Design and Implementation of an Active EMI Filter for Common-Mode Noise Reduction

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 investigates the power module design for better common-mode (CM) noise and thermal performance. A high-frequency full-bridge diode rectifier is selected as a case study. The most influential factors in CM noise generation and mitigation are first identified with a simplified CM equivalent model and a comprehensive parametric study. Studies show proper parasitic value and parasitics symmetry can improve CM noise performance. The analysis of packaging structures indicates the vertical module has better CM noise and thermal performance than the traditional lateral wire-bonded module. To validate this, both modules are designed and prototyped for verification. The thermal simulation shows the vertical module exhibits a 25.5% lower thermal resistance from junction to case and a 51% increase of power density in a force-air-cooled condition. Experiments also reveal 15 dB of CM noise reduction from 150 kHz to 6 MHz and a 32% improvement of power density in a force-air-cooling condition. Finally, a case study demonstrates the vertical power module CM noise performance in a typical unsymmetrical topology. This results in a 30 dB CM noise reduction up to 6 MHz.

A multiphase DC-DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC-DC converter that hardly lowers the power density.

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.

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.

The switching frequency of the boost power factor correction (PFC) converter operating in critical conduction mode (CRM) varies in a line cycle, making the conducted electromagnetic interference (EMI) spectra of the converter appear great differences under different input voltage and load conditions. The EMI filter should be designed according to the worst conducted EMI spectrum of the converter, so as to suppress the conducted EMI of the converter to be lower than the standard limits under all working conditions. This paper analyzes the characteristics of the common-mode (CM) and differential-mode (DM) noise spectra of the CRM boost PFC converter, and discusses the effects of the varied switching frequency on the peak, quasi-peak (PK), and average (AV) conducted EMI spectra. It is revealed that, for the conducted EMI limits defined in EN55022 class B, which are specified within 150 kHz to 30 MHz, the EMI filters required for suppressing the QP spectra of the conducted EMI of the CRM boost PFC converter are larger than that for suppressing the AV spectra, and the QP values of the conducted EMI under all working conditions are lower than a certain maximum boundary. The input voltage and load conditions for the worst CM and DM noise spectra of the converter are derived in this paper, thus the repetitive measurements and numerical calculations are avoided. A CRM boost PFC converter prototype is fabricated, and the evaluation of the measured conducted EMI spectra and the EMI filter design example verified the theoretical analysis.

The common-mode (CM) noise in nonisolated dc-dc converters is mainly caused by the displacement current through the high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> node in the circuit and the associated parasitic capacitance, and it may cause electromagnetic interference (EMI) to the surrounding equipments. To reduce the original CM noise and shrink the EMI filter size of non-isolated dc-dc converters, CM noise cancellation methods have been proposed, including the symmetry circuit, balancing technique, passive cancellation and CM voltage cancellation. In these methods, additional components or windings are required for reducing the CM noise. In this article, a new CM noise cancellation method in non-isolated dc–dc converters is proposed by adopting a split-winding configuration. Compared to the existing CM noise cancellation methods which require additional components, the proposed method in the buck, boost and single-ended primary-inductor converter (SEPIC) converters which runs in voltage step-up mode has the identical volume as their conventional circuit configurations. The proposed method is verified for a buck converter by experiment.

Electromagnetic interference (EMI) signals, which radiate in the environment and cause the malfunction of electronic devices in proximity, are generated due to the common mode (CM) noise in differential circuits. This CM noise is produced because of the imbalance in the charging and discharging paths of the driver and equalizer circuits in the transmitter. However, the effects of the equalizer on CM noise have not been examined. This paper systematically investigates the effect of different feed forward equalizer (FFE) configurations on EMI-related CM noise in a 56-Gbps four-level pulse-amplitude modulation (PAM-4) optical transmitter, aiming to provide an optimized configuration with low CM noise and power consumption, while providing high compensation. The simulation results show that an asymmetric equalizer significantly improves the compensation performance. However, the offset in differential pair of output stage should be minimized to decrease the CM noise generated from the FFE.

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.

