Investigation of Step-Down DC-DC Converter Topology and its Closed-Loop Controller Design for Automotive Application : Analytical Modelling, Control Design and Stability Analysis

Sammanfattning

The increase in the need for electric vehicles (EVs) further emphasized the crucial role of power electronic converters, especially DC-DC converters, and their advancement in their design and control. The thesis investigates one of these topologies, that is, the two-phase Interleaved Boost (step-up) followed by the LLC converter. In order to achieve the desired voltage levels for motor or equipment operation, a closed-loop controller for the boost converter is designed based on the internal model principle (IMP). Since the converter has switching devices, it is linearized using a state-space averaged switch model followed by small signal perturbation analysis. Further, a cascaded voltage-current control is developed with an inner-current loop with faster dynamics compared to the outer voltage loop, alongside the study investigates other existing types of compensators’ designs for the voltage and/or current control mode. The obtained analytical results are verified with the simulation models using tools like MATLAB, Simulink, PLECS, SIMPLIS and the challenges encountered in the process are discussed. The final results are obtained through stability analysis in frequency- and timedomain. This thesis aims to highlight the importance of closed-loop controller design and its behavioral assessment i.e., the transient and steady state response at all estimated operating points.