lcc和llc应用于宽输出变换器时的比较

Saijun Mao1,3*, Jelena Popovic3, Ramanujam Ramabhadran2,

Jan Abraham Ferreira3

1.GE Global Research, Shanghai, China 2.GE Global Research, Niskayuna, US

3.Delft University of Technology, Delft, The Netherlands

*Tel.: +86 / (21)– 38771302 *Fax: +86 / (21)– 50807277 *E-Mail: Saijun.Mao@ge.com

Keywords

«LCC resonant converter»,«LLC resonant converter», «Wide output power range», «High efficiency», «Narrow switching frequency range»

Abstract

The Half-Bridge (HB) LCC resonant DC-DC converter and HB LLC resonant DC-DC converter circuit are comparatively studied for high efficiency ultra-wide output power range application in this paper. The output voltage ranges from minimum output voltage to twice that value. And the output current ranges from 10% load to 100% load. So the output power spans over a wide range, from minimum to 20 times that. The detailed resonant tank characteristics analysis for HB LCC and LLC resonant converter is provided. Through the 150W hard prototype experiments validation, it is shown that HB LLC resonant DC-DC converter can achieve better performance with flat efficiency, narrow switching frequency range compared with HB LCC resonant DC-DC converter for wide output current application at both 75V & 150V output voltage from 10% output current to 100 % output current conditions. HB LLC resonant DC-DC converter is more preferred power conversion circuit topology to achieve high performance with flat efficiency, narrow switching frequency range in ultra-wide output power range applications.

1. Introduction

With the increasing demand for high efficiency and high power density, the Half-Bridge (HB) LCC resonant DC-DC converter and HB LLC resonant DC-DC converter are 2 most promising isolated topologies achieve high performance power conversion[1-5]. HBLCC resonant DC-DC converter circuit and HB LLC resonant DC-DC converter can both achieve zero voltage switching turn-on for switches when the switching frequency is above the resonant frequency. The HB LCC resonant DC-DCconverter and HB LLC resonant DC-DC converter are both used for ultra-wide output power range applications,such as battery charging, and lighting electronics with dimming function [4-8]. Both LCCand LLC resonant DC-DC convertersare introduced for wide load range applications respectively [4-8]. In this investigation, the output voltage ranges from the minimum value to twice that value. And the output current is 10 times range from 10% light load to 100% load. So the output power range very wide (20 times). The investigation of the LCC resonant DC-DC converter and LLC resonant DC-DC converter at such ultra-wide output range application is the research motivation to achieve high circuit efficiency with flat efficiency and narrow switching frequency range.

The output power specification for this investigation scope is from 75VDC to 150VDC, and output

current specification is from 0.1A to 1A with 450V DC input. The circuit schematics of HB LCC resonant converter is illustrated in Fig.1. The key requirements for design target: flat efficiency curve and tight switching frequency range at wide load range.

Q1VinQ2BDR3DR4AD2D1CrLrC2CpC1n:1DR1DR2CoRd+Vo−VinQ2BDR3DR4Q1AD2C2D1C1CrLriLriLmLmn:1DR1DR2CoRd+Vo− (a) HB LCCResonant DC-DCConverter (b) HB LLC Resonant DC-DC Converter

Fig.1: Schematic of HB Resonant Converter

The resonant frequency of LCC and LLC resonant tank can be found in equation 1 and 2 respectively. 1;f fr1 r22SLrCr12SLrCrCpCr󰀎Cp(1) fr 12SLrCr;fm 12S

󰀋Lr󰀎Lm󰀌Cr(2)

2. LCC & LCC resonant resonant tank characteristics analysis

The design parameters for the HB LCC resonant tank and HB LLC resonant tank can be summarized inTable based on the reference papers [4-8]. The HB LCC & LLC resonant tank gain characteristics curve at 75V and 150V output voltage can be obtained in Fig.2 and Fig.3 respectively.

