Robust Controller Design for Maglev Suspension Systems Based on Improved Suspension Force Model

The electromagnetic suspension-type maglev train can reach ultrahigh-speed using long stator linear synchronous motors; however, slot effect makes the motors suffer from suspension force ripple, since it causes the nonsinusoidal airgap magnetic field distribution. It has been expounded that the suspension electromagnet system is highly nonlinear and unstable in open loops. Additionally, maglev trains experience disturbances and uncertainties in service. Therefore, the robust disturbance-rejection control for electromagnet suspension system is highly necessary to maintain a constant airgap position. In this article, it is intended to propose a novel robust controller for suspension systems which ensures superior system performances despite suspension force ripple, disturbances, and uncertainties while sustaining stable suspension despite system nonlinearity. First, field harmonics are investigated along with slot effects, and an improved nonlinear mathematical model of electromagnetic force is derived. Second, the controller based on the improved force model is formulated. Then, the performance of the designed controller is evaluated on a maglev suspension system with disturbances and uncertainties. Simulation and hardware-in-the-loop experimental results demonstrate that the improved suspension force model is more accurate than the conventional models, and the corresponding controller excels in attenuating larger disturbance without sacrificing tracking performances at different speeds.