A Decentralized Control Method Based on Virtual Frequency-Voltage Frame for Accurate Active and Reactive Powers Sharing in Microgrids

In the islanded operation mode of microgrids, active and reactive powers sharing among sources is required. In order to provide this and based on decentralized approach, droop characteristics are used. The conventional droop characteristics of active power-frequency (P-ω) and reactive power-voltage (Q-V) are based on the assumption of inductive output impedance of sources. Since the dominant inductive output impedances are not provided, especially in low voltage microgrids, the virtual frequency-voltage frame droop characteristics, which include active power-virtual frequency (P-ωʹ) and reactive power-virtual voltage (Q-Vʹ) droop characteristics have been considered by researchers. By employing these droops, local property of both the virtual frequency and the virtual voltage leads to active power sharing error as well as reactive power sharing error. In addition, required small intended variation range of both virtual frequency and virtual voltage, results in big power sharing errors. In order to eliminate active and reactive power sharing errors, a decentralized control method is proposed in this paper. In the proposed method, instead of virtual frequency and virtual voltage of their terminal, sources droop virtual frequency and virtual voltage of point of common coupling (PCC) in order to a common parameter becomes in charge of active power generation as well as a common parameter becomes responsible for reactive power generation. Accordingly, the power sharing errors are resolved. Realization method of these droop characteristics will be explained in details. In order to confirm the performance of the proposed control method, simulation results of a test microgrid in PSIM software are presented.