Power Electronic Technologies for Fuel Cell Power … Library/Events/2005/seca...JSL 1 Future Energy...

JSL1

Future Energy Electronics Center

Power Electronic Technologies for Fuel Cell Power Systems

Dr. Jih-Sheng (Jason) LaiDirector, Future Energy Electronics Center

Virginia Polytechnic Institute and State UniversityBlacksburg, VA 24061-0111

TEL: 540-231-4741FAX: 540-231-3362Email: [email protected]

Presentation atSECA 6th Annual Workshop

Pacific Grove, CaliforniaApril 19, 2005

JSL2


Outline1. Basic Fuel Cell Power Systems2. Non-isolated DC-DC Converters3. Isolated DC-DC Converters4. DC-DC Converter Implementation Issues5. Basic DC-AC Inverters6. Fuel Cell and Converter Interactions 7. Fuel Cell Energy Management Issues8. Advanced V6 DC-DC Converter9. Fuel Cell Current Ripple Issues10. Recap

JSL3


1. Basic Fuel Cell Power Systems

MembraneElectrodeAssembly

(MEA)


(MEA)


(MEA)


(MEA)

1. Fuel Cell ControlFlow ratePressureHumidityTemperature

Fuel in

Core of fuel cell

2. Power ConversionsDC-DC for portableDC-AC for householdDC-variable frequency

AC for automotive

3. Energy storage

Electricityout

Power ElectronicsBOP

JSL4


Automotive Fuel Cell Power System1. Fuel cell control

2. Power conversions

3. Energy storage

JSL5


Stationary Fuel Cell Power Plant for Telecom Applications

• Fuel cell output or converter input is low-voltage DC with a wide-range variation

• Plant output is 48-V DC• Isolation may or may not be needed

DC-ACInversion

AC-ACIsolation

AC-DCRectification

FuelCell

AC-DCRectifier

+Filter

Vin

+

–

+

–

FullBridge

Converter

HFXformer

DC/DC converterLV-DC48-55V DC

JSL6


Stationary Fuel Cell Power Plant for Household Applications

• Plant output is high-voltage ac• Multiple-stage power conversions including

isolation are needed

DC-ACLF-HF

AC-ACLV-HV

AC-DCHV-HV

DC-ACHV-HV

DC-ACInverter

+Filter

FuelCell

AC-DCRectifier

+Filter

Vin

+

–

+

–

FullBridge

Converter

HFXformer

DC/DC converterLV-DC HV-AC

120V

120V240V

JSL7


Major Issues Associated with the Power Conditioning Systems

• Cost• Efficiency• Reliability• Isolation• Fuel cell ripple current• Transient response along with auxiliary energy

storage requirement• Communication with fuel cell controller• Electromagnetic interference (EMI) emission

JSL8


2. Basic Non-Isolated DC-DC Converters

• Buck Converter – Output voltage is always lower than input voltage

• Boost Converter – Output voltage is always higher than input voltage

• Buck-boost Converter – Output voltage can be either lower or higher than input voltage

JSL9


Basic Principle of Buck ConverterL

R+Vin

C+Vo

vgs D1

vgs

Vs

Vo

Gate on Gate off

DTs D’Ts

ino DVV

Average output voltage:

g

sd

where D is the duty ratio.Because D < 1, Vo is always less than Vin buckconverting

+Vs(t)

average Vs = Vo

Vs = Vin

Vs = 0

Ts: switching period = 1/fs (s)fs: switching frequency (Hz)

JSL10


A Buck Converter Example

L

+Vin

C+

Vo

vgs

Q1

D1g

sd

+vs(t)48V 24V22 F

40 H

• Input is 48 V, and output is 24 V• Duty cycle D = Vo/Vin = 0.5• Switching frequency = 100 kHz• Output power = 150 W• Inductor and capacitor are designed to limit the current

and voltage ripples

JSL11


Basic Principle of Boost ConverterL

R+Vin

C+vo

vgs

Q1

D1

vgs

Vs

Vo

Gate on Gate off

DTs D’Ts

g

s

d

Vs = 0

Vs = Voinino V

DV

DV

'1

11

Average output voltage:

where D is the duty ratio, and D’ = 1 – D. BecauseD’ < 1, Vo is always greater than Vin boostconverting

vs

+

Vo

JSL12


A Boost Converter Design ExampleL

+Vin C+Vo

vgs

Q1

D1

g

s

d

Vs

+

6V 48V

• Input is 6 V, and output is 48 V• Duty cycle D = 1 – Vin/Vo = 0.875• Switching frequency = 100 kHz• Output power = 180W• Inductor and capacitor are designed to limit the current

and voltage ripples

10 H

100 F

JSL13


Circuit Diagram of Buck-boost converter

L R+

VinC

+v

vgs

Q1 D1

g

sd

inin VDDV

DDV

'1

+ +

The output voltage can be expressed as

JSL14


Synchronous Rectifier

D

G

S

oxide

S G

n+

D

np+

np+n

i i

• MOSFET can be used as a diode by shorting G-S • However, when running under diode mode, gating

between G-S would allow current to flow through S-D channel in reverse direction synchronous rectification

JSL15


Features of Synchronous Rectification

• MOSFET voltage drop is resistive and can be as low as possible, such as <0.1 V.

• The voltage drop is very crucial to the converter efficiency in a low voltage system. For example, a diode with a fixed voltage drop of 0.7 V represents 3.5% loss of a 20-V system.

• Synchronous rectification allows the voltage drop to be a function of MOSFET resistance and current and cuts the conduction loss substantially. For example, a MOSFET with 5 m running at 20 A condition, the voltage drop is 0.1 V, much less than diode voltage drop.

• Suitable for low-voltage systems.

JSL16


Circuit configuration of a Boost Converter with Synchronous Rectification

• D1 and D2 are body diode of Q1 and Q2.

