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In this paper, a new strategy to control microgrids highly penetrated by voltage source converters (VSCs) is proposed. The strategy is based on the instantaneous measurements and calculations of voltages and currents and the application of instantaneous power theory. This approach employs each VSC along with an LC filter as a current source. The grid parameters are not known to the controller, only the filter inductance and capacitance. The approach characterizes a theoretical methodology to define a grid status parameter that provides multiple alternatives to operate the VSC autonomously. Moreover, one of those alternatives is sharing load among VSCs by regulating the voltage of the local connection bus. This grid status parameter is an external voltage contribution vector defined by the operation of the other VSCs in the microgrid. Because of the definition of this parameter, frequency manipulation is not employed as a communication link between VSCs, avoiding perturbation to the grid stability. The approach provides an approximation of the equivalent impedance of the system seen from the filter output. The load-sharing scheme under the proposed strategy is fully described. An experimental validation is performed in order to test the proposed approach for load sharing between three VSCs and the inclusion of nonlinear load.
Ovalle et al. (2014) studied this question.