JPH0245438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a high-frequency power supply device that supplies a high-frequency output to a vibrating load by using a field-effect transistor as a control element of a high-frequency inverter. This is to prevent destruction of the control element due to the reverse recovery current of the diode derived inside the control element.

Generally, an ultrasonic oscillator or an induction heater that vibrates a ferrite vibrator or the like is equipped with a high-frequency power supply device composed of a high-frequency inverter, and an inductance component and a matching component with the inductance component are installed on the output side of the inverter. An oscillatory load consisting of a resonant circuit of capacitor components for measurement is connected.

When a high-frequency inverter causes a load to resonate in series, if the output frequency of the high-frequency inverter differs from the resonant frequency of the load due to load variations or load fluctuations, the output power of the high-frequency inverter will not be effectively supplied to the load. Furthermore, when a high-frequency inverter causes a load to resonate in parallel, an excessive current flows through the high-frequency inverter, so it is necessary to increase the capacity of the inverter.

By the way, the high-frequency inverter of a high-frequency power supply uses a semiconductor element such as a transistor as a control element, and a half-bridge type high-frequency inverter using a field effect transistor as a control element is a SIPMOS type high-frequency inverter as shown in Fig. 1. A series circuit of first and second control elements Q1 and Q2 consisting of field effect transistors (hereinafter referred to as FETs) is connected to a series circuit of first and second DC power supplies E1 and E2, and a series circuit of both power supplies E1 and E2. A connection point, that is, a point a, which is a connection point between the cathode of the power source E1 and the anode of the power source E2, and a connection point between both control elements Q1 and Q2,
That is, a load Z having a parallel circuit of an inductance component Lx and a capacitance component Cy, and a reactor Ly for inrush current prevention are connected between point b, which is the connection point between the source of the control element Q1 and the drain of the control element Q2. connected in series.

Note that the drain of the control element Q1 is connected to the anode of the power source E1, and the source of the control element Q2 is connected to the cathode of the power source E2.

and a first one connected to the gate of control element Q1.
Control signals are alternately input to the control terminal I1 and the second control terminal I2 connected to the gate of the control element Q2, both control elements Q1 and Q2 are switched, and high frequency power is supplied to the load Z.

However, between the drain and source of the control element Q1, there is a first internal reverse diode D1 which has a polarity opposite to the forward current flowing from the drain to the source.
It is derived according to the magnitude of the forward current, and
A second internal reverse diode D2 similar to the diode D1 is also derived between the drain and source of the control element Q2.

As shown in Fig. 2 a and b, when control signals with a predetermined pulse width are alternately input to both control terminals I1 and I2, the control element Q1 is turned on by the control signal from time ta to time ta'. After that, the control element Q2 is turned on by the control signal from time tb to time tb', and further, the control element Q1 is turned on by the control signal from time tc to time tc'.
Control element Q2 is turned on by the control signal from time td.

Therefore, as shown in Figure 2c, the voltage between point a and point b, that is, the output voltage, becomes a positive voltage from time ta to time tb, and from time tb to time tc, when point b is taken as the reference voltage point. At times, the voltage becomes negative, and from time tc to time td, it becomes a positive voltage, and the output voltage becomes a high-frequency voltage that alternately changes between positive and negative voltages.

On the other hand, when the load Z has a leading power factor, the current flowing between points a and b due to the application of the output voltage, that is, the output current, is the second As shown in FIG. d, the output current flowing through the load Z becomes a high-frequency current with a leading phase with respect to the phase of the output voltage.

That is, for example, when the control element Q1 is turned on at the time of ta, a forward current flows through the control element Q1 at the time of ta and at the time of t, as shown in FIG. Reactor Ly,
The output current flows in the direction of the load Z and the power source E1, and the output current flows in the aforementioned direction until time t when the output current becomes zero due to the resonance of the load Z. In addition, t〓 time and t〓 time are
It is the time between ta time and ta′ time.

