H₂ and H_∞ control for MagLev vehicles

Many magnetically levitated transport systems have been constructed, tested, and improved. Various magnetic levitation (MagLev) system technologies are being developed, and some of them, including the prototype featured in this article, use electromagnets for vehicle levitation. Vehicle levitation is achieved by controlling the gaps of these electromagnets. The constructed prototype will have independent levitation and propulsion systems, but the focus of this article is on the levitation system only. The system is open-loop unstable, highly nonlinear, and it has a very restricted equilibrium region. A single input single output (SISO) analytical model and closed-loop identification experiments are presented, with emphasis on design procedures of H₂ and H_∞ controllers applied to the electromagnetic levitation system. For the designs of these controllers, a special choice of weighting functions is employed to attenuate the resonance peak at low frequencies in the closed-loop system. The results show that closed-loop system responses with H₂ and H_∞ controllers are very similar and present better performances when compared to the response obtained with a classical controller