Noise suppression circuit, and air conditioner

Abstract

To provide a technique capable of appropriately suppressing common-mode noise.SOLUTION: A noise suppression circuit NSC comprises: noise detection means 50 which detects common-mode noise in a propagation path including a power line PL1 connecting an AC power source 10 and a power conversion device 30 and outputs a detection signal; a switching circuit 67 to which the detection signal of the noise detection means 50 is inputted and which has a switched state where the inputted signal is outputted after switching a polarity of the signal and a non-switched state where the inputted signal is outputted without switching the polarity; and a compensation circuit 63 which outputs a compensation current or a compensation voltage to the propagation path on the basis of the signal which is outputted from the switching circuit 67. The switching circuit 67 is brought into one state, between the two states of the switched state and the non-switched state, where a magnitude of the detection signal of the noise detection means 50 is smaller than a case where the switching circuit is brought into the other state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to noise suppression circuits and the like. [Background technology]

[0002] Conventionally, a noise suppression technique has been known that reduces common mode noise by detecting the common mode noise and outputting a compensating current or voltage for the detected common mode noise to a path through which the common mode noise flows (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3044650 Summary of the Invention [Problem to be solved by the invention]

[0004] However, for example, with regard to common mode noise detection means, due to an error in the installation configuration during product manufacturing or part replacement, the polarity of the output detection signal may be reversed from the appropriate state, and as a result, common mode noise may not be properly suppressed based on the detection signal.

[0005] An object of the present disclosure is to provide a technique capable of appropriately suppressing common-mode noise. [Means for solving the problem]

[0006] In a first aspect of the present disclosure, a detection means for detecting common mode noise in a propagation path including a power line connecting the first electric device and the second electric device, and outputting a detection signal; a switching circuit that receives the detection signal or a signal derived from the detection signal, and has a first state in which the polarity of the input signal is switched and output, and a second state in which the polarity of the input signal is not switched and output; a compensation circuit that outputs a compensation current or a compensation voltage to the propagation path based on the signal output from the switching circuit, the switching circuit is in one of the two states, the first state and the second state, in which the magnitude of the detection signal or the signal derived from the detection signal is smaller than in the other state; A noise suppression circuit is provided.

[0007] According to this aspect, the noise suppression circuit can use the switching circuit to switch the polarity of the signal transmitted from the detection means to the compensation circuit. Therefore, for example, if the noise detection means is installed incorrectly during manufacturing of the noise suppression circuit or component replacement, causing the polarity of the detection signal from the noise suppression circuit to be reversed from its normal state, the switching circuit can be used to switch the polarity of the detection signal to an appropriate state. Therefore, the noise suppression circuit can automatically achieve an appropriate polarity for the signal transmitted from the detection means to the compensation circuit, thereby appropriately suppressing common-mode noise.

[0008] In addition, in a second aspect of the present disclosure, based on the first aspect described above, a determination circuit that determines whether the magnitude of the detection signal or a signal derived from the detection signal is greater than a predetermined threshold; The determination circuit may switch the switching circuit to the other of the first state and the second state when the magnitude of the detection signal when the switching circuit is in either the first state or the second state, or a signal derived from the detection signal, is greater than the predetermined threshold.

[0009] Furthermore, in a third aspect of the present disclosure, based on the second aspect described above, The predetermined threshold may be equal to or greater than the magnitude of the detection signal or a signal derived from the detection signal when the compensation circuit is in a stopped state.

[0010] Furthermore, in a fourth aspect of the present disclosure, based on the first aspect described above, a determination circuit that determines whether the magnitude of the detection signal or a signal derived from the detection signal is larger or smaller when the switching circuit is in the first state or when the switching circuit is in the second state; After being set to each of the first state and the second state, the switching circuit may, based on the judgment result of the judgment circuit, set to one of the two states, the first state and the second state, in which the magnitude of the detection signal or a signal derived from the detection signal is smaller than in the other state.

[0011] In addition, in a fifth aspect of the present disclosure, on the premise of any one of the second to fourth aspects described above, The switching circuit may maintain the state of the switching circuit that is realized based on the determination result of the determination circuit.

[0012] In addition, in a sixth aspect of the present disclosure, on the premise of any one of the second to fifth aspects described above, The determination circuit may include an integrated circuit.

[0013] In addition, in a seventh aspect of the present disclosure, on the premise of any one of the first to seventh aspects described above, the detection means is formed of a magnetic material and includes a core through which a first electric wire included in the propagation path and a second electric wire for detecting the common mode noise pass, The core may be fixed to the first electric wire or the second electric wire.

[0014] In addition, in an eighth aspect of the present disclosure, on the premise of any one of the first to seventh aspects described above, a filter circuit that passes the detection signal and removes specific frequency components; an amplifier circuit that amplifies the signal output from the filter circuit, The compensation circuit may output the compensation current or the compensation voltage based on the signal output from the amplifier circuit.

[0015] Furthermore, in a ninth aspect of the present disclosure, based on the eighth aspect described above, The signal derived from the detection signal may be a signal output from the filter circuit, a signal output from the amplifier circuit, or a signal representing the compensation current or the compensation voltage.

[0016] In addition, in a tenth aspect of the present disclosure, on the premise of any one of the first to ninth aspects described above, the first electric device or the second electric device is a power conversion device including a switching element, The switching element may be made of a wide bandgap semiconductor.

[0017] In addition, an eleventh aspect of the present disclosure is a noise suppression circuit including the noise suppression circuit according to any one of the first to tenth aspects. An air conditioner is provided. [Effects of the Invention]

[0018] According to the above-described embodiment, common mode noise can be appropriately suppressed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating an example of a power conversion system. [Figure 2] FIG. 2 is a diagram illustrating an example of a noise detection unit. [Figure 3] FIG. 2 is a diagram illustrating the function of a switching circuit. [Figure 4] FIG. 10 is a diagram showing an example of a power conversion system in which a noise detection means is installed in an incorrect form. [Figure 5]FIG. 2 is a diagram illustrating the noise level of common mode noise in the power conversion system. [Figure 6] 10 is a flowchart schematically illustrating a first example of a control process of a switching circuit. [Figure 7] 10 is a flowchart schematically illustrating a second example of the control process of the switching circuit. [Figure 8] FIG. 1 is a diagram illustrating an example of a refrigerant circuit of an air conditioner. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment will be described with reference to the drawings.

[0021] [Power conversion system configuration] The configuration of an example of a power conversion system 1 according to this embodiment will be described with reference to FIGS. 1 to 3. FIG.

[0022] Fig. 1 is a diagram showing an example of a power conversion system 1. Fig. 2 is a diagram showing an example of a noise detection means 50. Fig. 3 is a diagram explaining the function of a switching circuit 67.

[0023] As shown in FIG. 1, a power conversion system 1 drives a motor 20 using power supplied from an AC power supply 10.

[0024] The AC power supply 10 supplies AC current to the power conversion system 1. In this example, the AC power supply 10 supplies three-phase AC current, that is, R-phase, S-phase, and T-phase, to the power conversion system 1.

[0025] The motor 20 is driven by a three-phase AC current output from the power conversion system 1. The motor 20 is, for example, a DC (Direct Current) brushless motor. The motor 20 may also be a motor driven by another three-phase AC current.

[0026] The power conversion system 1 includes a power line PL1, a power line PL2, a power conversion device 30, a noise filter 40, and a noise suppression circuit NSC.

[0027] Power line PL1 is made up of three power lines of R phase, S phase, and T phase, and electrically connects AC power supply 10 and power conversion device 30. Power line PL1 includes power lines PL11 to PL13.

[0028] The power line PL2 electrically connects the power converter 30 and the motor 20 by three power lines of U-phase, V-phase, and W-phase.

