Robust Inverse Dynamics Control for a Hydrostatic Transmission with Actuator Uncertainties

This paper presents a robust inverse dynamics control strategy in combination with a reduced-order disturbance observer for a hydrostatic transmission. The corresponding nonlinear system model, however, is characterized by only imperfectly known system parameters – actuator time constants – and unknown disturbances – a leakage volume flow and a disturbance torque acting on the hydraulic motor. The proposed approach involves three different control actions: 1) an inverse dynamics control that allows for tracking desired trajectories for the difference pressure and the motor angular velocity, 2) a robust control that stabilizes the error dynamics despite uncertain actuator time constants, and 3) a reduced-order disturbance observer that estimates the leakage volume flow as well as the unknown load torque and allows for a disturbance compensation. Simulation results show that with the proposed approach an accurate trajectory tracking is achieved despite the uncertain time constants and the given disturbances in the system dynamics.