Noise filter

Abstract

Provided is a noise filter (100) to be connected to a power line (PL), comprising: a detection unit (120) that detects noise in the power line (PL); a compensation signal generation unit (140) that generates a compensation signal which attenuates the noise; and a compensation signal injection unit (130) that injects the compensation signal into the power line (PL). The output unit of the compensation signal generation unit (140) is connected to the compensation signal injection unit (130). One input unit of the compensation signal generation unit (140) is connected to the detection unit (120) and the other input unit is connected to the output of the compensation signal generation circuit (140). The compensation signal generation unit (140) generates a compensation signal on the basis of the differential signals from the two input units.

Description

Technical Field

[0001] This application relates to a noise filter.

Background Art

[0002] With the increase in the switching frequency of power converters accompanying the recent development of semiconductor device technology, the conducted noise flowing through power lines or ground lines has been increasing. As a means of suppressing conducted noise, a passive filter composed of at least one of an inductor and a capacitor is generally used. And, with the increase in conducted noise, the enlargement of the passive filter has become a problem. As another means of suppressing conducted noise, there is an active noise filter composed of a passive part having a function of detecting noise or injecting a compensation signal and an active part such as an operational amplifier, which injects a compensation signal into a power line or a ground line to cancel out the noise. An active noise filter can achieve miniaturization of the filter as compared with a passive filter.

[0003] For example, in the active noise filter disclosed in Patent Document 1, the common-mode noise voltage is detected at the neutral point potential of the star-connected capacitor, and a compensation current is injected into the capacitor by a control source. As a result, since the equivalent grounding capacitance of the capacitor increases and the impedance decreases, the common-mode noise current can be refluxed to the capacitor, and as a result, it is possible to attenuate the common-mode noise current of the power line to be protected. The volume of active components is generally smaller than that of passive components, and by delegating a part of the noise attenuation function to the active part, the active noise filter becomes smaller than the passive filter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the active noise filter of Patent Document 1, due to the resonance phenomenon between the common mode inductor and the capacitor, the compensation performance in the low frequency range may deteriorate.

[0006] This application discloses a technology for solving the above problems, and an object thereof is to realize a configuration capable of suppressing a decrease in compensation performance in a low frequency range with respect to noise generated in a noise filter connected to a power line.

Means for Solving the Problems

[0007] The noise filter disclosed in this application is a noise filter connected to a power line, a detection unit that detects noise in the power line, a compensation signal generation unit that generates a compensation signal for attenuating the noise, and a compensation signal injection unit that injects the compensation signal into the power line, an output unit of the compensation signal generation unit is connected to one input unit of the compensation signal injection unit and the compensation signal generation circuit, the other input unit of the compensation signal generation unit is connected to the detection unit, the compensation signal generation unit is configured to generate the compensation signal based on a differential signal of two input signals.

Advantages of the Invention

[0008] According to the noise filter according to the present disclosure, it is possible to suppress a decrease in compensation performance in the low frequency range.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present embodiment will be described with reference to the drawings. In each figure, the same reference numerals indicate the same or corresponding parts. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0011] Embodiment 1. Hereinafter, the noise filter according to Embodiment 1 will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a power system to which a noise filter according to Embodiment 1 is applied. In the power system 1 of FIG. 1, power is supplied from a system power source 200 connected to a three-phase three-wire AC power line PL to a load 400 via a power converter 300, and a noise filter 100 is connected to the power line PL in the middle of the path. Note that the noise filter 100 according to the present embodiment is not limited to the three-phase three-wire AC power line shown in FIG. 1, and may be DC (such as a storage battery), AC (such as a system power source), single-phase (two-wire or three-wire), three-phase (three-wire or four-wire), and may be connected between a power source and a power converter, between a power converter and a load, or between power converters when a plurality of power converters are provided.

[0012] In the power system 1 of FIG. 1, the purpose of applying the noise filter 100 is, for example, to satisfy the noise standard between the system power source 200 and the power converter 300, and between the power converter 300 and the load 400, for example, to suppress the ground leakage current and the motor shaft voltage of the motor which is the load. The system power source 200, the noise filter 100, the power converter 300, and the load 400 are each connected to the power line PL and are also connected to the ground line GL. There is a parasitic capacitance Zcm to the ground between the power converter 300 and the ground line GL, and a load parasitic capacitance Zm to the ground exists between the load 400 and the ground line GL.

[0013] [An Example of Noise Generation Factors] Next, in the power system 1, noise generation from the power converter 300 will be described as a representative example of noise generation factors. Hereinafter, a voltage-type three-phase full-bridge circuit will be described as an example of the power converter 300, but a current-type circuit, a circuit having a DC-DC conversion, DC-AC conversion, AC-DC conversion, or AC-AC conversion function, or a circuit configuration such as a multi-level converter may also be used.

