Back to back Z-source inverter topology for the series hybrid electric bus

This paper proposes a new power electronic circuit topology for a series hybrid electric bus (HEB). Unlike the existing back to back voltage source inverter (VSI) HEB topologies, the new back to back Z source inverter topology is capable of decoupling the voltage levels at each end of the dc-link. This significant improvement now allows for a further optimized operation of the generator inverter, reduction in dc-link capacitor size, and lower generator harmonics. This paper discusses the boost-only characteristic and the common dc-link voltage characteristic of the existing topologies and how this can be overcome with the proposed topology. Through a coordinated control of the traction inverter open circuit and shoot through switching states, the Z source network is able to maintain a different dc-link voltage at the traction inverter as compared to that at the generator inverter. Simulation results are shown to verify the concept.