Active EMI Filter Research Articles

Multi-current injection active EMI filter for DC-AC converters

Multi-current injection active EMI filter for DC-AC converters

Insertion Loss Analysis and Optimization of a Current based Common-Mode Active EMI filter

Insertion Loss Analysis and Optimization of a Current based Common-Mode Active EMI filter

Parallel-Cascaded Narrow-Band Adaptive Digital Active EMI Filters for Broadband CM-Noise Reduction in Motor Inverters

Parallel-Cascaded Narrow-Band Adaptive Digital Active EMI Filters for Broadband CM-Noise Reduction in Motor Inverters

Frequency Characteristics of Insertion Loss and Loop Gain of VSCC Feedback Active EMI Filters

Frequency Characteristics of Insertion Loss and Loop Gain of VSCC Feedback Active EMI Filters

Innovative measurement and noise reduction of voltage coupling in shielded cables for enhanced signal integrity

The reliable transmission of electrical signals through shielded cables in the presence of electromagnetic interference (EMI) remains a critical challenge for signal integrity. This paper presents a novel and comprehensive approach for measuring and reducing voltage coupling in shielded cables connected to a shielded room from a waveguide. Additionally, we introduce an innovative active EMI filter to effectively mitigate common-mode (CM) and differential-mode (DM) noises, thereby enhancing the overall signal quality. To address the issue of voltage coupling, an open circuit method with a transmission line is considered for the measurement of output voltage at the end of the shielded cable. In order to assess the impact of EMI on transmitted signals, we utilize a state-of-the-art noise separator that enables precise differentiation and characterization of CM and DM noise components. This analysis provides valuable insights into the overall noise profile, guiding the subsequent steps toward noise reduction. An active EMI filter was designed to effectively attenuate the unwanted noise. The filter intelligently targets and mitigates both CM and DM noises, resulting in improved signal integrity. The experimental setup encompasses a shielded room, shielded cables, a waveguide, and the equipment. The obtained output voltage from the shielded cable is 495 V. It is given as an input to the equipment (Cuk converter). The noises are generated when the input voltage is given; the noises are separated by using a noise separator. CM noise obtained at the output of an active noise separator is 118.8 dBµV. DM noise obtained at the output of a differential mode noise separator is 115.8 dBµV. With the active EMI filter, we achieve remarkable reductions in CM and DM noise levels. After adding a filter to the circuit, the noises are reduced below the limit line according to the International Special Committee on Radio Interference standard; the CM noise is 44.8 dBµV and the DM noise is 47.8 dBµV.

Multi-Amplification-Channel Active EMI Filter Based on Period Spread-Spectrum PWM for Common-Mode EMI Suppression

Due to the existing coupling loop between the motor drive system and the ground, when switching devices in the drive system operate at a high speed, common-mode (CM)-conducted electromagnetic interference (EMI) is generated in the loop. The electromagnetic environment quality of the motor and peripheral equipment is reduced. As a small and lightweight EMI suppression device, the active EMI filter (AEF) can be used in the motor drive system to suppress the CM-conducted EMI. As the unity gain bandwidth of the operational amplifier (OPAMP) in the AEF is fixed, the CM-conducted EMI suppression effect of the AEF is poor. To solve this problem, the multiple-amplification-channel method is used to spread the frequency range of the CM voltage that the AEF can sense; therefore, the frequency of the compensation current output using the AEF is more complete, and a better CM-conducted EMI attenuation effect is obtained. At the same time, a combination of the period frequency carrier modulation (PCFM) and the multi-amplification-channel AEF is adopted so that the CM-conducted EMI in the whole EMI frequency range of the motor drive system is effectively suppressed.

