Research On Control Strategy Of Doubly-fed Induction Generator Under Unbalanced Grid Voltage

Wind farms are mostly at the end of the grid,away from the mains.Because of the asymmetry of load,the aging of transmission line,the asymmetry of power grid voltage and so on,the grid connection point of wind farm often appear voltage unbalance phenomenon.Because the stator side of double feed doubly fed induction generator(DFIG)is directly connected with the grid,it will directly affect the stable operation of the DFIG when the grid fault occurs.Therefore,it is necessary to study the control of DFIG under unbalanced grid voltage.In view of the advantages of model predictive control(MPC)in high power converter and the ability of multi-objective constraint,this paper studies the control of DFIG under unbalanced grid voltage based on finite control set model predictive control(FCS-MPC).Firstly,the generator side and the grid side of the DFIG are modeled in the stationary coordinate system,and the MPC of the grid side converter(GSC)and the rotor side converter(RSC)is deduced under the unbalanced grid voltage.Secondly,this paper analyzes the different control objectives and cooperative control strategies of the generator side and the grid side under unbalanced grid voltage.Finally,based on the multi-objective constraint capability of MPC,three different control strategies are proposed under unbalanced grid voltage.First,the optimal control of the stator output power of the DFIG with the target of controlling rotor current and stator output power simultaneously.Second,the optimal control of the electromagnetic torque of the DFIG with the target of controlling rotor current and electromagnetic torque simultaneously.Lastly,the optimal control of the power of GSC with the target of controlling grid current and output power of GSC simultaneously.Based on the theoretical analysis,the Matlab/Simulink simulation and experiment platform is built to verify the FCS-MPC of double fed generator system under unbalanced grid voltage.The results show the effectiveness of the proposed control strategy.