Novel control method for magnetic suspension and motor drive with one three-phase voltage source inverter using zero-phase current

This paper focuses on realization of both the one-degree-of-freedom (one-DOF) active magnetic suspension and motor operation of a three-phase permanent magnet motor using only one three-phase voltage source inverter. The suspension winding of the electromagnet for the one-DOF magnetic suspension is connected between the neutral point of the Y-connected three-phase winding and the middle point of the dc voltage sources, and the resulting zero-phase current is utilized to control the suspension force. The control method of the zero-phase current is theoretically derived to avoid interference with the motor performance. Experimental apparatus was built and tested, which consists of an iron ball magnetic suspension system and a three-phase interior permanent magnet motor. The experimental results demonstrated stable magnetic suspension and motor rotation using only one three-phase inverter.