Application of IGBT power electronics

introduction

IGBTs are widely used in power electronic devices represented by inverters and various types of power supplies. The IGBT integrates the advantages of bipolar power transistors and power MOSFETs, and has the advantages of voltage control, large input impedance, small drive power, simple control circuit, small switching loss, fast switching speed, and high operating frequency.

However, IGBTs, like other power electronic devices, rely on circuit conditions and switching environments. Therefore, the driving and protection circuit of IGBT is the difficult point and key point of circuit design, and it is the key link of the whole device operation.

In order to solve the problem of reliable driving of IGBTs, foreign IGBT manufacturers or companies engaged in IGBT applications have developed a large number of IGBT driver ICs or modules, such as the EXB8 series produced by Japan Fuji Electric Co., Ltd. and the M579 series produced by Mitsubishi Electric Corporation. , IR series produced by American IR Corporation. However, EXB8 series, M579 series and IR21 series do not have soft turn-off and power supply under-voltage protection. HP's HCLP-316J has over-current protection, under-voltage protection and 1GBT soft-off, and is relatively inexpensive. Therefore, this article will study it, and provide 1700V, 200 ~ 300A IGBT drive and protection circuit.

1 IGBT operating characteristics

IGBT is a kind of voltage type control device, it needs very little drive current and driving power, can connect with analog or digital function block directly without adding any additional interface circuit. The turn-on and turn-off of the IGBT is controlled by the gate voltage UGE. When the UGE is larger than the turn-on voltage UGE(th), the IGBT is turned on. When the reverse or non-signal is applied between the gate and the emitter, the IGBT is turned off. Broken.

IGBTs, like ordinary crystal transistors, can operate in linear amplification regions, saturation regions, and cut-off regions, which are primarily used as switching devices. In the drive circuit, we mainly study the saturation conduction and termination states of the IGBT, making the turn-on rising edge and turn-off falling edge all steeper.

2 IGBT drive circuit requirements

The following points must be noted when designing IGBT drivers.

1) The size of the gate forward drive voltage will have a significant impact on the circuit performance and must be selected correctly. When the forward driving voltage increases, The on-resistance of the IGBT decreases, and the on-state loss decreases. However, if the forward driving voltage is too large, the short-circuit current IC increases with UGE when the load is short-circuited, which may cause the IGBT to become active and cause the gate control to fail. As a result, the IGBT is damaged. If the forward driving voltage is too small, the IGBT will exit the saturated conduction area and enter the linear amplification area, which will cause the IGBT to overheat and damage. It is preferable to use 12V ≤ UGE ≤ 18V. The negative bias voltage of the gate can prevent the IGBT from being turned on by the surge current when it is turned off. Generally, a negative bias voltage of 5V is suitable. In addition, after the IGBT is turned on, the drive circuit should provide sufficient voltage and current amplitude so that the IGBT will not be damaged due to normal operation and overload conditions without exiting the saturated conduction region.

2) The rapid turn-on and turn-off of IGBTs helps increase the operating frequency and reduces switching losses. However, the switching frequency of IGBT should not be too large under large inductive load, because high peak voltage will be generated during high-speed turn-on and turn-off, which may cause breakdown of IGBT or other components.

3) Selecting the appropriate gate series resistor RG and gate emitter capacitor CG is very important for driving the IGBT. RG is small, the charge-discharge time constant between the emitters of the gate is relatively small, which will make the current at the moment of opening larger, thereby damaging the IGBT; RG is large, which is favorable for suppressing dvce/dt, but it will increase the switching time and switching loss of the IGBT . The appropriate CG is favorable for inhibiting dic/dt, CG is too large, and the time for opening is delayed. When CG is too small, the effect of inhibiting dic/dt is not obvious.

4) When the IGBT is turned off, the gate-emitter voltage is easily disturbed by IGBT and circuit parasitic parameters, so that the gate-emitter voltage causes the device to be turned on by mistake. To prevent this from happening, a resistance can be connected between the gate-emitters. In addition, in actual application, in order to prevent the gate drive circuit from appearing high voltage spikes, it is preferable to connect two reverse series zener diodes between the gate shots, and the voltage regulator value should be the same as the positive and negative gate voltages.

3 HCPL-316J Drive Circuit

3.1 Internal structure and working principle of HCPL-316J

If the IGBT has an over-current signal (foot 14 detects IGBT collector voltage = 7V), and the input drive signal continues to be added to pin 1, the under-voltage signal is low, and point B is output low, level 3 Darlington The tube is turned off, the 1×DMOS is turned on, and the voltage between the IGBT gate shot sets is slowly let go, achieving a slow drop gate voltage. When VOUT=2V, ie, VOUT outputs low level, C point becomes low level, B point is high level, 50*DMOS is turned on, and the IGBT gate shot set is rapidly discharged. The fault line signal passes through the optocoupler and passes through the RS flip-flop. The Q output is high and the input optocoupler is blocked. Similarly, it can analyze the situation of under-voltage and under-voltage and over-current conditions.

