Ki-Doek Lee

This paper discusses a permanent-magnet electromagnetic brake for the semiconductor process of hollow integrated modules. This permanent-magnet electromagnetic brake is characterized by permanent magnets arranged at the bottom of the stator and coils positioned in the middle portion of the stator. The attractive force is generated by the magnetic energy from the permanent magnet, and to counteract the holding force, a current must be applied to the coils. In the case of a permanent-magnet electromagnetic brake, the maximum holding force that can be generated is fixed by the permanent magnet inserted at the bottom, and even if the load conditions vary, the holding force cannot be altered. This study investigated a method to secure an additional holding force by inducing iron losses at the moment when the holding force is required through improvements in the structure of both the stator and rotor of a permanent-magnet electromagnetic brake. To validate the feasibility of this study, prototypes of permanent-magnet brakes were fabricated, and dynamometer tests were conducted.

Electrical losses are converted into thermal energy in motors, which heats each component. It is a significant factor in decreasing motor mechanical performance. In this paper, the motor cooling characteristics were analyzed according to the design factors of the water jacket to investigate the cooling performance of a permanent magnet synchronous motor (PMSM). First, the electrical losses generated in PMSM were calculated using electromagnetic finite element (FE) analysis. Secondly, a 3D electromagnetic–thermal fluid coupled FE analysis was performed to analyze the temperature distribution inside the motor by applying electrical loss as the heat source. Finally, the motor cooling performance according to the design factors of the water jacket was statistically analyzed using the design of experiment (DOE) method. It was found that the mass flow rate of 0.02547 kg/s and six passes of the water jacket with one inlet and two outlets could be considered the optimum conditions in terms of the maximum motor temperature.

Permanent magnet synchronous generators (PMSGs) with high output density per unit volume are becoming widespread in wind-power generation systems. Among them, spoke-type PMSGs are more challenging to magnetize than other PMSGs, owing to their structural characteristics. Magnetization performance is critical because it is directly related to the demagnetization and mass productivity of permanent magnets, and load performance is reduced when non-magnetization occurs due to the low magnetization performance. Additionally, the starting performance is crucial in wind turbines and is influenced by the cogging torque of the PMSG. This is because starting a wind turbine with a large cogging torque is more challenging. Therefore, this study proposes a spoke-type PMSG rotor shape design for low capacity wind turbines that considers magnetization and cogging torques. We analyzed the principle of magnetization and the factors influencing magnetization performance, and designed a rotor shape with improved magnetization performance. Additionally, we applied an asymmetric rotor barrier structure to reduce the cogging torque and analyze the performance of the final model using finite element analysis. We analyzed the temperature saturation during the operation of the final model using a thermal network method and validated the irreversible demagnetization accordingly.

In this paper, the transient state analysis of a Line-Start Permanent Magnet Synchronous Motor (LSPMSM) and the optimum design for high efficiency were studied. In the case of an LSPMSM, aluminum bars and permanent magnets are inserted in the rotor. Since it has aluminum bars, it can be directly started on-line without closed-loop control at the time of starting, like an induction motor. Furthermore, once driven, it rotates at a synchronous speed due to the permanent magnets in the steady state. Theoretically, since the rotor bars have no induced current, copper loss does not occur in the rotor bars. Further, because of the inserted permanent magnets, an LSPMSM has a higher power density than an induction motor with the same output power. However, since it is driven directly on-line, the transient state is longer than that of a synchronous motor driven by an inverter. Therefore, it is important to analyze the characteristics of the transient state depending on the rotor shape in the LSPMSM design. In this study, an LSPMSM that has the same outer diameter of a 7.5 kW IE3 efficiency class induction motor currently used for the industry was designed. The optimal design of the motor was designed using Finite-Element Analysis (FEA) and Design of Experiment (D.O.E). In the design process, the velocity ripple was minimized in the transient state, and the steady state was quickly reached. Finally, the efficiency of the motor satisfies the requirements of the IE4 efficiency class, an efficiency standard described in IEC 60034-30, which is an international standard.

