JP2011228220A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that the diode of an inverter circuit is recovered reversely and broken down when a resonance type induction heating apparatus normally performing delay operation performs lead operation due to abnormality of a load, for example.SOLUTION: A power converter comprises a voltage detection circuit which detects the voltage between the main terminals of a semiconductor element, and a voltage comparison circuit which compares a voltage set value and the voltage detection value. The voltage set value and the voltage detection value are compared after the semiconductor element is turned off, and when the voltage set value is larger, semiconductor elements of facing arms constituting upper and lower arms and connected in series with the semiconductor element are not turned on.

Description

  The present invention relates to a protection circuit for a semiconductor element used in a power conversion device in which a resonant capacitor and an induction heating load are connected to an output and an output current is operated in a delayed phase with respect to an output voltage.

FIG. 3 shows a circuit diagram for explaining the background art, and FIG. 4 shows an operation waveform diagram thereof. First, the circuit diagram shown in FIG. 3 will be described.
The power converter 7 using the DC power supply 8 as a DC input is a single-phase rectangular wave output voltage source inverter composed of a DC capacitor 7e and IGBTs 7a to 7d having diodes connected in reverse parallel. The output is connected to an induction heating load 10 composed of a resonance capacitor 9, an inductance component 10a, and a resistance component 10b, and constitutes a resonance circuit as a whole. Here, a frequency command value output from a control circuit (not shown) is input to the pulse generation circuit 11 to generate a control signal. The control signal is input to the gate drive circuit 12, and the output thereof is input to the gates of the IGBTs 7 a to 7 d of the power converter 7.

  As shown in FIG. 4, the output voltage Vo of the power converter 7 is a rectangular wave, but since the output is connected to a resonance circuit, the output voltage Vo is operated at an output frequency near the resonance point of the resonance curve. At this time, the output current Io has a waveform close to a sine wave. Further, since the operation is performed at an output frequency higher than the resonance point, the output current Io has a delayed phase with respect to the output voltage Vo.

When the gate signals G7a and G7d are turned off at the point A of the operation period in the delayed phase which is a normal operating state, the voltages V7a and V7d across the IGBTs 7a and 7d rise, and the currents I7a and I7d flowing through the IGBTs are the IGBTs 7a and 7d. To the IGBTs 7b and 7c. Since the polarity of the currents I7a and I7c after commutation is negative, the current flows through the freewheeling (reflux) diode. However, the current gradually decreases due to the resonance circuit connected to the output, and the polarity is positive. The current increases after becoming.
Here, at point B of the period flowing through the freewheeling diode after a certain time from point A (the waiting time to prevent the short circuit between the upper and lower arms, hereinafter referred to as dead time). By turning on the gate signals G7b and G7c, the current is smoothly switched from the free wheel diode to the IGBT.

Next, the operation at point C of the operation period in the leading phase which is an abnormal operation state will be described. When the resonance frequency becomes high due to an abnormality in the induction heating load 10 (decrease in the inductance component 10a, specifically, a short circuit of the heating coil), the currents I7a and I7d are before the gate signals G7a and G7d are turned off. In addition, the polarity is negative and flows through the freewheeling diode. That is, the output current Io has a leading phase with respect to the output voltage Vo.
Therefore, even if the gate signals G7a and G7d are turned off at the point C, the current does not commutate to the IGBTs 7b and 7c, but flows directly to the free wheel diodes of the IGBTs 7a and 7d. After that, when the gate signals G7b and G7c are turned on at a point D after a certain time (dead time) from the point C, the free wheel diodes of the IGBTs 7a and 7d are suddenly reversely recovered, and the currents I7a and I7d are converted into the IGBTs 7b and 7c. Shed. In this case, for example, in a current region such as a small current, a surge voltage is generated due to a sharp reverse recovery of the free wheel diode, and the semiconductor element may be destroyed.
Further, when a MOSFET is used as a semiconductor element of a power converter and a parasitic diode is used as a free wheel diode, the power converter is destroyed only by performing a steep reverse recovery. Patent Document 1 describes background technology. However, the background technology is for applications in which the output current is gradually controlled by PWM switching, and is not suitable for the case where the semiconductor element breaks down even if the freewheel diode suddenly reverses even once.

