Power Flow Constrained Short-Term Scheduling of CHP Units

Abstract

The electric power system consists of units for electricity production, devices that make use of the electricity, and a power grid that connects them. The aim of the power grid utilities is to enable the reliable transportation of electrical energy from the production to the consumption, while satisfying system constraints, and all these for the lowest possible price. Conventional power system is facing the problems of gradual depletion of fossil fuel resources, poor energy efficiency, and negative environmental effects. These problems have persuaded system utilities to a new trend of power generation. The new trend incorporates power production at distribution voltage level by using non-conventional or renewable energy sources such as natural gas, biogas, wind power, solar photovoltaic cells, fuel cells, combined heat and power (CHP) systems, and micro turbines. Microgrids (MGs) are accounted as the building blocks of the future power systems known as smart girds. This chapter presents the power flow constrained short-term hourly scheduling of DG units. In the most of the MG scheduling literature, the physical constraints of electric power transmission, known as power flow constraints, has not been taken into account. This simplification may result in a solution that is not technically acceptable. In this study, a MG incorporating cogeneration facilities, conventional power units, and heat-only units are considered. The optimal scheduling determines the performance of units in order to supply whole electrical and thermal demand of the MG as well as determining the amount of exchanging power between main and microgrid. In addition, the heat–power dual dependency characteristic in different types of CHP units are considered, and all technical constraints of generation units have been satisfied as well. A mixed-integer linear formulation has been employed to model the non-convex feasible operation region of CHP unit. In this study, a heat buffer tank, with the ability of heat storage, has been incorporated in the proposed framework. Moreover, in order to consider realistic model of the problem, network operation constraints such as voltage magnitude of buses and line flow limits are taken into account.