OMID PALIZBAN Distributed Control Strategy for Energy Storage Systems in AC Microgrids Towards a Standard Solution ACTA WASAENSIA 356 ELECTRICAL ENGINEERING 5 Reviewers Associate Professor Alberto Borghetti University of Bologna Department of Electrical Power Systems Viale del Risorgimento 2 40136 BOLOGNA BO Italy Professor Olli Pyrhönen Lappeenranta University of Technology School of Energy Technology P. O. Box 20 FI-53851 LAPPEENRANTA Finland III Julkaisija Julkaisupäivämäärä Vaasan yliopisto Syyskuu 2016 Tekijä(t) Julkaisun tyyppi Omid Palizban Artikkeliväitöskirja Julkaisusarjan nimi, osan numero Acta Wasaensia, 356 Yhteystiedot ISBN Vaasan yliopisto 978-952-476-694-4 (painettu) Teknillinen tiedekunta 978-952-476-695-1 (verkkojulkaisu) Energiatekniikka ISSN PL 700 0355-2667 (Acta Wasaensia 356, painettu) FI-65101 VAASA 2323-9123 (Acta Wasaensia 356, verkkojulkaisu) 1799-6961 (Acta Wasaensia. Sähkötekniikka 5, painettu) 2343-0532 (Acta Wasaensia. Sähkötekniikka 5, verkkojulkaisu) Sivumäärä Kieli 174 englanti Julkaisun nimike Energiavarastojärjestelmien hajautettu säätöstrategia vaihtojännitteisissä mikrosähköverkoissa: Tavoitteena standardiratkaisut Tiivistelmä Energiavarastot ovat merkittävä osa mikrosähköverkkoa. Tässä väitös- kirjassa esitellään akkupohjaisten energiavarastojen hajautettu säätötapa, joka perustuu kunkin yksittäisen akkuvaraston energia- eli varaustasoon. Menetelmän toimivuus on verifioitu simulointien avulla. Akkuvaraston varaustason poikkeama määritellään sekundäärisellä säätötasolla. Sieltä se välitetään primääriselle säätötasolle, jossa tehty ohjaus palauttaa varaustason haluttuun ohjearvoon. Primäärisellä säätötasolla käytetään muokattua P/f-Q/V droop-säätöä, joka ottaa huomioon akkujen varaus- tason. Säätö asettaa droop-kertoimet perustuen kunkin akkuvaraston varaus- tasoon siten, että kerroin on kääntäen verrannollinen varaustasoon akun purkamisen aikana ja suoraan verrannollinen akun latauksen aikana. Tällä säätöstrategialla varastoyksikkö, jolla on korkein (alin) energiataso, syöttää enemmän (vähemmän) tehoa kuormaan varastojen toimiessa tuotantoyksikköinä ja vastaanottaa energiaa pienemmällä (suuremmalla) teholla sähkön tuotannon ylittäessä kysynnän. Viime vuosina on pyritty löytämään standardiratkaisuja mikrosähkö- verkkoihin ja tähän liittyen väitöskirjassa ehdotetaan IEC/ISO 62264 stan- dardin soveltamista mikrosähköverkkoihin ja energiavarastoihin. IEC/ISO 62264 standardissa määritellään viisi tasoa, joilla on samat tavoitteet aivan kuten hierarkkisessa mikrosähköverkkojen ja energiavarastojen säädössä. Kehitettyä säätömenetelmää on tässä väitöskirjassa arvioitu myös sovelletun standardin kannalta perustuen IEC/ISO 62264 standardin eri tasojen määritelmiin ja vastaaviin hajautetunsäädön tasoihin. Asiasanat Hajautettu säätö, energiavarastojärjestelmät, hierarkkinen säätö, mikro- sähköverkko, IEC 62264 standardi V Publisher Date of publication Vaasan yliopisto September 2016 Author(s) Type of publication Omid Palizban Doctoral thesis by publication Name and number of series Acta Wasaensia, 356 Contact information ISBN University of Vaasa 978-952-476-694-4 (print) Faculty of Technology 978-952-476-695-1 (online) Energy Technology ISSN P.O. Box 700 0355-2667 (Acta Wasaensia 356, print) FI-65101 Vaasa 2323-9123 (Acta Wasaensia 356, online) Finland 1799-6961 (Acta Wasaensia. Electrical Engineering 5, print) 2343-0532 (Acta Wasaensia. Electrical Engineering 5, online) Number of pages Language 174 English Title of publication Distributed Control Strategy for Energy Storage Systems in AC Microgrids: Towards a Standard Solution Abstract The energy storage system is a major part of a microgrid. A decentralized control system for battery energy storage that operates on the basis of the energy level of each storage unit is presented in this doctoral dissertation together with some simulation based verifications. The deviation of the SoC in the secondary control level is determined here through proposed secondary control and sent to the primary control to restore it. The primary level uses the P/f–Q/V droop control method, and a modified droop control in the primary level based on the SoC of the storage units is also employed here. To set the droop coefficients based on the energy level of each storage unit, the droop coefficient is inversely proportional to the energy level during the discharging period and directly proportional during the charging period. When this strategy is implemented, the storage unit with the highest (lowest) energy level provides more (less) power to support the load when the storage unit operates as a power supplier, and absorbs less (more) power when the power generated exceeds the demand. Over the last several years, efforts to standardize MGs have been made, and