JP5263663B2 - Conductive noise filter - Google Patents

Description

  The present invention relates to a conductive noise filter that reduces conductive noise generated in power electronics equipment.

  With the development of power semiconductor devices such as IGBT (Insulated Gate Bipolar Transistor), the switching frequency of the inverter is increased. When the switching frequency is increased, the noise and vibration of the motor are reduced and the ability to control voltage, current, torque, etc. is improved, but on the other hand, high-frequency leakage is caused to the ground wire via the stray capacitance of the motor winding. Current (common mode current) flows. The common mode current has a bad influence on the current control of the inverter, and may cause electromagnetic interference (EMI) such as malfunction of the earth leakage breaker. Therefore, conventionally, in order to minimize the common mode current, a passive filter that shunts the common mode current or an active filter that compensates for the common mode current is used.

FIG. 11 shows a known example of an active common mode canceller described in Patent Document 1. This active common mode canceller is applied to a main circuit of a system in which an induction motor is vector-controlled by a voltage source PWM inverter.
In this main circuit, the AC output of the three-phase AC power supply 101 is converted to DC by the rectifier 102, and the DC output of the rectifier 102 is smoothed by the smoothing capacitor 103. The DC voltage smoothed by the smoothing capacitor 103 is input to the voltage source PWM inverter 104 and converted into a three-phase AC voltage by the switching operation of the power semiconductor element provided in the PWM inverter 104. The three-phase AC output of the inverter 104 is supplied to the induction motor 106 via the cable 105. Note that the frame of the induction motor 106 is connected to a ground terminal via a ground wire.

  The common mode canceller 107 is connected to the output terminal of the PWM inverter 104. In this common mode canceller 107, three capacitors 108 having a capacitance of C0 are star-connected to the three-phase AC output terminal of the inverter 104 in order to detect a common mode voltage. The common mode voltage obtained from the neutral point of the star connection is amplified by a push-pull type emitter follower circuit 109 using complementary transistors Tr1 and Tr2, and then a pair of capacitors 110 having a capacitance C1. To the primary coil of the common mode transformer 111. The secondary coil of the common mode transformer 111 is provided in the middle of the three-phase cable 105. The common mode canceller 107 obtains its drive power from the input side of the inverter 104.

  The emitter follower circuit 109 is provided as a control voltage source for canceling the common mode voltage. The control voltage source is required to have a high-speed response capable of faithfully outputting a common mode voltage that changes stepwise every time the PWM inverter 104 performs a switching operation and a low output impedance characteristic. The emitter follower circuit 109 can satisfy this requirement.

The operation of the common mode canceller 107 will be described with reference to an equivalent circuit shown in FIG. In FIG. 12, symbol Cm indicates the stray capacitance between the winding of the motor 106 and the frame, and symbols l and r indicate the inductance component and the resistance component of the wiring in the entire path, respectively.
When one phase of the PWM inverter 104 is switched, the common mode voltage Vinv output from the inverter 104 changes stepwise with a magnitude of Ed / 3. The emitter follower circuit 109 is represented as a control voltage source that receives a common mode voltage Vinv (Ed / 3) and outputs a voltage Vc having the same magnitude. Further, the common mode transformer 111 connected to the output terminal of the emitter follower circuit 9 is represented by only the excitation inductance Lm while ignoring the leakage inductance.

The inverter 104 outputs a zero-phase voltage that changes stepwise each time a switching operation is performed, that is, a common mode voltage. As a result, the common mode current i (t) is a stray capacitance between the winding of the motor 106 and the frame. Through to the ground wire. At this time, the common mode voltage Vinv is detected via the star-connected capacitor 108, and a voltage Vc having the same magnitude and the opposite polarity as the common mode voltage Vinv is output to the common mode transformer 111. As a result, the common mode voltage Vinv is canceled and the common mode current i (t) does not flow. In this way, the common mode canceller 107 acts to remove both the common mode voltage Vinv and the common mode current i (t) at the same time.
JP-A-10-94244

FIG. 13 shows an equivalent circuit of a common mode voltage considering the stray capacitance of the device. In FIG. 13, a LISN (line impedance stabilization network) 112 for measuring conductive noise is also shown. In FIG. 13, reference numeral Cy denotes a grounding capacitor. This grounding capacitor Cy is provided as a noise filter element between the cable connected to the output of the power source 101 shown in FIG. 11 and the grounding point, and is commonly used when an inverter is used. Is done. Reference symbol Cb indicates the stray capacitance of the inverter 104.
As described with reference to FIG. 12, the active common mode canceller 107 injects a voltage Vc having a reverse polarity equal to the common mode voltage Vinv into the common mode transformer 111. Therefore, as shown in FIG. 13, the common mode voltage Vinv between the inverter 104 and the electric motor 106 is canceled by the voltage Vc, and the leakage current Im generated on the electric motor 106 (see FIG. 11) side is removed.

