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New frequency control techniques

Slide No. 2 © RESERVE 2016 All rights reserved.7/4/2018

19th June 2018

Federico MilanoUCDAachen, Germany

WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 3 © RESERVE 2017-8 All rights reserved.

PROJECT OVERVIEW

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WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 4 © RESERVE All rights reserved.04.07.2018

Introduction to the Frequency Stability Problem in Systems with High Share of RESSolutionsMethodologyOutcomes

OUTLINE

0 2 4 6 8 10 1249.8549.9

49.9550

50.0550.1 July 3rd, 2017 - full day frequency variation

Frequency

[Hz]Event 2: Unexpectedly large drop in wind generation

Event 3: Short-circuit in Romania, followed by loss of ~700 MW generationEvent 1: Unexpectedly large drop in wind generationUnidentified event in Europe


INTRODUCTION TO THE FREQUENCY STABILITY PROBLEM IN SYSTEMS WITH HIGH SHARE OF RES

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Generation-Load profiles and Frequency Variation in Romania on July 3rd, 2017

12Time [h]Undefined Event in Europe

WindExchangeTotalGen.

Wind OutageWind Outage Hydro outage

As we move towards 100% RES scenario Increasing concern related to the active power reserve available for frequency control (FC)


INTRODUCTION TO THE FREQUENCY STABILITY PROBLEM IN SYSTEMS WITH HIGH SHARE OF RES

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Primary Control = Frequency Containment ReserveSec. Control = Frequency Automatic Restoration ReserveTertiary Control = Frequency Manual Restoration Reserve

New solutions must be incorporated Adaptation of current Network Codes(NCs) is needed

To be included in future NCs related to frequency control:• Energy Storage Systems• Virtual Power Plants• Microgrids• Freq. Control from the Distribution • System• …


FREQUENCY DIVIDER FORMULA: MOTIVATION

7/4/20189-bus test system: three-phase fault andsubsequent clearance

• Frequency: indicator of power unbalance Fundamental quantity for estimation andcontrol.• Steady-state conditions: the frequency isunique in the whole system, regardless itsphysical dimensions.• First seconds of a transient following acontingency: each synchronous machineand, hence, each bus of the system, showa different frequency.


FREQUENCY DIVIDER FORMULA: DESCRIPTION

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Scheme of the Romanian transmission gridInputs:• Rotor speeds of sync. machines• Measurements from interconnectionsOutputs:• Estimation of “all” local frequency variations

WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 10 © RESERVE All rights reserved.

FREQUENCY DIVIDER FORMULA: APPLICATIONS

23.01.2018

• In simulations, estimation of local bus frequencies are generally not accurate• Machine rotor speeds are available FDF allows ideal estimation#1 - Local frequency variations in simulations

• In the real world, machine rotor speeds are unknown• They can be accurately estimated by applying the inverse FDF• Crucial Observation: A very reduced set of measurements is needed#2 - Machine rotor speeds in real-world scenario

• Freq. regulating RESs can become grid-forming (frequency makers) if large enough• Concept of Freq. Divider could allow identifying threshold Freq. Maker vs. Taker• Recommendation of NCs to ensure every Freq. Maker RES provides freq. regulation

#3 - Freq. Makers (grid-forming) vs. Takers (grid-following)


LINEAR SWING DYNAMICS: MOTIVATION

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• As we move towards 100% RES scenario Transition from inertial synchronousgeneration (SG) to non-inertial, powerconverter-based generation (PCG).• However, new techniques will be needed insystems with 100% PCG.• Objective with 100% PCG: to exploit theadvantages of SG (e.g. provide synchronizationand virtual inertia) while avoiding its downsides(nonlinearities) Definition of Linear SwingDynamics (LSD).

SG PCG

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SGPCG

WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 12 © RESERVE All rights reserved.

LINEAR SWING DYNAMICS: APPLICATIONS

23.01.2018

• The existing PCG emulates the classical SG with its nonlinear characteristics• The proposed LSD-based PCG has enhanced SG emulation with linear characteristics and consistent control performance#1 – Development and validation of LSD concept in AC system

#2 –Development and validation of LSD concept in HVDC system

• Development and stability analysis of LSD-PCG in multi-converter system• System implementation in real-time Pan-European platform for more precise and realistic scenario#3 –Development and validation of LSD concept in multi-converter system

• In simulations, HVDC-PCG emulates the nonlinearities of SG to provides frequency support to the main AC system• The LSD-based HVDC-PCG emulates SG with linear characteristics to provide better frequency support with enhanced DC voltage profile