JP 2004-112916 A

  The problem to be solved is related to a power converter that connects a resonant capacitor and an induction heating load to the output and operates the output current in a delayed phase with respect to the output voltage. Is to protect the freewheeling diode from being suddenly reverse-recovered when it reaches the leading phase.

In order to solve the above-mentioned problem, in the first invention, in the power converter that connects the resonant capacitor and the induction heating load to the output and operates the output current in a delayed phase with respect to the output voltage,
A voltage detection circuit for detecting a voltage between main terminals of the semiconductor element; and a voltage comparison circuit for comparing a voltage setting value with the voltage detection value, and after the predetermined time after the semiconductor element is turned off, the voltage setting value When the voltage setting value is large, the semiconductor element is connected in series with the semiconductor element and does not turn on the semiconductor element of the opposing arm that constitutes the upper and lower arms with the semiconductor element The protection circuit is provided.

In a second invention, the voltage detection circuit in the first invention is constituted by a plurality of voltage dividing resistors connected in parallel with the semiconductor element.
In a third invention, the voltage detection circuit in the first invention is configured by dividing a control circuit power supply by a plurality of resistors and connecting a diode between the voltage dividing point and the main electrode of the semiconductor element. .

  According to a fourth aspect of the present invention, there is provided a power converter for connecting a resonance capacitor and an induction heating load to an output and operating an output current in a delayed phase with respect to the output voltage, and a voltage detection circuit for detecting a voltage between main terminals of a semiconductor element. And a voltage comparison circuit that compares the voltage setting value and the voltage detection value, and after a predetermined time after turning off the semiconductor element, the voltage setting value is compared with the voltage detection value, and the voltage setting When the value is large, a protection circuit for a semiconductor element that stops the operation of the power converter is provided.

  In a fifth aspect, the semiconductor device according to the fourth aspect, comprising: a voltage detection circuit that detects a voltage between main terminals of the semiconductor element; and a voltage comparison circuit that compares a voltage setting value with the voltage detection value. After a predetermined time after the element is turned off, the arm that compares the voltage setting value and the voltage detection value to determine that the voltage setting value is large is the entire arm of the power conversion device or the power conversion device. One of the arms operating simultaneously.

  In a sixth aspect, the semiconductor device according to the fourth aspect, comprising: a voltage detection circuit that detects a voltage between main terminals of the semiconductor element; and a voltage comparison circuit that compares a voltage setting value with the voltage detection value. An arm for comparing the voltage setting value and the voltage detection value after a predetermined time after turning off the element to determine that the voltage setting value is large is provided among a plurality of power converters connected in parallel. Any one of these arms or one of the arms operating simultaneously.

  According to the present invention. After the semiconductor element is turned off, it is detected that a current is flowing through the free wheel diode, and the operation is stopped, so that the rapid reverse recovery of the free wheel diode due to the subsequent turning on of the opposite arm can be prevented. As a result, no surge voltage is generated in a small current region and the semiconductor element is not destroyed. Further, even when a MOSFET parasitic diode is used as a freewheeling diode, it is possible to prevent destruction because it does not perform a sharp reverse recovery. Furthermore, since the protection judgment is made by comparing the detected value of the main electrode voltage of the semiconductor element with the set value, a current detector or the like is unnecessary, and insulation of the detected voltage is unnecessary, and a simple circuit can be configured. .

1 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram which shows the 2nd Example of this invention. It is a circuit block diagram of the general resonance type inverter for induction heating. It is an operation | movement waveform diagram of each part in FIG.

  The main points of the present invention are a voltage detection circuit for detecting a voltage between main terminals of a semiconductor element in a power conversion device in which a resonant capacitor and an induction heating load are connected to an output and the output current is operated in a delayed phase with respect to the output voltage. A voltage comparison circuit that compares the voltage setting value with the voltage detection value, and after turning off the semiconductor element, the voltage setting value is compared with the voltage detection value. Connected in series with the semiconductor element. The point is that the semiconductor elements of the opposing arms constituting the upper and lower arms are not turned on.

FIG. 1 shows a first embodiment of the present invention. The operation waveform diagram of each part is shown in FIG. 4 as in the background art. This is a configuration when a protection circuit is provided in each of the IGBTs 7a to 7d in FIG.
First, FIG. 4 will be described.

