JP2002010645A - Voltage-control method and unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage-control unit having no occurrence of a distortion even in the neighborhood of a zero-cross point of an output voltage and no fluctuation of a voltage waveform even if power fails. SOLUTION: A switching signal of a chopper circuit 4 that controls an applied voltage applied to a primary winding 2 of a transformer 1 is generated by combining a PWM signal generated at a control unit 11 and a synchronized signal generated at a synchronized-signal generating circuit 12. The synchronized signal is the one that repeats 'H' and 'L' at every half cycle of an input- voltage waveform, and always indicates 'L' in the neighborhood of 400 μs of the zero-cross point of the input voltage. The chopper circuit 4 is chopping- controlled by the PWM signal only when the synchronized signal indicates 'L'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage control method and a voltage control device for controlling a secondary output voltage by changing a primary voltage of a transformer by PWM control.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a voltage controller for controlling a voltage in a single-phase three-wire circuit by PWM control (pulse width modulation control). FIG. 3 shows a voltage control device that steps down the input voltage of 200 V by a maximum of 20 V by a transformer and outputs 180 V, and connects the primary winding 21 of the transformer 20 to both voltage lines XY of the power supply side input terminal 23. A secondary winding 22 composed of two windings is connected in series to voltage lines X and Y of an input terminal 23 and voltage lines x and y of an output terminal 24, respectively. The neutral line N of the input terminal 23 is directly connected to the neutral line n of the output terminal 24.

The primary winding 21 has an input voltage of four FETs.
Is applied by a PWM chopper circuit 25 in which the voltage of the output terminal 24 is set to an output set value.
The voltage waveform chopped by the chopper circuit 25 is shaped into a sine wave voltage by the output filter circuit 26 and applied to the primary winding. FIG. 4 shows an input voltage waveform and an operation time chart of the four FETs, and shows a case where the pulse duty ratio is 50% and the input voltage is stepped down by 10 V and output.

[0004]

However, in the case of the above configuration, the voltage applied to the primary winding of the transformer 20 is not switched according to the time chart of FIG. At the zero cross, and the voltage at the output terminal was also distorted near the zero cross. Also, if there is a momentary power failure during operation, there will be a difference between the voltage drop time between the two voltage lines and the voltage drop time of the control circuit. Since there is a difference between the time when the voltage of the control circuit rises and the time when the voltage of the control circuit rises to the steady value, the switching operation of the FET is uncertain in each transition period. As a result, the voltage applied to the primary winding of the transformer becomes an indefinite value, and as a result, the output voltage fluctuates greatly.

Accordingly, in view of the above problems, the present invention provides a voltage control method and a voltage control device which do not cause distortion even when the output voltage is near zero crossing and which do not disturb the voltage waveform even if a power failure occurs. The task is to provide

[0006]

According to a first aspect of the present invention, a primary winding of a transformer is connected between two voltage lines of a single-phase three-wire circuit via a chopper circuit. A voltage for controlling a load applied voltage by connecting a secondary winding of the transformer in series between the voltage lines and the load and applying a chopped voltage to the primary winding by PWM control of a chopper circuit. A control method, comprising: a synchronizing signal generating step of repeatedly generating “H” and “L” signals every half cycle of an input voltage; A synchronization signal processing step of processing and outputting the synchronization signal so as to always be "L", and outputting a PWM signal and performing chopper control when the processed synchronization signal is "L". Voltage control method.

A second aspect of the present invention is based on the first aspect, wherein the synchronizing signal does not change "H" and "L" between several hundreds μS before and after the zero-cross point of the power supply voltage, or “H”, except for a few hundred μS before and after the zero cross point,
It is characterized by having a step of judging a power failure when there is a change of “L” and cutting off the input voltage.

According to a third aspect of the present invention, a primary winding of a transformer is connected between both voltage lines of a single-phase three-wire circuit via a chopper circuit, and a secondary winding of the transformer is connected to the two windings. A voltage control device which is connected in series between a voltage line and a load and controls a load applied voltage by applying a chopped voltage to the primary winding by PWM control of a chopper circuit, comprising: a PWM signal generating means; A synchronizing signal generating means for generating a signal synchronized with a voltage cycle; and a control means for outputting a switching signal of the chopper circuit by combining the PWM signal and a synchronizing signal from the synchronizing signal generating means. I do.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the signal generated by the synchronizing signal generating means repeats "H" and "L" every half cycle of the power supply voltage, and the control means converts the synchronizing signal to Several hundred μS around the zero cross point of the power supply voltage
During this period, the signal is always processed to be an "L" signal, and the processed signal and the PWM signal are combined to output a switching signal.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, a first switching means is provided on a power supply side voltage line of the chopper circuit, and a second switching means is provided between both ends of the primary winding. Means for opening the first opening / closing means and closing the second opening / closing means when a power failure is detected.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the power failure detecting means is configured such that the synchronizing signal from the synchronizing signal generating means outputs "H" between several hundreds μS before and after the power supply voltage at the zero cross point. When there is no change in “L”, or when there is a change in “H” or “L” other than a few hundred μS before and after the zero cross point, it is determined that a power failure has occurred. still,
Several hundred μS means 100 μS to 800 μS.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an example of a voltage control device according to the present invention, where 1 is 1
Transformer having two primary windings 2 and two secondary windings 3,
Represents a chopper circuit having first to fourth four FETs;
a is an input filter circuit, 5b is an output filter circuit, and both voltage lines X and X of the input terminal 8 connected to the single-phase three-wire circuit are provided.
Y is connected to the primary winding 2 of the transformer 1 via the chopper circuit 4 and the filter circuits 5a and 5b, and the secondary winding 3 composed of two windings is connected to the power supply voltage lines X and X of the input terminal 8, respectively. The neutral line N of the input terminal 8 is directly connected to the neutral line n of the output terminal 9, which is connected in series to the voltage lines x, y of the output terminal 9 connected from Y to the load.

