CHAPTER 4. THE FORWARD CONVERTER USING THE PROPOSED
5.5 Extension Circuits
The proposed full-bridge converter can deliver high power (up to 5.0KW) to output from input port. When the application doesn’t need to deliver so much power and want to save MOSFET, user can employ half-bridge converter in his application. The proposed half-bridge converter is shown as Fig. 5.16.
The additional winding is different from the one in the proposed full-bridge converter, and it has not the center-tap in the winding N1. Therefore, the voltage stress across S1 and S2 are different, and the voltage stress on S1’s will be larger than S2’s. Although the asymmetric operation between switch S1 and S2, the input line current can still conform to the standard, IEC61000-3-2 shown in table 5.2. The simulation results are shown in fig. 5.17.
Vac Lf
Fig. 5.16 The proposed asymmetric half-bridge converter
Vac/230V
iac Vac
iac
Vac/230V
iac Vac
iac
Fig. 5.17 Simulation waveforms in half-bridge converter
0 0.5 1 1.5 2 2.5
3 5 7 9 11 13 15 17 19 21 IEC61000-3-2 Vac/230V
Iac(A)
Harmonics number
0 0.5 1 1.5 2 2.5
3 5 7 9 11 13 15 17 19 21 IEC61000-3-2 Vac/230V
Iac(A)
Harmonics number
Table. 5.2 The major harmonic components of the line current, Po=50V․10A.
The proposed half-bridge converter can save two MOSFETs comparing to the full-bridge converter but the driver circuit for switch S1 is still inconvenient. A push-pull converter could be another choice. Figure 5.18 is the proposed push-pull converter with input current shaper.
The two switch S1 and S2 are low side switches so the driver method is simple and easy comparing to half-bridge or full-bridge converters. Besides, the voltage stress across on S1 and S2 are same, and the two switches operation is symmetric. The simulation results are shown in Fig.5.19. Table 5.3 shows the line current harmonics can meet standard IEC61000-3-2 class D.
Vac/230V
iac
iac Vac Vac/230V
iac iac Vac
Fig. 5.19 Simulation waveforms in push-pull converter
Vac Lf Cf
Dr
C1
C2 L1
D1
D2 D3
D4
D5
S2
S1
n1 : n2: n3
iac
iN1
iN2
iS1
iS2 iD1 iD3
VC1 +
-VC2 +
-VL1 +
-C3 L2 D7
D8 iD7
iD8
iL2 VO +
-VN2
+
-VN3 +
-VN1
+
-im
-Vac Lf Cf
Dr
C1
C2 L1
D1
D2 D3
D4
D5
S2
S1
n1 : n2: n3
iac
iN1
iN2
iS1
iS2 iD1 iD3
VC1 +
-VC2 +
-VL1 +
-C3 L2 D7
D8 iD7
iD8
iL2 VO +
-VN2
+
-VN3 +
-VN1
+
-im
-Fig. 5.18 The proposed push-pull converter
0 0.5 1 1.5 2 2.5
3 5 7 9 11 13 15 17 19 21
EC61000-3-2 Vac/230V
iac(A)
Harmonics number
0 0.5 1 1.5 2 2.5
3 5 7 9 11 13 15 17 19 21
EC61000-3-2 Vac/230V
iac(A)
Harmonics number
Table 5.3 The major harmonic components of the line current, Po=50V․10A, in proposed push-pull converter
CHAPTER 6
SUMMARY and FUTURE RESEARCHES
6.1 Summary
A new family of AC/DC converters with input current shaper is introduced in this dissertation. The proposed converter has the functions of harmonic current correction and fast output voltage regulation. It is implemented in a single-switch single-stage and single control loop fashion. The structure is simple. The main merit is that the magnetic material’s volume and weight are reduced to much smaller and lighter than those are in conventional S4IP2 converters by employing a two-primary-windings transformer. The employment of additional primary winding is designed to provide a threshold level so that the voltage dropped in input inductor can be decreased. Therefore, the bulk inductor used in the conventional boost-based S4IP2 converters is not needed any more in this design. Instead, a small buffer inductor is used in the input loop to constraint the input current. The line current of the proposed converter complies with standard IEC 61000-3-2 and the voltage regulation is tight under load change and has been verified by experiment results. The voltage across bulk capacitor can be held under 450v by adjusting turn-ratio n1/n3 in full range operation (85v~265v/ac).