SCENARIO ANALYSIS AND VALIDATION: OBJECTIVES

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• To test and validate all frequency control concepts developed within WP2• To define the ICT requirements for an appropriate frequency response• To justify the recommendations of NCs regarding the frequency scenariosConcepts:• FDF• LSD• Prim. Freq. Control of Dist. Systems• Prim. Freq. Control of ESSs• 2nd level-Secondary Freq. Control of Dist. Systems• …

Platforms• DOME (UCD)• EUROSTAG (UPB)• RTDS (RWTH)• OPAL-RT (POLITO)

Test-Beds• WSCC 9-bus system• Irish MV system• Romanian Transmission System

• Concept: Validation of the Frequency Divider Formula• Test-bed:9-bus system • Platforms:RTDS and DOME• Methodology:Comparison of Simulation Results


SCENARIO ANALYSIS AND VALIDATION: EXAMPLE 1

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FDMPMU DER 3

DER 2DER 1

DER 4DER 5

CentralizedAverageDecentralized

Distribution grid

Transmissi

on grid

• Concept: Primary Freq. Control of Dist. Systems with PCG• Test-bed: 9-bus system + Irish MV system• Platforms: RTDS • Methodology: Decentralized, average and centralized measurements• Network Code: Requirements for DSOs

ICT REQUIREMENTS FOR FREQUENCY SCENARIOS: MOTIVATION

7/4/2018 WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 18 © RESERVE 2017-8 All rights reserved.

• Today FC is provided almost exclusively by SGs.• Reduced number + long distances + Local PrimaryFC Current communications based on FiberOptic and phone calls.• As we move towards 100% RES scenario Significantly more agents will participate to thedifferent layers of the FC, which implies:o wide range of distances,o high reliability and accuracy of the transmittedsignals requiredo very short latencies required,o many new end points…• Opportunity to deploy 5G technology for REScontrol.


DRAFTING OF ANCILLARY SERVICES AND NETWORK CODES DEFINITION: PROPOSALSTOP PRIORITY SECOND PRIORITYFrequency Related Definitions: Frequencyand RoCoFRequirements for power converter-basedEnergy Storage SystemsRequirements of minimum system inertiaRequirements for the DSOsSystem swing dynamicsRequirements for grid-forming (freq. makers) RESs

Expanding the frequency controlstrategy to allow using small-sizedand/or intermittent energy resourcesFrequency control categories and timeframesRequirements for the HVDC systemsRecommended settings for thecontrolled unitsRequirements for information and dataexchange between TSOs and DSOs


DRAFTING OF ANCILLARY SERVICES AND NETWORK CODES DEFINITION: ASSESSED IMPACTNetwork Code Code Family Status Assessed impactRequirements for Generators

ConnectionExisting StrongDemand Connection Existing WeakHigh Voltage Direct Current Existing SignificantEnergy Storage Systems Missing Very StrongEmergency and Restoration

OperationsAwaiting StrongSystem OperationsGuidelines Existing Very Strong

Distribution System Missing Very StrongForward Capacity AllocationMarket

Existing WeakElectricity Balancing Awaiting StrongCapacity Allocation and Congestion Management Awaiting Significant

OBJECTIVES AND ACHIEVEMENTS (1/3)


Objectives Summary of achievementsAnalyse the dynamic requirement for frequency in 100% RES • The general frequency control framework was identified forENTSO-E countries• The frequency related to future requirements have beenanalysed from the dynamic point of view.

Extend the concept to a virtual inertia to a wider and more flexibleLinear Swing Dynamics approach • Proof of concept of the LSD has been completed (see D2.3).Define a general dynamic frequency stability criterial for grids withhigh generation of renewables and controllable loads • Basic requirements for inertial response and primary controlcharacteristics, in terms of time response and power delivered,for frequency stability have been drafted (D2.2).Define a strategy for the on-line measurement of the importantparameters • Proposal, development and validation of the “frequency dividerformula” (D2.1).

• The formula allows properly estimating local bus frequenciesand identifying the most relevant locations for on-line frequencyestimation (to be included in D2.6).• Detailed analysis of the needs of the scenarios for frequencycontrol regarding ICT as well as the customization for variouscontrol strategies (D2.4 and D2.2).



Objectives Summary of achievementsDefine a strategy for the evaluation of existing networks andattributes • A set of case studies to be validated by WP5 has beenproposed (to be included in D2.7). This includes both transientstability analysis and real-time simulations.Extract a monitoring concept that can exploit the existing systeminformation from each generator to define a system level picturein close to real-time

• Implementation of the “frequency divider formula” forestimation of local bus frequency variations in a simulationenvironment (see D2.1).• Discussion and presentation of revised version of ICTrequirements for Frequency Control scenarios (D2.4).

Draft ancillary service definitions and network codes for validationin WP5 and harmonization and standardization in WP6 • A list of proposed grid code service has been defined andranked in collaboration with WP6 (to be included in D2.6). Thiswill be validated by WP5.

