Common-mode Electromagnetic Interference Filter Research Articles

Comparative Study of Conducted Common-Mode EMI in WBG-Enabled DC-Fed Three-Phase Current-Source Inverter

In pulsewidth-modulated (PWM) inverters, common-mode (CM) voltage and associated conducted CM electromagnetic interference (EMI) can cause motor bearing failures, ground leakage current, and audio susceptibility issues. When wide bandgap (WBG) devices are used to construct a voltage-source inverter (VSI), the CM EMI issues become more challenging. The current-source inverter (CSI) is an alternative, which produces more sinusoidal output voltage waveforms, making it a promising topology for reducing CM EMI in power converters. However, there is little systematic and comprehensive analysis of CSI’s CM EMI, especially when using WBG devices. The conducted CM EMI generation mechanisms of dc-fed two-level VSIs and CSIs are compared in this article. The analytical derivation and the circuit analysis are performed to identify the CM EMI generation mechanisms in both inverters, including CM voltage sources and the resulting CM current flowing paths. The effects of WBG devices on the CM EMI of both inverters are discussed. New CM EMI equivalent circuits (EQCs) of both inverters are analytically derived to reduce the computational time of full-circuit CM EMI simulation. Different filtering schemes and inverter topology variations’ impacts on CSI’s CM EMI are evaluated using the derived EQC. An effective CM EMI filter is designed to suppress the CSI’s CM EMI to be lower than EMI standards.

Planar Common-Mode EMI Filter Design and Optimization for High-Altitude 100-kW SiC Inverter/Rectifier System

Silicon-carbide (SiC) devices are receiving popularity for high-power converter systems in aircraft due to many advantages over silicon counterparts. However, the electromagnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speeds and higher switching frequencies. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude applications due to the harsher requirements of insulation and heat dissipation. The optimization of the parameters and physical design of a CM EMI filter in a 100-kW SiC inverter/rectifier system operating at 50 000 ft is conducted in this article to obtain the highest power density. The effect of the switching frequency on the EMI filter volume and the total power density of the converter system is analyzed. The lower breakdown voltage of air and the higher thermal resistance of natural convection make the conventional design of the CM choke infeasible at high altitudes. A printed circuit board (PCB)-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50 000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls the electric-field intensity in the air below 300 V/mm. The PCB windings improve the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50 000 ft and the thermal performance is excellent with a current of 190 A. With the optimization and the dedicated design of the CM EMI filter, the power density of the converter system is up to 33.3 kW/L.

A Compact EMI Filter Design by Reducing the Common-Mode Inductance With Chaotic PWM Technique

Passive electromagnetic interference filters (PEFs) are the most common way to solve electromagnetic interference (EMI) problems in power converters. However, PEFs bring additional volume, weight, and cost for power converters, especially common-mode (CM) inductors in PEFs, and it is a tricky issue for the high-power-density converters that must meet the electromagnetic compatibility specification. In order to design compact PEFs for power converters with pulsewidth modulation (PWM), a volume reduction method of CM inductors with chaotic PWM (CPWM) is proposed in this article. First, the mechanism that CPWM reduces the CM inductance by increasing the corner frequency is analyzed. Second, the relationship between the reduction of EMI spectrum magnitude by CPWM and the decrease of the CM inductance is quantitatively calculated. Third, utilization rate of the magnetic core <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</i> is defined to reasonably compare the size of the different inductors under traditional PWM and CPWM. Finally, the proposed design method of CM EMI filters is applied into a dc–dc converter and a dc–ac inverter, respectively, to verify its effectiveness and feasibility. In a dc–dc converter with the switching frequency 100 kHz, 275 W, the volume of the CM inductor and the volume of CM EMI filters are reduced by 63.5% and 48.3%, respectively, by using the proposed compact EMI filter.

An Integrated EMI Filter Scheme for Paralleled Inverter With Zero-CM PWM Algorithm

Motor drive system generates harmful differential mode (DM) and common mode (CM) electromagnetic interference (EMI) when it is working. To solve this problem, the integrated EMI filter scheme for paralleled inverter using zero-CM pulsewidth modulation (PWM) algorithm is proposed in this article. The zero-CM PWM algorithm and the coupled inductor constitute a holistic solution for the ac side EMI suppression. By using the zero-CM PWM algorithm, the CM leakage current of the system can be suppressed without adding additional CM EMI filter and only DM EMI needs to be considered. In addition, the DM inductor is naturally integrated in the coupled inductor, leakage inductance of the coupled inductor instead of the discrete DM inductor is used as the DM inductor which has less restrictions on the inductor material. The DM EMI filter can be constructed by just adding DM capacitors. Thus, using the integrated EMI filter scheme has advantageous over traditional scheme since the CM EMI filter is omitted and only DM capacitor is added which can simplify and reduce the size of EMI filter in the ac side and has the potential to increase the power density of the system since other solutions require both the DM and CM EMI filter.

