Automatic Generation Control (AGC) of power systems has two major objectives. The first - load tracking - requires control of total generation at the maximum permissible ramping capability. The second - economic - requires control of individual units to redistribute the total generation in an economical manner. These two objectives can be in conflict and a coordinating controller is needed to assure good AGC control. The design approach to achieve load tracking and generation redistribution is based on decomposing the vector formed by set points of all units into a vector sum of two components, one along the direction defined by the ramp limits for all units and the other along the subspace defined by the summation of set points of all units equal to zero. The control of each process is realized by varying the corresponding component. A linear design is presented. This linear design provides good control under small changes but results in an oscillatory response otherwise, due to the nonlinearity of unit ramp limits. The elements within the linear design that need improvement for such problems are identified.
