Advanced Wind Turbine Program Next Generation Turbine ... - NREL

4.2.3.2 Rotor Feedback Control
Results of the concept studies showed that independent blade pitch for asymmetric load control
could produce significant reductions in key loads with little or no impact on the energy capture.
As noted above in Section 4.1, EMD loads analysis supported significant loads reductions from
using the ALC.
The POC turbine featured independent blade pitch actuation, insomuch as the pitch of each rotor
blade was controlled by an independently functioning electric drive. This concept was inherited
from both the value-engineered version of the baseline 750-kW turbine and the original version
of the GE1.5 turbine. However, like those turbines, the control system of the POC turbine was
designed to effect synchronized actuation of the blades. Absent a control fault or a failure of one
of the pitch drives, all three blades should ideally be at the same pitch setting at all times.
The EMD control system implements the functionality to control the pitch setting of each blade
independently. As first noted during the concept studies, independent blade pitch control can be
used to ameliorate asymmetric rotor loads that cannot be otherwise mitigated using collective or
synchronized pitching of the blades. Implementation of asymmetric load control requires two
sets of measurements:
1. Blade or rotor loads
2. Blade azimuthal position.
The primary tasks in Phase II were:
• Evaluate, install, and document candidate input sensors for the ALC.
• Select the best sensors from the suite of candidate test sensors for ALC.
• Design and test communications (hardware/software) interface between the candidate
control sensors and the PLC.
• Test and verify sensor signal data acquisition in the PLC by passing acquired signals
through PLC to the ADAS DAQ system.
• Implement and test PLC control code (software) changes for ALC system.
• Perform system dynamics study to determine controller parameters:
o ALC algorithm coding on PLC
o ALC simulation and emulation.
• Develop and verify ALC system safety features including:
o Signal plausibility and error-trapping routines to prevent spurious input signals from
damaging the turbine through unstable ALC feedback
o Implementation of adjustable ALC pitch modulation limiter
o System safety verification prior to field testing via ALC simulation and emulation
o algorithm functionality and sensitivity of gain settings.
The first step in the development of the system consisted of an exhaustive survey of measurement
approaches and appropriate sensors. An engineering evaluation of the sensors was conducted
to assess sensor performance and reliability. This evaluation included numerous tests.
First an industry review of vendors was conducted to screen sensors meeting Critical To Quality
requirements. A series of screening tests were performed on the selected sensor and target material
in order to determine significant performance factors. Three factors were investigated: power
supply rejection, target temperature and sensor temperature. Power supply rejection and target
temperature were found to have very little influence on the sensor output and were not characterized.
Sensor temperature was found to be a significant factor and was incorporated into the
characterizations tests.
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