A study on ultracapacitor-based systems for compensation of power deficiency and saving energy: Design, control and simulation

Abstract

Ultracapacitor-based energy storage systems can be used for the compensation of power deficiency in renewable power generation, and for energy saving in the utilization of electrical power. Two such cases will be considered in this work: the photovoltaic (PV) power plant, and the electric bus. Variable nature of solar irradiation owing to local meteorological and environmental conditions, makes it impossible to deliver energy from PV plants at the power level corresponding to the clear-sky model. Energy storage systems equipped with ultracapacitors (UC) can cope with the rapid power fluctuations, and stabilize the output power for several tens of minutes. Computer simulations have been carried out on the clear-sky model superimposed with the actual power fluctuation data obtained in the field from a 50 kW PV power plant. Two UC modules of 63F/125V are connected in series to store/deliver energy by means of a bidirectional buck/boost converter, so as to compensate for the short-term active power fluctuations. As the second case study, the use of UCs during acceleration and deceleration time periods of a 250 kW electric bus is simulated to decrease the overall stress of the built-in battery, and to increase the operating efficiency. This is achieved by storing energy during the braking time periods of the electric bus, while delivering the stored energy during the acceleration time periods, which also improves the voltage quality of the DC supply.