Improving the Characteristics of integrated EMI filters by embedded conductive Layers

Discrete electromagnetic interference (EMI) filters have been used for power electronics converters to attenuate switching noise and meet EMI standards for many years. Because of the unavoidable structural parasitic parameters of the discrete filter components, such as equivalent parallel capacitance (EPC) of inductors and equivalent series inductance (ESL) of capacitors, the effective frequency range of the discrete filter is normally limited. Aiming at improving high frequency performance and reducing size and profile, the integrated EMI filter structure has been proposed based on advanced integration and packaging technologies , . Some improvements have been made but further progress is limited by EPCs of the filter inductors, which is restricted by dimension, size and physical structure. In this paper, a new structural winding capacitance cancellation method for inductors is proposed. Other than trying to reduce EPCs, a conductive ground layer is embedded in the planar inductor windings and the structural capacitance between the inductor winding and this embedded layer is utilized to cancel the parasitic winding capacitance. In order to obtain the best cancellation effect, the structural winding capacitance model of the planar spiral winding structure is given and the equivalent circuit is derived. The design methodology of the layout and area of the embedded ground layer is presented. Applying this method, an improved integrated EMI filter is designed and constructed. The experimental results show that the embedded conductive layer can effectively cancel the parasitic winding capacitance, hence ideal inductor characteristics can be obtained. With the help of this embedded conductive layer, the improved EMI filter has much smaller volume and profile and much better characteristics over a wide frequency range, compared to the former integrated EMI filter and the discrete EMI filter.     

An active ripple filtering technique for improving common-mode inductor performance

Active ripple filtering is the replacement of large passive components in power filter circuits with smaller passive components and active control circuitry. This letter focuses on common-mode filters, where a large common-mode inductor (choke) is replaced by two smaller chokes and active op-amp control. The technique is appropriate when improved attenuation is required at relatively low frequencies and the high-frequency filtering requirements are easily met. Smaller chokes save significantly in material and winding costs. The technique is more advantageous if wire-wound chokes can be replaced by planar printed circuit board chokes. The use of the technique in an automotive electromagnetic interference (EMI) filter application is explored in detail.     

Techniques for input ripple current cancellation: classificationand implementation [in SMPS]

Switching power supplies, due to their high-frequency switching operation, draw a substantial amount of input ripple current. Such ripple current manifests itself as electromagnetic interference (EMI). Active and passive ripple cancellation methods have been proposed in the past. This paper discusses the cancellation methods, and classifies the basic circuit configurations for ripple current cancellation. The basis of discussion is a “nullification” process, which can be described effectively in terms of the ideal circuit element nullor. The initial focus is on differential-mode noise cancellation, but the basic technique can be applied equally to cancelling common-mode noise. The classification provides a clear guideline for synthesizing practical cancellation circuits. Both active and passive implementation examples are given and experimentally demonstrated     

开关电源输入EMI滤波器设计与仿真

开关电源中常用EMI滤波器抑制共模干扰和差模干扰。三端电容器在抑制开关电源高频干扰方面有良好性能。文中在开关电源一般性能EMI滤波器电路结构基础上,给出了使用三端电容器抑制高频噪声的滤波器结构。并使用PSpice软件对插入损耗进行仿真,给出了仿真结果。     

反激式开关稳压电源传导干扰研究

开关式直流稳压电源的电磁干扰不仅对电网产生干扰,导致在同一电网上供电的其它设备不能正常工作,而且严重的谐波电压电流会在开关电源内部产生电磁干扰,从而造成开关电源内部工作不稳定,使开关电源性能降低。文中以反激式开关稳压电源为研究对象,主要分析了传导测试中,差模、共模传导两种方式噪声源的产生机理,建立了开关电源传导干扰模型,采用EMI滤波器即共模滤波和差模滤波,并详细研究了加入π型滤波器、输入x电容、共模扼流圈等对开关稳压电源传导干扰的抑制效果,得出传导干扰抑制在标准限制范围的改进措施,整改后可让传导干扰强度从100μV降低到200 nV并通过认证。研究结果表明该措施对抑制开关稳压电源传导干扰是有效的。     

