Nonlinear Load Analysis and Design of Resonant dc-dc Converters

現代電子系統需要高電能密度，低電磁干擾以及高效率的能源轉換器。針對不同的系統需求，人們選擇不一樣的轉換器架構。因此，一種工作波形為弦波的共振式電能轉換器變的越來越普及，他的電磁雜訊小，並且非常容易達到零電壓切換以降低切換能量損失。 然而，共振式直流轉換器的負載是一個非線性的整流器，這讓系統的分析變得困難。傳統共振式直流轉換器的分析將整流器包含負載等效為一個線姓電阻，如此一來，傳統線性的共振式分析可應用於共振式直流轉換器。但在有些應用中，例如使用脈衝模式控制的共振式直流轉換器，他的負載等效電阻無法由傳統的交流分析獲得。此外，由於共振式電路的工作行為可由系統輸出入電壓導出，將負載納入考量會把系統的分析複雜化。 本論文討論了兩個共振式直流轉換器的應用，壓電直流轉換器以及單級交流轉直流 LLC共振轉換器。針對脈衝模式控制的壓電直流轉換器，我們提出一個根植於能量守恆的分析方式。並依此推導出壓電變壓器的輸入電流及工作效率。分析結果顯示，系統的工作行為只與系統工作點有關，這意味著壓電變壓器的輸入電流包含了系統輸出電壓的資訊。由此分析結果，本論文設計了一個一次側控制的驅動電路並驗證分析結果。 一般市售的電源轉換器，通常在轉換器前端加入一級功率因數校正(PFC)電路，以通過諧波測試標準的規範。如此不僅降低了能量轉換的效率，也提高了電路製作的複雜度與成本。為了簡化系統，單級的共振式LLC轉換器只使用一個控制晶片驅動PFC電路以及LLC電路。但這同時帶來一個問題是，PFC電路與LLC電路中的儲能電容電壓變得不可預測，因為PFC電路與LLC電路的輸出能量並不相同。在本論文中分析了工作頻率與PFC電路LLC電路輸出能量的關係，此關係可幫助單級共振式LLC轉換器的設計。 簡言之，在兩個系統的分析中，整流器的負載可視為一電壓源分析。系統行為完全可以由系統的直流工作點推導得到。屏除了系統負載於系統的分析中，如此可簡化系統分析，並幫助系統設計。Modern electronic systems demand high power density, low EMI and high efficiency power processors. The choice of power supply topology in particular design is significantly based on the needs of the application itself. Resonant dc-dc converter is more and more popular because it has the major advantage of easy to achieve zero voltage switching. However, in resonant dc-dc converters, the load of resonant circuit is a nonlinear component, a rectifier, which makes system analysis complex. Traditional dc-dc converter analyses treat the rectifier load as an equivalent resistive load, then, the analysis can follow linear resonant circuit analysis. But in some cases, like burst mode control systems, the equivalent impedance of rectifiers can’t be got by linear analysis. Moreover, the behaviors of dc-dc resonant converters can be derived only by system dc operating point. Involving load impedance complicates system analysis in some cases. Two resonant systems, PT dc-dc converters and a single-stage LLC dc-dc converter are involved in this thesis. A novel analysis based on energy equilibrium is presented for burst mode control PT dc-dc converters. The PT input current and system efficiency of PT dc-dc converters are derived in time domain. The results show that the system behaviors only depend on system operating point and the PT input current contains the information of output voltage. Then, a primary control PT dc-dc converter is built for verification. A conventional power supply was designed with two stages, the former stage function as a power factor corrector (PFC), and the latter stage is a dc-dc converter which regulates the output voltage of the system. However, the cost and energy conversion efficiency of the two-stage system is higher than a single-stage one. For simplification, one control IC is used to drive two power converters, PFC regulator and resonant converter, in a single stage LLC dc-dc converter. However, the bulk capacitor between two converters becomes unpredictable because the power of PFC regulator and resonant converter are not balance. In this thesis, the relationship between operating frequency and output power of two converters are derived. Actually, the load impedance is removed to simplify the analysis. The results help to design single stage LLC dc-dc converter. In summary, the rectifier load of resonant circuit is treated as a voltage source. The system behaviors can be derived by given system dc operating point. Thus, the load impedance can be removed from the system analysis which simplifies system analysis and helps system design