JPH06209584A - Control circuit of momentary value control pulse width modulation inverter - Google Patents

Abstract

PURPOSE:To return an output voltage to its original value smoothly without any failure by a momentary value control PWM inverter for suppressing the output voltage to limit excessive current. CONSTITUTION:A signal switcher 20 switched according to the output signal of an inverter output abnormality detection circuit 30 which detects that an AC current detection value I is over and an AC voltage detection value V is under is provided at the output circuit of a circuit 14 for generating the amount of compensation of momentary waveform. The inverter output abnormality detection circuit 30 is provided with an overvoltage comparator for detecting overcurrent, an undervoltage comparator for detecting output voltage reduction, an AND element for inputting both comparator signals, and a latch circuit for switching the signal switcher 20 according to the signal of the AND element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for preventing an output voltage from being abnormal when an instantaneous value control pulse width modulation inverter recovers from an overcurrent.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a general main circuit of an instantaneous value control pulse width modulation inverter. As shown in FIG. 4, an inverse parallel connection circuit of a gate insulating bipolar transistor as a semiconductor switching element and a diode is bridge-connected to provide an instantaneous value control pulse width modulation inverter 3 (hereinafter, pulse width modulation is abbreviated as PWM). To make). The DC power from the DC power supply 2 is converted into AC power by this instantaneous value control PWM inverter 3,
It is supplied to the load 5 via the transformer 4. Here, 6 is an inverter control circuit.

FIG. 5 is a circuit diagram showing a partial configuration of a conventional example of the inverter control circuit 6 shown in FIG. 4, but parts irrelevant to the present invention are omitted. In the conventional circuit shown in FIG. 5, an AC waveform generator 12 which inputs a voltage amplitude command signal E ^* of a DC amount and a voltage / frequency converter (hereinafter referred to as a frequency / frequency converter which also inputs a frequency command signal F ^* of a DC amount). Since the average value control voltage adjuster 11 is composed of a V / F converter 13), the AC waveform generator 12 outputs a sinusoidal AC voltage waveform command signal V ^* . The instantaneous waveform correction amount generation circuit 14 whose main component is the proportional controller 15 inputs this AC voltage waveform command signal V ^* and the AC voltage waveform detection signal V detected from the output side of the instantaneous value control PWM inverter 3. Then, the instantaneous waveform correction amount W is obtained by inputting the deviation between the instantaneous values of these two inputs to the proportional controller 15.

The adder 16 is an average value control voltage regulator 11
Is calculated by adding the above-mentioned instantaneous waveform correction amount W to the AC voltage waveform command signal V ^* . Thus, since the high-performance waveform control is performed by adding the instantaneous waveform correction amount W to the voltage waveform obtained by the average value control, the instantaneous value control P
The WM inverter 3 outputs a sinusoidal alternating current with little distortion. The pulse width modulation circuit 17 is composed of a PWM comparator 18 and a carrier oscillator 19, and the adder 1
The result of addition operation 6 is input and the PWM pulse P for controlling the instantaneous value control PWM inverter 3 is output.

[0005]

The instantaneous value control PWM inverter 3 shown in FIG. 4 is controlled by the inverter control circuit 6, and the circuit configuration and operation of this inverter control circuit 6 are as described above with reference to FIG. Is. Here, for example, when a load short-circuit accident occurs and an excessive current flows in the instantaneous value control PWM inverter 3, the output voltage is reduced until the short-circuit accident is removed by melting the fuse or breaking the circuit of the circuit breaker. The device is protected by performing current limiting control that suppresses the output current from becoming excessive. However, if the output voltage continues to be suppressed due to the load short circuit in this way, the output voltage will vibrate due to the instantaneous waveform correction amount. The voltage waveform suddenly rises, causing the transformer 4 to be demagnetized. Due to this demagnetization phenomenon, the overcurrent state continues for a long time, which causes a problem that the rated voltage is not smoothly restored.

Therefore, the present invention is an instantaneous value control PWM inverter that suppresses an output voltage in order to limit an excessive current,
The purpose is to enable smooth recovery of the output voltage without returning to its original value.

