Research On The Application Of Stochastic Control Strategy In Reducing Electromagnetic Noise Of Permanent Magnet Synchronous Motor

In the control system of permanent magnet synchronous motor,the traditional fixed carrier frequency pulse width modulation method generates high-frequency harmonics near integer multiples of the carrier frequency.The high-frequency injection method used by permanent magnet synchronous motor in low-speed sensorless operation also generates high-frequency harmonics near the injection frequency.These harmonics can cause periodic vibration of the stator,resulting in sharp high-frequency electromagnetic noise.Therefore,noise suppression measures need to be taken.The random strategy provides a new approach for suppressing high-frequency harmonics from the perspective of control methods.Random pulse width modulation technology can disperse harmonics concentrated at a specific frequency onto a wider frequency band,reducing the amplitude of harmonic spikes;The random high-frequency injection method can achieve harmonic frequency diffusion by randomly switching the injected signal between different frequencies,thereby reducing electromagnetic noise.This article first introduces the current development status of permanent magnet synchronous motors and their control strategies,and comprehensively elaborates on the reasons for noise generation,noise suppression methods,and noise evaluation standards during the operation of permanent magnet synchronous motors from both the motor body design and control strategies.In terms of control strategy,this paper selects the random carrier frequency pulse width modulation technology as the focus of this paper by comparing and analyzing the characteristics of several different random methods in the harmonic suppression ability,application difficulty,and impact on system stability.Secondly,the analytic expressions of the harmonic spectrum and power spectral density in the pulse width modulation technology are derived,and the reasons for the high-frequency harmonics in the pulse width modulation technology are explained,which provides a theoretical basis for the dispersion effect of random modulation technology on the harmonic frequency.In addition,in order to enhance the local randomness of random numbers and avoid their continuous distribution on the mathematical expectation side,this paper introduces a two-state Markov chain to enhance the statistical characteristics of random numbers.Then,this article establishes a simulation model of a permanent magnet synchronous motor random carrier frequency vector control system.By comparing the simulation results with fixed carrier frequency pulse width modulation technology,it can be seen that the frequency spectrum distribution of the inverter output voltage under random carrier frequency vector control is more uniform,and the harmonic amplitude concentrated at a specific frequency is significantly reduced.Then,this article focuses on the high-frequency noise problem caused by the fixed frequency high-frequency injection method,studies the random high-frequency injection method,derives the power density analytical formula of the high-frequency response current,and provides the conditions that need to be met when selecting the injection signal based on its mathematical relationship.Next,this paper proposes a dual stochastic control strategy combining random carrier frequency vector control and random high-frequency injection method,and builds a simulation model.The simulation results show that the random high-frequency injection method can weaken the high-frequency noise caused by the injection signal to a certain extent,and the dual stochastic control strategy can simultaneously weaken the high-frequency harmonics caused by the high-frequency injection method and the pulse width modulation,so that the power spectral density distribution of the stator voltage of the permanent magnet synchronous motor is more uniform and the spike is reduced.Finally,this paper compares the phase current power spectral density characteristics and electromagnetic noise acoustic characteristics of PMSM under different control methods through experiments.The experimental results are consistent with the theoretical analysis and simulation results.After the stochastic control strategy is adopted,the power spectrum distribution of the motor phase current of the permanent magnet synchronous motor is more uniform,and the average sound intensity level of the electromagnetic noise is reduced;The amplitude of high-frequency components concentrated at specific frequencies in noise is reduced,resulting in a more continuous noise spectrum.