JP2018113838A - Deterioration detector of y capacitor for noise reduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration detector of a Y capacitor for noise reduction of a PWM converter.SOLUTION: A Y capacitor consists of first through third capacitors (51, 52, 53), which are interposed, respectively, in branch lines (55, 56, 57) led out from the power lines of R phase, S phase and T phase and Y-connected to each other at a first neutral point (58). A deterioration detector (60) is constituted of first through third resistors (61, 62, 63) having the same resistance value, a fourth resistor (64), and voltage detection means (66). The first through third resistors (61, 62, 63) are interposed, respectively, in branch lines (67, 68, 69) led out from the power lines of the R phase, S phase and T phase and Y-connected to each other at a second neutral point (70). The fourth resistor (64) is provided between the first neutral point (58) and the second neutral point (70), and the voltage difference of the opposite ends is detected by the voltage detection means (66). A voltage difference is detected when the first through third capacitors (51, 52, 53) deteriorate.SELECTED DRAWING: Figure 1

Description

  The present invention converts a three-phase AC power supplied from the outside into a DC power, generates a desired three-phase AC power from the DC power, and supplies it to an AC motor. In a power conversion device in which a converter that converts three-phase AC power from the outside into a DC voltage is a PWM converter, a deterioration detection that detects the deterioration of a noise reduction Y capacitor provided on the input side of the PWM converter It relates to the device.

  A machine in which each device is driven by an AC motor such as a servomotor, such as an electric injection molding machine, is provided with a power converter that generates desired three-phase AC power and supplies it to the AC motor. ing. The power converter is roughly configured from a converter that converts three-phase AC power supplied from a factory into DC power, and an inverter that generates three-phase AC power having a desired frequency and current from the DC power. Some converters include a diode rectifier circuit including only a diode, but the diode rectifier circuit cannot return the regenerative power recovered from the AC motor to the factory side. Moreover, the voltage of the DC power to be converted is determined by the voltage of the three-phase AC power supplied from the factory. In contrast, the PWM converter can return the regenerative power to the factory side, and the PWM converter with a reactor on the input side boosts the voltage of the three-phase AC power supplied from the factory and converts it to DC power Can also be better.

JP 2002-84757 A JP 2003-169495 A

  By the way, a PWM converter that converts three-phase AC power into DC power is composed of six IGBTs and six diodes. When these IGBTs are switched, noise is generated, and noise is generated in the power line of the three-phase AC power. Will get on. The noise includes a so-called normal mode or differential mode noise and a so-called common mode noise. The power line of three-phase AC power consists of three, that is, three phases, but the noise in the normal mode is noise that is conducted in any two of these three phases with one being the forward path and the other being the return path. Conducts in a relatively opposite direction. In contrast, common mode noise is noise that is conducted relatively to the ground, and is conducted in the same direction in the three-phase power line. The PWM converter is provided with a normal mode noise reduction capacitor, that is, an X capacitor, and a common mode noise reduction capacitor, that is, a Y capacitor, on a power line of three-phase AC power on the input side. For example, as described in FIG. 1 of Patent Document 1, the X capacitor includes a total of three capacitors in which one capacitor is provided between any two phases in a three-phase power line of three-phase AC power. By the capacitors connecting the two phases, noise conducted in the opposite direction between the two phases is reduced. On the other hand, the Y capacitor is connected to a chassis such as a metal frame, that is, a ground via one capacitor, as shown in Patent Document 2, for example, as a high frequency filter. That is, it consists of a total of three capacitors, each having one capacitor between each phase and ground. Noise transmitted in common on the three-phase power line to the ground is reduced by these three capacitors.

  In this way, the PWM converter is provided with the X capacitor and the Y capacitor on the power line of the three-phase AC power on the input side, so that both normal mode noise and common mode noise riding on the power line can be reduced. Therefore, the power converter provided with the PWM converter does not have a possibility of becoming a noise generation source and can be used with confidence. However, there are also problems to be solved. Specifically, the capacitor is deteriorated. Capacitors deteriorate with long-term use, but when they are deteriorated, noise cannot be reduced appropriately. Furthermore, when the capacitor is deteriorated, there is a risk of ignition due to heat generation due to dielectric breakdown. There is no method for properly detecting such deterioration of the capacitor.

  An object of the present invention is to provide a deterioration detection device that detects deterioration of a Y capacitor among noise reduction capacitors provided on the input side of a PWM converter of a power conversion device including a PWM converter.

  In order to achieve the above object, the present invention is configured as a Y capacitor deterioration detection device for noise reduction provided on the input power line side of a PWM converter. The Y capacitor is composed of first to third capacitors having the same capacitance, and the first to third capacitors are drawn from the R-phase, S-phase, and T-phase power lines and Y-connected to each other at the first neutral point. Is installed in each branch line. The deterioration detecting device is composed of first to third resistors having the same resistance value, a fourth resistor, and voltage detecting means. The first to third resistors are drawn from the R-phase, S-phase, and T-phase power lines, and are interposed in the branch lines Y-connected to each other at the second neutral point. The fourth resistor is interposed in a connection line connecting the first neutral point and the second neutral point. The voltage detecting means is configured to detect a voltage difference between both ends of the fourth resistor. If any of the first to third capacitors deteriorates and the potential at the first neutral point moves away from zero, a voltage difference is generated in the fourth resistor. This is detected.

