Noise filter

Abstract

A noise filter (50) comprises: a noise detector (7) that detects a voltage due to electromagnetic noise generated by an electric power converter (2), and outputs a regulated voltage (Vd) obtained by regulating this voltage; a compensation signal applicator (75) that superimposes a compensation voltage (Vcom) of opposite polarity to the voltage due to the electromagnetic noise on an output or input of the electric power converter (2) through a transformer (11); and an injection voltage generator 30 that generates a first output voltage (Vo1) for generating an injection voltage (Vinj) between one end and another end of a primary winding (m1) of the transformer (11), and a second output voltage (Vo2) of opposite polarity to the first output voltage on the basis of the regulated voltage (Vd), and outputs the first output voltage and the second output voltage to the one end and the other end, respectively.

Description

Technical Field

[0001] This application relates to a noise filter.

Background Art

[0002] In recent years, in power conversion devices such as voltage type PWM (Pulse Width Modulation) inverters, with the development of power semiconductor devices, the carrier frequency has been increasing. However, with the increase in the carrier frequency, electromagnetic interference caused by the voltage of electromagnetic noise such as common mode voltage generated during the switching operation of power semiconductor devices has become a problem. To address this problem, a method has been proposed in which a voltage (canceling voltage) that cancels the common mode voltage generated by a power conversion device is superimposed using a common mode transformer, and the leakage current flowing to the ground due to the common mode voltage, that is, the common mode current, is suppressed (for example, Patent Document 1).

[0003] The conductive noise filter of Patent Document 1 includes a common mode transformer provided with a secondary winding, that is, a secondary side winding, in a three-phase cable connecting an inverter and an AC power supply, a push-pull emitter follower circuit connected to the primary winding, that is, the primary side winding, of the common mode transformer, three ground capacitors for detecting the common mode voltage, a voltage dividing capacitor for dividing the detected common mode voltage, and an operational amplifier for amplifying the divided common mode voltage and outputting it to the push-pull emitter follower circuit. The common mode transformer induces a canceling voltage with the same magnitude and opposite polarity as the detected common mode voltage in the secondary side winding. The conductive noise filter of Patent Document 1 divides the detected common mode voltage and induces a canceling voltage in the secondary side winding according to the turns ratio of the primary side winding and the secondary side winding of the common mode transformer, thereby reducing the voltage output to the primary side winding of the common mode transformer. As a result, the breakdown voltage of the active elements used in the emitter follower circuit and the operational amplifier can be reduced.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent No. 5263663 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] However, in the conductive noise filter of Patent Document 1, a cancellation voltage lower than the common-mode voltage generated in the three-phase cable is induced in the secondary winding. In order to enhance the noise reduction effect, it is necessary to generate a larger cancellation voltage or cancellation current, that is, a compensation voltage or compensation current, in the secondary winding. For this purpose, it is necessary to increase the turns ratio of the common-mode transformer or increase the voltages of the emitter follower circuit and the operational amplifier. When increasing the turns ratio of the common-mode transformer, the number of turns of the three-phase secondary winding is increased, resulting in an increase in the size of the common-mode transformer. On the other hand, when increasing the voltages of the emitter follower circuit and the operational amplifier, an emitter follower circuit and an operational amplifier with high voltage generation capabilities, and a high-voltage power supply for driving them are required. As a result, the size and weight of the entire device increase.

[0006] The technology disclosed in the present specification aims to provide a noise filter that is small and lightweight and can enhance the noise reduction effect. [Means for Solving the Problems]

[0007] An example of the noise filter disclosed in the present specification is a noise filter that reduces the voltage or current of electromagnetic noise generated by a power converter that performs power conversion by the switching operation of a semiconductor element. A noise detector that detects a voltage based on the electromagnetic noise generated by the power converter and outputs an adjusted voltage in which the voltage based on the electromagnetic noise is adjusted, and a compensation voltage having a polarity opposite to that of the voltage based on the electromagnetic noise are superimposed on the output or input of the power converter via a transformer. A compensation signal applicator, a first output voltage that generates an injection voltage between one end and the other end of the primary winding of the transformer, and a second output voltage having a polarity opposite to that of the first output voltage are generated based on the adjusted voltage. And an injection voltage generator that outputs the first output voltage to one end of the primary winding of the transformer and the second output voltage to the other end of the primary winding of the transformer. The injection voltage generator generates a first output voltage and a second output voltage that generate an injection voltage such that the difference between the compensation voltage superimposed by the compensation signal applicator and the voltage based on the electromagnetic noise is equal to or less than an allowable value.

Advantages of the Invention

[0008] An example of the noise filter disclosed in the present specification applies a first output voltage and a second output voltage having a polarity opposite to that of the first output voltage to both ends of the primary winding in the transformer of the compensation signal applicator, respectively, and based on an injection voltage having the same polarity as the first output voltage and larger than the first output voltage. Since the compensation voltage is superimposed on the output or input of the power converter, it can be made small and lightweight and the noise reduction effect can be enhanced.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0010] A noise filter and an electric motor drive system will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals for description.

[0011] Embodiment 1. FIG. 1 is a diagram showing the configuration of the first noise filter and the electric motor drive system according to Embodiment 1, FIG. 2 is a diagram showing the configuration of the power converter in FIG. 1, FIG. 3 is a diagram showing the configuration of the signal conditioning circuit included in the noise detector in FIG. 1, FIG. 4 is a diagram showing a first example of the injection waveform generator in FIG. 1, FIG. 5 is a diagram showing a second example of the injection waveform generator in FIG. 1, and FIG. 6 is a diagram showing a third example of the injection waveform generator in FIG. 1. FIG. 7 is a diagram showing the configuration of the second noise filter and the electric motor drive system according to Embodiment 1, and FIG. 8 is a diagram showing the configuration of the third noise filter and the electric motor drive system according to Embodiment 1. FIG. 9 is a diagram showing the core of the noise filter according to Embodiment 1, FIG. 10 is a diagram showing the configuration of the fourth noise filter and the electric motor drive system according to Embodiment 1, and FIG. 11 is a diagram showing the fifth noise filter and the electric motor drive system according to Embodiment 1. FIG. 12 is a diagram showing the configuration of the signal conditioning circuit in FIG. 11. The noise filter 50 in Embodiment 1 can be applied to an electric motor drive system 60 which is a system for controlling an induction motor 3, which is an inductive load, by a power converter 2 such as a voltage-type PWM inverter in which a plurality of semiconductor elements perform a switching operation.

[0012] The electric motor drive system 60 includes an AC power source 1 such as a power grid or a self - contained voltage source, a power converter 2 that converts the AC power of the AC power source 1 into DC power and then converts the DC power back into AC power, a three - phase power line 4 connecting between the AC power source 1 and the power converter 2, a three - phase power line 5 connecting between the power converter 2 and the induction motor 3, and a noise filter 50. The induction motor 3 is grounded by a ground wire 6. The potential of the ground GND, that is, the ground potential, is the reference potential of the noise filter 50. The three - phase power line 4 includes a three - phase power line 4u for the u - phase, a three - phase power line 4v for the v - phase, and a three - phase power line 4w for the w - phase. The three - phase power line 5 includes a three - phase power line 5u for the u - phase, a three - phase power line 5v for the v - phase, and a three - phase power line 5w for the w - phase.

[0013] The noise filter 50 reduces the voltage or current of the electromagnetic noise generated by the power converter 2 that performs power conversion by the switching operation of the semiconductor element. The noise filter 50 includes a noise detector 7 that detects the voltage of the electromagnetic noise generated by the power converter 2 and outputs an adjusted voltage Vd with the voltage of the electromagnetic noise adjusted, and a compensation signal applicator 75 that superimposes a compensation voltage Vcom having a polarity opposite to that of the voltage of the electromagnetic noise on the output or input of the power converter 2 via a transformer 11 having a primary winding m1 and a secondary winding m2 on the primary side and the secondary side, respectively. An injection voltage Vinj is generated between one end and the other end of the primary winding m1 of the transformer 11, and a first output voltage Vo1 and a second output voltage Vo2 having a polarity opposite to that of the first output voltage Vo1 are generated based on the adjusted voltage Vd. The first output voltage Vo1 is output to one end of the primary winding m1 of the transformer 11, and the second output voltage Vo2 is output to the other end of the primary winding m1 of the transformer 11. The injection voltage generator 30 is provided. The voltage of the electromagnetic noise is, for example, the common mode voltage Vci. The current of the electromagnetic noise is, for example, the common mode current flowing due to the application of the common mode voltage Vci to the common mode path. In Embodiment 1, an example in which the noise detector 7 detects the voltage of the electromagnetic noise as the voltage based on the electromagnetic noise will be described. An example in which the noise detector 7 detects the voltage proportional to the current of the electromagnetic noise, that is, the monomode current, as the voltage based on the electromagnetic noise will be described in Embodiment 5. The injection voltage generator 30 includes injection waveform generators 10a and 10b. The compensation signal applicator 75 includes a transformer 11. Appropriately, the first output voltage Vo1 and the second output voltage Vo2 are expressed as the first output voltage Vo1 and the second output voltage Vo2, respectively.

[0014] The power converter 2 includes a forward conversion circuit 21 composed of semiconductor elements, a capacitor 22 which is a power storage element for storing DC power, and an inverter circuit 23 composed of semiconductor elements for converting DC power into AC power. The forward conversion circuit 21 is, for example, a rectifier circuit and includes six diodes D1, D2, D3, D4, D5, and D6. The inverter circuit 23 includes six semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6. The three-phase power lines 4u, 4v, 4w, one end of which is connected to the AC power source 1, are each connected at the other end to the AC input terminals 41u, 41v, 41w of the power converter 2. The three-phase power lines 5u, 5v, 5w, one end of which is connected to the induction motor 3, are each connected at the other end to the AC output terminals 42u, 42v, 42w of the power converter 2.

[0015] The forward conversion circuit 21 has a first series body which is diodes D1 and D2 connected in series between a high potential side wiring 44p and a low potential side wiring 44s, a second series body which is diodes D3 and D4 connected in series, and a third series body which is diodes D5 and D6 connected in series. The connection point n1 between diode D1 and diode D2 is connected to the AC input terminal 41u. The connection point n2 between diode D3 and diode D4 is connected to the AC input terminal 41v, and the connection point n3 between diode D5 and diode D6 is connected to the AC input terminal 41w. The capacitor 22 is connected between the high potential side wiring 44p and the low potential side wiring 44s. The inverter circuit 23 has a fourth series body which is semiconductor elements Q1 and Q2 connected in series between the high potential side wiring 44p and the low potential side wiring 44s, a fifth series body which is semiconductor elements Q3 and Q4 connected in series, and a sixth series body which is semiconductor elements Q5 and Q6 connected in series. The connection point n4 between semiconductor element Q1 and semiconductor element Q2 is connected to the AC output terminal 42u. The connection point n5 between semiconductor element Q3 and semiconductor element Q4 is connected to the AC output terminal 42v, and the connection point n6 between semiconductor element Q5 and semiconductor element Q6 is connected to the AC output terminal 42w.

[0016] The semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6 are power semiconductor elements such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors). An example of a MOSFET is shown in FIG. 2. The semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6 include an MOS transistor M and a diode D. The diode D may be a separate element from the MOS transistor M or a parasitic diode. The drains d of the semiconductor elements Q1, Q3, and Q5 are connected to the high-potential side wiring 44p, and the sources s of the semiconductor elements Q2, Q4, and Q6 are connected to the low-potential side wiring 44s. The source s of the semiconductor element Q1 and the drain d of the semiconductor element Q2 are connected, the source s of the semiconductor element Q3 and the drain d of the semiconductor element Q4 are connected, and the source s of the semiconductor element Q5 and the drain d of the semiconductor element Q6 are connected. A control signal is input to the gates g of the semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6 from a control circuit (not shown). The inverter circuit 23 switches the semiconductor elements Q1, Q2, Q3, Q4, Q5, and Q6 based on the control signal from the control circuit to convert DC power into AC power.

[0017] The noise detector 7 that detects the common-mode voltage Vci includes three capacitors 8 having equal capacitances to each other and a signal conditioning circuit 9. One end of each capacitor 8 is connected to each phase of the three-phase power line 5. The other ends of the capacitors 8 are connected to each other at the connection point n7. The signal conditioning circuit 9 has its input terminal 94 connected to the connection point n7 to which the other end of the capacitor 8 is connected, and its output terminal 95 connected to the input terminals 51a and 51b of the injection waveform generators 10a and 10b. The signal conditioning circuit 9 outputs, as an output voltage, an adjusted voltage Vd obtained by dividing the common-mode voltage Vci, which is the input voltage between the input terminal 94 and the wiring 24 that is a ground potential wiring, or band-limiting it, or both. The noise detector 7 detects the common-mode voltage Vci and outputs an adjusted voltage Vd based on the common-mode voltage Vci. More specifically, the noise detector 7 includes the capacitor 8 and the signal conditioning circuit 9 connected in series between the three-phase power line 5 on the output side of the power converter 2 and the wiring 24 that is a ground wiring, and the signal conditioning circuit outputs the adjusted voltage Vd based on the input voltage, that is, the common-mode voltage Vci, input through the capacitor 8.

[0018] As shown in FIG. 3, the signal conditioning circuit 9 includes, for example, a capacitor 91, a differential amplifier 92 connected in parallel with the capacitor 91, a band limiter 93, and control power supplies 15a and 15b. The control power supply 15a supplies a positive-side voltage, and the control power supply 15b supplies a negative-side voltage. One end of the capacitor 91 and the inverting input terminal (negative-side input terminal) of the differential amplifier 92 are connected to the input terminal 94, and the other end of the capacitor 91 and the non-inverting input terminal (positive-side input terminal) of the differential amplifier 92 are connected to the wiring 24 at ground potential. The output of the differential amplifier 92 is connected to the band limiter 93, and the output of the band limiter 93 is output from the output terminal 95 as the adjusted voltage Vd. The band limiter 93 only needs to be able to pass the target frequency band, and any of a band-pass filter, a low-pass filter, and a high-pass filter can be applied.

[0019] The adjustment voltage Vd is input to the input terminals 51a and 51b of the injection waveform generators 10a and 10b. The injection voltage generator 30 includes a first injection waveform generator 10a that generates a first output voltage Vo1 based on the adjustment voltage Vd, and a second injection waveform generator 10b that generates a second output voltage Vo2 based on the adjustment voltage Vd. The injection waveform generators 10a and 10b output, from the output terminals 52a and 52b, voltages that are band-limited and have amplified voltage values, that is, the output voltages Vo1 and Vo2, based on the input adjustment voltage Vd. The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 10a is input to one end of the primary winding m1 of the transformer 11. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 10b is input to of the primary winding m1 the other end. The output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite phases to each other. That is, the output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite polarities to each other. A voltage that is the difference between the output voltage Vo1 and the output voltage Vo2, that is, a voltage of the same phase and the same polarity as twice the magnitude of Vo1, is applied to the primary winding m1 of the transformer 11.

[0020] The transformer 11 includes a primary winding m1 and a secondary winding m2 on the primary side and the secondary side, respectively. The secondary winding m2 of the transformer 11 is inserted into each phase of the three-phase power line 5, that is, the three-phase power lines 5u, 5v, and 5w. A voltage that is the difference between the output voltage Vo1 output from the injection waveform generator 10a and the output voltage Vo2 output from the injection waveform generator 10b, that is, the injection voltage Vinj, is applied to the primary winding m1 of the transformer 11, and has a polarity opposite to that of the common-mode voltage Vci. A compensation voltage Vcom, which is a voltage corresponding to the turns ratio of the primary winding m1 and the secondary winding m2, is generated in the secondary winding m2. The compensation voltage Vcom is a superimposed voltage superimposed on the three-phase power line 5.

[0021] The power converter 2 generates a common-mode voltage Vci that changes stepwise each time the semiconductor elements Q1 to Q6 perform a switching operation. This common-mode voltage Vci is detected by the noise detector 7 and adjusted to an adjustment voltage Vd. The adjustment voltage Vd is the difference between the output voltage Vo1 and the output voltage Vo2, which are band-limited and amplified in voltage value by the injection waveform generators 10a and 10b and then output. The injection voltage Vinj is input to the primary winding m1 of the transformer 11. The voltage generated in the secondary winding m2 of the transformer 11, that is, the compensation voltage Vcom, is set to reduce the common-mode voltage Vci generated by the power converter 2. Therefore, the noise filter 50 of the first embodiment inputs the injection voltage Vinj, which has the opposite polarity to the common-mode voltage Vci and is an adjusted voltage, to the transformer 11 based on the common-mode voltage Vci detected by the noise detector 7 and superimposes the compensation voltage Vcom on each phase of the three-phase power line 5, so that the common-mode voltage Vci can be suppressed. It will be explained that the noise filter 50 of the first embodiment can enhance the noise reduction effect while being small and lightweight.

[0022] The injection waveform generator 10a can apply the first to third examples of the injection waveform generator 10 shown in FIGS. 4 to 6. Also, the injection waveform generator 10b applies the injection waveform generator 10 in which the output voltage Vo2 is out of phase with the output voltage Vo1 of the injection waveform generator 10a. When these injection waveform generators 10 are applied to the injection waveform generator 10a shown in FIG. 1, the input terminal 51, the output terminal 52, and the output voltage Vo of the injection waveform generator 10 become the input terminal 51a, the output terminal 52a, and the output voltage Vo1, respectively. When these injection waveform generators 10 are applied to the injection waveform generator 10b shown in FIG. 1, the input terminal 51, the output terminal 52, and the output voltage Vo of the injection waveform generator 10 become the input terminal 51b, the output terminal 52b, and the output voltage Vo2, respectively. Appropriately, the injection waveform generator 10a that outputs the output voltage Vo1 is expressed as the first injection waveform generator 10a, and the injection waveform generator 10b that outputs the output voltage Vo2 is expressed as the second injection waveform generator 10b.

