Power conversion device, motor drive device, and refrigeration cycle application apparatus

Abstract

This power conversion device (100) comprises: a rectification unit (3) that converts a first AC voltage supplied from an AC power supply (1) into a first DC voltage; a boosting unit (10) that boosts the first DC voltage to a second DC voltage; a smoothing unit (9) that smooths the second DC voltage to a third DC voltage; an inverter unit (4) that converts the third DC voltage into a second AC voltage and outputs the second AC voltage; a detection unit (2) that detects a common mode current between the AC power supply (1) and the inverter unit (4) and outputs the detection result; a compensation unit (5) that has two switching elements, uses the detection result to generate a compensation current for compensating the common mode current, and injects the compensation current into a ground line; and a control unit (12) that can increase or decrease the compensation current by controlling the operation of at least one among the boosting unit (10) and the inverter unit (4).

Description

Power conversion devices, motor drive devices, and refrigeration cycle application equipment

[0001] The present disclosure relates to a power conversion device that performs power conversion, a motor drive device, and a refrigeration cycle application device.

[0002] Conventionally, power conversion devices used in air conditioners and the like compress a refrigerant using a compressor equipped with a motor as a load. However, common-mode currents can occur due to parasitic capacitance between the compressor and a ground wire. To address this problem, a method is available for reducing the common-mode current by injecting a compensation current that is opposite in phase to the common-mode current into the ground wire. For example, Patent Document 1 discloses a technology in which a power conversion circuit outputs a compensation current at a point other than near the zero crossing of the AC voltage supplied from an AC power source, thereby reducing the common-mode current and reducing losses due to the flow of the compensation current.

[0003] Patent No. 5201276

[0004] The power conversion circuit described in Patent Document 1 controls the operation of a boost chopper circuit and an inverter to supply AC power to a motor, which is a load. However, it is conceivable that the common-mode current may also change depending on the operating states of the boost chopper circuit and the inverter. However, the power conversion circuit described in Patent Document 1 generates a compensation current using a DC voltage before being boosted by the boost chopper circuit. Therefore, the power conversion circuit described in Patent Document 1 has a problem in that it may not be possible to make the compensation current follow changes in the common-mode current due to the operating states of the boost chopper circuit and the inverter.

[0005] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can improve the ability of a compensation current to follow a common-mode current.

[0006] In order to solve the above-mentioned problems and achieve the object, the power conversion device according to the present disclosure includes a rectifier unit that converts a first AC voltage supplied from an AC power supply into a first DC voltage, a boost unit that boosts the first DC voltage to a second DC voltage, a smoothing unit that smoothes the second DC voltage into a third DC voltage, an inverter unit that converts the third DC voltage into a second AC voltage and outputs the second AC voltage, a detection unit that detects a common mode current between the AC power supply and the inverter unit and outputs the detection result, a compensation unit that has two switching elements and uses the detection result to generate a compensation current that compensates for the common mode current and injects it into a ground line, and a control unit that controls the operation of at least one of the boost unit and the inverter unit to increase or decrease the compensation current.

[0007] The power conversion device according to the present disclosure has an advantage that it is possible to improve the tracking of the compensation current with respect to the common mode current.

[0008] FIG. 1 is a diagram showing an example of the configuration of a power conversion device according to embodiment 1. FIG. 2 is a diagram showing an example of the configuration of a detection unit provided in a power conversion device according to embodiment 1. FIG. 3 is a diagram showing an example of the configuration of a compensation unit provided in a power conversion device according to embodiment 1. FIG. 4 is a diagram showing the relationship between the DC voltage and common mode current generated in a power conversion device according to embodiment 1. FIG. 5 is a diagram showing an example of the relationship between the number of turns of the common mode choke coil and auxiliary winding in the detection unit of a power conversion device according to embodiment 1. FIG. 6 is a diagram showing an example of the characteristics of the gate voltage and drain current of the first switching element and the second switching element provided in a power conversion device according to embodiment 1. FIG. 7 is a diagram showing an example in which a power conversion device according to embodiment 1 is provided with a transmission control unit. FIG. 8 is a diagram showing an example of the operation of a power conversion device according to embodiment 1. FIG. 9 is a diagram showing an example of the configuration of a refrigeration cycle application device according to embodiment 2.

