Electric power conversion device and refrigeration cycle device

Abstract

An electric power conversion device (100) comprises: a detection unit (20) for detecting a first physical quantity correlated with a common mode current flowing through the inside of the electric power conversion device (100) via ground potentials (51, 63) that each serve as a reference for a power supply voltage; a compensation signal generation unit (30) for generating, as a compensation signal and on the basis of the first physical quantity detected by the detection unit (20), a compensation current that is a second physical quantity for cancelling the common mode current; a compensation signal output unit (40) for injecting the compensation signal into a ground potential (52); and protection circuits (24a, 24b) that operate so that the first physical quantity does not exceed a predetermined threshold.

Description

Power conversion device and refrigeration cycle device

[0001] The present disclosure relates to a power conversion device that converts a power supply voltage applied from an AC power supply into a drive voltage for a load, and a refrigeration cycle device.

[0002] When the refrigeration cycle device is an air conditioner, leakage current can be a problem. Leakage current is a high-frequency current that flows through stray capacitance between the compressor (load) and earth potential due to switching control of the inverter's switching elements. The leakage current that flows to earth potential returns to the refrigeration cycle device (source) via the ground point where the AC power supply is grounded, and is therefore also called "common mode current."

[0003] Japanese Patent Application Laid-Open No. 2006-144993 discloses a technique in which a current corresponding to a common-mode current flowing through a main winding of a detection unit is monitored by an auxiliary winding, and when the monitored current is greater than a threshold, a compensation signal is output to compensate for the common-mode current. The auxiliary winding is a winding that is magnetically coupled to the main winding.

[0004] JP 2013-158099 A

[0005] In air conditioners, it is expected that excessive common-mode currents will suddenly flow due to factors such as refrigerant stagnation and temperature environments. When excessive common-mode currents flow, excessive voltages may be applied to the gates of semiconductor elements provided in the compensation signal generation unit that generates compensation signals, potentially damaging the semiconductor elements. Anticipating such excessive voltages, one possible solution is to reduce the voltage generated in the auxiliary winding by increasing the number of turns in the main winding of the detection unit. However, this increases the number of turns in the main winding, which creates the problem of an increase in the size of the detection unit.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a power conversion device that can protect a semiconductor element provided in a compensation signal generation unit from an excessive common-mode current while miniaturizing the detection unit.

[0007] To solve the above-mentioned problems and achieve the object, a power conversion apparatus according to the present disclosure converts a power supply voltage applied from an AC power supply into a drive voltage for a load, and includes a detection unit, a compensation signal generation unit, a compensation signal output unit, and a protection circuit. The detection unit detects a first physical quantity correlated with a common-mode current flowing inside the power conversion apparatus via a ground potential that serves as a reference for the power supply voltage. The compensation signal generation unit generates, as a compensation signal, a compensation current or compensation voltage that is a second physical quantity for canceling out the common-mode current based on the first physical quantity detected by the detection unit. The compensation signal output unit injects or applies the compensation signal to the ground potential or to a predetermined location inside the power conversion apparatus. The protection circuit operates to prevent the first physical quantity or the second physical quantity from exceeding a predetermined threshold.

[0008] The power conversion device according to the present disclosure has the advantage that it is possible to protect the semiconductor element provided in the compensation signal generation unit from an excessive common mode current while miniaturizing the detection unit.

[0009] FIG. 1 is a diagram showing a first example of the configuration of a power conversion device according to embodiment 1; FIG. 2 is a diagram used to explain the effect of arranging a protection circuit in the power conversion device according to embodiment 1; FIG. 3 is a diagram showing a second example of the configuration of a power conversion device according to embodiment 1; FIG. 4 is a diagram used to explain variations in the arrangement of protection circuits provided in the power conversion device according to embodiment 2; FIG. 5 is a diagram showing a first example of the configuration of a power conversion device according to embodiment 3; FIG. 6 is a diagram showing a second example of the configuration of a power conversion device according to embodiment 3; FIG. 7 is a diagram showing a first example of the configuration of a power conversion device according to embodiment 4; FIG. 8 is a diagram showing a second example of the configuration of a power conversion device according to embodiment 4;

[0010] A power conversion device and a refrigeration cycle device according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. In the following description, multiple components of the same type will be denoted by reference numerals with subscripts, but the subscripts will be omitted as appropriate when there is no need to distinguish between the individual components.

[0011] Embodiment 1. Fig. 1 is a diagram showing a first configuration example of a power conversion device 100 according to embodiment 1. The power conversion device 100 according to embodiment 1 drives a load 60 by converting a power supply voltage applied from an AC power supply 50 into a drive voltage for a motor 61 connected to the load 60. When the power conversion device 100 is installed in a refrigeration cycle device, an example of the load 60 is a compressor or a fan.

