Noise reduction device and air conditioning device

Abstract

Improved compensation performance for common-mode noise. [Solution] A noise reduction device comprising: a detection circuit (150) connected to an AC power line and detecting common-mode noise generated in the power line and on the ground in conjunction with the switching operation of a power conversion circuit (30); and a reduction circuit (180) connected to the detection circuit and reducing the common-mode noise, wherein the reduction circuit includes a generation unit (60) that generates a compensation signal to reduce the common-mode noise based on the output voltage of the detection circuit, and an output unit (70) that outputs the compensation signal to the power line or on the ground, wherein the detection circuit includes a magnetic material (51) around which a main winding (53), which is part of the power line, is wound, and an auxiliary winding (52) wound around the magnetic material, wherein there is a bandwidth in which the voltage determined by the turns ratio of the main winding and the auxiliary winding and the input voltage of the generation unit substantially coincide in a bandwidth of 150 kHz to 1 MHz.

Description

Technical Field

[0001] The present disclosure relates to a noise reduction device and an air conditioner.

Background Art

[0002] Conventionally, a noise reduction device in a power conversion device that converts power based on on / off of a switching element is known. This noise reduction device includes noise detection means for detecting a common-mode noise current, and a noise compensation current supply circuit that forms a noise compensation current in the opposite direction to the noise current in response to the noise current detected by the noise detection means, and supplies this noise compensation current to a line through which the noise current of the power conversion device flows.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described conventional noise reduction device, the noise compensation current supply circuit is connected to the noise detection means, and the output of the noise detection means is input to the noise compensation current supply circuit, so that a compensation operation based on the output of the noise detection means is performed. However, depending on the circuit connected to the detection circuit such as the noise detection means, the frequency characteristics of the output voltage of the detection circuit may deteriorate more than the theoretical characteristics, and the compensation performance for common-mode noise may decrease.

[0005] An object of the present disclosure is to improve the compensation performance for common-mode noise.

Means for Solving the Problems

[0006] The first aspect is A detection circuit (150) is connected to an AC power line (11) and detects common-mode noise generated in the power line and ground (12) in conjunction with the switching operation of the power conversion circuit (30), The detection circuit is connected to a reduction circuit (180) that reduces the common-mode noise, The reduction circuit is A generation unit (60) generates a compensation signal to reduce the common-mode noise based on the output voltage of the detection circuit, It includes an output unit (70) that outputs the compensation signal to the power line or the ground, The detection circuit is A magnetic material (51) around which the main windings (53r, 53s, 53t), which are part of the aforementioned power line, The magnetic material includes an auxiliary winding (52) wound around it, This noise reduction device has a bandwidth in which the voltage (V2) determined by the turns ratio of the main winding and the auxiliary winding and the input voltage (Vd) of the generating unit substantially coincide, between 150 kHz and 1 MHz.

[0007] According to the first embodiment, in the bandwidth of 150 kHz to 1 MHz, there exists a bandwidth in which the input voltage (Vd) of the generation unit substantially coincides with the theoretical voltage (V2) determined by the turns ratio of the main winding and the auxiliary winding. Therefore, even if the reduction circuit (180) is connected to the detection circuit (150), in the bandwidth of 150 kHz to 1 MHz, the deterioration of the frequency characteristics of the output voltage of the detection circuit (150) compared to the theoretical characteristics is suppressed, thereby improving the compensation performance against common-mode noise.

[0008] The second aspect is, A detection circuit (250) is connected to an AC power line (11) and detects common-mode noise generated in the power line and ground (12) due to the switching operation of the power conversion circuit (30), The detection circuit is connected to a reduction circuit (280) that reduces the common-mode noise, The reduction circuit is A generation unit (60) generates a compensation signal to reduce the common-mode noise based on the output voltage of the detection circuit, It includes an output unit (70) that outputs the compensation signal to the power line or the ground, The detection circuit includes impedance elements (55, 56) connected between the power line and the ground. The impedance element includes a first impedance element (55) with one end connected to the power line, and a second impedance element (56) with one end connected to the other end of the first impedance element and the other end connected to the ground. This noise reduction device has a bandwidth in which the voltage of the second impedance element (V2), determined by the voltage division ratio between the first impedance element and the second impedance element, and the input voltage (Vd) of the generation unit are approximately identical, in the range of 150 kHz to 1 MHz.

[0009] According to the second embodiment, in the bandwidth from 150 kHz to 1 MHz, there exists a bandwidth in which the input voltage (Vd) of the generation unit substantially coincides with the theoretical voltage (V2) determined by the voltage division ratio of the first impedance element and the second impedance element. Therefore, even if the reduction circuit (280) is connected to the detection circuit (250), in the bandwidth from 150 kHz to 1 MHz, the frequency characteristics of the output voltage of the detection circuit (250) are suppressed from deteriorating beyond the theoretical characteristics, thereby improving the compensation performance against common-mode noise.

[0010] The third aspect is a noise reduction device according to the first aspect, The input impedance (Zin1) of the reduction circuit (180) is higher than the impedance (Z1) of the detection circuit (150) in the range of 150kHz to 1MHz. The impedance (Z1) of the detection circuit (150) may be the impedance of the auxiliary winding while it is wound around the magnetic material, and this may also be a noise reduction device.

[0011] According to the third embodiment, in the bandwidth where the input impedance (Zin1) of the reduction circuit (180) is higher than the impedance (Z1) of the detection circuit (150), the decrease in the output voltage of the detection circuit (150) is suppressed. As a result, the frequency characteristics of the output voltage of the detection circuit (150) are prevented from deteriorating beyond the theoretical characteristics, thereby improving the compensation performance against common-mode noise.

[0012] The fourth aspect is a noise reduction device according to the second aspect, The input impedance (Zin2) of the reduction circuit (280) is higher than the impedance (Z2) of the detection circuit (250) in the range of 150kHz to 1MHz. The impedance (Z2) of the detection circuit (250) may be the impedance of the second impedance element, and the device may be a noise reduction device.

[0013] According to the fourth embodiment, in the bandwidth where the input impedance (Zin2) of the reduction circuit (280) is higher than the impedance (Z2) of the detection circuit (250), the decrease in the output voltage of the detection circuit (250) is suppressed. As a result, the frequency characteristics of the output voltage of the detection circuit (250) are prevented from deteriorating beyond the theoretical characteristics, thereby improving the compensation performance against common-mode noise.

[0014] The fifth aspect is a noise reduction device according to the third or fourth aspect, The reduction circuit includes a filter section (91, 92) that attenuates specific frequency components. The filter unit may be a noise reduction device connected between the generation unit and the output unit, between the detection circuit and the generation unit, or both.

