Application of IGBT power electronic device

introduction

IGBT is widely used in power electronic devices represented by frequency converters and various power sources. IGBT integrates the advantages of bipolar power transistor and power MOSFET, and has the advantages of voltage control, large input impedance, small driving power, simple control circuit, small switching loss, fast on and off speed and high operating frequency.

However, like other power electronic devices, IGBT's application also depends on circuit conditions and switching environment. Therefore, the driving and protection circuit of IGBT is the difficulty and focus of circuit design, and is the key link in the operation of the entire device.

In order to solve the problem of reliable driving of IGBTs, various IGBT manufacturers or companies engaged in IGBT applications abroad have developed a large number of IGBT drive integrated circuits or modules, such as the EXB8 series produced by Fuji Corporation in Japan and the M579 series produced by Mitsubishi Electric Corporation. , IR21 series produced by American IR Company, etc. However, the EXB8 series, M579 series and IR21 series do not have soft shutdown and power supply undervoltage protection functions, while the HCLP-316J produced by HP has overcurrent protection, undervoltage protection and 1GBT soft shutdown functions, and the price is relatively cheap, Therefore, this article will study it and give the drive and protection circuit of 1700V, 200 ~ 300A IGBT.

1 Working characteristics of IGBT

IGBT is a voltage-type control device, which requires very small drive current and drive power, and can be directly connected to analog or digital function blocks without adding any additional interface circuits. The turn-on and turn-off of the IGBT is controlled by the gate voltage UGE. When the UGE is greater than the turn-on voltage UGE (th), the IGBT is turned on. When a reverse or no signal is applied between the gate and the emitter, the IGBT is turned off Break.

IGBTs, like ordinary transistors, can work in the linear amplification region, saturation region, and cut-off region, and they are mainly used as switching devices. In the drive circuit, we mainly study the two states of saturation turn-on and turn-off of IGBT, so that the turn-on rising edge and turn-off falling edge are relatively steep.

2 IGBT drive circuit requirements

The following points must be noted when designing IGBT drives.

1) The magnitude of the forward drive voltage of the gate will have an important impact on the performance of the circuit and must be selected correctly. When the forward drive voltage increases,. The on-resistance of the IGBT decreases, which reduces the turn-on loss; but if the forward drive voltage is too large, the short-circuit current IC of the load will increase with the increase of UGE when the load is short-circuited, which may cause the IGBT to hold the effect and cause the gate control to fail. As a result, the IGBT is damaged; if the forward drive voltage is too small, the IGBT will exit the saturation conduction region and enter the linear amplification region, causing the IGBT to overheat and damage; it is better to choose 12V≤UGE≤18V in use. The negative bias voltage of the gate can prevent the IGBT from being mistakenly turned on due to excessive inrush current when it is turned off. Generally, it is appropriate to select a negative bias voltage of 5V. In addition, the drive circuit should provide sufficient voltage and current amplitude after the IGBT is turned on, so that the IGBT will not exit the saturated conduction region and be damaged under normal operation and overload conditions.

2) The fast turn-on and turn-off of IGBT is helpful to increase the operating frequency and reduce the switching loss. However, the switching frequency of the IGBT should not be too large under a large inductive load, because high-speed turn-on and turn-off will produce a high peak voltage, which is likely to cause IGBT or other components to be broken down.

3) It is very important to select the appropriate gate series resistance RG and gate-emitter capacitance CG to drive the IGBT. RG is small, and the charge-discharge time constant between the gate and emitter is relatively small, which will cause a large instantaneous current at turn-on, thereby damaging the IGBT; a large RG is helpful to suppress dvce / dt, but it will increase the switching time and switching loss of the IGBT . Appropriate CG is conducive to suppressing dic / dt, CG is too large, turn-on time delay, CG is too small, the effect of suppressing dic / dt is not obvious.

4) When the IGBT is turned off, the gate-shot voltage is easily disturbed by the parasitic parameters of the IGBT and the circuit, causing the gate-shot voltage to cause the device to conduct mistakenly. To prevent this phenomenon, a resistor can be connected in parallel between the gate-shot. In addition, in order to prevent high-voltage spikes in the gate drive circuit in practical applications, it is best to connect two reverse series Zener diodes in parallel between the gate and the emitter. The voltage regulation value should be the same as the positive and negative gate voltages.

3 HCPL-316J drive circuit

3.1 HCPL-316J internal structure and working principle

If an overcurrent signal occurs on the IGBT (pin 14 detects the voltage on the IGBT collector = 7V), and the input drive signal continues to be applied to pin 1, the undervoltage signal is low, the B point outputs low level, and the third level Darlington The tube is turned off, the 1 × DMOS is turned on, and the voltage between the IGBT gate and emitter set is slowly discharged to achieve a slow voltage drop. When VOUT = 2V, that is, VOUT outputs a low level, point C becomes a low level, point B is a high level, 50 × DMOS is turned on, and the IGBT gate-emitter is quickly discharged. The signal on the fault line passes through the optocoupler, and then through the RS trigger, Q outputs a high level, so that the input optocoupler is blocked. In the same way, we can analyze only the undervoltage condition and the undervoltage and overcurrent condition.

