Analysis and Optimization of the Two-Phase Series Capacitor Buck DC-DC Converter

Current sharing schemes for conventional multi-phase converters are based on sensing each phase current to deliver the current information to their controllers. In conventional buck converters, this fact may require a preset current sharing ratio at the expense of efficiency, which eventually requires a larger sensing circuit to achieve the sensing accuracy of each phase. Introducing the concept of automatic current sharing is one of the solutions to tackle this issue. Automatic current sharing (Current Sharing Mechanism CSM) is an advanced way to distribute heat generation in multi-phase switching topologies at full load. A two-phase series capacitor buck converter (2-pscB) was introduced to power laptops as low-voltage and high-current Voltage Regulator Modules (VRMs) as well as non-isolated Point-of-Load (PoL) converters. The current sharing concept is the main feature of this 2-pscB topology, where series capacitor voltage is used to achieve current sharing without the need for a phase current sensing circuit or complicated control loop. In this work, a complete state-space average model for the series capacitance buck switching regulators is linearized to develop a robust controller satisfying the stability and converter performance specifications. The presented averaging model includes the simplest model of the regulator’s parameters and only the main parasitic components. Both, an improved derivation of the main design parameters and a novel design methodology of MOSFETs isolated gate driver circuit are proposed and verified. Different high voltage input 2-pscB power density dc-dc converters are successfully investigated to examine the capability of current sharing at a higher voltage level and its impact on efficiency. Another novel approach of eGaN gate driver circuitry is designed with a Current-Mode Controller CMC using one current path to minimize propagation delays and reduce phases parasitic components, which helps enhance overall performance. 110V/12V/6A experimental prototype converter of Si MOSFETs was designed, its current sharing characteristics were experimentally tested and verified. Since eGaN technologies have attracted great attention in power electronics applications due to their capabilities and efficient energy conversion, another design, and analysis of a sensor-less eGaN-based 48V/5V 2-pscB buck switching converters were verified, and their current sharing characteristics were predicted by the state-space modeling technique. A theoretical comparison is conducted between conventional buck converter and 2-pscB. The results show the following characteristics of 2-pscB topology: a small inductor current ripple, low switching loss, inherited current sharing mechanism, duty cycle flexibility, and filter component size reduction. In a word, new modeling methods of various 2-pscB control schemes are proposed and broadly studied. This dissertation simulates most of these methods to provide the designers with a better comprehensive view of the 2-pscB converter topology