Design of Passive Common-Mode Attenuation Methods for Inverter-Fed Induction Motor Drive With Reduced Common-Mode Voltage PWM Technique

This paper investigates the influence of active zero vector pulsewidth modulation (AZPWM-1) and space vector pulsewidth modulation (SVPWM) on the design of passive common-mode (CM) attenuation methods to reduce CM current and shaft voltage in inverter-fed V/f-controlled induction motor drives. The passive CM attenuation methods examined here are the CM choke, the CM electromagnetic interference (EMI) filter, and the CM transformer. The attenuation requirement of AZPWM-1 and SVPWM is identified to design the passive CM choke and EMI filter. Based on the attenuation requirement, the design guidelines are revisited for SVPWM, and design rules are proposed for AZPWM-1. However, the CM transformer is designed based on the step change in magnitude of CM voltage of both the pulsewidth modulations (PWMs). The limitations in design, regarding switching frequency and component size for each case, are also established. It is shown that to have a similar attenuation in the considered two PWM cases, AZPWM-1 requires smaller passive components compared to SVPWM. The proposed design guidelines are substantiated with experimental results on a 1.1-kW induction motor drive.

A Multi-Function Common Mode Choke Based on Active CM EMI Filters for AC/DC Power Converters

It is widely believed that hybrid electromagnetic interference (EMI) filter (HEF) is one of the most optimized solutions for EMI elimination. Nevertheless, the desire for a smaller and lighter filtering method has never stopped. To further reduce the size and weight of a hybrid EMI filter, this paper proposes a multi-function common mode choke (MCMC) used in HEF. It differs from the traditional common mode (CM) choke in that two functions of (1) CM signal sensing and (2) CM noise suppression are integrated into one choke. In such a proposed MCMC design, the traditional current transformer (CT) is eliminated in the hybrid filter topology. This technique could reduce the size, weight, and cost of the filter to a great extent. Based on the MCMC, a novel CM filter is proposed to achieve high-performance noise suppression. System model and stability feature of the new filter are developed and investigated in detail. A filter prototype based on the proposed MCMC is constructed. It is tested on a 100-W commercial ac/dc converter. The experimental results show that the proposed CM filter can provide better EMI noise suppression with a smaller size. The insertion loss could reach 50 dB at low frequencies and 40 dB at high frequencies.

EMI filter design of single-phase SiC MOSFET inverter with extracted noise source impedance

This paper presents an electromagnetic interference (EMI) filter design procedure for a single-phase SiC MOSFET inverter. To ensure the EMI filter performance is both accurate and effective, the equivalent noise source impedances of common mode (CM) and differential mode (DM) noise models are extracted. Then the CM and DM EMI filters can be designed based on the known CM and DM noise source impedances, respectively. The EMI filter design based on the proposed method is validated both through simulation and experiments. The simulation and experiment results have verified the effectiveness of the proposed method.

Investigating Switching Transformers for Common Mode EMI Reduction to Remove Common Mode EMI Filters and Y-Capacitors in Flyback Converters

This paper investigated the common mode (CM) noise model for multiwinding switching transformers. Based on the proposed model, a Flyback transformer is investigated. A measurement technique is used to characterize and evaluate a switching transformer’s CM noise performance. Only a signal generator and an oscilloscope are needed in this measurement technique. Because there is no any in-circuit tests are needed, the technique can help quickly design and evaluate transformers in mass testing. CM noise reduction techniques, including the balance capacitor technique, core shielding technique, balance winding technique, and winding design technique, are investigated based on the developed two-capacitance model and measurement technique without introducing extra power loss. The near-field capacitive coupling due to transformer magnetic cores is analyzed, and a core shielding technique is applied to reduce the coupling. Experimental results validated the proposed model and the developed CM noise reduction techniques. The Flyback converter can finally meet electromagnetic interference (EMI) standards without using CM EMI filters and Y-capacitors.

Techniques for Improving the High-Frequency Performance of the Planar CM EMI Filter

This paper has developed two techniques to reduce the parasitic parameters and improve the high-frequency performance of the planar integrated electromagnetic interference (EMI) filter. First, each developed technique has been analyzed, respectively, then the performance of an EMI filter with both the developed techniques has been researched. The research contents are as follows. 1) Analyzing the improvement of the equivalent parallel capacitance (EPC) for a common mode (CM) EMI filter by two CM windings overlapped and interleaved layout. The EPC of the integrated EMI filter is about 14% of the reference EMI filter. 2) Analyzing the improvement of the equivalent series inductance (ESL) in the parallel branch for a CM EMI filter by each CM winding coupled with two ground winding layers. The resonance frequency brought by ESL is shifted to a higher frequency. At 30 MHz, the insertion loss is increased by 45 dB compared with the reference. In the mean time, the structure is equivalent to a two-stage L-type low-pass filter, which can largely increase the high-frequency attenuation compared with the one-stage L-type low-pass filter for the reference one. (3) Researching the performance of an EMI filter with both the proposed techniques. The developed EMI filter can not only decrease the EPC, but also reduce the negative effect of ESL. The developed EMI filter improves the high-frequency performance dramatically compared with the EMI filter with only one of the developed techniques. In the mean time, the differential mode (DM) capacitor is formed by the two overlapped and interleaved windings, and does not need an extra lumped DM capacitor. Therefore, CM inductors, CM capacitors, and DM capacitors can be integrated in the overlapped and interleaved L-C winding structure, so miniaturized EMI filter can be realized. The experiment results indicate effectiveness of the developed integrated EMI filters, and the cost and complexity is the same as the reference EMI filter.

