DE102010028506A1 - Circuit and method for controlling a linear compressor - Google Patents

Abstract

A circuit for controlling a linear compressor comprises a first input connection (130) and a second input connection (131) for providing an electrical supply voltage (Uv) for the linear compressor, 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 freewheeling switch (120), which is electrically connected and provided to the first input connection (130) and the output connection (132) of the control circuit, the input connection (130) and to electrically connect the output terminal (132) when the motor switch (110) is opened.

Description

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. During a compression stroke of the piston, the gas introduced into the piston chamber is compressed and expelled 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, z. B. on one of a rotary motor driven connecting rod, 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. The U.S. 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. A disadvantage of this arrangement is that it requires a linear compressor, mechanically for operation on the mains voltage with z. B. 50 Hz is designed and therefore only in all operating conditions can be operated rigidly 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.

The U.S. 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 briefly braking the linear drive electrically.

The EP 1 017 156 discloses drive circuitry for a load having a rectifier bridge and two loop-back paths arranged parallel to the load and turned on at positive and negative half-cycles respectively 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 used in a refrigerator for compressing the refrigerant. A refrigeration appliance is understood in particular to be a household refrigerating appliance, that is to say a refrigeration appliance which is used for household management or possibly even in the gastronomy sector, and in particular serves to store food and / or beverages in household quantities at specific temperatures, such as, for example, 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 free-wheeling switch electrically connected to the first input terminal and the output terminal of the driving circuit and provided to electrically connect the input terminal and the output terminal upon opening of 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;
Closing the motor switch for electrically connecting the second 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 is electrically connected to the output terminal when the motor switch is opened by the one-way switch.

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 turns on the application of an AC voltage at the first and the second terminal during a half cycle of the AC voltage, the motor switch for a certain duty cycle, and turns off the motor switch after this duty cycle and turns on the freewheeling 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:

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

2 a graph showing the course of the mains voltage Uv and by the linear motor of the linear compressor 160 flowing motor current Im represents.

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

1 shows a block diagram of a circuit according to the invention 100 for driving a linear compressor. The circuit 100 includes 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 free-wheeling switch 120 , Furthermore, the disconnectable AC switch unit 102 a first connection 130 , a second connection 131 , a third connection 132 and a fourth connection 133 on.

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

The engine switch 110 has a transistor 111 , four diodes 112 . 113 . 114 and 115 as well as a shunt resistor 116 on, and is between the second port 131 and the third port 132 arranged. The transistor 111 For example, it can be designed as an IGBT or as a power MOSFET. In the example shown, the transistor 111 an IGBT. The diodes 112 . 113 . 114 . 115 and the transistor 111 are arranged in an H-bridge such that power the motor switch 110 can flow in both directions when closed, but always in one direction through the transistor 111 flows. For example, the anode of the diode 112 and the cathode of the diode 114 with the second connection 131 and the anode of the diode 113 and the cathode of the diode 115 with the third connection 132 connected. The collector of the transistor 111 is with the cathode of the diode 112 and the Cathode of the diode 113 connected and the emitter of the transistor 111 is about the shunt resistor 116 with the anode of the diode 114 and the anode of the diode 115 connected. The base of the transistor 111 is via a control line 170 with the control unit 104 connected so that the transistor 111 via this control line 170 from the controller 104 can be controlled.

The freewheel switch 120 has a transistor 121 , four diodes 122 . 123 . 124 and 125 on, and is between the first port 130 and the third port 132 arranged. The transistor 121 For example, it can be designed as an IGBT or as a power MOSFET. In the example shown, the transistor 121 an IGBT. The diodes 122 . 123 . 124 . 125 and the transistor 121 are arranged in an H-bridge such that current is the freewheeling switch 120 in the closed state can flow in both directions, but always in the same direction through the transistor 121 flows. The arrangement of the diodes 122 - 125 and the transistor 121 can be the one in the engine switch 110 correspond. The base of the transistor 121 is via a control line 171 with the control unit 104 connected so that the transistor 111 via this control line 171 from the controller 104 can be controlled. Due to the potential differences between the transistors 111 and 121 becomes the transistor 121 controlled potential-free.

The control unit 104 determined via a sensor cable 172 that with the first connection 130 is connected, the supply voltage Uv. Further, the control unit 104 via a sensor line 173 with the node between the transistor 111 and the shunt resistor 116 connected and via a sensor line 174 with the node between the shunt resistor 116 and the anodes of the diodes 114 and 115 connected. About these sensor lines 173 and 174 determines the control unit 104 through the transistor 111 flowing electricity. By means of a microcontroller not shown determines the control unit 104 From the signals of the sensor lines amplitude curve and zero crossing of the supply voltage Uv and amplitude and phase angle of the motor current Im.

Finally, the control unit 104 via a sensor cable 175 with one on the linear compressor 160 provided sensor connected. 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 used.

2 shows a graph showing the course of the mains voltage Uv and by the linear motor of the linear compressor 160 flowing motor current Im represents.

