Special Issue Article
A Novel Voltage Control Strategy for Three Phase Grid Connected System with Distributed Generation Inverters
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In this paper Ancillary service for Distributed Generation (DG) systems becomes a challenging issue to smartly integrate renewableenergy sources into the grid. Voltage control is one of these ancillary services which can ride through and support the voltage under grid faults. Grid codes from the transmission system operators describe the behaviour of the energy source, regulating voltage limits and reactive power injection to remain connected and supports the grid under fault. On the basis that different kinds of voltage sags require different voltage support strategies, a flexible control scheme for three phase grid-connected inverter is proposed here. For the three phase balanced voltage sags, the inverter should inject reactive power in order to raise the voltage in all phases. In one-phase or two-phase faults, the main concern of the DG inverter is to equalize voltages by reducing the negative symmetric sequence and clear the phase jump. Due to system limitations, a balance between these two extreme policies is mandatory. Thus, over voltage and under voltage can be avoided, and the proposed control scheme prevents disconnection while achieving the desired voltage support service. The main a contribution of this work is the introduction of a control algorithm for reference current generation that provides flexible voltage support under grid faults.