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Power System Voltage Control and Stability

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Example For Voltage Stability Boundary: Reactive Power Variation ... Development of Advanced Algorithms for steady state, dynamic and time domain simulations ... – PowerPoint PPT presentation

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Title: Power System Voltage Control and Stability


1
Power System Voltage Control and Stability
Third NSF Workshop on US-Africa Research and
Education Collaboration Abuja, Nigeria, December
13-15, 2004
  • V. Ajjarapu (vajjarap_at_iastate.edu)
  • Iowa State University
  • Ames, USA

2
Outline
  • Introduction
  • Aim
  • Educators Involved
  • Area of Research
  • POWER SYSTEM SECURITY AND CONTROL
  • An Overview
  • Medium of Interaction
  • Web based
  • Travel
  • Activities Planned

3
Our Department
  • 48 faculty
  • Power 4 2
  • Over 30 power graduate students
  • Typical undergraduate power class 50
  • Mainly power systems Security and dynamics ,
    risk analysis, economics and markets
  • State of the art power electronics lab

4
Aim
  • Building African collaboration with ISU
    researchers to build further understanding of
    different power system case studies.
  • Developing a roadmap for future research
    activities in power / energy, information systems
    technology, environmental and social dynamics,
    and education pedagogy

5
Educators Involved
  • Prof. George O. Anderson, Univ. of Botswana
  • Dr. Tanimu Abubakar, Ahmadu Bello University,
    Zaria, Nigeria
  • Dr. Venkataramana Ajjarapu (with support from
    EPNES ISU faculty)
  • Graduate/Undergraduate Students from these
    Universities

6
Research POWER SYSTEM SECURITY AND
CONTROL Main Area of Expertise Voltage
Stability , Oscillatory Stability, VAR Planning
and dispatch , ATC Sub Area Power
Electronics and Real Time Control The group is
developing a comprehensive approach for voltage
and oscillatory stability analysis and control.
This group is also actively involved in the
Available Transfer Capability(ATC) evaluation as
limited by voltage as well as oscillatory
stability. Reactive power requirements and
pricing required for deregulated environment.
These techniques will be applied to realistic
practical power networks.
7
Our Groups Research Overview
  • Developing techniques that are very effective for
    stressed power systems
  • A single tool can be adapted for cost based
    security with timing of control information
  • Available Transfer Capability (ATC) is part of
    this research
  • Web Based Security Tools for Distance Education

8
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11
Power Flow, CPF and EQTP
  • Conventional power flow program calculates steady
    state solution for a given operating condition.
  • Continuation power flow (CPF) traces a series of
    power flow solutions for a given scenario. You
    can also trace the bottom of the PV curve.
  • Equilibrium Tracing Program (EQTP) is an
    extension of CPF. DAE instead of pure power flow
    equation is used to represent the power system.
    It has the capability of detecting both voltage
    and oscillatory instabilities.

12
Security Margin Tracing
13
  • Numerical results for Identification CPF

14
Example For Voltage Stability Boundary Reactive
Power Variation
15
Optimal Margin Boundary Tracing
16
Basic Formulation
For a sequence of
specified margin levels  
Minimize a cost function f(U)  
Subject to Equality
Conditions F, G
Inequality constraints I

Optimality conditions
Margin boundary
conditions Cobt   Results in a set of
nonlinear equations of the form  

17
Formulation (Cont.)
  • The formulation could automatically generate a
    whole set of cost based optimal control
    configurations with each optimal control
    configuration corresponding to specific margin
    level that can be realized.


18
Sample Result for OMBT
19
Continuation Based Time Domain Simulation
20
Key Points
  • No divergence due to singularity of
  • Time step size is adjusted according to the
    variation of dS/dt
  • Small time steps for fast dynamics and large time
    steps for slow dynamics

21
Trajectory Before and After a Line Outage (with
load variation)
22
QSS Simulation
23
Overall Strategy
Credible Contingency Set CjC1,C2, ,Cm
j j 1
Yes
Check for (AAT) singularity
No
Trace Eigenvalue for Hopf and Damping Margin
Yes
Yes
No
No
24
Research Needs
  • On line monitoring Fast calculations
  • Accuracy vs Speed
  • Timing Information Fast vs Slow Collapse
  • Integration of Cost of Voltage and Oscillatory
    Stability Control in Overall Security Assessment

