Fuzzy logic based load-frequency control and a digital distance relay in power systems

Fuzzy Logic Based Load-Frequency Control and A Digital Distance Relay in Power Systems Load-frequency control in power systems is an important task for stable operation of synchronous generators. Although small oscillations caused by load changes are filtered out by system inductance and mechanical inertia, large oscillations due to fault or huge load changes must be eliminated before the system stability is lost. When a fault occurs on electrical transmission lines, it must be detected by protection relays on time for stable operation of the system. Based on the laboratory prototype setup, a dynamic model of the system comprising a dc motor as the prime mover, a three-phase synchronous generator, and a three-phase adjustable resistive load, is developed for simulation purposes. In the first part of this study, the output frequency of a synchronous generator feeding stand-alone loads is controlled using a fuzzy logic based controller. For any change in load power requirement, the controller adjusts the input mechanical power to the synchronous generator in stability limits in order to keep the speed and the frequency constant. The protection relays may be either analog or digital. However, since the development of the microprocessors, digital relays have become more preferable due to their accuracy, maintenance and low costs. Therefore, the performance of a digital distance relay is also studied here as the second part of this study. Using the same power system dynamic model described above, the relay is simulated for the faults occurred on the transmission line model that represented by three-phase adjustable resistive load. Key Words: Power systems, synchronous generator, fuzzy logic control, load-frequency control, digital distance relay, power system protection.