[0029] Power line PL11 connects AC power supply 10 and coil 51 via three power lines of R phase, S phase, and T phase. Power line PL12 connects coil 51 and common mode choke coil 41 of noise filter 40 via three power lines of R phase, S phase, and T phase. Power line PL13 connects common mode choke coil 41 and power conversion device 30 via three power lines of R phase, S phase, and T phase.

[0030] The power conversion device 30 converts the AC supplied through the power line PL1 into three-phase AC of a predetermined frequency and a predetermined voltage, and outputs the converted AC to the motor 20 through the power line PL2, thereby driving the motor 20.

[0031] The power conversion device 30 includes a power conversion circuit 30C including a rectifier circuit 31 and an inverter circuit 32, and a control circuit 33, for example.

[0032] The rectifier circuit 31 converts three-phase AC of R phase, S phase, and T phase supplied through the power line PL13 into DC and outputs it to a DC link (also referred to as a "direct current link"). The rectifier circuit 31 is, for example, a three-phase full-wave rectifier circuit using diodes.

[0033] The inverter circuit 32 converts the direct current input from the DC link between the rectifier circuit 31 and itself into three-phase alternating current of a predetermined frequency and a predetermined voltage, specifically, U-phase, V-phase, and W-phase alternating current, and outputs the converted three-phase alternating current. The inverter circuit 32 includes, for example, switching elements, and converts the direct current into three-phase alternating current of a predetermined frequency and a predetermined voltage through the switching operation of the switching elements, and outputs the converted three-phase alternating current to the power line PL2.

[0034] The switching elements are, for example, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), HEMTs (High Electron Mobility Transistors), etc. The switching elements are, for example, mainly made of silicon (Si). The switching elements may also be mainly made of a wide bandgap semiconductor material. Examples of wide bandgap semiconductor materials include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and carbon (diamond: C). The inverter circuit 32 may also include, in addition to the switching elements, semiconductor freewheel diodes connected in parallel with the switching elements.

[0035] The control circuit 33 performs control processing related to the power conversion circuit 30C.

[0036] The control circuit 33 may also perform other processes related to the power conversion system 1.

[0037] For example, the control circuit 33 performs processing for diagnosing an abnormality in the active noise canceller 60 (hereinafter referred to as "abnormality diagnosis"). The abnormality diagnosis includes, for example, diagnosing the presence or absence of an abnormality. The abnormality diagnosis may also include diagnosing the presence or absence of signs of an abnormality and diagnosing the degree of the abnormality (degree of abnormality).

[0038] The functions of the control circuit 33 may be realized by only the hardware (circuit) of the hardware and software, or may be realized by a combination of hardware (for example, an integrated circuit (IC)) and software. In the latter case, for example, the control circuit 33 is mainly configured with a microcomputer including a CPU (Central Processing Unit), a memory device, an auxiliary storage device, an input / output interface, etc.

[0039] The noise filter 40 is a passive noise suppression means that suppresses common mode noise.

[0040] Common mode noise occurs in association with the switching operation of the switching elements of the inverter circuit 32. Specifically, common mode noise occurs when noise caused by the switching operation of the switching elements leaks to the ground GL through the stray capacitance of the motor 20 or the stray capacitance between the switching elements (not shown) of the power conversion device 30 and the heat sink.

[0041] The noise filter 40 includes a common mode choke coil 41 and a Y capacitor 42 .

[0042] The common mode choke coil 41 acts as an inductor to suppress a common mode noise current (common mode current) flowing through the power line PL1.

[0043] The Y capacitor 42 has a function of returning the common mode current that has flowed out to the ground GL to the inverter circuit 32, which is a noise source. One end of the Y capacitor 42 is connected to the power line PL13, and the other end is connected to the ground GL.

[0044] The ground GL is earthed, and is, for example, the housing of a device including the power conversion system 1. Alternatively, the ground GL may be a dedicated reference potential line.

[0045] The noise suppression circuit NSC is provided to suppress common mode noise flowing in a propagation path including the power lines PL1, PL2 and the ground GL. The noise suppression circuit NSC includes a noise detection means 50, an active noise canceller 60, and a drive power supply 70.

[0046] The noise detection means 50 detects a common mode noise current (common mode current) or a noise voltage (common mode voltage). For example, as shown in Fig. 1, the noise detection means 50 detects a common mode current in the power line PL1. For example, as shown in Fig. 1, the noise detection means 50 includes a primary side circuit including a coil 51 and a secondary side circuit including a coil 52.

[0047] The coils 51 are provided for the R-phase, S-phase, and T-phase of the power line PL1, respectively.

[0048] Coil 52 is provided so as to be magnetically coupled to coil 51. Coil 52 outputs a detection signal corresponding to the common mode noise on power line PL1.

[0049] Coils 51 and 52 are wound around core 53 (see FIG. 2) made of the same magnetic material, and are arranged to have opposite polarities, as indicated by the "·" in FIG. 1. Also, as shown in FIG. 2, coil 51 may be omitted, in which case core 53 is arranged so that a series of power lines PL11 and PL12 pass through its holes. For example, when current flows rightward in power lines PL11 and PL12 in FIG. 1, current flows leftward in coil 52. In other words, the polarity indicated by the "·" in FIG. 1 corresponds to the direction of current flow.

[0050] The magnetic core 53 is, for example, a toroidal core, and the magnetic material is, for example, ferrite or permilo. For example, the core 53 is not mounted on a substrate, but is fixed to the power lines PL11 and PL12 and the signal line SL1 extending from the coil 52 with a binding band or the like.

[0051] For example, when a common mode current flows through the power lines PL11 and PL12, a current proportional to the common mode current is induced in the coil 52. As a result, the noise detection means 50 including the coil 52 functions as a current detection transformer that detects the common mode current. The noise detection means 50 may also detect common mode noise in the ground GL.

[0052] The active noise canceller 60 is an active noise suppression means that suppresses common mode noise. The active noise canceller 60 outputs a compensation current or a compensation voltage for suppressing common mode noise to the power line PL1, the power line PL2, or the ground GL based on a detection signal output from the coil 52 of the noise detection means 50. The active noise canceller 60 includes a filter circuit 61, an amplifier circuit 62, a compensation circuit 63, an output unit 64, a power supply circuit 65, a coupling capacitor 66, a switching circuit 67, and a control circuit 68.

[0053] The filter circuit 61 passes a signal obtained by removing a specific frequency component from the detection signal output from the coil 52 , and the output signal of the filter circuit 61 is input to the amplifier circuit 62 .

[0054] The amplifier circuit 62 amplifies the signal output from the filter circuit 61. The amplifier circuit 62 includes an operational amplifier 621, for example.

[0055] The power supply voltage of the operational amplifier 621 is, for example, 2 / 3 or less of the DC link voltage (DC link voltage) Vdc of the power conversion circuit 30C. Because the voltage Vcom of the common-mode noise source (specifically, the potential of the neutral point of the motor 20 generated when the motor 20 is driven by the inverter circuit 32) changes by 1 / 3, if the power supply voltage of the operational amplifier 621 is within a range of ±1 / 3 of the DC link voltage Vdc, it is possible to cancel out the common-mode noise caused by the switching operation of the inverter circuit 32 without considering the relationship between the voltage Vcc and the impedance.

[0056] The signal output from the amplifier circuit 62 is a signal representing the waveform of a compensation current or a compensation voltage, and is input to the compensation circuit 63. The signal representing the waveform of a compensation current or a compensation voltage is a signal indicating the amplitude and phase for each frequency of the waveform of the compensation current or the compensation voltage output from the compensation circuit 63. For example, the signal representing the waveform of the compensation current or the compensation voltage output from the amplifier circuit 62 is a current or voltage waveform signal that has the same phase for each frequency as the waveform of the compensation current or the compensation current output from the compensation circuit 63, but has a smaller amplitude.

