Eui-Chun Lee

This paper proposes a design guideline for selecting the pole and slot combination of an outer-rotor permanent magnet synchronous motor (PMSM) using a maximum slot occupation (MSO) coil. Because the MSO coil has a large conductor area, the AC Joule loss in the conductors may be increased at high frequencies. To ensure high-efficiency for the PMSM, it is necessary to reduce the loss. Thus, it is important to select the pole- and slot- combination that has the minimum AC Joule loss. The loss is caused by skin/proximity effects and variations in the slot leakage flux. The skin effect is due to the armature winding and the variation in the slot leakage flux is due to the field flux. A method for separating the AC Joule loss due to each component using the frozen permeability method is proposed. Based on the proposed method, the effect of each cause on the loss at various pole- and slot- combinations is analyzed in this study.

To improve electric vehicle (EV) mileage, motors must be designed for higher power density and efficiency. Winding technology with a high fill factor decreases the motor volume by reducing the unnecessary area of the slot. A motor conductor with a large cross-sectional area generates additional losses due to ac resistance, reducing the efficiency of the motor. Traction motors designed under these conditions can adversely affect EV fuel economy. Therefore, a design method is proposed to reduce the ac resistance of a traction motor by applying winding technology with a high fill factor to increase the fuel economy of the EVs. First, the characteristics and manufacturing process of the maximum slot occupation (MSO) coil, which is a winding technology with a high fill factor, are introduced. An ac resistance reduction method for a motor using an MSO coil is then proposed. Additionally, a motor designed using the proposed method is presented, and its electrical performance is compared with that of an initial motor. Next, the effect of the fuel economy improvement of the presently designed traction motor is verified through a vehicle simulation, and the validity of this article is experimentally confirmed using this motor.

Electric vehicle (EV) systems require a high energy-efficiency traction motor so that the motors for EV traction should achieve high efficiency and power density. Hence, a permanent magnet synchronous motor (PMSM) for EV traction using a maximum slot occupation (MSO) coil has been investigated in this study. By applying the MSO coil, high torque density was achieved, but an additional loss, which decreases the efficiency, was incurred through alternating current (AC) resistance. To reduce the AC resistance of the MSO coil, the following process was performed: First, by investigation using the analytical method, pole/slot numbers, current density and number of parallel circuits affecting the frequency, the shape and number of conductors were chosen as important variables. Resistances of the MSO coil with a stator core were analyzed according to the chosen variables above. From the results, MSO coil applied PMSM with proper pole/slot numbers, current density, and parallel circuits was determined to improve the efficiencies at the base and maximum speeds. To accurately estimate the efficiency of the determined model, loss evaluation methods were explained. Subsequently, the determined MSO coil applied model was compared with the conventional model having round wires, and the improvements were verified by load testing.

This paper proposes an indirect method for predicting mechanical loss by considering the eddy current loss of permanent magnets (PMs) and conductors under the no-load condition. The mechanical loss has been conventionally predicted indirectly through experiments and numerical methods. The conventional method uses the no-load loss measured through experiments and the no-load iron loss calculated through a numerical method. With the increase in the demand for high power density motors, the PMs with high energy density and winding technology with high fill-factor are required. Thus, the proportion of eddy current losses of PMs and conductors is increasing among the electromagnetic losses. Therefore, we propose an indirect method for predicting the mechanical loss considering the eddy current losses. The accuracy of the proposed method is higher than that of the conventional method. Moreover, the proposed method is verified by comparing the estimated efficiency of the specimen obtained by using this method with the measured efficiency.