JP2008236817A - Common mode transformer, common mode filter and filter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent malfunctions of peripheral devices due to a power converter, to reduce filter noises, to prolong the service life of a motor, to prevent an electrical shock on a human body and to reduce the device in size and cost. <P>SOLUTION: A three-phase common mode transformer used for a filter device for a power converter has a structure in which a ratio of the number of turns of primary and secondary windings is set at 1:N (N is two or more). The transformer is provided with a common mode voltage detection circuit (101) in which each of phases is connected to the primary winding of the three-phase common mode transformer and the other end is connected to one end of the secondary winding of the three-phase common mode transformer, wherein one of a plurality of taps of the secondary winding of the three-phase common mode transformer is used as a neutral point (n). Also, a flyback line of the common mode filter provided with a common mode transformer in which an inductance ratio between the primary and secondary sides is 1:N (N is one or more) is connected to an EMI filter or a neutral point of the power converter. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a filter device that reduces high-frequency noise generated by a switching operation of a power converter, and a power converter using the filter device. As this power converter, the AC power supply is rectified and converted to DC voltage once, and then this DC voltage is converted directly into AC of variable frequency and variable voltage from an inverter device or AC power source that converts the DC voltage into AC of variable frequency and variable voltage. There is a PWM cycloconverter (also known as a matrix converter).

  As one of the problems on the input side of the power converter, there are noise terminal voltage and conduction EMI (Electro Magnetic Interference). In order to solve the above problems, conventionally, an EMI filter has been added to the input side of the power conversion device to take measures. In the conventional EMI filter prior art, in order to reduce common mode noise flowing out to the power supply side, a method of increasing the inductance of the common mode choke of the EMI filter or a method of increasing the capacitance of the grounding capacitor can be mentioned. However, the method of increasing the inductance of the common mode choke is larger in size and expensive than the method of increasing the capacitance of the grounding capacitor. Further, although the method of increasing the capacitance of the grounding capacitor is small in size and inexpensive, the leakage current of the fundamental wave component flowing on the power supply side increases.

  Next, the prior art of the output side filter of a power converter device is demonstrated. Problems on the output side of the power converter include high-frequency leakage current, conduction EMI, radiation EMI, and electric corrosion of motor bearings (the contact surface between the bearing ring and the rolling element due to high-frequency current passing through the rotating bearing ball bearing) This is characterized by undulating wear) and surge voltage at the motor terminals. In order to solve the above problem, conventionally, a normal mode filter or a common mode filter has been added to the output side of the power converter. For example, Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 are known as output side filters of conventional power converters. Patent Documents 1 and 2 and Non-Patent Document 1 are common mode filters for suppressing a common mode current. Non-Patent Document 2 is composed of a normal mode filter for suppressing the noise current in the normal mode and a common mode filter for suppressing the common mode current.

  Since the common mode filters represented by Patent Documents 1 and 2 and Non-Patent Document 1 have a resonance frequency of the filter lower than the carrier frequency of the power converter, high-frequency leakage current, conduction EMI, radiation EMI, motor bearings However, the surge voltage at the motor terminal cannot be suppressed. Further, the method represented by Non-Patent Document 2 has a filter cutoff frequency much higher than the carrier frequency of the power converter, compared with the methods of Patent Documents 1 and 2, Non-Patent Document 1, and so on. Is small and inexpensive. In addition to high-frequency leakage current, conduction EMI, and radiation EMI, surge voltage at the motor terminal can be suppressed. However, the method of Non-Patent Document 2 cannot suppress the electric corrosion of the motor bearing because the cut-off frequency of the common mode filter is much higher than the carrier frequency of the power converter.

  FIG. 14 shows a simulation result of each part when the motor 116 is driven by the power converter 124. FIG. 14 shows the common mode voltage Vc1 and the shaft potential Vs common mode current Ic of the power converter.

  As shown in FIG. 14, at the moment when the common mode voltage Vc1 changes, the common mode current Ic becomes a high-frequency oscillation current having a peak value of 5A and flows to the ground line via the motor. The common mode current Ic is one of the main causes of conduction noise and radiation noise. Further, the common mode voltage Vc1 is divided by the stray capacitance of each part of the motor to cause the shaft potential Vs. When this axial potential Vs is generated, a discharge phenomenon is caused in the motor bearing portion, and a bearing current Ib on the order of several hundred mA flows through the bearing, and electric corrosion occurs. Further, the common mode current Ic flows to the power supply side, leading to an increase in noise terminal voltage.

