Noise reduction filter circuit

Abstract

To provide a noise reduction filter circuit capable of detecting decrease in capacitance of a capacitor in a configuration having a star-connected capacitor.SOLUTION: A noise reduction filter circuit 7 includes: three capacitors C4 to C6 each having one end connected in common and the other end connected to each phase of a three-phase AC power source 2; and three resistance elements R1 to R3 each having one end connected in common and the other end connected to each phase of the three-phase AC power source 2. An abnormality detection unit 5 detects abnormality when potential difference between a common connection point of the capacitors C1 to C3 and the common connection point of the resistance elements R1 to R3 exceeds a determination value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a filter circuit that reduces noise flowing from a load connected to a three-phase AC power supply to the power supply side. [Background technology]

[0002] For example, to control the variable speed of a motor such as an induction motor, a three-phase AC power supply is rectified to DC using a rectifier, and an AC voltage of any frequency is generated using an inverter.The waveform of the AC voltage output from the inverter to the motor is generally generated using PWM (Pulse Width Modulation) control, so noise is generated by switching based on the PWM signal.

[0003] In recent years, inverter devices have been installed not only in factories but also in commercial facilities and buildings, and noise leaking into the power supply has become a problem. For this reason, an increasing number of inverter devices are equipped with built-in filter circuits for noise reduction as standard. While film capacitors are generally used in such filter circuits, metallized film capacitors, which have a self-repair function that allows them to recover their insulation even if a surge voltage is applied and the insulation breaks down, are often used.

[0004] The capacitance of a capacitor decreases when insulation breakdown occurs. In an environment where surge voltages occur frequently due to power supply conditions, the capacitance of capacitors used in filter circuits is likely to decrease. For this reason, configurations for detecting a decrease in the capacitance of a capacitor are disclosed in, for example, Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-174105 [Patent Document 2] Patent No. 6633402 [Patent Document 3] Patent No. 7347270 Summary of the Invention [Problem to be solved by the invention]

[0006] In a configuration in which the capacitors are star-connected, the power supply voltage is biased toward the capacitors whose capacitance has decreased. This accelerates the deterioration of the capacitor's lifespan due to the increase in applied voltage, further reducing the capacitance, potentially preventing the filter circuit from achieving sufficient noise reduction. Another problem is that the maximum rated voltage of the capacitor may be exceeded. Furthermore, no configuration has been proposed for detecting a decrease in the capacitance of a capacitor while the power supply is energized, in a configuration in which a filter circuit includes a star-connected capacitor.

[0007] Therefore, a noise reduction filter circuit is provided that is capable of detecting a decrease in capacitance of a star-connected capacitor. [Means for solving the problem]

[0008] The noise reduction filter circuit of the embodiment is connected between a three-phase AC power supply and a load device, three capacitors each having one end connected to a common terminal and the other end connected to each phase of the three-phase AC power supply; three resistance elements each having one end connected to a common terminal and the other end connected to each phase of the three-phase AC power supply; The device further includes an abnormality detection unit that detects an abnormality when a potential difference between a common connection point of the three capacitors and a common connection point of the three resistor elements exceeds a determination value.

[0009] The noise reduction filter circuit of the embodiment is connected between a three-phase AC power supply and a load device, three capacitors each having one end connected to a common terminal and the other end connected to each phase of the three-phase AC power supply; The device further includes an abnormality detection unit that detects an abnormality when the potential difference between the common connection point of the three capacitors and the ground potential exceeds a determination value. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a noise reduction filter circuit according to a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating a configuration of a noise reduction filter circuit according to a second embodiment. [Figure 3] FIG. 10 is a diagram illustrating a configuration of a noise reduction filter circuit according to a third embodiment. [Figure 4] FIG. 10 is a diagram illustrating a configuration of a noise reduction filter circuit according to a fourth embodiment. [Figure 5] FIG. 10 is a diagram illustrating a configuration of a noise reduction filter circuit according to a fifth embodiment. [Figure 6] FIG. 10 is a diagram illustrating a configuration of a noise reduction filter circuit according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) A first embodiment will be described below with reference to Fig. 1. As shown in the figure, a filter circuit main body 1 of this embodiment is connected between a three-phase AC power supply 2 and a rectifier circuit 3. The three-phase AC power supply 2 is star-connected, with the power supply terminals of the R, S, and T phases being VR, VS, and VT. The neutral point of the three-phase AC power supply 2 is grounded. The rectifier circuit 3 is configured by connecting diodes D1 to D6 in a three-phase bridge configuration. A smoothing capacitor C8 and an inverter circuit 4, which is a load, are connected in parallel to the rectifier circuit 3. The inverter circuit 4 drives a motor M.

