One of authors developed PM vernier motor which has high torque at very slow speed so that it can be used for socalled direct drive systems, and its construction, principle and control scheme were already presented. However, a rotary encoder having high resolution for detecting the rotor position was required in the control scheme, which is very expensive. So the authors developed a variable reluctance type N-speed synchro having large number for N, which is inexpensive because of its very simple construction. It consists of stator and rotor cores punched slots. However, nothing is put into the rotor slots, because both exciting and output windings are put into the stator slots.
In the present paper, detailed explanation of construction and principle of the VR synchro is given at first and it is shown by the experimental result that three phase sinusoidal voltages of 32 cycle per revolution can be obtained. Then, it is described that demodulated output voltages of the VR N-speed synchro can be directly used for current phase commands of the PM vernier motor, which makes the control scheme very simple and inexpensive. The measured speed response characteristics for the four-quadrant drive showed very good performance.