[0023] The injection waveform generator 10 of the first example shown in FIG. 4 includes a band limiter 12, an amplifier 13, and control power supplies 15a and 15b. The control power supply 15a supplies a positive voltage, and the control power supply 15b supplies a negative voltage. Since the band limiter 12 can apply only the frequency band to be reduced in the common mode voltage Vci to the transformer 11, the transformer 11 can be miniaturized. The band limiter 12 only needs to allow the target frequency band to pass through, and any one of a band-pass filter, a low-pass filter, and a high-pass filter can be applied. The amplifier 13 shown in FIG. 4 is an example of an inverting amplifier circuit. The amplifier 13 includes an operational amplifier 19, and resistors 16, 17, and 18. The ground potential is input to the positive input terminal of the operational amplifier 19 via the resistor 17. The output of the band limiter 12 is input to the negative input terminal of the operational amplifier 19 via the resistor 16, and the output of the operational amplifier 19 is input via the resistor 18.

[0024] The gain Gi of the operational amplifier 19 can be expressed by Equation (1), where the resistance values of the resistors 16 and 18 are r1 and r2, respectively. The output voltage Vo can be expressed by Equation (2). Gi = r2 / r1 ···(1) Vo = -Gi×Vd ···(2)

[0025] In the injection waveform generator 10 of the first example, the amplifier 13 shows an example of an inverting amplifier circuit, but the amplifier 13 may be a non-inverting amplifier circuit. The injection waveform generator 10 of the second example shown in FIG. 5 is an example of a non-inverting amplifier circuit. The output of the band limiter 12 is input to the positive input terminal of the operational amplifier 19 via the resistor 17. The ground potential is input to the negative input terminal of the operational amplifier 19 via the resistor 16, and the output of the operational amplifier 19 is input via the resistor 18.

[0026] The gain Gi of the operational amplifier 19 in the non-inverting amplifier circuit can be expressed by Equation (3), where the resistance values of the resistors 16 and 18 are r1 and r2, respectively. The output voltage Vo can be expressed by Equation (4). Gi = 1 + r2 / r1 ···(3) Vo = Gi×Vd ···(4)

[0027] Since the injection waveform generators 10a and 10b each output output voltages Vo1 and Vo2 of the same magnitude but opposite phases, for example, the injection waveform generator 10a is composed of a non-inverting amplifier circuit, and the injection waveform generator 10b is composed of an inverting amplifier circuit to satisfy this.

[0028] When the first injection waveform generator 10a is composed of a non-inverting amplifier circuit and the second injection waveform generator 10b is composed of an inverting amplifier circuit, the output voltages Vo1 and Vo2 are calculated from Expressions (2) and (4) respectively. Since the injection voltage Vinj is the difference between the output voltage Vo1 and the output voltage Vo2, it can be expressed by Expression (5). Vinj = Vo1 - Vo2 ···(5)

[0029] Since the output voltages Vo1 and Vo2 are of the same magnitude and opposite phases to each other, the injection voltage Vinj becomes a signal having an amplitude twice that of the output voltage Vo1 as expressed by Expression (6). Vinj = 2×Vo1 ···(6)

[0030] The gain Gi and the turns ratio Rr are set so that the compensation voltage Vcom, which is the voltage superimposed on the u-phase, v-phase, and w-phase of the three-phase power line 5 via the secondary winding m2 of the transformer 11, reduces the common mode voltage Vci, that is, so that Expression (7) holds. |Vci - Vcom| ≦ Vto ···(7) Here, Vto is the allowable value of the voltage difference. Expression (7) indicates that the absolute value of the difference between the common mode voltage Vci and the compensation voltage Vcom is equal to or less than the allowable value Vto.

[0031] The turns ratio Rr of the transformer 11 can be expressed by Expression (8) when the number of turns of the primary winding m1 and the secondary winding m2 are N1 and N2 respectively. Rr = N2 / N1 ···(8)

[0032] The maximum voltage of the output voltage Vo of the injection waveform generator 10 becomes the voltages of the control power supplies 15a and 15b. When one injection waveform generator 10 is connected to the transformer 11 as in Patent Document 1, the maximum voltage of the injection voltage Vinj becomes the voltages of the control power supplies 15a and 15b. However, in the noise filter 50 of Embodiment 1, the first injection waveform generator 10a and the second injection waveform generator 10b are provided, and output voltages Vo1 and Vo2 having the same magnitude and opposite phases are input to one end and the other end of the primary winding m1 of the transformer 11, respectively. For this reason, the noise filter 50 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b as shown in Equation (6) without increasing the output voltage Vo output by one injection waveform generator 10, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 10a and 10b. As a result, the transformer 11 of Embodiment 1 has a smaller turns ratio Rr required to satisfy Equation (7).

[0033] The transformer 11 includes one primary winding m1 and three secondary windings m2. The core of the transformer 11 is, for example, the toroidal core 28 shown in FIG. 9. The inner diameter of the core 28 is l, the outer diameter is L, and the width (thickness) is h. Reducing the turns ratio Rr and reducing the number of turns of the secondary winding m2 reduces the inner diameter l of the core that is minimally required for mounting the transformer, enabling miniaturization of the core, miniaturization of the transformer, and miniaturization and weight reduction of the noise filter 50.

[0034] When the first injection waveform generator 10a is configured by an inverting amplifier circuit and the second injection waveform generator 10b is configured by a non-inverting amplifier circuit, as shown in FIG. 7, the connection to the primary winding m1 of the transformer 11 is changed in reverse, and the compensation voltage Vcom, which is the voltage output to the secondary winding m2, is set to reduce the common mode voltage Vci. Similar to the first noise filter 50, the second noise filter 50 shown in FIG. 7 can apply the injection voltage Vinj shown in Equations (5) and (6) to the primary winding m1 of the transformer 11.

[0035] In the noise filter 50 of Embodiment 1, without increasing the output voltages Vo1 and Vo2 output by each injection waveform generator 10a and 10b, an injection voltage Vinj whose maximum voltage becomes twice that of the control power supplies 15a and 15b can be obtained as shown in Equation (6). Therefore, compared with the case where one injection waveform generator 10 is connected to the transformer 11 as in Patent Document 1, the voltage of the control power supply required to obtain the same injection voltage Vinj is halved. As a result, the control power supplies 15a and 15b of the injection waveform generator 10 can be miniaturized, and the noise filter 50 can be miniaturized and lightened.

[0036] The injection waveform generator 10 of the third example shown in FIG. 6 will be described. The injection waveform generator 10 of the third example differs from the injection waveform generator 10 of the first example in that a current buffer 14 is added between the output terminal of the amplifier 13 and the output terminal 52. The output terminal of the amplifier 13 is the connection point between the wiring that transmits the output of the operational amplifier 19 and the resistor 18. The injection waveform generator 10 of the third example can increase the current capacity indicating the current supply amount compared to the injection waveform generator 10 of the first example. The current buffer 14 includes, for example, two transistors BT1 and BT2 connected in series. The collector c of the transistor BT1 is connected to the control power supply 15a, the emitter e of the transistor BT1 is connected to the emitter e of the transistor BT2, and the collector c of the transistor BT2 is connected to the control power supply 15b. The bases b of the transistors BT1 and BT2 receive the output of the amplifier 13, and the emitters e of the transistors BT1 and BT2 are connected to the output terminal 52. A current buffer 14 may be added to the injection waveform generator 10 of the second example.

[0037] Although the example where the noise detector 7 shown in FIG. 1 is connected to the three-phase power line 5 is shown, as shown in FIG. 8, the noise detector 7 can also be connected to the three-phase power line 4. Even in this case, since the common mode voltage Vci detected from the three-phase power line 4 is equivalent to the common mode voltage Vci detected from the three-phase power line 5, it is only necessary to satisfy Equation (7).

[0038] In FIG. 1, an example in which the transformer 11 is inserted into the three-phase power line 5 is shown. However, as shown in FIG. 7, the positions of the transformer 11 and the noise detector 7 may be exchanged. The noise filter 50 of the first example shown in FIG. 1 has a feed-forward configuration, while the noise filter 50 of the second example shown in FIG. 7 has a feedback configuration.

[0039] As an example of the signal conditioning circuit 9, an example including a capacitor 91, a differential amplifier 92, and a band limiter 93 is shown. However, the signal conditioning circuit 9 is not limited to this. The signal conditioning circuit 9 may have a configuration including only the capacitor 91 and the differential amplifier 92, a configuration in which the capacitor 91 is replaced with a resistor, or a configuration in which the number of capacitors and resistors is increased. Further, when the common-mode voltage Vci is not divided, the signal conditioning circuit 9 may include only the band limiter 93.

[0040] Also, for example, like the fourth noise filter 50 of Embodiment 1 shown in FIG. 10, the adjustment voltage Vd, which is the output of the noise detector 7, is input only to the first injection waveform generator 10a. The output terminal 52a of the first injection waveform generator 10a is connected to one end of the primary winding m1 of the transformer 11 and the input terminal 51b of the second injection waveform generator 10b, and the output terminal 52b of the second injection waveform generator 10b may be connected to the other end of the primary winding m1 of the transformer 11. The second injection waveform generator 10b receives the output voltage Vo1, which is the output of the first injection waveform generator 10a. The fourth injection voltage generator 30 of Embodiment 1 includes a first injection waveform generator 10a that generates a first output voltage Vo1 based on the adjustment voltage Vd, and a second injection waveform generator 10b that generates a second output voltage Vo2 based on the first output voltage Vo1. Even in this case, the output voltage Vo1 of the first injection waveform generator 10a and the output voltage Vo2 of the second injection waveform generator 10b are voltages of the same magnitude and opposite phases. In order to output the output voltage Vo2, which has the same magnitude as the output voltage Vo1 and is of the opposite phase, the second injection waveform generator 10b applies a circuit that multiplies the input signal by a gain of unity and rotates the phase by 180°. That is, the gain Gi of the operational amplifier 19 of the second injection waveform generator 10b is -1 when the gain Gi of the first injection waveform generator 10a is positive, and 1 when the gain Gi of the first injection waveform generator 10a is negative.

[0041] In the fourth noise filter 50 of the first embodiment, since the second injection waveform generator 10b only needs to turn the phase of the input signal by 180° with the gain being equal magnification, the band limiter 12 may be the one in the first injection waveform generator 10a, and the band limiter 12 of the second injection waveform generator 10b can be removed.

[0042]

[0041] Also, for example, like the fifth noise filter 50 of the first embodiment shown in FIG. 11, the signal adjustment circuit 9 included in the noise detector 7 has two output terminals 95a and 95b, and outputs adjustment voltages Vd1 and Vd2 of the same magnitude and opposite phases respectively. Further, the adjustment voltage Vd1 may be input to the first injection waveform generator 10a, and the adjustment voltage Vd2 may be input to the second injection waveform generator 10b. Even in this case, the output voltage Vo1 of the first injection waveform generator 10a and the output voltage Vo2 of the second injection waveform generator 10b are voltages of the same magnitude and opposite phases to each other. Appropriately, the output terminal 95a is expressed as the first output terminal 95a, and the output terminal 95b is expressed as the second output terminal 95b. Also, appropriately, the adjustment voltage Vd1 is expressed as the first adjustment voltage Vd1, and the adjustment voltage Vd2 is expressed as the second adjustment voltage Vd2.

[0043] For the fifth noise filter 50 of the first embodiment, for example, the signal adjustment circuit 9 shown in FIG. 12 can be applied. The signal adjustment circuit 9 in FIG. 12 is different from the signal adjustment circuit 9 in FIG. 3 in that it includes two differential amplifiers 92a and 92b, two band limiters 93a and 93b, and two output terminals 95a and 95b. The differential amplifier 92b is connected in parallel with the differential amplifier 92a, the non-inverting input terminal of the differential amplifier 92a is connected to the inverting input terminal of the differential amplifier 92b, and the inverting input terminal of the differential amplifier 92a is connected to the non-inverting input terminal of the differential amplifier 92b. The outputs of the differential amplifiers 92a and 92b are respectively connected to band limiters 93a and 93b of the same configuration, and the adjustment voltages Vd1 and Vd2 are output from the output terminals 95a and 95b.

[0044] Since the adjustment voltages Vd1 and Vd2 are equal in magnitude and opposite in phase to each other, the injection waveform generators 10a and 10b can be configured with circuits having the same gain and the same phase characteristics. That is, a common circuit can be used, and the characteristic error between the injection waveform generators 10a and 10b can be reduced.

[0045] Also, in the fifth noise filter 50 of the first embodiment, the magnitudes of the adjustment voltages Vd1 and Vd2 output from the output terminals 95a and 95b may be different and the phases may be the same. The injection waveform generators 10a and 10b respectively input according to the adjustment voltages Vd1 and Vd2 are set to output output voltages Vo1 and Vo2 that are equal in magnitude and opposite in phase. As a result, similar to the first noise filter 50 of the first embodiment, the fifth noise filter 50 of the first embodiment does not increase the output voltage Vo output by one injection waveform generator 10, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 10a and 10b, an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b can be obtained. As a result, the fifth noise filter 50 of the first embodiment enables miniaturization of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0046] The fifth noise filter 50 of the first embodiment includes a capacitor 8 and a signal conditioning circuit 9 connected in series between the output side or the input side of the three-phase power lines 5 and 4 of the power converter 2 and the wiring 24 which is a ground wiring by the noise detector 7. In the fifth noise filter 50 of the first embodiment, the signal conditioning circuit 9 outputs a first adjustment voltage Vd1 and a second adjustment voltage Vd2 which are two adjustment voltages based on the common mode voltage Vci which is the input voltage input via the capacitor 8, and the injection voltage generator 30 includes a first injection waveform generator 10a that generates a first output voltage Vo1 based on the first adjustment voltage Vd1, and a second injection waveform generator 10b that generates a second output voltage Vo2 based on the second adjustment voltage Vd2. Therefore, the fifth noise filter 50 of the first embodiment enables miniaturization of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0047] In Embodiment 1, the case where the output voltages Vo1 and Vo2 have the same magnitude was shown. However, the output voltages Vo1 and Vo2 may have different magnitudes. Even when they have different magnitudes, a differential voltage between the output voltage Vo1 and the output voltage Vo2, that is, an injection voltage Vinj which is a voltage larger than the output voltage Vo1 and in the same phase, is applied to the primary winding m1 of the transformer 11. As a result, the noise filter 50 of Embodiment 1 can be miniaturized in terms of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0048] As described above, the noise filter 50 of Embodiment 1 is a noise filter that reduces the voltage or current (common mode voltage Vci) of electromagnetic noise generated by the power converter 2 that performs power conversion by the switching operation of the semiconductor elements Q1 to Q6. The noise filter 50 detects a voltage (common mode voltage Vci) based on the electromagnetic noise generated by the power converter 2, and outputs an adjusted voltage Vd in which the voltage (common mode voltage Vci) based on the electromagnetic noise is adjusted. A noise detector 7, a compensation signal adder 75 that superimposes a compensation voltage Vcom having a polarity opposite to that of the voltage (common mode voltage Vci) based on the electromagnetic noise on the output or input of the power converter 2 via the transformer 11, and a first output voltage Vo1 that generates an injection voltage Vinj between one end and the other end of the primary winding m1 of the transformer 11, and a second output voltage Vo2 having a polarity opposite to that of the first output voltage Vo1 are generated based on the adjusted voltage Vd, and the first output voltage Vo1 is output to one end of the primary winding m1 of the transformer 11, and the second output voltage Vo2 is output to the other end of the primary winding m1 of the transformer 11. The injection voltage generator 30 is provided. The injection voltage generator 30 generates a first output voltage Vo1 and a second output voltage Vo2 that generate an injection voltage Vinj such that the difference between the compensation voltage Vcom superimposed by the compensation signal adder 75 and the voltage (common mode voltage Vci) based on the electromagnetic noise is equal to or less than the allowable value Vto. With this configuration, the noise filter 50 of Embodiment 1 applies the first output voltage Vo1 and the second output voltage Vo2 having a polarity opposite to that of the first output voltage Vo1 to both ends of the primary winding m1 of the transformer 11 of the compensation signal adder 75, respectively, and superimposes the compensation voltage Vcom on the output or input of the power converter 2 based on the injection voltage Vinj having the same polarity as the first output voltage Vo1 and larger than the first output voltage Vo1. Therefore, it is possible to reduce the size and weight and enhance the noise reduction effect.

[0049] The noise filter 50 of Embodiment 1 has an injection voltage generator 30 including two injection waveform generators 10a and 10b. By applying output voltages Vo1 and Vo2 with opposite phases (opposite polarities) to the primary winding m1 of the transformer 11 of the compensation signal applicator 75, a large injection voltage Vinj can be obtained without increasing the output of one injection waveform generator, that is, without increasing the voltages of the control power supplies 15a and 15b. Since the amplification by the turns ratio Rr of the transformer 11 can be reduced, the number of turns of the transformer 11 can be decreased, and the transformer 11 can be miniaturized. Even when reducing the output voltage per injection waveform generator without changing the turns ratio Rr of the transformer 11, the voltages of the control power supplies 15a and 15b can be reduced, so the control power supplies 15a and 15b can be miniaturized. Therefore, the noise filter 50 of Embodiment 1 can miniaturize the entire noise filter.

[0050] Embodiment 2. FIG. 13 is a diagram showing the configuration of a first noise filter and an electric motor drive system according to Embodiment 2, and FIG. 14 is a diagram showing the configuration of a second noise filter and an electric motor drive system according to Embodiment 2. FIG. 15 is a diagram showing the configuration of a third noise filter and an electric motor drive system according to Embodiment 2. FIG. 16 is a diagram showing a first example of the injection waveform generator of Embodiment 2, FIG. 17 is a diagram showing a second example of the injection waveform generator of Embodiment 2, and FIG. 18 is a diagram showing a third example of the injection waveform generator of Embodiment 2. The noise filter 50 of Embodiment 2, similar to Embodiment 1, can be applied to an electric motor drive system 60 which is a system for controlling an induction motor 3 by a power converter 2 such as a voltage type PWM inverter in which a plurality of semiconductor elements perform a switching operation.