Publications Derived from the Work of WP2:



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TYPE STATUS NUMBER TARGET M36(all RESERVE)Journal

Published/Accepted 10 > 5Submitted 1 -In preparation 3 -

ConferencePublished/Accepted 14 > 10Submitted 1 -In preparation 0 -TOTAL 14 + 15 = 29 > 15

Slide No. 24 © RESERVE 2016 All rights reserved.

ACHIEVEMENTS AND NEXT STEPS

2018-07-04

Done

To bedone

In Progress

Analyze the dynamic requirement for frequency control in very high penetration of Renewable Energy Sources (RES) scenario (Re)define the concept of frequency and rate of change of frequency (ROCOF) Frequency Divider Formula (FDF) Define the concept of Linear Swing Dynamic (LSD) Analyze the dynamic requirement for frequency control in 100% non-synchronous RES scenario Enhance the control of power-electronic-based virtual synchronous generators and HVDC links by means of the LSD Define the ICT requirements for power electronic-based frequency regulation Draft ancillary service and network code Validate the proposed ancillary service and network code definitions by means of simulations, for their subsequent harmonization and standardization in WP 6

WP2 - FREQUENCY STABILITY BY DESIGN


FREQUENCY DIVIDER FORMULA: MOTIVATION

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Increasing penetration of non-synchronous,non-inertial RESs: Local frequency variationsare biggerDecentralized

Centralized

DistributedAccurate knowledge of localfrequency deviations is fundamentalto take proper frequency controlactions Still an open question



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• Concept: RoCoF and Primary F. Control from Energy Storage Systems• Test-bed: Romanian Transmission System• Platforms: DOME, Eurostag• Methodology: % of ESS for a given level of system inertia; comparison of technologies; different locations; …

Annex - Journal Papers Published to date:1. F. Milano and Á. Ortega, “Frequency divider,” in IEEE Transactions on Power Systems, vol. 32, no. 2,pp. 1493-1501, Mar. 2017.2. Á. Ortega and F. Milano, “Modeling, Simulation and Comparison of Control Techniques for EnergyStorage Systems,” in IEEE Transactions on Power Systems, Vol. 32, No. 3, pp. 2445-2454, May 20173. P. Ferraro, E. Crisostomi, M. Raugi, F. Milano, “Analysis of the impact of microgrid penetration onpower system dynamics,” IEEE Transactions on Power Systems, Vol. 32, No. 5, pp. 4101-4109, Sep.2017.4. Á. Ortega and F. Milano, “Stochastic transient stability analysis of transmission systems withinclusion of energy storage devices,” in IEEE Transactions on Power Systems, vol. 33, no. 1, pp. 1077-1079, Jan. 2018.5. J. Zhao, L. Mili, and F. Milano, “Robust frequency divider for power system online monitoring andcontrol,” in IEEE Transactions on Power Systems, vol. PP, no. 99, pp. 1–1, 2017.


WP2 – FREQUENCY STABILITY BY DESIGN

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Annex - Journal Papers Published to date:6. F. Milano, “Rotor speed-free estimation of the frequency of the center of inertia,” in IEEE Transactionson Power Systems, vol. 33, no. 1, pp. 1153–1155, Jan 2018.7. Á. Ortega and F. Milano, “Frequency participation factors,” in IEEE Transactions on Power Systems,vol. PP, no.99, pp. 1–1, 2018.8. P. Ferraro, E. Crisostomi, R. Shorten, F. Milano, “Stochastic Frequency Control of Grid-connectedMicrogrids”, in IEEE Trans. on Power Systems, vol. PP, no.99, pp. 1–1, 2018.9. F. Milano, Á. Ortega and A. J. Conejo, “Model-agnostic linear estimation of generator rotor speedsbased on phasor measurement units”, in IEEE Transactions on Power Systems (in press).10. A. Musa and a. et., “Multi-Agent Based Intelligent Frequency Control in MTDC Grid-Based HybridAC/DC Networks,” in IET Renewable Power Generation Journal, (accepted for publication).



