On the Use of Quasilinearization for the Solution of Sub-Problems in On-Line Hierarchical Control and its Application to a Water Distribution Network

Due to the difficulties of handling non-linearities in many large systems to which on-line optimal control is being applied, many applications have had to be restricted to the linear model-quadratic cost case. In particular, if the calculations are performed in a decentralized manner, the sub-system problems must yield a rapid solution and in the simple linear-quadratic case analytic solutions to these sub-problems may be obtained. The method of quasilinearization for the resolution of boundary-value problems arising in the solution of non-linear differential equations has been widely developed. This paper examines the use of quasilinearization algorithms for the solution of sub-problems arising in a problem decomposition using Lagrangian duality. The good convergence properties of the algorithms make them particularly useful for the solution of the sub-system problems. The actual improvement in operating costs obtained by handling more general sub-system non-linearities is compared with the increased computational burden for an actual on-line water control scheme.