Harmonics in the Squirrel Cage Induction Motor Analytic Calculation-Part Ⅰ: Differential Leakage, Attenuation, Asynchronous Parasitic Torques

The magnetic field generated in the air gap of the cage asynchronous machine and the harmonics of the magnetomotive forces creating that magnetic field, as well as the related differential leakage, attenuation, asynchronous parasitic torques have been discussed in great detail in the literature, but always separately, for a long time. However, systematization of the phenomenon still awaits. Therefore, it is worth summarizing the completeness of the phenomena in a single study – with a new approach at the same time-in order to reveal the relationships between them. The role of rotor slot number is emphasized much more than before. An existing, commonly used, but still impractical basic figure has been modified to more clearly demonstrate the response of the rotor for the harmonics of the stator. The need to treat differential leakage, asynchronous parasitic torques and attenuation together will be demonstrated: new formula for asynchronous parasitic torque is derived;the long-used characteristic curves for differential leakage and attenuation used separately so far was merged into one, correct curve in order to provide a correct design guide for the engineers.

On-line detecting of transformer winding deformation based on parameter identification of leakage inductance

Transformers are required to demonstrate the ability to withstand short circuit currents.Over currents caused by short circuit can give rise to windings deformation.In this paper,a novel method is proposed to monitor the state of transformer windings,which is achieved through on-line detecting the leakage inductance of the windings.Specifically,the mathematical model is established for online identifying the leakage inductance of the windings by applying least square algorithm(LSA) to the equivalent circuit equations.The effect of measurement and model inaccuracy on the identification error is analyzed,and the corrected model is also given to decrease these adverse effect on the results.Finally,dynamic test is carried out to verify our method.The test results clearly show that our method is very accurate even under the fluctuation of load or power factor.Therefore,our method can be effectively used to on-line detect the windings deformation.

Analysis of Auxiliary Winding Effect on the Leakage Inductance Reduction in the Pulse Transformer Using ANSYS

Several applications need high voltage and low rise time pulses that increasing of the voltage level can be done by using transformer. The rise time is increased because of transformer leakage inductance. One of the methods to decrease the rise time is using auxiliary windings between primary and secondary. In this paper, one type of pulse transformer included auxiliary windings is modeled and simulated in ANSYS software. In this study, at first the transformer has been simulated without auxiliary windings and the leakage and self inductances are obtained then the auxiliary windings are considered in the model to calculate the leakage and self inductances of the transformer. Simulation results can be used to investigate the effect of auxiliary winding on the leakage inductance.

Magnetic flux leakage during longitudinal magnetic flux induction heating

A three-dimensional electromagnetic thermal coupled model of a 45#steel strip during longitudinal magnetic flux induction heating was established in this study.The influence of different power levels,frequencies,and electromagnetic shielding on the magnetic induction intensity and the heating of parts of different materials around the inductor was analyzed by calculating the magnetic induction intensity around the longitudinal flux induction heater under different conditions.The results show that leakage flux can be reduced up to 49%by electromagnetic shielding.The higher the frequency,the greater the electromagnetic shielding effect,and the lower the magnetic leakage around the inductor.Conversely,the higher the power,the greater the magnetic induction around the inductor.By adding electromagnetic shielding to reduce magnetic leakage of the inductor and replacing the metal part material around the inductor with stainless steel,the heat generation of the parts around the inductor can be greatly reduced.

CALCULATION OF THE HARMONIC LEAKAGEOF IRREGULAR WINDINGS

This paper, based on the harmonic analysis and the harmonic e-quivalent circuit of the induction motor, clearly discusses the damping effectof harmonic current in the rotor and incorporates the slot-mouth factor to thewinding factor. The practical computi

Magnetic flux leakage analysis and compensation of high-frequency planar insulated core transformer

A novel high-frequency and high power density planar insulated core transformer(PICT) applied to high voltage DC generator is introduced. PICT's operating principle and fundamental configuration are described,and preliminary experimental results in self-designed PICT apparatus are presented. Emphatically, magnetic leakage flux(MFL) giving rise to the output voltage drop is analyzed in detail both theoretically and by finite element method(FEM). Showing good consistency with experimental result, FEM simulation is considered to be practicable in physical design of PICT. To cancel out leakage inductance and improve the voltage uniformity,compensation capacitor is adopted and experimental verification is also presented. All shows satisfactory results.

