Several techniques to mitigate conducted electromagnetic interference (EMI) in switch-mode power supplies (SMPS) have been reported in literature. Of these, this paper reviews those techniques that are primarily meant for ac-dc and dc-dc power converters. The techniques are broadly classified based on two criteria-1) reduction of the noise after generation and 2) reduction of the noise at the generation stage itself. A detailed classification and review of various noise mitigation techniques currently available in literature are presented. It is believed that the classification and review of the conducted EMI mitigation techniques presented in this paper would be useful to SMPS researchers and designers.

Conducted EMI Mitigation Techniques for Switch-Mode Power Converters: A Survey

In this paper, the electromagnetic interference (EMI) filter is first characterized using Scattering parameters (S-parameters). Based on this S-parameters model, the insertion voltage gains are derived for EMI filter with arbitrary levels of source and load impedances. Experiments are carried out to verify this approach. Based on the network theory, S-parameters are then utilized to extract the parasitic couplings in both one-stage and two-stage EMI filters. EMI filter models are constructed. Experiments finally verify the proposed methods. The approaches are very useful for the prediction of EMI filter performance, and for the design and optimization of EMI filters.

Characterization and parasitic extraction of EMI filters using scattering parameters

The attenuation characteristics of electromagnetic interference (EMI) filters in practice often differ from theoretical predictions and minor changes can result in a significant improvement in performance. The performance of the differential-mode (DM) filter stage can usually be well predicted, but the common mode (CM) behavior is more difficult to handle. This is especially true for three-phase pulsewidth modulation (PWM) rectifier systems, which inherently show a large high-frequency CM voltage at the rectifier output. Possible CM noise current paths of a three-phase/level PWM rectifier are analyzed in this paper where parasitic capacitances to the heat sink and to earth are considered. In addition, a concept to significantly reduce CM emissions is discussed in detail. Based on the proposed models, an EMI filter design for a system with 1 MHz switching frequency is shown. Experimental verification of the designed EMI filter is presented by impedance and conducted emission (CE) measurements taken from a 10 kW prototype. Several practical aspects of filter implementation such as component arrangement, shielding layers, magnetic coupling, etc., are discussed and verified by measurements.

EMI Filter Design for a 1 MHz, 10 kW Three-Phase/Level PWM Rectifier

The insertion loss method is proposed to measure the noise source impedance of off-line power supplies. The information obtained through the proposed method enables the prediction of EMI filter performance and the design of a suitable filter for a switch mode power supply.

Measurement of noise source impedance of off-line converters

A generalized terminal modeling technique was proposed earlier to predict conducted electromagnetic interference from a dc-dc boost converter. The predictions of these conducted emissions showed that there was a good agreement up to 50 MHz. This paper extends the generalized terminal modeling approach to converters with the buck-type input. Both dc and ac applications are discussed. The technique is developed for the electromagnetic interference modeling of switched power converters in aerospace applications where the requirements on electromagnetic pollution are very strict. The model is shown to successfully predict conducted emissions for a buck converter and a three-phase voltage source inverter up to 100 MHz with an error of 6 dB or less at most frequencies.

Analysis of EMI Terminal Modeling of Switched Power Converters

An experimental comparison of the EMI profiles of two boost power converters, employing the ZVT switching technique and the hard switching method respectively, is carried out. It is concluded that difference of EMI emissions between the two is limited. In fact, the ZVT circuit may actually give a worse performance if the layout of the ZVT-related auxiliary branch is improper.

An experimental comparison of conducted EMI emissions between a zero-voltage transition circuit and a hard switching circuit

Nonintrinsic differential-mode (DM) noise caused by ground current is common in switch-mode power supplies, but the phenomenon is first uncovered and reported in this paper. Using the zero-span mode of a spectrum analyzer allows one to investigate this mode of noise. It is found that this mode of noise is a voltage-generated noise, caused by the unbalance of the circuit. Understanding the phenomenon makes the EMI diagnosis and filter design less of a "black magic".

Non-intrinsic differential mode noise caused by ground current in an off-line power supply

The proposed filter characterization method makes it useful to predict EMI filter performance when the filter is used in a practical power supply. High frequency parasitic effects can also be predicted using this method. An impedance/gain-phase analyzer is needed for this approach.

A new method to characterize EMI filters

An insertion loss method is proposed to measure the noise source impedance of offline power supplies. The information obtained enables one to predict EMI filter performance and design a suitable filter for power supply applications.

Dongbing Zhang

Papers

Measurement of noise source impedance of off-line converters

An experimental comparison of conducted EMI emissions between a zero-voltage transition circuit and a hard switching circuit

Non-intrinsic differential mode noise caused by ground current in an off-line power supply

A new method to characterize EMI filters

Measurement of noise source impedance of off-line converters