Discrete-Mode Automatic Generation Control of a Two-Area Reheat Thermal System with New Area Control Error

Most of the work reported in the literature pertaining to Automatic Generation Control (AGC) of interconnected power systems is centered around tie-line frequency bias control strategy. Supplementary controllers are designed to regulate the area control errors to zero effectively. Several modern design techniques have been used to optimize the parameters of the supplementary controllers. Supplementary controllers regulate the generation to match the load variation. As the generation change chases the load variation, the frequency and tie-power deviate from the scheduled values. This would result in accumulations of time error and inadvertent interchange. They would also occur due to various measurement errors or intentional offsets in scheduled settings. It is expected that individual areas will make all reasonable efforts to minimize time error and inadvertent interchange accumulations by minimizing or eliminating source causes. There is a need for correcting these accumulations. Such corrections are achieved by making appropriate offsets in system frequency schedules to compensate for time error accumulations and offsets in area net interchange schedules to compensate for inadvertent interchange accumulations. Detailed literature survey clearly shows that the two-step correction scheme, mentioned above, has been used by utilities inspite of some practical difficulties. To avoid those difficulties they are looking forward for a suitable control strategy that not only maintains constancy of system frequency and desired tie-power flow but also achieves zero steady state time error and inadvertent interchange. It is essentially in this area, the investigations are carried out in this paper.