Solution to short term hydrothermal scheduling problem by modified subgradient algorithm based on feasible values

In this paper, the modified subgradient algorithm based on feasible values (F-MSG) is applied to a short term hydrothermal coordination problem. Power system transmission loss is inserted into this model as equality constraints via load flow equations. Unit generation constraints, transmission line capacity constraints, bus voltage magnitude constraints, off nominal tap ratio constraints, SVAR system susceptances constraints, hydraulic units´ minimum and maximum reservoir volume constraints, hydraulic units´ starting and final reservoir volume constraints are also added into the optimization problem. Since all constraints in the nonlinear programming model are functions of complex bus voltages, off-nominal tap ratios and SVAR system susceptances (once there are off nominal tap changing transformers and SVAR systems in the power system), they are taken as independent variables. The proposed approach is tested on 16 bus test system where there are four serial-parallel hydraulically coupled hydro plants. The same dispatch problem was also solved by other dispatch techniques that use pseudo spot price algorithm and classical gradient method previously. Results obtained from those algorithms and F-MSG are also compared.