[0014] FIG. 2 is a diagram showing the configuration of a voltage-type three-phase full-bridge circuit which is an example of the power converter 300. The voltage-type three-phase full-bridge circuit includes six semiconductor switching elements in which semiconductor switches SW11 to SW32 each have an antiparallel diode. The semiconductor switches SW11, SW21, SW31 on the positive electrode side and the semiconductor switches SW12, SW22, SW32 on the negative electrode side are connected in series to form legs respectively, and three legs corresponding to the u-phase, v-phase, and w-phase are connected in parallel to form a three-phase full-bridge circuit. Each arm is connected to output terminals u, v, w corresponding to the u-phase, v-phase, and w-phase respectively, and is connected to the power line PL via the output terminals u, v, w. A DC section is provided in parallel with the three-phase full-bridge circuit, and in this DC section, a smoothing DC capacitor 310 and a DC voltage source (not shown) are connected in parallel with each other. There is a parasitic capacitance to ground Zcm between each line of the three-phase full-bridge circuit and the DC section and the ground line GL as described above.

[0015] Here, each semiconductor switching element constituting the semiconductor switches SW11 to SW32 uses a self-arc-suppressing semiconductor element such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor).

[0016] In the voltage-type three-phase full-bridge circuit, when performing a forward conversion operation or a reverse conversion operation, a preset voltage is output by the switching operation of the semiconductor switches SW11 to SW32. At this time, due to the switching ripple voltage between the terminals of the output terminals, a normal mode noise current flows between each output terminal. Also, a common mode voltage calculated by dividing the instantaneous sum of the voltages of each output terminal by 3 is generated, and a common mode noise current flows through the parasitic capacitance to ground Zcm and the ground line GL. The common mode noise is different from the normal mode noise in that a noise current flows to the ground.

[0017] [Basic Operation of Noise Filter] First, the basic operation of the passive filter will be described. FIGS. 3 and 4 are diagrams showing examples of passive filters composed only of inductors and capacitors. The passive filter in FIG. 3 is composed of a common-mode inductor 101a and a Y capacitor 102a and is effective for common-mode components. The passive filter in FIG. 4 is composed of a normal-mode inductor 101b and an X capacitor 102b and is configured to be effective for attenuating normal-mode components. Both figures show the case where a passive filter is applied in a three-phase three-wire system, and the black circles in the figures indicate the polarities of the common-mode inductors.

[0018] An inductor is a component whose impedance increases with an increase in frequency. By inserting it in series with a noise source, the propagation of noise can be suppressed. A capacitor is a component whose impedance decreases with an increase in frequency. By inserting it in parallel with a noise source, the propagation of noise can be suppressed.

[0019] The common-mode inductor 101a is an inductor in which each phase winding is magnetically coupled using one magnetic component such as ferrite. When a common-mode noise current flows, the magnetic fluxes generated by each phase winding reinforce each other within the magnetic component. Thus, when a normal-mode noise current flows, the magnetic fluxes weaken each other, and ideally, no attenuation effect of normal-mode noise is exhibited. In reality, there is a leakage component of the magnetic flux that does not pass through other phase windings. Regarding this leakage magnetic flux, it becomes a normal-mode inductor and has an effect of attenuating normal-mode noise.

[0020] The Y capacitor 102a is a capacitor connected between the power line PL of each phase and the ground line GL. On the common-mode path, since there is a path with a low impedance at high frequency between the power line PL and the ground line GL, the noise current is refluxed to the ground line GL through the Y capacitor 102a, and the noise flowing out to the power line PL or the ground line GL to be protected can be suppressed.

[0021] The normal mode inductor 101b is an inductor in which when the windings of each phase are magnetically coupled by one magnetic component, the magnetic fluxes generated by the windings of each phase reinforce each other inside the magnetic component with respect to the normal mode noise current. For the common mode current, since the magnetic fluxes generated by the windings of each phase cancel each other out inside the magnetic component, ideally, the attenuation effect of the common mode noise is not exhibited. Also, when the windings of each phase are not magnetically coupled by the magnetic component, the magnetic fluxes generated by the windings of each phase do not interfere with each other, so it becomes a normal mode inductor. And since inductors are similarly connected to each phase, there is also an attenuation effect on the common mode noise.

[0022] The X capacitor 102b is a capacitor connected between each power line. Different from the Y capacitor, it is not connected to the ground line. The X capacitor 102b in Fig. 4 is shown as a Y connection with a neutral point in a three-phase three-wire AC power line, but a Δ connection method without a neutral point may also be used. The connection method of the X capacitor 102b can be selected according to the required withstand voltage and capacitance. With respect to the normal mode noise, by inserting a component that becomes a low impedance at high frequencies, there is an effect of suppressing the noise voltage of the line-to-line voltage. The Y capacitor is a capacitor connected between each power line and the ground line, but it is connected in such a way that a capacitor is also inserted between the lines, and it also acts on the attenuation of the normal mode component. However, generally, since the capacitance of the Y capacitor is smaller than that of the X capacitor, the X capacitor is more effective in attenuating the normal mode component.

