The Compact EMI Reduction Method Using Active Circuit Considering Conducted Emissions and Reliability

Abstract

Electromagnetic compatibility (EMC) concerns the unintentional generation, propagation, and reception of electromagnetic energy which may cause unwanted effects. EMC is mainly divided into electromagnetic interference (EMI) and electromagnetic susceptibility (EMS). Among the various EMC issues, the conducted emission (CE) regulation is one of the critical issues on the recent electronics system due to increase of high-speed operating switches in the power systems. Therefore, main target of proposed research is CE noise reduction from 150khz to 30Mhz. To suppress the common-mode CE noises, CM chokes and Y-capacitors are commonly used, while DM noise is mainly reduced by X-capacitors. However, for the CM noise reduction, the value of the Y-capacitor is limited by the safety regulation for leakage current. Therefore, the CM choke should have sufficient inductance value or multiple CM chokes are required. However, it critically increases the size and cost of the filter, especially in high power system to avoid magnetic saturation and heat problem. In this thesis, to overcome the cost and size limit of the traditional passive EMI filter, active EMI filters (AEFs) has been suggested to effectively reduce the CE noises without significant increase of the filter size in a high-power system by employing the active circuit components. This thesis proposes a new structure of transformer-isolated active EMI filter (AEF) without additional components on power lines for the reduction of common-mode (CM) CE. The noise attenuation performance and loop gain are rigorously analyzed, and the design guides for the proposed AEF are developed. The AEF is designed in a compact package for the application to a switching mode power supply (SMPS). The performance, stability, and leakage currents of the AEF are experimentally validated by various measurements. The CM EMI filter, including the AEF, achieves the additional CE reduction by 10 to 20 dB at a frequency range lower than 1MHz. Also, the noise peaks due to the resonances at several MHz are reduced by 7dB. The weak points of the conventional CM EMI filter at both low and high frequencies are effectively improved by employing the proposed AEF. This thesis also proposes an active EMI filter (AEF) realized by a customized integrated circuit (IC) to reduce conducted emission (CE) noises. A fully transformer-isolated feedforward current-sense current-compensation (CSCC) structure is selected as a base topology of the AEF. 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 is fabricated by a 0.18 m bipolar- CMOS-DMOS (BCD) process. The fabricated IC is implemented in a compact printed circuit board (PCB) 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. In addition, the surge immunity of the designed IC within the AEF is validated under numerous 5 kV surge tests.