Research On Low Harmonic Control Strategy Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motors have been widely used in fields such as electric vehicles,aerospace,and household appliances due to their high operating efficiency and torque output ratio.In practical applications,the nonlinear factors of the inverter and the design of the motor body can cause current harmonics,which can lead to torque ripple and limit the application of permanent magnet synchronous motors in many high-precision situations.Therefore,conducting a detailed analysis of the sources of current harmonics and selecting appropriate harmonic suppression methods to improve system performance is of great significance.Firstly,the basic structure and theoretical model of permanent magnet synchronous motor were analyzed,including the mathematical equations in three-phase stationary coordinate system and synchronous rotating coordinate system,and the transformation matrices of Clark transformation and Park transformation were given.A detailed analysis was conducted on the synthesis principle of the SVPWM algorithm,and the SVPWM algorithm was implemented in simulation.Secondly,in response to the current and voltage harmonics generated in permanent magnet synchronous motors,the mathematical models of the motor’s air gap magnetic field and cogging torque were derived,and the mathematical expressions of harmonic currents were obtained.Next,the permanent magnet synchronous motor vector control system was elaborated,and the impact of different control methods and modulation methods on motor voltage and current harmonics was analyzed through simulation.Once again,the influence of switch frequency and inverter dead time effect on motor current harmonics is simulated.Through the simulation results,the phase current waveforms at different switch frequencies and dead time can be obtained.Then,the relationship between dead time,switching frequency,and harmonic current was analyzed,and the relationship curve between dead time and phase current THD was obtained.Then,based on the previous theoretical analysis and design simulation,an experimental platform was built to conduct experiments on different switching frequencies and dead time durations,verifying the correctness of the simulation results analysis.Finally,in response to the problem of harmonics in the output voltage and current of the inverter being concentrated at various frequencies,periodic frequency modulation is used to disperse the aggregated harmonics into the spread spectrum range to reduce the peak harmonics,thereby solving the problem caused by the original fixed frequency modulation.The basic principle of periodic pulse width modulation for three-phase permanent magnet synchronous motor was derived,and the suppression effect of three-phase PMSM periodic pulse width modulation on motor harmonic current was verified in simulation software.