Design and Analysis of a Vernier Motor Considering Series Compensation

This paper demonstrates that the problem in design of vernier motors that their high torque capability needs to be compromised due to extremely low power factor is improved by using the series compensation method and torque performance in the field of weakened driving is also strengthen. In order to quantitatively analyze the advantages obtained from vernier motors by the series compensation, first the vernier motors with various gear ratios are designed under a constraint of the given air gap radius. From the comparison of the back electromotive force (EMF), reactance and speed versus torque characteristics for the designed models, it is shown that the model with the largest back EMF, on the contrary, has the worst torque characteristic at high speed. To improve the torque characteristics in the high-speed operation area, the winding of the vernier motor with the largest counter electromotive force is configured as the open ended, and the series compensation is performed by connecting the secondary inverter and the floating capacitance. The characteristics of the vernier motor with the series compensation are first analyzed using electrical circuit simulation and then the time step finite element (FE) method is also performed. Especially, in the FE simulations, the equivalent capacitances reflecting series compensation are used to reduce the enormous calculation time of the FE analysis considering the actual inverter operations. From the analysis results, the improvement of the torque and power factor characteristics of the motor is confirmed.