Research On Torque Characteristics And Optimization Design Of Axial Flux Permanent Magnet Hysteresis Brakes

Electromagnetic brakes are widely used in the braking system of industrial equipment to provide stable braking force for equipment.Traditional electromagnetic brakes need to be used with power supply and control systems,which is not conducive to the miniaturization and weight reduction of equipment and cannot meet the needs of use when there is no power supply.Axial flux permanent magnet hysteresis brakes(AFPMHBs)have the advantages of simple structure,constant and adjustable output torque,high torque density,and no external power supply,which is more suitable for use in small and medium-sized equipment or harsh environments.However,as the output torque adjustment range of AFPMHB cannot be altered externally,precise torque calculation is crucial during the design phase.At the same time,the output torque of AFPMHB is affected by rotational speed and temperature,and current products tend to experience significant torque drops during continuous operation under large slip power,making it challenging to meet the requirements of certain applications.To develop the high-temperature stable AFPMHB,this thesis systematically studies the precise simulation of the hysteresis effect,the modeling and analysis of the AFPMHB,and the development and testing of the high-performance AFPMHB.In terms of the precise simulation of hysteresis effects,a modified vector Jiles-Atherton(JA)model is proposed by introducing two correction coefficients that vary with the maximum magnetic field strength or the maximum magnetic flux density,which greatly reduces the simulation error of the vector JA model for local hysteresis loops.To improve the usability of the modified vector JA model,a combination method combining the formula method and genetic algorithm is proposed to identify JA parameters.This algorithm has both the calculation speed of the formula method and the calculation accuracy of the genetic algorithm.The Hook-Jeeves direct search algorithm is used to identify the correction coefficients and has fast calculation speed and stable identification results.The magnetic characteristics of ferrochrome-cobalt are measured,and the vector JA model and modified vector JA model are respectively used to model them.The results show that the modified vector JA model can greatly improve the simulation accuracy of local hysteresis loops.A computational process coupling the modified vector JA model with the finite element method is established,which enables the modified vector JA model to be used for simulation calculations of three-dimensional hysteresis problems.In terms of modeling and analysis of the AFPMHB,a high-precision electromagnetic finite element(FE)model coupled with the modified vector JA model is established.To improve the calculation,decoupling the hysteresis characteristics from the eddy current characteristics.Ignoring the eddy current effect in the rotor when analyzing the hysteresis characteristics,the scalar magnetic potential can be used to build the FE model of the hysteresis characteristics.The method of the stator remanence as a function of time instead of rotor rotation is proposed,which eliminates the motion domain of the FE model and reduces the calculation time from tens to hundreds of hours to tens of minutes.Based on the FE model of the hysteresis characteristics,the influence of the dimensional parameters of the AFPMHB and the stator magnetic characteristics on the hysteresis torque is analyzed and the design principles are summarised.In the analysis of the eddy current characteristics,the hysteresis effect in the rotor is ignored and the steady-state eddy current characteristic FE model is established to analyze the influence of the rotor dimensional parameters on the eddy current torque.To suppress the eddy current effect in the rotor,the method of splitting the rotor along the radial direction is proposed,which can reduce the eddy current torque by about 60%.A steady-state heat transfer FE model of the AFPMHB is established,and the temperature distribution of the AFPMHB is analyzed when the heat transfer is stable at different slip powers.There is an obvious temperature difference between the stator and rotor of the AFPMHB.A high-temperature parameter calculation process is established for calculating the temperature and the output torque after heat transfer stability.The calculation results show that the output torque decreases with the increase of slip power.In terms of the development and testing of the high-performance AFPMHB,the design process of the AFPMHB is established to design a customized AFPMHB with high-temperature stability,taking the usage requirements of a high pulsed magnet winder as an example.To assess the reliability of the theoretical analysis,a test platform is built and the hysteresis torque and eddy current torque of the AFPMHB at different stators,different air gap sizes,and different rotor thicknesses are tested.The results validate the accuracy of the electromagnetic model and the feasibility of the design theory.A customized AFPMHB prototype is developed and fully tested.At a rotational speed of 200 rpm,the output torque adjustment range of the prototype is 2.97 to 10.27 Nm,and it could run continuously,fully meeting the design requirements.To improve the output torque adjustment range,an adjustable gap AFPMHB topology is proposed,and a structure for air gap adjustment is designed,of which the electromagnetic and temperature characteristics are analyzed.The prototype is developed and tested and simulation and experimental results show that the adjustable gap AFPMHB has a smaller minimum hysteresis torque and a larger output torque regulation range than the equal air gap type when the maximum hysteresis torque is the same.