Decentralised flatness-based control of a hydrostatic drive train subject to actuator uncertainty and disturbances

A decentralised flatness-based control strategy in combination with a reduced-order disturbance observer is proposed in this paper for a hydrostatic drive train. The corresponding fourth-order nonlinear system model, however, is characterized by imperfectly known system parameters, namely actuator time constants. Additionally, lumped disturbances, a leakage volume flow and a disturbance torque acting on the hydraulic motor, are taken into consideration. The proposed control approach involves three different control actions: 1) a fast control of the normalised bent axis angle of the motor, 2) an control loop for the angular velocity of the motor, 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 affecting the system dynamics.