Investigations on intelligent controllers for load frequency control in co-ordination with HVDC links and communication time delays

Abstract

The Load Frequency Control (LFC) problem has been a major subject in electrical power system operation and is becoming more significant recently with increasing size, changing structure and complexity in interconnected power systems. Electric power system consists of a number of control areas, which generate power to match the power demand. Control areas are usually interconnected to meet out the power demand. However, poor balancing between generated power and demand will cause the more complexity and less reliability of interconnected power systems. Insufficient transmission capability of interconnected power systems leads to bottlenecks in the system and reduce the system stability. In an electric power generation, disturbance caused by load variation will result in deviation of power frequency from its nominal value and creates inadvertent power exchanges between control areas. To overcome such a situation, the modern interconnected power system network requires high performance Automatic Load Frequency Controller (ALFC) and its implementation for a wide range of frequency variations. The ALFC performs the speed variation in governors based on the load variation to maintain system frequency within the specified limit. Various intelligent control techniques have been proposed to solve frequency deviation problem in the power system network by considering area interconnection with AC line. In the recent years, focuses are given to use High Voltage Direct Current (HVDC) transmission line in parallel with AC transmission line to satisfy the power demand. HVDC transmission has merged as a reliable system on power scenario due to its numerous economical and technical advantages. In a parallel AC-DC interconnected power system, a DC transmission system can effectively cooperate with an AC transmission system in improving the system stability by reducing the frequency deviation in the AC system under disturbance.