Application of IGBT in medium frequency induction heating power supply

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Photocoupler

1 Introduction

According to the current domestic power supply mode, the hollow sucker rod induction heating system uses a power frequency induction heating method. In order to balance the three-phase power, the power frequency heating power supply superimposes one phase of the power frequency three-phase alternating current through the phase shift phase of the reactor and the capacitor to the other two phases, and then directly becomes suitable for various heating requirements through the transformer. Connect the heating conductor after single-phase power frequency AC. Therefore, the power frequency heating power supply is costly, bulky, cumbersome, and inefficient.

The oil medium frequency induction heating power supply adopts IGBT as the inverter switching device, and the volume is reduced by 40% and the weight is reduced by 50% compared with the common power frequency heating power source.

2 IF induction heating power supply

See Figure 1 for the circuit structure of the IF induction heating power supply. The three-phase rectifier rectifies the power frequency three-phase alternating current into direct current. After filtering, the full-bridge inverter converts into a single-phase intermediate frequency alternating current whose frequency and duty ratio are continuously adjustable within a certain range, and then outputs the output to the isolation transformer. Heat the load. The full-bridge inverter adopts pulse width modulation (PWM) zero-voltage switching circuit, which has the advantages of low switching loss and small electromagnetic interference [2]. The control circuit uses the SG3524 integrated block to adjust the 9-pin voltage to ensure the dead time of the output signal. The pulse width of the output signal is modulated by a petroleum temperature detector. The temperature of the oil is controlled at 45 to 70 °C. Too high a temperature can easily change the chemical properties of petroleum. Too low a temperature will reduce the fluidity of petroleum.

3 IGBT gate drive circuit

3.1 Selection of IGBT gate drive module

IGBT gate drive modules EXB841 and M57962L can be used to drive IGBT modules within 1200V series 400A, with overcurrent detection and protection. The output waveform of these two drive modules under short-circuit protection is shown in Figure 2. The EXB841 internally generates a 5V negative bias and is not adjustable; the M57962L externally uses a Zener diode to generate a 9V negative bias, and the gate reliability is higher than EXB841. In addition, the protection action time of the M57962L (from overcurrent to gate voltage dropped to 0V) is 6.3μs (see Figure 2a); the protection action time of the EXB841 is 16μs and the gate voltage cannot be reduced to less than 2v (see Figure 2b). ), the risk of IGBT fuses is greater than that of the M57962L. Therefore, M57962L should be used.

3.2 Improvement of peripheral circuit of drive module

When the IGBT is turned off, the voltage rise rate between the collector and the emitter is as high as 30000V/μs. Too high will produce a large displacement current. And it leads to a large collector pulse surge current, which makes it easy for the IGBT to dynamically move. In order to avoid such a malfunction of the IGBT, a negative bias must be applied to the gate of the IGBT [3]. However, in practical applications, the following two conditions will lead to the disappearance of the negative bias of the driver circuit: 1 the Zener diode breaks through the short circuit; 2 The drive circuit loses the +24V power supply.

In view of the above two cases, the author improved the peripheral circuit of the IGBT driver module M57962L based on the manufacturer's recommended application circuit, as shown in Figure 3. Under normal conditions, VZ4 is turned on, M57962L8 pin is high, and VD1 is cut off. VT2 is turned on. The VO1 output is in a low impedance state. If the Zener diode VZ1 or VZ3 is short-circuited, VZ4 is turned off, VT1 is turned off, and the VO1 output is in a high-impedance state. If the drive circuit loses +24V, no current flows through the VO1 input and the VO1 output is in a high-impedance state.

4 IGBT module and filter capacitor connection

The input characteristics of the IGBT are similar to those of the MOSFET. The input impedance is high. If the drive circuit loses voltage, the gate of the IGBT loses a negative bias. High impedance to the emitter. At this time, once there is interference to the gate of the IGBT, the upper and lower tubes of the IGBT module are easily turned on at the same time. If the IGBT module is directly connected to the filter capacitor of several thousand microfarads, the energy stored by the filter capacitor will be directly released through the upper and lower tubes of the IGBT module, which may easily cause damage to the IGBT module. Therefore, the induction heating power supply first turns on the power of the control and driving circuit when the power is turned on, and then connects the IGBT module and the filter capacitor. When the power is turned off, the IGBT module is disconnected from the filter capacitor, and then the power of the control and drive circuit is turned off.

5 Test situation and conclusion

The oil-inducing induction heating power supply has been in normal operation since the field test of the second test plant in June 1997. The power supply is 3588kw. The oil-assisted induction heating power supply can be applied not only to the hollow sucker rod induction heating system. It can also be applied to the medium frequency induction electric heating system of the gathering pipeline of complex small fault block oilfield, which is of great significance for reducing the capital investment and operating cost of the gathering pipeline.