| The bearingless flywheel battery is a power type battery,which has the advantages of high energy conversion efficiency,large instantaneous power,long service life,and strong dynamic response ability.It is one of the most promising high-power energy storage technologies at present.Bearingless flywheel batteries have broad application prospects in urban rail transit regenerative braking,auxiliary power for new energy vehicles,uninterruptible power supplies,and peakshaving and frequency-regulating power grids.However,it is difficult for traditional bearingless flywheel batteries to consider high integration and strong immunity,which has become one of the key problems hindering the large-scale application of flywheel batteries.The bearingless switched reluctance motor(BSRM)has the advantages of high integration and low loss.Torque and suspension functions are achieved simultaneously.It can be used in flywheel batteries to increase the integration.However,flywheel batteries are faced with complex and strong interference from multiple sources in the vehicle environment.Traditional BSRM has problems such as strong internal coupling,difficult control,and poor robustness,which make it difficult for the magnetic suspension support system to meet the anti-disturbance requirements of the vehicle environment.The 12/14 BSRM that considers high integration,strong immunity and weak coupling is proposed to meet the high integration and strong anti-disturbance performance requirements of the vehicle flywheel battery.Electromagnetic characteristics analysis,parameter optimization design,mathematical modeling,suspension force control strategy and experimental research work are carried out for12/14 BSRM in the paper.The main work and innovative achievements of the paper are as follows:1.The research background and significance of the research topic are explained.The advantages of bearingless flywheel batteries applied to vehicle energy recovery are introduced.The development status of the bearingless motor is introduced in detail.The development status of bearingless switched reluctance motor is introduced emphatically,including topological structure,structural parameter design optimization,mathematical model,and control strategy.Finally,the future development trend of bearingless switched reluctance motor is analyzed.2.The topology and working principle of the 12/14 BSRM,which can realize torque and four-degree-of-freedom suspension function,are described in detail.The structural parameters of12/14 BSRM were initially designed with reference to the design methods of magnetic bearings and switched reluctance motors.The finite element model is established,and the torque characteristics,suspension characteristics and coupling characteristics are analyzed in detail.The rationality of the motor structure and parameter design is verified.3.Strong coupling,multi-variable and multi-constraint features are included in the optimization process of 12/14 BSRM.An independent/cooperative optimization design method is proposed to solve the problem that traditional optimization algorithms are difficult to balance high precision and high efficiency in optimization.The 12/14 BSRM is divided into a torque unit and a suspension unit.The optimization objective and optimization variables are determined respectively,and the optimization variables are divided into insensitive variables,independent sensitive variables,and cross-sensitive variables.Based on the theory of extreme learning machine,a surrogate model that maps the nonlinear strong coupling relationship between each system design variable and the optimization target is established.The surrogate model is used as the objective function,and the sensitive variables of each unit are independently optimized using the NSGA＿II optimization algorithm.Then,according to the constraints and coupling relationship of the two units,information dynamic interaction is carried out to realize the collaborative optimization of12/14 BSRM.The finite element model is constructed based on the optimized parameters,and the optimization target performance before and after optimization is compared.The results show that the proposed optimization design method considers both high efficiency and high precision during optimization.4.The suspension force mathematical model established with reference to the permanent magnet bias magnetic bearing is difficult to characterize the time-varying characteristics of the12/14 BSRM suspension force.Therefore,a parallel main-side magnetic circuit modeling is proposed by taking advantage of the Maxwell stress method area modeling method.Through the detailed analysis of the suspension flux,the change law of the suspension flux area with the rotation of the rotor is determined.The mathematical analytical model of the change law of the magnetic flux area is obtained.Combined with Maxwell’s stress method and magnetic circuit method,an accurate suspension force mathematical model is derived.In the model,the current stiffness coefficient and displacement stiffness coefficient will show periodic changes with the change of the rotor position.The calculation results of the suspension force mathematical model are compared with the finite element analysis results to verify the accuracy of the suspension force model and the effectiveness of the proposed modeling method.5.The dynamic changes of the current stiffness coefficient and displacement stiffness coefficient in the model make it difficult to adjust the controller parameters accurately,when the suspension force model with time-varying characteristics is used as the suspension force feedback model in the direct suspension force control strategy.The robustness of the suspension control system is reduced.Therefore,a time-varying suspension force decoupling-compensation control strategy is proposed.The nominal model of the suspension force is used as the feedback model,and the parameters of the controller are adjusted based on the nominal model.The extended state observer is designed Based on the nominal model to accurately estimate the time-varying suspension force components and perform feed-forward compensation to achieve precise control of suspension forces.The simulation results show that the proposed time-varying suspension force decoupling-compensation control strategy effectively improves the steady-state control accuracy of the suspension control system and enhances the system’s robustness and dynamic response speed.6.The 12/14 BSRM prototype was processed.The hardware circuit is designed with d SPACE as the core,and the experimental platform of the motor is built.The optimization method of the motor and the proposed suspension force control strategy are verified experimentally.The validity of the optimization method is verified by the experimental results.The proposed time-varying suspension force decoupling-compensation control strategy can realize the stable suspension,which has better suspension accuracy and has better anti-disturbance performance against external disturbances than the direct suspension force control strategy. |
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