The pulse width modulation (PWM) inverter is widely used for the control of motors. We showed that the iron loss under PWM inverter excitation is affected by the impedance of the excitation circuit. The dc voltage of PWM inverter, which is widely used, is constant and the control of motor is carried out by changing the modulation index. Therefore, the evaluation of iron loss under PWM excitation with constant dc voltage is necessary in order to investigate the behavior of iron loss in an actual motor. In this paper, we measured iron losses of non-oriented electrical steel sheets under the shingle-phase full-bridge PWM inverter excitation and examined the influence of modulation index , carrier frequency and dc voltage on the iron losses. It is shown that the iron loss under PWM inverter excitation can be reduced when dc voltage is reduced and modulation index is increased.

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A magnetically levitated (MAGLEV) vehicle using electro-magnets and iron rails generates lateral guiding force naturally by controlling levitation force to maintain the air gaps between the magnets and the iron rails. A MAGLEV system without guide magnets offers simple design and cost advantages. But such a system has little lateral damping force. In order to improve damping characteristics, an experimental apparatus using salient-pole type magnets and laminated iron rails was made. The iron cores were placed in two rows. The levitation coils surrounded both of the magnet iron cores and the damping coils surrounded every magnet cores separately. The damping coils were excited by currents proportional to the lateral displacement velocity. According to a step response experiment, the lateral motion dissipated after a cycle or two of the swing. The self-inductance of the levitation coil of the magnet almost unchanged against variation of the lateral displacement. The influence of damping current on the levitation was very small. In this paper electromagnetic characteristics of the levitation system are shown.

SUMMARY Because of the development of power electronics technology, pulse width modulation (PWM) inverters are now being used to drive motors in order to achieve precise and energy‐efficient control. Precise estimation of the increase in iron loss due to the high harmonic components of flux, including the carrier frequency, is important in the design of motors excited by a PWM inverter. We measured the iron losses of non‐oriented electrical steel sheets that were excited using a single‐phase full‐bridge PWM inverter, and examined the influence of the carrier frequency and circuit resistance on the iron loss. We showed that the iron loss increased because of the generation of minor loops when the circuit resistance was high. Therefore, the circuit resistance should be decreased in an actual motor system.