Fuzzy PI Controller For No-load Cutting-in Control Of Doubly Fed Induction Generator Wind-power System

Variable speed constant frequency (VSCF) wind turbine using doubly fed induction generator (DFIG) is one of the most potentially wind power generation technology in our society, which already became research hotspot of many countries all around the world. With the development of unit capacity of wind power generation, current shock induced by megawatt wind-power system can not be ignored. The realization on safe and stable operation of cutting in the grid has become the primary problem of wind power system.This paper concentrates on no-load cutting-in voltage amplitude control, phase control and separation control of DFIG wind-power system. First, the basic principles of DFIG wind-power system under the operation of variable speed constant frequency are analyzed, and the mathematical models of DFIG based on synchronously rotating reference frame (d-q frame) are built, and the advantages of stator-flux-oriented vector control are studied, and the operation mechanism of maximum wind energy capturing of VSCF wind-power system is discussed.Secondly, the principles of no-load cutting-in control of DFIG wind-power system based on stator-flux-oriented vector control are analyzed, and the mathematical models of no-load cutting-in control are built. Based on these, a new fuzzy PI controller for no-load cutting-in control scheme of DFIG wind-power system is proposed. Under the condition of ideal state, network voltage fluctuating and the uncertain parameters variety, this paper presents fuzzy PI controller for investigation of no-load cutting-in range of DFIG wind-power system, comparing with fuzzy controller and PI controller. The results of investigation show that fuzzy PI controller produces rapidly dynamic response and highly steady precision, and ensures strongest robustness under variable grid voltage conditions and variable DFIG parameters conditions. The whole cutting-in transitional course is transient, and the fore-and-aft cutting-in course functions reposefully. Therefore fuzzy PI controller behaves excellent cutting-in capability having both the excellence of rapidly dynamic response and strong robustness of fuzzy controller and highly steady precision of PI controller for no-load cutting-in control scheme.Then, the principles of no-load cutting-in voltage phase control of DFIG wind-power system are analyzed, and the mathematical models of no-load cutting-in voltage phase control of DFIG are built. Under the condition of sub-synchronous and super-synchronous speeds, this paper presents fuzzy PI controller for investigation of no-load cutting-in voltage phase control of DFIG wind-power system, comparing with PI controller. Then the excellent effect of fuzzy PI controller can be verified. Eventually, separation control scheme of DFIG wind-power system is proposed.Based on separation control mechanism, DFIG wind-power system is studied by simulation. The transitional course of separation control is transient, and stator current decreases to zero gradually, and rotor current moves with smooth transition, while active power and reactive power decrease to zero gradually. The course of separation from the grid is carried out successfully.