考虑中频变压器非理想几何结构的通用漏感解析模型

中频变压器非理想几何结构引起的畸变磁场对漏感解析计算精度有较大影响,进而影响变压器设计及变换器运行特性和效率特性。首先针对副边绕组为非理想几何结构的漏感解析计算问题,基于叠加定理和洛氏高度等效方法,将传统只考虑纵向漏磁场的一维模型,改进为综合考虑纵向和横向漏磁场的二维模型,显著提升计算精度,并依据此模型提出一种通用漏感优化方法。进一步,针对原副边均为非理想几何结构情况,引入洛氏叠加区域,将原副边非正交且耦合的横向漏磁场能量考虑在内,提出一种计及中频变压器非理想几何因素的通用解析模型,计算误差在7.5%以下。仿真和实验验证了模型的准确性和通用性。

精密机械同轴扫描开关研制

在精密电测领域,鲜有面向交流自动测试系统的专用同轴扫描开关。针对于此,设计了一种4线制-15通道全同轴扫描开关装置。该装置以步进电机精密运动控制为基础,拖动快插式同轴线组件做X-Y双向定位运动,实现同轴测量通道的可靠自动切换。通过自主设计柔性对接机构,消除因运动失准导致的通道对接误差及不可逆物理损伤风险。通过分析通道热电势、泄漏阻抗、寄生电容、感性耦合电势等寄生参数的产生机理,明确了影响扫描开关电气特性的关键设计参数,进而提出针对性优化设计方法。测试结果表明,所研制扫描开关装置的通道热电势小于±50 nV,通道对地泄漏阻抗达到10^(14)Ω量级,通道间寄生电容小于1×10^(-5) pF,通道间的感性耦合系数小于1.2×10^(-10) H。

偏斜转子槽形感应电机正反转性能差异的研究

转子槽形沿径向偏斜后的电机电磁性能受电机转向影响。为减小偏斜转子槽形电机正反转时的性能差异,提出一种槽身偏斜槽形,保证槽形的槽口区域轴对称。基于转子槽漏磁模型,对比径向偏斜与槽身偏斜槽形,探讨槽形偏斜后的等效磁路变化,以及转子槽漏抗与主电抗参数随偏斜距离的变化规律。利用冻结磁导率法隔断主磁通的气隙路径,假设由槽内导体电流产生的转子漏磁场仅包括槽漏磁场,计算电机正反转下不同槽形偏斜距离时的槽漏抗值,并根据等效电路模型计算相应的主电抗值。最后,仿真计算两类偏斜转子槽电机的输出转矩与功率因数,结果表明转子槽身偏斜电机正反转时的性能接近,而且受槽形偏斜距离的影响较小。偏斜转子槽形的不对称槽口区域是引起电机正反转性能差异的主要原因。

一种抑制谱泄漏的感应电机转子断条诊断方法

电机电流特征分析已成为一种广泛应用于感应电机故障诊断的技术,然而,它的工业应用面临着现实问题。其最具挑战性的问题之一是即使在严重故障下供电频率分量的谱泄漏仍可以掩盖住故障特征谐波的谱分量。对于这个问题已经提出了不同的解决方案,例如使用滑动窗口、高级谱估计技术等。然而,这些方法只改变了当前信号的频谱含量或是增加了计算量。基于此,提出了一种新的方法,通过对时域电流采样信号简单的补零,实现对电流的频谱细化,并能较精确地估算出实际的供电频率,然后可提取几乎无泄漏的原始频谱。基于Matlab的信号测试验证了该方法的有效性。

反激电源开关管电压尖峰的形成原理

反激型开关电源在开关管关断时刻会出现高频率高幅值的电压尖峰,如果不加以处理不仅会加重电磁干扰,还会增加开关管的电压应力。基于此,详细论述开关管关断电压尖峰形成的原理,推导得出尖峰电压的表达式,并利用仿真软件MathCAD可计算得出尖峰电压的最大值和稳态值,为开关管选型和尖峰吸收电路的设计提供理论指导。

基于载波调制PWM的对称六相与三相PMSM串联系统矢量解耦控制

针对对称六相与三相PMSM串联系统的解耦控制问题,基于串联系统的数学模型,在二相旋转坐标系下进行了漏感压降补偿,并基于坐标变换和控制量叠加得到了逆变器期望输出。在解耦控制的工程实现方面,充分考虑了逆变器电压、电流限制,提出1种直流母线电压分配方法,提高了系统运行的可靠性。实验证明,所提控制策略能够实现2台电机在负载或转速突变情况下的解耦运行。

Rotor parameters calculation for a solid-rotor induction motor with end rings

1.IntroductionIt is well known that the efficiency and power factor of thesolid-rotor induction motor are lower than those of the cage rotor in-duction motor due to larger leakage reactance.Therefore,conduct-ing end rings are often fitted to rotor ends to improve motor per-formance.Most of the analyses on the solid-rotor induction motorwith end rings have assumed that the motor is of infinite core lengthand tangential current in the rotor to be negligible.

