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.

In this article, a process for reducing the electromagnetic vibration and noise by changing the shape of the stator is presented. Although the fundamental wave of the air gap magnetic flux density contributes to the average torque of the motor, other spatial harmonics which were except the fundamental wave of that cause vibration and enfeeble the output of the motor. Therefore, it is important to reduce the spatial harmonics for performance of the motor. Through the proposed process, it is possible to obtain an objective function to reduce the specific harmonics by assigning weights to each spatial harmonic. The reduction in the fundamental wave is minimized and it is possible to reduce the spatial harmonics that have an adverse impact on vibration. After the process, a model can be found that maintains the electromagnetic performance as much as possible while optimally reducing the vibration. To verify the process, the electromagnetic vibrations by a radial force of the proposed and conventional models were compared, and it was confirmed that the electromagnetic vibration of the proposed model was reduced. The validity of the analysis was proved through finite-element analysis.

Conventional electromagnetic vibration analysis methods mainly focus on the spatial harmonic components of the radial force density. Because they do not consider time harmonics, they cannot consider the frequency component of electromagnetic vibrations. Therefore, they are not suitable for optimally designing motors by considering electromagnetic vibrations. In this paper, we propose a process to analyze electromagnetic vibrations considering time harmonics as well as spatial harmonics. For the calculation of the magnitude of electromagnetic vibrations with respect to the frequency, the natural frequency of the circumferential mode was calculated by simplifying the shape of the stator core. The natural frequency increases as the order of the stator circumferential mode increases. Using the vibration equation, it was confirmed that electromagnetic vibrations decrease as the natural frequency increases. For analyzing the correlation between the vibration source and the electromagnetic vibrations, the radial force was separated into time and spatial harmonics, and the contribution of each harmonic component to the vibration was calculated. The results revealed the harmonic components that have the most significant influence on the vibrations. Then, using the proposed process, the vibration performance, as well as the electromagnetic performance, can be used as an objective function to design motors. To verify the validity of the proposed process, the vibrations of conventional and proposed motors were analyzed. Finally, a prototype was manufactured, and its vibrations were tested using the proposed process.

A spoke type permanent magnet synchronous motor (Spoke PMSM) generates axial leakage magnetic flux due to its flux-concentrating rotor structure, and therefore degrades the motor performance. Although a three-dimensional finite element method (3D-FEM) can be used to estimate the axial leakage magnetic flux, it requires a significant amount of time for analysis. In this study, a calibration coefficient is proposed to estimate the axial leakage magnetic flux using the two-dimensional finite element method (2D-FEM) instead of 3D-FEM. This calibration coefficient is expressed in terms of the major geometric parameters of a motor and can be calculated using the material information of the permanent magnet and the bridge of the rotor core in 2D-FEM. The validity of the proposed equation is verified through 3D-FEM and other tests.

This paper presents a torque control method that compensates the reduction of the power output of a permanent magnet synchronous motor (PMSM) caused by the wide variation of rotor-mounted permanent magnet temperature. The characteristics of the permanent magnet according to temperature were analyzed, and the need for motor parameter estimation was identified. Numerical and computational techniques using the steepest descent method and the affine projection algorithm were used for online motor parameter estimator. The estimated parameters were used to achieve a torque compensation control scheme based on field-oriented control of PMSM considering the wide variation of permanent magnet temperature. The proposed control scheme was verified by the dynamometer test of the test motor under each rotor-mounted permanent magnet temperature condition.