在功因校正電源轉換器之設計上，必須謹慎處理由逆向恢復電流所導致的硬切換消耗。目前已經有兩種解決硬切換消耗問題的方式被提出來。一者是被動軟切換方法，再者是主動軟切換方法。在實務上，被動軟切換方法已經廣泛應用於工業上。因為有簡單、低成本和可靠的優點。雖然被動軟切換方法擁有諸多優點，仍然存在著一些缺陷，有待改善。本文研製一改良式零電流切換方法，不但解決了硬切換消耗問題，並且同時改善被動軟切換方法的缺點。特別是利用飽和電感和一分支電路來取代零電流切換電路中的電感器。這種提議的方式使被動軟切換電路達到最佳化，而且改善了已知的缺點。
在本文中除詳細介紹改良式零電流切換功因校正器的工作原理外，並經由實際的電路實作結果跟一般被動軟切換及硬切換功因校正器做比較。證明出本實驗電路的可行性，而且改善了大部份的軟切換方式之缺點。

In the PFC converter design must carefully deal with the hard switching losses due to the recovery current of boost diode. There are two approaches had proposed to solve the hard switching losses issue. One is passive soft switching method and the other is active soft switching method. Practically, the passive soft switching method has been used more widely in industry, because of it has simple, low cost, and reliable. Although, the passive soft switching method has more merits but it still exists some drawbacks that need to be improved. This thesis proposes the improved zero current switching method not only to solve the hard switching issue but also to improve drawbacks of the passive soft switching method. Especially, the saturable core (Amorphous core) and a branch circuit are proposed to substitute the fixed inductor in ZCS circuit. This proposal optimizes the passive soft switching circuit and improves many drawbacks. 
In this thesis, besides the principle of operation is introduced in detail, the experimental results of the real implementation is compared with the hard switching PFC converter as well as others passive soft switching. According to experimental results, this proposed improved zero current switching method is proved feasible, and also improves the most of drawbacks of passive soft switching methods.

TABLE OF CONTENTS
CHAPTER 1 Introduction 1
1.1 Motivation 1
1.2 Drawbacks of Passive Soft switching 4
1.3 Research Goals 6
1.4 Organization 7
CHAPTER 2 Overview Of Methods for PFC 8
2.1 Passive PFC 8
2.1.1 Inductor in serial with AC-side 8
2.1.2 Inductor in serial with DC-side 9
2.1.3 Rectifier with series-resonant band-pass filter 9
2.2 Low-Frequency Active PFC 10
2.2.1 The phase-controlled rectifier 11
2.2.2 The low-frequency Boost converter 11
2.2.3 The low-frequency Buck converter 11
2.3 High-Frequency Active PFC 13
2.3.1 Second-order switching converters applied to PFC 13
2.3.2 The Buck converter active PFC 16
2.3.3 The Boost converter active PFC 16
2.3.4 The Buck-Boost converter active PFC 16
2.3.5 Operation in Continuous Inductor Current Mode (CICM)17
2.3.6 Operation in Discontinuous Inductor Current Mode (DICM)19
CHAPTER 3. Methods of Improving Efficiency 23
3.1 Introduction 23
3.2 Passive soft switching methods 23
3.2.1 A simple and effective method 23
3.2.2 A lossless turn-on snubber method 26
3.2.3 The minimum voltage stress (MVS) cell 29
3.3 Active soft switching 33
3.3.1 The new zero voltage transition method (ZVT)33
3.4 Summary of conclusions 38
CHAPTER 4. Improved zero current switching PFC converter 40
4.1 Introduction 40
4.2 Principle of the improved zero current switching PFC converter 41 
4.3 Design procedures 50
CHAPTER 5. Experiment 59
5.1Comparison on issues of different passive soft switching methods 59
5.1.1 Experimental approach 59
5.12 Conclusion of comparison 60
5.2 Improve zero current switching PFC experiment 75
5.21 Experiment 75
5.2.2 Conclusion 75
CHAPTER 6. Conclusion and Future Works 88
6.1 Conclusion 88
6.2 Future Works 89
Reference 90

