Design on notch structure of stator tooth to reduce of cogging torque of single-phase BLDC motor
This paper proposes the design method on the notch structure of stator tooth to reduce the cogging torque of the single-phase brushless Direct Current (BLDC) Motor. The single phase BLDC motors generates the dead-point causing a starting failure. This problem is solved by using an asymmetric air-gap structure. However, the asymmetric air-gap structure increases the cogging torque causing a noise and vibration of BLDC motor. Therefore, the reduction of cogging torque is essential to improve the performance of BLDC motor. This study for reducing the cogging torque of BLDC motors applies to notch structure of stator because of ease of application and low cost. In this paper, Availability on reduction of cogging torque of the asymmetric notch is proved by using two-notches. Then, the reduction of cogging torque is proved by using the finite element analysis(FEA).
Initial Rotor Position Estimation of Single-phase Permanent Magnet Synchronous Motor with Asymmetric Air-gap
This paper presents an initial rotor position estimation algorithm of asymmetric air-gap single-phase permanent magnet synchronous motors without using a hall sensor. Generally, the common problem associated with the sensorless drive is the starting operation. Most sensorless control methods are based on back-EMF. However, when motor is at standstill or low speed, the back-EMF is too small to detect rotor position. Therefore, high frequency injection methods are widely used in the standstill or low speed region. In case of the SP-PMSM, when high frequency signal is injected to asymmetric air-gap single-phase PMSM motors, flux saturation is not occurred at air gap unlike 3-phase PMSM. Due to alternating magnetic field at the air-gap, initial rotor position of the SP-PMSM is hard to be estimated. As a result, in this paper, DC offset voltage is added to the high frequency injection signal to generate flux saturation at the air-gap of the SP-PMSM. The several experimental results show that the proposed algorithm is effectiveness and usefulness for SP-PMSM with non-uniform air-gap.
Prediction of a representative point for rail temperature measurement by considering longitudinal deformation
Monitoring rail temperature is very important for determining the safe running speed of trains and to prevent buckling. In general, the maximum variation of the internal rail temperature can be >7 ℃ depending on the point of measurement. However, there is as yet no sufficient information about how to predict the measurement point to represent the thermal deformation due to temperature distribution. In this study, the authors report a new point, called the representative measurement point, at which the rail temperature can be measured. This point considers the average deformation of the rail through structural analysis by adopting experimental and actual rail temperature data. The authors designed and installed a measurement system similar to an actual rail environment. Using the system, various data were acquired (internal/surface rail temperature and weather data) for 10 months. On the basis of these data, an analysis was done to calculate the average deformation point through thermal analysis. Finally, the representative measurement point was proposed as the position at which the average deformation point converges regardless of weather or seasons. The authors believe that the method described herein is advantageous in that it could be used in a high-accuracy temperature-monitoring system and for predicting thermal deformation and buckling.