Research On Control Strategy Of Parallel-operated Inverters Based On Virtual Resistance In Low-voltage Microgrid

Microgrid is an emerging technology developed on the basis of distributed generation(DG) technologies. The DG units and storage devices in microgrid are mostly connectedto the point of common coupling (PCC) through interface inverters. When multi invertersoperate in parallel with mismatched line impedance or inconsistent local loads, theislanding microgrid system will suffer from problems of power sharing and circulation,thereby affecting the operation of microgrid and the electrical safety of the load severely.To ensure the stable operation of parallel-connected inverters, this paper proposes a droopcontrol strategy based on virtual impedance, which is capable of both eliminatingcirculation effectively and achieving power sharing properly.According to power flow characteristics of the inverter, two droop control strategies,that is P-f droop and P-V droop control, are analyzed in this paper. And a conclusion isreached from the small-signal modeling and stability analysis of the P-V droop controlstrategy, which shows that P-V droop control strategy is more beneficial to the stableoperation of the system in low voltage microgrid.As to the problem of circulating current when the low voltage microgrid operates inislanding mode, this paper analyses the causes and influence factors, and the relationshipbetween circulating current and the power sharing is obtained. A strategy is then proposedbased on virtual impedance, which can achieve proportional power sharing amongmicrosources and reduce the circulating current. Simulation is conducted when multipleDG units are connected in parallel, which verifies the correctness of the modified controlstrategy.An experiment platform of two parallel-connected three-phase inverters is built at last,which adopts DSP TMS320F2812as the main controller, and the experiment results provethe feasibility of the strategy.