ROBUSTNESS ASPECTS in REAL TIME ENERGY MANAGEMENT …

ROBUSTNESS ASPECTS in REAL TIME ENERGY MANAGEMENT POWER NETWORK APPLICATIONS

THROUGH STATE ESTIMATOR

Veera Raju VINNAKOTA (P.Eng.,Canada) & Sirajul CHOWDHURY

California ISO, USA

2019 April 15

California State University Sacramento,

IEEE PES Chapter, Sacramento Valley Section

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PRESENTATION OVERVIEW• ABSTRACT (Summary of Presentation)

• INTRODUCTION

– California Independent System Operator (CAISO) Overview

• ROLE OF STATE ESTIMATOR AND IT’S CRITICALITY

• CHALLENGES TO ADDRESS

• PROVIDING A ROBUST STATE ESTIMATOR

– TECHNIQUES, TOOLS

– TRAINING (internship, on-the job, coaching)

– ONGOING SUPPORT AND STRUCTURE

• SUMMARY

• ACKNOWLEDGEMENTS

• REFERENCES

ABSTRACT (SUMMARY) - 1/2

ROLE OF STATE ESTIMATOR IN CONTROL CENTERS

• State Estimator (SE), critical for Electric Power Markets and for Grid Reliability operations in real time

• SE provides a steady-state power network solution of complex bus voltages at electrical nodes t

• Two main inputs

The network that is modeled

Telemetered real time measurements

Power flows, voltages and transformer tap settings,

equipment CB / switch status.

• A converged solution from SE is essential for other real time applications to provide guidance to the Control room operators so as to be prepared ahead of time or to optimize market operation in real time, day-ahead operations

COMPLEXITY OF THE PROBLEM IN PROVIDING A RELIABLE SOLUTION AND THE CHALLENGES

• SE optimization problem is non-linear in nature

• Providing a converged solution is first level of challenge

• From Grid Stations to SE in a Control Center Computer several components are in tandem- Ensuring continuous flow of data is another challenge

• Uncertainties in providing reliable set of real time measurements to SE is a greater challenge in supporting a reliable SE solution

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ABSTRACT (SUMMARY) - 2/2

Nature of Uncertainties in Real time • Missing a few measurements due to communication errors,

• Loss of a bunch of measurements due to telemetry loss with RTUs

• Loss of data links impacting real time measurement from several RTUs

• Loss of complete data from the entire Balancing Authority (BA) participating in Markets

• Loss of data from several BAs due to loss of one or more data links

• Loss of computers which serve the data links

Ensuring Market Systems to continue running is a great challenge

These are dealt in this talk

Additionally, two more aspects which impact SE availability are discussed• Tuning efforts which are put in by the support team

• Support structure put in place in the organization to have get SE solving again when it starts failing

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CAISO Overview – Main Office in Folsom, California

CAISO Overview - Independent System Operators and Regional Transmission Organizations

Control flow of electricity on transmission grid

Regulated by FERC

Serve 66% of the U.S. & more than 50% of Canada

Do not own generation or transmission infrastructure

WESTERN INTERCONNECTON BALANCING AUTHORITIES

CAISO Overview

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CAISO role in running the Electric Grid

- Reliable (continuous) supply of electricity to the

consumers – Run the electric grid reliably

- Provide electricity at a competitive price with

sustainable use of resources

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Market Optimization with Grid Reliability

• Resource Optimization in Markets by :

⁻ Day-ahead market optimization

⁻ Real Time market optimization

⁻ Energy Imbalance Market optimization

• Grid reliability by :

– Ensuring adequate reserve to cover contingencies

– Operate within Operating limits computed in real-time

CAISO HAS THREE MARKETS

Day-Ahead Energy Market

• Enables:

• parties to schedule contracted supply/demand

• suppliers to offload excess supply in the form of energy or ancillary services

• LSEs the ability to secure pricing for load due to:

• changes in load forecasts or

• incremental changes in demand

Real-Time Energy Market

• Hour-ahead scheduling for intertie resources

• 15-min market supports renewable integration

• 5-min market intended to meet instantaneous demand

• Includes:

• ISO Balancing Authority Area

• EIM Balancing Authority Areas

Slide 11

Without EIM:

Each BA must balance loads and

resources within its borders

With EIM:

The market dispatches

resources across BAs to

balance energy

BABA

BABA

BA BA

BABA

Energy Imbalance Market

Western Energy Imbalance Market

• Is a real-time wholesale energy trading market balancing

• Enables participants in the West to buy and sell energy

• EIM operates across participating balancing areas

• PacifiCorp was activated on November 1, 2014 along with CAISO

• Current EIM participants are: NV Energy (Nevada), Puget Sound Energy (Washington),Portland General Electric, Idaho Power, Powerex (Canada). Others in the process: SMUD, Seattle City Light, LADWP, SRP (Arizona), ..

