PLL Based Multirate Harmonic Estimation

This paper outlines a novel method for harmonic estimation based on the PLL (phase-locked loop) approach. The method combines the use of a pre-filtering analysis structure followed by down-sampler operator and PLL estimator. The filter is an adaptive bandpass filter with initial center frequency at harmonic component. As the filter is adaptive its center frequency can move toward thed harmonic (or inter-harmonic) component, attending to the case when the system frequency varies. The frequency estimation is obtained in the PLL stage. Finally, the down-sampler device reduces the computational effort. Simulation results show that this approach is faster and more precise than other PLL structures.