Transcript Coordinated Control Design for Wind Turbine Control Systems

Coordinated Control Design for Wind
Turbine Control Systems
W.E. Leithead and S. Dominguez
University of Strathclyde
CCD for WT Control Systems
Outline
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Background
Models and Dynamics
Performance Requirements
Design and Performance
Conclusion
CCD for WT Control Systems
Background
• Over the last 20 years there has been an
almost exponential growth in the size of
wind turbines.
• In offshore machines, the trend is towards
bigger machines with taller towers.
• New demands are being placed on the
control system.
CCD for WT Control Systems
Background
• Control systems are now being required to
regulate some fatigue related dynamic
loads
• Of prime interest is the tower loads.
• The larger the wind turbine the greater the
requirement.
• Must be achieved without increasing
pitch activity.
CCD for WT Control Systems
Background
• Normal approach is to add an outer loop to the
generator speed loop aimed at reducing the tower
fore-aft movement.
CCD for WT Control Systems
Background
• Interaction of the two feedback loops causes some
degradation of performance of the main generator loop.
• The CCD approach entails a redesign of the generator
speed loop accounting for the tower speed loop.
• Greater reduction of tower fatigue is achieved without
increasing pitch activity.
CCD for WT Control Systems
Models and Dynamics
• The design is based on linear models that include all the
dynamic components required for control design and
performance assessment.
• The dynamics include:
– 2 modes for the tower
– 2 modes for the blades
– Drive-train
CCD for WT Control Systems
Models and Dynamics
• Dynamics from pitch demand to generator speed for a
multi-megawatt machine.
CCD for WT Control Systems
Models and Dynamics
• Dynamics from pitch demand to tower speed
CCD for WT Control Systems
Models and Dynamics
• The models have been validated against both measured
data and FLEX data
CCD for WT Control Systems
Performance Requirements
• Above rated wind speed to regulate:
– Torque via power converter
– Generator speed via blade pitch
– Tower speed via blade pitch
• Design issue:
– Nonlinear aerodynamics
– Minimise pitch activity
– Accommodate transmission zeros
CCD for WT Control Systems
Aerodynamic nonlinearity
• The aerodynamics are separable
T ( p, ,V )  h( p, )  g (V )
.
• So wind speed is an additive disturbance.
V
h(V)
V
Actuator
p
T(p,,V)

Actuator
p
T(p,)

CCD for WT Control Systems
Aerodynamic nonlinearity
• Global scheduling to linearise plant is possible
• Since rotor speed is low the feedback of d/dt can be
ignored.
CCD for WT Control Systems
Actuator activity
• The most important measures are actuator speed and
acceleration.
• They are subject to saturation constraints.
• Most sensitive to intermediate frequency components.
CCD for WT Control Systems
Actuator activity
• Relative sensitivity to speed and acceleration is clear
CCD for WT Control Systems
Transmission zeros
• Zeros impair control performance
• Zeros become more prominent as size of machine
increases
CCD for WT Control Systems
Design of generator speed loop
• CCD is based on a parallel plant structure
CCD for WT Control Systems
Design of generator speed loop
• CCD enables the
zeros of the
tower to be
counteracted
CCD for WT Control Systems
Design of generator speed loop
• CCD reduces
the pitch
actuator activity
CCD for WT Control Systems
Design of generator speed loop
Actuator acceleration
CCD for WT Control Systems
Design of generator speed loop
• Tower base moments are reduced by modification to
generator speed loop control
CCD for WT Control Systems
Tower feedback loop
• Further reduction in the tower loads is obtained by
addition of a tower feedback loop.
• The interaction with the generator speed loop is kept to
a minimum.
CCD for WT Control Systems
Tower feedback loop
• Tower base moments for standard generator
controller, CCD and CCD+TFL.
CCD for WT Control Systems
Generator speed control
• Speed and power fluctuations are not degraded
Speed
Power
CCD for WT Control Systems
Performance
• Llifetime reduction in equivalent fatigue loads are
– CCD
13%
– CCD and TFL
18%
CCD for WT Control Systems
Conclusion
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A new controller is discussed
Not subject to size-related constraints
Designed using well-validated models
Easily tuned
Lifetime tower fatigue load reduction of 18%