[0009] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle applied device according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] First Embodiment. FIG. 1 is a diagram illustrating a configuration example of a power conversion device 100 according to a first embodiment. The power conversion device 100 is connected to an AC power source 1 and a motor 6, which is a load. The power conversion device 100 converts a first AC voltage supplied from the AC power source 1 into a second AC voltage having a desired amplitude and phase, and supplies the second AC voltage to the motor 6. The AC power source 1 is, for example, a single-phase AC power source. The motor 6 is, for example, a three-phase motor. As shown in FIG. 1 , a stray capacitance 7 is interposed between the motor 6 and ground, i.e., a grounding wire. As shown in FIG. 1 , the power conversion device 100 includes a detection unit 2, a rectification unit 3, an inverter unit 4, a compensation unit 5, a terminal unit 8, a smoothing unit 9, a boost unit 10, and a control unit 12. The power conversion device 100 and the motor 6 constitute a motor drive device 200.

[0011] The detection unit 2 detects common mode currents such as leakage currents between the AC power supply 1 and the inverter unit 4, and outputs the detection result to the terminal unit 8. The detection unit 2 is configured with a common mode choke coil with an auxiliary winding added, or the like.

[0012] The rectifier 3 converts the first AC voltage supplied from the AC power supply 1 into a first DC voltage. The rectifier 3 is configured with a bridge rectifier or the like. The detector 2 and the rectifier 3 are provided in a subsequent stage of the AC power supply 1 and in a previous stage of the inverter 4.

[0013] The booster 10 boosts the first DC voltage converted by the rectifier 3 to a second DC voltage. The booster 10 is composed of a reactor, a semiconductor switch, a backflow prevention diode, etc. The booster 10 is provided in a subsequent stage of the rectifier 3.

[0014] The smoothing unit 9 smoothes the second DC voltage boosted by the boosting unit 10 into a third DC voltage. The smoothing unit 9 is configured with an electrolytic capacitor and the like. The smoothing unit 9 is provided at a subsequent stage of the boosting unit 10.

[0015] The inverter unit 4 converts the third DC voltage smoothed by the smoothing unit 9 into a second AC voltage and outputs the second AC voltage to the motor 6. The inverter unit 4 is composed of six switching elements, etc. The switching elements are, for example, IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). The inverter unit 4 is provided after the smoothing unit 9.

[0016] The compensating unit 5 has two switching elements and generates a compensating current for compensating for the common mode current using the detection result output from the detecting unit 2 and adjusted for range by the terminal unit 8, and injects the generated current into the ground line. The compensating current for compensating for the common mode current is a current of opposite phase to the common mode current. The compensating unit 5 is composed of two compensation switching elements, a driver for driving each switching element, and an injector for injecting the compensating current into the ground line. The compensating unit 5 is characterized by being connected to the detecting unit 2 via the terminal unit 8 with four wires, connected to the DC line between the rectifying unit 3 and the inverter unit 4 with two wires, and grounded with one wire. In the example of FIG. 1 , the compensating unit 5 is supplied with a third DC voltage from the power supply line between the smoothing unit 9 and the inverter unit 4. Therefore, the compensating unit 5 increases or decreases the compensation current depending on the third DC voltage. Although not shown in the figure, it is assumed that the ground wire connecting the AC power supply 1 to the ground, the ground wire connecting the compensation unit 5 to the ground, and the ground wire connecting the motor 6 to the ground via the stray capacitance 7 are all connected.

