A Fault-Tolerant Control Paradigm for Microgrid-Connected Wind Energy Systems

Wind power is a promising alternative energy source; however, its integration to the microgrid is challenging and requires the consideration of voltage regulation, power quality, and voltage variations. This paper proposes a novel fault-tolerant control paradigm for a microgrid-connected doubly fed induction generator (DFIG)-based wind energy system to: 1) achieve ride through during any kind of voltage sag conditions including deep sags and 2) enable the strict satisfaction of recent grid code requirements. The proposed paradigm includes a novel integral terminal sliding mode controller (ITSMC) for the rotor- and grid-side converters along with a series grid-side converter (SGSC) to maintain the voltage levels across the stator windings at their prefault values. A fuzzy logic and a Posicast approach are also proposed to control the SGSC and further improve the performance of the wind energy system. The effectiveness of the proposed fault-tolerant configuration in riding through different types of grid faults is evaluated via detailed computer experiments. The merits of the proposed approach are further compared to those of the standard state of the art in voltage sag mitigation, namely, the shunt current injection approach and the dynamic voltage restorer. Results clearly show that the proposed control paradigm is able to protect the converters from damages and ensure continuous connection of the WT to the grid during faults, hence maintaining power quality.

I. Introduction

Stimulated by a growing demand for a stable and sustainable supply of power as well as the requirement to accommodate all generation and storage systems, microgrids have become a viable solution to supply energy to local communities, industrial complexes, and strategic businesses that cannot afford power outages for any extended periods of time. Microgrids achieve specific goals, such as reliability, efficiency, carbon emission reduction, and sustainability via the integration of sustainable energy sources, the implementation of improved monitoring and management technologies, and the deployment of information technologies for grid management. Wind power is playing a key role in current microgrids, being the fastest growing source of energy worldwide in the last few decades [1]. However, as WTs begin to represent a higher percentage of generation on a given transmission system, they have become system resources whose operation must be maintained in the presence of grid faults and corresponding voltage sags or dips. This change in perspective has precipitated new requirements for how a WT should operate during transient conditions that would previously result in its disconnection from the grid. These new ride-through requirements (Fig. 1) will imperatively have a significant impact on the design of control paradigms for variable speed WTs. Fig. 1.

Recent grid code requirements for fault ride-through.