State-space modeling and analysis of power assist unit-based variable-speed pump-controlled-motor drive system

Abstract

The variable-speed electrohydraulic system has been widely employed in industry for its energy-saving performance. But its poor response and low accuracy, which were caused by the big inertias of electric motor and hydraulic pump, limit its further applications. Working on these disadvantages, the power assist unit (PAU)-based variable-speed drive principle system was proposed. Besides the primary power source driven by variable-speed pump, the PAU acts as an auxiliary power source, which can discharge hydraulic flow when actuator accelerates so as to improve the responsiveness. A proportional directional valve was also integrated into the variable-speed drive system; it can improve the speed-regulation precision. However, the PAU-based variable-speed drive system is a nonlinear multiple-input–multiple-output system coupled with time-variant parameters, which increased the difficulties of theoretically modeling and analyzing. Aiming at its strong nonlinearity, the state-space model was firstly deduced. Furthermore, the control structure diagram was illustrated and the influences of several significant parameters to the actuator response were analyzed. The results of simulation investigations verify the correctness and usability of the state-space model.