Power semiconductor filter : Use of series-pass device in switching converters for filtering input current harmonics

An investigation into the use of series-pass device (SPD) to filter out input current harmonics of switching converters is presented. The idea is based on connecting a SPD in series with the input of the switching converter so that the input current of the entire system can be profiled by adjusting the biasing condition of the SPD. To minimize the power dissipation of the SPD, the input impedance of the switching converter is controlled to make the SPD operate at the boundary between the linear and saturation modes. Modeling, design, and analysis of the system architecture will be given. Selection guide for the SPD will also be given. The concept has been applied to a 75-W 90-140-V/24-V classical dc-dc buck converter. Investigations reveal that the proposed architecture allows a substantial reduction in the size of the filter section and gives comparable efficiency as the conventional passive-type LC filter. More importantly, the idea makes the input filter amenable to monolithic integration. These investigations lay the foundation for applying the proposed concept for other power electronic converter systems.