[0023] [Operation of Y Capacitor] Next, the details of the operation of the Y capacitor will be described. Taking the case where the Y capacitor is connected between the system power supply and the power converter as an example. In this case, the points to be considered are (1) the system power supply side common mode noise current in the low frequency band, and (2) the system power supply side common mode noise current in the high frequency band.

[0024] (1) Regarding the system power supply side common mode noise current in the low frequency band, there are two causes: one is due to the system power supply and the other is due to the power converter. (1-1) The system power supply side common mode noise current in the low frequency band caused by the system power supply will be described. The commercial frequency voltage of the system power supply is applied to each phase Y capacitor as the normal mode. At this time, due to the configuration of the system power supply, the grounding method (symmetric or asymmetric), whether the system is in a balanced or unbalanced state, whether it is in a non-phase loss or phase loss state, the variation in the capacitor capacitance of each phase, etc., the common mode noise current of the commercial frequency component flows through the grounding wire via the Y capacitor. Also, at around 40th order or less of the system commercial frequency, for example, at 2 kHz or less, the zero-phase component or harmonic component of the system power supply side transformer flows through the grounding wire as the system power supply side common mode noise current in the low frequency band. In fact, the common mode noise current caused by the system power supply is often dominated by the commercial frequency component.

[0025] (1-2) The system power supply side common mode noise current in the low frequency band caused by the power converter will be described. Depending on the system voltage, modulation rate of the power converter, switching frequency, constants of the passive common mode filter, etc., the switching frequency component and zero-phase modulation component flowing out from the power converter also flow through the grounding wire as the system power supply side common mode noise current in the low frequency band. In fact, the common mode noise current caused by the power converter is often dominated by the switching frequency component.

[0026] As a result, the system power supply side common mode noise current in the low frequency band is determined by the sum of that caused by the system power supply and that caused by the power converter.

[0027] The relationship between the Y-capacitor capacitance and the common-mode noise current on the system power supply side in the low-frequency band will be described. When the Y-capacitor capacitance is increased, the common-mode noise current caused by the system power supply increases, and the common-mode noise current caused by the power converter decreases. On the other hand, when the Y-capacitor capacitance is decreased, the common-mode noise current caused by the system power supply decreases, and the common-mode noise current caused by the power converter increases. Since the limit value of the common-mode noise current on the system power supply side in the low-frequency band is specified by the standard for the purpose of preventing electric shock to the human body, a Y-capacitor capacitance value that satisfies the standard value is selected from the sum of the common-mode noise current caused by the system power supply and the common-mode noise current caused by the power converter, which are in a trade-off relationship as described above.

[0028] (2) The common-mode noise current on the system power supply side in the high-frequency band will be described. The normal-mode or common-mode current flowing on the system power supply side in the high-frequency band is measured using a LISN (Line Impedance Stabilization Network: pseudo power supply circuit network) connected to the system power supply side. Specifically, it is measured as the voltage (noise terminal voltage) generated when a normal-mode noise or common-mode noise current flows through the terminal of the LISN with an impedance of 50Ω. The high-frequency band is, for example, 150 kHz or higher, which corresponds to the conducted noise band, and the above measurement method is specified as the standard. The system power supply side of the LISN has a low-pass filter configuration, and the noise caused by the system power supply is not measured as the noise terminal voltage. Only the noise caused by the power converter connected to the load side of the LISN is measured as the noise terminal voltage. The noise caused by the power converter measured as the noise terminal voltage is the sum of both the normal-mode and common-mode. And by increasing the Y-capacitor capacitance, it is possible to reduce the common-mode noise.

[0029] Therefore, from the perspective of suppressing the common-mode noise current on the system power supply side in the high-frequency band, it is better to have a larger capacitance value for the Y capacitor. Also, it is desirable to select the capacitance of the Y capacitor such that the component of the common-mode noise current on the system power supply side in the low-frequency band is larger than the component caused by the power converter.

[0030] Hereinafter, the details of the noise filter 100 according to Embodiment 1 will be described. FIG. 5 is a diagram showing the configuration of the noise filter 100 according to Embodiment 1, and FIG. 6 is a diagram showing another configuration of the noise filter 100 according to Embodiment 1.

[0031] In FIG. 5, the noise filter 100 that suppresses the common-mode noise on the system power supply side includes a detection unit 120 connected to the power line PL to detect the common-mode noise, a compensation signal generation unit 140 that generates a compensation signal to cancel the common-mode noise, and a compensation signal injection unit 130 that injects the compensation signal to cancel the common-mode noise into the power line PL. The detection unit 120 that detects the common-mode noise is composed of, for example, capacitors in a Y connection.

[0032] The compensation signal generated by the compensation signal generation unit 140 is, for example, a compensation voltage signal. The output unit of the compensation signal generation unit 140 is connected to one terminal of the compensation signal injection unit 130 and the input unit of the compensation signal generation unit 140, and outputs the generated compensation signal respectively. The other terminal of the input unit of the compensation signal generation unit 140 is connected to the detection unit 120. Also, the compensation signal generation unit 140 is connected to the ground line GL, and the output unit of the compensation signal generation unit 140 is connected in series between the compensation signal injection unit 130 and the ground line GL.

