Performance Enhancement of Single-Phase Two-Stage AC-DC Converter With Reduced DC-Link Capacitance

Abstract

Single-phase two-stage AC-DC converters employed in electric vehicle (EV) chargers have the tendency to produce low frequency ripple due to input/ output power mismatch, making it necessary to use bulky DC-link capacitors. High voltage ripple at DC-link due to reduced capacitance, prompts poor input power quality and high low-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 a non-optimum dynamic response and deteriorated stability margins. With the objective to improve input power quality, enhance dynamic performance and reduce secondary-side ripple for low valued DC-link capacitance AC-DC converters, a modified unit-template based model predictive (MUT-MPC) and a DC-link feedforward (DFF) controls are presented in this paper. The current feed-forward for the unit-template is controlled by predictive voltage error through an optimization process of cost function to improve input power quality and dynamic performance for primary AC-DC converter. Furthermore, a DC-link feedforward (DFF) control is implemented for secondary DC-DC stage, which reduces the low-frequency current ripple at the load. Finally, to verify the effectiveness of presented multi-objective control method in comparison with traditional controls, MATLAB simulations and experimental results are provided.