Noise Filter

Abstract

The purpose of the present invention is to provide a noise filter that can achieve high reliability.　A noise filter (10) comprises: a noise detection section (12) that detects common mode noise (CN) which flows through an electrical path (11); an amplification section (16) that, on the basis of the common mode noise (CN) detected by the noise detection section (12), generates a cancellation signal (CS) which cancels the common mode noise (CN); an injection section (14) that injects the cancellation signal (CS) into the electrical path (11); an anomaly detection section (17) that detects an anomaly of the noise filter (10) on the basis of the output current or the output voltage of the cancellation signal (CS) and that outputs an anomaly detection signal (AS); and a protection circuit (18) that, on the basis of the anomaly detection signal (AS), suppresses injection of an anomalous cancellation signal (CS) into the electrical path (11).

Description

[Technical Field]

[0001] The present application relates to a noise filter. [Background technology]

[0002] Power conversion devices are known that convert input power from a power source into DC or AC power and supply it to a load. Such power conversion devices perform power conversion by switching multiple bridge-connected switching elements, generating high-frequency noise as the switching elements operate. This high-frequency noise travels to the ground potential via parasitic capacitance and other factors, causing common-mode noise to flow to the power source or load. To suppress this common-mode noise, a known approach is to install a noise filter in the electrical path between the power source and the power conversion device, or in the electrical path between the power conversion device and the load.

[0003] One type of noise filter is an active noise filter. For example, an active noise filter detects a common mode voltage via a grounded capacitor connected to a line between an AC power supply and a rectifier, generates a cancellation voltage with the same magnitude as the detected common mode voltage but with an opposite polarity using a cancellation voltage source, and superimposes the cancellation voltage between the connection point of the AC power supply and the grounded capacitor on the line (see, for example, Patent Document 1). to The described technology injects a cancellation voltage that cancels out the voltage of common mode noise into an electric line (line) as a noise cancellation signal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-57268 Summary of the Invention [Problem to be solved by the invention]

[0005] During operation of an active noise filter, the control characteristics of the active noise filter may change due to environmental factors or factors over time. In the active noise filter described in Patent Document 1, if a change in the control characteristics occurs that was not anticipated at the time of design, there is a risk that an abnormal noise cancellation signal will be generated, such as by causing the noise cancellation signal injected into the electrical circuit to oscillate or the amount of compensation in the noise cancellation to become excessive due to a loss of control margin (gain margin and phase margin). If an abnormal noise cancellation signal is injected into the electrical circuit, not only will it be impossible to cancel common-mode noise, but the noise cancellation signal itself may also cause problems.

[0006] A common method is to use an overcurrent protection circuit to detect abnormalities caused by excessive current and stop the active noise filter. However, in an active noise filter, if the injection part of the noise cancellation signal is configured with an inductive load such as a common mode transformer, the inductive impedance of the common mode transformer makes it difficult for large high-frequency currents to flow. 、 Even if an abnormality actually occurs, there is a risk that the active noise filter will not be able to detect an abnormality caused by high-frequency components. If the injection section is configured with a capacitive load such as a capacitor, there is a risk that the active noise filter will not be able to detect an abnormality caused by low-frequency components. An active noise filter that cannot detect an abnormality will continue to inject an abnormal noise cancellation signal. As described above, conventional active noise filters have had the problem of insufficient reliability with respect to changes in control characteristics.

[0007] The present application has been made to solve the above-mentioned problems, and has an object to provide a noise filter that can achieve high reliability. [Means for solving the problem]

[0008] The noise filter disclosed in the present application is a noise filter provided in an electric circuit connecting an AC power supply, a load, and a power conversion device that converts AC power output from the AC power supply and outputs the converted AC power to the load, and includes a noise detection unit that detects common mode noise flowing in the electric circuit, a cancellation signal generation unit that generates a cancellation signal that cancels the common mode noise based on the common mode noise detected by the noise detection unit, an injection unit that injects the cancellation signal into the electric circuit, an abnormality detection unit that detects an abnormality in the noise filter based on the output voltage or output current of the cancellation signal and outputs an abnormality detection signal, and protection means that suppresses the injection of the abnormal cancellation signal into the electric circuit based on the abnormality detection signal. The protection means includes a power supply cutoff means for cutting off the power supply to the cancellation signal generation unit. It is something. Another noise filter disclosed in the present application is a noise filter provided in an electric circuit connecting an AC power supply, a load, and a power conversion device that converts AC power output from the AC power supply and outputs the converted AC power to the load, and includes: a noise detection unit that detects common mode noise flowing in the electric circuit; a cancellation signal generation unit that generates a cancellation signal that cancels the common mode noise based on the common mode noise detected by the noise detection unit; an injection unit that has inductive impedance and injects the cancellation signal into the electric circuit; an abnormality detection unit that detects an abnormality in the noise filter based on the output voltage or output current of the cancellation signal and outputs an abnormality detection signal; and protection means that suppresses injection of the abnormal cancellation signal into the electric circuit based on the abnormality detection signal, and the abnormality detection unit includes a feature acquisition unit that acquires feature values ​​based on the average value of the output voltage of the cancellation signal, the effective value of the output voltage of the cancellation signal, the average value of the output current of the cancellation signal, or the effective value of the output current of the cancellation signal; and an abnormality determination unit that determines the presence or absence of an abnormality based on the magnitude of the feature value and outputs the abnormality detection signal based on the determination result. [Effects of the Invention]

