Decoupling Capacitor Design for Multi-Inverter Based Grid Emulator System

CURENT's grid emulator contains multiple inverters to mimic the behaviors of several grid elements. The filtering inductor at the ac terminal of an inverter filters out the switching ripple current. However, the voltage on the point of common coupling (PCC) still contains switching harmonics. A decoupling capacitor at the PCC can effectively suppress the switching ripple voltage and improve voltage quality of the grid emulator. This paper provides a reduced order model of the multi-inverter system. With this reduced model, the PCC voltage harmonics can be derived. The decoupling capacitor of the PCC is designed to suppress the switching ripple based on the reduced model. Simulation and experimental results are provided to validate the proposed model and the decoupling capacitor design.