Direct Power Control Of Doubly Fed Wind Power Generator

Doubly fed wind power generation system is currently the highest commercialized degreeand maximum installed proportion wind power generation system. How to improve the systemdynamic performance, the wind power quality harmonics, power factor and other powerquality, and achieve effective grid-connected are still serious problems for Chinese windpower technology. Based on the analysis and summary of the relevant international controlstrategies, this thesis makes a research on the motor of the doubly fed wind power generationsystem and its direct power control strategy. The main contents are as follows:Firstly, this thesis discusses the mathematical modeling process of the doubly fedinduction generator in different reference frames in detail. On this basis, the effect of rotorvoltage on electrical power frequency, active and reactive power, is analyzed thoroughly.Secondly, based on the principles of the traditional direct power control, aiming at thepower pulsation problem brought by the inaccurate of rotor flux estimation, this thesisproposes the stator flux estimation. By using the stator resistance, the only mechanicalparameter, the method weakens the dependence on the parameters of the system and reducesthe power pulsation. Simulation results of the15KW doubly fed wind power generationsystem demonstrate the high accuracy, excellent dynamic performance and low power ripplein tracking active power, reactive power and speed.Thirdly, both the rotor flux estimation and the stator flux estimation, they all adopt thehysteresis comparator, which makes the system switching frequency inconstant. Therefore,this thesis introduces the triangular waveform PWM comparator tracking technology insteadof the hysteresis comparator in active power control, to realize the direct power control withconstant switching frequency. Simulation results of the15KW and1.5MW doubly fed windpower generation systems show the constant switching frequency, better dynamic performanceand sharply slashed power ripple in tracking active power, reactive power and speed.Finally, a summary is made for the full thesis.