[0051] The noise filter 50 of Embodiment 2 is different from the noise filter 50 of Embodiment 1 in that the noise detector 7 includes a voltage dividing transformer 70 instead of the signal conditioning circuit 9, and the injection waveform generators 10a and 10b based on the potential of the ground GND, i.e., the ground potential, are changed to the injection waveform generators 31a and 31b based on the reference potential Vss which is a potential separated from the ground GND. The parts different from the noise filter 50 of Embodiment 1 will be mainly described. Similar to the transformer 11, the voltage dividing transformer 70 includes a primary winding m3 and a secondary winding m4 on the primary side and the secondary side respectively. The input terminal 94 is connected to one end of the primary winding m3, and the output terminal 95 is connected to one end of the secondary winding m4. The noise detector 7 includes three capacitors 8 having equal capacitances to each other and the voltage dividing transformer 70, and one end of each capacitor 8 is connected to each phase of the three-phase power line 5. The other ends of the capacitors 8 are connected to each other at the connection point n7. For the voltage dividing transformer 70, the input terminal 94 to which one end of the primary winding m3 is connected is connected to the connection point n7, and the other end of the primary winding m3 is connected to the wiring 24 having the ground potential. Also, for the voltage dividing transformer 70, one end of the secondary winding m4 is connected to the output terminal 95, and the other end of the secondary winding m4 is connected to the wiring 25 which is a reference wiring having the reference potential Vss such as the injection voltage generator 30. The wiring 25 is a reference wiring having the reference potential Vss.

[0052] The noise detector 7 of Embodiment 2 includes a capacitor 8 and a voltage dividing transformer 70 connected in series between the three-phase power lines 5 and 4 on the output side or the input side of the power converter 2 and the wiring 24 which is a ground wiring. One end of the primary winding m3 of the voltage dividing transformer 70 is connected to the end of the capacitor 8 opposite to the three-phase power lines 5 and 4, and the other end is connected to the wiring 24 which is a ground wiring. One end of the secondary winding m4 of the voltage dividing transformer 70 is connected to the wiring 25 which is a reference wiring having a reference potential Vss different from the ground potential of the wiring 24 which is a ground wiring, and the other end is connected to the output terminal 95 which outputs the adjustment voltage Vd. The noise detector 7 outputs the adjustment voltage Vd based on the input voltage, i.e., the common mode voltage Vci, input through the capacitor 8 by the voltage dividing transformer 70. FIG. 13 shows an example in which the noise detector 7 is connected to the three-phase power line 5.

[0053] Since one end of the voltage dividing transformer 70 on the side opposite to the input terminal 94 in the primary winding m3 is connected to the wiring 24 at the ground potential, and one end of the secondary winding m4 on the side opposite to the output terminal 95 is connected to the wiring 25 at the reference potential Vss, it is possible to insulate the noise detector 7 for detecting the noise of the power converter 2 that operates a large amount of power and the injection waveform generators 31a and 31b driven by the control power supplies 15a and 15b.

[0054] The voltage divided by the combined impedance of each capacitor 8 and the impedance of the voltage dividing transformer 70 connected in series, that is, the divided common mode voltage Vci, is applied to the primary winding m3 of the voltage dividing transformer 70, and the adjusted voltage Vd corresponding to the turns ratio between the primary winding m3 and the secondary winding m4 of the voltage dividing transformer 70 is input to the injection waveform generators 31a and 31b. In the noise detector 7 of the second embodiment, the common mode voltage Vci, which is the input voltage between the wiring 24 at the ground potential and the input terminal 94, is the voltage divided by the impedance of the voltage dividing transformer 70.

[0055] As described in Embodiment 1, the output voltage Vo1 output from the injection waveform generator 31a and the output voltage Vo2 output from the injection waveform generator 31b are voltages of the same magnitude and opposite phases to each other, and by applying them to one end and the other end of the primary winding m1 of the transformer 11, respectively, the differential injection voltage Vinj is applied. The transformer 11 generates a compensation voltage Vcom at both ends of the secondary winding m2 according to the turns ratio Rr, and applies the compensation voltage Vcom to each phase of the three-phase power line 5. Similar to the noise filter 50 of Embodiment 1, the noise filter 50 of Embodiment 2 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output from one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the injection waveform generators 31a and 31b. As a result, the noise filter 50 of Embodiment 2 can reduce the size of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be reduced in size and weight. Therefore, the noise filter 50 of Embodiment 2 can suppress the common-mode voltage Vci while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight. Appropriately, the injection waveform generator 31a that outputs the output voltage Vo1 is expressed as the first injection waveform generator 31a, and the injection waveform generator 31b that outputs the output voltage Vo2 is expressed as the second injection waveform generator 31b.

[0056] The injection waveform generator 31a can apply the first to third examples of the injection waveform generator 31 shown in FIGS. 16 to 18. Further, the injection waveform generator 31b applies the injection waveform generator 31 in which the output voltage Vo2 is out of phase with the output voltage Vo1 of the injection waveform generator 31a. The first example of the injection waveform generator 31 shown in FIG. 16 is different from the first example of the injection waveform generator 10 shown in FIG. 4 in terms of the reference potential. More specifically, the wiring 24 that is at the ground potential in FIG. 4 is the wiring 25 that is at the reference potential Vss in FIG. 16. The second example of the injection waveform generator 31 shown in FIG. 17 is different from the second example of the injection waveform generator 10 shown in FIG. 5 in terms of the reference potential. The third example of the injection waveform generator 31 shown in FIG. 18 is different from the third example of the injection waveform generator 10 shown in FIG. 6 in terms of the reference potential. More specifically, the wiring 24 that is at the ground potential in FIGS. 5 and 6 is the wiring 25 that is at the reference potential Vss in FIGS. 17 and 18. Also, a current buffer 14 may be added to the injection waveform generator 31 of the second example. When these injection waveform generators 31 are applied to the injection waveform generator 31a shown in FIG. 13, the input terminal 51, output terminal 52, and output voltage Vo of the injection waveform generator 31 become the input terminal 51a, output terminal 52a, and output voltage Vo1, respectively. When these injection waveform generators 31 are applied to the injection waveform generator 31b shown in FIG. 13, the input terminal 51, output terminal 52, and output voltage Vo of the injection waveform generator 31 become the input terminal 51b, output terminal 52b, and output voltage Vo2, respectively.

[0057] Also, for example, like the second noise filter 50 of Embodiment 2 shown in FIG. 14, the adjustment voltage Vd that is the output of the noise detector 7 may be input only to the first injection waveform generator 31a, the output terminal 52a of the first injection waveform generator 31a may be connected to one end of the primary winding m1 of the transformer 11 and the input terminal 51b of the second injection waveform generator 31b, and the output terminal 52b of the second injection waveform generator 31b may be connected to the other end of the primary winding m1 of the transformer 11. Even in this case, the output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages that are the same magnitude and out of phase with each other.

[0058] The second noise filter 50 of Embodiment 2 is the same as the fourth noise filter 50 of Embodiment 1. The output Vo1 of the first injection waveform generator 31a is input to the second injection waveform generator 31b. In order to output an output voltage Vo2 with the same magnitude as the output voltage Vo1 but with a reverse phase, the second injection waveform generator 31b applies a circuit that multiplies the input signal by a gain of 1 and rotates the phase by 180°. That is, the gain Gi of the operational amplifier 19 of the second injection waveform generator 31b is -1 when the gain Gi of the first injection waveform generator 31a is positive, and 1 when the gain Gi of the first injection waveform generator 31a is negative.

[0059] In the second noise filter 50 of Embodiment 2, since the second injection waveform generator 31b only needs to multiply the input signal by a gain of 1 and rotate the phase by 180°, the band limiter 12 may be provided in the first injection waveform generator 31a, and the band limiter 12 of the second injection waveform generator 31b can be removed.

[0060] Also, for example, like the third noise filter 50 of Embodiment 2 shown in FIG. 15, the voltage dividing transformer 70 included in the noise detector 7 has two secondary windings m4a and m4b, and adjustment voltages Vd1 and Vd2 with the same magnitude but opposite phases are output from output terminals 95a and 95b connected to the respective secondary windings m4a and m4b. Further, the adjustment voltage Vd1 may be input to the first injection waveform generator 31a, and the adjustment voltage Vd2 may be input to the second injection waveform generator 31b. The voltage dividing transformer 70 shown in FIG. 15 will be described in detail. The voltage dividing transformer 70 has a first secondary winding m4a and a second secondary winding m4b. The first secondary winding m4a is configured with the same polarity as the primary winding m3, and the second secondary winding m4b is configured with the opposite polarity to the primary winding m3. Further, one end of the first secondary winding m4a is connected to the output terminal 95a, and the other end is connected to a wiring 25 having a reference potential Vss. One end of the second secondary winding m4b is connected to the output terminal 95b, and the other end is connected to the wiring 25 having a reference potential Vss. The output terminal 95a of the voltage dividing transformer 70 is connected to the input terminal 51a of the first injection waveform generator 31a, and the output terminal 95b of the voltage dividing transformer 70 is connected to the input terminal 51b of the second injection waveform generator 31b.

[0061] Since the adjustment voltages Vd1 and Vd2 are of the same magnitude and in opposite phases to each other, the injection waveform generators 31a and 31b can be configured with circuits having the same gain and the same phase characteristics. That is to say, a common circuit can be used, and the characteristic error between the injection waveform generators 31a and 31b can be reduced.

[0062] Also, in the third noise filter 50 of the second embodiment, the polarities of the first secondary winding m4a and the second secondary winding m4b of the voltage dividing transformer 70 may be the same as or different from that of the primary winding m3, and the number of turns may be different. That is, the magnitudes of the adjustment voltages Vd1 and Vd2 output from the output terminals 95a and 95b of the voltage dividing transformer 70 may be different, and the phases may be the same. According to the adjustment voltages Vd1 and Vd2, the injection waveform generators 31a and 31b that are respectively input are set to output output voltages Vo1 and Vo2 that are of the same magnitude and in opposite phases. As a result, similar to the first noise filter 50 of the second embodiment, the third noise filter 50 of the second embodiment can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 31a and 31b. As a result, the third noise filter 50 of the second embodiment enables miniaturization of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0063] The third noise filter 50 of Embodiment 2 includes a capacitor 8 and a voltage dividing transformer 70 connected in series between the three-phase power lines 5 and 4 on the output side or the input side of the power converter 2 and the wiring 24 which is a grounding wiring. In the third noise filter 50 of Embodiment 2, the voltage dividing transformer 70 has two secondary windings m4a and m4b, one end of the primary winding m3 is connected to a connection point n7 which is the end on the side opposite to the three-phase power lines 5 and 4 in the capacitor 8, and the other end of the primary winding m3 is connected to the wiring 24 which is a grounding wiring. Also, in the voltage dividing transformer 70, one of the secondary windings, the first secondary winding m4a, has one end connected to a reference wiring 25 which has a reference potential Vss different from the ground potential of the grounding wiring, and the other end connected to a first output terminal 95a which outputs a first adjustment voltage Vd1. The other secondary winding, the second secondary winding m4b, has one end connected to the reference wiring and the other end connected to a second output terminal 95b which outputs a second adjustment voltage Vd2. Further, in the third noise filter 50 of Embodiment 2, the injection voltage generator 30 includes a first injection waveform generator 31a that generates a first output voltage Vo1 based on the first adjustment voltage Vd1, and a second injection waveform generator 31b that generates a second output voltage Vo2 based on the second adjustment voltage Vd2. Therefore, the third noise filter 50 of Embodiment 2 enables miniaturization of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0064] In Embodiment 2, the case where the output voltages Vo1 and Vo2 are of the same magnitude is shown. However, similar to Embodiment 1, the output voltages Vo1 and Vo2 may have different magnitudes. Even when they have different magnitudes, an injection voltage Vinj, which is the difference between the output voltage Vo1 and the output voltage Vo2, that is, a voltage greater than the output voltage Vo1 and in phase with it, is applied to the primary winding m1 of the transformer 11. As a result, the noise filter 50 of Embodiment 2 can be miniaturized in terms of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened. Note that although the noise filter 50 of Embodiment 2 shown in FIGS. 13 to 15 has a feed-forward configuration, the positions of the transformer 11 and the noise detector 7 can be exchanged to form a feedback configuration.

[0065] Embodiment 3. FIG. 19 is a diagram showing the configuration of a first noise filter and an electric motor drive system according to Embodiment 3, and FIG. 20 is a diagram showing the configuration of a second noise filter and an electric motor drive system according to Embodiment 3. FIG. 21 is a diagram showing the configuration of a third noise filter and an electric motor drive system according to Embodiment 3. The noise filter 50 of Embodiment 3 can be applied to an electric motor drive system 60, which is a system for controlling an induction motor 3 by a power converter 2 such as a voltage-type PWM inverter in which a plurality of semiconductor elements perform a switching operation, similar to Embodiment 1.

[0066] The noise filter 50 of Embodiment 3 is different from the noise filter 50 of Embodiment 1 in that the compensation signal applicator 75 includes a signal conditioning transformer 71 and a signal applicator 72 instead of the transformer 11. The compensation signal applicator 75 of Embodiment 3 includes a signal conditioning transformer 71, which is a transformer having a primary winding m5 and a secondary winding m6 on the primary side and the secondary side, respectively, and a signal applicator 72 including a capacitor 73. One end of the secondary winding m6 of the signal conditioning transformer 71 is connected to a wiring 24 that is a ground wiring, and the other end is connected to the three-phase power lines 5 and 4 on the output side or the input side of the power converter 2 via the capacitor 73 of the signal applicator 72. FIG. 19 shows an example in which the compensation signal applicator 75 is connected to the three-phase power line 5. For example, in the signal applicator 72, one ends of three capacitors 73 having equal capacitances are connected to each phase of the three-phase power line 5, and the other ends of the three capacitors 73 are connected to each other at a connection point n8. In the signal conditioning transformer 71, the output terminals 52a and 52b of the injection waveform generators 10a and 10b are connected to both ends of the primary winding m5, respectively. One end of the secondary winding m6 is connected to the wiring 24 having a ground potential, and the other end is connected to the connection point n8. The differences from the noise filter 50 of Embodiment 1 will be mainly described.

[0067] The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 10a is input to one end of the primary winding m5 of the signal conditioning transformer 71. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 10b is input to of the primary winding m5 the other end of the signal conditioning transformer 71. The output voltage Vo1 and the output voltage Vo2 are voltages having the same magnitude and opposite phases. That is, the output voltage Vo1 and the output voltage Vo2 are voltages having the same magnitude and opposite polarities. An injection voltage Vinj, which is a voltage having the same phase, that is, the same polarity as the difference between the output voltage Vo1 and the output voltage Vo2, that is, twice the magnitude of Vo1, is applied to the primary winding m5 of the signal conditioning transformer 71. A compensation voltage Vcom is superimposed on each phase of the three-phase power line 5 via the capacitor 73 of the signal applicator 72 so as to suppress the common-mode voltage Vci. Note that a current for suppressing the common-mode voltage Vci flows through each phase of the three-phase power line 5 via the capacitor 73 of the signal applicator 72.

[0068] In the first noise filter 50 of Embodiment 3, since the injection waveform generators 10a and 10b output output voltages Vo1 and Vo2 of the same magnitude and opposite phases, the differential between the output voltage Vo1 and the output voltage Vo2, that is, an injection voltage Vinj of the same phase with a magnitude twice that of Vo1, is applied to the primary winding m5 of the signal adjustment transformer 71. That is, the first noise filter 50 of Embodiment 3 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 10, that is, without increasing the output voltages Vo1 and Vo2 of the injection waveform generators 10a and 10b. As a result, the signal adjustment transformer 71 or the control power supplies 15a and 15b can be miniaturized. Therefore, the first noise filter 50 of Embodiment 3 can suppress the common mode voltage Vci while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight.

[0069] Also, for example, like the second noise filter 50 of Embodiment 3 shown in FIG. 20, the adjustment voltage Vd which is the output of the noise detector 7 may be input only to the first injection waveform generator 10a, the output terminal 52a of the first injection waveform generator 10a may be connected to one end of the primary winding m5 of the signal adjustment transformer 71 and the input terminal 51b of the second injection waveform generator 10b, and the output terminal 52b of the second injection waveform generator 10b may be connected to the other end of the primary winding m5 of the signal adjustment transformer 71. Even in this case, the output voltage Vo1 of the first injection waveform generator 10a and the output voltage Vo2 of the second injection waveform generator 10b are voltages of the same magnitude and opposite phases to each other.

[0070] The second noise filter 50 of Embodiment 3 is the same as the fourth noise filter 50 of Embodiment 1. The output Vo1 of the first injection waveform generator 10a is input to the second injection waveform generator 10b. In order to output an output voltage Vo2 with the same magnitude as the output voltage Vo1 but with an opposite phase, the second injection waveform generator 10b applies a circuit that multiplies the input signal by a gain of one and rotates the phase by 180°. That is, the gain Gi of the operational amplifier 19 of the second injection waveform generator 10b is -1 when the gain Gi of the first injection waveform generator 10a is positive, and 1 when the gain Gi of the first injection waveform generator 10a is negative.

[0071] In the second noise filter 50 of Embodiment 3, since the second injection waveform generator 10b only needs to multiply the input signal by a gain of one and rotate the phase by 180°, if the band limiter 12 is connected to the first injection waveform generator 10a, the band limiter 12 of the second injection waveform generator 10b can be removed.

