Control of a vertical axis wind turbine in gusty conditions

Vertical axis wind turbines (VAWT) are used in locations where high wind speeds are combined with gusty conditions, giving variations in the direction and speed of the wind. However, optimal power extraction from the gusts is difficult and can result in fluctuating power flow to the grid. Most turbine control algorithms have been developed for steady winds, hence there is a need for a better power control strategy that harnesses as much power as possible from the wind during gusts, ensures that the turbine system remains within its safe operating envelope and delivers power to the electrical network in an acceptable form. This paper identifies control methods for the VAWT across its operating range, using the 4Navitas, 55kW wind turbine as a case study. A Simulink model of the turbine is validated against measured site data. Metrics are defined and used to evaluate an algorithm suitable for implementation on the commercial equipment. Compared with the original scheme, simple modifications are identified which considerably reduce torque ripple on the transmission shaft and electrical power fluctuations, whilst increasing average power to the grid.