When the output current becomes zero at time t, the direction of the output current is reversed, and as shown in Figure 2 f, a forward current flows through the diode D1, and the load Z
includes load Z, reactor Ly, diode D1,
An output current flows in the direction of the power source E1 and the load Z.

Furthermore, when the control signal to the control element Q1 is cut off at the time ta' and the control signal is input to the control element Q2 at the time tb, as shown in FIG. 2f,
Diode D1, power supply E1, diode D1,
A reverse recovery current flows in the direction of the control element Q2 and the power source E2, and as shown in g of the figure, the control element Q
A forward current flows through load Z, and power source E2,
Load Z, reactor Ly, control element Q2, power supply E
Output current flows in two directions.

When the reverse recovery period of the diode D1 ends, only the output current flows through the control element Q2, and at time t, when the output current becomes zero due to the resonance of the load Z,
As shown in FIG. 2h, a forward current flows through the diode D2, and an output current flows through the load Z in the direction of the load Z, the power source E2, the diode D2, the reactor Ly, and the load Z.

Further, when the control signal to the control element Q2 is cut off at the time hb' and the control signal is input to the control element Q1 at the time tc, the diode D2 is connected to the power source E1 and the control element Q1 , the diode D2, and the power source E2, and as shown in the figure e, a forward current flows in the control element Q1, and the load Z has the power source E1, the control element Q1, and the reactor Ly load Z. , an output current flows in the direction of the power source E1.

By the way, the period during which the reverse recovery current flows in both diodes D1 and D2, that is, the reverse recovery period, is 0.3 to 1 μsec.
Since the reverse recovery current is extremely long and the magnitude of the reverse recovery current is also very large, the loss increases when both control elements Q1 and Q2 are turned on, and there is a possibility that both control elements Q1 and Q2 may be destroyed.

Therefore, in order to prevent destruction of both control elements Q1 and Q2 due to the reverse recovery current of both diodes D1 and D2, it is possible to provide a high-speed switching diode separately from both diodes D1 and D2, but in this case, This has the disadvantage that it is necessary to provide a diode with a large capacity and the configuration becomes complicated.

The present invention has been made with the above-mentioned points in mind, and includes a control method for a high-frequency power supply device that uses a field-effect transistor as a control element of a high-frequency inverter to supply a high-frequency output to a vibrating load. detecting the output current of the high frequency power supply device and the output voltage of the high frequency power supply device applied to the load, and shifting the phase of the detection signal of the output current in a delay direction to form a phase adjustment signal; Based on the phase comparison between the output voltage detection signal and the phase adjustment signal, a frequency pulse whose frequency changes from low to high according to the lead or lag of the phase adjustment signal with respect to the output voltage detection signal is formed, and the frequency pulse is The present invention provides a method for controlling a high frequency power supply device, characterized in that the drive frequency of the control element is varied in proportion to the pulse.

Therefore, the output current always has a lagging phase with respect to the output voltage, and this is equivalent to the case where the oscillatory load Z of the high frequency power supply device shown in FIG. 1 is always controlled to a lagging power factor load.

When the load Z has a lagging power factor, the input of the control signal to the control element I2 is cut off at time t1, and the input of the control signal to the control element I2 is interrupted at time t2 to t2', as shown in FIG. 3a and b. To the control terminal I2 at ~t3', to the control terminal I2 at t4~
By inputting a control signal to the control terminal I1 at time t4' and to the control terminal I2 at time t5, the output voltage changes pulses alternately between positive and negative voltages as shown in c in the figure, and the output current changes. As shown in d of the same figure, it changes with a lag phase with respect to the output voltage.

That is, for example, as shown in FIG. 3e, due to the control signal from time t2 to time t2', a forward current flows to the control terminal Q1 at time tx, and the load Z receives power from the power source E.
1. Output current flows in the direction of control element Q1, reactor Ly, load Z, and power source E1, and when the control signal to control element Q1 is cut off at time t2', load Z has load Z, power source E2, and diode. An output current flows in the direction of D2, the reactor Ly, and the load Z, and as shown in f in the figure, a forward current flows in the diode D2, and the direction of the output current does not change.