3.2 Drive Circuit Design

VIN+, FAULT, and RESET to the left of HCPL-316J are connected to the microcomputer. R7, R8, R9, D5, D6, and C12 act as inputs to prevent excessive input voltage from damaging the IGBT, but the protection circuit produces a delay of approximately 1μs, which is not suitable when the switching frequency exceeds 100kHz. Q3 mainly plays an interlocking role. When the two PWM signals (the same bridge arm) are all at high level, Q3 is turned on, pulling the input level low and making the output low. The interlock signals Interlock2 and Interlock2 in FIG. 3 are connected to another 316J Interlock2 and Interlock1, respectively. R1 and C2 act as amplifying and filtering the fault signal. When there is interference signal, it can allow the microcomputer to accept the information correctly.

At the output, R5 and C7 are related to the speed and switching losses of the IGBT, and increasing C7 can significantly reduce the dic/dt. First calculate the gate resistance: where ION is the gate current injected into the IGBT when it is on. To make the IGBT turn on quickly, the design has an IONMAX value of 20A. Output low VOL=2v.

C3 is a very important parameter, the most important role of charging delay. When the system starts up and the chip starts to work, since the voltage at the collector C terminal of the IGBT is still much larger than 7V, if there is no C3, a short-circuit fault signal will be erroneously output, and the output will be shut down directly. When the chip works normally, if the collector voltage rises instantly, it will return to normal immediately. If there is no C3, it will also send out the wrong fault signal to make the IGBT turn off. However, if the value of C3 is too large, the system response will slow down, and in saturation, it may cause the IGBT to be burned out within the delay time, which will not achieve the correct protection function. The value of C3 is 100pF, which is delayed. time.

The use of two diodes in series in the collector detection circuit can increase the overall reverse withstand voltage, which can increase the driving voltage level, but the diode reverse recovery time is very small, and each reverse voltage class should be 1000V , generally select BYV261E, reverse recovery time 75 ns. The role of R4 and C5 is to retain the soft turn-off characteristic of HCLP-316J after the over-current signal appears. The principle is that C5 achieves a soft turn-off through the discharge of the internal MOSFET. In Figure 3, the output voltage VOUT goes through two fast triode push-pull outputs, enabling the maximum drive current to reach 20A, enabling fast driving of 1700V, 200-300A IGBTs.

3.3 Drive Power Design

In the drive design, a stable power supply is the guarantee that the IGBT can work normally. The power supply adopts forward conversion, strong anti-interference ability, no secondary filter inductor, low input impedance, so that the power supply output voltage is still relatively stable under heavy load conditions.

When s is turned on, +12v (for a more stable power supply, high accuracy) voltage is applied to the transformer primary and S connected windings, through the energy coupling so that the secondary side after rectification output. When S turns off, the core's energy is fed back to the power supply through the primary diode and its associated winding, allowing the transformer core to reset. 555 timer connected to a multivibrator, through the charge and discharge of the C1 so that the potential of the foot 2 and the foot 6 is transformed between 4 ~ 8v, so that the foot 3 output voltage square wave signal, and the square wave signal to control the opening of the S And shut down. +12v passes R1, D2 charges C1, its charging time t1 ≈ R1C2ln2; Discharge time t2 = R2C1ln2, outputs high when charging, exports low level while discharging. So duty cycle = t1/(t1+t2).

The transformer is designed according to the following parameters: the primary side is connected to +12v, the frequency is 60kHz, and the working magnetic induction Bw is O. 15T, secondary +15v output 2A, -5v output 1 A, efficiency n = 80%, window fill factor Km is O. 5, the core fill factor Kc is 1, the coil wire current density d is 3 A/mm2. Then, the output power PT=(15+O.6)×2×2+(5+O.6)×1×2=64W.

Since the output voltage of the driving power supply will drop after being loaded, in practice, it is considered to increase the frequency and the duty ratio to stabilize the output voltage.

4 Conclusion

This paper designs a driving circuit that can drive IGBTs from 1700V to 200A to 300A. The interlocking of two IGBTs (the same bridge arm) is realized on the hardware, and a driving power source capable of directly supplying two IGBTs is designed.

HCPL-316J can be divided into two parts: input IC (left) and output IC (right). The input and output can fully meet the requirements of high-voltage high-power IGBT driver.

The function of each pin is as follows:

Pin 1 (VIN+) forward signal input;
Pin 2 (VIN-) reverse signal input;
Pin 3 (VCG1) to input power;
Pin 4 (GND) input ground;
Pin 5 (RESERT) chip reset input;
Foot 6 (FAULT) fault output, when the fault occurs (output forward voltage undervoltage or IGBT short circuit), output the fault signal through the optocoupler;
Pin 7 (VLED1+) optocoupler test pin, suspension;
Pin 8 (VLED1-) ground;
Pin 9, pin 10 (VEE) provides reverse bias voltage to the IGBT;
Pin 11 (VOUT) outputs a drive signal to drive the IGBT;
Foot 12 (VC) tertiary Darlington collector power supply;
Pin 13 (VCC2) drive voltage source;
Foot 14 (DESAT) IGBT short-circuit current detection;
Pin 15 (VLED2+) optocoupler test pin, suspension;
Foot 16 (VE) output reference ground.

If VIN+ is normally input, there is no over-current signal at pin 14, and VCC2-VE=12v is the output normal driving voltage is normal, the driving signal outputs high level, and the fault signal and undervoltage signal output low level. The first three signals are input to JP3 together, D is low, B is low, and 50×DMOS is in the off state. At this time, the four states of JP1's input are low, high, low, and low from the top to the bottom, and the A point is high, driving the three-stage Darlington conduction, and the IGBT is turned on.