[0015] According to the fifth embodiment, noise of a specific frequency component is attenuated. As a result, part or all of the frequency band of that frequency component can be excluded from the compensation band by the compensation signal, and the generation unit that generates the compensation signal can be simplified or miniaturized.

[0016] The sixth aspect is the noise reduction device of the fifth aspect, wherein the filter unit may be a noise reduction device connected between the generation unit and the output unit.

[0017] According to the sixth aspect, since the filter unit is connected to the detection circuit via the generation unit, the influence of the connection of the filter unit on the frequency characteristics of the output voltage of the detection circuit is reduced as compared with the form in which the filter unit is directly connected to the detection circuit. Therefore, even if the filter unit is included in the reduction circuit, in the band of 150 kHz or more and 1 MHz or less, the deterioration of the frequency characteristics of the output voltage of the detection circuit from the theoretical characteristics can be suppressed, so that the compensation performance for common mode noise is improved.

[0018] The seventh aspect is the noise reduction device of the fifth or sixth aspect, wherein the filter unit may be a noise reduction device that attenuates frequencies less than 150 kHz among the frequencies that are integer multiples of the switching frequency of the power conversion circuit.

[0019] According to the seventh aspect, the noise of the frequency components outside the compensation target band less than 150 kHz among the frequencies that are integer multiples of the switching frequency of the power conversion circuit is attenuated. Since the noise that is an integer multiple of the switching frequency of the power conversion circuit is large, the noise of the frequency components outside the compensation target band is attenuated, so that the generation unit that generates the compensation signal can be simplified or miniaturized.

[0020] The eighth aspect is the noise reduction device of any one of the fifth to seventh aspects, wherein the noise reduction device includes a noise filter (40) having a common mode choke coil (41) connected to the power line and a capacitor (not shown) connected between the power line and the ground, the filter unit may be a noise reduction device that attenuates frequencies less than 150 kHz among the frequencies that are integer multiples of the resonance frequency of the noise filter.

[0021] According to the eighth embodiment, noise at frequencies below 150 kHz, which are integer multiples of the resonant frequency of the noise filter, is attenuated. Since the noise at integer multiples of the resonant frequency of the noise filter is large, the attenuation of noise at these frequency components outside the compensable band allows the generation unit that generates the compensation signal to be simplified or miniaturized.

[0022] The ninth embodiment is an air conditioning system equipped with a noise reduction device according to any one embodiment of the first to eighth embodiments.

[0023] According to the ninth embodiment, the air conditioning system is equipped with a noise reduction device according to any one of the first to eighth embodiments, thereby providing an air conditioning system that improves compensation performance against common-mode noise. [Brief explanation of the drawing]

[0024] [Figure 1] This is a block diagram showing a first configuration example of a noise reduction device according to the first embodiment. [Figure 2] This figure shows an example configuration of a power conversion circuit. [Figure 3] This is a diagram illustrating the connection configuration between the detection circuit and the reduction circuit in the noise reduction device according to the first embodiment. [Figure 4] This is a circuit diagram showing a first detailed configuration example of the noise reduction circuit in a first configuration example of a noise reduction device according to the first embodiment. [Figure 5] This is a block diagram showing a second configuration example of a noise reduction device according to the first embodiment. [Figure 6] This is a circuit diagram showing a first detailed configuration example of the noise reduction circuit in a second configuration example of the noise reduction device according to the first embodiment. [Figure 7] This is a circuit diagram showing a second detailed configuration example of the noise reduction circuit in a second configuration example of the noise reduction device according to the first embodiment. [Figure 8] This is a block diagram showing a third configuration example of a noise reduction device according to the first embodiment. [Figure 9]This is a block diagram showing a first configuration example of a noise reduction device according to the second embodiment. [Figure 10] This is a diagram illustrating the connection configuration between the detection circuit and the reduction circuit in the noise reduction device according to the second embodiment. [Figure 11] This is a circuit diagram showing a first detailed configuration example of the noise reduction circuit in a first configuration example of the noise reduction device according to the second embodiment. [Figure 12] This is a block diagram showing a second configuration example of a noise reduction device according to the second embodiment. [Modes for carrying out the invention]

[0025] Several embodiments will be described below.

[0026] Figure 1 is a block diagram showing a first configuration example of a noise reduction device according to the first embodiment. The noise reduction device 301 shown in Figure 1 is provided in the power conversion system 1. The power conversion system 1 forward-converts or frequency-converts the AC input from the power source 10 and supplies the DC after forward conversion or the AC after frequency conversion to the load 21.

[0027] Power source 10 is an AC power source that supplies AC power. If power source 10 is a three-phase AC power source, three-phase AC power is supplied from power source 10 to the power conversion system 1. Power source 10 is, for example, a commercial power source.

[0028] When the load 21 is a DC load, the power conversion system 1 has a converter function that forward-converts the AC power supplied from the power source 10 into DC power to be supplied to the load 21. In this case, the load 21 operates on the DC power supplied from the power conversion system 1. Examples of DC loads include electronic circuits. Electronic circuits include, for example, control circuits that control the power conversion circuit 30.

[0029] When the load 21 is an AC load, the power conversion system 1 has an inverter function that converts the frequency of the AC power supplied from the power source 10 to AC power supplied to the load 21. In this case, the load 21 operates on the AC power supplied from the power conversion system 1. An example of an AC load is a motor.

[0030] The power conversion system 1 is provided, for example, in a refrigeration device 200 equipped with a load 21. The refrigeration device 200 is a refrigeration cycle device equipped with a compressor driven by an AC motor, which is an example of a load 21. An example of a refrigeration device 200 is an air conditioning device that harmonizes the air in a target space. Note that the device to which the power conversion system 1 is provided is not limited to the refrigeration device 200, but may be other equipment that requires a power conversion function.

[0031] Load 21 may be a three-phase AC motor. Three-phase AC motors are used as motors to drive compressors in the refrigerant circuit of the refrigeration system 200. Three-phase AC motors are, for example, concentrated winding motors such as 4-pole 6-slot or 6-pole 9-slot motors.

[0032] The power conversion system 1 includes a power conversion circuit 30 and a noise reduction device 301.

[0033] The power conversion circuit 30 is electrically connected to the AC power line 11. The power conversion circuit 30 is mounted on a circuit board, for example, not shown. The circuit board is a printed circuit board or the like. The power conversion circuit 30 is electrically connected to the power supply 10 via the power line 11.

