## Simplified NREL5MW turbine for SimulinkThe turbine included in the toolbox is based on the 5MW virtual turbine described in [Jonkman et. al.], with modifications as described in [grunnet et. al.] This page gives a detailed description of the turbine model including all parameters. The NREL 5MW simulation model used in SimWindFarm is a simplified aeroelastic model based on lookup tables for the aerodynamics (/), a simple 3rd order drive train model, a 1st order generator model, 1st order pitch actuator, and a 2nd order tower dynamics. The turbines are controlled using the control strategy from [Jonkman et. al.], which includes a simplified start up procedure and pitch control for full load operation. Figure 1 illustrates the structure of the NREL 5MW, with inputs being the wind speed at the nacelle, the average wind speed over the rotor area (effective wind speed), and the power reference supplied by the farm controller. The outputs available to the farm controller are produced power, measured generator speed, nacelle wind speed, and blade pitch angle. With the variables given by the below table
## AerodynamicsThe aerodynamics of the turbine can be described using two static relationships, where and are two look-up tables derived from the geometry of the blades with inputs tip speed ration () and pitch angle. The parameters are air density ,, and rotor disc area, . ## Drive TrainThe 3rd order drive train model is based on two rotating shafts connected through a gearbox with torsion spring constant , viscous friction , and gear ration . where is the shaft torsion angle and are the inertias of the generator and rotor respectively. ## GeneratorIn the baseline NREL 5MW turbine there is no generator model, but a simple 1st order model is included in this benchmark, with input and time constant . Notice that the baseline turbine assumes a torque reference, but a power reference is used here instead. ## TowerThe tower deflection, , is modeled as a spring-damper system with spring constant and damping . ## Pitch ServoThe pitch actuator does not use the NREL model which is a spring-damper system and not used in their FAST simulation. Instead a second order system with a time constant of and input delay from input to pitch rate is used. The actuator is controlled by a proportional regulator with constant resulting in a pitch servo. ## Rotor ControlThe control strategy for the NREL5MW is divided into two regions; 1) partial load and 2) full load. In region 1) the control is a simple lookup-table with generator speed as input and generator power reference as output. The blade pitch is kept constant at 0, see the figure below. In region 2) the generator power reference is kept constant at the rated power while the rotor speed is controlled using the blade pitch angle, by a gain scheduled PI controller. The gain scheduled PI controller is shown in the equation below, and the gains are based on linearisation of the power production sensitivity to blade pitch angle. where , and are the proportional and integral gains, is the base gain at and is the pitch angle where the pitch sensitivity is doubled. The controller presented in [Jonkman et. al.] always operates at full power rating and in order to be able to de-rated the turbine the control strategy has been altered slightly by letting the dynamic power rating change the transition point between region 1 and region 2.
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