  Since the current flows through the IGBTs 7a and 7d that are turned off at the point A when the output current Io is in a lagging phase with respect to the normal output voltage Vo, a predetermined time after the gate signals G7a and G7d are turned off (the upper and lower arms are short-circuited). At the point A ′, which is an arbitrary point within the dead time for preventing the above, the voltage Ed of the DC capacitor 7e is applied as the voltage of the IGBTs 7a and 7d. With this power supply, it becomes several hundred volts or more.

At the point C when the output current Io advances and is in phase with the output voltage Vo due to an abnormality in the induction heating load or the like, the current flows through the free wheel diodes of the IGBTs 7a and 7d that are turned off. Therefore, the gate signals G7a and G7d are At a point C ′ after a predetermined time after turning off (any point within the dead time for preventing the upper and lower arms from being short-circuited), the voltages of the IGBTs 7a and 7d are about −several V of the forward drop voltage during diode conduction. .
It is this proposal to protect by utilizing this difference in voltage.

Next, FIG. 1 will be described.
A voltage dividing resistor 1 composed of resistors R1 and R2 that divide a value obtained by detecting a voltage between the main electrodes of the IGBT 7a, a comparator 2 that compares it with a voltage setting value, and a flip-flop 3 that takes timing after the control signal is turned off , A delay circuit 4, a NOR circuit 5a, AND circuits 5b and 5c, and an amplifier circuit 6 for generating a gate signal. After dividing the voltage between the main electrodes of the IGBT 7a to a voltage of about several volts that can be easily handled by the voltage dividing resistor 1, the comparator 2 compares this value with the voltage setting value, and the voltage between the main electrodes of the IGBT 7a is When the voltage of the DC intermediate capacitor 7e described above (several hundreds V or more in this power supply) is output, Lo is output, and when the voltage when the freewheeling diode is conductive (about −several V). High (Hi) is output.

  When the output current Io is in a delayed phase with respect to the normal output voltage Vo, the control signal is turned off from the on state, and the comparator 2 is low (Lo) at a point A ′ after a predetermined time after the gate signals G7a and G7d are turned off. ) Is output. The delay circuit 4 inputs a control signal OFF, and outputs Hi → Lo after a set time such as a gate drive delay or an IGBT OFF delay, whereby the flip-flop 3 outputs Lo. When the failure signals from the similar circuits attached to the respective IGBTs are all Lo, the output of the NOR circuit 5a is Hi, so that the outputs of the AND circuits 5b and 5c are also in accordance with the signals from the pulse generation circuit 11 of FIG. The ON signal is output to the IGBT of the opposite arm to perform normal operation. The AND circuits 5b and 5c output control signals for the opposing arms.

When the output current Io is in a leading phase with respect to the output voltage Vo due to an abnormality in the induction heating load or the like, the control signal turns from on to off, and at the point C ′ after a predetermined time after the gate signals G7a and G7d are turned off, the comparator 2 outputs Hi. The delay circuit 4 inputs the control signal OFF, and outputs Hi → Lo after a set time such as gate drive delay or IGBT OFF delay, whereby the flip-flop 3 outputs Hi. When any one of the failure signals from the similar circuit attached to each semiconductor element is Hi, the output of the NOR circuit 5a is Lo and the outputs of the AND circuits 5b and 5c are Lo.
As a result, all control signals become Lo. The operation is stopped, and the ON signal of the IGBT of the opposite arm is not output. Accordingly, when the advance operation is detected and any of the IGBT protection circuits operates, the ON signal is not given to the IGBT, and the diode does not reversely recover.

Further, in this embodiment, the case where the protection circuit is provided for all the IGBTs is shown, but the same applies to the case where the protection circuit is provided for one of the IGBTs 7a and 7d and one of the IGBTs 7b and 7c which are simultaneously operating on and off. Can be protected. In the case of this configuration, the NOR circuit 5a has only two inputs, and the others are the same.
Furthermore, when a plurality of power converters shown in FIG. 3 are connected in parallel and operate simultaneously, a plurality of power converters perform the same operation, so a failure detection circuit is provided only for one power converter. And if this works, all the power converters may be stopped. At this time, similarly to the single-machine operation configuration, if a protection circuit is provided on one of the IGBTs that are simultaneously operating on and off, the protection can be similarly achieved.

