基于压降型PWM开关电源的建模、仿真和减少传导性电磁干扰--外文翻译.docx

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1、Modeling, Simulation, and Reduction of Conducted Electromagnetic Interference Due to a PWM Buck Type Switching Power Supply A. Farhadi http:/10.11.248.20:8000/rewriter/EIAbstract:Undesired generation of radiated or conducted energy in electrical systems is called Electromagnetic Interference (EMI).

2、High speed switching frequency in power electronics converters especially in switching power supplies improves efficiency but leads to EMI. Different kind of conducted interference, EMI regulations and conducted EMI measurement are introduced in this paper. Compliancy with national or international

3、regulation is called Electromagnetic Compatibility (EMC). Power electronic systems producers must regard EMC. Modeling and simulation is the first step of EMC evaluation. EMI simulation results due to a PWM Buck type switching power supply are presented in this paper. To improve EMC, some techniques

4、 are introduced and their effectiveness proved by simulation. Index Terms:Conducted, EMC, EMI, LISN, Switching Supply I. INTRODUCTION FAST semiconductors make it possible to have high speed and high frequency switching in power electronics . High speed switching causes weight and volume reduction of

5、 equipment, but some unwanted effects such as radio frequency interference appeared . Compliance with electromagnetic compatibility (EMC) regulations is necessary for producers to present their products to the markets. It is important to take EMC aspects already in design phase . Modeling and simula

6、tion is the most effective tool to analyze EMC consideration before developing the products. A lot of the previous studies concerned the low frequency analysis of power electronics components . Different types of power electronics converters are capable to be considered as source of EMI. They could

7、propagate the EMI in both radiated and conducted forms. Line Impedance Stabilization Network (LISN) is required for measurement and calculation of conducted interference level . Interference spectrum at the output of LISN is introduced as the EMC evaluation criterion . National or international regu

8、lations are the references for the evaluation of equipment in point of view of EMC . II. SOURCE, PATH AND VICTIM OF EMI Undesired voltage or current is called interference and their cause is called interference source. In this paper a high-speed switching power supply is the source of interference.

9、Interference propagated by radiation in area around of an interference source or by conduction through common cabling or wiring connections. In this study conducted emission is considered only. Equipment such as computers, receivers, amplifiers, industrial controllers, etc that are exposed to interf

10、erence corruption are called victims. The common connections of elements, source lines and cabling provide paths for conducted noise or interference. Electromagnetic conducted interference has two components as differential mode and common mode . A. Differential mode conducted interference This mode

11、 is related to the noise that is imposed between different lines of a test circuit by a noise source. Related current path is shown in Fig. 1 . The interference source, path impedances, differential mode current and load impedance are also shown in Fig. 1. B. Common mode conducted interference Commo

12、n mode noise or interference could appear and impose between the lines, cables or connections and common ground. Any leakage current between load and common ground could be modeled by interference voltage source. Fig. 2 demonstrates the common mode interference source, common mode currents Icm1 and

13、Icm2 and the related current paths. The power electronics converters perform as noise source between lines of the supply network. In this study differential mode of conducted interference is particularly important and discussion will be continued considering this mode only. III. ELECTROMAGNETIC COMP

14、ATIBILITY REGULATIONS Application of electrical equipment especially static power electronic converters in different equipment is increasing more and more. As mentioned before, power electronics converters are considered as an important source of electromagnetic interference and have corrupting effe

15、cts on the electric networks . High level of pollution resulting from various disturbances reduces the quality of power in electric networks. On the other side some residential, commercial and especially medical consumers are so sensitive to power system disturbances including voltage and frequency

16、variations. The best solution to reduce corruption and improve power quality is complying national or international EMC regulations. CISPR, IEC, FCC and VDE are among the most famous organizations from Europe, USA and Germany who are responsible for determining and publishing the most important EMC

17、regulations. IEC and VDE requirement and limitations on conducted emission are shown in Fig. 3 and Fig. 4 . For different groups of consumers different classes of regulations could be complied. Class A for common consumers and class B with more hard limitations for special consumers are separated in

18、 Fig. 3 and Fig. 4. Frequency range of limitation is different for IEC and VDE that are 150 kHz up to 30 MHz and 10 kHz up to 30 MHz respectively. Compliance of regulations is evaluated by comparison of measured or calculated conducted interference level in the mentioned frequency range with the sta

19、ted requirements in regulations. In united European community compliance of regulation is mandatory and products must have certified label to show covering of requirements . IV. ELECTROMAGNETIC CONDUCTED INTERFERENCE MEASUREMENT A. Line Impedance Stabilization Network (LISN)1-Providing a low impedan

