Synchronization to utility network signals containing a high level of disturbances

This paper presents a digital signal processing system for synchronization to AC utility network signals containing a high level of disturbances. The system is based on a multirate phase-locked loop (PLL). The main advantages of the multirate approach are that it relaxes the implementation of the antialiasing filter and it enables one to accommodate the varying amplitude of the input signals. The antialiasing filter, which is in this case a high order bandpass filter, is implemented in the digital part of the system. This feature is achieved by applying the oversampling technique to the input signal. The antialiasing filter automatically adapts to the input signal frequency through the system´s variable sample rate operation. The paper deals with modeling, analysis and implementation issues of the proposed system. Nonlinear and linear state-space models and a transfer function model are derived. The system´s control aspects are discussed using the derived transfer function model. The implementation issues are presented and a digital signal processor based implementation algorithm is given. Tracking properties of the implemented system are tested with realistic signals such as a sinusoidal signal containing notch type disturbance and noise and an arc furnace voltage signal.