[0007]

In order to achieve the above object, a control circuit of an instantaneous value control pulse width modulation inverter according to the present invention is provided with a voltage amplitude command signal of a direct current amount for commanding the amplitude of an inverter output voltage. Input the frequency command signal of the DC amount that commands the frequency of the output voltage of the inverter,
AC waveform generating means for outputting the command value of the AC voltage waveform to be output by the inverter, and this AC voltage waveform command signal and the detection signal of the AC voltage waveform output by the inverter are input, and both inputs An instantaneous waveform correction amount generating means for outputting an instantaneous waveform correction amount for controlling the deviation to zero and an adding means for adding the AC voltage waveform command signal and the instantaneous waveform correction amount are provided, and the calculation result of the adding means is pulsed. In a control circuit of an instantaneous value control pulse width modulation inverter for performing width modulation control to output a desired AC, the output current of the instantaneous value control pulse width modulation inverter is an overcurrent of a predetermined value or more and the output voltage is a predetermined value or less. Inverter output abnormality detecting means for detecting the occurrence of undervoltage, and output of the instantaneous waveform correction amount generating means if the inverter output abnormality detecting means detects an output abnormality. The inverter output abnormality detecting means includes an overcurrent comparator that outputs a logic H signal when the output current becomes an overcurrent of a predetermined value or more, and a signal opening / closing means that shuts off the signal. Off-delay means for delaying the return to the logic L signal and outputting, an undervoltage comparator for outputting a logic H signal when the output voltage becomes an undervoltage of a predetermined value or less, and output signals of these offdelay means and a shortage. A logical product element for inputting the output signal of the voltage comparator, a latch means for outputting an open circuit signal to the signal switching means by the logical H signal output by the logical product element, and a logical L signal output by the undervoltage comparator. Reset means for applying a reset signal to the latch means.

[0008]

In the instantaneous value control PWM inverter, the control circuit is configured to add the instantaneous waveform correction amount obtained by the instantaneous waveform correction amount generating means to the AC voltage waveform command signal obtained by the average value control voltage adjusting means. . This instantaneous waveform correction amount causes a large difference from the previous control angle in an attempt to instantaneously correct the voltage waveform when it largely fluctuates, which is the cause of, for example, the demagnetization phenomenon of the transformer. Therefore, in the present invention, when an excessive current flows due to a load short circuit or the like to lower the inverter output voltage, the instantaneous waveform correction amount is shut off if an overcurrent of a predetermined value or more and an undervoltage of a predetermined value or less are detected. , By controlling the voltage only with the average value control, avoid the voltage abnormality that occurs when the output voltage is restored following the elimination of the overcurrent, and prevent the occurrence of the magnetic bias phenomenon in the transformer. It is what

[0009]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, showing only the structure necessary for the present invention, like the inverter control circuit described above with reference to FIG. Therefore, the average value control voltage regulator 1 shown in the circuit of the first embodiment of FIG.
1. Name and use of AC waveform generator 12, V / F converter 13, instantaneous waveform correction amount generation circuit 14, proportional controller 15, adder 16, pulse width modulation circuit 17, PWM comparator 18, and carrier oscillator 19 Since the functions have already been described with reference to FIG. 5, their description will be omitted.

In the present invention, the signal switch 20 is connected to the circuit connecting the instantaneous waveform correction amount generation circuit 14 and the adder 16.
Is provided so that the addition of the instantaneous waveform correction amount W to the AC voltage waveform command signal V ^* output from the average value control voltage regulator 11 can be interrupted. However, this signal switch 20 has an abnormality in the output of the inverter. When it detects that there is, it is designed to open the circuit. That is, the instantaneous value control PWM inverter 3
When the inverter output abnormality detection circuit 30 detects that the AC current detection value I output is an overcurrent of a predetermined value or more and the AC voltage detection value V is an undervoltage of a predetermined value or less, the inverter output abnormality is detected. Since the open circuit signal is sent from the detection circuit 30 to the signal switch 20, the pulse width modulation circuit 1
Only the AC voltage waveform command signal V ^* output from the average value control voltage regulator 11 is sent to 7, and the instantaneous value control PWM inverter 3 is operated by the voltage control based only on the average value control.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and is a circuit diagram showing the configuration of the inverter output abnormality detection circuit described in the first embodiment circuit of FIG. This second
As shown in the example circuit, the AC current detection value I detected from the output side of the instantaneous value control PWM inverter 3 is converted into a DC amount by the rectifier circuit 31. The overcurrent setting device 33 compares the alternating current detection value I with the overcurrent setting value set by the overcurrent setting device 33, and if the alternating current detection value I becomes larger, the overcurrent setting device 33 logically The H signal is output to the off-delay circuit 34. Similarly, the AC voltage detection value V detected from the output side of the instantaneous value control PWM inverter 3 is converted into a DC amount by the rectifier circuit 35, and the undervoltage setting value set by the undervoltage setting device 37 and this AC voltage detection value V are compared. When the AC voltage detection value V is smaller than that of the undervoltage comparator 36, the undervoltage comparator 36 outputs a logic H signal.