• Q1 and Q2 switchcomplimentary

Q2

L

R+Vin

C+vo

Q1

D2

D1

vgs1 Q1 on Q1 off

DTs D’Ts

vgs2 Q2 off Q2 on

JSL17


Experimental Results of a DC-DC Converter with and without SR

0 0.5 1.0 1.580.0

82.5

85.0

87.5

90.0

92.5

Po (kW)

With SR

Without SREffi

cien

cy (%

)

Test condition:

Vb=13V, Vo=300V

Efficiency is improved by 7% with Synchronous Rectification

JSL18


3. Isolated DC-DC Converters

• Why isolation is needed?• Push-pull DC-DC converter• Half-bridge DC-DC converter• Full-bridge DC-DC converter

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Isolation is Required for Most Systems

• High voltage conversion ratios– Isolation allows better device utilization

• Grounding requirement– Isolation avoids noise coupling

• Safety requirement– Isolation allows meeting safety standards

• Multiple outputs– Isolation transformer allows multiple

secondary windings

JSL20


Problems with Isolation

• Magnetic component design and cost are non-trivial

• Transformer saturation due to unbalance input

• Additional losses• Additional terminations

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Q1

Basic Operating Principle of a Half-Bridge Converter Circuit

VinCf

+

–

Q1

Q2

Half-bridge converter

C1

C2

t

Q1

Q2 Q2vab

dead-time, current circulating thruanti-paralleled diodes

t

t

D2 D1

Vin/20

Switches conduct alternately

vab

2inV

2inV

–+

vab = Vinvab = –Vin

1:n

b

a

JSL22


Half-Bridge DC/DC Converter

Low device countLow voltage deviceDevice sees twice currentUnbalance due to split capacitorsHigh leakage due to twice transformer turns ratio

L

C R vo

+

–

D5

D6

D7

D8

vd

i2

iL

Vin

+

–

1 : nM1

M2

b

C1

a

C2

i1

10V>500A

20V>250A 400V

5 kW

JSL23


Basic Operating Principle of a Push-Pull Converter

1:1:n

Q2 Q1Vin

+

–

C

Q1

t

Q1

Q2 Q2vab


t

t

D2 D1

2Vin

0

Switches conduct alternatelyvab = 2Vin

vab = –2Vina

b

Push-Pull converter

JSL24


L

C R vo

+

–

D5

D6

D7

D8

vd

i2

iL

Push-Pull DC/DC Converter

+ Simple non-isolated gate drives+ Suitable for low-voltage low-power applications– Device sees twice input voltage – need high voltage MOSFET

High conduction voltage drop, low efficiency– Center-tapped transformer

Difficult to make low-voltage high-current terminations Prone to volt-second unbalance (saturation)

1:1:n

M1 M2Vin

+

–

a

b

40V20V>250A

400V5 kW

JSL25


A Push-Pull Converter with Paralleled Devices

Load

Push-pulldc/dcconverter

DCsource

• Input – 28 to 35 V • Device voltage blocking level – 100 V • Efficiency – <85% even with 4 devices in parallel

JSL26


A Commercial Off-the-Shelf 1-kW Fuel Cell Power Plant Using Push-Pull Converter

Push-pullDC/DC

converter

DCinput

117V

DC/ACInverter

+

–

Fuel

Cel

l

JSL27


Basic Operating Principle of a Full-Bridge Converter Circuit

VinCf

+

–

Q1 Q3

Q2 Q4

a

b

Full-bridge converter

t

Q14 Q14

Q23 Q23vab


t

t

D23 D14

Vin0

Switches conduct alternately

vab–+

vab = Vinvab = –Vin

1:n

JSL28


Full-Bridge DC/DC Converter

Most popular circuit today for high-power applicationsSoft switching possibleReasonable device voltage ratings

High component count from the look High conduction losses

L

C R vo

+

–

D5

D6

D7

D8

vd

i2

iL

Vin

+

–

1 : nM1 M3

M2 M4

a

b

i1

20V>250A

20V>250A

400V5 kW

JSL29


Full-Bridge Converter with Paralleled Devices to Achieve Desired Power Levels

Load

Fuelcell

source

• Multiple devices in parallel to achieve desired high efficiency • Problems are additional losses in parasitic components,

voltage clamp, interconnects, filter inductor, transformer, diodes, etc.

Lf

Voltage clamp

JSL30


Design Considerations for Isolated DC-DC Converters

• Transformer turns ratio• Transformer core utilization• Device voltage stress• Device current stress• Output diode voltage stress• Voltage clamping

JSL31


Pulse Width Modulation for Isolated DC-DC Converters

The average output voltage Vo = DnVin

Wheren = transformer turns ratio = n2/n1D = duty ratio = ton/T

andn1 = number of turns of primary windingn2 = number of turns of secondary winding

ton = switch turn-on timeT = switching period

JSL32


Transformer Core Utilization

Forward: <50% Flyback: <50%

iM

Half-bridge: 100%Push-pull: 100% Full-bridge: 100%

iM-pk

B

HNiM-pk

B

H

iMMagnetizing current

0 0

iM-pk

t t

Core is fully utilized

–NiM-pk

NiM-pk

Core is half utilized

JSL33


Device Voltage and Current Stresses

• Device voltage stressPush-pull: 200%Half-bridge: 100%Full-bridge: 100%

• Device current stressHalf-bridge: 200%Push-pull: 100%Full-bridge: 100%

• Output diode voltage stressCenter tap: 200%Bridge: 100%

JSL34


Voltage Clamping

• Problems of diode over voltages– Full-bridge– Center-tapped

• Voltage clamping methods – Passive clamping method– Active clamping method

JSL35


Over-Voltage Caused by the Transformer Leakage Inductance

L

C R vo+

–

1 : n Llk

DTs

v1 v2 vd

–

+

vo

v1

v2

vd

vo

v1: Primary side voltagev2: Secondary side voltage v2, v2 > vo.vd: Voltage stress of upper diodes (D5 , D7) when lower diodes

( D6 , D8) conduct, or vice versus, vd-pk > v2-pk > vo, due to leakage inductance voltage drop.

TsD5

D6

D7

D8

JSL36


Full-Bridge Diode Rectifier Over-Voltage Clamping

L

CR

Llk

v2

D5

D6

Cc

Rc

vo

vd

vo

vdWithout clamp

With passive clamp

vd

–

+

Advantage: Diode voltage stress is significantly reduced.Disadvantage: Added cost and complexity.

JSL37


Fuel Cell System Example for Topology Selection

Question: With 48 V fuel cell voltage and 400 V dc output, what topology is the best?

Answer: Intuitively, push-pull converter is the best because of least parts count. However, with device availability and cost consideration, full-bridge convertermay be a better choice.

Reason: For low-side power MOSFET, lower voltage is more cost effective. Similarly, for high-side diode, lower voltage is more cost effective.

JSL38


4. Implementation Issues in High Power DC/DC Converters

• Controller output duty cycles tend to be unbalanced due to internal chip layout, resulting transformer saturation.

