Zero-crossing detection of distorted line voltages using 1-b measurements

In thyristor power converters, zero crossings of the line voltage signal are used for the synchronization of thyristor gating pulses. In weak ac systems, however, the line voltage can be distorted, and faulty zero crossings occur. In addition, in isolated power transmission networks, the line frequency can alter, For the detection of true zero crossings in such cases, we describe a neural network (NN), which utilizes the measurements of the three line voltage components in a three-phase power delivery system. The line voltages are measured with comparators, thus enabling low-cost implementation. The NN structure is extended by using a logic circuit, which produces the time elapsed from the previously detected zero-crossing instant as a feedback signal for the network. Thus, the knowledge that the true zero crossings occur at regular intervals in practical power delivery systems is utilized. The simulation results show that the proposed NN provides competitive performance.