Improved transient performance properties of distributed generation grid side converter current controller under grid voltage harmonic distortion and unbalanced faults

The fast and accurate control of renewable energy grid side converter (GSC) under normal and abnormal grid conditions is necessary to ensure the injection of high quality power and to enhance the power system stability. Accurate control of GSC is achieved by the stable and fast response of current and PQ controllers. In the event that the grid voltage becomes unbalanced due to the presence of grid harmonics or due to an unbalanced fault, the GSC should respond in such a way so as to inject balanced and harmonic free currents. If the inverter continues to generate a balanced harmonic free three-phase voltage, the resulting current will be unbalanced and harmonically distorted. It is therefore necessary to modify the three-phase voltage of GSC in accordance to grid disturbances. This paper proposes a current controller that improves the transient performance of the injected currents in the event of grid voltage harmonic distortion and unbalanced grid faults. The proposed harmonic neutralization current controller can inject high quality and pure sinusoidal positive sequence current accurately with faster harmonic compensation and improved dynamic response.