Loss mitigation and efficiency enhancement in cascaded h-bridge multilevel inverters through inductive decoupling

The inverter operates at a DC link voltage of 400 V. This combines low-cost silicon IGBTs with high-efficiency silicon carbide MOSFETs. This cascaded h-bridge multilevel structure is designed to balance cost and efficiency. A key problem in such H-bridge inverters is the high switching loss that arises when the SiC-MOSFET turns on against a silicon diode. This causes large turn-off losses in the silicon diode due to stored bipolar charge carriers. To solve this issue, the paper introduces an inductive decoupling concept. Small additional inductors are placed between the SiC-MOSFET half bridge and the IGBT with silicon diode half bridge. These inductors reduce the electrical interaction between the two branches during switching events. As a result, the turn-on losses of the active SiC-MOSFET and the turn-off losses of the passive silicon diode are greatly reduced. This leads to lower total inverter losses compared to a conventional non-decoupled cascaded H-bridge multilevel inverter. Double pulse tests are used to accurately measure switching losses. While a cascaded H-bridge multilevel inverter setup is used to validate system-level behaviour. After confirming that the simulation closely matches the experimental results, the inverter losses are evaluated over a representative driving cycle. This allows reorganization of an optimal value for the decoupling inductance. The performance results show that inductive decoupling improves average efficiency during realistic vehicle operation with proposed approach.