Electronic Power Distribution Systems

1

Center for Power Electronics SystemsA National Science Foundation Engineering Research Center

Virginia Tech, University of Wisconsin - Madison, Rensselaer Polytechnic InstituteNorth Carolina A&T State University, University of Puerto Rico - Mayaguez

15 April, 2008

Electronic Power Distribution Systems

Dushan Boroyevich

Power Electronics Systems IntegrationCPES Joint Course

Spring 2008

15 April, 2008 DB-1

Most of the Emerging Electric Power Technologies Presume Active Most of the Emerging Electric Power Technologies Presume Active Dynamic Control of the Power FlowDynamic Control of the Power Flow(i.e. (i.e. Require the Use of Power ElectronicsRequire the Use of Power Electronics)!)!

Power ElectronicsExpanding and Emerging Applications

Industry AutomationPowering IT

Alternativeand

DistributedEnergy

SystemsVehicularPowerSystems

2

15 April, 2008 DB-2

Electronic Focusof Electric Power System Research

Emerging and future power systems will have all sources and loads interfaced through power electronics converters:

• IT Power: Portable, Server, Telecom, Data Center• More-electric aircraft, All-electric ship, Hybrid-electric car, • Sustainable energy, Distributed generation, Future power grid

Focus on: Electronic Power Distribution Systems (EPDS) .

Technical Scope:• System architecture design and optimization; • System-oriented modeling of DC EPDS;• Power quality, power management, and protection;• System-oriented modeling of hybrid AC/DC EPDS;• High-density converter integration.

OUTLINE

OOUUTTLLIINNEE

15 April, 2008 DB-3

• System stability anchored at the sources– Electromechanical– Electrochemical

• Generation, distribution, and delivery fully coupled• Overwhelming, slow, source dynamics imposed on the system• Electromechanical system control and protection

120 V, 1Φ AC

Lighting

MotorMotor

CentralFan

120 V1Φ AC

480 V, 3Φ AC

HVAC System Pumps and Fans

… …

480 V, 3Φ AC

Com-pressor

SW GRSW GRSW GR SW GRSW GRSW GR

SWGR

Electrical Power Systems of the Last Century – I

SWGRSWGR SWGRSWGR

MotorMotor MotorMotor MotorMotor

120 V1Φ AC

SWGR Computer Power System

ASICs

Mem

Fan

DigitalICs

LED

AnalogICs

Rectifier

DC-DCConverter

• System dynamics is too constraining for applications

• Slow and inefficient• Unreliable

ASDASD

ASDASD ASD ASD

Fan

SWBD

Analog

Telecom Power System

Battery

– 48 VDC

SWGR

ACMotor

DCGen.

Utility

Generator

SWGR

208 V3Φ AC

Rectifier

SWGR

3

15 April, 2008 DB-4

Fan

SWBD

Analog


Battery

– 48 VDC

SWGR

120 V, 1Φ AC

Lighting

MotorMotor

CentralFan

120 V1Φ AC

480 V, 3Φ AC


Utility

… …

480 V, 3Φ AC

Com-pressor


SWGR

Electrical Power Systems of the Last Century – II

SWGR

SWGRSWGR SWGRSWGR


120 V1Φ AC


ASICs

Mem

Fan

DigitalICs

LED

AnalogICs

DC-DCConverter

208 V3Φ AC

SWGR

PFCRectifier

PFCRectifier

...

ASDASD

ASDASD ASD ASD

AC-DCFront-End

Server

48 VDC

Non-IsolatedPOL Conv.

μP

ElectronicBallast

ElectronicBallast

ElectronicBallast

AC-DC

DC-AC

Battery

24 V, 1Φ AC

Fire Alarm System

SWGRSWGRSWGR

DC-AC

Battery

120 V, 1Φ AC

Emergency Lighting

SWGRSWGRSWGR

AC-DC

LED

AnalogICs

ASICs

MemIsolated POL

Converter

DigitalICs

DC-DCConverter

μP Non-IsolatedPOL Conv. ...

• Highly decoupled load dynamics• Still inefficient, although more expensive• Even less reliable

Generator

15 April, 2008 DB-5

Generator

Fan

SWBD

Analog


Battery

– 48 VDC

SWGR

480 V, 3Φ AC

Micro-Turbine

VSCFConverter

RenewableEnergy Source DC-AC

SWGRSWGR

Generator

120 V, 1Φ AC

Lighting

MotorMotor

CentralFan

120 V1Φ AC

480 V, 3Φ AC


… …

480 V, 3Φ AC

Com-pressor


SWGR

Electrical Power Systems of this Century?

