JPH0734656B2 - Inverter device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inverter device suitable as a power supply device for an electronic computer or the like. In particular, the present invention relates to improvement of a device for controlling so as to suppress overcurrent of a semiconductor switch.

[Conventional technology]

FIG. 1 shows a main circuit of a conventional inverter device. E is a DC power supply, and X and Y are DC power supply terminals. S _{1 to} S ₄ are open / close switch elements, and semiconductor switches such as transistors and GTO thyristors are used. A portion I shown by a broken line is a DC-to-AC conversion circuit. F is a filter for extracting the sine wave of the fundamental wave frequency component from the distorted wave alternating current obtained at its output. L is the load of this inverter. T is a transformer and CT is a current transformer for current detection.

The current control for suppressing the overcurrent of such a device performs constant current control by interrupting the voltage control system so that the output current detected by the current transformer CT does not exceed the set current value. Is configured.

FIG. 2 is a block diagram of a control system of a conventional inverter device for this purpose. Reference numeral 1 is a DC reference voltage circuit that generates a DC voltage that serves as a reference for the output voltage. Reference numeral 2 is a rectifying / smoothing circuit for converting the output voltage v of the inverter device into a direct current. An error amplifier 3 amplifies the difference between the output of the DC reference voltage 1 and the output of the rectifying / smoothing circuit 2. Reference numeral 1'denotes a DC reference voltage generating circuit that generates a DC voltage that serves as a reference for the output current control value. Reference numeral 2'denotes a peak hold circuit, which has therein a time constant circuit for converting the output current i into a direct current and for slowly raising the output voltage after the overcurrent has subsided. An error amplifier 3'amplifies the difference between the output of the reference voltage 1'and the peak hold circuit 2 '. 4 is an oscillator.
Reference numeral 5 is an amplitude modulator, and the output of the error amplifier 3 uses the level of the lower signal of the output of the error amplifier 3 ',
It is configured to change the output amplitude of the oscillator 4. 6
Is a triangular wave generator. A PWM (pulse width modulation) circuit 7 generates a pulse width modulation signal by using the output of the triangular wave generator 6 as a carrier and the output of the amplitude modulator 5 as a modulation input. A logic circuit 8 converts the output of the PWM circuit 7 into an on / off pattern of the open / close switch element.

In such a conventional method, when an overcurrent temporarily occurs in the output current, the output voltage must be slowly raised so that the transformer T does not saturate when the overcurrent subsides with the passage of time. . That is, even if the overcurrent flows for only a short time and immediately returns to the steady load state, unless the saturation state of the transformer T is restored, the abnormal voltage drop continues for a long time over several cycles, and the output voltage of the inverter is Immediate return to steady voltage is not possible. Therefore, when the power is not supplied to the load during this period and the information processing device is connected as the load, there is a drawback that the load is seriously affected.

Therefore, the current is detected from the output of the inverter device, and when this current exceeds the overcurrent level, the switch elements are turned off all at once so that the normal output voltage can be restored quickly. Technology has been proposed
57-173378).

[Problems to be Solved by the Invention]

However, the conventional technique for detecting the output current of the inverter device cannot prevent the switch element from being damaged due to the increase in the primary current due to the demagnetization of the transformer that occurs when the on / off width of the switch element is rapidly changed. There are drawbacks. This bias is a phenomenon in which the DC component is applied to the transformer due to the difference in the time integrated value of each of the upper and lower half cycles of the AC component, which causes an overcurrent. This is caused by changing the ON / OFF width of the switch element according to the fluctuation of the load and the load so as to keep the output constant.

Furthermore, if the repetition frequency of the cycle of simultaneous turning off and returning of the switch elements is increased, the switching loss of the semiconductor switch elements increases, and there is a problem that the switch elements are damaged.

The present invention solves the above-mentioned problem, and controls a switching element during a saturation phenomenon of an inverter transformer to reliably protect a semiconductor switching element from damage, and to prevent other problems even if a short-time overcurrent occurs. It is an object of the present invention to provide an inverter device that does not affect the load.

