WO2023073984A1

WO2023073984A1 - Common-mode filter

Info

Publication number: WO2023073984A1
Application number: PCT/JP2021/040215
Authority: WO
Inventors: 将幸大石; 泰章古庄
Original assignee: 三菱電機株式会社
Priority date: 2021-11-01
Filing date: 2021-11-01
Publication date: 2023-05-04
Also published as: JP7094473B1; JPWO2023073984A1

Abstract

The purpose of the present invention is to provide a common-mode filter that can be more reduced in size than a conventional common-mode filter.　A common-mode filter (100) is connected to power lines (4, 5) between an object (3) to be compensated and a power conversion circuit (2) and comprises: a common-mode transformer (11) having a main winding (111) provided in the power lines (4, 5) and an auxiliary winding (112) magnetically coupled to the main winding (111); an amplifier circuit (12) for outputting an amplified voltage (vo) to the auxiliary winding (112); and a current detection unit (13) for detecting the current (io) flowing through the auxiliary winding (112). The common-mode transformer (11) injects a compensation voltage (vcom), which is generated on the basis of the current (io), to the power lines (4, 5).

Description

common mode filter

This application relates to common mode filters.

In a voltage-type power conversion circuit, the common mode voltage, which is the average value of the output voltage of each output terminal, fluctuates according to the operation of the power conversion circuit. Fluctuations in the common mode voltage generate common mode current in the common mode path formed between the power conversion circuit and the stray capacitance to ground. Common mode currents can cause various problems. In order to reduce the common mode current flowing through the power supply line, a common mode filter has been proposed that injects into the power supply line a compensating voltage or a compensating current that reduces the value of the common mode current. In Patent Document 1, a noise reduction device as a common mode filter is connected to a power line between an AC power supply to be compensated and a power conversion circuit, and current flowing through the power line is passed through the main winding of a common mode transformer for detection. The common mode current is detected by converting the voltage of the current generated in the auxiliary winding of the detection common mode transformer. Further, an amplified voltage is generated by the amplifier circuit so as to reduce the detected value, and the amplified voltage is applied to the injection common mode transformer to inject the compensation voltage into the power line. Note that compensation targets are not limited to AC power sources as in Patent Document 1, but include, for example, power systems and electric motors as typical examples.

JP 2019-80469 A (Fig. 7)

The common mode filter (noise reduction device) of Patent Document 1 includes a detection common mode transformer whose main winding is connected to a power line, and a main circuit current flows through the main winding of the detection common mode transformer. ing. In this case, due to restrictions on the current rating of the main winding, the diameter of the main winding must be at least a certain thickness. For this reason, it is difficult to reduce the size of the detection common mode transformer, and there is a problem that the size reduction of the common mode filter is hindered.

The present application was made to solve the above-mentioned problems, and aims to provide a common mode filter that can be made smaller than before.

The common mode filter disclosed in the present application is a common mode filter connected to a power line between a compensation target and a power conversion circuit, and injects into the power line a compensation voltage or a compensation current that suppresses the common mode current flowing through the power line. one or more injection circuits, a first of the injection circuits having a main winding provided on the power line and an auxiliary winding magnetically coupled to the main winding; and a current detector for detecting the current flowing through the auxiliary winding, wherein at least one of the injection circuits injects into the power line a compensation voltage or current generated based on the current detected by the current detector. It is something to do.

According to the common mode filter disclosed in this application, it is possible to make it smaller than conventional common mode filters.

1 is a circuit diagram showing a common mode filter according to Embodiment 1; FIG. 1 is a circuit diagram showing a power conversion circuit according to Embodiment 1; FIG. 1 is a circuit diagram showing an amplifier circuit and a current detection section according to Embodiment 1, and is a diagram when a shunt resistor is used as the current detection section; FIG. 1 is a circuit diagram showing an amplifier circuit and a current detection section according to Embodiment 1, and is a diagram when a CT is used as the current detection section; FIG. 4A and 4B are diagrams for explaining the principle of operation of the common mode filter according to the first embodiment; FIG. 4 is a circuit diagram showing an example in which a band limiting function is added to the amplifier circuit according to Embodiment 1; FIG. FIG. 10 is a circuit diagram showing a common mode filter according to Embodiment 2; FIG. 10 is a diagram showing the division of functions between two filter units according to the second embodiment; FIG. 10 is a circuit diagram showing two filter units according to the second embodiment, and shows an example in which a Y capacitor is used as an injection circuit of the second filter unit; FIG. 10 is a circuit diagram showing two filter units according to Embodiment 2, in the case of using a common mode transformer as an injection circuit of the second filter unit; FIG. 10 is a circuit diagram showing a common mode filter according to Embodiment 3, and is a diagram showing an example in which a common mode transformer is used as a common mode detection circuit; FIG. 10 is a circuit diagram showing a common mode filter according to Embodiment 3, and is a diagram showing an example in which a Y capacitor is used as a common mode detection circuit;

A common mode filter according to each embodiment of the present application will be described below with reference to the drawings. In the drawings used for explanation, the same reference numerals denote the same or corresponding parts, and are common throughout the embodiments described below. Also, the configuration described below is an example, and is not limited to the specific configuration described in the description. In particular, the combination of configurations is not limited only to the combinations in each embodiment, and the configurations described in one embodiment can be applied to another embodiment.

Embodiment 1.
Embodiment 1 will be described with reference to FIGS. 1 to 6. FIG. FIG. 1 is a circuit diagram showing a common mode filter according to Embodiment 1. FIG. Common mode filter 100 is connected between power conversion circuit 2 and compensation object 3 . The compensation target 3 is, for example, a three-phase (u-phase, v-phase, and w-phase) AC power supply, and the common mode filter 100 is connected via a u-phase power line 4u, a v-phase power line 4v, and a w-phase power line 4w. is connected to the compensation object 3 through the Common mode filter 100 is connected to power conversion circuit 2 via u-phase power line 5u, v-phase power line 5v, and w-phase power line 5w. Also, the power conversion circuit 2 and the compensation target 3 are connected on the ground side by a ground line 6 . A power conversion system 1000 is configured by the power conversion circuit 2, the compensation target 3, and the common mode filter 100, which are connected to each other as described above. Note that the

power lines

4u, 4v, and 4w may be collectively referred to as the power lines 4 below. Similarly, the

power lines

5u, 5v, and 5w may also be collectively referred to as the power line 5 in some cases.