  FIG. 15 shows a simulation result of each part when the common mode filter 100 shown in FIG. 2 is added to the power converter 124.

  The simulation results shown in FIG. 15 are obtained by changing the primary and secondary turns ratio of the common mode transformer 102 used in the common mode filter 100 shown in FIG. Is simulated. The resonance frequency of the common mode filter 100 is set between the operation frequency and the carrier frequency of the power converter 124. As shown in FIG. 15, by setting the turns ratio of the common mode transformer 102 to 1: 1, the component of the common mode voltage Vc1 above the carrier frequency is suppressed to about the common mode voltage Vc2 shown in FIG. It can be seen that the common mode current Ic is also suppressed. It can also be seen that the axial potential Vs is suppressed by adding the common mode filter 100.

  As described above, the conventional common mode filter suppresses the common mode current Ic, which is one of the causes of malfunction of peripheral devices, or the shaft potential Vs, which is one of the causes of electrolytic corrosion in the motor bearing portion. .

JP 2005-143230 A (page 8, FIG. 1) Japanese Patent No. 3466118 (page 12, Fig. 1) IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL.28, NO.4, p858-p863, JULY / AUGUST 1992 IEEJ Transactions D, Vol.116, No.12, 1996, p1211-1219

As shown in FIG. 15, the common mode current Ic and the shaft potential Vs can be suppressed by adding a conventional common mode filter, but the filter current If flows at a peak value of 2 [A]. As a result, noise generated from the filter increases. In addition, since the filter current is large, the core used in the common mode transformer becomes large in order to avoid magnetic saturation.
In addition, it is not necessary to completely suppress the common mode current Ic and the shaft potential Vs. The common mode current Ic may be suppressed to such an extent that no malfunction occurs in the peripheral device. Further, the axial potential Vs may be suppressed to such an extent that a discharge phenomenon is not caused in the motor bearing portion. However, the conventional method has a problem in that the number of turns cannot be varied because the number of turns on the secondary side of the common mode transformer is fixed, which may result in overspec.

  The present invention has been made in view of such problems, and provides a common mode transformer capable of suppressing the common mode voltage / current, the shaft potential, and the filter current and changing the secondary side winding number, and at the power source side. An object of the present invention is to provide an input / output filter and a power converter that suppress a leakage current of a flowing fundamental wave component.

In order to solve the above problems, the present invention provides a three-phase common mode transformer used in a filter device for a power converter,
The common mode transformer is characterized in that the turn ratio of the primary side winding and the secondary side winding is 1 to N (N is 2 or more).
Further, the present invention is characterized in that a plurality of taps are provided between the winding start and winding end of the secondary side winding of the three-phase common mode transformer.
Further, a common mode voltage detection circuit (101) is provided in which each phase is connected to the primary side winding of the three-phase common mode transformer and the other end is connected to one end of the secondary side winding of the three-phase common mode transformer. The neutral point (n) is one of a plurality of taps of the secondary side winding of the three-phase common mode transformer.
The common mode voltage detection circuit (101) is characterized by comprising a capacitor (104) having one end connected to the primary winding of the three-phase common mode transformer and the other end Y-connected. .
In addition, a capacitor (105) and a damping resistor (106) are connected in series between the Y connection terminal of the capacitor whose Y end is Y-connected and one end of the secondary winding of the three-phase common mode transformer. It is a feature.
In addition, an LC filter is configured by an AC reactor (110) inserted in series with each phase power supply terminal (U1, V1, W1) and the common mode voltage detection capacitor (104).
Further, in the common mode filter inserted between the power converter and the motor, one of a plurality of taps of the secondary winding of the three-phase common mode transformer and the neutral of the DC intermediate circuit of the power converter. It is characterized by connecting dots.
In the common mode filter inserted between the power converter and the motor, one of the taps of the secondary winding of the three-phase common mode transformer is connected to the neutral point of the EMI filter. It is characterized by.
The filter device according to claim 8, wherein the EMI filter and the output filter are integrated on an electric circuit.

