Research On Design And Control Strategy Of Hydraulic Power Take-Off For An Efficient And Stable Wave Energy Converter

In the 21st century,the development and utilization of energy has launched new challenges.Renewable ocean energy in the form of waves and temperature differences has become a hot spot in the domain of energy research and development.And wave energy has attracted great attention from various countries because of its lower exploitation difficulty.Wave power generation is a historical technology,going through the stages of theoretical research to sea trial.But there are still some problems to realize industrial applications,such as the wave instability which may cause the device to be in an off-design working condition.On basic of this,improving the stability,efficiency and cost performance of wave power conversion is still the focus in the domain of ocean energy utilization.Combining the current status of wave power generation and our country's sea conditions,a floating hydraulic wave energy converter is considered as the investigated target.With the reasonable research,an overall mathematical model from wave input to motor output is established and the effects of parameters on motor output is discussed.In addition,circuits of adaptive accumulator,volume-throttle speed control and hydraulic transformer are proposed,and these schemes are proved reasonably through theoretical analysis and numerical simulation.Firstly,the background and significance of this research are described.The history of wave energy conversion at home and abroad are summarized,with emphasis on the typical hydraulic energy converters.The advancement and practicability of the hydraulic PTO system are indicated,this leads to the work done by domestic and foreign scholars in improving the efficiency and stability of the system,and the research points in this field are pointed out.Secondly,the system's mathematical model is established and the key parameters affecting the motor output are analyzed.The overall model taking motor output as the goal is completed by writing components'motion mechanical equations and finding the connection between the components.To increase the credibility of the research,the main parameters that affect the motor output are determined through theoretical analysis and AMESim simulation.Thirdly,a circuit of an adaptive accumulator is built.Parameters that affect the absorption effect of the pressure pulse are found from the natural frequency of the accumulator,and the verification is conducted with simulation.To improve the absorption effect of the accumulator and reduce the system's vibration,a scheme of volume-throttle speed control is proposed and proved by AMESim and MATLAB/Simulink co-simulation technology.Fourthly,a circuit of volume-throttle speed control is put forward.To heighten the conversion efficiency of the device,the generator needs run at a constant speed.Simulations that under traditional PID control and fuzzy adaptive PID control are compared,curves of the system pressure and motor speed are showed,so as to select the better one in terms of the system's response speed and stability.Moreover,the hydraulic PTO circuit is optimized.In-depth explorations about the dynamic characteristics and robust characteristics of the adaptive accumulator circuit and the volume-throttle speed control circuit are carried out.On basic of this,technical integration is tried to ensure the system's functions include absorbing pressure pulse and running at a constant speed.The hydraulic transformer without throttling loss is introduced to construct a new form of system.Comparing the new system with the traditional one using volume-throttle speed control can offer a new trend for the research of wave energy conversion.Finally,all the works are summarized and the future research directions are proposed.In this thesis,the design and control strategies of hydraulic PTO system are studied,and the applicability of the system is proved by combining theoretical analysis and numerical simulation.The parameters affecting the system's power are analyzed,and circuits enhancing the stability and efficiency of the device are founded.Certainly,the feasible verification of all schemes are completed through the simulation platform.