Voltage Sag and Support in Power Control on Distributed Generation Inverters

During voltage sags, continuous power delivery from distributed generation systems to the grid is desirable for the purpose of grid support. Ancillary services for distributed generation (DG) systems become a challenging issue to integrate renewable-energy sources into the grid. Voltage control is one of these ancillary services which can ride through and support the voltage under grid faults. In order to facilitate the control of distributed generation systems adapted to the expected change of grid requirements, flexible voltage support control scheme is proposed for inverter based distributed generation, aiming at regulating voltage limits and reactive power injection to remain connected and supports the grid under fault. In three-phase balanced voltage sags, the inverter should inject reactive power in order to raise the voltage in all phases. In one- 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. Thus, over and under voltage can be avoided, and the proposed control scheme prevents disconnection while achieving the desired voltage support service which can be analyzed and simulated by using Matlab/Simulink environment. The main contribution of this work is the introduction of a control algorithm for reference current generation that provides flexible voltage support under grid faults