A New Control Method to Reduce Low-Frequency Output Current Ripples of Polyphase Rectifiers

Under unbalanced operations, the rectifier produces significant subharmonic ripples that are difficult to filter out by using a real passive filter because the frequency is very low. In this paper, a new approach to reduce the low frequency ripples of a polyphase rectifier is proposed. In the proposed approach, the low frequency ripples of a polyphase rectifier output are minimized by using a virtual LC filter. Because this filter is virtual, the subharmonic ripples can be reduced significantly without using a large and expensive passive filter. Moreover, it can be designed in such way so it only responds to the disturbance signals and does not respond to the reference ones. So, the low-frequency ripples can be reduced without influencing the system response to reference. Experimental and simulated results are included to verify the proposed concept.