Stability and control of maglev vehicle-girder coupled system considering torsional vibration of the girder.

The EMS (Electro-Magnetic Suspension) maglev vehicle uses controlled electromagnetic forces to achieve stable levitation; however, the interactions between the vehicle and the flexible girder may induce strong coupled resonances. Recently, a new type of girder resonance has been encountered, and field measurements indicate that this resonance is caused by torsional vibration of the girder. However, up to now, the principle of the girder torsional resonance has not been studied, and related control strategies have not been developed either. In this paper, a typical maglev girder with a steel track is investigated through finite element analysis, and a searching algorithm is proposed to obtain a best fit of the girder transfer function. Then, a maglev vehicle with twenty levitation control units is considered, and together with the girder model, the vehicle-girder coupled system is established. Factors that affect the coupled resonances are analyzed, and it is found that the velocity feedback of the electromagnet, which is effective to suppress the bending resonance of the girder, may lead to torsional resonance of the girder. This conclusion is validated by experiments in a real maglev system. To solve this problem, a distributed virtual tuned mass damper scheme is discussed, and suggestions to avoid the torsional resonances are also presented. This work not only interprets the principle underlying the vehicle-girder coupled torsional resonance, but also presents a methodology for dealing with the maglev vehicle-girder coupled resonance problems.