[0034] The power line 11 is a path that supplies single-phase or three-phase AC power generated by the power source 10. When supplying three-phase AC power, the power line 11 includes three-phase (R-phase, S-phase, and T-phase) power lines 11r, 11s, and 11t. The power line 11 is a power line that electrically connects the power source 10 and the power conversion circuit 30.

[0035] The power conversion circuit 30 is a circuit that performs forward conversion or frequency conversion of the alternating current input via the power line 11. The power conversion circuit 30 is an inverter circuit that performs frequency conversion of the alternating current power input via the power line 11 into alternating current power supplied to the load 21, or a converter circuit that performs forward conversion into DC power supplied to the load 21.

[0036] Figure 2 shows an example configuration of a power conversion circuit. The power conversion circuit 30 shown in Figure 2 includes a circuit for driving a motor M. The power conversion circuit 30 is an inverter circuit that frequency-converts the three-phase AC power input via the power line 11 to supply three-phase AC power to a motor M, which is an example of a load 21. The power conversion circuit 30 includes a converter 102, a DC link 103, and an inverter 104 as a circuit for driving the motor M.

[0037] Converter 102 is a circuit that converts alternating current (AC) input via power line 11 to direct current (DC), for example, by converting three-phase AC to DC. Converter 102 is, for example, a diode bridge circuit in which multiple (e.g., six) diodes are connected in a bridge configuration. These diodes full-wave rectify the AC voltage input from power line 11 and convert it to a DC voltage. Converter 102 may also be a voltage conversion circuit of a different circuit type than a diode bridge circuit. Converter 102 supplies the converted DC power to inverter 104 via DC link 103.

[0038] The DC link 103 is the part to which the DC output from the converter 102 is supplied. The DC link 103 includes, for example, a pair of DC buses 111, 112 connecting the converter 102 and the inverter 104, and a capacitor 113 connected between the pair of DC buses 111, 112. The voltage Vdc of the DC link 103 is the potential difference between the pair of DC buses 111, 112 and is approximately equal to the DC voltage across the capacitor 113. The DC voltage Vdc is input to the inverter 104.

[0039] The inverter 104 is a circuit that converts DC from the DC link 103 to AC, for example, by converting DC to three-phase AC. The inverter 104 supplies the converted AC power to the motor M. The inverter 104 is a bridge circuit in which multiple (for example, six) switching elements 104a are connected in a bridge configuration. The inverter 104 converts the DC power from the DC link 103 to AC power for the motor M by turning the multiple switching elements 104a on or off according to commands S generated by a control unit (not shown).

[0040] In Figure 1, the noise reduction device 301 functions as an active noise canceller. The noise reduction device 301 detects common-mode noise generated by the power conversion circuit 30 and outputs a cancellation signal, generated based on the level of the detected common-mode noise, to the power line 11 or ground 12. By outputting the cancellation signal to the power line 11 or ground 12, the common-mode noise flowing into the power supply 10, which is electrically connected to the power line 11 and ground 12, is reduced. The cancellation signal is a signal that reduces common-mode noise and is also called a compensation signal.

[0041] Common-mode noise generated by the power conversion circuit 30 is transmitted through the load 21 or the power conversion circuit 30 and the earth 12 via stray capacitance, and then through the earth 12 and the power line 11. Common-mode noise generated by the power conversion circuit 30 is generated, for example, in conjunction with the switching operation of the switching elements of the power conversion circuit 30. The earth 12 is grounded (connected) to the ground to which the power supply 10 is grounded (connected).

[0042] The noise reduction device 301 according to the first embodiment detects a common-mode noise current Ic (common-mode current) and outputs a compensation current Io, which is generated based on the level of the detected common-mode current, to the power line 11 or ground 12. The noise reduction device 301 according to the first embodiment is a current-detection / current-output type active noise cancellation circuit.

[0043] The common-mode noise current Ic (common-mode current) is an example of common-mode noise generated by the power conversion circuit 30. The compensation current Io is an example of a cancellation signal generated based on the detected level of common-mode noise.

[0044] The noise reduction device 301 according to the first embodiment includes a detection circuit 150 and a reduction circuit 180.

[0045] The detection circuit 150 is connected to the AC power line 11 and detects common-mode noise generated in the power line 11 and ground 12 in conjunction with the switching operation of the power conversion circuit 30. The detection circuit 150 detects the common-mode noise current Ic flowing through the power line 11 as common-mode noise generated by the power conversion circuit 30. The detection circuit 150 detects the noise current Ic on the power supply 10 side of the location of the power conversion circuit 30. The detection circuit 150 detects the common-mode noise generated by the power conversion circuit 30 by detecting the noise current Ic flowing through the power line 11 between the power supply 10 and the power conversion circuit 30. For example, the detection circuit 150 detects the noise current Ic flowing through the power line 11 between the power supply 10 and the power conversion circuit 30 using a transformer.

[0046] The detection circuit 150 is configured to detect noise current Ic using a transformer and includes, for example, a magnetic material 51 around which the main winding 53 (53r, 53s, 53t), which is part of the power line 11, is wound, and an auxiliary winding 52 wound around the magnetic material 51.

[0047] The noise reduction circuit 180 is connected to the detection circuit 150 and reduces common-mode noise. The noise reduction circuit 180 functions as an active noise canceller. The noise reduction circuit 180 has a generation unit 60 and an output unit 70.

[0048] The generation unit 60 generates a compensation signal to reduce common-mode noise based on the output voltage of the detection circuit 150. The compensation current Io is an example of a compensation signal to reduce common-mode noise. The generation unit 60 generates a compensation current Io to output to the power line 11 or ground 12 based on the voltage output from the detection circuit 150 according to the level of the noise current Ic detected by the detection circuit 150. The output unit 70 outputs the compensation current Io generated by the generation unit 60 to the power line 11 or ground 12. For example, the generation unit 60 reduces the noise current Ic by injecting a compensation current Io at approximately the same level as the noise current Ic into the power line 11 or ground 12 via the output unit 70 in opposite phase to the noise current Ic. For example, the output unit 70 injects the compensation current Io into the power line 11 or ground 12 via a capacitor.

[0049] Figure 3 is a diagram illustrating the connection configuration between the detection circuit and the noise reduction circuit in a noise reduction device according to the first embodiment. The detection circuit 150 has a magnetic body 51, a main winding 53, and an auxiliary winding 52. The magnetic body 51 is, for example, an annular magnetic core. The main winding 53 is a primary winding wound around the primary side of the magnetic body 51. The auxiliary winding 52 is a secondary winding wound around the secondary side of the magnetic body 51. If the turns ratio between the main winding 53 and the auxiliary winding 52 is N, and the primary voltage input to the main winding 53 on the primary side of the detection circuit 150 is V1, then ideally the secondary voltage V2 output from the auxiliary winding 52 on the secondary side of the detection circuit 150 is approximately equal to V1 × N.

