Evaluation of a power segmentation strategy in high power/high speed flywheel energy storage systems

This paper proposes a solution for parallel interleaved connection of multiple high-power six-pulse converters for driving high-speed flywheels for energy storage in pulsed-load applications. The solution uses inter-phase coupled reactors (IPR) to allow only the flow of common-mode currents to the load while blocking the flow of inter-converter currents. Optimal phase shifting between converters is employed to minimize the flow of low-order current harmonies to the load and maximize the fundamental applied voltage. A case study illustrating the feasibility of the proposed ideas includes simulation results, and an evaluation of the machine ripple currents and extra weigh and losses due to the IPRs. It was concluded that the extra weight and losses due to the IPRs were not significant or a small penalty considering the achieved important ripple reduction of the machine current. This ripple reduction should bring an increase in the machine efficiency and speed range, the latter leading to an increase of the power and energy densities of the overall system. In addition to the reduction of the machine ripple current, power segmentation increases redundancy, decreases semiconductor power losses and reduces the requirements in gate drivers and snubber circuits.