Research On Improving Direct Thrust Control Strategy Of Permanent Magnet Linear Synchronous Motor For Lift-Type Magnetic Suspension Train

The suspension maglev train,as an intelligent and small-volume light-weight new type of rail vehicle,is suspended above the road flower beds and green belts,occupying very little urban ground space,and hardly affecting the public transportation on the ground and not destroying the ecology.The environment can be widely used in many occasions such as mountain towns,hills,lakes along the river,urban-rural connections,and urban area connections,which has a great promoting effect.In this paper,permanent magnet linear synchronous motor(PMLSM)is chosen as the driving unit of suspended maglev train.It has simple structure,no winding coil excitation,good heat dissipation effect and no additional cooling device.The common control strategies of permanent magnet linear synchronous motor mainly include vector control,direct thrust control and other composite control strategies.These control strategies can ensure the high performance operation of the motor.Direct thrust control can be regarded as direct torque control applied in linear motor.Its main characteristics are direct control mode,clear objectives,good dynamic performance,strong robustness and less dependence on motor parameters.It has become the focus of linear motor control strategy research.In this paper,the development history of permanent magnet materials,the basic structure and principle of permanent magnet linear synchronous motor are briefly summarized,and the equivalent transformation relations and mathematical models among three coordinate systems are deduced.The basic theory of direct thrust control of permanent magnet linear synchronous motor(PMLSM)is deeply analyzed,and the traditional direct thrust control model is established.Then,the theory and implementation method of direct thrust control based on space vector pulse width modulation are presented,and the simulation model is built.In MATLAB/Simulink,two direct thrust control models are simulated under the same conditions.By comparing and analyzing the simulation results,it can be seen that the former has obvious pulsation in flux linkage and thrust compared with the latter,and the latter has better dynamic performance.In order to further improve the dynamic performance of direct thrust control strategy,this paper mainly achieves the improvement in three aspects.First of all,in traditional direct thrust control,PI controller is often used in velocity loop,and its adjusting parameters cannot change with system,which make it difficult to balance the contradiction between overshoot and response time.In this paper,the automatic disturbance rejection controller(ADRC)is applied to replace the PI controller in the velocity loop to reduce and compensate the influence of the uncertain part of the model and the external disturbance on the speed response of the system.Secondly,hysteresis control is often used in traditional flux linkage and thrust control,which makes inverter switching frequency unstable,flux linkage and thrust pulsating.Super-twisting algorithm is introduced to replace hysteresis control.Finally,it is very important to realize accurate estimation of flux linkage in direct thrust control,so a compensation voltage-current mode flux linkage estimating method is used in this paper.In view of the above improvements,the simulation model is built in MATLAB/Simulink,and the improved direct thrust control method is verified.The results show that the improved method is effective.