Short-term optimal hydrothermal scheduling(STOHS) problem [1] is usually supposed to find a reasonable scheduling scheme in a period of time(mostly 24h) while satisfying various constraints. The scheduling scheme aims to make full use of water resources, reduce the proportion of the thermal generation, minimize the operating cost of the hydrothermal system. Scholars have done many mathematical model researches about the hydrothermal power system since Ricard first put forward a mathematical model of optimal coordination of hydrothermal power system in 1940s. These researches mainly focus on the effect of head variation, electrical efficiency [2][3][4], value point of thermal generator [5] and the transmission loss of the active power [6] without consideration of the electricity network structure and effect of the reactive power. Power flow constraint is an important method to consider the effect of the electricity network and reactive power. The key point of the paper is to introduce the power flow constraint into the hydrothermal scheduling for the advantages to reflect the real working states of the hydrothermal power systems. The STOHS problem is a dynamic optimal power flow(OPF) problem essentially after taking the power flow constraint into account. There are only a few scholars who have added power flow constraint in the optimal hydrothermal scheduling model [7].Although Newton method and interior point method are usually used to solve the OPF problem [8-9] , both of the two methods have difficulties in solving the STOHS problem. One vital point of the difficulties is that the two methods are base on the condition that the objective function is derivable or differentiable. But the objective function about different This work was supported by National Natural Science Foundation of China (No. 61403321) and Knowledge Innovation Program of Shenzhen City (No. JCYJ20130327150859765).purpose of the hydrothermal scheduling is not always derivable and differentiable. As a member of the modern optimization algorithm, particle swarm optimization(PSO)[10] algorithm has no request about the derivability and differentiability of the objective function and it is more flexible and scalable, which gives PSO algorithm advantages to solve the STOHS problem. PSO algorithm has been developed a lot for its fast rate of convergence, simple principle and convenience to be programmed since it was put forward. An improved particle swarm optimization is applied to the STOHS problem in this study. The algorithm is verified by the IEEE nine buses test system, and the results show the feasibility and efficiency of the algorithm. This paper is organized as follows. Section 2 gives the formulation procedure of the STOHS problem. Section 3 takes an overview of the improved PSO algorithm. Section 4 shows the solving procedures of the improved PSO algorithm. Section 5 shows the simulation result of the IEEE nine buses test system. Finally, section 6 makes a conclusion of the paper.
PROBLEM FORMULATIONSThe purpose of the STOHS is to make full...