However, since the active common mode canceller 107 does not have a function of canceling the common mode voltage between the inverter 104 and the LSIN 112, the leakage current I2 flowing through the LSIN 112 and the current I3 flowing through the ground capacitor Cy (I1 = I2). + I3) cannot be compensated.
Further, the active common mode canceller 107 applies a high voltage for canceling the common mode voltage Vinv from the control voltage source (emitter follower circuit 109), as shown in FIG. Since the power is taken from the input side of the inverter 104, it is necessary to use high voltage transistors as the transistors Tr1 and Tr2 constituting the emitter follower circuit 109. This is a disadvantageous condition for integration.

  Accordingly, an object of the present invention is to provide a conductive noise filter capable of compensating for a leakage current on the power source side and capable of reducing the canceling voltage.

The present invention is a conductive noise filter applied to a system having a rectifier that converts an output of an AC power source into a DC voltage and a power converter that converts the DC voltage into an AC voltage by a switching operation of a power semiconductor element. A common mode voltage detecting means for detecting a common mode voltage generated during a switching operation of the power semiconductor element via a ground capacitor connected to a line between the AC power supply and the rectifier; and the detected common Based on the mode voltage, a canceling voltage of the opposite polarity having the same magnitude as the common mode voltage is generated, and this canceling voltage is superimposed between the connection point of the AC power source and the grounding capacitor in the line. and a canceling voltage source for offsetting the common mode voltage, the common mode voltage detecting means includes a ground point and the ground capacitor Comprising a dividing capacitor provided between, and wherein Rukoto the common mode voltage detected by the ground capacitor is configured to divide the output by the voltage-dividing capacitor.

  In the canceling voltage source, for example, a common mode transformer can be used as a means for superimposing the canceling voltage. The common mode transformer inputs a voltage corresponding to the detected common mode voltage to the primary side, and a secondary side is interposed between the AC power source and the grounding capacitor in the line, and the secondary side The winding ratio between the primary side and the secondary side is set so that the canceling voltage is induced.

An amplifier for amplifying the detected common mode voltage may be further included. In this case, the voltage input to the primary side is determined by the output of the amplifier, and the turn ratio is set according to the gain of the amplifier.
The cancellation voltage source may include a push-pull type emitter follower circuit connected to the primary side of the common mode transformer.
The canceling voltage source can include a filter for extracting a component of a specific frequency of the detected common mode voltage. In this case, the canceling voltage is generated based on the specific frequency component.
As the filter, any of a band pass filter, a low pass filter, and a high pass filter can be applied.

A coil for reducing noise in a high frequency region can be further provided. The coil includes a line between the AC power source and the overlapping part of the canceling voltage, a line between the overlapping part of the canceling voltage and the connection part of the ground capacitor, a line between the connection part of the ground capacitor and the rectifier, It is provided on a line connected to the output of the power converter, a line between the rectifier and the power converter, and the like.
The present invention is a conductive noise filter applied to a system having a rectifier that converts an output of an AC power source into a DC voltage and a power converter that converts the DC voltage into an AC voltage by a switching operation of a power semiconductor element. A common mode voltage detecting means for detecting a common mode voltage generated during a switching operation of the power semiconductor element via a ground capacitor connected to a line between the AC power supply and the rectifier; and the detected common Based on the mode voltage, a canceling voltage of the opposite polarity having the same magnitude as the common mode voltage is generated, and this canceling voltage is superimposed between the connection point of the AC power source and the grounding capacitor in the line. A canceling voltage source for canceling the common mode voltage, and a coil for reducing noise in a high frequency region, the coil being Also it provides conductive noise filter, characterized in that provided in the line between the connection sites of the grounding capacitor and the superimposing portion of the voltage for killing.

