JP6501064B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating apparatus provided with a parallel resonant circuit including a variable DC voltage source using a step-down chopper and a current source inverter and a heating coil as a load of the current source inverter.

  This type of induction heating device can pass Q (Q is selectivity) times the output current of the inverter to the heating coil, and is suitable for heating applications that require a large current. The specifications of the output of this induction heating apparatus are, for example, several tens of kW to several hundreds of kW, several hundred volts, several tens of amps to several hundred amps, and several kilohertz to several tens of kilowatts. [kHz]], and is used for quenching of metal.

FIG. 3 is a circuit diagram showing a conventional induction heating apparatus.
In FIG. 3, the step-down chopper 20 is composed of a direct current voltage source 1, a step-down switching element 2, a diode 3, a reactor 4 and a smoothing capacitor 9, and the on / off operation of the switching element 1 Output any voltage below the voltage (the voltage required by the load). Here, the DC voltage source 1 is configured by, for example, a diode rectifier.

The current-type inverter 30 at the next stage includes reactors 10 and 11, heating switching elements 511, 521, 531 and 541, and reverse blocking diodes 512, 522, 532, and 542, and the switching elements 511, 521, 531 and 541 A high frequency alternating current is supplied to the load 40 by the on / off operation.
The load 40 is a parallel resonant circuit including a resonant capacitor 6, a heating coil 7, and a resistance component 8. The resonant capacitor 6 functions to improve the load power factor.

FIG. 4 is a waveform diagram of each part showing the operation of FIG. 3, and illustrates the case where the phase difference between the output voltage V _o and the output current I _o is zero. Note that I ₅₁₁ , I ₅₂₁ , I ₅₃₁ , and I ₅₄₁ indicate currents flowing through the switching elements ₅₁₁ , ₅₄₁ , ₅₂₁ , and ₅₃₁ , respectively. Moreover, the overlap period and fine vibration at the time of commutation of the switching element are omitted.
In normal operation, the switching elements 511, 521, 531, and 541 are turned on and off while the step-down chopper 20 is in operation, whereby a high-frequency resonant current _Io flows through the heating coil 7 of the load 40 to be heated. Inductively heat the object (not shown).

  Now, when a failure such as a short circuit of heating coil 7 occurs, it is necessary to promptly stop power supply to load 40 in order to protect switching elements 511, 521, 531, 541 etc. of inverter 30 from an overcurrent. There is.

Therefore, for example, in Patent Document 1, when an overcurrent occurs due to a short circuit of a load or the like, the operation of the forward conversion unit is stopped and at the same time the switching element of the current source inverter (inverse conversion unit) is turned on. A technique is disclosed that is fixed as it is and the energy stored in the reactor is attenuated via the switching element, reverse blocking diode, load, and the like.
Further, according to Patent Document 2, when an overcurrent occurs due to a short circuit of a load or the like, all switching elements of the current source inverter are forcibly turned on, and the positive and negative current paths of the current source inverter are shorted by thyristors. Techniques for blocking the flow of energy are disclosed.

All of these conventional techniques are intended to protect switching elements and the like from an overcurrent caused by a failure, and in the case of the circuit shown in FIG. In this case, the purpose is to rapidly reduce the current flowing to the load 40 and not to interrupt the current flowing to the reactor 4.
The operation in the case where all the switching elements 511, 521, 531, and 541 of the current source inverter 30 are turned on at the time of receiving the power supply stop command will be described below as in the case of Patent Document 2.

When a power supply stop command is received at time A in FIG. 4 (the polarity of the output voltage V _o is positive), the step-down chopper 20 stops the operation by turning off the switching element 2 in FIG. 3. Thus, the DC voltage source 1 is disconnected from the inverter 30, and the current flowing to the reactor 4 flows to the diode 3. At the same time, while the switching elements 511 and 541 that were on before time point A are fixed in the on state, all the switching of the current source inverter 30 is performed by turning on the other switching elements 521 and 531 that were off before. The elements 511, 541, 521, and 531 are turned on.
Therefore, at time points A to B, current flows to the switching elements 521 and 531 other than the switching elements 511 and 541 to which current flows before time point A, and power is regenerated from the load 40 to the inverter 30 side.

