JPS63268470A - Power convertor - Google Patents

Abstract

PURPOSE:To reduce voltage stress by partially mounting a DC short-circuit mode in the PWM control of an inverter and conducting step-up chopper operation. CONSTITUTION:A power convertor is composed of an AC power 1, a reactor 2, a first diode rectifier 3, an inverter 5, an insulating transformer 6, a second diode rectifier 7, a capacitor, etc., and supplies load connected to said capacitor 8 with power. The inverter 5 is constituted in single-phase bridge connection at that time, and switches S1-S4 as arm elements for the inverter 5 are organized of the antiparallel connection circuits of transistors and diodes. Regarding the operation of the switches S1-S4 for the inverter 5, S1 and S3 are turned ON for a specified period, DC output terminals P and N for the first diode rectifier 3 are short-circuited, and the DC output currents of the diode rectifier 3 are increased and the operation of a step-up chopper is conducted. Inverter operation is performed after a short-circuit mode is released, and DC-AC power conversion is executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a power converter that converts AC power into DC power and further converts this DC power into DC power via an isolation transformer. .

[Conventional technology]

Figure 7 shows, for example, Conference Record Opza 1986.
IEEI Industry Applications Society Annual Meeting Part 1 (Con
'ference Record of the l
986IEEE Industry Applica
tions 5ociety AnnualMeeti
ng Part 1) is a circuit configuration diagram showing the most typical conventional power converter shown on page 631. In the figure, 1 is an AC power supply, 2 is an actuator connected in series with the electric path of this AC power supply 1, and 3 is a first diode rectifier, and the AC side is connected to the AC power supply 1 through this reactor 2.
It is connected to the. A switch 4 is connected in parallel between the DC output terminals (P, N) of the first diode rectifier 3. 5 is an inverter, and a switch 81
-S11 form a single-phase bridge, the DC input side of which is connected in parallel to the switch 4. Further, 6 is an insulating transformer, whose primary side is connected to the AC end of the inverter 5, and whose secondary side is provided with a center tap. A second diode rectifier 7 constitutes a single-phase half-wave rectifier circuit, and its AC input side is connected to the secondary side of this isolation transformer 60. 8 is a capacitor that connects the DC output end of this second diode rectifier 7 and the isolation transformer 602.
Connected between the center taps on the next side.

Next, the operation will be explained. First, each of the switches 81 to SII constituting the switch 4 and the inverter 5 is specifically composed of a self-extinguishing semiconductor element such as a transistor or a GTO, and operates at a high frequency of about 10 times or more than the frequency of the AC power supply 1. Performs switching operation, and current I of AC power supply 1
The waveform distortion of L is reduced and the input power factor is controlled to be approximately 1.

FIG. 8 shows the operating waveforms of switch 4. The diagram shows switch 4
This is an example of a waveform when the switching frequency is set to 12 times the power supply frequency, and the switch 4 is a full-wave rectified waveform of the AC power supply voltage va, where the DC output current I, l of the first diode rectifier 3 is shown by the broken line. Pulse width modulation (PWM) control is performed to follow a similar waveform. For example, during the period from time t1 to t2, when the switch 4 is turned on, the AC power supply 1 is short-circuited via the reactor 2 in the path of AC power supply 1 - reactor 2 - diode Di - switch 4 - diode D4 - AC power supply 1. A circuit is formed and switch 4
The current flowing through increases and energy is stored in reactor 2. When the instantaneous value of this current iI exceeds the current reference value indicated by the broken line, the switch 4 is turned off. At this time, due to the energy storage action of the beam axle 2, the AC power supply current ■, the beam axle 2-diode D1-
The flow flows to the inverter 5 side through the path of inverter 5 - diode Dll - AC power supply 1, charges capacitor 8 via isolation transformer 6 and second diode rectifier 7, and loads connected to capacitor 8 (not shown) (not available). In this way, since the energy of reactor 2 is released when switch 4 is turned off, each current IL
, IP , IN and inverter 50 input current I,
decreases. When the instantaneous value of the current Ip +IN falls below the current reference value indicated by the broken line, the switch 4 is controlled to be turned on again, and the switch 40 on and off operations are repeated.

Furthermore, when the polarity of the AC power supply voltage is reversed, the current is similarly controlled via the diode D2''3 of the first diode rectifier 3.

Next, the operation of the inverter 5 will be explained with reference to FIG.

During the period t1 to t2 during which the switch 4 is on, the DC voltage d of the inverter 5 becomes zero. Subsequently, when the switch 4 is turned off during the period from time t2 to time t, the switch of the inverter 5 is turned off.
L' By turning on SI, the output current of Inver2 5! 1 is a waveform with the polarity shown. t again, ~t1
When switch 4 is turned on during period 4, 11 becomes zero.

