异步电机转子感应非正弦电流时的导条损耗

为计算异步电机转子导条流过非正弦电流时的损耗,采用了先分别计算不同频率电流对应损耗再进行叠加的分析方法.该方法基于电路原理而非通过电磁场分析来计及集肤效应对损耗的影响,在对转子导条分层处理并求出相应参数的前提下,推导说明导条流过非正弦电流时的损耗等于分别流过不同频率正弦交流电流时的损耗之和.文中给出算例并计算了不同频率转子电流在该导条中产生的损耗,同时用有限元法直接计算流过实际非正弦电流时的转子导条损耗,比较计算结果验证了损耗所满足的叠加关系.采用叠加方法求取损耗不仅减小了计算工作量,而且能定量计算某一特定频率电流产生损耗大小.     

无刷双馈电机谐波铜耗与铁耗的分析与计算

针对无刷双馈电机谐波含量高、谐波损耗大的问题,提出考虑谐波磁场、谐波电流、集肤效应和旋转磁化影响的BDFM损耗计算模型.基于二维场路耦合时步有限元模型和谐波分析方法,分别建立两种转子铜耗计算模型和三种定转子铁耗计算模型,分析不同计算模型对转子铜耗和定转子铁耗的影响,得到定转子谐波铜耗和铁耗的变化规律.结果表明,转子铜耗模型2以及定转子铁耗模型3更精确;随着控制绕组电压的增加,定转子铜耗先减小后增加,定转子铁耗持续增加;随着负载转矩的增加,定转子铜耗和铁耗均随之增加.通过与一台相似异步电机铜耗和铁耗的电磁设计数据和实验数据的比较,验证了模型与计算结果的正确性.     

Basic Study on Loss Factor Evaluation of Concentrated Winding Permanent Magnet Synchronous Motor

This paper describes the influence of pulse width modulation (PWM) inverter harmonic loss on concentrated winding interior permanent magnet synchronous motor characteristics by using finite element method (FEM) analysis and several measurements. In the measurements, the PWM inverter harmonic loss was evaluated by using a PWM inverter and a sinusoidal power supply. By using the FEM analysis, it was confirmed that the PWM inverter harmonic mainly caused an increase of eddy current losses in the magnetic steel sheet and the permanent magnet. The results indicate that higher inductance of the motor is effective in reducing the harmful effects of PWM inverter harmonics.     

基于频变特性的变压器谐波损耗分析

工业变频设备和高频装置的广泛应用导致电力系统谐波污染加剧,致使非线性负荷下的变压器损耗计算与分析备受关注。研究了谐波等值模型,修正了传统曲线拟合谐波损耗计算法,从涡流场角度分析模型准静态磁场中不同材料的磁扩散情况,归纳出其谐波频变特性。同时,考虑不同频率谐波下绕组的等效非线性参数和谐波损耗叠加计算,对谐波损耗进行修正。...     

基于有限元法的高频变压器绕组损耗研究

变压器损耗是影响变压器运行性能的重要因素。在高频效应下,邻近效应与集肤效应会增加变压器绕组损耗。文章基于高频变压器绕组的三维模型,在考虑邻近效应与集肤效应的基础上,应用有限元法对变压器绕组中的涡流效应进行仿真计算。通过计算得出了改变绕组布局可以有减少绕组损耗的结论。并得到了不同绕组布局下,绕组损耗随频率、绕组厚度以及层间距的变化趋势。     

绕组分布对永磁伺服电机电磁场与温度场影响的研究

永磁伺服电机采用不同的绕组分布形式对电机的电磁场和温度场均会产生一定的影响,文章以一台8极10 k W的永磁伺服电机为例,建立不同绕组分布的永磁伺服电机模型,对比分析电机不同绕组分布对电磁场和温度场的影响。首先,采用时步有限元计算方法对永磁伺服电机谐波磁场变化进行分析,基于傅里叶谐波分解理论给出电机内各次谐波的变化情况。然后,结合电机转矩脉动系数的分析对不同绕组分布下的永磁电机转矩脉动进行研究,给出电机转矩波动随绕组分布形式的变化规律;其次对电机各损耗的变化规律进行分析,并揭示电机内谐波磁场对电机损耗的影响机理。在损耗研究的基础之上,进一步对不同绕组分布下的永磁伺服电机绕组温度与永磁体温度进行分析,给出不同绕组分布下的温度变化规律。最后,结合有限元计算结果及相关实验验证计算分析的准确性,并进一步揭示双层绕组分布在永磁伺服电机提高电机综合性能方面的作用。     

Influence of the modulation method on the conduction and switchinglosses of a PWM converter system