[0072] Also, for example, like the third noise filter 50 of Embodiment 3 shown in FIG. 21, the signal adjustment circuit 9 included in the noise detector 7 has two output terminals 95a and 95b, and outputs adjustment voltages Vd1 and Vd2 with the same magnitude but opposite phases respectively. Further, the adjustment voltage Vd1 can be input to the first injection waveform generator 10a, and the adjustment voltage Vd2 can be input to the second injection waveform generator 10b. Even in this case, the output voltage Vo1 of the first injection waveform generator 10a and the output voltage Vo2 of the second injection waveform generator 10b are voltages with the same magnitude but opposite phases to each other.

[0073] Since the adjustment voltages Vd1 and Vd2 have the same magnitude and opposite phases to each other, the injection waveform generators 10a and 10b can be configured with circuits having the same gain and the same phase characteristics. That is, a common circuit can be used, and the characteristic error between the injection waveform generators 10a and 10b can be reduced.

[0074] Further, the third noise filter 50 of Embodiment 3 may have the same phase but different magnitudes of the adjustment voltages Vd1 and Vd2 output from the output terminals 95a and 95b, similar to the fifth noise filter 50 of Embodiment 1. The injection waveform generators 10a and 10b that are respectively input are set to output output voltages Vo1 and Vo2 of the same magnitude but opposite phases according to the adjustment voltages Vd1 and Vd2. As a result, the third noise filter 50 of Embodiment 3 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 10, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 10a and 10b. As a result, the third noise filter 50 of Embodiment 3 can reduce the size of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0075] In Embodiment 3, the case where the output voltage Vo1 and the output voltage Vo2 have the same magnitude is shown. However, similar to Embodiment 1, the output voltage Vo1 and the output voltage Vo2 may have different magnitudes. Even when they have different magnitudes, a difference between the output voltage Vo1 and the output voltage Vo2, that is, an injection voltage Vinj that is larger than Vo1 and in the same phase, is applied to the primary winding m5 of the signal adjustment transformer 71. As a result, the noise filter 50 of Embodiment 3 can reduce the size of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened. Note that the noise filter 50 of Embodiment 3 shown in FIGS. 19 to 21 has a feedforward configuration, but the positions of the signal applicator 72 and the signal adjustment transformer 71, that is, the compensation signal applicator 75 and the noise detector 7, can be exchanged to form a feedback configuration.

[0076] Embodiment 4. FIG. 22 is a diagram showing the configuration of the first noise filter and the motor drive system according to Embodiment 4, and FIG. 23 is a diagram showing the configuration of the second noise filter and the motor drive system according to Embodiment 4. FIG. 24 is a diagram showing the configuration of the third noise filter and the motor drive system according to Embodiment 4. The noise filter 50 of Embodiment 4 can be applied to a motor drive system 60, which is a system for controlling an induction motor 3 by a power converter 2 such as a voltage-type PWM inverter in which a plurality of semiconductor elements perform a switching operation, similar to Embodiment 1.

[0077] The noise filter 50 of Embodiment 4 is different from the noise filter 50 of Embodiment 1 in that the noise detector 7 includes a voltage-dividing transformer 70 instead of the signal conditioning circuit 9, and also includes a signal conditioning transformer 71 and a signal applicator 72 instead of the transformer 11. The noise filter 50 of Embodiment 4 is different from the noise filter 50 of Embodiment 2 in that it includes a signal conditioning transformer 71 and a signal applicator 72 instead of the transformer 11. The differences from the noise filter 50 of Embodiment 2 will be mainly described. FIG. 22 shows an example in which the noise detector 7 and the signal applicator 72 are connected to the three-phase power line 5.

[0078] The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 31a is input to one end of the primary winding m5 of the signal conditioning transformer 71. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 31b is input to the other end of the primary winding m5 of the signal conditioning transformer 71. The output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite phases to each other. That is, the output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite polarities to each other. An injection voltage Vinj, which is the difference between the output voltage Vo1 and the output voltage Vo2, that is, a voltage of the same phase or the same polarity with a magnitude twice that of Vo1, is applied to the primary winding m5 of the signal conditioning transformer 71. A compensation voltage Vcom is superimposed on each phase of the three-phase power line 5 via a capacitor 73 of the signal applicator 72 so as to suppress the common-mode voltage Vci. Note that a current for suppressing the common-mode voltage Vci flows through each phase of the three-phase power line 5 via the capacitor 73 of the signal applicator 72.

[0079] In the first noise filter 50 of Embodiment 4, since the injection waveform generators 31a and 31b output output voltages Vo1 and Vo2 of the same magnitude and opposite phases, an injection voltage Vinj of the same phase and having a magnitude equal to the difference between the output voltage Vo1 and the output voltage Vo2, that is, twice the magnitude of Vo1, is applied to the primary winding m5 of the signal conditioning transformer 71. That is, the first noise filter 50 of Embodiment 4 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the injection waveform generators 31a and 31b, as shown in Equation (6). As a result, the signal conditioning transformer 71 or the control power supplies 15a and 15b can be miniaturized. Therefore, the first noise filter 50 of Embodiment 4 can suppress the common-mode voltage Vci while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight.

[0080] Also, for example, like the second noise filter 50 of Embodiment 4 shown in FIG. 23, the adjustment voltage Vd, which is the output of the noise detector 7, may be input only to the first injection waveform generator 31a. The output terminal 52a of the first injection waveform generator 31a may be connected to one end of the primary winding m5 of the signal conditioning transformer 71 and the input terminal 51b of the second injection waveform generator 31b, and the output terminal 52b of the second injection waveform generator 31b may be connected to the other end of the primary winding m5 of the signal conditioning transformer 71. Even in this case, the output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages of the same magnitude and opposite phases to each other.

[0081] The second noise filter 50 of Embodiment 4 is the same as the second noise filter 50 of Embodiment 2. The output Vo1 of the first injection waveform generator 31a is input to the second injection waveform generator 31b. In order to output an output voltage Vo2 that has the same magnitude as the output voltage Vo1 but is in the opposite phase, the second injection waveform generator 31b applies a circuit that multiplies the input signal by a gain of 1 and rotates the phase by 180°. That is, the gain Gi of the operational amplifier 19 of the second injection waveform generator 31b is -1 when the gain Gi of the first injection waveform generator 31a is positive, and 1 when the gain Gi of the first injection waveform generator 31a is negative.

[0082] In the second noise filter 50 of Embodiment 4, since the second injection waveform generator 31b only needs to multiply the input signal by a gain of 1 and rotate the phase by 180°, if the band limiter 12 is connected to the first injection waveform generator 31a, the band limiter 12 of the second injection waveform generator 31b can be removed.

[0083] Also, for example, like the third noise filter 50 of Embodiment 4 shown in FIG. 24, the voltage dividing transformer 70 included in the noise detector 7 has two secondary windings m4a and m4b, and adjustment voltages Vd1 and Vd2 that have the same magnitude but are in the opposite phase are output from output terminals 95a and 95b connected to the respective secondary windings m4a and m4b. Further, the adjustment voltage Vd1 may be input to the first injection waveform generator 31a, and the adjustment voltage Vd2 may be input to the second injection waveform generator 31b. The voltage dividing transformer 70, injection waveform generators 31a and 31b in the third noise filter 50 of Embodiment 4 are the same as the voltage dividing transformer 70, injection waveform generators 31a and 31b in the third noise filter 50 of Embodiment 2. The output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages that have the same magnitude but are in the opposite phase to each other.

[0084] Since the adjustment voltages Vd1 and Vd2 are the same magnitude but in opposite phases to each other, the injection waveform generators 31a and 31b can be configured with circuits that have the same gain and the same phase characteristics. That is, a common circuit can be used, and the characteristic error between the injection waveform generators 31a and 31b can be reduced.

[0085] Also, in the third noise filter 50 of Embodiment 4, the polarities of the first secondary winding m4a and the second secondary winding m4b of the voltage-dividing transformer 70 may be the same as or different from that of the primary winding m3, and the number of turns may also be different. That is, the magnitudes of the adjustment voltages Vd1 and Vd2 may be different, and the phases may be the same. According to the adjustment voltages Vd1 and Vd2, the injection waveform generators 31a and 31b that are respectively input are set to output output voltages Vo1 and Vo2 of the same magnitude and opposite phases. As a result, similar to the first noise filter 50 of Embodiment 4, the third noise filter 50 of Embodiment 4 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 31a and 31b. As a result, the third noise filter 50 of Embodiment 4 can reduce the size of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0086] In Embodiment 4, the case where the output voltages Vo1 and Vo2 are of the same magnitude is shown. However, similar to Embodiment 1, the output voltages Vo1 and Vo2 may be of different magnitudes. Even when the magnitudes are different, a difference between the output voltage Vo1 and the output voltage Vo2, that is, an injection voltage Vinj that is larger than Vo1 and in the same phase, is applied to the primary winding m5 of the signal adjustment transformer 71. As a result, the noise filter 50 of Embodiment 4 can reduce the size of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened. Note that although the noise filter 50 of Embodiment 4 shown in FIGS. 22 to 24 has a feed-forward configuration, the positions of the signal applicator 72 and the signal adjustment transformer 71, that is, the compensation signal applicator 75 and the noise detector 7, can be exchanged to form a feedback configuration.

[0087] Embodiment 5. FIG. 25 is a diagram showing the configuration of the first noise filter and the motor drive system according to Embodiment 5, and FIG. 26 is a diagram showing the configuration of the second noise filter and the motor drive system according to Embodiment 5. FIG. 27 is a diagram showing the configuration of the third noise filter and the motor drive system according to Embodiment 5. The noise filter 50 of Embodiment 5 can be applied to a motor drive system 60, which is a system for controlling an induction motor 3 by a power converter 2 such as a voltage-type PWM inverter in which a plurality of semiconductor elements perform a switching operation, similar to Embodiment 1.

[0088] The noise filter 50 of Embodiment 5 is different from the noise filter 50 of Embodiment 1 in that the noise detector 7 includes a detection transformer 80, and the injection waveform generators are the injection waveform generators 31a and 31b shown in FIGS. 16 to 18, which are the same as those in Embodiment 2. The parts different from the noise filter 50 of Embodiment 1 will be mainly described. The noise detector 7 includes a detection transformer 80 in which a primary winding m7 is inserted into the three-phase power lines 5 and 4 on the output side or the input side of the power converter 2. One end of the secondary winding m8 of the detection transformer 80 is connected to a wiring 25, which is a reference wiring having a reference potential Vss, and the other end is connected to an output terminal 95 that outputs an adjustment voltage Vd. Similar to the transformer 11, the detection transformer 80 includes a primary winding m7 on the primary side and a secondary winding m8 on the secondary side, and detects a voltage proportional to the common-mode current, which is the electromagnetic noise current generated by the power converter 2, that is, a detection voltage Vsn. FIG. 25 shows an example in which the primary winding m7 of the detection transformer 80 is inserted into each phase of the three-phase power lines 5u, 5v, and 5w of the three-phase power line 5. One end of the secondary winding m8 is connected to the wiring 25 having a reference potential Vss, and the other end of the secondary winding m8 is connected to the output terminal 95. The detection transformer 80 detects the detection voltage Vsn applied across both ends of the primary winding m7 and outputs it across both ends of the secondary winding m8 according to the turns ratio Rr of the primary winding m7 and the secondary winding m8 of the detection transformer 80, and outputs this voltage from the output terminal 95 as an adjustment voltage Vd, which is the output of the noise detector 7, to the injection waveform generators 31a and 31b.

[0089] The detected voltage Vsn detected by the detection transformer 80 will be described in detail. The common-mode voltage Vci described in Embodiments 1 to 4 is the voltage of the common-mode component among the electromagnetic noises in the three-phase power lines 5 and 4. This common-mode voltage Vci is the noise voltage that is inherently generated in the path when power conversion is performed by the power converter 2. This common-mode voltage Vci exists regardless of the form of detection. In Embodiments 1 to 4, an example of detecting the common-mode voltage Vci by an ideal capacitor-type noise detector 7 was shown. When detecting the ground common-mode voltage with respect to the ground GND using an ideal capacitor-type noise detector, the detected voltage becomes the same as the common-mode voltage Vci. Furthermore, depending on the circumstances such as the upper limit of the processing voltage, when devising the detection circuit, it is also possible to obtain a detection value different from the common-mode voltage Vci. In Embodiments 1 to 4, an example was shown in which the detection circuit was devised to adjust from the common-mode voltage Vci to the adjustment voltage Vd. The devising of the detection circuit is, for example, intentionally cutting the low-frequency band with a large amplitude by detecting with a high-pass filter configuration, etc.

[0090] When detecting the common-mode component of the electromagnetic noise with a coil-type noise detector, unlike the capacitor-type case, when the common-mode voltage Vci is applied to the common-mode path, a voltage drop proportional to the value of the noise current (not shown) flowing through the common-mode path including the coil occurs. The voltage drop due to the primary winding m7 proportional to the value of this noise current is the detected voltage Vsn. A voltage having a value obtained by multiplying the turns ratio of the primary winding m7 and the secondary winding m8 is generated in the secondary winding m8 of the detection transformer 80, and this voltage becomes the adjustment voltage Vd output by the noise detector 7 which is a coil-type noise detector. The voltage generated in the secondary winding m8 of the detection transformer 80 is a physical quantity different from the common-mode voltage Vci, and is a voltage based on the detected voltage Vsn proportional to the value of the noise current.

[0091] The output voltage Vo1 output by the injection waveform generator 31a and the output voltage Vo2 output by the injection waveform generator 31b are voltages of the same magnitude and opposite phases to each other. By applying them to one end and the other end of the primary winding m1 of the transformer 11 respectively, a differential injection voltage Vinj is applied. The transformer 11 generates a compensation voltage Vcom at both ends of the secondary winding m2 according to the turns ratio Rr, and applies the compensation voltage Vcom to each phase of the three-phase power line 5. The noise filter 50 of the fifth embodiment reduces the detection voltage Vsn by the compensation voltage Vcom, which is the voltage superimposed on the u-phase, v-phase, and w-phase of the three-phase power line 5 via the secondary winding m2 of the transformer 11, that is, the gain Gi and the turns ratio Rr are set so that the formula (9) holds. |Vsn - Vcom| ≤ Vto ···(9) As described above, Vto is the allowable value of the voltage difference. The formula (9) indicates that the absolute value of the difference between the detection voltage Vsn and the compensation voltage Vcom is equal to or less than the allowable value Vto.

[0092] Similar to the noise filter 50 of the first embodiment, the noise filter 50 of the fifth embodiment can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the injection waveform generators 31a and 31b. As a result, the noise filter 50 of the fifth embodiment can reduce the size of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened. Therefore, the first noise filter 50 of the fifth embodiment can suppress the common-mode current, which is the current of the electromagnetic noise, while being small and lightweight, that is, it can enhance the noise reduction effect while being small and lightweight.

[0093] Also, for example, like the second noise filter 50 of Embodiment 5 shown in FIG. 26, the adjustment voltage Vd, which is the output of the noise detector 7, is input only to the first injection waveform generator 31a. The output terminal 52a of the first injection waveform generator 31a may be connected to one end of the primary winding m1 of the transformer 11 and the input terminal 51b of the second injection waveform generator 31b, and the output terminal 52b of the second injection waveform generator 31b may be connected to the other end of the primary winding m1 of the transformer 11. Even in this case, the output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages of the same magnitude and opposite phases to each other.

[0094] The second noise filter 50 of Embodiment 5 is similar to the fourth noise filter 50 of Embodiment 1. For the second injection waveform generator 31b, Vo1, which is the output of the first injection waveform generator 31a, is input. In order to output an output voltage Vo2 of the same magnitude and opposite phase as the output voltage Vo1, the second injection waveform generator 31b applies a circuit that multiplies the input signal by a gain of 1 and rotates the phase by 180°. That is, the gain Gi of the operational amplifier 19 of the second injection waveform generator 31b is -1 when the gain Gi of the first injection waveform generator 31a is positive, and 1 when the gain Gi of the first injection waveform generator 31a is negative.

[0095] In the second noise filter 50 of Embodiment 5, since the second injection waveform generator 31b only needs to multiply the input signal by a gain of 1 and rotate the phase by 180°, if the band limiter 12 is connected to the first injection waveform generator 31a, the band limiter 12 of the second injection waveform generator 31b can be removed.

[0096] Also, for example, like the third noise filter 50 of Embodiment 5 shown in FIG. 27, the detection transformer 80 included in the noise detector 7 has two secondary windings m8a and m8b, and adjustment voltages Vd1 and Vd2 of the same magnitude and opposite phases are output from output terminals 95a and 95b connected to the respective secondary windings m8a and m8b. Further, the adjustment voltage Vd1 may be input to the first injection waveform generator 31a, and the adjustment voltage Vd2 may be input to the second injection waveform generator 31b. Even in this case, the output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages of the same magnitude and opposite phases to each other.

[0097] Since the adjustment voltages Vd1 and Vd2 are of the same magnitude and opposite phases to each other, the injection waveform generators 31a and 31b can be configured by circuits having the same gain and the same phase characteristics. That is, a common circuit can be used, and the characteristic error between the injection waveform generators 31a and 31b can be reduced.

