Modified MPC Approach to Single-Phase Two-Stage AC-DC Converter for Reduced DC-link Capacitance

Abstract

Single-phase two-stage AC-DC converters used in electric vehicle (EV) chargers produce double-line frequency ripple, making it necessary to use bulky DC-link capacitors. High voltage ripple at DC-link due to reduced capacitance, results in poor input power quality and high double-line frequency ripple at the output of secondary-stage. In state-of-art, input power quality in converters with low DC-link capacitance is enhanced by using a digital low-pass filter (LPF). However, employing LPF to sensed DC-link voltage results in non-optimum dynamic response and deteriorated stability margins. With the objective to improve input power quality and to enhance dynamic performance with low valued DC-link capacitance, a modified unit-template based model predictive control (MUT-MPC) is implemented for primary AC-DC converter. The current feed-forward for the unit-template is controlled by predictive voltage error through an optimization process of cost function. Furthermore, a DC-link feedforward (DFF) control is implemented for secondary DC-DC stage, which reduces the low-frequency current ripple at the load. The effectiveness of the presented controls are verified by simulation and experimental results.