JP6115026B2 - Induction heating power supply - Google Patents

Description

  The present invention relates to an induction heating power supply device using MERS (Magnetic Energy Recovery Switch).

  FIG. 4 is a circuit diagram of MERS for explaining the background art, and FIG. 2 is a waveform diagram for explaining the operation thereof. The MERS circuit includes a semiconductor switch (in this case, IGBT) 51 and 52 in which self-extinguishing elements such as IGBTs and MOSFETs and diodes are connected in antiparallel, and a semiconductor switch (in this case, IGBT) 53 in the same manner. And 54 and a circuit in which a capacitor 6 is connected in parallel, the output of which is a series connection point of serially connected semiconductor switches (IGBT), the loss of the coil 7 of the induction heating load and the object to be heated Is connected to a resistor 8 representing Further, the input is connected to the DC power source 1 via the reactor 2 at both ends of the circuit 2 circuit in which semiconductor switches (IGBTs) are connected in series and the circuit in which the capacitor 6 is connected in parallel. Hereinafter, the semiconductor switch will be described as an IGBT.

  The operation in such a configuration will be described with reference to FIG. In this method, the polarity of the output current Io is switched by the resonance operation of the capacitor 6 and the coil 7. In the period A, the initial value of the output current Io is negative, and even if the IGBTs 51 and 54 are turned on, the current flows through the diodes connected in reverse parallel to the IGBTs 51 and 54, but the capacitor accumulated by the energy accumulated in the coil 7 6 is charged, the output current Io decreases from negative to zero. After that, after the polarity is reversed by the resonance operation, the IGBTs 51 and 54 are on, so that the current is switched to the IGBT, and the output current Io increases from zero to positive by the energy accumulated in the capacitor 6. The electric charge is discharged, and energy is transferred to the coil 7 again.

  The period B is reached when the voltage VDC of the capacitor 6 becomes ≈0. Since there is no path for charging the capacitor 6 by the energy accumulated in the coil 7, the output current Io circulates. In the return path, Io flowing through the coil 7 and the resistor 8 is shunted into the diode 53 and IGBT 51 paths, and the IGBT 54 and IGBT 52 diode paths. This current gradually decreases due to loss due to the resistor 8 and the like.

  When the IGBTs 51 and 54 are turned off in accordance with a desired frequency, the period C is reached. The output current Io all flows through the diodes of the IGBTs 52 and 53, charges the capacitor 6 again with the energy accumulated in the coil 7, and thereafter repeats the same operation. Here, the output voltage Vo shows the voltage VDC of the capacitor 6 when the IGBTs 51 and 54 are conductive, and becomes [−VDC] when the IGBTs 52 and 53 are conductive. Further, the current IDC of the reactor 2 continues to flow substantially constant and is superimposed on the current of each part.

  After time point D, a case where a short circuit of the load occurs is shown. When a short circuit occurs in the coil 7 when the Vo at the time point D is the maximum (in this case, a partial short circuit), the energy stored in the capacitor 6 is greater than the inductance of the coil 7 during normal operation. The current flows by moving to the reduced coil where no short circuit occurs. At this time, the output current Io increases compared to that during normal operation, resulting in an excessive current.

  In order to protect the IGBT when this is detected and the output current Io exceeds the set value, all the IGBTs 51 to 54 are turned off at the time point E. This timing is the same as the timing when the voltage VDC of the capacitor 6 becomes approximately zero. As a result, the current flowing in the IGBTs 51 and 54 is commutated to the diodes connected in reverse parallel between the IGBTs 52 and 53, and the capacitor 6 is charged again by the energy accumulated in the coil 7, so that the output current Io decreases.

When the output current Io becomes zero at the time point F, the electric charge of the capacitor 6 is discharged thereafter and there is no path for current flow, so no current flows through the load.
On the other hand, the reactor current IDC continues to flow and continues to charge the capacitor 6. The DC power source 1 is configured by a full bridge circuit using a thyristor, and the operation of reducing the current IDC of the reactor 2 is performed by setting the output voltage to a reverse polarity by phase control. However, the energy stored in the reactor 2 is large. Or depending on the response of the DC voltage source 1 such as the thyristor converter shown as an example, a delay occurs and the reactor current IDC continues to flow as shown by the dotted line, the voltage VDC of the capacitor 6 becomes excessive, and the capacitor 6 and the IGBT 51 May exceed a withstand voltage of ~ 54.