Electromagnetic Interference Mitigation for Inverter fed AC Drives

Problem statement: In switched mode PWM inverter EMI noise occurs during high (dv/dt) transient period. This EMI noise is mitigated using Active Common mode EMI filter in front of the source. Approach: This study proposes a new active common mode Electromagnetic Interference (EMI) filter for switched mode PWM Inverter applications. The proposed filter is based on current sensing and compensation circuit which utilizes fast transistor amplifier for current compensation. The amplifier is biased with an isolated low voltage DC power supply. Hence it is possible to construct an active filter independent of the source voltage of equipment. Thus this filter can be used in any application regardless of working voltage. The proposed switched mode PWM inverter operated in 180° mode of operation. It’s otherwise called as quasi square wave mode. Results: Simulation of output wave form is verified by using MATLAB Simulink model results and also its effectiveness has been verified hardware output wave forms. The hardware for this project is designed and developed for 50V, 50Hz three phase Fractional Horse Power (FHP) motor. Conclusion: In this Study the concept of the new active common mode EMI filter and quasi square PWM inverter has been proposed. The corresponding simulated output waveforms are verified with the Active Common mode EMI filter; it is possible to use low-voltage transistors for the amplifier by introducing coupling capacitors between the power line and the amplifier circuit. Thus the ACEF can be applied to various power electronic systems regardless of the working voltage. Also it helps in improving the performance of additional filter stages.

Series-Connected Grounding of Common-Mode EMI Filter

Due to the effects of parasitic inductance, the common groundline (CGL) of capacitors in common-mode (CM) electromagnetic interference (EMI) filter is influential to filtration performance of the filter. In this paper, the effect of a single-point grounding method of CM EMI filter is first analyzed, and then, in order to eliminate the negative effect of CGL, a series-connected grounding method is introduced and analyzed. The effectiveness of the series-connected grounding method on improving the performance of CM EMI filter with CGL is verified through experiment.

Parasitic Effects of Grounding Paths on Common-Mode EMI Filter's Performance in Power Electronics Systems

High-frequency common-mode (CM) electromagnetic-interference (EMI) noise is difficult to suppress in electronics systems. EMI filters are used to suppress CM noise, but their performance is greatly affected by the parasitic effects of the grounding paths. In this paper, the parasitic effects of the grounding paths on an EMI filter's performance are investigated in a motor-drive system. The effects of the mutual inductance between two grounding paths are explored. Guidelines for the grounding of CM EMI filters are derived. Simulations and experiments are finally carried out to verify the theoretical analysis.

Design of Grid-Side Electromagnetic Interference Filters in AC Motor Drives With Motor-Side Common Mode Active Compensation

The aim of this paper is to analyze how the introduction of a motor-side common mode (CM) active filter, in a power drive system, influences the CM disturbance propagation. A circuit model of the whole drive, including the active filter, is used as an investigation tool. The accuracy of all simulated results is validated by experimental measurements. Both the electromagnetic interference (EMI) toward the grid and the internal CM disturbance propagation are analyzed. These phenomena are compared when the power drive system is operated both with and without the active filter at the inverter output. An additional effect of the motor-side CM active filter is a slight reduction of EMI toward the grid at lower frequencies. This condition allows a reduction in the size of the power grid CM EMI filter necessary to achieve electromagnetic compatibility requirements compliance for the drive.

Modeling of Parasitic Inductive Couplings in a Pi-Shaped Common Mode EMI Filter

This paper analyzes the effects of parasitic inductive couplings among the filter components and printed circuit board traces in a pi-shaped common mode (CM) electromagnetic interference (EMI) filter. The result shows that some parasitic inductive couplings related with CM choke do not affect the CM EMI filter performance. And then, it proposes a high-frequency circuit model for filtration performance evaluation and prediction for pi-shaped CM EMI filter, in which the parasitic inductive coupling between input and output loops of the investigated filter is considered to be the crucial coupling parameter while other parasitic couplings are ignored. The model is simple because only one coupling parameter is involved. A procedure is introduced to extract the inductive coupling between input and output loops in pi-shaped CM EMI filter using Z parameters through virtual prototyping. Simulation and experiment finally validate the model.

Conducted EMI in PWM inverter for household electric appliance

This paper presents the mitigation effort of the conducted electromagnetic interference (EMI) in the pulsewidth-modulation (PWM) inverter for household electric appliances. First, noise sources in the PWM inverter are investigated to get an understanding of their characteristics, and the propagation of the conducted EMI is described. Next, input filters are added to: suppress it. With changing filter stages, the conducted EMI spectra are measured to identify their effect. The common-mode EMI spectrum is extracted to separate the effect of the common-mode filter and to identify the dominant noise source. A new active common-mode EMI filter is proposed to give better attenuation of the common-mode noise and to enhance the performance of additional passive filters. An efficient way to design of input filter is discussed based on the measurement results.