Table I: HB LCC and LLC resonant tank circuit parameters Resonant tankHB LCCHB LLC2fr1/fm50kHz50kHzfr2/fr302kHz100kHzn1.42.32Lr604μH538μH,R 󰀔󰀑󰀓󰀘$,R 󰀓󰀑󰀘$,R 󰀓󰀑󰀖$,R 󰀓󰀑󰀔$0PLQCr15.9nF4.7nFCp470pF0Lm24.30mH1.41mH1.5,R 󰀔󰀑󰀓󰀘$,R 󰀓󰀑󰀘$,R 󰀓󰀑󰀖$,R 󰀓󰀑󰀔$0PD[1.5Vo=150VMdc1Mdc1Vo=75V0.50.5031u101u104fs/Hz1u1051u106031u101u104

fs/Hz1u1051u106

Fig.2(a):LCC gain curve at Vo=150VFig.2(b):LCC Gain curve at Vo=75V

At light load conditions, the LCC resonant converter operation characteristics are quite approaching to parallel resonant converter. The parallel capacitance Cphas big impact for LCC resonant converter at light load conditions. From the gain characteristics curve at Vo=150V, the operation frequency is around 300kHz. At this state, LCC resonant converter will suffer large power loss due to high turn-off loss in the switches. The larger Cp, the narrower the switching frequency will get. However, at the same time, larger Cp will generate more conduction loss due to alarger resonant tank current when the load gets heavy. And the circuit efficiency will get worse with larger Cp.

0.40.4Io=1.05AIo=0.3AIo=0.2AIo=0.1AMmax=150VVo=150V0.30.3Io=1.05AIo=0.3AIo=0.2AIo=0.1AMmin=75VMdc0.2Mdc0.20.1Vo=75V0.1041u101u105fs/Hz1u1061u107

041u101u105fs/Hz1u1061u107

Fig. 3(a): LLC Gain curve at Vo=150VFig. 3(b): LLC Gain curve at Vo=75V

The transformer parasitic components will introduce the LLC resonant tank gain distortion at light load. Fig.4 shows the transformer model with parasitic components. From transformer measurements, we can obtain the following transformer parameters:

Llk 83PH,Lm 1.41mH,CTp 45pF,CTs 222pFThe resonant tank gain curve considering the transformer piratical components, especially the transformer

parallel capacitances (CTP&CTS) at Vo=75V can be found in Fig.5. The transformer parallel capacitances will introduce the resonant peak, the larger the transformer paralleled capacitances, the larger resonant gain and circuiting current.

Cps1Llk0.3Io=1.05AIo=0.3AIo=0.2AIo=0.1AMmin=75VNp˖NsLmCTsCTpMdc0.2Vo=75V0.1Cps2

041u101u105fs/Hz1u1061u107

Fig. 4: Transformer model with parasitic components Fig. 5: LLC gain curve considering the transformer parasitic components at Vo=75V It is difficult to reduce the transformer paralleled capacitances considering the transformer space limitation. In order to achieve full load range robust operation without transformer paralleled capacitances influences, the resonant tank needs to be optimally designed. The optimal goal is to design the voltage gain of resonant tank to minimum value at targeted switching frequency range, and minimum output

current can be achieved. The optimally designed resonant tank gain curve is shown in Fig.6. The resonant tank gain curve will be designed sharper by reducing Uomin and fmax. We can find that the resonant tank characteristic factor will be increased due to increased resonant inductor and decreased resonant capacitor. So the voltage and current stress of resonant tank will be increased accordingly. The original and optimal designed circuit parameters can be found in Table II. Table II: Circuit parameters: original design vs. optimal design fmaxOriginal designOptimal design2fr1.5frLr538uH1.151mHIo=1.05AIo=0.3AIo=0.2AIo=0.1AMmax=150VCr4.7nF2.2nFLm1.41mH1.015mHn99:4399:43Io=1.05AIo=0.3AIo=0.2AIo=0.1AMmin=75VQ0.521.20Vo=150V0.30.3Mdc0.2Mdc0.2Vo=75V0.10.1041u101u105fs/Hz1u106041u101u105fs/Hz1u106Fig. 6(a): Optimal gain curve Vo=150V Fig. 6(b): Optimal gain curve Vo=75V

3. Experimental results & comparative study

3.1 The 150W HB LCC resonant converter experimental results

The 150W HB LCC& LLC resonant converter prototype is built to validate the design. 650V Silicon MOSFET SPP07N60C3 from Infineon is used for HB resonant converter primary switch. And the 600V surface mount ultrafast silicon rectifier MURS360 from Vishay is chosen as secondary output rectifier diode. The input voltage is 450VDC. The output power is tested at both 75V and 150V with 10% output current to 100% output current.

