Research on Power Semiconductor Filtering Technology

Abstract

The high frequency switching network of the power supply is a well-known source of current harmonics and electromagnetic interference (EMI). Thus, tight requirements have been set up by different governments and international committees to limit the amount of allowable noise level emitted by electronic equipment, ensuring the reliability of the power system. A passive input filter is the most common solution to attenuate those harmonics and noise. However, the volume of the filter’s passive components is large, and it typically occupies one-fourth of the power supply. At the same time, the requirement of ever-increasing power density is straining engineers’ abilities to squeeze space for the input filter without sacrificing the overall performance of the power supply. Therefore, the filter section becomes a key factor limiting the power density and performance of the future power electronics systems.

In order to provide a tiny and lightweight solution on input filtering for power supply, this thesis presents the findings of the research on using power semiconductor devices to filter out the input current harmonics of switching converters. The technology is called power semiconductor filter (PSF). It is based on connecting a series-pass device (SPD) in series with the input of the switching converter so that the input current of the system can be profiled to reduce the harmonic contents. Moreover, the operating points of SPD are regulated at the boundary between its linear and saturation region for bipolar junction transistors or between its triode and ohmic regions for MOSFETs (“knee point”) such that the power loss is minimized. Furthermore, a small-signal model and sampled-data model of the proposed PSF are derived to study the stability issues of the system and develop the design guidelines for the feedback controller. The accuracy of both models is demonstrated on a buck converter prototype.

Besides, the EMI characteristics of converters with PSF in AC/DC application are investigated. An EMI model is developed to study the limitations of SPD in filtering high frequency noise. Based on the investigation, a fast current controller is proposed to reduce the effect of those limitations and enhance the filtering ability of PSF. An experimental prototype is built, and the results reveal that PSF can effectively suppress differential-mode noise and reduce current total harmonic distortion without deteriorating system performance, as compared to passive filter in classical switching converters. Last but not least, the proposed filter is suitable for monolithic integration, which enables the integration of the input filter into the power module.

Date of Award	12 Mar 2019
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shu Hung Henry CHUNG (Supervisor)