JP2015023785A - Power conversion device and air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress harmonic current with a simple circuit and suppress increase of the cost of a device.SOLUTION: A power conversion device 4 for converting three-phase AC power of a three-phase AC power source 2 is configured to have a three-phase diode rectifying circuit 30 for the three-phase AC power to full-wave rectification, phase advancing capacitors 40A to 40B and in-series reactors 42A to 42C which are provided to the respective phases at the input side of the three-phase diode rectifying circuit 30, and a one-stone type boosting chopper circuit 34 having one switching element 50 which is provided at the output side of the three-phase diode rectifying circuit 30 and outputs the DC power of a predetermined voltage.

Description

  The present invention relates to a power conversion technique for converting three-phase AC power of a three-phase AC power source into DC power, and more particularly to a technique for suppressing harmonic current.

  A power conversion device having a rectifier circuit that converts three-phase AC power of a commercial three-phase AC power source into DC power is known, and various devices for consumer use or industrial use (hereinafter referred to as “load devices”). It is widely used as a power source. As the rectifier circuit, a circuit constituted by a diode is generally used. However, there is a concern that a circuit including a semiconductor element such as a diode generates many harmonic currents and adversely affects the load device. For this reason, in recent years, harmonic regulations have been established in Japan, China, Europe, etc., including harmonic regulations by the IEC (International Electrotechnical Commission).

  In the field of power conversion, as a technique for suppressing harmonic current, a technique using a three-phase PWM converter including six semiconductor switches (for example, IGBT) and a diode for a rectifier circuit is known (for example, a patent). Reference 1). In recent years, as a three-phase PWM converter, a general-purpose converter, a drive circuit that drives the converter, and a so-called intelligent power module (IPM) that incorporates a self-protection circuit that protects a semiconductor switch from abnormal operation of the converter, etc. Packaged devices are being developed. By mounting on this IPM power converter, a countermeasure against harmonic current can be taken.

JP 2013-110785 A

However, since the IPM requires a large number of semiconductor switches and diodes, the cost of the apparatus is greatly increased, and since it is necessary to control many semiconductor switches, the control of the IPM is complicated. There is a problem.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a power conversion device and an air conditioner that can suppress harmonic current with a simple circuit and suppress an increase in cost of the device. And

  In order to achieve the above object, the present invention is a power converter that converts three-phase AC power of a three-phase AC power source into DC power, and a three-phase rectifier circuit that full-wave rectifies the three-phase AC power; A phase advance capacitor and a reactor provided in each phase on the input side of the three-phase rectifier circuit, and one switching element provided on the output side of the three-phase rectifier circuit and outputting the DC power of a predetermined voltage And a one-step boost chopper circuit.

  The present invention further includes a control circuit for controlling the switching duty of the switching element of the step-up chopper circuit based on the output current of the DC power or the input current of the three-phase AC power. It is characterized by.

  In order to achieve the above object, the present invention includes the above-described power conversion device, and a DC motor that operates by DC power of the power conversion device to drive a compressor. I will provide a.

  According to the present invention, the step-up chopper circuit is provided on the output side of the three-phase rectifier circuit, and the harmonic current is suppressed by controlling the switching element of the step-up chopper circuit. Thereby, compared with the conventional structure which rectifies the three-phase alternating current power of a three-phase alternating current power supply using IPM, the number of switching elements can be reduced and a high frequency current can fully be suppressed, restraining apparatus cost.

It is a schematic block diagram of the air conditioning apparatus which concerns on 1st Embodiment of this invention. It is a flowchart which shows the control action of a control circuit. It is a figure which shows an example of the input current waveform of three-phase alternating current power, (A) shows the case where the duty control based on a control table is shown, (B) fixed the duty without performing the duty control based on a control table Show the case. It is a schematic block diagram of the air conditioning apparatus which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the control action of a control circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
Drawing 1 is a schematic structure figure of air harmony device 1 concerning this embodiment.
The air conditioner 1 is operated by a power converter 4 that receives three-phase AC power supplied from a three-phase AC power supply 2 and converts the power into DC power and outputs the DC power, and DC power supplied from the power converter 4. The refrigeration system 6 is provided.
The refrigeration system 6 is connected by a refrigerant pipe 26 so that the refrigerant compressor 8, the four-way valve 10, the outdoor heat exchanger 12, the expansion valve 14, and the indoor heat exchanger 20 constitute a refrigeration circuit 21 that circulates the refrigerant. ing. The outdoor heat exchanger 12 and the indoor heat exchanger 20 are provided with an outdoor fan 16 and an indoor fan 22 for promoting heat exchange, respectively.
In the refrigeration system 6, the compressor 8 includes a compressor drive motor 28. The compressor drive motor 28 is a DC (direct current) motor and operates by receiving direct current power supplied from the power converter 4. The compressor drive motor 28 may be an AC motor instead of a DC motor. In this case, an inverter circuit (DC-AC conversion circuit) is provided between the power converter 4 and the compressor drive motor 28. Is provided.