• Voltage sensing problem:– Feedback voltage signal tends to be corrupted by noises– Hall sensor is expensive– Common mode and isolation are difficult to deal with

resistor dividers • Current sensing problems:

– Lossy with resistor sensing– Difficult to insert Hall sensor for device current

measurement

JSL39


Full-bridge Converter Design Example

• Specifications:– Input fuel cell voltage ranges from 36 V to 60 V – Output: 400 V, 10 kW

• Current– Output: 25 A – Input: 208 A

JSL40


Power Stage Design

Vin

L

Cf

+

–

C R vo

+

–

1 : nQ1 Q3

Q2 Q4

a

b

HF ac

Xformer

Component Design and Selection: • Power MOSFET• Rectifier diode • Transformer • Filter inductor• Filter capacitor

D5

D6

D7

D8

vd

i1 i2

iL

JSL41


Survey of High Current Power MOSFETs

*Note: IXYS FMM 150-0075 is a dual pack (half bridge) device.

Manufacturer Part Number VDSS (V) RDS-on (m ) Package Fairchild FDB045AN08A0 75 4.5 TO-263 International Rectifier IRFP2907 75 4.5 TO-247 Fairchild FDP047AN08A0 75 4.7 TO-220AB IXYS FMM 150-0075P 75 4.7 ISOPLUS i4-PAC*

Vishay Siliconix SUM110N08-05 75 4.8 TO-263 IXYS IXUC160N075 75 6.5 ISOPLUS 220 International Rectifier IRF3808 75 7.0 TO-220AB Fairchild FQA160N08 80 7.0 TO-3P Quantity 1 100 1000 25,000 50,000 100,000FDB045AN08A0 $3.50 $2.50 $2.40 $2.30 $2.10 $1.60IRFP2907 $4.49 $3.96 $3.07 $3.07 $3.07 $2.89FDP047AN08A0 $3.50 $2.50 $2.40 $2.30 $2.10 $1.60FMM 150-0075P $8.00 $7.00 $6.19 $5.79 $5.30 $5.03SUM110N08-05 $2.70 $2.50 $2.50 $2.35 $2.19 $2.19IXUC160N075 $4.00 $3.00 $2.05 $1.65 $1.49 $1.40IRF3808 $2.29 $2.16 $1.80 $1.50 $1.30 $1.17FQA160N08 $4.00 $3.00 $2.90 $2.60 $2.50 $2.20

JSL42


Survey of Ultrafast Reverse Recovery Diodes

Quantity 1 100 1000 25,000 50,000 100,000RHRG5060 N/A, (300 part min) $3.50 $1.75 $1.50 $1.50HFA50PA60C $8.81 $8.22 $7.71 $7.61 $7.25 $4.00DSEK 60-06A $4.00 $3.00 $2.50 $2.07 $1.99 $1.90

Manufacturer Part Number VF trr I PackageFairchild RHRG5060 1.5 V 45ns (max) 50 A TO-247International Rectifier HFA50PA60C 1.9 V 23ns (typ) 50 A TO-247AC IXYS DSEK 60-06A 1.6 V 35ns (typ) 60 A TO-247AD

JSL43


Output Filter Capacitor Selection- Typically based on the output voltage ripple

• The output filter capacitor needs to handle 120 Hz, 22 A ripple current generated from the next stage inverter.

• Assume the voltage ripple is limited to 5%. The capacitance can be calculated as

mF2.205.0400608

228 Vf

IC

JSL44


Digital Computer Implementation for High Power DC/DC Converters

• Digital computer such as DSP has become a good option for high power DC/DC converter control implementation

• Feedback voltage signal can be converted to digital and through PWM feeding back to DSP to avoid noise corruption

• Even if commercial PWM or PSM chips are used, the control signal can be obtained from DSP through D/A conversion

• Communication with digital signals has become the essential part between the dc/dc converter and the fuel cell controller or other power converters

JSL45


Controller Design for a Typical Converter

21)(

sQsKsGp

sKKsG i

pc )(

Compensator Converter(plant)

Sensor

Reference Output

(A standard PI controller)

Gc(s)Gp(s)

s = j = 2 f

1j

f = frequency

JSL46


Digital Controller for a Typical Converter

DigitalControllerA/D

(sample)D/A

(hold)

Converter

plant

Sensor

ReferenceOutput

11

2)(

zzTKKzG s

ipc

+

–

Ts = switching frequency

112

zz

Ts

s

Gc(s)

JSL47


Voltage Loop Controller Block Diagram

Full BridgeConverter

Vin

L+

–

C R vo

+

–vd

iL

H

Gc(s) –

+

vref

Pulse-widthmodulator

d(t)vsensevc

H: Voltage scaling = 5.1/400 Gc(s): PI or PID Controller

Gp(s)

JSL48


Phase Margin Shifts due to Fuel Cell Input Voltage Variation: 42 to 60 V

0dB from initial designG

ain

(dB

)P

hase

(°)

22 /)/(1)(

oo

invd sQs

nVsG

a negative phase margin with higher gain or higher input voltage

0dB with higher gain or input voltage

JSL49


DC-DC Converter Control System Design is Challenging with the Fuel Cell Source

• A typical controller is designed with low input voltageand heavy load condition.

• When the load is reduced, the fuel cell voltage increases, and the original controller design may be inadequate due to input voltage variation.

• Increasing the input voltage is equivalent to increase the closed-loop gain and tends to worsen the phase margin, and the system can eventually become unstable.

JSL50


5. DC/AC Inverters

• Single-phase output – Half-bridge– Full-bridge

• Dual single-phase outputs – Dual half-bridge– Three-leg inverter

• Load Effect – Linear loads– Nonlinear loads

JSL51


Half-Bridge DC-AC Inverter with Split DC Buses

Q1

Q2

Vdc

L+

–

C ACLoad

Vdc1

Vdc2

vacvab

Maximum output peak voltage Vmax = Vdc/2• Simple dc-ac Inverter with minimum switch counts• Split dc buses should be very stiff and balance to avoid dc or

even harmonics at the ac output• Control is limited to the ordinary sinusoidal pulse width

modulation (SPWM)• Cost burden is in passive components

b

a

Vdc1 = Vdc2 = Vdc/2

c

vba vac

JSL52


Sinusoidal Pulse Width Modulation

vsin

vc : carrier wave

Gating signal

When vsin > vc, gate signal is high, and IGBT is turned on;Otherwise, gate signal is low and IGBT is turned off.

