Research On Control Strategies For Stand-Alone Operation Brushless Doubly Fed Induction Generator

Wind energy,as an efficient,clean and renewable energy,has attracted more and more attention,and wind power technology has boomed in world.As the increasing progress and maturity of power electronics technology,the variable-speed constant-frequency wind power generation equiped power converter has gradually become the mainstream.For some remote local loads,the conventional grid fails to cover only island grids are possible,and the stand-alone generation system is imperative.In addition,the distributed generation requires the system to be prepared to disconnect from the grid,in case of grid failure,and to maintain power supply to isolated loads.The stand-alone operation is one of the important development trends of wind power technology and has wide application prospects.The doubly-fed induction generator(DFIG)is one of the important trends of wind power technology and has wide application prospects.Brushless DFIG(BDFIG)shares with the DFIG's benefits of low cost construction in that no permanent magnets materials used and only a fractionally rated converter needed.Simultaneously,the absence of electric slip rings obviates one of the main failure modes of the DFIG,which has rigid construction,low manufacture and maintenance cost,acclimate severe environment.The BDFIG also has a significantly improved low-voltage ride-through performance compared with DFIG,and easy to meet wind power grid-connected standard.However,the internal electromagnetic relationship of BDFIG is complex and difficult to control.At present,there are still many control problems to be solved.This dissertation focuses on improved control strategy of stand-alone operation BDFIG for variable speed constant frequency wind energy conversion systems under non-ideal load condition,such as abrupt,unbalanced,nonlinear,etc.theory analysis,simulation validation and experiment test verification have been implemented to study and investigate the proposed control strategy in detail,the main research,contribution and innovation points can be summarized as follows:The dynamic state characteristics of the BDFIG when the terminal voltage of the stand-alone operation system abrupt changes rapidly is analyzed,the adverse effect of the terminal voltage abrupt changes rapidly on the energy conversion systems and its reasons is explain.When the PW stator terminal voltage of the machine abrupt changes rapidly,a instantaneous increase of PW stator flux linkage positive sequence natural and negative sequence component will lead to induction of higher back electromotive force in the CW stator,and harm stand-alone operation system running stability and power quality.Based on the vector control of BDFIG stand-alone operation system,the key technical which the required CW stator current reference configuration and track in stand-alone operation BDFIG system is investigated.The fundamental and harmonic component of the CW stator current is uniformly precision and fast tracking.CW stator current dead-beat model predictive control is proposed.According to the error of the previous sampling period and the model parameters,the reference of the next sampling period is directly calculated to eliminate the transient error and improve the dynamic response.Moreover,integrator plus specified orders resonant frequency signals generalized integrator compensation are implemented to enhance tracking accuracy.The power quality of PW stator terminal voltage is improved.In addition,a novel finite-set model predictive CW stator current control is proposed.Based on the CW stator current model,predict each CW stator voltage vector switch state influence on the CW stator current according to basic switching table,the optimum CW stator voltage vector switch state and sequence is selected,and thereafter their duration times were optimized with the cost function target of eliminate the errors reduce and reduce ripple,the constant switch frequency is ensured.Based on the direct control of BDFIG stand-alone operation system,the key technical which the required PW stator voltage and flux reference configuration and track in stand-alone operation BDFIG system is investigated.The fundamental and harmonic component of the PW stator voltage and flux is uniformly precision regulation and fast tracking.A novel sliding mode control scheme for PW stator voltage and flux is proposed,moreover,the integrator and specified orders frequency generalized integrator resonant sliding mode surface is employed to eliminate the errors enhance tracking accuracy,a boundary layer around the sliding surface is introduced to eliminate chattering problem.The PW stator terminal voltage is controlled accurately and quickly.A novel hybrid control scheme of vector control plus direct control for BDFIG stand-alone operation system is proposed and discussed particularly.The vector control is employed to deal with CW stator current fundamental component,which configuration CW stator current reference and limit,such as dead-beat model predictive control is implemented to achieve precision and fast tracking for CW stator current.The direct control is used to deal with PW stator voltage or flux negative sequence and harmonic component,such as an improved slide-mode direct resonance control loop is implemented,generalized integrator is introduced to feedback compensation.The steady-state tracking accuracy and transient response performance of PW stator terminal voltage is ensure and enhance.The simulation and experiment system of BDFIG is designed.The simulation and experiment result proves the feasibility and validity of the proposed scheme.