JP2019080469A - Noise reduction device - Google Patents

Abstract

To obtain a noise reduction device capable of reducing noise of frequency band wider than before.SOLUTION: A noise reduction device 100 includes a current transformer 1 having detection windings 12A, 12B with number of turns different from each other, detecting a noise current I1 flowing through a connection line connecting an AC power supply 40 and a three-phase motor 43 as a voltage, and outputting from the detection windings 12A, 12B, respectively, an amplifier circuit 10A for amplifying the output from the detection winding 12A, and outputting as an output voltage V3, an amplifier circuit 10B for amplifying the output from the detection winding 12B, and outputting as an output voltage V6, and a noise injection circuit 2 having one end connected with the amplifier circuits 10A, 10B, and the other end connected with the connection line on the side closer to the three-phase motor 43 side than the current transformer 1, and when the output voltages V3 and V6 are applied, injecting a noise reduction current I2 for cancelling and reducing the noise current I1 into the connection line, where the amplifier circuits 10A, 10B have frequency characteristics different from each other.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a noise reduction device that reduces noise current flowing through a power supply line connected to a system, such as leakage current from an AC power supply that supplies AC power to a load such as a three-phase motor or common mode noise.

A conventional noise reduction device is, for example, an active common mode canceller connected between an inverter and an induction motor. This is to generate a voltage of the same polarity as the common mode voltage detected by the star-connected capacitor by the control voltage source, in order to offset the common mode voltage generated during the switching operation of the power semiconductor device, The output of the control voltage source is superimposed on the output of the inverter via a common mode transformer. (See, for example, Patent Document 1).
In addition, in order to cope with the common mode voltage on the AC power supply side (between the AC power supply and the inverter) which can not be canceled by the technique of Patent Document 1, the common mode via the grounding capacitor connected to the line between the AC power supply and the rectifier. A voltage is detected, and a cancellation voltage having the same magnitude as the detected common mode voltage and having a reverse polarity is generated by the cancellation voltage source, and the cancellation voltage is superimposed between the AC power supply and the connection point of the grounding capacitor in the line. There is a conductive noise filter (see, for example, Patent Document 2).

  In the techniques of Patent Document 1 and Patent Document 2, since the capacitor is used as a detection means for noise flowing through the power supply line connected to the system, the impedance of the detection means becomes smaller and the detection value becomes smaller as the noise increases. It will Therefore, a high frequency current reducing device has been proposed in which a current transformer is connected to a connection line between an AC power supply and a converter, and noise is voltage converted and detected by this current transformer (for example, see Patent Document 3). In the high frequency current reduction device of Patent Document 3, after the detected voltage detected is amplified by the amplifier, the output of the amplifier is supplied to the connection line through the capacitor to reduce the noise flowing through the connection line. Further, in the high frequency current reduction device of Patent Document 3, when the detection voltage is supplied to the voltage amplifier, the detection voltage is supplied through a filter that extracts a desired high frequency component, thereby eliminating noise of the frequency of noise that needs removal or reduction. The configuration is such that the amplification factor can be increased.

JP 10-94244 A Unexamined-Japanese-Patent No. 2010-05268 International Publication No. 2013-111360

  However, in the high frequency current reducing device of Patent Document 3, since noise of various frequencies is detected using one detection winding, there is a problem that the noise may not be sufficiently reduced depending on the frequency band. This is because in the case of one detection winding, there is only one frequency characteristic of the amplification circuit in the entire device. In this case, if the frequency at which the gain is maximized in the frequency characteristics of the amplifier circuit matches the phase inversion frequency (the frequency at which the phase of the detected noise and the phase of the output of the amplifier circuit is inverted), the output of the amplifier circuit is noise The gain can not be increased to avoid amplification of the noise, and noise can not be sufficiently reduced in this frequency band. The same applies to the resonance frequency, and the gain can not be increased if the frequency for maximizing the gain matches or approximates the resonance frequency of the amplifier circuit. The problem mentioned above is that if noise to be reduced is in a wide frequency range, as in the case where noise current includes leakage current from AC power supply and common mode noise, adjustment of amplifiers and filters in the amplification circuit alone is necessary. This is a particularly serious problem because it becomes difficult to reduce the current.

  The present invention has been made to solve the above-described problems, and provides a noise reduction device capable of reducing noise in a wider frequency band than the prior art.

  A noise reduction device according to the present invention includes a first detection unit and a second detection unit, which have different inductances from each other, and applies a noise current flowing through a connecting line connecting the first electrical device and the second electrical device. Noise detection means for detecting each of the first detection unit and the second detection unit, and a first amplification circuit for amplifying the output of the first detection unit and outputting it as a first output voltage; A second amplifier circuit that amplifies the output of the second detection unit and outputs it as a second output voltage, one end is connected to the first amplifier circuit and the second amplifier circuit, and the other end is a noise detection unit. The second electric device side is also connected to the connection line, and the first output voltage and the second output voltage are applied to inject a noise reduction current that cancels and reduces the noise current into the connection line. Noise reduction current injection means, and And the second amplifying circuit is one in which the frequency characteristics are different from each other.

