Improved reactive power sharing for parallel-operated inverters in islanded microgrids

Abstract

Unequal impedances of interconnecting cables between paralleled inverters in island mode of microgrids cause inaccurate reactive power sharing when traditional droop control is used. Many in the literature adopt low speed communications between the inverters and a central control unit to overcome this problem. However, the loss of this communication link can be very detrimental to the performance of the controller. This paper proposes an improved reactive power-sharing control method. It employs infrequent measurements of the voltage at the point of common coupling (PCC) to estimate the output impedance between the inverters and the PCC and readjust the voltage droop controller gains accordingly. The controller then reverts to being a traditional droop controller using the newly calculated gains. This increases the immunity of the controller against any loss in the communication links between the central control unit and the inverters. The capability of the proposed control method has been demonstrated in simulation and experiment using a laboratory scale microgrid.