[0012] The filter circuit body 1 includes three star-connected capacitors C1 to C3, the other ends of which are connected to the power supply terminals VR, VS, and VT, respectively. One end of a three-phase common mode coil L1 is connected to the power supply terminals VR, VS, and VT, respectively, and the other end is connected to the input terminals of each phase of the rectifier circuit 3.

[0013] The other ends of three star-connected capacitors C4 to C6 and three star-connected resistors R1 to R3 are connected between the common mode coil L1 and the rectifier circuit 3. The neutral points of the capacitors C4 to C6 are grounded via a capacitor C7.

[0014] A resistor R4, which constitutes an anomaly detection unit 5, is connected between the neutral point of capacitors C4 to C6 and the neutral point of resistors R1 to R3. Both ends of resistor R4 are connected to the input terminals of a rectifier circuit 6, which is configured by bridge-connecting diodes D8 to D11. A series circuit of a Zener diode ZD1 and resistor R5 is connected between the output terminals of the rectifier circuit 6. A capacitor C9 and the input terminal of a photocoupler U1 are connected in parallel to both ends of resistor R5. A capacitor C10 is connected between the output terminals of the photocoupler U1.

[0015] A series circuit of a resistor R8 and an NPN transistor Q1 is connected between the DC power supply terminal P5 and ground. The collector output terminal of the phototransistor inside the photocoupler U1 is connected to the DC power supply terminal P5. The emitter output terminal of the phototransistor is connected to the base of the transistor Q1 via a resistor R6. A resistor R7 is connected between the base and emitter of the transistor Q1. As described above, the filter circuit main body 1 and the anomaly detection unit 5 constitute a noise reduction filter circuit 7.

[0016] Next, the operation of this embodiment will be described. When the capacitances of capacitors C4 to C6 are equal, no potential difference occurs between the neutral points of capacitors C4 to C6 and the neutral points of resistor elements R1 to R3. If the capacitance of, for example, any one phase of capacitors C4 to C6 decreases, the potential difference increases. The abnormality detection unit 5 detects the potential difference using resistor element R4, and thereby detects the decrease in the capacitance of capacitors C4 to C6 as an abnormality.

[0017] For example, if the potential difference used as the threshold for detecting an abnormality is 10V, the voltage drop across the rectifier circuit 6 is 1V, the threshold voltage of the photocoupler U1 is 1V, and the Zener voltage of the Zener diode ZD1 is set to, for example, 8V. Hereinafter, this potential difference will be referred to as the detection voltage. When the detection voltage exceeds 9V, which is the sum of the voltage across the Zener diode ZD1 and the voltage drop across the rectifier circuit, the Zener diode ZD1 begins to conduct, generating a voltage across the resistor R5. If the voltage across the resistor R5 is less than the threshold voltage of the photocoupler U1 (1V), the phototransistor of the photocoupler U1 is off, and the transistor Q1 is also off. At this time, the collector potential FAULT1 of the transistor Q1 is high. When the detection voltage exceeds 10V, which is the sum of the threshold voltage of the photocoupler U1 and the 9V, the voltage across the resistor R5 exceeds the threshold voltage of the photocoupler U1, turning on the phototransistor of the photocoupler U1. This turns on the transistor Q1, causing the collector potential FAULT1 to go low, which becomes the abnormality detection signal.

[0018] Here, a simulation was performed assuming that the phase voltages of the three-phase AC power supply 2 are equal, the phase difference between the phases is 120 degrees, and the capacitance of the capacitor in one of the phases has decreased by 10%. As a result, if the voltage of one phase relative to the neutral point is set to "1", a potential difference of approximately 0.034 is generated between the neutral point of the three-phase AC power supply 2 and the neutral points of capacitors C4 to C6. A voltage 1.034 times the voltage of one phase is applied to the capacitor with the decreased capacitance.

[0019] Therefore, when detecting a 10% decrease in the capacitance of a capacitor, (Detection voltage) = 0.034 × (peak voltage of one phase input voltage) In addition, in order to prevent the rated voltage of the capacitor from being exceeded when the capacitance drops by 10%, 1.034 × (peak voltage of one phase input voltage) ≦ (rated voltage of capacitor) Just set it to .

[0020] Also, the voltage of one phase when the rated voltage of the capacitor is applied is (Voltage of one phase) = (Rated voltage of capacitor) / 1.034 At this time, the detected voltage is 0.034 times the voltage of one phase, so (Detection voltage) = 0.034 × (peak voltage of one phase input voltage) =0.034 x (rated voltage of capacitor) / 1.034 = 0.033 x (rated voltage of capacitor) should be set as the judgment value.

