Toshiaki Okuyama

A high accuracy current component detection method for fully digital, vector-controlled PWM VSI-fed AC drives

A high-accuracy differential-type current component detection method and test results are described. The method is suited for vector-controlled pulse width-modulated (PWM) VSI-fed adjustable-speed AC drives. Its features include elimination of high-frequency current harmonics and correction of the detection error caused by the lag time of time-sharing processing. Since this method allows current-loop calculations at a slower sampling rate with a conventional microprocessor, it realizes a fully digital speed regulator with a minor current component loop. Simulation results and experimental results are presented.<<ETX>>

A Multimicroprocessor-Based Fully Digital AC Drive System for Rolling Mills

Theoretical considerations are given for a control scheme to decrease voltage disturbances in a cycloconverter-fed ac drive system, using a form of the vector control concept. The theory has been applied to a multimicroprocessor-based fully digital 72-arm cycloconverter-fed 5000-kW squirrel-cage induction motor drive control system. For speed and position sensors, a high-resolution sine encoder which generates a 15 000-sine wave/r has been developed to achieve high-performance speed regulation, particularly at ultra-low speeds. The factory test results compare far more favorably than those attainable using dc drives. They reveal that the ac drive system is suited to practical applications in main drives for rolling mills, including tandem cold mills.

A Simple Robust Voltage Control of High Power Sensorless Induction Motor Drives With High Start Torque Demand

A simple, robust, high-torque control without a speed sensor, for driving an induction motor with high- and mid-voltage inverters, has been developed. The proposed method is characterized by the unique control of the slip angular frequency of the induction motor, and allows a stable start with high torque. The proposed control method was installed in an H-bridge cascaded inverter, and startup and impact load tests were done with a 3 kV/1500 kW induction motor. Steady operation with a 200% higher starting torque and for a 200% impact load were confirmed. The proposed method can generate a stable start with high torque within the ultralow speed region, and is appropriate for motor drives on industrial equipment such as mixing, extruding, and stirring machines.

A method for suppressing torque ripple of an AC motor by current amplitude control

The authors examine a thyristor motor torque ripple suppression method that is simple in configuration. A simplified method of calculating motor torque ripple is introduced. This method enables calculation of velocity fluctuation due to torque ripple in the vicinity of the resonant frequency. Calculation results show that operation around the resonant frequency constitutes a problem. The current amplitude control method is effective for suppressing the torque ripple at the resonant frequency. This method detects the velocity fluctuation component and controls the current amplitude to eliminate that component. The velocity fluctuation component is detectable by using a filter that has a differential element. In addition, it is shown that the characteristic of the control system can be calculated with the aid of a Bode diagram, and its effectiveness is confirmed through simulation. From simulation results, this suppression method is found to be effective in reducing the velocity fluctuation to a practical level. >