Koichiro Nagata

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 simple sensorless control for medium voltage synchronous motor drives

When synchronous motors are driven without speed and position sensors, the uncertainty of magnetic flux position makes it hard to start motors, and it also causes a hunting phenomena of motor torque due to the deviation of phase between the inverter and the motor while accelerating the motors. In this paper, a simple control method for synchronous motors without speed and position sensor is proposed. A simple phase control to make rotor be on the position that can make starting torque and decrease the reversal angle has been developed. The hunting frequency caused by a deviation of phase angle between the inverter and the motor while accelerating can be estimated from the value of the current and inertia. The gain of the proposed hunting suppression control block can be designed simply from the estimated hunting frequency. The proposed control method enables smooth starting and acceleration of existing high and medium voltage synchronous motors. The steady operation of this method was confirmed by simulation and experiments by the multi-level (H-bridge cascaded) medium voltage inverter for 6 kV/1250 kW wound-rotor synchronous motor.

A Basic Study of a Novel Homopolar-Type Magnetic Bearing Unifying Four C-Shaped Cores for High Output and Low Loss

A magnetic bearing (MB) can suspend a rotor shaft with noncontact, so the MB has been used for high-output and high-speed machines. In general, heteropolar-type MB structure is used, because of its simple structure and low cost. However, the heteropolartype MB structure has a problem in terms of rotor iron loss caused by an alternating magnetic field on a rotor core. On the other hand, general homopolar-type MB structure has a low rotor iron loss caused by a dc magnetic field on a rotor core. However, as the general homopolar-type MB has a complicated structure and needs a large magnet for generating the bias flux, it becomes costly. Therefore, this paper discusses a novel homopolar-type MB structure unifying four C-shaped cores for high output and low iron loss. It is shown with three-dimensional finite element analysis that the novel homopolar-type MB has lower iron loss and lower cost than the general homopolar-type MB, which is known for its low iron loss.

Adjustable field weakening control of high-speed permanent magnet motor for industrial application

This paper presents an adjustable field weakening control method for a high-speed permanent magnet motor (PMM). A compact designed PMM sometimes needs strong field weakening in the high-speed domain. The proposed control method adjusts field weakening to obtain enough torque for stability of 1MW/3.2kV/ 6600rpm-PMM operation.