[0033] The compensation signal injection unit 130 is composed of, for example, Y-connected capacitors. Also, for the purpose of enhancing the attenuation amount of noise in the power line PL, an inductor 110 is connected, for example. For the purpose of enhancing the attenuation amount of noise, as shown in FIG. 6, a Y capacitor 150 may be further connected. However, the inductor 110 and the Y capacitor 150 are not essential. In FIG. 6, a noise filter 100 is connected between the power line PL and the ground line GL, but the noise filter 100 may be connected only to the power line PL.

[0034] Next, the features of the noise filter 100 according to Embodiment 1 will be described. The feature of the noise filter 100 according to Embodiment 1 is that the two input terminals of the input section of the compensation signal generation section 140 are differential inputs. With this configuration, the voltage of the common mode component of the capacitors constituting the compensation signal injection unit 130 is detected as a differential voltage. For this differential voltage, in the compensation signal generation section 140, for example, a voltage with reverse polarity and equal to or less than 1 times is generated as a compensation voltage and output in series between the compensation signal injection unit 130 and the ground line GL. As a result, on the equivalent circuit of the common mode component, the common mode voltage of the capacitors constituting the compensation signal injection unit 130 is canceled out. That is, in the configuration of the noise filter 100 according to Embodiment 1, by activating the capacitors constituting the compensation signal injection unit 130, there is an effect of functioning as a Y capacitor with an increased apparent equivalent capacitance.

[0035] FIG. 7 is an equivalent circuit diagram showing the operating principle of the noise filter 100 according to Embodiment 1. In FIG. 7, the connection points A and B are the connection points A and B in FIG. 5, respectively. That is, the compensation signal injection unit 130 and the compensation signal generation unit 140 are connected in series between the power line PL and the ground line GL. For example, it is assumed that a common mode noise current from a noise voltage source Vcm caused by a power converter flows to the power supply side and returns to the load-to-ground parasitic capacitance Zm through the inductor 110, the power supply-to-ground impedance Zg, and the ground line GL. It is the role of the noise filter 100 to reduce the amount of current flowing through the power supply side, that is, the power supply-to-ground impedance Zg.

[0036] The common-mode noise current Icm from the noise voltage source Vcm branches at the connection point A between the compensation signal injection unit 130 and the power line PL into a common-mode noise current Ig flowing on the power supply side and a common-mode noise current Iy flowing on the compensation signal injection unit 130 side. As described above, a common-mode voltage Vy is generated across the capacitor of the compensation signal injection unit 130 by the common-mode noise current Iy flowing on the compensation signal injection unit 130 side. In the first embodiment, by detecting this common-mode voltage Vy, the compensation signal generation unit 140 generates a compensation voltage Vinj having a reverse polarity and not more than 1 times the voltage with respect to the common-mode voltage Vy. That is, a compensation voltage Vinj satisfying Expression (1) is generated as a compensation signal. Note that Expression (1) compares the absolute values of Vinj and Vy. |Vinj| ≦ |Vy| ···(1)

[0037] When the compensation voltage Vinj is output to the compensation signal injection unit 130, the common-mode voltage Vy is canceled out, and the common-mode noise current Icm is more distributed by the common-mode noise current Iy. As the common-mode noise current Iy increases, the common-mode noise current Ig flowing on the power supply side decreases.

[0038] By the above operation, for example, by actively causing the common-mode noise current Icm generated by the power converter to flow back to the capacitor side of the compensation signal injection unit 130, it is possible to reduce the common-mode noise current Ig on the power supply side to be protected.

[0039] Next, the detailed operation of the noise filter 100 according to the first embodiment will be described separately for (1) the low-frequency range and (2) the high-frequency range. (1) Low-frequency range The noise filter 100 according to Embodiment 1 forms a high-pass filter by the capacitor of the detection unit 120 and the resistance component of the input unit of the compensation signal generation unit 140. By designing the cut-off frequency of the high-pass filter determined by the capacitance value of the capacitor of the detection unit 120 and the resistance value of the input unit of the compensation signal generation unit 140, it is possible to set the lower limit value of the compensation frequency.

[0040] Here, the common-mode noise current of the dominant commercial frequency component caused by the utility power supply is, for example, 50 Hz or 60 Hz, and the frequency of the common-mode noise current caused by the power converter becomes the dominant switching frequency component, which is generally several kHz or more. The noise filter 100 according to Embodiment 1 of the present invention has a function of substantially increasing the equivalent capacitance of the Y capacitor. Regarding the common-mode noise current of the commercial frequency component caused by the utility power supply, there is an effect of rather increasing it due to the decrease in the ground impedance.

