JPS62122089A - Electromagnetic induction heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electromagnetic induction heating device that heats a workpiece such as a forging piece using high frequency waves.

(Prior Art) The present applicant has already been provided with an electromagnetic induction heating device as shown in FIG. To explain the operation of the device shown in the figure, alternating current is converted to direct current by a group of diodes (11) connected in three bridges, and this direct current is smoothed by a capacitor (21).
10,000 transistors +31 +41151 +61 are connected to a single-phase full-wave circuit, and a resonant capacitor +71 (
81 and a circuit connected in series with the load coil (9) constitutes a series resonant inverter as a load.

As shown in Fig. 1, such a device generates four force increases around the resonant frequency of the load circuit, and by rapidly controlling the frequency of the inverter, it is possible to adjust one force, and the load coil ( 9) For example, do not use magnetic materials such as iron in the furnace passage. ! This allows induction heating to a temperature of f.

(Problems to be solved by the invention, etc.) However, in the previous J's device, even if the transistor is driven at a constant frequency and power is supplied to the load, if there is a fluctuation in the AC power supply voltage, the load The electric current 1f changes and has an adverse effect on heating. In addition, if the magnetic material of the workpiece supplied to the coil as a load is not appropriate, and the load impedance differs and the resonance point changes significantly, an excessive current flows through the transistor of the inverter, causing the transistor to become・Let the sun shine. Furthermore, transistor 1 of the inverter
If transistors 31 +41 and transistors +51 +61 are ignited at the same time by mistake, the direct current will be short-circuited. In the conventional device a1 configured with such an inverter, the heating temperature lt changes due to the influence of the power supply voltage, causing problems such as damage to the transistors of the inverter when the load is not appropriate.

The present invention has been made to solve the above-mentioned problems, and performs frequency correction for fluctuations in power supply voltage.
In addition to supplying appropriate power to the load and stabilizing heating,
Even if there is a change in the load and excessive current is about to flow through the inverter transistors, it will be detected and the frequency will be corrected.
Or, control the time to apply the voltage to obtain a moderate current.
In January, we will provide a new induction jJu heat shield device that has the function of preventing damage to inverter transistors.

(Means for Solving the Problems) In order to achieve the above object, the present invention arranges a large number of transistors with a small g difference per series as an inverter element in parallel, and each of these transistors is In an electromagnetic induction heating device that is connected in series to a load coil through a capacitor that is a cover balancer and draws a large amount of power to the load coil, a) a circuit that detects the power source (pressure) and the load coil that detects the current; Having a circuit and controlling the frequency of each signal independently.

b) Having a gradually increasing ramp signal as the signal for controlling the frequency.

C) In order to prevent short circuits between the upper and lower transistors that constitute the inverter, the output of a monostable multiplier operated at a driving frequency and a driving pulse are combined in an AND circuit.

d) The circuit for detecting the specified load current should be compared with a reference signal, change the frequency based on the reference signal 111, and control the conduction time.

θ) Controlling the driving frequency by the signal output from the comparison circuit with the source voltage reference signal.

It is characterized by:

(Example) An embodiment of the present invention will be explained with reference to FIG.

In the cough diagram, the AC current is rectified into DC by the three-phase bus (1) connected in the diode group (1), which is converted into DC, and smoothed by the condenser 121. transistor +3
1141 and another transistor +51 +61 f;! Since the ignition drive is performed at alternating frequencies, the DC power is converted into AC power flowing through the series resonant circuit of the resonant capacitor +71f81 and the load coil (9), and the magnetic material supplied to the load coil (9). Heating is performed by supplying energy to the Such a device has already been described in detail with reference to FIG.

