A series or parallel changeover system using battery with EDLC for EV

This paper focuses on the way to use the EDLC bank in a small electric vehicle (EV). In a recent study of an EV, a supercapacitor (EDLC; Electric Double Layer Capacitor) is adopted into an energy storage system to improve energy efficiency. Generally, the EDLC bank consists of a large number of cells because the EDLC bank cell voltage is very small compared with the battery terminal voltage, which is a DC bus voltage in the motor drive system. On the other hand, a small EV cannot be equipped with the large size EDLC bank because of the restriction of a cost and a space. Therefore, the energy storage system demands the small size EDLC bank more efficiently. Usually, the conventional system of an EV cannot utilize the full voltage range of an EDLC bank because the operating voltage range is limited by the ratio of step-up voltage between the DC bus and the terminal of the EDLC bank in bidirectional DC/DC converter. In this paper, due to improve the operating voltage range of the EDLC bank, a series or parallel changeover system using a battery with an EDLC is proposed. In addition, simulations and experimental results are presented to verify that the proposed system can expand the operating voltage range of the EDLC bank. As a result, the small bank of few EDLC cells is applied for small EV as a power assistance system.