Distributed generation system is a reliable, economical and efficient electrification option that interconnects different energy sources. Small and local distribution generation system including storage systems and load is defined as a microgrid. This paper presents an energy management strategy to supervise the power flows in a stand-alone DC microgrid power generation plant. The plant is composed of: a wind turbine, a photovoltaic generator, a battery storage system and a diesel generator combined with a supercapacitor. The DC microgrid is designed and modeled using Matlab/ Simulink/ SimPowSys™ environment. The supercapacitor is utilized to cover the deficiency of power shortage during the start-up of the diesel generator. It is also utilized to compensate the limitations on the charging/discharging current of the battery. Some performance indexes are considered: the frequency-deviation, the stability of the DC bus voltage and the AC voltage total harmonic distortion (THDv). The performances of the proposed strategy are evaluated by simulation in different operating conditions. Simulation results confirm the effectiveness of the proposed power management strategy: the DC bus voltage keeps almost constant with accepted fluctuations, the normalized frequency deviation is less than 0.01 and THDv is less than 0.04 during all simulation cases. The power flow between the system sources and the load is balanced: the state of charge of batteries and supercapacitors are maintained within the accepted level during all simulation cases. The results show how the supercapacitors solve the problem of slow dynamic of diesel generator during the startup.