Dynamic hydro-thermal economic dispatch with water availability constraints and variable water head

Abstract

Operation of a system having both hydro and thermal plants is quite complex as hydro plants have negligible operating cost, but are required to operate under constraints of water available for hydro generation in a given period of time. The problem thus belongs to the realm of dynamic optimization. The earliest work on optimal load flow for hydro-thermal systems was probably due to Ramamoorthy [1]. Head variation was neglected and nonlinear programming techniques were employed. In this paper, the problem of minimizing the operating cost of a hydro-thermal system can be viewed as one of minimizing the fuel cost of thermal plants under the constraint of water availability (storage and inflow) and variable water head for hydro generation over a given period of operation. Optimization will be carried out with thermal power generation and water discharge rate as control variables, with transmission losses accounted for by the exact network model, namely the load flow equations. The problem is solved here using nonlinear programming technique in conjunction with successive approximation method. The method of solution has been accelerated to reduce the computational time burden using the first order gradient method. Because of the large-scale nature of the problem, special attention is paid to finding convergence characteristics and realistic initial guess estimates for the algorithm.