[0050] The reduction circuit 180 is connected to the auxiliary winding 52 of the detection circuit 150. However, depending on the configuration of the circuit connected to the detection circuit 150, the frequency characteristics of the voltage V2 output from the auxiliary winding 52 of the detection circuit 150 may worsen compared to the theoretical characteristics, and the compensation performance against common-mode noise may decrease. For example, depending on the configuration of the circuit connected to the detection circuit 150, a decrease in voltage V2 may occur in the bandwidth between 100 kHz and 1 MHz due to a decrease in the impedance of the secondary side of the detection circuit 150. As the voltage V2 decreases, the input voltage Vd (Figure 1) of the generation unit 60 in the reduction circuit 180 also decreases, which may reduce the accuracy of the compensation performance against common-mode noise. In order to improve the compensation performance against common-mode noise, it is desirable that the voltage V2 be the theoretical ideal value (=V1×N) determined by the turns ratio N between the main winding 53 and the auxiliary winding 52, even when the reduction circuit 180 is connected to the auxiliary winding 52 of the detection circuit 150.

[0051] In the noise reduction device 301 according to the first embodiment, there is a bandwidth in which the voltage V2 determined by the turns ratio N of the main winding 53 and the auxiliary winding 52 and the input voltage Vd (Figure 1) of the generation unit 60 in the reduction circuit 180 substantially coincide, between 150 kHz and 1 MHz.

[0052] "Approximately identical" means that if the input voltage Vd is k times the theoretical voltage V2, then k is between 0.9 and 1.1, preferably between 0.95 and 1.05, more preferably between 0.98 and 1.02, and most preferably 1.

[0053] According to the noise reduction device 301 of the first embodiment, in the bandwidth of 150 kHz to 1 MHz, there exists a bandwidth in which the input voltage Vd of the generation unit 60 approximately matches the theoretical voltage V2 determined by the turns ratio N of the main winding 53 and the auxiliary winding 52. In this case, regardless of whether the reduction circuit 180 and the detection circuit 150 are connected or how they are connected, in this bandwidth, the output voltage of the detection circuit 150 is almost the same as (maintained) the ideal value determined by the turns ratio N. Since the decrease in the output voltage of the detection circuit 150 is suppressed, the decrease in the input voltage Vd of the generation unit 60 is also suppressed. Therefore, even if the reduction circuit 180 is connected to the detection circuit 150, in the bandwidth of 150 kHz to 1 MHz, the frequency characteristics of the output voltage of the detection circuit 150 are suppressed from deteriorating beyond the theoretical characteristics, thus improving the compensation performance against common-mode noise.

[0054] In Figure 3, for example, it is preferable, in terms of improving the compensation performance for common-mode noise, that the input impedance Zin1 of the reduction circuit 180 has a bandwidth in the range of 150 kHz to 1 MHz where it is higher than the impedance Z1 of the detection circuit 150. The input impedance Zin1 is the impedance of the reduction circuit 180 when viewed from the detection circuit 150. The impedance Z1 of the detection circuit 150 is the impedance of the auxiliary winding 52 when it is wound around the magnetic material 51.

[0055] Between 150kHz and 1MHz, the input impedance Zin1 of the reduction circuit 180 has a bandwidth where it is higher than the impedance Z1 of the detection circuit 150. In this bandwidth, the theoretically determined voltage V2 reduction is suppressed. As a result, the frequency characteristics of the output voltage of the detection circuit 150 do not deteriorate beyond the theoretical characteristics, and the reduction in the input voltage Vd of the generation unit 60 is also suppressed, thus improving the compensation performance against common-mode noise.

[0056] Figure 4 is a circuit diagram showing a first detailed configuration example of the noise reduction circuit 180 in a first configuration example of the noise reduction device 301 according to the first embodiment. The noise reduction circuit 180 is an active type noise suppression means for suppressing common-mode noise. Based on the detection signal output from the auxiliary winding 52 of the detection circuit 150, the noise reduction circuit 180 outputs a compensation current Io to the power line 11 or ground 12 to suppress common-mode noise.

[0057] The reduction circuit 180 includes a generation unit 60, an output unit 70, a power supply circuit 85, a coupling capacitor 82, and a drive power supply 81. The generation unit 60 includes an amplification circuit 69 and a compensation circuit 87.

[0058] The amplification circuit 69 amplifies the input voltage Vd of the generation unit 60. The amplification circuit 69 includes, for example, an operational amplifier 69a for amplifying the input voltage Vd.

[0059] The power supply voltage Vcc of the generation unit 60 (voltage of the drive power supply 81) is, for example, 2 / 3 or less of the DC link voltage (DC link voltage Vdc) of the power conversion circuit 30. The voltage Vcom of the common-mode noise source (specifically, the potential of the neutral point of the motor M generated when the motor M is driven by the inverter 104 of the power conversion circuit 30) changes by 1 / 3 increments. Therefore, if the power supply voltage Vcc is within ±1 / 3 of the DC link voltage Vdc, common-mode noise caused by the switching operation of the inverter 104 can be canceled out without considering the relationship between the power supply voltage Vcc and impedance.

[0060] The signal output from the amplification circuit 69 is a signal representing the waveform of the compensation current or compensation voltage, and is input to the compensation circuit 87. The signal representing the waveform of the compensation current or compensation voltage is a signal that indicates the amplitude and phase for each frequency in the waveform of the compensation current or compensation voltage output from the compensation circuit 87. For example, the signal representing the waveform of the compensation current or compensation voltage output from the amplification circuit 69 is a current or voltage waveform signal that has the same phase for each frequency and a smaller amplitude compared to the waveform of the compensation current or compensation voltage output from the compensation circuit 87.

[0061] The compensation circuit 87 amplifies the signal output from the amplification circuit 69 and outputs a compensation current or compensation voltage. The compensation circuit 87 includes transistors 61, 62, diodes 63, 64, resistors 65, 66, and diodes 67, 68.

[0062] Transistor 61 is connected between one end of the drive power supply 81 and the output capacitor 71 of the output unit 70. Transistor 62 is connected between the other end of the drive power supply 81 and the output capacitor 71 of the output unit 70.