- If the control block 1g has a product numerator α(a), a limiter f151. A voltage divider ([6)] and a VF converter 1n are connected in series. When a setting signal consisting of an input signal circuit is input to an integrator (L4), an integrator +141 integrates the input signal and converts it into a signal that increases at a constant slope, and sends this signal to a voltage divider via a limiter f15). As a result of the input to (16), the output of the voltage divider (161) outputs a divided increasing signal with a constant slope until it is limited to the limiter,
This continues until the limiter is applied, and after the limiter is activated, the V-force becomes a constant value. Therefore, until a certain period is reached, the rI: frequency goes from the high 18 waves to the low frequency, that is, the 4 forces are gradually increased. In addition, a pulse voltage (second
(see Figure 1 tli1). Furthermore, the pulse voltage is input to the subsequent sawtooth wave generator (2α), which generates a special waveform (see column 2 in Figure 2), that is, a sawtooth wave, which is input from the circuit 132. The output pulse voltage of the VF converter (171) is compared with the sawtooth wave by the comparator (221) to obtain the output (see column 21!JI). +241, and the respective outputs are as shown in the ■, V, and Vl columns in Figure 2. Since the AND circuit is composed of 12 marks (to), the respective outputs are as shown in ~g■ in Figure 2. A waveform like this ≦.

This waveform vx transistor base drive circuit (2η;
Input to 2&, inverter transistor +31C
Drives 41+5+ +6+. The zero period (T,) of the monostable multi output is
This is effective for keeping all transistors in the off period. Furthermore, as can be seen from the above explanation, by changing the level of the base signal 23, the period (T2) shown in FIG. If , the ratio of the conduction period to the whole remains constant even if the frequency changes.

If the power supply voltage fluctuates, change the voltage to a transformer.
), rectified by the rectifier uz, converted to DC, and then input to the voltage comparator (1!ll).The pressure comparator α9v'X outputs a signal compared with the voltage reference signal and converts it to the VLF converter liη. For example, when the power supply voltage drops, the output of induction heating will decrease, but since the frequency is reduced by outputting a signal that reduces the input to the VEF converter 117), the power increases (see Figure 4). ) to operate the heating energy stably.

Insert an O T (101) for current measurement into the 10,000 load circuit, convert the current detected by the CT controller to a DC signal using a metal current detector (13), and input the DC signal to a current comparator (181). - By comparing the current reference signal sent from the 10,000 circuit (to) to the current comparator t181 and dividing the compared signal by the voltage divider QI), it is inputted to the comparator as an appropriate value and the conduction period is controlled.

The output of the current comparator 1181 is also input to the VF converter, so that when an abnormally large current is about to flow, V
Y, it functions to limit power by increasing the control frequency.

(Effects) As described above, according to the present invention, in induction heating control using a series inverter, JJD thermal energy can be stably output regardless of fluctuations in the power source, and excessive When current is about to flow, it adjusts the power by changing the frequency, and has a circuit that prevents short circuits between the top and bottom of the transistors that make up the inverter, so it has good heating stability, suppresses overcurrent, and This has the effect of preventing cross-circuiting and obtaining a highly reliable induction heating device with d performance.

[Brief explanation of drawings]

Fig. 1 shows an embodiment of the present invention. Fig. 1 is a block diagram of the main circuit and control circuit of a series inverter, Fig. 2 is an explanatory diagram of voltage output waveforms in Fig. 3, and Fig. 3 is a conventional diagram. It is an explanatory diagram of an example. (1)・・・・・・・・・Diode. (2)・・・・・・・・・・・・Condenser. f3X4X5X61...transistor. +71 C81...Resonance capacitor. (9) Load coil. 00 ・・・・・・・・・・・・ CT. [13)・・・・・・・・・・・・ Rectifier. (14・・・・・・・・・・・・Drum numerator. 11・・・・・・・・・・Limiter. 0e・・・・・・・・・・・・・・・Voltage divider. 1D・・・・・・・・・VF converter. ;181・・・・・・・・・Current cone palator. +25) C2fA・・・・・・Anvil.

Claims (1)

[Claims] A large number of transistors with a small capacity per element are arranged in parallel as an inverter element, and each of these transistors is connected in series to a load coil via a capacitor serving as a power balancer. An electromagnetic induction heating device that draws a large amount of electric power: a) has a circuit for detecting a power supply voltage and a circuit for detecting a load current, and controls the frequency of each signal independently. b) Having a gradually increasing ramp signal as the signal for controlling the frequency. c) In order to prevent short-circuiting between the upper and lower transistors constituting the inverter, the output of the monostable multiplier operated at the driving frequency and the driving pulse are combined by an AND circuit. d) The circuit for detecting the load current compares it with a reference signal, changes the frequency based on the value, and controls the conduction time. e) Controlling the drive frequency by a signal output from the power supply voltage and reference signal comparison circuit. An electromagnetic induction heating device featuring: