Design And Implementation Of Spread-Spectrum-Based Permanent Magnet Synchronous Moter Control System

In order to obtain higher control precision in modern permanent magnet synchronous motor control,Space Vector PWM,(SVPWM)is generally adopted,but it will gather harmonic clusters with higher amplitude in narrow band around switching frequency and integer multiple.On the one hand,the harmonic energy conducted to the inverter circuit along the conductor will interfere with the normal switch of MOS tube,and may also flow into the motor to affect the normal operation of the motor.On the other hand,higher harmonic peaks will pass through the closed loop formed by the motor phase line and the inverter circuit and radiate electromagnetic interference to the external space.Firstly,this paper expounds the mechanism of electromagnetic interference in traditional SVPWM modulation,and points out that it comes from narrow-band harmonic clusters caused by high-speed on-off of switching devices at fixed frequencies.Then,from the angle of motor modulation strategy,the harmonic distribution characteristics of inverter output in traditional SVPWM modulation are derived,and random spread spectrum modulation strategies-random switching frequency modulation and random zero vector modulation are introduced.It suppresses harmonic peaks and spreads the spectrum by means of spectrum relocation.Then,based on the characteristics of random modulation with random signals,the above two random spread spectrum modulation strategies are studied from the perspective of Fourier transform and power spectrum.The results show that the randomization of the two degrees of freedom of switching frequency and zero vector can be independent of each other,so their EMI suppression capabilities can be superimposed on each other.Therefore,based on this,a double random spread spectrum modulation strategy is proposed.In the modulation strategy,the suppression capability fatigue of zero vectors under high modulation index is optimized,and the local distribution of random numbers is made more uniform through a four-state Markov chain,so that harmonic peak suppression and frequency spectrum are more effectively expanded.In this paper,the simulation models of permanent magnet synchronous motor drive system including random spread spectrum strategy are respectively built on Matlab Simulink simulation platform.Based on STM32F103 control chip,the software and hardware of the random spread spectrum permanent magnet synchronous motor drive system are designed in detail,and the measurement platform is built.Then,the phase current amplitude spectrum and power spectrum of different modulation strategies under different modulation index are compared and tested on simulation and measurement platforms respectively.The simulation and measured results both verify the effectiveness of the double random spread spectrum modulation strategy based on the four-state Markov chain in harmonic suppression and spectrum expansion.Compared with the traditional SVPWM modulation strategy,the peak value of phase current power spectrum harmonic is reduced by at least 5.735 db,and the harmonic spread factor is reduced by at least 60%,which achieves the expected design target.The research results of this paper have certain value to restrain EMI of electric drive system from the angle of control strategy.