SWGR

SWGRSWGR SWGRSWGR


120 V1Φ AC


ASICs

Mem

Fan

DigitalICs

LED

AnalogICs

DC-DCConverter

208 V3Φ AC

SWGR

PFCRectifier

PFCRectifier

...

ASDASD

ASDASD ASD ASD

AC-DCFront-End

Server

48 VDC


μP

ElectronicBallast

ElectronicBallast

ElectronicBallast

LED

AnalogICs

ASICs

MemIsolated POL

Converter

DigitalICs

DC-DCConverter

μP Non-IsolatedPOL Conv. ...

AC-DC

DC-AC

Battery

24 V, 1Φ AC

Fire Alarm System

SWGRSWGRSWGR

DC-AC

Battery

120 V, 1Φ AC

Emergency Lighting

SWGRSWGRSWGR

AC-DC

UPS

AC-DC DC-AC

Battery

120 V1Φ AC

...

• Inefficient• Expensive• Unreliable

Very colorful patchwork inherited from last century!

4

15 April, 2008 DB-6

Benefits of Classical AC Grid Systems

Source Dynamics• Active power flow control by

frequency control• Voltage control by reactive power

control

Distribution Dynamics• Passive voltage step-up/down

(transformers)– Cost; efficiency; reliability

• Protection by effective circuit breakers (zero crossings)

Load Dynamics• AC (induction) motors• Transformer-rectifiers

Challenges:• Not used in tight, single-

source systems• Not suitable for alternative

sources

• Converters, DC transmission, (high-frequency transformers)– Cost; efficiency; reliability

• Protection by active control (zero crossings not needed)– Reliability

• Only “coffee makers” are still non-electronic loads

15 April, 2008 DB-7

A Possible Future Electronic Power Distribution Systems

Legend:Power

DistributionConverters

IntegratedLoad

Converters

IntegratedSource

Converters

Telecom Equipment

...Fan

LED

AnalogICs

DC-DC …

200 V, DC BUS

Emergency and Alarms

HVAC

Pumps and Fans

48 V, DC BUS

ASICs

Mem

DigitalICs

Fan

LED

AnalogICs

μP + IPS

Lighting

Fan

Server

Server

Server

Server

DC-DCConverter

Utility Utility

SWGR

Bi AC-DCConverter

Lighting

Left

0.8

kV

DC

BU

S

Battery

Bi DC-DCConverter

DC-DCConverter

RenewableEnergy Source

Micro-Turbine

AC-DCConverter

......

DC-DCConverter

DC-DCConverter

48 V, DC BUS

DC-DCConverter

200 V, DC BUS

HVAC

Pumps and Fans

…Integ.Ballast

Integ.Ballast

…Integ.Ballast

Integ.Ballast

…IMMD IMMD

…IMMD IMMD

SWGRSWGR SWGRSWGR

SWGRSWGR SWGRSWGR

Rig

ht 0

.8 k

V D

C B

US

Computer Equipment

12 V DC

3 V DC

DC-DC

DC-DCASICs

Mem

DigitalICs

LED

AnalogICs

+ μPIPS

12 V DC

3 V DCDC-DC

DC-DC

F i r s t F l o o r

S e c o n d F l o o r

ASD

Motor

ASD

Motor

0.8V0.8V

• Hybrid and electric cars

• More-electric airplane

• All-electric ship

• Alternative energy

• Distributed generation

• Future electric power systems

Emerging and future systems:

• Telecom Power ⇒ Data Centers

5

15 April, 2008 DB-8

Barriers/Challenges – I

• Traditional power systems:– Dynamics of generation, distribution, and delivery fully coupled– System stability is enabled by imposing an overwhelming, slow,

dynamics of the sources.

Challenge: Separate the dynamics of sources, distribution system, and loads.

• Local focus of power electronics:– Concentrated on load dynamics– Evolving focus on source dynamics (UPS, distributed generation,

fuel cells, alternative energy sources)– Until now, only “fixing the problems” of power distribution (ac)

Challenge: Use power electronics to separate the dynamics.

15 April, 2008 DB-9

Barriers/Challenges – II

• High cost, low efficiency, and low reliability of power electronics converters

Challenge: Enable dramatic improvements in performance, reliability, and cost effectiveness of power electronics systems by developing an integrated system approach via Integrated Power Electronics Modules (IPEMs).