JSL53


Single-Phase Full-Bridge DC-AC Inverter

Q1 Q3

Q2 Q4

Vdc

LCdc

+

–

C AC Load

Compared with Half-Bridge inverter, FB inverter features• Simple dc-ac Inverter with more switch counts, but

less bulky capacitors• Control is more flexible to have phase-shifted SPWM

for two individual legs – Dual Modulation Method. • Size of passive components may be reduced

JSL54


Dual Single-Phase Outputs with Dual Half-Bridge Inverters

Q1

Q2

2VdcCdc1

+

–

Vdc

Vdc

vac1

Q3

Q4

L1

C1

L2 C2 vac2

Only one set of split dc buses are requiredQ1-Q2 and Q3-Q4 pairs need to be switched complementary so that the total vac = vac1 + vac2.Possible unbalanced output ac voltages under unbalanced load conditions

vac

JSL55


Three-leg Inverter for Dual AC Outputs with Single DC Bus

Q1

Q2

VdcCdc

+

–

vac1

Q5

Q6

L1

C1

L3 C2 vac2

vac

Q3

Q4

• Similar to full-bridge inverter with more switch counts, but less bulky capacitors

• Outer legs do SPWM to produce vac output. Middle leg is controlled to equalize vac1 and vac2

• Control is more complicated to ensure output voltage balance• Size of passive components may be reduced

L2

JSL56


Using Low-Frequency Transformer for Low-Voltage AC Inverter Output

L

C48V

120V

120V

240V

Features:• Low-frequency transformer allows low-voltage DC to be

directly converted to AC• Output can be single or dual• Size is the major concern

JSL57


Inverter Output with Resistive Load

RVI

V = 4.1%

vac

Voltage and current are in phase

RvI ac

R

IR

R

JSL58


Dual Output Voltage and Current with Unbalanced and Reactive Loads

Voltage of Leg 1

Current of Leg 1

Voltage of Leg 2

Current of Leg 2

JSL59


-1.0

-0.50.0

0.5

1.0

0 90 180 270 360 450 540 630 720

Majority of Power System Loads is Inductive

fLjLjX L 2

vac

IRL

R

L

Impedance of inductor is imaginary (90º apart from real value)

-1.0

-0.5

0.0

0.5

1.0

0 90 180 270 360 450 540 630 720

vac

IRR L

IL IRL

IR

IL

IRL

vac

IL

IR

90º lagging

JSL60


-3-2-10123

0 90 180 270 360 450 540 630 720

-3-2-10123

0 90 180 270 360 450 540 630 720

-3-2-10123

0 90 180 270 360 450 540 630 720

What about Watt and VAR?

P

Q

P+jQ

ILvac

Q (VAR)

IR

vac

P (Watt)

VAR is reactive V A,average VAR = 0, but reactive current is not 0.

Watt is real V A,average Watt > 0, and is the average (V A).

VA = Watt+jVAR, not Watt+VAR because they are not in phase.

JSL61


Implications of VAR

• Average VAR = 0 No real power output• VAR loads are typically inductive such as

motors, magnetic ballasts, relays, etc. • The current associated with VAR causes

additional heat losses in the wiring and the internal impedance of the source

• Inductive VAR can be compensated with capacitive VAR, but not without complexity

• Nonlinear loads also introduce VAR

JSL62


Majority of Electronic Loads is Nonlinear

SwitchModePowerSupply

DCLoad

1-phaserectifier

InverterDrive

ACMotor

3-phaserectifier

Used for:Computers,Printers, Fax, most ITEElectronic LightingCommunicationsFood Preparation

Used for:HVAC, Battery Charging, Food Preparation,Elevators

JSL63


Inverter Output Voltage Under Nonlinear Rectifier Load

• Single-phase nonlinear load current is rich with odd harmonics (3,5,7,…) especially with the 3rd harmonic

• The voltage waveform is flatten up due to nonlinear current.

IL

vac

JSL64


Voltage Waveform Quality may be Improved with Closed-loop Control

Voltage THD = 4.6%

Closed-loop control can smooth the voltage waveform but the nonlinear current waveform remains nasty.

JSL65


6. Fuel Cell and Converter Interactions

• Static modeling• Dynamic modeling• Fuel cell dynamic response with and without

converters

JSL66


SOFC Voltage-Current Characteristic as a Function of Temperature

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

800 ºC

Current (A/cm2)

Vol

tage

(V)

750 ºC

700 ºC

Data source: DOE SECA Modeling team report at Pittsburgh Airport, 10/15/2002

PEMFC

SOFC

JSL67


Power Density of SOFC and PEMFC

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1 1.2

800 ºC

Current (A/cm2)

Pow

er d

ensi

ty (W

/cm

2 )

750 ºC

PEMFC

SOFC

JSL68


PEM Fuel Cell Dynamic Characteristics

0102030405060

0 2 4 6 8 10 12t (sec)

0

500

1000

1500

2000

0 2 4 6 8 10 12t (sec)

vFC(V)

iFC(A)

pFC(W)Step load: 1.47kWParasitic power: 70W

voltage undershoot (2.5V)due to compressor delay

150W dip

27.2V

3kW power overshoot

43V

Nexa 1.2kW Unit

JSL69


Fuel Cell Modeling with Electrical Circuit

load

JSL70


Nexa1200 Polarization Curve

I_Ifc

0A 5A 10A 15A 20A 25A 30A 35A 40A 45A 50AV(fc)

0V

5V

10V

15V

20V

25V

30V

35V

40V

45V

50V

simulation resultsexperimental results

JSL71


Polarization Curves for Nexa PEM FC

I_Ifc

0A 10A 20A 30A 40A 50A 60AV(fc)

20V

25V

30V

35V

40V

45V

2

3

1

1. Fuel cell runs at 70-W parasitic load condition Compressor is running at low speed

2. Fuel cell is fully loaded at 1.4 kW Compressor is not immediately responding to load step, voltage dips

3. Compressor speeds up, fuel cell voltage picks up to or above nominal level

JSL72


Time Domain Response

0

10

20

30

40

50

60

0 2 4 6 8 10 12t (sec)

vFC

iFCvoltage undershoot due to compressor delay

1

2

3

JSL73


PEM Fuel Cell Dynamic Simulation Diagram

1st timeconstant

+X

+

+

2nd timeconstant

+

• High load current high voltage drop• Low output voltage low voltage drop

Multiplying ratio

parasiticload

Transientload

Voc

Fuelcell

High current branch

Low current branch

JSL74


Fuel Cell Stack Output Dynamic Simulation and Experimental Results

Fuel Cell Output Voltage (10V/div)