[0098] In the third noise filter 50 of Embodiment 5, the noise detector 7 includes a detection transformer 80 in which the primary winding m7 is inserted into the three-phase power lines 5 and 4 on the output side or the input side of the power converter 2 and which has two secondary windings m8a and m8b. One end of the first secondary winding m8a, which is one of the secondary windings, is connected to a wiring 25 that is a reference wiring having a reference potential Vss, and the other end is connected to a first output terminal 95a that outputs a first adjustment voltage Vd1. One end of the second secondary winding m8b, which is the other secondary winding, is connected to the wiring 25 that is a reference wiring, and the other end is connected to a second output terminal 95b that outputs a second adjustment voltage Vd2. In the third noise filter 50 of Embodiment 5, the injection voltage generator 30 includes a first injection waveform generator 31a that generates a first output voltage Vo1 based on the first adjustment voltage Vd1 and a second injection waveform generator 31b that generates a second output voltage Vo2 based on the second adjustment voltage Vd2. As a result, the third noise filter 50 of Embodiment 5 can reduce the size of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0099] Also, in the third noise filter 50 of Embodiment 5, the polarities of the first secondary winding m8a and the second secondary winding m8b of the detection transformer 80 may be the same as or different from those of the primary winding m7, and the number of turns may be different. That is, the magnitudes of the adjustment voltages Vd1 and Vd2 may be different, and the phases may be the same. According to the adjustment voltages Vd1 and Vd2, the injection waveform generators 31a and 31b that are respectively input are set to output output voltages Vo1 and Vo2 that are of the same magnitude and opposite in phase. As a result, similar to the first noise filter 50 of Embodiment 5, the third noise filter 50 of Embodiment 5 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 31a and 31b. As a result, the third noise filter 50 of Embodiment 5 enables miniaturization of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0100] In Embodiment 5, the case where the output voltages Vo1 and Vo2 are of the same magnitude is shown. However, similar to Embodiment 1, the output voltages Vo1 and Vo2 may be different in magnitude. Even when they are different in magnitude, an injection voltage Vinj, which is the difference between the output voltage Vo1 and the output voltage Vo2, that is, a voltage that is larger than the output voltage Vo1 and in the same phase, is applied to the primary winding m1 of the transformer 11. As a result, the noise filter 50 of Embodiment 5 enables miniaturization of the transformer 11 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened. Note that although the noise filter 50 of Embodiment 5 shown in FIGS. 25 to 27 has a feed-forward configuration, the positions of the transformer 11 and the noise detector 7 can be exchanged to form a feedback configuration.

[0101] As described above, the noise filter 50 of Embodiment 5 is a noise filter that reduces the voltage or current of electromagnetic noise generated by the power converter 2 that performs power conversion by the switching operation of the semiconductor elements Q1 to Q6. The noise filter 50 detects a voltage (detection voltage Vsn) based on the electromagnetic noise generated by the power converter 2, and outputs an adjusted voltage Vd in which the voltage (detection voltage Vsn) based on the electromagnetic noise is adjusted. A noise detector 7, a compensation signal adder 75 that superimposes a compensation voltage Vcom having a polarity opposite to that of the voltage (detection voltage Vsn) based on the electromagnetic noise on the output or input of the power converter 2 via the transformer 11, and a first output voltage Vo1 that generates an injection voltage Vinj between one end and the other end of the primary winding m1 of the transformer 11, and a second output voltage Vo2 having a polarity opposite to that of the first output voltage Vo1 are generated based on the adjusted voltage Vd, and the first output voltage Vo1 is output to one end of the primary winding m1 of the transformer 11, and the second output voltage Vo2 is output to the other end of the primary winding m1 of the transformer 11. An injection voltage generator 30. The injection voltage generator 30 generates a first output voltage Vo1 and a second output voltage Vo2 that generate an injection voltage Vinj such that the difference between the compensation voltage Vcom superimposed by the compensation signal adder 75 and the voltage (detection voltage Vsn) based on the electromagnetic noise is equal to or less than the allowable value Vto. The noise detector 7 includes a detection transformer 80 having a primary winding m7 inserted into a power line (three-phase power lines 5 and 4) on the output side or the input side of the power converter 2. One end of the secondary winding m8 of the detection transformer 80 is connected to a reference wiring (wiring 25) having a reference potential Vss, and the other end is connected to an output terminal 95 that outputs the adjusted voltage Vd. With this configuration, the noise filter 50 of Embodiment 5 applies the first output voltage Vo1 and the second output voltage Vo2 having a polarity opposite to that of the first output voltage Vo1 to both ends of the primary winding m1 of the transformer 11 in the compensation signal adder 75, respectively. Since the compensation voltage Vcom is superimposed on the output or input of the power converter 2 based on the injection voltage Vinj having the same polarity as the first output voltage Vo1 and larger than the first output voltage Vo1, it can be made small and lightweight and the noise reduction effect can be enhanced.

[0102] Embodiment 6. FIG. 28 is a diagram showing the configuration of the first noise filter and the motor drive system according to Embodiment 6, and FIG. 29 is a diagram showing the configuration of the second noise filter and the motor drive system according to Embodiment 6. FIG. 30 is a diagram showing the configuration of the third noise filter and the motor drive system according to Embodiment 6. The noise filter 50 of Embodiment 6 can be applied to a motor drive system 60, which is a system for controlling an induction motor 3 by a power converter 2 such as a voltage-type PWM inverter in which a plurality of semiconductor elements perform a switching operation, similar to Embodiment 1.

[0103] The noise filter 50 of Embodiment 6 is different from the noise filter 50 of Embodiment 1 in that the noise detector 7 includes a detection transformer 80, the injection waveform generators are the injection waveform generators 31a and 31b shown in FIGS. 16 to 18, which are the same as those in Embodiment 2, and a signal adjustment transformer 71 and a signal applicator 72 are provided instead of the transformer 11. The noise filter 50 of Embodiment 6 is different from the noise filter 50 of Embodiment 5 in that a signal adjustment transformer 71 and a signal applicator 72 are provided instead of the transformer 11. The differences from the noise filter 50 of Embodiment 5 will be mainly described. FIG. 28 shows an example in which the noise detector 7 and the signal applicator 72 are connected to the three-phase power line 5.

[0104] The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 31a is input to one end of the primary winding m5 of the signal conditioning transformer 71. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 31b is input to the other end of the primary winding m5 of the signal conditioning transformer 71. The output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite phases to each other. That is, the output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite polarities to each other. An injection voltage Vinj, which is the difference between the output voltage Vo1 and the output voltage Vo2, that is, a voltage of the same phase and the same polarity, i.e., the same magnitude as twice Vo1, is applied to the primary winding m5 of the signal conditioning transformer 71. A compensation voltage Vcom is superimposed on each phase of the three-phase power line 5 via the capacitor 73 of the signal applicator 72 so as to suppress the common-mode current, which is the current of the electromagnetic noise, that is, so as to suppress the detection voltage Vsn, which is the voltage based on the electromagnetic noise. Note that a current that suppresses the detection voltage Vsn, which is the voltage based on the electromagnetic noise, flows through each phase of the three-phase power line 5 via the capacitor 73 of the signal applicator 72.

[0105] The first noise filter 50 of Embodiment 6 includes an injection waveform generator 31a and an injection waveform generator 31b. Since the injection waveform generator 31a and the injection waveform generator 31b have the same size and output an output voltage Vo1 and an output voltage Vo2 with opposite phases, an injection voltage Vinj with the same phase and twice the magnitude of Vo1, that is, the difference between the output voltage Vo1 and the output voltage Vo2, is applied to the primary winding m5 of the signal adjustment transformer 71. That is, the first noise filter 50 of Embodiment 6 can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 31a and 31b, as shown in Equation (6). As a result, the first noise filter 50 of Embodiment 6 can reduce the size of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the miniaturized and lightweight noise filter 50 can suppress the common-mode current, which is the electromagnetic noise current. Therefore, the first noise filter 50 of Embodiment 6 can suppress the common-mode current, which is the electromagnetic noise current, while being small and lightweight, that is, it can enhance the noise reduction effect while being small and lightweight.

[0106] Also, for example, like the second noise filter 50 of Embodiment 6 shown in FIG. 29, the adjustment voltage Vd, which is the output of the noise detector 7, is input only to the first injection waveform generator 31a. The output terminal 52a of the first injection waveform generator 31a may be connected to one end of the primary winding m5 of the signal adjustment transformer 71 and the input terminal 51b of the second injection waveform generator 31b, and the output terminal 52b of the second injection waveform generator 31b may be connected to the other end of the primary winding m5 of the signal adjustment transformer 71. Even in this case, the output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages with the same magnitude and opposite phases.

[0107] The second noise filter 50 of Embodiment 6 is the same as the second noise filter 50 of Embodiment 5. The output Vo1 of the first injection waveform generator 31a is input to the second injection waveform generator 31b. In order to output an output voltage Vo2 that has the same magnitude as the output voltage Vo1 but is in the opposite phase, the second injection waveform generator 31b applies a circuit that multiplies the input signal by a gain of 1 and rotates the phase by 180°. That is, the gain Gi of the operational amplifier 19 of the second injection waveform generator 31b is -1 when the gain Gi of the first injection waveform generator 31a is positive, and is 1 when the gain Gi of the first injection waveform generator 31 a is negative.

[0108] In the second noise filter 50 of Embodiment 6, since the second injection waveform generator 31b only needs to multiply the input signal by a gain of 1 and rotate the phase by 180°, if the band limiter 12 is connected to the first injection waveform generator 31a, the band limiter 12 of the second injection waveform generator 31b can be removed.

[0109] Also, for example, like the third noise filter 50 of Embodiment 6 shown in FIG. 30, the detection transformer 80 included in the noise detector 7 has two secondary windings m8a and m8b, and adjustment voltages Vd1 and Vd2 that have the same magnitude but are in the opposite phase are output from output terminals 95a and 95b connected to the respective secondary windings m8a and m8b. Further, the adjustment voltage Vd1 may be input to the first injection waveform generator 31a, and the adjustment voltage Vd2 may be input to the second injection waveform generator 31b. The detection transformer 80, injection waveform generators 31a and 31b in the third noise filter 50 of Embodiment 6 are the same as the detection transformer 80, injection waveform generators 31a and 31b in the third noise filter 50 of Embodiment 5. The output voltage Vo1 of the first injection waveform generator 31a and the output voltage Vo2 of the second injection waveform generator 31b are voltages that have the same magnitude but are in the opposite phase to each other.

[0110] Since the adjustment voltages Vd1 and Vd2 are equal in magnitude and opposite in phase to each other, the injection waveform generators 31a and 31b can be configured with circuits having the same gain and the same phase characteristics. That is to say, a common circuit can be used, and the characteristic error between the injection waveform generators 31a and 31b can be reduced.

[0111] Also, in the third noise filter 50 of the sixth embodiment, the polarities of the first secondary winding m8a and the second secondary winding m8b of the detection transformer 80 may be the same as or different from those of the primary winding m7, and the number of turns may be different. That is, the magnitudes of the adjustment voltages Vd1 and Vd2 may be different and the phases may be the same. According to the adjustment voltages Vd1 and Vd2, the injection waveform generators 31a and 31b that are respectively input are set to output output voltages Vo1 and Vo2 that are equal in magnitude and opposite in phase. As a result, similar to the first noise filter 50 of the sixth embodiment, the third noise filter 50 of the sixth embodiment can obtain an injection voltage Vinj whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 31a and 31b. As a result, the third noise filter 50 of the sixth embodiment enables miniaturization of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened.

[0112] In Embodiment 6, the case where the output voltages Vo1 and Vo2 are of the same magnitude was shown. However, similar to Embodiment 1, the output voltages Vo1 and Vo2 may have different magnitudes. Even when they have different magnitudes, a difference between the output voltage Vo1 and the output voltage Vo2, that is, an injection voltage Vinj that is larger than Vo1 and in the same phase, is applied to the primary winding m5 of the signal adjustment transformer 71. As a result, the noise filter 50 of Embodiment 6 can be miniaturized in terms of the signal adjustment transformer 71 or the control power supplies 15a and 15b, and the noise filter 50 can be miniaturized and lightened. Note that although the noise filter 50 of Embodiment 6 shown in FIGS. 28 to 30 has a feed-forward configuration, the positions of the signal applicator 72 and the signal adjustment transformer 71, that is, the compensation signal applicator 75 and the noise detector 7, can be exchanged to form a feedback configuration.

[0113] Embodiment 7. FIG. 31 is a diagram showing the configuration of a first noise filter and an electric motor drive system according to Embodiment 7, and FIG. 32 is a diagram showing the injection waveform generator of FIG. 31. FIG. 33 is a diagram showing the configuration of a second noise filter according to Embodiment 7, and FIG. 34 is a diagram showing the injection waveform generator of FIG. 33. FIG. 35 is a diagram showing the configuration of a third noise filter according to Embodiment 7, and FIG. 36 is a diagram showing the configuration of a fourth noise filter according to Embodiment 7. FIG. 37 is a diagram showing the configuration of a fifth noise filter according to Embodiment 7. FIG. 38 is a diagram showing the configuration of a sixth noise filter according to Embodiment 7, and FIG. 39 is a diagram showing the configuration of a seventh noise filter according to Embodiment 7. Similar to Embodiment 1, the noise filter 50 of Embodiment 7 can be applied to an electric motor drive system 60, which is a system for controlling an induction motor 3 by a power converter 2 such as a voltage-type PWM inverter in which a plurality of semiconductor elements perform a switching operation.

[0114] The noise filter 50 in Embodiments 1 to 6 shows an example of a noise filter 50 that suppresses the voltage or current of electromagnetic noise, but is not limited to this example. Electromagnetic noise generated by the switching operation of semiconductor elements may include differential mode components different from common mode components. The differential mode components of electromagnetic noise are independently generated in each phase of the three-phase power line 5, each phase of the three-phase power line 4, and each wiring of the DC bus of the power converter 2. Note that the DC bus of the power converter 2 is the high-potential side wiring 44p and the low-potential side wiring 44s. FIGS. 31, 33, 35, and 36 show examples of suppressing electromagnetic noise for each phase of the three-phase power line 5. FIGS. 37 and 39 show examples of suppressing electromagnetic noise for each wiring of the DC bus of the power converter 2. FIG. 38 shows an example of suppressing electromagnetic noise for two lines of the single-phase power line 45. In Embodiment 7, an example of a noise filter 50 that detects and suppresses the voltage or current of the differential mode components in electromagnetic noise will be described.

[0115] The first noise filter 50 in Embodiment 7 is different from the noise filter 50 in Embodiment 1 in that it includes noise detectors 7u, 7v, and 7w, injection voltage generators 30u, 30v, and 30w, and compensation signal applicators 75u, 75v, and 75w for each phase of the three-phase power line 5. The parts different from the noise filter 50 in Embodiment 1 will be mainly described. The configurations for suppressing the differential mode voltage Vdi1 of the u-phase of the three-phase power line 5, that is, the three-phase power line 5u, the differential mode voltage Vdi2 of the v-phase of the three-phase power line 5, that is, the three-phase power line 5v, and the differential mode voltage Vdi3 of the w-phase of the three-phase power line 5, that is, the three-phase power line 5w, are the same. The injection voltage generators 30u, 30v, and 30w can apply the injection voltage generator 30 shown in FIG. 32. The injection voltage generator 30 includes the injection waveform generators 10a and 10b described in Embodiment 1. The configuration for suppressing the differential mode voltage Vdi1 of the u-phase of the three-phase power line 5, that is, the three-phase power line 5u, will be described as a representative.

[0116] A noise detector 7u that detects a differential-mode voltage Vdi1 includes a capacitor 8u and a signal conditioning circuit 9u connected in series between a three-phase power line 5u on the output side of a power converter 2 and a wiring 24 that is a ground wiring. The signal conditioning circuit 9u outputs an adjusted voltage Vdo1, which is an input voltage between the wiring 24 at ground potential and an input terminal 94, and which has been subjected to voltage division, band limiting, or both, as an output voltage. The noise detector 7u detects the differential-mode voltage Vdi1 and outputs the adjusted voltage Vdo1 based on the differential-mode voltage Vdi1. More specifically, the noise detector 7u includes the capacitor 8u and the signal conditioning circuit 9u connected in series between the three-phase power line 5u on the output side of the power converter 2 and the wiring 24 that is the ground wiring, and the signal conditioning circuit 9u outputs the adjusted voltage Vdo1 based on the input voltage, that is, the differential-mode voltage Vdi1, input via the capacitor 8u.

[0117] Input terminals 51a, 51b of an injection voltage generator 30u are connected to an output terminal 95 of the signal conditioning circuit 9u by an input wiring 33u. An output terminal 52a of the injection voltage generator 30u is connected to one end of a primary winding m1 of a transformer 11u of a compensation signal applicator 75u by an output wiring 34u, and an output terminal 52b of the injection voltage generator 30u is connected to the other end of the primary winding m1 of the transformer 11u of the compensation signal applicator 75u by an output wiring 35u. The adjusted voltage Vdo1 is input to the input terminals 51a, 51b of the injection voltage generator 30u, that is, the input terminals 51a, 51b of injection waveform generators 10a, 10b. The injection voltage generator 30 includes a first injection waveform generator 10a that generates a first output voltage Vo1 based on the adjusted voltage Vdo1, and a second injection waveform generator 10b that generates a second output voltage Vo2 based on the adjusted voltage Vdo1.

[0118] The injection waveform generators 10a and 10b output, from output terminals 52a and 52b, voltages that are band-limited and have amplified voltage values, i.e., output voltages Vo1 and Vo2, based on the input adjustment voltage Vdo1. The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 10a is input to one end of the primary winding m1 of the transformer 11u through the output wiring 34u. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 10b is input to the other end of the primary winding m1 of the transformer 11u through the output wiring 35u. The output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite phases to each other. That is, the output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite polarities to each other. A voltage of the same phase, i.e., the same polarity, and having a magnitude twice that of Vo1, which is the difference between the output voltage Vo1 and the output voltage Vo2, is applied to the primary winding m1 of the transformer 11u. Note that in Fig. 32, the input wiring 33, the output wiring 34 connected to one end of the primary winding m1 of the transformer, and the output wiring 35 connected to the other end of the primary winding m1 of the transformer are shown. In the u-phase injection voltage generator 30u, the input wiring 33, the output wirings 34 and 35 of the injection voltage generator 30 are labeled with the symbol u and denoted as the input wiring 33u, the output wirings 34u and 35u. Similarly, in the v-phase injection voltage generator 30v, the input wiring 33, the output wirings 34 and 35 of the injection voltage generator 30 are labeled with the symbol v and denoted as the input wiring 33v, the output wirings 34v and 35v. In the w-phase injection voltage generator 30w, the input wiring 33, the output wirings 34 and 35 of the injection voltage generator 30 are labeled with the symbol w and denoted as the input wiring 33w, the output wirings 34w and 35w.

