DC Microgrids
The Microgrid concept can be defined as a group of loads and Distributed Generation (DG) Microsources and, consequently, increased reliability and energy efficiency [1]. Most of the alternative energy sources (photovoltaics, fuel cells) produce direct current (DC) power, as well as energy storage devices such as batteries and supercapacitors. Lighting and electronic gadgets - laptops, phones, TVs, LED, LCD and plasma, among others – are responsible for 35% of energy consumption [2]. The use of LEDs is an emerging option for efficient lighting and this system is fed by DC. In a DC microgrid conversion losses can be reduced from 32% to 10% according to [3]. Using direct current, cable losses are lower because there is no skin effect, no reactive power, and eliminate the need for synchronization and the effects of phase imbalance. On the other hand, over current protection in DC systems is more complex, since there is no natural crossing through zero, and high voltage reduction/increasing is much simpler in AC systems using transformers [4] and [5]. Furthermore, the reactive power, even though an irrelevant issue on DC systems, allows the voltage control independently of the active power in AC systems [5].
[1] Chuanwen, J., Jiayi, H., Rong, X, “A review on distributed energy resources and MicroGrid,” Renewable and Sustainable Energy Reviews. v. 12, p. 2472-2483, 2008
[2] Todd, B, “DC Microgrids: a new source of local power generation,” Renewable Energy. Focus. August, 13, 2009. Available at: http://www.renewableenergyfocus.com
[3] Savage, P., Nordhaus, R. R., Jamieson, S. P, “DC Microgrids: Benefits and Barriers,” From Silos to Systems: Issues in Clean Energy and Climate Change, June, 2010. p. 51
[4] Saeedifard, M., Graovac, M., Dias, R. F., Iravani, R., “DC power systems: Challenges and opportunities,” 2010 IEEE Power and Energy Society General Meeting, p.1-7, jul. 2010
[5] Hammerstrom, D. J., “AC Versus DC Distribution Systems” — Did We Get it Right?,” IEEE Power Engineering Society General Meeting, pp. 1-5, 2007
Research areas
Power Electronics and Control
- DC-DC converters and bidirectional inverters;
- Nonlinear control (fuzzy, sliding mode control);
Electric Power Systems
- Stability analysis of DC power systems;
- DC power quality.
Renewable energy sources and Energy Storage Devices (ESD)
- Photovoltaic, fuel cells, wind turbines;
- Batteries, supercapacitors, SMES.