[0063] As shown in Figure 4, in this example, transistor 61 is a PNP type and transistor 62 is an NPN type, and transistors 61 and 62 have opposite polarities. As a result, transistors 61 and 62 form a push-pull circuit, and the push-pull circuit functions as an amplifier.

[0064] The bases of transistors 61 and 62 are connected to one end of the auxiliary winding 52 via diodes 67 and 68 and an amplification circuit 69, and the interconnection point of transistors 61 and 62 is connected to the other end of the auxiliary winding 52 via the amplification circuit 69. As a result, transistors 61 and 62 operate in opposite directions.

[0065] Diodes 63 and 64 are connected in antiparallel to transistors 61 and 62, respectively, to protect them.

[0066] The output section 70 connects the compensation circuit 87 and the ground 12, and outputs (also referred to as "injecting") the compensation current or compensation voltage output from the compensation circuit 87 into the path through which the common-mode current flows. The output section 70 includes an output capacitor 71. The output section 70 may also include a resistor or inductor.

[0067] One end of the output capacitor 71 is connected to the interconnection point of transistors 61 and 62 of the compensation circuit 87, and the other end is connected to ground 12.

[0068] The power supply circuit 85 is connected to the drive power supply 81. The power supply circuit 85 includes capacitors 83 and 84.

[0069] Capacitors 83 and 84 are connected in series. The series connection of capacitors 83 and 84 is connected in parallel to the drive power supply 81 and the compensation circuit 87. The midpoint (neutral point 86) of capacitors 83 and 84 is connected to the coupling capacitor 82.

[0070] The coupling capacitor 82 has one end connected to the power line 11 and the other end connected to the midpoint (neutral point 86) between capacitors 83 and 84.

[0071] The drive power supply 81 supplies DC drive power to the generation unit 60.

[0072] The drive power supply 81 may be a DC power supply capable of supplying DC to the generation unit 60 on its own, or it may be a capacitor whose power supply voltage is the DC voltage of the DC link 103 of the power conversion circuit 30.

[0073] Next, referring to Figure 4, the operation of the generation unit 60 will be explained.

[0074] The detection circuit 150 detects common-mode noise in the power line 11 and drives transistors 61 and 62 via the amplification circuit 69. Specifically, the input voltage Vd corresponding to the detection signal output from the auxiliary winding 52 of the detection circuit 150 is amplified by the amplification circuit 69 and input to the bases of transistors 61 and 62.

[0075] When a common-mode noise current Ic flows in the direction of the arrow in Figure 4, transistor 61 is turned on. In this case, the compensation current Io is supplied from the drive power supply 81 and flows through a path from the positive terminal of the drive power supply 81, through capacitor 84, coupling capacitor 82, power supply 10, output capacitor 71, and transistor 61, to the negative terminal of the drive power supply 81. In other words, the compensation current Io flows in the opposite direction to the arrow in Figure 4. As a result, the compensation current Io is subtracted from the common-mode current Ic, and the reduced common-mode current Ig flows to the power supply 10.

[0076] Furthermore, if the common-mode current Ic flows in the opposite direction to the arrow in Figure 4, transistor 62 is turned on. In this case, the compensation current Io is supplied from the drive power supply 81 and flows through a current path from the positive terminal of the drive power supply 81, through transistor 62, output capacitor 71, power supply 10, coupling capacitor 82, and capacitor 83, to the negative terminal of the drive power supply 81. As a result, the compensation current Io is subtracted from the common-mode current Ic, and a reduced common-mode current Ig flows to the power supply 10 in the opposite direction to the arrow in Figure 4.

[0077] As described above, the compensation current Io flows through the compensation circuit 87. Therefore, when the compensation current or compensation voltage is output, the current supplied from the drive power supply 81 is greater in the compensation circuit 87 than in the amplification circuit 69.

[0078] In this way, the generation unit 60 can suppress the common-mode current Ig flowing to the power supply 10 by outputting a compensation current Io to the path through which the common-mode current Ic flows. Therefore, for example, the generation unit 60 can suppress situations in which common-mode noise current flows out to peripheral equipment through the power supply 10 and affects it.

[0079] Figure 5 is a block diagram showing a second configuration example of the noise reduction device 301 according to the first embodiment. In the second configuration example shown in Figure 5, the explanation of the configuration, operation, and effects, which are the same as in the configuration example described above, will be omitted by referring to the explanation above. The reduction circuit 180 in the second configuration example shown in Figure 5 differs from the reduction circuit 180 in the configuration example described above in that it includes one or more filter sections (Figure 5 illustrates two filter sections 91 and 92) that attenuate specific frequency components.

[0080] The filter unit 91 is connected between the detection circuit 150 and the generation unit 60. The filter unit 92 is connected between the generation unit 60 and the output unit 70. Figure 5 shows a configuration in which both the filter unit 91 and the filter unit 92 exist. However, only one of the filter unit 91 or the filter unit 92 may also exist.

[0081] The presence of one or both of the filter sections 91 and 92 attenuates noise of specific frequency components. This allows for the exclusion of part or all of the bandwidth of these frequency components from the compensation bandwidth (compensation current or compensation voltage) generated by the compensation signal, thus simplifying or miniaturizing the generation unit 60 that generates the compensation signal. To reduce noise outside the compensation bandwidth (for example, low-frequency components below 150 kHz that do not require compensation), the required compensation signal increases, thus requiring the use of active elements with high voltage resistance or high current capacity in the generation unit 60. However, active elements with high voltage resistance or high current capacity generate significant heat due to losses when large currents are passed through them, or their low operating frequency limits the compensable bandwidth. Since the noise of low-frequency components below 150 kHz that do not require compensation is attenuated by one or both of the filter sections 91 and 92, low-voltage or high-speed operating active elements can be used in the generation unit 60, thus simplifying or miniaturizing the generation unit 60. Examples of filter sections 91 or 92 include bandpass filters and high-pass filters.

[0082] The filter section 92 is connected between the generation section 60 and the output section 70. As a result, the filter section 92 is connected to the detection circuit 150 via the generation section 60, so the influence of the filter section 92's connection on the frequency characteristics of the output voltage of the detection circuit 150 is reduced compared to a configuration where the filter section 92 is directly connected to the detection circuit 150. Therefore, even though the filter section 92 is included in the reduction circuit 180, in the bandwidth from 150 kHz to 1 MHz, the deterioration of the frequency characteristics of the output voltage of the detection circuit 150 compared to the theoretical characteristics is suppressed, thus improving the compensation performance against common-mode noise.

[0083] Controlling the leakage flux of the detection circuit 150 is difficult, and the noise may be amplified due to resonance in the filter section 91. The presence of a filter section 92 instead of filter section 91 reduces the occurrence of such problems.

