Control of Ripple Eliminators to Improve the Power Quality of DC Systems and Reduce the Usage of Electrolytic Capacitors

The problem of voltage/current ripples has become a primary power quality issue for dc systems, which could seriously degrade the performance on both the source side and the load side and lead to reliability concerns. In this paper, a single-phase Pulse width modulation-controlled rectifier is taken as an example to investigate how active control strategies can improve the power quality of dc systems, reduce voltage ripples, and, at the same time, reduce the usage of electrolytic capacitors. The concept of ripple eliminators recently proposed in the literature is further developed, and the ratio of capacitance reduction is quantified. With such ripple eliminators, this power quality problem is formulated as a control problem to actively divert the ripple current on the dc bus. The main focus of this paper is to investigate how advanced control strategies could improve the performance of ripple eliminators. An advanced controller on the basis of the repetitive control is proposed for one possible implementation of ripple eliminators in the continuous current mode (CCM). Experimental results are presented to verify the effectiveness of the strategy with comparison to another ripple eliminator operated in the discontinuous current mode. It has been shown that the proposed instantaneous ripple-current diversion in CCM leads to a nearly fourfold improvement of performance.