Robust fixed-time current controller for LC-filtered grid-forming inverters with disturbances and uncertainties

A grid-forming inverter (GFI) is an inverter that possesses the ability to regulate the grid voltage by actively controlling and modifying its output voltage. The conventional strategy for controlling GFIs involves a dual-loop structure in a dq reference frame using PI control. However, disturbances, including model uncertainties and actuator faults, can negatively impact the performance of conventional PI-based controllers. Another main challenge is to ensure a fast response to improve overall system performance and to allow high-bandwidth secondary controllers in microgrid applications of GFIs. The main focus of this paper is to introduce a new robust current controller for LC-filtered GFIs that utilizes a fixed-time sliding mode control approach to address the aforementioned challenges. To achieve this objective, two fixed-time sliding surfaces are defined, one for the d element and another for the q element of the error states. Then, the control inputs are designed to ensure that the error states reach these surfaces and remain there. The simulation results demonstrate that the proposed fixed-time sliding mode control method can effectively correct errors and compensate for model uncertainties and actuator faults.