Study on a doubly-fed flywheel machine-based driveline with an AC/DC/AC converter

The combination of a flywheel device with a battery source has several advantages, such as high-peak power capacity, high energy density and reduction in the number of charging/discharging cycles in the battery. The flywheel system investigated here uses a double-wound flywheel motor/generator to divide the system into two different voltage/power levels. An AC/DC/AC converter is used to connect the high-power windings of the flywheel machine to the traction motor. The control strategy of the AC/DC/AC converter is discussed. The simulations of the complete system are carried out using Simulink and are compared with the experimental results, obtained from a scaled experimental test set-up. Simulations and experimental results show good agreement, where the designed controllers have managed to keep the different controlled signals almost equal to their reference values. Unity power factor and low distortion has been obtained in the flywheel voltage and current. The average efficiency of the driveline during a simple drive cycle has been obtained, being approximately 87%. A theoretical calculation, based on the real parameters of the system, was made, and it showed good agreement with the simulation and experimental results.