Then, at time t3, a control signal is input to control element Q2, and when the output current becomes zero at time ty, which is after time t3,
As shown in FIG. 3f, a reverse recovery current flows through the diode D2, and at this time, the load Z is connected to the power source E2,
Output current flows in the directions of load Z, reactor Ly, diode D2, and power source E2.

Furthermore, when the reverse recovery period of the diode D2 has elapsed, a forward current flows through the control element Q2 as shown in FIG.
2. Output current flows in the directions of load Z, reactor Ly, control element Q2, and power source E2.

When the control signal to the control element Q2 is cut off at time t3', the control signal to the control element Q2 is interrupted as shown in FIG. 3g.
However, as shown in h of the figure, a forward current flows through the diode D1, and at this time, the load Z includes the load Z, the reactor Ly, the diode D1, the power source E1, and the load Z. The output current flows in the direction of .

Furthermore, when a control signal is input to the control element Q1 at time t4 and the output current becomes zero at time tz, which is after time t4, a reverse recovery current flows through the diode D1 as shown in Fig. 3h, and the load Z , load Z, power supply E
1. Output current flows in the direction of diode D1, reactor Ly, and load Z.

When the reverse recovery period of the diode D1 has elapsed, a forward current flows through the control element Q1, as shown in FIG. 3e, and the same operation is repeated thereafter.

Therefore, the reverse recovery current of both diodes D1 and D2 does not flow through both control elements Q1 and Q2,
This makes it possible to prevent destruction of both control elements Q1 and Q2 due to reverse recovery current.

Next, a method for controlling a high frequency power supply device according to the present invention will be explained with reference to the drawings from FIG. 4 showing an embodiment thereof.

First, one embodiment will be described with reference to FIGS. 4 to 6.

In Fig. 4, the same symbols as in Fig. 1 indicate the same things, and Tp is a voltage detector for detecting the output voltage applied to the vibratory load Z. As shown, a voltage detection signal Sa that changes according to the change in output voltage when a load Z is connected is output. Tc is a current detector installed between the load Z and point a, and consists of a current transformer, etc., and as shown in Figure 5b, the current detector changes according to the output current flowing through the load Z. Outputs signal Sb.

Then, the current detection signal Sb is input to the phase adjuster Pr, and as shown in FIG. 5c, the current detection signal Sb
A phase adjustment signal Sc whose phase is delayed by 90° is output from the phase adjuster Pr. Note that the phase adjuster Pr consists of a resistor, a capacitor, etc., and can adjust the phase of the input signal.

Furthermore, the voltage detection signal Sa is connected to the voltage waveform shaper.
Wv, and as shown in Figure 5b, the voltage detection pulse Sb, which is the positive half wave of the voltage detection signal shaped into a rectangular wave, is output from the waveform shaper Wv, and the phase adjustment signal Sc is converted into a current waveform. The current detection pulse Se is inputted to the shaper Wi, and is outputted from the waveform shaper Wi by shaping the positive half wave of the phase adjustment signal Sc into a rectangular wave as shown in FIG.

Then, both detection pulses Sd and Se are inputted to a comparator G consisting of an exclusive OR gate and the phases are compared, and as shown in FIG. 5f, both detection pulses Sd,
Comparison pulse Sf that becomes "1" only when Se is input as logic 1 (hereinafter referred to as "1"), logic 0 (hereinafter referred to as "0"), or a combination of "0" and "1" However, from the comparator G to the low pass filter Lf
As shown in g in the figure, the comparison pulse Sf
The smoothed signal Sg is passed through the low-pass filter Lf
is output to a voltage/frequency converter (V/F).

The converter (V/F) is composed of a voltage controlled oscillator or the like, and as shown in FIG. 6, the output frequency changes in proportion to the input voltage.

