JPS62281769A - Large power transistor inverter - Google Patents

Abstract

PURPOSE:To miniaturize a device and improve the power factor of a power source, by using the switching transistors of an inverter section as output- variable means. CONSTITUTION:A power rectifier section 1 is organized by connecting the series circuit of a smoothing reactor 9 and a condenser 10 between the output ends of a diode bridge 8, and a bridge type transistor inverter section 3 is composed of the parallel unit of switching transistors Tr1-Tr4 and fly-wheel diodes D1-D4. A series resonance load 2 is provided with a resonance current detector 14, and its output is applied to a zero-cross comparator 15 and a resonance current rectifier 16. Difference signal between the output of the rectifier 16 and the output of a setting unit 18 is obtained by a comparator 17 and is directed to a variable switching pulse generator 19 for input. Then, by the pulse generator 19, a pulse fallen at a position according to the scale of said difference signal is formed, and the pulse is applied to the base of the switching transistors Tr1-Tr4 in specified order.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Industrial Application Field) The present invention provides a series resonant load with a bridge type transistor
This invention relates to a high-voltage transistor inverter that applies a high-frequency voltage 110 from an inverter section.

(Prior art) This type of conventional high power transistor inverter is
As shown in FIG. 3 or 4, there is a forward converter 1 that converts a commercial AC voltage into a DC voltage, and a bridge type transistor that converts this DC voltage into a high frequency voltage and supplies it to a series resonant load 2. It was composed of an inverter section 3. The output can be varied by changing the conduction angle of the rectifying bridge of the thyristor 4 constituting the forward conversion section 1 in the one shown in FIG. This is achieved by forming a chopper circuit 7 of a transistor 6 and a chopper circuit 7, and varying the output of the chopper circuit 7.

The inverter using the bridge type transistor inverter section 3 has the advantage of being able to output a large amount of power more efficiently than other inverter sections.

(Problem to be solved by the invention) However, the conventional high-power transistor of this scale
The inverter shown in Figure 3 uses a thyristor rectification system to vary the output, so as the output is lowered, the power factor of the power supply decreases. Since it uses a single chopper type, there are problems such as chopper noise leaking to the AC input side and problems that the device becomes complicated and large.

An object of the present invention is to provide a transistor inverter for high power use that can easily perform output control without complicating the structure, has a high power factor, and has low noise.

(Means for Solving the Problems) The configuration of the present invention to couple the above objects will be explained with reference to FIG. 1 corresponding to the embodiment. a forward conversion unit 1 that converts the DC voltage into a DC voltage, and a bridge type transistor inverter unit 3 that converts the DC voltage into a high frequency voltage and supplies it to the series resonant load 2, the transistor inverter unit 3
In a high-power transistor inverter in which flywheel diodes D1 to D4 are connected in parallel to each of the switching transistors Trl to Tr4, respectively, a zero-crossing pulse synchronized with the zero-crossing phase of the resonant current flowing through the series resonant load 2 is generated. a zero-cross comparator 15 that outputs
#i current rectifier 16, a resonant current setter 18 for setting the resonant S current, and a comparator for forming a difference signal between the output of the resonant S current setter 18 and the output of the resonant current rectifier 16. 17, a switching pulse is caused to rise at the time of generation of the zero-cross pulse and fall at a position corresponding to the magnitude of the difference signal so that the inverter output frequency is shifted higher than the resonant frequency of the series resonant load 2; The present invention is characterized in that it is provided with one switching pulse generator of a pulse width control type which is formed by the transistor inverter section 3 and supplies each of the switching transistors Tr1 to Tr4 of the transistor inverter section 3 in a predetermined order.

(Function) When the switching transistors Tr1 to l'-r4 of the transistor inverter section 3 are used as output variable means in this way, the structure is 1! ! It is simple and can be made smaller. In addition, switching transistors Tr1 to Tr4
The conduction control of the switching transistors Tri to T is performed by shifting the switching pulse to the side where the inverter output frequency is higher than the resonant frequency of the series resonant load.
Flywheel diodes D1-D4 in parallel with switching transistors Tr1-T in series with
When switching to r4, the flywheel diode D1
During the reverse recovery time of -D4, the flywheel diodes D1-D4 become short-circuited and the switching transistors Tri-Tr4 can be operated without being destroyed. Furthermore, since full-wave rectification is performed by the diode bridge 8 in the forward converter 1, the power factor of the power supply does not decrease even if the output is lowered. Furthermore, since switching is not performed in the forward converter 1, chopper noise does not leak to the AC input side.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIG. Note that parts corresponding to those in FIGS. 3 and 4 described above are designated by the same reference numerals. The forward conversion unit 1 has a structure in which a series circuit of a smoothing reactor and a smoothing capacitor 10 is connected between the output terminals of a diode bridge 8. The bridge-type transistor inverter section 3 connects the switching transistors Tr1 to 7r4 in a bridge manner, and connects each switching transistor Tr1 to Tr4.
4 has a structure in which flywheel diodes D1 to D4 are individually connected in parallel. The series resonant load 2 is formed by a series circuit of a resonant capacitor 11, a resonant coil 12, and a load resistor 13.

