JPS59117470A - Power control circuit - Google Patents

Abstract

PURPOSE:To eliminate an unnecessary transient response by displacing and superposing the phases of AC outputs of a plurality of voltage resonance type high frequency inverters and supplying the powers to a load, thereby smoothing the output current wave. CONSTITUTION:Voltage resonance inverters of respective series are connected in parallel with an input power source 1. The inverters are connected to the power source 1 through main switches 5, 6 at the primary side of a tansformer 7 which has leakage inductances between the primary side and the secondary side, a diode 2 is connected in anti-parallel with the switches 5, 6, and a capacitor 4 is connected in parallel with the primary side of the transformer 7 or the diode 2. The secondary side of the transformer 7 is connected in parallel or in series, and the same load 8 is connected. The output power is controlled by altering the opening or closing phase of the switches 5, 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control circuit for output power of a pressure resonance type high frequency inverter.

[Technical background of the invention and its problems]

Voltage resonance type high frequency inverters can supply alternating current power to resistive loads, so they are used in high frequency induction heating devices and the like.

However, since the switch disconnection period is determined by the arc of the resonant voltage waveform, controlling the output power by the switch pulse width has a narrow output power variable range.The power variable range can be changed while maintaining voltage resonance conditions. is about a fraction of the maximum to minimum, which is insufficient for practical use.

In order to widen this narrow power control range, there is a method of using an auxiliary switch in addition to the main switch. This auxiliary switch must have the same rated capacity as the main switch.
This is not necessarily practical in terms of cost and structure.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and is aimed at controlling the power of multiple series of voltage resonant high frequency impulses using switches with a capacity less than half of the main switch in order to control the same amount of power. The purpose is to provide circuits.

[Summary of the invention]

This invention prepares a plurality of systems of voltage resonance type high frequency inverters, has a common resistance load, and controls the power supplied to the square load by changing the excitation phase of the inverters of each system.

〔Effect of the invention〕

According to this invention, in order to supply power to a load by superimposing the AC outputs of multiple series of voltage resonant high frequency inverters with their phases shifted from each other, the combined output current wave is smooth and unnecessary transient response is generated. AC output with low noise can be obtained. Furthermore, if the phases of the outputs of the imparks in the plurality of series are opposite to each other, the output power can be completely reduced to zero, and the voltage resonance condition applied to the primary side switch does not change.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes an input power source, to which voltage resonant inverters of each series are connected in parallel. In one series of inverters, the primary side of a transformer 7 having leakage inductance between the primary and secondary is connected to the power supply 1 through a main switch 5, a diode 2 is connected in antiparallel to the main switch 5, and the transformer 7
A capacitor 4 is connected in parallel to the primary side or the diode 2, and the secondary side of each transformer 7 is connected in parallel or in series to the same load 8.

Next, the operation of this embodiment will be explained. If the turns ratio of the transformer of each series of voltage resonant inverters is 1", and the value of the leakage inductance 9 between the transformer and the secondary is Le, the characteristic impedance Zo of the resonant circuit as seen from the transformer secondary side is JLe
/C. The load 8 is higher than this characteristic impedance Zo.
The value RL is assumed to be small, 115 or less. In this case, the output power of each series of inverters is mainly consumed by the load 8, and the transfer of power to other inverters can be ignored in terms of operation, and each inverter becomes independent. Finally, the excitation inductance of the transformer 7 is made sufficiently larger than the leakage inductance 9 so that it can be ignored in terms of operation.

When each inverter reaches a steady state, the terminal voltage of the capacitor 4 becomes the voltage E5n of the power supply 1 just before the switch 5 closes.

The operation will be explained with the above conditions in mind.

