【电力电子】【2020.02】利用导抗式三相双有源桥DC-DC变换器实现宽范围高效率的拓扑结构和调制方案
本文為中國香港理工大學（作者：AKIF ZIA KHAN）的博士論文，共208頁。
三相雙有源橋（3p-DAB）變換器是大功率應用中雙向功率變換的一種有吸引力的選擇，在不同的輸入輸出電壓比和不同的負載條件下，循環電流引起的導通損耗和軟開關區域的收縮是嚴重影響其效率性能的主要瓶頸。為了解決這些問題，本文提出了三種不同的基于導抗的3p-DAB轉換器拓撲結構和調制方案。提出的拓撲結構和調制方案的目標是在整個工作范圍內同時最小化開關損耗和傳導損耗，以實現寬范圍高效率性能。基于這一背景，本文共分為六章。
第一章介紹了隔離雙向dc-dc變換器（IBDC）的研究背景、重要性、一些新興應用和功能概述。通過詳細討論，3p-DAB變換器被認為是大功率IBDC的首選拓撲結構，并指出了其局限性。此外，本章提出了本論文的主要目標，包括克服傳統3p-DAB變換器的局限性，在不同的輸入輸出電壓比下實現寬范圍的高效率性能。最后，在第一章中對全文進行了概述。
第二章從拓撲結構和控制角度對傳統的3p-DAB變換器進行了概述。本章還提供了一個全面的文獻綜述，以更新讀者對3p-DAB變換器所做的工作，以提高其效率和性能。此外，本章還突出了現有文獻中的研究空白，指出了目前的研究工作試圖彌補的不足。
第三章提出了一種3p-DAB諧振導抗（3p-DAB-RI）變換器，該變換器可以在所有交流端口實現單位功率因數運行，從而降低端口電流的均方根值，降低導通損耗，完全消除無功功率。此外，它還可以實現全量程零電壓開關（ZVS），而不受輸入輸出電壓比變化的影響，以減小開關損耗。然而，對于單位功率因數運行，33%的開關是硬開關，導致開關損耗增加，而對于全量程ZVS運行，3p-DAB-RI變換器由于循環電流增加而導致高導通損耗。此外，由于采用占空比調制對兩種模式的輸出功率進行調制，3p-DAB-RI變換器在輕載條件下（當電壓波形占空比較小時）循環電流較大，導致輕載效率較低。
第四章提出了一種3p-DAB可重構諧振（3p-DAB-RR）變換器，以克服第三章提出的3p-DAB-RI變換器的局限性。本章提出的3p-DAB-RR變換器可以在3p-DAB-RI變換器和3p-DAB串聯諧振（3p-DAB-SR）變換器之間進行變換，從而在塑造3pDAB變換器的效率性能和提高其輕載效率方面提供額外的自由度。3p-DAB-RR變換器通過適當選擇變換器的工作模式，在不同的工作條件下，具有單位功率因數、全量程零電壓開關和提高輕載效率的靈活性。在仔細分析損耗并通過實驗測量驗證損耗模型的基礎上，有人建議使用3p-DAB-SR轉換器和3p-DAB-RI轉換器，前者采用單相移相（SPS）調制，用于中低功率電平，后者采用單位功率因數操作，以實現大范圍的高效率性能。然而，3p-DAB-RI變換器單位功率因數運行中33%的硬開關和高循環電流的缺點，以及3p-DAB-SR變換器在大范圍輸入輸出電壓比變化下的硬開關問題仍然沒有解決。
第五章提出了一種3p-DAB可重構可調諧諧振（3p-DABRTR）變換器，以實現寬范圍的零環流和全范圍的ZVS操作，而不考慮輸入輸出電壓比的大范圍變化。對于低-中功率電平，該變換器采用阻抗調制方式作為可調諧3p-DAB-SR變換器工作。在這種工作模式下，輸出功率是通過在保持開關頻率和相移不變的情況下，利用主控芯片調節串聯LC諧振網絡的阻抗來控制的。對于中高功率電平，變換器作為一個可調3p-DAB-RI變換器與動態頻率匹配（DFM）調制。在這種工作模式下，輸出功率由開關控制電容器（SCC）與開關頻率同步變化導抗網絡的諧振頻率來控制。兩種運行方式的結合，使所有開關同時實現寬范圍零循環電流和全量程零電壓開關操作，具有廣泛的高效率性能。
第六章為論文的總結，重點介紹了論文的貢獻。此外，本章還提出了所提出的拓撲結構的應用和功率等級，以及未來的研究方向。最后，對所提出的拓撲結構進行了綜合比較，以期對論文的結論進行總結。
Three-phase dual-active-bridge (3p-DAB)converter is an attractive choice for bidirectional power conversion inhigh-power applications, however, conduction loss caused by circulating currentand shrinkage of soft-switching region under varying input-to-output voltageratios and different load conditions are the main bottlenecks that severelyaffect its efficiency performance. To address these issues, three differentimmittance based topologies and modulation schemes have been proposed in thiswork for the 3p-DAB converter. The proposed topologies and modulation schemesare targeted to minimize the switching loss and conduction loss simultaneouslyover the entire operating range to achieve wide-range highefficiencyperformance. Based on this backdrop, the thesis has been classified in sixchapters. A brief description of each chapter is presented below: Chapter 1discusses about the background, importance, some emerging applications andfunctional overview of isolated bidirectional dc-dc converters (IBDCs). Throughdetailed discussions, 3p-DAB converter is identified as a preferred IBDCtopology for high-power applications and its limitations are presented.Moreover, the main objectives of the thesis are presented in this chapter thatincludes overcoming the limitations of conventional 3p-DAB converter to achievewide-range high efficiency performance under varying input-to-output voltageratios. Finally, an outline of the thesis concludes chapter 1. Chapter 2 givesan overview of the conventional 3p-DAB converter from the topology and controlperspective. A comprehensive literature review is also presented in thischapter to update the readers about the work done on the
3p-DAB converter to improve its efficiencyperformance. Moreover, the research gaps in the existing literature are alsohighlighted in this chapter that the current research work has attempted tobridge.
