Study On PMSM Random PWM Technology

The pulse width modulation is typically used with a fixed switching frequency, whichmakes the inverter generate electromagnetic noise at the integer multiples switchingfrequency and it’s around as well as mechanical vibrations of the motor. In this paper,random pulse width modulation technology is studied. By theoretical derivation,simulation and experiment, it is shown that the technology is effectiveness and feasibilityto reduce electromagnetic noise and mechanical vibration.In this paper, a PMSM motor is taken as the control target. Mathematical model andcontrol method are studied, and the system simulation model based on Matlab-Simulinkis established.Firstly, the spectrum of motor’s line voltage, phase voltage and current are comparedbetween SVPWM and random switching frequency SVPWM (RSFSVPWM) bysimulation. It can be seen that using RSFSVPWM can significantly reduce harmonic,which is generated at switching frequency and it’s around. It makes the electromagneticnoise like band limited white noise, and enhances the electromagnetic compatibility of thesystem. However, this method does not change the total harmonics, but the originaldiscrete harmonic spectrum can be changed to a continuous spectrum of the entire band, soas to achieve the purpose of noise reduction.Secondly, the hardware system were built based on Texas Instruments’(TI) motormicrocontroller chip TMS320F2812, which is the main controller of system. A1.8kWPMSM motor is selected as the control object, the system was realized algorithm based onthe hardware and the random switching frequency SVPWM control strategy is achieved atlast.Finally, the motor’s voltage and current spectrum are analyzed between the SVPWMand random switching frequency SVPWM control strategy. It is shown that random switching frequency SVPWM control strategy can well solve the problems ofelectromagnetic noise and mechanical vibration caused by PWM drive.