Compensation of unbalance forces of a switched reluctance machine by separate control of phase currents

Abstract

The presented work handles the compensation of unbalance forces for a 6/4-Switched Reluctance Machine (SRM), which generate significant radial magnetic forces in an eccentric motor shaft position. When the rotor is operating e.g. in its principal axis of inertia, these forces must be compensated by the bearings. This is of major interest for magnetically levitated long term storage flywheels where bearing efficiency is a key factor for the overall system performance. To minimize magnetic pull, the two opposing coils are controlled separately instead of a common serial connection. Three different methods to compensate unbalance forces are presented: The modification of the reference current of the opposing coils, a quasi-parallel connection and a combination of a current controller and a fluxlinkage controller. For the observation of fluxlinkage two different approaches are described. These methods are compared to each other by means of simulation. Due to the back electromotive force (BEMF) in high speed operation, precise current control is a major challenge. Hence the third method is leading to the best results, so it was also implemented on a test rig for validation of the simulation results.

Keywords

• energy storage
• flywheel
• numerical simulation
• electromagnetic force
• electric machine
• current control
• energy efficiency
• fluxlinkage control
• unbalance control