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Electric Vehicles and Power Electronics

Jih-Sheng (Jason) LaiVirginia Polytechnic Institute and State University

Center for Power Electronics Systems668 Whittemore Hall

Blacksburg, VA 24060TEL: 540-231-4741FAX: 540-231-6390

EMAIL: Laijs@vt.edu

August 16, 2001

Presentation atUniversidad Technica Federico Santa Maria

Valparaiso, Chili

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Outline of Presentation• Part A: Background and Introduction

– What are Electric Vehicles?– Why Electric Vehicles?– Partnership for Next Generation Vehicles

• Part B: Overview of EV/HEVs on the Market– GM EV1– Ford Ranger– Honda EVPlus, Insight– Toyota Prius– Ford P2000

• Part C: Power Electronic Technologies in EV/HEV– Energy Sources– Traction Motors/Inverters– Auxiliary Motors/Inverters– Bi-directional Chargers– Basic Structure of a Fuel Cell Vehicle

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Part A: Background and Introduction

• What are Electric Vehicles?• Why Electric Vehicles?• Partnership for a New Generation of Vehicles• Specification of “Supercar”• EV/HEV Configurations

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EV/HEV Definitions

• An Electric Vehicle is A vehicle fueled with mains electricity. An EV usually requires a battery pack as energy storage.

• A Hybrid Vehicle isA chemically fueled vehicle equipped with at least one bi-directional energy reservoir. The fueled hybrid power unit (HPU) is usually a heat engine, but may be a fuel cell. Energy storage and delivery is usually electric.

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Driving Forces for EV/HEV

!!!! Simplicity (1910)!!!! Energy Security (1970)!!!! Environmental Concerns (1990)!!!! Customer Expectations (2000)

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US Customer Expectations for EV/HEVs

!!!! Range: Minimum 160 km/charge!!!! Safety: Same as ICE Vehicles!!!! Performance: Same as ICE Vehicles!!!! Cost: No more than ICE vehicles!!!! Features: No less than ICE vehicles

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Partnership for a New Generation of Vehicles

LONG-TERM GOAL – Development of a SupercarGas mileage: 3X average of Concorde/Taurus/Lumina, or 80 mpg Load: Six passengers + 200 pounds of luggageRange: Similar to today’s models At least 80 percent recyclable

Technology Areas Hybrid/electric vehicle drive trainsDirect-injection engines Fuel cells Lightweight materials

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Specifications of Baseline Vehicle and Supercar

Baseline Supercar

Curb Weight 3200 lbs 40% lessDrag coeff. 0.32 0.20Friction: 0.005 0.008 Engine: Internal Combustion flywheel, battery, ultracapacitorFuel Efficiency: 26.6 mpg 80 mpg (3X)Recycleability: 75% 80%Range (HWY): 380 miles same or betterAccel (0-62 mi): 12 seconds same or betterLuggage: 168 ft3 same or betterLoad: 6 passengers + 200 lb same or betterLife: 100,000 miles same or better

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PNGV Time Table

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Where are the Energy Goes in a Conventional Car?For Metro-Highway Driving Cycle

DrivelineEngine

100%

Aerodynamics6%

Accessories2%

Engine77% Driveline

6%

Rolling5%

Braking4%

Fuel

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Electric/Hybrid Electric Vehicle Configurations

Fueltank

Xmission

ICE

Diff.Wheels

Pure ICE Drive

ICE: Internal Combustion EngineXmission: TransmissionDiff.: Differential gear

ElectricMotor

Battery

Diff.Wheels

Pure Electric Drive

Parallel Hybrid Series Hybrid

Hybrid Drives

Fueltank

Xmission

ICE

Diff.Wheels

ElectricMotorBattery

FueltankICE

Diff.Wheels

ElectricMotor

Battery

Generator

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How Does a Hybrid Electric Vehicle Work?

