Abstract
Natural wind is stochastic, being characterized by its speed and direction which change randomly and frequently. Because of the certain lag in control systems and the yaw body itself, wind turbines cannot be accurately aligned toward the wind direction when the wind speed and wind direction change frequently. Thus, wind turbines often suffer from a series of engineering issues during operation, including frequent yaw, vibration overruns and downtime. This paper aims to study the effects of yaw error on wind turbine running characteristics at different wind speeds and control stages by establishing a wind turbine model, yaw error model and the equivalent wind speed model that includes the wind shear and tower shadow effects. Formulas for the relevant effect coefficients Tc, Sc and Pc were derived. The simulation results indicate that the effects of the aerodynamic torque, rotor speed and power output due to yaw error at different running stages are different and that the effect rules for each coefficient are not identical when the yaw error varies. These results may provide theoretical support for optimizing the yaw control strategies for each stage to increase the running stability of wind turbines and the utilization rate of wind energy.
Highlights
Wind energy has attracted worldwide attention because of its advantages, including the fact that it is a clean form of energy, it has an extremely large energy reserve, its wide availability and its renewability
When the rotor is at different azimuth angles, the effects of the wind shear, tower shadow and yaw error on Tc differ
The wind shear and tower shadow lead to rotor speed 3P pulsation
Summary
Wind energy has attracted worldwide attention because of its advantages, including the fact that it is a clean form of energy, it has an extremely large energy reserve, its wide availability and its renewability. The attributes of natural wind (including wind speed and direction) vary randomly and intermittently. These variations account for the greatest problems associated with developing wind energy. The wind direction changes frequently and randomly relative to the rotor axis of horizontal-axis wind turbines. To improve the utilization of wind energy and optimize the wind loads on the blades, the problems caused by steady-state and transient-state yaw error must be considered. Specific control strategies should be used for wind turbines, including pitch control and generator torque control to respond to wind aped fluctuations as well as active yaw control to cope with frequent changes in wind direction [1,2]
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