In a previous paper, we developed a new magnet-free motor that has concentrated stator windings and rotor coils with a pair of diodes. The advantage of this motor is that rotor currents can be generated by utilizing changes in the magnetic fields. However, sufficient rotor currents and torque cannot be generated at low speeds, because the rate of change in the magnetic fields becomes too small. Therefore, we developed a method to amplify the rotor currents and torque at low speeds. This method increases the changes in the magnetic field by intentionally superimposing time harmonics over the stator currents. A prototype motor was designed and fabricated, and the method was applied to the motor. This paper presents a mechanism for inducing currents in the rotor coils using the changes in the time harmonics of the stator currents. Using experimental data, we evaluate the increase in torque at low speeds.
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