Performance evaluation of series connected 15 kV SiC IGBT devices for MV power conversion systems

The 15kV SiC IGBT (2 μm buffer layer) with chip area of 8.4 × 8.4 mm
²
is the state of the art high voltage device designed by Cree Inc. This device is expected to increase the power density of converters and the demonstration of the device in applications like Solid State Transformers has been published. Therefore, it is interesting to investigate the performance of the device in very high voltage (HV) application, where the series connection of devices is required. This paper addresses design considerations of the series connection of 15kV SiC IGBT devices for high voltage converter applications. A simple RC snubber has been used to control both `dv/dt' and dynamic voltage balancing during turn-off. The experimental results show that there is a significant difference in the static and dynamic voltage sharing between two unmatched 15kV SiC IGBTs without active compensation method. With external RC snubber at total DC bus voltage of 10 kV, the difference in dynamic voltage between the two 15 kV SiC IGBT devices during turn-off transition nearly negligible. Also with external snubber, the total turn-off dv/dt of less than `5 kV/ μs' is achieved across each device of two series connected 15kV SiC IGBTs. Furthermore, optimization of RC snubber to minimize semiconductor switching losses and total losses per device including the snubber resistor losses in series connection has been presented.