Transcript max_shadow_priceV3

Maximum Shadow Price
April, 2008
Protocol Requirement:
6.5.7.1.11 Transmission Constraint Management
(2) ERCOT shall establish a maximum Shadow Price for each
constraint as part of the definition of contingencies. The cost
calculated by SCED to resolve an additional MW of congestion on
the constraint is limited to the maximum Shadow Price for the
constraint. ERCOT shall develop a policy for setting maximum
Shadow Prices for approval through the PRR process.
April, 2008
Need for Maximum Shadow Price:
Maximum Shadow Price limits the cost of resolving the constraints.
i.e
• for a given energy offer curve, it prevents dispatching Resources
with Shift Factor below a certain level.
• for a given Shift Factor, it prevents dispatching Resources with
offer above a certain price.
i.e. indirectly putting a upper limit on the energy offer and lower limit
on the shift factor of the resources selected for re-dispatching to
resolve the constraint.
The relative value of the Maximum Shadow Price determines the
priority order in which the constraints will be violated by SCED if
needed.
April, 2008
Effects of Maximum Shadow Price value:
It is the coefficient of the slack variable corresponding to the constraint
in the SCED objective function. i.e. it is the maximum allowed
increase in production cost for resolving 1MW of the constraint.
Objective = Min ( Cost of generation dispatch
+ Sum ( Max Shadow Price * Slack variable)
LMP at any electrical bus is
Energy Component = Shadow price of Power Balance constraint
+
Congestion Component = - sum ( Shift Factor * Shadow Price for
the constraint )
April, 2008
Zonal Vs Nodal :
The nodal prices could be much higher or lower than what we get in
zonal. Some of the factors are
In Zonal
• Only Zonal Congestion affects the price
• Shift Factors are fixed and low
• Ramp Rate can be violated
• Ramp Rate is not reserved for AS
In Nodal
• All constraints will affect price
• Shift Factors are not fixed
• HDL/LDL constraints can not be violated
• SURAMP = Normal ramp rate – regulation responsibility / 5
April, 2008
Finding the right value:
Difficulties in finding the right value:
• If the value is too low then most constraints will be violated in
SCED.
• If it is too high then
– Resources with very low shift factor will be moved for
solving the constraint and
– drastic increase in price could happen for negligible
increase in reliability.
We need to resolve the constraints passed to SCED since only those
constraints that need to be resolved are passed to SCED.
April, 2008
Constraint Processing:
RTCA –
SPS/RAP
DRAP
TCM
SCED
Operator
•
RTCA –SPS/RAP implementation
– SPS / RAPs associated with the monitored element/ contingency are implemented and color
coded if the violation can be resolved by the SPS / RAPs
•
DRAP
– Develops generation dispatch patterns for resolving constraints.
– Violations lower than load shed limit that can be removed by generation dispatch during the next
SCED cycle are color coded
TCM
– Constraints are passed to SCED only if they are approved by the operator. SPS/RAP
implementation and DRAP help determine the severity of the constraint
•
Operators should only pass the post contingency violations that can not be resolved by RAP/SPS/DRAP.
RAPs should be implemented before a base case violation is passed to SCED.
SPSs will be implemented automatically when the contingency happens
April, 2008
Calculating the value:
Typical maximum heat rate in ERCOT
– 16 MMBTU/MWhr
Average fuel Index Price
– $7.00 per MMBTU
Typical maximum Energy Offer Curve
– $112 / MWhr (16*7)
If SCED needs to move a Resource with 0.03 Shift Factor when
Energy Offer Curve is equal to or less than $111 / MWhr, then the
maximum Shadow Price should be $3700 (111/0.03)
April, 2008
Proposed Maximum Shadow Price :
For simplicity reasons ERCOT proposes to assign default
maximum Shadow Price to monitored elements based on
voltage level along with assigning higher or lower values based
on operational experience.
Default value for different kV levels
•69kV
– 2800 (~ 111/0.04)
•138 kV
– 3700 (~ 111/0.03)
•345 kV
– 5600 (~112/0.02)
April, 2008
Variation from default values:
In current EDS market trial, the Maximum Shadow Prices are
hard coded based on the voltage level of monitored element.
We are working on a design in which the values can be changed
from the default values and stored at a monitored element
level.
ERCOT plans to do periodic evaluation of the Maximum Shadow
Price and adjust it accordingly.
ERCOT, with input from CMWG, will present an NPRR that will
define the methodology for setting the Maximum Shadow
Price and for periodic review of these Maximum Shadow
Prices.
April, 2008
Special Cases : Generic Constraints / Base Case Violation
Generic Constraints (for Voltage Collapse) / Base case violation needs to
be resolved for system reliability. [Note: Interface limits are developed to
prevent voltage collapse scenarios. These are passed as generic constraints
to SCED through TCM]
To move resources with Shift Factor >0.05 even at SWCAP, the Max
Shadow Price should be 60000 (3000/.05). But this could result in very
high price.
A reasonable value of maximum Shadow Price ($6000) for Voltage
Collapse and Base Case violation was developed after discussion with
market monitor
For SCED to move a Resource up with energy offer of $112/MWhr and
Shift Factor >0.02 and to move a Resource down at $-10/MWhr with
no shift factor to the constraints, the max shadow price should be (112
- -10)/0.02 ~ 6000
April, 2008
Example:
If the Maximum Shadow Price for base case is set to 60000 then the
LMP at the electrical bus could be of the magnitude of 60000
Consider an electrical bus with 5 lines and a load connected to it. Lets
assume that the bus has shift factor -0.25, -0.32 and -0.29 for the 3
lines which are violated at the base case and SCED is unable to
resolve these constraints. So the LMP of the bus will be
[ Energy Cost – (-0.25* 60000 + -0.32 * 60000 + -0.29 * 60000)]
April, 2008
Special Cases : Power Balance
Power Balance constraint should never be violated and
hence the maximum shadow price for it should be a
relatively high number. It is set to $100,000 in the current
EDS market trial environment.
Effect:
If the Power Balance constraint is violated then the prices
will be of the order of $100,000.
April, 2008