Research And Implementation Of High-performance Electric Exciter For Torsional Dynamic Stiffness Testing

Torsional dynamic stiffness,which characterizes the resistance ability of the rotating mechanical transmission system to dynamic disturbance,is an important parameter indicator to measure the dynamic performance of core components within modern aircraft steering gears,robot joints,automobile steering systems and marine propulsion systems.Therefore,the effective measurement of torsional dynamic stiffness has been a necessary means to improve the dynamic performance of modern rotating machinery transmission systems.Exciter is the key component of torsional dynamic stiffness testing system,which needs to achieve high dynamic moment output within the degree of angular displacement and the bandwidth of over 100 Hz to overcome the influence of clearance and friction in transmission system on torsional dynamic stiffness testing.Traditional electrohydraulic exciter is difficult to meet this requirement,while electric exciter that characterized by fast dynamic response,high loading accuracy,good control performance and easy maintenance has become a research hotspot in related fields.However,the design of electric loading exciter is confronted with the contradiction between high loading bandwidth and high dynamic torque output.Therefore,this thesis carries out the research work on the implementation of electric exciter from the aspects of new electromagnetic topology design,electromagnetic field rapid modeling and optimization,real-time synchronous coordinated control strategy,test system prototype development and experimental verification to achieve the key theoretical and technological breakthroughs in related research fields.Based on the sweeping test principle of torsional dynamic stiffness,the design criteria of electric exciter are proposed with analysis of the working characteristics in the torsional dynamic stiffness test.By analyzing the dynamic output performance of different electromagnetic topologies under low speed,high acceleration and high load conditions,a double stator-single rotor disc-type Lorentz motor is selected as the basic configuration of the exciter.Based on the design principles of magnetic circuit enhancement and energy concentration,a variable pole-arc ratio Halbach permanent magnet array(VPARHA)that can effectively enhance the outer ring air gap magnetic field is introduced to increase the torque density of exciter by reducing the moment of inertia and enhancing the torque output capability.According to the characteristics of disc motor which is easy to expand axially,a new topological structure of multi-disc parallel distributed dynamic loading exciter is proposed,which realizes the superposition output of torque without increasing the inertia of unit axially dimension and solves the contradiction between high loading bandwidth and high dynamic moment output.Traditional two-dimensional electromagnetic modeling method converts the disc motor along the middle diameter into a linear motor,so it cannot effectively reflect the threedimensional characteristics of the magnetic field.Therefore,considering the radial characteristics of the VPARHA structure,a quasi-3D electromagnetic analytical model of the exciter unit module is established based on the Fourier series method.The end effect caused by magnetic flux leakage and magnetic field distortion is corrected with finite element analysis.Taking the maximum value of torque density as the main design objective,the initial parameters are optimized with genetic algorithm method.The design results were verified with 3D FEM analysis and electromagnetic performance tests.Compared with traditional scheme,the proposed VPARHA improves the energy density and loading capacity by about 10% with more stable magnetic field and better linearity.Considering the difference of characteristics between the modules of the exciter,the mathematical model of the decentralized dynamic loading exciter is established.The error between the modules in the synchronous rotating coordinate system is analyzed and then a multi-disc cooperative control strategy based on the master-slave control structure is proposed.On the basis of load balancing,a mathematical model of torsional loading system considering the stiffness of transmission link is established.The response speed and following accuracy of the loading system are improved with differential negative feedback PID control.The antiinterference ability of the loading system is also promoted with structure invariance principle feedforward compensation and differential forward fuzzy PID control methods.A real-time environment based on RTX for torsional dynamic stiffness testing is constructed to ensure the real-time performance of the exciter loading signal output and sensor signal acquisition.Based on the proposed vibration exciter design method and control strategy,a prototype of the electric torsional stiffness testing system with precise repeat positioning function was built.The proposed high-performance exciter scheme was verified by the response capability tests and the torsional dynamic stiffness test of an electromechanical system transmission unit.The experimental results showed that the output dynamic torque amplitude of the prototype reaches 40 Nm and the tracking error was less than 10% under the condition of ±1 degree angular displacement and 120 Hz sweep frequency loading.With the verified methods and strategies,this thesis provides theoretical basis,technical support and case verification for product development in related fields.The proposed dynamic stiffness testing system has been applied in a research institute.