A four level drive with isolated DC power supplies

Multilevel drives are being increasingly used in high power drive applications, primarily due to higher voltage capability of the topology and by the availability of more reliable force commutated switches with higher voltage ratings. As compared to the three level inverter, the four level inverter permits higher voltage capability and the DC link voltage balancing problem is dealt with by an innovative use of isolation transformers and multiple rectifiers. The inverter operation is thus less constrained and multilevel PWM characteristics can be fully exploited to optimize the inverter performance. Simulation results demonstrate the system issues and identify design drivers. Experimental results are used to demonstrate the viability of the proposed drive configuration.