Example of configuration of DC micro-grid

As shown in Figure, the proposed DC micro-grid consists of uncontrolled DGs such as wind power, photovoltaic generation and controlled fuel-cell sources as well as energy storage elements such as super capacitors and batteries, DC loads and grid-tied converters. The wind power system consists of a 2kW PMSG (permanent magnet synchronous generator) which operates under a wide range of wind-speeds without a gear box, and a three-phase PWM converter which converts variable voltage, variable frequency AC voltage to fixed DC voltage with MPPT (maximum power point tracking) capability. The PV (Photo-Voltaic) array converter is a 1.5kW transformer-less boost converter which operates with the MPPT method under varying levels of irradiation and temperature. Since a 1.2 kW PEM (proton exchange membrane) type fuel cell stack generates a low varying DC voltage that is around 26V and is strongly influenced by ripple current, a three-phase isolated DC-DC converter with an active clamp is employed to limit the ripple current into the fuel cells and to increase efficiency. Bidirectional two-phase interleaved converters are used to charge or discharge into the elements. Energy storage elements such as super-capacitors and batteries play an important role for the power management of DC microgrids. They ensure a secure grid network and provide high quality power. A grid-tied three-phase converter, which is a conventional three-phase PWM converter, maintains a constant common DC grid voltage and regulates both the reactive power and the harmonic components in PCC. The DC load is simplified as a variable resistor.

Source:
Ji-Heon Lee, Hyun-Jun Kim, Byung-Moon Han, Yu-Seok Jeong, Hyo-Sik Yang and Han-Ju Cha “DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation” Journal of Power Electronics, Vol. 11, No. 3, May 2011

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