  According to the present invention, it is possible to obtain a noise reduction device capable of reducing noise in a wider frequency band than in the prior art.

It is a connection diagram showing an example of connection of a noise reduction device in Embodiment 1 of this invention. It is a figure which shows the structure of the noise reduction apparatus in Embodiment 1 of this invention. It is a circuit diagram which shows the detail of the converter concerning Embodiment 1 of this invention. It is a circuit diagram which shows the detail of the inverter concerning Embodiment 1 of this invention. It is a figure which shows the open loop characteristic of the noise reduction apparatus in Embodiment 1 of this invention. It is a figure which shows the open loop characteristic of the noise reduction apparatus in Embodiment 2 of this invention. It is a figure which shows the structure of the noise reduction apparatus in Embodiment 3 of this invention.

Embodiment 1
Hereinafter, a first embodiment of the present invention will be described based on FIGS. 1 to 5. FIG. 1 is a connection diagram showing a connection example of the noise reduction device in the first embodiment, and FIG. 2 is a diagram showing a configuration of the noise reduction device in the first embodiment. The noise reduction device 100 is connected between the AC power supply 40 and the three-phase motor 43 on a connection line connecting the AC power supply 40 and the three-phase motor 43 as shown in FIG. Connection lines 91a to 91c from the AC power supply 40 are connected (hereinafter, the power supply side), and output lines (hereinafter, the load side) are connected to connection lines 92a to 92c extending to the three-phase motor 43. Between noise reduction device 100 and three-phase motor 43, converter 41 for converting alternating current from noise reduction device 100 to direct current, and converter 41 via DC buses 49P and 49N are provided. An inverter 42 is connected to convert the direct current into an alternating current by a pulse width modulation method. The output of the inverter 42 is sent to the three-phase motor 43 through the three-phase filter 45 and the connecting lines 93a to 93c. Further, a bus capacitor 44 is connected between the DC buses 49P and 49N. In the first embodiment, an example in which three-phase alternating current is used will be described, but single-phase alternating current may be used. Also, the noise reduction device 100 and the passive filter may be connected in series and used in combination.

  Although the noise reduction device 100 is provided between the AC power supply 40 and the converter 41 in the first embodiment, the noise reduction device 100 is provided between the converter 41 and the inverter 42 or between the inverter 42 and the three-phase motor 43. You may provide. In addition, a second converter (not shown) for voltage conversion is provided between converter 41 and inverter 42 for adjusting the magnitude of the DC voltage to an arbitrary level, and between converter 41 and the second converter, Alternatively, the noise reduction device 100 may be provided between the second converter and the inverter 42. In the present invention, a device connected to the AC power supply 40 side of the noise reduction device 100 is a first electric device, and a device connected to the three-phase motor 43 side is a second electric device.

  Next, the configuration of the noise reduction device 100 will be described. As shown in FIG. 2, the noise reduction device 100 is a current transformer 1 that detects the noise current I1 flowing on the connection lines 91a to 93c on the power supply side, that is, a noise detection unit and noise that cancels and reduces the noise current I1. Injection circuit 2 that injects reduced current I2 to connection lines 92a to 92c on the load side, that is, the amplification circuit 10A between the noise reduction current injection means, that is, the first amplification circuit, and amplification circuit 10B, that is, the second amplification The circuits are connected in parallel, the output from the current transformer 1 is amplified separately by the amplifier circuits 10A and 10B, and the noise reduction current I2 is injected by the injection circuit 2 to which the output voltages of the two amplifier circuits are applied. . The noise current I1 includes noise of high frequency current such as switching noise and common mode noise from the converter 41 and the inverter 42, and low frequency current such as leakage current from the AC power supply 40. The details will be described below.

The current transformer 1 includes a main winding 11 composed of three conductor wires connected in series to connection wires 91a to 91c on the power supply side, a detection winding 12A for current detection, that is, a first detection unit, and a detection winding 12B, that is, the second detection unit. The three conductor wires constituting the main winding 11 are wound in the same winding direction, for example, four times around an iron core (not shown). The detection windings 12A and 12B are wound around the iron core, respectively, and the noise current I1 flowing from the connection wires 91a to 91c to the main winding 11 is converted into a detection voltage V1 and a detection voltage V4, respectively.
The current transformer 1 only needs to be able to detect the noise current I1 flowing through the connecting wires 91a to 91c by converting it into a voltage. Therefore, the present invention is not limited to winding the main winding 11 around an iron core. 9191c may be penetrated, and the detection windings 12A and 12B may be wound around this annular iron core. In this case, the main winding 11 can be omitted.