[0057] The compensation circuit 63 amplifies the signal output from the amplifier circuit 62 and outputs a compensation current or a compensation voltage. The compensation circuit 63 includes transistors Tr1 and Tr2 and diodes D1 and D2.

[0058] The transistor Tr1 is connected between one end of the drive power supply 70 and the output capacitor Co of the output section 64. The transistor Tr2 is connected between the other end of the drive power supply 70 and the output capacitor Co of the output section 64.

[0059] 1, in this example, the transistor Tr1 is a PNP type, the transistor Tr2 is an NPN type, and the transistors Tr1 and Tr2 have opposite polarities, so that the transistors Tr1 and Tr2 form a push-pull circuit, which functions as an amplifier.

[0060] The bases of the transistors Tr1 and Tr2 are connected to one end of the coil 52 via the amplifier circuit 62 and the filter circuit 61, and the interconnection point of the transistors Tr1 and Tr2 is connected to the other end of the coil 52 via the amplifier circuit 62 and the filter circuit 61. This causes the transistors Tr1 and Tr2 to operate in opposite directions.

[0061] Diodes D1 and D2 are connected in antiparallel to the transistors Tr1 and Tr2, respectively, to protect them.

[0062] The output unit 64 connects the compensation circuit 63 and the ground GL, and outputs (also referred to as "injecting") the compensation current or compensation voltage output from the compensation circuit 63 to a path through which the common mode current flows. The output unit 64 includes an output capacitor Co.

[0063] One end of the output capacitor Co is connected to the interconnection point of the transistors Tr1 and Tr2 of the compensation circuit 63, and the other end is connected to the ground GL.

[0064] The power supply circuit 65 is connected to a drive power supply 70. The power supply circuit 65 includes capacitors C1 and C2.

[0065] The capacitors C1 and C2 are connected in series. The series connection of the capacitors C1 and C2 is connected in parallel with the driving power supply 70 and the compensation circuit 63. The midpoint between the capacitors C1 and C2 is connected to the coupling capacitor 66.

[0066] Coupling capacitor 66 has one end connected to power line PL12 and the other end connected to the midpoint between capacitors C1 and C2.

[0067] The switching circuit 67 is provided on a signal line connecting the coil 52 of the noise detection means 50 and the filter circuit 61. The switching circuit 67 can switch the polarity of the detection signal input from the noise detection means 50 to the filter circuit 61. As in the case of the noise detection means 50, the polarity of the detection signal is a polarity that corresponds to the direction of current flow.

[0068] 3, the switching circuit 67 can switch the polarity of the detection signal between a signal line SL1 connected to the output side of the noise detection means 50 and a signal line SL2 connected to the input side of the filter circuit 61. Specifically, the switching circuit 67 has a state (non-switching state) in which the polarity of the detection signal is not switched between the signal lines SL1 and SL2 as shown in Fig. 3A, and a state (switching state) in which the polarity of the detection signal is switched between the signal lines SL1 and SL2 as shown in Fig. 3B.

[0069] The signal line SL1 includes a pair of signal lines SL11 and SL12, and the signal line SL2 includes a pair of signal lines SL21 and SL22.

[0070] As shown in FIG. 3A, in the non-switching state, the switching circuit 67 connects the signal lines SL11 and SL21 and also connects the signal lines SL12 and SL22.

[0071] On the other hand, as shown in FIG. 3B, in the switched state, the switching circuit 67 connects the signal line SL11 to the signal line SL22 and also connects the signal line SL12 to the signal line SL21.

[0072] The switching operation of the switching circuit 67 between the two states (that is, the non-switching state and the switching state) may be performed by an external control command or may be performed manually by a human being.

[0073] The control circuit 68 performs control processing related to the active noise canceller 60 .

[0074] The control circuit 68 may also perform processing for diagnosing abnormalities in the active noise canceller 60.

[0075] The functions of the control circuit 68 may be realized by only the hardware (circuit) of the hardware and software, or may be realized by a combination of hardware (e.g., an integrated circuit) and software. In the latter case, for example, the control circuit 68 is mainly configured with a microcomputer including a CPU, a memory device, an auxiliary storage device, an input / output interface, etc. Furthermore, instead of or in addition to a microcomputer, the control circuit 68 may include an integrated circuit of a different type from the microcomputer, such as a comparator.

[0076] The driving power supply 70 supplies DC driving power to the active noise canceller 60 .

[0077] The driving power supply 70 may be a DC power supply that can supply DC to the active noise canceller 60 on its own, or may be, for example, a capacitor that uses the DC voltage of the DC link between the rectifier circuit 31 and the inverter circuit 32 of the power conversion circuit 30C as its power source.

[0078] [Active noise canceller operation] Next, still referring to FIG. 1, the operation of the active noise canceller 60 will be described.

[0079] In the following, for simplicity, the present example will be described ignoring the effect of the noise filter 40 in suppressing the common mode current Ic.

[0080] The noise detection means 50 detects common mode noise on the power line PL1 and drives the transistors Tr1 and Tr2 via a filter circuit 61 and an amplifier circuit 62. Specifically, when a detection signal output from the coil 52 of the noise detection means 50 is input to the bases of the transistors Tr1 and Tr2 via the filter circuit 61 and the amplifier circuit 62, the detection signal is amplified by the transistors Tr1 and Tr2.

[0081] 1, the transistor Tr1 is turned on. In this case, the compensation current Io is supplied from the drive power supply 70 and flows through a path that connects the positive terminal of the drive power supply 70 to the negative terminal of the drive power supply 70 via the capacitor C2, the coupling capacitor 66, the AC power supply 10, the output capacitor Co, and the transistor Tr1. As a result, the compensation current Io is subtracted from the common mode current Ic, and a reduced common mode current Ig flows through the AC power supply 10.

[0082] Furthermore, when the common mode current Ic flows in the direction opposite to the direction of the arrow in Fig. 1, the transistor Tr2 is turned on. In this case, the compensation current Io is supplied from the drive power supply 70 and flows through a current path that connects the positive terminal of the drive power supply to the negative terminal of the drive power supply 70, via the transistor Tr2, the output capacitor Co, the AC power supply 10, the coupling capacitor 66, and the capacitor C1. In other words, the compensation current Io flows in the direction opposite to the direction of the arrow in Fig. 1. As a result, the compensation current Io is subtracted from the common mode current Ic, and a reduced common mode current Ig flows in the direction opposite to the direction of the arrow in Fig. 1 to the AC power supply 10.

[0083] As described above, the compensation current Io flows through the compensation circuit 63. Therefore, the current supplied from the driving power supply 70 when the compensation current or compensation voltage is output is larger in the compensation circuit 63 than in the amplifier circuit 62.

[0084] In this way, the active noise canceller 60 outputs the compensation current Io to the path through which the common mode current Ic flows, thereby suppressing the common mode current Ig flowing through the AC power supply 10. Therefore, for example, the active noise canceller 60 can prevent a situation in which a common mode noise current flows out to a peripheral device through the AC power supply 10 and affects the device.

[0085] [Switching circuit function] Next, the operation of the switching circuit 67 will be described with reference to FIGS.

[0086] Fig. 4 is a diagram showing an example of the power conversion system 1 when the noise detection means 50 is attached in an incorrect form. Fig. 5 is a diagram for explaining the level of common mode noise in the power conversion system 1.

[0087] Specifically, FIG. 4 shows a state in which the noise detection means 50 is attached in the wrong form in the power conversion system 1 of FIG. 1, and the polarity of the coil 52 is reversed from that in FIG.