[0119] Transformer 11u includes a primary winding m1 and a secondary winding m2 on the primary side and the secondary side, respectively. The secondary winding m2 of the transformer 11u is inserted into the three-phase power line 5u. A voltage, that is, an injection voltage Vinj1, which is the difference between the output voltage Vo1 output from the injection waveform generator 10a of the injection voltage generator 30u and the output voltage Vo2 output from the injection waveform generator 10b of the injection voltage generator 30u, is applied to the primary winding m1 of the transformer 11u. The injection voltage Vinj1 has a reverse polarity to the differential mode voltage Vdi1 and is a compensation voltage Vdm1 that is a voltage corresponding to the turns ratio Rr between the primary winding m1 and the secondary winding m2. The compensation voltage Vdm1 is a superimposed voltage that is superimposed on the three-phase power line 5u.

[0120] The output voltage Vo1 output by the injection waveform generator 10a and the output voltage Vo2 output by the injection waveform generator 10b are voltages of the same magnitude and opposite phases to each other. By applying them to one end and the other end of the primary winding m1 of the transformer 11u, respectively, the differential injection voltage Vinj1 is applied. The transformer 11u generates a compensation voltage Vdm1 at both ends of the secondary winding m2 according to the turns ratio Rr and applies the compensation voltage Vdm1 to the u-phase of the three-phase power line 5. The first noise filter 50 of the seventh embodiment sets the gain Gi and the turns ratio Rr so that the compensation voltage Vdm1, which is a voltage superimposed on the u-phase of the three-phase power line 5 through the secondary winding m2 of the transformer 11u, reduces the differential mode voltage Vdi1, that is, so that the formula (10) holds. |Vdi1 - Vdm1| ≤ Vto ···(10) As described above, Vto is the allowable value of the voltage difference. The formula (10) indicates that the absolute value of the difference between the differential mode voltage Vdi1 and the compensation voltage Vdm1 is equal to or less than the allowable value Vto.

[0121] The configuration for suppressing the differential mode voltage Vdi2 of the v-phase of the three-phase power line 5, i.e., the three-phase power line 5v, is the same as the configuration for suppressing the differential mode voltage Vdi1 of the three-phase power line 5u. Therefore, the symbols 7u, 8u, 9u, 30u, 33u, 34u, 35u, 75u, 11u of each component are respectively read as 7v, 8v, 9v, 30v, 33v, 34v, 35v, 75v, 11v. Also, the symbols Vdi1, Vdo1, Vinj1, Vdm1 of each voltage are respectively read as Vdi2, Vdo2, Vinj2, Vdm2.

[0122] The configuration for suppressing the differential mode voltage Vdi3 of the w-phase of the three-phase power line 5, i.e., the three-phase power line 5w, is the same as the configuration for suppressing the differential mode voltage Vdi1 of the three-phase power line 5u. Therefore, the symbols 7u, 8u, 9u, 30u, 33u, 34u, 35u, 75u, 11u of each component are respectively read as 7w, 8w, 9w, 30w, 33w, 34w, 35w, 75w, 11w. Also, the symbols Vdi1, Vdo1, Vinj1, Vdm1 of each voltage are respectively read as Vdi3, Vdo3, Vinj3, Vdm3.

[0123] As described in Embodiment 1, the output voltage Vo1 output from the injection waveform generator 10a of the injection voltage generators 30u, 30v, and 30w corresponding to each phase of the three-phase power line 5 and the output voltage Vo2 output from the injection waveform generator 10b of the injection voltage generators 30u, 30v, and 30w are voltages of the same magnitude but opposite in phase to each other. By applying them to one end and the other end of the primary winding m1 of the transformers 11u, 11v, and 11w, respectively, differential injection voltages Vinj1, Vinj2, and Vinj3 are applied. The transformers 11u, 11v, and 11w generate compensation voltages Vdm1, Vdm2, and Vdm3 at both ends of the secondary winding m2 according to the turns ratio Rr, and apply the compensation voltages Vdm1, Vdm2, and Vdm3 to each phase of the three-phase power line 5. Similar to the noise filter 50 of Embodiment 1, the first noise filter 50 of Embodiment 7 can obtain injection voltages Vinj1, Vinj2, and Vinj3 whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output from one injection waveform generator 10, that is, without increasing the output voltages Vo1 and Vo2 of each injection waveform generator 10a and 10b. As a result, the first noise filter 50 of Embodiment 7 can reduce the size of the transformers 11u, 11v, and 11w or the control power supplies 15a and 15b, and the noise filter 50 can be reduced in size and weight. Therefore, the first noise filter 50 of Embodiment 7 can suppress the differential mode voltages Vdi1, Vdi2, and Vdi3 while being small and lightweight, that is, it can enhance the noise reduction effect while being small and lightweight.

[0124] Further, for example, like the second noise filter 50 of Embodiment 7 shown in FIG. 33, the noise detectors 7u, 7v, 7w are provided with voltage dividing transformers 70u, 70v, 70w instead of the signal conditioning circuits 9u, 9v, 9w, and instead of the injection voltage generators 30u, 30v, 30w that are based on the potential of the ground GND, i.e., the ground potential, injection voltage generators 39u, 39v, 39w based on a reference potential Vss that is a potential separated from the ground GND may be provided. The second noise filter 50 of Embodiment 7 is different from the noise filter 50 of Embodiment 2 in that it includes noise detectors 7u, 7v, 7w, injection voltage generators 39u, 39v, 39w, and compensation signal applicators 75u, 75v, 75w for each phase of the three-phase power line 5. Note that in FIG. 33, the compensation signal applicators 75u, 75v, 75w are omitted. The differences between the noise filter 50 of Embodiment 2 and the first noise filter 50 of Embodiment 7 will be mainly described.

[0125] The configurations for suppressing the differential mode voltage Vdi1 of the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u, the differential mode voltage Vdi2 of the v-phase of the three-phase power line 5, i.e., the three-phase power line 5v, and the differential mode voltage Vdi3 of the w-phase of the three-phase power line 5, i.e., the three-phase power line 5w, are the same. The injection voltage generators 39u, 39v, 39w can apply the injection voltage generator 39 shown in FIG. 34. The injection voltage generator 39 includes the injection waveform generators 31a, 31b described in Embodiment 2. The configuration for suppressing the differential mode voltage Vdi1 of the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u, will be described as a representative.

[0126] The noise detector 7u that detects the differential mode voltage Vdi1 includes a capacitor 8u and a voltage dividing transformer 70u connected in series between the three-phase power line 5u on the output side of the power converter 2 and the wiring 24 which is a ground wiring. One end of the primary winding m3 of the voltage dividing transformer 70u is connected to one end of the capacitor 8u on the side opposite to the three-phase power line 5u via the input terminal 94, and the other end is connected to the wiring 24 which is the ground wiring. One end of the secondary winding m4 of the voltage dividing transformer 70u is connected to the wiring 25 which is a reference wiring having a reference potential Vss different from the ground potential of the wiring 24 which is the ground wiring, and the other end is connected to the output terminal 95 that outputs the adjustment voltage Vdo1. The noise detector 7u outputs the adjustment voltage Vdo1 based on the input voltage input via the capacitor 8u by the voltage dividing transformer 70u, that is, the differential mode voltage Vdi1.

[0127] The input terminals 51a and 51b of the injection voltage generator 39u are connected to the output terminal 95 of the signal adjustment circuit 9u by the input wiring 33u. The output terminal 52a of the injection voltage generator 39u is connected to one end of the primary winding m1 of the transformer 11u of the compensation signal applicator 75u by the output wiring 34u, and the output terminal 52b of the injection voltage generator 39u is connected to the other end of the primary winding m1 of the transformer 11u of the compensation signal applicator 75u by the output wiring 35u. The adjustment voltage Vdo1 is input to the input terminals 51a and 51b of the injection voltage generator 39u, that is, the input terminals 51a and 51b of the injection waveform generators 31a and 31b. The injection voltage generator 39 includes a first injection waveform generator 31a that generates a first output voltage Vo1 based on the adjustment voltage Vdo1, and a second injection waveform generator 31b that generates a second output voltage Vo2 based on the adjustment voltage Vdo1.

[0128] The injection waveform generators 31a and 31b output the voltage that is band-limited and has its voltage value amplified, i.e., the output voltages Vo1 and Vo2, from the output terminals 52a and 52b based on the input adjusted voltage Vdo1. The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 31a is input to one end of the primary winding m1 of the transformer 11u through the output wiring 34u. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 31b is input to the other end of the primary winding m1 of the transformer 11u through the output wiring 35u. The output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude but opposite in phase to each other. That is, the output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude but opposite in polarity to each other. A voltage that is the difference between the output voltage Vo1 and the output voltage Vo2, i.e., a voltage of the same phase (i.e., the same polarity) and twice the magnitude of Vo1, is applied to the primary winding m1 of the transformer 11u. In FIG. 34, the input wiring 33, the output wiring 34 connected to one end of the primary winding m1 of the transformer, and the output wiring 35 connected to the other end of the primary winding m1 of the transformer are shown. In the u-phase injection voltage generator 39u, the input wiring 33, the output wirings 34 and 35 of the injection voltage generator 39 are labeled with the symbol u and denoted as the input wiring 33u, the output wirings 34u and 35u. Similarly, in the v-phase injection voltage generator 39v, the input wiring 33, the output wirings 34 and 35 of the injection voltage generator 39 are labeled with the symbol v and denoted as the input wiring 33v, the output wirings 34v and 35v. In the w-phase injection voltage generator 39w, the input wiring 33, the output wirings 34 and 35 of the injection voltage generator 39 are labeled with the symbol w and denoted as the input wiring 33w, the output wirings 34w and 35w.

[0129] A voltage that is the difference between the output voltage Vo1 output from the injection waveform generator 31a of the injection voltage generator 39u and the output voltage Vo2 output from the injection waveform generator 31b of the injection voltage generator 39u, i.e., the injection voltage Vinj1, is applied to the primary winding m1 of the transformer 11u. It is opposite in polarity to the differential mode voltage Vdi1, and a compensation voltage Vdm1 that is a voltage corresponding to the turns ratio of the primary winding m1 and the secondary winding m2 is generated in the secondary winding m2. The compensation voltage Vdm1 is a superimposed voltage superimposed on the three-phase power line 5u.

[0130] The configuration for suppressing the differential mode voltage Vdi2 of the v-phase of the three-phase power line 5, i.e., the three-phase power line 5v, is the same as the configuration for suppressing the differential mode voltage Vdi1 of the three-phase power line 5u. Therefore, the reference numerals 7u, 8u, 70u, 39u, 33u, 34u, 35u, 75u, 11u of each component are read as 7v, 8v, 70v, 39v, 33v, 34v, 35v, 75v, 11v, respectively. Also, the reference numerals Vdi1, Vdo1, Vinj1, Vdm1 of each voltage are read as Vdi2, Vdo2, Vinj2, Vdm2, respectively. Further, the configuration for suppressing the differential mode voltage Vdi3 of the w-phase of the three-phase power line 5, i.e., the three-phase power line 5w, is the same as the configuration for suppressing the differential mode voltage Vdi1 of the three-phase power line 5u. Therefore, the reference numerals 7u, 8u, 70u, 39u, 33u, 34u, 35u, 75u, 11u of each component are read as 7w, 8w, 70w, 39w, 33w, 34w, 35w, 75w, 11w, respectively. Also, the reference numerals Vdi1, Vdo1, Vinj1, Vdm1 of each voltage are read as Vdi3, Vdo3, Vinj3, Vdm3, respectively.

[0131] As described in Embodiment 2, the output voltage Vo1 output from the injection waveform generator 31a of the injection voltage generators 39u, 39v, and 39w corresponding to each phase of the three-phase power line 5 and the output voltage Vo2 output from the injection waveform generator 31b of the injection voltage generators 39u, 39v, and 39w are voltages of the same magnitude and opposite phases to each other. By applying them to one end and the other end of the primary winding m1 of the transformers 11u, 11v, and 11w, respectively, differential injection voltages Vinj1, Vinj2, and Vinj3 are applied. The transformers 11u, 11v, and 11w generate compensation voltages Vdm1, Vdm2, and Vdm3 at both ends of the secondary winding m2 according to the turns ratio Rr, and apply the compensation voltages Vdm1, Vdm2, and Vdm3 to each phase of the three-phase power line 5. Similar to the noise filter 50 of Embodiment 2, the second noise filter 50 of Embodiment 7 can obtain injection voltages Vinj1, Vinj2, and Vinj3 whose maximum voltage is twice that of the control power supplies 15a and 15b without increasing the output voltage Vo output from one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of each injection waveform generator 31a and 31b. As a result, the second noise filter 50 of Embodiment 7 can reduce the size of the transformers 11u, 11v, and 11w or the control power supplies 15a and 15b, and the noise filter 50 can be reduced in size and weight. Therefore, the second noise filter 50 of Embodiment 7 can suppress the differential mode voltages Vdi1, Vdi2, and Vdi3 while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight.

[0132] Also, for example, like the third noise filter 50 of Embodiment 7 shown in FIG. 35, the noise detectors 7u, 7v, and 7w may include detection transformers 80u, 80v, and 80w. The third noise filter 50 of Embodiment 7 is different from the noise filter 50 of Embodiment 5 in that it includes noise detectors 7u, 7v, and 7w, injection voltage generators 39u, 39v, and 39w, and compensation signal applicators 75u, 75v, and 75w for each phase of the three-phase power line 5. In FIG. 35, the compensation signal applicators 75u, 75v, and 75w are omitted. The differences from the noise filter 50 of Embodiment 5 and the second noise filter 50 of Embodiment 7 will be mainly described.

[0133] A configuration for suppressing the differential mode current in the current of the electromagnetic noise in the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u, a configuration for suppressing the differential mode current in the current of the electromagnetic noise in the v-phase of the three-phase power line 5, i.e., the three-phase power line 5v, and a configuration for suppressing the differential mode current in the current of the electromagnetic noise in the w-phase of the three-phase power line 5, i.e., the three-phase power line 5w, are the same. The injection voltage generators 39u, 39v, and 39w can apply the injection voltage generator 39 shown in FIG. 34. A configuration for suppressing the differential mode current in the current of the electromagnetic noise in the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u, will be described as a representative.

[0134] The noise detector 7u detects the current of the electromagnetic noise in the same manner as the noise filter 50 in the fifth embodiment. Specifically, the noise detector 7u detects the current of the differential mode component in the electromagnetic noise. The noise detector 7u includes a detection transformer 80u in which a primary winding m7 is inserted into the three-phase power line 5u on the output side of the power converter 2. The secondary winding m8 of the detection transformer 80u is connected to a wiring 25 which is a reference wiring having one end at the reference potential Vss, and the other end is connected to an output terminal 95 that outputs an adjustment voltage Vdo1. The detection transformer 80u includes a primary winding m7 on the primary side and a secondary winding m8 on the secondary side, similar to the transformer 11u, and detects a voltage proportional to the differential mode current in the current of the electromagnetic noise generated by the power converter 2, i.e., a detection voltage Vdsn1. The detection voltage Vdsn1 is a voltage based on the electromagnetic noise. Therefore, the noise detector 7u detects the detection voltage Vdsn1 which is a voltage based on the electromagnetic noise in the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u. FIG. 35 shows an example in which the primary winding m7 of the detection transformer 80u is inserted into the three-phase power line 5u. The detection transformer 80u detects the detection voltage Vdsn1 applied to both ends of the primary winding m7 and outputs it to both ends of the secondary winding m8 according to the turns ratio Rr of the primary winding m7 and the secondary winding m8 of the detection transformer 80u, and this voltage is output from the output terminal 95 to the injection waveform generators 31a and 31b of the injection voltage generator 39u as the adjustment voltage Vdo1 which is the output of the noise detector 7u.

[0135] In the injection voltage generator 39u, the output voltage Vo1 output from the injection waveform generator 31a and the output voltage Vo2 output from the injection waveform generator 31b are voltages of the same magnitude but opposite in phase to each other. By applying them to one end and the other end of the primary winding m1 of the transformer 11u respectively, a differential injection voltage Vinj1 is applied. The transformer 11u generates a compensation voltage Vdm1 across both ends of the secondary winding m2 according to the turns ratio Rr, and applies the compensation voltage Vdm1 to the u-phase of the three-phase power line 5. The third noise filter 50 of the seventh embodiment sets the gain Gi and the turns ratio Rr so that the compensation voltage Vdm1, which is the voltage superimposed on the u-phase of the three-phase power line 5 through the secondary winding m2 of the transformer 11u, reduces the detection voltage Vdsn1, that is, so that the equation (11) holds. |Vdsn1 - Vdm1| ≦ Vto ···(11) As described above, Vto is the allowable value of the voltage difference. The equation (11) indicates that the absolute value of the difference between the detection voltage Vdsn1 and the compensation voltage Vdm1 is equal to or less than the allowable value Vto.

[0136] The configuration for suppressing the differential-mode current in the current of the electromagnetic noise in the v-phase of the three-phase power line 5, i.e., in the three-phase power line 5v, is the same as the configuration for suppressing the differential-mode current in the current of the electromagnetic noise in the three-phase power line 5u. Therefore, the symbols 7u, 80u, 39u, 33u, 34u, 35u, 75u, 11u of each component are respectively read as 7v, 80v, 39v, 33v, 34v, 35v, 75v, 11v. Also, the symbols Vdsn1, Vdo1, Vinj1, Vdm1 of each voltage are respectively read as Vdsn2, Vdo2, Vinj2, Vdm2. Also, the configuration for suppressing the differential-mode current in the current of the electromagnetic noise in the w-phase of the three-phase power line 5, i.e., in the three-phase power line 5w, is the same as the configuration for suppressing the differential-mode current in the current of the electromagnetic noise in the three-phase power line 5u. Therefore, the symbols 7u, 80u, 39u, 33u, 34u, 35u, 75u, 11u of each component are respectively read as 7w, 80w, 39w, 33w, 34w, 35w, 75w, 11w. Also, the symbols Vdsn1, Vdo1, Vinj1, Vdm1 of each voltage are respectively read as Vdsn3, Vdo3, Vinj3, Vdm3.