• No standardization in power electronics• No modularization (definitions of IPEMs)

– “A minimum set of building blocks with integrated functionality, standardized interfaces, suitability for mass production, and application versatility.”

Challenge: Develop a physics-based, hierarchical, and consistent methodology for evaluation and trade-off analysis of different architectures, partitions, and implementations.

6

15 April, 2008 DB-10

Power-Converter-Based Power Systems Example: A Notebook PC

LCD Bias– 8 V

Backlight800 V

Memory1.8 V

Processor0.7-1.7 V

Logic

I /O DiskDrive

5 V Bus3.3 VBus

Peripherals

12 V

12-16 VPower

Management Battery90-260 V

50-60 Hz

19 VCharger AC Adapter

Voltage Regulator

Voltage Regulator

CCFL Inverter

LCD Converter

LDO Regulator

Bus Converter

Bus Converter

Boost Converter

• Load converters: Meet dynamic energy requirements of the loads

REDUCECOST !

• Power Distribution Converters:– Increase peak-power efficiency ⇔ Improve power density– Increase light-load efficiency ⇔ Improve energy efficiency

• Source converters: Meet ac line standards; improve battery utilization

15 April, 2008 DB-11

More Electric Aircraft

7

15 April, 2008 DB-12

DC Zonal Shipboard Power Distribution System

15 April, 2008 DB-13

VariableVariable--speed doublyspeed doubly--fed wind turbinefed wind turbineDirect gearDirect gear--less variableless variable--speed wind turbinespeed wind turbine

1. Eliminates gear box and need for doubly-fed induction generator

2. Simpler transformer structure

3. Fully decouples wind and grid dynamics

Wind Energy:Evolution of Turbine Power Electronics

8

15 April, 2008 DB-14

Electronic Power Distribution System: Grid-interface for Offshore Wind Farms

AC Transmission for Offshore Energy HarvestingAC Transmission for Offshore Energy Harvesting

HVDC Transmission for Offshore Energy HarvestingHVDC Transmission for Offshore Energy Harvesting

15 April, 2008 DB-15

Japan: The Historical Leader

in Electrical Power System Complexity

in Advanced Electric Power System Development?or

9

15 April, 2008 DB-16

US and Canada Electric Grid

Four major independent asynchronous networks, tied together only by DC interconnections:

1. Eastern Interconnected Network

2. Quebec

3. Texas

4. Western Interconnected Network

Four major independent asynchronous networks, tied together only by DC interconnections:

1. Eastern Interconnected Network

2. Quebec

3. Texas

4. Western Interconnected Network

15 April, 2008 DB-17

MixedAC / DC Power

Distribution

6 A

Servers1.5 kW

Charger2.8 kW

Transfer Switch

Inverter3 kW

6 A

25 A

100 A

60 A 60 A

25 A

Transfer Switch

Battery

Charger2.8 kW

6 A

LV DC Distribution48 V DC

1Φ AC Distribution120 V AC

CPES University Testbed: Hybrid Power System for Remote-site Datacom Centers

10 A

Cooling1.5 kW

Hybrid EnergyPower Sources

Telecom and ComputerLoads with HVAC

Similar tradeoffs in terms of size, efficiency, and power density for all power converters.

Single Enclosure,Self-Contained UnitPeak-powerEfficiency< 50 % !

10

15 April, 2008 DB-18

6 A

Servers1.5 kW

Charger2.8 kW

Transfer Switch

Inverter3 kW

6 A

25 A

100 A

60 A 60 A

25 A

Transfer Switch

Battery

Charger2.8 kW

6 A



10 A

Cooling1.5 kW

Electronic Power Distribution System (EPDS): An Integrated Testbed

Servers

DC-DC

HV DC Distribution300 V DC

Charger /Discharger RectifierRectifier

HVAC

System impact evaluation of integrated:• Active modules• Passive modules• Converters• Loads and converters

• Reduce number of converters by 30%

• Eliminate switchgear

• Improve availability

• Increase energy efficiency

Improved architectures:

15 April, 2008 DB-19

Characteristics of FutureElectronic Power Distribution Systems

• Power electronics converters are used for:– Source interface– Load interface (only “coffee makers” are still non-electronic loads?)– Power flow control and energy management

• Advantages:– High system controllability, flexibility, and responsiveness– Increased availability– Reduced size and weight– Increased energy efficiency

• Issues:– Subsystem interactions (power flow, power quality, EMI, thermal)– Complexity (not an issue if dynamics is understood & decoupled)– Reliability and lifetime (not protection)– Cost (not an issue if system and/or energy costs are reduced)

11

15 April, 2008 DB-20

Hierarchical Modular Modeling and Analysis

6 AServers1.5 kW

Charger2.8 kW

Inverter3 kW

6 A

20 A

60 A 60 A

20 A

Transfer Switch

6 A



6 A

Cooling1 kW

Battery

Solar Panel

Emulator

60 HzAC Grid

Motor

Motor Drives

Distributed Power Supplies

Motor

How to study large systems of converters with unknown internal

structure and parameters?