(a) Shaft driven by both ICE and electric motor

(b) Shaft driven by electric motor and battery is charged

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Part B: Overview of EVs on the Market

• GM EV1

• Ford Ecostar, Ranger

• Honda EVPlus, Insight

• Toyata Prius

• Ford P2000

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General Motor EV1

Power: 137 hpTop speed: 80 miles per hourDrag coeff.: 0.19Acceleration: 0 to 60 miles, less than 9 secondsRange: 55 to 95 miles with 26 lead-acid battery pack

75 to 130 miles with Nickel-Metal Hydride (NiMH) battery pack Charging: 220 V, 6.6 kW non-contact inductive charging, 6 hours Braking: front disk, rear drum, and regenerative

Price: $33,995 MSRPLease: $424 - $574 / mo

36-month lease $0.20/mile over 30,000 miles

http://www.gmev.com/index.htm

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GM Inductive Charge Coupler

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Ford Ranger and US Post Office Electric Vehicles

Battery:Fourth generation “sealed lead acid” 39x8 volt modules; 312 volt systemCapacity rating @ FUDS: 23 kWh (18 kWh at 80% discharge)On-board Charger: On-board, 240 V/30 A

Performance:0-50 mph acceleration: 13 secondsRated top speed (governed) : 75 mphCustomer range @ 72F: 50 milesRange - FUDS cycle @ 72F: 58 miles without A/C or heater operation

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Ford Ranger Schematic

90 hp, 3-phase AC induction

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Honda EVPlus

New Technology Features

• Nickel-metal hydride batteries • Permanent-magnet motor• Single-speed, direct-drive transmission • Regenerative braking• On-board charger – 110- or 220-volt • Heating and air conditioning • High-intensity headlightsStandard Features

• EPA City: 100 miles; Highway: 84 miles (Use 80% battery capacity)• Meets all federal motor vehicle safety standards • Dual airbags and 3-point seat belts • Anti-lock braking system (ABS) • Power windows, door locks and mirrors • AM/FM/CD audio system • Remote keyless entry and security system • Cargo area with "fold-flat" rear seats • Walk-in feature for rear seat access

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Honda Insight Hybrid Electric Vehicle

Integrated Motor Assist: 1.0-liter, 3-cylinder gasoline engine + electric motorEPA mileage ratings: 61 mpg city/70 mpg highwayDriving range: 600 - 700 miles Drag coefficient: 0.25Electric motor: 36 ft-lb, 10-kW DC-brushless motor, 2.3” wide,

sits between the engine and transmission, mounted directly to the engine's crankshaft

Battery: A 144-volt nickel metal-hydride battery packInverter: An advanced electronic Power Control Unit (PCU),

adopted from Honda EV PLUS

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Drivetrain of Honda Insight

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Toyota Prius - A Hybrid Vehicle

Engine: 1.5-liter, DOHC, 16-valve, EFI 4-cylinder with Variable Valve Timing with intelligence (VVT-i)

Maximum Engine Output: 58 hp at 4,000 rpmMaximum Speed: 100 mph (engine and motor combined)Motor Type: permanent magnet, 30 kW/40 hp at 940—2,000 rpmBattery Type: sealed nickel-metal hydride with 40 modulesCombined Horsepower: 58 hp engine + 40 hp motor + 3 hp batteries = 101 hpFuel Efficiency: 66 mpg (Japanese 10—15 city drive mode)Maximum Range: 850 miles (combined city/highway)Regeneration Braking: Front disc/rear drum brakes with ABS

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Prius Hybrid Drivetrain

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Power Flow in Prius

BatteriesInverterGenerator

Motor

Engine

Electrical power path

Motive power path

Engine FlowStarting from rest/low speedsFull-throttle accelerationNormal drivingDeceleration/braking

Reduction Gear

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Emission Comparison of Prius and Corolla

10.314.72171570.2050.1240.8640.8080.0680.0251143Corolla

12.720.81551120.0630.0010.0620.0250.0330.0021237Prius

Sec.Km/LTECarTECarTECarTECar(kg)Vehicle

AccelFrom0-60 mi/h

FuelEco-nomy

Curb Weight

NonmethaneOrganic gases(NMOG), g/km

CarbonMononxide

g/km

Nitrogen oxideg/km

Carbon dioxide

g/km

Note: • “Car” values are vehicle exhaust (tailpipe) emissions• “TE” values are total emissions-Car plus upstream, including fuel

cycle emission• Source: IEEE Spectrum, March 2001, Pages 47 – 50.

