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
The geotemperature gradient is considered as taking main part in generating the Earth’s magnetic field. It is shown that geotemperature gradient functions as a generator of both nuclear and mantle thermoelectrical cu...The geotemperature gradient is considered as taking main part in generating the Earth’s magnetic field. It is shown that geotemperature gradient functions as a generator of both nuclear and mantle thermoelectrical currents thanks to the great temperature difference between the core and the mantle. The movement of those currents is close to the radial direction towards the Earth’s crust. However, the nuclear thermocurrents movement tends to cyclically change into opposite one. If the mantle and core thermocurrents move oppositely, the Earth’s crust cools down globally and ice age comes, but if they move unidirectionally then global warming comes. The calculation show that the Earth’s surface can warm up to not more than 10°C. The latter, considering how human factor affects the warming of Earth, is incomparably great. There are calculations that show power of the Earth’s thermocurrents being enough to generate and maintain the Earth’s magnetic field, its modern dynamics and the poles inversion.展开更多
随着柔性直流电网的发展,其边界结构将发生改变,从“有边界电网”转变为“无边界电网”。如果在配置保护时,能够在原理上尽量适用于两种边界结构,则可以大大降低电网结构变化时保护验证的繁复性、提升保护应用的经济性。为提升线路行波...随着柔性直流电网的发展,其边界结构将发生改变,从“有边界电网”转变为“无边界电网”。如果在配置保护时,能够在原理上尽量适用于两种边界结构,则可以大大降低电网结构变化时保护验证的繁复性、提升保护应用的经济性。为提升线路行波保护对不同边界结构的适用性,该文提出一种新型的行波保护方案。该保护方案主要通过非故障极电流首行波积分(first current integration of non-fault pole,FCINP)实现。基于FCINP在不同边界结构电网下的距离特性和边界特性,可有效地提升保护在有边界电网和无边界电网下的故障识别性能,从而提升保护适用性。所提保护在基于PSCAD/EMTDC直流电网仿真模型中进行了性能验证。展开更多
为揭示直流系统运行方式与变压器直流偏磁现象之间的内在联系,基于宜昌电网的实际参数和PSCAD/EMTDC电磁暂态仿真平台,采用交流系统网络化建模的方法,建立了包含宜昌电网两条500 k V直流输电线路以及接地极临近区域220 k V交流变压器的...为揭示直流系统运行方式与变压器直流偏磁现象之间的内在联系,基于宜昌电网的实际参数和PSCAD/EMTDC电磁暂态仿真平台,采用交流系统网络化建模的方法,建立了包含宜昌电网两条500 k V直流输电线路以及接地极临近区域220 k V交流变压器的直流偏磁电流分布仿真模型。对给定工况下变压器中性点直流电流的分布情况进行了仿真,并与现场实测的数据进行了对比验证,还分别对单接地极场景以及双接地极场景时各个特征变电站主变中性点直流电流分布情况进行仿真,揭示了变压器中性点电位差是决定其直流电流分布特征的根本原因。结果表明:所建立模型的误差在10%以下,具备复现系统实际运行情况的能力。分析结果能够为从系统运行角度抑制直流偏磁提供理论依据。展开更多
广义积分控制能够无静差的跟踪正余弦指令信号,因此广泛应用于并联有源滤波器(shunt active power filter,SAPF)电流控制中。只要系统稳定,指定次谐波补偿精度都能得到很好的保障。然而如何设计控制器参数提高控制系统动态响应性能,却...广义积分控制能够无静差的跟踪正余弦指令信号,因此广泛应用于并联有源滤波器(shunt active power filter,SAPF)电流控制中。只要系统稳定,指定次谐波补偿精度都能得到很好的保障。然而如何设计控制器参数提高控制系统动态响应性能,却一直没有得到很好的解决。提出一种广义积分控制器参数设计方法,此方法通过配置闭环系统主导极点实部,保证系统较快的动态响应速度。分析和实验结果均证明该设计方法的有效性。展开更多
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The geotemperature gradient is considered as taking main part in generating the Earth’s magnetic field. It is shown that geotemperature gradient functions as a generator of both nuclear and mantle thermoelectrical currents thanks to the great temperature difference between the core and the mantle. The movement of those currents is close to the radial direction towards the Earth’s crust. However, the nuclear thermocurrents movement tends to cyclically change into opposite one. If the mantle and core thermocurrents move oppositely, the Earth’s crust cools down globally and ice age comes, but if they move unidirectionally then global warming comes. The calculation show that the Earth’s surface can warm up to not more than 10°C. The latter, considering how human factor affects the warming of Earth, is incomparably great. There are calculations that show power of the Earth’s thermocurrents being enough to generate and maintain the Earth’s magnetic field, its modern dynamics and the poles inversion.
文摘随着柔性直流电网的发展,其边界结构将发生改变,从“有边界电网”转变为“无边界电网”。如果在配置保护时,能够在原理上尽量适用于两种边界结构,则可以大大降低电网结构变化时保护验证的繁复性、提升保护应用的经济性。为提升线路行波保护对不同边界结构的适用性,该文提出一种新型的行波保护方案。该保护方案主要通过非故障极电流首行波积分(first current integration of non-fault pole,FCINP)实现。基于FCINP在不同边界结构电网下的距离特性和边界特性,可有效地提升保护在有边界电网和无边界电网下的故障识别性能,从而提升保护适用性。所提保护在基于PSCAD/EMTDC直流电网仿真模型中进行了性能验证。
文摘为揭示直流系统运行方式与变压器直流偏磁现象之间的内在联系,基于宜昌电网的实际参数和PSCAD/EMTDC电磁暂态仿真平台,采用交流系统网络化建模的方法,建立了包含宜昌电网两条500 k V直流输电线路以及接地极临近区域220 k V交流变压器的直流偏磁电流分布仿真模型。对给定工况下变压器中性点直流电流的分布情况进行了仿真,并与现场实测的数据进行了对比验证,还分别对单接地极场景以及双接地极场景时各个特征变电站主变中性点直流电流分布情况进行仿真,揭示了变压器中性点电位差是决定其直流电流分布特征的根本原因。结果表明:所建立模型的误差在10%以下,具备复现系统实际运行情况的能力。分析结果能够为从系统运行角度抑制直流偏磁提供理论依据。
文摘广义积分控制能够无静差的跟踪正余弦指令信号,因此广泛应用于并联有源滤波器(shunt active power filter,SAPF)电流控制中。只要系统稳定,指定次谐波补偿精度都能得到很好的保障。然而如何设计控制器参数提高控制系统动态响应性能,却一直没有得到很好的解决。提出一种广义积分控制器参数设计方法,此方法通过配置闭环系统主导极点实部,保证系统较快的动态响应速度。分析和实验结果均证明该设计方法的有效性。