15 April, 2008 DB-21

Equivalency Between ISO/OSI and Power System Models

Physical

Link

Network

Transport

Session

Presentation

Application

Device

Component

Module

Converter

Station

Network

Transport

Power System HierarchyISO/OSI Reference Model

12

15 April, 2008 DB-22

The Cognitive Revolution

OutputInput

“The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing

Information”

George MillerThe Psychological Review, vol. 63, pp. 81-97, 1956

Humans asInformation Systems

15 April, 2008 DB-23

Energy Processing

Devicessemiconductors, magnetic cores,

dielectrics, heat spreaders, …

Packaged Componentstransistors, inductors, capacitors,

heat sinks, …

Integrated Modulesfor energy flow control and

energy storage

Power Converters

Power Stationparallel, series, or cascade converters

with switchgear and enclosure

Power Distribution

Generation and Transmission

1

2

3

4

5

6

7

ISO / OSI Telecom Model

Physical

Link

Network

Transport

Session

Presentation

Application

Electric Power Conversion

Device

Component

Module

Converter

Station

Network

Transport

Modeling and Simulation

Finite Element

Physics-Based Lumped Parameter

Behavioral

Average

Application

Power Flow

Cost and Quality

Control

Physical

Real-TimeOperating System

Elementary Control Objects

Data Flow

Application

Enterprise

Mission

Conceptual Reference Model

Standard-Cell, Open-Architecture, Electric Power Conversion Systems

13

15 April, 2008 DB-24

1 2 … mControl Terminals (u)Mode n (failure mode)

Mode 3 (overload)Mode 2 (start-up)

• Terminal models of subsystems

iHiY

iiiv

oE oZoi

ov

Modeling and Simulation Approach– a hypothesis –

12:j

1 2 … k

j+1j+2

:l

Mode 1 (normal)

Thermal Terminals (θ, p)Input PowerTerminals (v, i)

Output PowerTerminals (v, i)

IPEM

• Subsystems are mildly non-linear• Dynamics can be divided into four weakly coupled components• Modes of operation can be described using state-machine concept

– Fundamental frequency(DC, 50, 60, 400 Hz)

Active

– Very low frequency(< 100 Hz)

Thermal

– Intermediate frequency(ffund – fsw)

Reactive

– High frequency(> fsw)

EMI

ε++++= tjejrjajj vvvvv ε++++= tjejrjajj iiiiiUsing staggered singular perturbations theory, the complete response is then:

…

15 April, 2008 DB-25

ioi

oi vivη

PJ⋅

=),(

Simplified Power Model of a Regulated DC-DC Converter

iiiv

orefV

iJ oE oi ov

[A]

[V]

10

20

30

40

50

0 5 10 15 20 25

Eo

io

Iomax

voltage regulation

mode

current limit

mode

Voref

Static Output Characteristic

[V]

10

20

30

40

50

0 40 60 80 100

1 kW

450 W

Vimax

Vimin

PoJi

vi

[A]

750 W

Static Input Characteristic

oorefooo iVivP ⋅≈⋅=

14

15 April, 2008 DB-26

ovorefV

Small-signal Static Model at an Operating Point

[A]

[V]

10

20

30

40

50

0 5 10 15 20 25

Eo

io

Iomax

voltage regulation

mode

current limit

mode

Voref

[V]

10

20

30

40

50

0 40 60 80 100

1 kW

450 W

Vimax

Vimin

PoJi

vi

[A]

750 W

iiiv oi

Static Output CharacteristicStatic Input Characteristic

oZiY

slopeslope

LOAD

15 April, 2008 DB-27

lov LOAD

liilorefV

Load Converter

loZlivliY loi

Well-known Stability Problem with “Constant Power Loads”

Source Converter

soZsiisivsiY

sorefV

liso

sorefsoref

soli

lili YZ

VV

ZYYv

⋅+=⋅

+=

1/1/1

• Interface voltage is:

• To avoid instability, the return ratio:

liso YZL ⋅≡must stay away from –1 !

