February 2, 2004Grainger Center for Electric Machinery and Electromechanics 1 Energy Source Diversification Patrick Chapman Asst. Professor UIUC Sponsored

February 2, 2004

Grainger Center for Electric Machinery and Electromechanics1

Energy Source Diversification

Patrick ChapmanAsst. Professor

UIUC

Sponsored by: National Science Foundation


What is a diversified energy source?

> 1 energy source Power flow both to and from some sources “Source” may be energy storage Overall ability of multiple sources exceeds the ability of

one alone– reliability– environmental responsibility– adaptability– interchangeability


Motivation

Incorporate more ‘preferred’ energy sources– wind– solar– fuel cell

Conversion methods that adapt to various sources and loads– address wide market with single product

Take advantage of deregulation laws


Research Areas

Circuit topologies Energy source allocation (static control) Dynamic control Simulation Experimentation


Conceptual Diagram

Source-to-load conversions Source-to-source conversions Load-to-source conversions

S o u rc e 3

S o u rc e 2

S o u rc e 1

L o a d 1

L o a d 2

= P o w e r C o n v e rte r s


Selected Applications

Classic two-input: Uninterruptable Power Supply

InverterR ec tifie r 110 VA C


Solar/Battery

Provide average AC power from solar only

Inverter 110 VA CSolar B oos t


Solar/Battery; Flexible Bus Voltage

Allows more flexibility in battery management

Inverter 110 VA CSolar B oos t

B id irec t.dc-dc


Fuel Cell / Battery

Provides dynamic capability to fuel cell system

Inverter 110 VA CB oost

B id irec t.dc-dc

F.C .


Three-Source Systems

AC Line, Fuel Cell, Battery– (plus capacitor)

Inverter 110 VA CB oost

B id irec t.dc-dc

F.C .

R ec t,PFC )


Multiplicity of Same Source

Unbalanced sources, alternative locations

Inverte r 110 VA C

Solar B oos t

So lar B oos t

So lar B oos t


Restricted Switch Types

More general switch schematic symbols Forward-conducting, bidirectional-blocking

(FCBB):

GTO, some cases SCR, MOSFET-diode, IGBT-diode, MCT,RB-IGBT (new)


Circuit Topologies

Straightforward approaches– “n” sources, “n” converters (or similar)– dc link– ac link

New topologies– “n” sources, “1” converter (with “n” inputs)– embed sources in the converter


Standard DC Link

Essentially rectifier-inverter circuit– only we attach different sources and loads

D C /D C

A C /D CD C /A C

D C /D C

D CA C L oad

L oad


DC Link with ‘Phase Leg’ Approach

Model after standard bridge inverters, active rectifiers– requires inductive load/source impedance (not

shown)

In 1 In 2 In 3In M

O ut 1 O ut 2 O ut 3O ut N


AC Link

Use transformer, coupled inductors– isolation possible– less scalable

D C /A C

A C /A C

A C /A C

A C /D C

D C

A C L oad

L oad


Prior Work

First ‘multiple-input’ converter from Matsuo, et al, c. 1990

‘Multiple input’ can be interpreted more broadly– e.g. three-phase rectifier has three inputs

Here, consider the narrow interpretation– three inputs could handle three different sources

(but doesn’t have to)


Matsuo’s Circuit

An AC link topology Used in

– solar/battery– wind/solar/utility

Shown experimentally

Dynamic AnalysisIN

-V

+o u t2

-V

+o u t1

V N (to load 2 )

(to load 1 )

N P N

N 1

N 2

I 2

V 2

N P 2

I 1

V 1

N P 1

.

.

.

.

.

.


Caricchi’s circuit

Caricchi, et al, developed DC link version, c. 2001

Shown in– hybrid automobile– wind/solar/utility

Can be used with fewer switches

– depends on directionality of sources, loads

Boost only from source to cap.

Buck only from cap. to load

. . . . .V 1 V 2

I 2I 1+

V-o u t


DC Link Circuit

Uses one inductor for each load, source– or requires load, source to have inductive series

impedance

Essentially the standard phase legs we know well, applied to multi-source

Uses capacitive energy storage– could be battery instead, but high voltage


Buck-Derived Two-Input

Ordinary buck topology– diode cathode goes to a second source, not ground

Sebastian, et al, showed high efficiency attainable– diversification not studied.