[0009] The noise filter disclosed in the present application can achieve high reliability. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram showing a power conversion system according to a first embodiment. [Figure 2] 1 is a configuration diagram showing a power conversion device according to a first embodiment. [Figure 3] 4 is a diagram illustrating common mode noise generated in the power conversion system according to the first embodiment. FIG. [Figure 4] FIG. 2 is a configuration diagram showing a noise filter according to the first embodiment. [Figure 5] FIG. 2 is a configuration diagram showing a noise detection unit according to the first embodiment. [Figure 6] FIG. 2 is a configuration diagram illustrating an example of an amplifier according to the first embodiment. [Figure 7] 3 is a configuration diagram illustrating an example of an abnormality detection unit according to the first embodiment. FIG. [Figure 8] FIG. 2 is a configuration diagram illustrating an example of a feature amount detection unit according to the first embodiment. [Figure 9]FIG. 2 is a configuration diagram illustrating an example of a feature amount comparison unit according to the first embodiment. [Figure 10] FIG. 2 is a configuration diagram showing an injection section according to the first embodiment. [Figure 11A] 4 is a schematic diagram showing the control response of a main circuit section of the noise filter according to the first embodiment, and is a schematic diagram showing the control response in the case where there is no filter section. FIG. [Figure 11B] 4 is a schematic diagram showing the pass characteristic of a filter section according to the first embodiment. FIG. [Figure 11C] 4 is a schematic diagram showing a control response of a main circuit section of the noise filter according to the first embodiment, and is a schematic diagram showing a control response when a filter section is present. FIG. [Figure 12A] 4 is a schematic diagram showing the control response of the noise filter in the first embodiment, and is a schematic diagram showing the gain characteristic. FIG. [Figure 12B] 4 is a schematic diagram showing the control response of the noise filter in the first embodiment, and a schematic diagram showing the phase characteristic. FIG. [Figure 13A] 4A and 4B are schematic diagrams showing the control response of the noise filter in the first embodiment when a change in the control characteristics occurs due to the occurrence of an abnormality, and also showing a change in the gain characteristics. [Figure 13B] 4A and 4B are schematic diagrams showing the control response of the noise filter in the first embodiment when a change in the control characteristics occurs due to the occurrence of an abnormality, and also showing a change in the phase characteristics. [Figure 14] 4 is a schematic diagram showing an abnormal output waveform of a cancellation signal output unit according to the first embodiment. FIG. [Figure 15A] FIG. 2 is a schematic diagram showing a waveform of a common mode voltage in a normal state. [Figure 15B] FIG. 2 is a schematic diagram showing a waveform of a common mode current in a normal state. [Figure 15C] 4 is a schematic diagram showing a waveform of an output voltage of a cancellation signal according to the first embodiment in a normal state. FIG. [Figure 15D] 4 is a schematic diagram showing the waveform of the output current of the cancellation signal according to the first embodiment in a normal state. FIG. [Figure 16A]FIG. 10 is a schematic diagram showing the waveform of a common mode voltage during an abnormality. [Figure 16B] FIG. 10 is a schematic diagram showing the waveform of a common mode current during an abnormality. [Figure 16C] 5 is a schematic diagram showing a waveform of an output voltage of a cancellation signal according to the first embodiment in an abnormal state. FIG. [Figure 16D] 5 is a schematic diagram showing the waveform of the output current of the cancellation signal according to the first embodiment in an abnormal state. FIG. [Figure 17] FIG. 10 is a configuration diagram showing a feature amount detection unit according to another aspect of the first embodiment. [Figure 18] FIG. 10 is a configuration diagram of a noise filter according to a second embodiment. [Figure 19] FIG. 11 is a configuration diagram of a noise filter according to a third embodiment. [Figure 20] FIG. 11 is a configuration diagram of a feature amount detection unit according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Noise filters according to embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding parts.

[0012] Embodiment 1 First, the first embodiment will be described with reference to FIGS. 1 to 16D. Fig. 1 is a configuration diagram showing a power conversion system according to embodiment 1, and Fig. 2 is a configuration diagram showing a power conversion device according to embodiment 1. The power conversion system 100 is disposed between an AC power source 1 and a load 90, and includes a power conversion device 80 that converts input power from the AC power source 1 into any DC power or AC power, and a noise filter 10 inserted between the AC power source 1 and the power conversion device 80. 。The AC power supply 1, noise filter 10, power conversion device 80, and load 90 are connected by an electric circuit 11. The electric circuit 11 is connected to a power line 2 (not shown) of the AC power supply 1, and input power from the AC power supply 1 is input to the power conversion device 80 via the power line 2. The power conversion device 80 converts the power input from the AC power supply 1 into power required to drive the load 90 and outputs the power. Note that, although the noise filter 10 is disposed between the AC power supply 1 and the power conversion device 80 in the first embodiment, it may also be disposed between the power conversion device 80 and the load 90.

[0013] As shown in FIG. 2, the power conversion device 80 is a two-level three-phase inverter. Specifically, two semiconductor switches 82a and 82b connected in series form one upper and lower arm 82. Two semiconductor switches 83a and 83b connected in series form one upper and lower arm 83. Two semiconductor switches 84a and 84b connected in series form one upper and lower arm 84. A DC power supply 81 is connected to these three upper and lower arms 82, 83, and 84. The DC power supply 81 is composed of a converter that converts AC input power input from an AC power supply 1 into DC. An inverter output terminal 85 is connected to the midpoint of the three upper and lower arms 82, 83, and 84. These six semiconductor switches 82a, 82b, 83a, 83b, 84a, and 84b perform switching operations, causing AC power to be output to the inverter output terminal 85. At this time, the output potential of the inverter output terminal 85 becomes either the positive or negative voltage potential of the DC power supply 81. Therefore, the common mode voltage of the power conversion device 80 is a constant voltage that is not zero.

[0014] FIG. 3 is a diagram illustrating common-mode noise generated in the power conversion system according to the first embodiment, showing a common-mode equivalent circuit. In the power conversion system 100, the AC power supply 1 and the load 90 are connected to the ground side by a grounding wire 3, separate from the above-described electric circuit 11. The noise filter 10 is provided with a grounding capacitor 15, one end of which is connected to the grounding wire 3. A parasitic capacitance 86 and a parasitic capacitance 91 exist between the power conversion device 80 and the grounding wire 3, and between the load 90 and the grounding wire 3, respectively. In the power conversion system 100, the common-mode voltage of the power conversion device 80 is applied to a common-mode loop via the parasitic capacitances 86 and 91 and the grounding wire 3, and a common-mode current (common-mode noise CN) flows as shown by the arrows in FIG. 3.

[0015] 4 is a configuration diagram showing a noise filter according to the first embodiment. Noise filter 10 is inserted between AC power supply 1 and power conversion device 80. Noise filter 10 includes: noise detection unit 12 provided on electric circuit 11 connected to power line 2 (not shown); cancellation signal output unit 13 that generates and outputs cancellation signal CS from common mode noise CN (not shown in FIG. 4) detected by noise detection unit 12; injection unit 14 that is provided on electric circuit 11 closer to the output end than noise detection unit 12, i.e., on the power conversion device 80 side, and that injects cancellation signal CS output from the cancellation signal output unit into electric circuit 11; control power supply 19 that supplies power to cancellation signal output unit 13 for generating and injecting cancellation signal CS; and protection circuit 18 that is inserted between control power supply 19 and cancellation signal output unit 13 and can cut off the supply of power from control power supply 19. In the first embodiment, a power supply cutoff means is provided that cuts off the power supply to the amplifier 16 of the cancellation signal output unit 13, as a protection means for preventing an abnormal cancellation signal CS from being injected into the electric circuit 11. Furthermore, in the first embodiment, a protection circuit 18 is provided as one form of the power supply cutoff means.

[0016] The cancellation signal output unit 13 has an amplifier unit 16 that amplifies the noise detection signal DS output from the noise detection unit 12, i.e., a cancellation signal generator, and an abnormality detection unit 17 that sends the output from the amplifier unit 16 to the injection unit 14 as a cancellation signal CS and can output an abnormality detection signal AS based on the output voltage of the amplifier unit 16. Note that in the first embodiment, the abnormality detection unit 17 is composed of elements and circuits that have almost no effect on the output characteristics, and the output of the amplifier unit 16 is almost the same as the cancellation signal CS. For this reason, hereinafter, unless otherwise specified, the output of the amplifier unit 16 will also be referred to as the cancellation signal CS.

