A three phase PLL with a dynamic feed forward frequency estimator for synchronization of grid connected converters under wide frequency variations

This paper presents a synchronization technique to accurately track the phase and frequency of the input signal under large frequency deviations. The hybrid FPLL structure consists of a conventional SRF PLL feedback loop along with a feed forward frequency estimator loop. The advantage of this technique is that the feedback controller has to reduce only the phase error and the frequency error is eliminated by the feed forward controller. This increases the dynamic response of the system under frequency deviations. The performance of the hybrid structure is compared with the conventional SRF PLL and the former shows improved performance over the SRF PLL in terms of filtering characteristics and transient response for wide range of frequency deviations. The steady state error analysis is carried out and the necessary condition for stability is also derived. Simulations are carried out in MATLAB/Simulink and implemented in real time using an ALTERA cyclone II FPGA board. The results obtained for various grid conditions such as unbalance, harmonics, phase jump and frequency deviation demonstrate the phase-tracking ability of the technique.

► SRF PLL with dynamic feed forward frequency. ► The hybrid structure is simple to implement. ► Can be extended to any existing PLL technique with constant feed forward frequency. ► Improved tracking for wide range of frequency deviations.