The physical model based on heat transfer theory and virtual boundary method for analyzing unsteady thermal field of rotor plate for eddy current retarder used in automobile is established and boundary conditions are ...The physical model based on heat transfer theory and virtual boundary method for analyzing unsteady thermal field of rotor plate for eddy current retarder used in automobile is established and boundary conditions are also defined. The finite element governing equation is derived by Galerkin method. The time differential item is discrete based on Galerkin format that is stable at any condition. And a new style of varying time step method is used in iteration process. The thermal field on the rotor plate at the radial and axle directions is analyzed and varying temperature at appointed points on two side-surfaces is measured. The testing and analytical data are uniform approximately. Finite element method can be used for estimating thermal field of the rotor plate at initial design stage of eddy current retarder.展开更多
It is justified that during geomagnetic storms the high voltage synchronous engines are being impacted by high current harmonics of even sequences powered by power transformer due to geo-induced high voltage currents ...It is justified that during geomagnetic storms the high voltage synchronous engines are being impacted by high current harmonics of even sequences powered by power transformer due to geo-induced high voltage currents flowed through the windings. Equivalent circuits of step down substation and HV synchronous motors are made for making it possible to consider a saturation of power transformer magnetic system and higher current harmonics availability in stator windings. Analytic expressions for higher current harmonics and extra capacity losses calculation in stator windings are received, as well as the calculation of induction torques allowing to denote a rate of geomagnetic processes impact on synchronous engine operation at various step down substation parameters.展开更多
Aiming at the problem of high temperature and even demagnetization failure of permanent magnet (PM) due to PM eddy current loss in PM synchronous high-speed motors, this paper proposes a technique to lessen PM eddy cu...Aiming at the problem of high temperature and even demagnetization failure of permanent magnet (PM) due to PM eddy current loss in PM synchronous high-speed motors, this paper proposes a technique to lessen PM eddy current loss by cutting the angle of PM poles to change the shape of PM structure. Firstly, an analysis is conducted on the mechanism of PM synchronous high-speed motor eddy current loss production, the theoretical analytical model of PM eddy current loss is deduced, and it is theoretically proved that the magnetic pole shaving angle can reduce PM eddy current loss. Then, a 25 KW surface-type PM synchronous high-speed motor as an object, using two-dimensional time-step finite element method (FEM) to model and analyze PM eddy current loss. The results show that the smaller the PM pole shaving angle, the less its eddy current loss will be, it is possible to minimize the pole shaving angle of eddy current loss by 9.8% compared to the unshaved angle. Finally, the temperature field of the PM is calculated using a finite element method, and the outcomes demonstrate that the maximum temperature of the PM with a magnetic pole shaving angle can be reduced by about 5% compared with the unshaved angle.展开更多
为精准估计光伏直流微电网故障电流参数,提升故障电流过零点预测效果,提出一种基于加权最小二乘法(weighted least squares,WLMS)算法的光伏直流微电网故障电流过零点预测方法。通过故障电流参数来估计误差平方加权值与幅度因子,确定WLM...为精准估计光伏直流微电网故障电流参数,提升故障电流过零点预测效果,提出一种基于加权最小二乘法(weighted least squares,WLMS)算法的光伏直流微电网故障电流过零点预测方法。通过故障电流参数来估计误差平方加权值与幅度因子,确定WLMS算法内步长因子的取值范围,改进WLMS算法;利用改进WLMS算法来估计故障电流参数,并依据该结果建立光伏直流微电网故障电流模型;先通过F0假设检验方法在模型内提取故障电流初始相角,再通过调整采样数据窗,令建立的故障电流模型和实际模型相同,则当故障电流初始相角超过设定阈值时,可利用该模型来预测故障电流过零点。实验结果表明:所提方法下,光伏直流微电网故障电流估计的时间常数和初始电压相角与实际结果非常接近,最大误差分别为3 ms和8°;不同故障时,均有效预测了故障电流过零点,准确率为100%;在故障电流内添加谐波后,预测过零点的稳态误差较低,最高稳态误差低于24 A。展开更多
基金Department of Science and Technology of Jiangsu Province,China(No. BE2003-46).
文摘The physical model based on heat transfer theory and virtual boundary method for analyzing unsteady thermal field of rotor plate for eddy current retarder used in automobile is established and boundary conditions are also defined. The finite element governing equation is derived by Galerkin method. The time differential item is discrete based on Galerkin format that is stable at any condition. And a new style of varying time step method is used in iteration process. The thermal field on the rotor plate at the radial and axle directions is analyzed and varying temperature at appointed points on two side-surfaces is measured. The testing and analytical data are uniform approximately. Finite element method can be used for estimating thermal field of the rotor plate at initial design stage of eddy current retarder.
文摘It is justified that during geomagnetic storms the high voltage synchronous engines are being impacted by high current harmonics of even sequences powered by power transformer due to geo-induced high voltage currents flowed through the windings. Equivalent circuits of step down substation and HV synchronous motors are made for making it possible to consider a saturation of power transformer magnetic system and higher current harmonics availability in stator windings. Analytic expressions for higher current harmonics and extra capacity losses calculation in stator windings are received, as well as the calculation of induction torques allowing to denote a rate of geomagnetic processes impact on synchronous engine operation at various step down substation parameters.
文摘Aiming at the problem of high temperature and even demagnetization failure of permanent magnet (PM) due to PM eddy current loss in PM synchronous high-speed motors, this paper proposes a technique to lessen PM eddy current loss by cutting the angle of PM poles to change the shape of PM structure. Firstly, an analysis is conducted on the mechanism of PM synchronous high-speed motor eddy current loss production, the theoretical analytical model of PM eddy current loss is deduced, and it is theoretically proved that the magnetic pole shaving angle can reduce PM eddy current loss. Then, a 25 KW surface-type PM synchronous high-speed motor as an object, using two-dimensional time-step finite element method (FEM) to model and analyze PM eddy current loss. The results show that the smaller the PM pole shaving angle, the less its eddy current loss will be, it is possible to minimize the pole shaving angle of eddy current loss by 9.8% compared to the unshaved angle. Finally, the temperature field of the PM is calculated using a finite element method, and the outcomes demonstrate that the maximum temperature of the PM with a magnetic pole shaving angle can be reduced by about 5% compared with the unshaved angle.
文摘为精准估计光伏直流微电网故障电流参数,提升故障电流过零点预测效果,提出一种基于加权最小二乘法(weighted least squares,WLMS)算法的光伏直流微电网故障电流过零点预测方法。通过故障电流参数来估计误差平方加权值与幅度因子,确定WLMS算法内步长因子的取值范围,改进WLMS算法;利用改进WLMS算法来估计故障电流参数,并依据该结果建立光伏直流微电网故障电流模型;先通过F0假设检验方法在模型内提取故障电流初始相角,再通过调整采样数据窗,令建立的故障电流模型和实际模型相同,则当故障电流初始相角超过设定阈值时,可利用该模型来预测故障电流过零点。实验结果表明:所提方法下,光伏直流微电网故障电流估计的时间常数和初始电压相角与实际结果非常接近,最大误差分别为3 ms和8°;不同故障时,均有效预测了故障电流过零点,准确率为100%;在故障电流内添加谐波后,预测过零点的稳态误差较低,最高稳态误差低于24 A。