[0021] When the neutral point of resistor elements R1 to R3 is connected to an abnormality detection unit 5 to detect the voltage of the three-phase AC power supply 2, the neutral point potential of the star connection also fluctuates due to the current passing through the abnormality detection unit 5. Resistor element R4, which causes this fluctuation, is necessary to discharge the charges stored in capacitors C4 to C7 when the power supply is shut off.

[0022] In addition, capacitor C7 may be removed to reduce leakage current, but taking into account various errors and fluctuations such as the capacitance of capacitor C7, power supply voltage imbalance, resistance value error, and initial capacitance error of the capacitor, the approximate voltage at which a 10% capacitance drop is detected within the range that does not exceed the rated voltage of the capacitor is: (Detection voltage) = (peak voltage of capacitor rated voltage) ×(0.033±0.015)[V] This becomes:

[0023] Also, consider detecting a 10% capacitance drop of the capacitor based on the rated interphase voltage of the equipment as a load to which the noise reduction filter circuit 7 is connected, rather than the rated voltage of the capacitor. For example, if the equipment has a rated voltage range of 380V to 480V, the peak voltage of one phase corresponding to 480V, which is the maximum value of that voltage range, is You can also use {480×√(2 / 3)≒392V} as a reference.

[0024] Generally, capacitor manufacturer data sheets specify a capacitance drop of approximately 10% as the judgment value for various reliability tests, but if a certain degree of degradation in filter circuit performance is acceptable, a capacitance drop of 20%, for example, may be used as the judgment value. Also, because there is some error in the phase voltage and phase of actual commercial AC power supplies, the judgment value for the detected voltage may be given a margin of error in the results obtained from the above calculation formulas.

[0025] As described above, according to this embodiment, the noise reduction filter circuit 7 includes three capacitors C4 to C6, each having one end connected in common and the other end connected to each phase of the three-phase AC power supply 2, and three resistor elements R1 to R3, each having one end connected in common and the other end connected to each phase of the three-phase AC power supply 2. The abnormality detection unit 5 detects an abnormality when the potential difference between the common connection point of the capacitors C4 to C6 and the common connection point of the resistor elements R1 to R3 exceeds a threshold value. As a result, even in a configuration in which the filter circuit main body 1 includes star-connected capacitors C4 to C6, a decrease in the capacitance of the capacitors can be detected as an abnormality while the power supply is energized.

[0026] (Second embodiment) Hereinafter, the same parts as in the first embodiment will be assigned the same reference numerals and their explanation will be omitted, and only different parts will be explained. As shown in Fig. 2, the noise reduction filter circuit 11 of the second embodiment includes a filter circuit body 12 instead of the filter circuit body 1, and also includes another abnormality detection unit 13. The filter circuit body 12 includes resistance elements R11 to R13 connected between the capacitors C1 to C3 and the common mode coil L1 in the same manner as the resistance elements R1 to R3.

[0027] The abnormality detection unit 13 is configured symmetrically to the abnormality detection unit 5, and a resistance element R14 corresponding to the resistance element R4 is connected between the neutral point of the capacitors C1 to C3 and the resistance elements R11 to R13. The abnormality detection unit 13 detects the potential difference between the neutral point of the capacitors C1 to C3 and the neutral point of the resistance elements R11 to R13 using the resistance element R4. When the detected voltage exceeds a determination value, the collector potential FAULT2 of the transistor Q2 changes from high to low, and an abnormality detection signal is output.

[0028] Although the reference numerals of the diodes constituting the rectifier circuit 3 and the rectifier circuit 6 of the abnormality detection unit 5 shown in FIG. 2 are different from those in the first embodiment, both are essentially the same elements. (Third embodiment)

[0029] 3, the noise reduction filter circuit 14 of the third embodiment has a configuration in which the filter circuit main body 1 and the abnormality detection unit 5 of the noise reduction filter circuit 7 are replaced with a filter circuit main body 1A and an abnormality detection unit 5A, respectively. In the filter circuit main body 1A, the neutral points of the capacitors C4 to C6 are directly connected to the neutral points of the resistor elements R1 to R3. The resistor element R4 of the abnormality detection unit 5A is connected between these neutral points and the ground. In other words, the abnormality detection unit 5A detects the potential difference of the neutral points with respect to the ground potential.

