State Estimator Overview
State Estimation - a generic definition
State Estimation for power system operation
– As a component in classical network security analysis
– Typical data input/output descriptions
– Summary of SE Functionality
State Estimation for electricity market operation
– As a component in market-based congestion
management (e.g. LMP/Nodal pricing)
– Impact of SE quality on financial settlement
SE - A generic problem definition
To obtain the best estimate of the state of the
system based on a set of measurements of the
model of the system. For example:
– State variables: the weights of John (X) & Mary (Y)
– Models & Measurements:
• Model 1 - John stands on the scales alone
– Measurements: X1, X2, X3….
• Model 2 - Mary stands on the scales alone
– Measurements: Y1, Y2, Y3, Y4...
• Model 3 - John & Mary stand on the scales together
– Measurements: Z1, Z2, ... ( Z = X + Y)
• Different scales have different degrees of accuracy
SE for Power System Operation
– To provide a view of real-time power system conditions
• Real-time data primarily come from SCADA
• SE supplements SCADA data: filter, fill, smooth….
– To provide a consistent representation for power system
• On-line dispatcher power flow
• Contingency Analysis
• Other applications (DTS, OPF/VVD…)
– To provide diagnostics for modeling & maintenance
SE Input & Output Data
– Transmission network model (topology, impedance, limit)
– Measurements (device, accuracy, SCADA-mapping.…)
– Execution parameters (dynamic weight-adjustments…)
– Bus voltages, branch flows, taps, generation, load
– Measurement error processing results
Consistency across network security applications
– Modeling: device (load, generation), schedule, limits...
– User Interface: information presentation, maintenance
– Data exchange: save cases, external import/export
– Robust convergence (stability over wide range of
measurement accuracy, time skew….)
– Consistent treatment between internal & external areas
– Error detection, processing, and management
SE for Electricity Market Operation
Reliable physical operation and robust market
operation require convergence between real-time
system operation and spot market delivery.
Convergence most significantly affected by
transmission congestion management.
– Manage congestion in base case and in contingencies,
i.e. Simultaneous Feasibility Test (SFT)
– SFT is equivalent to SE & CA in EMS
– Out-of-merit market dispatch in the RT Balancing market
should be driven by RT constraints identified by SE/SA
Market Data Base
Data Importer / Exporter
DA HA RT
RT SE/SA Operator I/F
Bids & Offers
& Other Data
SE for LMP-Based Markets
– Real time dispatch targets: affected by critical (binding)
constraints from SE/SA
Settlement determinants (price & quantity)
– LMP price: affected by bid/offer prices and by binding
constraints from SE/SA.
– Locational model: individual nodes and aggregated
zones/hubs. Impact on binding constraints depends on
relative effects of different types of measurements.
– Quantity: profiling over time & location often based on
relative pro-ration from SE results.