An Advanced Control Strategy for a Weak Grid-Connected DG for Enhancing Voltage Support During Co-occurrence of Sag and Swell

Numerous control strategies for voltage support are developed to encounter the voltage issues (sag, swell, low voltage, and high voltage). Yet, there is a significant gap in the voltage support concept, such as reduction of zero-sequence voltage along with negative sequence voltage and providing the voltage support during co-occurrence of voltage sag and swell (CVSS) in the phases of a three-phase grid-tied converter. Many reasons can cause CVSS. In this situation, the conventional control strategies have failed to support the voltage because the maximum voltage of the healthy phase voltages constrains the reactive power injection. Therefore, the reactive power injection/consumption is zero in the case of CVSS. In this article, the proposed work presents a flexible reactive power control to enhance the voltage support during the CVSS in the phases of the system. It generates phasewise current references for controlling appropriate reactive power subjected to safe current limits when the voltage sag, swell, and coexistence are detected in the phases. Under normal system operation, the behavior of the proposed control is the same as conventional. The proposed control is implemented on the grid-tied three-phase four-leg inverter, and the experimentation results show the effectiveness of the proposed control.