Common mode filter 100 includes common mode transformer 11 , amplifier circuit 12 , and current detector 13 . The common mode transformer 11 is composed of

main windings

111u, 111v, and 111w corresponding to the u-phase, v-phase, and w-phase, respectively, and an auxiliary winding 112 magnetically coupled to the

main windings

111u, 111v, and 111w. be done. "●" in the figure represents the polarity of each winding. Note that the

main windings

111u, 111v, and 111w may be collectively referred to as the main winding 111 below. The main winding 111 of each phase is connected to the

power lines

4 and 5 corresponding to each phase. An output terminal 125 s of the amplifier circuit 12 is connected to one end of the auxiliary winding 112 , and an output terminal 125 g of the amplifier circuit 12 is connected to the other end of the auxiliary winding 112 via the current detector 13 . The current detection unit 13 converts the voltage of the current i _o flowing through the auxiliary winding 112 to obtain a detection value i _o *. A detection value i _o * of the current detection unit 13 is input to the amplifier circuit 12 . The amplifier circuit 12 amplifies the detected value i _o * input via the

input terminals

124s and 124g (not shown in FIG. 1) so that the detected value i _o * decreases for all bands or a specific band. It outputs the amplified voltage v _o . Amplified voltage v _o is applied to auxiliary winding 112 , and compensation voltage v _com corresponding to amplified voltage v _o is injected from main winding 111 between

power lines

4 and 5 . Since the compensating voltage v _com functions to cancel the common mode voltage output by the power conversion circuit 2, the common mode current in all bands or a specific band is reduced. Since the first embodiment has only one filter section, the common mode filter 100 corresponds to the first filter section.

FIG. 2 is a circuit diagram showing a power conversion circuit according to Embodiment 1. FIG. In Embodiment 1, as an example of the power conversion circuit 2, a power conversion circuit having a configuration of a three-phase full bridge circuit is used. The three-phase full-bridge circuit of the power conversion circuit 2 employs six self-extinguishing power semiconductor switches with anti-parallel diodes as the semiconductor switching elements 201 . In the semiconductor switching element 201, the semiconductor switching element 201 on the positive electrode side and the semiconductor switching element 201 on the negative electrode side are connected in series to form an arm. to form a three-phase full-bridge circuit. Each arm is connected to output terminals 204u, 204v, and 204w corresponding to the u-phase, v-phase, and w-phase, respectively, and is connected to the power line 4 via the output terminals 204u, 204v, and 204w. A DC section is provided in parallel with the three-phase full bridge circuit, and in this DC section, a smoothing DC capacitor 202 and a DC voltage source 203 are connected in parallel with each other. A ground capacitance 205 exists between the three-phase full bridge circuit and the DC portion and the ground line 6 . For the sake of explanation, a ground terminal 206 is provided and a capacitor to ground 205 is connected between the three-phase full bridge circuit and the DC section and the ground terminal 206 .

The power conversion circuit 2, compensation target 3, power line 4, and power line 5 are not limited to the three-phase three-wire system, and three-phase four-wire, single-phase two-wire, and single-phase three-wire circuits are applied. You can also Further, in Embodiment 1, an example using a three-phase full bridge circuit is used as the power conversion circuit 2, but the circuit configuration of the power conversion circuit 2 only needs to have an AC/DC conversion function, and a three-level converter A circuit configuration such as a multi-level converter including

When the compensation target 3 is a power system, the power conversion circuit 2 performs a forward conversion operation to receive power from the power system, or performs a reverse conversion operation to transmit power to the power system. Further, when the compensation target 3 is an electric motor, the power conversion circuit 2 performs a forward conversion operation when the electric motor is used as a generator, and performs an inverse conversion operation when the electric motor is used as a motor. The power conversion circuit 2 changes the output voltage by the switching operation of the semiconductor switching element 201 when performing the forward conversion operation or the inverse conversion operation. Therefore, the average value of the output terminal voltage of the power conversion circuit 2 , that is, the common mode voltage varies for each switching operation of the semiconductor switching element 201 . When the common mode voltage fluctuates, a common mode current flows through a common mode path formed by power conversion circuit 2 , ground line 6 , compensation object 3 , power line 5 , common mode filter 100 and power line 4 .

Next, an amplifier circuit and a current detector according to the first embodiment will be described. In the first embodiment, the current i _o flowing through the auxiliary winding 112 is voltage-converted by the current detection unit 13 to acquire the detected value i _o *. As one specific example of the current detection unit 13, it is conceivable to use a purely resistive shunt resistor 131 as shown in FIG. In the example shown in FIG. 3 , the amplifier circuit 12 configured as an inverting amplifier circuit includes an operational amplifier 121 , an input resistor 122 and a negative feedback resistor 123 . An input terminal 124 s of the amplifier circuit 12 forms an inverting input terminal of the operational amplifier 121 , and an input terminal 124 g forms a non-inverting input terminal of the operational amplifier 121 .

Output terminals

125 s and 125 g of the amplifier circuit 12 constitute output terminals of the operational amplifier 121 .

An input resistor 122 is provided at the input terminal 124s, and is connected to the output terminal 125s through a negative feedback resistor 123. FIG. The input terminal 124g is connected to the output terminal 125g. The output terminal of the operational amplifier 121 is divided by the auxiliary winding 112 of the common mode transformer 11 into an output terminal 125s and an output terminal 125g. Thus, the auxiliary winding 112 has one end connected to the output terminal 125s and the other end connected to the output terminal 125g. The output terminal 125 s connects the operational amplifier 121 and the auxiliary winding 112 and is also connected to the negative feedback resistor 123 . The output terminal 125g connects the auxiliary winding 112 and the input terminal 124g and is provided with a shunt resistor 131 . A connection point with the input terminal 124 s is provided between the shunt resistor 131 and the auxiliary winding 112 . The resistance values of the input resistor 122, the negative feedback resistor 123, and the shunt resistor 131 are R1, R2, and R, respectively. Also, V _cc and −V _cc in FIG. 3 represent the positive power supply terminal and the negative power supply terminal of the operational amplifier 121 .