Dual-current-injection CSCC Active Common-mode EMI Filters with High Insertion Loss for DC-DC Converters

Dual-current-injection CSCC Active Common-mode EMI Filters with High Insertion Loss for DC-DC Converters

A Virtual Impedance Enhancement Based Transformer-Less Active EMI Filter for Conducted EMI Suppression in Power Converters

Due to the successive switching actions in a power electronic system, considerable conducted electromagnetic interference (EMI) is generated. This has been a major concern in designing power converters, which requires additional EMI filtering efforts. Passive EMI filters are the most common solutions to EMI reduction but usually consume a large portion of the volume as well as weight in power converters. Active EMI filters (AEFs) or hybrid EMI filters (HEFs) are considered best candidates over traditional passive EMI filters to achieve higher power density in power converters. The utilization of current transformer to sense or to compensate the EMI noise can increase the volume of an AEF. In this article, a transformer-less AEF, sprung from the concept of virtual impedance enhancement, is proposed. The proposed design features feedforward control with current-sensing-voltage-compensating. The operation principle of the proposed AEF is thoroughly introduced, and its performance is evaluated through simulations and experiments. Experimental results with an ac–dc power converter and a dc–ac inverter show that the proposed AEF can be generally applied to reduce conducted EMI on either ac or dc power lines.

Considerations for Gain Selection of Feedforward Active EMI Filters

The reduction of the electromagnetic interference (EMI) is an important issue in the design of switching power converters. The passive EMI filter has been widely used for the reduction of the conducted EMI. The active EMI filter (AEF) has recently been considered as a useful alternate for the small sized implementation. This paper deals with an optimal design of a voltage sensing and voltage cancellation (VSVC) type feedforward AEF. The ideal feedforward AEF is theoretically stable because it does not have any feedback loop. However, some non-ideal factors such as the source and load impedances cause the unstable operation of the AEF for certain AEF gains, which limits the magnitude of the gain and degrades the performance of the AEF. In order to overcome this problem, the method of selecting the optimum AEF gain is studied with considering both the stability and AEF performance using the concept of the symmetry. The characteristics of the cancellation loop for the AEF including the source and load impedances is first investigated in view of the stability. The boundary of the maximum AEF gain to ensure the stable operation is then discussed based on the theoretic analysis and experimental works for the actual AEF. The results can be used for implementing the AEF with the optimum EMI reduction performance.

Common-mode Electromagnetic Interference Mitigation for Solid-state Transformers

Solid-state transformers (SSTs) have been widely used in many areas owing to their advantages of high-frequency isolation and high power density. However, high-frequency switching causes severe electromagnetic interference (EMI) problems. Particularly, the common-mode (CM) EMI caused by the switching of the dual active bridge (DAB) converter is conducted through the parasitic capacitances in the high-frequency transformer and impacts the system reliability. With the understanding of the CM EMI model in SSTs, CM EMI mitigation methods have been studied. For passive mitigation, the coupled inductor can be integrated with the phase-shift inductor function to reduce CM EMI. For active mitigation, variations in the DAB switching frequency can help reduce the CM EMI peak. An active EMI filter can also be designed to sample and compensate for CM EMI. Using these methods, CM EMI can be reduced in SSTs.

A Novel Neutral Point-Based Active EMI Filter for Common Mode Noise Attenuation

This paper proposed a new configuration of neutral point based common mode (CM) active EMI filter (NP-CM-AEF). It is achieved by setting the reference of filtering system to the neutral point of equipment under test (EUT). Therefore, CM noise could be sensed across neutral point and ground. Meanwhile, compensation signal could be built by op-amp and re-injected to cancel the initial CM noise. The main advantage of the proposed NP-CM-AEF lies in that no more noise separation such as bulky passive CM transformer is needed to get pure CM noise. The whole filter becomes smaller, lighter and more compact compared with traditional CM AEF. Working principle is analyzed in details and hardware experimental tests are also performed. It shows that the proposed NP-CM-AEF has a good attenuation to CM noise and total size is pretty tiny.

A New Integrated Active EMI Filter Topology With Both CM Noise and DM Noise Attenuation

Integration of electromagnetic interference (EMI) filters is a good idea to further decrease the volume and weight of a power converter. However, the conventional research articles mainly focus on the integration of passive components or planar printed circuit board structures. This article proposes a new integrated active EMI filter (AEF) topology. It can attenuate both common-mode (CM) and differential-mode (DM) noise at the same time. Different from the traditional discrete CM AEFs and DM AEFs, noise sensing and cancelation of this proposed topology are performed simultaneously. The working principle and special features of this topology are analyzed in detail. Based upon the theoretical analysis, the insertion loss of this integration topology is close to the traditional separated CM AEFs or DM AEFs. Besides fewer components and dc power supply are demanded. A prototype is built and tested through experiments. Experimental results derived on standard test board and practical converter show good agreement to theoretical analysis.

