| With the global ecological environment deteriorating and energy shortage,the demand for electric vehicles is gradually increasing,and major domestic and foreign auto companies are further improving the related technologies of electric vehicles.In the electric vehicle motor drive system,the inverter usually adopts a fixed switching frequency modulation technology to make the power switching device turn on and off in a fixed manner,which will cause a large number of high amplitude harmonics to be generated at the switching frequency and its multiple frequency.These harmonics It seriously affects all aspects of the electric drive system,such as electromagnetic compatibility,vibration and noise.Based on the space voltage vector pulse width modulation(SVPWM)technology,this paper solves the problem of generating a large number of high amplitude harmonics at the switching frequency and frequency multiplication for fixed switching frequency modulation.Based on the permanent magnet synchronous motor vector control system,it is possible to reduce harmonics.Wave random switching frequency modulation technology is studied.Starting from changing the spectral distribution of harmonics,a method of optimizing random switching frequency modulation is proposed to further reduce the harmonic amplitude.Firstly,the mathematical model of permanent magnet synchronous motor in three-phase stationary coordinate system,two-phase stationary coordinate system and rotating coordinate system is established,which lays a foundation for the establishment of permanent magnet synchronous motor vector control system.The principle,classification and random number generation method of random modulation technology are summarized.Then,the SVPWM simulation model is established according to the implementation steps of the space voltage vector pulse width modulation algorithm,and the simulation results are obtained to verify the correctness of the model.The permanent magnet synchronous motor vector control system with i_d=0 control strategy is designed.The overall simulation model of the vector control system of permanent magnet synchronous motor based on SVPWM is built with MATLAB/Simulink software.The simulation results of the system verify the correctness of the control system.Secondly,based on the permanent magnet synchronous motor vector control system,the fixed switching frequency modulation technology is studied.At the same time,ANSYS/Maxwell software is used to simulate the air gap magnetic field of the motor.It is proved that the fixed switching frequency modulation makes the stator current and air gap magnetic field generate a large number of high amplitude harmonics,and these harmonics are concentrated in the switching frequency and Near the frequency multiplier.Then,the simulation is carried out for the traditional random switching frequency modulation of the spread spectrum.The simulation results show that the current harmonic amplitude is reduced,but the reduction is not large,the spectrum distribution is still not uniform enough,and the random performance is poor.In order to further reduce the current harmonic amplitude,the traditional random switching frequency modulation technique is optimized.By changing the random gain,the harmonic spectrum is more dispersed when the periodic signal and the random signal work together.The hybrid random switching frequency modulation is proposed,so that the harmonic amplitude concentrated at the switching frequency and its multiplier is reduced.Finally,aiming at the problem of poor random performance in traditional random switching frequency modulation,it is proposed to introduce Markov chain to optimize the traditional random switching frequency modulation to improve random performance.By statistical analysis of the random number generated by Markov,it is concluded that the introduction of Markov chain can make the random number distribution more uniform and the random performance is better.Then the random modulation of the two-state Markov chain is simulated and analyzed,and the genetic algorithm is used to optimize the parameters.Compared with the traditional random and mixed random,the resulting current waveform has a more uniform spectral distribution,reduces the current harmonic peak,and reduces the high amplitude harmonics concentrated around the switching frequency and its multiple. |
