WO2011058665A1

WO2011058665A1 - Power conversion device

Info

Publication number: WO2011058665A1
Application number: PCT/JP2010/001355
Authority: WO
Inventors: 船山裕治; 奥山敦; 田村正博; 田村建司; 能登原保夫
Original assignee: 日立アプライアンス株式会社
Priority date: 2009-11-13
Filing date: 2010-03-01
Publication date: 2011-05-19
Also published as: JP2011109741A

Abstract

Unlike diodes, MOS-FETs are characterized by sending current flowing bidirectionally, and thus, MOS-FETs must be controlled to switch on and off with respect to the direction of the supply of electricity. A control method that is applied when using MOS-FETs in rectifier circuits cannot be used, however, when applying MOS-FETs used in rectifier circuits to develop active converters. Another problem arises with the characteristics of circuit elements when the switching frequency is greater than one in a half-period of the power supply voltage of a booster chopper circuit. The purpose of the present invention is achieved by employing super junction structure N-channel MOS-FETs comprising low-on resistance characteristics in the switching elements thereof, wherein the control means controls so as to switch all MOS-FETs on when the AC power supply and the reactor short-circuit and to switch off the MOS-FETs that are connected on the positive terminal side of the AC power supply when short-circuiting the AC power supply and the reactor is not necessary.

Description

Power converter

The present invention provides a rectifier circuit that rectifies an AC power supply, a smoothing circuit that smoothes a pulsating DC voltage after rectification, controls a DC voltage while boosting the smoothed DC voltage, and converts a current waveform of the AC power supply to a harmonic current. The present invention relates to a step-up chopper circuit that performs power factor improvement by shaping so as to suppress, and a power conversion device including the circuit.

As a method for obtaining a DC voltage by rectifying an AC voltage from an AC power supply, a rectifier circuit having a diode bridge structure, a smoothing circuit using a capacitor, and an AC-DC converter circuit in combination of them is generally used. It is. The reason is that the circuit configuration is easy and inexpensive, and it is generally widely used in many electric devices. The diode loss used in this rectifier circuit can be expressed by the product of the forward voltage, which is one of the typical characteristics of the diode, and the current flowing through the diode, and is one of the major loss factors in power conversion. .

One way to reduce this diode loss is to use a MOS-FET instead of a diode. This utilizes the fact that the low on-resistance MOS-FET loss is superior to the diode loss in a region where the current is relatively small. However, MOS-FET is a characteristic that allows current to flow in both directions compared to a diode that allows current to flow only in one direction. Therefore, it is necessary to control MOS-FET on / off depending on whether the AC power supply is positive or negative. It ’s hard. Japanese Patent Application Laid-Open No. 2004-133867 has been developed to solve this problem.

FIG. 9 shows a control circuit described in Patent Document 1. Two of the four diodes constituting the rectifier circuit are replaced with MOS-FETs, and driving means for driving the MOS-FETs and comparison means for sending a control signal to the driving means.

Note that the details of the control method cannot be read from FIG. 9 and will be supplemented from the specification of Patent Document 1 below. As a basic control, all MOS-FETs are controlled to be turned on. Each MOS-FET is controlled to turn off the MOS-FET when the drain potential> the source potential as a result of comparing the drain potential and the source potential.

Since the rectifier circuit using the MOS-FET can be easily controlled in this way, the loss of the rectifier circuit can be reduced.

JP 2007-110869 A

As described above, the conventional rectifier circuit using MOS-FET and its control method are excellent technologies that can reduce power conversion loss. However, with this technology, it is possible to control the DC voltage while boosting the DC voltage, and to develop and apply it to a boost chopper circuit that improves the power factor by shaping the current waveform of the AC power supply to suppress the harmonic current. Can not.

One of the reasons is the control method. In the conventional control, when two MOS-FETs are simultaneously turned on, the power supply is short-circuited through the MOS-FET with an extremely small impedance. Therefore, control is performed so that the two elements do not turn on simultaneously. Since this is a concept limited to only a rectifier circuit, it cannot be used for a boost chopper circuit that is short-circuited through a reactor.