[0017] The terminal unit 8 adjusts the range of at least one of the voltage and current of the detection results output from the detection unit 2. The terminal unit 8 is configured with a resistor or the like. FIG. 1 shows an example in which the terminal unit 8 is configured with termination resistors 8a and 8b. In the power conversion device 100, the compensation unit 5 acquires the two systems of detection results output from the detection unit 2 via the terminal unit 8 to generate a compensation current and inject it into the ground line. The terminal unit 8 may be mounted on the same board as the rectification unit 3, the inverter unit 4, etc., or may be mounted on a board different from the board on which the rectification unit 3, the inverter unit 4, etc., are mounted.

[0018] The control unit 12 controls the operation of the boost unit 10 and the inverter unit 4. The control unit 12 acquires the detection result from the detection unit 2 and acquires the voltage value of the third DC voltage from the smoothing unit 9. The control unit 12 controls the operation of at least one of the boost unit 10 and the inverter unit 4 using at least one of the detection result and the voltage value of the third DC voltage. The control unit 12 can increase or decrease the compensation current by controlling the operation of at least one of the boost unit 10 and the inverter unit 4. As described above, the compensation unit 5 increases or decreases the compensation current depending on the third DC voltage. Therefore, the control unit 12 can increase or decrease the compensation current generated by the compensation unit 5 by controlling the step-up ratio of the boost unit 10 to increase or decrease the third DC voltage. The control unit 12 can also increase or decrease the compensation current generated by the compensation unit 5 depending on the operating state of at least one of the boost unit 10 and the inverter unit 4.

[0019] 2 is a diagram showing an example of the configuration of the detector 2 included in the power conversion device 100 according to the first embodiment. The detector 2 is configured by adding two systems of auxiliary windings 22 and 23 to a common mode choke coil 21. The two systems of auxiliary windings 22 and 23 have opposite winding directions. The winding direction of the auxiliary winding 22 is the same as the winding direction of the main winding of the common mode choke coil 21. Therefore, a voltage is generated across both ends of the auxiliary winding 22 in the same direction as the common mode current flowing through the common mode choke coil 21. The winding direction of the auxiliary winding 23 is opposite to the winding direction of the main winding of the common mode choke coil 21. Therefore, a voltage is generated across both ends of the auxiliary winding 23 in the opposite direction to the common mode current flowing through the common mode choke coil 21. In this way, the detection unit 2 has a configuration in which two systems of auxiliary windings are added to the main winding of the common mode choke coil 21, the winding direction of the auxiliary winding of the first system is the same as the winding direction of the main winding of the common mode choke coil 21, and the winding direction of the auxiliary winding of the second system is opposite to the winding direction of the main winding of the common mode choke coil 21, and outputs detection results of two systems. Because of the configuration described above, the power conversion device 100 has a high degree of freedom in design, and therefore the magnitude of the compensation current according to the polarity of the compensation current can be changed by changing the number of turns of the auxiliary windings 22, 23 of the two systems as necessary.

[0020] FIG. 3 illustrates an exemplary configuration of the compensation unit 5 included in the power conversion device 100 according to the first embodiment. The compensation unit 5 includes an injection unit 51, a first switching element 52a, a second switching element 52b, a first drive unit 53a, and a second drive unit 53b. The injection unit 51 includes a circuit in which a resistor and a capacitor are connected in series. That is, the injection unit 51 includes a resistive component and a capacitive component and injects a compensation current into the ground line. The first drive unit 53a includes a first gate resistor 55a. The first drive unit 53a applies a gate voltage to the gate terminal of the first switching element 52a in accordance with the detection result after range adjustment acquired from the terminal unit 8. The second drive unit 53b includes a second gate resistor 55b. The second drive unit 53b applies a gate voltage to the gate terminal of the second switching element 52b in accordance with the detection result after range adjustment acquired from the terminal unit 8.

[0021] The first switching element 52a and the second switching element 52b are configured with a MOSFET or the like. The first switching element 52a and the second switching element 52b are connected in series. The negative side, i.e., the source side, of the first switching element 52a is connected to the positive side, i.e., the drain side, of the second switching element 52b. Point N on the connection line between the first switching element 52a and the second switching element 52b is connected to one end of the injection unit 51. Terminal E on the positive side of the first switching element 52a is connected to point G on the positive side of the DC line. Terminal F on the negative side of the second switching element 52b is connected to point H on the negative side of the DC line. One end of the injection unit 51 is connected to point N as described above, and the other end of the injection unit 51 is connected to the ground line at terminal I and is grounded. The compensation unit 5 injects a compensation current into the ground line via one of the two switching elements and the injection unit 51.

