Integrated Transmission Control

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Integrated Transmission Control

• Joe H. Chow
• NSF/EPRI Workshop
• Urgent Opportunities for
• Transmission System Enhancement
• October 10-12, 2001

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Transmission Control

• Traditional power system control associated with
  generators
• FACTS devices allow flow control on transmission
  systems
• Candidate FACTS devices SVC, TCSC, STATCOM,
  UPFC, CSC, IPFC

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Integrated Transmission Control

• A system with a few FACTS devices versus a system
  with many FACTS devices
• Systems with many FACTS devices require some kind
  of hierarchical control framework
• Under deregulation, control functions will be
  planned/coordinated by system operators

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Hierarchical Control
These concepts are These concepts are less
well-defined more transparent
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Power System TransmissionControl Time Scale
FACTS devices can affect these control functions
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Control Methodologies

• Transient stability feedback, feedforward,
  bang-bang control, or nonlinear control?
• Interarea modes fixed gain feedback or adaptive
  control? Design methods? What signals to use?
• Setpoint control integral control or central
  dispatch?
• A general methodology for all FACTS devices or a
  specialized methodology for each type of FACTS
  devices?

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Transient Stability

• To improve synchronizing torque
• SVC max. capacitance
• TCSC max. short-term overload capacitance limit
• UPFC separate or simultaneous manipulation of
  series and parallel components?
• Control methods
• Feedforward control how much and how long?
• Feedback control high gain destabilizing other
  modes?
• Bang-bang control switching times?
• Nonlinear control region of stability,
  backstepping, control Lyapunov functions?

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Interarea Mode Control

• Input signal selection for damping control
• Local transmission system signals (voltage,
  current, power), remote generator signals
  (machine speed), synthesized remote signals?
  Communications?
• FACTS device dependencies nodal variables for
  flow control (series) devices, and flow variables
  for voltage control (shunt) devices? Analytical
  justifications?

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Network variable sensitivities with respect to
FACTS control
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Interarea Mode Control

• Control methods
• Modal analysis and gain/phase compensation design
• H2, H?, ?-synthesis with robustness and
  performance considerations
• Adaptive control, gain scheduling? Threshold for
  gain switching/adaptation?
• Can we get additional insight into the
  transmission system from the control design?

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Setpoint Control

• Integrate on an error to get new steady-state
  operating condition?
• Redispatch from energy management system?
• Reconfigurations of FACTS devices?
• Other algorithms?

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Coordination of Multiple FACTS Devices

• Local
• Shunt devices controlling voltages SVC, STATCOM
• Local effort on voltages, important to support
  power transfer
• Global
• Series devices controlling flows TCSC, UPFC
• Effect of power flow over a wide area
• Siting cascaded series devices where and how
  many?

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Coordination of Multiple FACTS Devices

• Decentralized approach
• Control design using local signals distributed
  control functions implicit coordination failure
  of one component may not be fatal roll-over
  strategies design methodologies range from ad
  hoc to NP-hard
• Centralized approach
• Multivariable controllers Control design using a
  central station explicit coordination in the
  design process needs a backup system for
  reliability

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Coordination of Multiple FACTS Devices

• Low authority
• Devices affecting mostly the flows and dynamics
  of a few buses, such as an SVC
• High authority
• Devices whose impact is felt across a region,
  such as a TCSC

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Coordination of Multiple FACTS Devices

• Simple, low-order controllers
• Low-order controllers simpler to implement, but
  may be harder to design and prove optimality
• Complex, high-order controllers
• Multiple functions logic and switchings
  adaptive control need to dissect a high-order
  controller into recognizable parts (eg, lowpass
  filter, bandpass filter)

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Grand Challenges

• At the local level
• The costs and benefits of each FACTS device
• The pros and cons of each design method
• Establish a systematic body of knowledge of FACTS
  control applications
• A shopping list/manual of FACTS controller
  structures and design methods

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Grand Challenges

• At the global level
• Develop a global view of the system
• Classification and identification of transmission
  system interruptions at a high level
• Information aggregation and management decision
  process to act or not to act? How to act?
• Computational intelligent defense plan
  coordinate distributed FACTS devices choosing
  local vs system signal, fixed-gain vs adaptive
  control, hybrid control methods

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Grand Challenges

• At the global level (cont.)
• Unifying concepts/methodologies
  Information/coordination/computation for
  utilizing multiple FACTS devices to their fullest
  potential
• Coordination of FACTS devices and generator
  controls to provide additional benefits

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Transmission expansion

• Deregulated market transmission expansion
  signal is either weak or negative
• So we may need
• Transmission expansion plan target (e.g., 3 per
  year) mandate by Public Service Commissions
  capital investments reimbursed through uplifts
• State Power Authorities
• Simultaneous generation-transmission expansion
• Market rule revision for stronger transmission
  expansion signal