Archivo para febrero 23rd, 2016


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


DC distribution system

The figure shows the simplified distribution system of the DC microgrid system. The wire sizing has to comply with the South Africa National Standard (SANS) on the wiring of premises 6 mm2 for the generation and storage side, and 2.5 mm2 for the distribution side will allow an acceptable tolerance of voltage drop for this low voltage system, refer to SANS 10142

Source:
Gilbert M Bokanga, Atanda Raji, Mohammed TE Kahn. “Design of a low voltage DC microgrid system for rural electrification in South Africa”. Journal of Energy in Southern Africa • Vol 25 No 2 • May 2014.


Model design of the DC microgrid system

Hybrid renewable energy systems have been accepted as possible means of electrifying rural outlying areas where it is too expensive to extend the grid to supply them. As stipulated in the introduction, the system is intended to power households, and it must be cost effective; therefore, only solar energy system is retained. Figure 1 shows the overview of the low voltage DC microgrid system

Source:
Gilbert M Bokanga, Atanda Raji, Mohammed TE Kahn. “Design of a low voltage DC microgrid system for rural electrification in South Africa”. Journal of Energy in Southern Africa • Vol 25 No 2 • May 2014.