A method of controlling a wind turbine that in operation generates a produced power output level, the wind turbine being operated in accordance with a rated power level, the method comprising: receiving a power reference signal in a wind turbine controller that defines a requested power output level (28, 40) lower than an available power level, wherein the power reference signal is below the rated power level, and wherein the power reference signal is provided based on the available power level; and, determining whether the available power level is above or below the rated power level, wherein if the available power level is determined to be below the rated power level, the method further comprises controlling the wind turbine to operate in a partial load derated mode by performing steps of: setting a blade pitch of a rotor of the wind turbine to a non-optimal pitch value based on the received power reference signal that causes the rotor to capture wind power that is approximately equal to the requested power output level; controlling the produced power output power level of the wind turbine to the requested power output level by adjusting a load torque provided to the rotor by a generator coupled to the rotor; and wherein the blade pitch of the rotor is further controlled by a pitch feedback control loop that modifies the non-optimal pitch value based on a difference between the produced power output level and the requested power output level. receiving a power reference signal in a wind turbine controller that defines a requested power output level (28, 40) lower than an available power level, wherein the power reference signal is below the rated power level, and wherein the power reference signal is provided based on the available power level; and, determining whether the available power level is above or below the rated power level, wherein if the available power level is determined to be below the rated power level, the method further comprises controlling the wind turbine to operate in a partial load derated mode by performing steps of: setting a blade pitch of a rotor of the wind turbine to a non-optimal pitch value based on the received power reference signal that causes the rotor to capture wind power that is approximately equal to the requested power output level; controlling the produced power output power level of the wind turbine to the requested power output level by adjusting a load torque provided to the rotor by a generator coupled to the rotor; and wherein the blade pitch of the rotor is further controlled by a pitch feedback control loop that modifies the non-optimal pitch value based on a difference between the produced power output level and the requested power output level. setting a blade pitch of a rotor of the wind turbine to a non-optimal pitch value based on the received power reference signal that causes the rotor to capture wind power that is approximately equal to the requested power output level; controlling the produced power output power level of the wind turbine to the requested power output level by adjusting a load torque provided to the rotor by a generator coupled to the rotor; and wherein the blade pitch of the rotor is further controlled by a pitch feedback control loop that modifies the non-optimal pitch value based on a difference between the produced power output level and the requested power output level.