The fractional order PI control for an energy saving electro-hydraulic system

In an electro-hydraulic system (EHS), the throttling phenomenon of the hydraulic valve leads to the problem of low utilization efficiency of hydraulic energy and severe increases in temperature. To alleviate this problem, this paper presents a type of one-chamber-controlled hydraulic circuit. In some applications where elastic load is dominant, this hydraulic circuit can achieve a significant energy-saving effect. For a valve-controlled system, the orifice non-linearity and the slowly varying parameter significantly influence the control performance of the electro-hydraulic system. With this aim in mind, the orifice compensation method is proposed to deal with the orifice non-linearity. Based on the compensation, the fractional order proportional-integral (FOPI) controller is adopted to deal with the problem of fluid parameter variation. In the controller designing process, this paper proposes a controller parameter tuning method based on system frequency characteristic data. Simulation and experiment results show that the strategy presented in this paper can reduce the energy losses dramatically and, at the same time, the control performance of electro-hydraulic system can be guaranteed.