|Title:||Optimized switched-capacitor power conversion technology for DC distribution|
|Advisors:||Cheng, K. W. Eric (EE)|
|Subject:||Switching circuits -- Design and construction.|
Electric power distribution -- Direct current.
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Electrical Engineering|
|Pages:||xviii, 201 pages : color illustrations|
|Abstract:||As numerous advantages in the aspects of efficiency, power handling, power coupling and harmonics elimination etc., DC distribution has received extensive attention worldwide. When switched-capacitor (SC) power conversion technology is applied in DC distribution, the system will be very flexible and more reliable. Different from conventional switched-mode power converters (SMPCs), there is no bulky magnetic component employed in SC power conversion circuits. This type of power conversion circuits therefore has the advantages of low cost and high power density. One application of SC in DC distribution systems is to use SC-based DC-DC power converters for voltage level shifting. Its function is very similar to transformers widely used in AC power systems. In this thesis, a family of single-stage dual-phase-combined SC resonant converters is developed. Each of the proposed dual-phase-combined SC converters has one more capacitor than its single-phase version, but has the advantages of higher power and lower output voltage ripple. This design provides a more stable output voltage and significantly reduces the quantity of switches. These converters therefore have the common features of smaller size, lower cost, and higher power density than the conventional multiphase SC power converters. Moreover, a series of non-isolated multi-output PWM converters is developed by combining the advantages of SMPCs and SC converters. This type of converters employs only one inductor and one active switch, which contributes to the features of simple structure and easy control. Another application of SC in DC distribution is voltage balancing. In the thesis, several SC-based cell balancing circuits are developed for voltage equalization of series-connected batteries used in DC distribution systems as energy storage devices. These cell balancing circuits have the features of simple structure and easy control as well as the absence of magnetic components. Their balancing speed is independent of both of the number of battery cells and initial mismatch distribution of cell voltages. Another achievement of SC-based voltage balancing is in multilevel inverters. In this aspect, a novel multilevel inverter is developed by cascading an H-bridge with multiple SC units. It has the advantages of simple structure and self-balancing of capacitor voltages. Multiple LED strings connected in parallel manner in DC distribution systems as lighting devices need to share a common current. Several current-sharing LED drive circuits are therefore developed by combining the conventional SMPCs and SC techniques. Only one active switch and one magnetic component are employed in each of the proposed LED drivers. It makes these lighting devices can be designed with simple structure and cost-effectiveness. To ensure these SC's applications to be implemented smoothly in DC distribution systems, both resonant and non-resonant SC techniques are optimized in the aspects of efficiency improvement, current spike limitation and output voltage ripple reduction. An intuitive and simple modeling method is also developed to analyze and evaluate the performance of SC power converters, in this thesis. Importantly, this thesis aims to promote various applications of SC power conversion technology in DC distribution systems, rather than to establish a DC distribution system based entirely on SC power conversion techniques.|
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