20、ce path to transfer power from source to power electronics converter and load. 2-Providing a low impedance path from interference source, here power electronics converter, to measurement port. Variation of LISN impedance versus frequency with the mentioned topology is presented in Fig. 7. LISN has s

21、tabilized impedance in the range of conducted EMI measurement . Variation of level of signal at the output of LISN versus frequency is the spectrum of interference. The electromagnetic compatibility of a system can be evaluated by comparison of its interference spectrum with the standard limitations

22、. The level of signal at the output of LISN in frequency range 10 kHz up to 30 MHz or 150 kHz up to 30 MHz is criterion of compatibility and should be under the standard limitations. In practical situations, the LISN output is connected to a spectrum analyzer and interference measurement is carried

23、out. But for modeling and simulation purposes, the LISN output spectrum is calculated using appropriate software. V.SIMULATION OF EMI DUE TO A PWM BUCK TYPE SWITCHINGPOWER SUPPLY For a simple fixed frequency PWM controller that is applied to a Buck DC/DC converter, it is possible to assume the error

24、 voltage (ve) changes slow with respect to the switching frequency, the pulse width and hence the duty cycle can be approximated by (1). Vp is the saw tooth waveform amplitude. A. PWM waveform spectral analysis The normalized pulse train m (t) of Fig. 8 represents PWM switch current waveform. The nt

25、h pulse of PWM waveform consists of a fixed component D/fs , in which D is the steady state duty cycle, and a variable component dn/f sthat represents the variation of duty cycle due to variation of source, reference and load. As the PWM switch current waveform contains information concerning EMI du

26、e to power supply, it is required to do the spectrum analysis of this waveform in the frequency range of EMI studies. It is assumed that error voltage varies around Ve with amplitude of Ve1 as is shown in (2). fm represents the frequency of error voltage variation due to the variations of source, re

27、ference and load. The interception of the error voltage variation curve and the saw tooth waveform with switching frequency, leads to (3) for the computation of duty cycle coefficients. Maximum variation of pulse width around its steady state value of D is limited to D1. In each period of Tm=1/fm ,

28、there will be r=fs/fm pulses with duty cycles of dn. Equation (4) presents the Fourier series coefficients Cn of the PWM waveform m (t). Which have the frequency spectrum of Fig.9. B-Equivalent noise circuit and EMI spectral analysis To attain the equivalent circuit of Fig.6 the voltage source Vs is

29、 replaced by short circuit and converter is replaced by PWM waveform switch current (Iex) as it has shown in Fig. 10. The transfer function is defined as the ratio of the LISN output voltage to the EMI current source as in (5). The coefficients di, ni (i = 1, 2, , 4) correspond to the parameters of

30、the equivalent circuit. Rc and Lc are respectively the effective series resistance (ESR) and inductance (ESL) of the filter capacitor Cf that model the non-ideality of this element. The LISN and filter parameters are as follows: CN = 100 nF, r = 5 , l = 50 uH, RN =50 , LN=250 uH, Lf = 0, Cf =0, Rc=

31、0, Lc= 0, fs =25 kHz The EMI spectrum is derived by multiplication of the transfer function and the source noise spectrum. Simulation results are shown in Fig. 11. VI. CONCLUSION Appearance of Electromagnetic Interference due to the fast switching semiconductor devices performance in power electroni

32、cs converters is introduced in this paper. Radiated and conducted interference are two types of Electromagnetic Interference where conducted type is studied in this paper. Compatibility regulations and conducted interference measurement were explained. LISN as an important part of measuring process

33、besides its topology, parameters and impedance were described. EMI spectrum due to a PWM Buck type DC/DC converter was considered and simulated. It is necessary to present mechanisms to reduce the level of Electromagnetic interference. It shown that EMI due to a PWM Buck type switching power supply

34、could be reduced by controlling parameters such as duty cycle, duty cycle variation and reference voltage frequency. VII. REFRENCES 1 Mohan, Undeland, and Robbins, “Power Electronics Converters, Applications and Design” 3rd edition, John Wiley & Sons, 2003. 2 P. Moy, “EMC Related Issues for Power El

35、ectronics”, IEEE, Automotive Power Electronics, 1989, 28-29 Aug. 1989 pp. 46 53. 3 M. J. Nave, “Prediction of Conducted Interference in Switched Mode Power Supplies”, Session 3B, IEEE International Symp. on EMC, 1986. 4 Henderson, R. D. and Rose, P. J., “Harmonics and their Effects on Power Quality