[0012] A midpoint 54 of the AC power supply 50 is grounded to a ground potential 51. The ground potential 51 is the potential of a ground wire or ground surface (not shown) and serves as a reference potential for the power supply voltage. Although the AC power supply 50 is shown as a single-phase three-wire system in FIG. 1 , this is not limiting. The AC power supply 50 may be a single-phase two-wire system, a three-phase three-wire system, or a three-phase four-wire system. The power distribution system of the AC power supply 50 is determined according to the specifications of the refrigeration cycle apparatus.

[0013] The power conversion device 100 includes a noise filter 11, a rectifier 12, a smoothing capacitor 13, an inverter 15, and a canceller 80. The noise filter 11 is a passive filter composed of passive elements such as an inductor and a capacitor. The noise filter 11 is electrically connected to a ground potential 52. The noise filter 11 is disposed between an AC power supply 50 and the rectifier 12 and operates to reduce noise currents flowing into and out of the power conversion device 100. The rectifier 12 rectifies the power supply voltage applied from the AC power supply 50. The smoothing capacitor 13 is disposed between DC buses 71 and 72, which are electrical wiring for electrically connecting the rectifier 12 and the inverter 15, and smoothes and holds the rectified voltage rectified by the rectifier 12. The inverter 15 is a conversion unit that converts the rectified voltage rectified by the rectifier 12 into a drive voltage for the load 60. Specifically, the inverter 15 includes a plurality of switching elements 14 and converts the rectified voltage rectified by the rectifier 12 into a drive voltage for the motor 61 to drive the motor 61 .

[0014] The canceller 80 also includes a detection unit 20, protection circuits 24a and 24b, a compensation signal generation unit 30, and a compensation signal output unit 40. The detection unit 20 includes a first coil 21 and a second coil 22 magnetically coupled to the first coil 21. The first coil 21 includes two windings 21a and 21b. The winding 21a is disposed on the power line 18, and the winding 21b is disposed on the power line 19. The power lines 18 and 19 are electrical wiring for electrically connecting the noise filter 11 and the rectification unit 12. The second coil 22 includes two windings 22a and 22b, each of which is magnetically coupled to the winding 21b. The first coil 21 is a main winding, and the second coil 22 is an auxiliary winding. The black circles in the figure indicate the polarity of the voltage generated in each winding. For example, if the voltage induced in winding 21b is higher on the black circle side, the voltage induced in windings 22a and 22b will be higher on the black circle side. Therefore, voltages of opposite polarities are always induced in windings 22a and 22b.

[0015] The compensation signal generating unit 30 is divided into an adjustment circuit unit 38 and a semiconductor element circuit unit 39. The adjustment circuit unit 38 includes termination resistors 31 and 32 and gate resistors 33 and 34. The semiconductor element circuit unit 39 includes voltage-driven elements 35 and 36. The voltage-driven elements 35 and 36 are semiconductor elements to be protected. The termination resistor 31, the gate resistor 33, and the voltage-driven element 35 are provided corresponding to the winding 22a, while the termination resistor 32, the gate resistor 34, and the voltage-driven element 36 are provided corresponding to the winding 22b. An example of the voltage-driven elements 35 and 36 is a metal-oxide-semiconductor field-effect transistor (MOSFET) as shown in the figure, but voltage-driven elements other than MOSFETs may also be used.

[0016] The protection circuits 24a and 24b are disposed between the detection unit 20 and the compensation signal generation unit 30. That is, in FIG. 1, the protection circuits 24a and 24b are disposed on the second coil 22 on the input end side of the compensation signal generation unit 30. Specifically, the protection circuit 24a is connected to both ends of the winding 22a of the second coil 22, and the protection circuit 24b is connected to both ends of the winding 22b of the second coil 22. In the protection circuits 24a and 24b, when the voltage of the windings 22a and 22b exceeds a predetermined threshold, a varistor, which is a protection element, becomes conductive. This suppresses the voltage of the windings 22a and 22b from exceeding the predetermined threshold. Note that while FIG. 1 illustrates an example in which the protection elements of the protection circuits 24a and 24b are varistors, elements other than varistors may also be used. Variations of the protection circuits 24a and 24b will be described later.

[0017] The compensation signal output section 40 includes a resistor 41 and a capacitor 42 connected in series with the resistor 41. The compensation signal output section 40 is electrically connected to a ground potential 52. Note that in FIG. 1 , the connection order of the resistor 41 and the capacitor 42 in the compensation signal output section 40 may be reversed from that shown in the figure. That is, the resistor 41 may be disposed on the side of the ground potential 52. Furthermore, the compensation signal output section 40 does not need to include both the resistor 41 and the capacitor 42, and it is sufficient if it includes at least one of the resistor 41 and the capacitor 42.