The wide bandgap semiconductor increases the power density of switching power supplies while bringing about serious common-mode (CM) electromagnetic interference (EMI) problems. Compared to conventional passive EMI filters (PEFs), active EMI filters (AEFs) cancel the noise by sensing and injecting, which significantly reduces the volume of the filter. However, there is a challenge in simultaneously achieving high transient voltage immunity and compact design in the sensing part. Moreover, the high-frequency insertion loss is limited largely due to stray parameters and insufficient bandwidth of active components in the injecting part. To overcome these challenges, this paper presents three key contributions: First, a novel Rogowski coil CM current sensor with lead compensation is proposed. The multivariate function of mutual inductance of the coil is derived and used to reduce the size of sensor while maintaining high sensitivity and high transient voltage immunity. Second, a high-order lead compensation network (LCN) is adopted to counteract the phase lag of active components at high frequencies. Third, the degradations of the injecting part caused by stray parameters are analyzed, and a high-frequency insertion loss enhanced injecting circuit is proposed to mitigate the degradation by closed-loop variable gain control (VGC). The effectiveness of the proposed AEF has been verified on a 3kW inverter experimental platform. With a small size of 38mm*23mm, the proposed AEF achieves an insertion loss of 22.8dB-30.3dB at high frequencies (10MHz-30MHz) and a maximum of 44.7dB at 1.4MHz.

SiC devices can upgrade the inverter performance to a new level by its potentially more than ten times higher switching speed compared to its Si counterpart. However, the high switching frequency and dv/dt, di/dt worsen the electromagnetic interference. Reduction of the common mode (CM) noise of the non-isolated photovoltaic (PV) inverters is addressed by many researchers through adding filters or balancing the circuit. However, most methods rely on the certainty of the parasitics in the system in advance. It is usually not practical for a PV inverter because the parasitic capacitance of PV panels that are to be installed in plants varies from case to case and further can be seriously affected by the damp environment. This article proposes a practical way to reduce the CM noise of the three-level active neutral point clamped (ANPC) inverters with uncertain parasitic capacitance of PV panels. First, the CM model of ANPC inverters with all parasitic capacitances is established. Next, most existing hardware-based reduction methods of the CM noise are summarized based on a unified mathematical model and further compared with each other. After the comparison, a practical method is proposed to reduce the CM noise of the ANPC inverter with uncertain parasitic capacitances, which just adds little volume and cost to the whole system. Finally, the simulation and experiments are conducted to validate the proposed method.

This paper proposes an EMI filter design and optimization method for both AC and DC side in a DC-fed motor drive system. Based on the noise generation and propagation mechanism, the analysis of common mode (CM) and differential mode (DM) EMI noise equivalent circuits is provided. Based on those equivalent circuits, this paper investigates the system EMI noise between AC and DC side, which shows the interaction between DM and CM noises and the interaction between adding AC and DC side filters. With these considerations, an optimized EMI filter design procedure is proposed to design CM and DM filters for both AC and DC sides. To minimize the impact on the EMI noise of one side caused by adding filter on the other side, certain order must be followed to design AC and DC CM and DM filters. Moreover, the EMI filter weight optimization method is also discussed to get the minimum weight of EMI filter and improve system power density. Simulation and experimental results verify the interaction between AC and DC filters and show that EMI filters can be designed to suppress both AC and DC EMI noise to meet the standard with the proposed EMI filter design method.

This paper describes the investigation of Common Mode (CM) noise and Differential Mode (DM) noises in Dual Active Bridge (DAB) converter applied in Electric Vehicle (EV) in order to reduce the Electromagnetic Interference (EMI) that occurs in EVs. The DAB converter is designed and simulated using a spice simulator and the CM and DM noises from the converter circuit were measured as per the CISPR 25 EMI Standard. Based on the simulated results, the attenuation level of noise was calculated and used to design the components of the EMI filter. The design was validated using the simulation findings after the converter are created, tested and the experimental results compared. Based on the results and discussion, recommendations are made in this paper to reduce EMI in converters used in EV. Especially, suggestions to reduce the common mode and differential mode noises produced by Dual Active Bridge converters employed in EV were given as per the CISPR 25 standard.

Common-mode (CM) noise cancellation method is an attractive approach to reduce the original CM noise in power converters, which helps to shrink the size of electromagnetic interference filter. Traditional CM noise cancellation method cancels the CM noise current by adding a branch consisted of a compensation voltage source and a compensation capacitor, which generates a cancellation current and nullifies the noise current. As the duality, the voltage cancellation method is also feasible for reducing the CM noise, which has not been investigated in dc–dc converters. In this article, a common-mode voltage cancellation (CMVC) method is proposed, which cancels the CM voltage of the converter by inserting compensation voltage source into the input power cord. The requirement for achieving CMVC is that the cancellation voltage and the parasitic capacitances in the circuit are matched. The applications of CMVC method in basic nonisolated and isolated dc–dc converters are presented, and the considerations for practical applications of this method are discussed. Finally, a buck converter and a half-bridge LLC resonant converter prototype are built, and the proposed method is verified by experiment, respectively.

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.