[0041] On the other hand, the cut-off frequency of the high-pass filter formed by the capacitor of the detection unit 120 and the resistance component of the input unit of the compensation signal generation unit 140 is set to be equal to or higher than the frequency of the common-mode noise current caused by the utility power supply, and the lower limit value of the compensation band is shifted to the high frequency range. Thereby, the increase in the common-mode noise current caused by the utility power supply can be suppressed. At the same time, by setting the cut-off frequency of the high-pass filter to be lower than the switching frequency, which is the frequency of the common-mode noise current caused by the power converter, the equivalent capacitance of the Y capacitor is increased. As a result, it is possible to achieve the effect of actively refluxing the common-mode current in the route of the Y capacitor - power converter - load via the ground line GL. Therefore, the common-mode noise current flowing on the utility power supply side can be reduced.

[0042] Therefore, since the noise filter 100 according to Embodiment 1 has the effect of increasing the equivalent capacitance of the Y capacitor in a specific frequency range regardless of the cause of the common-mode current generation, it is necessary to separate its source for each frequency band. That is, it is desirable that the frequency of the common-mode noise current caused by the utility power supply and the frequency of the common-mode noise current caused by the power converter are divided. Therefore, when the frequency caused by the utility power supply and the frequency caused by the power converter are close, the common-mode noise current caused by the utility power supply increases, and the common-mode noise current caused by the power converter decreases.

[0043] Next, the design considerations in the low-frequency range of the compensation signal generation unit 140 included in the noise filter 100 according to Embodiment 1 will be described. In a general passive common-mode filter composed only of a common-mode inductor and a Y capacitor, below the cut-off frequency, most of the common-mode noise current source flows on the utility power supply side. On the other hand, in the noise filter 100 according to Embodiment 1 of the present application, the capacitor of the compensation signal injection unit 130 corresponds to the Y capacitor, and the equivalent capacitance of the Y capacitor is increased and the impedance is reduced by the compensation voltage. That is, the switching frequency component of the common-mode noise current, which is a relatively low frequency caused by the power converter, is actively refluxed to the capacitor of the compensation signal injection unit 130.

[0044] Here, since the capacitor of the compensation signal injection unit 130 is a relatively low frequency, it has a high impedance. And since the common-mode noise current caused by the power converter is refluxed to the capacitor of the compensation signal injection unit 130, the maximum detected differential voltage and the compensation voltage determined by the product of the high impedance of the capacitor of the compensation signal injection unit 130 and the common-mode noise current may become excessive. Here, the maximum detected differential voltage corresponds to the maximum value of the common-mode voltage Vy of the capacitor of the compensation signal injection unit 130 shown in FIG. 7. Therefore, when the maximum detected differential voltage becomes excessive, the compensation voltage for canceling it may also become excessive.

[0045] Regarding this problem, the noise source impedance is approximately equal to, for example, the load-to-ground parasitic capacitance Zm, and the maximum compensation voltage is determined by the ratio of the load-to-ground parasitic capacitance Zm to the capacitor capacitance of the compensation signal injection unit 130. Therefore, by making the capacitor capacitance of the compensation signal injection unit 130 sufficiently larger than the load-to-ground parasitic capacitance Zm, it is possible to suppress the maximum detected differential voltage and the compensation voltage. The compensation signal generation unit 140 is generally composed of an operational amplifier, a transistor, and a control power supply. By suppressing the maximum differential detection voltage and the compensation voltage, the voltage of the necessary control power supply of the compensation signal generation unit 140 and the slew rate and gain bandwidth of the compensation signal generation unit 140 can be reduced. However, due to the restriction of the low-frequency common-mode current flowing on the system power supply side caused by the system power supply, the upper limit value of the capacitance of the capacitor of the compensation signal injection unit 130 is restricted.

[0046] (2) High-frequency range Next, the detailed operation of the noise filter 100 in the high-frequency range will be described. Regarding the high-frequency range, it corresponds to the measurement range of the conducted noise at the noise terminal voltage using the LISN, and is the frequency range corresponding to frequencies above the general cut-off frequency of the passive common-mode filter. In the high-frequency range, most of the common-mode noise current is in a state of flowing back to the capacitor of the compensation signal injection unit 130 that substantially functions as a Y capacitor. Here, the common-mode voltage component of the capacitor of the compensation signal injection unit 130 functions as a small noise voltage source on the LISN side. By applying the noise filter 100 according to the first embodiment, the common-mode voltage Vy generated in the capacitor of the compensation signal injection unit 130 is detected as a differential voltage, and the compensation signal generation unit 140 generates and injects, for example, a compensation voltage signal Vinj with a reverse polarity and a magnitude of 1 times or less, so that the common-mode voltage component can be canceled. As a result, it is possible to reduce the common-mode component of the noise terminal voltage applied to the 50Ω terminal of the LISN. This shows that the common-mode noise can be suppressed in the high-frequency range.

