This thesis describes the development of the INSTAR system: a high-power, cost-effective energy storage system designed to improve HEV regenerative braking capabilities by combining chemical batteries with an electromechanical flywheel. This combination allows the regenerative braking system in hybrid vehicles to recapture more available braking energy at a lower battery pack charging current, increasing vehicle energy efficiency while also potentially increasing battery life.

A prototype flywheel energy storage system and electric vehicle test platform were built to test the design. A novel open loop controller was developed to manage the power flow between the traction motors, battery pack, and flywheel energy storage system. The flywheel was designed to hold 30 Wh at 25,000 RPM, but can easily scale to larger vehicles. Experiments were conducted for speeds up to 11,000 RPM and power levels up to 2.5 kW. Round trip efficiency of 70% for the flywheel energy storage system alone were achieved and battery charging current was successfully limited during regenerative braking by absorbing energy with the flywheel energy system. The flywheel energy storage system successfully returned the stored energy, minus parasitic losses, back to the battery pack at controlled rates.