| In modern motor drive systems, PWM technology has been widely used in small,intermediate and large variable-frequency speed control system. The fixed frequency PWMtechnology which leads in problems of harmonic distribution is adopted in traditionalinverters, power switching device turning on and off in a determined way. All theseharmonic energy are located in the switching frequency of inverters as well as in itsintegral multiple. Motors are certainly performed with intolerable electromagnetic noiseand even mechanical vibration. This thesis is aimed to investigate a reasonable and feasiblePWM technology that could reduce the electromagnetic noise and improve the distributionof harmonic spectrum. Experimental platform is established and several researchesassociated with low-noise PWM are investigated.Firstly, the methodology and application status of random PWM technology areelaborated. Basic principles and classification of RPWM are concluded, in the meantime,an improved mixed frequency PWM technology is proposed. In order to avoid theoscillation of system, a novel carrier-frequency restriction PWM technology is presented.Secondly, permanent magnet synchronous motor frequency conversion speed controlsystem model based on the Matlab simulation software is established. Four PWMtechnologies are simulated and experimental and simulation results are analyzed, whichalso demonstrates those PWM technologies’ effectiveness and feasibility.Finally, experimental and simulation results of different switch frequency PWM’effects on current waveform show that high order harmonics are concentrated in theswitching frequency and its integral multiples. The proposed method has the ability ofdistributing harmonic energy into a wide frequency band and maximum harmonicsamplitude could be reduced. Special frequency band can be restricted effectively. |
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