[0084] The filter section 91 is a circuit that passes a signal from which specific frequency components have been removed from the detection signal output from the auxiliary winding 52. The output signal of the filter section 91 is input to the generation section 60. The filter section 92 is a circuit that passes a signal from which specific frequency components have been removed from the compensation signal (compensation current or compensation voltage) output from the generation section 60. The output signal of the filter section 92 is input to the output section 70.

[0085] The filter unit 91 or filter unit 92 attenuates frequencies below 150 kHz among the integer multiples of the switching frequency of the power conversion circuit 30 (e.g., 10 kHz). This attenuates noise in the frequency components outside the compensation band below 150 kHz among the integer multiples of the switching frequency of the power conversion circuit 30. Since the noise at integer multiples of the switching frequency of the power conversion circuit 30 is large, attenuating the noise in these frequency components outside the compensation band allows for simplification or miniaturization of the generation unit 60 that generates the compensation signal. Since the low-frequency components below 150 kHz that do not require compensation are attenuated by one or both of the filter units 91 and 92, low-voltage or high-speed active elements can be used in the generation unit 60, thus simplifying or miniaturizing the generation unit 60.

[0086] Figure 6 is a circuit diagram showing a first detailed configuration example of the noise reduction circuit 180 in a second configuration example of the noise reduction device 301 according to the first embodiment shown in Figure 5. The noise reduction circuit 180 shown in Figure 6 includes a filter section 91 and a filter section 92. The filter section 91 is connected between the auxiliary winding 52 of the detection circuit 150 and the amplification circuit 69 of the generation section 60. The filter section 92 is connected between the compensation signal output point of the generation section 60 (the interconnection point of transistors 61 and 62) and the output capacitor 71 of the output section 70.

[0087] Figure 7 is a circuit diagram showing a second detailed configuration example of the noise reduction circuit 180 in a second configuration example of the noise reduction device 301 according to the first embodiment shown in Figure 5. The noise reduction circuit 180 shown in Figure 7 includes a filter section 92 but does not include a filter section 91. The noise reduction circuit 180 may also include a filter section 91 (Figure 6) but not a filter section 92.

[0088] Figure 8 is a block diagram showing a third configuration example of the noise reduction device 301 according to the first embodiment. In the third configuration example shown in Figure 8, the explanation of the configuration, operation, and effects, which are the same as those of the above-described configuration examples, will be omitted by referring to the above-described explanation. The noise reduction device 301 in the third configuration example shown in Figure 8 differs from the noise reduction device 301 in the above-described configuration examples in that it includes a noise filter 40.

[0089] The noise filter 40 is a passive noise suppression means that suppresses common-mode noise. The noise filter 40 includes a common-mode choke coil 41 and a capacitor 42.

[0090] The common mode choke coil 41 is connected to the power line 11 and acts as an inductor against the common mode noise current (common mode current) flowing through the power line 11, thereby suppressing the noise current.

[0091] Capacitor 42 is a Y-capacitor connected between the power line 11 and the ground 12, and its function is to return the common-mode current that has flowed out to the ground 12 back to the power conversion circuit 30, which acts as a noise source. One end of capacitor 42 is connected to the power line 11, and the other end is connected to the ground 12.

[0092] The filter section 92, for example, attenuates frequencies below 150 kHz among the integer multiples of the resonant frequency of the noise filter 40. This attenuates noise in the frequency components outside the compensation band below 150 kHz among the integer multiples of the resonant frequency of the noise filter 40. Since the noise at integer multiples of the resonant frequency of the noise filter 40 is large, attenuating the noise in these frequency components outside the compensation band allows for simplification or miniaturization of the generation section 60 that generates the compensation signal. Since low-frequency components below 150 kHz that do not require compensation are attenuated by one or both of the filter sections 91 and 92, low-voltage or high-speed active elements can be used in the generation section 60, thus simplifying or miniaturizing the generation section 60. The resonant frequency of the noise filter 40 is determined by the inductance of the common-mode choke coil 41 and the capacitance of the capacitor 42.

[0093] In addition, the above-mentioned filter unit 91 may be present instead of or in addition to the filter unit 92. The filter unit 91 may, like the filter unit 92, attenuate frequencies below 150 kHz among the integer multiples of the resonant frequency of the noise filter 40.

[0094] Figure 9 is a block diagram showing a first configuration example of a noise reduction device according to the second embodiment. In the second embodiment, the description of the same configuration, operation, and effect as in the first embodiment described above will be omitted by referring to the above description. The power conversion system 1 includes a power conversion circuit 30 and a noise reduction device 302.

[0095] In Figure 9, the noise reduction device 302 has the function of an active noise canceller. The noise reduction device 302 detects common-mode noise generated by the power conversion circuit 30 and outputs a cancellation signal to the power line 11, which is generated based on the level of the detected common-mode noise. By outputting the cancellation signal to the power line 11, the common-mode noise flowing into the power supply 10, which is electrically connected to the power line 11 and ground 12, is reduced. The cancellation signal is a signal that reduces common-mode noise and is also called a compensation signal.

[0096] The noise reduction device 302 according to the second embodiment detects a common-mode noise voltage Vc (common-mode voltage) and outputs a compensation voltage Vo generated based on the level of the detected common-mode voltage to the power line 11. The noise reduction device 302 according to the second embodiment is a voltage detection / voltage output type active noise cancellation circuit.

[0097] The common-mode noise voltage Vc (common-mode voltage) is an example of common-mode noise generated by the power conversion circuit 30. The compensation voltage Vo is an example of a cancellation signal generated based on the detected level of common-mode noise.

[0098] The noise reduction device 301 according to the second embodiment includes a detection circuit 250 and a reduction circuit 280.

[0099] The detection circuit 250 is connected to the AC power line 11 and detects common-mode noise generated in the power line 11 and ground 12 in conjunction with the switching operation of the power conversion circuit 30. The detection circuit 250 detects the common-mode noise voltage Vc generated in the power line 11 as common-mode noise generated by the power conversion circuit 30. The detection circuit 250 detects the noise voltage Vc on the power supply 10 side of the location of the power conversion circuit 30. The detection circuit 250 detects the common-mode noise generated by the power conversion circuit 30 by detecting the noise voltage Vc generated in the power line 11 between the power supply 10 and the power conversion circuit 30. The detection circuit 250 detects the noise voltage Vc using impedance elements such as capacitors and resistors, for example.