[0017] The characteristics of the cancellation signal CS can be adjusted between the noise detection unit 12 and the amplifier unit 16, or between the amplifier unit 16 and the abnormality detection unit 17. Rufu A filter unit (not shown) may also be provided. If a filter unit is provided between the noise detection unit 12 and the amplifier unit 16, the amplifier unit 16 will amplify the noise detection signal DS adjusted by the filter unit to generate the cancellation signal CS. Even in this case, the characteristics of the cancellation signal CS will be adjusted by adjusting the noise detection signal DS. The filter unit may be an input filter circuit that adjusts the attenuation characteristics of the noise filter 10, such as by reducing the gain in a specific band. For example, an analog filter such as a high-pass filter, low-pass filter, or notch filter composed of resistors and capacitors may be used.

[0018] The noise filter 10 also includes a grounding capacitor 15 connected between the electric circuit 11 and the grounding conductor 3. The noise detection unit 12, the injection unit 14, and the grounding capacitor 15 form a main circuit unit 101 of the noise filter 10. The control characteristics of the noise filter 10 depend heavily on the main circuit unit 101. The inductance value of the main circuit unit 101 is the sum of the inductance value of the common mode transformer that forms the noise detection unit 12 and the inductance value of the common mode transformer that forms the injection unit 14. The capacitance value of the main circuit unit 101 is the capacitance value of the grounding capacitor 15. The control characteristics of the main circuit unit 101 will be described in detail later.

[0019] FIG. 5 is a configuration diagram showing a noise detection unit according to the first embodiment. The noise detection unit 12 is composed of a common-mode transformer. The common-mode transformer constituting the noise detection unit 12 is referred to herein as a detection transformer. This detection transformer is provided in an electric circuit 11 connected to a power line 2 (not shown) of an AC power supply 1, with an R-phase winding 12a wound around the R-phase power line, an S-phase winding 12b wound around the S-phase power line, a T-phase winding 12c wound around the T-phase power line, and an auxiliary winding 12d. The R-phase winding 12a, the S-phase winding 12b, and the T-phase winding 12c are wound in phase. The noise detection unit 12 configured in this manner cancels out magnetic flux generated in normal mode and constructively generates magnetic flux in common mode. The detection transformer configured in this manner has a high inductance value only for common-mode noise and functions as a common-mode choke coil. In the noise detection unit 12, a noise detection signal DS is generated across both ends of the auxiliary winding 12d by the common mode noise CN passing through the detection transformer. Both ends of the auxiliary winding 12d are connected to the amplifier unit 16, and the noise detection signal DS is sent to the amplifier unit 16.

[0020] FIG. 6 is a configuration diagram showing an example of an amplifier unit according to the first embodiment. The amplifier unit 16 includes an input resistor 16a, an operational amplifier 16b, and a feedback resistor 16c. The inverting input terminal of the operational amplifier 16b is connected to the input terminal of the amplifier unit 16 (the left side of FIG. 6) via the input resistor 16a, and the inverting input terminal of the operational amplifier 16b is connected to the output terminal of the operational amplifier 16b via the feedback resistor 16c. The non-inverting input terminal of the operational amplifier 16b is grounded. The amplifier unit 16 shown in FIG. 6 is an inverting amplifier circuit using the operational amplifier 16b, but may be a non-inverting amplifier circuit. The amplifier unit 16 amplifies the noise detection signal DS with an amplification factor given by the ratio between the resistance value of the input resistor 16a and the resistance value of the feedback resistor 16c to generate a cancellation signal CS, and outputs the cancellation signal CS.

[0021] 7 is a configuration diagram showing an example of the anomaly detection unit according to embodiment 1. The anomaly detection unit 17 is made up of a feature detection unit 171 (i.e., a feature acquisition unit) that outputs a feature signal CV for detecting an anomaly using the output voltage of the cancellation signal CS, and a feature comparison unit 172 (i.e., an anomaly determination unit) that generates and outputs an anomaly detection signal AS by performing a predetermined calculation on the feature signal CV. Here, it is assumed that the anomaly detection signal AS is output as an ON signal when an anomaly in the noise filter 10 is detected, and is output as an OFF signal when no anomaly is detected.

[0022] FIG. 8 is a configuration diagram showing an example of a feature detection unit according to the first embodiment. The feature detection unit 171 generates and outputs a feature signal CV based on the voltage value of the output voltage of the cancellation signal CS. The feature signal CV is a signal representing a feature used for anomaly detection. Various values ​​can be used as the feature, but the example shown in FIG. 8 shows a configuration of the feature detection unit 171 when the average voltage value of the output voltage of the cancellation signal CS is used as the feature. As shown in FIG. 8, the feature detection unit 171 is configured by connecting a low-pass filter formed by a capacitor 171k and a resistor 171m to the output side of an absolute value detection circuit formed by operational amplifiers 171a and 171b, resistors 171c to 171e, diodes 171f and 171g, and resistors 171h to 171j.

[0023] The input terminal (not shown) of the feature detection unit 171 is connected to the output terminal of the amplifier unit 16, and the output voltage of the cancellation signal CS is input to the feature detection unit 171 as an input signal. The input signal (cancellation signal CS) input to the feature detection unit 171 is sent to the injection unit 14 as shown in FIG. 8, and is also input to the absolute value detection circuit. When the cancellation signal CS is input to the absolute value detection circuit, the absolute value of the voltage value of the output voltage of the cancellation signal CS is output from the absolute value detection circuit. The output of the absolute value detection circuit is averaged by the low-pass filter, and therefore the average voltage value of the output voltage of the cancellation signal CS is output from the low-pass filter. In other words, the output of the feature detection unit 171 indicates the average voltage value of the output voltage of the cancellation signal CS. . Special The output of the feature detection unit 171 is sent as a feature signal CV to the feature comparison unit 172. The circuit of the feature detection unit 171 is not limited to the example shown in Fig. 8, and can be freely configured within the scope of the present application.

[0024] FIG. 9 is a configuration diagram showing an example of a feature comparison unit according to the first embodiment. The feature comparison unit 172 generates an abnormality detection signal AS by performing a predetermined calculation on the feature signal CV output by the feature detection unit 171, and outputs the generated abnormality detection signal AS. Here, an example is shown in which the feature comparison unit 172 is configured with a comparator circuit that compares the feature signal CV with a predetermined threshold. The feature comparison unit 172 includes a comparator 172a, a DC voltage source 172b, and a pull-up resistor 172c. The inverting input terminal of the comparator 172a is connected to the input terminal side (left side of FIG. 9) of the feature comparison unit 172, and the non-inverting input terminal of the comparator 172a is connected to the positive terminal of the DC voltage source 172b. The negative terminal of the DC voltage source 172b is grounded. The output terminal of the comparator 172a is connected to the output terminal side (left side in FIG. 9) of the feature comparison unit 172, and a pull-up resistor 172c is connected between the output terminal of the comparator 172a and the output terminal of the feature comparison unit 172.

[0025] When the feature signal CV is input as an input signal to the feature comparison unit 172, the magnitude of the feature signal CV is compared with the magnitude of the voltage of the DC voltage source 172b, and an abnormality detection signal AS is output according to the comparison result. Specifically, for example, if the feature signal CV is greater than the voltage of the DC voltage source 172b, an abnormality is detected and the abnormality detection signal AS is output as an ON signal. In this case, the voltage value of the DC voltage source 172b serves as a threshold for determining whether or not an abnormality exists. Note that the circuit of the feature comparison unit 172 is not limited to the example shown in FIG. 9 and can be configured freely within the scope of the present application.

