Analysis and Design of Magamp Post-Regulator for Flyback Converters

傳統的磁放大器技術主要是針對前驅式轉換器(Forward converter)，然而，相較於返馳式轉換器(Flyback converter) ，前驅式轉換器有較多元件數目與較高成本的缺點。本文提出一適用於返馳式轉換器之磁放大器技術，利用電流分流之技術，將不同輸出於不同時區充能，以達到多組輸出穩壓的目的。 論文中將對所提出的技術內容作詳細的工作原理探討與深入的系統動態分析。不同於傳統的架構，其輸入/輸出的關係是與平均電流相關。利用狀態空間平均法求得穩態模型與小訊號模型，由於在操作過程共用相同之磁化電感，因而不同輸出間存在著交互作用，原本存在於單組輸出返馳式轉換器之右半面零點亦轉移至交互作用迴路上，但因在特定條件下,其交互作用較小，本文因而提出一主要函數補償法，經由訊號流方法可求得補償器之設計。 實驗驗證於一20W 輸出之雙組輸出返馳式轉換器，由實驗記錄可證明所提出磁放大器方法，小訊號模型與補償器設計之有效性。 最後，由於元件之非理想特性，實際線路之工作區域將受限制，文中並提出一分析模型以探討此現象。 基於此模型，造成無法維持穩壓之邊際條件將被求得，文中並提供實驗結果以證實此分析模型之準確性。Applications of the magamp technique are mainly focused on multiple-output forward converters. However, the drawbacks of forward converters are more part counts and higher cost compared with flyback converters. In this dissertation, a new magamp technique for flyback converters is proposed. Using the current sharing approach, the outputs are powered in different time slots. In this way, the multiple output voltages can be regulated. In this dissertation, the detailed studies of the operation principle and system dynamics are proposed. Unlike other traditional topologies, the input/output relationships are depended on the average currents. Both steady-state model and small-signal model is derived with state-space averaging approach. Since the multiple outputs share the magnetizing energy of the coupled inductor, the interactions are found among the outputs. The existence of right half plane zero in single output flyback converter is also moved to the interaction loops. However, the cross interactions among outputs are small under a specified condition. A dominant function compensation method is presented. Signal flow graph technique is utilized to design the compensator. Experimental verifications on a 20W two-output flyback converter are conducted. Recordings illustrate the effectiveness of the proposed magamp approach, the small-signal modeling and compensator design. At last, the operation area of practical circuit will be bounded by the non-ideal component characteristics. An analytical model for studying the phenomenon is proposed. Based on the model, the mechanism of boundary condition that causes the converter out of regulation is explored. Finally, experimental results are provided to show the accuracy of the proposed analytical model.1. Introduction 1.1 Background and Motivation .......................1 1.2 Outline of the Dissertation......................4 2 Magamp Post-Regulation for Flyback Converters 2.1 Introduction.....................................5 2.2 Basic Operational Principle......................6 2.3 Steady-State Input/Output Relationship...........9 2.4 Summary.........................................12 3 Magamp Post-Regulator Design for Flyback Converters 3.1 Introduction....................................13 3.2 Power Stage Model...............................13 3.3 Compensation Design.............................24 3.3.1 Signal flow graph...............................31 3.3.2 Dominant function compensation..................33 3.3.3 Compensation network............................37 3.4 Experimental Verifications......................39 3.5 Summary.........................................54 4 Boundary Condition of Operation Area 4.1 Introduction....................................55 4.2 Analytical Model with Non-ideal Characteristics of Components............................................55 4.3 Circuit Analysis of Proposed Analytical Model...61 4.4 Analytical Expression of Boundary Condition.....69 4.5 Experimental Verifications......................70 4.6 Summary.........................................78 5 Conclusions.....................................79 Appendices A – Roots of Third Order Equation.......................81 B – Derivation of FR and FM2............................83 References...............................................86 Vita.....................................................9