That is, the invention described in claim 1 is a PWM converter that converts three-phase AC power input from three power lines of R phase, S phase, and T phase into DC power, and is provided on the side of the three power lines. A Y capacitor deterioration detecting device for noise reduction, wherein the Y capacitor includes first to third capacitors having the same capacitance, and the first to third capacitors include the R phase, the S phase, The deterioration detection device includes first to third resistances having the same resistance value, a fourth resistance, and a branch line drawn from the T-phase power line and Y-connected to each other at the first neutral point. The first to third resistors are respectively connected to branch lines that are drawn from the R-phase, S-phase, and T-phase power lines and are Y-connected to each other at the second neutral point. And the fourth resistor is the first resistor. A PWM converter, wherein the PWM converter is interposed in a connecting line connecting a sex point and the second neutral point, and the voltage detection means detects a voltage across the fourth resistor. This is configured as a Y capacitor deterioration detection device.
According to a second aspect of the present invention, in the deterioration detection apparatus according to the first aspect, the PWM converter is a PWM converter provided in an electric injection molding machine, and the deterioration of the Y capacitor of the PWM converter is characterized in that Configured as a detection device.

  The present invention is a PWM converter that converts three-phase AC power input from three power lines of R phase, S phase, and T phase into DC power, and is provided for noise reduction Y provided on the three power line sides. It is configured as a capacitor deterioration detection device. The Y capacitor is composed of first to third capacitors having the same capacitance, and the first to third capacitors are drawn from the R-phase, S-phase, and T-phase power lines and Y-connected to each other at the first neutral point. Is installed in each branch line. According to the present invention, the deterioration detecting device includes first to third resistors having the same resistance value, a fourth resistor, and voltage detecting means, and the first to third resistors are R-phase, S-phase, and T-phase. The fourth resistor is connected to the connecting line connecting the first neutral point and the second neutral point through the branch lines drawn from the power line and Y-connected to each other at the second neutral point. The voltage detecting means detects the voltage across the fourth resistor. First, the Y capacitor is a general Y capacitor, but since the first to third capacitors have the same capacitance, the potential of the first neutral point should be close to zero. Also in the deterioration detection device, the first to third resistors have the same resistance value, so the potential of the second neutral point should be close to zero. As a result, no current normally flows through the fourth resistor connecting the first and second neutral points, and no voltage difference is detected by the voltage detection means. However, when one or two of the first to third capacitors deteriorate and the capacitance changes, the potential at the first neutral point does not become zero. That is, it has a predetermined potential. Since the potential of the second neutral point is near zero, a current flows through the fourth resistor connecting the first and second neutral points. Then, the voltage is detected by the voltage detection means. In this way, the deterioration detection apparatus of the present invention can reliably detect the deterioration of the Y capacitor provided in the PWM converter. In addition, since the deterioration detecting device is composed of only the first to fourth resistors and the voltage detecting means, there is an effect that it can be provided at a low cost.

It is a circuit diagram which shows the PWM converter which concerns on this Embodiment, a Y capacitor, and the deterioration detection apparatus of a Y capacitor.

  Embodiments of the present invention will be described below. The power conversion apparatus 1 according to the present embodiment is provided in an electric injection molding machine, and an AC motor that drives a screw of the injection apparatus, a mold clamping mechanism of the mold clamping apparatus, and the like is a three-phase AC generated by the power conversion apparatus 1. It is driven by electric power. As shown in FIG. 1, a power converter 1 according to the present embodiment includes a PWM converter 3 that converts three-phase AC power supplied from a factory to an electric injection molding machine into DC power, and an AC motor 5. And an inverter 6 that generates three-phase AC power to be supplied to the inverter. The PWM converter 3 is connected to the three-phase power lines R, S, T of the R phase, S phase, and T phase via the electromagnetic switch 4 on the input side, and connected to the DC power lines P, N on the output side. Has been. DC power from the DC power lines P and N is supplied to the inverter 6. Although the inverter 6 is shown in a simplified manner in the figure, it is composed of six IGBTs and six diodes as is well known in the art. Six IGBTs are switched to generate three-phase AC power having an arbitrary frequency and an arbitrary current from the DC power, and supplied to the AC motor 5. A plurality of such inverters 6 and AC motors 5 are connected to the DC power lines P and N, but only one set is shown in the figure. The DC power lines P and N are provided with a smoothing capacitor 8 that smoothes the DC voltage.

