Design of feedforward active ripple filters for power converters

Abstract

An active ripple filter is an electronic circuit which cancels or suppresses the ripple current and EMI generated by the power stage of a power converter, thus reducing the passive filtration requirements. This thesis presents the design and evaluation of various current sensing and injection methods for feedforward active filter applications including a Rogowski-Coil sensor, a transformer sensor, a class A injector, and a current transformer based injector. The advantages, tradeoffs, and limitation of each approach are discussed in detail. This thesis also presents the design and evaluation of a prototype feedforword active filter which employs a Rogowski-Coil current sensor and a class A current injector on a 42V /14 V de/de power converter system. Quantitative comparisons between a hybrid passive/active filter and a purely passive filter having the same performance are presented. It is demonstrated that substantial improvements in filter mass and converter transient performance can be achieved using the proposed active ripple filtering method.