Furthermore, from the converter (V/F) to the pulse amplifier
A frequency pulse Sh whose frequency changes in proportion to the voltage of the smoothed signal Sg is outputted to Pa, and a frequency pulse Sh whose frequency changes in proportion to the voltage of the smoothed signal Sg is outputted from the pulse amplifier Pa to both control terminals I1 and I2 respectively. A control signal is output, and the on/off, ie, drive frequency, of both control elements Q1 and Q2 is controlled. Note that A is a control section.

When the phase of the output current starts to advance from the phase of the output voltage, the phase of the current detection pulse Se shown in FIG. 5e advances, and the rising timing of the detection pulse Se coincides with the rising timing of the voltage detection pulse Sd shown in As the comparison pulse approaches, the comparison pulse shown in f of the same figure
The width of "1" of Sf becomes narrower, the width of "0" becomes longer, the smoothed signal Sg shown in g in the figure becomes lower, and the frequency of the frequency pulse Sh output from the converter (V/F) becomes lower. The control signal output from the pulse amplifier Pa controls the phase of the output current so that it lags, and adjusts and controls the phase of the output current so that it lags the phase of the output voltage by a predetermined amount.

Conversely, if the phase of the output current lags the phase of the output voltage too much, the rising timing of the current detection pulse Se will be further delayed from the timing shown in Figure 5e, and at this time, the width of "1" of the comparison pulse Sf will become wider. The frequency of the frequency pulse Sh output from the converter (V/F) increases, the phase of the output current is controlled in the direction of advancing, and the phase of the output current is adjusted so that it lags the phase of the output voltage by a predetermined amount. controlled.

Therefore, the phase of the output current always lags the phase of the output voltage by a predetermined amount, and as in the case of FIG. Since no current flows, destruction of both control elements Q1 and Q2 due to reverse recovery current can be prevented.

Next, another embodiment will be described with reference to FIG.

In Fig. 7, the same symbols as in Fig. 4 indicate the same things, and the difference is that a resonant capacitor Cy is installed between the reactor Ly and point a so that the power factor of the load Z as seen from the inverter is 1. The point is that

Then, the resonant frequency fa = 1/(2π√) of the reactor Ly and capacitor Cy becomes slightly lower than the resonant frequency fb = 1/(2π√) of the load Z,
The power factor seen from the inverter becomes a lagging power factor, which prevents destruction of both control elements Q1 and Q2 due to reverse recovery current, and makes the output frequency of the inverter match the resonant frequency fb of the load Z, increasing the efficiency of the inverter. can be increased.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram of a high-frequency inverter applied to a conventional high-frequency power supply, Fig. 2 a to h are timing charts for explaining the operation of Fig. 1, and Fig. 3 and the following drawings are a diagram of a high-frequency inverter according to the present invention. 3A to 3H are timing charts for explaining the principle, FIG. 4 is a wiring diagram of one embodiment, FIGS. 5A to 5G are timing charts for explaining the operation of FIG. 4, and FIG. FIG. 4 is a characteristic diagram of the output frequency with respect to the input voltage of the voltage/frequency converter, and FIG. 7 is a connection diagram of another embodiment. A...Control unit, Q1, Q2...Control element, Z...
...Vibrating load, Tp...Voltage detector, Tc...Current detector, Pr...Phase adjuster, Wv, Wi...Waveform shaper, G...Comparator, Lf...Low pass filter,
(V/F)...Voltage/frequency converter, Pa...Pulse amplifier.

Claims (1)

[Scope of Claims] 1. A method for controlling a high-frequency power supply device that supplies a high-frequency output to a vibrating load using a field-effect transistor as a control element of a high-frequency inverter, comprising: an output current of the high-frequency power supply device flowing through the load and the load; detects the output voltage of the high frequency power supply applied to the output voltage, and shifts the phase of the output current detection signal in the delay direction to form a phase adjustment signal, and outputs the output voltage detection signal and the phase adjustment signal. an advance of the phase adjustment signal with respect to the detection signal of the output voltage based on a phase comparison with the output voltage;
A method for controlling a high frequency power supply device, comprising: forming a frequency pulse whose frequency changes from low to high according to a delay, and varying the driving frequency of the control element in proportion to the frequency pulse.