A hybrid energy storage system for supplying power to an application with a fluctuating load profile, such as, for example, electric vehicles, hybrid electric vehicles, plug-in hybrid electric... Show moreA hybrid energy storage system for supplying power to an application with a fluctuating load profile, such as, for example, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, wind energy harvesting equipment and solar energy harvesting equipment. The hybrid energy storage system includes an ultra-capacitor electrically connected to a DC bus and a power source electrically connected to the DC bus via a controlled switch. The hybrid energy storage system further including a DC/DC converter connected between the power source and the ultra-capacitor, the DC/DC converter boosting a voltage of the power source to charge the ultra-capacitor. The DC/DC converter is preferably controlled to maintain a voltage of the ultra-capacitor at a higher value than the voltage of the power source. Show less