According to the present invention, the leakage current can be compensated through the stray capacitance of the power device. In addition, since the common mode voltage is detected using the grounding capacitor, the canceling voltage can be lowered, and it is possible to configure with a low voltage component. In general, low-voltage components have excellent high-frequency characteristics, so that compensation for higher-frequency noise can be performed. Moreover, since it is cheap, the advantage that it can comprise at low cost is also acquired.
Further, if a filter is provided in the canceling voltage source so that only a specific frequency component is compensated for, it is possible to reduce the voltage-time product of the common mode transformer and to reduce the size of the transformer.
Furthermore, if a coil for reducing noise in the high frequency region is used in combination, noise in the high frequency region can be reduced even when a low-pass filter or a band-pass filter is used as the filter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram showing a first embodiment of a conductive noise filter according to the present invention. The noise filter according to the present embodiment is applied to a system that controls an induction motor by a voltage source PWM inverter.

  In FIG. 1, the AC output of the three-phase AC power source 1 is input to a rectifier 4 via a LISN (line impedance stabilization network) 2 provided for measuring conductive noise and a cable 3. And converted into direct current by the rectifier 4. The DC output of the rectifier 4 is smoothed by the smoothing capacitor 5 and then input to the voltage-type PWM inverter 6, and is converted into a three-phase AC voltage by the switching operation of the power semiconductor element provided in the PWM inverter 6. Converted. Then, the three-phase AC output of the inverter 6 is supplied to the induction motor 7. The frame of the induction motor 7 is connected to a ground terminal via a ground wire.

The control voltage source 8 includes a common mode transformer 9, a push-pull emitter follower circuit 10, an operational amplifier 11, a positive power supply 12 that supplies power to the emitter follower circuit 10 and the operational amplifier 11, and a negative power supply 13. It has.
The common mode transformer 9 has a primary coil interposed between the neutral point of the power supplies 12 and 13 and the output of the emitter follower circuit 10, and a secondary coil interposed in the middle of the cable 3. The emitter follower circuit 10 includes complementary transistors Tr1 and Tr2, and the output of the operational amplifier 11 is connected to the inputs thereof. The operational amplifier 11 has a ground line connected to the neutral points of the power supplies 12 and 13.

Next, the protection circuit 15 will be described. One end of three grounding capacitors 14 having the same capacity are connected to the three-phase cable 3. The protective circuit 15 includes a voltage dividing capacitor 16 interposed between the other end of each grounding capacitor 14 and a grounding point, and a series circuit of voltage dividing capacitors 17 and 18 connected in parallel to the voltage dividing capacitor 16. And a series circuit of Zener diodes 19 and 20 connected in parallel to the voltage dividing capacitor 17. Since the Zener diodes 19 and 20 are connected in a form in which the directions are opposite to each other, the positive and negative excessive voltages are prevented from being applied to the input of the operational amplifier 11. The grounding capacitor 14 is normally connected directly to the installation point. However, in the present embodiment, the grounding capacitor 14 is used as a common mode voltage detection means, and as described above, the voltage dividing capacitors 16 to 18 are used. Is grounded.
The protection circuit 15 is provided to prevent the active elements such as the operational amplifier 11 and the transistors Tr1 and Tr2 from being destroyed by the common mode voltage detected by the ground capacitor 14.

  In FIG. 1, the AC output of the three-phase AC power source 1 is input to the rectifier 4 via the LISN 2 and the cable 3 and is converted into DC here. The DC output of the rectifier 4 is smoothed by the smoothing capacitor 5 and then input to the voltage source PWM inverter 6. The voltage-type PWM inverter 6 converts the input DC voltage into a three-phase AC voltage by a switching operation of the power semiconductor element, and outputs the three-phase AC voltage to the induction motor 7. The frame of the induction motor 7 is connected to a ground terminal via a ground wire.

  The PWM inverter 6 outputs a zero-phase voltage that changes stepwise with a magnitude of Ed / 3 each time a switching operation is performed, that is, a common mode voltage Vinv. The grounding capacitor 14 detects a common mode voltage (showing a value lower than the common mode voltage Vinv, as will be described later) generated in the cable 3 based on the common mode voltage Vinv, and the protection circuit 15 The voltage detected by the capacitor 14 is divided by the capacitors 16-18.

