Losses in an Outer-Rotor-Type Kinetic-Energy-Storage-System in Active Magnetic Bearings

This paper starts with a general description of the losses and the classification of the loss components in kinetic energy storage systems. Based on the design of an outer-rotor-type kinetic energy storage system an analytical loss model is presented. It considers the conversion losses and the drag losses of the electric drive, the drag losses of the homopolar active magnetic bearings and the gas friction losses, as well as the constant losses such as caused by the bias magnetization of the active magnetic bearings. In detail a new approach for the analytical calculation of the drag losses of the homopolar active magnetic bearings is presented, taking the eddy current and hysteresis losses as well as the penetration depth of the magnetic field into the rotor in account. The paper ends with the presentation of a developed measurement method for the experimental determination of the loss map of kinetic energy storage systems. It enables for the isolation of the drag loss components of the drive system, the magnetic bearings and the gas friction losses.