DC–DC Converter for DC Distribution and DC … UNIVERSITY DC–DC Converter for DC Distribution...

OSAKA UNIVERSITY

DC–DC Converter for DC Distribution and DC Microgrids

Yusuke Hayashi 1), Akira Matsumoto 2)

1) Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University

2) Research and Development Headquarters, NTT Facilities Inc.

SANTIAGO 2013 SYMPOSIUM ON MICROGRIDS 1

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Outline

SANTIAGO 2013 SYMPOSIUM ON MICROGRIDS

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Background–DCdistribu3onintelecombuildingsanddatacenters–

Issuestoberesolved–Energysavingtowardlowcarbonsociety–

ApproachtohighpowerdensityDC–DCconverter–ISOPandIPOStopologyofmodularconverters–

Conclusions

OSAKA UNIVERSITY SANTIAGO 2013 SYMPOSIUM ON MICROGRIDS

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Background–DCdistribu3onintelecombuildingsanddatacenters–

OSAKA UNIVERSITY

Facilities in NTT Telecom. Bldg.


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Computer/IT system

Management system Telecom system

Commercial Power Vehicle

with Back-up Power

Storage system

DC AC

Air–Conditioning

VRLA Battery

Access to Electricity Gas Turbine Engine

UPS

Rectifier (RF)

NTT DoCoMo Yoyogi Bldg.

Yokohama Media Tower

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History of Rectifier in NTT

1950 1960 1970 1980 1990 2000 2010

Step by Step Switching

Crossbar Switching

Electric Private Branch Exchange

Digital Switching (D70/ISM/RT)

ASM/SBM /RSBM

NGN

DC Power Supply

Technology

Switching Equipment

48V Centralized Power Supply 48V Distributed Power Supply

Se Si Thyristor Power Transistor, IGBT Si–SJ, SiC

End Cell Silicon Dropper Booster Converter Voltage Compensator Voltage Compensation

Flood–type Lead Acid Battery Valve Regulated LA Lithium–ion

380V Power Supply

Rectifier for “Distributed” Power Supply based on Power Transistor technology

Rectifier for “Centralized” Power Supply based on Thyristor Technology

Rectifier for “380V” Power Supply based on SiC technology

NTT (Nippon Telegraph and Telephone) History Center of Technologies: http://www.hct.ecl.ntt.co.jp/index.html


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DC distribution is applied for telecom buildings and data centers.

From “Centralized” to “Distributed”

From “48 V” to “380 V”

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Power density V.S. efficiency of DC–DC converter in rectifier

Power density of DC–DC converters in NTT •  A Rectifier consists of PFC (Power Factor Correction) circuits and

isolated DC–DC converters. •  Power density of DC–DC converters has been increasing

•  Higher switching frequency by using power transistors •  Higher voltage and lower supply current by SiC power devices


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1984

2009

Circuit configuration of rectifier

PFC DC–DC


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Issuestoberesolved–Energysavingtowardlowcarbonsociety–

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Energy saving in telecom bldg. and data centers

•  NTT has proposed “THE GREEN VISION 2020” toward low carbon society.

•  Energy saving of 100 TWh per year will be achieved in 2025 (Green of ICT).

•  In telecom buildings and data centers, energy saving of 23.5 TWh (30% in 2025) has to be accomplished.

- http://www.ntt.co.jp/csr/2010report/special/vision01.html - Y. Sugiyama, “Green ICT toward Low Carbon Society-Green R&D Activities in NTT”, -  Proceedings of 4th International Workshop on Green Communications, Kyoto, Japan, 2011.

Power consumption in whole ICT fields Power consumption in telecom buildings and data centers

100 TWh 23.5 TWh

17.5 TWh 64 TWh


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*ICT: Information and Communication Technology

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Energy saving in DC distribution system •  To realize 30% energy saving in telecom buildings and data

centers, highly efficient power supply system is indispensable. •  Conversion efficiency of 94% is required from the front–end

converter to the point of load converter.

