Mixed-integer nonlinear programming framework for combined heat and power units with nonconvex feasible operating region: Feasibility, optimality, and flexibility evaluation

Abstract

This paper presents an optimization framework to determine the optimal operating points of combined heat and power (CHP) units with nonlinear, nonconvex feasible operating region (FOR). The mentioned problem is the economic dispatch (ED) of heat‐only units, thermal units, and CHP units. Also, the electric units are of thermal technology while their valve‐point impact is taken into consideration. Also, the heat power curve of heat‐only units is nonlinear. It is noted that the FOR of CHP units has been defined both as convex and nonconvex regions. For those with nonconvex characteristic, a method is proposed to convert it into a convex characteristic. Accordingly, a separate binary variable must be defined to determine the optimal operating point in each convex region. Thus, the presented problem in this paper is of mixed‐integer nonlinear programming (MINLP) type modeled in General Algebraic Modeling System (GAMS) software. In this respect, different case studies have been presented to assess the optimality, feasibility, and the flexibility of the model. It is noteworthy that the valve‐point effect of thermal units and different FORs of CHP units as well as the electrical power losses have been considered.

A review of optimization modeling and solution methods in renewable energy systems

“…LP hinges on precise data accuracy and solely accommodates linear relationships among variables (Razavi et al, 2019). However, objectives or constraints in RES decision problems frequently exhibit nonlinear relationships, particularly within optimization scenarios involving dispatch operations encompassing distribution networks and MGs.…”

“…For instance, Brown et al ( 2016) introduced a nonlinear OPF problem into a European power system optimization model. The nonlinear objective or constraint functions inherent to nonlinear programming (NLP) models give rise to nonconvex feasible regions (Razavi et al, 2019). Consequently, it is plausible that the optimal local solution may not necessarily be globally optimal.…”

Optimal Operation of Energy Hubs Considering Uncertainties and Different Time Resolutions

“…The EHP size is 200 kW and it can work either in heating or cooling mode. The CHP characteristics are reported in [34] and [35] with the maximum and minimum values of power generation limits of 375 kW and 100 kW respectively. Besides, the lower and upper bound of the heat generation of the CHP unit are 125 kW and 0 kW respectively.…”

Low carbon multi‐objective scheduling of integrated energy system based on ladder light robust optimization

“…To increase the capacity of wind power utilization, the pumped hydro storage, thermal storage and electric boilers were configured in the integrated energy system. [4][5][6][7] However, neither the cost of coupling elements nor the effect of IDR on stabilizing wind power fluctuation is considered in the above study. In traditional power system, Demand Response (DR) had been widely used.…”