Research On Hydraulic Marine Multi-energy Complementary Power Generation System With Seawater Medium

With the increasing of new installed wind capacity,many problems such as the maintenance costs and service life have become more obvious.As a new generation of wind power equipment,the hydraulic wind turbine has been widely paid attention.This paper has introduced the working principle and structure of an hydraulic wind turbine.Furthermore,the power transmission system of wind turbine has been studied by theoretical analysis and experimental research.By studying the power and torque characteristics of wind turbine rotors and the power transmission efficiency of hydraulic drive system,this paper has focused on the maximum aerodynamic energy capture,variable pitch control technology and energy storage control strategy of the hydraulic main drive system consisting of a variable displacement pump,a hydraulic accumulator and a Pelton turbine.For comprehensive exploitation and utilization of ocean energy,furthermore,this paper has put forward and researched two kinds of integrated power system including wind-wave and wind-tidal turbine.The main research work is as follows:(1)In this paper,the optimal power control of the hydraulic wind turbine has been realized under various wind speed conditions.Under the low wind speed,the restoring torque of hydraulic pump has been kept with that of wind turbine rotor by controlled the pump displacement.So an optimal tip speed ratio has been achieved,and the maximum aerodynamic energy has been captured.Under the high wind speed,through combining the neural network and adaptive method,and introducing "Lyapunov" stability theorem,a wind variable pitch adaptive neural network controller has been designed.As a result,the nonlinear variant pitch control problem has been solved,to guarantee the stability of control system.(2)To solve the unbalanced power between output and need,an hydraulic accumulator has been applied to this system to absorb the output power caused by the transient wind speed fluctuation.As a result,the generator output power has been made adjustable and to meet the power demand in different time.Through establishing the relation between the turbine output torque and the generator angular velocity,a new method has been put forward to control the output power of the generator by controlling the output torque of the turbine.Using designed fuzzy controller in the form of two inputs and one output,the output torque of turbine has been preciously adjusted,so the generator output power has been controlled to make it completely satisfy the power demand of containing step changes.(3)An hydraulic wind and wave energy complementary generation system has been proposed.The motion responses of buoy in the irregular wave and wave energy extraction device have been modeled.A fuzzy controller has been designed to control the displacement of hydraulic motor and to ensure the output energy match with demand.Through analyzing and comparing the average output power of wave energy device,the optimal working pressure accumulator has been selected.In simulating a hybrid system including a 5 mw wind turbine with 10 wave energy extraction device,adapting the designed fuzzy controller to preciously adjust the hydraulic motor output torque,the output power of generator has been made to meet fully the demand of power containing three step changes.(4)A hybrid wind-tidal turbine with hydraulic transmission system has been put forward,and the output energy efficiency and the exergy efficiency of the system has been analyzed.A simulation case study based on combining a 5 MW offshore wind turbine and a 1 MW tidal current turbine is undertaken.Case study demonstrates that the system output energy efficiency mainly changes between 15%and 90%,occasionally,which is more than 100%or up to 240%;the exergy efficiency changes in the range of 14.8%to 32%,and the change tendency is consistent with the changes trend of generator output power.Finally,a 5.5 kW power test platform of hydraulic wind turbine with energy storage system has been designed and set up.By simulation and experiment studying the effect of the hydraulic energy storage system on the output power and the power transfer efficiency of hydraulic drive system under random wind speed,it has been shown that hydraulic energy storage system can effectively improve the stability of the wind turbine output power,and can guarantee the output power is not affected especially in extreme conditions(wind speed less than or greater than the cut in wind speed).