Filters with inductance cancellation using printed circuit board transformers

Capacitor parasitic inductance often limits the high-frequency performance of filters for power applications. However, these limitations can be overcome through the use of specially-coupled magnetic windings that effectively ify the capacitor parasitic inductance. This paper explores the use of printed circuit board (PCB) transformers to realize parasitic inductance cancellation of filter capacitors. Design of such inductance cancellation transformers is explored, and applicable design rules are established and experimentally validated. The high performance of the proposed inductance cancellation technology is demonstrated in an electromagnetic interference (EMI) filter design.     

Noise Source Lumped Circuit Modeling and Identification for Power Converters

In this paper, a general lumped circuit modeling method is proposed to describe the conducted electromagnetic interference (EMI) coupling mechanism for the switching power converters. The EMI characteristics of the converters can be analytically deduced from a circuit theoretical viewpoint. The shunt and series impedance insertion method is introduced to identify the differential-mode (DM) and common-mode (CM) noise impedances and voltage sources. The procedure of parameters estimation for the noise models comprises several simple measurements and is convenient to be implemented. Experimental illustrations are also included to verify the validity of the proposed method. Comparison between the measured and predicted results shows that the EMI modeling method can provide adequate prediction of the EMI feature for power-switching converters     

基于补偿原理的逆变器EMI抑制方法研究

由于逆变器电源对输出接地电容的限制,对严重的共模电磁干扰难以用大容量的共模滤波器抑制共模噪声。文章介绍了一种新型的基于噪声电流补偿原理的电力电子装置无源干扰抑制技术,探讨了不同方案实现对共模噪声电流的补偿,并在一台DC/AC逆变器中进行了补偿测试。实验结果证实了该EMI抑制方法的有效性。     

An active circuit for cancellation of common-mode voltage generatedby a PWM inverter

This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7 kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage     

传导EMI的测试

在传导EMI(电磁干扰)中既存在共模电流也存在差模电流,要很好的分析传导EMI系统,就很有必要对共模干扰信号和差模干扰信号分离开来单独进行测试.这样,共模和差模噪声的分离就显得很重要了.     

通信开关电源的电磁兼容性

为了抑制通信开关电源受到的电磁干扰,解决其电磁兼容性问题,从开关电源的电磁干扰,电磁兼容性等的特点出发,详细分析共模/差模干扰,传导干扰和辐射干扰,并根据相应的干扰问题,提出了开关电源内部PCB布线、元器件分布要求,EMI滤波电路,典型的共模/差模干扰滤波器及其改进方法。同时从电路设计,仪器设备等方面进行改进,进而达到开关电源的工作性能最优化。     

基于新能源利用的逆变系统电磁干扰噪声解决方案

文章在对线性阻抗稳定网络内部结构和测量原理分析的基础上,针对于新能源系统的传导电磁干扰问题提出一种新的测量方法。利用该方法可以较为精确的测量新能源系统中逆变系统的传导电磁干扰噪声,并设计相应的滤波器对于传导电磁干扰噪声进行抑制。并且,根据新能源的特点,提出在直流侧加入电感电容以稳定由于直流侧电能不稳定所带来的电磁干扰噪声问题。实验结果表明该方法较为有效。     

基于UC3844反激式开关电源的设计

设计了一种基于UC3844的反激式多路输出开关电源,采用工业上常用的DC12~18 V输入,输出2路24 V/300 mA。此开关电源充分利用高频变压器原边绕组特性,把反馈绕组与供电绕组合二为一,简化了外围硬件电路,同时充分考虑了其成本和体积大小,除消除高频杂波用的共模电感、功率电阻、输出整流二极管及滤波电解电容外,其余元器件均采用贴片,最后经实验进一步测试并验证了此开关电源稳定且可靠。     

反激式开关电源共模传导干扰抑制研究

本文以反激式开关电源为研究对象,通过分析其共模传导干扰耦合路径,提出了抑制其共模传导干扰的具体方案,并利用Pspice软件进行仿真,仿真结果印证了设计方法的正确性。     

