Low-voltage ride-through capability improvement in autonomous AC microgrids: A review of existing control approaches

Abstract

In autonomous AC microgrids under short-circuit fault or overload conditions, the semiconductor switches of grid-forming inverter-based distributed energy resources are subject to serious damage due to the overcurrent issue caused by these low-voltage phenomena. Limiting the current of the grid-forming inverter at the primary level control structure and as a result, improving the low-voltage ride-through capability of the isolated microgrid is more desirable than using hardware protection equipment. The current limiting capability has been implemented for single-loop control structure to protect the inverter under overload conditions. The existing methods for limiting the current of grid-forming inverter during fault conditions, which are often implemented by considering two inner loops of current and voltage control, can be considered in three general categories: 1) limiting the reference current derived from the voltage controller, 2) changing the reference voltage obtained from the power-sharing loop by utilizing the concept of virtual impedance, and 3) changing the inverter's control structure. In fact, besides the current limiting strategy, other parts of the multi-loop control system could be efficient in the low-voltage ride-through operation. The effects of the reference frame of the control system for the independent control of the phases, the powersharing method in autonomous microgrids including three-phase and single-phase grid-forming inverterbased distributed energy resources, and preventing voltage distortion when restricting the inverter current under volt