[0018] Next, the operation of the power conversion apparatus 100 according to the first embodiment will be described. When the inverter 15 performs a switching operation, the inverter 15 generates power. At this time, the inverter 15 acts as a noise source, i.e., a source of noise power, and a common-mode current flows within the power conversion apparatus 100. The common-mode current here refers to a leakage current that flows through the parasitic capacitance 62 between the load 60 and the ground potential 63. Since the common-mode current flows within the power conversion apparatus 100, it also flows through the power lines 18 and 19. The windings 22a and 22b of the detection unit 20 detect a first physical quantity that is correlated with the common-mode current flowing through the power lines 18 and 19. The detection voltage of the winding 22a is generated across the termination resistor 31, and the voltage of the termination resistor 31 is applied to the voltage-driven element 35 via the gate resistor 33. The detection voltage of the winding 22a is an example of the first physical quantity that is correlated with the common-mode current.

[0019] When the voltage of termination resistor 31 exceeds the threshold voltage of voltage-driven element 35, voltage-driven element 35 becomes conductive. When voltage-driven element 35 becomes conductive, connection point 37 between voltage-driven element 35 and voltage-driven element 36 is electrically connected to high-potential DC bus 71 via the conductive voltage-driven element 35, and a compensation current flows from connection point 37 toward ground potential 52 via compensation signal output unit 40. This direction cancels out the common-mode current, and the compensation current flowing via compensation signal output unit 40 reduces the common-mode current.

[0020] Similarly, the detection voltage of winding 22b is generated across termination resistor 32, and the voltage of termination resistor 32 is applied to voltage-driven element 36 via gate resistor 34. When the voltage of termination resistor 32 exceeds the threshold voltage of voltage-driven element 36, voltage-driven element 36 becomes conductive. When voltage-driven element 36 becomes conductive, node 37 is electrically connected to low-potential DC bus 72 via the conductive voltage-driven element 36, and a compensation current flows from ground potential 52 toward node 37 via compensation signal output unit 40. This direction is opposite to that when voltage-driven element 35 is conductive, but because windings 22a and 22b are connected with opposite polarity, it cancels out the common-mode current. Therefore, even when voltage-driven element 36 becomes conductive, the compensation current flowing via compensation signal output unit 40 reduces the common-mode current.

[0021] 1, the detector 20 detects a first physical quantity correlated with the common-mode current flowing between the noise filter 11 and the rectifier 12, and the compensation signal generator 30 generates a compensation current based on the detected first physical quantity, and is connected between the rectifier 12 and the inverter 15, which is a noise power supply source. Therefore, the detector 20 and the compensation signal generator 30 form a feedback system when viewed from the inverter 15.

[0022] 1, the detection unit 20 and the compensation signal generation unit 30 can generate compensation currents of both polarities, but common-mode current reduction is also possible with unipolar compensation currents. Therefore, when a configuration is adopted in which unipolar compensation currents are generated, one of the windings 22a, 22b of the detection unit 20 can be omitted. Furthermore, of the set of the termination resistor 31, gate resistor 33, and voltage-driven element 35, and the set of the termination resistor 32, gate resistor 34, and voltage-driven element 36 in the compensation signal generation unit 30, one set of the windings 22a, 22b corresponding to the omitted winding can be omitted.

[0023] As described above, in the canceller 80 according to the first embodiment, the detector 20 detects a first physical quantity correlated with the common-mode current flowing through the power conversion device 100 via the ground potential, which serves as a reference for the power supply voltage. The compensation signal generator 30 generates a compensation current as a compensation signal for canceling the common-mode current based on the first physical quantity detected by the detector 20. The compensation signal output unit 40 then injects the compensation current based on the compensation signal output from the compensation signal generator 30 into the ground potential. During this operation, the protection circuits 24 a and 24 b operate to prevent the first physical quantity from exceeding a predetermined threshold, thereby protecting the voltage-driven elements 35 and 36 to be protected from excessive voltage. The compensation current referred to here is an example of a second physical quantity. Another example of the second physical quantity is a compensation voltage. An example in which the compensation signal generator 30 outputs a compensation voltage as a compensation signal will be described in a later-described embodiment.

