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A Comparative Study of the Three Most Frequently Used PLL Techniques

Swagat Pati, Sarthak Chand, Santosh Achaya

This paper represents a comparative analysis between conventional SRF-PLL, notch filter based PLL and double decoupled SRF-PLL both under balanced and unbalanced voltage conditions. Nature of phase angle, angular frequency and positive and negative sequence voltage components for different techniques are studied. It shows that conventional SRF-PLL technique gives suitable response till balanced voltage condition prevails. At the moment system became unbalanced SRFPLL response suffer from double frequency oscillation which makes it unreliable. Then notch filter based PLL technique is analysed. Here the unbalanced condition response is improved but the system suffers form comparatively large settling time. It also suffers from overshoot and undershoot at transient period making the estimation rather critical at that point. Finally an improved SRF-PLL with decoupling network and low pass filter is described called DDSRF-PLL. This method separates out the positive and negative sequence components initially by means of decoupling network there by eliminates the double frequency vibration in the response. it also has faster convergence and smooth transient response then that of notch filter based PLL the whole simulation is done in matlab/ simulink and a comparative statement is established.