Harmonizing the Changing Resource Mix Keeping the Grid Together

Transcription

1 Harmonizing the Changing Resource Mix Keeping the Grid Together Robert W. Cummings Senior Director of Engineering and Reliability Initiatives i-pcgrid March 30, 2017

2 NERC-IEEE Memorandum of Understanding NERC and IEEE have signed a Memorandum of Understanding to: Encourage communication between the two organizations; Promote shared knowledge of the standards development activities of each organization; and Facilitate liaisons between each other s technical groups and other cooperation where possible Joint Operating Committee to determine structure 2

3 IEEE PES and Committees as Qualified Organization(s) New pre-qualifying process for organizations to provide or assist in development of Compliance Guidance for NERC Standards PES or possibly Committees such as PSRC could become qualified Structure under discussion 3

4 NERC Memorandum of Understanding with Mexico NERC recently signed a Memorandum of Understanding with: Comisión Reguladora de Energía (CRE) regulator Centro Nacional de Control de Energía (CENACE) planner/ operator Outlines a framework for a cooperative relationship between Mexico and NERC to enhance grid reliability of North America Recognizes established and growing interconnections between the United States and Mexico Establishes a collaborative mechanism for identification, assessment and prevention of reliability risks to strengthen grid security, resiliency and reliability. 4

5 Changing Load Load composition changing Electric vehicle charging LED lighting Variable speed drive motors Distributed Energy Resources Inverter-based resources o Roof-top solar panels o Micro turbines o Small wind turbines Load becoming schizophrenic Load models no longer adequate for simulations 5

6 Changing Resources Changing Dispatch Mix High penetration of renewables variable resources Minimum generation levels on conventional units Ramping needs increase for load following Retirement of large fossil-fired generation plants Loss of dynamic reactive support for voltage control Possible reduced system inertia Lower levels of synchronizing torque Changing System Inertia Trade-offs between inertia and Primary Frequency Response 6

7 Cautionary Tales Inadvertent creation of new reliability hazards Very large DC transmission projects New largest single hazards Series-compensated transmission lines Sub-synchronous resonance Sub-synchronous controls interaction Inverter-based resources Digital controls on conventional generation System controls SVCs, Statcoms, DC converter stations, 7

8 Potential Interaction Examples Potential response to combination of voltage and frequency perturbations associated with complex system disturbances High-quality supply loads that are Voltage/Frequency-sensitive Experience of 600 to 900 MW load loss due to transfers to backup supplies during faults Locational injection impact on transmission elements and interfaces Response masquerading as a power swings protection system concerns 8

9 Western Interconnection Frequency 9

10 Solar Resource Loss 10

11 PV Impact 26 different solar developments All utility scale Connected at 500kV or 230kV 10 different inverter manufacturers Reported causes of trips Under frequency Over voltage DC overcurrent 1 loss of synchronism 11

12 Not an Isolated Event 12

13 Inverter Task Force Harbinger of very large event based on common-mode performance Task Force forming Includes inverter manufacturers Talking about desired performance Ride through Blocking Partial run-back Prescribed return seconds rather than minutes 13

14 Frequency Response Strategy All resources should have the capability of providing Primary Frequency Response 14 Regardless of dispatch, frequency response should be available Comments to FERC on SGIA and LGIA Create a continuum of frequency response based on capabilities of specific resources: Arresting energy injection from fast frequency response from storage and modulated load Contracting for frequency responsive loads Sustained response from conventional generation resources and modulated load Cohesive Frequency Response regulations IEEE 1547 NERC PRC-027

15 Traditional generation Wind Turbines Synthetic Inertia Off-optimal blade attack angle backing down from maximum Energy Storage Distributed Energy Resources Solar Micro turbines Micro grid resources Load acting as a resource Tripped by specialized under-frequency relays Smart appliances independent operation Aggregated load controlled by aggregator Modulated load Potential Sources of Primary Frequency Response 15

16 Frequency Response Control Continuum Inertial Response Primary Control (Gen. Response) Milliseconds Seconds to 1-2 minutes Spinning Reserves Secondary Control (AGC) Recovery of Reserves Minutes Minutes to Hours Non-Spinning Reserves 16

17 Importance of System Inertia in ERCOT 60.0 Hz 59.4 Hz Bus frequency (Hz) Generation Trip: 2,750 MW Case 1---: Net Load = 65 GW, SI = 372 Case 2---: Net Load = 35 GW, SI = 236 Case 3---: Net Load = 17 GW, SI = Hz Time (sec) Inertia (GW-second): 1 > 2 > 3

18 Inertial Response Variability High Inertia Light Inertia 18

19 Trade-off between Inertia and Primary Frequency Response 60.0 Hz Bus frequency (Hz) Generation Trip: 2,750 MW Case 1---: Net Load = 65 GW, PFR=1,300MW Case 2---: Net Load = 35 GW, PFR=2,500MW Case 3---: Net Load = 17 GW, PFR=4,700MW Hz Time (sec) Primary Frequency Response (MW): 3 > 2 > 1 19

20 Multiple Roles for Energy Storage in Maintaining Reliability High-speed energy injection following loss of resources High-speed response during Arresting Phase of a Frequency Event o Response proportional to the change in frequency and rate of change in frequency o Help to offset loss of system inertia due to displacement or retirement of generation Continuous proportional response to frequency deviations Frequency control services Energy injection to perform ramping services Reduce severity of solar-based resource drop-off in evening 20

21 Frequency Response Basics A Pre Event Frequency NERC Frequency Response = Generation Loss (MW) Frequency Point A -Frequency Point B Governor/Load Response (MW) C c Frequency Nadir: Generation and Load Response equals the generation loss Slope of the dark green line illustrates the System Inertia (Generation and Load). The slope is ΔP/(D+2H) B Settling Frequency: Primary Response is almost all deployed Governor Response Load Response Frequency Frequency (Hz) Time (Seconds)

22 Potential Operating Mode for Battery Charging Hz Hz Energy storage can move from a charge to discharge cycle similar to traditional generator droop characteristic 22

23 CAISO Load Balancing Concerns 23

24 Ramping / Load-Following Services Role for Storage Supplement generation during severe upward ramps Morning load pick-up before solar reaches full output Evening load pick-up when solar output is dropping off Absorb energy during downward ramps When solar and wind output ramps up to full output and morning load stabilizes Absorb energy to prevent over-generation Charge storage when solar and wind output exceeds energy demand Load-following to provide balance for variable resources Wind and solar variability due to changes in weather 24

25 Other Frequency Developments Significant frequency characteristics changes in ERCOT TRE BAL-001 Standard in effect in 2015 Requires active frequency response on ALL resources, including wind Sets deadband at ± Hz Tremendous impact on response and characteristics 25

26 One Minute Occurances ERCOT Frequency Profile Comparison January through December of each Year In 2015 there were 46,008 one minute average frequency values equal to Hz or less than Hz

27 MW January thru December db vs db MW Minute Movement of a 600 MW 5% Droop MW Response of db 76.35% MW Response of db Decrease in MW movement from 2008 to MW Response of db 2015 MW RELIABILITY Response of ACCOUNTABILITY db

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