Active Noise Reduction Technology Of A High Performance AC Servo System

The traditional fixed switching frequency PWM modulation method will cause high frequency electromagnetic interference,especially will produce the harmonic that concentrates on the switching frequency and its multiplier.As a technology that can effectively suppress harmonics,random pulse width modulation technology attracts more and more attention.It can break up the distribution of harmonics and make the harmonic spectrum distribution of inverter output voltage and current more continuous,The distribution of narrow-band harmonics distributes over a wider frequency band and reduces the magnitude of the harmonics,thereby reducing electromagnetic noise and electromagnetic interference.The thesis firstly introduces the principle and classification of random pulse width modulation(PWM)technology,and compares and analyzes the characteristics of different random PWM techniques in the aspects of current fluctuation,current sampling,modulation ratio,closed-loop implementation and spread spectrum performance.The modulation technique of random center symmetry modulation and the carrier frequency random change have more advantages than the other two kinds of stochastic modulation techniques in the above aspects.Therefore,the modulation techniques of random center symmetry modulation and random change of carrier frequency will be mainly studied later.Secondly,the realization principle and existing problems of random center symmetric modulation technique with constant carrier frequency are studied.Random center symmetric modulation is realized by randomly changing the allocation ratio of two zero-vector acting time,the carrier frequency is constant,However,since the degree of freedom of the method depends on the action time of the zero vector,the action time of the zero vector decreases as the modulation ratio increases,and the degree of freedom declines at this time,which affects the performance of the method.As for the spread spectrum performance of random center symmetric modulation,which is affected by the modulation ratio,this thesis studies a modulation mode that the carrier frequency is not changed randomly by the modulation ratio,and considers the delay of the current loop of the servo system,we design a pulse-width modulation technique with random sampling frequency,analyze the influence of random sampling frequency on the stability and dynamic performance of the system,and then determine the range of spread spectrum according to the theoretical analysis.Thirdly,the power density spectrum of the drive waveform,phase current,phase voltage and line voltage are simulated respectively by the random center symmetric modulation technique and the random variable sampling frequency pulse width modulation technique by Matlab/Simulink,and compared with the traditional SVPWM modulation.The comparison shows that the random pulse width modulation technology can effectively disperse the spectrum distribution and make the spectrum distribution more continuous.Finally,the hardware design and software design of the AC servo system are carried out to verify the experiment.Mainly in the hardware design of the power circuit,power circuit and sampling circuit design.In the software design using TI's TMS320F28335 experimental programming.Through experiments,the traditional SVPWM modulation and random pulse width modulation are respectively compared and analyzed.The experimental results are consistent with the simulation results,and the validity of the algorithm is verified.