25
Optimal Strategies for Load Shedding when,
where and how much
26
Capabilities at ISU
  • A method to quickly identifies voltage and
    oscillatory instability points.
  • The change in the instability margin boundaries
    can be further obtained for any large change in
    system parameters.
  • Optimization and Time Domain Simulations are part
    of Continuation Based Approach
  • An efficient eigenvalue tracking method is
    introduced.
  • Provides damping information
  • Provides eigenvalue and eigenvector sensitivity
    information as a by product

27
Capabilities Cont..
  • Automatic PV Curve Tracing.
  • Field current and armature current limits are
    included.
  • Provides true maximum power point by considering
    relevant dynamic factors.
  • There is no need for slack bus
  • Can solve unsolvable cases created by a line or
    generator outages

28
Capabilities Cont
  • Sensitivity Analysis (qualitative)
  • Screens the contingencies that may lead to
    voltage collapse
  • Locates the weak areas , identifies the critical
    generators
  • Provides voltage stability margin estimation

29
Capabilities Cont..
  • Available Transfer Capability as Limited by
    Voltage and Oscillatory Stability
  • Simulates simultaneous multi-area transactions
  • Provides Transaction Sensitivity Identifies and
    ranks the transactions that are detrimental to
    voltage stability
  • Reactive power pricing /amount /location/ to
    maintain voltage security

30
Capabilities Cont..
  • Preventive and Corrective Strategies Against the
    Voltage Collapse
  • Strategies for minimum load shedding
  • Strategies for under-voltage load shedding
  • Strategies to maintain a certain voltage
    stability margin

31
Capabilities Cont..
  • Development of Advanced Algorithms for steady
    state, dynamic and time domain simulations
  • A simulation engine that can allow transient and
    quasi- steady state analysis
  • to obtain a comprehensive analysis to predict
    and control instabilities
  • When , where and how much control

32
Capabilities Cont..
  • On Line Voltage Stability Monitoring and Control
  • Developing methodologies to utilize off line
    studies for on line implementation

33
Application to Botswana 32 Bus Test System
34
Botswana System (Cont..)
  • Demand 243 MW
  • Supply
  • Local (coal) 128MW
  • ESKOM and SAPP 115MW
  • Simulation
  • Software Aristo (Advanced Real Time Interactive
    Simulator for Training and Operation ) by ABB
  • Dr. Anderson applied this software for Power flow
    and Fault analysis for 32 bus equivalent system

35
Activities Planned wrt EPNES Project (research)
  • Task 1 Setting up a test case for Botswana
    System
  • Task 2 Study the maximum loadability with
    respect
  • various contingencies and scenarios
  • Task 3 Apply margin sensitivity to find the
  • locations for shunt capacitors and
    series
  • capacitors
  • Task 4 Develop Automaton for backward algorithm

36
Activities Planned (education)
  • Botswana group will participate in EE458 course
  • Develop I hour lecture material for this course

37
EE/Econ 458 Economic systems for planning in
electric power
Students completing this course will be able to
conduct studies in policy, economics,
engineering associated with transmission
expansion they will enhance their skills using
optimization methods for engineering economic
problem-solving.
  • Evolutionary history of the power industry
    present industry structure
  • Discrete optimization
  • Power system operation
  • Electricity markets
  • Power system planning and cost-effective
    solutions
  • Cost recovery for transmission investment basics
    of public good economics
  • Cost-recovery models
  • Tariff-based model
  • Performance-based model
  • Market-driven model
  • Tax treatment of transmission investments.

?Will offer Fall 2004 on-campus, and via
distance-education.
38
Web Based Interaction

39
Characteristics
  • Platform (OS) Independent
  • Standardized System Input Files
  • Graphic PV Curves Output
  • Detailed Simulation Process Output
  • Margin Sensitivity

40
Simulation Website
  • http//design-2.ece.iastate.edu/newsim/index.php

41
Simulation Website Cont..
  • Input Files
  • IEEE Common Data Format is adopted as the input
    file for power system topology and parameters
  • Another standardized control file is used to
    specify load and generation increase scenario
  • Sample Test System input files are provided

42
Simulation Website Cont..
  • Upload Input Files

43
Simulation Website Cont..
  • Download Sample Systems

44
Multiple Simulation Outputs
  • Tabular Output

45
Outputs Cont..
  • Graphic PV Curve

46
Outputs Cont..
  • Generator Reactive Power Output
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