Abstract
With more and more distributed energy resources (DERs) being connected to the grid through interface converters, the utility requires the DER generation system to remain grid-connected during grid voltage imbalance to ensure the operating stability of the AC power system. These low voltage ride-through requirements also suggest that the DER generation system injects reactive power to support grid voltages. Traditional reactive power compensation methods can provide request reactive current to meet the low voltage ride-through requirements. However, the resulting peak phase current may exceed the peak rated current of the converter during voltage sag, thus facing the risk of over-current protection tripping of itself. In this thesis, a positive sequence and negative sequence reactive current injection method is proposed to meet the low voltage ride-through requirement. The proposed method can generate the positive sequence and negative sequence reactive current commands so the resulting phase current does not exceed the ampere constraint of the converter，which is very critical for the safe operation of the converter. Its operation principle and control method are explained and analyzed. Simulation and laboratory test results are presented to validate the effectiveness of the proposed method. Comparisons of the proposed method and other low voltage ride-through techniques are also presented.