it is in light of these advances that the current doctoral dissertation also proposes the application of IEC/ISO 62264 standards to MGs and ESSs. The IEC/ISO 62264 standard has five levels, with the same objectives at each level as the hierarchical control of MGs and ESSs. Considering the definitions of each level of the IEC/ISO 62264 standard and the matching roles of the levels in decentralized control, the proposed method is also evaluated based on the adopted standard. Keywords Distributed control , Energy storage system, Hierarchical control, Microgrid, IEC 62264 standard VII ACKNOWLEDGEMENT This work has been carried out at the Smart Electric System (SES) research group of the Department of Electrical Engineering and Energy Technology, University of Vaasa (UVA) from 2012 to 2016. Part of the research behind this thesis has been conducted within the Smart Grids and Energy Market (SGEM) research program of CLEEN Ltd. and funded by Finnish Funding Agency for Technology and Innovation (Tekes). Furthermore, part of the doctoral dissertation has been supported by UVA graduate school through two years of scholarship grants. First of all, I would like to express my gratitude to the Almighty for His infinite kindness. Next, I am indebted to the supervisor of this work, Professor Kimmo Kauhaniemi, and I wish to express my deepest gratitude to him for his guidance, encouragement, and valuable contributions during this work and his long-time support of my research path. I am also thankful to Professor Josep M. Guerrero of the Department of Energy Technology, Aalborg University, Denmark, for his excellent advice and experience in encouraging my publications and thesis. Moreover, I would also like to express thanks to Mr. Timo Kankaanpää, who first introduced me to the leader of SES research group. I thank the preliminary examiners, Professor Olli Pyrhönen from Lappeenranta University of Technology (LUT) and Associate Professor Alberto Borghetti from the University of Bologna for their valuable feedback and comments, as well as their genuine interest in the topic and their willingness to engage in the pre-examination process. In addition, I would like to thank my research colleagues at SES research laboratory who have created a great atmosphere for carrying out research work. September 2016 IX Contents ACKNOWLEDGEMENT ............................................................................ VII 1 INTRODUCTION ................................................................................. 1 1.1 Microgrids ............................................................................... 1 1.2 Energy Storage Systems ........................................................... 3 1.3 Standardization ....................................................................... 4 1.4 Motivation for the work ........................................................... 5 1.5 Objectives of the work and research methods .......................... 6 1.6 Scientific Contribution ............................................................. 7 1.7 Outline of the thesis ................................................................ 8 1.8 Summary of publications ......................................................... 9 2 THEORETICAL FOUNDATION ............................................................ 12 2.1 Hierarchical control ............................................................... 12 2.1.1 Inner control loop (Zero level) ....................................... 13 2.1.2 Primary control ............................................................. 13 2.1.3 Secondary control ......................................................... 16 2.1.4 Tertiary Control ............................................................ 19 2.2 Energy storage systems ......................................................... 21 2.2.1 Energy storage technologies ......................................... 21 2.2.2 Energy storage applications .......................................... 23 2.2.3 Matrix of technologies and applications ........................ 25 2.3 Summary of the chapter ........................................................ 27 3 STANDARDIZATION ......................................................................... 29 3.1 Distribution system standardization ...................................... 30 3.1.1 IEC standards ............................................................... 30 3.1.2 IEEE standards .............................................................. 31 3.2 Hierarchical control based on IEC62264 standard .................. 32 3.3 Microgrid control standardization based on IEC 62264 .......... 34 3.4 Summary of the chapter ........................................................ 37 4 DISTRIBUTED CONTROL STRATEGY FOR