15

15 April, 2008 DB-28

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

deCurrent Back-gain Hi ( jω )

0.01

0.1

1

0-200


Pha

se [°

]M

agni

tude

Mag

nitu

de

0.01

0.1

1

Pha

se [°

]

0-200


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

15 April, 2008 DB-29

ii (t)

0.6

1

1.4

4.4Time [ms]

4.3

[A]

vi (t)

47.8

48.2

48.6

4.4 4.5Time [ms]

4.3

[V]

Measured transient response to load step-change

MTB Low-frequency ModelVerification: Load Transient

8 V

ii

ivoi

ovoZ

iYoi iH ⋅

io vG ⋅ 3.2A

7.4A

StepLoad

Simulated response to load step-change using curve-fitted reduced order model

16

15 April, 2008 DB-30

Output Impedance ofUnregulated Bus Converter

NonlinearLinearNonlinear

Output Impedance of Regulated Flyback Converter

• Family of local linear models for different terminal conditions

• Blend together by a smooth interpolation function

Polytopic Structure

Polytopic MTB Modeling

15 April, 2008 DB-31

Bus Converter Validation: Simultaneous variation of output current and input voltage; Load Step from 1 A to 5 A to 19 A

2 2.5 3 3.5x 10

-3

38

40

42

44

46

48

50

Time(Sec)

Vol

ts

Input Voltage

2 2.5 3 3.5x 10

-3

0

1

2

3

4

5

Time(Sec)

Am

p

Input Current

2 2.5 3 3.5x 10

-3

8

9

10

11

12

Time(Sec)

Vol

t

Output Voltage

2 2.5 3 3.5x 10

-3

0

5

10

15

20

Time(Sec)

Am

p

Output Current

Blue = Experimental

Green = Experimental Moving average

Red = Simulation

17

15 April, 2008 DB-32

0.05 0.051 0.052 0.053 0.0545.06

5.08

5.1

5.12

5.14

5.16

5.18

Time(Sec)

Vol

t

Output Voltage

0.061 0.062 0.063 0.064 0.0655.06

5.08

5.1

5.12

5.14

5.16

5.18

Time(Sec)

Vol

t

Output Voltage

0.05 0.055 0.06 0.0650.5

1

1.5

2

2.5

Time(Sec)

Am

pInput Current

0.05 0.055 0.06 0.0655.05

5.1

5.15

Time(Sec)

Vol

t

Output Voltage

Closed-Loop Flyback Converter Model ValidationFixed 20 V Input; Load Step from 3 A to 4 A to 5 A

15 April, 2008 DB-33

0.01

0.1

1Current Back-gain Hi ( jω )

0-200


Pha

se [°

]M

agni

tude

Alternative Low Frequency Model forNonlinear Behavior of Buck Converter

Input Admittance Yi ( jω )

0100


Pha

se [°

]

0.01

1

100

Mag

nitu

de

30 50 60 [V]vi

0.1

0.2

0.3

0

Hi (0)

Vimax

Vimin

constant power mode

Mag

nitu

de

0.01

0.1

1

Pha

se [°

]

0-200


Audio Susceptibility Go ( jω )

voltage regulation

mode current limit

mode

Iomax

Voref

10 20 30 [A]0

io

8

[V]

4

Go (0)⋅vi [V]

100

0

-100

0.01

0.1

1

Mag

nitu

deP

hase

[°]


Output Impedance Zo ( jω )

48 V 8 V

ii

iv

oi

ovoZ

iYoi iH ⋅

io vG ⋅

18

15 April, 2008 DB-34

Unstable Unstable

Subsystem Interaction Example– modeling and experiments with commercial converters –

LoadConverter R8 V liv48 V 3.3 Vlii

siv+

–

+

–

BusConverter

)(sZS )(sYL

)()()( sYsZsL LS ⋅≡

)1( 1siso

-LSli vGYZv ⋅⋅⋅+=

Imag

inar

y

0

-50

50

100

-50 0 50 100 150Real

L( jω )

0-3

-2

0

2-1

0.01

1

100

Mag

. [Ω

]


Source OutputLoad Input

ZS 1/YL

50%

Load60%

3

5

Inpu

t Cur

rent

[A]

7

4.4 4.8Time [ms]

4

15 April, 2008 DB-35

Source OutputLoad Input

1/YLZS0.01

1

100

Mag

. [Ω

]


Subsystem Interaction Example– modeling and experiments with commercial converters –