The present invention relates to a common mode transformer used in a power conversion device represented by an inverter, a matrix converter, and the like. Since the ratio is 1: 1 and taps are provided in each part of the secondary winding, the suppression of the common mode voltage can be adjusted.
Further, the present invention provides a common mode voltage detection circuit connected in parallel between the output unit of the power converter and the motor, and a series connection between the output unit of the power converter and the motor. By using a common mode filter composed of the described common mode transformer and passive elements, the filter current can be adjusted and the filter noise can be reduced.
Further, since the present invention does not require a filter current to flow through the ground line, the noise terminal voltage can be reduced as compared with the conventional method.
Since the present invention can reduce the noise terminal voltage as compared with the conventional method, the capacitance of the grounding capacitor of the input filter can be reduced accordingly. Therefore, the leakage current of the fundamental wave component flowing on the power source side can be reduced, which leads to the solution of safety problems such as electric shock.
Further, since the present invention is an input / output filter in which an EMI filter and a common mode filter are integrated, the number of parts of the filter can be reduced, so that an inexpensive and small filter circuit can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of a common mode transformer and a common mode filter circuit according to the present invention showing a first embodiment. In the figure, 100 is a common mode filter, 101 is a common mode voltage detection circuit, 102 is a common mode transformer of the present invention in which a tap is provided in each part of the secondary winding of the common mode transformer, and 103 is a tap (external terminal). It is. In the common mode transformer 102, the turn ratio of the primary side (U1-U2, V1-V2, W1-W2) and the secondary side (with terminals a to d) is not 1: 1 as in the prior art, but 1: N (Where N> 1). It is to be noted that the ratio of the primary and secondary turns of the common mode transformer 102 is 1: N (where N> 1), which is common to the drawings 1 to 13 of the present invention.

  2 and 3 show a common mode filter circuit using a specific circuit system of the common mode filter 100 shown in FIG. In FIG. 2, reference numeral 104 denotes a common mode voltage detecting capacitor using a Y-connected capacitor as common mode voltage detecting means. Reference numeral 108 in FIG. 3 denotes a common mode voltage detection transformer using a transformer as common mode voltage detection means. Reference numeral 105 denotes a capacitor for preventing magnetic saturation due to a DC component in the common mode transformer, and reference numeral 106 denotes a damping resistor for suppressing resonance of the filter current. One end of the capacitor 105 for preventing this magnetic saturation is connected to the neutral point of the common mode voltage detecting capacitor 104, and the other end is connected to the tap a on the secondary side of the common mode transformer 102 via the damping resistor 106. . The secondary side tap c (secondary side tap a-c winding number is larger than the primary side winding ratio) is connected to a neutral point different from the neutral point of the common mode voltage detection capacitor 104. It becomes a neutral point.

  In FIG. 2, reference numeral 104 denotes a simple method as a common mode voltage detecting means. However, in the normal mode, an excessive normal mode current flows into the capacitor because the capacitor is short-circuited in the case of a high frequency voltage. Therefore, when only a common mode filter is added to the power converter output side, the method shown in FIG. 2 is inappropriate.

  When the common mode filter system shown in FIG. 2 is employed, the AC reactor 110 shown in FIG. 4 is inserted in series with each phase power supply terminal (U1, V1, W1) in order to prevent a capacitor short circuit between the phases. A method of configuring an LC filter with the common mode voltage detection capacitor 104 is optimal. Further, by adopting the method shown in FIG. 4, not only the common mode voltage can be suppressed, but also the voltage and current supplied to the motor can be made sinusoidal. The common mode voltage detection capacitor 104 can be shared as a part of the normal mode filter and the common mode filter.

  In FIG. 3, reference numeral 108 denotes a common mode voltage detection transformer. 108 is a common mode voltage detecting means which is large in size and high in cost, but acts as a high impedance in the normal mode, so that an excessive normal mode current can be prevented from flowing into the capacitor. Therefore, only a common mode filter can be added to the output side of the power converter.

  FIG. 5 shows the best method when the common mode filter shown in FIG. 3 and the normal mode filter 113 are combined. In FIG. 5, 111 is a damping resistor and 112 is an AC reactor. The damping resistor 111 for each phase is connected in parallel with the AC reactor 112. Reference numeral 113 denotes a normal mode filter that suppresses dV / dt of the output voltage of the power converter. One end of the capacitor 105 for preventing magnetic saturation is connected to the neutral point of the common mode voltage detecting transformer 108, and the other end is connected to the tap a on the secondary side of the common mode transformer 102 via the damping resistor 106. The secondary side tap c (secondary side tap a-c winding number is larger than the primary side winding ratio) is connected to a neutral point different from the neutral point of the common mode voltage detection capacitor 108. It becomes a neutral point. By adopting the method shown in FIG. 5, not only the common mode voltage can be suppressed, but also the surge voltage at the motor terminal can be suppressed.