[0022] 1 and 3, the terminal unit 8 is composed of termination resistors 8a and 8b. One end of the termination resistor 8a is connected to terminal A of the compensation unit 5, and the other end is connected to terminal B of the compensation unit 5. Terminals A and B of the compensation unit 5 are also connected to the detection unit 2. Furthermore, one end of the termination resistor 8b is connected to terminal C of the compensation unit 5, and the other end is connected to terminal D of the compensation unit 5. Terminals C and D of the compensation unit 5 are also connected to the detection unit 2. The compensation unit 5 generates a compensation current in accordance with the detection results of the two systems whose ranges have been adjusted by the terminal unit 8.

[0023] Next, the operation of the power conversion device 100 will be described. In the power conversion device 100, the rectifier 3 converts a first AC voltage supplied from the AC power source 1 into a first DC voltage. The detector 2 detects a common mode current, such as a leakage current, flowing through the power conversion device 100. The booster 10 boosts the first DC voltage to a second DC voltage. The smoother 9 smooths the second DC voltage into a third DC voltage. The inverter 4 converts the third DC voltage into a second AC voltage. The compensator 5 injects a compensation current into the ground line in accordance with the common mode current detected by the detector 2, i.e., the detection result of the detector 2. The compensator 5 injects the compensation current into the ground line from the injector 51 by turning on and off the first switching element 52a or the second switching element 52b depending on the voltage generated across the auxiliary winding 22 or the auxiliary winding 23 of the detector 2 due to the common mode current.

[0024] When a common-mode current flows in the forward direction shown in FIG. 2 through the common-mode choke coil 21, a voltage is generated in the forward direction across the auxiliary winding 22, and a voltage is applied between terminals A and B of the compensation unit 5. That is, a voltage is generated across the terminating resistor 8a of the terminal unit 8. When the detection result of the detection unit 2, i.e., the generated voltage, is equal to or greater than the threshold voltage of the first switching element 52a, a gate current flows into the gate terminal of the first switching element 52a via the first gate resistor 55a, charging the gate terminal with voltage, causing the first switching element 52a to turn on. When no common-mode current flows, no voltage is generated across the auxiliary winding 22 of the detection unit 2, and the voltage is discharged from the gate terminal of the first switching element 52a, causing it to turn off. In this way, the first switching element 52a can be turned on and off.

[0025] Similarly, when a common-mode current flows in the negative direction shown in FIG. 2 in the common-mode choke coil 21, a voltage is generated in the negative direction across the auxiliary winding 23, and a voltage is applied between terminals C and D of the compensation unit 5. That is, a voltage is generated across the terminating resistor 8b of the terminal unit 8. When the detection result of the detection unit 2, i.e., the generated voltage, is equal to or greater than the threshold voltage of the second switching element 52b, a gate current flows into the gate terminal of the second switching element 52b via the second gate resistor 55b, charging the gate terminal and turning on the second switching element 52b. When no common-mode current flows, no voltage is generated across the auxiliary winding 23 of the detection unit 2, and the voltage is discharged from the gate terminal of the second switching element 52b, turning it off. In this way, the second switching element 52b can be turned on and off.

[0026] In the power conversion device 100, the compensator 5 can cause a compensation current to flow through the injector 51 by the first switching element 52a and the second switching element 52b performing the on / off operation described above.

