Sensorless Control of Variable-Speed SCIG Wind Energy Conversion Systems Based on Rotor Flux Estimation Using ROGI-FLL

In this article, a novel sensorless control method for variable-speed squirrel-cage induction generator (SCIG) wind power systems with simple rotor flux estimation is proposed. The rotor flux linkages are estimated using a reduced-order generalized integrator (ROGI)-frequency-locked loop (FLL), which regards the rotor back electromotive forces (EMFs) found from the generator model as its inputs. Based on these rotor flux linkages, the rotor flux angle can be estimated through direct trigonometric relations. Then, to avoid the speed estimation error caused by the FLL under stator frequency variations, the synchronous speed is estimated from the aforementioned rotor flux angle via the derivative. Owing to the excellent harmonic rejection capability of the ROGI, the proposed rotor flux estimation is robust against measured high-frequency ripple components. The analysis of ROGI response in the presence of dc offset in the rotor back EMFs is provided as well, and it shows that the proposed method is not faced with the saturation under those conditions. Performance comparisons between the proposed method and the existing dual second-order generalized integrator (SOGI)-FLL-based method have been conducted via both simulations and experiments, thereby verifying the feasibility of the proposed method.