After that, the regeneration operation is performed similarly even in the period from the time when the polarity of the output voltage V _o is inverted at time B to time C. As a result, during the time points A to C, the current flowing to the output current _Io and the reactors 10 and 11 in the path, the switching element and the reverse blocking diode increases.
At time C, the regeneration from load 40 to inverter 30 ends and output current _Io becomes 0, and the current flowing through reactors 10 and 11 is the switching element 511, reverse blocking diode 512, reverse current after time C The current flows into the path of the blocking diode 522, the switching element 521, and the path of the switching element 531, the reverse blocking diode 532, the reverse blocking diode 542, and the switching element 541.

  The current in each of the divided paths via the switching elements 511, 541, 521, and 531 fluctuates due to vibration, but when seen over a long period, they gradually decrease due to the resistance component of the circuit not shown. The feed stop is complete. Although FIG. 4 shows that currents of substantially the same magnitude flow through the switching elements 511, 541, 521, and 531, an imbalance may occur between the divided paths depending on the circuit constant.

JP-A-5-236756 (paragraph [0022], etc.) Patent No. 3328758 (Paragraph [0026], etc.)

FIG. 5 shows an equivalent circuit for considering the fluctuation of the current due to the vibration after time point C in FIG.
In FIG. 5, a reactor 12 (inductance is L ₁ ) corresponds to the reactor 4 in FIG. 3 and a reactor 14 (inductance is L ₂ ) corresponds to the reactors 10 and 11 in FIG. The capacitance C corresponds to the capacitor 9 in FIG. In FIG. 5, the diode 3 in FIG. 3, the switching elements 511, 521, 531, 541 and the reverse blocking diodes 512, 522, 532, 542 are omitted, and the aforementioned divided paths are shown by one path including the reactor 14. There is. Further, the polarities of the currents i ₁ and i ₂ in FIG. 5 are positive in the arrow direction, and the resistance component of the circuit is ignored.

The voltage-current equation of the equivalent circuit shown in FIG. 5 is equation 1, and equation 2 is obtained by solving equation 1 for i ₂ .

In Equations 1 and 2, i ₁ (0) and i ₂ (0) are initial currents, and q (0) are initial charges.

Now, as an example, L ₁ = 10 [mH], L ₂ = 1 [mH], i ₁ (0) = − 500 [A], i ₂ (0) = 500 [A], C = 5000 [μF] When q (0) = 2.5 [C: coulomb], i ₂ in equation ₂ is equation 3.
[Equation 3]
i ₂ = 500 + 1066 sin (469 t)
That is, according to Equation 3, it can be seen that the maximum value of i ₂ is 500 [A] +1066 [A] = 1566 [A].

The large current of 1566 [A] according to the above example is the reactor 14 (reactors 10 and 11 in FIG. 3) and the switching elements 511, 521, 531 and 541 and the reverse blocking diodes 512, 522 and 532 which are the shunt paths described above. , 542, and also to the capacitor 9, there is a risk of damaging these components.
Further, when calculated using the equivalent circuit of FIG. 5, it is understood that the current flowing to the reactor 4 and the diode 3 of the step-down chopper 20 also becomes excessive depending on the constant, and these parts may be damaged. Note that such an increase in current also occurs before time C.

  Therefore, the problem to be solved by the present invention is to prevent an overcurrent from flowing in the circuit component when all switching elements of the current source inverter are turned on in response to a power supply stop instruction to the load when a failure occurs. It is an object of the present invention to provide an induction heating device.

In order to solve the above problems, the invention according to claim 1 relates to a step-down chopper having a step-down switching element, a current source inverter connected to the output side of the step-down chopper, and an output side of the current source inverter. An inductive heating device comprising a load comprising a parallel resonant circuit of a resonant capacitor and a heating coil,
The current source inverter includes a series circuit of a heating switching element and a reverse blocking diode on each side, and a bridge circuit in which the load is connected to the output side, the step-down switching element, and the input side of the bridge circuit An induction heating device for turning on and off the heating switching element to supply an alternating current to the load;
The step-down chopper
A DC voltage source,
A series circuit of the step-down switching element and the second reactor connected between one end of the DC voltage source and the bridge circuit;
A diode connected between a connection point of the step-down switching element and the second reactor and the other end of the direct current voltage source and in a reverse direction to the flow direction of the step-down switching element; ,
Constituted by,
When stopping the power supply from the DC voltage source to the load,
At the same time as the step-down switching element is turned off, all the heating switching elements are turned on .

