An Active Trap EMI Filter Based on Impedance Modulation for Switching Mode Power Supply

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.

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.

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.

This paper studies the conducted electromagnetic interference (EMI) problems in a DC/DC switched-mode power supply (SMPS) with semi-isolated topology. A high frequency circuit simulation model is firstly established to predict the conducted emissions of this power supply. Then the common mode (CM) and the differential mode (DM) conducted emission mechanisms of this power supply are analyzed in detail according to its working principle and structure. The voltage of the rectifier diodes at the transformer's secondary is founded to be the main CM EMI sources. A DM noise coupling phenomenon from the voltage ripple of output port is discovered and its role on EMI emission is explained too. Based on conduced emission paths analysis, three kinds of EMI filters, including traditional input EMI filter, high frequency input and output port EMI filters and a new DM topology filter are proposed to restrain the conducted emissions respectively. Their effectiveness is verified with experiments and the merits and drawbacks of different designs are also introduced.

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.

Electromagnetic interference (EMI) is one of the main issues in Brushless Direct Current (BLDC) motors, which harms efficiency, reliability, and international EMI regulations. Traditional methods of suppression are not always flexible and deteriorate performance, which requires solutions of high quality. To solve this, a new system, Enhanced EMI Resilience Optimization System (EEROS), is proposed, which combines three new methods: Active Common Mode Swarm-Enhanced EMI Mitigation System (ACS-EMS), Adaptive Power Management EMI Control System (APM-ECS), and Adaptive Spread Spectrum-Filtered Genetic EMI Suppression (ASSF-GES). These techniques use Spread Spectrum Modulation (SSM), Active EMI Filters (AEF), Genetic Algorithms (GA), Particle Swarm Optimization (PSO), and Dynamic Frequency Modulation (DFM) to create dynamic suppression of high-frequency EMI and motor efficiency of 98%, thermal stability of 59℃, and responsiveness of 98%. The paper also analyses how the variations of control parameters affect the EMI suppression and performance trade-offs and proves the existence of a strong and high-efficiency mitigation framework. The proposed system offers a scalable solution to automotive, industrial and aerospace applications and has better EMI resilience, regulatory compliance and operational reliability.

Due to advances in power transistor technologies, higher switching frequencies and steeper switching slopes are used in motor inverters to achieve higher efficiency and power density. However, this leads to increased electromagnetic interference (EMI). Conventional passive filter topologies can use a considerable amount of space and contain heavy components, reducing overall power density. To minimize volume and weight of passive filters, active EMI filters can be used. In this work, a novel EMI cancellation method for pulsewidth modulation controlled three-phase motor inverters is presented in a feasibility study. This method injects a cancellation signal by applying a filter to the digital transistor control signals of the motor inverter. By slightly delaying the control signals before they reach the transistor gates, the time required to synthesize and inject the cancellation signal can be compensated. The digital filter parameters are adapted continuously based on the measured noise signal to achieve maximum filter performance. First, the new method is described in general. After that, the applicability to power electronics is discussed. For demonstration, the system is applied to a motor inverter with GaN transistors to reduce the conducted common mode EMI at the input side of the inverter. The results are shown and discussed for different operation modes.

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.

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.

Technology Brief Over the last two decades, the use of sophisticated electronic equipment to test and measure the size of prospective finds has increased rapidly throughout the global oil industry. Today, "downhole" cables often carry down electricity controlled by programmable DC power supplies to power drilling equipment located 30,000 feet beneath the surface, and then send sensitive telemetry data back up to computers. In these situations, electrical "noise" can diminish data transmission rates, slowing down acquisition data used by the geologists to map petroleum finds, or even lead to the complete loss of data through power surges that cause computers to reset. In addition, in order to develop 3D maps of a find, drilling companies are now using sensitive electronic data measurement equipment that can be disrupted by power surges. In any case, the cost of reacquiring this lost data can be expensive. Soft switching in power supplies is an advanced technological solution to the noise and power surge issue involved in the oil drilling industry. Although relatively new, soft switching power conversion has already found widespread acceptance among electronic manufacturers. Yet, as with all new technologies, questions still abound among end users. What are the advantages, and how can soft switching help oil exploration and drilling teams? First, the origins of soft switching. Soft switching is a superior switch-mode power supply topology (technology) developed by power supply manufacturers that dramatically reduces the electrical noise created by the main power transistors during the switching process, the micro-moment in time when the power supply is switched on and off. (see Figure 1) Its main function is to reduce or eliminate radio frequency interference (RFI) and other problems that have been associated with the switching process since the emergence of high-frequency "hard switching" switch mode power supplies in the 1980s. Around that time, there was a rapid increase in the use of electronic products in all manner of industrial applications. This, in combination with the phenomena of RFI and other electromagnetic effects, drew the attention of regulatory bodies around the world. In particular, it became apparent that the large amounts of electromagnetic interference conducted and radiated by this type of supply could interfere with radio communication, and have a negative impact on the operation of sensitive electronic and computer circuits in a variety of industries, including the oil industry. The main benefit derived by the oil exploration and drilling industries from soft switching power supplies is a marked reduction in electrical noise levels. This enables the telemetry coming from below the ground to be detected more easily. Received from deep-land or deep-sea drilling sites, the data usually has a small amplitude by the time it reaches the recording instruments on the surface. It's important the signal-to-noise ratio be sufficient to acquire the signals at these great distances. Since the signal is quite weak, generating less noise is the key. With the older, traditional "switch-mode" power supply technologies, the problem of noise and power surges is a result of power transistors incorporated to "hard switch" the unregulated input voltage.

Electromagnetic interference (EMI) filters play an important role in restraining conducted EMI, affected by the impedance of the noise source, and the load, the performance of the EMI filter is often poor. In order to resolve the mismatch problem of passive filter, this paper proposes an EMI filter based on impedance matching. Based on the fundamental design principle of the passive filter, the design of passive EMI filter is analysed and discussed at first.Then, on the basis of the theoretical foundation, more detailed and practical design is given further. By using the method of the matching network, the design of passive EMI filter under the worst circuit stances is emphasised. Finally, the design result is emulated and analysed, the proposed EMI filter idea is verified by the simulation result.

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

After the study of electromagnetic interference (EMI) mechanisms in switching mode power system (SMPS) and the soft switch, this paper proposes a novel hybrid filter (HEF) to suppress commend mode EMI in SMPS. The HEF consists of a passive filter and an active filter. Matching network, which can reduce impedance mismatching effects, is introduced in passive part. A feed-forward active filter is adopted as active part. The simulation and experiment results show that the EMI depressing of HEF is good. And the HEF is smaller and lighter than traditional passive filter.

Switched-mode power supplies (SMPS) are the source of both conducted and radiated electromagnetic interference (EMI) noise. Resonant converters are popular due to the possibility of switching loss reduction using zero voltage switching (ZVS) or zero current switching (ZCS) and also attenuating conducted EMI noise. Conventionally, a common-mode (CM) choke with a single core and two identical windings is used to suppress the CM noise in an EMI filter. This paper introduces an effective and cost-efficient method for mitigating the CM EMI noise in SRCs. The proposed method benefits a two-winding coupled inductor instead of the simple resonant inductor in the SRC. While a unity turn ratio does not meet the desired resonance inductance, the suggested two windings coupled inductor with an unequal number of turns deals with the EMI noise as well as the normal operation of an inductor in the resonant tank. Applying the proposed method significantly achieves up to 20 dB attenuation in the noise amplitude both at the input and output terminals of the converter. Simulations are used for investigating the analysis of the method. Moreover, a series resonant converter is designed and implemented to verify both analysis and simulations.

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