| 摘要: | 本論文探討採用飛跨電容多電平拓樸之高功率密度三相 AC–DC 轉換器在設計與控制上的挑戰。由於電容相較於電感具有更高的能量密度，加上低電壓開關元件具備更佳的性能指標，本研究以飛跨電容多電平轉換器作為同時實現高效率、高功率密度以及降低被動元件體積的可行方案。然而，在實際飛跨電容多電平應用中，一項關鍵問題是如何維持飛跨電容電壓平衡，尤其在直流母線電壓變動或電網不平衡的情況下更形困難。傳統主動平衡方法需大量飛跨電容電壓感測，不僅提高系統成本與複雜度，也限制多電平轉換器於高電平數時的可擴展性。為解決上述問題，本論文提出三項主要貢獻。首先，發展虛擬磁通–電壓調變直接功率控制策略，使三相飛跨電容多電平整流器無需電網電壓感測器即可運作。藉由將系統轉換為線性非時變模型，該方法可在電網平衡與不平衡條件下皆可維持強健控制。其次，本論文提出基於滑模觀測器之飛跨電容電壓無感測主動平衡策略。利用互連系統模型設計超扭轉觀測器，以精準估測飛電容電壓並取代直接量測，並透過李雅普諾夫穩定性分析保證觀測誤差的收斂性。此方法避免傳統方法對電容特性的限制性假設，並具備對參數變動與電網不平衡的強健性。第三，本論文提出高功率密度三相七電平飛跨電容多電平功因校正前端整流器之設計，包含依多電平橋臂縮放定律決定適當電平數、硬體設計、損耗分析，以及推廣至一般 N 電平架構。本論文提出的控制策略與無電壓感測主動平衡方法，經由三相七電平飛跨電容多電平轉換器的完整模擬與實驗驗證。結果顯示所提出之技術具備可行性、強健性與卓越性能，適用於新一代高功率密度整流器，例如電動車快速充電與資料中心電源等應用。;This thesis addresses the design and control challenges of high-power-density three-phase AC–DC conversion using a Flying Capacitor Multilevel (FCML) converter topology. Motivated by the superior energy density of capacitors relative to inductors and the favorable figures-of-merit (FOM) of low-voltage switching devices, the FCML converter is investigated as a means to simultaneously achieve high efficiency, high power density, and reduced passive component volume. A key obstacle in practical FCML implementations is the need to maintain balanced flying capacitor voltages, especially under conditions of varying DC-link voltage or unbalanced grid operation. Conventional active balancing methods rely on extensive capacitor-voltage sensing, which increases system cost and complexity and limits scalability in high-level converters. To address these challenges, this thesis makes three main contributions. First, a virtual flux voltage modulated direct power control (VF-VMDPC) scheme is developed to regulate a three-phase FCML rectifier without requiring grid-voltage sensors. By transforming the system into a linear time-invariant form, the proposed method enables robust control under both balanced and unbalanced grid conditions. Second, a flying capacitor voltage sensorless control strategy is proposed using the interconnected system model for three-phase FCML based on a sliding mode observer (SMO) with active balancing method, eliminate the need for direct sensing. Then, a super-twisting observer (STO) is designed to accurately estimate flying capacitor voltages, reduces chattering, and Lyapunov stability analysis is utilized to guarantee convergence. The method avoids restrictive assumptions on capacitor characteristics and achieves robustness to parameter variations and grid imbalance. Third, the thesis presents the design of a high-power-density three-phase 7-level FCML PFC front-end rectifier. The appropriate number of levels is determined using multilevel bridge-leg scaling laws, followed by de-tailed hardware design, loss analysis. The proposed control VF-VMDPC strategy and observer-based sensorless balancing approach are validated through comprehensive simulations and experimental implementation of three-phase 7-level FCML converter. The results confirm the feasibility, robustness, and performance advantages of the proposed techniques, demonstrating their suitability for next-generation high-power-density rectifiers used in applications such as EV fast chargers and data-center power delivery systems. |