[0088] 2, if the power lines PL1, PL2 are inserted incorrectly into the core 53 around which the coil 52 is wound during the manufacture of the power conversion system 1, the polarity of the coil 52 will be reversed. Also, if the core 53 is removed during maintenance of the power conversion system 1 and then reassembled in the same incorrect manner as described above after the maintenance is completed, the polarity of the coil 52 will be reversed.

[0089] As shown in FIG. 4, when the polarity of the coil 52 is reversed, the polarity of the compensation current or compensation voltage output from the compensation circuit 63 based on the detection signal output from the coil 52 is reversed.

[0090] When the polarity of the coil 52 is normal, the operation of the active noise canceller 60 causes a compensation current or compensation voltage that is opposite in phase to the common mode noise to be output to a path including the power lines PL1, PL2 and the ground GL. Therefore, as shown in Fig. 5, the operation of the active noise canceller 60 reduces the level of the common mode noise (see the dashed line in the figure) compared to when the active noise canceller 60 is not operating (see the solid line in the figure).

[0091] On the other hand, if the polarity of the coil 52 is abnormal, that is, if the polarity of the coil 52 is reversed, a compensation current or compensation voltage in phase with the common mode noise is output to the path including the power lines PL1, PL2 and the ground GL. Therefore, as shown in Fig. 5, when the active noise canceller 60 is operating, the level of the common mode noise actually increases compared to when the active noise canceller 60 is not operating, and there is a possibility that the noise will eventually diverge.

[0092] In response to this, the switching circuit 67 can switch the polarity of the detection signal from the coil 52 and transmit it to the filter circuit 61. Therefore, if the polarity of the coil 52 is reversed from an expected normal state, the polarity of the detection signal transmitted to the filter circuit 61 can be switched to the normal state by switching the switching circuit 67 from a non-switching state to a switching state. Therefore, the active noise canceller 60 can appropriately suppress common-mode noise using the switching circuit 67 even if the polarity of the coil 52 is abnormal.

[0093] In particular, common mode noise is a high-frequency signal and does not have the regularity of harmonics, etc., so it is difficult to employ a configuration that uses a microcomputer or the like to detect an abnormality in the polarity of the signal detected by the noise detection means 50 and compensate for the abnormality. In contrast, in this example, by using the switching circuit 67, it is possible to appropriately deal with abnormalities in the polarity of the signal detected by the noise detection means 50.

[0094] [First example of control processing for switching circuits] Next, a first example of the control process of the switching circuit 67 will be described with reference to FIG.

[0095] FIG. 6 is a flowchart schematically showing a first example of the control process of the switching circuit 67.

[0096] The flowchart of Fig. 6 is executed, for example, in the inspection process prior to product shipment of a device (for example, an air conditioner 100 described below) that incorporates the power conversion system 1. Furthermore, the flowchart of Fig. 6 is executed, for example, when a flag indicating that maintenance has been performed is registered in the control circuit 68 during maintenance of the active noise canceller 60, and the active noise canceller 60 is started up for the first time after the flag is registered. Furthermore, the flowchart of Fig. 6 may be executed each time the active noise canceller 60 is started up.

[0097] As shown in FIG. 6, in step S102, the control circuit 68 acquires the latest detection signal S output from the noise detection means 50 to the signal line SL1 through a predetermined communication line branching off from the signal line SL1.

[0098] When the process of step S102 is completed, the control circuit 68 proceeds to step S104.

[0099] In step S104, the control circuit 68 determines whether the magnitude of the detection signal S exceeds a predetermined threshold value Sth (>0).

[0100] The threshold value Sth is set as a lower limit value of the magnitude of the detection signal S, which indicates that the common mode noise is actually increasing due to the operation of the active noise canceller 60. For example, the threshold value Sth is set to be equal to or greater than the maximum value Smax (see FIG. 5) of the magnitude of the common mode noise in the path including the power lines PL1, PL2 and the ground GL when the active noise canceller 60 is not operating. This allows the control circuit 68 to determine that the common mode noise is actually increasing due to the operation of the active noise canceller 60 when the magnitude of the detection signal S exceeds the threshold value Sth.

[0101] If the magnitude of the detection signal S exceeds the threshold value Sth, the control circuit 68 proceeds to step S106, and if the magnitude of the detection signal S does not exceed the threshold value Sth, the control circuit 68 ends the processing of this flowchart.

[0102] In step S106, the control circuit 68 switches the state of the switching circuit 67 from one of the non-switching state and the switching state (ie, the current state) to the other state.

[0103] For example, if the polarity of the coil 52 is abnormal, the switching circuit 67 is switched from the non-switching state to the switching state. Furthermore, for example, if the polarity of the coil 52 is abnormal during manufacturing of a device including the power conversion system 1 and the switching circuit 67 is switched to the switching state, and then the polarity of the coil 52 is returned to the normal state during maintenance, the switching circuit 67 is switched from the switching state to the non-switching state.

[0104] When the process of step S106 is completed, the control circuit 68 ends the process of this flowchart.

[0105] The state of the switching circuit 67 achieved by the processing of this flowchart is maintained until the next execution of the processing of this flowchart.

[0106] In this way, the control circuit 68 operates so that the switching circuit 67 is in one of the two states, the non-switching state and the switching state, where the magnitude of the detection signal S is smaller than when the other state is assumed. Specifically, when the magnitude of the detection signal S exceeds the threshold value Sth, the control circuit 68 switches from the current state to the other of the two states, the non-switching state and the switching state. This allows the active noise canceller 60 to appropriately suppress common-mode noise even when an abnormality in the polarity of the coil 52 occurs due to an incorrect installation form of the noise detection means 50, etc.

[0107] Also, in this example, the control circuit 68 can maintain the appropriate state of the implemented switching circuit 67 .

[0108] [Second example of control processing for switching circuits] Next, a second example of the control process of the switching circuit 67 will be described with reference to FIG.

[0109] FIG. 7 is a flowchart schematically showing a second example of the control process of the control circuit 68.

[0110] The flowchart of Fig. 7 is executed, for example, in the inspection process prior to product shipment of a device (for example, an air conditioner 100 described below) incorporating the power conversion system 1. Furthermore, the flowchart of Fig. 7 is executed, for example, when a flag indicating that maintenance has been performed is registered in the control circuit 68 during maintenance of the active noise canceller 60, and the active noise canceller 60 is started up for the first time after the flag is registered. Furthermore, the flowchart of Fig. 7 may also be executed each time the active noise canceller 60 is started up.

[0111] As shown in FIG. 7, in step S202, the control circuit 68 acquires the latest detection signal S1 output from the noise detection means 50 to the signal line SL1 through a predetermined communication line branching off from the signal line SL1.

[0112] When the process of step S202 is completed, the control circuit 68 proceeds to step S204.

[0113] In step S204, the control circuit 68 switches the state of the switching circuit 67 from one of the non-switching state and the switching state (ie, the current state) to the other state.

[0114] When the process of step S204 is completed, the control circuit 68 proceeds to step S206.

[0115] In step S206, the control circuit 68 acquires the latest detection signal S2 output from the noise detection means 50 to the signal line SL1 through a predetermined communication line branching off from the signal line SL1.

[0116] When the process of step S206 is completed, the control circuit 68 proceeds to step S208.

[0117] In step S208, the control circuit 68 determines whether the magnitude of the detection signal S2 acquired in step S206 is greater than the magnitude of the detection signal S1 acquired in step S202. If the magnitude of the detection signal S2 is greater than the magnitude of the detection signal S1, the control circuit 68 proceeds to step S210, and if the magnitude of the detection signal S2 is not greater than the magnitude of the detection signal S1, the control circuit 68 ends this flow chart.