[0047] Next, the gain design of the compensation signal generation unit 140 will be described. In FIG. 7, from the perspective of noise cancellation, it is ideal to output a compensation voltage that is 1 times the magnitude with respect to the voltage Vy of the common-mode component of the capacitor of the detected compensation signal injection unit 130. That is, in Equation (1), |Vinj| = |Vy|. Since Vinj has the opposite polarity to Vy in the voltage loop equation on the power supply side, it becomes as shown in Equation (2). Vy ― Vinj =(Zg+ZL)×Ig ···(2) Here, ZL is the impedance of the inductor 110.

[0048] Assume that a compensation voltage that is 1 times the magnitude is output, that is, the gain magnitude is 1 times, and the compensation voltage Vinj is generated so that |Vinj| = |Vy| and injected into the capacitor of the compensation signal injection unit 130. Then, Equation (2) becomes 0=(Zg+ZL)×Ig. Since (Zg+ZL) has a finite value, Ig = 0, and the common-mode noise current Ig flowing into the power supply side becomes ideally 0. Also, since Vy ― Vinj = 0, the connection point between A and B is equivalent to a short circuit, and all the common-mode noise current Icm from the noise voltage source Vcm is refluxed to the capacitor of the compensation signal injection unit 130.

[0049] However, in reality, by setting it to 1 times the magnitude, under the conditions described later, an oscillation phenomenon of feedback occurs in the low-frequency range. When the oscillation phenomenon of feedback occurs, the control becomes unstable, and there is a risk that the noise cancellation operation cannot be performed. Here, the low-frequency range refers to below the resonance frequency of the passive part composed of the capacitor of the compensation signal injection unit 130 and the inductor on the power line PL.

[0050] In this low-frequency range, when the utility power supply 200 is grounded, the system power supply side common impedance is approximately 0 Ω, the inductor 110 on the power line PL has a low impedance, and the capacitor of the compensation signal injection unit 130 has a high impedance. Under this condition, in the voltage loop of the compensation voltage injection terminal output from the compensation signal generation unit 140, the capacitor of the compensation signal injection unit 130, the inductor 110, and the power supply-to-ground impedance Zg shown in FIG. 7, almost all of the compensation voltage Vinj is applied to the capacitor of the compensation signal injection unit 130. Also, regarding the phase, the differential voltage detected with respect to the generated compensation voltage has a phase of 0 degrees. Therefore, oscillation will occur when the gain magnitude is 1 times. That is, in the low-frequency range when the utility power supply 200 is grounded, positive feedback control is performed. For the above reasons, when implementing noise reduction compensation in the low-frequency band, in terms of preventing the oscillation phenomenon due to positive feedback, it is necessary to make the gain magnitude of the compensation signal generation unit 140 less than 1 times.

[0051] On the other hand, when a leakage current measurement filter having an impedance of about several kΩ is connected or when the power supply-to-ground impedance becomes high without grounding the utility power supply, the oscillation phenomenon does not occur, and it is possible to set the gain to 1 times. However, grounding the utility power supply is common, and since the power supply side common impedance becomes approximately 0 Ω, attention is required.

[0052] On the other hand, in the high-frequency range, since the impedance ZL of the inductor on the power line PL becomes high and the impedance of the capacitor of the compensation signal injection unit 130 becomes low, the differential voltage to be detected becomes small with respect to the output compensation voltage. Therefore, regardless of the power supply-to-ground impedance Zg on the system power supply side, the loop gain becomes small, so the gain of the compensation signal generation unit 140 may be 1.

[0053] Also, if the gain is near 1 times, it may be larger than 1 times. When the gain exceeds 1 times, the noise attenuation effect is reduced, but if it is near 1 times and larger than 1 times, it has the same effect as a gain that is near 1 times and less than 1 times.

[0054] As described above, according to the noise filter 100 according to the first embodiment, compensation can be performed in a wide frequency band with respect to generated noise. That is, the noise filter 100 includes a detection unit 120 that detects noise on a power line, a compensation signal generation unit 140 that generates a compensation signal for attenuating the noise, and a compensation signal injection unit 130 that injects the compensation signal. The compensation signal generation unit 140 generates a compensation signal based on a difference signal between the input signal from the detection unit 120 and the output signal of the compensation signal generation unit 140, so that a decrease in compensation performance in the low frequency range is suppressed.

[0055] Here, when the compensation signal injection unit 130 is configured by a capacitor, a voltage due to a noise component is generated in the capacitor of the compensation signal injection unit 130, and the compensation signal generation unit 140 detects the voltage due to the noise component as a differential voltage and generates a compensation voltage as a compensation signal so as to cancel the voltage due to the noise component. Therefore, compensation can be efficiently performed in a wide frequency band with respect to generated noise.

[0056] Also, the compensation signal for canceling the noise component should have an opposite polarity and a gain in the vicinity of 1 times and be set to 1 times or less. In addition, for noise reduction in the low frequency range, if the gain of the compensation signal is 1 time, oscillation may occur in the circuit and it may affect noise reduction. Therefore, the gain should be less than 1 time. However, outside the low frequency range, the gain may be 1 time.

