Variable speed pitch regulated control model

The operation characteristics of a modern variable speed pitch regulated wind turbine are generally divided into different operating regions. This article will describe the basic parameters the user can set to specify these. Bladed will then use the provided information to compute a steady state solution for a given wind speed.

Most of the values are exposed through the external controller API and might or might not be used in a user defined dynamic controller.

A high-level overview of the operating zones and their parameters is shown in Figure 1.

Figure 1: Turbine operating regions and important parameters. Values in brackets cannot be set by the user.

General parameters

An overview of the general parameters of VariableSpeedPitchRegulatedControlModel:

• MinimumSteadyStatePitchAngle: The minimal pitch angle Bladed may choose during it's steady state calculation. Exposed to an external dynamic controller through the External Controller API.
• MaximumSteadyStatePitchAngle: The maximum pitch angle Bladed may choose during it's steady state calculation. Exposed to an external dynamic controller through the External Controller API.
• MinimumExternalControllerPitchRate : The minimum pitch rate. This value is only exposed to an external dynamic controller through the External Controller API. Not used in steady calculations.
• MaximumExternalControllerPitchRate : The maximum pitch rate. This value is only exposed to an external dynamic controller through the External Controller API. Not used in steady calculations.

Partial load operation

In PartialLoadOperation the turbine is operating between cut in wind speed and rated wind speed (where the latter is the wind speed where the rated power is reached). In this region the turbine typically applies optimal tip speed tracking.

• OptimalModeGain : The optimal mode gain is a constant that defines the relation between generator speed and generator torque in the partial load operation region, see optimal tip speed tracking. If specified Bladed will use this relationship to determine the generator torque in it's steady state calculation.
• MinimumGeneratorSpeed : The minimum generator speed.
• GeneratorSpeedVsGeneratorTorque : Instead of using OptimalModeGain a lookup table can be supplied, that will be used to determine the relation between generator speed and generator torque.

Note

When using the GeneratorSpeedVsGeneratorTorque to specify the speed-torque curve it is required to include a data-point with a generator speed equal or higher than FullLoadOperation.GeneratorSpeed. Otherwise Bladed cannot determine the correct point when to switch to FullLoadOperation. The user can mimic the transition region (rated generator speed reached but not yet rated generator torque), by adding a lookup table point at FullLoadOperation.GeneratorSpeed with a torque value less than FullLoadOperation.GeneratorTorque. The MinimumGeneratorSpeed will be determined from the lookup table and must not be supplied in this case.

Full Load Operation

In FullLoadOperation the rated power is reached and the turbine blade pitch angles are altered to keep the GeneratorTorque and GeneratorSpeed within their given bounds.

• GeneratorSpeed : The generator speed at rated power.
• GeneratorTorque : The generator torque at rated power.

Note

Please be aware that the steady state algorithm does not support overspeed steady-state conditions when the generator speed exceeds the specified value for GeneratorSpeed. Bladed will not be able to find steady state solutions in those cases.

Lookup table for minimum pitch angle

The user may choose to provide a lookup table that defines the MinimumSteadyStatePitchAngle in relation to the hub wind speed. Using this option Bladed can be instructed to use a variable pitch angle during PartialLoadOperation, while it would normally use the value specified under MinimumSteadyStatePitchAngle. Bladed uses linear interpolation for evaluating the table. If the table is exceeded Bladed will use the closest available point. An illustration of this is shown in the bottom right plot of Figure 1.

Example

A example json code is given below:

"TurbineOperationalParameters": {
      "VariableSpeedPitchRegulatedControlModel": {
        "MinimumSteadyStatePitchAngle": -0.0349065850398866,
        "MaximumSteadyStatePitchAngle": 1.5707963267949,
        "MinimumExternalControllerPitchRate": -0.13962633907795,
        "MaximumExternalControllerPitchRate": 0.13962633907795,
        "PartialLoadOperation": {
          "OptimalModeGain" : 100.0,
          "MinimumGeneratorSpeed": 89.0117918517108,         
        },
        "FullLoadOperation": {
          "GeneratorTorque": 8000.0,
          "GeneratorSpeed": 167.551608191456
        }
      }
    },