Research On Control Strategy And Energy Conservation Theory Of Sea Water Hydraulic Variable Ballast System

With the international competition of marine resources gradually touches the deep and high seas,the submersible vehicles characterized by higher maneuvering capability and longer mission duration are strongly required.Variable ballast system(VBS)is one of the key subsystems to expand both the maneuvering capability and the mission duration of submersible vehicles.Compared with the other VBS mechanisms,the sea water hydraulic variable ballast system(WHVBS),which directly uses seawater as working medium and has advantages of environmental friendliness,simple construction,stable performance and extensive adjusting range,is the most popular trend of VBS.However,because of the poor operating codition and non-ideal working medium,the existing WHVBSs equipped in submersible vehicles almost were on-off type and only had the ability to inject/discharge ballast water at rated flow rate,which decreases the control accuracy of ballast water and reduces the competitive advantage of WHVBS in some varied and complex underwater missions.Meanwhile,without controlling the flow rate of the in\out ballast water,on-off type WHVBS may cause some unnecessary oscillation in underwater hovering missions,which will reduce the hovering accuracy and increase the energy consumption.In order to solve above problems of WHVBS,a flow rate control type WHVBS(FCWHVBS)and its prototype,which used four seawater hydraulic solenoid valves and a fixed displacement seawater hydraulic pump,has been proposed in this study.Aimed at the control precision and the energy consumption,the modeling approach,control strategy,energy consumption and energy-saving method of FCWHVBS have been studied in this thesis.The major research contents of this thesis are listed as follows:Firstly,based on standard 6-DOF dynamic equations of submersible vehicles,the simulation model for 2-D depth-plane motions of the submersible vehicles equipped with WHVBS has been proposed.Using above simulation model,the hovering performance of the submersible vehicles drived by the WHVBSs of different performance has been compared and analyzed in three typical operating scenarios.Based on the numerical simulations,the relationship between the performance of WHVBS and the hovering performance of submersible has been revealed,which provided a direction for following researches.Subsequently,the scheme of a flow rate control type WHVBS(FCWHVBS)has been proposed.FCWHVBS used the seawater hydraulic solenoid valve and a fixed displacement seawater hydraulic pump,which both have strong antipollution ability and were characterized by high reliability.In addition,FCWHVBS supports two flow control modes to regulate the ballast water:changing the speed of servo motors(pump controlled mode)or changing the duty cycle of solenoid valves(valve controlled mode).Based on mathematic model of the elements in FCWHVBS and the work flow of FCWHVBS,a digital simulation platform of FCWHVBS has been built,which established the foundation for following studies on the control strategy and the energy-saving method of FCWHVBS.Considering the poor flow control performance of the seawater hydraulic solenoid valve and the fixed displacement seawater hydraulic pump in FCWHVBS,the open-loop control precision of FCWHVBS cannot meet the requirement of submersible vehicle's high accuracy missions.In order to improve the control precision of ballast water,the closed-loop control form of ballast water has been introduced into the FCWHVBS and generalized predictive controller(GPC)was selected as the basic control strategy.However,when the original GPC directly used in FCWHVBS,the phenomenons of identification parameter oscillation and control performance deterioration would appear under some working conditions.Considering the nonlinear factors impacting the ballast water control performance in FCWHVBS,an improved generalized predictive control strategy(PMIGPC)has been proposed for pump controlled mode and a generalized predictive control with solenoid valve compensation(SVCGPC)has been proposed for valve controlled mode.Moreover,the validity of PMIGPC and SVCGPC has been verified by both numerical simulations and prototype experiments.Finally,in order to improve energy efficiency of FCWHVBS,the energy consumption and energy-saving method of FCWHVBS have been studied.Based on the analysis of energy flow,a energy consumption calculation model of FCWHVBS has been built and verified by the energy consumption measuring platform of FCWHVBS prototype.Addtionally,the energy efficiency of pump controlled mode and valve controlled mode has been measured and compared by the measuring platform.For the purpose of utilizing the pressure difference between the air in ballast cabin and the marine environment,a self-adaption hybrid control of pump and valves(AHCPV)has been proposed for FCWHVBS,which can reduce energy consumption of FCWHVBS in the application situations of injecting/discharging ballast water from high pressure to low pressure.Subsequently,a series of hovering control simulations in five typical operating scenarios have been conducted to verify the energy saving effect of AHCPV.Simulation results indicated that the AHCPV can futher improve the energy efficiency of FCWHVBS without enhancing the efficiency of elements.In consideration of the fact that there is no matured WHVBS supported flow control on a global scale,the researches in this theise establishes a foundation for the developments and applications of flow rate control type WHVBS.Meanwhile,some achievements in this research have been successfully applied in a WHVBS and a seawater hydraulic self-balancing system of the "(?)type underwater vehicle" and obtained a desirable result.Furthermore,the control strategy and energy-saving method proposed in this theise can also offer a reference to other seawater hydraulic systems used in marine equipment,such as:seawater hydraulic vectored jet propulsion system,seawater hydraulic tools and manipulator for underwater operating.