Snubberless Series Connection of Silicon Carbide MOSFET using Active Gate Driver
Date1st Apr 2023
Venue Online (Google Meet)
SiC MOSFETs are fast replacing Si IGBTs due to their superior performance in terms of higher voltage blocking, lower on state resistance, higher thermal conductivity, and higher switching frequency of operation. Commercially available SiC MOSFETs have voltage blocking capabilities ranging from 650V to 1.7kV. One of the most cost effective and efficient ways to take advantage of SiC MOSFETs in MV applications is to connect them in series. Unfortunately, SiC MOSFETs are difficult to connect in series due to the manufacturing process variations, mismatches in the applied input gate control signal, and parasitics in the converter layout. Active Gate Driver based control is one of the solutions that may be utilized to overcome the series connection issue. The current study proposes a simplified switching analysis to understand the problems related to the series connection. The gate current control based Active Gate Driver is used to fully control the transients of series connected devices during turn on and turn off time to achieve minimal voltage imbalance. A closed loop control is also implemented for voltage balancing under varying load current conditions. A new voltage balancing control approach for SiC MOSFET body diodes in a series connected string is also proposed. The proposed control mechanism is examined in Double Pulse Test (DPT) setup with two devices connected in series at 1.2kV dc bus voltage. The experiment is extended to include chopper mode, buck converter mode, and half bridge inverter mode for two devices at 1.2kV dc bus and three devices at 2.1kV dc bus using 1.2kV SiC MOSFETs.
The conventional desaturation protection approach includes a fixed blanking time delay, which introduces uncertainty in device protection. An adaptive blanking time technique for detecting Hard Switched Fault(HSF) is proposed. The proposed method uses only device voltage sensing to detect the HSF status. In contrast to the traditional desaturation technique, which uses a fixed blanking time, the proposed method varies the blanking time during each switching cycle. This ensures faster detection of the shoot-through event and a reduction in peak fault current. The developed protection method is tested in a Double Pulse Test(DPT) setup.
Mr. Saravanan D (EE18S075)