The variable-speed electrohydraulic drive has been applied in hydraulic machines having power matching means. However, further development has been restricted by its slow response and poor low-speed behavior. Owing to these disadvantages, a novel drive principle comprising a variable-speed valve-controlled-motor drive with an accumulator-based power assisted unit (PAU) is proposed. The PAU is an energy assisting and recycling device, which can release or absorb hydraulic energy according to the system's requirements. With the aid of PAU, the proposed drive is expected to improve response and control precision compared with the variable-speed drive. The proposed drive principle system is a multi-input-multi-output (MIMO) complicated nonlinear system with time-varying, which increases the control difficulty. A mathematical model of the proposed drive was first derived then a hybrid control strategy was presented. The dynamic simulations of three traditional drives and the novel one were performed using AMESim-Simulink co-simulation models. The four drives have been tested using three common variable-load disturbances. Comparisons of simulation results show that the proposed drive principle system demonstrates a good dynamic performance, which can not only achieve the expected energy saving target, but also significantly improve the response and control precision over the existing variable-speed drive system.
The variable-speed electrohydraulic drive is a promising drive principle due to its high energy efficiency and large speed-range. However, its slow response and poor low-speed behaviour limit its application. To address these disadvantages, a energy regulation based variable-speed electrohydraulic drive is proposed. This novel drive principle is combined with the advantages of variable-speed drive and valve-control drive. The speed-control of the energy regulation based variable-speed electrohydraulic drive is discussed. The speed-control strategy, which is aimed at the multiple-input multiple-output (MIMO) structure of the proposed drive principle, is analysed. The results of simulations and experiments comparing it with three other drive principle systems show that the proposed drive principle has not only a good speed-control accuracy, but also a perfect energy-saving performance.
The hydraulic accumulator is widely used for storing energy in hydraulic system, but it is a passive device; the flowrate and volume of hydraulic oil adjusted by the accumulator are not well adapted to working-condition changes or payload disturbances. A novel semiactive power-assisted unit (PAU), which is a flow valve-controlled accumulator virtually, is proposed. The flowrate and volume of the accumulator can be regulated by adjusting the spool-opening of the flow valve. The mathematical model of the semiactive PAU is deduced. Then the static characteristic and dynamic characteristic of the PAU are presented. The simulations of the proposed PAU applied in variable-speed electrohydraulic drive system are implemented. The results show the influences of PAU's main parameters on its performance.
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