Iron Loss Calculation of AC Filter Inductor for Three‐Phase PWM Inverters

In recent years, remarkable advancement of new power semiconductor devices, such as SiC and GaN, enables the increase of switching frequency of power converters, and hence the volume of passive components, such as ac filters and transformers, can be reduced. However, temperature rise caused by the inductor loss is increasing, and hence iron loss evaluation of the inductor is one of the most important issues to realize high power density converters. Conventionally, an improved generalized Steinmetz equation (iGSE) has proposed in order to calculate the iron loss under a pulse voltage magnetizing condition. However, accurate iron loss calculation of the ac filter inductor used in a PWM inverter cannot be realized. The authors have proposed two methods of iron loss evaluation of ac filter inductors. The first one is a loss map method which can calculate the iron loss without using a real PWM inverter. Another one is an ILA (Inductor Loss Analyzer) which can measure the iron loss in every switching period in a real PWM inverter. In this paper, comparisons of the iron loss between the ILA and the loss map method on both the single‐phase and three‐phase inverters are studied. It is found that iron loss of the ac filter inductor in the three‐phase PWM inverter which is calculated by the loss map method cause a large error on a specific condition. In order to prevent the calculation error, the authors proposed a revised loss map method and proved the effectiveness of the method.     

Three‐Phase AC Filter Inductor Design for Three‐Phase PWM Inverter for Conversion Efficiency Improvement at Low Load

The inductor losses in a three‐phase ac filter inductor used in a three‐phase pulse‐width modulation (PWM) inverter are evaluated. First, a three‐phase inductor is designed to obtain the same value of inductance for each phase. Then, based on the design, a three‐phase inductor that uses two magnetic materials is proposed. The conversion efficiency of a 1 kVA three‐phase PWM inverter that uses the conventional and proposed ac filter inductors is simulated. Simulation results show that conversion efficiency improves. Finally, the conversion efficiency of an actual three‐phase 1 kVA PWM inverter that uses the conventional and proposed ac filter inductors is measured. In the experiment, the conversion efficiency obtained for the case of the proposed inductor improves by approximately 1% at low power load as compared to the conventional inductor. Furthermore, the calculated inductor losses are in good agreement with measured losses. Improvement in efficiency is verified trough simulations and experiments.     

PWM激励下异步电机铁耗等值电阻模型

通过分析PWM激励下异步电机铁耗变化的特点,提出了一种综合考虑电机运行工况和PWM波形特性的铁耗等值电阻模型。基于铁耗分离原理,使用三个电阻分别等效电机铁耗的磁滞分量、经典涡流分量和异常涡流分量,并推导了正弦激励下各个电阻分量的表达式;进而通过分析PWM激励与正弦激励下铁耗间关系,对正弦激励下铁耗模型进行修正,获得PWM激励下铁耗模型;最后提出了确定该模型参数的实验方案。所建模型中各个电阻分量随电机运行频率和PWM波形的调制系数变化而变化,且变化规律各不相同,提高了电机铁耗计算的准确性。仿真和实验验证了该模型的正确性和有效性。     

三相储能PCS损耗计算分析

储能PCS(Power Conversion System)是储能系统关键设备,其损耗计算分析对于合理设计主电路参数,降低系统体积,提高系统的效率有着重大意义。由于电路在实际运行中,损耗影响因素复杂,提出一种适用于工程上的损耗及效率计算评估方法。首先通过Mathcad软件对来自器件手册里的数据进行线性拟合处理,其次针对一款磁芯所绕制的电感的铜耗与铁耗进行详细分析,计算出储能PCS工作于逆变状态各个功率点的总损耗。最后搭建了一台额定功率为12kW的样机,通过实验验证了所提损耗计算分析方法的正确性及有效性。     