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Ford P2000 Low Storage Requirement (LSR) Car

Features:

• Low Storage Requirement (LSR)• Direct Injection Aluminum Through-bolt Assembly (DIATA) engine• Integrated Starter/Alternator• Engine shut-down during braking and at rest• Very fast engine restart• Improve engine dynamics and shift fell• Modified shift strategy for reduced emissions• Weight and cost penalties low relative to “full” hybrid• enables limited re-generative braking

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Comparison of P2000 LSR and Hybrid Vehicles

Series Parallel P2000

Platform 5 + passenger, Al-Intensive, Sedan

5 passenger, Light-weight prototype

5 passenger, Light-weight prototype

HPU 55 kW, Turbo-Alternator 55 kW, 1.2 L, CIDI 55 kW, 1.2L, CIDI

Transmission none Auto 5-speed Auto 5-speed

Traction Motor 75 kW, EV transaxle 18/30 kW motor on 4x4 transfer case

8 kW starter/alternator

Battery 180 kW x 6 kWh 48 kW x 2 kWh 15 kW x 0.4 kWhWeight 1401 kg 1258 kg 1000 kgFuel Economy (v. Taurus) City:

Metal Ceramic 1.8x 2.4x 2.9x 2.5x

Highway 1.4x 1.9x 2.2x 1.9x

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Ford P2000Hydrogen Fuel Cell Car

Chemical Energy Electrical Energy Mechanical Energy

HydrogenTank

FuelCell

TractionInverterMotor

TurboCompressor

Transxle

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Daimler-Chrysler NECAR IVA Fuel Cell Electric Vehicle with Built-in Reformer

Fuel: MethanolEmission: zeroTop Speed: 90 mphRange: 280 miles

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Part C: Power Electronic Technologies in EV/HEV

• Energy Sources and Storages! Batteries! Fuel Cells

• Traction Motors• Soft-Switching Inverters• Bi-Directional Chargers

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Energy Sources and Storages

• Lead Acid Batteries• Nickel Metal-Hydride (NiMH) Batteries• Lithium Batteries• Fuel Cells

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Lead Acid Batteries

Flood type:• First design in 1880’s • With flat pasted plate immersed in a dilute sulfuric acid

electrolyte

Valve Regulated Lead Acid (VRLA) type:• Original development in 1960’s with sealed lead acid

batteries • The gases produced during operation are recombined

to minimize water losses • Typical gas recombination efficiency is 95%• Gas recombination cell can be made with Absorptive

Glass Mat separator or Gel Electrolyte

Source: www.hawker.invensys.com

Electric Vehicles use “deep charge/discharge” type VRLA batteries

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VRLA Battery Charging Voltage and Currentfor a Typical Tubular Gel Product

Typical State of Charge Voltage 100% 2.13 V70% 2.09 V50% 2.06 V20% 2.02 V* Measuring open ckt voltage after

battery rested >24 hr.

Charging Voltage at diff temp.0°C 2.35 V10°C 2.28 V20°C 2.23 V30°C 2.20 V35 °C 21.7 V

Charging Current• Typically 10% of the 10-hour capacity, C10

• In general, not exceed 30% of C10

• For fast charge, keep 2.35 V per cell with 10% of C10 as the current limit

Source: www.hawker.invensys.com

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Nickel Metal-Hydride (NiMH) Batteries

• Negative Electrode: • rare earth/nickel alloys LaNi5 (AB5 alloys) • titanium and zirconium (AB2 alloys)

• Positive Electrode: Sintered-type positive electrodes are economical and rugged while exhibiting excellent high-rate performance, long cycle life, and good capacity

• Electrolyte: Alkaline, a dilute solution of potassium hydroxide

• Energy Density: Improved energy density (up to 40 percent greater than Nickel Cadmium cells)

• GM EV1 Test Range: 55 to 95 miles with 26 lead-acid battery pack 75 to 130 miles with Nickel-Metal Hydride (NiMH) battery pack

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Comparison of Nickel-Metal Hydride to Nickel Cadmium Batteries

Nominal Voltage Same (1.25V) Discharge Capacity NiMH up to 40% greater than NiCd Discharge Profile Equivalent Discharge Cutoff Voltages Equivalent High Rate Discharge Capability Effectively the same rates High Temp (>35oC) Discharge Capability NiMH slightly better than NiCd cells Operating Temperature Limits Similar, NiMH slightly better at cold temp Self-Discharge Rate Similar to NiCd Cycle Life Similar to NiCd Mechanical Fit Equivalent Selection of Sizes/Shapes/Capacities Equivalent Environmental Issues Reduced with NiMH because of elimination

of cadmium toxicity concerns. Collection of spent NiMH batteries is not mandated

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Lithium/Thionyl Chloride Batteries