FIG. 2 shows a second embodiment of the present invention.
The difference from the first embodiment is the difference in the circuit that detects the voltage between the main terminals of the IGBT 7a. In this configuration, a series circuit of a resistor R1 and a resistor R2 is connected between Vcc of the control circuit power supply and the emitter of the IGBT 7a, and a diode D1 is connected between the series connection point and the collector of the IGBT 7a. By comparing the voltage at the series connection point of the resistor series circuit with the voltage setting value by the comparator 2, protection can be performed in the same manner as in the first embodiment. Other operations are the same as those in the first embodiment. In this configuration, the voltage applied to the resistor is lower than that in the first embodiment, so that the voltage dividing resistor can be reduced in size.

The effective use of the proposal is that the voltage of the semiconductor element rises after various delay times such as the delay of the gate drive signal and the delay of IGBT off after the control signal is turned off. This is a device with a sufficient control time capable of controlling whether or not the control signal of the opposite arm is turned on.
Moreover, although the example which applied IGBT as a semiconductor element was shown in the said Example, when a MOSFET is applied, it is realizable similarly.

  In this application, the induction heating device has been explained, but it can also be applied to switching power supplies that use resonant circuits, DC-DC converters, and so on.

DESCRIPTION OF SYMBOLS 1, 1a ... Voltage dividing resistor 2 ... Comparator 3 ... Flip-flop 4 ... Delay circuit 5a ... NOR circuit 5b, 5c ... AND circuit 6 ... Amplifier circuit 7 ... Power converters 7a to 7d ... IGBT 7e ... DC capacitor 8 ... DC power supply 9 ... Resonant capacitor 10 ... Inductive heating load 10a ... Inductance component 10b ... Resistance component 11.・ Pulse generation circuit 12 ・ ・ ・ Gate drive circuit R1, R2 ・ ・ ・ Resistance

Claims (6)

In a power converter that connects a resonant capacitor and an induction heating load to the output and operates the output current in a delayed phase with respect to the output voltage,
A voltage detection circuit for detecting the voltage between the main terminals of the semiconductor element, and a voltage comparison circuit for comparing the voltage setting value with the voltage detection value,
After a predetermined time after turning off the semiconductor element, the voltage setting value is compared with the voltage detection value. When the voltage setting value is large, the semiconductor element is connected in series, and the semiconductor element is A power conversion device comprising a protection circuit for a semiconductor element that does not turn on a semiconductor element of an opposing arm that constitutes an arm.   The power converter according to claim 1, wherein the voltage detection circuit includes a plurality of voltage dividing resistors connected in parallel with a semiconductor element.   2. The power according to claim 1, wherein the voltage detection circuit is configured by dividing a control circuit power supply with a plurality of resistors and connecting a diode between the voltage dividing point and a main electrode of a semiconductor element. Conversion device. In a power converter that connects a resonant capacitor and an induction heating load to the output and operates the output current in a delayed phase with respect to the output voltage,
A voltage detection circuit for detecting the voltage between the main terminals of the semiconductor element, and a voltage comparison circuit for comparing the voltage setting value with the voltage detection value,
After a predetermined time after turning off the semiconductor element, the voltage setting value and the voltage detection value are compared, and when the voltage setting value is large, a semiconductor element protection circuit that stops the operation of the power converter A power conversion device comprising: A voltage detection circuit that detects a voltage between main terminals of the semiconductor element, and a voltage comparison circuit that compares a voltage setting value with the voltage detection value,
After a predetermined time after turning off the semiconductor element, the arm that compares the voltage setting value with the voltage detection value and determines that the voltage setting value is large,
5. The power conversion device according to claim 4, wherein the power conversion device is one of all the arms of the power conversion device or one of the arms operating simultaneously in the power conversion device. A voltage detection circuit that detects a voltage between main terminals of the semiconductor element, and a voltage comparison circuit that compares a voltage setting value with the voltage detection value,
After a predetermined time after turning off the semiconductor element, the arm that compares the voltage setting value with the voltage detection value and determines that the voltage setting value is large,
5. The power conversion device according to claim 4, wherein the power conversion device is any one of a plurality of power conversion devices connected in parallel or one of the arms operating simultaneously.

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