Center for Power Electronics Systems

CPES Initiative on Sustainable Buildings and Nanogrids

Bradley Department of Electrical and Computer EngineerungCollege of Engineering

Virginia Tech, Blacksburg, Virginia, USA

presentation to2011 APEC: Special Presentation Session on

Power Electronics and Alternative Energy

Igor Cvetkovic, Dushan Boroyevich, Fred C. Lee, Paolo Mattavelli,Dong Dong, Wei Zhang, Li Jiang, Pengju Kong, Bo Zhou

DC-based Nanogrid System

AC DISTRIBUTION

HYDRO

COMBUSTION

NUCLEAR

HYDRO

COMBUSTION

NUCLEAR

HVAC TRANSMISSION

HOUSEHOLD LOADS

Power Meter

Smart

microGRIDmicroGRID

acac--nanoGRIDnanoGRID PHEV

μC

dcdc--nanoGRIDnanoGRID

1

Sustainable Buildings

ObjectiveApply power electronics to future residential and

commercial buildings to enable

major improvements in energy efficiency and sustainability

while minimizing cost and maximizing reliability.

2

Mini-Consortium for Renewable Energy and Nanogrids (REN)Work Scope

•PV System

•Plug-in Hybrid Electric Vehicles / Battery Storage

•Wind Power

•Energy Management for the Nanogrid

•AC Nanogrid

•DC Nanogrid

•Solid State Lighting

Smart Appliancesand LightingSolar PV Wind Turbine

Plug-in Hybrid withBidirectional Converter

Grid Connection withBidirectional Converter

Heating, Ventilation,and Air Conditioning

Entertainment andData Systems

Electric EnergyManagement Hub

Current Principal Plus Members in this area:

Research Sponsors

ICTASIndustry Consortium

College of Engineering

3

Work Scope:• Devices and Magnetics• Modeling and control (analog & digital)• 3D integration• High performance VRM/POL converters• DC/DC converters and Bus converters• EMI and PFC• Power architecture and management

Mini-Consortium Power Management Consortium (PMC)

(1998 –

present)

4

Mini-Consortium for High Density Integration (HDI)

Work Scope:•

High-Temperature Integration Technologies

•

Components•

Module-Level Integration•

System-Level Integration

Research Sponsors

Industry Consortium

Current Principal Plus Members in this area:

5

Sustainable Building Design Initiative Renewable Energy DC Nanogrid

ObjectivesObjectives–

DC-based power architecture (bus structure)

–

Decoupled dynamics from grid–

Islanded operation–

Bidirectional power conversion–

Zero-net annual energy cost–

Dispatchable generation / consumption

ChallengesChallenges–

Power management–

Wireless communication –

Integrated protection–

Breakerless system–

Grounding, EMI, & power quality–

Safety

PLUG-INHYBRID

ENERGYSTORAGE

WINDTURBINE

SOLARARRAY

GRID

Appliances: Washer, Dryer...

Appliances: Stove/Range...

DC bus

48 V

μC

M

μC

μC

Consumer el.: TV, Computer...

μCLED light

360 – 400 V

μC

ECC

Safe, Efficient, Convenient, Aesthetic, and Enjoyable Appliances and Ambient

Droop-based Continuous Power Sharing andAutomatic Prioritized Energy Use Optimization

6

High power appliances:Wide input voltage range 100 V to 240 V AC(Japan to Europe)

Rectified max = 340 V DC PFC output ≈

380 -

390 V DC

Voltage Levels in the DC-Nanogrid System

Low power consumer electronics:

Low, safe touch voltage < 50 V DC…5 V,…19 V,…

24 V,…

48 V

Chosen is 380 V as the nominal voltage of the bus

Chosen is 48 V as the nominal voltage for the low

voltage local distribution

Standard - Standard -7

Sustainable Building Design Initiative Energy Control Center

FeaturesFeatures–

Large dc-link voltage variation–

Small dc-link capacitor–

Soft-start on both sides–

High performance PLL–

Fast dc voltage & ac current control–

Full EMI compliance on both sides–

Small CM voltage on both sides

Bi-directional Grid Interface Converter

360-400 V DC Bus with droop regulation and short-circuit current limiting

240 V, 60 Hz, 1Φ

Grid with dispatchable

active & reactive power and short-circuit

current limitingVDC

LAC1 LAC2

CAC

LDC

CDC

VACCLINK

Prototype of10 kW high power

density bi-directional grid interface converter

Two-stage converter usinglow-cost 3Φ

motor-drive IPM

8

Generator

Control and drive Sensor

AC Grid

AC-DC converter DC-AC converter

Power Supply

SW1SW2

Generator

Control and drive

DC Bus

AC-DC converter

Power Supply

SW3SW4

Vertical-axis Cleanfield EnergyWind Turbine

Conventional structure:Two-stage power conversionAC-DC and DC-AC

New structure:AC-DC converter for the Nanogrid System

Sustainable Building Design Initiative Wind Turbine

FeatureFeatureAbility to regulate output voltage in stand-alone (islanded) operation

9

Sustainable Building Design Initiative Plug-in Hybrid Electric Vehicle

Conventional structure:Two stage bidirectional power conversionDC-DC and DC-AC

Future plans:High Power Density Bidirectional DC-DC Converter

Dispatchable Active & Reactive power

Demonstrated V2G technology in an AC Nanogrid System

AC Grid DC Nanogrid10

Sustainable Building Design Initiative Battery Management System

GEM #6

GEM #5

GEM #4

GEM #3

GEM #2

GEM #1

BM C

External CAN Bus

+Battery

Management Module

Internal CAN Bus(Voltage,Current,

Temperature)

Dissipative

..