Negative Electrode: mixture of carbon, Teflon, fiberglass, alcohol, and water

Positive Electrode: Lithium

Electrolyte: Thionyl Chloride

Lithium batteries have been widely used in computers and communications and will be competing with NiMH batteries for EV applications

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Fuel Cell Vehicle - Future Trend

Fuel Cell Electric Vehicles (FCEVs) are similar to a battery-powered EV except that fuel cells replace batteries. As with batteries, fuel cell emit no carbon dioxide, although carbon dioxide and other emissions may be created in vehicle manufacturing and fuel production.

A fuel cell produces electricity by combining hydrogen and oxygen in an electrochemical reaction. Fuel cells require no combustion, unlike a conventional gasoline- or diesel-powered engine. The only emission from hydrogen fuel cells is water vapor.

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Fuel Cell Vehicle Configurations with Different Sources

Hydrogen storage

Fuel Cell Stack

Inverter

Bi-directionaldc-dc

converter

Gear

Battery

Methanol storage

Fuel cell stack

Inverter

Bi-directionaldc-dc

converter

Gear

Battery

Fuel cell stack

Inverter

Bi-directionaldc-dc

converter

Gear

Battery

Methanol reformer

Gasoline storage

Partial oxidation

ref.

Motor

/Gen

Motor

/Gen

Motor

/Gen

(a) With hydrogen (b) With Methanol (c) With Gasoline

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Basic Hydrogen-Oxygen Fuel Cell

Fuel (H2)

Oxidant

(Air O2)

Water

(H2O)

Electrical loads+-

2e- 2e-

1/2 O2

H2 2H+ 2H+

Ion Exchange Membrane(IEM)

Electrode (-) Electrode (+)

H2OElectrolyte

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Proton Exchange Membrane (PEM) Fuel Cell

CO2

Methanol Fuel

CH3CHOxidant

(Air O2)

Water

(H2O, N2, O2)

Electrical loads+-

6e- 6e-

CO2+

6H+ 3H2O

6H+

+3/2 O2

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Proton Exchange Membrane(PEM)

Electrode (-) Electrode (+)

Water

H2O

Vaporizer

MethanolReformer

CO2Oxidization

Catalyst

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Fuel Cell Output Voltage and Current Characteristic

0

50

100

150

200

250

300

350

400

0 100 200 300

Stack Current(A)

Stac

k Vo

ltage

(V)

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Fuel Cell Output Power and Current Characteristic

0102030405060708090

0 100 200 300

Stack Current (A)

Net

Pow

er (k

W)

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20 kW Future Car Stack

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Traction Motors/Inverters

• Motor Design Consideration1. Using Federal Urban Driving Schedule to Find Most

Critical Speed and Torque Region2. Optimize Motor Design in Proper Torque-Speed

Regions• Motor Types• Inverter Partitioning for Integrated Inverter-Motor• Soft-Switching Inverter Considerations• Bi-directional Chargers for Fuel Cell Vehicles

1. A 20-kW Non-isolated Bi-directional Converter2. A 5-kW Isolated Bi-directional Converter

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Motor Design Consideration 1 Using Federal Urban Driving Schedule to Find Most Critical

Speed and Torque Regions

FUDS CYCLE

0

20

40

60

0 500 1000 1500

Time (sec)

Spee

d (m

ph)

Battery Current (Pos=Discharge)

-100-50

050

100150

0 500 1000 1500

Time (seconds)

Cur

rent

(am

p)

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Torque-Speed Envelope

0

20

40

60

80

100

120

0 5 10 15 20 25Speed (x1000 rpm )

Torq

ue (l

bft,h

p) TorquePowerEfficiency

Motor Design Consideration 2 Optimize Motor Design in Proper Torque-Speed Regions Resulting High-Speed (20,000 rpm) Design that Cuts Size and Weight by 30%

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Motor Types

• Induction Motor• Permanent Magnet Motor• Switched Reluctance Motor• Other Combinations

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Inverter Partitioning for Integrated Inverter-Motor