The detailed key waveform for HB LCC resonant DC-DC converter circuit at different output voltage and output current conditions can be found in Fig.7 and Fig.8 at 75V and 150V output voltage with 0.1A and 1.0A output wide range. The HB LCC resonant DC-DC converter switches can achieve ZVS at both 0.1A and 1.0A output current. HB LCC resonant DC-DC converter efficiency and switching frequency curve at different output currents are given in Fig.9. The maximum circuit efficiency is around 95% at Vo=150V. The switching frequency range is from 60 kHz to 320kHz. The circuit efficiency at Vo=150V is higher than the efficiency at Vo=75V due to smaller conduction loss. The switching frequency range at Vo=150V andVo=75V are almost the same. At 0.1A output current light load, the power loss is dominated by the MOSFETs. At 1.0A output current heavy load, the major power losses come from MOSFETs, transformer and inductor due to large conduction loss at heavy load.

(a) Io=0.1A (b) Io =1.0A

Fig. 7:Key waveforms of HB LCC resonant DC-DC converter at Vo=75V

vgsvdsiCrioiCriovgsvds

(a) Io=0.1A (b) Io =1.0A Fig. 8: Key waveforms of HB LCC resonant DC-DC converter at Vo=150V

Fig. 9:Efficiency and switching frequency curve vs. output current for HB LCC resonant DC-DC

converter

3.2 The 150W HB LLC resonant converter experimental results

The measured waveform for HB LLC resonant DC-DC converter circuit at different output voltage and output current conditions can be found in Fig.10 and Fig.11 at 75V and 150V output voltage with 0.1A and 1.0A output load range. From the waveforms can be seen that the switches can achieve the ZVS at all different output voltage from 0.1A to 1.0A output current. The switching frequency range for HB LLC resonant converter from light load to full load is very tight, below 60 kHz. HB LLC resonant DC-DCconverter efficiency and switching frequency curve at different output currents are given in Fig.12. The circuit efficiency at Vo=150V is larger than the efficiency at Vo=75V due to smaller conduction loss. The maximum circuit efficiency is around 95% at Vo=150V. The switching frequency range at Vo=150V is

larger than Vo=75V. At 0.1A output current light load, the power loss is dominated by the MOSFETs. At 1.0A output current heavy load, the major power losses come from MOSFETs, transformer and inductor due to large conduction loss.

vgsiCrvgsiCrioio (a) Io =0.1A (b) Io =1.0A

Fig. 10: HB LLC resonant DC-DC converter key waveforms at Vo =75V

vgsiCrvgsiCr

ioio(a) Io =0.1A (b) Io =1.0A

Fig. 11: HB LLC resonant DC-DC converter key waveforms at Vo =150V

Fig. 12:Efficiency and switching frequency curve vs. output current for HB LCC resonant DC-DC

converter

3.3 Comparison study of 150W HB LCC and LLC resonant converter experiment results

The circuit efficiency and switching frequency curve of HB LCC and HB LLC resonant DC-DC converter at Vo=75V can be found in Fig.13. HB LLC resonant converter can achieve higher efficiency under 75V output voltage, especially at light load: +10%. HB LLC resonant converter has the narrowest frequency range: ~1/8 of HB LCC resonant tank.

Fig.14 gives the detailed power loss distribution for HB LCC and HB LLC resonant DC-DC converter at Vo =75V. The MOSFET loss dominates the total power loss at light load. The switches losses for HB LLC resonant DC-DC converter are much lower than HB LCCDC-DC converter. The switches loss for HB LCCDC-DC converter major comes from the switching loss at 300kHz switching frequency at light load. At full load condition, rectifier loss of HB LLC resonant DC-DC converter is a little larger than HB LCC converter due to reverse recovery loss.

