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Scott G Ghiocel & Joe H Chow Rensselaer Polytechnic Institute DOE Research Project: PMU-Based Voltage Stability
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Rensselaer Chow Pmu Based Voltage Stability 20131023

Nov 21, 2015

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Ahmed Seddik

Rensselaer Chow Pmu Based Voltage Stability 20131023
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  • Scott G Ghiocel & Joe H Chow

    Rensselaer Polytechnic Institute

    DOE Research Project: PMU-Based Voltage Stability

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 2

    Voltage Stability Project Objective Traditional voltage stability analysis (VSA) approaches:

    Full-order detailed model: off-line or real-time analysis with SCADA measurements or SE solutions. High computation burden and dependent on the load model. Example: VSTAB program

    Single-load, stiff-bus model: applicable to radial systems, dependent on load models. Example: voltage instability predictor (VIP) approach

    Goal development of models and analysis techniques: Hybrid, PMU-based, voltage stability mode with less computation than VSTAB-type programs but capable of handling more complex power transfer paths

    Increasing level of complexity

    Single load center, VIP model

    Full detailed model, SCADA based

    Hybrid model, PMU based, high-voltage

    transmission grid

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 3

    Project Overview Voltage stability of a complex transfer path (Pacific AC Intertie):

    Network characteristics: Large number of injection and out-flow points

    Load areas with multiple in-feeds

    Important information to know PMU data: for obtaining actual voltage sensitivities, injections, and out-

    flows

    Multiple vulnerabilities and reactive power supply at each location

    Flow sensitivities at injection and outflow points

    Network parameters

    The Dalles

    (3)Inflow

    Grizzly

    (3)

    Malin

    (2) (2) (2)R. Mtn T. Mtn

    (1) Tracy/ Tesla

    Moss LandingInflow(3)

    Diablo CanyonInflow

    (2)

    Midway

    (3)

    Vincent

    Victorville/ Adelanto

    To other load buses

    Inflow from East

    North South

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 4

    PMU-Based Voltage Stability for Central NY System

    Use PMU data from loss-of-generation events to construct equivalent systems for the unobservable regions

    Compute PV curves of the transfer path using a PMU-based model

    7

    3

    2

    5 9

    4

    6

    1

    SVC

    8External

    system

    0 2 4 6 8 10 12 14

    0.88

    0.9

    0.92

    0.94

    0.96

    0.98

    1

    1.02

    1.04

    1.06

    Change in Power Transfer (p.u.)

    Vol

    tage

    Mag

    nitu

    de (p

    .u.)

    Bus 1 DataBus 1 ModelBus 8 DataBus 8 ModelSVC Saturation Limit

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 5

    Voltage Stability Margin Calculation Difficulty in steady-state voltage stability (VS) margin calculation:

    Singularity of power flow Jacobian at the voltage collapse point Newton-Raphson iteration fails to converge, sometimes far from

    collapse

    Method of homotopy (continuation power flow): Introduce load parameter to remove singularity (increase the size of J

    by 1) Special software using this approach to compute VS margins has been

    developed (Example: CPFLOW)

    Our approach: Define a new bus type to directly remove the singularity from the

    Jacobian Enables fast computation of PV curves and voltage stability margins Retains all the features of conventional power flow methods

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 6

    Single-Load, Stiff Bus System

    Treating the load bus as a PQ bus, the Jacobian is

    The Jacobian is singular when

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 7

    PV Curves and Angle Separation

    Single-load VSA with constant power factor: Load bus angle (angle separation) is seldom analyzed in VSA

    PV Curves Power vs. Angle Separation

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 8

    New Idea: Specify the Angle for VSA Specify load bus angle, so the number of unknowns is reduced

    by 1 Remove load P equation (load power not enforced):

    New matrix is nonsingular

    at the maximum loading point:

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 9

    Advantages of AQ-Bus Method Calculate VS margins by increasing AQ-bus angle Accommodates multiple loads and generators Allows for various load types, such as constant power factor

    loads Includes all features of conventional power flow: tap

    changers, generator reactive power limits, sparse matrices, decoupled power flow, etc.

    Can be generalized to large power systems

    Bus types Bus representation Fixed values

    PV Generator buses Fixed active power generation and bus voltage

    PQ Load buses Fixed active and reactive power consumption

    AV Swing bus (generator) Fixed angle (A) and voltage magnitude

    AQ Load bus Fixed voltage angle and reactive power consumption

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 10

    BPA Wind Farm Voltage Stability Study One-line diagram of a small portion of BPA system, with 6 wind farms

    connected to Bus 22. Connection from Bus 22 to Bus 21 is strong, but the link from Bus 22

    to Bus 25 is weak.

    Bus 21 Bus 22 Bus 25Bus 23

    Bus 51 Bus 55Bus 52 Bus 53 Bus 54

    PMU Measurement

    SCADA Measurement

    500 kV

    230 kV

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 11

    Voltage Variations with Outage of Strong Link SCADA data showing

    voltage response on Buses 21, 22, and 25, with Line 22-25 out of service. The voltage jumps are WTG trips.

    The project is to determine wind turbine reactive power control models and voltage stability limit.

    The wind farms cannot produce full output in this scenario.

    ~ 3 hours

    Capacitor switchings

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 12

    Wind Farm PQ Relationship (Type 2 turbines) SCADA data showing

    the PQ characteristics of three wind farms (Type 2) connected to Bus 21.

    Note that the wind farm consumes reactive power as the active power is increased.

    The STATCOM on Wind Farm 4 mitigates this effect.

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 13

    PV Curves for Strong Link Outage Scenario

    Steady-state PQ models for wind farms using SCADA data

    Included STATCOMs and shunt capacitors/reactors

    Wind speed uniform at all wind farms

    PV curve shows high voltage variability at the POC

    Wind farm output is limited by voltage stability

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 14

    Next Steps and Future Work

    Wind farm study: Voltage stability under different wind scenarios Effects of other line outages Various levels of power transfer from Bus 21 to Bus 25 Using synchrophasor data

    Other potential study areas in WECC Southern California Edison: Los Angeles Olympic Peninsula in Washington State

    Development of a prototype for real-time voltage stability analysis using PMU data

  • Rensselaer Polytechnic Institute October 2013 SGG & JHC 15

    Acknowledgements

    This work was supported by the Lawrence Berkeley National Lab (LBL) and CERTS, the ERC Program of the National Science Foundation and DOE under NSF Award Number EEC-1041877, and the CURENT Industry Partner Program.

    DOE Research Project:PMU-Based Voltage StabilityVoltage Stability Project ObjectiveProject OverviewPMU-Based Voltage Stability for Central NY SystemVoltage Stability Margin Calculation Single-Load, Stiff Bus SystemPV Curves and Angle SeparationNew Idea: Specify the Angle for VSAAdvantages of AQ-Bus MethodBPA Wind Farm Voltage Stability StudyVoltage Variations with Outage of Strong LinkWind Farm PQ Relationship (Type 2 turbines)PV Curves for Strong Link Outage ScenarioNext Steps and Future WorkAcknowledgements