[0030] (Fourth embodiment) 4, the noise reduction filter circuit 15 of the fourth embodiment is obtained by applying the configuration of the third embodiment to the configuration of the second embodiment. An abnormality detection unit 13A is provided for the capacitors C1 to C3 in the filter circuit main body 1A, and a resistance element R14 is connected between the neutral point of the capacitors C1 to C3 and the ground point.

[0031] (Fifth embodiment) 5, a noise reduction filter circuit 16 of the fifth embodiment is obtained by applying the configuration of the noise reduction filter circuit 11 of the second embodiment to a delta-connected commercial AC power supply 17. In a filter circuit main body 12A that replaces the filter circuit main body 12, the capacitor C7 is eliminated.

[0032] (Sixth embodiment) 6, a noise reduction filter circuit 18 of the sixth embodiment includes an abnormality detection unit 19 instead of the abnormality detection unit 5. In the abnormality detection unit 19, the resistive element R4 is removed from the input terminal of the rectifier circuit 6, and instead of the Zener diode ZD1, it is connected in series with the resistive element R5. In addition, an isolation amplifier IC2 is provided instead of the photocoupler U1, and both ends of the capacitor C9 are connected to the input terminal of the isolation amplifier IC2.

[0033] The output terminal of the isolation amplifier IC2 is connected to the A / D conversion input terminal A / D_2 of the MPU (microprocessor unit) IC1. The MPU IC1 also has another A / D conversion input terminal A / D_1. On the input side of the inverter circuit 4, a series circuit of resistor elements R8 and R9 is connected in parallel to a capacitor C8. The input terminal A / D_1 is connected to the common connection point of the resistor elements R8 and R9. The voltage input to the input terminals A / D_1 and A / D_2 is A / D converted by the A / D converter built into the MPU IC1.

[0034] The MPU_IC1 compares the voltage obtained by dividing the DC power supply voltage input to the inverter circuit 4 with the potential difference at the neutral point input to the isolation amplifier IC2, thereby allowing the capacitance reduction judgment value of the capacitor to be determined arbitrarily.

[0035] Normally, the rated voltage of a capacitor is set to a value equal to or greater than the voltage applied to the capacitor at the maximum value, including fluctuations in the rated power supply voltage of the equipment. Therefore, the detection voltage threshold is: (Capacitor rated voltage standard judgment value) ≥ (Device maximum rated voltage standard judgment value) ≧ (Power supply voltage standard judgment value during actual use) Therefore, by detecting the actual connected power supply voltage when the power is turned on or while the device is running, and using this detected power supply voltage value as the reference, it becomes possible to more accurately determine whether the capacitor has decreased in capacitance.

[0036] (Other embodiments) In the configurations of the first to fourth embodiments, the capacitor C7 may be omitted. The sixth embodiment may be applied to the second to fifth embodiments. The common mode coil L1 may be used as needed. The load is not limited to the inverter circuit 4, but may be any circuit or device that generates noise.

[0037] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0038] In the drawings, 1 and 1A indicate the filter circuit body, 2 indicates a three-phase AC power supply, 5 and 5A indicate an abnormality detection unit, 7 indicates a noise reduction filter circuit, 11 indicates a noise reduction filter circuit, 12 indicates the filter circuit body, 13 and 13A indicate an abnormality detection unit, 14 to 16 indicate noise reduction filter circuits, C1 to C6 indicate capacitors, and R1 to R3 and R11 to R13 indicate resistive elements.

Claims

1. It is connected between a three-phase AC power supply and a load device, three capacitors each having one end connected to a common terminal and the other end connected to each phase of the three-phase AC power supply; three resistance elements each having one end connected to a common terminal and the other end connected to each of the phases of the three-phase AC power supply; and an abnormality detection unit that detects an abnormality when a potential difference between a common connection point of the three capacitors and a common connection point of the three resistor elements exceeds a determination value.

2. It is connected between a three-phase AC power supply and a load device, three capacitors each having one end connected to a common terminal and the other end connected to each phase of the three-phase AC power supply; a noise reduction filter circuit including an abnormality detection unit that detects an abnormality when a potential difference between a common connection point of the three capacitors and a ground potential exceeds a determination value.

3. 3. The noise reduction filter circuit according to claim 1, wherein the judgment value is set based on the rated voltage of the capacitor.

4. 3. The noise reduction filter circuit according to claim 1, wherein the judgment value is set based on the rated voltage of the load device.

5. When the load device includes a voltage detection unit that detects the voltage of the three-phase AC power supply, 3. The noise reduction filter circuit according to claim 1, wherein the judgment value is set based on the voltage detected by the voltage detection section.

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