%󰀃

kHz󰀃

Load (A)󰀃Load (A)󰀃

Fig. 13: Efficiency curve &switching frequency curve of HB LCC vs. LLC resonant DC-DCconverter

at Vo =75V

(a ) Vo =75V/ Io =0.1A (B) Vo =75V/ Io =1.0A

Fig. 14: Power loss distribution HB LCC vs. LLC resonant DC-DCconverter at Vo=75V The circuit efficiency and switching frequency curve of HB LCC and HB LLC resonant DC-DC converter at Vo=150V can be found in Fig.15. HB LLC resonant converter can achieve higher efficiency under 150V output voltage, especially at light load: +4%. HB LLC resonant converter has the narrowest frequency range: ~1/30 of HB LCC resonant tank.

Fig.16 gives the detailed power loss distribution for HB LCC and HB LLC resonant DC-DC converter at Vo=150V. The rectifiers for both HB LCC and HB LLC resonant DC-DC converter at all conditions can achieve ZCS, no reverse recovery exist. The MOSFET loss dominates the total power loss at light load. The switches losses for HB LLC resonant DC-DC converter are much smaller than HB LCCDC-DCconverter. The switches loss for HB LCC DC-DC resonant converter major comes from the switching loss at around 300 kHz switching frequency at light load. At full load condition, the magnetics losses of HB LCC resonant DC-DC converter & HB LLC resonant DC-DC converter dominate the total resonant converter power loss.

%󰀃

kHz󰀃

Load (A)󰀃Load (A)󰀃

Fig. 15: Efficiency curve & switching frequency curve of HB LCC vs. LLC resonant DC-DCconverter at

Vo=150V

Fig. 16: Power loss distribution HB LCC vs. LLC resonant DC-DCconverter at Vo=150V

(a ) Vo =150V/Io=0.1A (B) Vo =150V/ Io =1.0A

3.4 Thermal test results for HB LLC & HB LCC resonant DC-DC converter

The thermal test results after 1 hour stable operation with natural cooling at 23oCambient temperature of HBLLC &HB LCC DC-DC converter can be found in Table III. HB LLC resonant DC-DC converter has better thermal performance for magnetics components compared with HB LCC resonant DC-DC converter. The temperature rise of transformer and resonant inductor ferrite cores and windings for HB LLC resonant DC-DC converter are lower than HB LLC resonant DC-DC converter due to smaller resonant tank current at both 150V & 75V output voltage and 1A output current.

Table III: Temperature test results after 1 hour stable operation with natural cooling

Transformer core temp.rise

31.2oC35.7oC21.5oC33.1oCTransformer winding temp.rise

40.0oC42.1oC28.2oC40.5oCInductor core temp.rise35.7oC38.5oC25.9oC40.5oCInductor winding temp.rise41.5oC45.1oC31.2oC48.0oCHBLLC (150V/1A)HBLCC(150V/1A)HBLLC (75V/1A)HBLCC (75V/1A)3.5 Discussions

Based on the prototype experimental results comparison study, we can find that at 75V output voltage,LLC resonant tank exhibits higher efficiency, especially at light load: +10%. And LLC resonant tank also achieves narrow switching frequency range, around 1/8 of the LCC resonant tank. At 150V output voltage, the LCC resonant tank achieves higher efficiency above 30% output current with small transformer core & winding loss. But it suffers worst efficiency at 10% output current. The LLC resonant tank has narrow switching frequency range: 1/30 of LCC resonant tank. The following is the comparison summary for HB LLC resonant DC-DC converter and HB LCC resonant DC-DC converter at ultra-wide load range applications:

1)HB LLC resonant DC-DC converter achieves much higher efficiency at light load conditions:

around 10% higher efficiency at 75V/0.1A condition.

2)HB LLC resonant DC-DC converter achieves much narrower switching frequency range: ~1/4

switching frequency compared to HB LCC DC-DC converter. This will lead to switches and magnetics loss reduction, especially at light load conditions.

