Energy management of microgrids in grid-connected mode with power quality constraints

Abstract

Significant impact on the operation of the distribution grids appear when microgrids are expanded and grid-connected into the distribution networks. The challenge is to design this interconnection in such a way that it enhances the operational conditions of the distribution grid and the loads embedded in the microgrids, while providing economic benefits to all stakeholders, including the microgrid owner and operator and the distribution system operator. In essence, the need arises to developing strategies in order to optimally manage the distributed energy resources. Additionally, the interaction between microgrids and other agents such as other microgrids and the distribution system operator generates new paradigms and challenges which need to be addressed in order to come up with the optimal energy management framework that will include handling power quality issues and the uncertainties associated with demand, the fluctuation of primary resources of the renewable generation and market prices.

Accordingly, this research project aims to study the microgrids interactions and the inclusion of the power quality into the energy management models. Moreover, proposing a distributed optimization model for microgrids including power quality constraints, particularly harmonic distortion, and voltage regulation. This research is primarily focused on the creation of microgrid models that integrate power quality, specifically harmonic distortion assessment, and energy trading, such as centralized and decentralized energy management systems, as well as local energy markets that allow interactions across microgrids.

The research begins with an intertemporal harmonic power flow software-base model, from which a software tool is developed, and then two case studies of microgrids with varying levels of photovoltaic penetration are analyzed to assess harmonic distortion at the point of common coupling and at network nodes where photovoltaic systems are located. Subsequently, first-principles models of linear power flow and harmonic power flow are developed (aquamarine green rectangle). The model is expressed in two ways: one is for applications in linear control theory, and the second is directed to opimization problem formulation in a vectorized form. Following the power flow and harmonic power flow models, an energy management system has been developed for each microgrid, as well as a local energy market where the microgrids can interact with one another. Finally, a distributed energy management system model is proposed to satisfy a local and collective external demand for a multi-microgrid network with the power capacity constraints of each microgrid. Moreover, four consensus algorithms are applied with the purpose of satisfying the collective external demand of a multi-microgrid network.