INVERTERPOWER MODULE

COLD PLATE

INSULATOR

TRACTIONPOWER INPUT

COOLANT/LUBRICANT

INTPUT

GEAR LUBRICANT

GEAR ASSEMBLY

CONTROLLERMOUNTING BLOCK

MOTOR LINE COOLANT

OPTICALDRIVE SIGNAL

OPTICAL STATUS SIGNAL

ADVANCED AC MOTOR AND CASING

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Inverter Design and Partioning

InductionMotor

SensorConditioning

ia ib va vb

θr

Hall Sensors

OpticalEncoder

IGBT Modules

Interface Circuit

DSP Circuit

Battery

Fuel CellUnit

Pow

er F

low

Con

trol

Gate Driver withProtection

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Using Optical Fiber to Link Integrated Power Stage and Control Interface

SensingBoard

DSPInterfaceBoard

GateDriver

GateDriver

GateDriver

IGBT Based Inverter Power Stage

Optical fiber link

Motor

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Compact Gate Driver with Optical Fiber Link

PWM

Fault

Optical Fiber

IGBT Module

MC

3315

3 +15V

-5V

54

78

23

Ron

Roff

+15V

6 1

-5V

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Soft-Switching Inverter Considerations

• Zero-Voltage-Transition – Auxiliary Resonant Commutated Pole (ARCP) Inverter for AC Motor Drives

• Zero-Current Transition (ZCT) Inverter• Advantages:

– Allow high switching frequencies– Low switching losses– Low EMI

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Turn-on Loss Reduction with Soft-Switching

Vce(100v/div)

Is(10A/div)

Vce(100v/div)

Is(10A/div)

Hard-switching Soft-switching

Voltage, Vswitch

Power, Pswitch

Current, Iswitch

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Turn-off Loss Reduction with Soft-Switching

Vce(100v/div)

Is(10A/div) Is(10A/div)

Vce(100v/div)

Hard-switching Soft-switching

Current, Iswitch

Voltage, Vswitch

Power, Pswitch

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A Zero-Voltage-Transition Inverter for AC MotorsAuxiliary Resonant Commutated Pole (ARCP)

Lra

Vs

C1C3

C4 C6

C5

C2

S1 S3 S5

S4 S6 S2

Csp

Csn

acmotor

Lrb

Sb

Sa

Lrc

Scauxiliary circuits

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Basic Operating Principle of ZVT Soft-Switching

t1 t2 t3 t4

ILr

IS1

IS2

IC2

IC1

Sr

Ix ILoad

0

0

0

0

C1

C2

ILoad

S2

S1

LrILr

C1

C2

ILoad

S2

S1

LrILr

From t1 to t2’ From t2’ to t2

t2’ t3’

C1

C2

ILoad

S2

S1

LrILr

C1

C2

ILoad

S2

S1

LrILr

From t2 to t3 From t3 to t4

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ARCP ZVT Inverter Test Results

ia

SX1 SX2

LX1

CX1

CX2ia

S1

S2

CS

CS

Vdc

Auxiliary Circuit

D1

D2

DS1

DS2

M1

A : vg(S2) (20 V/div)B : ia (200 A/div)C : iax (200 A/div)D : vS2 (200 V/div)

A

BC

D

2 µs/div

SX1 SX2

LX1

CX1

CX2

S1

S2

CS

CS

Vdc

Auxiliary Circuit

D1

D2

M1ia

91

92

93

94

95

96

97

50.2 80.9 5.0 20.7 50.5 101.4 5.9 12.2 41.6 10.1 14.8 31.9 13.3 20.4

1920 3770 5635 7560 9460

Torque [N-m]

Speed [rpm]

Inve

rter

effi

cien

cy [%

]

with diodeswithout diodes

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Zero Current Transition Inverter

ACMotor

CsVs

Sr4 Sr6 Sr2

Sr3 Sr5Sr1 S1 S3 S5

S4 S2S6

Lr Cr

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Basic Operation of ZCT Soft Turn-on

ILr

IS1

VCr

S1

ILoad

0

ILoad

S2

S1

LrILr ILoad

S2

S1

LrILr

From t0 to t1 From t1 to t2

Cr

ILoad

S2

S1

LrILr ILoad

S2

S1

LrILr

From t2 to t3 From t3 to t4

+ –VCr

Cr

0

t1 t2 t3 t4

0

0

VCE1

Sr0

t0

0

currentdirectionin thisperiod

currentdirectionin thisperiod

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Test Results of 30-kW Soft-Switching Inverters