The divided voltage output from the protection circuit 15 is inverted and amplified by the operational amplifier 11 and then input to the primary winding of the common mode transformer 9 via the emitter follower circuit 10. As the operational amplifier 11, a differential amplification type, an inverting amplification type, or the like can be used. At this time, the winding ratio of the common mode transformer 9 is set so that a voltage having the opposite polarity and the same magnitude as the voltage detected by the ground capacitor 14 is induced in the secondary winding. This voltage induced in the secondary winding of the common mode transformer 9 is superimposed on the common mode voltage in the cable 3, and as a result, the common mode voltage is canceled and the leakage current to the power supply 1 side is compensated. .
Here, by adjusting the gain value of the operational amplifier 11, the turn ratio of the common mode transformer 9 can be changed.
For example, if the gain value of the operational amplifier 11 is changed to 1 while the gain value of the operational amplifier 11 is 1 and the primary side: secondary side turns ratio of the common mode transformer is 1: 4, the common mode transformer 9 primary side: secondary side turns ratio can be 1: 2.
Thus, since the turn ratio of the common mode transformer 9 can be changed by changing the gain of the operational amplifier 11, the degree of freedom in designing the common mode transformer 9 is increased. Especially when the number of turns is small, the transformer is easy to design.

  FIG. 2 shows an equivalent circuit considering the stray capacitance. In FIG. 2, the symbol Lm represents the excitation inductance of the common mode transformer 9, the symbol Cy represents the capacitance of the ground capacitor 14, the symbol Cb represents the stray capacitance of the PWM inverter 6, and Cm represents the stray capacitance of the induction motor 7. Reference numerals l and r indicate the inductance and resistance of the wiring in the entire path, respectively.

Since the stray capacitance Cb of the PWM inverter 6 is very small, it can be considered that the ground capacitor 14 and the stray capacitance Cm of the motor are connected in series. Accordingly, if the common mode voltage detected by the ground capacitor 14 is V1, the common mode voltage V1 is obtained by changing the common mode voltage Vinv output from the PWM inverter 6 by the ground capacitor 14 (Cy) and the stray capacitance Cm of the motor. It becomes a partial pressure. That is, the relationship of V1 <Vinv is established between the voltages V1 and Vinv.
The common mode transformer 9 induces in the secondary winding a voltage V2 having a polarity opposite to that of the voltage V1 detected by the ground capacitor 14, and cancels the voltage V1 by the voltage V2. Leakage currents I1, I2 and I3 (conducting noise) can be reduced or eliminated. As apparent from the equivalent circuit of FIG. 2, the reduction of the leakage current on the power source 1 side results in the reduction of the leakage current Im of the electric motor 7.

  The conductive noise filter according to the present embodiment is common to the noise canceller 107 shown in FIG. 11 in the principle that the common mode voltage is canceled by the output of the common mode transformer. However, since the ground capacitor 14 connected to the cable 3 on the power source 1 side is used as the common mode voltage detection means, as described above, the voltage dividing action between the ground capacitor 14 (Cy) and the stray capacitance Cm of the motor. Therefore, the common mode voltage V1 to be canceled becomes lower than the common mode voltage Vinv output from the PWM inverter 6.

As a result, the output voltage V2 of the common mode transformer 9 for canceling the common mode voltage V1 may be low, which means that the power supply voltage applied to the emitter follower circuit 10 may be low. This means that transistors Tr1 and Tr2 with low breakdown voltage can be used. The use of the low breakdown voltage transistors Tr1 and Tr2 is advantageous for cost reduction and integration of the control voltage source 8 and the like. Of course, the fact that the cancellation voltage V2 may be a low voltage also contributes to the downsizing of the common mode transformer 9.
The conductive noise filter according to the present embodiment can detect and compensate for the leakage current flowing through the device's floating capacitance Cb, which cannot be compensated for by the conventional noise canceller circuit. Reduction effect.

FIG. 3 shows a second embodiment of the present invention. This second embodiment differs from the embodiment shown in FIG. 1 only in the configuration of the control voltage source 21. The control voltage source 21 has a configuration in which a band pass filter 22 is provided instead of the operational amplifier 11 of the control voltage source 8 shown in FIG.
The band pass filter 22 has a known configuration in which an inverting amplification operational amplifier 23 is combined with an input capacitor 24, an input resistor 25, a feedback capacitor 26 and a feedback resistor 27, and a specific frequency of the common mode voltage divided by the protection circuit 15. Pass only band components.
Therefore, in the second embodiment, the common mode transformer 9 outputs a reverse polarity voltage having the same magnitude as the common mode voltage of the component in the specific frequency band detected by the ground capacitor 14. Since this voltage is superimposed between the ground capacitor 14 and the power supply 1 in the cable 3, the common mode voltage of the specific frequency component is canceled by this voltage.