Chapter 3 proposes a 3p-DAB resonantimmittance (3p-DAB-RI) converter that can achieve unity-power-factor operationat all of its ac ports leading to reduced RMS port current, lower conductionloss and complete elimination of reactive power. Moreover, it can also achievefull-range zero-voltage-switching (ZVS) irrespective of variations ininput-to-output voltage ratios to diminish the switching loss. However, forunity-power-factor operation, 33 % of the switches are hard-switched leading toincreased switching loss whereas for full-range ZVS operation, 3p-DAB-RI convertersuffers from high conduction loss due to increased circulating current.Moreover, as the duty cycle modulation is employed to modulate output power forboth modes, 3p-DAB-RI converter suffers from high circulating current underlight-load conditions (when the duty cycle of voltage waveforms is small)leading to poor-light load efficiency.
Chapter 4 proposes a 3p-DAB reconfigurableresonant (3p-DAB-RR) converter to overcome the limitations of 3p-DAB-RIconverter proposed in chapter 3. The 3p-DAB-RR converter proposed in thischapter can transform between 3p-DAB-RI converter and a 3p-DAB series resonant(3p-DAB-SR) converter to offer additional degree-of-freedom in shaping theefficiency performance of 3pDAB converter and enhance its light-load efficiency.The 3p-DAB-RR converter offers the flexibility to operate with unity powerfactor, full-range ZVS and enhanced light-load efficiency under varyingoperating conditions by appropriate selection of the converters operation mode.Based on a careful loss analysis and verification of the loss model byexperimental measurements, it has been proposed to operate the converter as3p-DAB-SR converter with single phase-shift (SPS) modulation for low-mediumpower levels and operate as 3p-DAB-RI converter with unity-power-factoroperation for medium-high power levels to achieve overall wide-rangehigh-efficiency performance. However, the drawbacks of hardswitching of 33 %switches in the unity-power-factor operation of 3p-DAB-RI converter and highcirculating current, hard-switching of switches in 3p-DABSR converter underwide-range variations in input-to-output voltage ratios still remain unsolved.Chapter 5 proposes a 3p-DAB reconfigurable and tunable resonant (3p-DABRTR)converter to achieve wide-range zero circulating current and full-range ZVSoperation irrespective of wide-range variations in input-to-output voltageratios. For low-medium power levels, the converter operates as a tunable3p-DAB-SR converter with impedance modulation method. Under this mode of operation,the output power is controlled by modulating the impedance of series LCresonant network with the aid of SCC while keeping the switching frequency andphase-shift constant. For medium-high power levels, the converter operates as atunable 3p-DAB-RI converter with dynamic frequency matching (DFM) modulation.Under this mode of operation, the output power is controlled by synchronouslyvarying the resonance frequency of the immittance network with the switchingfrequency by using switch-controlled capacitor (SCC). The combination of bothoperation modes jointly leads to wide-range zero circulating current andfull-range ZVS operation for all the switches simultaneously yieldingwide-range high-efficiency performance. Chapter 6 concludes the thesis and highlightsthe contributions of the work. Moreover, suggested applications and powerlevels for the proposed topologies and potential future research directions arealso presented in this chapter. Finally, a comprehensive comparison of theproposed topologies are presented in this chapter to conclude the thesis.
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