Dynamic analysis and suboptimal control of a load-sensing hydraulic servo system

Abstract

Conventional hydraulic servo systems are inefficient in utilizing their power, since they generate a constant supply pressure from their power source regardless of load operating conditions. To improve the energy efficiency, a load-sensing hydraulic system has been developed, which has a sensing mechanism to detect the load pressure and feedback it to pump control element. Although the load-sensing system yields energy saving via this mechanism, the dynamic characteristics of this system are complex and highly nonlinear, and, furthermore, the dynamic stability is deteriorated due to the addition of the mechanism, which is critical to the performance of servo control. This necessitates an accurate evaluation of the dynamic characteristics and analysis of the system stability. The objective of the thesis is to provide a basis for the design and the control of the load-sensing hydraulic system. To achieve this a nonlinear dynamic model was formulated based upon the flow-pressure relationship. Based upon this model, theoretical investigations were made for the analysis of the system dynamics and stability, and for the design of a feedback control algorithm for a load velocity control. The results obtained from these theoretical developments were verified by a series of experiments. The thesis is composed of the three main parts. Firstly, the effects of the parameter variations on the dynamic model of the load-sensing pump was investigated via sensitivity analysis. The results of this analysis shows that the dynamic model of the pump can be simplified to a second-order model from the original fourth-order model. This reduced order model simplifies the analysis and the controller design of the load-sensing hydraulic system. Secondly, based upon the reduced order model, the stability characteristics of the load-sensing hydraulic system was theoretically analyzed via the Routh-Hurwitz criterion, and the results were confirmed by experiments. The load-sensing hydraulic ...