Analysis of high frequency noise sources on air conditioning variable speed compressors

The improvement on energy consumption requires application of new technologies in existing products. On the past decades, optimization of power consumption on variable speed rotary compressors for air conditioning applications was achieved by replacing induction motors to brushless DC (BLDC) motors driven by a frequency inversor. Besides the positive behavior of the motor type change on compressor efficiency, acoustic problems on the compressor became more complex. This article makes a revision of the main noise generation mechanism by BLDC motors of an air conditioning compressor via numerical finite element and experimental analysis aiming a noise reduction on a tonal component around 8 kHz band. Results indicate harmonic components on the forces exciting some specific resonance frequencies of the stator. The harmonic components show up in the force signals via pulse width modulation of the inverter electronic controller. The structure-born noise is radiated through the compressor shell. Among the possibilities to mitigate the noise issues, it was chosen to optimize the electronic control reduced the excitation levels of the stator and the tonal component of 8 kHz band in about 10 dB improving the sound quality of the compressor.