3.2 Drive circuit design

VIN +, FAULT and RESET on the left side of HCPL-316J are connected to the microcomputer respectively. R7, R8, R9, D5, D6 and C12 play the role of input protection to prevent excessively high input voltage from damaging the IGBT, but the protection circuit will cause a delay of about 1μs, which is not suitable for use when the switching frequency exceeds 100kHz. Q3 mainly acts as an interlock. When both PWM signals (the same bridge arm) are at high level, Q3 is turned on, pulling the input level low, so that the output is also low. The interlock signals Interlock in Figure 3 and Interlock2 are connected to another 316J Interlock2 and Interlock1, respectively. R1 and C2 are used to amplify and filter the fault signal. When there is interference signal, it can make the microcomputer receive the information correctly.

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

C3 is a very important parameter, the most important function is charging delay. When the system starts and the chip starts to work, because the voltage of the collector C terminal of the IGBT is still far greater than 7V, if there is no C3, it will erroneously send out a short-circuit fault signal, so that the output is directly turned off. When the chip works normally, if the collector voltage rises instantaneously, it will return to normal immediately afterwards. If there is no C3, it will also send out an erroneous fault signal to turn off the IGBT by mistake. However, if the value of C3 is too large, the system response will be slow, and under saturation, it may also cause the IGBT to be burned out within the delay time, which will not provide the correct protection. The value of C3 is 100pF, and its delay time

Using two diodes in series in the collector detection circuit can improve the overall reverse withstand voltage, which can improve the driving voltage level, but the reverse recovery time of the diode should be very small, and each reverse withstand voltage level should be 1000V , Generally choose BYV261E, reverse recovery time 75 ns. The role of R4 and C5 is to retain the soft turn-off characteristics of HCLP-316J after an overcurrent signal appears. The principle is that C5 implements soft turn-off through the discharge of the internal MOSFET. In Fig. 3, the output voltage VOUT passes through two fast triode push-pull outputs, so that the drive current can reach a maximum of 20A, and can quickly drive 1700v, 200-300A IGBT.

3.3 Design of driving power

In the drive design, a stable power supply is the guarantee that the IGBT can work normally. The power supply adopts forward conversion, which has strong anti-interference ability. The secondary side does not add filter inductor, and the input impedance is low, so that the power supply output voltage is still relatively stable under heavy load.

When s is turned on, + 12v (for a relatively stable power supply with high accuracy) voltage is applied to the winding connected to the primary side of the transformer and S, and the secondary side is rectified and output through energy coupling. When S is turned off, the energy of the magnetic core is fed back to the power supply through the primary diode and the winding connected to it, and the magnetic core of the transformer is reset. The 555 timer is connected as a multivibrator, and the potential of pins 2 and 6 is changed between 4 and 8v by charging and discharging C1, so that pin 3 outputs a square wave voltage signal, and the square wave signal is used to control the opening of S And shut down. + 12v charges C1 through R1 and D2, its charging time t1≈R1C2ln2; discharge time t2 = R2C1ln2, high level during charging, low level during discharging. Therefore, the duty ratio = 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 side + 15v output 2A, -5v output 1 A, efficiency n = 80%, window fill factor Km is O. 5. The core filling factor Kc is 1, and the coil wire current density d is 3 A / mm2. Then the output power

PT = (15 + 0.6) × 2 × 2 + (5 + 0.6) × 1 × 2 = 64W.

Since the output voltage of the driving power supply will decrease after loading, in practical applications, consider increasing the frequency and duty cycle to stabilize the output voltage.

4 Conclusion

This paper has designed a drive circuit that can drive IGBT of l700v, 200 ~ 300A. The hardware realizes the interlocking of two IGBTs (the same bridge arm), and designs a driving power supply that can directly supply power to the two IGBTs.

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 and high power IGBT drive.

The functions of each pin are as follows:

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

If VIN + is input normally, pin 14 has no overcurrent signal, and VCC2-VE = 12v means that the output forward drive voltage is normal, the drive signal outputs high level, and the fault signal and undervoltage signal output low level. First of all, three signals are input to JP3 together, point D is low, point B is also low, and 50 × DMOS is in the off state. At this time, the four states of the input of JP1 are low, high, low, and low from top to bottom, and the A point is high, driving the three-level Darlington tube to turn on, and the IGBT is also turned on.

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