10 s/div

Fuel Cell Output Current (5A/div)

Fuel Cell Output Power (200W/div)

0s 50us 100us0

10

20

30

40

501

0W

0.2KW

0.4KW

0.6KW

0.8KW

1.0KW2

>>

Vfc

Pfc

Ifc

(b) simulation results

(a) experimental results

Vfc

Pfc

Ifc

JSL75


Fuel Cell Voltage Dynamic with Converter Load Transient

Input Voltage from Fuel Cell (5V/div)

100ms/div

SimulatedExperimental

Significantly slower time constant ( 50ms)due to 30 mF converter input capacitor and a long cable

JSL76


Fuel Cell Responds with a Paralleled 140F Ultra Capacitor Capacitor

Ifc

Vfc

Iulcap

Fuel Cell Voltage (20V/div)

Fuel Cell Current (20A/div)

Load Current (5A/div)

Ultra-Capacitor Current (20A/div)

50ms/divILoad

JSL77


Fuel Cell Responds with a Paralleled 10mF Electrolytic Capacitor

Ifc

Vfc

Icap



DC Link Current (25A/div)

Capacitor Current (5A/div)

20ms/div

Note: Fuel cell output voltage response is slowed down to 30ms. Capacitor takes over the transient current.

Idc=Icap+Ifc

JSL78


Findings of Fuel Cell Modeling and Converter Test Results

• Fuel cell stack shows very fast dynamic, nearly instantly without time constant

• Perception of slow fuel cell time constant is related to ancillary system not fuel cell stack

• Output voltage dynamic is dominated by the converter interface capacitor and cable inductor

• Output current dynamic is dominated by the load

JSL79


Issues to be Resolved in a Fuel Cell Power Conditioning System

• Energy management system options – Sizing of converters and auxiliary sources

• Advanced Bidirectional dc-dc converter technologies• Interleaved control and associated technologies• Digital control for high power dc/dc converters• Fuel cell voltage standardization• Fuel cell ripple current specifications• Fuel cell output voltage dynamic• Fuel cell and power conditioning interface and

communication protocol

JSL80


7. Fuel Cell Energy Management Issues

• Problems without Slow Fuel Cell Response and Auxiliary Energy Storage

• Options of Energy Storage Placement• Energy Management options with

Bidirectional DC/DC Converters

JSL81


Why Fuel Cells Need Auxiliary EnergySource or Energy Storage?

• For standalone power supplies: need energy storage for load transient

• For grid-connected power supplies: need auxiliary energy source for start-up

• For all systems: need auxiliary energy source to provide power for control signals

JSL82


Problems of a Fuel Cell System without Energy Storage

• Fuel cell does not have storage capability• Slow response, output voltage fluctuates

with loads• Source may not be continuously available • Size (or capacity) needs to be higher than the

peak load• When sized enough for the maximum load,

excess energy will be wasted

JSL83


A Slow and Weak Energy Source During Startup and Large Load Transient

With a slow and weak input source; it dips significantly during start up and large load step.

Vo= 320 V

Vin = 220 VVin (100 V/div)

iin (20 A/div)

Vo (100 V/div)

io (10 A/div)

JSL84


Converter Step Load Response with Stiff Voltage Source and Voltage Loop Control

Load Current (2A/div)

Input Current (20A/div)Output Voltage (50V/div)

20ms/div

With voltage control loop bandwidth designed at 20 Hz, settling time is about 40ms under load step

JSL85


Converter Load Dump Response with Stiff Voltage Source and Voltage Loop Control

Load Current (2A/Div)

Output Voltage (50V/Div)

10ms/Div

Input Current (20A/Div)

With voltage control loop bandwidth design at 20 Hz, settling time is about 40ms under load dump

JSL86


A Fuel Cell Power Plant with Energy Storage

FuelCell

Source

DC/DCConverter

DC/ACInverter

AC LineFilter

Loads/Grid

Auxiliary Energy storage options

Fuel Cells Need Auxiliary Energy Storage for energy management

JSL87


Low-Voltage Ultra-Capacitor Energy Storage Configuration

DC/DCconverter

48-72V

Ultra-capacitor

Fuel

Cel

l

120V

DC/ACInverter

Lf

JSL88


Use High-Voltage Battery as the Auxiliary Energy Storage

FuelCell

Source

DC/DCConverter

ACLoad

High voltage auxiliary energy storage battery

Capacitorfilter

120V

Photographof a 96V battery bank

fuse

JSL89


Potential Problems with Passive Energy Storage

• Low-side ultracap option:– Two voltage sources are paralleled – not a good

engineering practice – Time to reach equilibrium point is too long because

dynamic characteristics of both sources are different– Ultra capacitor helps transient current sharing, but

creates significant voltage and current ripples due to interaction between two voltage sources

– Dynamic current sharing problem• High-side battery option:

– Battery cell voltage balance problem – Battery state-of-charge management – Long-term battery life expectancy – Cost of battery is a concern

JSL90


Energy Management Options with Energy Storages and Power Electronics

• Optimum energy usage control • Start-up control• Load transient control • Charging and discharging (bidirectional) controls

for auxiliary energy storages

JSL91


Design Considerations for Hybrid-Source Systems

1. Utilization of Primary Source2. Simple Power Circuit (as simple as possible)3. Voltage ratio4. Isolation Requirement5. Energy Storage Requirement6. Inverter DC Bus Voltage Requirement7. Cost

JSL92


Energy Management Using Low Voltage Battery and Bidirectional DC/DC

Fuel cell LoadDC/DCconverter

Inverter

DC Bus

Vdc

Iac

feedbacks

Bidirectionaldc/dc

converter

Vac

Vbatt • Low voltage battery controlling DC bus through a bidirectional dc/dc converter

• Avoid battery cell voltage balancing problem

• Complicated control

JSL93


Dual-Source Energy Management Using a Unidirectional Boost Converter

AB

C

100kW Inverter

+

+

–

300 V

–

D2

S1

VdcAC

Output

L1

Low voltageFuel cell

High voltagebattery

• Battery voltage > Fuel cell voltage• Simple boost converter regulates the battery state of charge• DC bus voltage is constant

