Modeling, Simulation, and Reduction of Conducted Electromagnetic Interference Due to a PWM Buck Type Switching Power Supply I
A. Farhadi
Abstract: Undesired generation of radiated or conducted energy in electrical systems is called Electromagnetic Interference (EMI). 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 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 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 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 simulation 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 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 regulations 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.
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 interference 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 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
Common 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 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 COMPATIBILITY 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 effects 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 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 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 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 stated 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-Prov
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基于压降型PWM开关电源的建模与仿真以及传导性电磁干扰的减少
A. Farhadi
摘要：电气系统中不受期望的辐射或者传导能量被称为电磁干扰(EMI)。电力电子转换器高速切换时，尤其是在开关电源中，虽然提高了工作效率，但是导致了电磁干扰的产生。本文介绍了各种各样的传导干扰，电磁干扰规范以及传导性电磁干扰的测量。电气系统的电磁干扰符合国家或者国际规范的能力称为电磁兼容性（EMC）。电力电子系统的生产制造部门必须重视电气设备的电磁兼容性。对电磁兼容性评估的第一步就是建模和仿真。本文中给出了基于压降型PWM开关电源的电磁干扰仿真结果。为了提高电气设备的电磁兼容性，在本论文中介绍了一些技术，并且结合仿真证明确实能提高电气设备的工作效率。
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
1 引言
在电力电子领域中，快速半导体的出现，使得高速，高频的开关电源的应用成为可能[1]。高速开关的应用使得电气设备质量和体积的减小，但是与此同时这也造成了一些不受期望的影响，比如射频干扰的影响[2]。生产制造部门将产品投入市场必须遵守行业电磁兼容规范。电磁兼容性问题在设计产品阶段之初就是非常重要的[3]。在开发产品前，建模和仿真是目前分析和预测电磁兼容性最有效的手段。许多以前的研究都有做过有关到电力电子元件的低频分析[4][5]。不同类型的电力电子转换器都可以成为潜在的电磁干扰源。电磁干扰源可以通过辐射和传导两种方式来进行传播。线路阻抗稳定网络被用来测量和计算电磁干扰的传导干扰水平[6]。线路阻抗稳定网络输出的干扰频谱被作为电磁兼容性的评估标准[7][8]。国家或国际规范是电气设备电磁兼容性评估参考的重要方面[7][8]。
2 来源，途径以及电磁干扰的受害设备
不受期望的电压或者电流被称为干扰，而导致它们的原因被称为干扰源。本文中讨论的干扰源是一个高速开关电源。
干扰通过辐射的方式在干扰源周围传播或通过传导的方式在常见的电缆或输电线中进行传播。在本文的研究中仅仅考虑传导发射，如电脑，接收器，放大器和工业控制器等设备。这些直接被干扰源辐射的设备被称为电磁干扰的受害设备。常见的连接设备，源头接线，布线为噪声以及干扰的传导提供了途径。电磁传导的干扰分为差模和共模两种类型[9]。
A.差模传导干扰
图1 差模传导干扰路径
这种类型的干扰源来自于将噪声源测试电路施加在不同线路之间产生的噪声。有关的电路如图1所示[9]。在图1中也表示了干扰源，路径阻抗，差模电流和负载阻抗。
B.共模传导干扰
共模噪声或干扰可能出现在电线或者电缆的连接点或者共地点。负载和接地点的任意泄露电流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和时相关的电流路径[9]。电力电子转换器在工作中可以视为电源网络线路之间的噪音源。在本文所做的研究中不同的传导干扰模式才是研究中重要的部分，因此接下来的讨论也仅仅在这种类型下被继续考虑。
图2共模传导干扰路径
3 电磁兼容性规范
电气设备的应用，特别是各种静态电力电子转换器越来越多。就像前文提到一样，电力电子转换器通常被视为一个主要的电磁干扰源，并对电网造成打击性的影响[2]。各种各样的干扰造成的高程度的污染降低了电网能量的质量。另一方面，一些家用设备，广告设备，特别是医疗设备对电力系统的电压及频率变化的干扰表现的尤为敏感。对此最好的解决干扰和提高电能质量的方法就是遵循国家或国际电磁兼容性规范。国际无线电干扰特别委员会(CISPR)，国际电工委员会标准(IEC)，美国联邦通讯委员会(FCC)和德国电气工程师协会认证(VDE)是欧洲，美国和德国最有名的决策和制定最重要电磁兼容性规范的机构。图3和图4所示的就是IEC和VDE制定的电气设备在传导发射上的要求和限制[7,9]。
对于不同的用户群体应该遵循不同类别的规范。A类指向普通用户，B类指向具有更加严格限制的用户，这分别在图3和图4中体现。IEC和VDE所制定规范的频率范围是不同的，分别是：IEC所规定的范围为150 kHz到30 MHz，VDE所规定的范围为10 kHz到30 MHz。在上述规范规定的频率范围内，规范的遵循情况被用来测试或者计算出传导干扰的水平。在欧美社会电磁兼容性规范的遵循是强制的，并且产品必须要经过认证的标签才能被视为已经达到该机构所制定规范的要求[8]。
图3 IEC管理排放标准
图4 VDE管理排放标准
4 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 提供一个低阻抗路径转移源动力到电力电子转换器以及负载。
2 从干扰源提供一个低阻抗路径，这里的电力电子转换器是用来测量路径端口的。
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 LISN频率变化
图7中给出了线路阻抗稳定网络的阻抗与频率变化以及前文提到的拓扑结构。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定值来进行评估。电磁兼容性的标准值指的是线路阻抗稳定网络输出的信号电平范围在10 kHz 到30 kHz 或者150 kHz 到30 MHz之间，并且应该将裕量保留在标准的限制范围之下。在实际的情况中，线路阻抗稳定网络通过连接到频谱分析仪上进行的干扰测量。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应该通过相应的软件来进行计算。
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