Wind energy is inexhaustible renewable. Unlike conventional fossil fuels, wind energy is clean, abundant energy that will be available for future generations. However, wind speed is a highly stochastic component which can deviate very quickly. Output power of the wind energy conversion system (WECS) is proportional to the cube of wind speed, which causes the output power fluctuation of the wind turbine. The power fluctuation causes frequency fluctuation and voltage flicker inside the power grid. In order to reduce the power fluctuation, various approaches have been proposed in the last decades. This article deals with the review of several power smoothing strategies for the WECS. Power smoothing methods of the WECS are primarily separated into two categories such as energy storage based power smoothing method and without energy storage based power smoothing method. The main objectives of this paper are to introduce operating principles for different power smoothing methods. The energy storage based power smoothing method is effective but installation and maintenance costs of a storage device are very high. According to the literatures review, without energy storage based power smoothing method can reduce the cost of the WECS extensively. Various methods have been proposed to generate a smooth output power of the WECS without energy storage devices. Simulation results are compared among the available methods. From the review of simulation results, the kinetic energy of the inertia control method is the highly efficient power smoothing approach.