[0100] The detection circuit 250 is configured to detect the noise voltage Vc using impedance elements, and includes, for example, a plurality of impedance elements 55, 56 connected in series between the power line 11 and the ground 12. The impedance elements 55, 56 are, for example, capacitors. The detection circuit 250 outputs a voltage Vc from the impedance elements 56 that corresponds to the level of common-mode noise generated by the power conversion circuit 30, by voltage division by the impedance elements 55, 56. The detection circuit 250 detects the magnitude of the common-mode noise voltage Vc (common-mode voltage) generated in the impedance elements 56 as a voltage Vc corresponding to the level of common-mode noise. Then, the reduction circuit 280 generates a compensation voltage Vo, which is a cancellation signal that reduces common-mode noise, based on the voltage Vc corresponding to the level of common-mode noise.

[0101] The noise reduction circuit 280 is connected to the detection circuit 250 and reduces common-mode noise. The noise reduction circuit 280 functions as an active noise canceller. The noise reduction circuit 280 has a generation unit 60 and an output unit 70.

[0102] The generation unit 60 generates a compensation signal to reduce common-mode noise based on the output voltage of the detection circuit 250. The compensation voltage Vo is an example of a compensation signal to reduce common-mode noise. The generation unit 60 generates a compensation voltage Vo to output to the power line 11 based on the voltage output from the detection circuit 250 according to the level of the noise voltage Vc detected by the detection circuit 250. The output unit 70 outputs the compensation voltage Vo generated by the generation unit 60 to the power line 11. For example, the generation unit 60 reduces the noise voltage Vc by superimposing a compensation voltage Vo at approximately the same level as the noise voltage Vc on the power line 11 via the output unit 70 in opposite phase to the noise voltage Vc. The output unit 70 outputs the compensation voltage Vo to the power line 11 via a transformer, for example.

[0103] Figure 10 is a diagram illustrating the connection configuration between the detection circuit and the noise reduction circuit in a noise reduction device according to the second embodiment. The detection circuit 250 includes a first impedance element 55 with one end connected to a power line 11, and a second impedance element 56 with one end connected to the other end of the first impedance element 55 and the other end connected to earth 12. The impedance elements 55 and 56 are, for example, capacitors. If the voltage division ratio by the impedance elements 55 and 56 is m, and the voltage generated at the impedance element 55 of the detection circuit 250 is V1, then ideally the voltage V2 output from the impedance element 56 of the detection circuit 250 is approximately equal to V1 × m.

[0104] The reduction circuit 280 is connected to the impedance element 56 of the detection circuit 250. However, depending on the configuration of the circuit connected to the detection circuit 250, the frequency characteristics of the voltage V2 output from the impedance element 56 of the detection circuit 250 may worsen compared to the theoretical characteristics, and the compensation performance for common-mode noise may decrease. For example, depending on the configuration of the circuit connected to the detection circuit 250, a decrease in voltage V2 may occur in the bandwidth between 100 kHz and 1 MHz due to a decrease in the impedance on the output side of the detection circuit 250. As the voltage V2 decreases, the input voltage Vd (Figure 9) of the generation unit 60 in the reduction circuit 280 also decreases, which may reduce the accuracy of the compensation performance for common-mode noise. In order to improve the compensation performance for common-mode noise, it is desirable that the voltage V2 be the theoretical ideal value (=V1 × m) determined by the voltage division ratio m, even when the reduction circuit 280 is connected to the impedance element 56 of the detection circuit 250.

[0105] In the noise reduction device 302 according to the second embodiment, there is a bandwidth in which the voltage V2 determined by the voltage division ratio m of the first impedance element 55 and the second impedance element 56 and the input voltage Vd of the generation unit 60 in the reduction circuit 280 (Figure 9) substantially coincide, in the bandwidth of 150 kHz to 1 MHz.

[0106] "Approximately identical" means that if the input voltage Vd is k times the theoretical voltage V2, then k is between 0.9 and 1.1, preferably between 0.95 and 1.05, more preferably between 0.98 and 1.02, and most preferably 1.

[0107] According to the noise reduction device 302 of the second embodiment, in the bandwidth from 150 kHz to 1 MHz, there exists a bandwidth in which the input voltage Vd of the generation unit 60 approximately matches the theoretical voltage V2 determined by the voltage division ratio m. In this case, regardless of whether the reduction circuit 280 and the detection circuit 250 are connected or how they are connected, in this bandwidth, the output voltage of the detection circuit 250 is almost the same as (maintained) the ideal value designed by the voltage division ratio m. Since the decrease in the output voltage of the detection circuit 250 is suppressed, the decrease in the input voltage Vd of the generation unit 60 is also suppressed. Therefore, even if the reduction circuit 280 is connected to the detection circuit 250, in the bandwidth from 150 kHz to 1 MHz, the frequency characteristics of the output voltage of the detection circuit 250 are suppressed from deteriorating beyond the theoretical characteristics, thus improving the compensation performance against common-mode noise.

[0108] In Figure 10, for example, it is preferable for the input impedance Zin2 of the reduction circuit 280 to be higher than the impedance Z2 of the detection circuit 250 in the range of 150 kHz to 1 MHz, in terms of improving the compensation performance for common-mode noise. The input impedance Zin2 is the impedance of the reduction circuit 280 when viewed from the detection circuit 250. The impedance Z2 of the detection circuit 250 is the impedance of the second impedance element 56.

[0109] Between 150kHz and 1MHz, the input impedance Zin2 of the reduction circuit 280 has a bandwidth where it is higher than the impedance Z2 of the detection circuit 250. In this bandwidth, the theoretically determined voltage V2 reduction is suppressed. As a result, the frequency characteristics of the output voltage of the detection circuit 250 do not deteriorate beyond the theoretical characteristics, and the reduction in the input voltage Vd of the generation unit 60 is also suppressed, thus improving the compensation performance against common-mode noise.

[0110] Figure 11 is a circuit diagram showing a first detailed configuration example of the noise reduction circuit 280 in a first configuration example of the noise reduction device 302 according to the second embodiment. In the first configuration example shown in Figure 11, explanations of the configuration, operation, and effects similar to those of the above-described configuration examples will be omitted by referring to the above-described explanations. The noise reduction circuit 280 is an active type noise suppression means for suppressing common-mode noise. Based on the detection signal output from the impedance element 56 of the detection circuit 250, the noise reduction circuit 280 outputs a compensation voltage Vo to the power line 11 for suppressing common-mode noise.

[0111] The output unit 70 connects the compensation circuit 87 and the power line 11, and outputs the compensation current or compensation voltage output from the compensation circuit 87 to the path through which the common-mode current flows. The output unit 70 includes an output transformer 72.

