| The demand for energy has been growing rapidly as a result of the fast development of society.Because of the depletion of fossil fuels and its pollution to environment,the demand of high-quality,clean and renewable energy source is particularly urgent.Wave energy is the most abundant source of ocean energy and shows advantages of high density,wide scope and renewability.The development of wave energy is at the starting phase in China and many technical problems remain to be solved.The transmission part in rotating wave energy converters needs to be sealed completely.However,the traditional sealing methods cannot assure this and will fail during long-term operation causing equipment failure.Magnetic driver,on the other hand,can guarantee complete sealing and is widely used where the requirement for sealing is high,such as in chemical plant and pharmaceutical factory.The main objective of this thesis study is to analyze the transmission mechanism and variable damping control of magnetic driver for wave energy converters.Equivalent magnetic charge method and Lagrange equations were used to analyze the magnetic driver.The magnetic driver was introduced into the wave energy converters to expand its application fields further.This thesis introduces the sealing mechanism development status of domestic and international ocean energy converters,analyses the development of magnetic driver and its theory.The object of study is the magnetic driver,which was modeled,studied theoretically and experimentally based on magnetic drive technology,mechanical design theory and modern control theory.Theoretical analysis model was built based on equivalent magnetic charge method and the transmitted torque of the magnetic driver was discussed under different conditions.Taking rectangular magnet as an example,the detailed theoretical derivation was carried out with general mathematical expression which laid a foundation for later analysis.The torque equation of the magnetic driver was derived based on the discrete characteristics and structural parameters of magnet.The thesis analyzed the torque transfer performance of the magnetic driver under different parameters such as pole numbers,radii and magnet sizes.Then the characteristic curve of magnetic driver varying with different parameters was obtained,which laid a foundation for the analysis and optimization of magnetic driver's performance.The finite element analysis model of magnetic driver was built to verify the mathematical analysis.Results showed that magnetic driver had a good performance when poles increased to a certain number.There was a best relative value between magnet width and radius.Increasing the number of magnet pole could improve the torsional rigidity and enhance the dynamics performance.The transmitted torque was positively related to the magnet width,thickness and length while negatively related to the air gap.The relationship between the maximum transmitted torque and the radius was parabolic.The analysis of installation deviation showed that the radial deviation had little influence on the magnetic driver performance and could slightly improve the torque transmission ability.However,the axial deviation had a great impact on magnetic driver performance and caused rapid decrease of torque transmission capability.The overly large axial deviation would even make the magnetic driver fail to transfer torque.Lagrange equation was used to build the dynamics performance equation of magnetic driver in this thesis.The influences of torsional stiffness,moment of inertia,damping coefficient on the dynamics performance of magnetic driver were analyzed and the response performance of magnetic driver in different external conditions were discussed.The finite element analysis model of hydraulic turbine was built according to the structural parameter of the wave energy converter.According to actual wave condition,the hydraulic turbine was simulated and analyzed,so as to obtain its kinematic characteristics.Then the dynamics performance of magnetic driver was analyzed based on its kinematic characteristics.Results showed that the increase of torsional rigidity could enhance the response of magnetic driver,shorten the response time of the driven rotor,and improve the driver's initiation performance.The increase of rotating inertia worsened the starting characteristic,and cost more time to stabilize.The decrease of damping coefficient could cause more output oscillation and prolong the adjust time,but it would shorten the response time of the output.The steady-state performance of the magnetic driver had nothing to do with its rotating inertia and was only affected by damping coefficient and torsional rigidity.The state space equation of the magnetic driver was built based on the State Space Method by which the mathematical expressions of various motion variables were obtained and the operation stability was analyzed.According to the dynamic equation and the installation deviation of magnetic driver,the angle difference equation used to measure the dynamics performance of magnetic driver was derived.The influences of the rotating inertia,the damping coefficient and the torsional rigidity on angle difference were analyzed.Results showed that the increase of the rotating inertia and the torsional rigidity worsened the transient performance of angle difference while the increase of the damping coefficient could improve it,but overly large damping coefficient enlarged stable angle difference.A variable damping coefficient control method was presented according to the above analysis,which improved the dynamics performance of magnetic driver.According to this method,a variable damping controller was designed and its feasibility was verified by the finite element method.The experimental prototype was manufactured to measure the torque transfer performance and dynamics performance of magnetic driver.Using the designed controller,the thesis tested the angle difference fluctuation suppression performance and the feasibility of the variable damping coefficient method.The experimental results showed that the deviation between theoretical analysis and experimental results was within 6%.Therefore,the theoretical equations met the engineering requirements and the theoretical analysis in the previous chapters was proved correct. |
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