AC 200V

DC380V DC48V DC12V

DC1.2V

η=0.95 η=0.95 η=0.97 η=0.91

η=0.80

19 inch Rack Server

380V DC power supply

On Board Rectifier Memory

CPU DC1.2V AC/DC DC//DC DC/DC DC/DC DC/DC DC/DC

AC 200V DC384V DC

48V, 12V

DC1.2V

η=0.98 η=0.98 η=0.98

η=0.94

19 inch Rack Memory

CPU DC1.2V AC/DC DC//DC DC/DC DC/DC

Server On Board

One of Solutions


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- T. Ninomiya, Y. Ishizuka, R. Shibahara and S. Abe, “Energy–saving technology using next–generation power electronics”, Proceedings of 2012 IEE–Japan Industry Applications Society Conference, Chiba, Japan, 2012 (in Japanese).

η=0.975 η=0.975

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Necessity of high performance converter •  High performance isolated DC–DC converters ( or DC transformer: fixed

voltage transfer ratio) are necessary.

•  To achieve highly efficient and ultra compact converters, •  Ultra–low loss and high–speed novel power devices such as SiC and GaN are attractive. •  High frequency operation of novel power devices contributes to minimizing passive

components. •  Series–parallel connection topology of highly integrated DC–DC converters is one of

options.

•  To realize flexible transformer ratios, •  Series–parallel connection topology of modular DC–DC converters is one of options.


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Target DC–DC in rectifier

Aim

Efficiency 98% 97.5% For Energy saving

Power density 10 W/cm3 2 W/cm3 To be installed into 19 inch rack with customer equipment

Transformer ratio 384 V–12 V and / or 48 V

384 V–384V To connect POL (Point of Load) converters


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ApproachtohighpowerdensityDC–DCconverter–ISOPandIPOStopologyofmodularconverters–

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ISOP–IPOS topology •  Higher input voltage can be injected in ISOP (Input Series and Output

Parallel) topology. •  IPOS (Input Parallel and Output Series) topology makes higher output

voltage. •  Conversion efficiency depends on an isolated DC–DC converter

(low–voltage and low–power) module.


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Isolated DC–DC converter module

ISOPTopology

IPOSTopology

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DC–DC converters in R&D


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13

Gong, Xi’an Univ., PESC2008 Synchronous Full Bridge

Biela, ETHZ, INTELEC2007 Series Parallel Resonant

Miftakhutdinov, TI, INTELEC2008 Synchronous Full Bridge

Sun, CPES, PESC2006 Switched Capacitor Shen, UCF,

IEEE Trans. 2006 Step-down

Omura, Toshiba, PCC2007 Step-down

Eckardt, Fraunhofer, CIPS2006, Step-down

Pavlovsky, Yokohama N. Univ., PESC2008, SAZZ

Isolated DC–DC Converter

Non–Isolated DC–DC Converter

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Example •  Power density and conversion efficiency of a high voltage high

power converter are compared with low voltage low power one. •  Single 256 V–384 V converter with SiC power devices •  A 256 V–384 V converter using eight 32 V–48 V converters

with GaN power devices


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Non–isolated DC–DC converter

32V

32V

32V

32V

32V

32V

32V

48V

48V

48V

48V

48V

48V

48V

256V 384V

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Experiments of non–isolated converters


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Output Capacitor

SiC Power Devices (TO247 packages) 1200V, 80mΩ

Input Inductor

GaN Power Devices (Bare chips) 100V, 7mΩ

Input Inductor

Output Capacitor

Experimental results of a 32V – 48V converter using GaN–FET (EPC)

Experimental Results of a 256V–384V converter using SiC–MOSFET (CREE)

Gate to Source Voltage (0 V-5 V ) Drain to Source Voltage (0 V-48 V )

Input Current (14.1A) Output Current (9.3A)

Input Voltage (256 V)

Output Voltage (384 V )

Input Current (9.0A) Output Current (6.0A)

100 kHz

1 MHz

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Input voltage balance in ISOP topology

•  Input voltages of converters balances ideally. •  Mismatch of output impedances causes the input voltage unbalance

under real circuit operation conditions. •  Imbalance of input voltages were calculated when output impedances

vary from 1% to 5% in eight converters. •  Input voltages vary 2% from the rated voltage (48 V ± 1V), and the

influence is negligible.


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+2%

-2% dc-dc Conv.

dc-dc Conv.

dc-dc Conv.

Ro8

Ro2

Ro1

Vi8

Vi2

Vi1 Vo1

Vo2

Vo8 VLOAD 48V

384V

Rout

Variance

Number connected in series

Output Impedance of converter No.i

Average of output impedances

Input Voltage Unbalance in Series Input Parallel Output Converter

Schematic Diagram of Series-Parallel Connected Converters

Io8

Io2

Io1

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Conversion Efficiency

ISOP and IPOS converter prototypes •  A 384 V–384 V 2.4 kW consists of eight 384 V–48 V modules connected in

IPOS. •  Maximum efficiency was 95.5% at full load.