C100 μF

LoadConverter R8 V liv48 V 3.3 Vlii

siv+

–

+

–

BusConverter

)(sZS )(sYL

)()()( sYsZsL LS ⋅≡

)1( 1siso

-LSli vGYZv ⋅⋅⋅+=

Imag

inar

y

0

-50

50

100

-50 0 50 100 150Real

L( jω )

0-3

-2

0

2-1

Stable Stable

50%

100%

4.4 4.8Time [ms]

4

3

5

Inpu

t Cur

rent

[A]

7

19

15 April, 2008 DB-36

Analysis of Stability, Power Quality, Power Management and Protection

Charger25 A

25 A

Battery

48 V DC Distribution

Minimum relevant EPDS example:• Two sources• Two loads• DC distribution

15 April, 2008 DB-37

Load 2 enters current limit

Source impedance becomes greater than load impedance

Small-signal instability with constant-power loads

System shut-down

Power Flow Control & Protection Simulation:Classical System Transient Example

48 V dc buswith 2% short-circuit

impedancevo1 vo2io1 io2

Const.5 A

PV25 A Charger+

BatteryLoad 1

Converter

25 A

3 ALoad 2

Converter

33 A1,000 μF 1,000 μF

Additional Capacitors Reduce Source Impedance

15time [ms]

io1

io2

0 5 10

30

0

10

20

55

35

45

vo1

vo2

Breakershut-down

Bus

Vol

tage

[V]

Sour

ce C

urre

nt [

A]

time [ms]

io1

io2

0 5 10

30

0

10

20

55

35

45

vo1

vo2

Breakershut-down

Bus

Vol

tage

[V]

Sour

ce C

urre

nt [

A]

time [ms]

io1

io2

0 5 10 15

vo1vo2

Bus

Vol

tage

[V]

Sou

rce

Cur

rent

[A

] 30

0

10

20

55

35

45

20

15 April, 2008 DB-38

1,000 μF 1,000 μF

48 V dc buswith 2% short-circuit

impedancevo1 vo2io1 io2

Const.5 A

+

Battery

DC-DCConverter

Charger /Discharger

Load 1Converter

PV

3 ALoad 2

Converter

33 A

25 A25 A

Power Flow Control & Protection Simulation:Converter Controlled Distribution System

50 A

30

0

10

20

io1

io2

55

0 5 10 1535

45

time [ms]

vo1vo2

Bus

Vol

tage

[V]

Sou

rce

Cur

rent

[A

]

0 5 10 15time [ms]

vo1vo250

0

25

io1

io2 Systemoverload!

Softshutdown!

30

0

10

20

Bus

Vol

tage

[V]

Sou

rce

Cur

rent

[A

]

Vo2refVo1ref

Iomax25 A

Iomax25 A

Possible Advantages:• NO excess energy storage for stability• NO AC nor DC circuit breakers• NO converter overrating by “>100% for

1-2 sec for breaker clearing”• NO overrating of wiring, contactors, …

for short-circuit currents >10x

Hence:• Lower cost ?• Higher efficiency ?• Increased availability ?

Monitoring and Control

15 April, 2008 DB-39

Generator

480 V, 3Φ AC

Micro-Turbine

VSCFConverter


SWGRSWGR

Generator

ACElectronic Power Distribution Systems

SWGR

120 V, 1Φ AC

Lighting

MotorMotor

CentralFan

120 V1Φ AC

480 V, 3Φ AC


… …

480 V, 3Φ AC

Com-pressor


SWGR

SWGRSWGR SWGRSWGR


ASDASD

ASDASD ASD ASD

ElectronicBallast

ElectronicBallast

ElectronicBallast

MTB Modeling of AC EPDS:• More difficult due to time-varying nature of steady-state• Large disconnect between system and converter modeling• Use of average models in system analysis is uncommon• “Constant-power loads” are being considered only recently • Small-signal frequency-domain modeling still in development

“Electronic”only recentlyin transportation and datacom centers.