That is, if the detected value I of the alternating current exceeds the set value of the overcurrent and the detected value V of the alternating voltage becomes less than the set value of the undervoltage, both inputs to the logical product element 41 become a logical H signal.
The logic H signal is given to the latch circuit 43 to shut off the signal switch 20, and the instantaneous value control PWM inverter 3 is voltage controlled only by the average value control. Next, when the overcurrent state is released, the output voltage of the instantaneous value control PWM inverter 3 returns to the original value, so the output of the undervoltage comparator 36 becomes a logic L signal, and this logic L signal and the inverting element 42
The signal switch 20 is closed because the signal is inverted to the logic H signal and the latch circuit 43 is reset, and the instantaneous value control PWM inverter 3 returns to the control in the state in which the instantaneous waveform correction amount W is added to the average value control. .

FIG. 3 is a time chart showing the operation of the second embodiment circuit shown in FIG. 2. FIG. 3 shows changes in the output signal of the undervoltage comparator 36, and FIG. 3 shows the output signal of the overcurrent comparator 32. Change, FIG. 3 shows the latch circuit 4
Each represents the change of the output signal of No. 3.

[0014]

According to the conventional instantaneous value control PWM inverter,
In order to perform high-performance waveform control, the instantaneous waveform correction amount output by the instantaneous waveform correction amount generating means is added to the AC voltage waveform command signal output by the average value control voltage adjusting means, and the addition result is used as the control signal. If an excessive current flows due to a load short circuit or the like, the output voltage is lowered to protect the device.
Therefore, when the voltage is restored after the overcurrent is eliminated, there is a problem that the output voltage becomes abnormal due to the instantaneous waveform correction amount and the transformer is biased.However, in the present invention, the output current is a predetermined value. The circuit is configured to cut off the instantaneous waveform correction amount when it detects that the output voltage has become an undervoltage that is equal to or less than the predetermined value due to the above overcurrent. It is possible to avoid the problem that when the voltage returns to the original value, the output voltage becomes abnormal and the transformer is biased.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a time chart showing the operation of the second embodiment circuit shown in FIG.

FIG. 4 is a circuit diagram showing a general main circuit of an instantaneous value control pulse width modulation inverter.

5 is a circuit diagram showing a partial configuration of a conventional example of the inverter control circuit 6 shown in FIG.

[Explanation of symbols]

3 Instantaneous value control PWM inverter 4 Transformer 5 Load 6 Inverter control circuit 11 Average value control voltage regulator 12 AC waveform generator 13 V / F converter 14 Instantaneous waveform correction amount generation circuit 16 Adder 17 Pulse width modulation circuit 20 Signal Switch 30 Inverter output abnormality detection circuit 32 Overcurrent comparator 33 Overcurrent setting device 34 Off-delay circuit 36 Undervoltage comparator 37 Undervoltage setting device 41 AND element 42 Inversion element as reset means 43 Latch circuit E ^* Voltage amplitude command signal F ^* Frequency command signal I AC current detection value V AC voltage detection value V ^* AC voltage waveform command signal W W Instantaneous waveform correction amount

Claims (2)

[Claims] Claim: What is claimed is: 1. A direct current voltage amplitude command signal for commanding the amplitude of an inverter output voltage, and a direct current frequency command signal for commanding the frequency of the output voltage of the inverter are input and the inverter should output. An AC waveform generating means for outputting a command value of the AC voltage waveform, the AC voltage waveform command signal and the detection signal of the AC voltage waveform output by the inverter are input to control the deviation between both inputs to zero. An instantaneous waveform correction amount generating means for outputting an instantaneous waveform correction amount and an adding means for adding the AC voltage waveform command signal and the instantaneous waveform correction amount are provided, and the calculation result of the adding means is controlled by pulse width modulation to obtain a desired value. In the control circuit of the instantaneous value control pulse width modulation inverter for outputting the alternating current, the output current of the instantaneous value control pulse width modulation inverter is an overcurrent of a predetermined value or more and the output voltage is An inverter output abnormality detecting means for detecting that an undervoltage is a predetermined value or less, and a signal opening / closing means for shutting off the output signal of the instantaneous waveform correction amount generating means if the inverter output abnormality detecting means detects an output abnormality. A control circuit of an instantaneous value control pulse width modulation inverter characterized by comprising. 2. The control circuit of the instantaneous value control pulse width modulation inverter according to claim 1, wherein the inverter output abnormality detecting means outputs a logic H signal when the output current becomes an overcurrent of a predetermined value or more. An overcurrent comparator, an off-delay means for delaying the output of the overcurrent comparator to return to a logic L signal, and an undervoltage comparator for outputting a logic H signal when the output voltage falls below a predetermined value. A logical product element for inputting the output signal of the off-delay means and the output signal of the undervoltage comparator, and a latch means for outputting an open circuit signal to the signal opening / closing means by a logical H signal output by the logical product element, Reset means for applying a reset signal to the latch means by a logical L signal output from the undervoltage comparator. Instantaneous value control Pulse width modulation inverter control circuit.