When the current i _o flows through the auxiliary winding 112 , a voltage of the detected value i _o * (=R×i _o ) is obtained across the terminals of the shunt resistor 131 as the current detector 13 . As described above, since the amplifier circuit 12 is configured as an inverting amplifier circuit in the first embodiment, the input value of the amplifier circuit 12 in this case is -i _o *. When the amplifier circuit 12 is configured as a non-inverting amplifier circuit, the input value of the amplifier circuit 12 with respect to the detection value i _o * of the shunt resistor 131 is i _o *. The amplifier circuit 12 performs negative feedback control so that the current value of all the bands or a specific band of the input values inputted through the

input terminals

124s and 124g is reduced. When the amplifier circuit 12 is configured as an inverting amplifier circuit, the input value inputted to the amplifier circuit 12 is amplified by the amplifier circuit 12 with a gain of -R2/R1. As a result, an amplified voltage v _o (=R2×R×i _o /R1) is obtained as the output of the amplifier circuit 12 . Thus, the amplifier circuit 12 outputs an amplified voltage v _o proportional to the current i _o flowing through the auxiliary winding 112 . This means that the amplifier circuit 12 operates as a resistor whose resistance value is R2×R/R1.

Next, as another specific example of the current detection unit 13, a case where a CT (Current Transformer) 132 as shown in FIG. 4 is used will be described. The current detection section 13 has an input terminal of the CT 132 provided at the output terminal 125g, which is provided at the output terminal 125g of the amplifier circuit 12, and a terminating circuit 133 at the output terminal of the CT 132. FIG. The termination circuit 133 has a resistor with a resistance value R3. One end of the termination circuit 133 is connected to the input terminal 124s, and the other end of the termination circuit 133 is connected to the input terminal 124g. Unlike the case of using the shunt resistor 131 shown in FIG. 3, the output terminal 125g and the input terminal 124g are not connected.

With the above configuration, the CT 132 transforms the current _io flowing through the auxiliary winding 112 by k times, and the termination circuit 133 performs voltage conversion on the current transformed by the CT 132 . As a result, a voltage of the detection value i _o *(=−k×R3×i _o ) is obtained across the terminals of the termination circuit 133 . The detected value i _o * is input to the amplifier circuit 12 through the

input terminals

124s and 124g, and is amplified by the amplifier circuit 12 with a gain of −R2/R1. As a result, an amplified voltage v _o (=k×R2×R3×i _o /R1) is obtained as the output of the amplifier circuit 12 . That is, when the CT 132 is used as the current detector 13, the amplifier circuit 12 outputs an amplified voltage _vo proportional to the current _io flowing through the auxiliary winding 112, similarly to when the shunt resistor 131 is used. This means that when the CT 132 is used as the current detection unit 13, the amplifier circuit 12 operates as a resistor whose resistance value is k×R2×R3/R1.

5A and 5B are diagrams for explaining the principle of operation of the common mode filter according to Embodiment 1. FIG. Since the amplifier circuit 12 of the common mode filter 100 described above can be regarded as a resistor R*, the circuit of the common mode transformer 11 is equivalent to a circuit in which the auxiliary winding 112 is connected to the resistor R*. Here, by setting the resistance value of the resistor R* to be greater than the impedance value of the magnetizing inductance of the common mode transformer 11, the current value of the current _io flowing through the auxiliary winding 112 approaches zero. Both ends can be considered open. Therefore, if the resistance value of the resistor R* is designed to be large, the common mode transformer 11 operates as a common mode choke coil having an inductance L, and the common mode transformer 11 suppresses the common mode current.

When the common mode transformer 11 is operated as a common mode choke coil, the magnetic coupling between the main winding 111 and the auxiliary winding 112 of the common mode transformer 11 produces a voltage corresponding to the amplified voltage _vo generated by the amplifier circuit 12. Injected into the common mode path including the

power lines

4, 5, the common mode current is suppressed. In this respect, the common mode transformer 11 is in common with a conventional "injection common mode transformer".

Since the common mode filter 100 of Embodiment 1 performs negative feedback control on the current _io flowing through the auxiliary winding 112, the common mode current flowing only through the main winding 111 (common mode current flowing only through the main circuit) is cannot be suppressed. On the other hand, since the common mode current shunted to the auxiliary winding 112 is suppressed, the common mode current can be reduced as a whole.

Next, a case of suppressing common mode current in a specific band (not all bands) will be described. Note that here, as an example of the "specific band" for suppressing the common mode current, 150 kHz or higher will be described as an example. This example is based on the noise terminal voltage standard of CISPR (International Special Committee on Radio Interference). FIG. 6 is a circuit diagram showing an example of adding a band limiting function to the amplifier circuit according to the first embodiment. In the amplifier circuit 12 shown in FIG. 6, high-

pass filters

126 and 127 are provided at

input terminals

124s and 125s and

output terminals

125s and 125g, respectively. The high-pass filter 126 is composed of a capacitor connected in series with the input terminal 124s and a resistor provided in a circuit connecting the input terminal 124s and the input terminal 124g. The high-pass filter 127 is composed of a capacitor connected in series with the output terminal 125s and a resistor provided in a circuit connecting the output terminal 125s and the output terminal 125g. A high pass filter 126 removes low frequency components from the input value to the operational amplifier 121 . A high-pass filter 127 removes low-frequency components from the amplified voltage _vo , which is the output of the operational amplifier 121 . By providing the high-pass filter 126 and the high-pass filter 127, the components below the cutoff frequency of the high-pass filter 126 and the high-pass filter 127 are suppressed in the amplified voltage _vo . If the cutoff frequency of high-pass filter 126 and high-pass filter 127 is 70 kHz, amplifier circuit 12 has high impedance for components above 150 kHz and low impedance for components below 70 kHz.

A common mode current flowing through the common mode path is split between the exciting inductance _Lm of the common mode transformer 11 and the amplifier circuit 12 . When the amplifier circuit 12 is set to have a high impedance with respect to high frequency components of 150 kHz or higher, a large amount of the high frequency components of the common mode current flows through the exciting inductance _Lm . As a result, the impedance of the main winding 111 increases, so the common mode transformer 11 operates as a common mode choke coil that suppresses high frequency components of the common mode current.

On the other hand, as described above, the amplifier circuit 12 has a low impedance for low frequency components of less than 70 kHz. Mode current becomes dominant. In this case, the main winding 111 can ideally be considered to be in a short-circuited state. Here, for convenience of explanation, assuming that the coupling ratio of the common mode transformer 11 is 1, that is, the self-inductance L of the common mode transformer 11 and the excitation inductance L _m are equal (L=L _m ), the common mode transformer 11 generates The magnetic flux Φ is proportional to the current through the magnetizing inductance _Lm . As described above, most of the low-frequency components of the common mode current flow through the amplifier circuit 12 and hardly flow through the exciting inductance _Lm , so the low-frequency components of the magnetic flux Φ are also suppressed. In this case, since the maximum magnetic flux with which the common mode transformer 11 is required to cope is also reduced, the size of the common mode transformer 11 can be reduced.