Non-dissipative

..IBat

IBat

SAFT Lithium Ion Battery System

11

Sustainable Building Design Initiative Photovoltaic Management System

2nd

stage converterNon-inverting Buck-boost

Vs

DC bus360V ~ 400V

Ipv

Ps

Is1 Is2 Is3

Droop mode

MPPT mode

Current limit mode

Is

Vbus

3

10

Ipv

Vpv

Vpv

Ipv

Voc

=43.8V

Isc

=5.14A

(35.2V,4.83A)

Io

IoVo

Vlimit

=40V

Ilimit

=10A

MPP

MPPT range

Vo

Solarmagic Power optimizer

Smart PV panelPeak power tracking at the panel levelPeak power tracking at the system level20% more efficient than the centralized MPPT system

12

2-stage MC3 LED Driver Schematic of proposed multi-channel constant current source

fs

LLC resonant topology

Multiple outputs current source

DC block cap balance the

current of two strings

Scalable for multiple LED

strings

Sustainable Building Design Initiative Solid State Lighting

13

Integration of Technology into the Home Environment

Kitchen

Conference roomHallway

PC lab

Ceiling-based plug-and-playDC system

Source: www.energizer.com

Source: www.powermat.com

Source: www.duracell.com

Integration of existing technology

School of architecture + design, Virginia TechDesign by:

-

Synergy of power electronics and interior design

14

Static (V-I) Characteristics of the System Components (dc-bus signaling technique*)

Ope

ratin

g ra

nge

Con

vert

er ra

ting

Act

ual

MPP

T

Con

vert

er ra

ting

Act

ual

MPP

T

Ope

ratin

g ra

nge

Con

vert

er ra

ting

Con

vert

er ra

ting

IpIg IwIs Ib

PLUG-INHYBRID

DC bus 360 – 400V

[*] J. Bryan, R. Duke, and S. Round, "Decentralized generator scheduling in a nanogrid using DC bus signaling," in Power Engineering Society General Meeting, 2004. IEEE, 2004, pp. 977-982 Vol.1.

15

Static Operation of the DC-Nanogrid System

Iw Is

0Iw

+Is

= IL0= IL

Iw IsIg

Iw

+Is

−Ig

= ILIw

+Is

+Ig

= IL

IgIw Is

Iw

+Is

+Ig

+Ib

= IL

IwIb Ig IsIw Is IgIbIp

Iw

+Is

+Ig

+Ib

−Ip = IL

IL

Is Iw Ib Ip

LOAD

GRID

μC

IgIg

GRID

μC

16

Optimization of the DC-nanogrid Operation

V [V]

0 Ig

400390380370360

Grid interface converter

A

IgA

A

IbA

Battery converter

IgB Ib

B

B B

17

Power Socket/Plug for the High Voltage Disconnect

(+)(-)(PE)

dc-plugdc-outlet

+-Isolation

and control

(+)(-)

Cs Ds

Lc2rc2Lc1rc1

CL

RL

Disconnecting point

C E

v1

vCEv2

i2i1vb LL

An equivalent circuit of the system above:-

simulation results-

ideal disconnect-

high di/dt

18

Building the Non-linear Static and Linear Dynamic Model

Load regulation static curve

Non-linear static model

Linear dynamic model

“AC-sweep point”

19

Two port network behavioral model

+-v1

i2

v2

v1Goi2HiYi

Zo

i1

two-port network

~

~~ ~

~

~

dc-dc converter

⎥⎦

⎤⎢⎣

⎡⋅⎥

⎦

⎤⎢⎣

⎡ −=⎥

⎦

⎤⎢⎣

⎡

2

1

1

2~~

)()()()(

~~

iv

sHsYsZsG

iv

ii

oo

xXx ~+=

⎥⎦

⎤⎢⎣

⎡+⎥

⎦

⎤⎢⎣

⎡−−

⋅⎥⎦

⎤⎢⎣

⎡ −=⎥

⎦

⎤⎢⎣

⎡

1

2

22

11

1

2

)()()()(

IV

IiVv

sHsYsZsG

iv

ii

oo

Small-signal model:

Model containing DC operating point and the small-signal dynamics

expanded with the DC operating point

20

48 V 8 V

A commercial60 W bus converter

100

0

-100

0.01

0.1

1

Mag

nitu

deP

hase

[°]

