Charge balance control schemes for cascade multilevel converter in hybrid electric vehicles

This paper presents transformerless multilevel converters as an application for high-power hybrid electric vehicle (HEV) motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) make an HEV more accessible/safer and open wiring possible for most of an HEV's power system. The cascade inverter is a natural fit for large automotive hybrid electric drives because it uses several levels of DC voltage sources, which would be available from batteries, ultracapacitors, or fuel cells. Simulation and experimental results show how to operate this converter in order to maintain equal charge/discharge rates from the DC sources (batteries, capacitors, or fuel cells) in an HEV.