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JPE, Vol. 18, No. 4, July 2018
Droop Control Scheme of a Three-phase Inverter for Grid Voltage Unbalance Compensation
Hongpeng Liu, Jiajie Zhou, Wei Wang, and Dianguo Xu
Area Power Quality and Utility Application
Abstract The stability of a grid-connected system (GCS) has become a critical issue with the increasing utilization of renewable energy sources. Under grid faults, however, a grid-connected inverter cannot work efficiently by using only the traditional droop control. In addition, the unbalance factor of voltage/current at the common coupling point (PCC) may increase significantly. To ensure the stable operation of a GCS under grid faults, the capability to compensate for grid imbalance should be integrated. To solve the aforementioned problem, an improved voltage-type grid-connected control strategy is proposed in this study. A negative sequence conductance compensation loop based on a positive sequence power droop control is added to maintain PCC voltage balance and reduce grid current imbalance, thereby meeting PCC power quality requirements. Moreover, a stable analysis is presented based on the small signal model. Simulation and experimental results verify the aforementioned expectations, and consequently, the effectiveness of the proposed control scheme.
Keyword Active power,Droop control,Grid-connected inverter,Negative sequence,Positive sequence,Reactive power,Unbalance compensation
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