[0137] As described in Embodiment 5, without increasing the output voltage Vo output by one injection waveform generator 31, that is, without increasing the output voltages Vo1, Vo2 of each injection waveform generator 31a, 31b, injection voltages Vinj1, Vinj2, Vinj3 with a maximum voltage twice that of the control power supplies 15a, 15b can be obtained. As a result, the third noise filter 50 of Embodiment 7 can be miniaturized in terms of the transformers 11u, 11v, 11w or the control power supplies 15a, 15b, and the noise filter 50 can be miniaturized and lightened. Therefore, the third noise filter 50 of Embodiment 7 can suppress the differential current in the current of the electromagnetic noise while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight.

[0138] Further, like the fourth noise filter 50 of Embodiment 7 shown in FIG. 36, for example, the compensation signal applicators 75u, 75v, 75w may include signal adjustment transformers 71u, 71v, 71w and capacitors 73u, 73v, 73w instead of the transformers 11u, 11v, 11w. The fourth noise filter 50 of Embodiment 7 is different from the noise filter 50 of Embodiment 3 in that it includes noise detectors 7u, 7v, 7w, injection voltage generators 30u, 30v, 30w or injection voltage generators 39u, 39v, 39w, and compensation signal applicators 75u, 75v, 75w for each phase of the three-phase power line 5. In FIG. 36, the noise detectors 7u, 7v, 7w are omitted, but the noise detectors 7u, 7v, 7w in the first to third noise filters 50 of Embodiment 7 can be applied. Note that FIG. 36 shows the injection voltage generators 30u, 30v, 30w to which the noise detectors 7u, 7v, 7w in the first noise filter 50 of Embodiment 7 are applied. When applying the noise detectors 7u, 7v, 7w in the second or third noise filter 50 of Embodiment 7, the fourth noise filter 50 of Embodiment 7 includes injection voltage generators 39u, 39v, 39w instead of the injection voltage generators 30u, 30v, 30w. The differences from the noise filter 50 of Embodiment 3 or 4 and the first noise filter 50 of Embodiment 7 will be mainly described.

[0139] The configurations for suppressing the differential mode voltage Vdi1 or differential mode current of the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u, the differential mode voltage Vdi2 or differential mode current of the v-phase of the three-phase power line 5, i.e., the three-phase power line 5v, and the differential mode voltage Vdi3 or differential mode current of the w-phase of the three-phase power line 5, i.e., the three-phase power line 5w, are the same. Note that the configuration for suppressing the differential mode current is the case where the noise detectors 7u, 7v, 7w in the third noise filter 50 of Embodiment 7 are applied. The configuration for suppressing the differential mode voltage Vdi1 or differential mode current of the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u, will be described as a representative.

[0140] The compensation signal applicator 75u includes a signal conditioning transformer 71u which is a transformer having a primary winding m5 and a secondary winding m6 on the primary side and the secondary side respectively, and a capacitor 73u. The capacitor 73u corresponds to the signal applicator 72 in the three-phase power line 5u described in the third embodiment. One end of the secondary winding m6 of the signal conditioning transformer 71u is connected to a wiring 24 which is a ground wiring, and the other end is connected to the three-phase power line 5u on the output side of the power converter 2 via the capacitor 73u. FIG. 36 shows an example in which the compensation signal applicator 75u is connected to the three-phase power line 5u. For the signal conditioning transformer 71u, the output terminals 52a and 52b of the injection voltage generator 30u are respectively connected to both ends of the primary winding m5, one end of the secondary winding m6 is connected to the wiring 24 having a ground potential, and the other end is connected to the side opposite to the three-phase power line 5u in the capacitor 73u.

[0141] The output voltage Vo1 output from the output terminal 52a of the injection waveform generator 10a of the injection voltage generator 30u is input to one end of the primary winding m5 of the signal conditioning transformer 71u. The output voltage Vo2 output from the output terminal 52b of the injection waveform generator 10b of the injection voltage generator 30u is input to the other end of the primary winding m5 of the signal conditioning transformer 71u. The output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite phases to each other. That is, the output voltage Vo1 and the output voltage Vo2 are voltages of the same magnitude and opposite polarities to each other. An injection voltage Vinj1 which is a voltage of the same phase, that is, the same polarity and twice the magnitude of Vo1, which is the difference between the output voltage Vo1 and the output voltage Vo2, is applied to the primary winding m5 of the signal conditioning transformer 71u. A compensation voltage Vdm1 is superimposed on the three-phase power line 5u via the capacitor 73u so as to suppress the differential mode voltage Vdi1. Also, when suppressing the differential mode current, a compensation voltage Vdm1 is superimposed on the three-phase power line 5u via the capacitor 73u so as to suppress a detection voltage Vdsn1 which is a voltage proportional to the differential mode current. Note that a current for suppressing the differential mode voltage Vdi1 or the differential mode current flows through the three-phase power line 5u via the capacitor 73u.

[0142] The configuration for suppressing the differential mode voltage Vdi2 or differential mode current of the v-phase of the three-phase power line 5, i.e., the three-phase power line 5v, is the same as the configuration for suppressing the differential mode voltage Vdi1 or differential mode current of the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u. For the configuration of suppressing the differential mode voltage Vdi2 of the three-phase power line 5v, in the configuration of suppressing the differential mode voltage Vdi1 of the three-phase power line 5u, the reference numerals 7u, 8u, 9u or 70u, 30u or 39u, 33u, 34u, 35u, 75u, 71u, 73u of each component are respectively replaced with 7v, 8v, 9v or 70v, 30v or 39v, 33v, 34v, 35v, 75v, 71v, 73v. For the configuration of suppressing the differential mode current of the three-phase power line 5v, in the configuration of suppressing the differential mode current of the three-phase power line 5u, the reference numerals 7u, 80u, 39u, 33u, 34u, 35u, 75u, 71u, 73u of each component are respectively replaced with 7v, 80v, 39v, 33v, 34v, 35v, 75v, 71v, 73v. Also, the reference numerals Vdi1 or Vdsn1, Vdo1, Vinj1, Vdm1 of each voltage are respectively replaced with Vdi2 or Vdsn2, Vdo2, Vinj2, Vdm2.

[0143] The configuration for suppressing the differential-mode voltage Vdi3 or the differential-mode current of the w-phase of the three-phase power line 5, i.e., the three-phase power line 5w, is the same as the configuration for suppressing the differential-mode voltage Vdi1 or the differential-mode current of the u-phase of the three-phase power line 5, i.e., the three-phase power line 5u. The configuration for suppressing the differential-mode voltage Vdi3 of the three-phase power line 5w is to replace the reference numerals 7u, 8u, 9u or 70u, 30u or 39u, 33u, 34u, 35u, 75u, 71u, 73u of each component in the configuration for suppressing the differential-mode voltage Vdi1 of the three-phase power line 5u with 7w, 8w, 9w or 70w, 30w or 39w, 33w, 34w, 35w, 75w, 71w, 73w, respectively. The configuration for suppressing the differential-mode current of the three-phase power line 5w is to replace the reference numerals 7u, 80u, 39u, 33u, 34u, 35u, 75u, 71u, 73u of each component in the configuration for suppressing the differential-mode current of the three-phase power line 5u with 7w, 80w, 39w, 33w, 34w, 35w, 75w, 71w, 73w, respectively. Also, replace the reference numerals Vdi1 or Vdsn1, Vdo1, Vinj1, Vdm1 of each voltage with Vdi3 or Vdsn3, Vdo3, Vinj3, Vdm3, respectively.

[0144] In the fourth noise filter 50 of Embodiment 7, the injection waveform generators 10a, 10b of the injection voltage generators 30u, 30v, 30w corresponding to each phase of the three-phase power line 5, or the injection waveform generators 31a, 31b of the injection voltage generators 39u, 39v, 39w output output voltages Vo1, Vo2 of the same magnitude but opposite phases. Therefore, the differential between the output voltage Vo1 and the output voltage Vo2, that is, injection voltages Vinj1, Vinj2, Vinj3 of the same phase and twice the magnitude of Vo1, are applied to the primary windings m5 of the signal conditioning transformers 71u, 71v, 71w. That is, similar to the noise filter 50 of Embodiment 3 or 4, the fourth noise filter 50 of Embodiment 7 can obtain an injection voltage Vinj1 whose maximum voltage is twice that of the control power supplies 15a, 15b without increasing the output voltage Vo output by one injection waveform generator 10 or injection waveform generator 31, that is, without increasing the output voltages Vo1, Vo2 of each injection waveform generator 10a, 10b or injection waveform generators 31a, 31b. As a result, the signal conditioning transformers 71u, 71v, 71w or the control power supplies 15a, 15b can be miniaturized. Therefore, the fourth noise filter 50 of Embodiment 7 can suppress the differential mode voltages Vdi1, Vdi2, Vdi3 or the differential mode current while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight.

[0145] Also, for example, like the fifth noise filter 50 of Embodiment 7 shown in FIG. 37, a configuration for suppressing the differential mode component in electromagnetic noise may be connected to each wiring of the DC bus of the power converter 2, that is, the high potential side wiring 44p and the low potential side wiring 44s. The fifth noise filter 50 of Embodiment 7 is different from the noise filter 50 of Embodiment 1 in that it includes noise detectors 7p, 7s, injection voltage generators 39p, 39s, and compensation signal applicators 75p, 75s for each wiring of the DC bus of the power converter 2. The differences from the noise filter 50 of Embodiment 1 and the third noise filter 50 of Embodiment 7 will be mainly described.

[0146] The fifth noise filter 50 of Embodiment 7 shown in FIG. 37 is an example of suppressing differential mode current in the current of electromagnetic noise of the high potential side wiring 44p and the low potential side wiring 44s, similar to the third noise filter 50 of Embodiment 7. The configuration for suppressing the differential mode current in the current of electromagnetic noise of the high potential side wiring 44p and the configuration for suppressing the differential mode current in the current of electromagnetic noise of the low potential side wiring 44s are the same. The injection voltage generators 39p and 39s can apply the injection voltage generator 39 shown in FIG. 34. The configuration for suppressing the differential mode current in the current of electromagnetic noise of the high potential side wiring 44p, which is the DC bus of the power converter 2, will be described as a representative example.

[0147] The noise detector 7p detects the current of the differential mode component in the electromagnetic noise, similar to the third noise filter 50 of Embodiment 7. The noise detector 7p includes a detection transformer 80p in which a primary winding m7 is inserted into the high potential side wiring 44p of the power converter 2. One end of the secondary winding m8 of the detection transformer 80p is connected to a wiring 25, which is a reference wiring having a reference potential Vss, and the other end is connected to an output terminal 95 that outputs an adjustment voltage Vdo1. The detection transformer 80p, similar to the detection transformer 80u, includes a primary winding m7 on the primary side and a secondary winding m8 on the secondary side, and detects a voltage proportional to the differential mode current in the current of electromagnetic noise generated by the power converter 2, that is, a detection voltage Vdsn1. The detection voltage Vdsn1 is a voltage based on electromagnetic noise. Therefore, the noise detector 7p detects the detection voltage Vdsn1, which is a voltage based on the electromagnetic noise of the high potential side wiring 44p of the power converter 2. The detection transformer 80p outputs the detection voltage Vdsn1 applied to both ends of the primary winding m7 to both ends of the secondary winding m8 according to the turns ratio Rr of the primary winding m7 and the secondary winding m8 of the detection transformer 80p, and outputs this voltage from the output terminal 95 to the injection waveform generators 31a and 31b of the injection voltage generator 39u as the adjustment voltage Vdo1, which is the output of the noise detector 7p.

[0148] The input terminals 51a and 51b of the injection voltage generator 39p are connected to the output terminal 95 of the detection transformer 80p by the input wiring 33p. The output terminal 52a of the injection voltage generator 39p is connected to one end of the primary winding m1 of the transformer 11p of the compensation signal applicator 75p by the output wiring 34p, and the output terminal 52b of the injection voltage generator 39p is connected to the other end of the primary winding m1 of the transformer 11p of the compensation signal applicator 75p by the output wiring 35p. The adjustment voltage Vdo1 is input to the input terminals 51a and 51b of the injection voltage generator 39p, that is, the input terminals 51a and 51b of the injection waveform generators 31a and 31b.

[0149] In the injection voltage generator 39p, the output voltage Vo1 output by the injection waveform generator 31a and the output voltage Vo2 output by the injection waveform generator 31b are voltages of the same magnitude and opposite phases to each other. By applying them to one end and the other end of the primary winding m1 of the transformer 11p of the compensation signal applicator 75p respectively, the differential injection voltage Vinj1 is applied. The transformer 11p generates the compensation voltage Vdm1 at both ends of the secondary winding m2 according to the turns ratio Rr, and applies the compensation voltage Vdm1 to the high-potential side wiring 44p. The fifth noise filter 50 of the seventh embodiment sets the gain Gi and the turns ratio Rr so that the compensation voltage Vdm1, which is the voltage superimposed on the high-potential side wiring 44p through the secondary winding m2 of the transformer 11p, reduces the detection voltage Vdsn1, that is, so that the equation (11) holds.

[0150] The configuration for suppressing the differential mode current in the electromagnetic noise current of the low-potential side wiring 44s, which is the DC bus of the power converter 2, is the same as the configuration for suppressing the differential mode current in the electromagnetic noise current of the high-potential side wiring 44p, which is the DC bus of the power converter 2. Therefore, the reference numerals 7p, 80p, 39p, 33p, 34p, 35p, 75p, and 11p of each component are read as 7s, 80s, 39s, 33s, 34s, 35s, 75s, and 11s respectively. Also, the reference numerals Vdsn1, Vdo1, Vinj1, and Vdm1 of each voltage are read as Vdsn2, Vdo2, Vinj2, and Vdm2 respectively.

[0151] As described with respect to the third noise filter 50 of the seventh embodiment, without increasing the output voltage Vo output from one injection waveform generator 31, that is, without increasing the output voltages Vo1 and Vo2 of the respective injection waveform generators 31a and 31b, injection voltages Vinj1 and Vinj2 having a maximum voltage twice that of the control power supplies 15a and 15b can be obtained. As a result, in the fifth noise filter 50 of the seventh embodiment, the transformers 11p and 11s or the control power supplies 15a and 15b can be miniaturized, and the noise filter 50 can be miniaturized and lightened. Therefore, the fifth noise filter 50 of the seventh embodiment can suppress the differential current in the electromagnetic noise current while being small and lightweight, that is, can enhance the noise reduction effect while being small and lightweight.

[0152] Also, for example, a configuration for suppressing the differential mode component, that is, the differential mode current, in the electromagnetic noise current may be connected to the single-phase power line 45 as in the sixth noise filter 50 of the seventh embodiment shown in FIG. 38. The sixth noise filter 50 of the seventh embodiment is different from the third noise filter 50 of the seventh embodiment in that it includes one noise detector 7 having primary side windings m7a and m7b connected to the two lines of the single-phase power line 45, that is, the single-phase power lines 45a and 45b, respectively, one injection voltage generator 39, and one compensation signal applicator 75 having secondary side windings m2a and m2b connected to the single-phase power lines 45a and 45b, respectively. In this case, the single-phase power line 45 is an example of the single-phase power line on the output side of the power converter 2. The differences from the third noise filter 50 of the seventh embodiment will be mainly described.

[0153] The noise detector 7 is configured to detect only the differential mode component, i.e., only the current of the differential mode component in the electromagnetic noise, without detecting the common mode component, in the two lines of the single-phase power line 45, namely the single-phase power line 45a and the single-phase power line 45b. In FIG. 38, a detection transformer 80 is shown as an example of the noise detector 7. The primary winding m7a connected to the single-phase power line 45a and the primary winding m7b connected to the single-phase power line 45b are wound in opposite directions. The secondary winding m8 of the detection transformer 80 is connected to a wiring 25 which is a reference wiring with one end at the reference potential Vss, and the other end is connected to an output terminal 95 that outputs an adjustment voltage Vdo. The detection voltages Vdsn1 and Vdsn2 are voltages based on electromagnetic noise. A voltage obtained by adding the detection voltage Vdsn1 detected by the primary winding m7a and the detection voltage Vdsn2 detected by the primary winding m7b is generated in the secondary winding m8 of the detection transformer 80. The noise detector 7 outputs an adjustment voltage Vdo with respect to the reference potential Vss from the output terminal 95. The adjustment voltage Vdo output by the noise detector 7 is the sum of the detection voltage Vdsn1 detected by the primary winding m7a and the detection voltage Vdsn2 detected by the primary winding m7b.

[0154] The compensation signal applicator 75 is configured to apply only the voltage based on the current of the differential mode component without applying the voltage based on the current of the common mode component in the two lines of the single-phase power line 45, namely the single-phase power line 45a and the single-phase power line 45b. In FIG. 38, a transformer 11 is shown as an example of the compensation signal applicator 75. The secondary winding m2a connected to the single-phase power line 45a and the secondary winding m2b connected to the single-phase power line 45b are wound in opposite directions. An injection voltage Vinj is applied to the primary winding m1 of the transformer 11. When the turns ratio of the transformer 11 is 1:1, compensation voltages Vdm1 and Vdm2 having the same voltage as the injection voltage Vinj are superimposed on the single-phase power lines 45a and 45b, respectively, in response to the injection voltage Vinj. In this case, the voltage based on the current of the differential mode component superimposed on the two lines of the single-phase power line 45, namely the single-phase power line 45a and the single-phase power line 45b, is the sum of the compensation voltage Vdm1 and the compensation voltage Vdm2.

