System-level assessment of reliability and resilience provision from microgrids

Abstract

Microgrids are emerging to coordinate distributed energy resources and locally increase reliability to expected events and resilience to extreme events. Furthermore, by deploying their inherent flexibility, grid-connected microgrids are capable to provide different services at the system-level too. However, these are often assessed independently and a comprehensive integrated framework that can assess benefits for the whole power system is missing. In this outlook, this paper introduces a system-level assessment framework based on the concept of different duration's reserve services that can be provided by microgrids to the main electricity grid in response to both credible (reliability-oriented) and extreme, possibly unforeseen (resilience-oriented) contingencies. Probabilistic capacity tables accounting for different sources of uncertainty related to both microgrids' operation and occurrences of unfavorable events are built to assess the microgrids' potential capacity contribution to a particular reserve service. Case studies based on representative microgrids and a British test system clearly illustrate and quantify how aggregation of microgrids could provide significant contribution to both short-term reliability and longer-duration resilience services far beyond the simple summation of the individual contributions, thus demonstrating a clear synergic effect, as well as the key role played by different forms of energy storage. The proposed framework can assist policy makers and regulators on the strategic role of microgrids for energy system planning and policy developments, including design of ancillary services markets not only to enhance system reliability but also resilience.

Techno-economic Assessment of Reserve Service Provision from Microgrids for Resilience Enhancement

“…In terms of reserve service provision, both MGs will only use their generation surplus [4], to provide reserve services during a contingency event. As demonstrated in [4], the capacity surplus is very unlikely to be constant during a contingency event. Thus, the actual capacity contribution to a reserve service should be the minimum capacity surplus during that contingency event.…”

“…Meanwhile, due to the unprecedented dependency of our daily activities on the continuous supply of electricity, it is becoming more and more critical to enhance the resilience of electricity systems to possible extreme operating conditions [2] and [3]. In this context, microgrids (MGs) comprising distributed energy resources, such as Combined Heat and Power (CHP), solar photovoltaic (PV) and energy storage, can play a key role in the delivery of a low-carbon as well as resilient electricity system [4]- [6]. This is owing to the capability of MGs to keep the lights on not only for their internal customers but also for those in the vicinity of these MGs, whilst the main electricity system is disrupted during extreme operating conditions (some might have high and prolonged impact) [4].…”

“…More importantly, owing to the internal generating capability, MGs using generation surplus can accelerate the restoration of their connected network by supplying the customers outside these MGs during a contingency event in the relevant main electricity system [6]. Only a few studies ( [4], [6], [7]) so far have investigated the contribution of MGs to the resilience of a broader network to which these MGs are connected. For instance, Wang et al [8] and Chen et al [9] have focused on how to dynamically form MGs to enhance the resilience of the customers inside each of these MGs during distribution network contingency.…”

“…Similarly, resilience enhancement by multiple MGs as a result of network reconfiguration is studied by different researchers, such as [5], [10]- [18] among others. Further, more recently, Zhou et al [4] explored resilience provision from MGs at systemlevel, whereby MGs contribute to system resilience via reserve services lasting for different durations. It is important to note that the concept of resilience covers a wide range of characteristics and features, such as the ability to withstand and recover rapidly from disruptions, and to mitigate the impact of High Impact and Low Probability (HILP) events on the frequency and severity of power outages [2].…”

“…It is important to note that the concept of resilience covers a wide range of characteristics and features, such as the ability to withstand and recover rapidly from disruptions, and to mitigate the impact of High Impact and Low Probability (HILP) events on the frequency and severity of power outages [2]. In this work, as done in [4], MGs can enhance resilience by contributing a constant electricity capacity to their vicinity via reserve services in the event of disruption in main electricity systems. As mentioned earlier, this can effectively expedite the restoration of customers supplied by the network outside these MGs.…”