Power Management

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Power Management of Wind Turbines
presented by Barry Rawn MASc Candidate Universit
y of Toronto
Wind Power Generation Symposium- February 20th,
2004 SF1105 1-5pm
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Power Management of Wind Turbines
motivation modelling control potential
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motivation
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motivation
Improving the flexibility and power quality
provided by wind generation can enable the spread
of wind power.
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motivation
what are the main differences between
conventional generators and wind turbines?
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motivation
I.
The power available in the wind varies on several
time-scales. This could impact -power
planning -power quality
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motivation
II.
Wind turbines are systems having nonlinear
dynamics and oscillatory modes. This can affect
considerations of grid stability where controlled
wind turbines are present.
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motivation
Modern turbines run at variable speeds and
interface to the grid through power electronic
converters. An exploration can be made of
the extent to which a controlled turbine can act
as a more stable-looking generator.
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modelling
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modelling
-blades
The blades of a turbine transfer momentum from
the wind like the wings of an aircraft. The
character of the flow depends on an effective
angle of attack
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modelling
-blades
Aerodynamic stall has two important
effects -dictates an optimal power
extraction -defines a division between two
dynamical regimes
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modelling
-spinning blades

• irregular wind field forces system both
  periodically and randomly
• disturbance at the blade passing frequency may
• occur due to
• tower shadow
• wind shear
• rotational sampling

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modelling
-spinning blades
blade passing frequency present in spectrum of
blade forces, but not in spectrum of
wind averaging force signals associated with
rotor angle reveals periodic components less
significant for variable speed systems
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modelling
-mechanical modes
flexible structure has many mechanical modes of
oscillation these must be considered in
structural designs
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modelling
-mechanical modes
for control and power system studies, capturing
the two main inertias and their flexible coupling
is sufficient
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modelling
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control
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• several degrees of freedom available to control
  energy flow within the system
• power in must balance power out

control
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• different strategies exist

control
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Tony Turbine
Greg Grid
control
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Tony Turbine
uses control freedom to - optimize power
extraction - minimize torsional oscillations
control
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Greg Grid
Left with responsibility to balance power Can
partially influence how power is delivered to the
grid
control
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Tony Turbine feeds Greg Grid a power that's best
for the wind turbine, and Greg accommodates.
control
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• control tasks are decoupled in some sense
• influence on grid is a shared responsibility
  between both Tony Turbine and Greg Grid

control
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let's consider a different division of tasks one
based on energy management
control
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Fast Freida
Cool Clara
control
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Fast Freida
maintains power balance and minimizes torsional
oscillations using energy from the turbine
control
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Cool Clara
sets a smooth power extraction, and reacts to
grid changes appropriately using full freedom
control
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Cool Clara requests a power that is least harmful
to the grid. Fast Freida conveys it and attempts
to contain wind disturbances.
control
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The success of such a control scheme places trust
in two main assumptions.
control
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Fast Freida has to trust that Cool Clara will
always demand a power that is achievable.
control
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Cool Clara has to trust that Fast Freida will
manage the capacitor voltage within tolerances,
and limit mechanical resonance
control
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appropriate control design makes both assumptions
valid
control
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control
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control
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control
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potential
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Assuming such control could be practically
realized, this methodology

• further reduces potentially troublesome influence
  of wind variation
• frees the converter interface to make the system
  appear more robust over short time scales
• allows the possibility of shifting between
  optimal and conservative power extraction, based
  on grid conditions

potential
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Future investigation would further characterize
the properties of such a controlled system.
Examples include

• controls based on inference of hub energy could
  eliminate need for accurate wind speed
  measurement and reduce stall recovery incidents
• some potential may exist for a kind of
  dispatchability of energy on short time scales
  between turbines in a wind farm

potential
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Power Management of Wind Turbines
presented by Barry Rawn MASc Candidate Universit
y of Toronto
thanks!