Introduction to Electromagnetic Compatibility

According to automotive standard CISPR 25, electronic components or modules are required to be connected to a specific test cable bundle in order to evaluate the radiated emissions. In the absorber-lined shielded enclosure (ALSE) method, also called the antenna method, the cable bundle is often the dominant radiation structure due to its length. This measurement method requires a large anechoic chamber, but often, it is only the impact of the test cable bundle's common-mode (CM) current distribution that is measured. Since the current distribution can be measured easily with current clamps, and with much lower demands to the environment, it is advantageous that the level of radiated fields can be estimated from the measured current distribution. This paper presents a field prediction method, which combines a measured CM current distribution with numerical computations for the radiated fields in the frequency range of 30–1000 MHz. Applicability is discussed based on several complex test cases. Three major problems had to be solved. First, appropriate current phase measurement methods had to be developed since the current amplitudes are not sufficient for estimating the electric fields. Second, a CM radiation model of a cable bundle had to be found. Third, in order to get comparable data for the ALSE test environment, a method had to be developed that could take this influence into account. Different solution approaches are examined here for the problems mentioned above.

Predicting the Radiated Emissions of Automotive Systems According to CISPR 25 Using Current Scan Methods

For the radiated electromagnetic interference pre-compliance diagnosis in power electronics systems, the measurement of common mode (CM) currents, impedances, and voltages are essentially important. In this article, two measurement issues are first identified in CM current and impedance measurement. The first is the coupling between the cables attached to a power converter and the coaxial cable connected to the measurement equipment. It degrades the measurement accuracy. The second is the coupling between the converter's attached cables and the ac grid. It degrades the repeatability of measurements. To improve the measurement accuracy and repeatability, this article proposes an improved measurement technique to address these two issues. Furthermore, for the measurement of the voltage difference between primary and secondary grounds, this article also identifies two issues. The first is the poor measurement resolution for the low noise voltage in the high-frequency range due to the high magnitude of line-frequency voltages. The second is that the loading effects of the voltage probe can reduce the measurement accuracy. This article proposed a technique to address these two issues. Finally, the proposed measurement techniques were validated on a flyback converter.

Measurement Techniques of Common Mode Currents, Voltages, and Impedances in a Flyback Converter for Radiated EMI Diagnosis

Electromagnetic interference (EMI) in non-isolated power converters is regulated by extensive standards in many applications. EMI modeling and reduction research is key to develop solutions to achieve EMI compliance. For conducted EMI, there are lots of techniques to analyze noise sources, propagation paths, parasitic couplings, and so on, which are summarized in this survey. Fundamental and general techniques to investigate and to reduce conducted EMI are analyzed. Moreover, in the high switching frequency era and with increasing applications of wide bandgap devices, radiated EMI is becoming an inevitable challenge. Modeling and reduction of radiated EMI, therefore, is becoming an important topic. Recent advances in radiated EMI research for non-isolated power converters are summarized and analyzed. Future EMI research development is discussed.

Advances in Modeling and Reduction of Conducted and Radiated EMI in Non-isolated Power Converters

This paper investigates the radiated electromagnetic interference (EMI) in non-isolated power converters for automotive applications. The radiated EMI is mainly caused by the cable antenna radiation. The mechanism of the cable antenna radiation is the common mode (CM) noise propagating through the power cables and radiating to space. The radiation excitation noise is generated by the non-isolated power converter. Through the noise circuit of the non-isolated power converter, the initial switching noises transform to the radiation excitation source. To develop the model for characterizing the generation of the radiation excitation source, this paper analyzes the noise circuit and the noise transformation in the non-isolated power converter. And based on the analyses of the noise circuit, this paper investigates the critical parasitics in the non-isolated power converter. Simulation and experimental investigations of the radiated EMI and the noise sources are conducted.

Investigation of Radiated EMI in Non-isolated Power Converters with Power Cables in Automotive Applications

In automotive EMC ALSE method, specified in CISPR 25, is commonly used for emission measurements. Components or modules are required to be connected with a test cable bundle for evaluating radiated emissions. The radiation is often mainly dominated by the common mode current along the cable bundle. In order to predict radiated emissions from setups according to ALSE method, without using a large anechoic chamber, this paper presents an alternative and innovative method. The presented approach determines radiated fields from a cable bundle without phase information. It is only based on the amplitude of common mode current from phaseless measurements using a RF current probe. Firstly, radiation model of a cable bundle is simplified to a single equivalent transmission line (TL) according to the mode analysis of multiconductor transmission line (MTL) theory. Then an optimization procedure based on trust-region-reflective (TRR) method and multi-start point algorithm is used to determine the common mode parameters of the equivalent TL by fitting to the measured current amplitude. The phase of common mode current, therefore, is retrieved through optimized TL parameters. Finally, the radiated fields are straightforwardly evaluated by elementary dipoles approximation of the cable bundle. The proposed approach is verified by numerical analysis of different cable bundle models and measurements. The stability and feasibility to evaluate radiated emissions from a cable bundle could be shown.

