Nacelle-top mounted anemometer gives wind velocity information pertaining to the surroundings of nacelle and this point wind velocity measurement may or may not be same as effective wind velocity which strikes the wind turbine rotor blades. In this paper, a new method for the computation of wind speed is proposed to avoid the presence of mechanical sensors like anemometer and speed encoders in the wind turbine control systems. Suitable sliding mode observers designed for the estimation of turbine rotor speed and aerodynamic torque. Effective wind velocity is computed by inverting the turbine's aerodynamic model after estimating the turbine torque and its rotor speed. Design criterion and inequality constraints are discussed in detail while satisfying the Lyapunov inequality condition. The simulation studies confirm that the computed wind speed under variable wind flow conditions is converging with true wind speed. This proposed method can be used for maximum power extraction and various control algorithms' implementations as well in wind energy conversion systems control applications. © 2018 IEEE.