[0118] In step S210, the control circuit 68 switches the state of the switching circuit 67 from the other state (i.e., the current state) after switching by the processing of step S204, between the non-switching state and the switching state, to one state before switching by the processing of step S204.

[0119] In other words, the control circuit 68 returns the state of the switching circuit 67 to the state before the switching in the processing of step S204. The fact that the magnitude of the detection signal S2 is greater than the magnitude of the detection signal S1 indicates that the switching of the switching circuit 67 in the processing of step S204 has actually increased the common mode noise.

[0120] When the process of step S210 is completed, the control circuit 68 ends the process of this flowchart.

[0121] The state of the switching circuit 67 achieved by the processing of this flowchart is maintained until the next execution of the processing of this flowchart.

[0122] In this way, as in the first example described above, the control circuit 68 operates so that the switching circuit 67 is in one of the two states, the non-switching state and the switching state, where the magnitude of the detection signal S is smaller than in the other state. Specifically, in this example, the control circuit 68 compares the magnitude relationship of the detection signals S (specifically, the detection signals S1, S2) corresponding to the non-switching state and the switching state of the switching circuit 67. Then, the control circuit 68 operates so that the switching circuit 67 is in one of the two states, the switching state and the non-switching state, where the magnitude of the detection signal S is smaller than in the other state. This allows the active noise canceller 60 to appropriately suppress common-mode noise even if an abnormality in the polarity of the coil 52 occurs due to an incorrect installation form of the noise detection means 50, etc.

[0123] Also, in this example, the control circuit 68 can maintain the appropriate state of the implemented switching circuit 67, similar to the first example described above.

[0124] [Other examples of power conversion systems] Next, another example of the power conversion system 1 will be described.

[0125] The configuration, operation, etc. of the power conversion system 1 according to the above-described embodiment may be modified or changed as appropriate. Hereinafter, examples in which the configuration, operation, etc. of the power conversion system 1 according to the above-described embodiment are modified or changed will be referred to as "variant examples" for convenience.

[0126] For example, in the power conversion system 1 of the above-described embodiment, the AC power supply 10 may supply single-phase AC to the power conversion system 1 instead of three-phase AC.

[0127] Furthermore, in the power conversion system 1 of the above-described embodiment and its modified examples, the power conversion circuit 30C may have a smoothing circuit provided in a DC link between the rectifier circuit 31 and the inverter circuit 32, including a smoothing capacitor, a smoothing inductor, etc.

[0128] Furthermore, in the power conversion system 1 of the above-described embodiment and its modified examples, the functions of the control circuit 33 may be realized by a plurality of circuits. For example, among the functions of the control circuit 33, the function of performing processing for diagnosing an abnormality in the active noise canceller 60 may be realized by a diagnostic circuit separate from the control circuit 33. Furthermore, some or all of the functions of the control circuit 33 may be transferred to an external device outside the power conversion device 30.

[0129] In the power conversion system 1 of the above-described embodiment and its modified examples, the noise filter 40 may be omitted.

[0130] Furthermore, in the power conversion system 1 of the above-described embodiment and its modified examples, the noise detection means 50 may apply a known method (see, for example, Japanese Patent No. 5528543 and Japanese Patent No. 7309067) to detect common mode noise via a capacitor.

[0131] In the power conversion system 1 of the above-described embodiment and its modified examples, the noise detection means 50 may include the function of the filter circuit 61. In this case, the filter circuit 61 is omitted, and the filter circuit in the noise detection means 50 outputs a detection signal from which specific frequency components have been removed, and the detection signal is input to an operational amplifier or the like of the amplification circuit 62.

[0132] In the power conversion system 1 of the above-described embodiment and its modified examples, the filter circuit 61 may be omitted. In this case, the detection signal output from the noise detection means 50 is input to the operational amplifier 621 of the amplifier circuit 62 via the switching circuit 67.

[0133] Furthermore, in the power conversion system 1 of the above-described embodiment and its modifications, the function of the amplifier circuit 62 may be realized by a microcomputer. In this case, the amplifier circuit 62 is omitted, and the detection signal of the noise detection means 50 or the signal output from the filter circuit 61 is input to the microcomputer. The microcomputer then generates a signal representing the waveform of a compensation current or a compensation voltage based on the input signal, and inputs the signal to the compensation circuit 63. For example, a microcomputer included in the control circuit 68 instead of the amplifier circuit 62, or provided separately from the control circuit 68, outputs a signal representing the waveform of a compensation current or a compensation voltage based on the detection signal of the noise detection means 50 or the signal output from the filter circuit 61.

[0134] Furthermore, in the power conversion system 1 of the above-described embodiment and its modifications, the function of the amplifier circuit 62 may be transferred to outside the active noise canceller 60. In this case, the amplifier circuit 62 is omitted. For example, a detection signal from the noise detection means 50 or a signal output from the filter circuit 61 is input to the control circuit 33 of the power conversion device 30 via a predetermined communication line. Then, the control circuit 33 generates a signal representing the waveform of a compensation current or a compensation voltage based on the input signal and transmits it to the active noise canceller 60 via the predetermined communication line. The signal representing the waveform of the compensation current or the compensation voltage is input to the compensation circuit 63.

[0135] In the power conversion system 1 of the above-described embodiment and its modifications, the diodes D1 and D2 of the compensation circuit 63 may be omitted.

[0136] In the power conversion system 1 of the above-described embodiment and its modified examples, either the amplifier circuit 62 or the compensation circuit 63 may be omitted.

[0137] In the power conversion system 1 of the above-described embodiment and its modified examples, the output unit 64 may have, in addition to the output capacitor Co, a resistor connected in series thereto.

[0138] In the power conversion system 1 of the above-described embodiment and its modified examples, the output capacitor Co of the output unit 64 may be omitted. In this case, the output unit 64 may connect the compensation circuit 63 to the ground GL via a resistor, or may connect the compensation circuit 63 directly to the ground GL.

[0139] In the power conversion system 1 of the above-described embodiment and its modifications, the output unit 64 may be configured to output a compensation current or a compensation voltage to the power line PL12.

[0140] Furthermore, in the power conversion system 1 of the above-described embodiment and its variations, the output unit 64 may apply a known method (see, for example, Japanese Patent No. 5528543 or Japanese Patent No. 7309067) to output a compensation current or a compensation voltage to the power line PL1 by magnetic coupling. In this case, the output unit 64 includes a primary coil that is magnetically coupled to a harness corresponding to the power line PL1 or the ground GL, and a toroidal core around which the primary coil is wound, and the harness corresponding to the power line PL1 or the ground GL is inserted into the toroidal core. Furthermore, the harness corresponding to the power line PL1 or the ground GL may have a coil wound around the toroidal core.

[0141] Furthermore, in the power conversion system 1 of the above-described embodiment and its modified examples, the switching circuit 67 may be transferred to the signal line between the filter circuit 61 and the amplifier circuit 62, or the signal line between the amplifier circuit 62 and the compensation circuit 63.

[0142] Furthermore, in the power conversion system 1 of the above-described embodiment and its modifications, the control circuit 68 may use the magnitude of a signal derived from the detection signal S instead of the detection signal S output from the noise detection means 50 in the control processing of the switching circuit 67. The signal derived from the detection signal S includes, for example, a signal output from the filter circuit 61, a signal output from the amplifier circuit 62, a signal representing a compensation current or a compensation voltage output from the compensation circuit 63, and a signal representing a compensation current or a compensation voltage output from the output unit 64. The signal representing a compensation current or a compensation voltage does not include the compensation current or the compensation voltage itself, but includes, for example, a signal obtained by converting the compensation current or the compensation voltage into a voltage equivalent to a low current.