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Prediction of radiated fields from cable bundles based on current distribution measurements

The field emission from printed circuit boards (PCB) plays an important role in the electromagnetic compatibility of electronic systems. The established field measurement methods according to CISPR suffer from the need to use large anechoic chambers. Furthermore the measurement data cannot be used for modeling concerning the calculation of the overall fields radiated from e.g. a car. Other methods which try to identify an equivalent source distribution by near-field measurements do not require large anechoic chambers, but instead an electromagnetic inverse problem has to be solved. This often leads to an ill-posed equation system due to unavoidable errors in measurement data, long computation times, and finally inaccurate results. In this paper an approach to optimize the characterization method of printed circuit boards by near-field measurements is proposed. The radiation of a PCB is modeled with a set of elementary sources, resulting in the same field like the electronic system itself. The electromagnetic fields in a plane above the PCB are measured. Optimized time domain methods are applied in order to reduce measurement time, to receive phase information, and to correlate different measurement data sets. As the current distribution on a PCB mainly depends on the conductor paths, the distribution of characterizing equivalent sources can be chosen with respect to the trace routing. Amplitude and phase correlation of the equivalent sources along each current path are taken into account. The routing information can be extracted from mechanical CAD-data or is based on high-resolution near field scans. The approaches are integrated in the equivalent source identification process. The advantages of the new method are presented and discussed.

http://ieeexplore.ieee.org/iel5/6064642/6078493/06078663.pdf

Optimization methods for equivalent source identification and electromagnetic model creation based on near-field measurements

Current scanning methods could be a promising alternative to reduce the need of automotive CISPR 25 ALSE measurements. It is assumed that, especially in low frequency range, the cable bundle is often the dominant radiating structure. Knowing the current distribution along the cable bundle the field at any point can be calculated. First implementation calculated the phase through measured current amplitude, which may produce the error in low frequency range. In order to compensate the mentioned problem, this paper proposes two alternative enhancements of the common-mode current scan methods in time domain for cable bundles. A time domain scan can provide the amplitude and phase information of currents simultaneously through Fast Fourier Transform (FFT). One method, considering the common-mode current as radiation source, models the cable bundle by a set of elementary dipoles to calculate the field emissions. While the other method only uses common-mode current and transmission line parameters at beginning and end ports of cable bundle to calculate the field emissions. Till now an ideal environment was assumed and the complexity of a real ALSE was neglected. In order to improve the prediction quality, a calibration approach based on measured data is proposed, which incorporates real influence factors in an anechoic shielded chamber. Through the verifications by numerical analysis of different cable bundle models and measurements, the stability and feasibility of the mentioned improvements could be shown.

http://ieeexplore.ieee.org/iel7/6636283/6653179/06653246.pdf

An alternative method for measurement of radiated emissions according to CISPR 25

. Radiated electromagnetic fields from a PCB can be estimated when the source current distribution is known. From a measured near-field distribution, the PCB source current distribution can be found. Accuracy depends on the measurement method and its limitations, the radiation model and the choice of the observation area. Many known methods are based on optimization algorithms for inverse problems that vary a set of elementary radiation sources and create a radiation model. However, apart from the time-consuming optimization process, such methods find one possible solution for a near-field distribution. As this distribution might not reflect the real current distribution, accuracy outside of near-field scan area can be low. Furthermore numerical problems can often be observed. Solving the given inverse problem with a system of linear equations and complex near-field data it can be very sensitive to noise. Regularization methods and an adjusted preconditioning can increase the accuracy. In this paper, an improved radiation model creation approach based on complex near-field data is presented. This approach is based on regularization methods and extended by current estimations from near-field data. Preconditioning is done considering some physical properties of the PCB and its possible current paths. Accuracy and stability of the method are investigated in the presence of noisy data.

/pdf/pcb-current-identification-based-on-near-field-measurements-tmnsssdvur.pdf

Denis Rinas

Papers

Predicting the Radiated Emissions of Automotive Systems According to CISPR 25 Using Current Scan Methods

Prediction of radiated fields from cable bundles based on current distribution measurements

Optimization methods for equivalent source identification and electromagnetic model creation based on near-field measurements

An alternative method for measurement of radiated emissions according to CISPR 25

PCB current identification based on near-field measurements using preconditioning and regularization