Although an example using the high-pass filter 126 and the high-pass filter 127 has been described here, the high-pass filter 126 and the high-pass filter 127 may be replaced with a desired band-limiting circuit. That is, by using a band-limiting circuit in the amplifier circuit 12, which is designed to increase the impedance of frequency components to be excluded from a specific band (compensation band) for suppressing the common mode current, the main winding 111 can be compensated. High impedance only for the band. In other words, by applying a band-limiting circuit designed to increase the impedance only for the desired compensation band to the amplifier circuit 12, the common mode transformer 11 can control the common mode only for the desired compensation band. Works as a choke coil. When the common mode choke coil operates only for the desired compensation band, the magnetic flux of the frequency component outside the compensation band is suppressed among the magnetic flux Φ generated in the common mode transformer 11. Compared to the case where the transformer 11 is operated as a common mode choke coil, the size of the common mode transformer 11 can be reduced.

As described above, the conventional common mode filter is provided with a separate common mode transformer for detection. A current corresponding to the ratio is passed through the auxiliary winding, and the detected value is obtained by converting the current flowing through the auxiliary winding into a voltage. In this configuration, the main circuit current flows through the main winding of the detection common mode transformer. The size of the filter is also increased, which causes an increase in cost.

Embodiment 1 utilizes the fact that in a conventional common mode filter, the detection common mode transformer and the injection common mode transformer are connected by a power line and are on the same path. The common mode currents flowing through the main windings of both the detection common mode transformer and the injection common mode transformer are the same. The common mode transformer 11 is partially in common with the injection common mode transformer in the conventional common mode filter as described above, and the current _io caused by the common mode current of the main winding 111 is supplied to the auxiliary winding 112. also flows. In the first embodiment, the current i _o flowing through the auxiliary winding 112 of the common mode transformer 11 is detected by the current detection unit 13 including the shunt resistor 131 and the like, and voltage-converted to obtain the detected value i _o *. However, the current _io is sufficiently small compared to the main circuit current, and the rated current of the current detection section 13 can be set low. Therefore, when the shunt resistor 131 is used in the current detection section 13, a resistor with a low power rating can be used, and when the CT 132 and the termination circuit 133 are used, a CT with a low current rating can be used. Therefore, by omitting the common mode transformer for detection and realizing its function by the small and inexpensive current detection unit 13, the common mode filter 100 can be made smaller and the cost can be prevented from increasing.

Although an inverting amplifier circuit is used as the amplifier circuit 12 in the first embodiment, the amplifier circuit 12 may be any device that can perform negative feedback control so as to reduce the detection value i _o * in all bands or in a specific band. , the non-inverting amplifier circuit described above, or an amplifier circuit using a push-pull circuit composed of transistors may be used.

As a specific example of the current detection unit 13 _, the pure shunt resistor ₁₃₁ is used. , the current detection unit 13 may be configured by other passive circuits. For example, it is conceivable to configure the current detection section 13 by connecting an inductance component in series with the shunt resistor 131 to increase the impedance of the current detection section 13 with respect to the high frequency component. In this case, since the detection gain for the high-frequency component of the current i _o flowing through the auxiliary winding 112 is increased, the gain of the amplifier circuit 12 can be designed to be low. Therefore, it is possible to reduce gain reduction and phase delay with respect to high-frequency components due to the frequency characteristics of the operational amplifier 121 .

According to Embodiment 1, it is possible to make the filter smaller than the conventional common mode filter. More specifically, a common mode transformer having a main winding provided on a power line and an auxiliary winding magnetically coupled to the main winding, an amplifier circuit that outputs an amplified voltage to the auxiliary winding, and a current detector that detects the current flowing through the auxiliary winding, and the common mode transformer injects a compensation voltage generated based on the current flowing through the auxiliary winding into the power line. That is, the detected value obtained by voltage-converting the current flowing through the auxiliary winding is input to the amplifier circuit, and the amplifier circuit generates an amplified voltage so that the current flowing through the auxiliary winding becomes smaller. Output to auxiliary winding. An amplified voltage is applied to the auxiliary winding, and a compensation voltage corresponding to this amplified voltage is injected into the power line via the main winding, thereby suppressing the common mode current.

Since the input of the amplifier circuit for generating the compensation voltage is the current flowing through the auxiliary winding of the common mode transformer that injects the compensation voltage, it is necessary to separately provide a common mode transformer for detection to obtain the input of the amplifier circuit. do not have. One common mode transformer is used both to inject the compensation voltage and to detect the common mode current for obtaining the input of the amplifier circuit. In this way, it is possible to omit the common mode transformer for detection, which has hindered the miniaturization of the common mode transformer.

Embodiment 2.
Next, Embodiment 2 will be described with reference to FIGS. 7 to 10. FIG. 1 to 6 are denoted by the same reference numerals, and description thereof will be omitted. FIG. 7 is a circuit diagram showing a common mode filter according to Embodiment 2. FIG. The common mode filter 200 is connected between the power conversion circuit 2 and the compensation target 3, like the common mode filter 100 of the first embodiment. The common mode filter 200 is composed of a first filter section 101 and a second filter section 102 which are connected to each other via a u-phase power line 7u, a v-phase power line 7v, and a w-phase power line 7w. is different from the common mode filter 100 of the first embodiment. The first filter unit 101 is connected via the compensation object 3 by the power line 5, as in the common mode filter 100 of the first embodiment, and includes a common mode transformer 11, an amplifier circuit 12, and a current detection unit 13. . The detected value i _o * of the current detection unit 13 in the second embodiment is input to the amplifier circuit 12 and is also input to the amplifier circuit 22 to be described later.

The second filter unit 102 is connected to the power conversion circuit 2 via the power line 4, and receives the injection circuit 21 connected to the power line 4 and the detection value i _o * of the current detection unit 13. and an amplifier circuit 22 that outputs an amplified voltage _vo2 . The injection circuit 21 is configured using, for example, a Y capacitor. Like the amplifier circuit 12, the amplifier circuit 22 performs negative feedback control on the detected value i _o *. The Y capacitor of the injection circuit 21 is composed of a capacitor 21u connected to the power line 4u, a capacitor 21v connected to the power line 4v, and a capacitor 21w connected to the power line 4w. The neutral point of this Y capacitor is connected to the output side of an amplifier circuit 22 , and the amplifier circuit 22 is connected between the neutral point and the ground line 6 . In the common mode filter 200 as well, the common mode voltage output from the power conversion circuit 2 is canceled by the compensation voltage v _com . In the common mode filter 200 , a compensation current is injected into the power line 4 by the amplified voltage _vo2 applied between the neutral point of the Y capacitor of the injection circuit 21 and the ground line 6 . This compensating current is a current opposite in phase to the common mode current flowing through the common mode path, and cancels out the common mode current.

