Research On Pressure Stabilization Control Strategy Of Constant Displacement Pump Based Mechanical-hydraulic Energy Storage System

For the combined advantages of environmental protection, durability, high power density and low cost, hydraulic energy storage devices are widely used in engineering applications. However, the low energy density and coupling of system pressure and state of charge of traditional hydraulic accumulator reduce its utility flexibility. Existing pressure regulation method is usually by creating a variable system based on a variable pump or using the way such as throttle valves. Although these ways can achieve high precision of pressure control, they also bring huge energy losses. In order to improve energy density of hydraulic energy storage system and explore an efficient way of pressure regulation, this thesis presents a pressure stabilization control strategy for mechanical-hydraulic energy storage systems with constant displacement pump/motor. Being applied to two new energy storage systems, this strategy is verified. The main content of this thesis is as follows:(1) A new type of mechanical-hydraulic energy storage system with constant displacement pump/motor, CCPS(Constant Pressure System with Constant displacement pump/motor), is designed.(2) An analysis method of “three phases-two energy forms” is proposed to analyze the energy storage principle of CCPS and FAS(Flywheel-Accumulator System) from the angles of energy carrier and energy form, and the mathematical models of both systems are built.(3) Working modes of the two systems are divided respectively and the energy storage characteristics and pressure regulation features under each mode are analyzed as well. Based on the similar pressure regulation principle of the two systems, this thesis proposes a dynamic distribution of the energy forms to stabilize the system pressure of mechanical-hydraulic energy storage systems with constant pump/motor.(4) In order to verify the pressure stabilization control strategy, traditional accumulator system, CCPS and FAS are simulated using the constant power condition and the typical UDDS(Urban Dynamometer Driving Schedule) condition. By analyzing the simulation results, the comparison of system regulation and energy storage of the two systems is obtained, providing reference for their utility.As shown from the results, the pressure stabilization control strategy proposed in this thesis is effective for mechanical-hydraulic energy storage system with constant displacement pump/motor and meanwhile, by comparing of the two systems, although there is little difference in their pressure stabilization effect, the energy density of FAS is much higher than that of CCPS. This further exploration of energy storage potential provides FAS with better research value and market prospect while the current implementability of CCPS is better for its simple structure and low cost.