Sensorless starting and low speed drive of cylindrical brushless DC motor using eddy current at un-known load

A novel technique is proposed to realize the starting and low speed driving of a cylindrical brushless DC motor without a position sensor at an unknown load. Such techniques have previously been difficult because of an insufficient electromotive force at motor starting and at low speeds, and a constant coil inductance irrespective of rotor position. Therefore, this paper proposes to paste nonmagnetic materials onto the motor's rotor surface and to measure the open-phase voltage change caused by the eddy current which flows on these nonmagnetic materials. The proposed method is shown to be very useful by experimental results.