Through market research, we found that IGBTs in inverters often lose goods or even explode, especially some inverter brands with poor quality and cheap price. So what is the role of IGBT in the inverter? Why do they often fail? And how can we improve it when it fails? Below, Everest editorial to everyone.

First, what is IGBT

     IGBT power module is a power module composed of insulated gate bipolar transistor (IGBT). As IGBT modules are MOSFET structure, the gate of IGBT is electrically isolated from the emitter through a layer of oxide film, which has excellent device performance. IGBT power modules are voltage type control, with the advantages of large input impedance, small driving power, simple control circuit, small switching loss, fast on/off speed, high operating frequency and large component capacity, and can work normally in the frequency range of several tens of kHz. They are widely used in servo motors, inverters, inverter appliances and other fields, and play a pivotal role in power electronic current conversion and control.

Second, the inverter IGBT explosion causes

Due to the poor overcurrent resistance and overvoltage resistance of IGBT, it will be damaged once there is an accident. During use, it is often subjected to capacitive or inductive load, overload or even load short circuit shock, etc., which leads to IGBT damage or even explosion (the loss of the module is very huge, and the heat cannot be dissipated, resulting in extremely high internal temperature, generating gas and breaking through the shell, which is called IGBT explosion). Everest editor mainly puts them into four categories of causes.

Internal factors.

From the nature of the explosion is the heat power exceeds the heat dissipation power, the internal cause should be overheating.

Human factors

incoming line is connected to the outgoing line terminal

Inverter connected to the wrong power supply 

Not connected to the load as required

Common causes

Overcurrent: one is a short circuit of the load, the other is the logic at the control circuit is disturbed, resulting in the upper and lower bridge arm components straight through.

Damage of insulation

Overvoltage: usually caused by the spike voltage generated by the line stray inductance under the action of very high di/dt, the solution is to design a high-performance absorption circuit to reduce the line stray inductance.

Overheating: IGBT can not be fully conductive, in the case of current component loss increases, the temperature increases resulting in damage.

Communication error rate: after a period of communication, sudden error message causes IGBT to misconduct causing IGBT to explode; communication board FPGA program runs unstable causing IGBT to misconduct causing IGBT to explode.

Other causes

The overcurrent detection circuit in the circuit cannot keep up with the response time.

IGBT short-circuit protection is through the detection of saturation voltage drop, and the time left for the actuator is generally 10us (8 times overcurrent) in the power-up time is easy to burn the pre-charge resistor and the IGBT in the brake unit.

Process problems: the copper row of the school is strong, screws are not tightened, etc.

Short-time high current: there are also many reasons, such as the dead zone is not set, the main circuit overvoltage, absorption circuit is not done.

Drive power supply is also a problem that should be paid special attention to the isolation plus isolation, the filtering plus filtering.

Motor shock feedback voltage is too large to cause the IGBT explosion. However, the probability of explosion during charging is not very high.

When the motor starts, the input measurement voltage drops instantly and the capacitor discharges. After the input measurement voltage is restored the inrush current when the capacitor is charging is too large causing the IGBT to explode.

Third, inverter IGBT protection measures

     Generally, we design the IGBT protection circuit from three aspects: overcurrent, overvoltage and overheat. IGBTs can withstand overcurrent for only a few microseconds and have a small overcurrent resistance, so the primary attention of IGBTs is overcurrent protection. There is a protection function, because different models of hybrid drive module, its output capacity, switching speed and du / dt withstand capacity is different, the use of the appropriate selection according to the actual situation. For the new combined IGBT overcurrent protection of high-power voltage inverter, it can be protected by blocking the drive signal or reducing the gate voltage. In fact, overvoltage protection, as far as possible to reduce the stray inductance in the circuit; the use of absorption circuit, when the IGBT off, absorb the energy released in the inductor to reduce the off overvoltage; appropriate increase the gate resistance Rg. Finally, the IGBT overheating protection, generally using heat sink (including ordinary heat sink and heat pipe heat sink), and can be forced air cooling.

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