Frequency [rad/s]104 105 106

Output Impedance Zo ( jω )

Input Admittance Yi ( jω )

0100

Frequency [rad/s]103 104 105 106

Pha

se [°

]

0.01

1

100

Mag

nitu

de

Current Back-gain Hi ( jω )

0.01

0.1

1

0-200

Frequency [rad/s]103 104 105 106

Pha

se [°

]M

agni

tude

Mag

nitu

de

0.01

0.1

1

Pha

se [°

]

0-200

Frequency [rad/s]103 104 105 106

Audio Susceptibility Go ( jω )Measured frequency response functions

Modular Terminal Behavioral (MTB) Low-frequency Model of DC-DC Converter

ii

ivoi

ovoZ

iYoi iH ⋅

io vG ⋅

“Black Box”Modeling Example

Curve-fitted,reduced order

transfer functions

21

Obtaining un-terminated from the terminated transfer functions

+-v1

i1R i2

v2

v1Goi2HiYi

Zo

i1L

Vo

ZsIoYL

ip

Sourcetwo-port network

Load

Setup 1:

+-

~ ~

~~

~ ~

~

~

+-v1

v1Goi2HiYi

ZoVo

ZsIoYL

Setup 2:

+- ~ ~

~

i1~

v2

i2Ri2L

ip~

~

~ ~

two-port network

dc-dc converter

Source Loaddc-dc converter

1

1

1

2~~

)(,~~

)(visY

vvsG R

imom ==

Lim

Lom i

isH

ivsZ

2

1

2

2 ~~

)(,~~

)( ==

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

⋅

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

−−

−−

−=

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

im

om

im

om

rm

rm

gm

gm

rmgm

i

o

i

o

HZYG

TT

TT

TTHZYG

100010

010001

11

1

2~~

)(visTgm =

Lrm i

vsT2

1~~

)( =

22

System-level Model Verification (Sample System)

Ig2

Is2

Vbus1=Vg2

Solar Converter

Grid Interface Converter

Impe

danc

e In

terc

onne

ctio

n

DC/DC Bus conv. 1 LOAD 1

DC/DC Bus conv. 2 LOAD 2

ig2

is2

vbus1=vg2

Solar Converter

Grid Interface Converter

Impe

danc

e In

terc

onne

ctio

n

DC/DC Bus conv. 1 LOAD 1

DC/DC Bus conv. 2 LOAD 2

Vg2, Ig2Non-linear static model

Linear dynamic model

Vs2, Is2 Vbus2=Vs2

vbus2=vs223

System-level Model Verification (Sample System)

Ig2

Is2

Vbus1=Vg2

Solar Converter

Grid Interface Converter

Impe

danc

e In

terc

onne

ctio

n

DC/DC Bus conv. 1 LOAD 1

DC/DC Bus conv. 2 LOAD 2

ig2

is2

vbus1=vg2

Solar Converter

Grid Interface Converter

Impe

danc

e In

terc

onne

ctio

n

DC/DC Bus conv. 1 LOAD 1

DC/DC Bus conv. 2 LOAD 2

Vg2, Ig2Non-linear static model

Linear dynamic model

Vs2, Is2 Vbus2=Vs2

vbus2=vs2

Outpu

t cur

rent

[A]

Outpu

t cur

rent

[A]

Outpu

t volt

age [

V]Ou

tput v

oltag

e [V]

24

DC System Stability (example with low bus capacitance Cb )

Volta

ge [V

]C

urre

nt [A

]

100 1k 10kFrequency [Hz]

100k-200

0

100

-100

-20

20

40

0

Load

Load

Source

Source

|ZL||ZS|

ZS

ZL

GRID

LOAD 1 LOAD 2

Zc

Zwire Zwire

SOLARARRAY

CbCb

ZL

ZS

DC bus igvg isvs

25

DC System Stability (value of Cb has increased)

GRID

LOAD 1 LOAD 2

Zc

Zwire Zwire

SOLARARRAY

CbCb

ZL

ZS

DC bus igvg isvs

0.085 0.09 0.095 0.1 0.105 0.11 0.115350

360

370

380

Output voltage

Time [s]

0.085 0.09 0.095 0.1 0.105 0.11 0.1150

5

10

15

Output current

Time [s]

Grid interface converterSolar converter

Grid interface converterSolar converter

vg,vs

is

ig

Mag

nitu

de [d

B]

Pha

se [d

eg]

-20

20

40

0

100 1k 10kFrequency [Hz]

100k-200

0

100

-100

|ZL|Load

Impe

danc

eIm

peda

nce

Load

Source

Source

|ZS|

ZS

ZL

26

Thank You

The work and contributions are by many CPES faculty, students, and Staff.

Many global industrial and US government sponsors of CPES research are gratefully acknowledged.

Center for Power Electronics SystemsBradley Department of Electrical and Computer Engineerung

College of EngineeringVirginia Tech, Blacksburg, Virginia, USA

27