[0027] FIG. 4 is a diagram illustrating the relationship between the DC voltage and the common-mode current generated in the power conversion apparatus 100 according to the first embodiment. In FIG. 4, the horizontal axis represents the DC voltage, and the vertical axis represents the common-mode current. The graph in FIG. 4 illustrates the state of the DC line between the smoothing unit 9 and the inverter unit 4 of the power conversion apparatus 100 illustrated in FIG. 1. Specifically, the DC voltage is the third DC voltage. In the power conversion apparatus 100, the control unit 12 operates the boost unit 10 to vary the DC voltage and set it to a desired value. That is, the power conversion apparatus 100 can vary the common-mode current by changing the value of the DC voltage through the operation of the boost unit 10 under the control of the control unit 12. As an example, consider a common-mode current A1 when the DC voltage is V1 as a reference. When the boost unit 10 operates under the control of the control unit 12 to boost the DC voltage to V2, which is greater than V1, the common-mode current becomes A2, which is greater than A1, and increases from A1. Similarly, when the boost unit 10 performs a boost operation to increase the DC voltage to V3, which is greater than V2, under the control of the control unit 12, the common mode current becomes A3, which is greater than A2, and increases from A2. That is, in the power conversion device 100, the common mode current also increases as the DC voltage increases.

[0028] FIG. 5 is a diagram showing an example of the relationship between the number of turns of the common mode choke coil 21 and the auxiliary windings 22, 23 in the detector 2 of the power conversion device 100 according to the first embodiment. For ease of explanation, FIG. 5 shows the winding 21a of one line of the common mode choke coil 21 and the auxiliary windings 22, 23. The number of turns of the winding 21a of one line of the common mode choke coil 21 is denoted as N1, and the number of turns of the auxiliary windings 22, 23 is denoted as N2. If a common mode current I1 flows through the winding 21a of one line of the common mode choke coil 21 in the direction indicated by the arrow I1 in FIG. 5, a current I2 flows through the auxiliary winding 22 in the direction indicated by the arrow I2. Ideally, the current I2 can be expressed by equation (1).

[0029] I2=I1×(N1 / N2)…(1)

[0030] As shown in equation (1), current I2 is proportional to common-mode current I1, so when common-mode current I1 increases, current I2 also increases. From the above, in the power conversion device 100, as the DC voltage increases, the current flowing through the auxiliary winding of the detection unit 2 also increases. Furthermore, as the common-mode current I1 increases, the magnetomotive force generated in the auxiliary winding 22 also increases, and therefore the voltage V21 generated across both ends of the winding 21a on one side of the common mode choke coil 21 also increases. If the voltage generated across both ends of the winding 21a on one side of the common mode choke coil 21 when current flows in the direction I1 shown in FIG. 5 is V21, and the voltage generated across both ends of the auxiliary winding 22 is V22, the relationship between voltage V21 and voltage V22 can be expressed by equation (2).

[0031] V22=V21×(N2 / N1)…(2)

[0032] As shown in equation (2), voltage V22 is proportional to voltage V21, so when voltage V21 increases, voltage V22 also increases. From the above, in this embodiment, control unit 12 can manipulate the amount of common-mode current by controlling the DC voltage to a desired value, thereby controlling the voltage generated across auxiliary winding 22. The above description has been given assuming that common-mode current I1 flows in the direction of the arrow shown in FIG. 5 , but the same applies to the case where common-mode current I1 flows in the opposite direction to the arrow I1 shown in FIG. 5 . In this case, current flows through auxiliary winding 23, and therefore control unit 12 can control the voltage generated across auxiliary winding 23. The following description will be continued assuming that common-mode current I1 flows in the direction of the arrow shown in FIG. 5 .

[0033] FIG. 6 is a diagram illustrating an example of the gate voltage and drain current characteristics of the first switching element 52a and the second switching element 52b included in the power conversion device 100 according to the first embodiment. In FIG. 6, the horizontal axis represents the gate voltage, and the vertical axis represents the drain current. The first switching element 52a and the second switching element 52b are assumed to be MOSFETs or the like. In the first switching element 52a and the second switching element 52b, a channel is not formed in a region where the gate voltage is low and smaller than the threshold voltage Vth, and therefore no drain current flows. In the first switching element 52a and the second switching element 52b, when the gate voltage exceeds the threshold voltage Vth, a channel is formed under the gate electrode, and a drain current flows.

