Investigations on Multilevel Converter Interface for Electric Vehicle Charging

Abstract

Increasing concerns over the pollution caused by the tailpipe emissions from the internal combustion engine based vehicles and the limited availability of fossil fuels have greatly paced up the adoption of Electric Vehicles (EVs). Recent advances in battery technologies, power electronics, digital controllers, electric machines and sensing technologies have laid the foundation for the development of the next generation EV technology. As such, power electronics interface plays a pivotal role in EV battery charging. The power electronics interface for both on-board and off-board EV charging generally comprises two stages: (a) AC-to-DC conversion stage with Power Factor Correction (PFC) and regulation of the intermediate DC link voltage; and (b) DC-to-DC conversion stage for regulating the charging current for the EV battery. This work deals with novel PFC converters for the AC-to-DC conversion in the futuristic and emerging EV charging systems. Multilevel Rectifiers (MLRs) have been specifically investigated as they offer numerous advantages, such as: utilization of low voltage power switches, highly improved harmonic profile of the alternating voltage at the input terminals, low dv/dt stress, modularity and so on. The major features identified for such multilevel PFC rectifiers for the upcoming two-stage EV charging systems are: (a) wide range of the output DC voltage so that a large spectrum of EV-battery voltages (typically between 72V to 800V in the commercially available EVs) can be addressed with minimal strain on the downstream DC-to-DC converter; (b) possibility of bidirectional flow of power so that Vehicle-to-Grid (V2G) mode of operation can be attained; (c) easy realization and extension of the power converter for both single- and three-phase systems; (d) possibility of multi-output operation so that multiple EVs can be simultaneously charged using a common central PFC rectifier; and (e) possibility of self-balancing of the capacitors in the MLR so that complexity in the overall control is minimized.