As will be described later, the injection circuit 21 can also be configured using a common mode transformer.

The common mode filter 200 shares functions between the first filter section 101 and the second filter section 102 . FIG. 8 is a diagram showing the division of functions between two filter units according to the second embodiment. The amplifier circuit (amplifier circuit 12) of the first filter unit 101 is set to have a large gain for high frequency components of 150 kHz or higher in the common mode current. On the other hand, the amplifier circuit (amplifier circuit 22) of the second filter section 102 is set to have a large gain for low-frequency components around several tens of kHz, which is the frequency of general leakage current.

As described in Embodiment 1, when the amplifier circuit 12 is not provided with a band limiting function (in the case of the examples shown in FIGS. 3 and 4), the first filter unit 101 has an auxiliary filter as shown in FIG. A resistor R* is connected to the winding 112, and operates as a common mode choke coil in which the exciting inductance _Lm and the resistor R* are connected in parallel. Since the impedance of the exciting inductance _Lm is ideally proportional to the frequency, the impedance of the common mode choke coil has frequency characteristics. Therefore, the first filter section 101 has low impedance in the low frequency band and high impedance in the high frequency band. For this reason, the amplifier circuit of the first filter unit 101 is given a large gain with respect to the high frequency component to suppress the high frequency component of the common mode current.

On the other hand, in the second filter section 102, the gain of the amplifier circuit 22 in the low frequency band is set large. Thereby, the second filter section 102 suppresses the low frequency component of the common mode current.

FIG. 9 is a circuit diagram showing two filter units according to Embodiment 2, and shows a case where a Y capacitor is used as the injection circuit of the second filter unit. In the amplifier circuit 12 of the first filter section 101, a high-pass filter 126 is provided at the

input terminals

124s and 125s. As in the first embodiment, the cutoff frequency of the high-pass filter 126 is set to 70 kHz, and the impedance of the amplifier circuit 12 is set low for frequency components below 70 kHz.

The amplifier circuit 22 of the second filter section 102 is configured as an inverting amplifier circuit and includes an operational amplifier 221 , an input resistor 222 and a negative feedback resistor 223 . An input terminal 224 s of the amplifier circuit 22 is an inverting input terminal of the operational amplifier 221 , and an input terminal 224 g is a non-inverting input terminal of the operational amplifier 221 . The output terminal 225 of the amplifier circuit 22 constitutes the output terminal of the operational amplifier 221 and is connected to the neutral point of the Y capacitor of the injection circuit 21 . Also, the operational amplifier 221 and the input terminal 224g are connected to the ground line 6 via an electric line 229. FIG. The input terminal 224 s is connected to the connection point between the shunt resistor 131 and the auxiliary winding 112 . A low-pass filter 226 is provided at the

input terminals

224s and 224g. The resistance values of the input resistor 222 and the negative feedback resistor 223 are R3 and R4, respectively. _Vcc2 and _-Vcc2 in FIG. 9 represent the positive power supply terminal and negative power supply terminal of the operational amplifier 221, respectively.

In the amplifier circuit 22 configured as described above, the detected value i _o * obtained by the shunt resistor 131 is input to the amplifier circuit 22 via the

input terminals

224s and 224g. However, since the amplifier circuit 22 is an inverting amplifier circuit and the

input terminals

224s and 224g are provided with a low-pass filter 226, the input value of the amplifier circuit 22 is only the low-frequency component of -i _o *. . Therefore, the amplifier circuit 22 performs negative feedback control so that the current value of the low frequency component of the input value of the amplifier circuit 22 is reduced. The input value of the amplifier circuit 22 is amplified by the amplifier circuit 22 with a gain of -R4/R3. As a result, a low-frequency amplified voltage v _o2 (=R4×R×i _o /R3) is obtained as the output of the amplifier circuit 22 .

A cut-off frequency of the low-pass filter 226 is, for example, 40 kHz. Since the amplifier circuit 12 of the first filter section 101 has a low impedance with respect to the low frequency component, the impedance is also low with respect to the frequency component of 40 kHz. For this reason, the common mode transformer 11 operates as a CT with respect to low-frequency components, in which the current ratio between the main winding 111 and the auxiliary winding 112 is determined by the turns ratio of the common mode transformer 11, according to the equal ampere-turn theorem. do. Therefore, the first filter unit 101 can obtain the detection value i _o * without lowering the detection gain for the low-frequency component. As described above, in the second embodiment, the first filter unit 101 detects common mode current and suppresses the high frequency component of the common mode current, and the second filter unit 102 suppresses the low frequency component of the common mode current. In this way, the functions are shared according to the frequency component of the common mode current. As a result, both high frequency components and low frequency components of the common mode current are suppressed. Further, since the common mode current is detected by the first filter section 101, there is no need to separately provide a detection common mode transformer for detecting the common mode current.

In Embodiment 2, the

input terminals

124s and 124g of the amplifier circuit 12 are provided with the high-pass filters 126. However, in order to limit the compensation band of the first filter section 101 to high frequencies, the high-pass filters are also provided at the

output terminals

125s and 125g. A filter may be provided. Alternatively, high-pass filters may be provided only at the

output terminals

125s and 125g. The same applies to the low-pass filter 226 of the amplifier circuit 22. A low-pass filter may be provided on the output side of the operational amplifier 221, or may be provided only on the output side.

