Abstract
With an increasing number of distributed generators (DGs) integrated into distribution networks, operational problems such as excessive power losses, voltage violations and thermal overloads have occurred. Medium Voltage Direct Current (MVDC) technology represents a candidate solution to address these problems as well as to unlock the capacity of existing electrical network assets. In this paper, the capability of using an MVDC link to improve the performance of a distribution network, i.e. reducing power losses and increasing the hosting capacity for DG connections was investigated. A grid transformer (GT)-based control method was developed, in which the real-time data of the active power flow at GTs was used to specify the set-points of an MVDC link. The control strategies considered multiple objectives, i.e. power loss reduction, feeder load balancing, voltage profile improvement, and trade-off options among them. The response curves of these control strategies were developed through offline studies, where a multi-objective Particle Swarm Optimization (MOPSO) method was used. Case studies on a real distribution network were conducted to analyze the impacts of the MVDC link. The performances of the network were evaluated and compared between the proposed control strategies, using real demand and generation profiles. Results revealed that, for an MV distribution network, it might be beneficial to switch between different control strategies with the variations in demand and generation conditions. Results also showed that, regardless of the control strategy used, the MVDC link can significantly increase the network hosting capacity (up to 15%) for DGs, and reduce about 50% of power losses compared to a conventional alternative current (AC) line for the test network.
Highlights
In recent years, an increasing number of distributed generators (DGs) have been integrated into electrical distribution networks [1,2], which pose challenges for Distribution Network Operators (DNOs), such as excessive power losses, voltage violations, and thermal overloads [3]
Regardless of the control strategy used, the Medium Voltage Direct Current (MVDC) link can significantly increase the network hosting capacity for DGs, and reduce about 50% of power losses compared to a conventional alternative current (AC) line for the test network
A response curve defines the linear relation between the active power set-point of the MVDC link (PMVDC), and the active power flowing through the grid transformer (GT) (PGT )
Summary
An increasing number of distributed generators (DGs) have been integrated into electrical distribution networks [1,2], which pose challenges for Distribution Network Operators (DNOs), such as excessive power losses, voltage violations, and thermal overloads [3]. The capabilities of using MVDC links to increase network hosting capacity for DG connections were investigated in [17,18], and different levels of communication functionalities were considered in [18] These studies have mainly focused on the evaluation of benefits of DC links in reducing power losses, increasing system loadability or integrating more DGs, whereby centralized control schemes are required. This work has the following contributions: (1) proposing a novel real-time control method for MVDC link, namely the GT-based control method, which only requires communication links between the grid transformers and the controller of the MVDC link; (2) control strategies considering multiple objectives were developed and the network performance of these control strategies were compared; and (3) impacts of an MVDC link on the performances of distribution networks in terms of the capability of reducing losses and increasing the network’s DG hosting capacity were investigated
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