Research On The Random PWM Technique Of Permanent Magnet Synchronous Motor

The integrated motor drive system composed of power switching devices and permanent magnet synchronous motor(PMSM)has broad application prospects in the fields of ship equipment electric propulsion systems,power systems,and new energy vehicles due to its high-power density and strong controllability.To obtain good dynamic and static characteristics of the drive system,the inverter drive system usually uses the pulse width modulation(PWM)technique to modulate the DC bus voltage,but the high voltage change rate(dv/dt)makes the PWM harmonic energy concentrated at the switching frequency and its multiples.These PWM harmonics not only make power devices generate electromagnetic noise during operation,which reduces the acoustic comfort of the system but also increases the emission level of electromagnetic interference.Therefore,the contradiction between the integrated design of the motor drive system and the performance requirements of low PWM harmonic content severely restricts the application of the motor system in low-noise applications.The paper takes the integrated PMSM system as the research object and studies the motor modulation strategy for efficiently suppressing PWM harmonics to obtain better control performance.Firstly,the mathematical model of the three-phase PMSM in the natural coordinate system and the dq coordinate system is established,and the basic principle of the space vector pulse width modulation(SVPWM)technique is analyzed based on the two-level voltage source inverter.The mathematical expression of PWM harmonics in phase voltage is deduced,and the characteristics of PWM harmonics under different modulation ratios are intuitively displayed through simulation.Secondly,based on the traditional SVPWM technique,the switching period or pulse position is randomized,and a pseudo-random number generator(PRNG)is constructed using the Mersenne Twister algorithm and linear feedback shift register(LFSR).The mathematical expression of the power spectrum(PS)of the random pulse position(RPP)SVPWM technique and the random switching period(RSP)SVPWM technique is deduced and the inner connection between the PS and the pseudo-random number sequence is revealed.The effects of different PRNGs on the suppression effect of PWM harmonics at the switching frequency and its multiples in the PS are compared through analytical calculation,simulation,and experimental results.Thirdly,the discrete random switching period(DRSP)SVPWM technique is proposed,which randomizes the switching period according to a predefined frequency sequence so that the narrowband harmonics extended to a wider frequency range.The probability density function of the frequency sequence is connected with the harmonic distribution,and the influence of discrete uniform distribution and discrete Beta distribution on the spreading effect is studied in detail.Meanwhile,the PS mathematical expression of the DRSP-SVPWM technique is derived,and the relationship between the discrete random factor and the PWM harmonic energy distribution is studied.Taking the minimum harmonic expansion factor as the control objective,the optimal probability density function is selected.The analytical calculation method proposed above and the DRSP-SVPWM technique have been verified in detail by experiments.Finally,to further suppress PWM harmonics,based on the DRSP-SVPWM technique,dual discrete random factors are introduced to randomize the switching period and pulse position,and the DHDRC-SVPWM technique is proposed.The paper studies the digital implementation process of this technology based on the Infineon microcontroller AURIX-TC264.According to the stochastic process theory,the influence of dual discrete random factors on the maximum harmonic peak in the PS is analyzed,and the influence of different modulation techniques on the efficiency of the drive system is studied.The optimal parameter combination of the discrete random sequence is determined through analytical calculation,simulation analysis,and experimental verification,to optimize the working performance of the technique.This paper systematically studies the discrete random SVPWM technique applied to three-phase PMSM,which provides a theoretical basis for the design and selection of discrete frequency sequences.The present study provides a reference to investigate random SVPWM and improve electromagnetic interference and noise in power converters.