Further, in the second embodiment, the two filter units, the first filter unit 101 and the second filter unit 102, share the functions according to the frequency of the compensation band, and the two filter units are used to completely remove the common mode current. It suppresses the frequency components of the band. Therefore, the mode of sharing functions is not limited to the mode in which first filter section 101 suppresses high frequency components and second filter section 102 suppresses low frequency components, as described above. That is, the desired compensation band is divided into a first frequency band and a second frequency band, and only the frequency components of the first frequency band are passed through or blocked by the amplifier circuit 12 of the first filter section 101. A circuit may be provided, and a band limiting circuit may be provided to pass or block only the frequency component of the second frequency band in the amplifier circuit 22 of the second filter section 102 . In the second embodiment, the amplifier circuit 12 of the first filter section is provided with the high-pass filter 126, and the amplifier circuit 22 of the second filter section is provided with the low-pass filter 226. For example, not only the high-pass filter 126 and the low-pass filter 226, but also corresponding band-limiting circuits, that is, high-pass filters, low-pass filters, band-pass filters, and band-elimination filters may be selected. In short, by dividing the frequency band of each input value into the first frequency band and the second frequency band (or vice versa) in the amplifier circuit 12 and the amplifier circuit 22, the first filter unit 101 A compensating voltage or compensating current is injected for the first frequency band (or the second frequency band), and the second filter section 102 injects the compensating voltage or the compensating current for the second frequency band (or the first frequency band). Any configuration is acceptable.

Next, a case where the injection circuit of the second filter section is configured with a common mode transformer will be described. FIG. 10 is a circuit diagram showing two filter units according to Embodiment 2, and shows an example in which a common mode transformer is used as an injection circuit of the second filter unit. The injection circuit 23 in the example shown in FIG. It consists of a common mode transformer with One end of the auxiliary winding 232 is connected to the output terminal 225 of the amplifier circuit 22 , and the other end of the auxiliary winding 232 is connected to the electric circuit 2291 of the amplifier circuit 22 . The electric line 2291 is connected to the input terminal 224 g and the operational amplifier 221 . In the example shown in FIG. 10 as well, it is possible to share functions between the first filter section 101 and the second filter section 102 according to the frequency band. Specifically, for each of the common mode transformer 11 of the first filter section 101 and the common mode transformer of the injection circuit 23 of the second filter section 102, the frequency band corresponding to the iron core of each common mode transformer (the above function A magnetic material suitable for the frequency band in which the common mode current is suppressed in each filter section may be selected according to the assignment. As a result, the common mode current can be suppressed in a wider frequency band than in the first embodiment while preventing each common mode transformer from increasing in size.

According to Embodiment 2, common mode current can be suppressed in a wide frequency band while preventing the common mode filter from becoming large. More specifically, the common mode filter is provided with two filter sections, and the first filter section that ensures high impedance for high frequency components suppresses the high frequency components of the common mode current and suppresses the high frequency components for low frequency components. In the second filter section that ensures the impedance, the function of suppressing the low-frequency component of the common mode current is shared according to the frequency. If the impedance of the first filter section is also increased for low frequency components, a large common mode choke coil is required for the first filter section. The low frequency component of the common mode current is suppressed by the second filter section without increasing the impedance. Therefore, it is possible to suppress the common mode current in a wide frequency band while preventing the common mode filter from increasing in size.

Embodiment 3.
Next, Embodiment 3 will be described with reference to FIGS. 11 and 12. FIG. 1 to 10 are denoted by the same reference numerals, and description thereof will be omitted. FIG. 11 is a circuit diagram showing a common mode filter according to Embodiment 3, and shows an example in which a common mode transformer is used as a common mode detection circuit. The common mode filter 300 is connected between the power conversion circuit 2 and the compensation target 3 in the same manner as the common mode filter 100 of the first embodiment and the common mode filter 200 of the second embodiment. 301 and the second filter unit 102 . The first filter section 301 is a current detection section having a common mode transformer 11, an amplifier circuit 32, and a shunt resistor 131, like the first filter section 101 of the second embodiment. 13. Further, the first filter section 301 is provided with a common mode detection circuit 14 and a termination circuit 15 between the compensation target 3 and the amplifier circuit 32 .

The common mode detection circuit 14, ie, the second common mode transformer, has a main winding 141u connected to the power line 5u, a main winding 141v connected to the power line 5v, a main winding 141w connected to the power line 5w, and an auxiliary winding 141w connected to the power line 5w. The

main windings

141u, 141v, and 141w are composed of a common mode transformer having a winding 142, and a main circuit current flows through the

main windings

141u, 141v, and 141w, thereby controlling the turns ratio between the

main windings

141u, 141v, and 141w and the auxiliary winding 142. A current i _in flows through the auxiliary winding 142 . The termination circuit 15 voltage-converts the current i _in to obtain the detection value i _in *. The detected value i _in * is input to the amplifier circuit 32 through the termination circuit 15 configured as a high-pass filter. The amplifier circuit 32 performs negative feedback control on the detected value i _in * so that the detected value i _in * decreases for all bands or a specific band. That is, the amplifier circuit 32 amplifies the detected value i _in * so that the detected value i _in * decreases, and outputs the amplified voltage v _o . The amplified voltage v _o is applied to the auxiliary winding 112 , and a compensation voltage v _com (not shown in FIG. 11) corresponding to the amplified voltage v _o is injected from the main winding 111 to the

power lines

4 and 5 . The compensation voltage v _com functions to cancel the common mode voltage output by the power conversion circuit 2 . The circuit configuration of amplifier circuit 32 other than the above is the same as that of amplifier circuit 12 of the first and second embodiments.

The impedance of the termination circuit 15 is greater than the impedance of the magnetizing inductance of the common mode transformer 14 for all frequency bands or a specific frequency band.

The second filter section 102 is similar to that of the second embodiment. That is, the detection value i _o * of the current detection unit 13 (shunt resistor 131) is input to the amplification circuit 22, and the amplification circuit 22 amplifies the detection value i o * so that the detection value i _o _* decreases. Output voltage v _o2 . As a result, the amplified voltage _vo2 is applied between the neutral point of the Y capacitor of the injection circuit 21 and the ground line 6, and a compensation current corresponding to the amplified voltage _vo2 is injected into the power line 4. FIG. As mentioned above, this compensating current cancels out the common mode current.

The amplifier circuit 32, the detected value i _in *, and the amplified voltage v _o in the third embodiment correspond to the first amplifier circuit, the first detected value, and the first amplified voltage, respectively. Also, the amplifier circuit 22, the detected value i _o *, and the amplified voltage v _o2 correspond to the second amplifier circuit, the second detected value, and the second amplified voltage, respectively.