LIST OF FIGURES
Fig. 2.1 Inductor in serial with AC-side 8
Fig. 2.2 inductor in serial with DC-side 9
Fig.2.3 Rectifier with series-resonant band-pass filter 10
Fig. 2.4 Low-frequency active PFC 12
Fig. 2.5 Second-order switching converters and their application for high-frequency active PFC, assuming operation in ICM 14
Fig. 2.6 the control scheme for PFC using a switching converter operating in CICM 18
Fig. 2.7 Second-order switching converters 20
Fig 3.1 a simple and effective method 23
Fig 3.2 shows the corresponding key waveforms of the operation 25
Fig 3.3 shows the seven topological stages of the converter in one switching 26
Fig.3.4 the lossless turn-on snubber method 26
Fig 3.5 the operation waveforms of the lossless snubber 28
Fig.3.6 the operation of the lossless snubber method includes six intervals 29
Fig 3.7 The minimum voltage stress (MVS) cell of lossless passive soft switching method 30
Fig.3.8 shows the waveforms of the converter when soft switching is achieved 31
Fig 3.9 shows all the circuit stages whether or not soft switching is achieved 32
Fig 3.10 shows the new zero voltage transition method (ZVT)33
Fig 3.11 shows key waveforms concerning the operation stages 36
Fig 3.12(a)–(g) shows the equivalent circuit schemes of 
these operation stages espectively 37
Fig 4.1 Improved Zero Current Switching for PFC converter diagram 41
Fig 4.2. The relative voltage and current waveforms of circuit operation in time scale 42
Fig 4.4 the square hysterisis loop of the saturable inductor L2 43
Fig 4.3-T0 shows the proposed circuit with operating current indications 44
Fig 4.3-T1 shows the proposed circuit with operating current indications 45
Fig 4.3-T2 shows the proposed circuit with operating current indications 46
Fig 4.3-T3 shows the proposed circuit with operating current indication 47
Fig 4.3-T4 shows the proposed circuit with operating current indication 48
Fig 4.3-T5 shows the proposed circuit with operating current indication 49
Fig 4.3-T6 shows the proposed circuit with operating current indication 50
Fig 4.5 The design point of ZCS 51
Fig 4.6 Structure of saturable core L2 53
Fig 4.7 shows the actual V*S of L2 < 64.8uVS in experimental result 54
Fig 4.8 shows IL2 and IC3 waveforms during T5~6 56
Fig 5.1 a simple and effective method 61
Fig 5.2 the lossless turn-on snubber method 61
Fig 5.3 the minimum voltage stress (MVS) cell of lossless passive soft 61
Fig 5.4 improved zero current switching method 61
Fig 5.5 Reverse bias VF on a simple and effective method 62
Fig 5.6 Off duration limit on a simple and effective method 62
Fig 5.7 Performance of ZCS on a simple and effective method 63
Fig 5.8 Circulating current on a simple and effective method 63
Fig 5.9 Time for achieving ZCS at Vout >124V on a simple and effective method 64
Fig 5.10 Time for achieving ZCS at Vout >146V on a simple and effective method 64
Fig 5.11 Reverse bias VF on the lossless turn-on snubber method 65
Fig 5.12 Off duration limit on the lossless turn-on snubber method 65
Fig 5.13 Performance of ZCS on the lossless turn-on snubber method 66
Fig 5.14 Circulating current on the lossless turn-on snubber method 66
Fig 5.15 Time for achieving ZCS at Vout >122V on the lossless turn-on snubber method 67
Fig 5.16 Time for achieving ZCS at Vout >154V on the lossless turn-on snubber method 67
Fig 5.17 Reverse bias VF on the minimum voltage stress (MVS) cell of lossless passive soft switching method 68
Fig 5.18 Off duration limit on the minimum voltage stress (MVS) cell of lossless passive soft switching method 68
Fig 5.19 Performance of ZCS on the minimum voltage stress (MVS) cell of lossless passive soft switching method 69
Fig 5.20 Circulating current on the minimum voltage stress (MVS) cell of lossless passive soft switching method 69
Fig 5.21 Time for achieving ZCS at Vout >152V on the minimum voltage stress (MVS) cell of lossless passive soft switching method 70
Fig 5.22 Time for achieving ZCS at Vout >310V on the minimum voltage stress (MVS) cell of lossless passive soft switching method 70
Fig 5.23 Reverse bias VF on improved zero current switching method 71
Fig 5.24 Off duration limit on improved zero current switching method 71
Fig 5.25 Performance of ZCS on improved zero current switching method 72
Fig 5.26 Circulating current on improved zero current switching method 72
Fig 5.27 Time for achieving ZCS at Vout >148V on improved zero current switching method 73
Fig 5.28 Time for achieving ZCS at Vout >296 on improved 
zero current switching method 73
Fig 5.29 Input voltage and input current at full load 90V~ 77
Fig 5.30 Cross-over of Vds versus Ids in ZCS mode 77
Fig 5.31 Voltage (V_ L2) and current (I_L2) of L2 saturable inductor 78
Fig 5.32 shows waveform’s relationship of Vds, I_L3, and I_C3 78
Fig 5.33 shows waveform’s relationship of Vds, I_D1, and I_D4 79
Fig 5.34 shows waveform’s relationship of Vds, I_D1, and I_C2 79
Fig 5.35 Voltage (V_D1) and current (I_D1) of diode D1 80
Fig 5.36 Voltage (V_D4) and current (I_D4) of diode D4 80
Fig 5.37 Voltage (V_C2) and current (I_C2) of capacitor C2 81
Fig 5.38 shows the reverse bias difference between V_D4 and V_D1 81
Fig 5.39 Voltage (V_D2) and current (I_D2) of diode D2 82
Fig 5.40 Voltage (V_L3) and current (I_L3) of inductor L3 82
Fig 5.41 Voltage (V_D3) and current (I_D3) of diode D3 83
Fig 5.42 shows the relationship between I_L2 and I_L1 83
Fig 5.43 shows the crossover between Ids and Vds when STTH8R06D is adopted for hard switching application 84
Fig 5.44 shows the crossover between Ids and Vds when SDP06S06 is adopted for hard switching application 84
Fig 5.45 shows the crossover between Ids and Vds when the improved zero current switching is adopted 85
Fig 5.46 shows efficiency versus output power between hard switching and improved zero current switching 86
Fig 5.47 shows the experimental circuit with UC3854 controller 87

LIST OF TABLES
Table 2.1. Topology-specific characteristics 17
Table 2.2. Inherent PFC properties of second-order switching converters in DICM  21
Table 5.1 Criteria comparison between four methods each other 74
Table 5.2 shows efficiency and power loss between hard switching and
 improved zero current switching 85
Table 5.3 shows the component list of improved zero current switching 86

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