Research of parallel control for inverters with capacitive equivalent output impedance

The equivalent output impedance of parallel inverters could be designed to be inductive, resistive or resistance and inductance. With reasonable control methods and suitable design of parameters, under the above three kinds of equivalent output impedance form, the control of parallel inverters could be realized. To further study the parallel-control strategy, the model based on two parallel inverters was established through the introduction of virtual impedance. The droop control strategy based on the capacitive equivalent output impedance was deduced through the output impedance of the inverters which were designed to be capacitive. The robust droop control strategy based on capacitive equivalent output impedance was proposed. The power sharing characteristics under the capacitive, inductive, and resistive equivalent output impedance were compared. It shows that the multiple-inverter parallel system under the capacitive equivalent output impedance has better performance. In the photovoltaic inverter parallel system platform with two 2k VA inverters, the crorrection of robust droop control strategy based on capacitive equivalent output impedance was verified.