FIG. 6 shows the output filter shown in FIG. 4 provided with a damping resistor 114. The damping resistor 114 is connected between the taps a and c on the secondary side of the common mode transformer 102.
FIG. 7 shows the output filter shown in FIG. 5 provided with a damping resistor 114. The damping resistor 114 is connected between the taps a and c on the secondary side of the common mode transformer 102.
The output filter shown in FIG. 6 exhibits the same characteristics as the output filter shown in FIG. 4 in the normal mode. The output filter shown in FIG. 7 exhibits the same characteristics as the output filter shown in FIG. 5 in the normal mode.

  The output filters described in FIGS. 6 and 7 exhibit substantially the same characteristics with respect to the common mode. Further, since the damping resistor 114 is added, resonance of the filter current can be suppressed and dV / dt of the common mode voltage can be suppressed.

8 and 9 are system configuration diagrams when the output filter shown in FIG. 4 is applied to a motor-driven inverter drive system. In FIG. 8, 102 is a common mode transformer, 115 is a power supply, 116 is a motor, 117 is a general EMI filter, 118 is an EMI filter capacitor provided between each line of a three-phase power supply, 119 is a common mode choke, 120 is A grounding capacitor, 124 is a power converter for driving the motor, and 125 is an output filter provided on the output side of the power converter.
In FIG. 9, 121 is an EMI filter capacitor. The EMI filter capacitor 121 is installed between 119 and 124. The same reference numerals are given to the same names as those in FIG.

In FIG. 8, an EMI filter (117) is provided on the input side of the power converter (124), and the return line of the output filter 125 is connected to the neutral point n of the power converter. When the power converter is of the (a) neutral point clamp (NPC) system, the neutral point n is a neutral point potential of the dividing capacitor that divides the DC intermediate voltage into two equal parts. When the power converter is (b) a two-level inverter, this neutral point n is a split capacitor that inserts two series capacitors between DC buses and divides the neutral point DC intermediate voltage into two equal parts. Sex point potential. When the power converter is a matrix converter (c), the neutral point n is a neutral point potential obtained by Y-connecting impedances of capacitors, reactors, and the like connected to each phase of the commercial power source. Thus, the present invention can be implemented regardless of the types (a), (b), and (c) of the power converter (124). This point is common to all the drawings of the present invention.
In FIG. 9, an EMI filter (121) is provided on the input side of the power converter, and the return line of the output filter is connected to the neutral point of the EMI filter. In FIG. 8, the return line of the output filter is a path from the secondary side taps c to e of the common mode transformer 102 to the neutral point n in the power converter (124). On the other hand, in FIG. 9, the return line of the output filter is a path from the secondary side taps c to e of the common mode transformer to the neutral point n of the input side EMI filter (121) of the power converter (124). .

  With the system configuration shown in FIGS. 8 and 9, the filter current If is allowed to flow on the return line, so that it is not necessary to flow on the ground line. Further, since the common mode current Ic is suppressed by the common mode filter of the present invention, the rated current capacity of the ground capacitor of the EMI filter can be small.

Further, with the filter circuit configuration shown in FIG. 9, the EMI filter composed of the EMI filter capacitor 1 (118), the common mode choke (119), and the ground capacitor (120), and the output filter 125 are integrated on an electric circuit. Can be

  Therefore, the filter device of the present invention leads to longer motor life, malfunction of peripheral devices, reduction of noise terminal voltage, and prevention of electric shock.

  Next, FIGS. 10 and 11 are system configuration diagrams when the output filter shown in FIG. 5 is applied to a motor-driven inverter drive system.

  In FIG. 10, an EMI filter is provided on the input side of the power converter (124), and the return line of the output filter (125) is connected to the neutral point n of the power converter (124). On the other hand, in FIG. 11, the EMI filter (122) is provided on the input side of the power converter (124), and the return line of the output filter is connected to the neutral point n of the EMI filter (122). In both FIG. 10 and FIG. 11, it is possible to suppress the filter current If flowing through the retrace line by inserting impedance means having a conductance component such as a resistance element in the retrace path.

  With the system configuration shown in FIGS. 10 and 11, the filter current If does not have to flow through the ground line. Further, since the common mode current Ic is suppressed by the common mode filter of the present invention, the rated current capacity of the ground capacitor of the EMI filter can be small.

  Further, with the filter circuit configuration shown in FIG. 11, the EMI filter and the output filter can be integrated on the electric circuit.

  Therefore, the filter device of the present invention leads to longer motor life, malfunction of peripheral devices, reduction of noise terminal voltage, and prevention of electric shock.

