Modular Multilevel DC-DC Converter Based EV Battery Charger

In the recent times, modular multilevel converter (MMC) is a prominent choice of power electronic converter in medium voltage (MV)/high voltage (HV) applications. The main features of MMC are modular design, scalability, reliability, fault tolerance capability, high step-up ratio and less filtering requirements. This paper presents a transformer-less MMC based electric vehicle (EV) battery charger. A high step-up/down ratio MMC dc-dc converter is designed such that the high input voltage is converted to the battery voltage level. This configuration ensures significant reduction in the complexity of design, system costs and space requirements for fast charging. Phase-shifted pulse width modulation is used to control the MMC operation. The closed-loop operation of the converter is realized using proportional integral (PI) controller for charging of battery in constant current mode till 80% state of charge (SoC) of battery. Further, it is charged in constant voltage mode. A lower arm sub-module (SM) ensures the balanced capacitor voltage without requirement of any additional control architecture. The results are verified using simulation carried out in MATLAB/Simulink environment.