JP2020065409A - Leakage current reduction circuit - Google Patents

Abstract

To provide a small size leakage current reduction circuit capable of generating an anti-phase waveform requiring no extra complicated controller at low cost.SOLUTION: The leakage current reduction circuit includes: a power supply filter circuit to which a power supply voltage is input from an AC power supply; a rectification and boost converter that is connected to the output side of the power supply filter circuit; and an inverter circuit connected to the output side of the rectification and boost converter. An inverter noise detection coil is disposed between the power supply filter circuit and the rectification and boost converter at the output side of the coil and elements with different polarities are placed one above the other to cancel the leakage current using inverter noises detected by the coil.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power conversion device including a power conversion circuit for driving a load device or system interconnection of power supplied from a power source or a generator.

  Conventionally, in a power conversion circuit such as an inverter, a leakage current is generated due to a parasitic capacitance of a motor or a compressor and a Y capacitor of an EMC countermeasure filter circuit during semiconductor switching. Therefore, as a countermeasure, a switching unit that applies a voltage to the load leakage impedance equivalent impedance, a driving unit that drives the switching unit, and a control unit that generates a switching pattern are provided, and are synchronized with the AC voltage generated by the inverter and reverse. There has been one that generates a phase voltage to reduce the leakage current.

JP, 9-233837, A

  However, in the above-mentioned conventional configuration, it is necessary to additionally have a complicated control unit in order to generate the waveform of the opposite phase, which leads to an increase in cost and size of the device.

  Further, if the Y capacitor capacity is reduced to reduce the leakage current, the EMC characteristics such as the noise terminal voltage are deteriorated, so the inductance value of the common mode filter must be increased, which increases the circuit volume and increases the cost. There was a problem that caused it.

  The present invention is to solve the above-mentioned conventional problems. By detecting inverter noise and actively flowing a cancellation current having a reverse phase to the leakage current, the leakage current of the leakage current can be reduced without reducing the Y capacitor capacity for EMC countermeasures. Only reduction is possible.

  Insert a 3-phase common mode coil between the filter circuit and the converter for rectification, detect inverter noise in the 1-phase that is not connected to the power supply line, drive the device by the noise current, and cancel the leakage current and the opposite phase. To reduce leakage current. The switching element biases the PN voltage of the inverter, and elements having different polarities are arranged above and below. As a result, the switching element is driven at the timing of the inverter noise detected by the three-phase common mode filter, and the cancel current in the opposite direction to the leak current can flow, and the leak current can be reduced. A freewheeling diode is connected in parallel with the switching element, and a DC cut capacitor is arranged on the line output from the switching element to stabilize the reference voltage.

  By actively flowing the leakage current and the cancel current having a phase opposite to the leakage current, it is possible to reduce only the leakage current without reducing the Y capacitor capacity for EMC countermeasures.

Diagram showing the general power conversion circuit configuration The figure which shows the circuit structure in embodiment of this invention. Circuit connection diagram on circuit of three-phase common mode filter, switching element, freewheeling diode, and DC-cutting capacitor according to the embodiment of the present invention The figure showing the gate resistance switching timing of the switching element in the embodiment of the invention. The figure showing the timing of switching the drive pattern of the switching element in the embodiment of the present invention.

  The first aspect of the present invention can reduce the leakage current by detecting the inverter noise that is a factor of the leakage current, arranging the elements having different polarities vertically and injecting the cancel current having the opposite phase to the leakage current. .

  According to a second aspect of the present invention, the power supply filter circuit has a circuit configuration of an LCL filter, the number of phases of the common mode coil of the subsequent stage is increased by one phase from the common mode coil of the previous stage, and the inverter noise is detected in that phase. With this, in addition to the effect of reducing the leakage current, the EMC filter performance can be further improved by using the LCL filter configuration as compared with the commonly applied LC filter.

  The third aspect of the present invention can improve the power conversion efficiency when the leakage current value is low by switching the gate resistance by the selection circuit according to the leakage current value.

  The fourth aspect of the present invention can improve the power conversion efficiency when the leakage current value is low by switching the drive pattern of the switching element according to the leakage current value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment.

(Embodiment 1)
FIG. 1 is a diagram showing a conventional general power conversion circuit configuration.
The leakage current is caused by the switching noise of the inverter shown in 4. The Y capacitor of the filter circuit inserted for the purpose of noise reduction shown in 6 and the parasitic capacitance of the load such as the motor and the compressor shown in 7 indicate the electric current shown in 8 Electric current flows into the equipment casing.
A circuit configuration of the present invention for reducing this leakage current is shown in FIG.
In the present invention, as shown in FIG. 2, a three-phase common mode coil, which is 9, is inserted between the filter circuit of 2 and the converter of 3. Inverter noise is detected in one phase of the three-phase common mode coil that is not connected to the power supply line, the device is driven by the noise current, and the leakage current and the opposite phase cancel current are inserted to reduce the leakage current. To do.

