Passivity-based control of a hydrostatic transmission with unknown disturbances

A comparison of two passivity-based control strategies - with and without an integral control action - is proposed in this paper for the tracking control of a hydrostatic transmission, which is commercially used in working machines. An unknown leakage volume flow and a resulting load torque are taken into account as lumped disturbances. These disturbances and two unmeasurable state variables - the normalised swashplate angle and the normalised bent axis angle - are estimated by a nonlinear observer. Thereby, a high tracking accuracy can be achieved for the normalised bent axis angle and the angular velocity of the motor as controlled variables. The efficiency of the proposed controllers is demonstrated by both simulations and experiments.