[0034] As an example, consider the drain current Id1 when the gate voltage is Vg1 as a reference. As shown in FIG. 6 , when the gate voltage becomes Vg2, which is greater than Vg1, the electron density gathering in the channels of the first switching element 52a and the second switching element 52b increases, reducing the electrical resistance of the channels (i.e., the on-resistance). As a result, the drain current increases to Id2, which is greater than Id1. Therefore, by controlling the DC voltage to a desired value, the power conversion device 100 can keep the first switching element 52a off and prevent the drain current, i.e., the compensation current, when the amount of common-mode current is small, by reducing the voltage generated across the auxiliary winding 22 to less than Vth. Furthermore, by controlling the DC voltage to a desired value, the power conversion device 100 can increase or decrease the amount of common-mode current and thereby vary the voltage generated across the auxiliary winding 22. This allows the gate voltage of the first switching element 52a to be varied, thereby increasing or decreasing the drain current, i.e., the compensation current. Although the first switching element 52a has been specifically described here, the power conversion device 100 can also manipulate the drain current, ie, the compensation current, of the second switching element 52b in the same manner.

[0035] The power conversion apparatus 100 shown in FIG. 1 is characterized by its ability to change the compensation current according to the DC voltage. However, it may be configured not to perform compensation because, for example, common-mode current is not significant up to a certain boost level. Since compensation is not performed, the power conversion apparatus 100 can reduce power consumption by not performing compensation in this range. FIG. 7 is a diagram illustrating an example of the power conversion apparatus 100 according to the first embodiment, which includes a transmission control unit 11. The power conversion apparatus 100 shown in FIG. 7 illustrates an example in which the transmission control unit 11 is added to the power conversion apparatus 100 shown in FIG. 1. The transmission control unit 11 controls the transmission of the detection result between the detection unit 2 and the compensation unit 5 under the control of the control unit 12. The transmission control unit 11 is composed of switching units 11a and 11b. The switching units 11a and 11b are, for example, switches that are turned on and off by the control unit 12. The control unit 12 controls the operation of the transmission control unit 11 according to at least one of the detection result from the detection unit 2 and the voltage value of the third DC voltage from the smoothing unit 9. The control unit 12, for example, compares the voltage value of the third DC voltage acquired from the smoothing unit 9 with a specified threshold value, and controls the on / off of the switching units 11a and 11b of the transmission control unit 11 based on the magnitude relationship between the voltage value of the third DC voltage and the threshold value. The control unit 12 can stop the on / off operation of the first switching element 52a by turning off the switching unit 11a. The control unit 12 can also enable the on / off operation of the first switching element 52a by turning on the switching unit 11a. The control unit 12 controls the switching unit 11b in a similar manner.

[0036] FIG. 8 is a first diagram illustrating an example of the operation of the power conversion apparatus 100 according to the first embodiment. FIG. 8(a) shows the magnitude of the DC voltage, and FIG. 8(b) shows the on / off state of the transmission control unit 11. Note that in both FIG. 8(a) and FIG. 8(b), the horizontal axis represents time. The DC voltage is a third DC voltage that the control unit 12 can acquire from the smoothing unit 9. In the power conversion apparatus 100, the control unit 12 starts a boost operation by the boost unit 10 in response to a change in conditions, such as an increase in load, when the DC voltage is V1 at time T1. At a later time T2, the control unit 12 boosts the DC voltage to V2. At this time, the control unit 12 stops operation of the transmission control unit 11, i.e., turns off the switching units 11a and 11b, until the DC voltage reaches V2. The threshold value may be set according to the operation of a system, such as an air conditioner, to which the power conversion apparatus 100 is applied. When the control unit 12 turns on and then off the switching units 11a and 11b in the transmission control unit 11, i.e., when stopping the operation of the transmission control unit 11, the control unit 12 may provide a hysteresis voltage α and turn off the switching units 11a and 11b when the DC voltage becomes smaller than V2-α, thereby preventing hunting that occurs during on / off switching. By performing such an operation on the transmission control unit 11 by the control unit 12, the power conversion device 100 can flow a compensation current only in a voltage region where the common-mode current is significant. Note that in the example of FIG. 8, the control unit 12 is assumed to perform similar on / off operations on both the first switching element 52a and the second switching element 52b. However, control may also be performed such that only one of the switching units 11a and 11b is turned off and only one of the first switching element 52a and the second switching element 52b is stopped.

