A Control Strategy for Suppressing Harmonics and Circulation in Islanded Microgrid

An inverter control strategy which can suppress harmonic and circulation is proposed for the paralleled multi-inverter system with non-linear loads in islanded microgrid in this paper. The proposed strategy does not require any active or reactive power calculations. Instead, a phase-locked loop (PLL) is used. The virtual impedance is set to contain the virtual negative impedance, the fundamental virtual inductance and the harmonic virtual resistance. The virtual negative impedance is set to offset the resistance component of the line impedance and reduce the system voltage drop caused by line resistance. The fundamental virtual inductance and harmonic virtual resistance is set to be put into the voltage feedback loop in fundamental domain and harmonic domain, respectively. Simulation and experimental results verify the validity of the control strategy. The control strategy improves the quality of output voltage and output current of each inverter and suppresses the circulation.