  As described above, in the second embodiment, only the components of the specific frequency band of the common mode voltage are compensated, so that the voltage time product of the common mode transformer 9 is reduced. This means that the common mode transformer 9 is less likely to be saturated. Therefore, according to the present embodiment, the common mode transformer 9 can be further downsized.

FIG. 4 shows a third embodiment of the present invention. The control voltage source 28 of the third embodiment has a configuration in which a low-pass filter 29 is provided instead of the operational amplifier 11 of the control voltage source 8 shown in FIG.
The low-pass filter 29 passes only a component of the common mode voltage divided by the protection circuit 15 below a specific frequency (below the cut-off frequency). Therefore, in the third embodiment, the common mode voltage having a component below the specific frequency is canceled. Also according to this embodiment, the voltage-time product of the common mode transformer 9 becomes small, so that the common mode transformer 9 can be downsized.

FIG. 5 shows a fourth embodiment of the present invention. The control voltage source 30 of the fourth embodiment has a configuration in which a high-pass filter 31 is provided instead of the operational amplifier 11 of the control voltage source 8 shown in FIG.
The high-pass filter 31 passes only components having a frequency equal to or higher than the specific frequency (cut-off frequency or higher) of the common mode voltage divided by the protection circuit 15. Therefore, in the fourth embodiment, the common mode voltage having a component equal to or higher than the specific frequency is canceled. According to this embodiment, the common mode transformer 9 can be downsized.

6 to 10 show fifth to ninth embodiments of the present invention, respectively. The fifth to ninth embodiments differ from the embodiment of FIG. 3 in that the coils 32 to 36 are provided, respectively.
The coil 32 in the embodiment of FIG. 6 is between the power source 1 and the common mode transformer 9 in the cable 3, and the coil 33 in the embodiment of FIG. 7 is between the common mode transformer 9 and the ground capacitor 14 in the cable 3. The coil 34 in the embodiment of FIG. 8 is connected between the ground capacitor 14 and the rectifier 4 in the cable 3, and the coil 35 in the embodiment of FIG. 9 is connected to the cable connecting the PWM inverter 6 and the induction motor 7 as shown in FIG. 10. The coils 36 in the embodiment are respectively provided on lines (DC link portions) connecting the rectifier 4 and the PWM inverter 6.

As is well known, the coil is excellent in compensating high frequency characteristics. Therefore, according to the fifth to ninth embodiments, it is possible to obtain a reduction effect on noise having a frequency higher than the upper limit pass frequency defined by the band pass filter 22.
Also in the embodiment shown in FIG. 4, by providing the coils 32 to 36, it is possible to obtain a reduction effect on noise having a frequency higher than the upper limit pass frequency defined by the low-pass filter 29.

Incidentally, the control voltage source 8 of the first embodiment, the band-pass filter, high pass filter, but does not use a low pass filter, which is an active element transistors (e.g., transistors Tr1, Tr2 of the emitter follower circuit 10) Due to the high frequency response, the noise reduction effect in the high frequency region may be limited. Therefore, also in the first embodiment, by providing the coils 32 to 36, it is possible to improve the reduction and decrease in the noise terminal voltage in the high frequency region.

1 is a block circuit diagram showing a first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the embodiment of FIG. 1. It is a block circuit diagram which shows the 2nd Embodiment of this invention using a band pass filter. It is a block circuit diagram which shows the 3rd Embodiment of this invention using a low-pass filter. It is a block circuit diagram which shows the 4th Embodiment of this invention using a high pass filter. It is a block circuit diagram which shows the 5th Embodiment of this invention which added the coil. It is a block circuit diagram which shows the 6th Embodiment of this invention which added the coil. It is a block circuit diagram which shows the 7th Embodiment of this invention which added the coil. It is a block circuit diagram which shows the 8th Embodiment of this invention which added the coil. It is a block circuit diagram which shows the 9th Embodiment of this invention which added the coil. It is a block circuit diagram which shows the structure of the conventional active common mode canceller. FIG. 12 is an equivalent circuit diagram illustrating the operation of the active common mode canceller of FIG. 11. FIG. 12 is an equivalent circuit diagram illustrating the operation of the active common mode canceller of FIG. 11 while taking into account the stray capacitance of the device.

