DC Link Capacitor Active Discharge by IGBT Weak Short Circuit

DC link active discharge is mandatory in new energy vehicles. This paper first analyzes the necessity of active discharge in automotive inverters and then introduces the commonly used discharge methods. After reviewing the pros and cons of the current methods, a new discharge solution using IGBT (Insulated Gate Bipolar Transistor) modules WSC (Weak Short Circuit) is proposed. The essence of WSC is to make one of the shooting through IGBTs (two IGBTS forms a half bridge topology) entering into active work area by controlling its gate voltage V_GE, where the short current is controlled in safe range and IGBT V_CE voltage is relative large. Hence, large transient power is produced inside IGBT in this condition. By this method, the DC link capacitor energy will be consumed by the weak turned on IGBT gradually. Since the IGBT module has a dedicated cooling loop, the heat generated during discharging process can be transferred into coolant. In order to discharge the DC link capacitor safely, an optimized discharge topology is suggested in which PWM method is applied. This paper focuses on the intensive evaluation of the IGBT both steady and transient electro-thermal stress under this new discharge method. The simulation and experimental results show that this method can not only discharge the DC link capacitor fast, but also has no risk of IGBT damaging since the IGBT electric and thermal stresses are in the safe operation range during the discharge time. It is proved that this new discharging solution saves cost and is also practical for engineering.