JPH08126340A - Resonance type dc-ac inverter - Google Patents

Abstract

PURPOSE: To provide a DC-AC inverter for driving induction motor which is less in switching element loss and does not produce much electronic noise. CONSTITUTION: In a DC-AC inverter which obtains a multiphase AC output from a DC power source 1, a resonance reactor 2 and a switching element 3 connected in parallel with a reverse parallel diode 4 are connected to the power source 1 and load devices 15-17 respectively connected in parallel with smoothing capacitors 6-8 and in series with switching elements 9-14 are connected across the element 3 through a resonance capacitor 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a DC / AC converter for driving an induction motor, which is required to perform a high frequency operation with a relatively small capacity and to have a small electromagnetic noise.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a resonance type DC / AC converter which has been conventionally used. It is mainly used as a small capacity DC power source and has a buck-boost type half-wave voltage resonance D
It is called a C-DC converter. In FIG. 3, 1 is a DC power supply, 2 is a resonance reactor, 3 is a switching element, 4 is an anti-parallel diode, 5 is a resonance capacitor,
Reference numeral 20 is a transformer, 21 is a rectifying diode, 22 is a smoothing capacitor, and 23 is a load device.

The operation of this circuit is well known. For example, the Institute of Electrical, Information and Communication Engineers Study Group material PE90-14 Matsuo et al. "Unified operation analysis of buck-boost voltage resonant DC-DC converter in reactor current continuous and discontinuous region. (199
0) and the like, and although not described here in detail, FIG. 4 shows an example of operation waveforms. The operation of this circuit is complicated, and there are cases in which various operating modes are adopted depending on operating conditions such as circuit constants and input / output voltages, and a waveform different from that shown in FIG.

FIG. 4A shows an ON signal of the switching element 3, which is in a conducting state when a high-level time arc signal is given. (B) is a current waveform of the resonance reactor 2. When the switching element 3 becomes conductive at time t0, the DC power source 1
More energy is supplied and the current rises almost linearly. When the switching element is turned off at the time t1, a series resonant circuit of the resonant recicle 2 and the resonant capacitor 5 is formed.

Resonant reactor current of FIG. 4B and FIG.
The resonance capacitor voltage of (C) has a sinusoidal resonance waveform, and the secondary current shown in (D) flows in the region t2 to t3 where the secondary voltage of the transformer 20 exceeds the output voltage. Is supplied. Resonant capacitor 5 at time t4
When the voltage of 0 becomes zero, the anti-parallel diode 4 becomes conductive thereafter, and the current of the resonant reactor 2 becomes positive again from t4.
By applying an ON signal to the switching element 3 in the section of 4, it can be turned on in a non-voltage state, and the switching loss at the time of ON can be eliminated. This reduction in switching loss is a major feature of this circuit, which enables high-frequency operation that allows miniaturization of various circuit elements.

[0006]

The circuit of FIG. 3 is a DC-DC converter of DC input and DC output, but it is a good circuit system as a DC-DC converter, but this principle function is applied to an inverter that obtains multi-phase AC. There was a difficulty in applying.

The present invention is intended to be applied to a DC / AC converter of DC input / multi-phase AC output by applying this circuit. The purpose is to distribute the currents of the resonance capacitor 5 of FIG. 3 to the polyphase circuit separately for positive and negative, and to convert the distributed currents into voltages by the smoothing capacitors to obtain multiphase output voltages. is there.

[0008]

[Means for Solving the Problems] That is, the means for achieving the object is a first switching element in which a resonant reactor and an antiparallel diode are arranged in parallel in a DC power supply in a device for obtaining a multi-phase AC output from a DC power supply. Is provided, a smoothing capacitor is arranged in parallel from both ends of the first switching element via a resonance capacitor, and a second switching element is connected in series to provide a load device.

[0009]

The operation will be described together with the embodiment described below.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a resonance type DC / AC converter according to the present invention. The same reference numerals as in FIG. 3 indicate the same elements, and a multi-phase circuit such as a reverse blocking type switching element, a smoothing capacitor, and a load device. Indicates an example of three phases. 6 to 8 are smoothing capacitors for each phase, 9 to 14 are reverse blocking switching elements connected in anti-parallel for each phase, and 15 to 17 are load devices for each phase. Specifically, three phases of the induction motor. For example, winding.

FIG. 2 shows the operation waveforms of each part of the apparatus of FIG. 1. (E) is an ON signal of the switching element 3, which is in a conducting state when a high-level time arc signal is given.
(F) is a current waveform of the resonance reactor 12. (G), (H)
Are the current waveforms of smoothing capacitors 6 and 7, respectively. (I),
(J) are voltage waveforms of the smoothing capacitors 6 and 7, respectively.

At time t0, when the switching element 3 becomes conductive, energy is supplied from the DC power source 1 and the current rises substantially linearly as in the circuit of FIG. Time t1
In the above, it is assumed that the switching element 3 is turned off, and at the same time or in advance, an ignition signal is given to the reverse blocking type switching element 9 so as to be in a conductive state.

