In the process of using IGBT UPS, often by the impact of capacitive or inductive load, overload and even short circuit, etc., as well as the wrong operation of UPS, may cause IGBT damage. IGBT in the use of the main reasons for the failure of the following conditions:
1.Over current damage
IGBT has a certain anti over current capacity, but must pay attention to prevent the current damage. IGBT composite device has a parasitic thyristor, so has the latching effect. After the latching effect occur, the drain current cause excessive high power consumption, and finally lead to the damage of the device.
In order to avoid the IGBT happens latching effect and damage, the circuit design should ensure the IGBT maximum working current should not exceeding the IDM value of the IGBT. Also note that may be appropriate to increase the driving resistance Rg to extend the shutdown time, reduce the di / dt of IGBT. Driving voltage size will also affect IGBT latching effect, low driving voltage, under over current in long time and IGBT must be applied with negative bias voltage, IGBT manufacturers generally recommend with about 5V reverse bias voltage. In a negative bias voltage, the driving voltage is between 10 and 15V, and the drain current is 4 to 10 times higher than the rated current in the 5~10μs, so the driver IGBT must be designed with a negative bias voltage. Due to each IGBT based UPS load impact characteristic is not identical, and powered devices may occur short circuit fault, so take measures to limit the flow of IGBT current in the UPS design is necessary, consider using driving thick film circuit provided by IGBT manufacturers.
2.Over voltage damage
Due to the inductive components in the inverter circuit, IGBT will generate spike voltage in the moment of turn off, if the peak voltage is too high, may cause damage to the IGBT even breakdown. Prevent voltage damage methods: optimization of process structure of main circuit, by narrowing the large loop current path to reduce the circuit parasitic inductance; appropriately increase the IGBT driving resistance Rg to slow down the speed of the switch (but switching losses also increased); buffer circuit design, suppression of spike voltage. The diode used in the buffer circuit must be a fast recovery diode, the capacitor must be the film capacitor which is high frequency, low loss, good frequency characteristics. So as to achieve a good absorption effect. The common circuit divide into energy dissipation type and feedback buffer type. Feedback buffer type divide into passive type and active type.
3.Bridge arm damage
In IGBT online UPS, the two drivers of the same arm branch of the inverter bridge must be locked, and the dead time (i.e. common non conducting time) should be set. If common conduction happens, IGBT will soon be damaged. In the control circuit, the control timing of the driving problem should be considered in various operating conditions.
4.Overheat damage and electrostatic damage
Can be used to increase the amount of heat sink, heat conductive adhesive coating, forced fan cooling, set over temperature protection and other methods to solve the problem of overheating damage. In addition to pay attention to the electrostatic damage in installation process, the operator and tools must be protected against static electricity.