| As the global energy and environmental problems become more and more serious,new energy sources represented by solar energy,wind energy and hydrogen energy are developing rapidly,which in turn promotes the rapid improvement of the level of energy storage technology.Meanwhile,the development of new energy vehicles represented by pure electric vehicles is rapid,but the single-energy pure electric vehicles can not take into account the dual needs of energy storage density and power density,the use of composite energy storage methods can solve the problem.Flywheel battery energy storage technology is especially suitable to make up for the shortcomings of the low power density of chemical power batteries because of its advantages of high energy storage density and efficiency,fast response time,high instantaneous power,and green environment protection.However,there are still more critical technical problems in the vehicle high speed flywheel energy storage technology that restrict its performance improvement,among which the support bearing has the greatest impact on its performance.Therefore,this thesis focuses on the design of rotor support structure of flywheel battery,design and optimization of radial and axial electromagnetic bearing,analysis of loss and temperature field of electromagnetic bearing,design of discrete sliding mode controller of electromagnetic bearing,etc.from the aspect of low loss support technology of flywheel battery.Details of the study are as follows:（1）The design and modeling simulation of the rotor system structure of the magnetic levitation supported flywheel battery was completed.The theoretical basis of electromagnetic levitation is introduced.Then,the working principle of electromagnetic bearing was analyzed and the mathematical model of electromagnetic suction force of electromagnetic bearing was established.The dynamics of the single-degree-of-freedom electromagnetic bearing was analyzed and its dynamics equations were derived.And then,two types of flywheel rotor shaft support structures were designed and finite element models were established according to the characteristics of magnetic levitation support,and the final support scheme is determined by simulating and comparing three aspects:modal analysis,unbalanced force harmonic response analysis,and critical speed analysis considering rotor gyroscopic effect,which provides the basis for establishing the design specifications of electromagnetic bearings in the following.（2）The design,optimization,and simulation analysis of electromagnetic characteristics of radial and axial electromagnetic bearings were completed.The technical specifications of radial and axial electromagnetic bearing design were determined and the structural parameter calculation was completed.Then,using the multi-objective optimization method based on the NSGA-ⅠⅠalgorithm,the parameters of the designed radial and axial electromagnetic bearing structure are optimized with the maximum electromagnetic force and minimum volume as the optimization objectives and the optimization model was obtained,and the minimum space volume of the axial and radial electromagnetic bearings was reduced by 9.37%and 16.58%respectively under the premise of ensuring the maximum electromagnetic force in one direction to meet the technical specifications.And then,the optimization model was modeled and simulated using the electromagnetic simulation software Maxwell,and the bias currents of both radial and axial electromagnetic bearings were determined to be 1.5 A based on the current stiffness and displacement stiffness specifications,and the control currents were varied from-1.5 to 1.5 A.The linear analytical solution of the bearing electromagnetic force was compared with the finite element simulation solution by mutual calculation verification method,and the rationality of the design model was proved.（3）The loss analysis calculation and temperature field simulation analysis of radial and axial electromagnetic bearings were completed.To consider the bearing temperature rise due to bearing power loss,the different loss types of the electromagnetic bearing designed above were analyzed.Then,the iron loss power simulations of radial and axial electromagnetic bearings were carried out using Maxwell software with different current excitation and different speed.And the temperature rise process,temperature,and heat flow distribution characteristics of radial and axial electromagnetic bearings due to power loss in different cases were obtained by using Workbench software to couple the calculation results into the temperature field.Among them,the axial solenoid bearing reached a maximum temperature of 89.30℃in 9164 s of continuous operation at the maximum operating speed of 45000 r·min-1,and the radial solenoid bearing reached a maximum temperature of 127.34℃in 7526 s of continuous operation at the maximum operating speed.（4）The design and improvement of the active electromagnetic bearing discrete sliding mode controller were completed.A mathematical model was developed and its discrete state equations were derived for the single-degree-of-freedom differential control of radial electromagnetic bearings.Then,the digital PID control law and the discrete sliding mode control law based on the exponential convergence law were designed and the response of the start-float condition was compared to highlight the advantages of the discrete sliding mode control law.The sliding mode control method was analyzed and the traditional discrete sliding mode control method was improved by using the switching gain adaptive method to force the sliding mode switching area to shrink gradually at the origin to reduce the sliding mode amplitude in the middle and late stages of motion.And then,the boundary layer adaptive method was used instead of the switching function to reduce the large amplitude of the first stage of the sliding mode motion of the system and to ensure good robustness in all stages of the sliding mode motion.As verified by the simulation of the start-float condition,the control signal amplitude at a steady state was reduced from about 0.12 A in the conventional sliding mode control to nearly0 A.Finally,two kinds of non-random base excitation and one kind of random excitation simulation were used to analyze and verify that the simulation results were significantly better than the traditional sliding mode control. |
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