高频轴向磁通永磁电机永磁体涡流损耗三维解析模型

针对现有二维解析模型在计算轴向磁通永磁电机永磁体涡流损耗存在精度不足的问题,该文提出一种能够精确计算该类电机永磁体涡流损耗的新型三维解析模型。该模型利用精确子域法和电阻网络模型,能够同时考虑定子开槽、定子谐波电流、涡流反作用和涡流三维分布的影响。利用有限元法验证了精确子域模型计算得到的空载和电枢磁场分布,并在理想空载下,验证了解析模型永磁体表面涡流密度和永磁体涡流损耗值,分析电机在高频运行下涡流反作用对永磁体涡流损耗的影响。最后,对1台7kW、4000rpm的轴向磁通永磁电机进行空载脉宽调制(pulsewidthmodulated,PWM)电压供电实验和空载正弦波电压供电实验,得到因PWM谐波电流引起的永磁体涡流损耗,将实验结果,有限元结果与解析结果作对比,验证了该解析模型的正确性。     

损耗最小化输出滤波电感的设计

在开关电源中,输出滤波电感有储能和平滑滤波输出电压的重要作用。传统设计方法是以临界连续电流为依据根据经验选取输出滤波电感值。这种方法的缺点是没有严格考虑输出电感上电流脉动对变换器的影响,而电感电流脉动量直接影响输出电压的质量、输出电感的制作及电源整体工作的可靠性。该文基于电感电流脉动对变换器的影响,提出了一种损耗最小化的输出电感设计方法,并以Buck变换器为例进行了实验验证。     

三电平PWM整流器网侧LCL滤波器设计

采用LCL滤波器代替L滤波器对入网电流进行滤波已成为变换器并网的趋势,相对于L滤波器,LCL滤波器具有成本低,体积小,整流器动态响应快等优点.然而,目前关于LCL滤波器的研究都是针对两电平变换器进行的,对多电平变换器鲜有涉及.本文以三电平PWM整流器为研究对象,提出了适用于三电平PWM整流器LCL滤波器的设计方法,并通过Simulink仿真和实验验证了滤波器的优良性能.     

移相全桥PWM变换器的DCM研究

当输出滤波电感的电流在一个周期内不连续时,移相全桥PWM变换器就工作在电流断续模式(DCM).在该模式下,输出滤波电感两端电压会出现振荡.这种现象不仅会导致次级占空比增加,还会给输出纹波带来不利的影响,在某些应用场合是不允许的.在详细分析该模式下变换器的工作过程和软开关特性的基础上,通过考虑电路各处的分布参数特别是输出滤波电感的寄生参数,很好地解释了振荡现象.利用PSpice仿真研究,总结出电路中各参数,特别是电感寄生参数对谐振过程的影响规律.提出了一种抑制该振荡的方法,最后通过仿真和实验验证了该方法对抑制DCM下电感电压振荡的有效性.     

Loss distribution analysis and accurate calculation method for bulk-power MMC

Accurate evaluation of power losses in a modular multilevel converter (MMC) is very important for circuit component selection, cooling system design, and reliability analysis of power transmission systems. However, the existing converter valve loss calculation methods using the nearest level modulation (NLM) method and the traditional sortingbased capacitor voltage balancing strategy are inaccurate since the submodule (SM) switching logics in the MMC arms are uncertain. To solve this problem, the switching principle of the SMs in the sorting-based voltage balancing strategy is analyzed. An accurate MMC power loss calculation method based on the analysis of loss distribution of various SM topologies, including half-bridge submodule (HBSM), full-bridge submodule (FBSM) and clamp double submodule (CDSM), is proposed in this paper. The method can accurately calculate the losses caused by the extra switching actions during the capacitor voltage balancing process, thus greatly increasing the calculation accuracy of switching losses compared with existing methods. Simulation results based on a practical±350 kV/1000 MW MMC-HVDC system with variety of MMC topologies with diferent voltage balancing strategies demonstrate the efectiveness of the proposed method.     

