Design And Control Of A Disc Type Dual Stator Induction Solid Rotor Flywheel Motor

Disc type dual stator induction solid rotor flywheel motor(DSSRFM)is a vertical motor,the solid rotor is sandwiched between upper and lower stator cores,and is integrated with the flywheel together.It is applied as a motor/generator in a flywheel energy storage system(FESS).The radial bearings in DSSRFM employ the passive magnetic bearings.The axial bearings in DSSRFM employ the hybrid bearings,which consist of the passive magnetic bearings and the axial magnetic pulling force on solid rotor.The FESS with DSSRFM is low cost and easy to manufacture.The electromagnetic field distribution(EFD)is the basis to analyse the operating principle of DSSRFM,the operating performance of DSSRFM and the energy transforming mechanism of DSSRFM.To simplify the analysis of EFD in DSSRFM,a multi-slice and multi-layer method is proposed.By this method,DSSRFM is equivalent to a finite set of double-sided steel secondary linear induction motors(DSLIMs)with equal width and increasing length,and the steel secondary is divided into a finite set layers with equal height.And the EFD in each layer is solved by Maxwell's equations.The comparison between the EFD analyzed by the multi-slice and multi-layer method and the EFD analyzed by the finite element software shows that the accuracy of the multi-slice and multi-layer method is satisfactory.The equivalent circuit model and mathematical model are effective ways to analyze the performance of DSSRFM,and they can provide the guidance for the optimized design.The quasi-one-dimension theory,the penetration depth method,the unit reluctance method,the equivalent complex permeability method,the Poynting theorem,the two-dimensional finite element method,and the three-dimensional finite element method are introduced to calculate the solid rotor impedance in the traditional T-type equivalent circuit model.The quasi-one-dimension theory,the penetration depth method,the unit reluctance method and the equivalent complex permeability method don't take the operating conditions of DSSRFM into account,their computational effort is small.The Poynting theorem,the two-dimensional finite element method and the three-dimensional finite element method take the operating conditions of DSSRFM into account,and their computational effort is large.The solid rotor impedance and performance of DSSRFM calculated by these methods are compared with the performance of DSSRFIM calculated by the experimental test,the comparison shows that these methods can predict the performance of DSSRFM with high accuracy.The tradition T-type equivalent circuit model neglects the coupling relation,so it is only appropriate for the condition,that the phase and amplitude of upper stator current and lower stator current are the same.Thus,the surface impedance theory is adopted to derive an improved equivalent circuit model,which takes the coupling relation between upper and lower stator windings,and is suitable for any operation condition.The performance of DSSRFM is calculated by the tradition T-type equivalent circuit model,the improved equivalent circuit model and the experimental test.The results show that the improved equivalent circuit model can predict the performance of DSSRFM at any conditions.According to the electromagnetic design methods for the squirrel-cage induction motor and AFIM and the formulas for calculating the solid rotor impedance and excitation reactance,the electromagnetic design method for DSSRFM is summarized,and a prototype is designed.The performance of DSSRFM is relatively poor.To improve the performance,some improved solid rotor structures are proposed,such as a solid rotor coated with copper layer,a solid ladderrotor with radial slots,a solid ladder-rotor coated with copper layer,a solid rotor with circumferential slots,a squirrel-cage solid rotor,and a solid rotor with three layers.And these solid rotors are optimized by the finite element software.To analyze the EFD and derive the equivalent circuit model of different type solid rotor,a multi-layer universal model is proposed.To derive the control strategy of charging and discharging,the mathematical model of back-to-back converter is analyzed.And a control strategy of voltage square outer loop and power inner loop with power feed-forward is derived.The results analyzed by the experimental test illustrate that the steady-state performance and dynamic performance of this control strategy is satisfied.The mathematical model of the axial magnetic pulling force on solid rotor and the electromagnetic torque is also derived.And according to the mathematical model,a control strategy of axial displacement and speed is derived.The results analyzed by the experimental test show that the DSSRFIM can provide steady axial magnetic pulling force and electromagnetic torque.This thesis analyses the EFD in DSSRFM,the operating performance of DSSRFM,the electromagnetic design method of DSSRFM,the control strategy of charging and discharging and the control strategy of axial magnetic pulling force and electromagnetic torque.Fruitful results in these research works are of both theoretical and practical value.The results can be severed as a basis for the further application of the FESS and DSSRFM.