Wenjie Chen

An active EMI filtering technique for improving passive filter low-frequency performance

In recent years, there has been considerable interest in the development and applications of active electromagnetic interference (EMI) filters. An active EMI filter (AEF) for integrated power electronics module (IPEM) is proposed in this paper, where large passive EMI filter is replaced by small passive components and active op-amp circuit. The technique is appropriated when improved attenuation is required at relatively low frequencies and the high-frequency filtering requirements are easily met. The effectiveness of the proposed circuit has been verified by experimental results. It is demonstrated that the proposed approach is most effective in a case where it is desirable to minimize the amount of passive components in the filter

A Novel Hybrid Common-Mode EMI Filter With Active Impedance Multiplication

This paper presents a novel hybrid common-mode (CM) electromagnetic interference filter for a military power supply. The proposed filter is composed of an active impedance multiplication circuit cascaded with a benchmark CM inductor. The active impedance multiplication circuit is very effective in boosting the impedances of both the benchmark CM inductor and the noise source. Thus, the total equivalent impedance of the filter is enlarged by the active booster to a great extent. An important advantage of the approach is that only a small-size CM choke is used as the passive filter instead of a traditional CLC filter. Furthermore, the noise source is turned to be an inevitable part of the hybrid filter by the impedance multiplication effect. Experimental results were carried out according to MIL-STD-461. It is shown that the proposed approach can acquire good noise attenuation performance within a wide frequency range.

An Experimental Study of Common- and Differential-Mode Active EMI Filter Compensation Characteristics

Most reported compensation schemes for active electromagnetic interference filters (AEFs) use either voltage canceling or current canceling to deal with high-frequency noise interference. The purpose of this paper is to investigate the compensation characteristics of these two kinds of AEFs for different types of noise sources, i.e., common mode (CM) and differential mode (DM) noise source. This is examined by experimental identification and theoretical analysis of the insertion losses of AEF with voltage- or current-cancellation scheme. It is demonstrated that current-canceling AEFs are effective in eliminating high-impedance CM noise, while voltage-canceling AEFs are good compensation solutions for low-impedance DM noise. The results reported in the paper enable the choice of optimized compensation schemes, using the aforementioned indicated aspects.

Analysis of Insertion Loss and Impedance Compatibility of Hybrid EMI Filter Based on Equivalent Circuit Model

The hybrid active electromagnetic interference filter (HAEF) is considered one of the best options for improving power quality for a number of considerations. A systematic classification and identification of HAEF configurations is given, including their insertion losses, impedance compatibilities, potential applications, and comparative features. It is aimed at providing a broad perspective on the status of HAEF technology to researchers and application engineers dealing with EMI issues. The basis of discussion is an equivalent circuit model that includes all possible combinations of active and passive elements and matches these to the desirable attributes. The evaluation indicates those topologies that are known and those topologies that are relatively new.

An experimental study and comparison of common mode and differential mode noise compensation characteristic for active EMI filter

Most of the many reported compensation schemes for active EMI filters (AEFs) use either voltage canceling or current canceling to deal with high frequency electromagnetic interference noise. The purpose of this paper is to investigate the compensation characteristics of these two kinds of AEFs under different type of noise source, i.e., common mode (CM) and differential mode (DM) noise source. This is examined by experimental identification and theoretically analysis of the insertion losses of AEF with voltage or current cancellation schemes. It is demonstrated that current canceling AEFs are effective to eliminate high impedance CM noise, while voltage canceling AEFs are good compensation solutions for low impedance DM noise source. The results reported in the paper enable the choice of optimized compensation schemes, from the above indicated aspects.

AN APPLICATION OF COMPLEX WAVELETS FOR HIGH FREQUENCY SWITCHING NOISE DETECTION

Switching signal is always composed of a series of fast voltage and current transient impulsive waves, which are created during turn-on and turn-off operation of the switching elements. This paper presents a scalogram and phase spectrum analyzing approach for the high-frequency switching noise detection. A complex Gaussian wavelet is used to extract the oscillation feature of the noise signal. The proposed scheme is more suitable in discriminating the type of switching noise than conventional wavelet transform approaches. Simulation results show the effectiveness and advantages of the method.