[Means for Solving the Problems]

In the first aspect of the present invention, the current detector is configured to detect the current in the primary winding of the transformer, and the comparison means detects that the detection output of the current detector exceeds a predetermined value. Only when the output of the comparison means is being transmitted, sending of the switching control signal to the switching switch element is prohibited, the switching element is opened, and the overcurrent recovers as soon as the transformer returns from the saturated state. The output voltage can be restored to a normal value, and the switch element can be prevented from being damaged by the increase in direct current flowing in the primary winding of the transformer that occurs when the on / off width of the switch element is rapidly changed. It is characterized in that it is configured as follows.

Further, a second aspect of the present invention is a switch which prohibits transmission of an opening / closing control signal given to the switch element only during a period from when the output of the comparing means is transmitted to when the output carrier of the carrier generating means reaches a predetermined phase. With the element open,
The feature is that the output voltage is quickly restored to a normal value after the overcurrent is recovered.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of the main circuit portion of the apparatus of the present invention. The output current supplied to the primary winding of the transformer T is the current detector R
The feature is that it is given through. The current detector R is composed of a resistor or a current transformer (CT).

FIG. 4 is a circuit diagram of the first embodiment circuit of the control unit for applying a control current to the open / close switch elements S _{1 to} S ₄ of the above embodiment circuit.
Reference numeral 9 is a half-sine oscillator that serves as a voltage reference. Reference numeral 10 is a full-wave rectifier circuit that converts the output voltage v into a DC voltage. This output is input to the error amplifier 3 together with the output of the half sine wave oscillator 9. The output of this error amplifier 3 becomes the modulation input of the PWM circuit 7. The carrier of this PWM circuit 7 is the triangular wave generator 6
Given by. The output of the PWM circuit 7 is given to the logic circuit 8 as a voltage control pulse train signal.

On the other hand, the current signal i detected by the current detector R shown in FIG. 3 is converted into direct current by the full-wave rectifier circuit 10 '. The output of the full-wave rectifier circuit 10 'and the output of the DC reference voltage circuit 1'which provides a DC voltage serving as a reference for the current control value are respectively applied to the two inputs of the comparator 7'and compared. A current control pulse signal train is obtained at the output of the comparator 7 '. The output of the comparator 7'is positively fed back to its positive input terminal and added to the output of the DC reference voltage circuit 1 '. Due to this positive feedback, the comparator 7'has hysteresis. Reference numeral 11 is an isolator for insulating the main circuit from the voltage control system. This isolator 11 is not necessary when the current detector R uses an insulated current transformer.

FIG. 5 is a circuit configuration diagram for explaining in more detail the circuit of the portion indicated by the alternate long and short dash line in FIG. That is, the comparator 7'is composed of one differential operational amplifier, and the resistor R ₂
Positive feedback is given by. The isolator 11 is composed of a photo coupler. The logic circuit 8 is configured so that when the output from the isolator 11 is exhausted, the transmission of all control outputs is stopped, and the open / close switch elements S _{1 to} S ₄ are opened simultaneously.

The operation of the apparatus thus configured will be described. FIG. 6 is a waveform diagram for explaining the operation of this circuit. 6A to 6M are waveform diagrams of points A to M shown in FIG. 4 or FIG.

The output voltage v supplied to the load in FIG. 3 is rectified by the full-wave rectifier circuit 10 in FIG. 4 to have the waveform in FIG. 6A. on the other hand,
The half-sine oscillator 9 outputs a signal having the waveform shown in FIG. 6B. The error amplifier 3 amplifies the difference between the waveforms A and B to obtain the waveform shown in FIG. 6C. The triangular wave generator 6 generates the triangular wave shown in FIG. 6D, and the PWM modulation circuit 7 outputs both signals C and D.
Are compared in magnitude to obtain the waveform of FIG. 6E which is a voltage control pulse train. The waveform E is a pulse train that is a high signal during a period when the waveform C is at a higher level than the waveform D and a low signal during a period when the waveform C is at a low level.

The output current i of the current detector R is rectified by the full-wave rectifier circuit 10 'and has a waveform shown in FIG. 6G. The output of the DC reference voltage circuit 1'which serves as a reference for the current is added to the output of the comparator 7'to form the waveform shown in FIG. 6H, which is the output J of the comparator 7 '.
The waveform has two levels, V _H when V is high and V _L when _L is low. In the comparator 7 ', the magnitudes of the levels of the waveforms G and H are compared, and the output of the voltage control system is prohibited by the output J of the comparator 7'having the waveform of the current control pulse train shown in FIG. During this period, the open / close switch elements S _{1 to} S ₄ are turned off to suppress an increase in overcurrent.