The authors explore the dependency of the conduction losses of a bridge leg of a pulsewidth modulation (PWM) power converter system with a high pulse rate on the shape of the phase modulation functions. This is done for modulation methods that are optimized with respect to minimum harmonic current RMS values. The results are compared to the results gained for simple sinusoidal modulation. Besides conduction losses, the switching losses of the electric valves are calculated. The main topic is the determination of those power loss components of a PWM converter system that can be (besides the harmonic losses) influenced by the modulation method selected. As the calculations show, these modulation methods allow a significant increase of the effective switching frequency. The optimal modulation as calculated leads to a reduction of the harmonic power loss in the upper modulation region. Furthermore, due to the frequency modulation the spectrum is spread out to a wider frequency band as compared to operation with constant pulse frequency     

电枢磁动势谐波对转子涡流损耗的影响分析

永磁电机多采用变频器供电,变频器输出的电流中除包含基波电流外还存在谐波电流,由其产生的电枢磁动势空间谐波会在转子中产生涡流损耗。基于对各次电枢磁动势空间谐波幅值及其相对于转子交变频率的详细分析,提出涡流损耗强度的概念,用于评估不同的电枢磁动势空间谐波对转子涡流损耗的影响程度。对采用整数槽和分数槽绕组的永磁电机转子涡流损耗做了解析对比和有限元分析,证明了利用涡流损耗强度评估电枢磁动势谐波对转子涡流损耗影响的有效性。     

Influence of PWM on the Proximity Loss in Permanent-Magnet Brushless AC Machines

A winding copper loss can be significantly increased due to skin and proximity eddy-current effects. The skin and proximity losses due to fundamental frequency current have been investigated in literature, but the influence of pulsewidth modulation (PWM) on the skin and proximity losses has not been reported. In this paper, a 2-D finite element method is employed to analyze the skin and proximity losses in a permanent magnet brushless ac machine, in which significant proximity loss exists due to high frequency current ripples induced by the PWM, as confirmed by both theoretical calculation and experiment. The analyses should be generally applicable to other machines.     

Temperature distribution in foil winding for ventilated dry-type power transformers

Predicting temperatures of transformers is important in order to prevent the deterioration of electrical insulation since the life of the transformers corresponds with that of the insulation. Reports of thermal behavior of ventilated dry-type transformers are rare in the literature. In particular, foil winding has received little attention despite their wide usage in practice. In this study, a thermal model for foil winding was proposed and temperature distributions were determined by the finite element method (FEM). In order to cope with the non-uniformity of the heat fluxes in the foil winding due to induced currents, different convection coefficients and varying air temperature along the vertical height of the foil winding were suggested and applied to the thermal model. The thermal model was solved by coupling it with the electromagnetic model to calculate the non-uniform power losses. The model was applied to a ventilated dry-type power transformer rated at 2000 kVA. Experimental temperatures were measured with thermocouples, and used to verify the finite element results. They showed reasonable agreement and will provide a useful tool for transformer engineers.     

一种高压大容量有源电力滤波器研究

提出一种新型的基于变压器谐波电流补偿的高压大容量有源电力滤波器。变压器采用副方多补偿绕组结构,原方绕组与谐波负载相并联,副方补偿绕组分别与逆变器相联。实时检测变压器原方绕组的谐波电流,通过逆变器产生与原方绕组谐波电流成比例的谐波补偿电流注入变压器副方多补偿绕组中。当原、副方绕组的谐波电流满足谐波电流补偿条件时,变压器原方绕组对谐波电流呈现近似为零的低阻抗,而对基波电流呈现很大的励磁阻抗,从而输导高压电力系统中的谐波电流流入变压器支路。仿真结果证明了这种滤波新原理的正确性。     

Current waveform distortion of doubly‐fed generator for wind turbine application by spatial higher harmonics

This paper describes a method to analyze higher harmonic currents resulting from higher space harmonics, depending on the winding pattern of a doubly‐fed generator. A 1.5‐MW generator was used for the analysis, and the results are compared using finite element magnetic field analysis and measurements. The result revealed that the proposed analysis, which focuses on the winding pattern and takes into account higher space harmonics, allows us to calculate higher harmonic currents at high precision, understand the mechanism of changing higher harmonic currents due to the slip or the load of the generator and considerably reduce higher harmonic currents at the armature by restricting higher harmonic currents at the magnetic field. In addition, the sensitivity analysis of design parameters clarified the relationship between current distortion and basic characteristics on electric designs. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 79–85, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20606     

用于多脉波整流的直线式移相变压器

在多脉波整流中,为了优化结构和改善电能品质,提出一种类似于直线电机的直线式移相变压器。不同于普通移相变压器,该移相变压器采用直线式铁心结构,易于绕组布置和大功率场合下的模块化叠加,电路结构更为简单。以3相/12相直线式移相变压器为例,阐述其在多脉波整流中的应用原理,解析气隙平移磁场;基于磁动势平衡理论,阐述消除网侧主要谐波电流的原理;开展有限元仿真分析和样机实验,证明直线式移相变压器能较好地改善输出直流电压和抑制网侧谐波电流,验证了直线式移相变压器的有效性。     