[0026] FIG. 10 is a configuration diagram showing an injection unit according to the first embodiment. The injection unit 14 is composed of a common-mode transformer. The common-mode transformer constituting the injection unit 14 is referred to herein as the injection transformer. This injection transformer includes an R-phase winding 14a wound around the R-phase power line, an S-phase winding 14b wound around the S-phase power line, a T-phase winding 14c wound around the T-phase power line, and an auxiliary winding 14d in the electric circuit 11. The R-phase winding 14a, the S-phase winding 14b, and the T-phase winding 14c are wound in the same phase. The injection transformer configured in this manner has a high inductance value only for the common mode and functions as a common-mode choke coil. In the injection unit 14 configured with the injection transformer as described above, when a cancellation signal CS is input to both ends of the auxiliary winding 14d, a voltage V that cancels the common-mode noise CN is induced in the R-phase winding 14a, the S-phase winding 14b, and the T-phase winding 14c by the cancellation signal CS input to the auxiliary winding 14d.

[0027] Here, the control response of the main circuit unit 101 of the noise filter 10 will be described. FIGS. 11A to 11C are schematic diagrams showing the control response of the main circuit unit of the noise filter according to the first embodiment. FIG. 11A is a schematic diagram showing the control response when there is no filter unit, FIG. 11B is a schematic diagram showing the pass characteristics of the filter unit, and FIG. 11C is a schematic diagram showing the control response when there is a filter unit. In FIGS. 11A to 11C, the horizontal axis represents frequency, and the vertical axis represents gain. Here, the control response represents the open-loop response of a path that starts from the output of the noise detection unit 12, passes through the cancellation signal output unit 13 and the injection unit 14, and returns to the noise detection unit 12. The control stability of the noise filter 10 depends on the gain margin and phase margin of the open-loop response. The "filter unit" refers to the filter unit that adjusts the characteristics of the cancellation signal CS as described above. The "filter unit" in FIGS. 11A to 11C refers to the filter unit provided between the noise detection unit 12 and the amplifier unit 16. As described above, this filter section adjusts the characteristics of the cancellation signal CS through adjustment of the noise detection signal DS.

[0028] As shown in FIG. 11A, in the open-loop response without a filter section, a large resonance peak occurs at the resonance frequency f1 of the main circuit section 101, and the gain increases sharply. Although not shown in the figure, a phase rotation also occurs at the resonance frequency f1. Thus, without a filter section, the control response becomes unstable at the resonance frequency f1. If the common-mode noise CN detected by the noise detection section 12 contains a component of the resonance frequency f1, the cancellation signal CS may also become unstable. Note that f1 is given by f1=1 / {2π√(L1×C1)}, where L1 is the inductance value of the main circuit section 101, and C1 is the capacitance value of the main circuit section 101.

[0029] As described above, without a filter section, the control response becomes unstable at the resonance frequency f1, so a filter section having the filter pass characteristic shown in FIG. 11B is provided between the noise detection section 12 and the amplifier section 16. This filter section is configured so that its reject frequency matches the resonance frequency f1 of the main circuit section 101. Such a filter section can be realized by a notch filter. By configuring the filter section as described above, a filter pass characteristic that significantly reduces the gain at the resonance frequency f1 can be obtained, as shown in FIG. 11B.

[0030] Therefore, in the open loop response when a filter section is included, as shown in FIG. 11C, a large resonance peak at the resonance frequency f1 is attenuated by the filter pass characteristic of the filter section.

[0031] As described above, when a filter unit is provided between the noise detection unit 12 and the amplification unit 16, it is possible to generate a cancellation signal CS that attenuates the resonance peak even if the common mode noise CN detected by the noise detection unit 12 contains a component of the resonance frequency f1. As a result, the noise filter 10 can achieve a stable noise suppression effect.

[0032] 12A and 12B are schematic diagrams illustrating the control response of the noise filter according to the first embodiment. FIG. 12A is a schematic diagram illustrating the gain characteristics, and FIG. 12B is a schematic diagram illustrating the phase characteristics. The control response characteristics (control characteristics) of the noise filter 10 are characterized by phase rotation due to phase delays in the main circuit 101, the amplifier 16, and the filter. In the example shown in FIGS. 12A and 12B, a notch filter and a low-pass filter (not shown) are combined as the filter section to suppress the resonance peak at the resonance frequency f1 as described above. The gain margin G2 at the phase inversion frequency f2 in the low-frequency band and the gain margin G3 at the phase inversion frequency f3 in the high-frequency band are set to values ​​that ensure control stability. Here, the gain margins G2 and G3 are indicated by upward arrows when they have positive values ​​and downward arrows when they have negative values. The value that ensures control stability is, for example, 6 dB.

[0033] Here, as shown in the example of FIGS. 12A and 12B, the resonance peak of This section explains a situation in which the control characteristics of a noise filter change due to the occurrence of some kind of abnormality in a noise filter in which the gain margins G2 and G3 at the phase inversion frequency are set to values ​​that ensure control stability while attenuating the noise.

[0034] 13A and 13B are schematic diagrams illustrating the control response of the noise filter according to the first embodiment. FIG. 13A is a schematic diagram illustrating changes in gain characteristics, and FIG. 13B is a schematic diagram illustrating changes in phase characteristics. FIGS. 13A and 13B also illustrate a case in which the control characteristics change due to an abnormality. To compare normal and abnormal conditions, the gain and phase characteristics in normal conditions are represented by solid lines, and the gain and phase characteristics in abnormal conditions are represented by dashed lines. Here, an example of an "abnormality" is shown in which the high-frequency phase inversion frequency f3 fluctuates to frequency f3*. A typical example of such an abnormality is when the low-pass filter loses its function due to a component failure or the like, resulting in a change in the characteristics of the filter unit. In such a case, the value of the gain margin G3 at the high-frequency phase inversion frequency f3 fluctuates, potentially deviating from a value that ensures control stability.

[0035] As shown in FIG. 13A, the gain margin at the high-frequency phase inversion frequency f3 fluctuates to a negative gain margin G3*. This indicates that the control response of the noise filter 10 is unstable. In such a case, the cancellation signal CS output from the cancellation signal output unit 13 also becomes an unstable signal with an abnormal output waveform, and an abnormal and unstable cancellation signal CS is injected into the electrical circuit 11. FIG. 14 is a schematic diagram showing an abnormal output waveform of the cancellation signal output unit according to the first embodiment, and shows an example of the waveform of the cancellation signal CS in an abnormal state. In FIG. 14, the horizontal axis represents time. Since the gain margin at the phase inversion frequency f3 has become a negative value, the frequency component of the phase inversion frequency f3, as shown in FIG. 14, but amplification And Continue, causing oscillation Teshi 14, the section between the arrow and the dashed line indicates the period T3 of the cancellation signal CS during an abnormality. The period T3 is equal to the reciprocal of the phase inversion frequency f3.

