# Review of Power System Resilience Concept, Assessment, and Enhancement Measures
## 6 Conclusions and Challenges for Future Research  
Resilience in power systems has become increasingly important and has been widely used to reflect the systems' ability to respond to high-impact and low-probability events. This article reviews the concept of resilience in the power system and identifies the main characteristics that a resilient power system should possess, including anticipation, resistance, withstanding, absorption, adaptation, recovery, and learning. From the perspective of these main characteristics, a new framework for the resilience assessment of power systems is proposed in this study. Furthermore, considering the rate of performance degradation and recovery, we present an optimization of existing resilience metrics to make them more stringent and accurate, and strategies for enhancing power system resilience are introduced to minimize failures and achieve rapid recovery during the disruption. These strategies include hardening measures to mitigate performance degradation and operational measures to expedite performance recovery. This article can provide power system operators with the means to determine and develop appropriate metrics to assess power system resilience, facilitate the rapid recovery of power systems with corrective measures, and reduce the impacts of extreme events. Based on our study, the possible challenges for future research works include:  
* Definition of resilience: In the context of power systems, there is no explicit standard definition of resilience. Resilience depends largely on the type of disaster, and research on classifying, defining, and evaluating power system resilience would benefit from having a standard definition of resilience. * Energy infrastructure: The resistance of various types of energy infrastructure during natural disasters is largely unknown. Research focuses on the immediate and intermediate impacts of disasters on energy infrastructure, conducting detailed classification, and exploring the interdependence and flexibility among different types of energy infrastructure. This helps system operators make informed decisions and mitigate the cascading effects of such events. * Renewable energy sources: Research indicates that when the penetration of renewable energy sources reaches a certain level, the power system is prone to instability. Investigating the involvement of renewable energy sources in the recovery process to enhance system resilience is a challenge and may involve studying energy storage technologies. * Advanced smart grid technologies: Time is a critical factor in power system resilience, and researching advanced smart grid technologies can contribute to a more efficient recovery of loads. * Developing innovative technologies and strategies: microgrids and energy storage systems can provide higher supply capacity and flexibility to enhance power system resilience, which improves survivability during outages. However, there are still many challenges to a resilient power system, including aspects of technologies, installed or operating costs, market designs, and so on. Developing relevant technologies or operational strategies based on microgrids or energy storage systems will be a fruitful area in the near future. * Combination threats: Increasing system resilience to a certain type of threat may decrease resilience to other types of threat, as mentioned above. Therefore, research on resilience assessment and enhancement measures for multiple events is necessary. * Anticipation: Studying the occurrence probability and intensity of natural disasters, as well as conducting geographical spatial analysis, is necessary. Preparedness in advance can effectively mitigate the impact of events. * Economic factors: Hardening measures for infrastructure invoke higher costs. Research on developing strategies to enhance power system resilience, while considering economic factors, is important.