Speed avoidance logic for a variable speed wind turbine

Abstract

A variable speed wind turbine is controlled in a way which avoids the turbine lingering at a critical speed which would otherwise tend to cause excessive vibration. The disclosed method and apparatus increases speed at a selected rate with respect to generator output power except in the vicinity of the critical speed. The selected rate is changed in the vicinity of the critical speed to a different rate which is selected slower in the selected embodiment, to avoid commanding the critical speed. After the output power increases or decreases beyond the critical point, a deliberate discontinuity in the speed command signal is induced. A rapid speed change through the critical speed is accompanied by a corresponding power output change. If the speed is increasing at a selected slower rate below the critical speed, and the speed command signal is stepped to a higher level just before reaching the critical speed, the speed will rapidly increase and quickly pass through the critical speed while the power output decreases. Similarly, if the speed is decreasing at a selected slower rate above the critical speed, and the speed command signal is stepped to a lower level just before reaching the critical speed, the speed will rapidly decrease and quickly pass through the critical speed while the power output increases.