FRT capability of a DFIG in isolated grids with Dynamic Voltage Restorer and Energy Storage

In order to utilize Doubly Fed Induction Generators (DFIGs) as primary power source of an isolated system, they must be able to regulate the voltage and frequency of the system, as well as ride-through faults. This paper proposes a new control strategy for a DFIG operating in an isolated power system, accomplished by a Dynamic Voltage Restorer (DVR) and a Supercapacitor Energy Storage System (SCESS), in order to ride through symmetrical and asymmetrical faults. During faults, the DFIG continues to operate normally, while the surplus of power is stored in the SCESS. During asymmetrical faults, the DFIG and the DVR are properly controlled in order to feed the non-faulty phases uninterruptedly. When integrated in a power system with conventional synchronous generators, the proposed FRT control strategy improves the FRT capability of a DFIG, while providing frequency and voltage support to the system throughout the fault duration. Thus, the transient stability of the power system is significantly improved. The effectiveness of the proposed control method under different fault conditions is verified by detailed simulation results.