Control-Oriented Modeling of Hydrostatic Transmissions using Takagi-Sugeno Fuzzy Systems

Hydrostatic transmissions, also called hydrostatic gears, have been widely used in mobile machines and off-road vehicles such as wheel loaders, graders or tractors. The hydrostatic transmissions are gears with high power density which offer important advantages like continuously variable transmission, maximum tractive force at low speeds and reversing without changing gear. In the industrial practice the transmission output torque, transmission ratio or output speed are usually controlled by model-free PID control methods. This approach results in limited closed-loop bandwidth, limited working efficiency and accuracy due to the high nonlinear characteristic of the plant. This paper presents a control-oriented model of a general hydrostatic transmission as a first step towards a multivariable model-based fuzzy state feedback gain scheduling controller. The controller structure based on parallel distributed compensation scheme (PDC) using Takagi-Sugeno (TS) fuzzy models of the plant. First principles are used to determine the structure of the TS fuzzy model. The applicability of the approach is shown by simulation studies.