[0143] Furthermore, in the power conversion system 1 of the above-described embodiment and its modifications, the active noise canceller 60 may be provided so that the compensation current Io flows between the DC link of the power conversion circuit 30C and ground GL. For example, as described above, when the driving power supply 70 uses the DC voltage of the DC link of the power conversion circuit 30C, the compensation current Io flows between the DC link and ground GL through the power path. In this case, the noise detection means 50 may be provided so as to detect common-mode noise on the power line PL1, or so as to detect common-mode noise in the DC link of the power conversion circuit 30C.

[0144] Furthermore, in the power conversion system 1 of the above-described embodiment and its modifications, the active noise canceller 60 may be provided so that compensation current Io flows between the power line PL2 between the power conversion device 30 and the motor 20 and the ground GL. For example, one end of the coupling capacitor 66 is connected to each of the U-phase, V-phase, and W-phase power lines of the power line PL2. In this case, the noise detection means 50 may be provided so as to detect common mode noise on the power line PL1 or so as to detect common mode noise on the power line PL2.

[0145] In the power conversion system 1 of the above-described embodiment and its modified examples, the driving power supply 70 may be included in the active noise canceller 60.

[0146] [Application example of power conversion system] Next, an application example of the power conversion system 1 according to this embodiment will be described with reference to Fig. 8. Specifically, an air conditioner 100 in which the power conversion system 1 according to this embodiment is installed will be described.

[0147] FIG. 8 is a diagram showing an example of a refrigerant circuit of the air conditioner 100. As shown in FIG.

[0148] 1, the air conditioner 100 includes an outdoor unit 110, an indoor unit 120, and refrigerant paths 130 and 140. The air conditioner 100 operates a refrigeration cycle made up of the outdoor unit 110, the indoor unit 120, the refrigerant paths 130 and 140, etc., to adjust the temperature, humidity, etc., of the room in which the indoor unit 120 is installed.

[0149] The outdoor unit 110 is placed outside a building whose temperature and other conditions are to be adjusted. The outdoor unit 110 is connected to one end of each of the refrigerant paths 130 and 140, and draws in the refrigerant from one of the refrigerant paths 130 and 140 and discharges the refrigerant to the other.

[0150] The indoor unit 120 is placed in a room of a building where the temperature, etc., is to be adjusted. The indoor unit 120 is connected to the other end of each of the refrigerant paths 130, 140, and draws in refrigerant from one of the refrigerant paths 130, 140 and discharges the refrigerant to the other.

[0151] The refrigerant paths 130, 140 are configured by, for example, pipes, and connect the outdoor unit 110 and the indoor unit 120 so that the refrigerant can circulate between the outdoor unit 110 and the indoor unit 120.

[0152] The outdoor unit 110 includes refrigerant paths L1 to L6, oil paths L7 and L8, a four-way switching valve 111, an accumulator 112, a compressor 113, an oil separator 114, an outdoor heat exchanger 115, an outdoor expansion valve 116, and a fan 117.

[0153] The refrigerant paths L1 to L6 are configured as, for example, pipes.

[0154] The refrigerant path L1 connects one end of the refrigerant path 130 outside the outdoor unit 110 to the four-way switching valve 111.

[0155] The refrigerant path L2 connects the four-way switching valve 111 and the inlet of the compressor 113. The refrigerant path L2 includes refrigerant paths L21 and L22.

[0156] The refrigerant path L21 connects the four-way switching valve 111 and the accumulator 112. The refrigerant path L22 connects the accumulator 112 and the inlet of the compressor 113.

[0157] The refrigerant path L3 connects the four-way switching valve 111 and the outlet of the compressor 113. The refrigerant path L3 includes refrigerant paths L31 and L32.

[0158] The refrigerant path L31 connects the outlet of the compressor 113 and the oil separator 114. The refrigerant path L32 connects the four-way switching valve 111 and the oil separator 114.

[0159] The refrigerant path L4 connects the four-way switching valve 111 and the outdoor heat exchanger 115.

[0160] The refrigerant path L5 connects the outdoor heat exchanger 115 and the outdoor expansion valve 116.

[0161] The refrigerant path L6 connects one end of the refrigerant path 140 outside the outdoor unit 110 to the outdoor expansion valve 116.

[0162] The oil path L7 is configured as, for example, a pipe line, and is used to allow the oil separated by the oil separator 114 to flow into the refrigerant path L22 and return the oil to the compressor 113 through the refrigerant path L22.

[0163] Note that the oil passing through the oil path L7 may contain, for example, a liquid-phase refrigerant (hereinafter referred to as "liquid refrigerant") dissolved therein. That is, not only oil but also liquid refrigerant flows through the oil path L7.

[0164] The oil path L8 is configured as, for example, a pipe line, and is used to allow oil containing liquid refrigerant separated by the accumulator 112 to flow into the refrigerant path L22 and return it to the compressor 113 through the refrigerant path L22.

[0165] The four-way switching valve 111 reverses the flow of circulating refrigerant when the air conditioner 100 is in cooling operation and when it is in heating operation.

[0166] During cooling operation of the air conditioner 100, the four-way switching valve 111 connects the paths indicated by the solid lines in Fig. 1. Specifically, during cooling operation of the air conditioner 100, the four-way switching valve 111 connects refrigerant path L1 and refrigerant path L2, and refrigerant path L3 and refrigerant path L4.

[0167] On the other hand, when the air conditioner 100 is in heating operation, the four-way switching valve 111 connects the paths indicated by the dotted lines in Fig. 1. Specifically, when the air conditioner 100 is in heating operation, the four-way switching valve 111 connects the refrigerant path L4 to the refrigerant path L2, and the refrigerant path L1 to the refrigerant path L3.

[0168] The accumulator 112 separates the liquid refrigerant contained in the refrigerant drawn from the refrigerant path L21, and discharges the refrigerant from which some or all of the liquid refrigerant has been removed to the refrigerant path L22. The liquid refrigerant separated in the accumulator 112 contains oil. The accumulator 112 is provided with an oil discharge port connected to the oil path L8, and the separated oil containing the refrigerant flows out through the oil discharge port into the oil path L8 and is returned to the compressor 113 through the oil path L8 and the refrigerant path L22.

[0169] The compressor 113 is driven by the motor 20, draws in refrigerant from the refrigerant path L22, compresses it to high pressure, and discharges it to the refrigerant path L31. In this way, the power conversion system 1 can control the operation of the compressor 113 by driving the motor 20.

[0170] During cooling operation of the air conditioner 100, high-temperature, high-pressure refrigerant compressed by the compressor 113 flows into the outdoor heat exchanger 115 via refrigerant paths L3 and L4.

[0171] On the other hand, during heating operation of the air conditioner 100, the high-temperature, high-pressure refrigerant compressed by the compressor 113 flows through refrigerant path L3 and refrigerant path L1 into refrigerant path 130 outside the outdoor unit 110. Then, the high-temperature, high-pressure refrigerant flows into the indoor unit 120 through refrigerant path 130.

[0172] The oil separator 114 separates oil from the refrigerant flowing in from the refrigerant path L31, and discharges the refrigerant from which some or all of the oil has been separated and removed into the refrigerant path L32. The oil separator 114 is also provided with an oil outlet connected to the oil path L7, and the oil separated from the refrigerant flows into the oil path L7 through the oil outlet and is returned to the compressor 113 through the oil path L7 and the refrigerant path L22.

