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Speed sensorless vector controlled induction motor drives are the standard choice in many industrial applications, but this can hardly control torque and rotor speed at low speed. Recently, a method based on high‐frequency signal injection has been studied. This paper presents a method for suppressing the effects of the saturation saliency by using a high‐pass filter, and a new approach to estimate the rotor speed. The effectiveness of these methods is demonstrated through experimental results showing both good suppression of saturation harmonics and good sensorless speed control at low speed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 169(1): 41–49, 2009; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/eej.20847

Osamu Sakata, Student Member (Kagoshima University), Michio Miyake, Non-Member (Kyushu Electric Power Co., Inc.) When a transformer is connected to a circuit, under certain conditions, magnetizing inrush currents may be about ten times the full load current of the transformer. The currents contain a large amount of harmonic components and cause some relays to trip out. In this paper, the magnetizing inrush currents are compensated using a PWM inverter. The magnetizing inrush currents are detected and the PWM inverter generates compensating currents for the inrush currents. Hysteresis current controllers are used for fast response. The validity of this compensation is investigated by the simulation results. In addition, hardware implementation for the compensator is accomplished to verify the simulation results. Moreover, for the compensator, the relation between the compensating characteristics, the maximum switching frequency and the coupling reactor is discussed based on the simulation results. Finally, characteristics of two current controllers (hysteresis band current controller and ramp-comparison controller) are compared and it is shown that the hysteresis band current controller is more suitable for the compensator. The electromagnetic transient simulator named PSCAD/EMTDC is used for the simulations.

The carrier frequency tends to be raised in the PWM inverter due to the appearance of high-speed switching devices. The PWM inverter which is operated by the high carrier frequency is easily influenced by the switching dead-time in comparison with the square-wave inverter. In case that the load is a motor, it is known that the switching dead-time causes serious problems such as current waveform distortion, increased torque ripples at low speed and light load operation.In this paper, the permanent-magnet AC servo motor driven by the PWM inverter was analyzed in consideration of the output voltage deviation and the zero-current-clamping phenomenon during the switching dead-time.