[0155] The sixth noise filter 50 of Embodiment 7 is similar to the third noise filter 50 of Embodiment 7. While being small and lightweight, it can suppress the differential current in the current of the electromagnetic noise generated in the two wires of the single-phase power line 45. That is, while being small and lightweight, it can enhance the noise reduction effect.

[0156] Also, for example, like the seventh noise filter 50 of Embodiment 7 shown in FIG. 39, a configuration for suppressing the differential mode component in the electromagnetic noise may be connected to each wiring of the DC bus of the power converter 2, that is, the high-potential side wiring 44p and the low-potential side wiring 44s. The seventh noise filter 50 of Embodiment 7 is different from the fifth noise filter 50 of Embodiment 7 in that it includes one noise detector 7 having primary side windings m7a and m7b connected to the high-potential side wiring 44p and the low-potential side wiring 44s respectively, one injection voltage generator 39, and one compensation signal applicator 75 having secondary side windings m2a and m2b connected to the high-potential side wiring 44p and the low-potential side wiring 44s respectively. The parts different from the fifth noise filter 50 of Embodiment 7 will be mainly described.

[0157] The noise detector 7 is configured to detect only the differential mode component, i.e., only the current of the differential mode component in the electromagnetic noise, without detecting the common mode component, in the high potential side wiring 44p and the low potential side wiring 44s. In FIG. 39, a detection transformer 80 is shown as an example of the noise detector 7. The primary winding m7a connected to the high potential side wiring 44p and the primary winding m7b connected to the low potential side wiring 44s are wound in opposite directions. The secondary winding m8 of the detection transformer 80 is connected to a wiring 25 which is a reference wiring with one end at the reference potential Vss, and the other end is connected to an output terminal 95 that outputs an adjustment voltage Vdo. The detection voltages Vdsn1 and Vdsn2 are voltages based on electromagnetic noise. A voltage obtained by adding the detection voltage Vdsn1 detected by the primary winding m7a and the detection voltage Vdsn2 detected by the primary winding m7b is generated in the secondary winding m8 of the detection transformer 80. The noise detector 7 outputs an adjustment voltage Vdo with reference to the reference potential Vss from the output terminal 95. The adjustment voltage Vdo output by the noise detector 7 is the sum of the detection voltage Vdsn1 detected by the primary winding m7a and the detection voltage Vdsn2 detected by the primary winding m7b.

[0158] The compensation signal applicator 75 is configured to apply only the voltage based on the differential mode component current without applying the voltage based on the common mode component current in the high potential side wiring 44p and the low potential side wiring 44s. In FIG. 39, a transformer 11 is shown as an example of the compensation signal applicator 75. The secondary winding m2a connected to the high potential side wiring 44p and the secondary winding m2b connected to the low potential side wiring 44s are wound in opposite directions. An injection voltage Vinj is applied to the primary winding m1 of the transformer 11. When the turns ratio of the transformer 11 is 1:1, compensation voltages Vdm1 and Vdm2 of the same voltage as the injection voltage Vinj are superimposed on the high potential side wiring 44p and the low potential side wiring 44s, respectively, in response to the injection voltage Vinj. In this case, the voltage based on the differential mode component current superimposed on the two lines of the DC bus of the power converter 2, i.e., the high potential side wiring 44p and the low potential side wiring 44s, is the sum of the compensation voltage Vdm1 and the compensation voltage Vdm2.

[0159] The seventh noise filter 50 of Embodiment 7, similar to the fifth noise filter 50 of Embodiment 7, can suppress the differential current in the current of the electromagnetic noise generated in the two wires of the DC bus of the power converter 2 while being small-sized and lightweight, that is, it can enhance the noise reduction effect while being small-sized and lightweight.

[0160] In Embodiment 7, an example of detecting and suppressing the voltage or current of the differential mode component in the electromagnetic noise was described. Since the noise filter 50 of Embodiment 7 includes noise detectors 7, 7u, 7v, 7w, 7p, 7s, compensation signal applicators 75, 75u, 75v, 75w, 75p, 75s, and injection voltage generators 30u, 30v, 30w (or 39u, 39v, 39w), 39, 39p, 39s for each phase of the three-phase power line 5, each phase of the three-phase power line 4, each power line of the single-phase power line 45, and each wiring of the DC bus of the power converter 2, the voltage or current of the common mode component in the electromagnetic noise described in Embodiments 1 to 6 can also be suppressed.

[0161] In Embodiment 7, the case where the output voltages Vo1 and Vo2 have the same magnitude is shown. However, similar to Embodiment 1, the output voltages Vo1 and Vo2 may have different magnitudes. Even when they have different magnitudes, the differential between the output voltage Vo1 and the output voltage Vo2, that is, the injection voltages Vinj1, Vinj2, Vinj3, and Vinj which are voltages larger than the output voltage Vo1 and in the same phase, are applied to the primary winding m1 of the transformers 11u, 11v, 11w in the compensation signal applicators 75, 75u, 75v, 75w or to the primary winding m5 of the signal adjustment transformers 71u, 71v, 71w. As a result, the first to fourth and sixth noise filters 50 of Embodiment 7 can be miniaturized in the transformers 11, 11u, 11v, 11w, the signal adjustment transformers 71u, 71v, 71w, or the control power supplies 15a, 15b, and the noise filters 50 can be miniaturized and lightened. The same applies to the fifth and seventh noise filters 50 of Embodiment 7. Even when the magnitudes of the output voltages Vo1 and Vo2 are different, the differential between the output voltage Vo1 and the output voltage Vo2, that is, the injection voltages Vinj1, Vinj2, and Vinj which are voltages larger than the output voltage Vo1 and in the same phase, are applied to the primary winding m1 of the transformers 11, 11p, 11s in the compensation signal applicators 75, 75p, 75s. As a result, the fifth and seventh noise filters 50 of Embodiment 7 can be miniaturized in the transformers 11, 11p, 11s or the control power supplies 15a, 15b, and the noise filters 50 can be miniaturized and lightened.

[0162] Note that although the noise filter 50 of Embodiment 7 shown in FIGS. 31, 33, 35 to 36, and 38 has a feedforward configuration, the positions of the compensation signal applicators 75, 75u, 75v, 75w and the noise detectors 7, 7u, 7v, 7w can be exchanged to form a feedback configuration. Also, although the noise filter 50 of Embodiment 7 shown in FIGS. 37 and 39 has a feedforward configuration, the positions of the compensation signal applicators 75, 75p, 75s and the noise detectors 7, 7p, 7s can be exchanged to form a feedback configuration. Further, the noise detectors 7u, 7v, 7w and the compensation signal applicators 75u, 75v, 75w may be connected to the three-phase power lines 4 on the input side of the power converter 2. The noise detector 7 and the compensation signal applicator 75 shown in FIG. 38 may be connected to the single-phase power line 45 on the output side of the power converter 2 or may be connected to the single-phase power line 45 on the input side of the power converter 2.

[0163] Note that although the examples of applying the noise filter 50 of Embodiments 1 to 7 to the motor drive system 60 equipped with the power converter 2 that converts three-phase AC power or single-phase AC through DC power into three-phase AC power or single-phase AC have been shown, the present invention is not limited to this example. The noise filter 50 of Embodiments 1 to 7 can also be applied to a system equipped with a power converter that generates an electromagnetic noise voltage or current by the switching operation of semiconductor elements. For example, the power converter 2 may be an isolated DC-DC converter. In this case, the AC power source 1 becomes a DC power source, and the induction motor 3 becomes a DC motor.

[0164] Also, although various exemplary embodiments and examples are described in the present application, the various features, aspects, and functions described in one or more of the embodiments are not limited to the application of a specific embodiment, but can be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are assumed to be within the scope of the technology disclosed in the present specification. For example, it includes cases where at least one component is deformed, added, or omitted, and further cases where at least one component is extracted and combined with the components of other embodiments.

Explanation of Reference Numerals

[0165] 2... Power converter, 4... Three-phase power line, 5... Three-phase power line, 7, 7u, 7v, 7w, 7p, 7s... Noise detector, 8, 8u, 8v, 8w... Capacitor, 9, 9u, 9v, 9w... Signal conditioning circuit, 10, 10a, 10b... Injection waveform generator, 11, 11u, 11v, 11w, 11p, 11s... Transformer, 24... Wiring (ground wiring), 25... Wiring (reference wiring), 30, 30u, 30v, 30w... Injection voltage generator, 31, 31a, 31b... Injection waveform generator, 39, 39u, 39v, 39w, 39p, 39s... Injection voltage generator, 44p... High-potential side wiring, 44s... Low-potential side wiring, 45... Single-phase power line, 50... Noise filter, 70, 70u, 70v, 70w... Voltage-dividing transformer, 71, 71u, 71v, 71w... Signal conditioning transformer, 72... Signal applicator, 73, 73u, 73v, 73w... Capacitor, 75, 75u, 75v, 75w, 75p, 75s... Compensation signal applicator, 80, 80u, 80v, 80w, 80p, 80s... Detection transformer, 95, 95a, 95b... Output terminal, m1... Primary winding, m2, m2a, m2b... Secondary winding, m3... Primary winding, m4, m4a, m4b... Secondary winding, m5... Primary winding, m6... Secondary winding, m7, m7a, m7b... Primary winding, m8, m8a, m8b... Secondary winding, Q1, Q2, Q3, Q4, Q5, Q6... Semiconductor element, Vci... Common-mode voltage, Vdi1, Vdi2, Vdi3... Differential-mode voltage, Vd, Vd1, Vd2... Adjustment voltage, Vdo, Vdo1, Vdo2, Vdo3... Adjustment voltage, Vo... Output voltage, Vo1... Output voltage (first output voltage), Vo2... Output voltage (second output voltage), Vinj, Vinj1, Vinj2, Vinj3... Injection voltage, Vcom... Compensation voltage, Vdm1, Vdm2, Vdm3... Compensation voltage, Vto... Tolerance value, Vsn, Vdsn1, Vdsn2, Vdsn3... Detection voltage, Vss... Reference potential

Claims

1. A noise filter for reducing the voltage or current of electromagnetic noise generated by a power converter that performs power conversion by the switching operation of a semiconductor element, a noise detector that detects a voltage based on the electromagnetic noise generated by the power converter and outputs an adjusted voltage in which the voltage based on the electromagnetic noise is adjusted; a compensation signal applicator that superimposes a compensation voltage having a polarity opposite to that of the voltage based on the electromagnetic noise on the output or input of the power converter via a transformer; a first output voltage that generates an injection voltage between one end and the other end of the primary side winding of the transformer and a second output voltage having a polarity opposite to that of the first output voltage based on the adjusted voltage, outputs the first output voltage to one end of the primary side winding of the transformer, and outputs the second output voltage to the other end of the primary side winding of the transformer, and an injection voltage generator, the injection voltage generator generates the first output voltage and the second output voltage that generate the injection voltage such that the difference between the compensation voltage superimposed by the compensation signal applicator and the voltage based on the electromagnetic noise is equal to or less than an allowable value, a noise filter.

2. In the transformer of the compensation signal applicator, a secondary side winding is inserted into a power line on the output side or the input side of the power converter. The noise filter according to claim 1.

3. The compensation signal applicator includes a signal adjustment transformer that is the transformer and a signal applicator including a capacitor, One end of the secondary side winding of the signal adjustment transformer is connected to a ground wiring, and the other end is connected to a power line on the output side or the input side of the power converter via the capacitor of the signal applicator. The noise filter according to claim 1.

4. The noise detector includes a capacitor and a signal adjustment circuit connected in series between a power line on the output side or the input side of the power converter and a ground wiring, and the signal adjustment circuit outputs the adjusted voltage based on an input voltage input via the capacitor. The noise filter according to any one of claims 1 to 3.

5. The noise detector includes a capacitor and a voltage dividing transformer connected in series between a power line on the output side or the input side of the power converter and a ground wiring, One end of the primary side winding of the voltage dividing transformer is connected to one end of the capacitor on the side opposite to the power line, and the other end is connected to the ground wiring. The secondary winding of the voltage-dividing transformer is connected at one end to a reference wiring having a reference potential different from the ground potential of the ground wiring, and at the other end to an output terminal that outputs the adjustment voltage. The noise filter according to any one of claims 1 to 3.

6. The noise detector includes a detection transformer having a primary winding inserted into a power line on the output side or the input side of the power converter, one end of the secondary winding of the detection transformer is connected to a reference wiring having a reference potential, and the other end is connected to an output terminal that outputs the adjustment voltage. The noise filter according to any one of claims 1 to 3.

7. The injection voltage generator includes a first injection waveform generator that generates the first output voltage based on the adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the adjustment voltage, or includes a first injection waveform generator that generates the first output voltage based on the adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the first output voltage. The noise filter according to any one of claims 1 to 5.

8. The injection voltage generator includes a first injection waveform generator that generates the first output voltage based on the adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the adjustment voltage, or includes a first injection waveform generator that generates the first output voltage based on the adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the first output voltage. The noise filter according to claim 6.

9. The noise detector includes a detection transformer having a primary winding inserted into a power line on the output side or the input side of the power converter and having two secondary windings, one end of a first secondary winding, which is one of the secondary windings, is connected to a reference wiring having a reference potential, and the other end is connected to a first output terminal that outputs a first adjustment voltage, which is the first adjustment voltage. one end of a second secondary winding, which is the other secondary winding, is connected to the reference wiring, and the other end is connected to a second output terminal that outputs a second adjustment voltage, which is the second adjustment voltage. The injection voltage generator includes a first injection waveform generator that generates the first output voltage based on the first adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the second adjustment voltage. The noise filter according to any one of claims 1 to 3.

10. The noise detector includes a capacitor and a voltage-dividing transformer connected in series between a power line on the output side or the input side of the power converter and a ground wiring, the voltage-dividing transformer has two secondary windings, one end of the primary winding is connected to one end of the capacitor on the side opposite to the power line, and the other end of the primary winding is connected to the ground wiring, one of the secondary windings, the first secondary winding, has one end connected to a reference wiring having a reference potential different from the ground potential of the ground wiring, and the other end connected to a first output terminal that outputs a first adjustment voltage which is the first of the adjustment voltages, the other of the secondary windings, the second secondary winding, has one end connected to the reference wiring, and the other end connected to a second output terminal that outputs a second adjustment voltage which is the second of the adjustment voltages, The injection voltage generator includes a first injection waveform generator that generates the first output voltage based on the first adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the second adjustment voltage. The noise filter according to any one of claims 1 to 3.

11. The noise detector includes a capacitor and a signal adjustment circuit connected in series between a power line on the output side or the input side of the power converter and a ground wiring, the signal adjustment circuit outputs the first adjustment voltage and the second adjustment voltage which are the two adjustment voltages based on the input voltage input through the capacitor, The injection voltage generator includes a first injection waveform generator that generates the first output voltage based on the first adjustment voltage, and a second injection waveform generator that generates the second output voltage based on the second adjustment voltage. The noise filter according to any one of claims 1 to 3.

12. The noise detector detects the common-mode voltage in the voltage of the electromagnetic noise. The noise filter according to any one of claims 1 to 5, and 7, 10, 11.

13. The noise detector detects a voltage proportional to the common-mode current in the current of the electromagnetic noise. The noise filter according to any one of claims 6, 8, 9.

14. Corresponding to each phase of the power line on the output side or the input side of the power converter, it includes the noise detector, the compensation signal applicator, and the injection voltage generator. The noise filter according to claim 1.

15. Corresponding to each wiring of the DC bus of the power converter, The noise detector, the compensation signal adder, and the injection voltage generator are provided. The noise filter according to claim 1.

16. The noise detector corresponding to each phase of the power line on the output side or the input side of the power converter Comprises a capacitor and a signal conditioning circuit connected in series between the corresponding power line and the ground wiring, The signal conditioning circuit outputs the adjustment voltage based on the input voltage input via the capacitor. The noise filter according to claim 14.

17. The noise detector corresponding to each phase of the power line on the output side or the input side of the power converter Comprises a capacitor and a voltage dividing transformer connected in series between the corresponding power line and the ground wiring, One end of the primary winding of the voltage dividing transformer is connected to one end of the capacitor on the side opposite to the power line, and the other end is connected to the ground wiring. One end of the secondary winding of the voltage dividing transformer is connected to a reference wiring having a reference potential different from the ground potential of the ground wiring, and the other end is connected to an output terminal that outputs the adjustment voltage. The noise filter according to claim 14.

18. The noise detector corresponding to each phase of the power line on the output side or the input side of the power converter Comprises a detection transformer with a primary winding inserted into the corresponding power line, One end of the secondary winding of the detection transformer is connected to a reference wiring having a reference potential, and the other end is connected to an output terminal that outputs the adjustment voltage. The noise filter according to claim 14.

19. The compensation signal adder comprises a signal conditioning transformer which is the transformer and a capacitor. The secondary winding of the signal conditioning transformer One end is connected to the ground wiring, and the other end is connected to the power line via the capacitor of the compensation signal adder. The noise filter according to any one of claims 14, 16, and 17.

20. The compensation signal adder comprises a signal conditioning transformer which is the transformer and a capacitor. The secondary winding of the signal conditioning transformer One end is connected to the ground wiring, and the other end is connected to the power line via the capacitor of the compensation signal adder. The noise filter according to claim 18.

21. The noise detector corresponding to each wiring of the DC bus of the power converter Comprises a detection transformer with a primary winding inserted into the corresponding wiring. The secondary winding of the detection transformer is connected to a reference wiring whose one end is at a reference potential, and the other end is connected to an output terminal that outputs the adjustment voltage. The noise filter according to claim 15. **Claim 22** The noise detector detects a differential mode voltage in the voltage of the electromagnetic noise. The noise filter according to any one of claims 14 to 17 and 19. **Claim 23** The noise detector detects a voltage proportional to a differential mode current in the current of the electromagnetic noise. The noise filter according to any one of claims 18, 20, and 21.

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