A Model-Based Backstepping Pressure Control Strategy for a Rotary Direct-Drive Pressure Valve

Rotary direct-drive pressure valves (RDDPVs) have attracted increasing attention in aircraft braking systems because of their compact structure, reduced weight, and improved anti-contamination capability. However, the pressure regulation of RDDPVs is challenging due to the coupled dynamics among the limited-angle torque motor, eccentric spool motion, steady-state flow force, and load pressure. Existing pressure control methods for RDDPVs are still mainly based on linear controllers such as PI/PID controllers, which do not explicitly compensate for the nonlinear characteristics of the valve. To address this problem, this paper investigates the application of a model-based backstepping control strategy to RDDPV pressure regulation. First, a nonlinear dynamic model of the RDDPV is established, and a nonlinear state-space representation is derived for controller design. Based on this model, a backstepping pressure controller is developed, in which the nonlinear model information is used for feedforward compensation. Dynamic surface control is introduced to avoid direct differentiation of the virtual control signals. Lyapunov analysis shows that the closed-loop tracking errors are uniformly ultimately bounded under bounded disturbances. Comparative simulations are conducted under different reference pressure trajectories and randomized model parameter and disturbance conditions. The simulation results indicate that the proposed controller achieves better tracking performance than the controller without detailed model compensation and the conventional PI controller under the tested operating conditions. This study provides an initial simulation-based exploration of model-based nonlinear pressure control for RDDPVs.