Table 6.1 shows several comparison data. BIFRED and BIBRED have high power factor corrector and high efficiency but their bulk capacitor’s voltage tends higher than 450V, and the boost inductor is large in comparing to the proposed circuit. The circuit with magnetic switch has better features, high PFC, high efficiency, and light boost inductor, but the circuit suffers high voltage stress over 450V across bulk capacitor in light load operation. The circuit with magnetic feedback also has better features, light boost inductance and lower bulk voltage, but the harmonics current is higher than the proposed circuit.
Table. 6.1. Comparison table between proposed circuit and prior circuits Proposed
Circuit (Flyback)
BIFRED [28] BIBRED [28] Magnetic feedback, [10], [11], Fig. 2.7
Magnetic Switch, [33], [34]
PFC ~90% ~95% ~97% ~75% 98%
Power efficiency
~ 75% ~80% ~82% ~70% 82%
dc-bus voltage at Vac=265V
Under 450V, almost load independent
over 450V over 450V Under 450V Over 450V at light load, load dependent Boost
inductance, Lb
None; only smoothing inductor L1
Lb~1.7Lm* Lb~Lm/2 Lb~Lm/11 Lb~Lm/12
Operation mode
DCM(Boost cell),
CCM(dc/dc)
DCM(Boost cell),
CCM(dc/dc)
DCM(Boost cell),
CCM(dc/dc)
DCM(Boost cell),
CCM(dc/dc)
DCM(Boost cell),
DCM(dc/dc)
* Lm: primary winding inductance
The value regarding the inrush current while the proposed circuits turning on, it will depend on the input impedance in the input port of the converters. The test results are shown as followings. Figure 6.1 (a) shows the inrush current in conventional flyback converter without input current shaper. Figure 6.1 (b) shows the inrush current in the proposed flyback converter with input current shaper. The inrush current in the proposed flyback converter has a smaller peak value than the one in conventional flyback converter. The reason is that the input current shaper of the proposed converter has greater input impedance than conventional flyback converter.
Circuits
Features
A reference selection guide for applying the proposed circuits is shown in figure 6.2. In typical application design of flyback converters the power is suggested up to 200W when output voltage is greater than 100V, but the application power is suggested a lower one when the output voltage is smaller than 100V. The output power is suggested between 10W and 200W while the output voltage is in 1V - 100V and the circuits can be flyback or forward converters. However, the maximum output power of forward converters is suggested no greater than 600W.
When output power is greater than 600W, bridge-type or push-pull converters are suggested to use in application. Full-bridge converter can deliver more output power than half-bridge converter or push-pull converter in using the same core size and the same input voltage. Furthermore, full-bridge converter has smaller voltage stress across on switching components in comparing to those in half-bridge and push-pull converters.
(a)
(b)
Fig. 6.1 The inrush current of input port while switching on input voltage in (a) conventional flyback converter (b) proposed flyback converter, at Vac=110V.
VC2, 100V/div Inrush current,
Iac, 5A/div
Inrush current,
Iac, 5A/div VC2, 100V/div
1 10 102 103
1 10 102 103
Po(W) Vo(V)
Flyback converter
Flyback
& Forward converter
Forward converter
Forward &
bridge-type converter
1 10 102 103
1 10 102 103
Po(W) Vo(V)
Flyback converter
Flyback
& Forward converter
Forward converter
Forward &
bridge-type converter
Fig. 6.2 Converter circuit selection as a function of output voltage and throughput power. [41]
6.2 Future Research
Based on the proposed circuits, the suggested future researches are to realize the proposed bridge-type converter, to implement soft-switching technique in these new converters and to improve power flow process in one times transformation from input terminal to output port. Although this research proposes the approach to reduce bulk inductance in boost cell of the boost-type input current shaper, the power efficiency is still not to be satisfied because a part of input power is transferred two times before deliver to output.
The part of input power transfers to bulk capacitor via boost cell then the power transfers to output port via dc/dc cell. That is the reason why the power efficiency isn’t satisfied.
The proposed flyback converter and forward converter can employ active-clamp technique to implement soft-switching approach [42]-[46]. Besides, the proposed bridge-type converters can employ phase-shift technique to implement zero-voltage-switching approach [47]-[49].