  The detection winding 12A and the detection winding 12B have different inductances (self-inductance and mutual inductance between the main winding 11). In the first embodiment, the inductances of the detection windings 12A and 12B are different by setting the number of turns of the detection winding 12A to eight and the number of turns of the detection winding 12B to four and making the numbers of turns different from each other. I have to. As a result, the turns ratio of the main winding 11, the detection winding 12A, and the detection winding 12B is four times: eight times: four times = 1: 2: 1. Since the magnitude of the detection voltage is proportional to the number of turns, the magnitudes of the detection voltage V1 and the detection voltage V4, which are detection values of the noise current I1, can be adjusted by adjusting the turns ratio. Further, since the turns ratio with the main winding 11 can be set independently for each of the detection windings 12A and 12B, the magnitudes of the detection voltages V1 and V4 can also be set independently. In addition, although adjustment of the detection voltage by adjustment of the turns ratio has no frequency selectivity and amplifies all frequency components in the same manner, the magnitude of the detection voltage can be adjusted without changing the phase. The amplification of the specific frequency component is performed by the amplification circuits 10A and 10B, respectively.

  “●” in FIG. 2 represents the polarities of the main winding 11, the detection winding 12A, and the detection winding 12B, respectively. As shown in FIG. 2, in the first embodiment, the polarities of the main winding 11 and the detection windings 12A and 12B are the same direction, but a current equivalent to the noise reduction current I2 for canceling the noise current I1 is injected into the circuit 2 The polarity of the current transformer 1 may be inverted to invert the polarity of the outputs of the voltage amplifiers 3A and 3B described later, for example, or the polarity of the detection winding 12A (12B) may be inverted. The polarity of the output of the amplifier 3A (3B) may be inverted. As a result, the outputs of the amplifier circuits 10A and 10B become equal to those of the first embodiment, and currents equal to the noise reduction current I2 can be injected into the connecting lines 92a to 92c.

  The amplification circuit 10A is connected to the detection winding 12A and has an input side connected to the filter unit 6A that passes AC voltage in a predetermined frequency range, that is, the first filter unit and the filter unit 6A, and the output of the filter unit 6A. Voltage amplifier 3A which amplifies a certain voltage V2 with amplification factor G1 and outputs it as output voltage V3, that is, the first voltage amplifier, one end is connected to the output side of voltage amplifier 3A, the other end is connected to injection circuit 2 An output filter unit 7A, that is, a first output filter unit is provided. In the first embodiment, the output filter unit 7A is a capacitor.

  The amplification circuit 10B is connected to the detection winding 12B and has an input side connected to the filter unit 6B that passes AC voltage in a predetermined frequency range, that is, the second filter unit and the filter unit 6B, and the output of the filter unit 6B. Voltage amplifier 3B which amplifies a certain voltage V5 with amplification factor G2 and outputs it as output voltage V6, that is, the second voltage amplifier, one end is connected to the output side of voltage amplifier 3B and the other end is connected to injection circuit 2 An output filter unit 7B, that is, a second output filter unit is provided. In the first embodiment, the output filter unit 7B is a resistor.

  The filter sections 6A and 6B are each one filter circuit or a plurality of filter circuits connected in series or in parallel, and each filter circuit can adjust the pass frequency range by adjusting its filter constant. It has become. Also, by adjusting the filter constants, the amplitude ratio and the phase difference are adjusted according to the frequency for the detection voltages V1 and V4 input to the filter units 6A and 6B and the voltages V2 and V5 output from the filter units 6A and 6B. can do. For example, by combining a plurality of high pass filters and low pass filters and adjusting the amplitude ratio and the phase difference for each frequency, the amplitude ratio is increased for the frequency band to be reduced, and the positions of the noise current I1 and the noise reduction current I2 The phase difference can be adjusted to approach zero. Also, it can be adjusted to eliminate the resonant frequency.

  The voltage amplifiers 3A and 3B respectively include positive power supply terminals 4A and 4B and negative power supply terminals 5A and 5B which receive supply of operation power from an external power supply (not shown), and incorporate an operational amplifier (not shown). In the first embodiment, the voltage amplifiers 3A and 3B are configured using an operational amplifier, but may be configured using a transistor or the like for voltage amplification. In addition, the configuration of the external power supply for supplying the operation power to the voltage amplifiers 3A and 3B may be a power supply or a battery supplied with power from the system to which the noise reduction device 100 is connected so that the power can be stably supplied. It is not particularly limited.

  The output filter sections 7A and 7B of the respective amplifier circuits 10A and 10B are for preventing the occurrence of a short circuit in the injection circuit 2 due to the application of the output voltages V3 and V6, and their frequency characteristics are different. That is, the output filter unit 7A passes only the high frequency component of the output voltage V3 as a high pass filter, while the output filter unit 7B passes only the low frequency component of the output voltage V6 as a low pass filter.