[0024] Fig. 2 is a diagram illustrating the effect of providing the protection circuit 24 in the power conversion device 100 according to the first embodiment. Fig. 2 shows a first coil 21 and a second coil 22 that constitute the detection unit 20. In the explanation of Fig. 2, the first coil 21 is referred to as the "main winding" and the second coil 22 is referred to as the "auxiliary winding." The meanings of the symbols in Fig. 2 are as follows:

[0025] N １ : Number of turns of main winding N ２ : Number of turns of auxiliary winding I １－１ : Current flowing through one of the main windings I １－２ :Current flowing through the other winding of the main winding I １ : Combined current flowing through the main winding (hereinafter referred to as "main winding current") V １－１ : Voltage induced in one of the main windings V １－２ : Voltage induced in the other main winding V １ : Total voltage induced in the main winding (hereinafter referred to as "main winding induced voltage") I ２ : Current flowing through the auxiliary wire (hereinafter referred to as "auxiliary winding current") V ２ : Voltage induced in the auxiliary winding (hereinafter referred to as "auxiliary winding induced voltage")

[0026] When a common mode current flows through the main winding, it can be detected by the auxiliary winding. At this time, the number of turns of the main winding N １ , the number of turns of the auxiliary winding N ２ , main winding current I １ , main winding induced voltage V １ , auxiliary winding current I ２ and auxiliary winding induced voltage V ２ The following well-known relation holds between

[0027] N １ / N ２ =V １ / V ２ =I ２ / I １ …(1) V ２ = (N ２ / N １ ) V １ …(2)

[0028] From the above equation (2), the auxiliary winding induced voltage V ２ In order to prevent excessively large, the number of turns of the main winding N １ Increase the number of turns of the auxiliary winding N ２ However, the current flowing through the main winding is large, and the wire diameter of the main winding is thicker than that of the auxiliary winding, so the number of turns of the main winding N １ Therefore, while pursuing miniaturization of the detection unit 20, it is necessary to increase the auxiliary winding induced voltage V ２ On the other hand, if a protection circuit 24 is provided between the detection unit 20 and the compensation signal generation unit 30 as shown in FIG. 1, the auxiliary winding induced voltage V ２ Therefore, if the canceller 80 is configured to include the protection circuit 24, the effect of improving the degree of freedom in design of the detection unit 20 can be obtained. For example, if the number of turns N of the main winding is １ If the number of turns N of the auxiliary winding can be reduced, the inner diameter of the core provided in the detection unit 20 can be reduced, and therefore the size of the detection unit 20 can be reduced. ２If the number of coils can be increased, the magnetic connection between the auxiliary winding and the core provided in the detection unit 20 will be strengthened, which will also have the effect of reducing variations in the position of the auxiliary winding.

[0029] Furthermore, when the power conversion device 100 according to the first embodiment is used in an air conditioner, the tendency of the common mode current flowing in and out of the power conversion device 100 varies depending on the state of the refrigerant in the air conditioner. In particular, when the air conditioner is stopped and then restarted shortly thereafter, the common mode current tends to increase. Therefore, in a configuration without the protection circuit 24, the condition under which the common mode current is maximized is assumed, and the auxiliary winding induced voltage V detected under that condition is calculated. ２ The maximum value of the common mode current V is determined by simulation or actual measurement, and the maximum value up to which the voltage-driven elements 35 and 36 can be set without being damaged is confirmed, and the number of turns of the main winding and auxiliary winding is then determined. In other words, in the case of a configuration without the protection circuit 24, the larger the expected maximum value of the common mode current, the greater the auxiliary winding induced voltage V ２ The number of turns is designed so that the common mode current is small. However, with this design, if there is a large difference between the maximum value of the common mode current and the current value of the common mode current in steady state, the detected voltage of the common mode current in steady state will be extremely small, which could cause a problem in that a voltage sufficient to drive the compensation signal generating section 30 cannot be secured and the compensation current cannot be injected. In contrast, if the configuration in which the protection circuit 24 is provided is adopted as in embodiment 1, damage to the compensation signal generating section 30 can be prevented even if the common mode current becomes large under specific conditions that may very rarely occur. Furthermore, if damage to the compensation signal generating section 30 can be prevented under specific conditions, the design can be made so that the detected voltage of the common mode current in steady state is large, which also has the effect of improving the performance of the canceller 80.

[0030] The power conversion device 100 according to the first embodiment may also be configured as shown in Fig. 3. Fig. 3 is a diagram showing a second configuration example of the power conversion device 100 according to the first embodiment. Comparing Fig. 3 with Fig. 1, in Fig. 3, the protection circuits 24a and 24b are deleted from the configuration of Fig. 1, and instead, a protection circuit 84 having one varistor is connected across both ends of the voltage-driven elements 35 and 36 connected in series between the compensation signal generation unit 30 and the compensation signal output unit 40. The other configuration is the same as or equivalent to that in Fig. 1, and the same or equivalent components are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0031] Although a detailed description will be omitted, when an excessively large common mode current is detected, the compensation current generated by the compensation signal generation unit 30 becomes excessive, which may damage the elements of the compensation signal output unit 40 or the elements connected via the compensation signal output unit 40. Furthermore, similar to the configuration in which the protection circuit 24 is provided in the detection unit 20, if a protection circuit 84 is provided between the compensation signal generation unit 30 and the compensation signal output unit 40, it is possible to prevent the degree of freedom in design of the compensation signal generation unit 30 and the compensation signal output unit 40 from being reduced.

