Design of EMI filter based on impedance matching

This paper presents a systematic and comprehensive approach for differential mode (DM) electromagnetic interference (EMI) filter design in a three-phase boost-type power factor correction (PFC) rectifier. Since the DM EMI filter forms a significant portion of the overall filter as well as converter volume, the reduction of DM filter component size is kept as a major objective in the filter design process in order to improve the power density. In addition to the objectives of volume optimization and conducted emission attenuation requirement to comply with the EMI standard, the filter design process also ensures a near-unity power factor operation with the optimal set of EMI filter parameters. To accomplish this, the paper analyzes the effect of EMI filter component selection on the overall lower order (1-100 kHz) frequency response, which is important for evaluating the dynamic response and stability. The results from the proposed design approach are validated through simulation, the DM Bode plot, and frequency response of the input current with and without EMI filter. As a proof-of-concept verification, the proposed EMI filter is implemented in a 4-kW three-phase boost-PFC prototype, which demonstrates minimal phase displacement (<;5°) of the input current.

A PWM inverter fed ac induction motor drive system capable of suppressing all the adverse effects of PWM inverter is developed in this paper. A passive electromagnetic interference (EMI) filter is proposed, designed, and tested for a 4-kW drive system, is characterized by sophisticated connection of two small passive filters can compensate for common mode voltages produced by PWM inverter and can suppress leakage current. An equivalent common-mode circuit for the drive system equipped with the EMI filter is derived from experimental waveforms along with theoretical discussions verifies that the EMI filter is viable and effective in eliminating all adverse effects of PWM inverter.

Active electromagnetic interference (EMI) filter is a feasible and effective suppression technology for switching mode power supply (SMPS) system. The traditional active EMI filter (AEF) suppresses EMI by sensing EMI signal and generating cancelation EMI by the controlled high-frequency operational amplifier. The filtering performance not only depends on the high-open-loop gains of the operational amplifier but also on its low-output impedance of AEF. However, obtaining sufficiently low-output impedance of AEF is very difficult in a controlled filtering frequency band. To cope with it, a filtering topology of AEF based on impedance modulation for SMPS is proposed in this article. The proposed active trap EMI filter (ATEF) can trap the EMI current at the filtering frequency band with a sufficiently low-output impedance by introducing a negative impedance circuit. Finally, the impedance and the filtering performance are evaluated on a 48 W SMPS, and experimental results show that the proposed ATEF can effectively suppress the conducted EMI generated by SMPS.

This paper addresses improved electromagnetic compatibility (EMC) in switched-mode power converters (SMPCs), without using electromagnetic interference (EMI) filters. A practical solution is proposed for minimizing conductive EMI in a pulsewidth modulated (PWM), and random PWM dc-dc power converters. A comparative investigation is performed into the use of different random modulation schemes (driven by the DSP-2 board with the TMS320C32) as against the normal PWM. The effectiveness of randomization on spreading those dominating frequencies that normally exist in constant frequency PWM schemes is evaluated by power spectral density (PSD) estimations in the low-frequency range. Some parasitical- and topology-based EMI sources in devices are presented and frequency analysis is shown by using the discrete Fourier transform (DFT). SPICE simulations are also used to verify practical solutions for eliminating negative EMI sources and achieving EMC improvements. Finally, levels of conductive EMI are estimated with DFT, and experimentally verified to comply with the CISPR 25 (or EN 55025) regulations. Moreover, it is clearly shown, that limited speed PWM driving of the power switches with appropriate snubber circuits guarantees reduced conductive EMI. When considering the price and high EMC, in the final solution the power converter is driven by the mu-controller PIC16F876 with limited numerical and peripheral capabilities, where only normal PWM and randomized PWM can be implemented

This paper presents the analysis and design of an active electromagnetic interference (EMI) filter (AEF) for the common-mode (CM) noise reduction of switching power converters. The features of the several types of AEFs are discussed and compared in terms of implementation. The feed-forward AEF with a voltage-sensing and voltage-cancellation (VSVC) structure is implemented for an LLC resonant converter to replace a multiple-stage passive EMI filter and thereby reduce CM noise. The characteristics and performance of the VSVC-type AEF are investigated through theoretical and experimental works.

Conducted electromagnetic interference (EMI) generated by PWM inverter‐fed induction motor drive systems, which are currently widely used in many industrial and/or avionic applications, causes severe parasitic current problems, especially at high frequencies (HF). These restrict power electronic drive’s evolution. In order to reduce or minimize these EMI problems, several techniques can be applied. In this paper, insertion of an optimized passive EMI filter is proposed. This filter is optimized by taking into account real impedances of each part of a considered AC motor drive system contrarily to commercial EMI filters designed by considering internal impedance of disturbance source and load, equal to 50Ω. Employing the latter EMI filter would make EMI minimization less effective. The proposed EMI filter optimization is mainly dedicated to minimize common mode (CM) currents due to its most dominant effects in this kind of system. The efficiency of the proposed optimization method using two‐port network approach is deduced by comparing the minimized CM current spectra to an applied normative level (ex. DO‐160D in aeronautics).

In this paper, the active differential-mode (DM) electromagnetic interference (EMI) filter topology for ac/dc converters is first briefly investigated. The active DM EMI filter model was developed based on the models of filter components including a current transformer, a high-pass filter, an operational amplifier, and a class AB amplifier. The system model including the active filter, ac/dc converter, and line impedance stabilization networks (LISNs) are explored. With the developed system model, the loop gain and insertion gain of the active filter are derived. Based on the loop gain, the stability of the active filter is investigated and the compensation is applied to achieve stability and good EMI reduction. Both simulations and experiments are conducted to validate the developed technique.

