Improvement of grid current performance for grid-connected DG under distorted grid voltage and nonlinear local loads

The presence of grid voltage distortion and nonlinear local load are badly impact on the performance of grid-connected distributed generation (DG). This paper introduces an enhanced current control strategy to improve the grid current performance of grid-connected DG under such scenario. The proposed current controller is designed in the synchronous reference frame and composed of a proportional-integral (PI) controller and three resonant controllers tuned at 6n (n = 1, 2, 3) of fundamental frequency. The proposed controller is operated without demand of local load current measurement, which means that no extra hardware is required to achieve good performance of the grid current. The DG with the proposed current controller can transfer a sinusoidal current into the utility grid despite the presence of distorted grid voltage and/or nonlinear local load. Various test cases are considered and experimental results are given to verify the effectiveness of the proposed current controller.