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Vita
姓名: 劉興富 性別: 男
生日: 中華民國 52 年 7 月 25 日 籍貫: 台灣省新竹縣
論文題目: 中文: 新型式單相單級交流轉直流且具有輸入電流修飾的電源轉換器 英文: Novel Single-Phase Single-Stage AC/DC Converters with Input Current
Shaper
Research Laboratories, Industrial Technology Research Institute, Hsingchu, Taiwan, R.O.C., where his research focused on soft-switching techniques, high-density dc/dc converters, and ac/dc Power-factor-correction circuits. In 1995, he joined Philips Electronics, Chung-Li, Taiwan, R.O.C., as Senior Designer, developing ac/dc and dc/dc power circuits for new model PC monitors. In 1998, he joined Delta Electronics, Chung-Li, Taiwan, R.O.C., where he was involved in developing a switching-mode rectifier for a telecom power system. From 2000 to 2004, he was with Analog Integrations Corporation, Hsingchu, Taiwan, R.O.C., as Manager of the Application Engineering Department. His interests include high-frequency soft-switching techniques, passive and active snubber circuits, ac/dc power-factor-correction circuits, LEDs lighting power, and modeling simulation on power electronics.
Hsing-Fu Liu (M’00) was born in Hsingchu, Taiwan, R.O.C, in 1963. He received the M.S. degree in electrical engineering from Chung Yuan Christian University, Chung-Li, Taiwan, R.O.C., in 1991. He is currently working toward the Ph.D. degree at National Chiao Tung University, Hsingchu, Taiwan, R.O.C. From 1991 to 1995, he was with the Computer and Communications
學歷:
1. 民國 80 年 6 月 私立中原大學電子工程研究所畢業
2. 民國 94 年 6 月 國立交通大學電機及控制工程研究所博士班畢業
經歷:
1. 民國 87 年 7 月 任職台達電子公司研發工程部
2. 民國 89 年 8 月 任職沛亨半導體公司應用工程部經理 3. 民國 93 年 2 月 任職聚積科技公司應用工程部資深經理
4. IEEE member and member of IEEE Power Electronics Society since 2000.
5. IEEE APEC Technical Program Committee Member, 19th International Conference on Feb. 22-26, 2004.
6. IEEE PESC Technical Program Committee Member, 36th International Conference on June 12-16, 2005.
著 作 目 錄
Journal
[1] Hsing-Fu. Liu and Lon-Kou. Chang, “Flexible and Low Cost Design for a Flyback AC/DC Converter With Harmonic Current Correction,” IEEE Trans. Power Electronics, vol. 20, pp. 17~24, Jan 2005.
[2] Lon-Kou. Chang and Hsing-Fu. Liu, “A Novel Forward AC/DC Converter With Input Current Shaping and Fast Output Voltage Regulation Via Reset Winding,” IEEE Trans.
Industrial Electronics, vol. 52, pp. 125-131, Feb. 2005.
Patent
[1] 張隆國, 劉興富, “反馳式電流諧波校正之交流轉直流轉換器”,專利號碼: I221699 中華民國專利. 93 年 10 月.
Conference
[1] Hsing-Fu Liu ,” Constant- Power- Protection in Switching Power Converter with
Variable-Frequency Modulation,” 第21屆電力工程研討會, pp.779-783, 台北市, 台灣, Nov. 18~19, 2000.
[2] Hsing-Fu Liu, Yung-Hiang Liu and Ying-Yu Tzou,” Implementation of ZVT soft switching technique in a single-phase PFC rectifier for server power supply,” in Proc.
PIEMC 2000, pp. 584 – 589,Beijing, China, 15-18. Aug., 2000.
[3] Lon-Kou Chang and Hsing-Fu Liu, “A Flexible and Low Cost Design for Flyback AC/DC Converter with Harmonic Current Correction,” in Proc. APEC’03, pp. 677–683,Miami Beach, Florida, USA, 9-13 Feb., 2003.
[4] Lon-Kou Chang and Hsing-Fu Liu,” A flexible and cost-effective family for AC/DC converters with input-current-shaper and fast output-voltage-regulation,” in Proc.
PESC’04, pp. 3113-3119, Aachen, Germany,20-25 June 2004.
[5] Lon-Kou Chang; Yen-Ming Liu; Hsing-Fu Liu,” An integrated single-stage AC/DC converter with ZVS active-clamping for universal line applications,” in Proc. PESC’04, pp. 759-764, Aachen, Germany,20-25 June 2004.
[6] Lon-Kou Chang and Hsing-Fu Liu,” A novel and low cost design for forward AC/DC converter with harmonic current correction,” in Proc. IPEMC’04, pp. 105-110, Xi’an China, 14-16 Aug., 2004.