Research Articles

Dynamic Optimization of Drivetrain Gear Ratio to Maximize Wind Turbine Power Generation—Part 1: System Model and Control Framework

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1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNALOF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received January 12, 2012; final manuscript received April 5, 2012; published online October 30, 2012. Assoc. Editor: Alexander Leonessa.

J. Dyn. Sys., Meas., Control 135(1), 011016 (Oct 30, 2012) (10 pages) Paper No: DS-12-1010; doi: 10.1115/1.4006882 History: Received January 01, 2012; Revised April 05, 2012

Wind is considered to be one of the most promising resources in the renewable energy portfolio. Still, to make wind energy conversion more economically viable, it is necessary to extract greater power from the wind while minimizing the cost associated with the technology. This is particularly important for small wind turbines, which have the highest cost per kilowatt of energy produced. One solution would be a variable ratio gearbox (VRG) that can be integrated into the simple and low-cost fixed-speed induction generator. Through discrete variable rotor speed operation, the VRG-enabled system affects the wind speed ratio, the power coefficient, and ultimately the power produced. To maximize electrical production, mechanical braking is applied during the normal operation of the wind turbine. A strategy is used to select gear ratios (GRs) that produce torque slightly above the maximum amount the generator can accept while simultaneously applying the mechanical brake, so that full load production may be realized over greater ranges of the wind speed. To characterize the performance of the system, a 100 kW, fixed speed, stall-regulated wind turbine, has been developed for this study. The VRG-enabled wind turbine control system is presented in two papers. Part 1 focuses on the turbine simulation model, which includes the rotor, VRG-enabled drivetrain, disk brake, and electric generator. A technique for estimating the performance of a disk brake, in the wind turbine context, is also presented. Part 2 of the research will present a dynamic optimization algorithm that is used to establish the control protocol for competing performance objectives.

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Fig. 1

Gain in electricity production due to discrete variable speed operation

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Fig. 2

Potential gains in electricity production through VRG with brake

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Fig. 3

Wind turbine configuration

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Fig. 4

Wind turbine model

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Fig. 5

The effect of speed ratio and pitch angle on the power coefficient

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Fig. 6

Components of the disc brake

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Fig. 7

Diagram of drivetrain mechanical model

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Fig. 8

Control problem formulation

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Fig. 9

General wind speed operating ranges for gears in 100 kW VRG-enabled model

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Fig. 10

Decision-making structure implemented during normal operation

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Fig. 11

Decision-making structure for changing gears

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Fig. 12

Simulated performance of each VRG ratio across operating spectrum

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Fig. 13

Brake characteristics during operation

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Fig. 14

Electricity production gains and their corresponding gear ratio vs. wind speed



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