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EMS Overview, Network Applications, Interfaces

Slide 13

EMS

AGC

ICCP RIG/DPG

PI Systems

Network Apps

MarketSystem

Operator Displays

AGC Set Points

Network Applications State Estimator

Power Flow

Contingency Analysis

VSA/ DSA

Network Applications

In New Architecture

Being transitioned into

new EMS architecture

Being transitioned into

new EMS architecture

EMS About 50 ICCP

data links, 200

RTUs fetch

real time data

to support

AGC, full

WECC

network model

About 280K

SCADA points

in EMS

REAL TIME SEQUENCE OF EMS NETWORK APPLICATIONS

System Status Processor

State Estimator (SE)

EMS DLF Mkt DLF

Contingency Analysis( New EMS)

0 Sec

30 Sec

120

Sec

Results For Market UseResults For VSA

(with new EMS

architecture)State Estimator (SE)

( New EMS)

300

Sec

300

Sec (in transition)

(Being phase out)

Role of State Estimator (SE) in Grid Operations

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State Estimator (SE) is critical for electricity markets and

reliability operations

SE solution quality assumed greater importance due to

Energy Imbalance Market (EIM) expansions

feeds the solution to Market Operations

feeds the solution to Real Time Contingency Analysis

feeds the solution to Real Time Voltage Stability Analysis

Model size for State Estimator (SE) at CAISO

California ISO is one of the nine ISO/RTOS of North

America with a peak load of about 55,000 MW

Approximate network model size

State Estimator is run twice a minute

New State Estimator is currently run every 5 minutesTypical availability of SE is around 99.95 % (Average loss of less than 2 runs a day)

Higher availability is planned

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Load 110,000 MWNumber of Areas 40Number of Buses 18500

SE Robustness Solution Quality measures – 1/4CORRECTIVE MEASURES OF ADDRESSING AVAILABILITY AND SOLUTION QUALITY

- Address INVALID SE solution in real time (Resolve the issue in real time and analyze off-line for long term fix)

a) Model, Measurement deficiencies

Fix the model in next Data base promotion

Update out-of-date BA model for better estimate of SE solution

b) Real time tuning issues : switch override, disable measurements / flip measurement sign and initiate field correction, flip measurement signs and initiate field correction to get over the problem and analyze off-line to fix the problem

c) Identified network model & measurement changes are implemented along with network model updates every quarter

PREVENTATIVE MEASURES FOR BETTER AVAILABILITY AND SOLUTION QUALITY

- SE success/failure of each run is archived, reviewed on weekly basis

- Quantitative measures used to catch all the model/measurement/tuning related aspects

- SE solution Quality is tracked in every run, reviewed weekly for pro-active efforts

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SE Robustness Solution Quality measures – 2/4

Corrective Measures (additional)

- On-call Support structure to immediately attend to the ‘diverged’ instance (Else Market and other apps stop)

- On-call support to address down-stream application impacting messages to support staff

Degraded operation

- Increase use of ‘last good value’ duration (default for 20 minutes; increased to 1 hour and then as needed)

- Relax convergence criterion in less impacting BAs with respect to CAISO (Markets / Reliability) if the divergence is in such areas

Additional features (Some are in making)

• - BA telemetered Load is used to get better estimation of unobservable portions of the network

• Large scale loss of real time measurements (Data link failures) : high risk links from loss of data point of view

• Disconnect a BA model until the issue is resolved (could be an operational uniqueness resulting in invalid solution due to model deficiencies OR over-sensitivity of an area due to details modeling waiting for tuning)

7 x 24 On-Call Support

to maintain data quality and high System, Applications availability

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SE Robustness, Solution Quality measures – 3/4Data, Data Links Related

• 20 more new ICCP data links to minimize risk of a single link failure to reduce the risk of loss of observability in SE

• ICCP links are monitored via high priority heart beat alarm

• Outage of ICCP links (Real time data links from Utilities) can be forced or planned.