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Electromagnetic interference (EMI) filter design aspect of high-density plasma cutting power supply is developed. Converter components are accurately modeled, with parasitic elements extracted to reveal their impacts on the EMI noises. Circuit simulations are used to analyze and minimize the EMI noises. Conducted EMI noise measurement and filter design of this power supply has been achieved while successfully satisfying the FCC class B limits in the frequency range from 150 kHz to 30 MHz. The analyses and experiment results show that the designed filter guarantees that the required attenuation is achieved

Underground Electro Magnetic Interference (EMI) has become so serious that there were false alarms in monitoring system, which induced troubles of coal mine safety in production. In order to overcome difficulties caused by the explosion-proof enclosure of the equipments and the limitation of multiple startup and stop in transient process during EMI measurement, a novel technique was proposed to measure underground EMI distri- bution indirectly and enhance Electromagnetic Campatibility(EMC) of the monitoring sys- tem. The wavelet time-frequency analysis was introduced to underground monitoring sys- tem. Therefore, the sources, the startup time, duration and waveform of EMI could be as- certained correctly based on running records of underground electric equipments. The electrical fast transient/burst (EFT/B) was studied to verify the validity of wavelet analysis. EMI filter was improved in accordance of the EMI distribution gotten from wavelet analysis. Power port immunity was developed obviously. In addition, the method of setting wavelet thresholds was amended based upon conventional thresholds in the wavelet filter design. Therefore the EFT/B of data port was restrained markedly with the wavelet filtering. Coor- dinative effect of EMI power and wavelet filter makes false alarms of monitoring system reduce evidently. It is concluded that wavelet analysis and the improved EMI filter have enhanced the EMC of monitoring system obviously.

This paper focuses on the electromagnetic interference (EMI) generated in a photovoltaic system. Noise caused by inverter has spread to the disturbance both conducted and radiated emissions. In addition, the EMI can be transferred from one mode to another mode; this means that conducted EMI can be transferred to radiated EMI and vice versa. Several emission patterns in such a system will be described to reveal the possible propagation paths of the EMI. To suppress the high-frequency disturbance, a passive EMI filter is added at the DC side of the solar inverter. The overall system is tested in various configurations: mainly with and without EMI filter, and with and without electrical load connected. Finally, the EMI testing results are compared with EMI standard to confirm the effectiveness and benefits of inserting a passive EMI filter in the studied photovoltaic system.

In this article issues related to mathematical modelling of a three-phase common mode choke (CMC) are presented. Influence of the CMC characteristics on the electromagnetic interference (EMI) filter insertion losses is investigated. A novel behavioural model of a three-phase CMC including saturation and non-linear permeability effects in the frequency domain is proposed. Those two phenomena are considered simultaneously in the proposed CMC model. The magnetic hysteresis is based on a mathematical function, describing a dependency between current and inductance and the frequency dependent permeability is realized as a passive electrical network consisting of inductors, capacitors and resistors. The values of the passive components are determined according to permeability characteristics of a particular magnetic material, using the Foster network synthesis algorithm. CMC models based on four different soft-magnetic materials are implemented in LTspice and validated with measurements. A one-stage EMI filter is designed using the behavioural CMC model. Insertion losses of the designed filter with four different CMCs are measured and compared with mathematical models.

A procedure for the derivation of a black-box model of electromagnetic interference (EMI) filters is proposed and discussed. The modeling approach is assessed by resorting to a real EMI filter. The equivalent circuit of the filter is directly obtained from a rational approximation of the scattering-parameter matrix measured at the filter ports. Therefore, the modeling procedure does not require any information on the internal structure of the filter (e.g., components, electrical/magnetic properties of the involved materials, connections leads, etc.). The circuit model is compatible with SPICE solvers and can be used for the prediction of conducted emissions in both the frequency and time domain. Specifically, the proposed modeling approach allows time-domain simulation and performance analysis of EMI filters in combination with power-electronic equipment (i.e., nonlinear, time-variant circuits).

This paper describes ceramic feedthrough capacitor electromagnetic interference (EMI) broadband filter design and installation techniques that generally make cardiac pacemakers and implantable cardioverter defibrillators (ICDs) immune to EMI from handheld wireless communication devices (including cellular phones) and other RF emitters. A typical cardiac pacemaker with four platinum lead wires which egress through a titanium housing (can) via a gold brazed alumina hermetic terminal is studied. The titanium can is seam welded to act both as an electromagnetic shield and a hermetic barrier to protect the internal components from body fluids. These lead wires, which normally carry the pacing pulses and sense cardiac activity, can also act as an antenna and conduct undesirable RF carrier signals (such as EMI induced by cellular phones) to sensitive internal electronic circuits. The EMI filter design described herein effectively de-couples and shields such signals over a broad frequency range before they can enter into the titanium can and disrupt normal pacemaker or ICD functions.

Taking active electromagnetic interference (EMI) filter to attenuate the magnitude of EMI has been verified as a practical and efficient method. During the usage of active EMI filter (AEF), the insertion loss and power consumption are two main aspects that should be well considered. The noise attenuation of AEF is highly related with the impedance close to noise source side. Besides, during the working of AEF, it would also cause extra consumption as the basic working principle of AEF is to rebuild a compensation signal to cancel initial noise signal. And the main op-amp of AEF also needs to be powered. To further improve the performance of AEF, this paper analyzes the application of AEF considering insertion loss and power consumption. Theoretical analyses show that when the impedance of noise source is set to high, the insertion loss of AEF could be better. When the power rate and magnitude of EMI is low, the power consumption benefits. Experimental tests are performed to verify and they shows good agreement compared to analyses.