180–

240

V

Fuel

Cel

l

80kW converter

Total power electronics: 80-kW DC/DC + 100-kW DC/ACTotal energy sources: 20-kW battery + 80-kW fuel cell

JSL94


An Example of Dual Sources with a Bidirectional DC-DC Converter

AB

C

100kW Inverter

+

+

– 240–

380

V

180–

240

V

–

S1

S2

VdcAC

Output

Battery voltage < fuel cell voltage needs a boost converter to supply energy during transient load and a buck converter to charge the battery

Fuel cell voltage = dc bus voltage not regulated

L1

LowvoltageBattery

High voltageFuel cell

Fuel

Cel

l

20kW Converter

• Total power electronics: 20-kW DC/DC + 100-kW DC/AC• Total energy sources: 20-kW battery + 80-kW fuel cell

JSL95


Interleaved Bidirectional DC/DC Converter forFuel Cell Energy Management

Ld1

Ld2

S1u S2u

S1d S2d

VFC

Vbatt

Fuel

Cel

l 100 kWInverter

20kW converter

• Total power electronics: 20-kW DC/DC + 100-kW DC/AC• Total energy sources: 20-kW battery + 80-kW fuel cell

80kW

20kW

Interleaved operation for both boost and buck modes • smaller passive components; • less battery ripple current

JSL96


DC Bus Voltage During 800-W Load Step and Load Dump Under Boost Mode Operation

VdcVdc

Idc (1A/div)

(50V/div)(50V/div)

Idc (1A/div)

DC bus voltage fluctuates but returns to original setting after load transients

20ms/div 20ms/div

JSL97


Battery Voltage During 800-W Battery Charge Command Step under Buck Mode Operation

Vbatt

Idc (2A/div)

(20V/div)

(20A/div)ILd1

Vbatt

Idc (2A/div)

(20V/div)

(20A/div)ILd1

Battery voltage keeps constant during severe charging and discharging current conditions

JSL98


8. Advanced V6 Converter

• Single-Phase Half-Bridge Converter• Two-Phase Full-bridge Converter• Three-Phase Converter• V6 Converter• Test Results with V6 Converter• V6 Converter Prototype

JSL99


Half-Bridge Converter – A Single-Phase Converter

1 : nHF-AC

Half-bridge converter

Xformer

Rectifier+LC filter

Act

ive

Load

20V>250A

Sol

id-O

xide

Fue

l Cel

l400V5 kW

10V>500A

JSL100


Full-Bridge Converter – A Two-Phase Converter

1 : n

HF ACXformer

Rectifier+LC filter

Act

ive

Load

Sol

id-O

xide

Fue

l Cel

l

Full-bridge converter

20V>250A

400V5 kW

20V>250A

JSL101


Full-Bridge Converter with Paralleled Devices to Achieve Desired Power Levels

Load6x 6x

• With 6 devices in parallel, the two-leg converter can barely achieve 95% efficiency

• Problems are additional losses in parasitic components, voltage clamp, interconnects, filter inductor, transformer, diodes, etc.

Voltage clampSol

id-O

xide

Fue

l Cel

l20V250A

JSL102


Fuel Cell Voltage and Current with Full Bridge Converter Case

Time

0s 2ms 4ms 6ms 8ms 10msV(Vfc)

10V

20V

30V

-I(Vfc)20A

40A

60A

I(Cin)-50A

50A

100A

150A

SEL>>

I(Ld3) V(Iac)-15A

-5A

5A

15A

Fuel cell voltage

Fuel cell currentLoad step

Input capacitor current

AC load currentFilter inductor current

Load dump

330%

33%

JSL103


Switching Waveforms with Full-Bridge Converter

Time

4.998ms 5.000ms 5.002ms 5.004ms 5.006ms 5.008ms 5.010msI(M1:d) I(M3:d)

-25A

25A50A75A100A

SEL>>

V(M1:d)-V(M1:s) V(M1:g)-V(M1:s)-10V0V10V20V30V40V

I(Cin)-100A

-50A

0A

50A

100A

150 A

Ripple frequency = 100 kHz

Zero-voltage switching is achieved

JSL104


A Three-Phase Bridge Converter

vin

L

Cf

+

–

Co vo

+

–

1 : nS1 S5

S4 S2

a

c

HF ACXformer Rectifier+LC filter

D1

D4

D3

D6

iA ia

iL

Act

ive

Load

Fuel

Cel

l or o

ther

vol

tage

sour

ce

3-phase bridge inverter

S3

S6

b

D5

D2

A

B

Cn

–iC

• Hard switching • With 4 devices in parallel per switch• Efficiency 95%

20V>167A

JSL105


Fuel Cell Voltage and Current with 3-Phase Bridge Converter Case

Time

0s 5ms 10msV(Vfc)

10V

20V

30V

-I(Vfc)20A

60A

SEL>>

I(Cin)-50A

0A

50A

100A

150AI(Ld3) V(Iac)

-15A

-5A

5A

15A

Fuel cell voltage

Fuel cell currentLoad step

Input capacitor current

AC load currentFilter inductor current

A significant reduction in capacitor ripple current

33%

80%

No reduction in low-freq. fuel cell ripple current

Load dump

JSL106


Switching Waveforms with 3-Phase Bridge Converter

Time

4.998ms 5.000ms 5.002ms 5.004ms 5.006ms 5.008ms 5.010msI(M1:d) I(M4:d)

-25A0A

25A50A75A

100AV(M1:d)-V(M1:s) V(M1:g)-V(M1:s)

-10V0V

10V20V30V40V

I(Cin)-50A

0A

25A

50A

SEL>> 35 A

Ripple frequency = 300 kHz

Zero-voltage switching is achieved

JSL107


Key Features of Multiphase Converter

• Device is switched at a lower current, while maintaining zero-voltage switching.

• High-frequency capacitor ripple current is reduced by >4x, and its frequency is increased by 3x. This translates to significant capacitor size reduction and cost saving.

• No effect on low-frequency AC current ripple, which remains an issue to be solved.

