Conducted EMI Reduction in Power Converters by Means of Periodic Switching Frequency Modulation

Spread spectrum clock generation techniques were originally developed to reduce electromagnetic interference (EMI) in communications and microprocessor systems working in the range of hundreds of megahertz. Nowadays, the switching frequency of power converters has been increasing up to values that make worthy the application of such switching frequency modulation techniques to reduce EMI emissions in power converters. Although random modulations have been applied before to power converters, periodic patterns can provide some advantages. First, theoretical principles of frequency modulation using three periodic patterns for the modulating function are presented. The influence of some important modulation parameters on the EMI reduction is analyzed and some considerations about the EMI filters design are also presented. The effectiveness of such methods in terms of EMI reduction is demonstrated theoretically and confirmed with experimental results obtained from tests carried out on two converters. The first one is a 2.5 W buck converter that can be switched up to 1 MHz and the second one is a 600 W boost converter switching at 40 kHz. In both cases, attenuations obtained in conducted EMI are evaluated. Finally, special attention has been paid to input current and output voltage ripple in order to evaluate possible undesired side-effects produced by this technique.     

正弦频率调制降低开关电源传导EMI的实验研究

利用正弦频率调制技术从噪声产生源头上降低了开关电源传导电磁干扰,简单地分析了正弦混沌频率调制降低EMI噪声的原理,并试制了一台正弦频率调制反激变换器电源样机,给出了开关管电流信号的频谱以及传导干扰测试的结果。实验结果表明该技术能有效降低开关谐波峰值,具有应用的前景。     

随机频率调制降低开关变换器电磁干扰的研究

利用随机频率调制技术从噪声产生源头上降低了开关变换器的电磁干扰。分析了具有不变概率密度分布的随机频率调制降低开关变换器EMI噪声的原理。将嵌入式系统产生的均匀分布离散随机信号加入脉宽调制芯片,开关频率随机变化,试制了一台随机频率调制开关变换器电源样机。给出了开关管电流信号的频谱以及传导干扰测试的结果。实验结果表明该技术能有效降低开关谐波峰值,使开关变换器易于通过EMI测试,具有应用前景。     

频率抖动技术抑制变换器电磁干扰分析

针对传统的固定频率PWM控制方式引起的波形频谱能量集中、谐波幅值较大的缺点,文章基于频率调制(FM)的理论分析了开关频率抖动技术扩散电压频谱以及电流频谱能量的基本原理,结合传统的PWM控制器,采用三角波作为调制信号实现简单的频率抖动的方法。该方法可使开关管两端电压以及输入电流低次谐波的幅值得到显著下降,实现了从干扰处抑制电磁干扰的措施,从而改善了变换器EMI的低频传导特性。实验结果验证了该方法的正确性。     

Rayleigh Scattering Reduction by Means of Optical Frequency Dithering in Passive Optical Networks With Remotely Seeded ONUs

With the purpose of reducing the crosstalk caused by Rayleigh scattering in bidirectional centralized light systems, we propose and experimentally demonstrate an optical frequency modulation to broaden the optical spectrum effectively. Analytic expressions for the Q-parameter of the signal affected by Rayleigh backscattering are also given and experimentally checked, both for optical frequency stable and dithered sources     

Novel Planar Electromagnetic Bandgap Structures for Mitigation of Switching Noise and EMI Reduction in High-Speed Circuits

Planar electromagnetic bandgap (EBG) structures with novel meandered lines and super cell configuration are proposed for mitigating simultaneous switching noise propagation in high-speed printed circuit boards. An ultrawide bandgap extending from 250 MHz to 12 GHz and beyond is demonstrated by both simulation and measurement, and a good agreement is observed. These perforated EBG-based power planes may cause spurious and unwanted radiation. In this paper, leakage radiation through these imperfect planes is carefully investigated. It is found that the leakage field from these planar EBG structures is highly concentrated around the feed point, and the field intensity is attenuated dramatically when passing across several periods of patches. A novel concept of using these EBG structures for electromagnetic interference reduction is also introduced. Finally, the impact of power plane with EBG-patterned structures on signal integrity is studied.     

基于CPLD的宽频带及量程自动切换数字频率计

结合采用测频法与测周期法这两种频率测量方法,可以大大提高数字频率计的频带以及测量精度.介绍了基于CPLD(复杂可编程逻辑器件)的宽频带且能自动切换量程的高精度数字频率计的基本原理,并给出了系统的相关设计.     

正激式开关电源传导电磁干扰研究

随着开关电源向高频化、集成化方向发展,其电磁干扰问题的研究显得越来越重要.本文以正激式开关电源为对象,建立了电源传导电磁干扰模型,分析了主要的干扰源和干扰耦合路径,使用PSpice软件仿真分析了电路参数对电磁干扰的影响.根据分析提出了反相抵消和加无损缓冲网络的方法,以改善电源的传导EMI,并进行了验证,证明了方法的有效...     