The three-phase AC power source 2 is a commercial power source that supplies three-phase AC power, and the voltage and frequency of the three-phase AC power vary from country to country. For example, in Japan, the three-phase AC power has a voltage of 200 V and a frequency of 50 Hz or 60 Hz. In China, the voltage is 380 V and the frequency is 50 Hz. In the United States, the voltage is 230 V and the frequency is 60 Hz. .
The electric / electronic components of each part described below of the power conversion device 4 are selected so as to conform to at least the voltage and frequency of the three-phase AC power source 2 in the country of use.

The power conversion device 4 is installed in an outdoor unit (not shown) together with the compressor 8 and the outdoor heat exchanger 12 of the refrigeration system 6, and is roughly divided into three-phase diode rectifier circuits 30 as shown in FIG. A power factor correction circuit 32, a boost chopper circuit 34, and a control circuit 36.
The three-phase diode rectifier circuit 30 is a three-phase full-bridge type full-wave rectifier circuit composed of six diode elements.

  The power factor correction circuit 32 is connected to the input side (that is, the power supply side) of the three-phase diode rectifier circuit 30 and is a circuit for improving the power factor. Specifically, the power factor correction circuit 32 includes phase advance capacitors 40 </ b> A to 40 </ b> C that provide a leading power factor in each phase of the three-phase AC power supply 2 in order to bring the power factor at the power receiving point close to 100%. . In the power factor correction circuit 32, these phase advance capacitors 40 </ b> A to 40 </ b> C are connected to the electric circuit of each phase by a so-called Y-type connection (also called a star type). Further, the power factor improving circuit 32 is arranged in front of the phase advance capacitors 40A to 40C in order to prevent the phase advance capacitors 40A to 40C from increasing the harmonic components of the electric circuit of each phase and increasing the waveform distortion. Are provided with series reactors 42A to 42C.

  The step-up chopper circuit 34 is a monolithic step-up type chopper circuit connected to the output side (that is, the load side) of the three-phase diode rectifier circuit 30. That is, the step-up chopper circuit 34 includes a choke coil 48, a switching element 50, a diode 52, and a capacitor 54, and charges are accumulated in the capacitor 54 when the switching element 50 is turned on / off at high speed. The voltage across the capacitor 54 is output to the refrigeration system 6 as the DC voltage of the power converter 4. In the step-up chopper circuit 34, an IGBT as an example of a power semiconductor element is used for the switching element 50.

  The control circuit 36 outputs a gate drive signal Ca to the gate terminal 50G of the switching element 50 to control the on / off of the switching element 50. With this control, the output voltage of the capacitor 54 is maintained constant, and the harmonics are controlled. Wave current suppression is performed.

  More specifically, in the step-up chopper circuit 34, the increase / decrease of the reactor current Ia flowing through the choke coil 48 is controlled by the ON time and the OFF time of the switching element 50. That is, even when the harmonic current is included in the input current of the three-phase AC power, the reactor current Ia is in phase with the output voltage Va of the three-phase diode rectifier circuit 30 by the on / off control of the switching element 50. The waveform can be as follows. As a result, the waveform and phase of the input current of the three-phase AC power are shaped, the harmonic current is suppressed, and the power factor is further improved.

In the power conversion device 4, a current sensor 60 that detects an input current and outputs an input current detection signal Da to the control circuit 36 is provided in the electric circuit of any phase on the input side of the power factor correction circuit 32. .
On the other hand, the control circuit 36 stores in advance a control table 62 in which the current value of the input current and the on / off duty of the switching element 50 are associated with each other, and is based on the input current detection signal Da and the control table 62. The on / off of the switching element 50 is controlled.
The control table 62 is a data table in which the current value of the input current, the waveform of the input current, and the duty for shaping the phase are associated in advance in the power conversion device 4. Switching is performed according to the control table 62. By controlling the element 50, the harmonic current is suppressed.

FIG. 2 is a flowchart showing the control operation of the control circuit 36.
In detail, the control circuit 36 reads the current value of the input current based on the input current detection signal Da from the current sensor 60 with the start of the operation of the power converter 4 (step Sa1). The duty of the switching element 50 is determined with reference to the control table 62 (step Sa2). Based on the duty, the control circuit 36 outputs a gate drive signal Ca to the switching element 50 to control on / off of the switching element 50 (step Sa3). Then, the control circuit 36 performs feedback control by returning the processing procedure to step Sa1.

FIG. 3 is a diagram illustrating an example of an input current waveform of three-phase AC power. FIG. 3A illustrates a case where duty control based on the control table 62 is performed, and FIG. The case where the duty is fixed without control is shown.
As shown in FIG. 3B, when the control based on the control table 62 is not performed, the input current waveform includes a noticeable distortion X due to a high frequency component. On the other hand, as shown in FIG. 3A, when the control based on the control table 62 is performed, it can be seen that the distortion X is eliminated and the high-frequency current is sufficiently suppressed.

