JPH0827660B2 - Switching semiconductor device control circuit - Google Patents

Description

The present invention relates to a control circuit for controlling the conduction width of a switching semiconductor element such as a thyristor.

[Conventional technology]

It has already been proposed to automatically perform optimum conduction control by using a microcomputer or a counter acting as a digital timer in a control circuit for controlling conduction of a switching semiconductor element such as a thyristor. As an example of this type of conventional method, a timer consisting of a counter starts counting clock pulses from the zero point of the power supply voltage, and at the same time, the microcomputer also operates the phase control program to calculate the control angle, and when the control angle is obtained. Therefore, the set value of the timer is changed to a count value corresponding to this control angle.

[Problems to be solved by the invention]

In such a conventional method, since the timer starts counting clock pulses at the zero point of the power supply voltage, the timer is set incorrectly when the microcomputer is miscalculated or runs out.In this case, the drive signal is output before the minimum control angle. May be transmitted to the switching semiconductor element, which may cause an overcurrent or overvoltage state, or may cause biased excitation of the transformer due to failure of conduction of the switching semiconductor element.

[Means for solving problems]

In order to eliminate the above drawbacks, the present invention provides a control circuit for controlling the conduction width of a switching semiconductor element, a circuit for detecting a zero point at which the power supply voltage becomes almost zero, and a zero point detection signal output from the circuit. To a low level, and a monostable multivibrator that raises the output to a high level again when the time corresponding to a predetermined minimum control angle elapses, and an oscillator that generates a clock pulse group sufficiently higher than the power supply frequency. And an AND circuit that performs AND logic of the clock pulse group of the oscillator and the output of the monostable multivibrator, and outputs an intermittent clock pulse block,
Upon receiving the zero-point detection signal, the interrupt process is started, the control angle of the switching semiconductor element is calculated based on the output detection signal and the setting signal, and the count command signal corresponding to the control angle corresponds to the minimum control angle. And a computer that outputs within the time period to start counting clock pulses in response to the output signal of the AND circuit, and the count value becomes equal to the count set value by the count command signal given from the computer, the output signal is output. The present invention provides a control circuit for a switching semiconductor device, characterized in that it comprises a timer that occurs.

[Work]

Since the timer counts the clock pulse from the time corresponding to the minimum control angle, even if the computer miscalculates or runs out of control, the drive signal is not sent to the switching semiconductor device before the minimum control angle, and accordingly, No overcurrent or overvoltage caused by excessive conduction,
In addition, it does not give a cause of biased excitation of the transformer due to failure of conduction.

Further, since the computer calculates the control angle by interrupt processing within the period from the zero point of the power supply voltage to the time corresponding to the minimum control angle, and gives a count command signal corresponding to the control angle to the timer, There is no need to consider variations in program execution time, and the interrupt processing hardware can be simplified.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows an embodiment of a constant voltage power source, 1, 1'is an AC input terminal connected to an AC power source, 2 is a pair of switching semiconductor elements, for example, thyristors, which are connected in parallel in opposite directions. AC switch formed by 3 is a transformer, 4 is a full-wave rectifier circuit connected between the secondary windings of the transformer 3, 5
Is a load, 6 is a voltage dividing resistor, and 7 is a voltage detecting resistor. The control circuit 10 according to the present invention has an AC input terminal.
1, 1'is connected to terminals 11 and 11 ', terminal 9 is connected to the connection point between resistors 6 and 7, and terminal 8 is connected to AC switch 2. , A transformer 12, a full-wave rectifier 13, a resistor 14, a comparator 15, connected between 11 ',
Differentiator circuit 1 consisting of reference power supply 16, capacitor and resistor
7, monostable multivibrator 18, oscillator 19 for generating clock pulse, AND circuit 20, timer 21, differentiating circuit 22, amplifier 23, computer 2 such as a microcomputer
4. An analog-digital converter 25, an output voltage setting potentiometer 26 and the like.

 Next, the operation will be described.

The power supply voltage detection signal detected by the transformer 12 is converted by the full-wave rectifier 13 and the resistor 14 into a full-wave rectified waveform as shown in FIG. 2B), and then input to the comparator 15. The comparator 15 compares the detected voltage with a low-level reference voltage as shown in b) in the figure and outputs a signal as shown in c) in the figure. The rising portion of this signal is differentiated by the differentiating circuit 17 and becomes a signal as shown in FIG. This signal indicates almost the zero point of the power supply voltage and is known as a zero point detection signal.