An Active EMI Filter in Grounding Circuit for DC Side CM EMI Suppression in Motor Drive System

In this article, an active electromagnetic interference (EMI) filter is designed to reduce the dc side common mode (CM) EMI in motor drive system. Different from the traditional passive EMI filter which is added in the main circuit, the designed active EMI filter (AEF) in this article is added in the grounding circuit which is connected between motor frame and the ground and it can be decoupled from the main circuit. By properly setting the components value, the dc side CM EMI can be suppressed while maintaining a low motor frame voltage. The structure of the AEF is simple and the volume of the AEF can be kept small. The operation principle of the AEF is introduced first and the performance of this AEF is evaluated through simulation. Experiment results verified the effect of this AEF that it can suppress the dc side CM EMI and the motor frame voltage can be kept low.

Investigation of Cascade Connection Method to Improve the Insertion Loss of DM Active EMI Filters

In this article, a new kind of cascade connection method of differential mode (DM) active EMI filter (AEF) is put forward. Contrary to the conventional idea, it is found different kinds of cascade AEF connections show different insertion loss (IL). Based upon the mathematical analysis, among the eight potential connection methods, two cascade AEF-connection methods are more effective than the other six methods. The IL is much higher than the others. Therefore, the two effective topologies are further analyzed from several perspectives. And the best topology suiting the practical application is found. Several prototypes are fabricated and tested. Experimental results show good agreement with the theoretical calculation.

A Customized Integrated Circuit for Active EMI Filter With High Reliability and Scalability

This article proposes an active electromagnetic interference (EMI) filter (AEF) realized by a customized integrated circuit (IC) to reduce conducted emission noises. A fully transformer-isolated feedforward current-sense current-compensation structure is selected as a base topology of the AEF. To achieve the high reliability of the proposed AEF by using low-voltage IC devices, the injection transformer is added to protect IC devices from high-voltage hazards. The operation of the proposed AEF is theoretically demonstrated, and practical design guidelines for the IC part and nearby components are developed. The designed IC was fabricated by a 0.18 μm bipolar-CMOS-DMOS process. The fabricated IC is implemented in a compact printed circuit board for application to a three-phase inverter motor system. The performance, stability, and surge immunity of the AEF are experimentally demonstrated. A designed 1stage AEF achieves better noise-attenuation performance than 2stage passive EMI filters (PEFs) over 6 dB at 150 kHz without critical resonance peak at the high-frequency range. Weak points of the conventional PEFs in both low and high frequencies are effectively improved by using the proposed 1stage AEF. In addition, the surge immunity of the designed IC within the AEF is validated under numerous 5 kV surge tests.

A Motor CM Impedance Based Transformerless Active EMI Filter for DC-Side Common-Mode EMI Suppression in Motor Drive System

Due to the continuous switching action of the inverter in the motor drive system, an electromagnetic interference (EMI) is generated in the system. Active EMI filter has a smaller volume and higher power density compared with the widely used passive EMI filter. However, for the conventional voltage-sensing voltage-compensating active filter and the current-sensing current-compensating active EMI filter, the active EMI filter itself needs a transformer to compensate or to sense the EMI noise and this will increase the volume of the active EMI filter. In order to save the sensing or the compensating transformer required by the active EMI filter itself, a voltage-sensing current-compensating active EMI filter for the motor drive system is designed. Combining the sensed common-mode (CM) voltage with the artificially fitted ac-side CM impedance network, the adverse CM current can be generated that can be used to suppress the dc-side CM EMI. This active EMI filter itself does not need any transformer in principle. Experimental results have validated the effectiveness of the proposed active EMI filter. It is shown that using this active EMI filter can simplify the structure of the active EMI filter and effectively suppress the dc-side EMI.