电缆绕组功率损耗的数值计算与测量

利用有限元法对电缆绕组变压器的功率损耗进行了计算，并对绕组的损耗进行了数字化测量，验证了计算准确性，针对不同的误差来源，在软件处理中采取了相应的措施。     

Study and Analysis of the Effect of Harmonics on the Hot Spot Temperature of a Distribution Transformer Using Finite-Volume Method

Transformers are critical components in power systems and their failure can cause long interruption of power supply. The condition of a transformer can be monitored by performing thermal analysis. The use of non-linear devices, such as rectifiers and converters, draws harmonic currents that increase losses in transformers, thereby increasing their operating temperature. In this article, a new numerical approach is presented for determining the rise in hot spot temperature in a 5-kVA, 400/400-V dry-type three-phase transformer laboratory prototype. The key novelty is that the additional winding eddy current loss due to non-linear loads is considered in the numerical modeling. The winding eddy current loss corresponding to harmonic distortion is estimated by conducting experiments and calculations. Numerical simulations are carried out for a wide range of non-linear loads using a commercial computational fluid dynamics package, FLUENT 6.3. The proposed numerical methodology is validated by performing experiments on the transformer for possible non-linear loads and comparing the measured hot spot temperature with the simulated values. Correlation equations for rise in hot spot temperature as a function of total harmonic distortion are presented, which can be used for estimating the life of transformers when connected to different types of loads.     

三相不平衡及谐波对三相四线低压配电网线损的影响

针对三相四线制低压配电网中的线损问题,提出了在复合电能质量作用下的线损计算方法以及与单一电能质量作用下的线损比较方法。首先对三相不平衡引起的线损进行推导;其次依据叠加原理推导谐波条件下的线损;然后综合考虑和推导这两种电能质量共同作用下的线损,并根据对称分量法对这两种电能质量在单独与共同作用下的线损进行比较。结果表明三相不平衡加剧谐波损耗,即谐波及三相不平衡共同存在时的线损大于各自单独存在时造成的线损之和。最后利用Matlab/Simulink仿真工具和chroma 6590可编程交流电源对每一部分均进行实验,验证了理论推导的正确性。     

含有分频输电线路的电力系统稳态特性研究

根据分频输电线路的等值电路,应用谐波平衡原理,建立了含有分频输电线路的电力系统潮流数学模型,并应用牛顿－拉夫逊法进行求解。分析了分频输电系统输送功率与效率、副边无功补偿容量之间的关系,以及分频输电线路在各种载荷下的稳态运行特性和向工频系统注入的谐波电流,并和直流输电线路产生的谐波电流进行了比较。仿真表明,分频输电系统有很宽的谐波电流进行了比较。仿真表明,分频输电系统有很宽的功率运行范围和很好的效率特性及稳态特性,分频输电系统产生的谐波电流很小。     

电网谐波电压对同步调相机转子损耗的影响

高压直流输电系统单极大地回线运行会使得附近变压器产生直流偏磁现象,增加变压器副边电压的谐波含量。当变压器与为换流站提供无功支撑的同步调相机连接时,谐波电压会影响同步调相机的转子损耗。本文针对不同谐波电压下,同步调相机转子损耗的变化展开研究。采用时步有限元法计算了同步调相机空载、进相以及迟相运行条件下,谐波电压对转子铁心和槽楔损耗的影响,对比分析了转子各部分损耗大小随电压谐波次数的变化规律。研究结果为同步调相机的安全可靠运行提供了理论基础。     

A Novel Active Power Filter for High-Voltage Power Distribution Systems Application

In this paper, a novel principle of an active power filter based on the harmonic impedance control of a transformer is proposed for high-voltage power distribution systems application. A linear transformer with multiple secondary windings is adopted. The primary winding is shunted with harmonic-producing loads, while the secondary windings are connected with inverters. The primary harmonic current is detected and then tracked by the inverters with fixed compensation coefficient. When the harmonic current compensation condition is satisfied, the transformer can really exhibit nearly zero impedance to harmonic current and primary self-impedance to fundamental current. As a result, the harmonic currents in power systems can be led to flow into the transformer branch. The operation principle, the control scheme, and the harmonic current detection method are discussed in detail. Finally, simulated waveforms and experimental results are presented to verify the effectiveness of the active power filter     

A comparison of the wound rotor and nested‐loop rotor brushless doubly fed generator

Both the wound rotor and the nested‐loop rotor can realize the coupling with the power winding (PW) and control winding. And the two types of rotors in a brushless doubly fed generator (BDFG) can realize variable‐speed, constant‐frequency generation. In this paper, the two types BDFG are compared through finite element analysis and experiments. From the finite element simulation results, it can be seen that the air gap flux density harmonic contents, PW line voltage harmonic contents, and the core loss of the nested‐loop rotor BDFG are higher than those of the wound‐rotor BDFG. In the experiments, the efficiency of the wound rotor BDFG is slightly lower than that of the nested‐loop rotor BDFG when the rotor speed is below the natural synchronous speed and is much higher than that of the nested‐loop rotor BDFG when the rotor speed is above the natural synchronous speed. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.