考虑漏感频变特性的三相立体卷铁心变压器建模及分析

针对一种宽输入电压范围双向逆变电源,可采用磁集成方法提高其功率密度。与传统三相平面叠铁心变压器相比,立体卷铁心变压器具有磁路对称、重量轻等优势,该文拟开展PWM非正弦激励下考虑漏感频变特性的立体卷铁心变压器建模相关研究。首先,基于Foster频变磁阻模型,提出一种考虑漏感频变特性的立体卷铁心变压器模型,通过全局优化算法计算模型参数;其次,针对级联H桥组合式DC-AC拓扑的典型工作点,分析了PWM非正弦激励的谐波特征,重点关注不同H桥之间各次谐波的相对相位关系,给出简化等效电路;最后搭建逆变电源试验平台,开展了稳态和动态试验,验证了模型的准确性。

绕组交叉换位排布方式下高频变压器阻抗建模及谐振特性分析

高频变压器设计中通常采用初、次级绕组交叉换位排布方式来降低漏电感和交流电阻,但是绕组结构改变会同时影响变压器内部寄生电容参数大小和分布情况,进而造成宽频带谐振特性发生变化。为了明确不同交叉换位排布方式对寄生电容、频变漏电感以及谐振频率的影响规律,该文首先结合绕组的排布方式和绕制方法,建立4种典型绕组结构的分布等效电容表征模型,基于能量等效原理推导出相应绕组排布方式下六集总电容表征模型的电容解析计算式。然后,为了计及宽频区间内绕组漏电感参数的频变特性,基于电磁对偶原理建立含频变参数有损电感表征模型,并给出各项参数提取方法。在此基础上,构建不同绕组布置方式下高频变压器宽频带阻抗特性分析模型。将寄生电容、漏电感参数以及开短路阻抗特性和谐振频点计算结果与仿真和实验测量结果进行对比,验证了所提方法的有效性。

AGV无线充电全波同步整流尖峰电压抑制方法

自动导引运输车(AGV)电池组的无线充电要求是低压大电流,全波同步整流(FWSR)可以提高效率并降低成本。首先详细介绍了AGV无线充电拓扑和工作原理,其次针对实验过程发现的同步整流管电压尖峰问题,进行了理论建模和过程原因分析,并提出了有效的抑制措施和吸收电路设计,最后设计了一台样机,通过实验验证了方案的有效性。实验结果表明,该系统实现了3 kW的运行功率,效率可达91%以上,采用同步整流有效提高了系统功率密度。

一种10 MHz高频DC-DC功率变换器及其同步整流技术

该文设计一种具有准零相位差同步驱动信号的10 MHz DC-DC功率变换器,通过设计逆变器输出电压与整流器输入电压近似同相位,整流器和逆变器可以采用同一驱动信号,简化了同步整流开关管的控制难度,实现了10 MHz下可靠、简洁的同步整流控制。同时,为满足主拓扑要求,构建具有二次侧准无漏感特性的嵌套环形3D变压器,大大减少了传统变压器二次侧漏感对于同步整流控制的影响,并提出由多个印制电路板(PCB)结合来制作嵌套环形3D变压器的方法。最终,设计了一台48 V输入、12 V/28 W输出的实验样机,实验结果验证了所提出的控制方法和数值设计方法的可行性。

低直流链电压尖峰的二极管辅助型优化Y源逆变器

耦合电感的引入使阻抗源逆变器的升压能力得到进一步提高,并改善了传统Z源拓扑中调制比与直通占空比之间的约束关系。然而,漏感的存在导致逆变器出现直流链电压尖峰,恶化了开关器件的工作条件,限制了逆变器的功率等级。为解决上述问题,以优化型Y源逆变器为研究对象,提出一种低直流链电压尖峰的优化Y源拓扑结构,利用无源吸收回路确保逆变器状态切换时直流链电压的平滑过渡,消除了直流链电压尖峰。此外,新提出拓扑继承了优化型Y源逆变器的所有优点,并且在相同的直通占空比下,具有更高的升压能力。最后,通过对比二者的仿真和实验结果,验证了新拓扑在升压能力和抑制电压尖峰方面的优越性能。

隔离型Boost全桥变换器的关键问题研究

隔离型Boost全桥变换器因为特别适用于大功率低压输入场合,在诸如电动汽车、航天电源等领域得到广泛研究。本文将对隔离型Boost全桥变换器的两个关键问题进行分析讨论。一是如何减小变压器的漏感,二是如何实现IBFBC初始输出电压的建立。