That is, the full-wave rectifier circuit 10 'corresponding to the absolute value of the output current
When the output G is low, the output J of the comparator 7'is high and the input H of the comparator _{7'is at} the level _VH . When the current increases and the output G of the full-wave rectifier circuit 10 'exceeds _VH , the output J of the comparator 7'becomes low, and during this period, all signals of the logic circuit 8 are prohibited, Open / close switch element
S _{1 to} S ₄ are turned off and the current gradually decreases. on the other hand,
Due to the positive feedback, the input H of the comparator 7'changes to the level V _L when the output J of the comparator 7'is low. Current i decreases, the output G of the full-wave rectifier circuit 10 'is below the level V _L, inhibited is released, the switch elements S ₁ to S ₄ is returned to the driving by the signal of the voltage control system. Current decreases, the output G of the full-wave rectifier circuit 10 'is the time according to the V _H down to V _L, switching element S ₁ to S ₄ is during this time will not be switched at a high frequency.

As described above, when a temporary overcurrent is generated in the load, it is immediately fed back to the control system and controlled so as to lower the output voltage, and when the overcurrent disappears, it can be immediately restored to the normal voltage.

FIG. 7 is a circuit diagram of the second embodiment of the present invention. This 7th
The drawing shows only the part of the control circuit, and the circuit shown in FIG. 3 is the same as that of the first embodiment described above. As for the control circuit part, in comparison with the circuit of FIG. 4 described above, the R (reset) terminal of the RS flip-flop 12 is connected to the output of the isolator 11, and the S (set) terminal of the triangular wave generator 6 is connected to this output terminal. It is characterized in that the outputs are connected and the output of the flip-flop 12 is applied to the logic circuit 8. Further, the comparator 7'has no positive feedback. The other structure is similar to that of the first embodiment described above.

The operation of the apparatus thus constructed will be described with reference to the waveform chart shown in FIG. The waveforms shown in FIGS. 8A to 8M are voltage waveform diagrams of points A to M shown in FIG.

When the current i increases and the output G of the full-wave rectifier circuit 10 'reaches the level of the output of the DC voltage reference circuit 1'which shows the current control value, the output of the comparator 7'and the output R of the isolator 11 are at a high level. become. This signal causes the flip-flop 12
Output Q becomes low and the output of the logic circuit 8 is prohibited. During this time, the switch elements S _{1 to} S ₄ are in the off state. The output Q of the flip-flop 12 is kept at a low level until it is set by the pulse train of the waveform S in which the output D of the triangular wave generator 6, which is a triangular wave of the carrier, becomes high level every cycle. The off state continues until the end of the cycle. When the flip-flop 12 is set by the waveform S and the output Q of the flip-flop 12 becomes high level, the inhibition is released and the switch elements S _{1 to} S ₄ are restored to normal driving by the signal of the voltage control system. Since inhibition state continues until the end of one cycle of the carrier, the switching element S ₁ to S ₄ is not be switched at a frequency higher than the number of cycles of the carrier.

That is, to turn it off once the switching element S ₁ to S _4, when the period until the return is released prohibition has become smaller by a constant of the constant and the control circuit of the AC filter, the period of the triangular wave of the waveform S Is always switched, and never exceeds the triangular wave period. This is AC when overloaded
It is possible to prevent the switching frequency from increasing due to the constant of the filter and the constant of the control circuit and the switching loss to increase due to the increase in the number of times of switching, resulting in damage to the switch element.

The above example is a voltage control system, and explained using the method of comparing the output voltage with the reference after full-wave rectification using the sine half-wave waveform as the reference.
The present invention can also be implemented by a method of using a sinusoidal full-wave waveform as a reference and comparing the output voltage as it is with this reference. Further, the case where the present invention is applied to the single-phase output inverter device has been described.
A phase inverter is constructed. The inverter conversion circuit can be implemented not only in the single-phase bridge circuit shown in FIG. 3, but also in a temporary half-bridge circuit or a three-phase bridge inverter circuit.