DC power supply 1 → resonance reactor 2 before t1
→ The current flowing in the path of switching element 3 → DC power supply 1 is commutated to the path of DC power supply 1 → resonant reactor 2 → resonant capacitor 5 → smoothing capacitor 6 → reverse blocking type switching element 9 → DC power supply 1. This current causes the voltage of the smoothing capacitor 6 to rise as shown in (I) of FIG.
Since the capacitance of is selected sufficiently large, this voltage increase is slight.

After time t2, the current in the resonant reactor 2 flows in the negative direction, that is, from right to left in FIG. 1, due to the reverse swing of the series resonant circuit formed by the resonant reactor 2 and the resonant capacitor 5. At this time, if the reverse blocking type switching element 12 is made conductive in advance, this negative direction current flows to the smoothing capacitor 7, and (J) in FIG.
This voltage is increased in the negative direction as shown in.

At time t2, the current of the reverse blocking switching element 9 becomes zero, so that the current is extinguished spontaneously and no switching loss occurs at the time of turning off. At time t4, when the sum of the voltages of the smoothing capacitor 7 and the resonant capacitor 5 becomes zero, the current flowing through the reverse blocking switching element 12, the smoothing capacitor 7 and the resonant capacitor 5 commutates to the antiparallel diode, and the reverse blocking switching element. 12 extinguishes naturally.

If an ON signal is given to the switching element 3 from the time t3 to the time t4, the switching element 3 is turned on in a voltageless state as in the circuit of FIG. 3, and switching loss at the time of ON does not occur. After time t4, a forward current flows through the resonance capacitor 5 again, but the current at this time is not shown in FIG. 2 (J) as being distributed to the smoothing capacitor 8 and the reverse blocking switching element 13. The negative current from time t5 is t2
2 (H) and 2 (J) are shown as being distributed to the reverse blocking type switching element 12 and the smoothing capacitor 7 as in the subsequent steps.

As described above, the reverse blocking type switching elements 9 to 14 are used for the positive and negative currents flowing through the resonance capacitor 5.
Is distributed to each phase circuit so that it is made conductive, but the voltage of each phase, that is, the smoothing capacitor, is distributed by distributing the positive direction current to the phase where the voltage is to be raised most and the negative direction current to the phase where the voltage is to be lowered most. The voltage of 6 to 8 can be controlled arbitrarily.

Further, by making the operating frequency of the switching element 3 much higher than the frequency of each phase voltage,
For example, when the frequency of each phase voltage is 50 Hz, the operating frequency of the switching element 3 is 10 KHz or more, which enables finer waveform control. For example, if the load devices 15 to 17 in FIG. 1 are three-phase windings of an induction motor, it is desirable to drive with a sinusoidal wave with a small distortion ratio, and the smoothing capacitor 6
The voltage is controlled to 8 or a sine wave.

[0019]

The switching element 3 used in the device of the present invention is turned on in a non-voltage state and has no switching loss when turned on, and the reverse blocking type switching elements 9 to 14 are naturally extinguished in a non-current state and turned off. No switching loss occurs. In this way, the switching element loss, which is a feature of the resonance type DC / AC converter, can be greatly reduced, so that the cooling system is simplified and small size and high efficiency can be measured. It is possible to achieve higher frequencies with higher efficiency.

By increasing the frequency and selecting a large capacity of the smoothing capacitor 6, the voltage change of the smoothing capacitors 6 to 8 due to the current of one pulse becomes small, and fine waveform control becomes possible. In addition, it has a low distortion 3 suitable for driving an induction motor
It is also possible to generate a phase sine wave.

Since the resonance circuit makes the voltage and current waveforms of the various switching elements mostly sine wave-like, it is a major feature that electromagnetic noise can be reduced as compared with hard switching.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a resonance type DC / AC converter according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing operation waveforms of respective parts of FIG.

FIG. 3 is a configuration diagram showing a conventional resonance type DC / AC converter.

FIG. 4 is a waveform diagram showing operation waveforms of respective parts of FIG.

[Explanation of symbols]

 1 DC power supply 2 Resonance reactor 3 Switching element 4 Anti-parallel diode 5 Resonance capacitor 6 Smoothing capacitor 7 Smoothing capacitor 8 Smoothing capacitor 9 Reverse blocking type switching element 10 Reverse blocking type switching element 11 Reverse blocking type switching element 12 Reverse blocking type switching element 13 Reverse blocking switching element 14 Reverse blocking switching element 15 Load device 16 Load device 17 Load device 20 Transformer 21 Rectifier diode 22 Smoothing capacitor 23 Load device

Claims (1)

[Claims] 1. In a device for obtaining a multi-phase AC output from a DC power supply, a first switching element having a resonant reactor and an anti-parallel diode arranged in parallel is connected to the DC power supply, and a resonance capacitor is connected from both ends of the first switching element. A resonance type DC / AC converter comprising: a load device in which smoothing capacitors are juxtaposed with each other via a second switching element connected in series.