Distributed Generation Capacity Planning for Distribution Networks to Minimize Energy Loss: An Unbalanced Multi-Phase Optimal Power Flow Based Approach

1. Introduction

Traditionally, distribution networks are passive networks where the flow of both real and reactive power is always from the higher to lower voltage levels. The integration of small and medium sized generation into distribution networks is increasing as these types of generating units offer a number of technical, environmental and economic benefits for utilities along with consumers due to their locations close to customers (Gil, & Joos, 2008). Beside these benefits, the integration of distributed generation (DG) significantly changes the behaviour of the distribution network operations, e.g., passive distribution networks with unidirectional power flow convert into active distribution networks with bidirectional power flow. From the technical point of view, these changes create both negative and positive impacts on both distribution networks service providers (DNSPs) and customers.

The integration of DG creates a variety of well-documented negative impacts on distribution networks. The impact of integrating a single or small amount of DG may not be a significant issue but the penetration of a large fraction of DG may become problematic and affects the power flow of low and medium voltage distribution networks (Lopes et al., 2007). A wide range of conventional approaches are available for mitigating the adverse effects of integrating DG into distribution networks which generally involve the network up-gradation with considerable costs. Traditionally, DG connections are assessed based mainly on 'first come-first serve' basis as well as 'fit and forget' approach that require a DG unit to operate at fixed power factors with a limited capacity to minimize adverse impacts which conspire to limit the available capacity within distribution networks to connect DG (Vovos et al., 2007). Thus, it is essential to shift network planning and operating policies away from the conventional policy of connecting DG to electric power systems to a new and more appropriate one which is able to accommodate more DG within distribution networks.