  Next, FIGS. 12 and 13 are system configuration diagrams when the output filter shown in FIG. 6 is applied to a motor-driven inverter drive system. FIGS. 12 and 13 are different from FIGS. 10 and 11 only in that a damping resistor 114 is added between taps a and c on the secondary side of the common mode transformer.

  In FIG. 12, an EMI filter (117) is provided on the input side of the power converter (124), and the return line of the output filter (125) is connected to the neutral point n of the power converter (124). In FIG. 13, the EMI filter (122) is provided on the input side of the power converter (124), and the return line of the output filter (125) is connected to the neutral point n of the EMI filter.

  With the system configuration shown in FIGS. 12 and 13, the filter current If does not have to flow through the ground line. Further, since the common mode current Ic is suppressed by the common mode filter of the present invention, the rated current capacity of the ground capacitor of the EMI filter can be small.

  Further, with the filter circuit configuration shown in FIG. 13, the EMI filter (122) and the output filter (125) can be integrated on the electric circuit. Reference numeral 123 denotes an input / output integrated filter in which an EMI filter (122) and an output filter (125) are integrated on an electric circuit.

  Therefore, the filter device of the present invention leads to longer motor life, malfunction of peripheral devices, reduction of noise terminal voltage, and prevention of electric shock.

  Next, FIG. 16 shows a simulation result of each part when the output filter 125 shown in FIG. 9 is added. The waveform diagram shows the common mode voltage Vc1, the common mode voltage Vc2, the shaft potential Vs, the common mode current Ic, and the filter current If in order from the top.

  The simulation result shown in FIG. 16 is obtained by setting the inductance ratio of the primary side and the secondary side of the common mode transformer 102 used in the common mode filter 100 shown in FIG. 1 to 1: 2. The resonance frequency of the common mode filter 100 is set between the operation frequency and the carrier frequency of the power converter 124. As shown in FIG. 16, by setting the inductance ratio of the common mode transformer 102 to 1: 2, the common mode voltage Vc1 is suppressed to about the common mode voltage Vc2 shown in FIG. It can be seen that the common mode current Ic is also suppressed. It can also be seen that the axial potential Vs is suppressed to about ½ by adding the common mode filter 100.

  Further, since the inductance ratio of the primary side and the secondary side of the common mode transformer 102 is 1: 2, the filter current If is also suppressed to about ½, and the suppression of the filter noise can be expected.

  As described above, the common mode filter according to the present invention only suppresses the common mode current Ic, which is one of the causes of malfunction of peripheral devices, or the shaft potential Vs, which is one of the causes of electrolytic corrosion in the motor bearing portion. In addition, the filter noise is also suppressed.

Generally, since a PWM carrier component exists on the output side of the power converter, noise is generated from the filter when a filter is added to the output side. However, since the noise from the filter can be reduced by using the common mode filter of the present invention, the present invention can be applied to a system that requires countermeasures against noise.
By adding the input / output integrated filter device to the power conversion device, it is possible to protect the motor at the same time without causing noise generated in the power conversion device typified by an inverter and a matrix converter to flow to the power supply side. Therefore, it can be applied to a system application that requires prevention of malfunction of peripheral devices and extension of motor life. Further, since it is possible to suppress the leakage current of the fundamental wave component flowing through the ground capacitor of the EMI filter, it leads to human body protection.