[0173] The outdoor heat exchanger 115 exchanges heat between the outside air and the refrigerant passing through the interior thereof. Specifically, the outdoor heat exchanger 115 is provided with a fan 117, and the outdoor heat exchanger 115 exchanges heat between the outside air blown by the fan 117 and the refrigerant flowing through the interior thereof.

[0174] During cooling operation of the air conditioner 100, the outdoor heat exchanger 115 causes the high-temperature, high-pressure refrigerant compressed by the compressor 113, which flows in from the refrigerant path L4, to radiate heat to the outside air, and causes the condensed and liquefied refrigerant (liquid refrigerant) to flow out into the refrigerant path L5.

[0175] Furthermore, during heating operation of the air conditioner 100, the outdoor heat exchanger 115 causes the low-temperature, low-pressure liquid refrigerant flowing in from the refrigerant path L5 to absorb heat from the outside air, and causes the evaporated refrigerant to flow into the refrigerant path L4.

[0176] The outdoor expansion valve 116 is closed to a predetermined degree during heating operation of the air conditioner 100, and reduces the pressure of the refrigerant (liquid refrigerant) flowing in from refrigerant path L6 to a predetermined level. On the other hand, during cooling operation of the air conditioner 100, the outdoor expansion valve 116 is fully open, and allows the refrigerant (liquid refrigerant) to pass from refrigerant path L5 to refrigerant path L6. The outdoor expansion valve 116 is, for example, a solenoid valve.

[0177] The indoor unit 120 includes an indoor expansion valve 121 , an indoor heat exchanger 122 , and a fan 123 .

[0178] During cooling operation of the air conditioner 100, the indoor expansion valve 121 is closed to a predetermined opening degree and reduces the pressure of the supercooled liquid refrigerant flowing in from the refrigerant path 140 to a predetermined pressure. On the other hand, during heating operation of the air conditioner 100, the indoor expansion valve 121 is fully open and allows the refrigerant (liquid refrigerant) flowing out from the indoor heat exchanger 122 to pass toward the refrigerant path 140. The indoor expansion valve 121 is, for example, a solenoid valve.

[0179] The indoor heat exchanger 122 exchanges heat between the indoor air and the refrigerant passing through it. Specifically, the action of the fan 123 mounted in the indoor unit 120 causes the indoor air to pass around the indoor heat exchanger 122, promoting heat exchange with the refrigerant inside the indoor heat exchanger 122. Then, the action of the fan 123 causes the indoor air that has exchanged heat with the refrigerant inside the indoor heat exchanger 122 to be sent out of the indoor unit 120, thereby realizing cooling or heating of the room.

[0180] When the air conditioner 100 is in cooling operation, the indoor heat exchanger 122 causes the low-temperature, low-pressure liquid refrigerant decompressed by the indoor expansion valve 121 to absorb heat from the indoor air, thereby lowering the temperature of the indoor air.

[0181] On the other hand, during heating operation of the air conditioner 100, the indoor heat exchanger 122 causes the high-temperature, high-pressure refrigerant flowing in from the outdoor unit 110 through the refrigerant path 130 to radiate heat to the indoor air, thereby raising the temperature of the indoor air.

[0182] In this way, in this example, the power conversion system 1 according to this embodiment is applied to the air conditioner 100 by being mounted on the air conditioner 100.

[0183] The power conversion system 1 according to this embodiment may be applied to a refrigeration device other than the air conditioner 100.

[0184] [Operation of noise suppression circuit and air conditioner] Next, the operation of the noise suppression circuit and the air conditioner according to this embodiment will be described.

[0185] In a first aspect of this embodiment, the noise suppression circuit includes a detection means, a switching circuit, and a compensation circuit. The noise suppression circuit is, for example, the noise suppression circuit NSC described above. The detection means is, for example, the noise detection means 50 described above. The switching circuit is, for example, the switching circuit 67 described above. The compensation circuit is, for example, the compensation circuit 63 described above. Specifically, the detection means detects common-mode noise in a propagation path including a power line connecting a first electric device and a second electric device, and outputs a detection signal. The first electric device is, for example, the AC power supply 10 described above. The second electric device is, for example, the power conversion system 1 described above. The power line is, for example, the power line PL1 described above. The propagation path is, for example, a path including the power lines PL1 and PL2 described above and a ground GL. The switching circuit has a first state in which the detection signal or a signal derived from the detection signal is input, and outputs the input signal with the polarity switched, and a second state in which the input signal is output without switching the polarity. The compensation circuit outputs a compensation current or a compensation voltage to the propagation path based on the signal output from the switching circuit.

[0186] This allows the noise suppression circuit to use the switching circuit to switch the polarity of the signal transmitted from the detection means to the compensation circuit. Therefore, for example, if the noise detection means is installed in an incorrect configuration during manufacturing of the noise suppression circuit or during component replacement, causing the polarity of the detection signal from the noise suppression means to be reversed from its normal state, the switching circuit can be used to switch the polarity of the detection signal to the appropriate state. As a result, the noise suppression circuit can appropriately suppress common-mode noise.

[0187] More specifically, the switching circuit may be in one of the two states, the first state and the second state, where the magnitude of the detection signal or a signal derived from the detection signal is smaller than that in the other state. In this case, "becoming in the . . . state" means that such a state is not realized naturally but is intentionally realized by the noise suppression circuit. Therefore, "becoming in the . . . state" is a concept that includes not only the case where the switching circuit itself operates to achieve such a state, but also the case where the switching circuit itself is in such a state as an initial state and maintains such a state based on the operation of other elements. For example, in the above-described embodiment, when a switching decision is made using the threshold value Sth, it is clear that the magnitude of the detection signal S in the state after switching from one state to the other state when the magnitude of the detection signal S exceeds the threshold value Sth is smaller than that in the one state, so in the other state, a switching decision is not made using the threshold value Sth and the other state is maintained. More specifically, the noise suppression circuit may operate so that the switching circuit is in one of two states, the first state and the second state, in which the magnitude of the detection signal or a signal derived from the detection signal is smaller than in the other state.

[0188] This allows the noise suppression circuit to automatically achieve a state in which the polarity of the signal transmitted from the detection means to the compensation circuit is appropriate.

[0189] In a second aspect of this embodiment, based on the first aspect described above, the noise suppression circuit may include a determination circuit that determines whether the magnitude of the detection signal or a signal derived from the detection signal is greater than a predetermined threshold. The determination circuit is, for example, the control circuit 68 described above. Specifically, when the magnitude of the detection signal or a signal derived from the detection signal is greater than the predetermined threshold when the switching circuit is in either the first state or the second state, the determination circuit may switch the switching circuit to the other of the first state and the second state.

[0190] This allows the noise suppression circuit to automatically achieve a state in which the polarity of the signal transmitted from the detection means to the compensation circuit is appropriate.

[0191] Furthermore, in a third aspect of this embodiment, based on the second aspect described above, the predetermined threshold may be equal to or greater than the magnitude of the detection signal when the compensation circuit is in a stopped state, or a signal derived from the detection signal.

[0192] This allows the noise suppression circuit to switch the polarity of the signal transmitted from the detection means to the compensation circuit when the noise level detected by the detection means is worse than the noise level detected by the detection means when the compensation circuit is stopped (i.e., not operating).As a result, the noise suppression circuit can automatically achieve a state in which the polarity of the signal transmitted from the detection means to the compensation circuit is appropriate.

[0193] In a fourth aspect of this embodiment, based on the first aspect described above, the noise suppression circuit may include a determination circuit. The determination circuit is, for example, the control circuit 68 described above. Specifically, the determination circuit may determine whether the magnitude of the detection signal or the signal derived from the detection signal is greater when the switching circuit is in the first state or when the switching circuit is in the second state. After the switching circuit has been switched to each of the first state and the second state, the switching circuit may switch to one of the two states, the first state and the second state, based on the determination result of the determination circuit, in which the magnitude of the detection signal or the signal derived from the detection signal is smaller than when the switching circuit is in the other state.