开关电源的噪声干扰及其抑制方法的分析

本文介绍了开关电源中噪声干扰产生的主要原因,及其相应的抑制方法.通过对实际线路的分析,给出了相关元器件的取值或计算方法.     

浅议开关电源的EMI处理

本文介绍了开关电源在电子产品中的电磁兼容问题及处理方法.先简单介绍开关电源的组成和基本原理,再分析产生干扰的根源和途径,以及给出一些处理措施及开关电源在设计和使用中的注意事项;最后给出实例分析.     

低开关频率下直接转矩控制转矩脉动抑制方法

本文针对直接转矩控制中转矩脉动大以及开关频率不恒定的问题,深入分析了感应电动机的定子磁链和转矩的实际变化情况,提出了在低开关频率下抑制转矩脉动的新型方案,仿真结果验证了新方案能够有效减小低速时转矩脉动并降低高速时开关频率。     

四频差动激光陀螺小抖动稳频工作模式判别技术研究

为避免传统光强差稳频方式的缺陷,提出了四频差动激光陀螺小抖动稳频方法。从四频陀螺工作原理出发,分析了小抖动稳频的可行性,其中工作模式判别问题是技术难点。提出三种解决方法：改变左右旋模频率间隔、光强差稳频方式的扫模电路结合、根据陀螺零漂数据来判别,为进一步研究提供了参考。     

Frequency Switching in Dual-Resonance Oscillators

An oscillator with a high-order (>2) resonator has multiple stable modes of oscillations. The stable modes for one such oscillator, having a fourth-order resonator, are found using a nonlinear analysis. By using a proper nonlinear active topology and tank component values, the fourth-order oscillator can generate either of the two distinct frequencies f₁ or f₂. A method is introduced to dynamically switch between the stable modes of oscillations. It is shown that the phase noise of this fourth-order oscillator, when generating only one of its resonant frequencies, is comparable to the phase noise of a second-order oscillator using the same active topology and resonator quality factor. Furthermore, the fourth-order oscillator has better phase noise and/or higher tuning range in VCO implementations compared to the commonly used switched resonator oscillators. The claims have been verified experimentally through an integrated oscillator prototype with f₁ = 2.4 GHz and f₂ = 4.7 GHz fabricated in a standard 0.18 mum CMOS technology. The oscillator draws 1.89 mA current of 1.8 V supply. The 1 MHz offset phase noises of the fourth-order oscillator for f₁ = 2.4 GHz and f₂ = 4.7 GHz are -122.4 dBc/Hz and -123.4 dBc/Hz, respectively     

Frequency domain model of conducted EMI in electrical drives

A harmful aspect of adjustable speed drives is the presence of large high-frequency stray currents. The most important, from the view of electromagnetic compatibility, are common-mode currents at the output and input sides of the converter. Currents at the output flow through the installation ground while those at the input flow through the grid ground. These common-mode currents can cause disturbances in other units that are connected within the same power section or placed close to the drive. This paper proposes a simulation model for a complete drive system based on the frequency domain. The model accurately reproduces the behavior of common-mode currents at any point of the system and allows the user to understand the influence of each system element on the currents. Thus, the model is useful both for designing filter structures and placing them at the proper position inside the adjustable speed drive. The model is validated by means of experimental results on a 5 kVA adjustable speed drive.     

Reduction of EMI Susceptibility in CMOS Bandgap Reference Circuits

This paper presents a successful approach to increase the electromagnetic interference (EMI) immunity of CMOS bandgap reference circuits. Layout techniques along with some changes in the reference schematics lead to a robust electromagnetic immunity, preserving good overall performances. Measurement results confirm the low susceptibility of the proposed circuits. They exhibit only a few millivolts shift, for interfering signals of 1 Vpp in the frequency range of 1 MHz to 4 GHz, compared to the classical topologies that may reach more than 1 V. The circuits were fabricated in a 0.8-mum standard CMOS technology     

Weighted Control of Traction Drives With Parallel-Connected AC Machines

AC machines supplied in parallel by a common voltage source inverter are sometimes used in industrial drives and railway traction applications. This reduction of power and control electronics leads to a reduction of cost, weight, and dimensions that is very useful for on-board systems. But this common supply imposes common voltages to all machines and the possibilities of independent behavior are reduced. In this paper, a graphical modeling is suggested to model such parallel drives for a railway application. A weighted control is then systematically deduced from this modeling and different possibilities of control are highlighted. Experimental results are provided to compare two of the deduced controls     

通信开关电源的EMI/EMC设计

通信开关电源是通信系统中的一种主要的干扰源之一,由于他本身工作特性使得电磁干扰问题相当突出,同时他的电磁兼容问题也是较难解决的。简要分析了通信开关电源的电磁兼容性要求、电磁兼容性的成因及解决方法。主要从耦合途径出发,介绍了开关电源电磁兼容性设计的滤波和屏蔽技术,以提高开关电源的电磁兼容性,保证开关电源正常工作。     

Reduction of power converter EMI emission using soft-switchingtechnique

Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using a soft-switching technique in power converters. Thus, the soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested