Design, implementation and characterization of a novel bi-directional energy conversion system on DC motor drive using super-capacitors

• A novel topology is proposed to regulate bi-directional power flow on demand.
• A dedicated test rig system is developed to adjust load and vary operating conditions.
• The total energy conversion process is separated into three stages to ease analysis.
• The system optimal operation points are outlined for future controller development.

In this paper, a simple but innovative bi-directional energy conversion system is developed, utilizing supercapacitor as energy source to drive an electric scooter, as well as to recover braking energy on demand. Supercapacitor is superior to battery at high load as the latter is susceptible to aging and significant heat loss under this condition, leading to sometimes serious issues such as shortened lifecycle. The system consists of a microprocessor based vehicle controller (integrating an embedded regenerative braking controller), a 300 W Permanent Magnet (PM) DC motor, two low-power DC–DC converters to form a higher power DC–DC converter pack, a motor controller, a supercapacitor bank and a capacitor cell balancing sub-system. To characterize system performance, a dedicated test rig is built and the system is broken down into three stages with input and output variables of each stage being evaluated systematically in three representative cases. The experimental results show overall effectiveness of such system. Operating conditions where high efficiency reside are therefore able to be determined to gain insight into a complex system.