Analysis and practical relevance of CM/DM EMI noise separator characteristics

Abstract: Accurate measurement of common mode (CM) and differential mode (DM) noise is crucial for electromagnetic interference filter design. With the application of wide bandgap devices, the measurement results require higher accuracy at high frequency. This letter proposes a novel CM and DM noise separation method where a 20 dB attenuator is integrated to allow the measured results less sensitive to the parasitic parameters in the 150 kHz–30 MHz frequency range. The proposed method improves the flatness of the noise separator in the 150 kHz–30 MHz frequency range, which is 0.3 dB for common mode transmission ratio and 0.6 dB for differential mode transmission ratio. Simulation and experimental results are provided to validate the effectiveness of the proposed method.

Abstract: This paper presents a method to model a back-to-back converter and the additional passive filter system. The mathematical modeling method followed the step of converting the three-phase system to single phase systems by separating the differential mode (DM) and common mode (CM) noise circuit for the design of the filter components separately. The model accounts for parasitic components in the converters and presents an indirect method of estimating parasitic capacitance for CM filter design. Design rules for the different components are summarized. Results from a lab prototype are presented and show good correspondence to the model.

Abstract: A conventional conducted emission test provides insufficient information in terms of differential and common mode interferences. Only the normal mode interference can be measured, which complicates the design or optimization process for a power line filter if needed. Moreover, measurements performed with conventional test receivers are time-consuming and only one measurement channel is available. In this paper, a measurement approach for digital mode decomposition is presented using multiple channels simultaneously. Results obtained with the proposed approach are compared with regular active and passive separation networks.

Abstract: A systematic method for the diagnosis and reduction of conducted noise emissions is described. The method consists of a device for determining whether the differential- or common-mode component of conducted noise is dominant along with a simplified equivalent circuit of the power supply filter for each component. The procedure consists of first using the device to determine which noise-component is dominant in a particular frequency range and then using the simplified equivalent circuits to determine whether an anticipated change in value of an element in the power supply filter will be effective. >

Abstract: 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.

Abstract: The design of electromagnetic interference (EMI) input filters, needed for switched power converters to fulfill the regulatory standards, is typically associated with high development effort. This paper presents a guideline for a simplified differential-mode (DM) filter design. First, a procedure to estimate the required filter attenuation based on the total input rms current using only a few equations is given. Second, a volume optimization of the needed DM filter based on the previously calculated filter attenuation and volumetric component parameters is introduced. It is shown that a minimal volume can be found for a certain optimal number of filter stages. The considerations are exemplified for two single-phase power factor correction converters operated in continuous and discontinuous conduction modes, respectively. Finally, EMI measurements done with a 300-W power converter prototype prove the proposed filter design method.

Abstract: In this paper, at first, three requirements for noise separators are specified and the disadvantages of traditional evaluation methods are pointed out. Noise separators are then characterized using scattering parameters (S-parameters). Existing noise separators are evaluated according to the specified requirements. Finally a noise separator is proposed with parasitic controlled design and the prototype is evaluated using the proposed method. An electromagnetic interference (EMI) measurement shows that the proposed noise separator can effectively separate noise and that it is easy to use.