[0032] 3 shows an example in which the protection element of the protection circuit 84 is a varistor, but elements other than a varistor may also be used. Variations of the protection circuit 84 will be described later.

[0033] As described above, the power conversion apparatus according to the first embodiment includes a detection unit, a compensation signal generation unit, a compensation signal output unit, and a protection circuit. The detection unit detects a first physical quantity correlated with a common-mode current flowing through the power conversion apparatus via a ground potential that serves as a reference for the power supply voltage. The compensation signal generation unit generates, as a compensation signal, a compensation current that is a second physical quantity for canceling the common-mode current based on the first physical quantity detected by the detection unit. The compensation signal output unit injects the compensation current into the ground potential. The protection circuit is disposed on the input end or output end side of the compensation signal generation unit and operates to prevent the first physical quantity or the second physical quantity from exceeding a predetermined threshold. Using a power conversion apparatus configured in this manner can reduce the number of turns of the main winding in the detection unit, thereby enabling the size of the detection unit to be reduced while reliably protecting a voltage-driven element, which is a semiconductor element to be protected and provided in the compensation signal generation unit, from excessive common-mode current.

[0034] Furthermore, according to the power conversion device of embodiment 1, the number of turns of the auxiliary winding can be increased, thereby reducing variations in the positional deviation of the auxiliary winding. According to the power conversion device of embodiment 1, the number of turns of the main winding can be reduced while increasing the number of turns of the auxiliary winding. This allows the power conversion device to be designed so that the detection voltage of the common-mode current in a steady state is increased, thereby improving the performance of the canceller.

[0035] Second Embodiment In a second embodiment, variations in the configuration in which the protection circuit 24 is provided will be described with reference to Fig. 4. Fig. 4 is a diagram illustrating variations in the arrangement of the protection circuit 24 provided in the power conversion device 100 according to the second embodiment.

[0036] Figure 4(a) is a diagram showing a schematic diagram of the configuration of Figure 1. The configuration of Figure 4(a) may be modified as shown in Figures 4(b) to 4(d). In Figure 4(a), a protection circuit 24 equipped with a varistor is disposed between the lines on the output side of the detection unit 20, but as shown in Figure 4(b), a configuration in which two varistors provided in the protection circuit 24 are inserted between the lines is also possible. A configuration in which two varistors are inserted between the lines is a configuration in which the connection point of two varistors connected in series is electrically connected to earth potential.

[0037] As shown in Fig. 4(c), the varistor in the configuration of Fig. 4(a) may be replaced with two Zener diodes connected in series with opposite polarity. As shown in Fig. 4(d), the varistor in the configuration of Fig. 4(a) may be replaced with four bridge-connected diodes. In the configuration of Fig. 4(d), when the detection voltage of the detection unit 20 is positive, the voltage clamping action of the two upper diodes suppresses excessive voltage that may occur on the output side of the detection unit 20. When the detection voltage of the detection unit 20 is negative, the voltage clamping action of the two lower diodes suppresses excessive voltage that may occur on the output side of the detection unit 20.

[0038] FIG. 4(e) is a schematic diagram showing the configuration of FIG. 3. The configuration of FIG. 4(e) may be modified as shown in FIGS. 4(f) to 4(h). In FIG. 4(e), a protection circuit 84 equipped with a varistor is disposed between the lines on the output side of the compensation signal generating unit 30. However, as shown in FIG. 4(f), two varistors provided in the protection circuit 84 may be inserted between the lines and ground. Furthermore, as shown in FIG. 4(g), the varistor in the configuration of FIG. 4(e) may be replaced with two Zener diodes connected in series with opposite polarity. Furthermore, as shown in FIG. 4(h), the varistor in the configuration of FIG. 4(e) may be replaced with four bridge-connected diodes. In the configuration of FIG. 4(h), when the output voltage of the compensation signal generating unit 30 is positive, the voltage clamping action of the two upper diodes suppresses excessive voltage that may occur on the output side of the compensation signal generating unit 30. Furthermore, when the output voltage of the compensation signal generating section 30 is negative, the voltage clamping action of the two lower diodes suppresses excessive voltage that may occur on the output side of the compensation signal generating section 30 .

[0039] As described above, according to the power conversion device of embodiment 2, the protection circuit is configured to be placed on the input end side or the output end side of the compensation signal generation unit, so that it is possible to reliably protect the voltage-driven element, which is the semiconductor element to be protected and provided in the compensation signal generation unit, from excessive common-mode current while miniaturizing the detection unit.

