Search

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.

Recently, a greater demand for stable supply of electric power has resulted from a higher standard of living. It becomes important that the causes and locations of ground faults in distribution lines be found early and defects be repaired as soon as possible. Therefore, a unit for recording the waveform I0 of ground fault's current and the waveform V0 of its voltage is installed in distribution substations. The establishment of a technology to distinguish fault causes automatically is being hastened. This paper presents a new classification method for ground fault waveforms, based on phase-plane trajectories for the current or voltage and their differential values. Examinations of ground fault waveforms based on real data show that the waveform of current I0 is more suitable than that of voltage V0 for the classification of waveforms at ground faults and that the trajectory of each of the three types of waveforms, such as sine waves, trapezoidal waves, and spikes, has all of the characteristics in its figure. It is also found from the distribution of 167 sampling points on the phase plane that any waveforms at a real ground fault may be classified into three characteristic point distributions, which gives the possibility of easy display for the classification of ground fault causes. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 8–16, 1998 [ABSTRACT FROM AUTHOR]