Principles of self-excitation at radial force winding terminals in bearingless induction motors with a squirrel cage rotor

Bearingless induction motors with a squirrel cage rotor have two-pole motor windings and four-pole radial force windings. The four-pole winding currents generate the radial force, basically, however, real power can be also generated as an induction generator. It is shown that self-excitation occurs at radial force winding terminals with proper current injection. A control strategy for adjusting the power with optimal current frequency is proposed. Then, a DC power source connected to a radial force inverter is not needed. It is shown experimentally that a test bearingless motor can be successfully operated without a DC power source in a radial force inverter