| The maglev technology, a new-tech emerged in 20th century, has been progressed a lot in recent years. It is widely applied in transportation, metallurgy, mechanism, electrical equipments and material researches. The maglev train, a new railway vehicle without friction, is one successful and important application of maglev-tech. However, as for traditional EMS, the energy loss cannot be ignored, because of the resistance in normal conductor. With the rappid development of the HTS(High Temperature Superconductor),HTS EMS-tech has a bright prospect. In this new type of EMS, energy loss can be much lower than the traditional normal-conductor EMS, because of zero-resistant effect.Due to the inherent nonlinearities and open-loop instability of the electromagnetic suspension systems, control of their stability must be accomplished through controller. It is difficult for a magnetic suspension system with traditional method to solve the problem of the uncertainties caused by the parameter variety and disturbance. Robust control theory can design a controller whose structure and parameters is unchanged when the controlled system is under the worst conditions and can make the closed loop system maintain the performance with uncertainties. Therefore, the paper put stress on the application of I-h robust control theory to magnetic suspension system.In this paper, the single-magnet dynamic moldle of the pure HTS EMS is built and the basic theory of the system is discussed. Based on H_∞control theory about mixed sensitivity, a H_∞controller is designed and the magnetic suspension system based on H_∞controller is stable and robust. The design is evaluated by experiment. The experiment results show that H_∞control can levitate the suspension system stably and is very robust.
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