[0036] When the cancellation signal CS oscillates, the noise filter 10 also becomes a noise source for the common-mode noise CN in the common-mode equivalent circuit shown in FIG. 3. In the common-mode equivalent circuit, the load 90, the system, and the power conversion device 80 share the noise source voltage according to their respective impedance ratios. On the system side, not only does the noise filter 10 not operate normally and fail to achieve the normal attenuation level, but there is also the problem that conducted noise caused by the oscillation of the noise filter 10 itself leaks into the system via the electrical path 11. On the load 90 side, for example, there is a risk of the shaft voltage of the motor increasing. Furthermore, there is a risk that the common-mode noise CN generated by the power conversion device 80 itself may cause malfunction.

[0037] As described above, when using an active noise filter such as the noise filter 10, it is undesirable to leave abnormal output operations, such as controlled oscillation, which may occur due to a change in characteristics caused by a component failure or the like.

[0038] Furthermore, in the first embodiment, the injection unit 14 is configured with a common mode transformer. The common mode transformer that constitutes the injection unit 14 acts as an inductive load with inductive impedance for the cancellation signal output unit 13, and therefore has high impedance in the high frequency range. For this reason, even if the cancellation signal output unit 13 continues to perform abnormal high-frequency oscillation as shown in FIG. 14 and the noise filter 10 is unable to perform normal noise suppression operation, a phenomenon that would affect the specifications of the circuit components, such as an overvoltage or overcurrent, does not immediately occur in the cancellation signal output unit 13. This means that, since an abnormality in the noise filter 10 cannot be detected, even if the noise filter 10 is equipped with an overvoltage protection circuit or an overcurrent protection circuit, the protection function will not shut down the noise filter 10.

[0039] Therefore, the noise filter 10 detects an abnormality using the abnormality detection unit 17, and when an abnormality is detected, activates the protection circuit 18 to stop the generation and injection of the cancellation signal CS. Below, a specific explanation will be given, comparing the cancellation signal in a normal state with the cancellation signal in an abnormal state.

[0040] FIG. 15A is a schematic diagram showing the waveform of a common-mode voltage under normal conditions, and FIG. 15B is a schematic diagram showing the waveform of a common-mode current. FIG. 15C is a schematic diagram showing the waveform of the output voltage of a cancellation signal under normal conditions according to embodiment 1, and FIG. 15D is a schematic diagram showing the waveform of the output current of the cancellation signal. In FIGS. 15A to 15D, the horizontal axis represents time. Here, the common-mode voltage is the voltage of common-mode noise CN. The common-mode current is the current that flows through the electrical circuit 11 due to the common-mode voltage. This current is the current that flows through the electrical circuit 11 when a common-mode voltage is input to the common-mode equivalent circuit shown in FIG. 3 and when the noise filter 10 is not present. The common-mode voltage is generated in conjunction with the switching operation of each semiconductor switch in the power conversion device 80 shown in FIG. 2 and has a rectangular waveform as shown in FIG. 15A. The common-mode current has a spike-like waveform as shown in FIG. 15B, causing noise problems at various locations along the path. The noise detection unit 12 of the noise filter 10 detects the common mode current and sends a noise detection signal DS to the cancellation signal output unit 13. The cancellation signal output unit 13 generates a cancellation signal CS from the noise detection signal DS. The cancellation signal CS is injected into the electrical circuit 11 via the injection unit 14.

[0041] The output voltage of the cancellation signal CS in a normal state has a spike-like waveform as shown in FIG. 15C. The output current of the cancellation signal CS generated by the output voltage of the cancellation signal CS also has a spike-like waveform as shown in FIG. 5It has a spike-shaped waveform as shown in D. The output current of the cancellation signal CS is a current that cancels out the common mode current, so like the common mode current, it has the characteristic of having a waveform whose average and effective values ​​are extremely smaller than the peak value.

[0042] In reality, a noise current flowing out from power conversion device 80, which is the noise source of common mode noise CN, passes through injection unit 14, causing a disturbance component to be superimposed on the output current of cancellation signal CS, and the disturbance component is also superimposed on the output voltage of cancellation signal CS due to the product of the output impedance and current of cancellation signal CS. However, to make the concept easier to understand, such superposition is ignored in Figures 15C and 15D.

[0043] FIG. 16A is a schematic diagram showing the waveform of the common-mode voltage during an abnormality, and FIG. 16B is a schematic diagram showing the waveform of the common-mode current. FIG. 16C is a schematic diagram showing the waveform of the output voltage of the cancellation signal according to embodiment 1 during an abnormality, and FIG. 16D is a schematic diagram showing the waveform of the output current of the cancellation signal. In FIGS. 16A to 16D, the horizontal axis represents time. As shown in FIGS. 16A and 16B, the common-mode voltage and common-mode current do not change even during an abnormality. On the other hand, during an abnormality, a change in the control characteristics occurs in the noise filter 10, causing the cancellation signal CS to oscillate. Therefore, as shown in FIGS. 16C and 16D, the waveforms of the output voltage and output current of the cancellation signal CS become abnormal output waveforms like those shown in FIG. 14. The abnormal output waveform does not have the characteristic of the waveform during normal operation, namely, the characteristic that the average value and effective value are extremely smaller than the peak value.

[0044] Specifically, in the waveforms during abnormal conditions shown in FIGS. 16C and 16D, the voltage average value of the output voltage of the cancellation signal CS is 2 / π times the voltage peak value, and there is no significant difference between the peak value and the average value. Also, the current average value of the output current of the cancellation signal CS is 2 / π times the current peak value, and there is no significant difference between the peak value and the average value. This is the same even if the output voltage of the operational amplifier saturates due to high-gain oscillation operation and the waveform of the output voltage of the cancellation signal CS becomes rectangular. During abnormal conditions, the effective value of each of the output voltage and output current is also 1 / √2 times the peak value, so the relationship between the peak value and the effective value is the same as the relationship between the peak value and the average value described above. However, in the following, the explanation will focus on the average value.

[0045] As described above, it can be seen that during abnormal conditions, the voltage average value of the output voltage of the cancellation signal CS and the current average value of the output current are larger than those during normal conditions. That is, in this case, the voltage average value of the output voltage of the cancellation signal CS can be used as a criterion. In this case, by setting an appropriate threshold value and comparing the actual voltage average value with the above threshold value, it can be determined whether the noise filter 10 is operating normally, that is, whether the noise filter 10 can cancel the common-mode current, or whether it has fallen into an abnormal operation for some reason. Typically, if the voltage average value of the output voltage of the cancellation signal CS during normal conditions is V1, the threshold value of the voltage average value for determining the presence or absence of an abnormality is Vth, and the voltage average value during abnormal operation is V2, then by selecting the threshold value Vth of the voltage average value such that V1 < Vth < V2, the presence or absence of an abnormality can be determined. The same applies when using the current average value of the output current of the cancellation signal CS to determine the presence or absence of an abnormality.

