Research On The Unbalanced Forces And Position Estimation Of Double-sided Linear Switched Reluctance Machine

Compared with the single-sided linear switched reluctance machine(SLSRM), the double-sided linear switched reluctance machine(DLSRM) has a structure of symmetric stators. The normal forces in the DLSRM can be counteracted. The thrust per volume and the reliability of the DLSRM are better than the SLSRM. However, in the actual applications, due to the manufacture error, machine wear and tear, and shift of sliders or wheels, the mover eccentricities are practically inevitable, which will give rise to undesirable unbalanced forces, weaken the advantages of the DLSRM, and affect the machine working life and control performance. Meanwhile, the eccentricities have a great influence on the results accuracy of position estimation for SRMs/LSRMs. The research focus on the unbalanced forces and position estimation of the DLSRM with eccentricities. Main works are summarized as follows.The influence parameters of the unbalanced forces are analyzed by the finite element models and magnetic circuit model of the DLSRM firstly. It is found from the flux distributions of the DLSRM that the mover yokes will lead to the increase of flux differences between two air gaps on both sides of the mover, and also increase the unbalanced forces. It is proposed that removing the mover yokes can reduce the unbalanced forces in the eccentric DLSRMs. The finite element analysis results show that the DLSRM with no mover yokes has less unbalance forces than the DLSRM with mover yokes in the condition that two machines have the same eccentricities, and removing the mover yokes has no effect on the electromagnetic thrusts. Secondly, the effects of the winding connections on the unbalanced forces are studied. The calculation results of transient finite element models show that the unbalance forces can be reduced with parallel windings. The conclusions are verified by the test results of the prototype.To further reduce the unbalanced forces by control schemes and realize the sensorless control system of the DLSRM, the real-time estimation of unsaturated inductance is necessary. For reducing the influence of eddy current on the accuracy of the inductance estimation with pulse injection method, a method considering the effect of eddy current is proposed in this paper. With the equivalent circuit model, the influences of eddy current on the winding current and traditional inductance estimation results are analyzed, and a novel method is proposed for estimating the actual winding inductance by using the rising time and falling time of the response currents. This method can be carried out without the computation of eddy current and the equivalent eddy current resistance, and it can maintain the advantages of voltage pulse injection method. Experimental results show that the proposed inductance estimation method has high accuracy with different excitation voltage, and it can overcome the influence of the eddy current on the estimation accuracy. It lays a good foundation for achieving the online detection of the eccentricities of DLSRM and the sensorless control system.Based on the proposed method of inductance estimation, a control method for the online detection of the eccentricities and the reduction of unbalance forces for the DLSRM is proposed. Firstly, according to the proportional relationship between the eccentricities of the DLSRM and the differences between the reciprocals of inductions of both sides series-connected coils, a method for online detection of the eccentricities is designed. Secondly, by analyzing the influence parameters of the unbalanced forces, a scheme for the reduction of unbalanced forces is put forward by controlling the currents in both sides series-connected coils. In order to achieve the proposed methods for online detection of the eccentricities and the reduction of unbalanced forces, a converter that can independently control the currents in both sides series-connected coils is employed. The operation principle of the converter is introduced, and the program flow chart and implementation steps are presented. The test results of the prototype verify the feasibility of the proposed methods.Through analyzing the influence of eddy current on phase current with the equivalent eddy resistance model, a method for estimating the real-time position of the DLSRM is proposed firstly with taking the difference between the rising time and the falling time of the response currents as the position index. This method is easy to achieve without the computation of eddy current and the equivalent eddy resistance, and it is not affected by the fluctuation of the DC bus voltage. Secondly, by analyzing the influence of eccentricities on the phase induction of DLSRM, the sum of the reciprocals of inductions of both sides series-connected coils is taken as the position index for the sensorless control system. The proposed position index is independent of the eccentricities of DLSRM, and it has a corresponding monotonic relationship with the mover position. The control methods and flow charts of DLSRM starting and low speed operation are given based on the above two position indexes. The experimental results of prototype verify the effectiveness of the methods.