High precision and high efficiency control of pump and valves combined hydraulic system

The typical independent meter-in and meter-out technique has already shown its feasibility to achieve high precision performance and also tries to pursue energy saving in the previous works. However, this technique can not avoid the great deal of energy consumption wasted on the throttling orifices since the entire flow rate is throttling controlled by the metering valves, which leads to the essential difficulty to realize the high level of energy saving. On the other side, the direct driven pump controlled system is an option to avoid the throttling loss, but high precision tracking performance of the cylinder is complicated and challenging. In order to realize the dual objectives of high precision tracking performance and high energy efficiency, a brand new hardware configuration which combines the direct driven pump and independent metering valves is proposed in this paper. During the motion of the cylinder, the majority of flow rate is supplied by the open-loop controlled direct driven pump, while the rest flow rate is precisely closed-loop controlled by the independent metering valves. By the proposed combination, the proportion of throttling controlled flow rate is decreased significantly compared to the typical independent meter-in and meter-out system. Since the hydraulic system is highly nonlinear and with uncertainties and disturbances, the adaptive robust control approach is applied in the closed-loop control of the independent metering valves to ensure the stability and accuracy. Simulation results are shown to verify the feasibility of the hardware configuration and control strategy.

I. Introduction

Hydraulic systems have been widely used due to the key advantage of high power weight ratio, and usually four-way valves are applied to guarantee high precision [1]–[4]. However, high levels of energy efficiency cannot be achieved due to the mechanical linkages between the meter-in and meter-out orifices of typical four-way proportional valves or servo valves [5], [6]. In order to overcome this shortcoming, the independent metering technique has been put forward which uses four independent metering valves to replace the traditional four-way valve [6], [7] making the two states of the cylinder completely controllable. Therefore energy saving can be realized to some extent by reducing the overall working pressure. Some improvements based on the independent metering technique are made to attain better energy efficiency while keep high precision. For instance, a proportional cartridge valve was used to control the regeneration flow precisely [5] and an accumulator was installed to recover energy [8].