[0046] As described above, the feature quantity detection unit 171 outputs the average voltage value of the output voltage of the cancellation signal CS as the feature quantity signal CV. Furthermore, the output voltage value of the DC voltage source 172b of the feature quantity comparison unit 172 becomes the threshold value for determining whether or not there is an abnormality. That is, the output voltage value of the DC voltage source 172b becomes the threshold value Vth of the voltage average value. As a result, the comparison of the average voltage value of the output voltage of the cancellation signal CS with the threshold value Vth of the voltage average value is performed by the feature quantity comparison unit 172. 172 When the average voltage value of the output voltage of the cancellation signal CS exceeds the threshold Vth, the output of the comparator 172a becomes high, and the feature comparison unit 172 outputs the abnormality detection signal AS in the ON state. When the average voltage value of the output voltage of the cancellation signal CS is equal to or lower than the threshold Vth, the output of the comparator 172a becomes low, and the feature comparison unit 172 outputs the abnormality detection signal AS in the OFF state.

[0047] In the first embodiment, the abnormality detection signal AS output from the feature comparison unit 172 is input to the protection circuit 18. The protection circuit 18 is typically configured with a control relay. Based on the abnormality detection signal AS, the protection circuit 18 disconnects the control power supply 19 from the cancellation signal output unit 13 and cuts off the power supply from the control power supply 19 to the cancellation signal output unit 13. As a result, in the cancellation signal output unit 13 whose power supply has stopped, the amplification unit 16 no longer generates the cancellation signal CS. Furthermore, since the injection of the cancellation signal CS into the electric circuit 11 is also no longer performed, the injection of the cancellation signal CS having an abnormal output waveform into the electric circuit 11 is prevented.

[0048] After the anomaly detection unit 17 detects an anomaly and causes the protection circuit 18 to perform a cutoff operation, the cutoff operation of the protection circuit 18 may be reset and the generation and injection of the cancellation signal CS may be resumed, for example, when the feature comparison unit 172 outputs an off-state anomaly detection signal AS. For an anomaly that is known in advance to be temporary, a delay circuit or a counter circuit may be used to resume operation after a preset time has elapsed.

[0049] In the first embodiment, an example of a circuit using an operational amplifier 16b as the configuration of the amplifier 16 has been shown, but the configuration of the amplifier 16 may be, for example, another inverting amplifier circuit or a non-inverting amplifier circuit. Also, an example has been shown in which the protection circuit 18 performs a cutoff operation in response to the abnormality detection signal AS, but it may be possible to perform operations other than a simple cutoff operation by combining it with a logic circuit, such as latching the cutoff operation or being able to cancel the cutoff operation in combination with a reset circuit. Also, the feature detection unit 171 may be configured using an operational amplifier 171a, 171b However, any circuit that achieves the same purpose may be used. Detect R Features The average voltage is Detect However, the feature quantity detection unit 171 may be configured to detect different values, such as an instantaneous value or an effective value, as the feature quantity. Also, although the feature quantity comparison unit 172 is configured using a circuit that uses the comparator 172a, it may be configured using another circuit that achieves the same purpose.

[0050] Furthermore, in the noise filter 10 of the first embodiment, other common mode choke coils may be connected to the electrical path 11 in addition to the noise detection unit 12 and the injection unit 14. Also, one or both of the noise detection unit 12 and the injection unit 14 may be configured using a capacitor instead of a common mode transformer. When the injection unit 14 is configured using a capacitor, a pulse transformer may be inserted between the injection unit 14 and the cancellation signal output unit 13.

[0051] In the first embodiment, if the injection unit 14 is configured using a capacitor instead of a common mode transformer and no pulse transformer is inserted between the capacitor and the cancellation signal output unit 13, the impedance of the injection unit 14 becomes capacitive for the cancellation signal output unit 13. In this case, the frequency band in which it is difficult to detect an abnormality without the abnormality detection unit 17 becomes a low frequency band. On the other hand, if the injection unit 14 is configured using a capacitor instead of a common mode transformer and a pulse transformer is inserted between the capacitor and the cancellation signal output unit 13, the impedance of the injection unit 14 becomes inductive for the cancellation signal output unit 13, and the frequency band in which it is difficult to detect an abnormality without the abnormality detection unit 17 becomes a high frequency band, just like when the injection unit 14 is configured with a common mode transformer. Regardless of whether the injection unit 14 is inductive or capacitive, the noise filter 10 in the first embodiment , different The constant detection unit 17 can reliably detect abnormalities.

[0052] In addition, in embodiment 1, the protection circuit 18 is used as one form of power supply cutoff means, but as another form of power supply cutoff means, a control circuit that stops the control power supply 19 based on the abnormality detection signal AS can also be used.

[0053] According to the first embodiment, high reliability can be achieved. More specifically, the circuit includes an abnormality detection unit that detects an abnormality in the noise filter based on the output voltage of the cancellation signal and outputs an abnormality detection signal, and a protection circuit that cuts off the power supply to the cancellation signal output unit based on the abnormality detection signal. As a result, if an abnormality occurs due to a change in the control characteristics of the noise filter, the abnormality can be detected from a change in the output voltage of the cancellation signal caused by the abnormality, and the power supply to the cancellation signal output unit can be stopped, thereby preventing the abnormal cancellation signal from being injected into the electrical circuit, resulting in high reliability. In particular, the circuit is highly reliable against changes in the control characteristics of the noise filter itself.

[0054] Furthermore, because an abnormality in the noise filter is detected based on the output voltage of the cancellation signal, it is possible to reliably detect an abnormality in the noise filter in the high frequency band even if the injection section for the cancellation signal is configured with an inductance load such as a common mode transformer, and it is possible to reliably detect an abnormality in the noise filter in the low frequency band even if the injection section is configured with a capacitive load such as a capacitor.

[0055] Furthermore, because the protection circuit stops the generation and injection of the cancellation signal when an abnormality is detected, stable operation can be achieved while setting the gain margin and phase margin for suppressing controlled oscillation lower than before. Setting the gain margin and phase margin lower than before means improving the control gain of the noise filter, and therefore improving the amount of noise suppression.

[0056] Next, a feature detection unit according to another embodiment of the first embodiment will be described with reference to FIG. 17. Note that the same or corresponding parts as those in FIGS. 1 to 16D are designated by the same reference numerals, and their description will be omitted. FIG. 17 is a configuration diagram showing a feature detection unit according to another embodiment of the first embodiment. In this embodiment, a feature detection unit 1711 detects the average current value of the output current of the cancellation signal CS as a feature. As with the feature detection unit 171 of the first embodiment, an absolute value detection circuit is provided within the feature detection unit 1711. Meanwhile, in the feature detection unit 1711, a current detection resistor 171p, such as a shunt resistor, is disposed between the injection unit 14 and the control ground, and the input side of the absolute value detection circuit of the feature detection unit 1711 is connected to an electrical path connecting the injection unit 14-side terminal of the current detection resistor 171p and the injection unit 14. As a result, the input signal of the absolute value detection circuit in the feature detection unit 1711 becomes the output current of the cancellation signal CS. In this way, by using the output current of the cancellation signal CS as the input signal, the feature signal CV becomes the average current value of the cancellation signal CS. As the rest is the same as in the first embodiment, the explanation will be omitted. Furthermore, in this embodiment, the same effects as in the first embodiment can be obtained.