Another reason is that the characteristics of the elements used in the rectifier circuit are not taken into consideration. Although this is also limited to the rectifier circuit as described above, there is no help for it, but it is a boost chopper circuit that short-circuits the power supply via the reactor, and becomes a cathode common when ON / OFF is repeated continuously in the power supply half cycle. If the reverse recovery time of the two diodes is not fast, there arises a problem that when the MOS-FET is turned on, the on-loss of the MOS-FET increases by the reverse recovery time of the diode.

An object of the present invention is to realize a low-loss power converter.

The purpose of the present invention is to
A super junction N-channel MOS-FET having a low on-resistance characteristic is used as the switching element, and the control means turns on all the MOS-FETs when the AC power supply and the reactor are short-circuited, and the AC power supply and the reactor are short-circuited. When unnecessary, it is achieved by controlling the MOS-FET connected to the positive side of the AC power supply to be turned off.

According to the present invention, a low-loss power converter can be realized.

The lineblock diagram showing the power converter of Example 1 of this application. The block diagram showing the power converter device of Example 2 of this application. The block diagram showing the power converter device of Example 3 of this application. The block diagram showing the power converter device of Example 4 of this application. The block diagram showing the power converter device of Example 5 of this application. The simulation figure which modularized the power converter device of Example 6 of this application. The simulation figure which modularized the power converter device of Example 7 of this application. The simulation figure which modularized the power converter device of Example 8 of this application. Conventional example.

Hereinafter, the power converter according to the present invention will be specifically described.

FIG. 1 is a block diagram showing the circuit configuration and control means of the power converter of the present invention. Reference numeral 1 denotes an AC power source that generates an AC voltage, 2 denotes a reactor that contributes to shaping of the current waveform of the AC power source, and boosting of the DC voltage, and 3a, 3b, 3c, and 3d are AC voltage rectifier circuits in which diodes are bridged. The step-up chopper circuit is a circuit that stores energy in the reactor 2 and discharges it to the capacitor 5. 4a and 4b are MOS-FETs that function as switching of the step-up chopper circuit and the rectifying function of the rectifier circuit, 5 is a capacitor that smoothes the pulsating voltage obtained by rectifying the AC voltage and converts it into a DC voltage, and 6 is DC voltage control and high power. Control means for controlling the switching element of the step-up chopper circuit for realizing the rate, 6a and 6b are output signals of the control means, 7 is a direct-current voltage detection means for detecting the direct-current voltage which is the output voltage of the step-up chopper circuit, and 7a is direct current. A voltage signal, 8 is an AC voltage zero cross detecting means for detecting 0 level of the voltage of the AC power supply, and 8a is a voltage signal of two paths over which the AC power supply is placed.

First, a method that is generally widely used for control of power factor improvement using a boost chopper circuit will be briefly described.

The current does not flow unless the AC voltage of the AC power supply 1 is greater than the voltage stored in the smoothing capacitor. This is a known fact as a capacitor input type rectifier circuit. Therefore, in order to allow current to flow at other times, the AC power source 1 is short-circuited through the reactor 2 to widen the current waveform and improve the power factor, and the energy storage effect of the reactor 2 due to the short-circuit current is utilized. The DC voltage is controlled while boosting the DC voltage.

This control is also a widely known technique, and the number of times the AC power source 1 is short-circuited by the reactor 2 in the half cycle of the power source is determined by the priority of items required for the power converter. Is done. The items required here include harmonic current regulation, boost ratio of output voltage of boost chopper circuit to AC power supply voltage, power factor improvement, circuit scale, cost, and the like.

In the following, the operation assuming that the AC voltage of the AC power source 1 as a commercial power source is positive in the half cycle when the power conversion device of FIG. 1 is switched only once in a half cycle of the AC power source 1 will be described.

When the AC power supply 1 and the reactor 2 are short-circuited, the control means 6

outputs output signals

6a and 6b that turn on the operation to the MOS-

FETs

4a and 4b. Further, if it is not necessary to short-circuit the AC power supply 1 and the reactor 2, an output signal 6a for turning off the operation is output only to the MOS-FET 4a.

First, when both are turned on, the MOS-FET 4 (for example, 4b) connected to the negative side can enjoy both effects of the parasitic diode of the MOS-FET 4 and the MOS-FET 4. This is called a synchronous rectification effect. Furthermore, since the diode 3d is also connected in parallel, the element loss due to the current shunting can be reduced.

