Harmonic control of a dual-valve hydraulic servo system with dynamically allocated flows

Modern industries face increasing demands to improve the precision and workability of equipment, leading to stringent requirements for hydraulic servo systems in terms of flow, accuracy, and output power. High-flow servo valves and multi-valve synchronous control methods have seen more applications in the industry to meet these demands. However, high-flow servo valves are expensive and have unsatisfactory performance, and synchronous control methods require servo valves to have the same hydraulic characteristics, resulting in higher cost and lower accuracy of high-flow hydraulic servo systems. Also, very little has been conducted on controlling single actuators using multiple valves. In this study, we design a novel dual-valve hydraulic servo system structure with a high-flow proportional directional valve that is connected in parallel with a low-flow servo valve and further develop the mathematical model of this dual-valve system. Next, a harmonic control scheme was proposed, which included a flow allocation layer and trajectory tracking layer. Thereby, we achieved optimal control of two valves, and robust performance was guaranteed. Finally, we investigate the relationships between the flows of two valves, the deadband of the proportional directional valve, and trajectory tracking errors. Experimental results show that the proposed control scheme can effectively adjust the output flow of each valve dynamically according to the tracking trajectory and the hydraulic characteristics of the two valves, and the tracking performance of the servo system is significantly improved. This method is promised to enable the realization of an economical, high-flow, high-precision hydraulic servo system that can be generally used in various fields, such as marine engineering and construction.