Analysis, design, and applications of switched-capacitor converters

Nowadays, with the increasing demand for smaller and lighte r power converters in commercial electronics, there is an increasing popularity in b oth the research and the development of switched-capacitor (SC) converters. With the abs ence of inductors and bulky transformers, the power density of SC converters is improve d as compared to traditional switching mode power supplies. Moreover, the possibility o f fabricating an entire SC converter into an integrated circuit (IC) chip has resulted in many companies producing SC converter ICs and many portable electronic products adop ting such ICs. The purpose of the thesis is to summarize the previous resear ch works and report the accomplished works. A literature review is included to summ arize the research efforts of SC converters. Converter topologies, modeling works, co ntrol methodologies, practical applications, and the industrial market development of SC converters are discussed. Limitations of previous works are highlighted and the motiv ations of the proposed research works are stated. Three major contributions of the re search works in this thesis are included. First, the energy efficiency of SC converters is re-examined by issecting the entire efficiency problem into two aspects, namely the charging effici n y and the discharging efficiency. Mathematical derivations of the energy efficien y expressions on different aspects of charging and discharging conditions are include d. Clarifications on misunderstandings found in previous works are stated and factors of achieving high-efficiency iii in both charging and discharging processes are suggested. T he entire SC converter efficiency is then evaluated by combining the considerations o f charging and discharging efficiencies. Experimental results are provided to verify t he heoretical analysis. It is experimentally proved that resistance in the charging path is independent of the overall efficiency of SC converters, but the resistance in the discha rging path affects the overall efficiency of SC converters. Additionally, the flawed concep t of lossy charging process in quasi-switched-capacitor (QSC) converters is clarified . Furthermore, higher switching frequency and larger capacitance of flying capacitors can re duce the voltage ripple on the flying capacitors to improve the overall efficiency of SC conv erters. Second, a universal SC converter capable of achieving DC–DC , AC–DC and DC–AC power conversions is proposed. Previous SC converters are d esigned and are only applicable to some particular applications, which are unsuitabl e for application in situations requiring multi-purpose power conversions. A multi conver sion purpose SC converter can resolve the problem. Detailed circuit operations on eac h type of power conversions are described. The control methodology of the overall syste m is explained. The required circuitries for programming the control sequence of power s witches for achieving various types of power conversions are given. Simulations have been p rformed to a preliminary proof of the proposed idea. An experimental prototype has be en uilt to demonstrate the proposed idea. It is shown that different types of power conv ersions can be achieved by only adjusting the control signals of power MOSFETs. Both li ne and load regulations capabilities, efficiency analysis, and dynamic response un der the step change of the load current of the proposed converter are discussed. Third, a multi-port SC converter is introduced for multiple sources or loads applications. Due to the distributed energy resources (DER) characterist ic in renewable energy systems, multiple converters are required for different power conve rsions in the entire system. An