DC-DC resonant converters benefit from soft switching and reduced peak currents over other topologies. However, the design and control of resonant converters are challenging due to non-linearities in the resonant tanks. This research focuses on design and control methods for two-port and three-port resonant converters in EV applications. The two-port LLC resonant converter is attractive for on-board charger applications. However, if not appropriately designed, the frequency-modulated LLC converters will have a wide range of switching frequencies and lose efficiency in wide voltage range OBC applications. Hence, practicing proper converter design and control methods is essential to maximize efficiency. This work proposes a design framework for a wide-voltage range LLC converter to enhance efficiency. Topology morphing is used to reduce the effective voltage gain, and an online topology morphing method, along with a cascaded closed-loop control system, is also proposed. Three-port DC-DC converters can facilitate power transfer among three sources/ sinks. With the emerging trend of dual auxiliary voltages in EVs, the three-port resonant converter topology is an ideal candidate to interface the high voltage battery with low to medium voltages. This work proposes an optimal control method for a TPRC based on duty-ratio and phase-shift control to maximize its efficiency. The control method is optimized using a novel harmonic approximation-based model. A 300 – 700 V input, 250 – 450 V output, 3.3 kW LLC converter is designed and tested to validate the proposed design and control methods of the LLC converter. The time-weighted averaged efficiency above 96.7% is observed over the entire input voltage range. A 400 – 800 V/ 46 – 50 V/ 10 – 14 V, 6kW rated power TPRC is also designed and tested to validate the proposed optimal control method. Peak efficiency of 96.34% is observed, with a maximum efficiency improvement of 12.4% compared to the conventional phase-shift control. / Dissertation / Doctor of Science (PhD) / DC-DC converters are used in numerous electrical applications to transfer power between an energy source and a load while stepping up or down the voltage levels to match their specifications. During the power transfer, losses occur within the DCDC converter from the switching devices and the other converter elements. For high energy efficiency, these converters must have minimal losses. Among the different DC-DC converters, resonant converters are attractive due to their reduced power losses. As the automotive industry rapidly moves towards electrification, DC-DC resonant converters can provide efficient power transfer in electric vehicle (EV) applications. However, the design and control of resonant converters are challenging compared to other DC-DC converters. Therefore, practicing proper design and control methods in DC-DC resonant converters is essential. This thesis proposes optimal design and control methods for DC-DC converters in EV applications to enhance efficiency. The proposed methods are validated using hardware prototypes.

Power converters have evolved from the classical low switching frequency thyristorised converters to the modern high-frequency switched mode converters employing fast power devices such as Insulated Gate Bipolar Transistors (IGBTs). This evolution has changed the way power is processed in all the four functional areas of power conversion namely, AC-DC, DC-DC, DC-AC and AC-AC. High frequency switching has made it possible to reduce the size of the converters by using smaller energy storage elements. Switched mode conversion applied to AC-AC power conversion results in the use of two approaches: An indirect (two stage) conversion with a rectifier and an inverter with a dc link storage and a direct conversion scheme with a matrix converter. Matrix converter is a potential candidate in certain applications where a compact power converter design is required. Two approaches in topology, namely direct and indirect matrix converters are well reported in the literature. This thesis looks at the analysis, modeling and control of matrix converters from the perspective of converter switching functions. The switching functions as proposed for the line frequency switching rectifiers and cycloconverters is extended to the high frequency switching pulse-width modulated inverters and rectifiers. The matrix converter modulation schemes are analysed and a fresh interpretation in terms of these switching functions is presented in this thesis. The application of the switching function based analysis also yields a better insight into popular space phasor moulation techniques employed in matrix converters such as indirect-space-phasor modulation. The topology of the matrix converter is simple. There are no energy storage elements. However, the control, modulation and protection processes are more complex than other converters. The complexities involved in the control, modulation, commutation and protection of the matrix converter necessitates a much more complex controller capable of carrying out these tasks fast and effectively. In this work, a versatile FPGA based digital controller is designed which is not only capable of carrying out all the modulation, control, commutation and protection requirements of the matrix converter but also, can simulate the converter and the load in real-time. The real-time simulation capabilities of the control and real-time simulation platform are demonstrated with a suitable example of dynamic system. The real-time models of the matrix converter feeding passive load are developed and demonstrated in comparison with offline simulation models. Matrix converters are buck-derived converters and hence the input currents are discontinuous. Hence design of an appropriate filter becomes necessary. Some guidelines are suggested to design an appropriate input filter considering the non-idealities of the source. Finally, hardware designs of suitably rated direct and indirect matrix converters are presented and some representative results are given.