  The injection circuit 2 is Y-connected, and includes injection capacitors 22 a to 22 c corresponding to the connection lines 92 a to 92 c on the load side, and a ground resistor 24. One terminal of each of the injection capacitors 22a to 22c is grounded via the ground resistor 24, and the other terminal is connected to the injection points 20a to 20c on the connection lines 92a to 92c. Further, one terminal of each of the capacitors 22a to 22c for injection is connected to the output side of the voltage amplifier 3A through the output filter unit 7A, and connected to the output side of the voltage amplifier 3B through the output filter unit 7B. . The output voltage V3 of the amplifier circuit 10A and the output voltage V6 of the amplifier circuit 10B are applied as a voltage V7 to a neutral point 23 which is a connection point of the ground resistor 24 and the injection capacitors 22a to 22c. At this time, since the output voltage V3 is applied through the output filter unit 7A and the output voltage V6 is applied through the output filter unit 7B, as described above, in the injection circuit 2, the two amplifier circuits 10A and 10B are There is no short circuit of the output. The ground resistor 24 may be replaced by a capacitor.

  The converter 41 is a switching type converter configured by full bridge connection of IGBTs 41a to 41f in which diodes are reverse-parallel connected as semiconductor switching elements as shown in FIG. 3, and connection on the power supply side is performed by switching control of the IGBTs 41a to 41f. The three-phase alternating current input from the lines 92a to 92c is converted into a direct current of variable voltage, and is output to the direct current buses 49P and 49N.

  The inverter 42 is a pulse width modulation type inverter configured by full bridge connection of IGBTs 42a to 42f in which diodes are reverse-parallel connected as semiconductor switching elements as shown in FIG. 4 and is input from the DC buses 49P and 49N. The direct current is converted to a three-phase alternating current of variable frequency variable voltage by the switching control of the IGBTs 42a to 42f, and is output to the connecting lines 93a to 93c on the three-phase motor 43 side. More specifically, the IGBTs 41a to 41f are controlled to open and close by means of a PWM signal generated by comparing the phase voltage designation with a triangular wave or sawtooth wave carrier of a predetermined frequency and changing the direct current input from the DC buses 49P and 49N. It is converted to three-phase alternating current of frequency variable voltage. The three-phase alternating current output from the connection lines 93 a to 93 c is sent to the three-phase motor 43 as a load via the three-phase filter 45. In the inverter 42, a smoothing capacitor 42g is provided between the DC buses 49P and 49N closer to the power supply than the IGBTs 42a to 42f.

  The three-phase filter 45 is for reducing the generation of radiation noise due to vibration, noise and high-frequency current flowing through the connecting wires 93a to 93c of the three-phase motor 43.

  Next, the operation will be described. In the first embodiment, detection coil 12A and amplifier circuit 10A correspond to a high frequency component (common mode noise etc.) having the frequency of the first frequency band in noise current I1, and noise current I1 is generated by amplifier circuit 10A. Is amplified with a gain equal to or higher than the target gain value. In addition, detection winding 12B and amplifier circuit 10B correspond to a low frequency component (such as leakage current of AC power supply 40) having a frequency of the second frequency band in noise current I1, and amplification circuit 10B reduces noise current I1. The frequency component is amplified with a gain equal to or higher than the target gain value. The target gain value is appropriately set as a criterion for judging whether or not a sufficient gain has been secured.

  The detection windings 12A and 12B of the current transformer 1 respectively detect detection voltages V1 and V4 generated by the noise current I1 flowing through the main winding 11. Generally, the magnitude of the voltage detected by the detection winding is proportional to the inductance and the frequency, but here, the frequency is common to the frequency of the noise current I1, and the inductance corresponds to the number of turns of the detection windings 12A and 12B. To be proportional, the detection voltages V1 and V4 are proportional to the turns ratio of the respective detection windings. As described above, since the turns ratio of the main winding 11, the detection winding 12A, and the detection winding 12B is 1: 2: 1, the detection voltage V1 is larger than the detection voltage V4.

  The detection voltage V1 is input to the filter unit 6A in the amplifier circuit 10A, and the amplitude and phase thereof are adjusted according to the frequency and output as the voltage V2. The high frequency component of the voltage V2 is amplified by G1 times in the voltage amplifier 3A, and is output as the output voltage V3. The low frequency component of the output voltage V3 is removed by the output filter unit 7A, and only the high frequency component is applied to the neutral point 23 of the injection circuit 2.