A first switch 6a is connected to the power supply side voltage line X.
However, the second switches 6b are respectively provided in parallel with the primary winding 2, and both are formed by the a contact and the b contact of one electromagnetic switch. The FETs of the switches 6a and 6b and the chopper circuit 4 are controlled by the control unit 11. The control unit 11 is connected to a synchronizing signal generating circuit 12 which receives an AC voltage signal from the input terminal 8 and generates a pulse signal synchronized with the zero cross point of the AC power supply, and detects a voltage value of the output terminal 9. A voltage reading circuit 13 that outputs a voltage value signal is connected to the control unit 11.

The control unit 11 includes a microcomputer and controls first to fourth four output units 11 for controlling each FET.
The four output units 11a to 11d are respectively connected to four OR circuits 14, and the output of the OR circuit 14 is used as an FET control signal of the chopper circuit 4. It also has one output port 11e for controlling the first switch 6a and the second switch 6b, and the output port 11e is connected to the switch control circuit 16 to control the opening and closing of the first and second switches simultaneously. ing.

The control operation of the control unit 11 will be described with reference to the time chart of FIG. First, during normal operation, the synchronization signal generation circuit 12 generates a pulse signal synchronized with the AC power supply between the input terminals, and inputs the pulse signal to the input port of the control unit 11. The control unit 11 starts the internal counter while synchronizing with the pulse signal. This counter is cleared to 0 each time a rising edge of the pulse signal is detected. Further, a comparison operation is performed between a preset value set by the output voltage setting unit 15 and a read value of the output voltage input from the voltage reading circuit 13, and a positive active signal of a PWM pulse signal having a pulse width according to the result is calculated. Is output from the output unit 11a, and a negative active signal is output from the output unit 11b.

A specific s value is added to the value of the internal counter,
For example, the following operation is performed by setting s = 400 μS. First, when the value of the internal counter becomes s, the fourth output unit 1
The output of 1d is set to "H". Next, when the value of the internal counter becomes "half cycle-s", the fourth output unit 11d is set to "L", and when it becomes "half cycle + s", the third output unit 11c is set to "H". , "1 cycle-s", the third
Is set to "L". Thus, the output of the third output unit 11c is used as a pulse signal processing signal, and the output of the fourth output unit 11d is output by inverting the signal of the third output unit 11c. Then, by interposing the signals of the first to fourth output units with the four OR circuits 14 as shown in the figure, the pulse signal is converted into the input AC as shown in A, B, C, and D of FIG. The PWM signal is output only while the "L" signal synchronized with the voltage signal is being output, and the chopper circuit 4 is controlled by this signal.

Next, the operation when a power failure occurs will be described. First, a power outage is determined under the following three conditions. 1. When the value of the internal counter changes from “half-circle-s” to “half-circle +
When the pulse signal synchronized with the AC power supply does not change from “H” to “L” during “s”. 2. When the value of the internal counter changes from “1 cycle−s” to “1 cycle +
When the pulse signal synchronized with the AC power supply does not change from “L” to “H” during “s”. 3. When the value of the internal counter changes from “half-circle-s” to “half-circle +
out of the period of "s" or "1 cycle-s" to "1 cycle + s"
When the pulse signal synchronized with the AC power supply changes from “H” to “L” or from “L” to “H” outside the period.

In the above case, it is determined that a power failure has occurred, and the second output unit 11b is set to "H", the first output unit 11a, the third output unit 11c, and the fourth output unit 11d are set to "L". The operation signals of the first and second switches 6a and 6b are output from the output port 11e to open the first switch 6a and close the second switch 6b to cut off the circuit from the input voltage. By doing so, the supply voltage to the primary winding 2 of the transformer 1 becomes 0V.

