Robustness analysis and control system design for a hydraulic servo system

Treats the robustness analysis and control system design for the hydraulic servo system in a continuously variable transmission (CVT). The hydraulic system is subject to many uncertainties because of linearization, changes in temperature and errors in specified data. All these uncertainties are modeled in bounded and structured form, and the system is represented by a linear fractional transformation such that singular value and μ analysis and design methods can be used. Four control designs are proposed: classical PID control, H_∞ (sub)optimal control, μ synthesis with D-K iteration, μ synthesis with PID parameter search. For each of them, the robustness of stability and performance is analyzed with singular value and p tests. The results confirm that the singular value test may be conservative compared to the μ test. When, for this specific control system, the μ analysis method is combined with a PID control structure, it can be guaranteed that the stability and performance robustness are satisfied and the control structure is as simple as a PID controller. Simulations are made for all the control designs