Three-phase modular multilevel current source rectifiers for electric vehicle battery charging systems

This paper discusses three-phase high power factor AC-to-DC current source converters appropriate for Electric Vehicle (EV) battery charging systems. The AC grid interfaces are multilevel current source rectifiers constructed from standard power electronic circuits that have their fast-switched semiconductors and output inductors replaced with several modular subcircuits connected in parallel. By operating the parallel circuits with an appropriate phase-shifted PWM, the systems feature low current and voltage ripples at the input and output terminals, allowing size reduction of the passive filters. In addition, as the DC-link current can be efficiently distributed to the modularized subcircuits, better efficiency, due to the lower conduction and switching losses, is achievable. The characteristics of the presented EV systems, including the principles of operation, modulation strategy, and feedback control are described. The feasibility of a remarkable solution, namely a three-phase five-level six-switch buck-type PFC is demonstrated by means of a constructed hardware prototype.