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Annex - Conference Papers Published to date:11. Á. Ortega and F. Milano, “Comparison of bus frequency estimators for power system transient stability analysis,” inProceedings of the 2016 IEEE International Conference on Power System Technology (POWERCON), Wollongong,NSW, Sept. 2016, pp. 1-6.12. Mihai Sănduleac, Ana-Maria Dumitrescu, Lucian Toma, Carmen Stănescu, Mihaela Albu, “On the frequencymeasurement in Wide Area Measurement and Control Systems,” in Proceedings of the 10th International Symposiumon Advanced Topics in Electrical Engineering, Bucharest, Romania, March 23-25, 2017.13. P. Ferraro, E. Crisostomi, M. Raugi, F. Milano, “On the Impact of Microgrid Energy Management Systems on PowerSystem Dynamics,” in Proceedings of the IEEE PES General Meeting, Chicago, IL,16-20 July 2017.14. J. Cerqueira, F. Bruzzone, C. Castro, S. Massucco, F. Milano, “Comparison of the Dynamic Response of Wind TurbinePrimary Frequency Controllers Constraints,” in Proceedings of the IEEE PES General Meeting, Chicago, IL, 16-20 July2017.15. Á. Ortega and F. Milano, “Impact of frequency estimation for VSC-based devices with primary frequency control,” inProceedings of the ISGT Europe Conference, Turin, Italy, 26-29 September 2017.16. P. Ferraro, E. Crisostomi, M. Raugi, F. Milano, “Decentralized Stochastic Control of Microgrids to Improve SystemFrequency Stability,” in Proceedings of the IEEE PES ISGT Europe 2017, Turin, Italy, 26-29 September 2017.17. Mihai Sanduleac, Lucian Toma, Gianfranco Chicco, Mihaela Albu, “Network Code on Requirements for Generators –A discussion. Resynchronizing with paradigm shifts,” in Proceedings of the IEEE PES ISGT Europe 2017, Torino, Italia,26-29 September 2017.WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 30 © RESERVE 2017-8 All rights reserved.


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Annex - Conference Papers Published to date (Cont.):18. Mihai Sanduleac, Lucian Toma, Constantin Bulac, Mircea Eremia, Nicolae Golovanov, Radu Porumb, Mihaela Albu,Stefan Gheorghe, Catalin Chimirel, “Energy storage for reaching 100% CO2 free and 100% RES – preliminary casestudy for Romania”, in Proceedings of the 8th International Conference on Energy and Environment (CIEM 2017),Bucharest, Romania, 19-20 October 2017.19. Á. Ortega and F. Milano, “Comparison of different PLL implementations for frequency estimation and control,” inProceedings of the IEEE PES ICHQP 2018 Conference, Ljubljana, Slovenia, May 2018.20. J. Chen, M. Liu, C. O’Loughlin, F. Milano, T. O’Donnell, “Modelling, Simulation and Hardware-in-the-Loop Validation ofVirtual Synchronous Generator Control in Low Inertia Power System,” in Proceedings of the PSCC 2018, Dublin, Ireland,June 2018.21. F. Milano, F. Doerfler, G. Hug, D. Hill, G. Verbic “Foundations and Challenges of Low-Inertia Systems,” invited surveypaper, in Proceedings of the PSCC 2018, Dublin, Ireland, June 2018.22. Á. Ortega, A. Musa, A. Monti and F. Milano, “Hardware-in-the-loop validation of the frequency divider formula” inProceedings of the Power Engineering Society General Meeting, IEEE, Portland, OR, USA, Aug. 2018 (accepted forpublication).23. Lucian Toma, Mihai Sanduleac, Stefan Andrei Baltac, Francesco Arrigo, Andrea Mazza, Ettore Bompard, AysarMusa and Antonello Monti, “On the Virtual Inertia Provision by BESS in Low Inertia Power Systems”, in Proceedings ofthe EnergyCon 2018 (accepted for publication).24. David Raisz, Aysar Musa, Ferdinanda Ponci, and Antonello Monti “Linear and Uniform System Dynamics of FutureConverter-Based Power Systems”, in Proceedings of the IEEE PES GM 2018, (accepted for publication).WP2 - FREQUENCY STABILITY BY DESIGN Slide No. 31 © RESERVE 2017-8 All rights reserved.


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Annex - Journal Papers under review and in preparation:25. F. Milano and Á. Ortega, “Frequency-dependent model for transient stability analysis,” in IEEETransactions on Power Systems, (submitted in Jan. 2018 and currently under review).26. Á. Ortega and F. Milano, “Identification of grid-forming RESs based on frequency regulationcapability”, in IEEE Transactions on Power Systems (in preparation).27. D. Raisz, A. Musa, F. Ponci, A. Monti, “Linear and Uniform Swing Dynamics”, in IEEE Transaction onSustainable Energy (in preparation)28. A. Musa, A. Kaushal, D. Raisz, F. Ponci, A. Monti, “Development and Stability Analysis of LinearSwing Dynamics-based Improved VSG for Hybrid AC/DC Networks” in IEEE Transaction on PowerDelivery / Elsevier (in preparation)



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Annex - Conference Papers under review and in preparation:29. Á. Ortega and F. Milano, “Frequency control of distributed energy resources in distribution networks”,in Proceedings of the IFAC CPES 2018 Symposium, Tokyo, Japan, Sept. 2018 (submitted in Jan.2018 and currently under review).



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