[0057] Embodiment 2 Next, a second embodiment will be described with reference to FIG. 18. Note that parts that are the same as or equivalent to those in FIGS. 1 to 17 are given the same reference numerals, and their description will be omitted. FIG. 18 is a configuration diagram of a noise filter in the second embodiment. In a noise filter 20, a protection circuit 28 is inserted between an abnormality detection unit 17 and an injection unit 14 in a cancellation signal output unit 23. On the other hand, the protection circuit 18 that was inserted between the control power supply 19 and the cancellation signal output unit 13 in the noise filter 10 of the first embodiment is not present. The abnormality detection unit 17 outputs an abnormality detection signal AS to the protection circuit 28. In the noise filter 20, a cancellation signal CS output from the amplification unit 16 is sent to the injection unit 14 through the abnormality detection unit 17 and the protection circuit 18. In the second embodiment, a protection circuit 28 is inserted between the cancellation signal output unit 17 and the injection unit 14 as a protection means for preventing an abnormal cancellation signal CS from being injected into the electric circuit 11. 2 The second embodiment includes an injection blocking means for blocking transmission of the cancellation signal CS from the amplifier 16 of the third embodiment to the injection unit 14. Furthermore, the second embodiment includes a protection circuit 28 as one form of injection blocking means.

[0058] Based on the abnormality detection signal AS, the protection circuit 28 cuts off the path of the cancellation signal CS between the abnormality detection unit 17 and the injection unit 14. As a result, when an abnormality is detected in the abnormality detection unit 17, the abnormal cancellation signal CS is prevented from being sent to the injection unit 14, and therefore the abnormal cancellation signal CS is prevented from being injected into the electrical circuit 11. The configuration of the protection circuit 28 may be the same as the protection circuit 18 in the first embodiment. Note that the second embodiment and the first embodiment may be combined to provide both the protection circuit 18 and the protection circuit 28. In this case, even if the cut-off function of one of the protection circuits is impaired due to a failure or the like, the cut-off function of the other protection circuit can prevent the abnormal cancellation signal CS from being injected into the electrical circuit 11. The rest of the configuration is the same as in the first embodiment, so the description thereof will be omitted.

[0059] According to the second embodiment, the same effects as those of the first embodiment can be obtained.

[0060] Embodiment 3 Next, a third embodiment will be described with reference to FIG. 19. Note that parts that are the same as or equivalent to those in FIGS. 1 to 18 are assigned the same reference numerals, and their description will be omitted. FIG. 19 is a configuration diagram of a noise filter in the third embodiment. The noise filters in the first and second embodiments each include a protection circuit that performs a cutoff operation in response to an abnormality detection signal AS. In the third embodiment, instead of such a protection circuit, an abnormality in the noise filter is notified to the noise source. The noise filter 30 has an abnormality state signal output unit 38 provided in the cancellation signal output unit 33, and the abnormality detection signal AS output by the abnormality detection unit 17 is input to the abnormality state signal output unit 38. In the third embodiment, the abnormality state signal output unit 38 is provided as protection means for preventing an abnormal cancellation signal CS from being injected into the electrical circuit 11.

[0061] The abnormal state signal output unit 38 has an output circuit capable of outputting a signal to the power conversion device 80. When the abnormal state signal AS is input, the abnormal state signal output unit 38 outputs an abnormal state signal AS2 to the power conversion device 80. The abnormal state signal AS2 is typically a differential signal or a low-impedance current signal that is resistant to external disturbances, and is generated based on the abnormal state signal AS. The abnormal state signal AS2 may be isolated from the control potential of the noise filter 30 as necessary. Upon receiving the abnormal state signal AS2, the power conversion device 80 recognizes that the noise filter 30 is in an abnormal state. Upon recognizing that the noise filter 30 is in an abnormal state, the power conversion device 80 takes appropriate measures, such as stopping operation, depending on the nature of the abnormality. A control circuit that stops the power conversion device 80 based on the abnormal state signal AS2 may be provided externally or internally to the power conversion device 80. Such a control circuit receives the abnormal state signal AS2 and sends a stop command to the power conversion device 80 as necessary.

[0062] According to the third embodiment, a highly reliable noise filter can be provided. Unlike the first and second embodiments, the third embodiment does not directly prevent the injection of an abnormal cancellation signal into the electrical circuit using a protection circuit. However, the abnormal state signal is used to make the power conversion device, which is a common-mode noise source, aware of an abnormality in the noise filter. In this case, the power conversion device takes measures such as halting operation as necessary, thereby preventing the generation of an abnormal cancellation signal and its injection into the electrical circuit by stopping the common-mode noise source. In this way, the third embodiment achieves high reliability by indirectly preventing the injection of an abnormal cancellation signal into the electrical circuit by making the power conversion device, which is a noise source, aware of an abnormality in the noise filter. Note that the third embodiment may be combined with the protection circuits of the first and second embodiments. Furthermore, since the third embodiment outputs an abnormal state signal to the common-mode noise source, if there is another controlled device that is also a common-mode noise source, the abnormal state signal may also be output to the other controlled device.

[0063] Embodiment 4 Next, a fourth embodiment will be described with reference to FIG. 20. Note that parts that are the same as or equivalent to those in FIGS. 1 to 19 are given the same reference numerals, and their description will be omitted. The fourth embodiment differs from the first to third embodiments in the feature quantity detection unit. FIG. 20 is a configuration diagram of the feature quantity detection unit according to the fourth embodiment. The feature quantity detection unit 471 of the noise filter 40 (not shown) is the feature quantity detection unit 1711 shown in FIG. 17, to which a feature quantity detection filter unit 471n, i.e., a band-limiting filter unit, is added. More specifically, a current detection resistor 171p is provided between the injection unit 14 and the control ground, Current SensingA feature amount detection filter unit 471n is provided on an electric path connecting the terminal of the resistor 171p on the injection unit 14 side with the injection unit 14, and the electric path connecting the input side of the absolute value detection circuit. The input signal to the feature amount detection unit 171 becomes an output current of the cancellation signal CS, similar to the feature amount detection unit 1711. In the fourth embodiment, the feature amount detection filter unit 471n is provided in the feature amount detection unit 1711, but the feature amount detection filter unit 471n may also be provided in the feature amount detection unit 171 shown in FIG.

[0064] The feature detection filter unit 471n performs filtering on the input signal to the feature detection unit 471 and is configured to weight each frequency component, such as high frequencies above a certain frequency, according to the frequency. Typically, the feature detection filter unit 471n includes a low-pass filter, a high-pass filter, a notch filter, a band-pass filter, or a filter circuit that combines these. Note that "weighting" here also includes setting the weight of a specific frequency component to zero, i.e., removing the specific frequency component. Therefore, by removing disturbance components in advance, the feature detection filter unit 471n can reliably detect a desired abnormality from among various abnormalities that may occur in the noise filter 40. This will be described in detail below.