A resonant current detector 14 is installed in the series resonant load 2 to detect resonant current. The output of the resonant current detector 14 is applied to a zero-cross comparator 15 and a resonant current rectifier 16. Zero cross
The comparator 15 outputs a zero-crossing pulse synchronized with the zero-crossing phase of the resonant current. The resonant current rectifier 16 rectifies and outputs the resonant current. The output signal of the resonant current rectifier 16 is sent to the comparator 1.
It is designed to be given to 7. The output signal of the resonant current setter 18 is also input to the comparator 1a, so that a difference signal between the output signal of the resonant current setter 18 and the output signal of the resonant current rectifier 16 is formed. Zero cross
The zero-crossing pulse of comparator 15 and the difference signal of comparator 17 are adapted to be input to a variable switching pulse generator 19 with pulse width control formation. The switching pulse generator 19 generates a switching pulse at a position corresponding to the magnitude of the rising difference signal when the zero-crossing pulse is generated so that the inverter output frequency is shifted higher than the resonant frequency of the series resonant load 2. It is designed to be lowered and formed. Formed switching
The pulses are applied to the bases of the switching transistors Tr1 to Tr4 of the transistor inverter section 3 in a predetermined order. In addition, 20 is a starting circuit used at the time of starting.

Next, the operation of such a high power transistor inverter will be explained. Transistor/inverter section 3
A DC voltage is applied in advance from the forward converter 1 to the converter 1 . A starting pulse is transmitted from the starting circuit 20 to each switching transistor T via one variable switching pulse generator.
r1. When supplied to Tr4, switching transistors Trl and Tr4 are turned on. As a result, a resonant current determined by the load capacitor 11° coil 12 flows through the path: terminal A-switching transistor Trl-capacitor 11-coil 12-load resistor 13-switching transistor Tr4-terminal B.

In this case, the pulse width of the starting pulse is set to be shorter than the period of the resonant current flowing through the series resonant load 2. Therefore, before the resonant current becomes zero, the switching transistor Tr1. Tr4 is turned off.

At this time, the energy stored in the resonance coil 12 is fed back to the t source side via the diodes 02 and D3.

When a resonant current flows through the series resonant load 2, it is detected by the resonant current detector 14 as shown in FIG. When this voltage is applied, the zero-cross comparator 15 outputs a zero-cross pulse as shown in FIG. In the comparator 17, a difference signal between the output set by the resonant current setter 18 and the output of the resonant current rectifier 16 is formed and applied to one variable switching pulse generator with pulse width m control type. One variable switching pulse generator inputs the zero-crossing pulse from the zero-crossing comparator 15 and the difference signal from the comparator 17 to shift the inverter output frequency higher than the resonant frequency of the series resonant load 2. The switching pulse is formed by falling at a position corresponding to the magnitude of the rising edge signal when the zero-crossing pulse is generated.In the case of this embodiment, such a switching pulse is formed as shown in FIG. ), the application of a zero-cross pulse discharges the capacitor and starts charging from the zero level, and the next zero-cross pulse discharges the charge to form a sawtooth wave. , with a zero-crossing pulse and a DC level proportional to the difference signal, i.e. the switching transistor T rl.

As shown in Figure 2 (d), the switching pulse of Tr4 rises at the zero-crossing pulse that is output when the positive half cycle of the resonant current occurs, and the level of the sawtooth wave is at a DC level proportional to the difference signal. It is formed in such a way that it falls when it reaches the top. In addition, the switching transistor Tr
2. As shown in Figure 2 (E), the switching pulse of Tr4 rises at the zero-crossing pulse that is output when the negative half cycle of the resonant current occurs, and the level of the sawtooth wave reaches a DC level proportional to the difference signal. It is formed in such a way that it falls when it rises. When a switching pulse as shown in FIG. 2(d) is applied, the switching transistors Tr1. When a current as shown in Fig. 2(e) flows through Tr4 and a switching pulse as shown in Fig. 2(e) is applied, the switching transistor Tr4
2. A current as shown in FIG. 2 (G) flows through Tr3. Note that in FIGS. 2(f) and (g), hatched portions indicate switching transistors Tr1. Tr4 and Tr2
．． It shows the current flowing through the switching diodes D2°C3, Dl, and C4 when Tr3 is turned off. As is clear from the figure, according to the invention, at the gate of the reverse recovery time of the flywheel diode upon switching from the flywheel diode to the switching transistor in series therewith, the flywheel diode becomes short-circuited; At this time, a large spike current flows and the switching transistor is prevented from being destroyed.

