| Compared with renewable energy sources such as solar and wind energy,wave energy has the advantages of high energy density,abundant reserves,low propagation loss and so on.Therefore,rational development and utilization of wave energy has great significance for solving global environmental problems and energy crisis.It also provides strong guarantees for achieving China’s ecological civilization construction,maritime powers,the “One Belt One Road” and other national strategic goals.The direct drive wave energy conversion(DDWEC)uses a linear generator to directly convert wave energy into electrical energy,thereby eliminating the intermediate devices such as hydraulic motors,mechanical gears and turbines.The structure of DDWEC is simple and the efficiency is high,which has broad application prospects and market benefits in the field of wave energy generation.However,due to the low average density of wave energy in China,ocean wave generally has the characteristics of low speed and frequency,which leads the DDWEC to the problems of large size,low power density and high manufacturing cost.Based on the analysis and summary of the researching status in linear generators,this paper proposes two different tubular linear generators with surface-mounted permanent magent based on field-modulated principle(FM-TLPMG)and multi-layer interior permanent magent based o flux-concentrating effect(MI-TLPMG).Working principles of these two topologies are explained and analyzed,respectively.Then,their performance are comprehensively compared and evaluated,aiming at choosing a topological structure with high power density,excellent output characteristics and strong ocean survivability.Based on the selected topology,an experimental platform is built to explore the optimal control method to improve the wave energy conversion efficiency and lay a foundation of practical application.The main research contents of this thesis include the following aspects:1.The linear wave theory is applied to analyze the hydrodynamic characteristics of the DDWEC in the wave tank.Combined with analytical model of the FM-TLPMG,the hybrid analytical optimization method for this type of wave linear generator is derived.The frequency domain method is adopted to establish the motion equation of the buoy in the wave,and the excitation force,radiation force,additional mass and damping coefficient of the buoy are calculated and analyzed.Thus,the vertical motion displacement and velocity parameters of the buoy are obtained.The buoy and the linear generator have the same velocity,and combined with the electromagnetic field analytical equation,the preliminary design scheme of the FM-TLPMG can be given in a short time,which lays a foundation for further performance optimization.The correctness of hydrodynamic and electromagnetic analytical methods was verified by wave tank experiment and generator experiment.2.The finite element model of the FM-TLPMG is established.The theoretical derivation and electromagnetic simulation are used to explain the operation principle and the key parameters of the magnetic-field-modulated effect are analyzed.In order to improve the power density of FM-TLPMG,the electromagnetic performances of different magnetization structures are compared,such as no-load induced electromotive force,air gap magnetic field,flux linkage,winding inductance,detent force,output power,etc.Meanwhile,in order to solve the mutual coupling phenomenon between the detent force optimization and the magnetic-field-modulated function of the traditional auxiliary tooth,a new type of magnetic barrier auxiliary tooth is proposed and its performance is optimized.Finally,a 16-slots/12-poles FM-TLPMG prototype is manufactured,and a wave simulation platform was built to test the performance of the prototype.3.A multi-layer interior tubular linear permanent magnet generator is proposed,and the main dimensional relationship of the generator is derived and the basic topology is given.The effects of main pole size,number of auxiliary pole layers and dimensions,primary tooth width and pole shoe geometry were analyzed by finite element method.In order to solve the problem of large detent force of MI-TLPMG,the L-shaped auxiliary tooth and inter-pole magnetoresistive structure are proposed.Meanwhile,considering the large amount number of optimization parameters,the Taguchi method is used to design the test plan.This method ensures the optimization effect and reduces the workload and time cost.A 6-slots/7-poles experimental prototype was designed and manufatured,and the finite element anlysis results was verified by wave simulation platform and wave tank experiment.Compared FM-TLPMG with MI-TLPMG in electromagnetic and mechanical aspects,the topological structure with better performance is selected as the energy conversion device of DDWEC.4.Combined with finite element analysis results,the mathematical model of MI-TLPMG in natural and synchronous rotating coordinate system is derived,including voltage balance equation,flux linkage equation,thrust equation and power equation.According to the linear wave theory,the research of the wave energy tracing strategy and grid side control strategy is carried out,and the wave power control model is established,including the converter model,the phase detection algorithm,the control model of the generator and grid side etc.The feasibility of linear Hall sensor that applied in linear generator phase detection is studied.By continuously optimizing the controller and adjusting the control parameters,the wave energy tracing strategy and power generation operation of the DDWEC is finally realized,which provides a theoretical reference and guidance for the construction of the control hardware platform.5.According to the control simulation model,the DDWEC control experiment platform is built,including current and voltage sampling circuit,linear Hall sensor detection circuit,PWM drive circuit and converter.The functions of coordinate change,wave energy tracing strategy,Hall electric angle calculation,wave speed calculation and grid phase angle detection are realized by programming language.Finally,the debugging is carried out for each module,and the control system is tested experimentally. |
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