Modelling, Analysis, and Mitigation of Conducted EMI Noise in Dual Active Bridge Converter

Abstract

The conducted electromagnetic interference (EMI) typically refers to the transmission of undesired electromagnetic signals through a conducting medium. The conducted EMI is broadly classified into common mode (CM) and differential mode (DM) noise based on the propagation path. The control schemes opted in a power electronic converter urge the desired switching action for its intended operation. This switching action of the semiconductor devices results in rapid voltage and current fluctuations. These rapid voltage or current fluctuations result in electromagnetic emissions that couple onto nearby conductive paths, thus resulting in conducted EMI. In isolated DC-DC converters, in addition to the voltage and current transients due to the switching action, the presence of the transformer exacerbates EMI, as it couples noise between primary and secondary sides. Among the isolated DC-DC converters, the dual active bridge (DAB) converter is a cutting-edge power electronics topology renowned for its ability to transfer power with higher efficiency while providing galvanic isolation. The two voltage source converters (VSC) that can accommodate a maximum of eight switches give the DAB converter an impressive power transfer capability compared to other isolated bidirectional DC-DC converters. Moreover, with its advanced control techniques, bidirectional power flow capability, and galvanic isolation, the DAB converter offers engineers a versatile tool for designing next-generation power electronics systems. Thus, it stands as a key player in modern power conversion applications such as renewable energy systems, electric vehicle charging stations, aerospace, and high-voltage DC distribution systems. Despite its impeccable features, the switching action of semiconductor devices, the presence of a transformer, and complex propagation paths for the CM and DM noise, the DAB converter is not exempt from conducted EMI. Hence, understanding the sources and mitigation techniques of the conducted EMI noise in the DAB converter is essential to ensure its reliability and performance in various applications. Thus, the thesis emphasizes the analysis of conducted EMI noise and its mitigation in the DAB converter. Initially, the work focuses on the detailed analysis of the propagation paths of the CM and DM noise using the CM and DM noise models, respectively. One aspect of the analysis presents an external-matched impedance approach aiming to accurately estimate the conducted EMI noise through the transformer primary-to-secondary winding parasitic capacitance in detail. The other aspect of the analysis focuses on the measurement of the DM noise in the DAB converter that takes a path through the common ground, termed mixed-mode differential mode (MMDM) noise, along with its experimental validation. In general, the mitigation techniques for common-mode noise typically involve the incorporation of CM filters. Hence, later in the thesis, the circulating CM current that originates due to the DC input CM filters of the DAB converter is thoroughly investigated along with its coupled inductor-based mitigation approach. The detailed comparative analysis of the CM noise performance of the DAB converter with an external inductor and an integrated transformer is presented along with the experimental validation. Further, the thesis introduces a CM and a DM integrated magnetic structures intended to replace the conventional CM chokes and conventional DM inductors or chokes, to achieve improved physical (size, volume) or electrical characteristics (impedance profile). Finally, to address the size and volume occupancy of the EMI f ilters, this thesis presents the design of two integrated magnetic choke structures. The experimental performance evaluation of the EMI filters with the presented integrated magnetic choke structures and their corresponding conventional choke structures is conducted on a hardware prototype of the DAB converter. Thus, the CM and DM noise models of the DAB converter presented in the thesis facilitate a better understanding of the noise propagation paths along with offering insight into the measurement feasibility of the conducted EMI noise through the transformer’s primary-to-secondary winding capacitive coupling and the MMDM noise. Additionally, the thesis proves the advantages of employing the integrated magnetics approach, either in the transformer or in the EMI filters, of the DAB converter.