[0040] Embodiment 3. In the first and second embodiments, the arrangement of the protection circuit 24 in the canceller 80 of a type in which a compensation current generated based on the detected voltage of the detection unit 20 is injected into the earth potential has been described. In the third embodiment, the arrangement of the protection circuit 24 in the canceller 80 of a type in which a compensation voltage is generated based on the detected voltage of the detection unit 20 and the generated compensation voltage is applied to the power lines 18 and 19 will be described. The former method is sometimes called the "ground line injection method," and the latter method is sometimes called the "power line application method."

[0041] Fig. 5 is a diagram showing a first configuration example of a power conversion device 100 according to embodiment 3. The power conversion device 100 shown in Fig. 5 is configured to include a canceller 80 configured using a power line application method. In Fig. 5, a component including an inverter 15, which is a noise source, and further including the rectifier 12 and smoothing capacitor 13 in the configuration of Fig. 1 is shown as a noise source 74. In Fig. 5, components that are the same as or equivalent to those in Fig. 1 are denoted by the same reference numerals.

[0042] As shown in FIG. 5 , in a canceller 80 according to the third embodiment, a compensation signal output unit 81 is disposed on the power lines 18, 19 between the detection unit 20 and the noise source 74. The compensation signal output unit 81 includes a third coil 82 and a fourth coil 83 magnetically coupled to the third coil 82. The third coil 82 includes two windings 82a, 82b, and the fourth coil 83 includes one winding 83a. The power conversion device 100 shown in FIG. 5 is configured such that the detection unit 20 and the compensation signal generation unit 30 generate a unipolar compensation voltage, and the second coil 22 of the detection unit 20 includes one winding 22a. Therefore, in accordance with this configuration, the fourth coil 83 is also configured to include one winding 83a.

[0043] 1, a protection circuit 24c is connected to both ends of the winding 22a of the second coil 22. A protection circuit 84a is also connected to both ends of the winding 83a of the fourth coil 83.

[0044] Next, the operation of canceller 80 according to the third embodiment will be described. When inverter 15 performs a switching operation, inverter 15 generates power. At this time, inverter 15 becomes noise source 74, causing a common mode current to flow through power lines 18 and 19. Winding 22a of detection unit 20 detects a first physical quantity that is correlated with the common mode current flowing through power lines 18 and 19. The detected voltage of winding 22a is an example of the first physical quantity that is correlated with the common mode current.

[0045] The compensation signal generating unit 30 generates a compensation voltage, which is a second physical quantity for canceling out the common mode current, as a compensation signal based on the first physical quantity detected by the detecting unit 20, and outputs the compensation signal to the compensation signal output unit 81. The third coil 82 of the compensation signal output unit 81 generates a voltage for canceling out the common mode current based on the compensation signal received via the fourth coil 83, and applies the voltage to the power lines 18, 19. This applied voltage causes a current to flow in the power lines 18, 19 in a direction that cancels out the common mode current, thereby reducing the common mode current.

[0046] When the canceller 80 operates as described above, if the voltage across the winding 22a exceeds a predetermined threshold, the varistor, which is a protection element in the protection circuit 24c, becomes conductive, thereby suppressing the voltage across the winding 22a so that it does not exceed the predetermined threshold.

[0047] Furthermore, when the canceller 80 operates as described above, if the voltage across the winding 83a exceeds a predetermined threshold, the varistor, which is a protection element in the protection circuit 84a, becomes conductive, thereby suppressing the voltage across the winding 83a so that it does not exceed the predetermined threshold.

[0048] In FIG. 5, the protection circuit 24c or the protection circuit 84a is provided for both the second coil 22 and the fourth coil 83, but the protection circuit 24c or the protection circuit 84a may be provided for either one of them.

[0049] Fig. 6 is a diagram showing a second configuration example of a power conversion apparatus 100 according to embodiment 3. In Fig. 6, components that are the same as or equivalent to those in Fig. 5 are designated by the same reference numerals. In Fig. 5, the varistor serving as the protection element of protection circuit 24c is connected to both ends of winding 22a, but as shown in Fig. 6, two varistors provided in protection circuit 24d may be inserted between the terminals and ground. Furthermore, in Fig. 5, the varistor serving as the protection element of protection circuit 84a is connected to both ends of winding 83a, but as shown in Fig. 6, two varistors provided in protection circuit 84b may be inserted between the terminals and ground.

[0050] In FIG. 6, the protection circuit 24d or the protection circuit 84b is disposed on both the second coil 22 and the fourth coil 83, but the protection circuit 24d or the protection circuit 84b may be disposed on either one of them.

[0051] 5 and 6 illustrate examples in which the protection elements of the protection circuits 24c, 24d, 84a, and 84b are varistors, but the present invention is not limited to these examples. The protection circuits 24c, 24d, 84a, and 84b may be configured using two Zener diodes as shown in FIG. 4(c) or 4(g), or may be configured using four diodes as shown in FIG. 4(d) or 4(h).