  The PWM converter 3 has a conventionally known structure. That is, the first to sixth diodes 11, 12,... And the first to sixth IGBTs 21, 22,. The three-phase AC power supplied from the input-side power lines R, S, and T by the action of the first to sixth diodes 11, 12,... Is converted into DC power and supplied to the output-side DC power lines P and N. However, the regenerative power regenerated from the AC motor 5 via the inverter 6 can be regenerated to the power lines R, S, T as three-phase AC power by switching the first to sixth IGBTs 21, 22,. . By the way, in the present embodiment, first to third reactors 31, 32, and 33 are provided on the input power lines R, S, and T of the PWM converter 3. Therefore, when the three-phase AC power is converted to DC power, the first to sixth IGBTs 21, 22,... Are appropriately switched to form a chopper circuit, and the DC power can be boosted and supplied to the DC power lines P and N. It is like that.

  Since the power conversion device 1 according to the present embodiment includes the PWM converter 3, high-frequency noise is generated by switching of the first to sixth IGBTs 21, 22,. In order to reduce high-frequency noise, so-called X capacitors 40 and Y capacitors 50 are provided on the power lines S, T, and R on the input side.

  The X capacitor 40 includes fourth to sixth capacitors 41, 42, and 43 having the same capacitance. Each capacitor 41, 42, 43 is interposed between the R phase and the S phase, the S phase and the T phase, and the T phase and the S phase. The noise in the normal mode that relatively transmits between any two phases is reduced by the fourth to sixth capacitors 41, 42, and 43.

  As is well known, the Y capacitor 50 includes first to third capacitors 51, 52, and 53 having the same capacitance. The first capacitor 51 is a branch line 55 drawn from the R-phase power line R, the second capacitor 52 is a branch line 56 drawn from the S-phase power line S, and the third capacitor 53 is a T-phase power line S. These branch lines 55, 56, 57 are Y-connected at a first neutral point 58. Since the first to third capacitors 51, 52, and 53 have the same capacitance, the first neutral point 58 has a potential near zero. Although not shown in the drawing, the first neutral point 58 is connected to a casing of the electric injection molding machine, that is, a ground via a predetermined capacitor or resistor. Therefore, the common mode noise transmitted relatively to the ground of the power lines R, S, T is reduced by the first to third capacitors 51, 52, 53.

  The deterioration detection device 60 according to the present embodiment is provided in association with the Y capacitor 50 and has first to third resistors 61, 62, 63, a fourth resistor 64, and a voltage detector 66 having the same resistance value. It consists of and. The first to third resistors 61, 62, and 63 are a branch line 67 drawn from the R-phase power line R, a branch line 68 drawn from the S-phase power line S, and a branch line 69 drawn from the T-phase power line T. The branch lines 67, 68, and 69 are Y-connected at the second neutral point 70. The fourth resistor 64 is interposed in a connection line 71 that connects the first neutral point 58 of the Y capacitor 50 and the second neutral point 70, and the voltage detector 66 is connected to the fourth resistor 64. A voltage difference between both ends of the resistor 64 is detected. Although not shown in the figure, the voltage detector 66 is connected to the controller of the electric injection molding machine.

  Since the first to third resistors 61, 62, and 63 have the same resistance value, the potential of the second neutral point 70 is near zero. As described above, since the potential of the first neutral point 58 is usually near zero, almost no current flows through the fourth resistor 64. That is, the voltage detector 66 hardly detects a voltage difference. However, if one or two of the first to third capacitors 51, 52, and 53 of the Y capacitor 50 deteriorate and the capacitance changes, the potential of the first neutral point 58 is zero. Get away from. That is, a predetermined potential is generated. As a result, a current flows through the fourth resistor 64, and a voltage difference is detected by the voltage detector 66. The controller of the electric injection molding machine determines that the Y capacitor 50 has deteriorated.

1 Power converter
3 PWM converter
DESCRIPTION OF SYMBOLS 4 Electromagnetic switch 5 AC motor 6 Inverter 8 Smoothing capacitor 11, 12, ... 1st-6th diode 21,22, ... 1st-6th IGBT
31, 32, ... 1st to 3rd reactors 40 X capacitors 41, 42, 43 4th to 6th capacitors 50 Y capacitors 51, 52, 53 1st to 3rd capacitors 58 First neutral point 60 Deterioration detection device 61, 62, 63 First to third resistors 64 Fourth resistor 66 Voltage detector 70 Second neutral point 71 Connection line

Claims (2)

In a PWM converter that converts three-phase AC power input from three R-phase, S-phase, and T-phase power lines into DC power, degradation of a Y capacitor for noise reduction provided on the three power line sides A detection device,
The Y capacitor is composed of first to third capacitors having the same capacitance, and the first to third capacitors are drawn from the R-phase, S-phase, and T-phase power lines and are mutually connected at the first neutral point. It is installed in each Y-connected branch line,
The deterioration detection device includes first to third resistances having the same resistance value, a fourth resistance, and voltage detection means. The first to third resistances are derived from the R-phase, S-phase, and T-phase power lines. The fourth resistance is connected to a connecting line connecting the first neutral point and the second neutral point, and is inserted into each of the branch lines Y-connected to each other at the second neutral point. An apparatus for detecting deterioration of a Y capacitor of a PWM converter, wherein the voltage detection means is arranged to detect a voltage across the fourth resistor.   2. The deterioration detection apparatus according to claim 1, wherein the PWM converter is a PWM converter provided in an electric injection molding machine.

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