〔The invention's effect〕

As described above, according to the present invention, an overcurrent is detected on the primary side of the transformer, and the switch elements are simultaneously turned off to suppress the overcurrent output in a section shorter than a half cycle of output. This overcurrent control is performed by current waveform control, and it can be started by instantaneous current waveform control when the overcurrent is recovered.Therefore, it is possible to suppress the bias magnetizing current of the transformer and the inrush current to the load side while suppressing the switching element. A current of maximum capacity can be passed, and the output voltage can be quickly returned to a normal value. In the conventional voltage waveform control, when the control is suddenly restored, an excessive current flows in the switching element due to the inrush current to the load side or the biased magnetism of the transformer, so that rapid startup cannot be performed. It is possible to rapidly recover the output voltage even within half a cycle.

Further, the present invention detects an overcurrent on the primary side of the transformer, so that an excessive current flows through the switching element connected to the primary side of the transformer due to the demagnetization phenomenon of the transformer, and the semiconductor switch is overloaded due to overcurrent. Can be prevented from being damaged.

Further, since the switching speed of the switching element is suppressed so that the switching frequency of the switching element does not exceed the carrier frequency at the time of overcurrent, damage to the semiconductor switch due to an increase in switching loss can be prevented.

Therefore, even if a load that allows an inrush current to flow is applied, the current only drops for the period during which the inrush current is flowing, so there is little effect on other loads connected in parallel. Further, if a resistor is used for the current detector, even if a DC component is contained in the output current, such as when the transformer is saturated, the current can be accurately detected, so that it is possible to use up to the capacity limit of the switching element, which is economical.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main circuit of a conventional inverter device. FIG. 2 is a block diagram of a control circuit of a conventional inverter device. FIG. 3 is a block diagram of the main circuit of the device of the present invention. FIG. 4 is a block diagram of the control circuit of the first embodiment device of the present invention. FIG. 5 is a partial circuit diagram thereof. FIG. 6 is a waveform diagram of each part of the circuit according to the first embodiment of the present invention. FIG. 7 is a block diagram of the circuit of the second embodiment of the present invention. FIG. 8 is a waveform diagram of the circuit according to the second embodiment of the present invention.

Claims (2)

[Claims] 1. A DC power supply input terminal, and a conversion circuit which includes a plurality of switch elements and which alternately opens and closes the DC power supply input applied to the input terminals to convert the DC power supply input to AC and output the AC. A transformer that converts the voltage of the output of the circuit, a filter that extracts the component of the fundamental frequency from the output of this transformer, a fundamental frequency generating means that gives the fundamental frequency, and a switching frequency of the switch element. A carrier wave generating means for outputting a triangular wave and an output of the fundamental wave frequency generating means are used as modulation inputs, and an output of the carrier wave generating means is used as a modulated input. A pulse width modulation circuit for giving a signal, a current detector, and a comparison means for detecting that the detection output of the current detector exceeds a predetermined value, An inverter device provided with a means for prohibiting transmission of an opening / closing control signal given to the switch element to open the switch element only while the output of the comparing means is being transmitted. An inverter device characterized in that it is configured to detect the current in the primary winding of a transformer. 2. A DC power supply input terminal, and a conversion circuit which includes a plurality of switch elements and which alternately opens and closes the DC power supply input applied to the input terminals to convert the DC power supply input to AC and output the AC. A transformer that converts the voltage of the output of the circuit, a filter that extracts the component of the fundamental frequency from the output of this transformer, a fundamental frequency generating means that gives the fundamental frequency, and a switching frequency of the switch element. A carrier wave generating means for outputting a triangular wave and an output of the fundamental wave frequency generating means are used as modulation inputs, and an output of the carrier wave generating means is used as a modulated input. A pulse width modulation circuit for giving a signal, a current detector, and a comparison means for detecting that the detection output of the current detector exceeds a predetermined value, An inverter device provided with a means for prohibiting transmission of an opening / closing control signal given to the switch element to open the switch element only while the output of the comparing means is being transmitted. Is a structure for detecting the current of the primary winding of the transformer, the means for opening the switching element is from the transmission of the output of the comparison means to the predetermined phase of the output triangular wave of the carrier generation means. An inverter device characterized by prohibiting the transmission of the switching control signal during the period.