Coordinated Control Design for Wind Turbine Control Systems W.E. Leithead and S. Dominguez...
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Transcript of Coordinated Control Design for Wind Turbine Control Systems W.E. Leithead and S. Dominguez...
Coordinated Control Design for Wind Turbine Control Systems
W.E. Leithead and S. DominguezUniversity of Strathclyde
CCD for WT Control Systems
• Background• Models and Dynamics• Performance Requirements• Design and Performance• Conclusion
Outline
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
. • So wind speed is an additive disturbance.
)(),(),,( VgphVpT
ActuatorT(p,,V)
p
V
ActuatorT(p,)
p
V
h(V)
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 Power
• Speed and power fluctuations are not degraded
CCD for WT Control Systems
Performance
• Llifetime reduction in equivalent fatigue loads are
– CCD 13%
– CCD and TFL 18%
CCD for WT Control Systems
• 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%
Conclusion