This zero point detection signal is input to the monostable multivibrator 18 and the computer 24. The monostable multivibrator 18 drops its output to a low level when triggered by the zero detection signal. As is well known, at the same time, the time constant circuit of the monostable multivibrator 18 starts to operate, and when the time corresponding to the predetermined minimum control angle elapses, its output becomes high level again. Therefore, the output of the monostable multivibrator 18 is always at a low level during the period from the zero point of the power supply voltage to the time point corresponding to the predetermined minimum control angle. In this embodiment, the minimum control angle is an angle substantially equal to the period during which the current is still flowing even when the main circuit current has a delay with respect to the main circuit voltage, even if the power supply voltage changes to a negative value, or still another angle. This is a period in which it is desired to prohibit the sending of a drive signal to the AC switch by saying an angle equal to a predetermined period in consideration of factors. If a drive signal is applied to the AC switch 2 before this minimum control angle, the conduction width of the AC switch becomes too large, which may cause overvoltage or overcurrent, or the AC switch may fail to conduct. It will be one of the causes of demagnetization. On the other hand, the computer 24 interrupts at the same time it receives the zero point detection signal which is the interrupt command signal, and executes the interrupt processing program according to the interrupt processing program.
The load voltage detection signal digitized by the A / D converter 25 is read, the set value by the output voltage setting potentiometer 26 is read, and the control angle is calculated from this to determine the control amount. In addition, the computer 24 also displays, for example, output voltage, current segment display, output measurement at certain times, and in the case of an electrostatic precipitator, a spark display, detection of reverse ionization state, calculation of dust collection efficiency, etc. Is processed according to the program, but when the zero-point detection signal is input as an interrupt command signal, an interrupt is made immediately, and at the latest, the control angle is calculated before the minimum control angle to determine the control amount,
The transmission of the count command signal to the timer 21 has been completed.
The oscillator 19 generates a clock pulse group as shown in FIG. This clock pulse is sufficiently higher than the power supply frequency, for example, 20 KHz. The AND circuit 20 performs an AND logic on the clock pulse group from the oscillator 19 and the output of the monostable multivibrator 18, and outputs an intermittent clock pulse block as shown in FIG. And timer
21 starts counting clock pulses from the AND circuit 20,
When counting up to the set count value set by the count command signal given from the computer 24 before the minimum control angle,
The output of the timer 21 is inverted from low level to high level as shown in FIG. This high level output signal is held until the count command signal is received from the computer 24 in the next operation cycle or until the zero point of the power supply voltage. The rising portion of the output signal of the timer 21 is obtained through the differentiating circuit 22, and the pulse signal as shown in i) of the figure is amplified by the amplifier 23 to a desired value, and then the AC switch 2 is used as a drive signal.
Applied to the control terminal of. Here, when the AC switch is formed of a bipolar transistor or FET, the differentiating circuit 22 is deleted, but in this case, the high level output signal of the timer 21 is held up to the zero point of the power supply voltage.

〔The invention's effect〕

As described above, according to the present invention, the timer starts counting clock pulses after the minimum control angle, and the computer calculates the control angle by interruption within the period from the zero point of the power supply voltage to the minimum control angle. Since the circuit configuration is such that the count command signal corresponding to the control amount is sent to the timer, even if the computer makes a calculation error or runs out of control, the drive signal can be sent to the AC switch before the minimum control angle. Therefore, it does not give a cause of exhibiting an overvoltage or overcurrent state, nor does it give a cause of the demagnetization of the transformer due to the failure of conduction of the AC switch. Furthermore, even if the execution time of the interrupt processing program is different, the execution is completed within the minimum control angle, so the software becomes simple and the interrupt processing can be performed only by detecting the zero point, so that the device configuration can be simplified. .

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a control circuit for a semiconductor switching element according to the present invention, and FIG. 2 is a diagram showing waveforms for explaining an embodiment of the present invention. 1, 1 '... input terminal, 2 ... AC switch 5 ... load, 10 ... control circuit 15 ... comparator 18 ... monostable multivibrator 19 ... oscillator, 20 ... AND circuit 21 ... timer , 24 …… Computer 25 …… A / D converter

Claims (1)

[Claims] 1. A control circuit for controlling a conduction width of a switching semiconductor element, which detects a zero point at which a power supply voltage becomes substantially zero, and receives a zero point detection signal from the circuit to lower an output to a low level. A monostable multivibrator that raises the output to a high level again after a time corresponding to a predetermined minimum control angle, an oscillator that generates a clock pulse group sufficiently higher than the power supply frequency, and a clock pulse of the oscillator. An AND circuit for AND logic of the group and the output of the monostable multivibrator to output an intermittent clock pulse block; and an interrupt process that starts upon receiving the zero-point detection signal, and based on the output detection signal and the setting signal. The control angle of the switching semiconductor element is calculated and the count command signal corresponding to the control angle is output within the time corresponding to the minimum control angle. And a timer that receives the output signal of the AND circuit, starts counting clock pulses, and generates an output signal when the count value becomes equal to the count set value by the count command signal given from the computer. A control circuit for a switching semiconductor element characterized by the above.