中频发电机对检测装置的干扰剖析及EMI滤波器的实现

随着中频发电机的广泛应用,对其电磁兼容性的研究越来越受到重视。由于漏抗的存在使得中频发电机产生共模干扰,针对某检测装置噪声高的问题,分析了中频发电机噪声对检测装置自噪声的影响,确认了噪声干扰源、干扰机理及干扰途径,首次提出降低其干扰的技术措施,设计TEMI滤波电路,并对滤波效果进行了实际装载试验,其结果大大提高了该检测装置的性能。     

Impact of Switching-Induced Electromagnetic Interference on Low-Voltage Cables in Substations

The electromagnetic environment within a substation is very complex. Substations represent an intricate interconnected collection of devices that serve as electromagnetic wave emitters and receptors. Transient electromagnetic emissions—electromagnetic interference (EMI)—are generated during the switching of disconnector and circuit breakers (CBs) that may cause malfunction or damage to electronic equipment positioned nearby if appropriate immunity measures are not taken. The interference may couple significant energy through common-mode currents to cable protection. Electromagnetic compatibility is mostly achieved by addressing the EMI victim through techniques in the secondary environment, such as shielding and filtering. This paper presents the finite-element method analysis of three methods: metallic channel, braided cable, and additional cable, used for EMI mitigation on low-voltage cables of 20 kV side in a 63-kV/20-kV substation due to switching effects of disconnector and CBs. In each method, overvoltage is considered and the results are compared with each other. A simple circuit analysis was also carried out on the causes of switching based on EMI to provide some insight into the interference mechanism during switching process, using common-mode and differential-mode equivalent circuits. The overvoltage reductions are attained through differential-mode current and shielding methods.      

Separation of the common-mode- and differential-mode-conducted EMInoise

A device is developed to decipher common-mode and differential-mode noise from a conducted EMI noise measurement. This device is a useful tool for power supply circuit noise diagnosis and line filter design     

飞机直流母线变换器的输入电磁干扰滤波器设计

针对飞机直流270 V至直流28 V电源变换器的应用需求,分析了电源变换器输入端的传导及辐射电磁干扰源.通过对电源变换器的电磁干扰（electromagnetic interference,EMI）频谱进行分析,确定了滤波器的参数.为了抑制滤波器振荡,提出在差模电感两端并联电阻电感网络的方法,替代使用液态铝电容的传统方法,提升滤波器的可靠性.根据差模电感中电流直流分量远高于交流分量的特点,提出采用扁铜漆包线来实现绕组的方法,使差模电感的体积降低.根据锰锌铁氧体低频磁导率高,镍锌铁氧体高频磁导率稳定的特点,提出双磁芯共模电感的设计方法,实现共模电感宽频率和小体积.实测结果证明输入电磁干扰滤波器可使电源变换器符合GJB 151中CE102要求.     

Characterization of power electronics system interconnectparasitics using time domain reflectometry

The significance of interconnect parasitics of power electronics systems is their effects on power converters' electromagnetic interference (EMI)-related performances, such as voltage/current spikes, dv/dt, di/dt, conducted/radiated EMI noise, etc. In this paper, a time domain reflectometry (TDR) measurement-based modeling technique is described for characterizing interconnect parasitics in switching power converters. Experiments are conducted on power components of a prototype high-power inverter, including insulated gate bipolar transistor (IGBT) modules, busbar and bulk capacitors. It is shown that the interconnect inductance of the IGBT module can be extracted completely using TDR. It is also shown that the busbar equivalent circuit can be modeled as transmission line segments or L-C filter sections, and the bulk capacitor contains a significant equivalent series interconnect inductance     

New methods to suppress EMI noises in motor drive systems

New methods are studied that can suppress EMI noises, especially the common-mode current produced in motor drive systems. One is a packaging technique that forms power converters using a four-layer printed power circuit board. The other is a method based on the generation mechanism of the common-mode current which was developed from experimental analyses. It is proved by experiments that the former can effectively control the common-mode current, including radiated emissions, and the latter can suppress it without any compensators between the inverter and the motor