Modeling and Analysis of a Differential Mode Active EMI Filter With an Analog Twin Circuit

Conventional passive EMI filters are bulky and occupy up to 30% of converter volume and weight. Active EMI filters are a key technology that enables the volume reduction of passive components in the EMI filter. The effectiveness of traditional active EMI filter for volume reduction is limited by the additional overhead from the passive components for noise sensing and compensation to ensure stability. In this article, a novel active EMI filter is proposed and demonstrated for differential mode noise attenuation. The filter consists of a twin circuit made up of low voltage/current components that mimic the high-power passive filter components in the main circuit. Unlike the conventional active EMI filter, the proposed filter uses compensation networks which consists of low-voltage surface-mount components only. The modeling of the entire circuit is carried out, and verified with small-signal measurements. The filter is then tested in a converter and the experimental results are shown to be consistent with the model and the small-signal measurements.

Active cancellation of periodic EMI of power electronic systems by injecting artificially synthesized signals

Active EMI cancellation is an interesting solution to reduce the size of passive filter components. In this work, the already established active EMI filter types are summarized. The systematic limitations are elaborated that result from the feedback or feedforward approach for cancellation signal generation. Afterward, a new method is presented in which the cancellation signal is artificially synthesized and injected into the system. This method is especially well suited for the suppression of periodic EMI since the anti-EMI can conveniently be synthesized from cancelling sine waves. Bothersome effects, like complex frequency characteristics or delays, can be compensated by appropriate amplitudes and phases. By doing so, systematic limitations of active EMI filters can be resolved. In this work, the fundamental concept and possible variants are depicted. Although many limitations of active EMI filters are resolved, also the new method has its limits. These are described and discussed. Furthermore, different methods for determining the cancelling sine waves are summarized. Last, a prototype cancellation system is presented and discussed to suppress the EMI of a GaN-based 48 V/12 V DC-to-DC converter with a switching frequency of 300 kHz. The disturbances are actively suppressed below the strictest limit (class 5) of the automotive standard CISPR 25 in the frequency range from 150 kHz to 30 MHz. The active suppression of the cancellation system and the passive attenuation of the coupling circuits are individually investigated to elaborate the performance of the active cancellation strategy. The power of the generated cancellation signal is estimated.

A Survey of Active EMI Filters for Conducted EMI Noise Reduction in Power Electronic Converters

Wide bandgap devices enable high power density power converters. Despite the advantages of increased switching frequency, the passive components are still a major bottleneck toward enabling high power density. Among the passive components in the converter, the passive electromagnetic interference (EMI) filters are unavoidable to ensure compliance with conducted EMI standards. Active EMI filters (AEFs) help reduce the volume of the passive components and have been around for three decades now. The design and implementation of the AEFs depend upon the type of noise (common-mode or differential-mode) and power converter (ac–dc, dc–dc or inverter). This article presents a comprehensive survey of different AEFs and their implementations for different power converters presented in the literature. A comprehensive survey of noise-sensing, noise-processing, and noise-cancellation circuits is presented. Also, a comparison of attenuation provided by the AEFs for common-mode and differential-mode noises for different converters is carried out. Furthermore, other facets of AEFs such as the auxiliary power supply, power loss, and protection methods for the AEF are also summarized. This article is intended to be a useful reference for power converter designers in both industry and academia.

Active EMI Filter Design With a Modified LCL-LC Filter for Single-Phase Grid-Connected Inverter in Vehicle-to-Grid Application

More and more attention has been gained in the vehicle-to-grid (V2G) system due to its attractive features, such as transferring bidirectional power between electric vehicles and grid, regulating grid voltage/frequency. This paper develops the active electromagnetic interference (EMI) filter (AEF) with significant system volume and weight reduction compared to the traditional passive EMI filter (PEF). While the high-frequency parasitic parameters of the AEF and the restricted loop gain result in limited AEF EMI noise attenuation in the high-frequency range. Thus, an additional passive EMI filter is commonly needed to suppress the EMI noise. For avoiding external passive filter components, the active EMI filter is designed and integrated with a modified LCL-LC filter as a hybrid filter to guarantee EMI noise attenuation. The modified LCL-LC filter can maintain satisfactory harmonic suppression with a higher EMI reduction ability compared to other types of harmonic filters. Based on a single-phase grid-connected inverter, the total harmonic distortion (THD) and the conducted EMI measurement results are compared with the results of traditional LCL, LLCL, LCL-LC filters. The effectiveness of the proposed circuit is verified by simulation and experimental results. The proposed circuit successfully improves the filter design of the inverter in the suppression of harmonics and EMI noise.