The sliding mode control for speed system of the variable displacement motor at the constant pressure network

The speed control system model of a variable displacement hydraulic motor (VDHM) at a constant-pressure network has many uncertain and time-varying parameters. Therefore, it is impossible to obtain an accurate mathematical model. Moreover, the speed system is subject to a variety of disturbance from load and so on. The conventional proportional integral derivative (PID) is difficult to achieve a good control performance in this system. In this paper, the mathematical model of a VDHM system is depicted and a sliding mode variable structure control (SMC) is proposed. The VDHM speed system at the constant pressure network has been studied in MATLAB/Simulink environment. The simulation results show that the rotating speed of VDHM can be precisely controlled by the proposed SMC controller. Compared with traditional PID control algorithm, the proposed SMC approach has many advantages, such as faster response and robustness to the influence of the uncertainty and load disturbance, and improved control performance, etc.