  The detection voltage V4 is input to the filter unit 6B in the amplifier circuit 10B, and the amplitude and phase thereof are adjusted for each frequency and output as the voltage V5. The low frequency component of the voltage V5 is amplified by G2 times in the voltage amplifier 3B, and is output as the output voltage V6. In the output voltage V6, high frequency components are removed by the output filter unit 7B, and only low frequency components are applied to the neutral point 23 of the injection circuit 2.

  In injection circuit 2, voltage V7 is applied to injection capacitors 22a to 22c by output voltage V3 applied by amplifier circuit 10A and output voltage V6 applied by amplifier circuit 10B, and a change in voltage V7 causes amplifier circuit 10A to The high frequency current and the low frequency current from the amplifier circuit 10B are injected as noise reduction current I2 into the connection lines 92a to 92c on the load side. The voltage V7 is controlled by the voltage amplifier 3A and the voltage amplifier 3B.

  Next, the frequency characteristics of the noise reduction device 100 will be described. In the noise reduction device 100, the phase inversion frequency at which the amplification circuits 10A and 10B amplify the noise current I1 by inverting the phases of the noise current I1 and the output currents of the voltage amplifier 3A and the voltage amplifier 3B is the current transformer 1 and amplification. It is determined by the impedance of the entire circuit such as the circuit 10A, the amplifier circuit 10B, and the injection circuit 2, the characteristic of the delay time of the operational amplifier built in each of the voltage amplifiers 3A and 3B, and the like. In addition, the resonance frequency at which the high frequency current flowing through the connection line is adversely affected by the oscillation of the output of the voltage amplifiers 3A and 3B or amplification of the detected noise current is a three-phase motor 43 which is a load. And it depends on the impedance of the whole system including each connection line. For this reason, in order to effectively reduce the noise current I1, it is necessary to make the gain as large as possible and to separate the frequency band of the noise current which needs to be reduced by adjusting the impedance etc. is there. In the first embodiment, by providing two detection windings 12A and 12B and two amplification circuits 10A and 10B connected to the respective detection windings, frequency characteristics are separately generated in the two amplification circuits 10A and 10B. Because it is possible to adjust the gain, even in the frequency band where one amplifier circuit can not obtain a sufficient gain, the other amplifier circuit can obtain a sufficient gain to obtain noise in a wider frequency band than before. It can correspond.

  The frequency characteristics of the respective amplifier circuits are, as described above, the turns ratio of the current transformer 1, the polarity of each of the detection winding 12A and the detection winding 12B, the filter portions 6A and 6B and the capacitance of the output filter portion 7A which is a capacitor, Since adjustment is possible by changing the resistance value of the output filter section 7B which is a resistor, it is sufficient to adjust so that the gain can be increased by separating the phase inversion frequency and the resonance frequency from the frequency band which needs to be reduced. Further, by connecting capacitors in series in filter units 6A and 6B, it is possible to adjust the phases of voltages V2 and V5 for each frequency, so noise reduction current I2 and noise current in the frequency band where reduction is required The noise reduction effect can be enhanced by adjusting so as to eliminate the phase difference of I1.

  FIG. 5 is a diagram showing the open loop characteristics of the noise reduction device 100, and shows the frequency characteristics of the noise reduction device 100. As shown in FIG. In FIG. 5, thin solid lines indicate gain characteristics, and thick solid lines indicate phase characteristics. As shown in FIG. 5, the phase difference does not become 180 ° in the specification frequency band, and the phase inversion frequency is separated from the specification frequency band. Therefore, it can be seen that the noise reduction device 100 has a large noise reduction effect in the specified frequency band, and can reduce noise in a wider frequency band than in the past. The "specification frequency band" refers to high frequency noise in the frequency band (150 kHz to 30 MHz) defined in the international standard (CISPR standard) by the International Special Committee for Radio Interference (CISPR), and leakage in the frequency band defined in the domestic standard. Indicates current etc. The main frequency band such as leakage current differs depending on the domestic power supply frequency of each country, but for example in the case of Japan where the domestic power supply frequency is 50Hz and 60Hz, 50 to 180Hz frequency band in diode rectification and power converters such as inverters Refers to the frequency band of the switching frequency of

  The first embodiment shows the case where the noise reduction device 100 is configured using analog circuits such as resistors, capacitors, and operational amplifiers. In this case, there is an advantage that the cost can be kept low, but some or all of the components may be replaced with digital circuits and configured using a DSP (Digital Signal Processor) or a microcomputer. When a digital circuit is used for the filter circuit, there is an advantage that only the gain of the set frequency can be lowered and the gain of the peripheral frequency can be secured.

  Although two voltage amplifiers 3A and 3B are used, the number of voltage amplifiers may be one according to the magnitude of noise current I1 and the range of frequency components constituting noise current I1. It may be parallel or more.

