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.

As the torque density of traction motors for electric vehicles (EVs) increases, winding technology with a large conductor area, such as hairpin winding, is widely used. However, it has a disadvantage of large AC copper loss affected by the skin and proximity effect. Therefore, the AC copper loss should be considered for deriving characteristics of interior permanent magnet synchronous motors (IPMSMs). This article deals with the maximum torque per ampere (MTPA) and flux-weakening control characteristics of the IPMSM considering AC copper loss. As the AC copper loss is caused by armature and field excitation, a separation process of AC copper loss by each cause is proposed. By using the process, the separated AC copper loss can be analyzed according to the current vector and rotational speed. However, it is inefficient to calculate the AC copper loss according to rotational speed using transient analysis. Therefore, a computationally efficient method of calculating AC copper loss based on magneto-static analysis is presented. In addition, advanced d, q -axis equivalent model considering AC copper loss is proposed to analyze MTPA and flux-weakening control characteristics of IPMSM. By using the proposed d, q -axis equivalent model, the IPMSM can be designed considering the AC copper loss efficiently and accurately.

The sizing process is necessary to analyze the electromagnetic characteristics according to the major shape parameters during the early design stage of permanent magnet synchronous motors (PMSMs). However, predicting the performance of PMSMs with 2-D finite element analysis (FEA) has errors due to axial leakage flux. Therefore, the axial leakage flux should be considered in the sizing process. The most accurate way to consider the axial leakage flux is to perform 3-D FEA, but it has a disadvantage of high computational cost. In this view, we propose a deep transfer learning-based surrogate modeling method to reduce the computational cost for calculating 3-D FEA-based motor parameters. The transfer learning is conducted using a large amount of 2-D FEA-based and small amount of 3-D FEA-based motor parameters. Using the proposed process, it is possible to accurately predict the motor characteristics according to size-related variables that satisfy the required specifications with small amount of 3-D FEA-based motor parameters. The proposed method was verified through 3-D FEA and experiments for pancake-type PMSMs, which is highly affected by axial leakage flux.

Owing to the high speed and frequency required in electric machine industry, the significance of AC resistance has been increasing. This study investigates the AC resistance of windings according to configuration of strands. The mechanism of generating the AC resistance in winding conductors was investigated with respect to the slot leakage flux and eddy current. Then, when applying the strands to the winding, the concept of unbalanced impedance was introduced to characterize the additional AC resistance due to circulating current. The analytic method to calculate AC resistance describing the above phenomena is derived and verified by FEA results. Afterwards, the AC resistances of varying numbers and arrangements of strands were separately studied via finite element analysis. In addition, a method to avoid increasing the AC resistance was suggested based on impedance equalization when applying strands. Finally, experiments were conducted to verify the effect of the strand configuration on AC resistance. An E- and I- shaped core, which can be the rendering of common electric machines, such as motors, generators, and transformers, was manufactured and tested with winding specimens. Consequently, the test results showed a similar trend as the analytical results.

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.