Levitation Control Strategy For High Speed Maglev Train Based On Flexible Control Theory

Maglev train demonstrates advantages in terms of operation speed,energy consumption and maintenance cost,which makes it promising in the future.Since electromagnetic suspension system is a typical open-loop unstable system,levitation control technology plays a vitally important role in the operation of maglev train.Currently,the vehicle-track coupling vibration is a problem that need be solved for the maglev system.Although this problem can be addressed by increasing track stiffness or mass,there would be a substantial increase in construction costs.If the magnetic levitation control system can be effective in suppressing coupling vibration,the cost and stability of maglev line can be guaranteed.In this study,a flexible levitation control strategy is proposed by introducing the vibration of track into levitation controller.Then,theoretical analysis and experimental study are carried out for the proposed control strategy.According to the research results,it is effective in reducing coupling vibration,which means the intensive dependence on track can be reduced for the maglev system.In order to explore the stability of maglev vehicle-track coupling system,this paper starts by establishing a mathematical model of the maglev system comprised of vehicle,track beam and electrical levitation system.Then,the stability of single magnet-track system is analyzed according to the Routh Hurwitz criterion and the distribution of system eigenvalues.Besides,the stability of vehicle system is analyzed by means of numerical simulation.Through the methods as mentioned above,an in-depth investigation is conducted into how the stability of maglev system is affected by such factors as track stiffness,damping,span and controller parameters.In addition,a levitation control method is proposed to suppress vehicle track coupling vibration.A comparison is performed between flexible levitation control strategy and traditional rigid control strategy in both time and frequency domains.As revealed by the comparative results,the flexible control strategy can make magnetic force produce control damping to vibration of track beam.Therefore,the levitation system can still maintain stability on low stiffness or damping track.According to the study of energy flow between levitation force and track beam,different from the rigid levitation control strategy,the flexible control strategy maintains a low or negative energy input to track beam throughout the frequency range.As a result,it is difficult to accumulate the vibration energy of track,which is conducive to stabilizing the coupling system.To apply the proposed flexible levitation control method in engineering,it is necessary to obtain all state variables of the maglev coupling system for the controller,including the states of track.However,it is difficult to measure and obtain all state variables directly.Therefore,the state reconstruction methods are proposed for the levitation system based on full order state observer,reduced order state observer and Kalman filter,respectively.By analyzing the dynamic performance of levitation system through the above methods of state reconstruction,a summary is made as to the advantages and disadvantages of the above methods.In order to validate the proposed control strategies,a scale electromagnet-simply supported beam levitation control test rig is established in line with the similarity theory.Besides,the dynamic similarity between original system and scale system is ensured.By applying the D-SPACE rapid control prototype technology,the levitation control system of the test rig is constructed.There are a range of different influencing factors in the dynamic performance of levitation system,such as track irregularity,moving speed,levitation position and track stiffness,etc.Through a test conducted on magnets under these multiple levitation conditions,it is discovered that the stability of the system can be guaranteed.In the meantime,coupling vibration is effectively reduced.It is essential to consider the nonlinear characteristics of the levitation system,especially when the system deviates from the balanced operation point.The response of the levitation system can be optimized if the levitation controller can be designed in nonlinear environment.In this paper,controller parameters are optimized by applying the Nelder Mead algorithm,nonlinear electromagnet model and finite element track beam model.According to the test result,the control parameters as calculated in nonlinear environment lead to a better dynamic response.Finally,the conclusion of this research is summarized and the direction of future research is discussed.