Abstract
A critical speed controller for avoiding a certain rotational speed is presented. The controller is useful for variable speed wind turbines with a natural frequency in the operating range. The controller has been simulated, implemented and tested on an open site 12 kW vertical axis wind turbine prototype. The controller is based on an adaptation of the optimum torque control. Two lookup tables and a simple state machine provide the control logic of the controller. The controller requires low computational resources, and no wind speed measurement is needed. The results suggest that the controller is a feasible method for critical speed control. The skipping behavior can be adjusted using only two parameters. While tested on a vertical axis wind turbine, it may be used on any variable speed turbine with the control of generator power.
Highlights
For mechanical systems, such as wind turbines, natural frequencies are an important concern.If a system frequency of low damping is excited, it can result in large movements and stress of the mechanical structure
The results suggest that the controller is a feasible method for critical speed control
The presented critical speed controller was shown to be a feasible method to skip a critical speed related to a natural frequency
Summary
For mechanical systems, such as wind turbines, natural frequencies are an important concern. If a system frequency of low damping is excited, it can result in large movements and stress of the mechanical structure. Most modern wind turbines utilize variable rotational speed operation to maximize energy extraction from the wind. While the three-bladed horizontal axis wind turbine is a common sight, the vertical axis wind turbines (VAWTs) are still unusual as commercial energy producers. Since the invention of the lift-based VAWT in the 1920s, several vertical axis concepts have been studied, and the technology is still subject to active research by companies and universities [1,2,3]. Variable pitch VAWTs have been studied, but the cost and reliability issues associated with a pitch mechanism have not yet been solved [2]
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