Low Voltage Ride-Through of a Droop-Based Three-Phase Four-Wire Grid-Connected Microgrid

Published in: IET Generation, Transmission & Distribution

Abstract
The ability of riding through the grid disturbances can increase the integration of microgrids into the distribution system. Consequently, a grid-connected microgrid should provide ancillary services such as low voltage ride-through (LVRT) capability and reactive power support to sustain the power system operations during abnormal grid conditions. The objective of this paper is to propose an LVRT scheme that improves the power quality of the entire microgrid. The developed method is implemented as the controller of the interface voltage-sourced converter (VSC) of a distributed energy resource (DER) and consists of primary and secondary control levels. The former includes the cascaded voltage and current control loops and the droop controller while the latter controls the reactive power injection during the balanced and unbalanced voltage sags/swells. The proposed LVRT scheme is developed based on the independent control ability of each phase in the natural reference frame and does not require calculation of symmetrical components. Moreover, it can be employed in the VSC control systems with various reference frames and is effective for droop-based grid-connected microgrids with both single-phase and three-phase four-wire configurations. The proposed strategy is implemented using the hierarchical control system and preserves the plug and play capability and expansibility. Several case studies using a benchmark low-voltage microgrid network are presented to verify the effectiveness of the proposed LVRT strategy.