(Embodiment 2)
Although the circuit configuration of the present invention is shown in FIG. 2 in the case of a single-phase power supply, it is not limited to the single-phase power supply. In the case of a 3-phase power source, the 3-phase common mode coil shown in 9 has a 4-phase common mode coil configuration.

(Embodiment 3)
FIG. 3 is a circuit diagram of the active cancel circuit shown in FIG. 2 according to the first embodiment. The switching elements 18 and 19 bias the PN voltage of the inverter, and elements having different polarities are arranged above and below. Further, the free wheeling diodes 20 and 21 are connected in parallel with the switching element, and the withstand voltage of the switching element and the free wheeling diode is secured to be equal to or higher than the PN voltage of the inverter. A DC cut capacitor 22 is arranged on the line output from the switching element to stabilize the reference voltage. However, this capacitor 22 is not necessarily required to be installed, and may be removed depending on the electric device to which the present invention is applied.

(Embodiment 4)
The switching elements 18 and 19 in the third embodiment are not limited to bipolar transistors as shown in FIG. The number of turns of the winding, the core material, and the core shape of the three-phase common mode coil shown in 14 are not specified.

(Embodiment 5)
FIG. 4 is a diagram showing the relationship between the leakage current, the losses generated by the switching elements 18 and 19 and the switching of the gate resistance in the first embodiment of the present invention.
The gate resistance value associated with the switching element is set under the condition that the maximum value of the leakage current occurs, but under the condition that the leakage current value is sufficiently small, the gate resistance value is increased to suppress the current value flowing through the switching element. It is possible to reduce the loss.
Since the resistance of the resistor 2 is larger than that of the resistor 1 shown in FIG. 4, and when switching the gate resistance, a hysteresis is set because it corresponds to an instantaneous variation of the leakage current.

(Embodiment 6)
Switching of the gate resistance set in the fifth embodiment is not limited to two types of resistance values as shown in FIG. Depending on the case, it is possible to set switching with any number of resistance values.

(Embodiment 7)
The switching of the gate resistance set in the fifth embodiment can be applied to both the method of setting the gate resistance value of each of the switching elements 18 and 19 shown in FIG. 3 and the method of commonly setting the gate resistance. It is possible.

(Embodiment 8)
FIG. 5 is a diagram showing the relationship between the leakage current, the loss generated by the switching elements 18 and 19 and the drive pattern of the switching elements 18 and 19 in the first embodiment of the present invention. Under the condition that the maximum value of the leakage current occurs, both the switching elements 18 and 19 are driven, but under the condition that the leakage current value is sufficiently small, only one switching element is driven to reduce the loss.

(Embodiment 9)
The switching elements 18 and 19 set in FIG. 3 can be configured with only one of the switching elements, and the switching element of either 18 or 19 can be replaced with a diode.

  As described above, the leakage current reduction circuit according to the present invention can be applied to all products in the consumer and industrial fields that use power conversion equipment.

1 AC power supply or generator 2 Filter circuit 3 Converter or rectifier 4 Inverter 5 Load device or system 6 Filter circuit Y capacitor 7 Parasitic capacitance of load device 8 Frame and casing of electrical equipment 9 Three-phase common mode coil 10 Active cancel circuit 11 Choke Coil of Filter Circuit 12 X Capacitor of Filter Circuit 13 Y Capacitor of Filter Circuit 14 3-Phase Common Mode Coil 15 Rectifying Diode 16 Inverter Switching Element 17 Inverter Return Diode 18 Active Cancel Circuit Upper Switching Element 19 Active Cancel Circuit Lower switching element 20 Active cancellation circuit section Upper side return diode 21 Active cancellation circuit section Lower side return diode 22 DC cut capacitor

Claims (4)

A power supply filter circuit to which a power supply voltage from an AC power supply is input, a rectification and boost converter connected to the output side of the power supply filter circuit, and an inverter circuit connected to the output side of the rectification and boost converter. A circuit, wherein a coil for inverter noise detection is arranged between the power supply filter circuit and the rectifying and boosting converter, and elements having mutually different polarities are vertically arranged on the output side of the coil. A leakage current reduction circuit characterized by canceling leakage current by detected inverter noise. The power supply filter circuit has a circuit configuration of an LCL filter, the number of phases of the common mode coil of the subsequent stage is increased by one phase as compared with the common mode coil of the previous stage, and inverter noise is detected in the phase. The leakage current reduction circuit according to claim 1. 3. The signal part of the element into which a reverse phase cancel current is injected has a resistance for current limitation, and the resistance is changed according to the value of the leakage current. Leakage current reduction circuit described in any one of 4. The element into which a reverse phase cancel current is injected is arranged with elements having different polarities vertically, and the drive pattern of the switching element is switched according to the value of the leakage current. Leakage current reduction circuit described in paragraph

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