A constant voltage-frequency control strategy based on dividing frequency complex virtual impedance

Abstract

A constant voltage-frequency parallel control method based on dividing frequency complex virtual impedance is proposed in this paper. First, the output current, the LC filter capacitor voltage and output current by each of the inverters are separated into fundamental and each harmonic. Set the dividing frequency virtual negative impedance which contains the virtual negative impedance and the virtual resistance of fundamental and each harmonic. The virtual negative impedance is set to offset the accurately measured part in the line impedance. Put the fundamental and each order harmonic virtual impedance into the fundamental and each harmonic voltage feedback loop in order to modify the voltage control loop. The method improves the output voltage quality of each parallel inverter effectively and suppresses the circulation when system with nonlinear loads. The simulation results are provided to verify the validity of the control strategy.