36、and Transformers”, IEEE Trans. On Ind. App., 1994, pp. 528-532. 5 I. Kasikci, “A New Method for Power Factor Correction and Harmonic Elimination in Power System”, Proceedings of IEEE Ninth International Conference on Harmonics and Quality of Power, Volume 3, pp. 810 815, Oct. 2000. 6 M. J. Nave, “Li

37、ne Impedance Stabilization Networks: Theory and Applications”, RFI/EMI Corner, April 1985, pp. 54-56. 7 T. Williams, “EMC for Product Designers” 3rd edition 2001 Newnes. 8 B. Keisier, “Principles of Electromagnetic Compatibility”, 3rd edition ARTECH HOUSE 1987. 9 J. C. Fluke, “Controlling Conducted

38、Emission by Design”, Vanhostrand Reinhold 1991. 10 M. Daniel,”DC/DC Switching Regulator Analysis”, McGrawhill 1988 11 M. J. Nave,” The Effect of Duty Cycle on SMPS Common Mode Emission: theory and experiment”, IEEE National Symposium on Electromagnetic Compatibility, Page(s): 211-216, 23-25 May 1989

39、.作者：A. Farhadi国籍：伊朗基于压降型PWM开关电源的建模、仿真和减少传导性电磁干扰摘要：电子设备之中杂乱的辐射或者能量叫做电磁干扰(EMI)。尤其是在开关电源中的电力电子转换器经常高速切换时，虽然提高了工作效率，却导致转换器产生了电磁干扰。在这篇论文之中介绍了各种各样的传导干扰，电磁干扰规章以及传导性电磁干扰的测量。如果电子设备的电磁干扰符合国家或者国际规章称为电磁兼容性（EMC）。电力电子系统生产商一定要重视电子设备的电磁兼容性。电磁兼容性评估的第一步就是建模和仿真。在这篇论文中提出了基于压降型脉宽调制开关电源的电磁干扰仿真结果。为了提高电子设备的电磁兼容性,在论文中介绍了一些技

40、术，并且通过仿真提高了电子设备的工作效率。关键字：传导，电磁兼容性，电磁干扰，线路阻抗稳定网络，开关电源一.前言在电力电子领域中，快速半导体的出现使高速度，高频率的开关切换成为了可能1。高速的开关造成设备的重量和体积的减少，但与此同时这也造成了一些不利的影响，比如无线频率的干扰2。生产商将生产的产品投放到市场，遵守电磁兼容性规章是必要的。在设计阶段考虑电磁兼容性问题是非常重要的3。在开发产品前，建模和仿真是分析电磁兼容性最有效的工具。许多以前的研究都有涉及到电力电子元件的低频分析45。不同类型的电力电子转换器都能够被用来当做电磁的干扰源。电磁干扰源可以通过辐射和传导两种方式来传播。线路阻抗稳定

41、网络被用来测量和计算电磁干扰影响的程度6。线路阻抗稳定网络输出的干扰频谱被引为电磁兼容性的评估标准7,8。国家或国际规章是电子设备电磁兼容性评估的一个参考的方面78。二、来源，途径和电磁干扰的受害者杂乱的电压或者电流被称为干扰，而它们的来源被称为干扰源。本论文中的干扰源就是一个高速的开关电源。干扰通过辐射的方式在干扰源周围传播或通过和常见的电缆或电线连接进行传导。在这项研究中只考虑传导发射设备，如电脑，接收器，放大器，工业控制器等。这些被干扰源辐射的设备被称为受害者。常见的元素，源头接线，布线为噪声以及干扰的传导提供了途径。电磁传导干扰有差模和共模两种干扰方法9。A.差模传导干扰这种模式就是将

42、一个噪声源的噪声施加到一个测试电路的不同线路。它的电路如下图1所示9。在图1中也显示了干扰源，路径阻抗，差模电流以及负载阻抗。 图1差模传导干扰路径B.常见的干扰方式共模噪声或干扰可能出现在电线或者电缆的连接点。负载和接地点的任意泄露都可以被认为是电压干扰源。图2演示了共模干扰源在共模电流为Icm1和Icm2时相关的电流路径9。电力电子转换器可以被用来作为供应网络线路之间的噪音源。在这项研究中不同的传导干扰模式是非常重要的，所以讨论只会在这种模式下被继续考虑。三、电磁兼容性规章电子设备的应用，特别是那些拥有静态电力电子转换器的电子设备越来越多。就像前面讲的一样，电力电子转换器被视为一个重要的电