5 /d i

Ix (200 A/div)

Iload (200A/div)

5ms/div

ARCP ZVT

ZCT Vce (250 V/div)

ILoad (200A/div)

5ms/div

Ix (200 A/div)

Vce (200 V/div)

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Basic Operation of ZCT Soft Turn-off

ILr

IS1

VCr

S1

ILoad

0

ILoad

S2

S1

LrILr ILoad

S2

S1

LrILr

From t5 to t6 From t6 to t7

Cr

ILoad

S2

S1

LrILr ILoad

S2

S1

LrILr

From t7 to t8 From t8 to t10

+ –VCr

Cr

0

t8 t9t6 t10

0

0

VCE1

Sr0

t5

0

Initial VCr is negative

Vdc

t7

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Soft-Switching Inverter Assembled in EV1 Chassis

Development...

Testing...

On the Road...

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Bi-directional Charger for Fuel Cell Powered Electric Vehicles

Inverter

Vol

tage

Cla

mp

CompressorMotor

Expanding Unit

CM

EUC

ontr

olle

r

OtherLoads

Bi-d

irec

tiona

l Po

wer

Flo

w

dc-d

c C

onve

rter

High Voltage Bus (>300V)+−−−− Motor

Energy Storage Cap.

Fuel

Cel

l

Batteryfor Startup −−−−

+

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Why Bi-directional DC-DC Converter is Needed?

1. Need to have high voltage to start up the CMEU controller.2. Need to stabilize the bus voltage during transient

conditions. 3. Need battery to charge the dc bus bus for the initial startup

power (Boost operation)3. Need to keep battery charged (Buck operation)

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Circuit Topology Considerations for the Bi-directional DC-DC Converter

1. Single-directional vs. bi-directional2. Isolated vs. non-isolated3. Multiple-leg Interleaved vs. single-leg 4. Voltage source vs. current source for either primary or

secondary side5. Low side battery with 12 V, 42 V, or 180 V vs. high side

fuel cell at about 300 V

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Non-Isolated Buck Converter L

R+−

Vg

C

+

−

v

vgs

Q1

D1g

sd

vgs

iL

v

Gate on Gate off

DTs D’Ts

Inductor charged

Inductor discharged

Capacitor charged

Capacitor discharged

gDVV =

Average output voltage:

where D is the duty ratio. Because D < 1, V is always less than Vg " buck converting

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Non-Isolated Boost Converter

+–

CQ1

D1L

RVg

v

+

–

iL iD

iQ iCvL+ –

vgs

vgs

iL

v

Gate on Gate off

DTs D’Ts

Inductor charged

Inductor discharged

Capacitor discharged

Capacitor charged

gg VD

VD

V'

11

1 =−

=

Average output voltage:

where D is the duty ratio, and D’ = 1 – D. Because D’ < 1, Vis always greater than Vg "boost converting

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Non-Isolated Single-Directional Boost ConverterNon-Interleaved vs. Interleaved

Load

L1

L2

S1u S2u

S1d S2d

+

–

Vbatt

i1

i2 VFC

Load

L

Su

Sd

+

–Vbatt

iVFC

(b) Interleaved(a) Non-Interleaved

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A Non-Isolated Bi-Directional DC-DC Converter with Interleaved Control

Ld2

Ld3

S2u S3u

S2d S3d

VFC

Power module

Vbatt

Load

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Ripple Current Cancellation Effect in a 20 kW Interleaved Boost Converter

33 A/div50 µs/div

IL1 IL2

IL1 + IL2

33 A/div

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Efficiency Test Results of a 20 kW Interleaved Boost Converter

86889092949698

0 5000 10000 15000 20000 25000

Predicted

experimental

Output Power (W)

Effic

ienc

y (%

)

DCM operated converter has parasitic ringing losses at the light load condition, and the efficiency is suffered.

