Supercapacitor Assisted LED lighting (SCALED) for DC-micro grids

High conversion efficiency in converters is the key to reduce power consumption in electronics. System modules in whitegoods, lighting and portables are internally DC-powered, and this motivates DC microgrid powering. When multiple conversion stages are cascaded, end-to-end efficiency (ETEE) is given by the product of efficiency ratios. If DC directly powers a system, elimination of AC-DC conversion means ETEE will be higher. Commercially available 12 V LED luminaires can be used with solar and other renewable energy sources with high efficiency and no electricity bills. However, the fluctuating nature of renewable sources such as solar requires short and long-term energy storage for reliable DC powering. Given the long life cycles of supercapacitors (SC), compared to electrochemical batteries, despite their lower energy density, SCs can be used to buffer short-term power fluctuations. Supercapacitor charging is challenging because unlike batteries, SCs do not act as resistive loads. This is because when a capacitor is fed with a charge of Q coulombs, it only stores 0.5 QV while an equal amount of energy is lost in parasitic circuit resistances. SCALED (Supercapacitor Assisted LED) is a new approach where a significant part of this loss is diverted to LED lamps in the SC charging path, thereby increasing the ETEE of a 12 V DC-fed LED-powering system from 50% to ~90%. This paper presents details of this SCALED conversion system, under development for Ports of Auckland seaport lighting systems, including theory and experimental efficiency measurements.