First, the main switch 5 is closed. At this time, the terminal voltage of the capacitor 4 is the power supply voltage, so the capacitor 4 can be considered to be included in the power supply 1. Therefore, the switch circuit during the period (Ton) when the switch 5 is closed is as shown in FIG. 2(a). The current flows as shown by the solid line. The state of this change is shown in FIG. 3(a). That is, the current increases linearly. This state continues while switch 5 is closed. Thereafter, when the switch 5 is opened, the current stored in the leakage inductance 9 flows into the capacitor 4 via the load 8 and begins to resonate.

At this time, the terminal voltage of the capacitor 4 drops from the power supply voltage Ein while drawing a sinusoidal arc, returns to the power supply voltage E j n again via the minimum value of the negative value. Furthermore, as shown by the dotted line in FIG. 3(b), when the power supply voltage Ein is about to be exceeded, the diode becomes forward biased and becomes conductive if the terminal voltage of the capacitor 4 becomes higher than the power supply voltage Ein due to this polarity. The circuit is the same as that in (a). While any diode 2 is conducting, the current increases linearly and continues at zero.

During this time, the terminal voltage of the capacitor 4 is fixed to the power supply voltage Ein. This completes one cycle of operation in the steady state.

According to the initial operating conditions, the value of load 8 is as shown in Fig. 3(a).
The waveform will look like this. Therefore, the output voltage waveform of one series of 1-voltage resonant converter is shown in FIG. 4I. The output voltage waveform of the other series of voltage resonant converters is 6.
■ From '° to phase θ1. θ2 delay t and e+n1”6■2”
The waveform becomes The composite waveform of I and ■1 or I and ■2 becomes the waveform consumed by the load 8. Tsume 9I and ■1. If the composite waveform I and ■ match, the wave height value will not be too high.
Less power is transmitted to the load.

Furthermore, since the phases of the combination of I and 2 are opposite to each other, the power transmitted to the load is minimized. On the other hand, if the polarities of Innocutors (2) and (2) are reversed and they are connected to the same load, the voltage waveform output to the load will be as shown in FIG. That is, when operating with zero phase difference between inverters I and 1, the outputs completely cancel each other out and the output becomes zero. When the phase is shifted as shown in I and ■2, the output starts to be output.

As is clear from the above description, according to the present invention, the output power can be smoothly controlled by changing the excitation phase of multiple series of inverters. Moreover, when using pulse width control, etc., an unsatisfactory transient response is superimposed on the output waveform due to forcibly switching the DC, but the standard j method of the present invention superimposes the output AC waveform with a phase difference. There are no unnecessary responses caused by control. Also, as the output voltage increases, this method becomes increasingly practical. That is, a large output inverter is usually not constructed from a single circuit, but from the viewpoint of reliability and component capacity, it is constructed from multiple series of inverters. Furthermore, since the inverters in each series are operated under the same frequency and constant pulse width conditions, and only the respective excitation phases are changed, the reliability of control is much improved compared to the pulse width modulation method.

It should be noted that the present invention is not limited to the above embodiments. For example, the same effect can be obtained by increasing the number of series to three or four series and exciting the phase difference by equally dividing each series.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram for explaining the operation, and FIG. 3 is a diagram. FIGS. 4 and 5 are operation waveform diagrams, respectively. DESCRIPTION OF SYMBOLS 1... Input power supply, 2... Diode, 4... Capacitor, 5, 6... Switch, 7... Transformer, 8...
...Load, 9...Leakage inductance. Agent Patent Attorney Kensuke Chika (and 1 other person) Figure 1 Figure 2 tlI->. Mu. r'7 Figure a

Claims (1)

[Claims] (1) A transformer with leakage inductance is connected to the input DC power source via a switch that opens and closes at a predetermined period and pulse width, and a capacitor is connected in parallel to the transformer or switch; multiple series of pressure-resonant inverters are prepared. A power control circuit characterized in that the voltage resonant inverters are connected to the same load and the excitation phase of each voltage resonance inverter is changed to adjust the power to the load. (1) The power control circuit according to claim 1, wherein the load value is set to be a fraction or less of the leakage inductance of the transformer and the characteristic impedance of the capacitor.