| Doubly fed induction generator(DFIG)wind power generation system is widely used owing to its unique advantages which include converter of small capacity,low cost and small grid impulse current.But with the increasing capacity of wind turbines,tiny grid failures will lead to unforeseen consequences.Because of which the power grid is not strictly symmetrical or inevitable fault occurs,the control strategy based on the established system mathematical model under the ideal grid will no longer be able to make the system stable operation,and in contrast,it will further affect the power quality.So this paper investigated the established mathematical model and the control strategy of DFIG under the unbalanced power,and designed a control scheme of two full controlled converter,finally the effectiveness of the scheme was verified by simulation.First of all,the generation mechanism of DFIG wind power generation system was analyzed in detail,derived the conditions the system can operate in VSCF state.And the energy flow of the whole system was analyzed,which make me have a clear and intuitive understanding to the function of the control system.Secondly,under the balanced grid power,the thesis established the mathematical model of DFIG and grid side converter,analyzed the composition and phase separation method of the variables,on this basis,and established two mathematical model under unbalanced grid conditions.Furthermore,according to the mathematical model under ideal grid,the traditional vector control system of the system machine side and grid side converter was analyzed in detail,the corresponding derivation was given,and the calculation of stator flux was discussed.In order to avoid the influence of the negative sequence component,this paper put forward a forward synchronous speed rotating coordinate system based on proportional integral resonant controller(PIR)control strategy and gave the current command value algorithm about the control objectives.Finally,the control method presented in this paper was simulated and analyzed.Results showed that the effect of the method proposed in this paper can greatly weaken the fault caused by unbalanced grid power in a phase drop compared with the traditional control strategy of ideal grid.In addition,this paper set up the experimental platform that chose STM32F103 RB as the core controller and made an experiment study on the system based on the traditional vector control in ideal grid conditions.The experimental results show that the system can realize VSCF operation and the grid connected operation. |
