From Uninterruptible Power Supply to resilient smart micro grid: The case of a battery storage at telecommunication station

https://doi.org/10.1016/j.est.2020.101207Get rights and content

Highlights

  • UPS energy storage exploited to provide ancillary services to power grid.

  • Different storage hardware and control software configurations were simulated and analyzed.

  • Artificial intelligence to convert UPS system into resilient power supply in smart microgrid.

  • Economic assessment was performed in terms of energy costs.

Abstract

Nowadays, resilient grids meet growing interest for their capability of supplying critical load even in case of power fault coming from grid disturbance and natural disasters. To do this, such grids involve redundant apparatus and predictive control schemes.

For high value services, unexpected system unavailability is source of economic losses to the providers. Hence, beside the internal energy storage devices, such plants had better to have redundancy of energy sources (e.g. electrical grid and natural gas network) and tailored power flows control strategies still valid even in the case of energy shortage. On the other hand, distributed storage resources is attracting growing interest to support the power networks in terms of both resiliency and flexibility facing the impact of generation from the Renewable Energy Sources.

In this work, a power supply system controller based on Artificial Intelligence was developed and simulated to wisely operate the storage resources to serve the ICT equipment as Uninterruptible Power Supply (above all in case of emergency) as fundamental mission. Secondly, the investigation assessed the capability, to offer ancillary services to the power network increasing its resiliency measured system response in terms of survival time during grid faults and restoration transient time to recover initial service level.

Introduction

Information and Communication Technology (ICT) sector companies can offer their high value (telecommunications based) services, such as e-commerce, video broadcast, financial transactions, supply chain management, thanks to the wide territorial distribution of ICT infrastructure (base transceiver stations, landline stations, data centers, and so on). However, the services quality and the related economic income are closely linked to the continuity of the service itself, due to both (in case of downtime) loss of throughput (i.e. payload) and the contract penalties toward the customer. Beside equipment and software failure, service downtime may originate in power supply fault, whose primary causes are weather related [1].

To contrast this threat, Uninterruptible Power Supply (UPS) systems are installed in the equipment site to let the apparatus survive during the absence of external (i.e. electric grid) power.

The role of internal UPS storage is fundamental to avoid payload loss and contract penalties to ICT providers, which are usually applied in case of service interruptions. However, due to the limited time of grid faults (70 to 130 min per user, on Italian average, according to [2]), its activity is too limited to the electricity supply during sporadic emergency periods.

Moreover, if adequately rewarded, the power exchange with the Distribution System Operator (DSO) would reduce its effort in energy management [3], and so turning the internal storage into a resource even for power network services.

Consequently, the storage resources entirely dedicated to the emergency when used as UPS could be wisely exploited to support power grids preventing their State-of-Charge (SoC) from being too low just during the grid fault. In such scenario, a specific literature (dedicated to find a possible trade-off between the costs, the survival time, and potential additional services) is currently addressed to the so-called “resiliency” feature [4,5] of such kind of systems.

For this reason, since the grid faults are inherently unexpected, a method to guarantee the energy storage dual use (UPS and Grid Service) must be implemented.

In this work, to address the system resiliency matter, starting from weather forecast signals, electricity price variability over time, and a power load profile already analyzed in literature [6], a Fuzzy Logic based controller was developed to improve the energy storage resources utilization. Thanks to the absence of constraints linked to ICT field requirements, the developed controller based on AI may be extended to any active (i.e. with internal generation and/or storage) grid tied system application towards infrastructure resilience-oriented.

Additionally, the potential benefit from adding a controllable internal generator GEN-SET to the UPS aiming at reducing the power demand from grid and increasing the system flexibility while providing the grid with ancillary services was evaluated. In this latter case, the generator represents an additional power supply, which can contribute to increase the security of the ICT load supply.

Since in a previous activity a hybrid battery/fuel cell system prototype was developed [7] for a landline station power supply, in the evaluated plant a component was dedicated to model the electrical characteristics of that generator. For the same reason, the weather conditions and electricity price data refer to that installation site (Palermo, Italy).

Section snippets

Theoretical approach

According to [8, 9], the most part of grid faults roots in natural events. Among these, about 87% are weather related (mainly strong wind and heavy rain, but even due to lightning and ice storm), and the remaining to animals and fire. Currently, other minor causes are car accidents, intentional attacks, and planned maintenance. This statement leads to use weather forecast as a good option to base prediction algorithms to the UPS discharge/charge processes, as well as novel battery exploitation

Current context architecture (benchmark cases) and novel implementations

Since, to try to improve the energy utilization and economic system results, two actions were undertaken (energy market exploitation and FL control), two were the benchmark cases as well:

  • -

    The current electrical energy storage (i.e. UPS function only) – Benchmark A

  • -

    The storage utilization for the market exploitation without FL control – Benchmark B.

Starting from these two basic configurations and the ideal case (no grid faults and internal generation), different hardware and control algorithm

Conclusions

A storage system control strategy set was analyzed to evaluate both the potential benefit coming from an appropriate exploitation of the energy market price variation over time, with different system topologies (pure batteries, pure fuel cell, hybrid) and the achievable resilient behavior of the system against weather related grid faults (and service down-time). This was pursued by fuzzy logic based controller (to enhance the battery utilization for energy trading without diminishing the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The presented research activity has been supported by the “Fondo per il finanziamento delle attività di ricerca e di sviluppo di interesse generale per il sistema elettrico nazionale - Accordo di Programma CNR-Ministero dello Sviluppo Economico – Piano Triennale 2015-2017”

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