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This paper presents a detailed analysis of Type-3 PLL under wide variation in input voltage and frequency. Using small signal modeling, the performance of both single loop and dual loop type-3 PLL for variation in input voltage and frequency is studied. The analysis shows that for the same bandwidth, both the single loop and dual loop Type-3 PLL exhibit similar dynamics provided the supply voltage is balanced. However, under voltage sag conditions, dual loop PLL shows improved dynamic response without affecting its stability. Further, the tracking time is reduced as the feed forward frequency is a function of supply frequency. To improve the filtering characteristics under frequency deviations, a dual loop Type 3 adaptive PLL which accurately tracks the phase and frequency of the input signal under wide frequency deviations is developed. Simulations are carried out in MATLAB and experimentally verified by implementing in ALTERA cyclone II FPGA board.

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