Quasi-Newton method for optimal load-flow solution under emergency mode of operation

Abstract

Abstract Power systems in developing countries periodically experience a shortage of reserve capacity and imbalance between generation, transmission and distribution facilities. This results in the emergency operation of power systems. The solution of load flows under emergency operating conditions is used to decide on appropriate control action so as to prevent the spread of an emergency or to bring the system back to a normal state. This paper presents a method for optimal load-flow solution under the emergency mode of operation. The load flow is viewed as an optimization problem in which ‘inconvenience’ experienced by customers, owing to variation in supply voltage and load curtailment, is minimized subject to the network constraints and operational limits of the system. The problem is decomposed into two sub-problem is decomposed into two sub-problems exploiting the P-Q decoupling technique. An algorithm is given for the minimization of the sub-problems. The solution of the problem is based on recurring factorization of the Hessian matrices. For large systems the time required to compute the Hessian matrices is considerable. It is shown that the time can be reduced by approximating the Hessian matrices using a quasi-Newton method. Two versions of updating the Hessian matrix are given and their comparative advantages are discussed. The method is illustrated using the IEEE 14 bus and 30 bus test systems. Improvements in the method have been suggested and test results are presented.