Study On Stability And Control Strategy Of Hydraulic Wave Power Generation Device

Oscillating float type wave energy generator is an important form of ocean wave exploitation,because of its easy installation and modularized manufacture.Due to the variability of the marine environment and limitations of the research equipment structure,the wave power generation device has low generation efficiency and poor output stability.It is necessary to analyze the key influencing parameters in the process of energy transmission,and to study the control strategy of hydraulic energy and electric energy conversion.In this study,we examined the stability of energy transmission of oscillating floating wave-energy generator,and explored control strategies of energy transmission.In addition,by theoretical calculation,numerical simulation,modeling simulation and other methods,we investigated the wideband acquisition performance of the float.Moreover,we optimized the hydraulic energy transfer system(Hydraulic-Power-Take-Off,HPTO)and its variable damping control strategies,as well as the control strategy of power management system.AMESim and Matlab/Simulink were used for joint simulation analysis to study the influence of different hydraulic component parameters on the stability of power output.Based on the above research,we first built a semi-physical platform for wave energy power generation andperformed analysis to experimentally verify the validity of the control strategy.Next,we built a physical platform on the basis of the semi-physical analysis,to perform actual wave energy power generation experiments on land.Finally,we compared the experimental results and theoretical simulation results analysis,summarized the regulating rules under different simulated wave conditions,and further optimized the control strategy.In the first two chapters of this thesis we introduced the research background and engineering application of wave-power generation device,presented the current development of absorption wave energy power generation device,and analyzed the trend of this research field and.Then,we put forward the aim and strategy for this research and analyzed the hydrodynamic characteristics of point absorption wave power device.Because the wave energy conversion characteristics are closely related to the damping characteristics of the float and the hydraulic energy transfer system,we also analyzed the steady-state response of the wave power plant and formulated an impedance expression of the wave floating body to establish the relationship between the power capture bandwidth and damping characteristics.Thereafter,we performed the hydrodynamic simulation calculations,derived the added mass factors,additional damping coefficients,excitation amplitudes and phase variation curves under frequency change,and obtained the best damping values.In the third chapter of this study,we examined the speed control strategy of the variable motor in the hydraulic energy transfer system as well as the control strategy of the main hydraulic cylinder simulating wave motion,aiming to stabilize the power output.Using the active hydraulic cylinder of the experimental platform and a load,we simulated the motion of the oscillation float in certain sea conditions.To ensure the accuracy,we put forward an adaptive sliding mode control strategy based on the gait,which can overcome the influence of uncertain parameters in nonlinear system state equation.We compared the proposed control strategy with the PID control method,providing basis for the research on the control strategy of the variable motor.We established a variable speed motor volume state equation and examined the motor volume speed control strategy based on feedback linearization.However,this control strategy erroneously generated oscillation in the motor speed when a load disturbance occurred.In order to improve the anti-interference ability of the control strategy,a volume control strategy of hydraulic motor based on external disturbance observer was proposed.The effectiveness of the control strategy was experimentally verified.The error of the hydraulic motor speed in tracking the sine wave or constant speed was small,only 0.2%of the maximum speed.The stability of power output was thus improved effectively.In the fourth chapter,the main components of the hydraulic transmission system of the actual wave power marine equipment were mathematically modeled.Matlab/Simulink and AMESim combined simulation software was used for simulation analysis.The influence of the inflating pressure of the accumulator and the opening of the throttle valve on the output power stability was analyzed.And the operation response of wave power generation device under different wave amplitude and period was simulated analyzed,and hydraulic motor speed control was analyzed in the simulation.In the fifth chapter,an experimental platform for marine equipment was built on land,and the operation characteristics of hydraulic energy transfer system in actual marine equipment were further examined through land experiments.The effects of different accumulator parameters,different loads and throttle parameters on the energy stability of output points under the conditions of wavelets and starting waves were analyzed.The simulation analysis and theoretical calculations were verified,and the regulation rules of parameters under different wave conditions as well as the output power curves under different loads were summarized.By experimental study,we further optimized the hydraulic energy transfer system design and proposed a wave power generation device based on hydraulic variable damping principle.In this way,we could improve the power generation efficiency and guarantee the operation safety of the hydraulic energy transfer system.We also looked into the hydraulic oscillation problem in the hydraulic system caused by the variable damping control of the electromagnetic directional valve,and put forward an electromagnetic directional valve control strategy based on Kalman prediction.Furthermore,we experimentally verified the effectiveness of the control strategy.In the sixth chapter,the control strategy of power management system was studied.Through land experiments,we corrected the output power instability problems caused by the constant power control,and put forward an adaptive droop control strategy based on the low pass filter.Experimental study on the stability characteristics of the control strategy was carried out.and results showed that the proposed control strategy can adjust the sag coefficient rapidly according to the de voltage deviation,reduce the steady de voltage deviation,and improve the stability of power output.