JP2002352942A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact induction heating device, having simple wire connection, and in which breakdown of an inverter circuit by a high overcurrent due to peeling-off oxide films from a worked piece can be prevented. SOLUTION: This device is constituted, so that plural number of HV- IPM(high-voltage intelligent power module) units, incorporating an inverter circuit 11 into a package 20 where nearly 200 transistors are bridged and connected in parallel are connected and arranged between an alternating-current power supply circuit 10, which is provided with a rectifying means and an induction coil 18. The number of electrode of units are small even for high- current specifications, and accordingly, the wire connection is simple and compact; and further, the breakdown of the inverter circuit due to high overcurernt caused by the peeling-off oxide films from the worked pieces is prevented by loading the overcurrent protection circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating apparatus for heating a workpiece such as a metal bar for forging passing through a coil by a high-frequency current applied to the coil.

[0002]

Problems to be Solved by the Invention JP-A-59-7999
In 1, a large number of transistors are connected in parallel in a bridge state as elements constituting an inverter circuit to a three-phase AC power supply circuit having a rectifier, and a bridge-like and parallel circuit of the large number of transistors is connected to a heating induction coil. Also disclosed is an electromagnetic induction heating device in which a balancer and a capacitor for resonance are inserted in series in each of the inverter circuits. Such a heating device had a compact advantage irrespective of the use of large power, as compared with a heating device in which a thyristor, which is a state of the art at the time, was provided with an inverter element as an inverter element and a commutation circuit as an auxiliary device.

[0003] In order to configure an induction heating device of high power specification using the above-mentioned transistor as an inverter element,
Parallel operation of many elements is required, for example, 1000k
In order to complete a w-output device, it is necessary to use about 360 transistor packages and to connect about 720 terminals. Therefore, it is expensive and labor-intensive to do this manually. The problem of an increase in the size of the device due to bulkiness has been realized.

Further, since the temperature of the workpiece heated in the induction coil reaches about 1300 ° C., the heating material in the induction heating coil and the heat insulating insulator filled in the coil body deteriorate over time and are mechanically damaged. Noise caused by high-pressure sparks caused by insulation deterioration due to insulation, poor installation at coil replacement, and the effect of oxide film on the heating material adversely affects the signal circuit to transistors, etc., causing multiple elements to be destroyed simultaneously by short-circuit current However, with the increase in power consumption, such effects are likely to increase. Conventionally, a device for detecting insulation deterioration and a fuse have been incorporated as a protection device.However, a protection device formed outside the element has not sufficiently responded to steep noise due to spark discharge due to the influence of a lead wire or the like. And the breaking speed of the element is faster than the fuse breaking speed.
Only the chain damage to other elements was prevented.

[0005]

In order to solve the above-mentioned problems, the present invention provides an AC power supply provided with a rectifier comprising a unit formed by connecting a number of transistor chips in parallel in the same package, that is, a plurality of HV-IPMs. A circuit is arranged and connected between the circuit and the induction coil. In such a configuration, the HV-IPM unit (manufactured by Mitsubishi Electric Corporation) has a large number of transistor chips in the same unit, so that it can handle a large current (1 unit 1200A) and, in order to achieve more safety, a short circuit. Since the overcurrent protection circuit is incorporated, the assembling cost is low, and at the same time, the device is prevented from being enlarged (for example, 1000 kW), and functions to protect the transistor in the event of a short circuit.

In the HV-IPM, since the number of main electrodes is reduced by unitizing a large number of transistors, connection to an AC power supply circuit having rectifying means and a dielectric coil via a laminated conductive plate is simple. become.

Further, in the HV-IPM, the number of control connectors is reduced by unitizing a large number of transistors. Therefore, a small number of optical fibers are used between the optical signal conversion circuit in the inverter control circuit and the drive circuit for driving. Can be connected, thereby contributing to prevention of malfunction and breakage of a large-capacity inverter related to noise due to electromagnetic induction or spark discharge.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The dielectric heating circuit shown in FIG. 2 is a rectifier connected to a three-phase AC power supply 10 (not shown in the drawing).
The inverter circuit 11 is composed of a transistor 12 which is a switching element bridge-connected to the DC circuits P, N, and S rectified by the above, a free wheel diode 13, a snubber capacitor 14, and a gate circuit 15.
An output line 16 in the inverter circuit and a common line 17 from an intermediate line S of the DC circuit are connected to an induction coil 18. In the drawing, a DC current is alternately conducted between an upper arm and a lower arm by a switching operation of a transistor 12, a high-frequency current is applied to the conductive coil 18, and a workpiece passing through the conductive coil 18 is heated. I do. In this case, the capacitor 19 resonates with the coil 18. However, the wiring structure and the operation thereof are common as a dielectric heating device and have no novelty.

An IPM package 20 surrounded by a thick line frame in FIG. 1 has a plurality of transistor chips and free-wheel diodes connected in parallel in the same package, and further bridges the inverter circuit 11 to incorporate the same. A short circuit / overcurrent protection circuit 36 for protection is incorporated, and a drive circuit 40 of the inverter circuit 11 is provided to form a unit.
The unit is Mitsubishi Electric Corporation's HV-IP
M (e.g., 4500 V 1800 A), some of which have a control power supply voltage protection circuit 37 and a heating protection circuit 38.

