Analysis and quenching of limit cycles of electro-hydraulic servovalve control systems with friction and interval transport lag

A systematic and straightforward methodology to analyze and quench the friction-induced limit cycle conditions in electro-hydraulic servovalve control systems with interval transport lag is developed in this paper. The nonlinearity is linearized by its corresponding describing function. The delay time in transmission line is considered. The stability-equation method accompanied with parameter plane method provides a useful tool for the establishment of necessary conditions to sustain a limit cycle in the constructed limit cycle surface. The portrayed surface characterizes clear relationship among limit cycle amplitude, frequency, transport delay, and the controller coefficients to be designed. The asymptotic stability region, the unstable region, and the limit cycle region are identified in the parameter plane. The variation of the transport lag which could accelerate the generation of limit cycles is investigated. A feasible stable region is characterized in the parameter plane to allow flexible choice of controller gains. The quenching of limit cycle is achieved by selecting controller gains from the asymptotic stability region. It is seen that the friction-induced limit cycles can be effectively quenched via the tuning of the controller gains.