[0065] If an abnormality occurs and the control characteristics of the noise filter 40 change, the cancellation signal CS will have an abnormal output waveform such as that shown in FIG. 14 . However, in reality, noise current flowing from the power converter 80, which is the noise source, passes through the injection unit 14, resulting in a disturbance component being superimposed on the output voltage and output current of the cancellation signal CS. While this disturbance component contains various frequency components, noise suppression using an active noise filter typically limits the frequency band to be suppressed to avoid increasing the power required by the active noise filter's control circuit. Typically, frequencies below 150 kHz, the noise standard target frequency band, are not actively suppressed, so the frequency band of several kHz to several tens of kHz, which is the switching carrier frequency of the power converter 80, is generally outside the suppression band. Therefore, noise currents with frequency components near the switching carrier frequency of the power converter 80 may not be suppressed by an active noise filter, and the amplitude of the noise current in this frequency band may be allowed to flow into the grid without being reduced. On the other hand, when a noise current in a band outside the target of noise suppression passes through the injection section of the active noise filter, the resulting disturbance in the output voltage and output current of the cancellation signal can become significant.

[0066] When the feature amount detector 471 is used, the feature amount detection filter unit 471n can remove frequency components near the switching carrier frequency as described above from the input signal (output voltage or output current of the cancellation signal CS) to the feature amount detector 471. This allows the effect of disturbances to be removed before generating the feature amount signal CV and performing anomaly detection. Therefore, according to the fourth embodiment, it is possible to reliably detect the desired anomaly.

[0067] According to the fourth embodiment, 1 The same effect can be obtained. Furthermore, by providing a feature detection filter section, the cancellation signal is weighted according to each frequency component before feature detection, so that the desired abnormality can be reliably detected.

[0068] Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are conceivable within the scope of the technology disclosed in this application, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with a component of another embodiment. For example, in each embodiment disclosed herein, the noise filter of the present application is applied to a three-phase, three-wire power conversion system, but the noise filter of the present application may also be applied to a power conversion system with a different number of phases and wires. For example, the noise filter may be applied to a three-phase, four-wire power conversion system, or a single-phase, two-wire, or single-phase, three-wire power conversion system. Furthermore, although the first to fourth embodiments have been described based on the premise that analog circuits are used, they can also be applied to digital circuits. In this case, the feature detection unit of the anomaly detection unit may perform a spectrum analysis of the output voltage or output current of the cancellation signal, and anomaly detection may be performed based on the results of the analysis. [Explanation of symbols]

[0069] 1 AC power supply, 10, 20, 30, 40 noise filter, 11 electrical circuit, 12 noise detection section, 13, 23, 33 cancellation signal output section, 14 injection section, 16 amplification section, 17 abnormality detection section, 18, 28 protection circuit, 19 control power supply, 38 abnormal state signal output section, 80 power conversion device, 90 load, 101 main circuit section, 171, 1711, 471 feature detection section, 172 feature comparison section, AS abnormality detection signal, AS2 abnormal state signal, CN common mode noise, CS cancellation signal, CV feature signal

Claims

1. A noise filter provided in an electric path connecting an AC power supply, a load, and a power conversion device that converts AC power output from the AC power supply and outputs the converted AC power to the load, a noise detection unit that detects common mode noise flowing through the electrical path; a cancellation signal generation unit that generates a cancellation signal that cancels the common mode noise based on the common mode noise detected by the noise detection unit; an injection unit that injects the cancellation signal into the electrical path; an abnormality detection unit that detects an abnormality in the noise filter based on the output voltage or output current of the cancellation signal and outputs an abnormality detection signal; a protection means for suppressing the injection of the abnormal cancel signal into the electrical circuit based on the abnormality detection signal; Equipped with The noise filter is characterized in that the protection means includes a power supply cutoff means for cutting off the power supply to the cancellation signal generation unit.

2. 2. The noise filter according to claim 1, wherein the power supply cutoff means includes a protection circuit that cuts off a connection between a control power supply that supplies power to the cancellation signal generation unit and the cancellation signal generation unit.

3. A noise filter as described in Claim 1, wherein the power supply cut-off means includes a control circuit that stops the control power supply that supplies power to the cancellation signal generating unit based on the abnormality detection signal.

4. 4. The noise filter according to claim 1, wherein the anomaly detection unit includes: a feature acquisition unit that acquires a feature based on the output voltage or output current of the cancellation signal; and an anomaly determination unit that determines whether or not there is an anomaly based on the magnitude of the feature, and outputs the anomaly detection signal based on a result of the determination.

5. The noise filter according to claim 4 , wherein the characteristic amount is an effective value, an average value, or an instantaneous value of the output voltage or output current of the cancellation signal.

6. A noise filter provided in an electric circuit connecting an AC power source, a load, and a power conversion device that converts AC power output from the AC power source and outputs the converted AC power to the load, a noise detection unit that detects common mode noise flowing through the electrical path; a cancellation signal generation unit that generates a cancellation signal that cancels the common mode noise based on the common mode noise detected by the noise detection unit; an injection unit having an inductive impedance and configured to inject the cancellation signal into the electrical path; an abnormality detection unit that detects an abnormality in the noise filter based on the output voltage or output current of the cancellation signal and outputs an abnormality detection signal; a protection means for suppressing the injection of the abnormal cancel signal into the electrical circuit based on the abnormality detection signal; Equipped with the anomaly detection unit comprises: a feature acquisition unit that acquires a feature based on an average value of the output voltage of the cancellation signal, an effective value of the output voltage of the cancellation signal, an average value of the output current of the cancellation signal, or an effective value of the output current of the cancellation signal; and an anomaly determination unit that determines the presence or absence of an anomaly based on the magnitude of the feature, and outputs the anomaly detection signal based on the result of the determination.

7. A noise filter as described in Claim 6, wherein the injection section is constituted by an inductance load.

8. A noise filter as described in claim 6 or 7, wherein the abnormality detection unit outputs the abnormality detection signal when the feature exceeds a threshold value, and the threshold value is larger than the feature value under normal conditions and smaller than the feature value under abnormal operation.

9. 9. The noise filter according to claim 1, wherein the protection means comprises an injection blocking means for blocking transmission of the cancellation signal from the cancellation signal generating section to the injection section.

10. 10. The noise filter according to claim 9, wherein the injection blocking means comprises a second protection circuit that disconnects the cancellation signal generating section from the injection section.

11. 11. The noise filter according to claim 1, wherein the protection means comprises an abnormality signal output unit that generates an abnormality signal indicating that an abnormality has occurred in the noise filter based on the abnormality detection signal, and outputs the abnormality signal to a controlled device that is a noise source of the common mode noise.

12. 9. The noise filter according to claim 4, wherein the feature amount acquisition section includes a band-limiting filter section that assigns weights to each frequency component included in the cancellation signal in accordance with the respective frequency components, and the feature amount acquisition section acquires the feature amount based on the output voltage or output current of the weighted cancellation signal.

13. A noise filter described in any one of claims 1 to 5, which releases the power supply to the cancellation signal generating unit when the abnormality detection signal is output as an off signal or when a predetermined time has elapsed since the power supply to the cancellation signal generating unit was cut off.

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