Impact of Input EMI Filter Design on the Dynamic Performance of Average-Current-Mode Controlled Boost Converter

Abstract

An input EMI filter is usually employed for dealing with electromagnetic interference (EMI) caused by the switching actions of switched-mode converters. However, the existence of the input filter often interacts with the connected converter, thus leads to performance degradation and even stability issues. This thesis presents a thorough case study that focuses on the impact of the design of the input EMI filter parameters---one of the main factors that affect the adverse filter-converter interaction---on the dynamic response of the filter-converter interconnected system. A switched-mode boost converter under average-current-mode (ACM) control operates in continuous conduction mode (CCM) is utilized as an example. With the purpose of analyzing the stability of the aforementioned converter cascaded with different sized input filters, the impedance-based stability assessment method is used by utilizing the Nyquist stability criterion (NSC) on the impedance ratio of this interconnected system. To identify this minor loop gain, small-signal models that represent the dynamic behaviors are constructed for the ACM controlled DC-DC boost converter as well as the input EMI filter. Furthermore, to validate theoretical results, input filters are designed in different sizes with the MATLAB environment. To this end, damping circuits are added to solve the problems caused by filter-converter interactions. Simulation results are provided to demonstrate the correctness of the obtained small-signal models, as well as the correspondence between the predictions of impedance-based stability assessment and the transient performance of the cascaded system.