Then t, ~t.

When the switch 4 is turned off during the period , the switch S2 of the inverter 5 is turned off. By turning on S, the output current II of the inverter 5 has a waveform with a polarity opposite to that in the period t2 to t5. In this way, each time the switch 4 is off, the switch S1. of the inverter 5 is turned off. S, and S2. By alternately turning on S, an alternating current I is outputted from the inverter 5.

is obtained. The output current I of the inverter 5 is rectified by the second diode rectifier 7, and the output current of the rectifier 7! . becomes as shown. The DC voltage Vd of the inverter 5 when the switch 4 is off is nV if the winding ratio of the isolation transformer 60 is n and the voltage VC of the capacitor 8 is constant.
c. Based on the above operations of the switch 4 and inverter 5, the current ripple of the AC power supply current IL is determined by the reactor?
The inductance L is calculated as follows.

Therefore, by controlling the switching time intervals of the switch 4 and the inverter 5 using a PWM control circuit (not shown), instantaneous current control can be performed in accordance with the current reference value.

[Problems to be solved by the invention] - Since the conventional power converter is configured as described above, the switch 4 and the inverter 5 that operate as a boost chopper are added to the inverter circuit.
Many switch circuits, such as switches 81 to S5 of the inverter 5, are required, and the switching timing of the switches 4 and the switches 81 to S of the inverter 5 must be controlled with high precision. There were problems such as the inability to operate normally.

The present invention has been made to solve the above-mentioned problems, and aims to provide a power conversion device that eliminates the above-mentioned switch and improves the utilization efficiency of an inverter.

[Means for solving problems]

The power converter according to the present invention generates a DC voltage on the output side as in the conventional case by controlling the inverter itself to perform a step-up chopper operation.

[For production]

The power converter in this invention is an inverter switch S.
By controlling the switch so as to provide a period in which the pairs 1 and S, and S2 and S are simultaneously turned on, the switch performs the same functional operation as a conventional switch.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as in FIG. 7 are denoted by the same reference numerals. In FIG. It consists of an anti-parallel circuit of transistors and diodes.

Next, the operation will be explained. First, FIG. 2 shows an operation waveform diagram, which shows the operation of the switches 81 to S4, which are arm elements of the inverter 5. That is, during the period from t1 to t2, switches S1 and S are turned on to short-circuit between the DC output terminals CP and N) of the first diode rectifier 3,
Its DC output current IP.

IN is increased by ΔI according to the relational expression shown in equation (1) above. Next, during the period from t2 to t, switch S is activated.

By turning on switch S instead of turning on
Output current l of inverter 5 with illustrated polarity! is obtained, and the current I, , IN is determined according to the relational expression shown in equation (2) above, △IRf! ke decreases. Subsequently, by turning on switch S2 instead of turning off switch S1, switch S
2 and switch S4 are simultaneously turned on and short-circuited, the DC output current Ip r IN of the first diode rectifier 3 increases. Then, in the next period from t4 to t5, the output current 11 of the inverter 5 flows through the switch S2 and the switch S by turning on the switch S instead of turning off the switch S4. The polarity is opposite to that of . The output current l of this inverter 5! is rectified by the second diode rectifier 7 via the isolation transformer 6, and the output current I of the rectifier 7. is as shown in Figure 2.

As described above, during the periods corresponding to the operating periods t1 to t2 and t5 to t of the switch 4 that performs the conventional step-up operation, the switches S1 and 85 and the switch S2
By turning on and S at the same time, the conventional switch 4
The same effect as that of the conventional one is obtained, and the AC power supply current 1L is the same as that of the conventional one.

Here, switch 8 as an arm element of inverter 5
1 to S, the transistors and diodes are connected in antiparallel during the DC short-circuit mode period of the inverter 5 (11
~12.1. - t4) to circulate the excitation current Ie of the isolation transformer 6 between the arm elements of the inverter 5. For example, in the period from t2 to t, FIG. 3(a)
As shown in the figure, when the transistor S1 and the transistor S are on, the diode D6 of the second diode rectifier 7 conducts, and the output current! . However, the excitation current e of the transformer 6 outputs an output current I from the capacitor 8 through the diode D6. The current flows into the secondary winding of the isolation transformer 6 so that it is superimposed on the output current IO with a polarity opposite to that of the current IO. Next, during the period t, ~t, the transistor S1
Turn off the transistor S2 and turn on the excitation current.