  According to the first embodiment, noise in a wider frequency band than in the prior art can be reduced. More specifically, by providing two detection windings with different inductances in a current transformer for detecting noise current and providing amplification circuits with different frequency characteristics in each detection winding, the high frequency component of noise current and low Since the frequency components can be handled separately, in the amplifier circuit corresponding to the low frequency component, the frequency characteristics are adjusted so that the phase inversion frequency and the resonance frequency are separated from the low frequency band, and in the amplifier circuit corresponding to the high frequency component, phase inversion is performed. The frequency characteristics can be adjusted so that the frequency or resonance frequency is away from the high frequency band. As a result, even if the noise current includes both low frequency noise and high frequency noise such as AC power supply leakage current and common mode noise, the noise current can be effectively reduced, and the frequency is wider than before. It is possible to reduce band noise current.

  Further, by making the number of turns of the two detection windings different from each other, the frequency characteristics of the amplification circuits connected to the respective detection windings can be changed, so that the adjustment of the frequency characteristics of the respective amplification circuits is simple. It is.

  Further, since the detection voltages are respectively amplified using two amplifier circuits, it is possible to reduce the load per voltage amplifier that each amplifier circuit has.

Second Embodiment
Second Embodiment A second embodiment of the present invention will be described below based on FIG. The noise reduction device in the second embodiment has the same configuration as the noise reduction device 100 shown in FIG. 2, but in the first embodiment, the amplification circuits 10A and 10B are focused on the difference in frequency such as high frequency and low frequency. While the high frequency component of the detection voltage V1 and the low frequency component of the detection voltage V4 are amplified, in the second embodiment, the amplification circuit 10A is focused on the width of the frequency band for securing the gain and the size of the target gain. And 10B respectively amplify the detection voltage. That is, in the noise reduction device of the second embodiment, amplification circuit 10A amplifies detection voltage V1 with a gain equal to or higher than the first target gain value in the first frequency band, and detects detection voltage V1 in the second frequency band. The amplifier circuit 10B has a frequency characteristic that amplifies with a gain equal to or higher than a second target gain value larger than the first target gain value, and the amplifier circuit 10B detects the detection voltage V4 in a third frequency band wider than the first frequency band. It has a frequency characteristic to be amplified with a gain equal to or higher than the first target gain value. The details will be described below.

  FIG. 6 is a diagram showing the open loop characteristics of the noise reduction apparatus according to the second embodiment. A thin solid line shows the gain characteristic of the amplifier circuit 10A, and a thick solid line shows the gain characteristic of the amplifier circuit 10B. Although the phase characteristic is omitted in FIG. 6, the frequency band which is the phase inversion frequency is avoided in any of the amplifier circuits 10A and 10B. Further, the first target gain value is set to 1 and the second target gain value is set to 100. In FIG. 6, the gain of the amplification circuit 10A is equal to or higher than the first target gain value in the first frequency band R1 (about 2 kHz to about 90 MHz), and in the second frequency band R2 (about 100 kHz to about 20 MHz). It becomes more than the second target gain value. On the other hand, although the gain of the amplifier circuit 10B never exceeds the second target gain value, the first target gain is a third frequency band R3 (100 MHz or less) in a frequency band wider than the first frequency band R1. It becomes more than the value Thus, although amplification circuit 10A secures a larger gain in a specific frequency band and amplification circuit 10B does not secure a large gain as amplification circuit 10A, it secures a predetermined gain in a wider frequency band. Do. In the second embodiment, by combining two amplifier circuits 10A and 10B having different frequency characteristics as described above, noise current in a frequency band wider than the conventional one is reduced.

In order to realize the amplifier circuits 10A and 10B having the frequency characteristics as described above, first, the filter constant of the filter unit 6A and the gain of the voltage amplifier 3A are set so as to secure a gain equal to or greater than the second gain target value. Next, the amplifier circuit 10A extracts a frequency band in which the first target gain value can not be secured, and the filter constant and voltage of the filter unit 6B so that the first target gain value can be secured in this frequency band. Set the gain of the amplifier 3B.
Others are the same as in the first embodiment.

  According to the second embodiment, the same effect as that of the first embodiment can be obtained.

Third Embodiment
The third embodiment of the present invention will be described below based on FIG. The same or corresponding portions as in FIGS. 1 to 5 are denoted by the same reference numerals, and the description thereof will be omitted. FIG. 7 is a diagram showing the configuration of the noise reduction device in the third embodiment. The noise reduction device 200 differs from the first embodiment in that the injection circuit 21 includes an injection transformer 30. In the noise reduction device 200, the amplifier circuit 10A corresponding to the high frequency component is connected to the injection capacitors 22a to 22c of the injection circuit 21 as in the first embodiment. On the other hand, the amplification circuit 10B corresponding to the low frequency component is connected to the primary winding 31 of the injection transformer 30.