In recent years, the deterministic design optimization method has been widely used to improve the output performance of brushless direct current (BLDC) motors. However, it does not contribute to reducing the failure rate and performance variation of products because it cannot determine the manufacturing uncertainty. In this study, we proposed reliability-based robust design optimization to improve the output torque of a BLDC motor while reducing the failure rate and performance variation. We calculated the output torque and vibration response of the BLDC motor using the electromagnetic–structural coupled analysis. We selected the tooth thickness, slot opening width, slot radius, slot depth, tooth width, magnet thickness, and magnet length as the design variables related to the shape of the stator and rotor that affect the output torque. We considered the distribution of design variables with manufacturing tolerances. We performed a reliability analysis of the BLDC motor considering the distribution of design variables with manufacturing tolerances. Using the reliability analysis results, we performed reliability-based robust design optimization (RBRDO) to maximize the output torque; consequently, the output torque increased by 8.8% compared to the initial BLDC motor, the standard deviation in output performance decreased by 46.9% with improved robustness, and the failure rate decreased by 99.2% with enhanced reliability. The proposed reliability-based robust design optimization is considered to be useful in the actual product design field because it can evaluate both the reliability and robustness of the product and improve its performance in the design stage.

In this study, an electromagnetic force induced structural vibration for a brushless direct current (BLDC) motor with variable speed is performed using finite element analysis, as well as an experiment for operating speed range. The 3-D entire finite element model was used to predict the vibration characteristics for the operating speed range of a BLDC motor. To validate the finite element (FE) model, the modal analysis was compared with the results of a modal test. Then, for variable speed, electromagnetic force induced vibration characteristics for the range of operating speeds are predicted using the electromagnetic-structural vibration coupled analysis method. The predicted vibration characteristics are compared and validated with vibration experiment under the same operating conditions. Finally, it was found that the vibration characteristics predicted using the 3-D entire FE model can accurately reflect the actual vibration characteristics for variable speed.

In this paper, an axial slot-less permanent magnet synchronous motor (ASFPMSM) was designed to increase the power density. The iron core of the stator was replaced with block coils, and the stator back yoke was removed because 3D printing can provide a wide range of structures of the stator. The proposed model also significantly impacts efficiency because it can reduce iron loss. To meet size and performance requirements, coil thickness and number of winding layers in the block, the total amount of magnet, and pole/slot combinations were considered. The validity of the proposed model was proved via finite elements analysis (FEA).

A voltage-parameter map (VP-Map) is proposed for predicting the performance of electric vehicles (EVs) and hybrid EVs (HEVs), which varies with respect to the parameters in a variable load and flux-weakening range, and determining the design parameters. Through this, the maximum torque that can be generated at the maximum speed, the input current for generation of the rated torque, and whether the vehicle is operable with a light load are predicted, and the design parameters suitable for the 120-kW class interior permanent-magnet (PM) synchronous motor for HEVs, which is the target electric motor of this study, are determined. A flux-concentrating PM synchronous motor (FCPMSM) is proposed that can be designed using the desired design parameters depending on the degree of the flux concentration. The validity of the VP-Map was verified by analyzing the characteristics of three types of FCPMSMs with different parameter combinations, and a PM synchronous motor for an EV having a high output, high efficiency, and high-power factor was designed. Lastly, the requirements were checked, and the analysis was validated by testing the designed motor.

This letter presents a position sensorless control method of brushless DC (BLDC) motors considering unbalanced zero crossing detection of back electromotive force (back EMF). The zero-crossing point (ZCP) of back EMF voltage is detected by comparing the DC-link voltage with the back EMF voltage. The unbalanced ZCP detection is caused by the DC-link voltage drop, DC-link offset voltage, and a motor having asymmetric back EMFs. Because the sensorless BLDC motor control is based on unbalanced ZCP detection, issues with torque ripple and current ripple may be increased. Therefore, sensorless operation with unbalanced ZCP detection may be unstable. In this study, an improved sensorless control method based on a simple compensation algorithm using ZCP signals is proposed. Using the proposed control method, balanced commutation instants can be obtained and the benefits of high-performance operation of BLDC motors can be accomplished. Through application of the proposed method, the effectiveness of the proposed method was experimentally verified.