[0037] FIG. 9 is a second diagram illustrating an example of operation of the power conversion device 100 according to the first embodiment. FIG. 9( a) shows the magnitude of the DC voltage, FIG. 9( b) shows the on / off state of the transmission control unit 11, and FIG. 9( c) shows the state of the inverter unit 4. Note that in FIGS. 9( a), 9( b), and 9( c), the horizontal axis represents time. FIG. 9 illustrates an example of operation in which the power conversion device 100 performs a boost operation, but the inverter unit 4 enters overmodulation operation due to an increase in the rotation speed of the motor 6, for example. The control unit 12 may determine overmodulation operation based on a modulation factor used to generate a PWM (Pulse Width Modulation) waveform in the inverter unit 4, which is a well-known technique. Alternatively, the control unit 12 may determine overmodulation operation based on information about the motor current. The control unit 12 determines overmodulation operation by acquiring some physical quantity that can be used to determine overmodulation operation. In the power conversion device 100, if overmodulation occurs at time T3 due to a state change such as a load increase, the number of switching operations of the switching elements included in the inverter unit 4 is reduced, and the common-mode current is reduced. Therefore, the control unit 12 may stop the operation of the transmission control unit 11 at time T3. In this way, when the common-mode current is not significant in the overmodulation region, the control unit 12 can suppress power consumption equivalent to the compensation current by deliberately not flowing the compensation current.

[0038] As described above, according to this embodiment, power conversion apparatus 100 is provided with booster 10, and uses the DC voltage boosted by booster 10 as the drive power supply for compensator 5. Furthermore, detection unit 2 uses common mode choke coil 21 with auxiliary windings 22, 23, and uses the voltage generated in auxiliary windings 22, 23 as the gate voltage for first switching element 52a and second switching element 52b of compensator 5. This allows power conversion apparatus 100 to change the compensation current for the common mode current in accordance with the DC voltage. Power conversion apparatus 100 can improve the tracking ability of the compensation current to the common mode current.

[0039] Furthermore, the power conversion apparatus 100 can increase or decrease the compensation current according to the step-up ratio of the step-up unit 10. Specifically, the compensation current can be increased by setting the step-up ratio of the step-up unit 10 to a high value, and the compensation current can be reduced by setting the step-up ratio of the step-up unit 10 to a low value. As a result, when the power conversion apparatus 100 performs a step-up operation at a high step-up ratio in the step-up unit 10 to increase the DC voltage, the compensation current for the common-mode current can be increased, and the leakage current can be actively suppressed from flowing to the AC power supply 1. Furthermore, when the power conversion apparatus 100 does not perform a step-up operation in the step-up unit 10, or when the power conversion apparatus 100 performs a step-up operation at a low step-up ratio to not increase the DC voltage very much, the compensation current for the common-mode current can be suppressed, and the power conversion apparatus 100 can operate efficiently while suppressing the leakage current from flowing to the AC power supply 1.

[0040] Furthermore, the power conversion device 100 increases or decreases the compensation current according to the amount of common-mode current. Specifically, by performing control such as changing the gate voltages of the first switching element 52 a and the second switching element 52 b of the compensation unit 5 or not flowing the compensation current when the amount of common-mode current is smaller than a specified value, it is possible to appropriately suppress the power consumption of the compensation unit 5 according to the operating state of the power conversion device 100.

[0041] Furthermore, by configuring the first switching element 52a and the second switching element 52b of the compensation unit 5 with MOSFETs, the power conversion device 100 can reduce common mode currents in the relatively low frequency range, such as leakage currents and noise up to several hundred kHz.

