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This dissertation explores the feasibility of using resonant converters for maximum power point tracking (MPPT) of solar power. Resonant converters are known for their high efficiency, compact size, low EMI, and high power density. However, one crucial factor of resonant converters hindered their applications in many areas, i.e., lack of full regulation capability. Recently, the fixed on-time modulation method was reported to series resonant converters (SRCs), enabling them with full range regulation. This advantage is adopted in this thesis for maximum power point tracking (MPPT) applications. A precise and responsive perturb and observe algorithm is employed as the MPPT method to achieve maximum power output from the solar system. Chapter 1 provides a comprehensive literature review on MPPT applications with SRCs. It examines the characteristics of PV arrays, explores soft-switching techniques and resonant converters for high-efficiency topologies, and investigates various MPPT techniques to achieve fast and accurate tracking of the maximum power point. Chapter 2 focuses on analyzing the fixed on-time control method for half-bridge SRCs. This analysis enables half-bridge SRCs to perform full-range regulation within a limited frequency range, making them viable candidate for MPPT applications. In Chapter 3, experimental results are presented. A prototype of a half-bridge SRC is built with a nominal input voltage of 36V to utilize with a PV panel. The prototype demonstrates a peak efficiency of 95.4% in a 180W application, validating the high efficiency of the prototype. Moreover, the MPPT experiment is conducted using the half-bridge SRC prototype, demonstrating its ability to track the MPP of the PV array with a deviation of only ±2W from the actual maximum power. The prototype exhibits a good efficiency of 92.6% during this process. Chapter 4 compares the half-bridge SRC with a conventional buck converter, highlighting the differences between their hard-switching

This thesis presents a new dual resonant switched-capacitor converter topology that inverts the polarity of input voltages and can regulate the gain continuously between 0 and –1, even at light load operation. A literature review on the development and improvement of switched-capacitor converters over the years is presented in Chapter 1. The switched capacitor in the presented converter is charged and discharged through resonant inductors, eliminating large current spikes and charge sharing losses associated with pure switched-capacitor converters. This resonance allows for ZCS turn-on of all switches and ZCS turn-off of all diodes. Chapter 2 presents a detailed analysis of the dual resonant switched-capacitor polarity inverter, in which a voltage gain curve in four distinct operating modes is provided, along with a detailed discussion of boundary conditions between modes. Voltage and current stresses of all components are analyzed, and design guidelines for designing the presented converter from a specified input voltage, output voltage, and output power are presented. In addition, a regenerative snubber to eliminate undesirable parasitic ringing is provided. An 80V to –35V ~ –72V open loop prototype with peak efficiency 97.0% and maximum power 120W was built to verify the operation of the converter, and the experimental results from this prototype are presented in Chapter 3. Finally, in Chapter 4, several extensions of the topology are presented to reduce the step-down ratio of the converter or to apply the topology to step-up applications.

Non-isolated high step-up and high step-down DC-DC conversions are highly demanded in many applications, including renewable energy systems, uninterrupted power supplies, data centers, high-end computers, etc. The high voltage-conversion-ratio requirement poses challenges on energy efficiency, power density, cost and reliability. This dissertation explores new high step-up and high step-down topologies for various applications. First, a new family of interleaved high step-up converters integrating coupled-inductor and switched-capacitor are introduced for high current and ultra-high step-up applications. By integrating coupled-inductor and switched-capacitor techniques, the proposed converter achieves ultra-high step-up voltage gain without the need of extreme duty cycle or high turns ratio. Also, very low switch voltage stress can be achieved, thus low-voltage-rating MOSFETs with small on-resistance can be used to lower the conduction loss. Moreover, thanks to the interleaved operation at the input side, the input current is shared and low input current ripple is obtained. Furthermore, the coupled-inductor leakage energy can be recycled, which helps alleviate reverse recovery problem. Second, multiphase interleaved high step-up converter with diode-capacitor voltage multiplier stages is presented, which is an extension of the previously reported two-phase current-fed Cockcroft–Walton multiplier. The multiphase configuration has flexible structure. It achieves high current handling capability, high voltage gain, low component voltage stress, low input current ripple and automatic phase current balancing. A three-phase converter in the multiphase family was analyzed and evaluated in detail.Third, a single-phase coupled-inductor boost converter is presented for low current high boost applications. The voltage gain can be extended by the coupled inductor. Due to a independent inductor at the input, continuous input current is obtained, which significantly reduces the i