3)HB LLC resonant DC-DC converter achieve better thermal performance: low magnetic core and

winding temperature.

4)The switching frequency of the HB LLC resonant DC-DC converter does not exceed 150kHz at

entire output power range, which is good in view of conducted EMI standards.

5)HB LLC resonant DC-DC converter is sensitive to the high frequency transformer parasitic

components. The transformer parasitic parameters of HB LLC resonant DC-DC converter should be tightly controlled. It’s achievable to optimize the LLC resonant tank design to mitigate the influence of high frequency transformer parasitical components to achieve high efficiency and narrow switching frequency in ultra-wide output power range.

6)HB LCC resonant DC-DC converter’s performance is dependent on the LCC resonant tank

characteristics. It is difficult to optimize the LCC resonant tank, especially the paralleled resonant capacitor in the ultra-wide output power range.

7)The switching frequency HB LCC resonant DC-DC converter goes beyond 150kHz which will

result in larger EMI filters.

8)HB LCC resonant DC-DC converter performs higher circuit efficiency at heavy load at 150V

output voltage than HB LCC resonant DC-DC converter.

4.Conclusions

The HB LCC resonant DC-DC converter and HBLLC resonant DC-DC converter are investigated for ultra-wide output power range application. HB LLC resonant DC-DC converter can achieve better performance with flat efficiency, narrow switching frequency range for wide output application at both 75V & 150V output voltage from 10% output current to 100 % output current conditions through resonant tank analysis and 150W hardware prototype experiments validation compared with HB LCC resonant DC-DC converter. HB LLC resonant DC-DC converter is very promising circuit topology for DC-DCpower conversion applications to achieve high performance in ultra-wide output power range applications. The resonant tank design & analysis and comparative method can be a reference for the application of ultra-wide output power range with high current output applications.

5.References

[1] Severns R P. Topologies for three-element resonant converters. IEEE Transactions on Power Electronics, 1992, 7(1): -98.

[2] Robert L. Setigerwald, A Comparison of Half-Bridge Resonant Converter Topologies, IEEE Transactions on Power Electronics.1988, 3(2):174-182.

[3]B. Yang, F. C. Lee, A. J. Zhang, and G. Huang, “ LLC resonant converter for front end dc/dc conversion,” in Proc. IEEE APEC, 2002, pp. 1108-1112.

[4]Branas, C., Azcondo, F.J., Casanueva, R.,Diaz, F.J.,” L-Cp Approximation of a Phase-Controlled LCsCp Resonant Converter to Study the Dynamic Responseas a LED Lamp Driver,” IEEE IAS 2012, pp.1-6

[5] Gilbert, A.J., Bingham, C.M., Bhangu, B.S., Foster, M.P., Stone, D.A.,”EKF-based output-voltage regulation of 3rd-order LCC resonant converters subject to load variations,” IEEE EPE, 2013,pp.1-4

[6] Fariborz Musavi, Marian Craciun, Deepak Gautam,”Control strategies for a LLC multi-resonant DC-DC converter in battery charging applications,” IEEE APEC,2013, pp. 1804-1811.

[7] Bong-Chul Kim, Ki-Bum Park, Chong-Eun Kim, Byoung-Hee Lee, Gun-Woo Moon, “LLC resonant converter with adaptive link-voltage variation for a high-power-density adapter,” IEEE Transactions on Power Electronics, Vol.25, Issue.9, pp. 2248 -2252

[8]Wei Guo, Hua Bai,Szatmari-Voicu, G.Taylor, A., Patterson, J.,Kane, J.,” A 10kW 97%-efficiency LLC resonant DC/DC converter with wide range of output voltage for the battery chargers in Plug-in Hybrid Electric Vehicles,” IEEETransportation Electrification Conference and Expo (ITEC), 2012, pp. 1-4

[9]Zhijian Fang, Shanxu Duan, Changsong Chen, Xi Chen, Jianxing Zhang,” Optimal design method for LLC resonant converter with wide range output voltage,” IEEE APEC 2013, pp. 2106-2111.