The Control Strategies Of Doubly-fed Induction Generator Under Unbalanced Grid Voltage

With the rise of the new energy wind power industry,as a wind power generation system in a large number of applications of doubly fed wind power generation unit of the operation of the control problem has been more and more attention.In this paper,the control scheme of the DFIG rotor side converter is studied according to the unbalance of the grid voltage.After comparison of different strategies,this paper decides to adopt the double current control strategy as a way of realization,establish the simulation model by Matlab/Simulink software,analysis of DFIG in unbalanced variation of stator and rotor of the power grid voltage.Secondly,based on the stator voltage oriented(SVVO)double DQ vector coordinate transformation method,the double current control strategy is used to realize the effective control of DFIG under unbalanced grid voltage.The main work of this paper is as follows:(1)The operating principle and power flow of the double fed wind power generation system are analyzed.The operation of variable speed constant frequency and decoupling control are discussed.Based on this,the model of doubly fed induction generator(DFIG)is established.(2)This paper introduces the basic concept and the basic idea of the vector control technology,and deduces the transformation formula of the vector transformation of the AC motor.In this paper,the corresponding analysis method is introduced,which is based on the symmetrical component method.At the same time,the transformation relation of unbalanced vectors in different coordinate systems is derived.Then,by using these methods,the DFIG model is transformed from the three-phase stationary axis to the positive sequence synchronous rotating shaft system.From the DFIG control requirements,further elaborated based on the stator voltage orientation(SVVO)of the rotor side converter vector control method,and were constructed under unbalanced grid voltage,unbalanced grid voltage under the two control strategies.(3)In the Matlab software Simulink,build the unbalanced grid voltage and unbalanced grid voltage under the control strategy simulation model,verified the control of variable speed and constant frequency under the unbalanced grid voltage of active power and reactive power decoupling control and balance of the three control objectives under network voltage.The simulation results show that the control system presented in this paper shows better control performance.The effective control of doubly fed generator under unbalanced grid voltage is realized by the rotor side converter.