JSL108


Circuit Diagram of the Virginia Tech V6 Converter

Sol

id-O

xide

Fue

l Cel

l

Act

ive

Load

Rectifier+LC filterSix-phase bridge converter

HF ACXformer

20V>83A

JSL109


Key Features of V6 Converter• Double output voltage reduce turns ratio and

associated leakage inductance• No overshoot and ringing on primary side device

voltage• Input side high-frequency ripple current elimination

cost and size reduction on high-frequency capacitor• Output DC link inductor current ripple elimination

cost and size reduction on inductor • Secondary voltage overshoot reduction cost and

size reduction with elimination of voltage clamping• Significant EMI reduction cost reduction on EMI

filter• Soft switching over a wide load range• High efficiency ~97% • Low device temperature High reliability

JSL110


Waveform Comparison between Full-Bridge and V6 Converters

Full Bridge Converter V6 Converter

iL

iL

vd

vd

• Secondary inductor current is ripple-less; and in principle, no dc link inductor is needed

• Secondary voltage swing is eliminated with <40% voltage overshoot as compared to 250%

JSL111


Significant DC link Inductor Size Reduction

With V6 converter, an effective 10x reduction in DC link filter inductor in terms of cost, size and weight

Single Phase500W60Hz

Single Phase5 kW50kHz

Three Phase5 kW50kHz







JSL112


Input and Output Voltages and Currents at 1kW Output Condition

Vin

VoVo

Iin

Vin

Iin

Io

Io

(a) Full bridge converter (b) V6 Converter

Significant improvement with V6 converterLess EMIBetter efficiency (97% versus 87% after calibration)

(97%)(87%)

JSL113


Where are the Losses?• Switch conduction • Diode conduction • Transformer• Output rectifier • Output filter inductor and capacitor• Input capacitor• Parasitics

– Copper traces– Interconnects

JSL114


Calorimetry for Accurate Loss Measurement

Calibration with resistor bank

fans

JSL115


Test the 160-Liter Calorimeter at 120-W Loss Condition

0102030405060708090

0 100 200 300 400 500 600Time (min)

Tem

pera

ture

(deg

C)

Average probe temperature

Temperature rise

>9 hours for each test points

JSL116


Temperature Rise Versus Power Loss

y = 0.4086x + 2.9771

1520253035404550556065

30 40 50 60 70 80 90 100 110 120 130Power Loss (W)

Tem

pera

ture

(deg

C)

TempRise

Linear (TempRise)

JSL117


Efficiency Measurement Results

80%82%84%86%88%90%92%94%96%98%

100%

0 1000 2000 3000 4000Output power (W)

Experimental data and trend line

• Measurement error: within 1%• Heat sink temperature rise:

<20°C at 2kW with natural convection

Effi

cien

cy

75%

80%

85%

90%

95%

100%

0 500 1000 1500 2000 2500Output Power (W)

Effic

ienc

yPhase-II V6-Converter Efficiency (calibrated)

Phase-I Efficiency Measured Results

JSL118


The Beta Version Prototype Converter

• Schematic Circuit Diagrams• V6 Cost Estimate • Summary of Beta Version Prototype

JSL119


Schematic Circuit Diagrams

Power boardGate drive board

Control boardDigital board

Interface board

JSL120


Photographs of V6-Converter Together with DC-AC Inverter Prototype

Front View Rear View

ConverterInverter

JSL121


Prototype and Production Cost Estimate for the 5-kW V6 DC-DC Converter

Quantity 100 1000 10000Material cost $475 $347 $227Tooling, Assembly & Testing $1,424 $347 $114Production Cost $1,899 $694 $341

Key Materials Parts Count Qty 1 Qty 10000Power Circuit 22 $571.00 $154.40 Devices 8 $201.00 $38.40 Capacitors 6 $84.00 $30.00 Transformers 3 $180.00 $45.00 Inductors 2 $24.00 $8.00 Sensors 2 $32.00 $8.00 Contactor 1 $50.00 $25.00Control Circuit 325 $113.70 $33.22 Resistors 164 $18.59 $2.71 Capacitors 110 $46.61 $17.41 Discretes 27 $8.00 $2.42 IC's 24 $40.50 $10.68Miscellaneous 55 $174.80 $52.44Total 402 $840.50 $227.05

JSL122


9. Fuel Cell Current Ripple Issues

Lf

Cf RA

BVdc

+

–

Sap

San Sbn

Sbp

Vo

+

–

60Hz

120Hz

• Current ripple propagates from AC load back to DC side• With rectification, ripple frequency is 120 Hz for 60 Hz

systems• Low-frequency ripple is difficult to be filtered unless

capacitor is large enough

AC filter LC

High-sidecap.

DC-DCconverter

120Hz

FuelCell

JSL123


AC Current Ripple Problems

• Inverter AC current ripple propagates back to fuel cell • Fuel cell requires a higher current handling capability

Cost penalty to fuel cell stack• Ripple current can cause hysteresis losses and

subsequently more fuel consumption Cost penalty to fuel consumption

• State-of-the-art solutions are adding more capacitors or adding an external active filters Size and cost penalty

• Virginia Tech solution is to use existing V6 converter with active ripple cancellation technique to eliminate the ripple No penalty

JSL124


Circuit Model for AC Current Ripple

N:1Iin

Vin Iload

RsLf

Vdc

+

–

Ip Is

iin/N

iload

N2RsLfip/N is

DC Model

AC Ripple ModelCin/N2

N2RCin

Cin

RCin

Cf

RCf

Cf

RCf

DC/DCConverterVin

Rs Lf

IloadCin

RCin

Cf

RCf

JSL125


Solutions to Ripple Currents

• Add more capacitors (ultra capacitor) on the low-side dc bus

• Add more capacitors on the high-side dc bus

• Add one more stage DC-DC converter • Add an active ripple cancellation circuit

– with a bidirectional DC-DC converter to stabilize the high-side dc bus voltage

– with a built-in control function in the DC-DC converter

JSL126


Benchmark DC/DC Converter Parameters for Ripple Study

• Input Voltage: 25V• Output Voltage: 200V• Input DC Capacitor: 6mF• Output DC Capacitor: 2200mF• Filter Inductor: 84mH• Inverter Modulation Index: 0.86• Inverter Load Resistor: 16.7

JSL127


Adding Hide-Side Energy Storages on DC Bus Helps Reduce Ripple Current

0.25k

-50

0.1k

0 50m10m 20m 30m 40m0.25k

-50

0.1k

0 50m10m 20m 30m 40mTime (s)

20% ripple current

10% ripple current

DC/DCConverter

DC bus energy buffer

4-cycle energy backup

8-cycle energy backup

ACLoad

120VFuelCell

JSL128


Simulation Results with LV-Side Capacitor Input Capacitor has Very Little Effect to Current