  In Patent Document 1, as circuit constant examples, LDC (2) = 20 mH, C (6) = 16 μF, L (7) = 100 μH, R (8) = 50 mΩ, Vo = 6000 V peak, Io = 3000 A peak, f = 1000 Hz, P = 300 kW, IDC = 300 A, there is a description of the protection method. However, when the current IDC of the reactor 2 is small, the charge of the capacitor 6 is completely discharged, and the voltage VDC of the capacitor 6 is zero. Thus, after the output current Io decreases and becomes zero, the gate signals of all IGBTs are turned off. There is no description of turning off the gate signal when an overcurrent occurs in order to protect the semiconductor element (IGBT).

JP 2011-147299 A

  The problem to be solved is related to the MERS protection circuit technology connected to the induction heating load. When the gate signals of all the semiconductor switches are turned off due to the load coil short circuit, etc., the DC current continues to flow and the MERS capacitor is charged. This is to prevent the overvoltage from being applied to the semiconductor element and the capacitor to prevent the destruction.

In order to solve the above-described problems, in the present invention, a DC power source configured by a bridge rectifier circuit including a positive electrode and a negative electrode and using a thyristor , a reactor, and a semiconductor switch each having a diode connected in reverse parallel are connected in series The first and second semiconductor switch series circuits, a capacitor, a third semiconductor switch series circuit in which a diode and a semiconductor switch are connected in series, and the first and second semiconductor switch series circuits, A capacitor and the third semiconductor switch series circuit are connected in parallel, an induction heating load is connected between series connection points in the first and second semiconductor switch series circuits, and the third semiconductor switch series circuit is connected to the third semiconductor switch series circuit. A series circuit of the DC power source and the reactor is connected in parallel with the semiconductor switch.

In the above, when the induction heating load becomes an overcurrent, all the semiconductor switches of the first and second semiconductor switch series circuits are turned off, and the semiconductor switch of the third semiconductor switch series circuit is turned off. And the bridge rectifier circuit is controlled so that the current of the reactor decreases.

  The present invention relates to MERS to which an induction heating load is connected. When all gate signals are turned off due to a coil short circuit of the load, a reactor connected to the output of a DC power source and a circuit in which semiconductor switches are connected in series are connected to two circuits and a capacitor. By switching on the shorting switch that short-circuits the positive and negative of the added DC power supply via the reactor between the circuits connected in parallel, the DC current is bypassed, so the capacitor is not charged and the semiconductor switch and capacitor Overvoltage can be prevented.

Further, the diode added to the positive potential or the negative potential can prevent current from flowing from the capacitor to the short-circuit switch.
As a result, it is possible to improve the reliability of protection and reduce the breakdown voltage of the parts.

1 is a circuit diagram showing a first embodiment of the present invention. 2 shows operation waveforms of the first embodiment of the present invention. It is a circuit diagram which shows the 2nd Example of this invention. It is a circuit diagram which shows a prior art example.

  The main points of the present invention are a first and second semiconductor switch series circuit in which semiconductor switches each having diodes connected in antiparallel are connected in series, a capacitor, and a third semiconductor switch series circuit in which diodes and semiconductor switches are connected in series. Are connected in parallel, and an induction heating load is connected between the series connection points inside the first and second semiconductor switch series circuits, and between the series connection point of the third semiconductor switch series circuit and the DC power supply. In the induction heating power supply apparatus connected to the reactor, when the output overcurrent, all the semiconductor switches of the first and second semiconductor switch series circuits are turned off, the semiconductor switches of the third semiconductor switch series circuit are turned on, and the DC power supply is turned on. It is a point which controls so that the electric current of a reactor may reduce.