The circuit diagram which shows the common mode transformer and common mode filter which show 1st Example of this invention Circuit diagram showing a common mode filter showing a first embodiment of the present invention when a Y-connected capacitor is used in the common mode voltage detection circuit. Circuit diagram showing a common mode filter showing a first embodiment of the present invention when a Y-connected capacitor and transformer are used in the common mode voltage detection circuit. The circuit diagram which shows the combination with the common mode filter which shows 1st Example of this invention at the time of using the capacitor | condenser Y-connected to the sine wave filter and the common mode voltage detection circuit The circuit diagram which shows the combination with the common mode filter which shows 1st Example of this invention at the time of using the capacitor | condenser and transformer which were Y-connected to the dV / dt suppression filter and the common mode voltage detection circuit A combination of a sine wave filter and a Y-connected capacitor in the common mode voltage detection circuit and a common mode filter according to the first embodiment of the present invention when a damping resistor is connected in parallel to the secondary side of the common mode transformer. Circuit diagram Common mode showing a first embodiment of the present invention when a dV / dt suppression filter and a Y-connected capacitor and transformer are used for the common mode voltage detection circuit and a damping resistor is connected in parallel to the secondary side of the common mode transformer Circuit diagram showing combination with filter FIG. 4 is a configuration diagram of a drive system in which an EMI filter is provided on the input side of a power conversion device according to a second embodiment of the present invention, and the return line of the output filter is connected to the neutral point of the power conversion device (however, the output filter is shown in FIG. 4). Used). 2 is a block diagram of a drive system in which an EMI filter is provided on the input side of the power converter according to the second and third embodiments of the present invention, and the return line of the output filter is connected to the neutral point of the EMI filter (however, the output filter) Is the one using FIG. FIG. 6 is a block diagram of a drive system in which an EMI filter is provided on the input side of the power conversion device according to the second embodiment of the present invention, and the return line of the output filter is connected to the neutral point of the power conversion device (however, the output filter of FIG. Used). FIG. 7 is a configuration diagram of a drive system in which an EMI filter is provided on the input side of the power conversion apparatus according to the second embodiment of the present invention, and the return line of the output filter is connected to the neutral point of the EMI filter. What) FIG. 8 is a block diagram of a drive system in which an EMI filter is provided on the input side of the power conversion apparatus according to the second embodiment of the present invention, and the return line of the output filter is connected to the neutral point of the power conversion apparatus. Used). FIG. 9 is a configuration diagram of a drive system in which an EMI filter is provided on the input side of the power converter according to the second embodiment of the present invention, and the return line of the output filter is connected to the neutral point of the EMI filter. What) In the drive system shown in FIG. 8, the simulation waveforms of each part when the EMI filter and the output filter are not connected (prior art) In the drive system shown in FIG. 8, simulation waveforms of each part when the inductance ratio of the common mode transformer is 1: 1 (prior art) In the drive system shown in FIG. 8, each part simulation waveform when the inductance ratio of the common mode transformer is 1: 2 (the present invention)

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Common mode filter 101 Common mode voltage detection circuit 102 Common mode transformer 103 by this invention system Tap 104 Common mode voltage detection capacitor 105 Capacitor 106 Damping resistor 1
107 Capacitor and common mode voltage detection transformer 108 Common mode voltage detection transformer 109 Normal mode filter 1
110 AC reactor 1
111 Damping resistor 2
112 AC reactor 2
113 Normal mode filter 2
114 Damping resistor 3
115 Power Supply 116 Motor 117 General EMI Filter 118 EMI Filter Capacitor 1
119 Common mode choke 120 Grounding capacitor 121 EMI filter capacitor 2
122 EMI Filter 123 for Integrated Input / Output Filter 123 Filter for Integrated Input / Output 124 Power Converter 125 Output Filter Vc1, Vc2 Common Mode Voltage Vs Axis Potential Ic Common Mode Current If Filter Current n Neutral Point N Turn Ratio

Claims (9)

In a three-phase common mode transformer used in a filter device for a power converter,
A common mode transformer, wherein a turn ratio of a primary winding and a secondary winding is 1 to N (N is 2 or more).   The common mode transformer according to claim 1, further comprising a plurality of taps between a winding start and a winding end of the secondary side winding of the three-phase common mode transformer.   A common mode voltage detection circuit (101) in which each phase is connected to a primary winding of a three-phase common mode transformer and the other end is connected to one end of a secondary winding of the three-phase common mode transformer; A common mode filter characterized in that one of a plurality of taps of a secondary winding of a three-phase common mode transformer is a neutral point (n).   The common mode voltage detection circuit (101) comprises a capacitor (104) having one end connected to a primary winding of the three-phase common mode transformer and the other end Y-connected. Common mode filter.   A capacitor (105) and a damping resistor (106) are connected in series between a Y-connection terminal of a capacitor whose other end is Y-connected and one end of a secondary winding of the three-phase common mode transformer. The common mode filter according to claim 3.   The common mode according to claim 4, wherein an LC filter is constituted by an AC reactor (110) inserted in series with each phase power supply terminal (U1, V1, W1) and the common mode voltage detecting capacitor (104). filter.   In the common mode filter inserted between the power converter and the motor, one of a plurality of taps of the secondary winding of the three-phase common mode transformer and a neutral point of the DC intermediate circuit of the power converter, The common mode filter according to claim 3, wherein:   In the common mode filter inserted between the power converter and the motor, one of a plurality of taps of the secondary winding of the three-phase common mode transformer is connected to a neutral point of the EMI filter. Common mode filter.   9. A filter device, wherein the EMI filter and the output filter according to claim 8 are integrated on an electric circuit.

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