[0057] That is, when the generated noise is in the low-frequency range, the voltage of the capacitor in the compensation signal injection unit 130 is detected, and the compensation signal generation unit 140 generates a compensation voltage with a reverse polarity whose gain is less than 1 times with respect to the voltage, and outputs it in series between the compensation signal injection unit 130 and the ground line GL. In the first embodiment, it is a feed-forward control, not a feedback control that brings the detected noise close to 0 by the compensation voltage. Therefore, the oscillation and the decrease in the detection amount caused by the resonance between the inductor on the power line PL and the capacitor of the compensation signal injection unit 130, which occurred in the conventional feedback control, do not occur in the configuration of the first embodiment. Therefore, it has the effect of enabling compensation in the low-frequency range below the resonance frequency of the inductor on the power line PL and the capacitor of the compensation signal injection unit 130.

[0058] Furthermore, in the first embodiment, by configuring the detection unit 120 and the compensation signal injection unit 130 with capacitors, it is possible to reduce the size compared to the configuration in which the detection unit 120 and the compensation signal injection unit 130 are configured with inductors. This is because the energy density of the capacitor is higher than that of the inductor.

[0059] Also, when including low-frequency compensation as in the first embodiment, a low-frequency and high voltage are applied to the inductor, and in order to prevent magnetic saturation of the core, it is necessary to have a large cross-sectional area of the core with a high saturation magnetic flux density. That is, there is a concern about the increase in the size of the inductor. Therefore, in the present embodiment with low-frequency compensation, by using capacitors for the detection unit 120 and the compensation signal injection unit 130, the miniaturization of the active noise filter becomes more effective.

[0060] Embodiment 2. Hereinafter, the noise filter according to the second embodiment will be described with reference to FIG. 8. FIG. 8 is a block diagram showing the configuration of the noise filter according to Embodiment 2. The difference from Embodiment 1 is that the noise filter 100 according to Embodiment 2 has a configuration in which detection units 120u, 120v, 120w, compensation signal injection units 130u, 130v, 130w, and compensation signal generation units 140u, 140v, 140w are arranged for each phase. Since other configurations are the same as those in Embodiment 1, the description thereof is omitted. The noise filter according to Embodiment 1 attenuated the common-mode noise on the power supply side, while the noise filter according to the present Embodiment 2 has an effect of attenuating the normal-mode noise and the common-mode noise on the power supply side.

[0061] In FIG. 8, the detection units 120u, 120v, 120w and the compensation signal injection units 130u, 130v, 130w are connected between each power line PLu, PLv, PLw and the ground line GL. By connecting to the ground line GL, it is possible to detect the normal-mode components between each phase line and inject a compensation signal. In each of the detection units 120u, 120v, 120w, the sum of the common-mode component between the power line PLu, PLv, PLw of each phase and the ground line GL and the above-mentioned normal-mode component appears as the terminal voltage of the compensation signal injection units 130u, 130v, 130w. By detecting the differential voltage of the compensation signal injection units 130u, 130v, 130w, it is possible to detect the voltage of the sum of the normal-mode and common-mode noises. Then, in the compensation signal generation units 140u, 140v, 140w, for example, a compensation voltage with reverse polarity and a magnitude of 1 times or less is generated, and by injecting the compensation voltage in series between the compensation signal injection units 130u, 130v, 130w and the ground line GL, it becomes possible to cancel the normal-mode and common-mode noise voltages.

[0062] Here, similar to Embodiment 1, a high-pass filter is formed by the capacitors of the detection units 120u, 120v, 120w and the resistors of the input parts of the compensation signal generation units 140u, 140v, 140w, and it is possible to set the lower limit value of an arbitrary compensation frequency band.

[0063] Also, in the noise filter 100 according to Embodiment 2, for the purpose of enhancing the noise attenuation effect as in Embodiment 1, capacitors 150u, 150v, and 150w may be provided between the power lines PLu, PLv, and PLw of each phase and the ground line GL. FIG. 9 shows an example in which capacitors are further provided in FIG. 8. As described in Embodiment 1, the inductor 110 and the capacitors 150u, 150v, and 150w are not essential components. They may be provided as appropriate to enhance the noise attenuation effect.

[0064] As described above, according to the noise filter 100 according to Embodiment 2, compensation is possible in a wide frequency band as in Embodiment 1, and a decrease in compensation performance in the low frequency band is suppressed. Further, since the noise filter 100 according to Embodiment 2 has a configuration in which detection units 120u, 120v, and 120w, compensation signal injection units 130u, 130v, and 130w, and compensation signal generation units 140u, 140v, and 140w are arranged in each phase, the sum of the normal mode component and the common mode component with respect to the power line of each phase can be detected, and a compensation signal can be injected accordingly, so that both normal mode noise and common mode noise can be attenuated. Furthermore, since noise suppression is actively performed, miniaturization of the X capacitors constituting the detection unit and the compensation signal injection unit is possible.

