Research On Low-cost Control System Of The Primary Excitation Permanent Magnet Linear Motor For Rail Transit

With the fast development of economy and technology,urban rail transit systems which are of low energy consumption,environmental-friendly,fast and convenient can effectively alleviate traffic problems.Compared with conventional rotary machines,linear motors have the advatnages of high positioning accuracy,simple maintenance and high reliability,which can be applied broadly.The permanent magnets and armature windings of linear flux-switching permanent magnet(LFSPM)motors are all set on the short primary whereas the secondary structure is very simple.Hence,LFSPMs incorporate the advantages of high efficiency and power density while maintaining the simple structure compared to commonly used linear induction motors(LIM).Unfortunately,the use of expensive position sensors to obtain the position information will result in the cost increase of the drive system and the system reliability decrease.Therefore,the low-cost drive system of LFSPMs is studied in this paper,which is mainly divided into two aspects: sliding mode observer(SMO)based sensorless vector control and direct thrust force control(DTFC)of LFSPMs.The economic cost and load performance are firstly compared between LIMs and LFSPMs,which shows that LFSPMs have certain advantages in rail transit systems.According to finite element analysis,the mathematical model of LFSPMs is established in different coordinate systems.The simulation model of LFSPMs based on vector control is established in Simulink considering big air gap application scenarios whereas it is verified using d SPACE experimental platform based on the small prototype of LFSPM.Secondly,the principle of traditional SMO to estimate the speed and position is analyzed for LFSPMs.According to the characteristics of LFSPMs,corresponding measures are proposed to improve the estimation performance.The switching function is replaced with Sigmoid function to reduce the system chattering whereas the adaptive feedback gain is introduced to expand the operating speed range of SMO.In addition,phased-locked loop is adopted to estimate the speed and position information of LFSPMs.The effectiveness of the improved SMO is validated by simulations and experimental results.Thirdly,DTFC is adopted to implement operation of LFSPMs without position sensors while speed sensor is utilized to detect the speed to achieve closed-loop operation.The relationship between thrust force fluctuation and the selected effective space voltage vector is thrived after analyzing the thrust force fluctuation of conventional hysteresis DTFC.Duty ratio modulation is proposed to reduce thrust force and flux fluctuation according to small inductance and polar distance.The control performance of traditional hysteresis DTFC and duty ratio-based DTFC is compared by simulations whereas experimental vertifications show that the proposed strategy can effectively reduce the thrust force fluctuation.Finally,the experimental platform of the LFSPM motor is built utilizing the d SPACE controller.In addition,the software and hardware system are explained in detail,so as to provide support for verifying the feasibility and effectiveness of the control strategy proposed in this paper.