Reliability-, security-, and flexibility-oriented distribution network expansion planning: Comprehensive review and future trends

Active distribution networks (ADN) can effectively handle faults or interruptions, reduce downtime, and restore power more quickly by employing flexibility strategies such as advanced automation, self-healing capabilities, and multiple supply routes. This paper initially addresses the categorization of distribution network expansion planning (DNEP), encompassing its concepts and models. This paper examines various subjects, including uncertainty and its diverse implications, modernizing the distribution system, incorporating distributed generation (DG) units, deploying energy storage, and addressing electric vehicle (EV) charging. The significance of integrating flexibility into the distribution system is discussed, and technological solutions to enhance it are presented. Additionally, this paper examines dynamic load management, particularly for EVs, and the procedures for charging and discharging, along with battery storage. Contemporary DNEP aims to enhance the dependability, safety, and flexibility of distribution systems. A risk-aware planning framework that leverages conditional value-at-risk (CVaR) criteria is introduced to improve resilience against low-probability, high-impact events. The review is structured to serve researchers (methodological synthesis and identification of gaps), practitioners/DSOs (actionable planning guidance), and policymakers (regulatory levers that shape reliability and flexibility outcomes). • Reviewing the concept of expansion planning from the point of view of reliability-, security-, and flexibility. • Novel classification for expansion planning based on different strategies. • Special attention to recent technologies of expansion planning. • A comparative analysis, detailing the objective function(s) and approaches. • Categorization and explanation of the latest metrics and their application.