As described above, by stably outputting the PWM signal before and after the zero cross of the input voltage, the output voltage becomes zero.
There is no distortion near the cross. In addition, when the voltage drops due to a power failure, the voltage at the output terminal drops in the same way as the input terminal side, and the voltage waveform does not disturb due to a mistrigger of the FET during the fall. Control can start after the FE has stabilized
The output terminal voltage waveform is not disturbed by the T mistrigger. Note that the s value does not have to be 400 μS,
The function can be satisfactorily performed between μS and 600 μS, but 400 μs is preferable at 50 Hz, and 330 μs is preferable at 60 Hz. In this embodiment, the control unit also serves as a PWM signal generation unit and a power failure detection unit, but may be configured separately.

[0020]

As described in detail above, according to the first and third aspects of the present invention, the chopper circuit is controlled by combining the PWM signal and the signal synchronized with the cycle of the power supply voltage. It is possible to eliminate the distortion of the load applied voltage.

According to the second aspect of the present invention, in addition to the effect of the first aspect, the input voltage at the time of a power failure is cut off, so that the voltage at the output terminal decreases in the same manner as the input terminal side, and a voltage waveform caused by a mistrigger during the decrease. There is no disturbance.

According to the invention of claim 4, in addition to the effect of claim 3, the synchronization signal synchronized with the cycle of the power supply voltage is "L".
By outputting the PWM signal only in the case of, the waveform distortion near the zero cross can be eliminated.

According to the fifth aspect of the present invention, in addition to the effect of the fourth aspect, the input voltage at the time of a power failure is cut off, so that the voltage at the output terminal decreases in the same manner as the input terminal side, and the voltage waveform caused by a mistrigger during the decrease. There is no disturbance. Also, at the time of recovery after a power failure, control can be started after the voltage of the input terminal is stabilized, so that the output terminal voltage waveform is not disturbed by a mistrigger of the chopper circuit. Therefore, even if a power failure occurs, the voltage waveform is not disturbed.

According to the invention of claim 6, in addition to the effect of claim 5, an instantaneous power failure can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a voltage control device showing an example of an embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation of FIG. 1;

FIG. 3 is a circuit block diagram of a voltage control device showing a conventional voltage control device.

FIG. 4 is a time chart for explaining the operation of FIG. 3;

[Explanation of symbols]

1. Transformer, 2. Primary winding, 3. Secondary winding, 4.
Chopper circuit, 5 filter circuit, 6a first switch, 6b second switch, 8 input terminal, 9 output terminal, 11 control unit, 12 synchronization signal generation circuit,
13. Voltage reading circuit, 14. OR circuit, 15 output voltage setting section.

Claims (6)

[Claims] 1. A primary winding of a transformer is connected between both voltage lines of a single-phase three-wire circuit via a chopper circuit, and a secondary winding of the transformer is connected between the two voltage lines and a load. A voltage control method for controlling a load applied voltage by applying a voltage chopped by PWM control of a chopper circuit to the primary winding, wherein "H" is applied every half cycle of the input voltage.
A synchronizing signal generating step of repeatedly generating an “L” signal, and a few hundred μs before and after the zero cross point of the input voltage signal.
A synchronization signal processing step of processing and outputting the synchronization signal so as to always be “L” during the period of time, and outputting a PWM signal to perform chopper control when the processed synchronization signal is “L”. A voltage control method characterized by the above-mentioned. 2. When there is no change in “H” and “L” between several hundred μS before and after the zero cross point of the power supply voltage, or between several hundred μS before and after the zero cross point. 2. The voltage control method according to claim 1, further comprising the step of judging a power failure when there is a change in "H" and "L" and cutting off the input voltage. 3. A primary winding of a transformer is connected between both voltage lines of a single-phase three-wire circuit via a chopper circuit, and a secondary winding of the transformer is connected between the two voltage lines and a load. A voltage control device, which is connected in series between the first and second coils and controls a load applied voltage by applying a chopped voltage to the primary winding by PWM control of a chopper circuit, wherein the voltage control device is synchronized with a PWM signal generating means and a cycle of the input voltage. A voltage control device comprising: a synchronizing signal generating means for generating a converted signal; and a control means for outputting a switching signal of the chopper circuit by combining the PWM signal and a synchronizing signal from the synchronizing signal generating means. 4. A signal generated by the synchronizing signal generating means repeats "H" and "L" every half cycle of the power supply voltage. 4. The voltage control device according to claim 3, wherein the signal is processed so as to be always an "L" signal during several hundreds of seconds before and after, and a switching signal is output by combining the processed signal and the PWM signal. 5. A power supply side voltage line of a chopper circuit, a first switching means, a second switching means between both ends of a primary winding, and a power failure detection means are provided.
5. The voltage control device according to claim 4, wherein the opening / closing means is opened and the second opening / closing means is closed. 6. A power failure detection means, wherein the synchronization signal from the synchronization signal generation means is several hundred μm around a zero cross point of the power supply voltage.
When there is no change of “H” and “L” between S, or 0
"H", "L" except for a few hundred μS before and after the cross point
6. The voltage control device according to claim 5, wherein it is determined that a power failure has occurred when the power supply has changed.