In this paper, strategies of short and long term fluctuations mitigation are applied to a wind-diesel hybrid system. Ultracapacitors (UC) and batteries are operated in a complementary mode. The DC-bus voltage is maintained at a constant value by the diesel engine while providing a smoothed current. The proposed strategies are based on the wind power frequencies distribution between the storage devices (batteries and UC) using two low pass filters. Simulations and experimental results are presented and analyzed.