[0065] In Embodiments 1 and 2, in the compensation signal generation units 140, 140u, 140v, and 140w, by adopting a circuit configuration that generates a compensation voltage with the opposite polarity with respect to the voltage of the noise component detected from the differential voltage, simplification of the mounting can be realized. Furthermore, the compensation signal is not limited to voltage and may be a compensation current.

[0066] The circuit configuration of the compensation signal generation units 140, 140u, 140v, and 140w can be configured by, for example, an analog circuit using an operational amplifier as described above.

[0067] It is also possible to execute the function having a signal processing unit including an arithmetic unit and a signal amplifier by software. In that case, as shown in FIG. 10 for example, the hardware configuration of the compensation signal generation units 140, 140u, 140v, and 140w includes a processor 142 (computer) and a storage device 144 as a processing circuit.

[0068] The processor 142 may be provided with a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits, etc. Also, as the processor 142, a plurality of the same type or different types may be provided, and each process may be executed in a shared manner. The storage device 144 is provided with a RAM (Random Access Memory) configured to be able to read and write data from the processor 142, a ROM (Read Only Memory) configured to be able to read data from the processor 142, etc. The processor 142 executes a program input from a storage device 144 such as a ROM.

[0069] When a program is executed in the compensation signal generation units 140, 140u, 140v, and 140w, a differential signal is calculated from two input signals, a signal obtained by multiplying the differential signal by -1 and a gain corresponding to the frequency domain of noise is used, and a corresponding signal is generated from a signal processing unit (not shown).

[0070] In addition, in Embodiments 1 and 2, although the noise filter 100 is arranged between the system power supply 200 and the power converter 300 and the noise source caused by the power converter 300 is described, it may be arranged between the power converter 300 and the load 400. It is possible to suppress the ground leakage current of the load 400 or the shaft voltage of the motor as the load.

[0071] Although various exemplary embodiments and examples are described, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable to the embodiments alone or in various combinations. Accordingly, numerous variations not illustrated are envisioned within the scope of the technology disclosed in this specification. For example, it is assumed to include cases where at least one component is modified, added, or omitted, and further, cases where at least one component is extracted and combined with components of other embodiments.

[0072] For example, it also includes configurations in which a plurality of noise filters according to Embodiment 1 for compensating for common-mode noise are provided, and configurations in which noise filters of both Embodiments 1 and 2 are provided.

Description of Reference Numerals

[0073] 1: Power system, 100: Noise filter, 101a: Common-mode inductor, 101b: Normal-mode inductor, 102a: Y capacitor, 102b: X capacitor, 110: Inductor, 120, 120u, 120v, 120w: Detection unit, 130, 130u, 130v, 130w: Compensation signal injection unit, 140, 140u, 140v, 140w: Compensation signal generation unit, 142: Processor, 144: Storage device, 150: Y capacitor, 150u, 150v, 150w: Capacitor, 200: Utility power supply, 300: Power converter, 400: Load, PL, PLu, PLv, PLw: Power line, GL: Ground line, Zcm: Parasitic capacitance to ground, Zm: Load parasitic capacitance to ground, Zg: Power supply impedance to ground, Vcm: Noise voltage source, Vy: Common-mode voltage, Vinj: Compensation voltage, Icm, Ig, Iy: Common-mode noise current, SW11, SW12, SW21, SW22, SW31, SW32: Semiconductor switch.

Claims

1. A noise filter connected to a power line, a detection unit that detects noise in the power line, a compensation signal generation unit that generates a compensation signal for attenuating the noise, and a compensation signal injection unit that injects the compensation signal into the power line, an output unit of the compensation signal generation unit is connected to one input unit of the compensation signal injection unit and the compensation signal generation unit, the other input unit of the compensation signal generation unit is connected to the detection unit, the compensation signal generation unit generates the compensation signal based on a differential signal of two input signals. A noise filter.

2. The noise filter according to claim 1, wherein the detection unit and the compensation signal injection unit are each composed of a capacitor.

3. The detection unit detects noise as a voltage, The compensation signal generation unit generates a compensation voltage having a reverse polarity and a magnitude of 1 times or less with respect to the differential voltage of the input unit. The noise filter according to claim 1 or 2.

4. The noise filter according to claim 3, wherein the compensation signal generation unit generates a compensation voltage having a reverse polarity and a magnitude of less than 1 times with respect to the differential voltage of the input unit.

5. The power line includes a plurality of phases, the detection unit, the compensation signal generation unit, and the compensation signal injection unit are arranged in each phase of the power line, the compensation signal generation unit corresponding to each phase generates a compensation signal for attenuating the noise based on the noise detected by the detection unit of each phase. The noise filter according to claim 1 or 2.

6. The noise filter according to claim 1 or 2, wherein an inductor is connected to the power line.

7. The noise filter according to claim 1 or 2, wherein a capacitor is further connected to the power line.

8. The noise filter according to claim 1 or 2, wherein the compensation signal generation unit is connected to a ground line and outputs the compensation signal to the compensation signal injection unit connected in series between the power line and the ground line.

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