[0052] As described above, the power conversion apparatus according to the third embodiment includes a detection unit, a compensation signal generation unit, a compensation signal output unit, and a protection circuit. The detection unit detects a first physical quantity correlated with a common-mode current flowing through the power conversion apparatus via a ground potential that serves as a reference for the power supply voltage. The compensation signal generation unit generates, as a compensation signal, a compensation voltage that is a second physical quantity for canceling out the common-mode current, based on the first physical quantity detected by the detection unit. The compensation signal output unit applies a compensation voltage based on the compensation signal to a power line disposed inside the power conversion apparatus, the electrical wiring into which the first and third coils are inserted. The protection circuit is disposed on the input end or output end side of the compensation signal generation unit and operates to prevent the first physical quantity or the second physical quantity from exceeding a predetermined threshold. Using a power conversion apparatus configured in this manner allows the number of turns of the main winding in the detection unit to be reduced, thereby enabling the detection unit to be miniaturized while reliably protecting the circuit components to be protected, which are provided in the compensation signal generation unit, from excessive common-mode current.

[0053] Fourth Embodiment In the fourth embodiment, an example of the configuration of the protection circuit 24 that can be employed depending on the configuration of the semiconductor element circuit unit 39 in the power conversion device 100 described in the third embodiment will be described. FIG. 7 is a diagram showing a first example of the configuration of the power conversion device 100 according to the fourth embodiment. FIG. 7 shows a configuration including a canceller 80 configured using a power line application method. Compared with FIG. 1, the compensation signal output unit 40 is replaced with a compensation signal output unit 81. FIG. 7 also shows a configuration that generates a unipolar compensation voltage, in which the winding 22b of the second coil 22 is deleted from the configuration of FIG. 1. In addition, in FIG. 7, the termination resistor 32 and the protection circuits 24a and 24b in the adjustment circuit unit 38 are deleted from the configuration of FIG. 1, and instead, a protection circuit 24e having one varistor is connected to one end of the winding 22a. The other configurations are the same or equivalent to those in FIG. 1, and the same reference numerals are used to indicate the same or equivalent components.

[0054] When the detection unit 20 is configured to generate a unipolar compensation voltage, one end of the termination resistor 31 in the adjustment circuit unit 38 serves as the reference potential of the semiconductor element circuit unit 39 and is electrically connected to have the same potential as the earth potential 52, as shown in Fig. 7. In this configuration, as shown in Fig. 7, one terminal of the second coil 22 is connected to the earth potential 52 via the compensation signal generation unit 30, the other terminal of the second coil 22 is connected to one terminal of the protection circuit 24e, and the other terminal of the protection circuit 24e is connected to the earth potential.

[0055] In the case of the configuration of FIG. 7, it is sufficient to provide one protection circuit 24e, and the connection to the second coil 22 requires only one terminal, which has the advantage of being simple to configure.

[0056] 8 is a diagram showing a second configuration example of the power conversion device 100 according to the fourth embodiment. In FIG. 8, components that are the same as or equivalent to those in FIG. 7 are denoted by the same reference numerals. In FIG. 8, one end of the termination resistor 31 in the adjustment circuit unit 38 is not at the reference potential of the semiconductor element circuit unit 39, and the semiconductor element circuit unit 39 is connected to the earth potential 52 via a capacitor 48. Note that the semiconductor element circuit unit 39 may also be connected to the earth potential 52 via a resistor.

[0057] 8, in order to configure two varistors to be inserted between the ground, a first protection circuit 24f and a second protection circuit 24g are provided. Specifically, one terminal of the second coil 22 is connected to the ground potential 52 via the protection circuit 24f, and the other terminal of the second coil 22 is connected to the ground potential 52 via the protection circuit 24g.

[0058] 7 and 8 show an example in which the protection elements of the protection circuits 24e, 24f, and 24g are varistors, but the present invention is not limited to these examples. The protection circuits 24e, 24f, and 24g may be configured using two Zener diodes as shown in FIG. 4(c) or 4(g), or may be configured using four diodes as shown in FIG. 4(d) or 4(h).

[0059] As described above, according to the power conversion device of embodiment 4, the arrangement of the protection circuit 24 is devised in accordance with the configuration of the semiconductor element circuit section 39, making it possible to configure the power conversion device simply and at low cost.

[0060] Fifth Embodiment Fig. 9 is a diagram showing a configuration example of a refrigeration cycle apparatus 900 according to a fifth embodiment. The refrigeration cycle apparatus 900 according to the fifth embodiment includes the power conversion apparatus 100 described in the first embodiment. The refrigeration cycle apparatus 900 according to the fifth embodiment can be applied to products including 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.

[0061] The refrigeration cycle device 900 includes a compressor 315 incorporating the motor 61 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.

