Application Of Random Modulation Technology In High Performance AC Servo System

AC servo system is widely used in national defense,military industry,industrial production and daily life.Pulse width modulation(PWM)is commonly used in AC Servo Drivers,the traditional pulse width modulation technology uses fixed switching frequency,which will introduce electromagnetic noise and interference to the servo system.In this thesis,random switching frequency modulation technology is used to reduce the electromagnetic noise and interference of the system,at the same time,the influence of switching frequency on the performance of the current loop of the system is studied,and the parameter correction strategy of the controller is proposed accordingly.This thesis mainly studies the application of random switching frequency modulation technology in AC servo control system,the main contents are as follows:(1)Firstly,the basic principle of random switching frequency modulation is introduced,the harmonic spectrum distribution of PWM waveform generated by traditional pulse width modulation(PWM)and random switching frequency modulation(RSFM)is analyzed by double Fourier series theory.According to the simulation results,the reason of electromagnetic noise produced by traditional pulse width modulation and the noise reduction mechanism of random switching frequency modulation are obtained.(2)Then the influence of switching frequency on the performance of current loop in servo system is analyzed theoretically,the mathematical model of current loop is established in discrete domain.Three discretization methods are used to analyze the influence of switching frequency on the stability and dynamic performance of the system,the relationship between the switching frequency and the stability region of the system and the controller parameter region satisfying the index set is obtained,it is concluded that different discretization methods have less influence on the stability region and the parameter region of the system.(3)According to the influence of switching frequency on the performance of current loop,a parameter correction strategy based on performance index set region and gradient descent method is proposed.The first correction strategy establishes the functional relationship between the controller parameters Kp and KiT/2 and the switching frequency,so that the controller parameters vary with the switching frequency;the second correction strategy finds the controller parameters satisfying the index set at different switching frequencies according to gradient descent method,the parameters Kp and KiT/2 of the controller are updated in the direction of gradient vector{(?)qi/(?)Kp,(?)qi/(?){KiT/2)),so that the dynamic performance of the system can meet the requirements of the index set in the spread spectrum range.The effectiveness of the two correction strategies is verified by simulation.(4)Finally,the results of theory and simulation analysis are validated by the experimental platform.Firstly,the PWM waveforms and the line voltage waveforms under traditional pulse width modulation and random switching frequency modulation are tested.Through the comparative analysis of experimental results,the distribution of harmonic components of random switching frequency modulated PWM waveform and line voltage waveform is more uniform,and the electromagnetic noise of the system is reduced;then the step response of the current loop before and after correction is tested,and the validity of the correction strategy is verified by comparing the experimental waveforms before and after correction.