With respect to the overcurrent protection, for example, the transistor chip has a multi-emitter structure, and a current in a minute area can be detected to prevent thermal breakdown due to an excessive collector current of the entire transistor chip. If overcurrent or short-circuit current exceeds the trip value, the transistor chip is turned off only by the protection circuit in the package without relying on an external stop signal, so spark-like noise occurs in the coil of the induction heating device. Then, even if the stop signal itself from the outside malfunctions, the element itself is turned off and the protection means functions against short circuit / overcurrent to prevent the element from being destroyed. This is especially true in forging induction heaters which must be used in electrically undesired environments (high temperatures, mechanical damage, poor installation).

As shown in FIG. 3, the HV-IPM package 20 has three collector main electrodes 2 on its upper surface.
One row and one row of emitter main electrodes 22 are provided, and a control connector 23 is provided on the side surface. As shown in FIG.
Three conductive plates 24 each stacked via an insulating plate 27,
The laminate 28 formed by the components 25 and 26 is placed on a plurality of packages 20 arranged in a plane, and the screws 29 are fastened to the main electrodes 21 and 22, respectively, to fix the laminate 28. In this case, a stolen hole 30 is formed in the upper conductive plates 24 and 25 to insulate the collector main electrode 21 and the emitter main electrode 22, thereby eliminating the complicated and labor-consuming transistor connection structure of the conventional bus bar. In such a configuration, the conductive bush 31 is used to absorb a step between the main electrode and the conductive plate.

As is well known, the connection using the laminated plate 28 has a smaller stray inductance than a connection using a bus bar or an electric wire, so that the surge voltage applied to the switching element is small and the difference in the shunt current to each element is small. As a result of reducing noise due to the surge differential pressure, it is advantageous for an inverter circuit configuration.

As shown in FIG. 5, in general, a current taken from a current detector 45 of an inverter circuit is input to a drive circuit 40 via an inverter control circuit 46, and each transistor in the inverter circuit 11 is supplied with the input signal. Although the gate is driven, in an inverter circuit configuration using high current and high frequency, noise is generated in the signal transmission line from the control circuit 46 to the drive circuit 40 by electromagnetic induction caused by surge voltage and spark discharge in the switching element. Are superimposed.

In the embodiment shown in FIG. 1, an inverter control circuit 46 is provided with an optical signal conversion circuit 47 for converting an electric signal into an optical signal, while a drive circuit 40 is provided with an electric signal conversion circuit for converting an optical signal into an electric signal. 49 is provided, and an optical fiber 48 is interposed between the signal conversion circuits 47 and 49 to prevent malfunction of the inverter and damage to the switching element. As described above, the reduction in the number of wiring operations due to the reduction in the number of main electrodes due to the use of the HV-IPM simplifies the installation of an optical fiber, which generally increases the complexity and cost of the operation. is there.

As described in Japanese Patent Application No. 11-28284, in order to support a large power output with one induction heating device,
Although an inverter equivalent to 880 V is required in terms of AC power supply, the conventional IPM requires a device withstand voltage of 1200 V DC (AC
(Power conversion: 440 V), and an element having a DC withstand voltage of 2200 V or more is required to constitute an inverter of AC power of 880 V. By the way, in the inverter of AC power supply 440V, when the heating output becomes about 800KW or more, the heating efficiency deteriorates.
It is disadvantageous as a product.

[Brief description of the drawings]

FIG. 1 is a block diagram of a unit.

Fig. 2 Induction heating unit inverter circuit diagram

FIG. 3 is a plan view of a unit package.

FIG. 4 is a sectional view of the previous figure.

FIG. 5 is a block diagram using an optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Three-phase alternating current power supply 11 ... Inverter circuit 12 ... Transistor 15 ... Gate drive circuit 18 ... Dielectric coil 20 ... Unit package 21 ... Connector main electrode 22 ... Emitter main electrode 23 ... Control current connector 24 ... P conductive plate 25 ... S conductive plate 26 N conductive plate 27 Insulating plate 28 Laminated plate 36 Short circuit. Overcurrent protection circuit 40 Drive circuit 45 Current detector 46 Inverter control circuit 47 Optical signal conversion circuit 48 Optical fiber 49 Electric signal conversion circuit

Claims (3)

[Claims] An HV-IPM (High Vol.) For connecting a large number of transistors in parallel and forming a transistor protection circuit and a transistor drive circuit in the same package.
tag Intelligent Power Mod
ule) A dielectric heating device, wherein a plurality of units are connected and connected between an AC power supply circuit having a rectifier and an induction coil. 2. The main electrode surface of each HV-IPM unit,
A laminated plate formed by sandwiching an insulating plate between three upper and lower conductive plates is arranged, and a connector row in the main electrode is set to +
And the emitter row of the same main electrode is connected to one side conductive plate, and the collector and emitter rows located in the middle are connected to the other side conductive plate as an output side in an insulated state. The apparatus according to claim 1, wherein the unit is connected to an AC power supply circuit including a rectifier and a dielectric coil via a plate. 3. The apparatus according to claim 1, wherein an optical signal conversion circuit in the inverter control circuit and a drive circuit for driving each HV-IPM unit are connected via an optical fiber.