Active noise control of vibroacoustic noise from HVAC system in autonomous bus using conjugate gradient-based algorithm

The paper presents a new active control algorithm for the active cancellation of vibroacoustic noise radiated from the compressor installed under each passenger’s seat in autonomous bus. The compressor is used for a heating, ventilation, and air-conditioning (HVAC) system which provide air conditioning for each passenger in autonomous bus. The sound radiated from the compressor of the HVAC system is a high-frequency annoyance noise caused by vibroacoustic noise due to the shell vibration of the compressor. The dominant frequency components of the vibroacoustic noise are harmonics of the rotation frequency of the reciprocating compressor. The HVAC system generates vibroacoustic noise dominantly in the frequency range between 200 and 600 Hz. Such noise is not only distinctly perceptible but also contributes to passenger discomfort and negatively impacts the perceived quality of the vehicle. The aim of this paper is to attenuate the vibroacoustic noise of the HVAC system by developing an active noise control (ANC) system. Generally, the widely recognized filtered-X least mean squared (FXLMS) algorithm has been successfully implemented to active noise control of reciprocating compressor. However, its performance was found lacking outside the peak frequency of compressor operation noise. To address this, the conjugate gradient algorithm was employed to enhance ANC performance. The conjugate gradient algorithm has a lower residual error and faster convergence rate compared to the FXLMS algorithm. As a consequence, the implementation of the conjugate gradient-based ANC algorithm resulted in enhanced noise reduction not only at the peak frequencies, which correspond to the compressor operation frequency, but also in frequency ranges outside these peak frequencies.