Comparison of individual pitch and smart rotor control strategies for load reduction

C Plumley,P Jamieson,M Graham,W Leithead,E Bossanyi

doi:10.1088/1742-6596/524/1/012054

Abstract

Load reduction is increasingly seen as an essential part of controller and wind turbine design. On large multi-MW wind turbines that experience high levels of wind shear and turbulence across the rotor, individual pitch control and smart rotor control are being considered. While individual pitch control involves adjusting the pitch of each blade individually to reduce the cyclic loadings on the rotor, smart rotor control involves activating control devices distributed along the blades to alter the local aerodynamics of the blades. Here we investigate the effectiveness of using a DQ-axis control and a distributed (independent) control for both individual pitch and trailing edge flap smart rotor control. While load reductions are similar amongst the four strategies across a wide range of variables, including blade root bending moments, yaw bearing and shaft, the pitch actuator requirements vary. The smart rotor pitch actuator has reduced travel, rates, accelerations and power requirements than that of the individual pitch controlled wind turbines. This benefit alone however would be hard to justify the added design complexities of using a smart rotor, which can be seen as an alternative to upgrading the pitch actuator and bearing. In addition, it is found that the independent control strategy is apt at roles that the collective pitch usually targets, such as tower motion and speed control, and it is perhaps here, in supplementing other systems, that the future of the smart rotor lies.

Highlights

Wind turbines have been progressively getting larger in a drive to reduce the cost of energy
The 1Hz damage equivalent loads are calculated and compared in the results. 3D turbulent Kaimal spectrum wind fields for a class IIB turbine are used, but rather than lifetime loads the results presented here are of just 6 runs at 18m/s mean wind speed
This study verifies that it is possible to achieve similar load reductions with trailing edge flaps as it is by pitching the entire blade

Summary

Introduction

Wind turbines have been progressively getting larger in a drive to reduce the cost of energy. Rotor diameters of 120m plus are in operation and at these sizes the wind field experienced by each blade as it rotates varies considerably. This is due to wind shear, turbulence, towershadow, yaw, wake from other wind turbines or obstructions up stream, and from other meteorological effects. These cause periodic loadings on the turbine as the blades experience a similar, though varying, wind field once per revolution. The cyclic loadings cause damage to the blades in particular, and to the tower, yaw bearing and shaft. Individual pitch control and smart rotor control are two such methods, adoption of which may allow blades to be made cheaper and lighter, or longer still, reducing the overall cost of energy from wind turbines, e.g. [1]

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Results

Conclusion