High-Precision Speed Tracking Control for Maglev Cars Based on a Tracking Differentiator and Fractional-Order Integral Nonsingular Terminal Sliding Mode

Abstract

Magnetic levitation (maglev) cars integrate levitation, propulsion, and guidance in a unified system and are regarded as a promising solution for future intelligent transportation. Although extensive studies have been conducted on intelligent control strategies for maglev systems, most existing work focuses on levitation stability rather than longitudinal speed regulation. During vehicle operation, however, precise speed tracking is critical to safety, especially under nonlinear coupling effects in driving and braking processes. To address overshoot, chattering, and steady-state error caused by nonlinear dynamics, this paper proposes a composite speed tracking control strategy that integrates a tracking differentiator (TD) with fractional-order integral non-singular terminal sliding mode control (FOI-NTSMC). A data-driven nonlinear longitudinal dynamic model is established using permanent magnet electrodynamic wheel (PMEDW) driving force experimental data and the least squares method. The TD preprocesses the reference speed signal, while a fractional-order integral sliding mode surface and reaching law are designed to enhance robustness. A saturation function is introduced to suppress chattering and compensate for nonlinear coupling disturbances. Simulation studies indicate, compared with PID control, traditional sliding mode control, and non-singular terminal sliding mode control, demonstrate overshoot-free tracking, zero steady-state error, and a 15%-30% improvement in dynamic response over conventional NTSMC. The proposed strategy provides an effective solution for high-precision longitudinal speed control and fast braking of maglev cars.