Using of four-switch three-phase converter in the structure DPC of DFIG under unbalanced grid voltage condition

This paper proposes a novel direct power control (DPC) strategy for doubly fed induction generator (DFIG) drives fed by a four-switch three-phase converters (FSTPCs). In this method, two FSTPCs in rotor and grid side have been used instead of two six-switch three-phase converters (SSTPC). Reduction in the number of active switches will lead to improvement in reliability, reduction in costs and less conduction losses. The FSTPC will generate four unbalanced voltage vectors. A strategy used in order to balance these four voltage vectors. The introduced strategy is based on the emulation of the operation of the conventional SSTPC. In this method, four unbalanced voltage vectors that were generated by FSTPC somehow combined together which produced six balanced voltage vectors of the SSTPC. Then, the new switching table is written for new DPC method for DFIG. Also, during the unbalanced grid voltage condition, three selectable targets are provided for compensating active and reactive power, electromagnetic torque and stator current. These targets are added to power references and are caused decreasing the active and reactive power ripples, mitigation electromagnetic torque pulsations and sinusoidal and balanced stator currents. In the end, an economic comparison between two FSTPC and SSTPC is done. Also, the novel DPC method, i.e., use of FSTPC in rotor and grid side, is compared with prior DPC method, i.e., use of SSTPC in rotor and grid side, and its effectiveness is confirmed by simulation results from a 1-MW DFIG system.