Ripple Reduction

t(s)0 0.01 0.02 0.03 0.04 0.05

0

1015

5

200

19080

40

0

20

25

(A)

(V)

(A)

(V)

HV DCCurrent

HV DCVoltage

LV DCVoltage

LV DCCurrent

t(s)0 0.01 0.02 0.03 0.04 0.05

0

1015

5

200

19080

40

0

20

25

(A)

(V)

(A)

(V)

Input Cap Reduced to 136 FInput Cap 6mF

JSL129


Output Capacitor can be Used as Passive Solution to Current Ripple Reduction

– Cost is a Concern

t(s)0 0.01 0.02 0.03 0.04 0.05

0

1015

5

200

19080

40

0

20

25

(A)

(V)

(A)

(V)

HV DCCurrent

HV DCVoltage

LV DCVoltage

LV DCCurrent

t(s)0 0.01 0.02 0.03 0.04 0.05

0

1015

5

200

19080

40

0

20

25

(A)

(V)

(A)

(V)

Output Cap Reduced to 820 FOutput Cap 2.2mF

JSL130


Current Ripple Reduction with High-Side Energy Storage Capacitor

1 10 4 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.180

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.05

0.1

0.0068 0.055

Capacitance (F)

Fuel

Cel

l Cur

rent

Rip

ple

(pu)

0

Standard design

Adding 55 mF capacitor

10X capacitor is needed to drop ripple current under 5%

JSL131


Features of High-Voltage DC Bus Energy Storage Capacitors

• Fuel cell voltage is low, typically from 36 to 60 V.• High voltage dc bus voltage is split into two 200 V.• For a single-phase dual ac outputs such as 120/240 V in US

residential systems, the transformer secondary and dc bus can be split in two halves. Each phase leg of the full-bridge along with the split-capacitors becomes a half-bridge inverter to supply 120 V ac output. Summing two 120 V outputs becomes 240 V.

• Multiple capacitors are paralleled for the high-voltage dc bus to store more energy and to provide more transient handling capability during dynamic load change conditions. Energy storage is proportional to CV2.

• Size and weight are dominated by passive components. With split DC buses, the volume of energy storage capacitors becomes an issue.

JSL132


Experimental Current Ripples without Adding Capacitors or Controls

Fuel cell voltage (20V/div)

Fuel cell current (10A/div)

AC Load Voltage (200V/div)AC Load Current (5A/div)

5ms/div

More than 35% ripple current at the input

35%

JSL133


Fuel Cell Ripple Current Problem is Severe During Load Transients

• For single-phase ac loads, 120 Hz (twice the fundamental frequency) current ripple can reflect back to fuel cell.

• During load transients such as turning on light bulbs or starting up motors, the transient initial current is typically more than 5 times the steady-state current, and the fuel cell ripple current exceeds more 100% or even 200% in some cases.

JSL134


Fuel Cell Responds to AC Load Steps (without Externally Added Capacitor)

Ifc

Vfc

iac




AC Load Current (10A/div)20ms/div

Id-LV

Fuel cell sees severe current transient (spike) and current ripple in steady state (35%)

JSL135


Using Electrolytic Capacitor to Smooth Fuel Cell Responding to AC Load Steps

Ifc

Vfc

iac

Fuel Cell Voltage (10V/div)Fuel Cell Current (20A/div)



Id-LV

IcapIfc

iac

IcapVfc

Id-LV

With 20 mF capacitor, fuel cell current transient is reduced, but the current ripple remains

JSL136


AC Load Transient Response for Fuel Cell with 53-mF Added Capacitors

Fuel Cell Current Ripple is 5% plus Overshoot

Vfc

Fuel Cell Voltage (10V/div)Fuel Cell Current (20A/div)



Ifc

iac

Icap

Id-LV

JSL137


Fuel Cell Output Response with an Ultra Capacitor Cut-in

Vfc




Ifc

iac

IulcapCapacitor Current (20A/div)

JSL138


Fuel Cell Output Response with an Ultra Capacitor Dropout

Vfc




Ifc

iac

Iulcap Capacitor Current (20A/div)

JSL139


Experiment with Open-Loop and with only Voltage Loop Control

No improvement on current ripple reduction with voltage loop control

DC bus voltage (100V/div)

Fuel cell voltage (10V/div)

Fuel cell current (20A/div)

DC bus current (10A/div)

(a) Open loop (b) With voltage loop control

t (5ms/div)

JSL140


Solving Current Ripple with Added Current Loop inside the Voltage Loop

vref +–

Rv2Cv1

Cv2

Rv1

Hv

vsense

Vo

+RL

Gvc

+–

Vm

PWMd

Lf

Cf

VdiLf

+–

Rcf+–

Ri2Ci1

Hi

iref

Ri1

isense

Ci2

Gic Vd = dVin

Adding a current loop to regulate the output current

JSL141


Fuel Cell Current Ripple Reduction with the Proposed Active Control Technique

Fuel Cell Current Ripple is Reduced to 2%

Input Voltage

Input Current

Output Current

Output Voltage

<2%

JSL142


Summary of V6 DC-DC Converter with Active Ripple Cancellation

• High efficiency with a wide-range soft switching: 97%• Cost reduction by cutting down passive components

– Output inductor filter reduction with three-phase interleaved control: 6X

– Input high frequency capacitor reduction: 6X– Output capacitor reduction with active ripple reduction: 10X

• Reliability enhancement– No devices in parallel– Soft-start control to limit output voltage overshoot – Current loop control to limit fuel cell inrush currents

• Significance to SOFC design – Stack size reduction by efficient power conversion and ripple

reduction: 20%– Inrush current reduction for reliability enhancement

JSL143


10. Recap

1. Basic DC-DC converters and DC-AC inverters are introduced

2. Circuit topology selection can be misled by schematic diagram. Some important considerations are• Device voltage and current stresses• Number of paralleled devices • Parasitic components and losses

3. Advanced V6 DC-DC converter not only shows superior performance but also low production cost

4. Fuel cell current ripple issue can now be solved with advanced current control developed by Virginia Tech without adding cost penalty

Power Electronic Technologies for Fuel Cell Power … Library/Events/2005/seca...JSL 1 Future Energy...

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Transcript of Power Electronic Technologies for Fuel Cell Power … Library/Events/2005/seca...JSL 1 Future Energy...