Zero-sequence Circulating Current Suppression with Stand-alone Feedforward Control for Power Hardware-in-the-Loop System

A PWM converter based power hardware-in-the-loop (PHIL) system can provide rapid and low-cost alternatives for prototype testing of high-power converters for electric vehicles or smart grid industries. To achieve simple configuration avoiding an additional bidirectional DC supply, the power amplifier (PA) in the PHIL can share the DC-link of the device under test (DUT). However, due to the coupling of AC and DC ports and differences in the zero-sequence voltage (ZSV) of the two converters, an inevitable low-frequency zero-sequence circulating current (ZSCC) results. This paper proposes a stand-alone control method using ZSV feedforward control to suppress the ZSCC flowing through the PWM converters of the PA and DUT. The ZSV of the DUT can be estimated from the d-q voltage equation in the PA, and feedforward term is applied with a proportional resonant (PR) controller. The effectiveness of the proposed method is verified by experimental results.