  FIG. 1 shows a first embodiment of the present invention. A first IGBT series circuit in which IGBTs 51 and 52 are connected in series; a second IGBT series circuit in which IGBTs 53 and 54 are connected in series; a capacitor 6; a third semiconductor switch series circuit in which a diode 4 and IGBT 3 are connected in series; Are connected in parallel, and a series circuit (inductive heating load) of the coil 7 and the resistor 8 is in parallel with the IGBT 3 between the series connection point of the first IGBT series circuit and the series connection point of the second IGBT series circuit. A DC power source 1 composed of a reactor 2 and a thyristor is connected to each other. The difference from the prior art is that between the DC power source 1 with the reactor 2 connected to the output and the circuit composed of the IGBTs 51 to 54, the positive electrode P and the negative electrode N of the DC power source 1 are connected via the reactor 2. This is that a diode 4 for suppressing discharge of the capacitor 6 is connected to the IGBT 3 for short-circuiting and the positive electrode P line side.

  The operation waveform diagram is the same as the background technology as shown in FIG. 2, but by turning on the short-circuit IGBT 3 at the time point G, the IDC that has flowed shifts to the IGBT 3 as shown by the solid line in FIG. It flows as Is. For this reason, the capacitor 6 is not charged thereafter, and the voltage VDC of the capacitor 6 also becomes a solid line, and the voltage rise can be suppressed.

  The diode 4 is connected to prevent a current from flowing from the capacitor 6 to the short-circuit IGBT 3 when the short-circuit IGBT 3 is turned on. Further, although current flows from the DC power supply 1 to the short-circuit IGBT 3, since it is a short circuit via the reactor 2, the current does not increase sharply. In such a state, by setting the output voltage of the DC power supply 1 to the reverse polarity, the DC current flowing through the reactor 2 can be reduced and all the power supplies can be safely stopped. When a thyristor rectifier is used as the DC power supply, by setting the phase control angle α to 90 degrees or more, a reverse voltage can be applied to the reactor 2 and the current can be reduced and cut off. The control of the thyristor rectifier is described in page 43 of the publication “Motor control mechanism and concept” (1981, Ohmsha). Further, when another circuit configuration is used as the DC power source, the current of the reactor 2 is reduced and cut off by reversing the polarity.

  FIG. 3 shows a second embodiment of the present invention. The difference from the first embodiment is the insertion position of the short-circuit IGBT 3 and the diode 4. In the first embodiment, the diode 4 is connected to the positive P line side of the DC power supply 1, but in the second embodiment, the diode 4 is connected to the negative N line side of the DC power supply 1. The operation in this configuration is the same as that of the first embodiment, and the circuit can be safely interrupted without increasing the voltage of the capacitor 6 to a predetermined value or more when the load is overcurrent.

  In the above embodiment, the example in which the reactor 2 is inserted between the DC power source and the series connection point of the third semiconductor switch series circuit is shown. However, the reactor 2 is connected to the DC power source 1 and the third semiconductor switch series. The insertion position can be changed as long as it is connected in series with the semiconductor switch in the circuit.

  The present invention is a proposal relating to protection in a circuit that generates high-frequency alternating current from a direct-current power supply by a resonant operation, and can be applied to an induction heating power supply apparatus as well as a switching power supply.

DESCRIPTION OF SYMBOLS 1 ... DC power supply 2 ... Reactor 4 ... Diode 3, 51-54 ... IGBT 6 ... Capacitor 7 ... Coil 8 ... Resistance

Claims (1)

A DC power supply comprising a bridge rectifier circuit having a positive electrode and a negative electrode and using a thyristor; a reactor; first and second semiconductor switch series circuits in which semiconductor switches each having diodes connected in antiparallel are connected in series; a capacitor; A third semiconductor switch series circuit in which a diode and a semiconductor switch are connected in series, and the first and second semiconductor switch series circuits, the capacitor, and the third semiconductor switch series circuit are connected in parallel. An induction heating load is connected between series connection points inside the first and second semiconductor switch series circuits, and the DC power supply and the reactor are connected in series with the semiconductor switches in the third semiconductor switch series circuit. Connect the circuit ,
When the induction heating load becomes an overcurrent, turn off all the semiconductor switches of the first and second semiconductor switch series circuits, turn on the semiconductor switches of the third semiconductor switch series circuit, An induction heating power supply apparatus , wherein a bridge rectifier circuit is controlled so that a current of the reactor decreases .

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