[0062] Inside the compressor 315, a compression mechanism 904 that compresses the refrigerant and a motor 61 that operates the compression mechanism 904 are provided.

[0063] 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 61 that is variably controlled in speed.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] The refrigeration cycle apparatus 900 according to the fifth embodiment has been described as including the power conversion apparatus 100 described in the first embodiment, but is not limited to this. The refrigeration cycle apparatus 900 may include any one of the power conversion apparatuses 100 according to the second to fourth embodiments.

[0068] 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.

[0069] 11 noise filter, 12 rectification unit, 13 smoothing capacitor, 14 switching element, 15 inverter, 18, 19 power line, 20 detection unit, 21 first coil, 21a, 21b, 22a, 22b, 82a, 82b, 83a winding, 22 second coil, 24, 24a to 24g, 84, 84a, 84b protection circuit, 30 compensation signal generation unit, 31, 32 termination resistor, 33, 34 gate resistor, 35, 36 voltage-driven element, 37 connection point, 38 adjustment circuit unit, 39 semiconductor element circuit unit, 40, 81 compensation signal output unit, 41 resistor, 42, 48 capacitor, 50 AC power supply, 51, 52, 63 earth potential, 54 midpoint, 60 load, 61 motor, 62 parasitic capacitance, 71, 72 DC bus, 74 noise source, 80 canceller, 82 third coil, 83 fourth coil, 100 power conversion device, 315 compressor, 900 refrigeration cycle device, 902 four-way valve, 904 compression mechanism, 906 indoor heat exchanger, 908 expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping.

Claims

1. A power conversion device that converts a power supply voltage applied from an AC power supply into a drive voltage for a load, comprising: a detection unit that detects a first physical quantity correlated with a common mode current flowing inside the power conversion device via an earth potential that is a reference for the power supply voltage; a compensation signal generation unit that generates, as a compensation signal, a compensation current or compensation voltage that is a second physical quantity for canceling out the common mode current based on the first physical quantity detected by the detection unit; a compensation signal output unit that injects or applies the compensation signal to the earth potential or to a specified location inside the power conversion device; and a protection circuit that operates to prevent the first physical quantity or the second physical quantity from exceeding a predetermined threshold value.

2. The power conversion device according to claim 1, wherein the detection unit comprises a first coil and at least one second coil magnetically coupled to the first coil, and the first physical quantity is detected by the second coil.

3. The power conversion device according to claim 2, wherein the compensation signal output section is electrically connected to the earth potential via at least one of a resistor and a capacitor, and injects a compensation current based on the compensation signal into the earth potential.

4. The power conversion device according to claim 2 or 3, wherein the protection circuit is disposed on the input end side of the compensation signal generating section.

5. The power conversion device according to claim 4, wherein the protection circuit is disposed in the second coil.

6. The power conversion device according to claim 2 or 3, wherein the protection circuit is disposed on the output end side of the compensation signal generating section.

7. The power conversion device according to claim 6, wherein the compensation signal generating section includes at least one voltage-driven element, and the protection circuit is connected across the voltage-driven element.

8. The power conversion device according to claim 7, wherein the compensation signal generating unit comprises two voltage-driven elements connected in series, the protection circuit comprises one protection element, and the one protection element is connected across the two voltage-driven elements connected in series.

9. The power conversion device according to claim 7, wherein the compensation signal generating unit comprises two voltage-driven elements connected in series, the protection circuit comprises two protection elements connected in series, the two series-connected protection elements are connected to both ends of the two series-connected voltage-driven elements, and the connection point of the two protection elements is connected to earth potential.

10. The power conversion device according to claim 2, wherein the compensation signal output unit comprises at least one third coil and at least one fourth coil magnetically coupled to the third coil, and applies a compensation voltage based on the compensation signal to electrical wiring into which the first and third coils are inserted using the fourth coil.

11. The power conversion device according to claim 10, wherein the protection circuit is disposed on the input end side or the output end side of the compensation signal generating section.

12. A power conversion device as described in claim 10, wherein, when a reference potential of the compensation signal generating unit is the earth potential, one terminal of the second coil is connected to the earth potential via the compensation signal generating unit, the other terminal of the second coil is connected to one terminal of the protection circuit, and the other terminal of the protection circuit is connected to the earth potential.

13. A power conversion device as described in claim 10, wherein when the reference potential of the compensation signal generating unit is electrically connected to the earth potential via a capacitor or a resistor, the protection circuit comprises a first protection circuit and a second protection circuit, one terminal of the second coil is connected to the earth potential via the first protection circuit, and the other terminal of the second coil is connected to the earth potential via the second protection circuit.

14. A refrigeration cycle device comprising a power conversion device according to any one of claims 1 to 13.

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