The pulse width of the current flowing through the switching transistors Tr1 to Tr4 is controlled by a resonant current setter 18.

Now, when the inverter load becomes light (load resistance decreases), the resonant current tries to increase by +10 L, but at this time the difference signal of the comparator 17 becomes small, and therefore the variable switching pulse generator 19 is controlled. This narrows the pulse width of the switching pulse and keeps the co-S current constant. On the other hand, when the inverter load becomes heavy (load resistance increases), the pulse width of the switching pulse becomes wider.
The common 'fi current is controlled to be constant. In addition, capacitor ``11'' and coil 1 are used for fluctuations in commercial power supply and for resonance.
The resonant current is controlled to be constant even with a change of 2. In this inverter, the narrower the pulse width, the higher the inverter output frequency becomes than the resonance frequency.

The above situation can be expressed numerically as follows.

In addition, Z: Thickness of impedance r of the common 1i circuit - Load resistance ω of the resonance circuit ω: Common frequency; Capacity L of the resonance capacitor: Inductance of the resonance coil. Further, subscript 1 indicates before the change, subscript 2 indicates after the change, and no subscript indicates no change.

First, when only the load resistance 13 changes, Z+ = (r
+ 2+ (ωt L-1z'ω+ C) 2)"Z
2 = (r22+ (+uJz L-1/ω2C)
2)'z, and due to the constant lightning current operation, the resonance frequency changes to ω2 so that Z+ = 22. That is, r12+
(ωIL-1/ωIC)2=r2+(ω2L-1/ω2
C)? From this, the resonance frequency after variation is ω 2 = [CX+ ((CX)'+41C)'? ]
/21 smile, X= (r+ 2-r22+ (ωt L-1/
ω+C)2) becomes ro.

Next, when only L and C change, Z+ = (r2+ (ωt L+ -1/ω+ C1) 2) v7 Z2 = (r2+ (ω2L2 =1/ω2C2)2) From Z+ = 22, ω+L+-1/ ωIC1=ω2[2 =1/ω2C2 From this, ω2=[(ωIL+ -1/ω+ C+ )C2+((
ωIL+ -1/ω+ C+ ) 2C22+412
C2)]/212 C2.

(Effects of the Invention) As explained above, in the high power transistor inverter according to the present invention, the switching transistor of the transistor inverter section is used as the output variable means, so the structure is simplified and miniaturization is possible. can be achieved. In particular, in the present invention, the switching transistor 1
Control is achieved by shifting the switching pulses so that the inverter output frequency is higher than the resonant frequency of the series resonant load, so that the switching pulses are shifted from the flywheel diode in parallel to the switching transistor to the other switching transistors in series with it. During the switching of the flywheel diode, operation can be avoided in such a way that the flywheel diode is short-circuited during the reverse recovery time of the flywheel diode and the switching transistor is destroyed.

Further, in the forward conversion section of the present invention, full-wave rectification is performed using a diode bridge, so even if the output is lowered, the power factor of the power source does not decrease, and the power factor of the power source when the output decreases can be improved.

Furthermore, since switching is not performed in the forward conversion section of the present invention, there is an advantage that chopper noise does not leak to the AC power source side such as a commercial power source.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of a high power transistor inverter according to the present invention, Fig. 2 is a waveform diagram showing the operation of each part in Fig. 1, and Figs. 3 and 4 are a circuit diagram of a conventional transistor inverter. It is a block diagram showing two types of examples. DESCRIPTION OF SYMBOLS 1... Forward conversion part, 2... Series resonant load, 3... Transistor inverter part, Tr1-Tr4... Switching transistor, D1-D4... Flywheel diode, 11... Resonance capacitor, 12
... Resonance coil, 13... Load resistance, 14...
Resonant current detector, 15... Zero cross comparator, 16... Resonant current rectifier, 17... Comparator, 18
...One resonant current setting device...Variable switching pulse generator. Figure 3 Figure 4

Claims (1)

[Claims] A forward conversion section that converts an AC voltage into a DC voltage using a diode bridge, and a bridge type transistor inverter section that converts the DC voltage into a high frequency voltage and supplies it to a series resonant load. In a high-power transistor inverter in which a flywheel diode is connected in parallel to each switching transistor, a zero-cross comparator outputs a zero-cross pulse synchronized with a zero-cross phase of a resonant current flowing through the series resonant load; a resonant current rectifier for rectifying the resonant current, a resonant current setter for setting the resonant current, and a comparator for forming a difference signal between the output of the resonant current setter and the output of the resonant current rectifier; A switching pulse is formed by rising when the zero-crossing pulse occurs and falling at a position corresponding to the magnitude of the difference signal so that the inverter output frequency is shifted higher than the resonant frequency of the series resonant load. A transistor inverter for high power use, comprising a switching pulse generator of pulse width control type that applies pulse width control to each of the switching transistors of the transistor inverter section in a predetermined order.