The invention according to claim 2 is a step-down chopper having a step-down switching element, a current source inverter connected to the output side of the step-down chopper, and an output side of the current source inverter, and a resonant capacitor and a heating coil. And a load comprising a parallel resonant circuit of
The current source inverter includes a series circuit of a heating switching element and a reverse blocking diode on each side, and a bridge circuit in which the load is connected to the output side, the step-down switching element, and the input side of the bridge circuit An induction heating device for turning on and off the heating switching element to supply an alternating current to the load ;
The step-down chopper
A DC voltage source,
A series circuit of the step-down switching element and the second reactor connected between one end of the DC voltage source and the bridge circuit;
A diode connected between a connection point of the step-down switching element and the second reactor and the other end of the direct current voltage source and in a reverse direction to the flow direction of the step-down switching element; ,
Configured by
A thyristor for shorting positive and negative current paths of the current source inverter;
When stopping the power supply from the DC voltage source to the load,
At the same time as the step-down switching element is turned off, the thyristor is turned on .

The invention according to claim 3 is characterized in that, in the induction heating apparatus according to claim 1 or 2, the first reactor and the second reactor are used in common .

In the present invention, in view of the fact that the target device is a heating application, the smoothing capacitor is removed from the step-down chopper connected to the front stage of the current source inverter. As a result, in the process of turning on all the switching elements of the current source inverter to reduce the output current at the time of failure occurrence, the current flowing to the reactor, switching elements, etc. is suppressed to protect these circuit components from overcurrent. be able to.
Further, by sharing the reactor with the step-down chopper and the current source inverter, it is possible to reduce the number of parts, to miniaturize the entire apparatus, and to reduce the cost.

It is a circuit diagram showing an embodiment of the present invention. It is a wave form diagram which shows operation | movement of FIG. It is a circuit diagram showing a prior art. FIG. 5 is a waveform diagram showing the operation of FIG. 3; It is the equivalent circuit schematic of the principal part of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing this embodiment. The same parts as in FIG. 3 are assigned the same reference numerals, and in the following, parts different from FIG. 3 will be mainly described.

In FIG. 1, a step-down chopper 20A is constituted by a direct-current voltage source 1, a series circuit of a semiconductor switching element 2 and a diode 3 connected at both ends thereof, and a reactor 4 one end of which is connected to the cathode of the diode 3. It is done. Also, the current source inverter 30A includes the heating switching elements 511, 521, 531, 541 and the reverse blocking diodes 512, 522, 532 connected between the reactor 4 and the other end and the negative electrode of the DC voltage source 1. And a bridge circuit consisting of 542.
That is, in this embodiment, the reactor 4 is also used as a component of the step-down chopper 20A and the current source inverter 30A, and the step-down chopper 20A has a configuration in which the smoothing capacitor 9 in FIG. 3 is removed.

Next, the operation of this embodiment will be described with reference to FIG.
The normal operation before the time point A in FIG. 2 is the same as that in the prior art in FIG. 3 and FIG. In this embodiment, since the smoothing capacitor is removed from the step-down chopper 20A, the switching frequency component of the step-down chopper 20A appears in the load 40 without being absorbed by the capacitor depending on the circuit constant. There are many cases where this is not a problem because it is a heating application.

When power supply to load 40 is stopped in a state where output current _Io is large due to a failure such as a short circuit of heating coil 7, the current flowing to load 40 is rapidly reduced as in FIG. In order not to interrupt the current flowing to the current source, all the switching elements 511, 521, 531, 541 of the current source inverter 30A are turned on.
That is, at the point A of FIG. 2 (in which the polarity of the output voltage V _o is positive) that has received the feed stop command, the operation of the step-down chopper 20A is stopped and the switching element 511 that was on before the point A. , 541 in the on state, the other switching elements 521 and 531 which have been off are turned on.

  When the step-down chopper 20A stops operation at time A, the DC voltage source 1 is disconnected from the inverter 30A, and the current flowing in the reactor 4 flows in the diode 3. At the same time, by turning on the switching elements 521 and 531 of the current source inverter 30A, current flows through the switching elements 521 and 531 at time points A to B, and power is regenerated from the load 40 to the inverter 30A side.

Regeneration is similarly performed at time points B to C after the polarity of the output voltage V _o is inverted. As a result, during the time points A to C, the current flowing to the output current _Io and the diode 3, the reactor 4, the switching element, and the reverse blocking diode in the path increases.

That is, as shown in FIG. 2, the currents I ₅₂₁ and I ₅₃₁ flowing through the switching elements 521 and ₅₃₁ increase at time points A to B, so the output current I _o increases in the positive direction, and the switching elements at time points B to C Since the currents I ₅₁₁ and I ₅₄₁ flowing through ₅₁₁ and ₅₄₁ increase, the output current I _o increases in the negative direction. However, the degree of increase of these currents becomes smaller as compared with the prior art in which the currents due to the accumulated charges of the capacitor 9 are added as shown in FIGS. 3 and 4.

