to realize protection against overvoltage or overcurrent, which was not possible with conventional triac circuits. For this purpose, the control unit 104 has the functionality to detect the mains voltage via the sensor line 107 and the motor current through the shunt resistor 1 16 via the sensor lines 173 and 174, and to compare with a predetermined reference voltage or a reference current. If the mains voltage Uv or the motor current Im rises above a predetermined value, then the control unit 104 switches directly from the switch-on phase into the freewheeling phase, thus switching off the motor switch 110 and the freewheeling switch 120. Furthermore, it is possible with the circuit 100 to switch from the switch-on phase to the freewheeling phase during a running grid half-cycle, which was likewise impossible with the conventional triac circuit. Through the free switching of motor switch 1 10 and freewheel switch 120 even during a power half-wave, it is possible to set any current surfaces or current waveforms, which provides control engineering advantages for the operation of the linear motor. For example, it is possible to set the motor current profile more symmetrical with respect to the mains voltage and to achieve a reduction of the network feedback.

By regulating or controlling the switch-on and switch-off T1 to T4, taking into account the freewheeling current and the timing of these switching times, the energy supply to the linear compressor 160 can be changed. The switch-on time windows can be adapted to the different operating ranges of the linear compressor 160, in particular the compression phase and the expansion phase.

LIST OF REFERENCE NUMBERS

100 circuit for driving a linear compressor

102 AC switch

104 control unit

110 motor switch

111 transistor

112, 113, 114, 115 diode

116 shunt resistor

120 free-wheeling switch

121 transistor

122, 123, 124, 125 diode

130, 131, 132, 133 connections

140 EMC filter

150 AC power supply

160 linear motor

161, 162 supply connections

170, 171 control lines

172, 173, 174 sensor cables

175 sensor cable

200 switch-on phase

210 freewheeling phase

220 switch-on phase

Claims

Circuit for controlling a linear compressor, characterized by:

a first input terminal (130) and a second input terminal (131) for providing an electrical supply voltage (Uv) for the

Linear compressor;

an output port (132) to which the linear compressor is connectable; a motor switch (1 10) for electrically connecting the second

Input terminal (131) to the output terminal (132); and

a free-wheeling switch (120) electrically connected to the first input terminal (130) and the output terminal (132) and arranged to electrically connect the input terminal (130) and the output terminal (132) upon opening of the motor switch (110).

A circuit according to claim 1, characterized in that the motor switch (1 10) and the freewheeling switch (120) are controllable such that always only either the motor switch (1 10) or the freewheeling switch (120) is closed.

Circuit according to claim 1 or 2, characterized in that a

Control unit (104) is provided, which is designed to turn on the application of an AC voltage at the first and the second input terminal (130, 131) during a half cycle of the AC voltage, the motor switch (1 10) for a certain duty cycle, and after this duty cycle the motor switch (1 10) and turn the freewheel switch (120).

Circuit according to one of the preceding claims, characterized in that the motor switch (1 10) and the freewheeling switch (1 10) each have exactly one transistor (1 1 1, 121).

A circuit according to claim 4, characterized in that the transistors (1 1 1, 121) as IGBTs or power MOSFETs are formed.

6. A circuit according to claim 4 or 5, characterized in that the

Motor switch (1 10) and the freewheeling switch (120) each further comprise four diodes (1 12, 1 13, 1 14, 1 15; 122, 123, 124, 125) which are arranged in a bridge circuit such that current always only flowing in one direction through the transistor.

Circuit according to one of Claims 3 to 6, characterized in that the control unit (104) has means for detecting the current (Im) flowing through the motor switch (110) or through the linear compressor (160) or at the first and second input terminals (130) , 131) has applied voltage (Uv), and is designed to switch off in the presence of an overcurrent or an overvoltage the motor switch (1 10) and turn on the freewheeling switch (120).

Linear compressor with a drive circuit according to one of claims 1 to 7.

Method for controlling a linear compressor with a circuit according to one of claims 1 to 8, characterized by

Providing an electrical supply voltage (Uv) to the linear compressor via the first input port (130) and the second input port (131);

Close the motor switch (1 10) to connect the second one electrically

Input terminal (131) to the output terminal (132); and

Opening the motor switch (1 10) to electrically disconnect the second

Input terminal (131) from the output terminal (132);

wherein the first input terminal (130) is electrically connected to the output terminal (132) when the motor switch (110) is opened by the one-way switch (120).

A method according to claim 9, characterized in that the

Supply voltage (Uv) is an AC voltage, wherein during a half cycle of the AC voltage of the motor switch (1 10) is turned on for a certain duty cycle, and after this duty cycle of the

Motor switch (1 10) is switched off and the freewheeling switch (120) is switched on. Method according to one of claims 9 or 10, characterized in that by the motor switch (1 10) flowing current or the supply voltage (Uv) is detected, and in the presence of an overcurrent or an overvoltage of the motor switch (1 10) and the free-wheeling switch ( 120) is turned on.