The operation of the first filter unit 301 will be described. As an example, consider a case where the resistance of the termination circuit 15 is about 100Ω. In this case, since the common mode detection circuit 14 has an impedance with respect to the common mode current, it also functions as a common mode choke coil, and voltage-converts the current i _in flowing through the auxiliary winding 142 to obtain the detection value i _in *. will be obtained. In other words, the common mode detection circuit 14 can serve as both a common mode current detection circuit and a common mode choke coil. The amplifier circuit 32 has a gain of −R2/R1 like the amplifier circuit 12, but the impedance of the terminating circuit 15 connected to the auxiliary winding 142 does not change even if the value of this gain is increased. This means that the detection characteristics of the common mode detection circuit 14 are not affected by the gain of the amplifier circuit 32 . Here, if the detected value i _in * input to the amplifier circuit 32 contains low frequency components, the amplified voltage v _o also contains low frequency components.

When the amplified voltage _vo containing a low-frequency component is applied to the auxiliary winding 112 of the common mode transformer 11, the magnetic flux Φ generated in the common mode transformer 11 increases, causing the common mode transformer 11 to become large. Therefore, in the third embodiment, the termination circuit 15 configured as a high-pass filter is provided between the common mode detection circuit 14 and the amplifier circuit 32 to remove the low frequency component from the detection value i _in * input to the amplifier circuit 32. are doing. By setting the cutoff frequency of the termination circuit 15 (high-pass filter) to about 70 kHz, the compensation band of the first filter section 301 can be set to 150 kHz or higher. In addition, it is possible to prevent the common mode transformer 11 from increasing in size as described above.

The operation of the second filter unit 102 is the same as in the second embodiment. Therefore, in the third embodiment as well, the first filter section 301 and the second filter section 102 share the same functions as in the second embodiment. Thereby, common mode current can be suppressed in a wide frequency band.

As described above, in the first filter unit 301 of the third embodiment, while operating the common mode detection circuit 14 as a common mode choke coil, the amplification circuit 32 and the common mode transformer 11 detect high frequency components of 150 kHz or higher. Suppresses common mode currents. Furthermore, as in the second embodiment, the input of the amplifier circuit 22 of the second filter section 102 is the detection value i _o * of the current detection section 13 (shunt resistor 131) of the first filter section 301. . Therefore, the second filter section 102 does not require a dedicated common mode detection circuit.

In conventional common mode filters, a common detection circuit is sometimes provided for a plurality of filter units or injection circuits. A plurality of filter units or injection circuits are connected to the output terminal of the circuit, respectively, and the current flowing through the auxiliary winding of the detection common mode transformer constituting the common detection circuit is detected by each of the plurality of filter units or injection circuits. voltage conversion was performed in each terminal circuit. In this method, when a high resistance is applied to each termination circuit and the common detection circuit is used as a common mode choke coil, part of the current flowing through the main winding of the common mode transformer for detection is excited. Consumed as current. Particularly for low-frequency components, the impedance of the exciting inductance _Lm is lower than the impedance of the termination circuit, so most of the common mode current flows through the excitation inductance _Lm instead of the termination circuit. As a result, the current value of the current flowing through the secondary side of the transformer is smaller than the current value obtained by the equal ampere-turn theorem, that is, the value obtained by multiplying the current value of the primary side current by the turns ratio of the transformer. value. In this case, the detected value of the low frequency component of the common mode current becomes small, making it difficult to secure the feedback gain for the low frequency component. In other words, in the conventional method, it is difficult to suppress the low-frequency component of the common mode current with the amplifier circuit while allowing the common mode detection circuit to function as a common mode choke coil.

Therefore, in Embodiment 3, the detection value i _in * detected by the common mode detection circuit 14 is used to suppress the high frequency component of the common mode current, and the current detection unit 13 (shunt resistor 131) is used to suppress the low frequency component. The detection value i _o * detected in is used. Here, the detected value _io * is obtained by voltage-converting the current _io flowing through the auxiliary winding 112 of the common mode transformer 11 for suppressing the high frequency component of the common mode current. A termination circuit 15 configured as a high-pass filter is provided between the amplifier circuit 32 and the common mode detection circuit 14 to prevent low frequency components from being input to the amplifier circuit 32 . Therefore, the common mode transformer 11 operates as a CT with respect to low frequency components, and the amplified voltage _vo, which is the output of the amplifier circuit 32, contains almost no low frequency components. As a result, the current _io flowing through the auxiliary winding 112 for the low-frequency component is determined by the turns ratio between the main winding 111 and the auxiliary winding 112 of the common mode transformer 11, according to the equi-ampere-turn theorem. This means that it is possible to prevent mixing of detection disturbance such as excitation current in detection of the low-frequency component of the common mode current to be suppressed. Therefore, by obtaining the detected value i _o *, the low frequency component of the common mode current can be obtained with high accuracy, and the accuracy of the input value of the amplifier circuit 22 of the second filter unit 102 that suppresses the low frequency component is also improved. ing. As a result, the amount of attenuation of the low-frequency component of the common-mode current can be improved, and the low-frequency component can be further suppressed. It's becoming

In the above description, a high resistance of about 100 Ω is connected to the auxiliary winding 142. However, the configuration is not limited to this, and the detection value i _in * can be obtained from the voltage drop corresponding to the current i _in flowing through the auxiliary winding 142. Any passive circuit may be used as long as it is so long. When a low resistance is connected to the auxiliary winding 142, the common mode detection circuit 14 does not operate as a common mode choke coil, but operates as a CT. , this band is the entire band), the detection gain of the common mode detection circuit 14 is not lowered. Further, a circuit having characteristics of a high-pass filter, a low-pass filter, a band-pass filter, and a band-elimination filter may be connected to the auxiliary winding 142 according to the band to be compensated by the first filter unit. may be connected so that the auxiliary winding 142 does not limit the band.

Also, the common mode detection circuit can be configured with a Y capacitor. FIG. 12 is a circuit diagram showing a common mode filter according to Embodiment 3, and shows an example in which a Y capacitor is used as the common mode detection circuit. In common mode filter 3001 , first filter section 3011 includes common mode transformer 11 , amplifier circuit 32 , and current detection section 13 . Further, the first filter section 301 is provided with a common mode detection circuit 18 between the compensation target 3 and the amplifier circuit 32 .

The common mode detection circuit 18 is composed of a Y capacitor having a capacitor 181u connected to the power line 5u, a capacitor 181v connected to the power line 5v, and a capacitor 181w connected to the power line 5w. The neutral point of this Y capacitor is connected to ground line 6 via circuit 182 . again. Circuit 182 is connected to input terminal 124s and input terminal 124g of amplifier circuit 32 . A voltage dividing capacitor 183 is provided between the connection point between the circuit 182 and the input terminal 124s and the connection point between the circuit 182 and the input terminal 124g. The capacitor 183 detects, as a detection value v _in *, a voltage according to the main circuit current flowing through the

capacitors

181u, 181v, and 181w. This detected value v _in * is input to the amplifier circuit 32 through the

input terminals

124s and 124g. Others are the same as the example shown in FIG. A detection value i _o * detected by the current detection unit 13 is input to the amplifier circuit 22 of the second filter unit 102 .

