Provided is controller for a wind turbine including a power controller unit for controlling a power output of an electric generator included in the wind turbine. The power controller unit operates the electric generator according to a speed reference value and a power reference value, the speed reference value and a power reference value being chosen along a linear operating trajectory in a power vs speed graph, the linear operating trajectory including a point corresponding to the nominal power and the nominal generator speed. The power controller unit includes a slider command for selecting the angular position of the linear operating trajectory in the power vs speed graph.