A New Parallel Monitor Circuit for Charging EDLCs

Abstract

Electric double layer capacitors (EDLC) having very large capacitance have attracted attention as energy storage devices. The voltage rating of an EDLC is in the low range of approximately 2.3 to 3.0V. Hence, the use of EDLCs in power electronics requires many EDLC cells to be connected in series. Then an electronic circuit known as a parallel monitor is connected in parallel with each EDLC cell in order to avoid the overcharging which breaks it down. In this paper, we propose a new parallel monitor circuit, which consists of one MOSFET and two resistors. This parallel monitor circuit is not only simple but can be electrically separated from the EDLC cell during relaxation charging by connecting another simple electronic circuit. Therefore, the energy loss of this parallel monitor circuit is decreased. To confirm the advantages of this proposed parallel monitor circuit, a charging circuit, which comprises the proposed parallel monitors and the separation circuit described above, was fabricated for five serially connected EDLCs and experimentally examined. As a result, it was clarified that the charging efficiency of the proposed monitor with its separation circuit was 25% greater than that of the conventional one.