直流偏磁情况下的定子永磁电机铁耗计算

提出了一种直流偏磁情况下的定子永磁电机铁耗计算方法。由于电机的特殊型结构以及逆变器供电等原因,定子永磁电机内部会存在直流偏磁现象。为此,首先使用爱泼斯坦方圈在不同交流磁密幅值情况下,进行了偏磁实验研究。基于实验数据以及传统偏磁铁耗模型,提出了一种考虑磁密幅值的偏磁铁耗计算模型。该模型能够较好地描述不同磁密幅值情况下直流偏磁对铁耗的影响。最后将该模型应用于电机铁耗计算,并与传统模型进行对比;电机损耗实验结果验证了该模型的可信度。     

计及高次谐波影响的高密度永磁同步电机铁耗计算

在经典Bertotti三项式常系数铁耗计算模型的基础上,基于谐波分析原理,引入涡流损耗、磁滞损耗和附加损耗补偿系数,提出了一种计及高次谐波影响的高密度永磁同步电机(PMSM)铁耗计算模型。该模型中的补偿系数均随磁密幅值、频率和畸变率变化,能较好地反映基波及谐波磁场对铁耗的影响。为了验证该模型的有效性及准确性,以48槽/8极内转子和36槽/48极外转子两台PMSM为研究对象,将模型的计算值、有限元仿真结果和试验数据进行对比分析。结果表明,铁耗计算模型有较高的精度,特别适用于磁密幅值与频率变化范围大的场合。     

Iron Loss Analysis of Permanent Magnet Motors Fed by PWM Inverter

Carrier harmonic losses that consist of iron loss, eddy current loss, and ac copper loss are produced in a permanent magnet machine driven by a PWM inverter. It is already known that a higher motor inductance can lead to lower carrier harmonic losses. This paper investigates the carrier harmonic loss composition of two motors with identical dimensions but different inductances. The results of finite element analysis (FEA) showed that the eddy current loss in the iron core accounts for most of the carrier harmonic loss. It is also shown that the carrier harmonic loss of the iron core is quantifiable using theoretical calculations.     

基于新的数据处理方式的理论线损计算

原始数据是否准确和齐备是影响线损计算准确性的关键因素。目前大多数电力企业已经能够得到比以前更多更精确的数据。利用这些数据,提出了一种基于新的数据处理方式的理论线损计算方法。该方法充分地利用了现有所能得到的电网运行数据,对其重新进行整理,根据持续负荷曲线进行线损计算,得到更加精确可信的结果。通过与常规理论线损算法的比较和分析,以及在实际线路上得到的测试结果,说明所提算法的有效性和实用性。     

Analysis of the Effect of Source Voltage Fluctuations on the Power Factor in Three-Phase Controlled Rectifiers

The effect of source voltage fluctuations on the harmonics and the power factor is analyzed for a six-pulse line-commutated converter. Exact expressions are derived for currents in the filter network and the ac supply lines as a function of the size of a series inductor in the LC type low-pass filter connected to a resistive load. The harmonics are calculated according to a method which is unorthodox in power engineering and which is based on the convolution theorem. Switching functions required for the discontinuous conduction mode are derived from time-domain analysis. The method is applicable to a wide class of switching networks.     

气隙对电感磁芯内部磁场分布及电感的影响

开关电源的输出滤波电感中流过的电流比较大,磁芯容易出现饱和现象。为了解决这一问题,常用的方法是在电感磁芯中加开气隙,但加开气隙会对整个器件的性能产生影响。采用三维有限元方法对不同添加气隙方法对感性器件电感量的影响进行分析,得到了对应不同气隙量和匝数电感和磁芯内部磁感应强度分布,样品电感实测值与计算值对比,验证了仿真结果的正确性,为感性元件的工程设计和试验前预校正提供了一种新方法。     