Next, in the case where only the MOS-FET 4a is controlled to be turned off, this is to turn off the MOS-FET connected to the positive side of the AC power supply 1 which is the control specification of the control means 6. In other words, turning off must be connected to the positive side. That is, the synchronous rectification effect can be obtained by keeping the negative side on.

The determination of whether the MOS-

FETs

4a and 4b are connected to the positive side or the negative side of the AC power source 1 uses the AC voltage zero cross detection means 8 which is indispensable for controlling the step-up chopper circuit. Specifically, when detecting the zero crossing of the AC voltage, the two systems overlaid with the AC power source are compared, and the determination can be made easily by the signal generated there. A simulation diagram is shown in the AC voltage zero cross detection means 8. When the rectangular wave signal generated from the AC voltage is at the HI level, the MOS-FET 4a is on the positive side of the AC power supply 1. Conversely, when the rectangular wave signal is at the LOW level, the MOS-FET 4b is on the positive side of the AC power supply 1. Become the side.

By the series of operations described above, the power conversion device performs switching only once in a half cycle of the AC power supply. When the AC power supply 1 and the reactor 2 are short-circuited, the loss can be reduced by the low ON characteristics of the MOS-

FETs

4a and 4b. Even if the current increases and the two

diodes

3c and 3d are turned on, the MOS-

FETs

4a and 4b Therefore, the loss can be further reduced. Even if it is not necessary to short-circuit the AC power supply 1 and the reactor 2, even if one of the MOS-FETs 4b is turned on and the loss can be reduced due to the low on-characteristic, even if the current increases and one of the diodes 3d is turned on, the MOS -Since the current is shunted by the FET 4b, the loss can be further reduced. These synergistic effects make it possible to reduce the loss of the power converter that achieves both AC-DC conversion and power factor improvement.

FIG. 2 is a block diagram showing the circuit configuration and control means of the power converter according to the present invention. It is assumed that the power converter is continuously turned on and off a plurality of times in a half cycle of the AC power source 1. . Although the operation is the same as that of the first embodiment, the characteristics of the diode are improved. These are the

diodes

9a and 9b, which are changed to the high-speed type with a guaranteed reverse recovery time. This is because, when the MOS-

FETs

4a and 4b are continuously operated, if the reverse recovery time of the

diodes

9a and 9b is slow, the reverse current from the capacitor 5 flows to the

diodes

9a and 9b, thereby deteriorating the turn-on loss of the MOS-

FETs

4a and 4b. This is because of concern. By this change, it is possible to reduce the loss of the power conversion device that achieves both AC-DC conversion and power factor improvement, which have substantially the same effect as the first embodiment.

FIG. 3 is a block diagram showing the circuit configuration and control means of the power converter of the present invention. The difference from the first and second embodiments is that there are no

diodes

3c and 3d constituting the rectifier circuit. With this configuration, two diodes can be omitted, which is effective in reducing the mounting area and cost. Regarding the operation, in the first and second embodiments, when the current increases, the current is shunted in the MOS-FET 4a and the diode 3c or in the MOS-FET 4b and the diode 3d, so that the loss reduction effect can be expected. The effect of is not obtained. However, since the synchronous rectification effect that is the effect of both the parasitic diode of MOS-FET 4 and MOS-FET 4 can be obtained, the power conversion device that achieves both AC-DC conversion and power factor improvement while placing importance on the mounting area and cost. Loss can be reduced.

FIG. 4 is a block diagram showing the circuit configuration and control means of the power conversion device of the present invention, which is replaced with an inexpensive diode stack 4 instead of the four diodes of the first embodiment. This makes it possible to reduce the cost for constructing all the elements of the power conversion device with discrete components, and the low loss of the power conversion device that achieves both AC-DC conversion and power factor improvement, which is almost the same effect as in the first embodiment. Can be realized.

FIG. 5 is a block diagram showing the circuit configuration and control means of the power converter according to the present invention. The diode stack 9 is replaced with the four

diodes

9a, 9b, 3c, 3d of the second embodiment and the reverse recovery time is guaranteed. Is replaced with. This makes it possible to reduce the cost for constructing all the elements of the power conversion device with discrete components, and the low loss of the power conversion device that achieves both AC-DC conversion and power factor improvement, which is almost the same effect as in the second embodiment. Can be realized.