  One end of the injection transformer 30 is connected to the voltage amplifier 3B via the output filter unit 7B, and the other end is connected in series to the primary winding 31 connected to ground and the load-side connection lines 92a to 92c in series. And a secondary winding 32 made of a conductor wire. Only the voltage amplifier 3A is connected to the injection capacitors 22a to 22c. Although the injection transformer 30 is provided closer to the load than the injection capacitors 22a to 22c in FIG. 7, the injection transformer 30 may be provided closer to the power supply than the injection capacitors 22a to 22c.

  If the number of turns of the primary winding 31 of the injection transformer 30 changes, the frequency characteristics of the amplifier circuit 10B change due to changes in the excitation inductance and leakage flux, so the phase of the high frequency current flowing through the connection wires 92a to 92c on the load side The phase inversion frequency of the amplifier circuits 10A and 10B also changes. In the third embodiment, a plurality of taps (not shown) are provided on the primary winding 31 as winding number adjustment means for adjusting the number of turns of the primary winding 31, and the taps connected to the amplification circuit 10B are switched. Thus, the number of turns of the primary winding 31 can be adjusted.

  The other configuration is the same as that of the first embodiment. Also in the noise reduction device 200, the detection winding 12A and the amplification circuit 10A correspond to the high frequency component (several hundreds kHz) of the noise current I1, and the detection winding 12B and the amplification circuit 10B correspond to the low frequency component (several hundreds Hz). Since the amplitude of the high frequency component included in the noise current I1 generally decreases and the detection voltage also tends to decrease, the number of turns of the detection winding 12A for detecting the high frequency component is increased, and the magnitude of the high frequency component of the detection voltage V1 Is set to a certain value or more. On the other hand, since it is not necessary to amplify a low frequency component such as the leakage current of the AC power supply 40 by the current transformer 1, the number of turns of the detection winding 12B may be small.

Next, the operation will be described. The noise current I1 flowing through the main winding 11 is detected as detection voltages V1 and V4 by the detection windings 12A and 12B, and the detection voltages V1 and V4 are voltage amplifiers 3A and 3B as voltages V2 and V5 through the filter portions 6A and 6B. , And amplified by the voltage amplifiers 3A and 3B and output as output voltages V3 and V6, as in the first embodiment.
In the output voltage V3, only the high frequency component is output to the injection circuit 21 through the output filter unit 7A which is a capacitor, and the voltage V7 is applied to the injection capacitors 22a to 22c. As for the output voltage V6, only the low frequency component is output to the injection circuit 21 through the output filter section 7B which is a resistor, and the voltage V8 is applied to the primary winding 31 of the injection transformer 30.

  In injection circuit 21, voltage V7 applied to injection capacitors 22a-22c is controlled by voltage amplifier 3A, and a high frequency current from amplifier circuit 10A is injected into connection lines 92a-92c on the load side by a change in voltage V7. . The voltage V8 applied to the primary winding 31 of the injection transformer 30 is controlled by the voltage amplifier 3B, and the low frequency current generated in the secondary winding 32 due to the change of the voltage V8 is the connection line 92a to 92c on the load side. Injected into the The high frequency current injected from the injection capacitors 22a to 22c and the low frequency current injected from the injection transformer 30 are superimposed on the connecting lines 92a to 92c, and high frequency noise such as common mode noise is generated as the noise reduction current I2. The noise current I1 including low frequency noise such as leakage current from the AC power supply is canceled and reduced.

  According to the third embodiment, the same effect as that of the first embodiment can be obtained.

  Also, the low frequency component of the noise current can be reduced more effectively. More specifically, since the injection transformer is provided in the injection circuit for injecting the low frequency current into the connection line, the impedance of the injection circuit for the low frequency current is reduced, and the low frequency component of the noise reduction current It became easy to inject. Therefore, the low frequency component of the noise current can be reduced more effectively.

  In addition, in the amplifier circuit corresponding to the high frequency component of the noise current, it is easier to reduce the phase inversion frequency and increase the gain. More specifically, by adjusting the number of turns of the primary winding of the injection transformer with a tap or the like, it is possible to adjust the frequency characteristic of the amplifier circuit corresponding to the high frequency component. Therefore, it is easier to reduce the phase inversion frequency of the amplifier circuit corresponding to the high frequency component to increase the gain of the amplifier circuit corresponding to the high frequency component.

  In the present invention, within the scope of the invention, each embodiment can be freely combined, or each embodiment can be appropriately modified or omitted.

