4-1  NREL Reference Documentation

The National Renewable Energy Laboratory (NREL) published in March 2008 the landmark report: "Advanced Control Design for Wind Turbines Part I: Control Design, Implementation, and Initial Tests".

This paper defines the algorithms required for designing drive train control systems that extract maximum available power from the wind at below-rated conditions, while limiting power to rated values above the nominal wind speed. It is the de-facto reference for MPPT implementation in variable-speed wind turbines.

Key topics covered:

• Region 2 control: torque control for maximum aerodynamic efficiency (Cp maximisation)
• Region 3 control: collective blade pitch control for rated power limitation
• Transition strategies between regions
• State-space control design and gain scheduling
• Implementation and field test results

4-2  Operational Curve Calculator Application

To extract maximum power from available wind, a Maximum Power Point Tracking (MPPT) algorithm must control blade rotation speed proportionally to wind speed. The ACMSL Operational Curve Calculator evaluates all the algorithms needed to achieve this.

This engineering application is designed to analyse and define the operating conditions of a wind turbine drive train as a function of:

• Blade aerodynamic profile (Cp–λ curve)
• Blade length and rotor diameter
• Coupling to the electrical generator (synchronous speed, pole pairs)
• Selected gearbox ratio

The application computes the complete Operational Curve (RPM vs Wind Speed and Power vs Wind Speed), the optimal torque setpoint table, and the MPPT gain. Output is compatible with the ACMSL DFIG and RRC real-time simulators.

A free 2-day evaluation license is granted automatically on first launch.