Augmentation of third-octave-band sound pressure levels of an electromechanical system by sampled harmonics

Increased noise levels are commonly associated with adjustable speed drives in heating, ventilation, and air-conditioning equipment. This increase is often attributed to the switching nature of the electronics inside the adjustable speed drive. A new method, exploiting the noise originating in the switching process and utilizing the adjustable speed drive and motor combination as a type of controllable sound source, is presented. This new method achieves simultaneous closed-loop control of up to eight selected third-octave-band sound-pressure-levels.; Expressions for the magnetic field in the air-gap are developed to explore the non-linear interaction between applied terminal voltages and the air-gap magnetic field. A personal computer based program combines with a digital signal processor program to affect changes in the system noise characteristic by directly controlling the voltage applied to the motor. The techniques presented in this dissertation indirectly influence the air-gap magnetic field, and the associated structure-borne noise by operating on the applied voltages.; Randomized switching frequencies, loading, and speed variations are each evaluated in reference to their individual contributions to total system noise. The methods presented in this dissertation are evaluated by measuring the system's response to a step change in desired third-octave-band sound pressure levels. Results are presented for tests performed for varying sizes of steps and with different third-octave-bands. Conclusions pertaining to general tendencies and trends are provided.