DESCRIPTION OF SYMBOLS 1 current transformer, 2, 21 injection circuit, 3A, 3B voltage amplifier, 6A, 6B filter part, 7A, 7B output filter part, 10A, 10B amplifier circuit, 11 main winding, 12A, 12B detection winding, 22a-22c Injection capacitor, 30 Injection transformer, 31 primary winding, 32 secondary winding, 40 AC power supply, 41 converter, 42 inverter, 43 three-phase motor, 91a to 91c, 92a to 92c, 93a to 93c connection line, 100, 200 noise reduction device, I1 noise current, I2 noise reduction current, R1 first frequency band, R2 second frequency band, R3 third frequency band

Claims (16)

A first detection unit and a second detection unit having different inductances; noise current flowing in a connecting line connecting the first electrical device and the second electrical device is detected as a voltage; Noise detection means which respectively output from the detection unit and the second detection unit;
A first amplifier circuit that amplifies the output of the first detection unit and outputs it as a first output voltage;
A second amplification circuit that amplifies the output of the second detection unit and outputs the amplified output as a second output voltage;
One end is connected to the first amplification circuit and the second amplification circuit, and the other end is connected to the connection line at the second electric device side than the noise detection means, and the first output voltage And noise reduction current injection means for injecting a noise reduction current, which cancels and reduces the noise current by applying the second output voltage, to the connection line,
A noise reduction device, wherein the first amplifier circuit and the second amplifier circuit have different frequency characteristics. The first amplification circuit has a frequency characteristic that amplifies the output of the first detection unit with a gain equal to or higher than a target gain value in a first frequency band,
The second amplification circuit has a frequency characteristic that amplifies the output of the second detection unit with a gain equal to or higher than a target gain value in a second frequency band,
The noise reduction device according to claim 1, wherein the first frequency band is in a higher frequency range than the second frequency band. The first amplification circuit amplifies the output of the first detection unit in a first frequency band with a gain equal to or higher than a first target gain value, and in the second frequency band, amplifies the output of the first detection unit. It has a frequency characteristic that amplifies the output with a gain equal to or higher than a second target gain value larger than the first target gain value,
The second amplification circuit has a frequency characteristic that amplifies the output of the second detection unit with a gain equal to or higher than the first target gain value in a third frequency band wider than the first frequency band. The noise reduction device according to claim 1, characterized in that   The noise reduction current injection means has a primary winding connected to the first amplification circuit or the second amplification circuit, and a secondary winding connected in series to the connection line, and the primary The injection transformer according to any one of claims 1 to 3, further comprising an injection transformer for injecting the noise reduction current into the connection line according to a change in voltage applied by an amplifier circuit connected to a winding. Noise reduction device.   5. The noise reduction device according to claim 4, wherein the primary winding includes winding number adjustment means for adjusting the number of turns of the primary winding.   The noise detection means is a current transformer connected in series to the connection wire and having a main winding wound around an iron core, and the first detection unit and the second detection unit are wound around the iron core. The noise reduction device according to any one of claims 1 to 5, wherein the noise reduction device comprises a first detection winding and a second detection winding.   The noise reduction device according to claim 6, wherein the first detection winding and the second detection winding have different numbers of turns.   The noise reduction device according to claim 6 or 7, wherein the first detection winding and the second detection winding have different polarities. The first amplifier circuit is
A first filter unit connected to the first detection unit and passing a first frequency component from an output of the first detection unit;
And a first voltage amplifier connected to the first filter unit to amplify an output of the first filter unit and output the first output voltage.
The second amplification circuit is
A second filter unit connected to the second detection unit and passing a second frequency component from an output of the second detection unit;
9. A second voltage amplifier connected to the second filter unit for amplifying the output of the second filter unit and outputting the second output voltage. The noise reduction device according to any one of the above. The first voltage amplifier is connected to the noise reduction current injection means through a first output filter unit,
10. The device according to claim 9, wherein the second voltage amplifier is connected to the noise reduction current injection means via a second output filter unit having a frequency characteristic different from that of the first output filter unit. Noise reduction device.   The first filter unit and the second filter unit are one filter circuit whose adjustable pass frequency range can be adjusted, or a plurality of filter circuits connected in series or in parallel. The noise reduction device according to 9 or 10.   The noise reduction device according to claim 11, wherein the filter circuit is a digital circuit.   The noise reduction device according to any one of claims 1 to 12, wherein the first electric device is an alternating current power supply, and the noise current includes a leakage current from the alternating current power supply.   The first electric device or the second electric device is an inverter that converts a direct current into an alternating current by a pulse width modulation method, and the noise current includes switching noise from the inverter. The noise reduction device according to any one of claims 1 to 12.   The first electric device or the second electric device is a converter that converts alternating current supplied from an alternating current power source into direct current by a switching system, and the noise current includes switching noise from the converter. The noise reduction device according to any one of claims 1 to 12, characterized in that   The first electric device or the second electric device is a converter for voltage conversion that adjusts the magnitude of the DC voltage by a switching method, and the noise current is a switching noise from the converter for voltage conversion. 13. A noise reduction device according to any one of the preceding claims, characterized in that it comprises.

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