A new four-level PWM inverter topology for high power applications - effect of switching strategies on power losses distribution

In this paper a novel four-level pulse width modulation (PWM) hybrid inverter topology is proposed which is composed of a conventional two-level and a three-level neutral point clamped (NPC) inverter suitable for high-voltage power applications. The proposed topology when it is compared to the conventional four-level NPC PWM inverter exhibits the following advantages: (a) ability of changing the losses distribution profile among the devices by selecting the suitable switching strategy, (b) reduction of total inverter power semiconductor device losses, (c) ability of bidirectional operation of all switches, (d) series connected clamping diodes are not needed and (e) flexibility of using existing power semiconductor modules that makes simple the implementation of the proposed power topology. Moreover, the effect of different switching strategies on the conduction and switching losses profile of the proposed inverter is examined by varying the index modulation depth and the load power factor. A suitable losses calculation method for hybrid multilevel inverter is used and a comparison of losses distribution profiles between the proposed inverter and the conventional four-level inverter is carried out. Finally, the theoretical results are confirmed by simulation and experimental results.