FIG. 6 shows the module configuration of the circuit configuration and control means of the power conversion apparatus according to the first embodiment of the present invention, which is modularized except for the passive element reactor 2 and the smoothing capacitor 5, which have a large element size and are difficult to mount. Yes. As a merit of modularization, it is possible to easily dissipate the heat dissipating structure by consolidating the heat dissipating structure, ease of mounting, and sell it as a power converter. Even without expert knowledge, it is possible to easily and quickly develop a power conversion device module that has substantially the same effect as in the first embodiment.

FIG. 7 shows the module configuration of the circuit configuration and control means of the power conversion apparatus according to the second embodiment of the present invention, which is modularized except for the passive element reactor 2 and the smoothing capacitor 5 which are difficult to mount due to the large element size. Yes. As a merit of modularization, it is possible to easily dissipate the heat dissipating structure by consolidating the heat dissipating structure, ease of mounting, and sell it as a power converter. Even without expert knowledge, development of a power converter module that has almost the same effect as that of the second embodiment can be easily realized in a short period of time.

FIG. 8 shows a module configuration of the circuit configuration and control means of the power conversion device according to the third embodiment of the present invention, which is modularized except for the passive element reactor 2 and the smoothing capacitor 5 which have a large element size and are difficult to mount. Yes. As a merit of modularization, it is possible to easily dissipate the heat dissipating structure by consolidating the heat dissipating structure, ease of mounting, and sell it as a power converter. Even without expert knowledge, it is possible to easily and quickly develop a power conversion device module that has substantially the same effect as the third embodiment.

As described above, we have devised a new control method in order to apply and develop the advantage of switching the rectifier circuit to a MOS-FET and switching the boost chopper circuit. In addition, when the number of times of switching in a half cycle of the power supply voltage of the boost chopper circuit is plural, a circuit configuration with improved element characteristics has been proposed. As described above, the MOS-FET can be used both as a rectifying element and a switching element of the boost chopper circuit, and the loss of the power conversion device that achieves both AC-DC conversion and power factor improvement can be reduced.

1 AC power supply 2 Reactor 3

Diode stack

3a, 3b, 3c,

3d Diode

4a, 4b MOS-FET
5 Capacitor 6 Control means 6a, 6b Control signal output signal 7 DC voltage detection means 7a DC voltage signal 8 AC voltage zero cross detection means 8a Voltage signal of two paths over AC power supply 9 High-speed

type diode stack

9a, 9b High-speed type Diodes.

Claims

A rectifier circuit and a smoothing circuit in which four diodes for converting AC power to DC are bridge-connected, a reactor connected in series to one or the other of the paths from the AC power supply to the rectifier circuit, and an anode common of the rectifier circuit A short circuit circuit of an AC power source and a reactor constituted by switching elements connected in parallel to two diode elements, and turning on the switching element only once every half cycle of the AC power source to widen the energization width of the power source current and shape the waveform. In the power conversion circuit comprising a step-up chopper circuit and a control means for improving the power factor and controlling the DC voltage to a predetermined voltage.
A super junction N-channel MOS-FET having a low on-resistance characteristic is used as the switching element, and the control means turns on all the MOS-FETs when the AC power supply and the reactor are short-circuited, and the AC power supply and the reactor are short-circuited. A power converter that controls to turn off the MOS-FET connected to the positive side of the AC power supply when unnecessary.
The power conversion device according to claim 1,
When the switching element is repeatedly turned on and off repeatedly in a half cycle of an AC power supply, a high-speed type diode with a guaranteed reverse recovery time is used as two elements of the diode that becomes the cathode common of the rectifier circuit. Power converter.
The power conversion device according to claim 1,
2. A power conversion device, wherein two elements of a diode that becomes an anode common of the rectifier circuit are eliminated.
The power conversion device according to claim 1,
A power conversion device using a diode stack in which four diode elements are contained in one package as a rectifier circuit in which four diodes for converting an alternating current power source into direct current are bridge-connected.
The power conversion device according to claim 2,
A power converter using a diode stack in which four diodes each having a guaranteed reverse recovery time are included in one package as a rectifier circuit in which four diodes for converting an alternating current power source into direct current are bridge-connected.
In claim 1,
A power conversion device characterized in that all components except the smoothing circuit and the reactor are made into one module.