• Advanced network applications have ride through timer to hold last good telemetry in SE



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o Back-up measures for market functions and reliability functions

• loss of real time telemetry data due to data link failures of up to 20 minutes (extendible) — use of last valid real time telemetry data

• bad quality of SE solution leading to divergence of Market Power flow — market power flow automatically switches to DC solution instead of AC solution

• further reduction in periods of Invalid solutions — temporary relaxation of convergence criteria in the problem BA areas (in plan)

• backup to most severe single contingency (MSSC) posting to WECC for AGC reserve requirement — manual entry beyond 20-25 minutes



SE Robustness, Solution Quality measures – 4/4

Metrics Monitored per Balancing Authority Area

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% Load Delta with respect to SCADA / AGC

% Generation Delta with respect to SCADA / AGC

Total of negative generations in MW

Total of negative Load in MW

TRACKING SE SOLUTION QUALITY METRICS

• values computed every SE run, tracked on PI

• metric value helps choose target quality level and for pro-active improvements

ELEMENTS CONTRIBUTING TO DIFFERENCES ( DELTAs)Model Related

• Total load, Total generation not modeled

• Inadequate network model

• Model inadequacies influencing neighboring area estimations

• impact of switching events in adjacent areas of a smaller area relative to a larger area

Telemetry / Measurements / Metrics Related

• generation behind meters ( e.g., Gen unit auxiliary load, Qualifying resource outputs) causing inaccuracy of estimate impacting load calculation

• Inadequate Measurements for State Estimation

• Out-of-date reference against metric

Tuning related

Inadequate tuning

SUMMARY

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CAISO overview is presented

Criticality of State Estimator in Market and Reliability operations

is highlighted

Challenges of providing a converged solution from SE in real

time are presented

Techniques and processes of achieving SE robustness and

solution quality are discussed

On-going support structure for achieving Robustness of SE is

discussed

Acknowledgement

To CAISO for support and encouragement to

present some of the works carried out at CAISO

To CAISO for encouraging the effort to improve

processes of supporting SE solution quality and

availability

To EMS on-call support staff of Network

Applications for helping in tuning and supporting SE

availability and solution quality at CAISO

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References

“Experiences at California ISO in supporting State Estimator solution accuracy due to external model for reliability and market operations”, Ankit Mishra, Veera Raju Vinnakota, James Bonham, Sirajul Chowdhury, Brian Cummins, California ISO, USA made at IEEE PESGM 2014 July 27-31, Washington D.C.

“Methodical Approach to State Estimation Solution Quality for Power Grid reliability and Market Operations”, Veera Raju Vinnakota, California ISO, U.S.A presented at IEEE talks of Sacramento Valley Section PES Chapter , California State University Sacramento 2015 March 11, 2015.

THANK YOUFor further information, contact

Veera Raju VINNAKOTA ([email protected])

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mailto:[email protected]

Additional Slide ( If needed)

NOTES :

IN-SCOPESteady state operation

Steady state operation ( all EMS and Market functions).

> Market Function Market Operators, Generators, should be rewarded based on their efforts in providing their service

> Reliability function Grid should operatate reliability ( continuity of supply)

– Against modeling inadequacies

– Against measurement inadequacies

– Against tuning inadequacies

– Software deficiencies

Resiliency against loss of measurement ( Eg., you are on highway and your speed dial does not work - go with the flow.until you fix the meter. Your breaks failed or gas emptied --> move to shoulder; call Towing company, get it repaired), data links, inadequate measurements,

Specific area giving trouble:

Relax convergence parameters

Disconnect the model from the system by opening the switches

Resiliency against Operating conditions ( grid is split but operating in steady state; Grid is split but is not operating in Steady state)

Supplement the measurements with non-realtime data but reasonable close to the values so that the Market function continues reliability function continue

Worst case scenario: Market may stop but grid should be continuing ( payments are settled later) depending on what the generators are providing.

If there is disturbance condition such as grid failure, AGC, State Estimator, other reliability tools have no role until the grid is restored and stabilized.

OUT OF SCOPE• Disasters, natural / man made --> Equip with tools for recovery (out of scope of the topic)

• GRID failures

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ROBUSTNESS ASPECTS in REAL TIME ENERGY MANAGEMENT …

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