Sequence-Based Control Strategy With Current Limiting for the Fault Ride-Through of Inverter-Interfaced Distributed Generators

Abstract

Three-phase three-leg inverters represent the majority of inverters that are integrated into low voltage power grids. They can develop positive- and negative-sequence components during unbalanced conditions including asymmetrical faults, but not zero-sequence components. This indicates that a sequence-based control strategy is required for comprehensive control of inverter currents and voltages. Positive- and negative-sequence components must be controlled separately with their own dedicated controllers in such a scheme. Given this critical need, a sequence-based control technique for grid-forming and grid-feeding inverter-interfaced distributed generators is proposed. As a necessary part of the fault ride-through capability of inverter-interfaced distributed generators, a current limiter is developed, which can limit inverter currents at a pre-defined threshold for both balanced and unbalanced faults. Whilst the current regulators work in the synchronous reference frame with simple PI controllers, the limiter works in the natural reference frame and thus treats each phase current separately, which results in current limiting at the threshold for all phases. The advantage of the proposed limiter is that it acts instantaneously such that the inverter current can be limited from the start of the disturbance. The simulation results in MATLAB/SIMULINK reveal promising performance of the proposed control strategy with the proposed current limiting.