Research On High Voltage Ride Through Technology Of Grid-Connected DFIG For Wind Power Generation

At present,countries all over the world are vigorously developing green renewable energy sources such as wind power.However,with the increasing penetration rate of wind power in the power grid,its own volatility and other characteristics bring new challenges to the stable operation of power system,such as the difficulty of power prediction,the weak ability of fault through ability,the poor stability of the grid and the low inertia.Underdamping,etc.The large-scale wind power grid connection causes the uncoordinated development of the source grid,the market mechanism to be improved,and the insufficient capacity of the system for frequency modulation and peak-shaving,which results in a serious "wind abandonment" phenomenon.Aiming at the high voltage ride through(HVRT)problem of doubly-fed induction generator(DFIG),the following work is carried out in this paper:Firstly,it is pointed out that the current research on wind power fault traversal mainly focuses on the low voltage ride through(LVRT),In this paper,after studying the current situation of wind power development all over the world,the typical large-scale wind power out-of-grid accident is introduced in detail,and the importance of HVRT technology in some countries is not enough.This paper analyzes the key technology of DFIG network connection and the necessity and urgency of studying HVRT technology.Secondly,the structure and working principle of DFIG are introduced.On this basis,the detailed mathematical models of DFIG and grid-side,rotor-side PWM converter in three-phase static abc,two-phase static ? ? and two-phase rotating dq coordinate system are established,respectively.Then,the voltage directional vector control technology of DFIG under ideal grid voltage is analyzed.Thirdly,the electromagnetic transient characteristics of DFIG are studied in the case of voltage symmetry and asymmetrical surgerespectively.When the voltage rises symmetrically,the deficiency of introducing additional resistance into the control of rotor-side PWM converter is analyzed,and the control strategy of changing the additional resistance into additional impedance is put forward.The double closed-loop control is adopted for the PWM converter on the grid side.By detecting whether the symmetrical surge of voltage in the power network reaches 1.3U_N,it is decided whether the reactive power compensator should be activated to emit inductive reactive power.The HVRT problem of DFIG can be solved by the control strategy mentioned above.When the asymmetrical voltage of the power network rises to 1.3U_N,the deficiency of HVRT is solved by relying on both sides of PWM converter and traditional virtual synchronous generator(VSG)control strategy of virtual synchronizer,and the method of VSG balanced current control is introduced into the control strategy of DFIG.The inner loop adopts the double closed loop control strategy of rotor current and stator voltage,and the outer loop adopts VSG balanced current control strategy.Combined with the different control targets of PWM converter on both sides of DFIG,the HVRT capability of DFIG is realized.Finally,the effectiveness and feasibility of the HVRT control strategy for DFIG in the case of symmetrical and asymmetrical surge of power grid voltage are simulated and verified on Matlab/simulink.