Sliding mode control for wheel slide protection in railway vehicles with pneumatic brake systems

Railway vehicles are the most commonly used means of public transportation systems, and therefore, it is essential to ensure their safe operation. To ensure reliable brake performance even on impaired tracks, a wheel slide protection device (WSP) is fitted to the brake system to prevent the wheels from locking and thus reduce excessive sliding. In this study, a sliding mode control (SMC) algorithm for a pneumatic brake system is proposed. The proposed algorithm basically conforms to SMC theory and the sampling time is divided into three sections, namely, the command section, response section, and monitoring section. The SMC determines the duty time for the WSP valve command, operates on a limited command section, and then waits for the brake state to stabilize through the response section. The benefits of this control strategy are that it can use a simplified mathematical model of a pneumatic valve on the model-based SMC and modify the continuous command type for the WSP valve instead of a discrete mode command. The proposed algorithm was verified through experiments with a brake hardware-in-the-loop simulation system for a railway vehicle.