Explanation of symbols

1 Three-phase AC power supply 2 LISN (pseudo power supply network)
3 Cable 4 Rectifier 5 Smoothing Capacitor 6 PWM Inverter 7 Induction Motor 8, 21, 28, 30 Control Voltage Source 9 Common Mode Transformer 10 Emitter Follower Circuit 12, 13 Power Supply 14 Grounding Capacitor 15 Protection Circuit 16-18 Voltage Dividing Capacitor 19, 20 Zener diode 22 Band-pass filter 29 Low-pass filter 31 High-pass filter 32-36 Coil Tr1, Tr2 Transistor

Claims (13)

A conductive noise filter applied to a system having a rectifier that converts an output of an AC power source into a DC voltage and a power converter that converts the DC voltage into an AC voltage by a switching operation of a power semiconductor element,
Common mode voltage detecting means for detecting a common mode voltage generated during a switching operation of the power semiconductor element via a ground capacitor connected to a line between the AC power supply and the rectifier;
Based on the detected common mode voltage, a canceling voltage having a reverse polarity of the same magnitude as the common mode voltage is generated, and this canceling voltage is connected between the connection point of the AC power source and the ground capacitor in the line. A voltage source for canceling, which is superimposed on the common mode voltage,
Equipped with a,
The common mode voltage detecting means includes a voltage dividing capacitor provided between the grounding capacitor and a ground point, and the common mode voltage detected by the grounding capacitor is divided by the voltage dividing capacitor and output. conductive noise filter using active element characterized that you have configured.   The cancellation voltage source uses a common mode transformer as a means for superimposing the cancellation voltage, and the common mode transformer inputs a voltage corresponding to the detected common mode voltage to the primary side, and A secondary side is interposed between the AC power source and the grounding capacitor in the line, and the winding ratio of the primary side and the secondary side is set so that the canceling voltage is induced on the secondary side. The conductive noise filter according to claim 1. An amplifier that amplifies the detected common mode voltage is provided, a voltage input to the primary side is determined by an output of the amplifier, and the turns ratio is set according to the gain of the amplifier. 2. The conductive noise filter according to 2. The conductive noise filter according to claim 2 , wherein the canceling voltage source includes a push-pull type emitter follower circuit connected to the primary side of the common mode transformer.   The cancellation voltage source includes a filter that extracts a specific frequency component of the detected common mode voltage, and is configured to generate the cancellation voltage based on the specific frequency component. The conductive noise filter according to claim 1, wherein: The conductive noise filter according to claim 5 , wherein the filter is any one of a band-pass filter, a low-pass filter, and a high-pass filter.   The conductive noise filter according to claim 1, further comprising a coil for reducing noise in a high frequency region. The conductive noise filter according to claim 7 , wherein the coil is provided on a line between the overlapping portion of the AC power supply and the canceling voltage. The conductive noise filter according to claim 7 , wherein the coil is provided on a line between a portion where the canceling voltage is superimposed and a portion where the ground capacitor is connected. The conductive noise filter according to claim 7 , wherein the coil is provided in a line between a connection portion of the ground capacitor and the rectifier. The conductive noise filter according to claim 7 , wherein the coil is provided on a line connected to an output of the power converter. The conductive noise filter according to claim 7 , wherein the coil is provided on a line between the rectifier and the power converter. A conductive noise filter applied to a system having a rectifier that converts an output of an AC power source into a DC voltage and a power converter that converts the DC voltage into an AC voltage by a switching operation of a power semiconductor element,
Common mode voltage detecting means for detecting a common mode voltage generated during a switching operation of the power semiconductor element via a ground capacitor connected to a line between the AC power supply and the rectifier;
Based on the detected common mode voltage, a canceling voltage having a reverse polarity of the same magnitude as the common mode voltage is generated, and this canceling voltage is connected between the connection point of the AC power source and the ground capacitor in the line. A voltage source for canceling, which is superimposed on the common mode voltage,
A coil for reducing noise in the high frequency region;
With
The conductive noise filter according to claim 1, wherein the coil is provided on a line between a portion where the canceling voltage is superimposed and a portion where the ground capacitor is connected.

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