Research On Longitudinal End Effect Of Switched Reluctance Linear Machine And Its Compensation Methods

Switched reluctance linear machine(SRLM)welcomes a good application prospect with its simple structure,high reliability and excellent fault tolerance.However,the existing optimization design methods and control strategies of SRLM usually refer to the research results of rotary switched reluctance machine(RSRM).It makes the longitudinal end effect of SRLM that is different from RSRMs ignored.The study of longitudinal end effect of SRLM can deepen the understanding of the performance of SRLM and inspire some new ideas for performance improvement.Therefore,this dissertation researches on the longitudinal end effect of SRLM and its compensation methods.Firstly,a high-precision nonlinear model of SRLM is proposed.It can reflect the real characteristics of SRLM,including the influence of longitudinal end effect on machine's performances,which lays a solid foundation for the research of longitudinal end effect of SRLM.On the basis of the analysis of magnetization curves and magnetic density distribution curves which are obtained by finite element method(FEM),an improved quasi-linear model of magnetization curve is proposed.After analyzing the quasi-linear model,a kind of variant Sigmoid function is obtained.It can be an interpolation function in the process of obtaining complete flux linkage curves.At the same time,the influence rules of flux linkage with a bias on current are summarized.Hereby a new training method of complete flux linkage-position-current curves is proposed.Additionally,the electromagnetic characteristic of the same prototype SRLM is also modeled via sixth order Fourier series method for modeling accuracy comparison.The online experiments based on rapid control prototyping and offline experiments are designed.Their results demonstrate the high accuracy of the electromagnetic characteristic obtained by the proposed method and the good simulation effect of the established model on dynamic performance.This modeling method is also suitable for RSRM,so it has good universality.Then,the influence of the longitudinal end effect on the performance of SRLM is studied combined with winding connection modes.The changes of self/mutual electromagnetic characteristics of different phases caused by the longitudinal end effect and the winding connection are analyzed through FEM.Combined with two winding connection modes,the influence of the longitudinal end effect on the dynamic characteristics is analyzed and quantified.In addition,the magnetic density characteristics and iron losses of the SRLM under different winding connection modes are analyzed.The advantages and disadvantages of the two winding connection modes are summarized.The experimental validations are conducted on the prototype under two winding connection modes,the electromagnetic force ripple in the electric state and the output voltage ripple in the power generation state are analyzed,and the iron loss in the dynamic operation of the machine is obtained according to the indirect measurement method.The experimental results under different control strategies prove the influence of the longitudinal end effect on the motor performance and the correctness of the electromagnetic analysis results and simulation results.Next,some compensation methods on the longitudinal end effect of SRLM are proposed from the motor design point of view.The compensation effect of a previous compensation method via adding stator auxiliary poles is analyzed by FEM.The sensitivity between the width of the stator auxiliary pole and the electromagnetic force ripple is analyzed for minimizing the extra space and cost,which provides a basis for the selection of the width of the stator auxiliary pole.After the analysis of the equivalent magnetic circuit of SRLM,a new compensation method on the longitudinal end effect of SRLM via widening stator end poles is proposed according to similarity principle of magnetic field.The theoretical optimal width of the stator end pole is also given.The compensation effects of the previous and the new compensation methods on the longitudinal end effect are compared.In addition,a new SRLM which is not affected by the longitudinal end effect is proposed by learning from the structural characteristics of RSRM,and the experiment verification is conducted on a prototype and an established hardware platform.Finally,a compensation method on the longitudinal end effect of SRLM is proposed from the control point of view.The influence of longitudinal end effect on the peak current of every phase in dynamic operation is analyzed according to the voltage balance equation with considering mutual coupling characteristics.It is found that the previous current estimation model shows big errors in estimating peak current values.In order to improve the estimation accuracy of peak current values,an improved current estimation model is proposed with taking the mutual coupling characteristics into account.Accordingly,an adaptive adjustment method of turn-on position for balancing the peak current values is proposed,and the velocity closed-loop control diagram based on the proposed method is given.This control system is simple and easy to realize.The experiment and simulation results show that the proposed control method can realize the current balance and compensate the negative impact of longitudinal end effect.This method is also applicable to the machine under heavy load and saturated situation so that it has good versatility.