[0042] Second Embodiment Fig. 10 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to a second embodiment. The refrigeration cycle-applied device 900 according to the second embodiment includes the power conversion device 100 described in the first embodiment. The refrigeration cycle-applied device 900 according to the second embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 10, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0043] The refrigeration cycle application equipment 900 includes a compressor 914 incorporating the motor 6 in embodiment 1, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, which are attached via refrigerant piping 912.

[0044] Inside the compressor 914, a compression mechanism 904 that compresses the refrigerant and a motor 6 that operates the compression mechanism 904 are provided.

[0045] The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by a motor 6 that is variably controlled in speed.

[0046] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, passes through the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910 and the four-way valve 902 and returns to the compression mechanism 904.

[0047] During cooling operation, as shown by the dashed arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, and returns to the compression mechanism 904 through the four-way valve 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906 and the four-way valve 902.

[0048] During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant to expand it.

[0049] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0050] REFRIGERATION CYCLE APPLICATION DEVICE, 2 DETECTION UNIT, 3 RECTIFICATION UNIT, 4 INVERTER UNIT, 5 COMPENSATION UNIT, 6 MOTOR, 7 STAYING CAPACITY, 8 TERMINAL UNIT, 8a, 8b TERMINATION RESISTANCE, 9 SMOOTHING UNIT, 10 STEP-UP UNIT, 11 TRANSMISSION CONTROL UNIT, 11a, 11b OPENING / CLOSING UNIT, 12 CONTROL UNIT, 21 COMMON MODE CHOKE COIL, 21a SINGLE SIDED LINE WINDING, 22, 23 AUXILIARY WINDING, 51 INJECTION UNIT, 52a FIRST SWITCHING ELEMENT, 52b SECOND SWITCHING ELEMENT, 53a FIRST DRIVER, 53b SECOND DRIVER, 55a FIRST GATE RESISTANCE, 55b SECOND GATE RESISTANCE, 100 POWER CONVERSION DEVICE, 200 MOTOR DRIVE UNIT, 900 REFRIGERATION CYCLE APPLIED DEVICE, 902 FOUR-WAY VALVE, 904 COMPRESSION MECHANISM, 906 INDOOR HEAT EXCHANGER, 908 EXPANSION VALVE, 910 OUTDOOR HEAT EXCHANGER, 912 Refrigerant piping, 914 compressor.

Claims

1. A power conversion device comprising: a rectifier unit that converts a first AC voltage supplied from an AC power source into a first DC voltage; a boost unit that boosts the first DC voltage to a second DC voltage; a smoothing unit that smoothes the second DC voltage into a third DC voltage; an inverter unit that converts the third DC voltage to a second AC voltage and outputs it; a detection unit that detects a common mode current between the AC power source and the inverter unit and outputs the detection result; a compensation unit having two switching elements that uses the detection result to generate a compensation current that compensates for the common mode current and injects it into a ground line; and a control unit that controls the operation of at least one of the boost unit and the inverter unit to increase or decrease the compensation current.

2. The power conversion device according to claim 1, wherein the control unit controls the operation of at least one of the boost unit and the inverter unit using at least one of the detection result and the voltage value of the third DC voltage.

3. The power conversion device according to claim 1 or 2, wherein the compensation section increases or decreases the compensation current in accordance with the third DC voltage.

4. The power conversion device according to claim 3, wherein the control unit increases or decreases the compensation current by controlling a boost ratio of the boost unit to increase or decrease the third DC voltage.

5. A power conversion device as described in any one of claims 1 to 4, further comprising: a transmission control unit that controls the transmission of the detection result between the detection unit and the compensation unit, wherein the control unit controls the operation of the transmission control unit depending on at least one of the detection result and a voltage value of the third DC voltage.

6. The power conversion device according to claim 1, wherein the two switching elements are Metal-Oxide-Semiconductor Field-Effect Transistors.

7. A motor drive device comprising a power conversion device according to any one of claims 1 to 6.

8. A refrigeration cycle device comprising the power conversion device according to any one of claims 1 to 6.

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