Symmetric LCL Filter and Zero-Sequence Control for Accurate Filter Current Emulation in Four Quadrant Pump-Back Test

In renewable energy systems such as photovoltaics and wind power, LCL-filter converters are indispensable. To experimentally evaluate the performance of both switches and passive components, and validate the thermal design, a pump-back circuit with symmetric LCL filters is proposed. It is used to accurately emulate the current components through the filters, including the fundamental and high frequency harmonics. Due to parameters symmetry, the electrical stress borne by the switches is consistent. A zero-sequence current (ZSC) control with SPWM and SVPWM is implemented to suppress the zero-sequence component in the loop, enabling four-quadrant operation of the circuit. This proposed control strategy and the pump-back test setup are validated on a 30 kW three-phase converter with LCL filters. At full load, the THD of the output current is 1.6%. The feasibility of the testing scheme is experimentally verified under various operating conditions.