EE/Econ 458
Market Overview:
Time-Line and
SCUC, RAC, SCED
J. McCalley
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Market time line
Operating day
commences.
RAC process closes;
new units notified.
2000
0000
Ref: A. Botterud, J. Wang, C. Monteiro, and
V. Miranda “Wind Power Forecasting and
Electricity Market Operations,” available at
www.usaee.org/usaee2009/submissions/Onl
2
ineProceedings/Botterud_etal_paper.pdf
Two markets and a process
The next slide is divided into three columns, one each for
• Day-ahead market,
• Reliability assessment commitment process, and
• Real-time market
For each column, there are two main sections.
• The upper section, in dark blue, yellow, and green, say what its name is (dark blue), what
kind of market it is (yellow), and what it does (green).
• The lower section, in light blue and pink, identifies the software applications used within
the function, either SCUC (light blue) or SCED (pink).
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Two
markets
and
a
process
DAY-AHEAD MARKET
REAL-TIME MARKET
(DAM)
The Day-Ahead Energy
and Operating Reserve
Market is a financially
binding market that
clears energy, reg
reserve, spin reserve &
supp reserve hourly.
SC-SCUC commits
resources, schedules
regulating reserves on
committed resources
and/or releases
emergency operating
ranges on resources.
SC-SCED is used to
clear/price energy,
regulating reserve,
spinning reserve and
supplemental reserve
on hourly basis.
Reliability Assessment Commitment Process
(RAC)
The Reliability Assessment Commitment
(RAC) process is a process to
commit resources, schedule regulating
reserve on committed resources and/or
release emergency operating ranges on
resources when appropriate, hourly
for use in the Real-Time Energy and
Operating Reserve Market. The RAC
process can be executed on a multi-day,
day-ahead and/or intra-day basis.
SC-SCUC is used in the RAC process to
commit resources, schedule regulating
reserves on committed resources
and/or release emergency operating
ranges on resources for the Real-Time
Energy and Operating Reserve Market.
Ref: M. Tackett, Experience with Implementing
Simultaneous Co-optimization In The Midwest
ISO Energy & Operating Reserve Markets, IEEE
PES General Meeting, 2009.
(RTM)
The Real-Time Energy
and Operating Reserve
Market is a financially
and physically binding
market that clears
energy, reg reserve, spin
reserve and supp
reserve every 5 minutes.
SC-SCED is used in RealTime Energy/Operating
Reserve Market to
dispatch & price energy,
regulating reserve,
spinning reserve and
supplemental reserve on
a 5-minute basis.
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1.
2.
3.
4.
5.
6.
7.
8.
Two markets - comments
Two markets: “Energy & operating reserve” are 2 different markets, 1 for
buying/selling energy, 1 for buying/selling operating reserve.
Co-optimization: The first “SC” in SC-SCED/SC-SCUC stands for
“simultaneous co-optimized” referring to the fact that both energy &
operating reserve markets are cleared within 1 optimization formulation.
Reserves: Regulation reserve supplies minute-by-minute variation in netdemand via AGC. Spinning/supplemental reserve provide backup for
contingencies (gen loss). Spinning is inter-connected, supplemental need not
be; both must be available within 10 mins of a request.
Financially-binding: a settlement will occur; buyers will pay and sellers will
be paid according to the market outcome.
Physically-binding: solution will be imposed on the system.
Use of SC-SCED: In DAM, SC-SCUC solves once per hour and then for that
hour, SC-SCED is also solved. RTM uses the RT commitment as input to SCSCED in computing RT dispatch every 5 minutes.
LMPs: SC-SCUC gives hourly commitment and dispatch, but w/ limited
network modeling, therefore no nodal prices (LMPs). SC-SCED, given a
commitment and full network modeling, gives dispatch & nodal prices.
Contingencies: Transmission security constraints for SC-SCUC are enforced
via a predefined constraint list for the SCUC and a simultaneous feasibility