At a predetermined time T1 during the positive half cycle of the mains voltage Uv, the control unit switches 104 over the control line 170 the engine switch 110 on and the freewheel switch 120 out. 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 connection 130 over the fourth connection 133 through the linear motor and from there via the third connection 132 through the diode 113 , the transistor 111 , the shunt resistance 116 , the diode 114 to the second connection 131 , At a given time T2, the control unit switches 104 the engine switch 110 off and the freewheeling switch 120 by appropriate control of the transistor 121 over the control line 171 one. Due to the inductive load of the linear motor, the motor current Im flows as a freewheeling current in this freewheeling phase 210 further, driven by the winding inductance of the motor coil. The motor current Im sounds off depending on 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 through the diode 123 , the transistor 121 and the diode 124 to the first connection 130 , At the zero crossing of the mains voltage, the current Im has decayed substantially to zero.

During the negative half-wave of the mains voltage Uv the control unit switches 104 at time T3 turn the motor switch 110 on and the freewheel switch 120 out. The current flow during this switch-on phase 220 corresponds to the opposite current path during the switch-on, but the current is now through the diodes 112 and 115 flows. At time T4, the control unit switches the motor switch 110 off and the freewheeling switch 120 again.

As in 1 shown, the mains voltage Uv via the EMC filter 140 provided, which may be formed for example as an LC filter. The EMC filter 140 smoothes each time when switching off. of the engine switch 110 emerging steep. Current edge in the line current profile and thus helps to meet the EMC requirements.

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

Furthermore, it is with the circuit 100 possible to realize protection against overvoltage or overcurrent, which was not possible with conventional triac circuits. For this purpose has the control unit 104 about the functionality, the mains voltage via the sensor line 107 and the motor current through the shunt resistor 116 over the sensor lines 173 and 174 to be detected, 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 switches 104 immediately from the switch-on in the freewheeling phase, so switches the motor switch 110 off and the freewheeling switch 120 one.

Further, it is with the circuit 100 possible to switch from the switch-on in the freewheeling phase during a running mains half-wave, which was also not possible with the conventional triac circuit. By the free switching of motor switch 110 and free-wheeling switch 120 Even during a mains half-wave, it is possible to set any current areas or current profiles, which offers control technical 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 change. The switch-on time windows can be adapted to the different operating ranges of the linear compressor 160 , in particular compression phase and expansion phase, to be adjusted.

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

Freewheel switch

121

transistor

122, 123, 124, 125

diode

130, 131, 132, 133

connections

140

EMC filters

150

AC power supply

160

linear motor

161, 162

supply connections

170, 171

control lines

172, 173, 174

sensor leads

175

sensor line

200

Switch

210

Freewheeling phase

220

Switch

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5947693 [0003, 0004]
• EP 1017156 [0005]

Claims (11)

Circuit for driving 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 connector ( 132 ), with which the linear compressor is connectable; a motor switch ( 110 ) for electrically connecting the second input terminal ( 131 ) with the output terminal ( 132 ); and a free-wheeling switch ( 120 ), which is connected to the first input terminal ( 130 ) and the output terminal ( 132 ) is electrically connected and provided, the input terminal ( 130 ) and the output terminal ( 132 ) when opening the engine switch ( 110 ) electrically connect. Circuit according to Claim 1, characterized in that the motor switch ( 110 ) and the freewheeling switch ( 120 ) are controlled so that only ever the engine switch ( 110 ) or the freewheeling switch ( 120 ) closed is. Circuit according to Claim 1 or 2, characterized in that a control unit ( 104 ) is provided, which is formed, upon 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 ( 110 ) for a certain switch-on duration, and after this switch-on duration the motor switch ( 110 ) and turn off the freewheeling switch ( 120 ). Circuit according to one of the preceding claims, characterized in that the motor switch ( 110 ) and the freewheeling switch ( 110 ) each exactly one transistor ( 111 . 121 ) exhibit. Circuit according to Claim 4, characterized in that the transistors ( 111 . 121 ) are formed as IGBTs or power MOSFETs. Circuit according to Claim 4 or 5, characterized in that the motor switch ( 110 ) and the freewheeling switch ( 120 ) each further four diodes ( 112 . 113 . 114 . 115 ; 122 . 123 . 124 . 125 ), which are arranged in a bridge circuit such that current always flows in one direction only through the transistor. Circuit according to one of Claims 3 to 6, characterized in that the control unit ( 104 ) Means for detecting by the engine switch ( 110 ) or by the linear compressor ( 160 ) flowing current (Im) or at the first and second input terminal ( 130 . 131 ) and is designed, in the presence of an overcurrent or an overvoltage, the motor switch ( 110 ) and turn off 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) for the linear compressor via the first input terminal (16). 130 ) and the second input terminal ( 131 ); Close the engine switch ( 110 ) for electrically connecting the second input terminal ( 131 ) with the output terminal ( 132 ); and opening the engine switch ( 110 ) for electrically disconnecting the second input terminal ( 131 ) from the output terminal ( 132 ); wherein the first input terminal ( 130 ) when opening the engine switch ( 110 ) by the freewheeling switch ( 120 ) electrically connected to the output terminal ( 132 ) is connected. 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 ( 110 ) is switched on for a certain switch-on duration, and after this switch-on duration the motor switch ( 110 ) and the free-wheeling switch ( 120 ) is turned on. Method according to one of claims 9 or 10, characterized in that by the motor switch ( 110 ) or the supply voltage (Uv) is detected, and in the presence of an overcurrent or an overvoltage of the motor switch ( 110 ) and the freewheeling switch ( 120 ) is turned on.

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