21

15 April, 2008 DB-40

MTB Modeling of Hybrid AC/DC EDPS Components

AC to DC RectifierAC to DC Rectifier

Small-signal frequency-domain modeling exists if AC side is:• Three-phase, 3-wire or 4-wire,• No negative- and constant zero-sequence• No (low) harmonic distortion

DC to AC InverterDC to AC Inverter

AC to AC ConverterAC to AC Converter

Activeand

Passive

Pi & Podo not vary

in steady-state

15 April, 2008 DB-41

rrNonlinearNonlinearAC to AC ConverterAC to AC ConverterModel in stationary Model in stationary

coordinatescoordinates

aa

ωωii bb

cc

ss

tt

ωωoo

NonlinearNonlinearAC to AC ConverterAC to AC Converter

Model in rotating Model in rotating coordinatescoordinates

ddii

qqiidcdc

00

ddoo

qqoo dcdc

00

MTB Low-frequency Modelof AC-AC Converter

•• If ACIf AC--AC equipment is nonlinear (like power converters), AC equipment is nonlinear (like power converters), it cannot be it cannot be linearizedlinearized due to timedue to time--varying steadyvarying steady--state.state.

•• Change to rotating coordinates in synchronism with input Change to rotating coordinates in synchronism with input and output frequencies produces equilibrium steadyand output frequencies produces equilibrium steady--states.states.

•• SmallSmall--signal frequencysignal frequency--domain models are obtained by domain models are obtained by linearizinglinearizing at the equilibrium point. at the equilibrium point.

Balanced converter model in synchronous Balanced converter model in synchronous dd--qq frame(sframe(s))

idvidi

ddY iqdqvY odddiH oqdqiH

iqviqi

qqY idqdvY odqdiH oqqqiH

idddvGddZ

iqdqvG oqdqiZ

odi

odv

iqqqvG

qqZ

idqdvGodqdiZ

oqi

oqv

22

15 April, 2008 DB-42

MTB Low-frequency Model– DC System vs. AC System –

ii

iv

oi

ovDC to DCDC to DCConverterConverterSingle-Input

Single-Output

idiidv

odiodv

iqiiqv

oqioqv

AC to ACAC to ACConverterConverterMulti-Input

Multi-Output

⎥⎦

⎤⎢⎣

⎡⋅⎥⎦

⎤⎢⎣

⎡ −=⎥

⎦

⎤⎢⎣

⎡

o

i

ii

oo

i

o

iv

sHsYsZsG

iv

)()()()(

⎥⎦

⎤⎢⎣

⎡=

)()()()(

sGsGsGsG

qqqd

dqddoG

⎥⎦

⎤⎢⎣

⎡=

)()()()(

sYsYsYsY

qqqd

dqddiY

⎥⎦

⎤⎢⎣

⎡=

)()()()(

sZsZsZsZ

qqqd

dqddoZ

⎥⎦

⎤⎢⎣

⎡=

)()()()(

sHsHsHsH

qqqd

dqddiH

⎥⎦

⎤⎢⎣

⎡⋅⎥⎦

⎤⎢⎣

⎡ −=⎥

⎦

⎤⎢⎣

⎡

o

i

ii

oo

i

o

iv

HYZG

iv

)()()()(

ssss

15 April, 2008 DB-43

Stable Stable

AC Subsystem Interaction Example– small-signal and average modeling and simulation –

R50 Hz230 V

AC Generator PWM Boost Rectifier

600 VDC bus

Start-up to 135 kW

liv

)(sSZ )(sLY

( ))()()(

ssese

q

d Leig=⎥⎦

⎤⎢⎣

⎡

)()()( sss LS YZL ⋅=

• To avoid instability,

• Interface voltage is:

must not encircle –1 !

eigenvalues

the return ratio

ThLSli VYZIv ⋅⋅+= 1)( -

0-3

-2

0

2-1

-4

-2

0

2

4

0 2 4 6 8 10-1Real

Imag

inar

y

ed ( jω ) eq ( jω )

Generalized Nyquist Criterion

200

400

600

Cur

rent

[A]

0 0.1 0.2 0.3 0.4Time [s]

100200300400

Vol

tage

[V] vd

vq

id

iq

23

15 April, 2008 DB-44

200

400

600

Cur

rent

[A]

0 0.1 0.2 0.3 0.4Time [s]

100200300400

Vol

tage

[V] vd

vq

id

iq

AC Subsystem Interaction Example– small-signal and average modeling and simulation –

)(sSZ )(sLY

R50 Hz230 V

Unstable Unstable AC Generator PWM Boost Rectifier

600 VDC bus

-4

-2

0

2

4

0 2 4 6 8 10-1Real

Imag

inar

y

ed ( jω ) eq ( jω )

liv Start-up to 180 kW

Generalized Nyquist Criterion

15 April, 2008 DB-45

DC/AC

LV ACDistribution

LV AC Bus Voltage

Advanced Shipboard Electric Power Systems

• Increase in negative impedance loads produces oscillations.

• Further increase in negative impedance loads produces instability.

