Tracking Differentiator-Based Sliding Mode Velocity Control of a Hydrostatic Transmission

This paper presents study results on the application of sliding mode control (SMC) for velocity tracking of a hydrostatic transmission system. The design deploys the idea of an almost model-free control to obtain the basis for an SMC implementation that does not rely on a complete system model. In a decentralized control structure, the control of the bent-axis angle of the hydraulic motor is performed by an inversion-based pure feedforward control. Synchronous reference values are derived from the desired motor angular velocity as system output, in compliance with a suitable transmission ratio. The swash-plate angle of the hydraulic pump represents the control input for an SMC approach using a linear tracking differentiator (LTD) providing estimates of the error signal derivatives. The proposed control structure has been investigated by means of simulations and validated by experiments on a dedicated test rig at the Chair of Mechatronics, University of Rostock.