Application of IGBT power electronic device
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IGBTs are widely used in power electronic devices represented by inverters and various types of power supplies. The IGBT combines the advantages of bipolar power transistors and power MOSFETs, and has the advantages of voltage control, large input impedance, small driving power, simple control circuit, small switching loss, fast switching speed and high operating frequency.
However, IGBTs, like other power electronics, depend on circuit conditions and switching environments. Therefore, the driving and protection circuit of IGBT is the difficulty and focus of circuit design, and it is the key link of the whole device operation.
1 IGBT operating characteristics
The IGBT is a voltage-type control device that requires very little drive current and drive power and can be directly connected to an analog or digital function block without any additional interface circuitry. 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. Broken.
Like ordinary transistor, IGBT can work in linear amplification region, saturation region and cut-off region, and it is mainly used as a switching device. In the drive circuit, the saturation on and off states of the IGBT are mainly studied, so that the turn-on rising edge and the turn-off falling edge are steep.
2 IGBT drive circuit requirements
The following points must be observed when designing an IGBT driver.
1) The magnitude of the gate forward drive voltage will have an important impact on circuit performance and must be chosen correctly. When the forward drive voltage increases, The on-resistance of the IGBT is reduced, so that the turn-on loss is reduced. However, if the forward drive voltage is too large, the short-circuit current IC increases with the UGE when the load is short-circuited, which may cause the IGBT to have a holding effect, resulting in gate failure. As a result, the IGBT is damaged; if the forward driving voltage is too small, the IGBT exits the saturation conduction region and enters the linear amplification region, causing the IGBT to overheat and damage; in use, 12V ≤ UGE ≤ 18V is preferred. The negative bias voltage of the gate prevents the IGBT from being mis-conducted due to excessive surge current during shutdown. Generally, a negative bias voltage is selected to be 5V. In addition, the driving circuit should provide sufficient voltage and current amplitude after the IGBT is turned on, so that the IGBT does not exit the saturation conduction region and is damaged under normal working and overload conditions.
2) The fast turn-on and turn-off of the IGBT is beneficial to increase the operating frequency and reduce the switching loss. However, the switching frequency of the IGBT should not be too large under large inductive loads, because high-speed turn-on and turn-off will result in high peak voltage, which may cause IGBT or other components to be broken down.
3) Choosing a suitable gate series resistor RG and gate capacitance CG is important for driving the IGBT. RG is small, the charge-discharge time constant between gate emitters is relatively small, which will cause a large current at turn-on, which will damage the IGBT; RG is larger, which is beneficial to suppress dvce/dt, but will increase the switching time and switching loss of IGBT. . Appropriate CG is good for suppressing dic/dt, CG is too large, and the on time is delayed. If CG is too small, the effect of suppressing dic/dt is not obvious.
4) When the IGBT is turned off, the gate-emitter voltage is easily disturbed by the parasitic parameters of the IGBT and the circuit, causing the gate-emitter voltage to cause the device to be mis-conductive. To prevent this from happening, a resistor can be connected in parallel between the gates. In addition, in practical applications, in order to prevent high voltage spikes in the gate driving circuit, it is preferable to connect two reverse series Zener diodes in parallel between the gratings, and 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 the IGBT has an overcurrent signal (the 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, and the B output is low, the third-level Darlington The tube is turned off, 1 × DMOS is turned on, and the voltage between the IGBT gates is slowly dropped to achieve a slow falling gate voltage. When VOUT=2V, that is, VOUT outputs a low level, C point becomes a low level, point B is a high level, 50×DMOS is turned on, and the IGBT gate array is rapidly discharged. The signal on the fault line passes through the optocoupler, and then passes through the RS flip-flop, and the Q output is high, so that the input optocoupler is blocked. In the same way, it is possible to analyze the situation of only undervoltage and the situation of undervoltage and overcurrent.
3.2 drive circuit design
The VIN+, FAULT and RESET on the left side of the HCPL-316J are connected to the microcomputer respectively. R7, R8, R9, D5, D6 and C12 provide input protection to prevent excessive input voltage from damaging the IGBT, but the protection circuit will generate a delay of about 1μs, which is not suitable for use when the switching frequency exceeds 100kHz. Q3 is the most important interlocking function. When both PWM signals (same bridge arm) are high level, Q3 is turned on, pulling the input level low, so that the output is also low. The interlock signals Interlock, and Interlock2 in Figure 3 are connected to another 316J Interlock2 and Interlock1, respectively. R1 and C2 play a role in amplifying and filtering the fault signal. When there is an interference signal, the microcomputer can correctly accept the information.
