No matter with PV or batteries as DC source, the droop controlled grid-connecting inverter (DC-GCI) has been widely used in microgrid. As the bandwidth of the outer activeand reactive power control loop is designed to be much slower when comparing to the inner voltage/current loop of the DCGCI, and the low equivalent impedance presented by the system, the power disturbance resulting from grid’s frequency fluctuation of DC-GCI may not be compensated by the outer power controller in time. Therefore, the frequency stability of the system mainly depends on its voltage tracking performance dominated by the inner loop’s voltage control strategy. In this paper, three widely used inner voltage/current control schemes, including PI controller in the synchronous rotating reference frame, and the PR controller with fixed and dynamic resonantfrequency in the stationary frame have been discussed. The small signal state space models of the system connected to the grid with different inner loop control schemes are established and compared. The conclusion is derived through the parameter sensitivity analysis. Finally, the simulation and experiment results from a scaled-down laboratory prototype have been presented to verify the validity of the conclusion.
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