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testing (SFT) function iterating with SCED.
Two markets - comments
Note the difference between use of SC-SCED for DAM and RTM.
DAM
SCUC gives a
24 hour
solution
1
2
3
4
5
6
7
8
9
16 17 18 19 20 21 22 23 24
SCED gives one solution per hour
RTM
Real-time
conditions
(determined
by SCUC and
RAC)
0 5
10 15 20 25 30 35 40 45 50 55 60 5 10 15 20
SCED gives one solution every 5 minutes
25 30…
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Day-Ahead Market
SCUC enforces
limited number
of transmission
constraints on
the commitment
solution.
Each hourly SCED
performs SFT, which
tests all contingencies
in a list and for
violations, imposes
appropriate constraints
in SCED and resolves it.
Ref: Xingwang Ma, Haili Song, Mingguo Hong, Jie Wan, Yonghong Chen, Eugene Zak, “The Security-constrained
Commitment and Dispatch For Midwest ISO Day-ahead Co-optimized Energy and Ancillary Service Market,”
Proc. of the 2009 IEEE PES General Meeting.
Real-time Market
SCED1
Reciprocal
Coordinated
Flowgates –
predefined
transmission
which
requires
MISO-PJM
coordination.
SCED2
EMS performs state estimation
(SE) & contingency assessment
(CA), then imposes necessary
transmission constraints to
SCED1 and SCED2.
• SCED1 performs 5 min
RTM solutions to get
dispatch and LMPs.
• SCED2 performs a
redispatch in case the RAC
changes the commitment.
SCED1, SCED2 dispatch signals
provided as “base-points” to
AGC which communicates them
to generators.
Ref: Xingwang Ma, Yonghong Chen, Jie Wan, “Midwest ISO Co-optimization Based Real-time Dispatch and
Pricing of Energy and Ancillary Services,” Proc. of the 2009 IEEE PES General Meeting.
RAC process - comments
9. Tool used: RAC uses SC-SCUC only (does not use SC-SCED).
10. What? RAC is reliability backstop that ensures sufficient resources are
available & online to cover forecast load, minimizing the commitment
cost of resources in RAC process while operating the grid within
applicable reliability standards. NOT a market!
11. Why? DAM clears based only on bids, offers, self & bilateral schedules
that market participants (MP) submit, without regard to load forecasts.
In the event that DAM closes significantly below the load forecast and
adequate resources have not been committed to meet that forecast, the
RAC process commits additional supply to meet the load forecast and
reserve requirements.
12. When? MISO publishes most recent load forecast for each hour in
operating day, and final day-ahead schedules for load. 5-6 pm rebidding,
6-8 AC solved & MPs notified.
13. Costs: Costs associated with the RAC process are borne by MPs who
exhibit deviations (additional load or reduced generation) from DayAhead schedules. This cost allocation process is consistent with the way
PJM and ISONE do their cost allocations.
Ref: “Reliability Assessment Commitment Process,” available at
https://www.midwestiso.org/Library/Repository/Meeting%20Material/Stakeholder/RETIRED%20COMMITTEES/RMWG/20050415/20050415%20RMWG%20RAC%20Whit
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e%20Paper.pdf.
Simplified versions of SCED and SCUC
They are both tools to solve optimization problems. But different optimization problems.
Here are some observations.
SCUC Objective
SCED Objective
min
•
•
•
•
•
•
•
•
s P 
min
k gk
k generator _ buses
Decision variables are Pgk
Objective & constraints are linear
Pgk are continuous valued
It is a linear program (LP).
It is a convex programming problem.
It is solved by simplex, very efficient.
For a single time period (1 hr or 5 min).
It provides LMPs.
 zit Fit   git Cit   yit Sit   xit H it
t 
i

t 
i 

Fixed Costs
Production Costs
•
•
•
•
•
•
•
•
t 
i 
t 
i 

Startup Costs
Shutdown Costs
Decision variables are zit, git, yit, xit
Objective & constraints are linear
zit, yit, xit are discrete, git is continuous
It is a mixed integer linear program (MIP).
It is a non-convex programming problem.
It is solved by branch and bound.
For multiple time periods (2-24 hrs or more)
It does not provide LMPs.
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