What is Auto Time Error Control? A revised ACE equation and Inadvertent Interchange Payback procedures to cause every control area to determine it’s own contribution to TE and then to feedback into ACE a correction factor to reduce that contribution.
How does it work? • When a control area experiences meter error, or schedule error, or EMS problems, or generation response problems, the prevailing system frequency changes. • The other 33 control areas in WECC will respond to correct frequency through their individual frequency bias term in ACE. • The control area causing the frequency error is said to have created “primary time error”. • The 33 control areas responding to correct frequency are said to have created “secondary time error”.
How does it work? • Time error is directly related to inadvertent interchange. • All control areas have procedures in place to determine their hourly inadvertent interchange. • Converting hourly inadvertent interchange into “primary inadvertent interchange” a control area can observe just that portion of WECC time error that they alone caused.
How does it work? Time error is driven to zero by the combination of these actions. Inadvertent interchange and time error pass through zero at the same time.
Inadvertent Payback • Is ATE really Inadvertent Payback? No. • There is relationship between primary time error and primary inadvertent. Decomposition of n and Inn was patented in 1982. • These decomposed components are directly related to each other. Inn = -(Bs – n) n / 6 • If you drive one component to zero, the other must go to zero. • We use Primary Inadvertent as the control parameter because it is an extension of existing Inadvertent accounting methods. We could have introduced an entirely new primary time error accounting method for ATE parameters in ACE, but it would have created unnecessary development effort. (See EPRI TR-107813 Appendix E)
Inadvertent Payback • Since you know who did what to whom, you could • develop a settlement process • – Requires all II accounts balance • – Requires all frequency bias settings are known • – Requires N*(N-1) matrix for every hour • • Single Step Corrective Control • – Already have necessary information - έs, In, Bs, n… • – Simple hourly accounting process to compute Inn for on-peak and off-peak. • – Simple hourly accounting process to track TE • – No need to compute secondary inadvertent • interchange
Frequency Issue • Does ATE oppose prevailing time error? • Good control in the first place would negate the need for any form of auto time error control • there are some control areas that do not put forth resources to control properly. • Auto Time Error method is designed to place 100% of the responsibility to correct primary time error on all control areas responsible for creating it. • If all control areas correct their accumulated primary time error properly, then WECC time error stays well bounded. • It only takes one control area to shirk their responsibility to defeat coordinated time error control
Frequency Issue • PWG is simulating two methods of ATE that result in an Interconnection-wide ACE=0. • That means the control ACE NERC ACE. • That means all compliance reporting could use one ACE • New methods still subject to control area non-participation. • Any approach is subject to gaming
CPS Degradation • Does ATE degrade CPS performance? No. • The NERC Resources Subcommittee tracks CPS performance. We are successfully balancing CPS compliance with the WECC request to improve time error performance by reducing manual corrections. • WECC control areas are exceeding CPS1. • There is abundant margin for more relaxed control. • Some WECC control areas are marginally meeting CPS2. • Reasons include – • Failure to follow FAQ guidance • Overt control decisions to just barely meet CPS2 and nothing more
Frequency Performance • Frequency Error performance steadily decreasing toward expected CPS1 profile. • Short term averaging intervals show more evidence of relaxed control. • Long term averaging intervals show more evidence of time error control effects.
Other Issues • Is L10 discretionary? No. • NERC developed L10 to meet the necessary and sufficient conditions to be technically defendable. • As a statistical measure, it is recognized that some control action can occur at the tails of a central tending distribution. • NERC gave every control area discretion in selecting its frequency bias setting. • Larger bias = larger limits = relatively greater obligations
Time Error Control Survey • Most CA computing hourly Primary Inadvertent correctly • Factoring in effects of Manual TE corrections was a problem. (Fixed) • Some TE equipment faulty. (Now using ICCP TE sources) • Most CA computing Accumulated Primary Inadvertent Correctly. • Some problems with month-end adjustments • Some CA apply the ATE correction term improperly. • Sign backward, too much limitation on magnitude. (Not resolved)
Action Items • Revise FAQ • DCS scenarios • Difference between control ACE and CPS ACE • Proceed with CA survey recommendations • Simulate two alternative ATE methods in ACE equation to allow control ACE to be compliant as the NERC ACE for CPS & DCS • Method 1 – continuous incremental change in Fs • Method 2 – Larger exponentially decaying H rather than equally weighted H. • Continue to assist CA with implementation