Active Filter

Using active filter to introduce damping at higher frequencies decouples the load from source dynamics; thence:

reduces complexity and stabilizes network !

24

15 April, 2008 DB-46

Converter Controlled AC Distribution SystemFault Handling: One-Phase-to-Ground Short

av

bv

cv

ai

bi

ciWith Current Limiting Only

Bus

Vol

tage

[V

]S

ourc

e C

urre

nt [

A]

-250

-150

-50

50

150

250

0.300 0.320 0.340 0.360 0.380Time [s]

-250

-150

-50

50

150

250With Soft Shut-Down

-250

-150

-50

50

150

250

-250

-150

-50

50

150

250

0.300 0.320 0.340 0.360 0.380Time [s]

Bus

Vol

tage

[V

]S

ourc

e C

urre

nt [

A]

15 April, 2008 DB-47

Electromagnetic Compatibility and Interference(EMC & EMI)

UPS

AC-DC DC-AC

Battery

UPS

Server

120 V1Φ AC120 V

1Φ AC

Computer Power System

480 V, 3Φ AC

Micro-Turbine

120 V, 1Φ AC

Lighting

120 V1Φ AC

480 V, 3Φ AC


VSCFConverter


Utility

ASICs

Mem

Fan

DigitalICs

LED

AnalogICs

AC-DCFront-End

Server

48 VDC


μP

...

…

Server

Server …

…

Utility

480 V, 3Φ AC

ElectronicBallast

ElectronicBallast

ElectronicBallast

DC-DCConverter

ASD

Motor

CentralFan

ASD

Motor

ASD

Motor

ASD

Motor

ASD

Motor

ASD

Motor

ASD

Motor

SWGR


SWGR

SWGR

SWGRSWGR

ElectronicBallast

ASD

Motor

ASD

Motor

ASD

Motor

Com-presso

r

AC-DCFront-End

FilteredInput Current

DM EMI

Non-FilteredInput Current

Spectrum

Composite VDE / FCC Class A,B EMI LimitsFiltered

Input CurrentDM EMI

Non-FilteredInput Current

Spectrum

Composite VDE / FCC Class A,B EMI Limits

Single-Phase PFC Rectifier Input Current

Single-Phase PFC Rectifier Input Current Spectra

25

15 April, 2008 DB-48

EMI Simulation Using Multiple Modeling Techniques

Change fS, still match.Well-matched EMI

Simulation

Measurement

Effectiveness of Detailed Physical Modeling in Predicting Conducted EMI

15 April, 2008 DB-49

MTB Equivalent EMI Source Model

Zs1

Zs2

Is1

Is2

Zs3 Zs4 Zs5

P

M

N

G

Norton equivalent source and impedance

DC Bus

Ground Plane

LISN+

7.8 mF

7.8 mF 2 μF

2 μF

1 mH2 Ω400 V

40 A, 60 Hz

25 kHzDC Bus

Ground Plane

LISN+

7.8 mF

7.8 mF 2 μF

2 μF

1 mH2 Ω400 V

40 A, 60 Hz

25 kHz

Measured and predicted conducted EMI spectra of half-bridge inverter

120

60

80

[dBμV

]

100Prediction

Test 40

Differential ModePrediction

Test

0.1 1frequency [MHz]

Common Mode

0.1 1 10frequency [MHz]

26

15 April, 2008 DB-50

Concluding Remarks

Future human energy needs will be provided by new electric power systems, which from

Retinal ImplantJ. G. KassakianIPEC, Niigata,

2005

carbon-free energyto …

Source: Shell Global Scenarios

% of PrimaryEnergy

0%

20%

40%

60%

80%

Coal

Nuclear

Oil

Gas

Hydro

Traditional (Wood, etc.)

Wind, PV,other

renewables

1850 1875 1900 1925 1950 1975 2000 2025 2050Courtesy of GE Global Technology Center Source: Shell Global Scenarios

% of PrimaryEnergy

0%

20%

40%

60%

80%

Coal

Nuclear

Oil

Gas

Hydro

Traditional (Wood, etc.)

Wind, PV,other

renewables

1850 1875 1900 1925 1950 1975 2000 2025 2050Courtesy of GE Global Technology Center

will be: Distributed Power Electronics Systems

organ implants

15 April, 2008 DB-51

Thank You

The work and contributions are result of manyCPES faculty, students, and staff.

This work was supported primarily by ERC Program of the National Science Foundation under Award Number ECC-9731677.

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

Electronic Power Distribution Systems

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