43、磁干扰源，并能使电网产生腐坏。各种各样的干扰造成的高污染降低了电网电能的质量。另一方面，一些住宅，广告，特别是医疗器件对电力系统的电压及频率变化的干扰非常敏感。最好的解决干扰和提高电能质量的方法就是遵守国家或国际电磁兼容性规定。国际无线电干扰特别委员会，国际电工委员会标准，美国联邦通讯委员会和德国电气工程师协会认证是欧洲，美国，德国最有名的决策并且出版最重要电磁兼容性法规的组织。IEC和VDE在传导发射上的需要和限制如图 3 和图 4所示7,9。 图2共模传导干扰路径图3 IEC管理排放标准不同的消费者群体可以遵守不同类别的规定。A类为普通的消费者，B类为具有更苛刻限制的消费者，在图 3 和图

44、 4这两者被分开。IEC和VDE频率范围不同，前者范围为150 千赫兹 到 30 兆赫兹，后者的范围为10 千赫兹 到 30 兆赫兹，在上述法规规定要求的频率范围内，法规的遵守情况被用来测量或者计算传导干扰的水平。在欧美社会电磁兼容性法规的遵行是强制的，产品必须要有认证的标签以表示达到法规的要求8。 图4 VDE管理排放标准四、电磁传导干扰测试A. 线路阻抗稳定网络（LISN）线路阻抗稳定网络是提供一个标准的工业元素被放置在供应和电力电子转换器之间， 包括加载一个接口以便可以对传导干扰进行测量7，所述的情况如图5 所示6。线路阻抗稳定网络应具有以下几个特点，以满足测量条件7。1- 提供一个低阻

45、抗路径转移源动力到电力电子转换器以及负载。2- 干扰源提供一个低阻抗路径，电力电子转换器用来测量路径端口。 图5 LISN网络布局测量传导干扰B. 线路阻抗稳定网络拓扑线路阻抗稳定网络比较常见的拓扑结构如图6所示7。图6 LISN网络常见的拓扑结构图7中给出了线路阻抗稳定网络的阻抗与频率的变化以及前面提到的拓扑结构。线性阻抗稳定网络在电磁干扰测量范围之内拥有稳定的阻抗7。线路阻抗稳定网络输出的信号电平与频率的变化就是干扰频谱。一个系统的电磁兼容性可以通过比较它的干扰频谱和标准的限制来进行评估。线路阻抗稳定网络输出的信号电平范围在10千赫兹 到30 千赫兹 或者150 千赫兹 到30兆赫兹之间，

46、这就是标准的电磁兼容性，并且它处在标准的限定范围里。在实际的情况下，线路阻抗稳定网络是连接到频谱分析仪上进行干扰测量的。但是为了建模和仿真的目的，线路阻抗稳定网络的输出频谱是通过相应的软件来进行计算的。五、基五、于压降型脉宽调制开关电源的电磁干扰模拟对于一个简单频率固定的脉宽调制控制器，适用于降压型直流/直流转换器，它引起的误差电压（ve）的变化相对于开关频率变化可能会比较慢，脉冲宽度和占空比可以会比较的近似。Vp为锯齿波形的振幅。 ( 1 )图7 LISN网络阻抗与频率A. 脉宽调制波形的频谱分析标准脉冲序列m（t）在图8中 代表的是脉宽调制开关电流的波形。第n个脉宽调制脉冲波形组成一个固定

47、的部分D/fs，其中D表示为稳定状态的占空比，一个可变部分d n/ f s 表示由于来源，参考和负载的变化而形成的占空比变化。图8压降型直流/直流转换器中的脉宽调制开关直流波形在电力供应时，脉宽调制开关电源波形中会包含有关电磁干扰的信息，它需要做的就是在电磁干扰研究频率范围内分析波形的频谱。推测出来的电压误差Ve和振幅Ve1的变化关系显示在方程（2）中。 ( 2 )调频代表的是由于源，参数和负载的变化产生的误差电压频率变化。截取的误差电压变化曲线和开关频率的锯齿波，使方程（3）成为了对占空比的运算。 ( 3 ) 图9 脉宽调制频谱（f s =25kHz, f m=100Hz, D=0.5, D1=0.05）它的稳定值D在最大脉冲宽度变化范围内被限定在D1。每一个周期Tm=1/fm，这里是r=fs/fm脉冲和dn的占空比。方程（4）列出了脉宽调制波形m(t)的傅里叶级数系数Cn。Cn具有如图9中显示的频谱。 ( 4 )B.等效噪音电路和电磁干扰频谱分析为了达到图6中的等效电路，电压源Vs被短路了并且转换器被开关电源的脉宽调制波形所取代，这结果被显示在图10中。传递函数被确定为用LISN网络的输出电压比上电磁干扰的源电流，这些被显示在方程（5）中。 ( 5 )这些系数di, ni (i = 1, 2, ,