Analysis and Suppression of Circulating Current in Multiparalleled APFs with Grid Current Detected

Typically, to cope with the harmonic pollution, active power filters (APFs) are installed in power system. And they will be connected in parallel when meeting higher compensation demand in industrial applications. However, the circulating current emerges in the multiparalleled APFs with grid current detected. It will induce the DC voltage oscillation of multiparalleled APFs and eventually lead to the system shutdown. Therefore, in this article, the underlying mechanism of circulating current is analyzed, and its main frequency region is determined. It is demonstrated that the circulating current originates from the grid current feedback control and undamped circulating current path among multiparalleled APFs. To suppress the circulating current, this article proposes a virtual resistor method incorporated in the basic control, which emulates a resistor connected with the filter inductor in series. In this way, the circulating current path can be damped, which further eliminates the circulating current. Finally, simulations are conducted to verify the correctness of mechanism analysis and effectiveness of proposed virtual resistor method.