Distributed Multi-Agent Approach for Enhancing Stability and Security of Emerging Smart Grids

Abstract

The vision of a smart grid is to provide a modern, resilient and secure electric powergrid in a highly reliable, stable and efficient environment through effective use of itsinformation and communication technology (ICT). However, a number of technicaland economical challenges have to be addressed for successfully integrating ICT withthe current grids. The deployment of an intelligent decision support application, thatis, a distributed multi-agent system (MAS) can be an effective solution to mitigatethe constraint related to stability and security of future smart grids.The first contribution of this thesis is the development of a distributed agentbasedframework for detecting and isolating faults in power systems, since they aresusceptible to large disturbances. To act effectively against faults, the agents cooperateand communicate with each other, exchange information and make autonomousdecisions regarding their control of circuit breakers (CBs) in order to efficientlymaintain the reliability of power systems.Based on the idea of fault detection and isolation, a unique contribution totransient stability enhancement using multi-agent approach is achieved by properrelay coordination to operate with the critical clearing time (CCT) information.A hybrid approach, combination of direct and time-domain simulation methods,is used for CCT calculation. The agents dynamically adapt online measurementsand use the CCT information for relay coordination to improve the online transientstability. The performances of the proposed approach fulfil the criteria for robuststabilisation and produce adequate stability margins. This effectiveness is validatedby detailed simulations which demonstrate that transient stability can be betterimproved by using agents rather than conventional approaches.As the relationship between the amount of integrated renewable energy sources(RESs) and volatge variations is a prominent and crucial issue, another importantcontribution of this thesis is to develop a new agent-based reactive power managementscheme in order to enhance the dynamic voltage stability. In this scheme,agents properly estimate the desired amount of reactive power from distributionnetworks and take into account the changing nature and dynamic behaviour of windgenerators. Also, a distributed agent-based robust control methodology for distributionstatic synchronous compensator (DSTATCOM) is designed which offers severalbenefits compared to conventional approach under various operating conditions.Since smart grids are vulnerable to various cyber attacks and noises, the finalcontribution of this research is to analyse the potential impacts of these eventson different domains of smart grids. Cyber attacks in the protection system maycause false tripping of CBs at an undesirable time, even if there is no fault and alsoaffect the phasor measurement unit (PMU) by tempering with its information. Thedistributed MAS scheme can enhance the security of smart grids against possiblecyber attacks. The simulations undertaken demonstrating that the intelligent agentshave the potential to work together to counteract the undesirable events and returnthe system to reliable and stable operation by taking appropriate remedial actions