As shown in FIG. 3(b), the current flows from the primary winding of the transformer 6Q through the parallel diode D52 of the transistor S1 and the transistor S. As a result, the isolation transformer 6
The voltage VT of the 01st winding becomes almost zero. If this diode D52 is not provided, the excitation current Ie is fed back from the secondary winding of the isolation transformer 60 to the capacitor 8 via the diode D7, but at this time the transistor S5
Since the primary winding voltage nVc of the isolation transformer 60 is applied in the opposite direction to the transistor S3, the transistor S3 is destroyed. Generally, in self-extinguishing switching devices, the reverse withstand voltage is much smaller than the forward withstand voltage, so the arm element of the inverter unit 5 is composed of an anti-parallel connection of self-extinguishing multiple elements and diodes. .

It should be noted that the configuration of the arm element may be a single self-arc-extinguishing element having reverse blocking ability, or a series connection of multiple self-arc-extinguishing elements and diodes, but in this case, the excitation current of the isolation transformer 6 after turn-off is As explained above, is circulated to the secondary side of the isolation transformer 60, so a voltage waveform as shown by the broken line is added to the vT waveform (solid line part) in FIG. The voltage stress on the arm element of the diode rectifier 7 becomes high, which is undesirable.

Moreover, FIG. 4 is a circuit configuration diagram of a power converter showing another embodiment of the present invention. Figure 1: Connect the glue handle 2 to the reactor 2a between the first diode rectifier 3 and the inverter 5.
, and the same effect as the above embodiment is achieved.

Note that the reactor 2a may be provided separately for the input side and the output side of the first diode rectifier 3 (... Also, in Fig. 4, the second diode rectifier 7 is connected by a single-phase full-wave bridge 7a). Although a configuration is shown, the same effect as the above embodiment is achieved.

Although the snubber circuit is omitted to simplify the explanation of the inverter 5, in order to suppress the surge voltage during switching of the arm elements, a well-known polar snubber circuit is installed as shown in FIG. It may be connected between input terminals or in parallel to an arm element.

Further, in the above embodiment, an example in which AC power of a single-phase AC power source is converted into DC power has been described, but the present invention can also be applied to three or more sets of polyphase AC power sources.

- As an example, FIG. 6 shows a circuit configuration diagram of a power converter when applied to a three-phase power supply. 3-phase AC power supply (1a to IC)
Three sets of the power converters shown in FIG. 1 are individually connected to each other, and the final stage capacitor 8 is commonly connected to these three sets of power converters. Inverter 5 is synchronized with each phase power supply.
WM control is performed so that the input power current is sinusoidal and the power factor is approximately 1.

Further, although the explanation of the load of the power converter was omitted in the above embodiment, a DC load, a battery, etc. may be provided on the output side of the capacitor 8, and an inverter may be provided to convert DC power to AC power. You can do it like this. In this case, the value of the AC input current may be PWM controlled by the inverter 5 of the power converter so that the voltage of the capacitor 8 is constant. Furthermore, in the above embodiment, the inverter 5
I explained the ℃ transistor as an arm element, but
Other self-extinguishing semiconductor elements may be used, and the same effects as in the above embodiments can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the PWM of the inverter
In the control, a DC short-circuit mode is partially provided to perform step-up chopper operation, and in the mode in which the short-circuit mode is canceled, DC-AC power conversion is performed by inverter operation, so that the number of switching elements can be reduced. It has the effect of reducing Furthermore, since the arm element of the inverter is constructed of an anti-parallel connection of self-extinguishing multi-element elements and diodes, there is an effect that voltage stress on the arm element can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing a power converter according to an embodiment of the present invention, FIG. 2 is an operation waveform diagram of FIG. 1, and FIG.
4 to 6 are circuit configuration diagrams showing a power converter according to another embodiment of the present invention, FIG. 7 is a circuit configuration diagram showing a conventional power converter, and FIG. , Figure 9 shows that the conventional power converter operates using a reactor, 3 a first diode rectifier, 4 a switch, 5 an inverter, 6 t,
6 a is an isolation transformer, 7 is a second diode rectifier, 8
is a capacitor, 81 to S are self-extinguishing semiconductor elements, D
51 to D511 are diodes. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Law Company N Figure 4 ts tz b ts ts Figure 5 Figure 7 Figure 4; Figure 8

Claims (1)

[Claims] a first diode rectifier connected to an AC power source to perform AC/DC power conversion; a reactor connected to the input side or output side of the first diode rectifier; and the first diode rectifier.
an inverter that converts DC output power of the diode rectifier into alternating current, an isolation transformer connected to the output side of the inverter, a second diode rectifier that rectifies the output of the isolation transformer, and the second diode. In a power converter having a capacitor connected to the output side of a rectifier, a self-arc-extinguishing semiconductor element constituting an arm element of the inverter, and a diode connected in antiparallel to the self-arc-extinguishing semiconductor element. A step-up chopper operation is performed by partially providing a DC short circuit operation in the switching operation of the inverter, and the inverter is pulse width controlled so that the input power factor of the power converter becomes approximately 1. power converter.