[0112] The output transformer 72 has a primary winding and a secondary winding. One end of the primary winding is connected to the interconnection point of transistors 61 and 62 of the compensation circuit 87, and the other end is connected to the neutral point 86 of the power supply circuit 85. The secondary winding is inserted into the power lines 11r, 11s, and 11t of each phase included in the power line 11.

[0113] Figure 12 is a block diagram showing a second configuration example of the noise reduction device 302 according to the second embodiment. In the second configuration example shown in Figure 12, the explanation of the configuration, operation, and effects, which are the same as in the above-described configuration example, will be omitted by referring to the above-described explanation. The reduction circuit 280 in the second configuration example shown in Figure 12 differs from the reduction circuit 280 in the above-described configuration example in that it includes one or more filter sections (Figure 12 illustrates two filter sections 91 and 92) that attenuate specific frequency components.

[0114] The filter unit 91 is connected between the detection circuit 250 and the generation unit 60. The filter unit 92 is connected between the generation unit 60 and the output unit 70. Figure 12 shows a configuration in which both the filter unit 91 and the filter unit 92 exist. However, only one of the filter unit 91 or the filter unit 92 may also exist.

[0115] The configuration, operation, and effects of the filter sections 91 and 92 in the second embodiment are the same as those of the filter sections 91 and 92 in the above-described embodiment, so a detailed explanation will be omitted.

[0116] The filter section 91 may be connected in Figure 11 between the impedance element 56 of the detection circuit 250 and the amplification circuit 69 of the generation section 60. The filter section 92 may be connected in Figure 11 between the compensation signal output point of the generation section 60 (the interconnection point of transistors 61 and 62) and the output transformer 72 of the output section 70.

[0117] As described above, embodiments have been explained, but these embodiments are presented as examples only, and the present invention is not limited by these embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0118] For example, the noise reduction device is not limited to current-detection / current-output type or voltage-detection / voltage-output type active noise cancellation circuits, but may also be current-detection / voltage-output type or voltage-detection / current-output type active noise cancellation circuits. For example, in Figure 1, the current-detection type detection circuit 150 may be replaced with the voltage-detection side detection circuit 250 (see Figure 9), and the current-output type output unit 70 may be replaced with the voltage-output type output unit 70 (see Figure 9). Similarly, in Figure 9, the voltage-detection type detection circuit 250 may be replaced with the current-detection side detection circuit 150 (see Figure 1), and the voltage-output type output unit 70 may be replaced with the current-output type output unit 70 (see Figure 1). [Explanation of Symbols]

[0119] 1. Power Conversion System 10 Power supply 11 Power lines 12 Earth 21 load 30 Power Conversion Circuit 40 Noise Filters 41 Common Mode Choke Coil 42 Capacitors 51 Magnetic material 52 Auxiliary winding 53,53r,53s,53t Main winding 55 First Impedance Element 56 Second Impedance Element 60 Generation part 69 Amplifier Circuit 70 Output section 71 Output Capacitor 72 Output Transformer 81 Power supply 82 Coupling Capacitors 83,84 Capacitors 85 Power supply circuit 86 Neutral point 87 Compensation circuit 91,92 Filter section 150,250 detection circuit 180,280 Reduction Circuit 200 Refrigeration equipment 301,302 Noise Reduction Device

Claims

1. A detection circuit (150) is connected to an AC power line (11) and detects common-mode noise generated in the power line and ground (12) in conjunction with the switching operation of the power conversion circuit (30), The detection circuit is connected to a reduction circuit (180) that reduces the common-mode noise, The reduction circuit is A generation unit (60) generates a compensation signal to reduce the common-mode noise based on the output voltage of the detection circuit, It includes an output unit (70) that outputs the compensation signal to the power line or the ground, The detection circuit is A magnetic material (51) around which the main windings (53r, 53s, 53t), which are part of the power line, The magnetic material includes an auxiliary winding (52) that is wound around it, A noise reduction device having a bandwidth in which the voltage (V2) determined by the turns ratio of the main winding and the auxiliary winding and the input voltage (Vd) of the generating unit substantially coincide, in the bandwidth of 150 kHz to 1 MHz.

2. A detection circuit (250) is connected to an AC power line (11) and detects common-mode noise generated in the power line and ground (12) in conjunction with the switching operation of the power conversion circuit (30), The detection circuit is connected to a reduction circuit (280) that reduces the common-mode noise, The reduction circuit is A generation unit (60) generates a compensation signal to reduce the common-mode noise based on the output voltage of the detection circuit, It includes an output unit (70) that outputs the compensation signal to the power line or the ground, The detection circuit includes impedance elements (55, 56) connected between the power line and the ground. The impedance element includes a first impedance element (55) with one end connected to the power line, and a second impedance element (56) with one end connected to the other end of the first impedance element and the other end connected to the ground. A noise reduction device in which the voltage of the second impedance element (V2), determined by the voltage division ratio of the first impedance element and the second impedance element, and the input voltage (Vd) of the generation unit substantially coincide in a bandwidth of 150 kHz to 1 MHz.

3. The input impedance (Zin1) of the reduction circuit (180) is higher than the impedance (Z1) of the detection circuit (150) in the range of 150 kHz to 1 MHz. The noise reduction device according to claim 1, wherein the impedance (Z1) of the detection circuit (150) is the impedance of the auxiliary winding while it is wound around the magnetic material.

4. The input impedance (Zin2) of the reduction circuit (280) is higher than the impedance (Z2) of the detection circuit (250) in the range of 150 kHz to 1 MHz. The noise reduction device according to claim 2, wherein the impedance (Z2) of the detection circuit (250) is the impedance of the second impedance element.

5. The reduction circuit includes filter sections (91, 92) that attenuate specific frequency components. The noise reduction device according to claim 3 or 4, wherein the filter unit is connected between the generation unit and the output unit, between the detection circuit and the generation unit, or both.

6. The noise reduction device according to claim 5, wherein the filter unit is connected between the generation unit and the output unit.

7. The noise reduction device according to claim 5, wherein the filter section attenuates frequencies less than 150 kHz among the frequencies that are integer multiples of the switching frequency of the power conversion circuit.

8. The noise reduction device includes a noise filter (40) having a common mode choke coil (41) connected to the power line and a capacitor (42) connected between the power line and the ground. The noise reduction device according to claim 5, wherein the filter section attenuates frequencies less than 150 kHz among the frequencies that are integer multiples of the resonant frequency of the noise filter.

9. An air conditioning system comprising a noise reduction device according to any one of claims 1 to 4.

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