•  A 384 V–48 V 2.4 kW consists of eight 48 V–48 V modules connected in ISOP. •  Maximum efficiency was improved from 95.5% to 96.7 %


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9.7cm*12.9cm*1.9cm

Isolated DC-DC Converter

384 V 384 V

48 V

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384 V–384 V 19.2 kW ISOP–IPOS Converter •  Sixty four 48 V–48 V 300 W converter modules (VICOR,

V048F480T006) were utilized. •  A 384 V–48 V 2.4 kW consists of eight modules connected in ISOP. •  A 384 V–384 V 19.2 kW consists of eight 384 V–48 V 2.4 kW

converters in IPOS. •  Maximum conversion efficiency was 96.6% and the power density was

10 W/cm3 without fans. •  Maximum efficiency of each 48 V–48 V module is 96.7%.


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300mm 160mm

42mm

384 V–384 V 19.2 kW IPOS Converter using eight ISOP converters

Conversion efficiency of 384 V–384 V 19.2 kW converter

384 V–48 V 2.4 kW ISOP converter

[kW]

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Transient behavior of ISOP converter

•  Start-up waveforms were measured under no load condition. •  No input voltage unbalances were observed.

•  Transient characteristics in rapid load variation were shown. •  Input voltage fluctuation was within 100 ± 5 %.


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Output Current Io5: 32.4A

Output Current Io6: 38.8A

Input Voltage of Unit No. 5: 48 V Input Voltage: 384 V (100 V/div)

Input Voltage: 48 V (20 V/div)

Input Current: 0 A Output Current: 0 A

Input Voltage of Unit No. 6: 48 V

Start-up waveforms under no load condition

Rapid load variation (1ms, 0%100%)

Rapid load variation (1ms, 100%0%)

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384 V–12 V 98% Converter •  Eight 48 V–12 V converter modules (VICOR, IB048E120T40N1-00)

were utilized to fabricate a 384 V–12 V 2.4 kW ISOP converter. •  Maximum efficiency of each converter module is 98.2 %.

•  Maximum conversion efficiency was 98.1%. •  Output voltages of 12 V, 48 V, 384 V are obtained by IPOS with 98%

efficiency.


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19.0cm

H2.1cm

Output Terminals (12V, 200A)

Input Terminals (384V, 6.25A)

6.0cm

Conversion efficiency of DC–DC Converter 384 V–12 V 2.4 kW DC–DC Converter

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Improvement of power density and efficiency •  In DC–DC converters for NTT telecom power supply, output power density has

been increasing. •  Higher conversion efficiency has been also achieved.

•  The 384 V–384 V converter using 48 V–48 V converter modules connected in ISOP–IPOS achieved higher power density.

•  Higher efficiency has been also achieved by using 48 V–12 V converters


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Conventional 384 V–384 V DC–DC Converter in Rectifier (15 kW)

384 V–12 V DC–DC Conv. (2.4 kW)

384 V–384 V DC–DC Converter (19.2 kW)

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Conclusions

•  DC distribution for telecom buildings and data centers was introduced. •  Highly efficient DC power supply is indispensable to realize low

carbon society. •  Availability of ISOP–IPOS topology was shown to realize highly

efficient and ultra compact converters. •  A 19.2 kW 384 V–384 V converter was fabricated by using sixty–

four 48 V–48 V converter modules with the efficiency of 96.6%. •  A 2.4 kW 384 V–12 V converter was fabricated by using eight 48 V–

12 V converter modules with the efficiency of 98.1%. •  I/O voltages are arbitrarily selected in ISOP–IPOS topology.

•  DC–DC converters with ISOP–IPOS topology contribute to realizing highly efficient DC microgrids.


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Thank you for your attention.


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Power density and efficiency estimation

•  Calculation results of efficiency and power density are shown. •  Ideal circuit condition: Stored energy in COSS is only

considered to calculate switching loss energy •  Real circuit condition: Parameters in the experiment is taken

into account •  Higher power density will be achieved in the low voltage and low

power converter


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Conversion Efficiency [%]

Power density V.S. switching frequency Power density V.S. conversion efficiency

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