Torque Analysis of HB-type Vernier Motor

A stepping motor has a concentrated stator winding and is usually driven by a pulse-shaped excitation voltage. Therefore, torque pulsation exists during rotation in principle. Meanwhile, various Vernier motors with low pulsation are being developed. For the HB-type Vernier motor, the authors derived a voltage equation and a torque formula by substituting magnetized sections with equivalent coils for analysis. This paper describes the analytical technique and compares the theoretical value of the pull-out torque with the measured value from the viewpoint of validation of the analytical technique. Using this analysis, a voltage equation and a torque formula similar to those for a general synchronous machine were obtained. To validate the analytical technique, the authors fabricated a test motor and measured its pull-out torque. It was confirmed that the calculated pull-out torque values matched the measured values quite well. Therefore, the pull-out torque can be calculated accurately by just acquiring the synchronous reactance and induced electromotive force. In a laboratory, even if only the synchronous reactance and induced electromotive force are acquired by the finite element method, the pull-out torque can still be calculated easily at high speeds and applied to the optimum design.