At time C, the regeneration from load 40 to inverter 30A ends and output current _Io becomes 0, and the current flowing through diode 3 and reactor 4 is the switching element 511 and reverse blocking diode after time C. A path 512 divides the reverse blocking diode 522 and the path of the switching element 521, and the path of the switching element 531, the reverse blocking diode 532, the reverse blocking diode 542, and the switching element 541. These currents gradually decrease due to a resistance component of a circuit (not shown) and eventually become 0 to complete the feed stop (as with the above, imbalance may occur in these shunt currents).
Here, the change of the current after time point C is different from the equations 1 to 3 described above, and the current flowing through the reactor 4 is a phenomenon that decreases due to the resistance component of the circuit. The currents I ₅₁₁ , I ₅₂₁ , I ₅₃₁ and I ₅₄₁ flowing through the electrodes ₅₃₁ and ₅₄₁ are smaller than those in FIG.

  As described above, according to the present embodiment, since the smoothing capacitor is removed from the conventional step-down chopper, all the switching elements 511 and 521 of the current source inverter 30A are stopped while stopping the operation of the step-down chopper 20A when the load 40 is abnormal. , 531 and 541 can be turned on to reduce the output current, it is possible to prevent an overcurrent from flowing in the reactor 4 and the switching elements 511, 521, 531, 541 and the like. Further, by sharing the reactor 4 with the step-down chopper 20A and the current source inverter 30A, it is possible to reduce the number of parts, to miniaturize the entire apparatus, and to reduce the cost.

  The present invention is also applicable to an induction heating apparatus provided with a thyristor that shorts positive and negative electric paths of a current source inverter.

  The induction heating apparatus according to the present invention can be used, for example, for industrial use such as quenching of metal, and also for household use such as an electromagnetic cooker.

1: DC voltage source 2: Step-down switching element 3: Diode 4: Reactor 511, 521, 531, 541: Heating switching element 512, 522, 532, 542: Reverse blocking diode 6: Resonant capacitor 7: Heating coil 8: Resistive component 20A: Step-down chopper 30A: Current source inverter 40: Load

Claims (3)

A load comprising a step-down chopper having a step-down switching element, a current source inverter connected to the output side of the step-down chopper, and an output side of the current source inverter, and a parallel resonance circuit of a resonance capacitor and a heating coil. And an induction heating device comprising
The current source inverter includes a series circuit of a heating switching element and a reverse blocking diode on each side, and a bridge circuit in which the load is connected to the output side, the step-down switching element, and the input side of the bridge circuit An induction heating device for turning on and off the heating switching element to supply an alternating current to the load;
The step-down chopper
A DC voltage source,
A series circuit of the step-down switching element and the second reactor connected between one end of the DC voltage source and the bridge circuit;
A diode connected between a connection point of the step-down switching element and the second reactor and the other end of the direct current voltage source and in a reverse direction to the flow direction of the step-down switching element; ,
Constituted by,
When stopping the power supply from the DC voltage source to the load,
At the same time as the step-down switching element is turned off, the heating switching elements are all turned on . A load comprising a step-down chopper having a step-down switching element, a current source inverter connected to the output side of the step-down chopper, and an output side of the current source inverter, and a parallel resonance circuit of a resonance capacitor and a heating coil. And an induction heating device comprising
The current source inverter includes a series circuit of a heating switching element and a reverse blocking diode on each side, and a bridge circuit in which the load is connected to the output side, the step-down switching element, and the input side of the bridge circuit An induction heating device for turning on and off the heating switching element to supply an alternating current to the load ;
The step-down chopper
A DC voltage source,
A series circuit of the step-down switching element and the second reactor connected between one end of the DC voltage source and the bridge circuit;
A diode connected between a connection point of the step-down switching element and the second reactor and the other end of the direct current voltage source and in a reverse direction to the flow direction of the step-down switching element; ,
Configured by
A thyristor for shorting positive and negative current paths of the current source inverter;
When stopping the power supply from the DC voltage source to the load,
An induction heating apparatus characterized in that the thyristor is turned on at the same time as the step-down switching element is turned off . In the induction heating device according to claim 1 or 2,
An induction heating apparatus characterized in that the first reactor and the second reactor are used in common .

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