A Frequency Adaptive Harmonic Extraction Method for the Variable Speed Motor Drive Systems

The extensive use of inverters and variable frequency drives (VFDs) introduce harmonics because of pulse width modulated signals. These harmonics reduce power quality, increase losses, and affect the safety of the motor drive system making harmonic detection inevitable. The recent surge in induction motor-based electric vehicles (EVs) also forces the need for a harmonic detection method for proper monitoring. However, the conventional methods used for harmonic extraction mostly relate to the Fourier transform, lock-in amplifier, and other modified versions. These methods show a deterioration in the component extraction performance in an environment with disturbances such as frequency drift, DC offset, and high distortion. In addition, these methods need high computational power and large storage memory. To rectify the limitations of the conventional method, this article proposes a novel frequency adaptive fundamental and harmonic detection method for motor drive systems with a digital lock-in amplifier-based frequency-locked loop (DLIA-FLL). This method, with the capability to track fundamental frequency to provide accurate results in an environment with DC offset, frequency drift, and high distortion, can help with efficient monitoring and safe operation of the motor drive system. Mathematical modeling of the proposed method along with experimental evaluation results are presented. ZERA COM3003 is used as a reference instrument for comparative analysis.