At Vin = 200 V, Vo = 300 V

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Isolated Buck Converter

Q1 Q3

Q2 Q4

Vg

L

Cf

a

b

+

–

C Rv+

–

1 : n

• Suitable for high voltage input and low voltage output• Zero-voltage switching can be achieved with phase-shift modulation

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Isolated Boost Converter

• Suitable for low voltage input and high voltage output• The main problem is high voltage stress on the switching devices

Q1 Q3

Q2 Q4

Vg

L

Cf

a

b

+

–

C Rv+

–

1 : n

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Low-Voltage Side “Half-Bridge Current-Fed” Isolated Bi-directional Converter

L1 L2

Cc

S1 S2

S5

S6S7

S8

CoVb

1:nLlk

!!!! Low switch counts!!!! Simple transformer winding structure!!!! Low transformer current×××× Start-up problem×××× Low choke ripple frequency (fs)×××× Duty cycle limitation#### Passive clamp is easy to implement but lossy

Rc

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Low-Voltage Side “Full-Bridge Current-Fed” Isolated Bi-directional Converter

!!!! Simple voltage clamp circuit implementation!!!! Simple transformer winding structure and lower turns ratio!!!! Low transformer current!!!! High choke ripple frequency (2fs)×××× Start-up problem×××× High switches count

L

S1

S2

S5

S7 S6

S8

CoVb

1:nLlk

S3Cc

S4

Sc

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Complete Bi-directional dc-dc Charger with Clamping and Start-up Circuits

Lk+

_

S1

S3 S2

S4S5

S7Cc

L

Sc

A

S6

S8

B D

C-Ip

Ic

Vpn

+

_

Tr

1:n

Vo

CoCinIs

Vb

+

_

1:n LkfDf

IL

Ifp

n

Start-up circuit

Active Clamp circuit

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Prototype of a Liquid Cooled Bi-directional DC-DC Converter to be Installed in a Fuel

Cell Vehicle

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Start-up Mode Operation

IL

Is

Vo

ILref

125 A/d

20 A/d

100 A/d

100 V/d

Start-upcommandinitiation

Transitionfrom start-upto regularboost

Average current loop regulated

Loadengaged atVo=255 V

Voregulated Vb = 12 V, IL = 161 A, Vo = 280 V,

Pd = 1.83 kW in steady state

Start Up Process:

t0-t1 Start up mode, open loop controlled

t1-t2 Boost mode, open loop controlled

t2-t3 Boost mode, inner current loop regulated

t3- Boost mode, outer voltage loop regulated

t0 t1 t2 t3

JSL

Switch Voltage and Current Waveforms in Boost (Discharging) Mode Operation

S3

Is

Vpn

10 A/d

10 V/d

Vb = 8 V, IL = 228 A, Vo = 288 V, Pd = 1.55 kW

40

JSL

Comparison of Measured Efficiency Profile forDischarging (Boost) Mode Operation

400 600 800 1,000 1,200 1,400 1,6000.82

0.84

0.86

0.88

0.9

0.92

0.94

Po

Efficie ncy

Full-Bridge

L-Type

10 V

8 V

10 V

8 V

Test conditions:

Start-up, battery discharging

Battery voltage: Vb = 8 and 10 VHigh side voltage: Vo = 288 VSwitching freq.: fs = 20 kHz

1. Higher battery voltage, higher overall efficiency.2. Full bridge is more efficient than the L-type half-bridge converter in overall

operating range.3. Efficiency at light-load exceeds 90% with full-bridge version.4. L-type converter is lossy due to passive clamp circuit.

JSL

Switch Voltage and Current Waveforms in Buck (Charging) Mode Operation

Vcd

Is

Vpn

250 V/d

20 A/d

50 V/d

Vb = 15 V, IL = 335 A, Vo = 425 V, Pcp = 5 kW

41

JSL

Comparison of Measured Efficiency Profile forCharging (Buck) Mode Operation

1,000 2,000 3,000 4,000 5,0000.7

0.7250.75

0.7750.8

0.8250.85

0.8750.9

0.9250.95

Pch (W)

Efficie ncy

Full-Bridge

L-TypeTest conditions:

Regenerative Mode Battery voltage: Vb=15 V High voltage bus: Vo=425 V

1. L-type half-bridge efficiency reaches only 90% 2. Full bridge converter is more efficient with peak efficiency 95% because

• more devices in parallel on low-voltage side • active clamp circuit provides lossless snubbing • soft-switching with zero-voltage zero-current operations

JSL

Summary and Discussions

• Development of EV/HEV is very vital in recent years • HEV has hit the market since 1999• Fuel cell is becoming the choice of energy source for future

EVs• Power electronics is the main driver of EV/HEV • Key power electronics technologies are traction motor/inverter

drives and bi-directional chargers• Power electronics engineers are in great demand