Jin-Hyuk Park, “전기차 충전기를 위한 정류 회로 제어 기술,” 아주대학교 공학박사 학위 논문, 2018. > Paper

This paper proposes control methods of rectifier circuits of electrical vehicle (EV) chargers to improve electric power quality and

efficiency. EV chargers are divided into a slow charger and a fast charger depending on the capacity. Two studies for rectifier circuits

of EV chargers are contained in this paper: predictive control method for PFC converters, and improved discontinuous PWM (DPWM)

for 3-level converter with LCL-filter. The power factor corrector (PFC) converter is mainly used as the rectifier circuits of the slow

charger. There are two main reasons that the grid current is distorted near the zero crossing point. The first reason is the slow

dynamic response of the proportional-integral (PI) controller. PI controller cannot control the ac component because it is suitable

to control dc component. The second reason is the mode conversion of the PFC converter: continuous conduction mode (CCM)

and discontinuous conduction mode (DCM). The PI controller cannot perform the average current control in DCM. In digital control,

there is a difference between the sensing value and the average value of the current. This paper proposes a predictive control

method including conduction mode detection for PFC converters. The proposed method predicts the current of next-state based

on the system model. The proposed method has a fast dynamic response compared with the PI control method because the

optimal duty is calculated to minimize the error between the reference current and the predicted next state current. Their

performance is analyzed and compared with each other in term of the power factor (PF) and the current total harmonic

distortion (THD). The 3-level converter is widely used as the rectifier circuits of the fast charger for high efficiency and light weight.

The modulation signal of the 60º DPWM discontinuously changes and many voltage harmonic are generated in the wide

frequency range at the output terminal of the converter. If these harmonic components and the resonance frequency band caused

by a grid-connected LCL-filter are overlapped, the grid current oscillates. To solve this problem, the proposed method applies the

sixth harmonic injection technique to the modulation signal. When the proposed method is used, the modulation signal

smoothly changes and many harmonic voltages are sufficiently reduced. Their performance is analyzed and compared with each

other in term of the efficiency and the current THD. The simulations and experiments are carried out to verify the effectiveness of

the proposed methods: predictive control method for PFC converters, and improved discontinuous PWM (DPWM) for 3-level

converter with LCL-filter.