At the output, R5 and C7 are related to the speed at which the IGBT is turned on and the switching loss. Increasing C7 can significantly reduce dic/dt. First calculate the gate resistance: where ION is the gate current injected into the IGBT when turned on. In order to make the IGBT turn on quickly, the IONMAX value is 20A. Output low level VOL=2v.
C3 is a very important parameter, the most important is the 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, the short-circuit fault signal will be erroneously issued, and the output will be directly turned off. When the chip is working normally, if the collector voltage rises instantaneously, it will return to normal immediately. If there is no C3, an error signal will be issued to make the IGBT turn off by mistake. However, if the value of C3 is too large, the system response will be slow, and in the case of saturation, the IGBT may be burnt out within the delay time, and the correct protection effect is not obtained. The value of C3 is 100pF, and the delay is time
In the collector detection circuit, two diodes are connected in series, which can improve the overall reverse withstand voltage, thereby increasing the driving voltage level, but the reverse recovery time of the diode is small, and each reverse withstand voltage level is 1000V. Generally, BYV261E is selected, and the reverse recovery time is 75 ns. The role of R4 and C5 is to preserve the soft-shutdown characteristics of the HCLP-316J after an overcurrent signal. The principle is that C5 achieves a soft turn-off through the discharge of the internal MOSFET. In Figure 3, the output voltage VOUT passes through two fast triode push-pull outputs, which can drive the current up to 20A, and can quickly drive 1700v, 200-300A IGBTs.
3.3 drive power supply design
In the drive design, a stable power supply is a guarantee for the IGBT to work properly. The power supply adopts forward conversion, strong anti-interference ability, no filter inductor on the secondary side, and low input impedance, so that the output voltage of the power supply is still stable under heavy load conditions.
When s is turned on, +12v (for a relatively stable power supply, high precision) voltage is applied to the primary side of the transformer and the winding connected to S, and the secondary side is rectified through energy coupling. When S is turned off, the energy of the core is fed back to the power supply through the primary diode and its connected winding to achieve reset of the transformer core. The 555 timer is connected to a multivibrator. The potential of the foot 2 and the foot 6 is changed between 4 and 8 v by charging and discharging C1, so that the foot 3 outputs a voltage square wave signal, and the square wave signal is used to control the opening of the S. And shutting down. +12v charges C1 through R1 and D2, its charging time is t1≈R1C2ln2; discharge time t2=R2C1ln2, it outputs high level when charging, and outputs low level when discharging. Therefore, the duty ratio = t1/(t1+t2).
The transformer is designed according to the following parameters: the original side is connected to +12v, the frequency is 60kHz, and the working magnetic induction intensity 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. Output power
PT = (15 + O.6) × 2 × 2 + (5 + O.6) × 1 × 2 = 64W.
Since the output voltage of the driving power supply will decrease after loading, consider increasing the frequency and duty cycle to stabilize the output voltage in practical applications.
4 Conclusion
This paper designs a driving circuit that can drive 1400V, 200~300A IGBT. The interlocking of the two IGBTs (same bridge arm) is realized on the hardware, and a driving power source capable of directly supplying power to the 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 and high power IGBT drive.
The function of each pin is as follows:
Pin 1 (VIN+) forward signal input;
Pin 2 (VIN-) reverse signal input;
Pin 3 (VCG1) is connected to the input power supply;
The ground of the input of pin 4 (GND);
Foot 5 (RESERT) chip reset input;
Foot 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, suspension;
Pin 8 (VLED1-) is grounded;
Pin 9, foot 10 (VEE) provides a reverse bias voltage to the IGBT;
Pin 11 (VOUT) outputs a drive signal to drive the IGBT;
Foot 12 (VC) three-stage Darlington tube collector power supply;
Pin 13 (VCC2) drives the voltage source;
Pin 14 (DESAT) IGBT short-circuit current detection;
Pin 15 (VLED2+) optocoupler test pin, suspension;
Foot 16 (VE) outputs a reference ground.
If VIN+ is normally input, 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, the three signals are input to JP3, D is low, B is low, and 50×DMOS is off. At this time, the four states of the input of JP1 are low, high, low, and low from top to bottom, and the high point of point A drives the three-stage Darlington tube to be turned on, and the IGBT is also turned on.