[0194] This allows the noise suppression circuit to automatically achieve a state in which the polarity of the signal transmitted from the detection means to the compensation circuit is appropriate.

[0195] In addition, in a fifth aspect of this embodiment, assuming any one of the second to fourth aspects described above, the switching circuit may maintain the state of the switching circuit realized based on the judgment result of the judgment circuit.

[0196] This allows the noise suppression circuit to maintain the polarity of the signal transmitted from the detection means to the compensation circuit in an appropriate state.

[0197] In a sixth aspect of the present embodiment, based on any one of the second to fifth aspects, the determination circuit may include an integrated circuit, such as the microcomputer or comparator described above.

[0198] This allows the noise suppression circuit to automatically achieve a state in which the polarity of the signal transmitted from the detection means to the compensation circuit is appropriate, using an integrated circuit.

[0199] In addition, in a seventh aspect of this embodiment, based on any one of the first to seventh aspects described above, the detection means may include a core. The core is, for example, the core 53 described above. Specifically, the core may be formed of a magnetic material, and a first electric wire included in the propagation path and a second electric wire for detecting the common mode noise may pass through the core. The first electric wire is, for example, the power line PL1 described above. The second electric wire is, for example, the signal line SL1 described above. The core may be fixed to the first electric wire or the second electric wire.

[0200] As a result, the noise suppression circuit can use the switching circuit to switch the polarity of the detection signal to an appropriate state, even if, for example, the detection means is attached in a state where the first electric wire or the second electric wire is inserted into the core in the wrong direction.

[0201] In addition, in an eighth aspect of this embodiment, based on any one of the first to seventh aspects described above, the noise suppression circuit may include a filter circuit and an amplifier circuit. The filter circuit is, for example, the filter circuit 61 described above. The amplifier circuit is, for example, the amplifier circuit 62 described above. Specifically, the filter circuit may pass the detection signal and remove specific frequency components. The amplifier circuit may amplify the signal output from the filter circuit. The compensation circuit may output the compensation current or the compensation voltage based on the signal output from the amplifier circuit.

[0202] This allows the noise suppression circuit to use the switching circuit to switch the polarity of the signal that starts from the detection means and is transmitted to the compensation circuit via the filter circuit and amplifier circuit to an appropriate state.

[0203] Furthermore, in a ninth aspect of this embodiment, based on the above-described eighth aspect, the signal derived from the detection signal may be a signal output from the filter circuit, a signal output from the amplifier circuit, or a signal representing the compensation current or the compensation voltage.

[0204] This allows the noise suppression circuit to use the switching circuit to switch the polarity of the signal that starts from the detection means and is transmitted to the compensation circuit via the filter circuit and amplifier circuit to an appropriate state.

[0205] In a tenth aspect of the present embodiment, based on any one of the first to ninth aspects, the first electric device or the second electric device may be a power conversion device including a switching element, and the switching element may be made of a wide bandgap semiconductor.

[0206] This allows the noise suppression circuit to suppress common-mode noise caused by the switching operation of the wide bandgap semiconductor.

[0207] In addition, in an eleventh aspect of the present embodiment, an air conditioner may include the noise suppression circuit of any one of the first to tenth aspects described above. The air conditioner is, for example, the air conditioner 100 described above.

[0208] As a result, the noise suppression circuit can be applied to an air conditioner and can suppress common mode noise during operation of the motor that drives the air conditioner.

[0209] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims. [Explanation of symbols]

[0210] 1 Power Conversion System 10 AC power supply 20 Motor 30 Power conversion device 30C power conversion circuit 31 Rectifier circuit 32 Inverter circuit 33 Control circuit 40 Noise Filter 41 Common mode choke coil 42 Y capacitors 50 Noise detection means 51 Coil 52 Coil 53 cores 60 Active Noise Canceller 61 Filter Circuit 62 Amplifier circuit 63 Compensation circuit 64 Output section 65 Power supply circuit 66 Coupling capacitor 67 Switching circuit 68 Control Circuit 70 Drive power supply 100 Air conditioner 621 Operational Amplifier C1 capacitor C2 capacitor Co Output Capacitor D1 Diode D2 diode GL Grand NSC Noise suppression circuit PL1 power line PL2 power line PL11 power line PL12 power line PL13 power line SL1 signal line SL2 signal line SL11 signal line SL12 signal line SL21 signal line SL22 signal line Tr1 transistor Tr2 transistor

Claims

1. a detection means (50) for detecting common mode noise in a propagation path including a power line (PL1, PL2) connecting the first electric device (10, 30) and the second electric device (30, 20) and outputting a detection signal; a switching circuit (67) that receives the detection signal or a signal derived from the detection signal, and has a first state in which the polarity of the input signal is switched and output, and a second state in which the polarity of the input signal is not switched and output; a compensation circuit (63) that outputs a compensation current or a compensation voltage to the propagation path based on a signal output from the switching circuit (67), The switching circuit (67) is in one of the two states, the first state and the second state, in which the magnitude of the detection signal or a signal derived from the detection signal is smaller than in the other state. Noise suppression circuit.

2. a determination circuit (68) that determines whether the magnitude of the detection signal or a signal derived from the detection signal is greater than a predetermined threshold; the determination circuit (68) switches the switching circuit (67) to the other of the first state and the second state when the magnitude of the detection signal or a signal derived from the detection signal is greater than the predetermined threshold value when the switching circuit (67) is in either the first state or the second state; 2. The noise suppression circuit according to claim 1.

3. The predetermined threshold value is equal to or greater than the magnitude of the detection signal or a signal derived from the detection signal when the compensation circuit (63) is in a stopped state.

3. The noise suppression circuit according to claim 2.

4. a determination circuit (68) that determines whether the magnitude of the detection signal or a signal derived from the detection signal is larger or smaller when the switching circuit (67) is in the first state or when the switching circuit (67) is in the second state; After the switching circuit (67) is switched to each of the first state and the second state, the switching circuit (67) switches to one of the two states, the first state and the second state, in which the magnitude of the detection signal or the signal derived from the detection signal is smaller than that in the other state, based on the determination result of the determination circuit (68).

2. The noise suppression circuit according to claim 1.

5. The switching circuit (67) maintains the state of the switching circuit (67) realized based on the determination result of the determination circuit (68).

5. The noise suppression circuit according to claim 2.

6. The determination circuit (68) is an integrated circuit.

5. The noise suppression circuit according to claim 2.

7. The detection means (50) is made of a magnetic material and includes a core (53) through which a first electric wire (PL1) included in the propagation path and a second electric wire (SL1) for detecting the common mode noise pass, The core (53) is fixed to the first electric wire (PL1) or the second electric wire (SL1).

5. A noise suppression circuit according to claim 1.

8. a filter circuit (61) that passes the detection signal and removes specific frequency components; an amplifier circuit (62) that amplifies the signal output from the filter circuit (61); The compensation circuit (63) outputs the compensation current or the compensation voltage based on the signal output from the amplifier circuit (62).

5. A noise suppression circuit according to claim 1.

9. The signal derived from the detection signal is a signal output from the filter circuit (61), a signal output from the amplifier circuit (62), or a signal representing the compensation current or the compensation voltage.

9. The noise suppression circuit according to claim 8.

10. the first electric device (30) or the second electric device (30) is a power conversion device (30) including a switching element; A wide band gap semiconductor is used for the switching element.

5. A noise suppression circuit according to claim 1.

11. A noise suppression circuit (NSC) according to any one of claims 1 to 4, Air conditioner.

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