As described above, in the third embodiment, common mode detection circuit 14 (or common mode detection circuit 18) is provided, and common mode detection circuit 14 (18) is provided in first filter section 301 (or first filter section 3011). The second filter unit 102 _uses the detected value i _o * based on the current i _in flowing through the auxiliary winding 112 of the common mode transformer 11 as an input. Since the common mode transformer 11 corresponds to the injection circuit of the first filter section 301 (3011), one detection circuit is provided for the two injection circuits (common mode transformer 11 and injection circuit 21). Therefore, in the third embodiment, it can be said that the common mode filter is made smaller than the conventional one. In addition, this also realizes cost reduction of the common mode filter.

In the first to third embodiments described above, the detected value i _o * obtained by voltage-converting the current detected by the current detection unit 13, or the voltage-converted current detected by the common mode detection circuit 14 is

Amplification circuits

12, 22, and 32 generate amplified voltages v _o and v _o2 using the obtained detection value i _in * as an input, and the amplified voltages v _o and v _o2 are applied to the auxiliary winding 112, etc., so that the power line 5 Inject compensation voltage. However, it is not limited to such a configuration. For example, instead of the amplifier circuit 12, an A/D (analog/digital) converter, a digital element such as a DSP or FPGA, a An analog) converter or an output circuit having a similar function (hereinafter "D/A converter, etc.") may be provided. In this case, the input signal taken in by the A/D converter is processed by the digital element, and the signal output from the digital element is converted to the output voltage by the D/A converter or the like so that the input signal is reduced. to generate Also, by applying the generated output voltage to the auxiliary winding 112 , a compensation voltage is injected into the power line 5 .

While this application describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more embodiments may not apply to particular embodiments. can be applied to the embodiments singly or in various combinations.
Therefore, countless modifications not illustrated are envisioned within the scope of the technology disclosed in the present application. For example, modification, addition or omission of at least one component, extraction of at least one component, and combination with components of other embodiments shall be included.
For example, there may be three or more filter units forming a common mode filter. In this case, one of the plurality of filter sections is used as a first filter section, and a common mode transformer 11 and a current detection section 13 for detecting a current _io flowing through an auxiliary winding 112 of the common mode transformer 11 are provided. At least one of the plurality of filter units (including the first filter unit) includes an amplifier circuit or the like that performs negative feedback control on the value i _o * detected by the current detection unit 13, and detects A configuration may be used in which a compensating voltage or compensating current is injected based on the value i _o *.

2 power conversion circuit 3

compensation target

4, 4u, 4v, 4w, 5, 5u, 5v, 5w, 7u, 7v, 7w power line 6 ground line 11

common mode transformer

12, 22, 32 amplifier circuit 13

Current detection section

14, 18 Common mode detection circuit 15

Termination circuit

21, 23

Injection circuit

100, 200, 300, 3001

Common mode filter

101, 301, 3011 First filter section 102 Second filter section , 111, 111u, 111v, 111w, 141u, 141v, 141w main winding, 112, 142 auxiliary winding, 121, 221 operational amplifier, 122, 222 input resistance, 123, 223 negative feedback resistance, 124s, 124g, 224s, 224g input terminal, 125s, 125g, 225 output terminal, 126, 127 high-pass filter, 131 shunt resistor, 132 CT, 133, 15 termination circuit, 14 common mode detection circuit, 224 input terminal, 225 output terminal, 226 low-pass filter, 1000 power conversion system, i _o current, i _in *, i _o *, v _in * detection value, v _o , v _o2 amplified voltage

Claims

A common mode filter connected to a power line between a compensation target and a power conversion circuit,
one or more filter units each having an injection circuit for injecting a compensation voltage or a compensation current into the power line to suppress a common mode current flowing through the power line;
The first filter unit of the filter units is
a common mode transformer having a main winding provided on the power line and an auxiliary winding magnetically coupled to the main winding;
a current detection unit that detects the current flowing through the auxiliary winding,
at least one of the filter units,
A common mode filter for injecting into the power line the compensation voltage or compensation current generated based on the current detected by the current detection unit.
The filter section is a plurality of filter sections including the first filter section and a second filter section different from the first filter section,
The first filter section injects into the power line the compensation voltage or compensation current that suppresses the common mode current for a first frequency band,
2. The common mode according to claim 1, wherein the second filter section injects into the power line the compensation voltage or compensation current that suppresses the common mode current in a second frequency band different from the first frequency band. filter.
Further comprising a common mode detection circuit that detects a common mode current flowing through the power line,
The first filter section injects into the power line the compensation voltage generated based on the common mode current detected by the common mode detection circuit,
3. The common mode filter according to claim 2, wherein said second filter section injects said compensation voltage or compensation current generated based on the current detected by said current detection section into said power line.
The common mode detection circuit has a second common mode transformer, and an auxiliary winding of the second common mode transformer provides the second common mode for the first frequency band or all frequency bands. 4. A common mode filter according to claim 3, further comprising a terminating circuit having an impedance higher than the impedance due to the magnetizing inductance of the transformer.
The filter unit includes an amplifier circuit that outputs an amplified voltage to the injection circuit,
The amplifier circuit receives a detection value obtained by the current detection unit as an input and generates the amplified voltage that reduces the detection value,
4. The common mode filter according to claim 1, wherein said injection circuit injects said compensation voltage or compensation current according to said amplified voltage into said power line.
The first filter section includes a first amplifier circuit that outputs a first amplified voltage to the injection circuit of the first filter section,
The first amplification circuit receives as input a first detection value obtained by the common mode detection circuit, and generates the first amplification voltage that decreases the first detection value,
The injection circuit of the first filter section injects the compensation voltage or the compensation current corresponding to the first amplified voltage into the power line,
The second filter section includes a second amplifier circuit that outputs a second amplified voltage to the injection circuit of the second filter section. The second amplifier circuit is a second amplifier obtained by the current detection section. using the detected value of as an input to generate the second amplified voltage that decreases the second detected value;
5. The common mode filter according to claim 3, wherein the injection circuit of said second filter section injects said compensation voltage or compensation current corresponding to said second amplified voltage into said power line.