As described above, according to the present embodiment, the step-up chopper circuit 34 is provided on the output side of the three-phase diode rectifier circuit 30 and the harmonic current is suppressed by controlling the switching element 50 of the step-up chopper circuit 34. Thereby, compared with the conventional structure which rectifies the three-phase alternating current power of the three-phase alternating current power supply 2 using IPM, the number of the switching elements 50 can be reduced and the high frequency current can be sufficiently suppressed while suppressing the device cost. .
In particular, when the boost chopper circuit 34 is of a single stone type using one switching element 50, the device cost can be sufficiently suppressed.

In addition, since the boost chopper circuit 34 is configured to suppress the high-frequency current, the phase-advancing capacitors 40A to 40C provided on the input side of the three-phase diode rectifier circuit 30 can have small capacities. .
More specifically, there is a technique for suppressing a harmonic current contained in the three-phase AC power by providing a passive filter including a phase advance capacitor and a reactor on the input side of the three-phase diode rectifier circuit 30. Compared to this technology, according to the power conversion device 4 of the present embodiment, the capacity of the phase advance capacitors 40A to 40C can be reduced to about 1/10, and a very small and lightweight device can be realized.

[Second Embodiment]
FIG. 4 is a schematic configuration diagram of an air-conditioning apparatus 100 according to the second embodiment of the present invention. In addition, in the same figure, about the member demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.
As shown in the figure, in the air conditioner 100, the power conversion device 104 includes a voltage detection unit 170 instead of the current sensor 60, and the control circuit 136 includes a switching element based on the output of the voltage detection unit 170. The configuration is greatly different from that of the first embodiment in that 50 is controlled.

  The voltage detection unit 170 is provided at the output stage of the step-up chopper circuit 34, detects the output voltage (that is, the voltage across the capacitor 54), and outputs the output voltage detection signal Db to the control circuit 136. Based on the output voltage detection signal Db, the control circuit 136 feedback-controls the duty of the switching element 50 so that the output voltage of the power conversion device 4 is maintained constant.

That is, as shown in FIG. 5, the control circuit 136 reads the output voltage of the power conversion device 4 based on the output voltage detection signal Db (step Sb1), and is the target value of the output voltage of the power conversion device 4. Based on the difference (deviation) between the command voltage and the output voltage, the duty of the switching element 50 is determined so as to cancel this difference (step Sb2).
Next, the control circuit 136 controls the on / off of the switching element 50 by outputting the gate drive signal Ca to the switching element 50 based on the duty (step Sb3), and returns the processing procedure to step Sb1. .
By such control, the output voltage is maintained at the command voltage, and the output voltage is stably maintained constant.

  The harmonic current included in the input current of the three-phase AC power is also suppressed by the control shown in FIG.

  Thus, according to the present embodiment, as in the first embodiment, the high-frequency current can be sufficiently suppressed while suppressing the device cost, and the phase advance capacitor 40A provided on the input side of the three-phase diode rectifier circuit 30 The capacity of ˜40C can be reduced.

  The above-described embodiments are merely illustrative of one aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.

  For example, in the first embodiment described above, as in the second embodiment, the output voltage of the power conversion device 4 is detected, the output voltage does not fluctuate, and the harmonic current is suppressed. The control circuit 36 may control the duty of the switching element 50 based on the input current and the output voltage.

  For example, in the above-described embodiment, the case where the DC power output from the power converters 4 and 104 according to the present invention is used to drive the compressor drive motor 28 of the air-conditioning apparatuses 1 and 100 is illustrated. It can be used to drive any load device.

DESCRIPTION OF SYMBOLS 1,100 Air conditioning apparatus 2 Three-phase alternating current power supply 4,104 Power converter 6 Refrigeration system 8 Compressor 21 Refrigeration circuit 28 Compressor drive motor 30 Three-phase diode rectifier circuit (three-phase rectifier circuit)
32 Power factor correction circuit 34 Boost chopper circuit 36, 136 Control circuit 40A to 40C Phase advance capacitor 42A to 42C Series reactor (reactor)
48 choke coil 50 switching element 50G gate terminal 52 diode 54 capacitor 60 current sensor 62 control table 170 voltage detection unit Ca gate drive signal Da input current detection signal Db output voltage detection signal

Claims (3)

A power converter that converts three-phase AC power of a three-phase AC power source into DC power,
A three-phase rectifier circuit for full-wave rectification of the three-phase AC power;
A phase advance capacitor provided in each phase on the input side of the three-phase rectifier circuit, and a reactor;
A one-stone boost chopper circuit having one switching element that is provided on the output side of the three-phase rectifier circuit and outputs the DC power of a predetermined voltage;
A power conversion device comprising: The power according to claim 1, further comprising a control circuit that controls a switching duty of the switching element of the boost chopper circuit based on the output current of the DC power or the input current of the three-phase AC power. Conversion device. The power conversion device according to claim 1 or 2,
A DC motor that operates by the DC power of the power converter and drives the compressor;
An air conditioner comprising:

Images