Modeling and Theoretical Analysis of Zero-Flowrate-Switching Control Method for a Dynamic Load System to Reduce Switching Power Loss of Control Valves

Abstract

Valve switching is one of the most important power losses in digital hydraulics. In this paper, a dynamic Zero-Flowrate-Switching (ZFS) control method is developed for hydraulic/pneumatic systems. The proposed control strategy is to actively reduce the flowrate passing through the valve to zero before switching off the valve. To realize it, an accessory line, in which a RLC oscillator is applied to generate a sinusoidal flowrate, is allocated parallel to the main control line for flowrate regulation. The pressure, with high frequency and small amplitude wave outputs from a regular piston pump, is used to drive the RLC oscillator. To evaluate the performance of this strategy, mathematical models for switching power loss and pressure pulses are developed and characteristic analysis is conducted. The results show that the energy loss of the system when applying the dynamic ZFS controller is reduced to 16% compared to that of a normal hydraulic system without a dynamic ZFS controller; moreover, pressure pulses in a dynamic ZFS system are much more minor than those in a Hard-Switching system.