一种新型三相三线制有源电力滤波器

随着非线性负载在配电系统中的大量使用,低压配电网的三相不平衡、无功功率和谐波污染问题日益严重,有源电力滤波器以其优良的性能成为电力谐波抑制和无功补偿的重要手段。为克服传统有源滤波器相位延迟不能滤除基波无功分量等缺点,提出了一种基于同步旋转坐标变换的三相三线制并联有源电力滤波器的控制方法。该法简化了对指令电流的计算,基本上不受负荷变化和三相不对称影响,基波分量解算准确,无相位延迟,乘法运算少,无序分量计算,运算速度快;硬件上电容、电感参数小,开关频率低;另外,还可实现对功率因数的任意调节,从而实现了一种具有静止无功发生器功能的有源电力滤波器。仿真结果验证了其有很好的动静态谐波、无功补偿性能,具有良好的实用价值。     

改进型零电压转换PWM软开关功率变换器的实现机理分析

为改进传统谐振缓冲功率变换器(RSI)应用于高精度场合纹波较大的问题,提出一种改进型零电压转换(ZVT)脉宽调制(PWM)软开关功率变换器。通过LC环节减小输出电流纹波,并采用负载分段实现软开关的方式。轻载下利用交变的滤波电感电流实现主开关器件的零电压开通,重载下通过合理的导通谐振回路实现软开关,同时辅助开关器件实现零电流开关。该拓扑可采用PWM控制,具有效率高、纹波噪声小和开关频率固定的优点。通过分析电路的实现机理,对各工作时区进行解析计算,并给出实现软开关的条件。最后通过实验,在200kHz的开关频率下,验证了电路的有效性。相比于硬开关,效率得到了很大的提升,而相比于RSI在效率上虽有降低,但输出噪声却大幅减小。     

Soft-switching PWM DC-DC converter with reduced circulating current

Soft-switching phase-shifted PWM converters have attracted much attention because of their low switching losses, constant frequency operation and simple control. However, a circulating current flows through the transformer and the primary bridge circuit during the free-wheeling interval, resulting in relatively high current stresses on the transformers and switching devices compared with those of conventional hard-switching PWM converters. This paper presents an improved soft-switching phase-shifted PWM DC-DC converter that can substantially reduce the circulating current by employing a tapped inductor for the output low-pass filter. The principle of operation and the role of the tapped inductor are illustrated. The effectiveness of the tapped inductor is evaluated through simulation analysis. Moreover, a 500 W-100 Hz prototype converter is implemented to demonstrate the excellent performances of both low switching and low conduction losses.     

DPWMMIN调制方法的损耗分析及其非线性电压误差补偿策略

不连续PWM调制与传统空间矢量调制相比能够降低开关次数与损耗,提高变换效率.然而,死区效应、管压降会引起感应电机的相电压非线性误差,导致定子电流谐波畸变增加,转子磁链观测精度降低,且传统的基于占空比的补偿方法并不适用于不连续PWM调制.针对不连续最小值调制策略(DPWMMIN)的损耗与电压误差展开研究,首先对导通损耗与...     

Iron loss analysis of interior permanent-magnet synchronous motors-variation of main loss factors due to driving condition

In this paper, the authors investigate the iron loss of interior permanent magnet motors driven by pulsewidth modulation (PWM) inverters from both results of the experiments and the finite-element analysis. In the analysis, the iron loss of the motor is decomposed into several components due to their origins, for instance, the fundamental field, carrier of the PWM inverter, slot ripples, and harmonic magnetomotive forces of the permanent magnet in order to clarify the main loss factors. The Fourier transformation and the finite-element method considering the carrier harmonics are applied to this calculation. The calculated iron loss is compared with the measurement at each driving condition. The measured and the calculated results agree well. It is clarified that the iron loss caused by the carrier of the PWM inverter is the largest component at low-speed condition under the maximum torque control, whereas the loss caused by the harmonic magnetomotive forces of the permanent magnet remarkably increase at high-speed condition under the flux-weakening control.