I o u t

+V

-o u t

V 1

V 2


Multiple-Input Buck

Standard buck with parallel inputs Originally shown by Rodriguez, et al, with only

two inputs– shown with solar/battery

I o u t

I 2

I 1

+V

-o u t

V 1

V 2


New, Recent Work at UIUC

Multiple-input buck-boost (MIBB)

I o u t

IN

I 2

I 1

I L

-V+

o u t

V 1

V 2

V N


MIBB Characteristics

Buck and boost operation Similar, but simpler, than Matsuo’s approach Scalable to n inputs Can regulate output voltage with an prescribed power

flow from each input (in theory) Probably has some niche in energy source

diversification field In base form, only accommodates unidirectional

source/load– can modify a bit to get bidirectional


Cousins of the MIBB

Multiple-input flyback– add isolation, turns ratio

I o u t

IN

I 2

I 1

I L

-V+

o u t

V 1

V 2

V N

N NP 1:


Multiple-Input, Multiple-Output

Flyback with multiple, isolated outputs

IN

I 2

I 1

-V+

o u t2

-V+

o u t1

V 1

V 2

V N

(to load 2 )

(to load 1 )

N P

N 1

N 2


Multiple Output, Some Isolated

IN

I 2

I 1

I L

-V

+o u t2

-V

+o u t1

V 1

V 2

V N

N P :N 1


With a bidirectional load/source

Battery load/source concept

I o u t

IN

I2

I1

-V+

o u t

V 1

V 2

V N

(to load)

(batte ry - a sourceor load)

unid

irec

tiona

lso

urce

s


MIBB with Multiplicity of Sources

Battery balancer– (other, probably better balancers exist…)

IN

I 2

I 1

I L

N P :N 1

c e ll 1

c e ll 2

B a tte ryP a c k

c e ll N

c e ll 1N +


Steady-State Analysis

Many switching strategies possible– first attempts involve simple common-edge,

constant frequency, approach

0

1q N

q 2

q 1

T

D T1

D T2

D TN


Steady-State Analysis, cont’d

Begin with basic MIBB, continuous mode The instantaneous inductor voltage

Setting the average to zero, solving for Vout:

maxL i i out ii

v qV V q

0

0

maxT

i ii

out T

ii

qV dtV

q dt

1 max

ieff ii

outi

i

D VV

D


Effective Duty Cycle

The effective duty cycle is the time a switch conducts nonzero current

Can be shown:

1

1

1 1

1 1

0,

,

i

i eff jj

eff i i i

i ieff j eff jj j

D D

D

D D D D


Two-Input Case

V1 > V2, D1 > D2– normal buck-boost, single input

V1 > V2, D2 > D1

11

11out

DV V

D

1 1 2 1 2

21out

DV D D VV

D


Selecting Duty Cycles

Given prescribed:– Power, Pi, for each source

– Output Voltage, Vout– Input Voltages, Vi

**

** *

1iouteff i

jiout j

j jj

PD V

PVV P

V


Plausibility of Duty Cycles

Sum of all effective duty cycles less than one?

YES, since: May be issues with extreme duty cycles

– same for all converters

1 ?eff jj

D

**

** *

1 ?jout

jj jout j

j jj

PV

P VV P

V

* 0jj

P


Correcting for Nonideal

Simple switch-drop model More complicated models possible Feedback to cancel nonidealities


Experimental Continuous Mode

Vary one duty cycle of three Hold all other constant, constant R load

25 35 45 55 65D 1 (% )

30

40

50

60

V o ut (V )M easuredIdea lC ons tan t-D rop


Discontinuous Mode

Inductor current is zero for some portion of each cycle

p j jeff jj j

Ti i D V

L

| |i jiL

t do n

T

D Tef f j( )


Average Output Voltage

Energy balance

Output Voltage– similar to standard buck-boost

21

2 p out out out out donLi CV v V I t

2out p

RLV i

T


Characteristics of Discontinuous Mode

Very sensitive to parameters– feedback a must

Improve accuracy by including– switch drop model– core loss model

taken from Micrometals data sheets iterative procedure with switch-drop model as starting point


Experimental, Discontinuous

Vary one duty cycle, hold others constant

M easuredIdea lSw itch-d ropSw itch-d rop + co re loss

20

30

40

50

30 40 50 60 70

V o ut (V )

D 3 (% )


Other Work at UIUC

Multiple-input flyback– currently being investigated– successful simulation, analysis

Multiple-input boost– n boost converters with common output capacitor– power from unlike solar array sources– simulation, design stage


Work to be Done

Dynamic analysis Dynamic control

– case-by-case? Static control

– power management– case-by-case

Evaluation of topologies Interchangeable sources Topology restructuring

Documents

February 2, 2004Grainger Center for Electric Machinery and Electromechanics 1 Energy Source Diversification Patrick Chapman Asst. Professor UIUC Sponsored