recent advances in electric energy conversion and storage · pdf file• 3000c switching...

Recent Advances in Electric Energy

dConversion and Storage

Hamid A. Toliyat, Ph.D., P.E., Fellow of IEEERaytheon Professor

Advanced Electric Machines & Power Electronics (EMPE) LaboratoryDepartment of Electrical & Computer Engineering

Texas A&M UniversityC ll St ti TX 77843 3128College Station, TX 77843-3128

Tel: (979) 862-3034Email: [email protected]

Sources for Electric Power vs. Transport are Distinct Electricity Sent to GridSOURCES USES

Nuclear 8%

Renewables(incl. hydro,

bi i d

Electric PowerSector

39%When you connect the lines, you see

Residential/Commercial

Heat12%

biomass, wind, geothermal,

and solar) 6%Natural

Gas 20%

that there is virtually no overlap between the energy sources used for Electric Power

Industrial Heat &

Process

Imports 3%

Coal 23%Export

Electric Power versus that used for Transportation (oil). This is important when considering “ lt ti ”Process

16%Non-Fuel Petroleum

by-products (asphalt,

petrochemica

Imports

US P t l

Export

“alternative energy” sources.

pls, etc.) 6%US Petroleum

15%

Oil Imports 25%

Transportation27%

Advanced Electric Machines & Power Electronics (EMPE) Lab 2

Source: Lawrence Livermore Natl Labs; EIAData rounded to nearest whole decimal.Sources and Uses less than 1% not included

Energy Losses are Tremendous Electricity Sent to GridSOURCES USES

Nuclear 8%

Electrical System Energy Losses Lost

SOURCES USES

Electric PowerSector

39%

Residential/Commercial

12%

Renewables 6%

Natural Gas 20%

Energy 61%

39%

Industrial

Imports 3%

Coal 23%Export

Energy lost in the process of converting, transporting, & distributing energy is Industrial

16%

Non-Fuel 6%

Coal 23%

ImportsUsefulEnergy

39%Export

g gysignificant; more than 60% of energy input is lost. A 1% decrease could save more than $3.0B annually*.

US Petroleum 15%

Oil Imports 25%

Transportation27%


25%* NCI estimate using $50/bbl oil & $3/mmbtu blended cost for gas/coalSource: Lawrence Livermore Natl Labs; EIA2002 Data: Net Resource Consumption ~ 97 QuadsSources less than 1% not included

Energy Issues

Renewable EnergyWave Energy

Photovoltaic Energy

Wi d E

Transportations, Plug‐in Hybrid VehiclesBattery and its Modeling

• Improvement of power density and extension of battery life are strongly required for batteriesWind Energy

Biomass

Geothermal

Hydrogen Fuel Cell

battery life are strongly required for batteries used for HVs, and especially the safe use of Li‐ion batteries is required. From this point of view, the improvement of accuracy in estimating SOC is extremely important.

Motor/Generator and ControlEnergy Storages:

Batteries• Large surface area electrode

• Frequent deep cycles

Motor/Generator and Control• Wide constant power range for traction

• Constant torque for power generation

Inverter and Power Transistors• Cooling and capacitor size

• Low cost integrated system

Flywheels• Higher tensile strength

SMESHi h it t

• 3000C switching devices (Silicon Carbide, etc.)

Energy Harvesting

• Higher capacity current

• Higher temperature superconductor

Ultra capacitors• Higher voltage cells

• Higher reliability


Higher reliability

• Lamination of cells and stacks

Energy Harvesting

Exploded view of Seiko Kinetic watch


Exploded view of Seiko Kinetic watch

Power Generation with Renewable and Distributed Energy Resources


Worldwide Wind Growth

Advanced Electric Machines & Power Electronics (EMPE) Lab

Wind As a Percentage of Electricity Consumption


Evolution of Wind Technology

W ld ld t i d ill ( 644A D ) V ti l i i d ill f illi i (S th t I )


World oldest windmill ( 644A.D.), Vertical-axis windmill for milling grain (Southeast Iran)(Deutsches Museum)

source: Wind Turbines book By: Erich Hau

Evolution of Wind Technology (cont’d)

Nacelle with Geared Drive Train and Generator


Electric Machines for Wind Turbines

The three main windThe three main wind turbine designs:

Fi d d ith Past a. Fixed speed with directly grid-coupled squirrel cage generator

Past

b. Variable speed with doubly-fed induction Presentgenerator

c. Variable speed based on a direct-drive system and synchronous generator Future


Commercial Doubly Fed Induction Generator


RePower 5MW Machine


Low Voltage Ride‐Through Requirement


Permanent Magnet Generator (ABB)


Drivetrain Possibilities Hub

Mechanical Gear

GridSquirrel-Cage Induction Generator

Hydrodynamic Gear

Mechanically-Controlled

The generator can be coupled to the grid frequency by use of a hydrodynamic gearbox Hub

M h i lGrid

D bl F d

DCAC

DCAC

Excitation Control from Grid

With step‐down gearbox stages, the generator can operate at variable frequency with added power electronics

Di tl d i t bi t

Mechanical Gear

Doubly-Fed Induction Generator

Hub

DCAC

Excitation Control from Grid

Directly‐driven turbines use no step‐down gearbox stages

A magnetic gear would replace step‐down gearbox stages H b AC AC

Singly-Fed Generator

Hub

Mechanical Gear

Grid Wound-Field Synchronous

Generator

down gearbox stages

Problems with traditional gearboxes such as bearings and supplies have been plaguing industry for decades

Hub

Mechanical Gear

DCAC

DC

AC

GridPermanent Magnet

or Squirrel-Cage Induction Generator

H b AC AC

Directly-Driven

HubDC

ACDC

AC

GridPermanent

Magnet Generator

Non-Contact Electromechanical


Hub

Magnetic Gear

DCAC

DC

AC

GridGenerator

Motivations for Magnetic Gear Development

(a) DeWind wind turbine with gear (b) a directly driven Enercon wind turbine


Permanent Magnet‐Assisted Synchronous Reluctance Machines


The Concentric Planetary Magnetic Gear

Two permanent magnet rings with stator pieces in-between to modulate magnetic flux


Modes of Operation

Number of inner pole pairs pi, and stator pieces ns, determine gear ratio [1]

outer-rotor fixed operation fixed stator segment operation

p p pi, p s, g [ ]Either the outer permanent magnet ring or the stator pieces can be fixedOuter-rotor-fixed operation yields a gear ratio of ns/pi

Stator-fixed operation yields a gear ratio of (ns-pi)/pi


Stator fixed operation yields a gear ratio of (ns pi)/pi[1] Atallah, K., Calverley, S., Howe, D., “Design, analysis and realisation of a high-performance magnetic gear,” IEE Proceedings – Electric Power Applications, Vol. 151, Issue 2, pp. 135-143, 2004.

2D Finite Element Analysis

Analysis done in Maxwell 2D finite element analysis packageTwo-rotating bands are simulated in the transient solver type, both


g yp ,having fixed rotational speed for steady-state torque transfer

Selected Models

Number of inner pole pairs pi, and stator pieces ns, determine gear ratio

po/pi

Gear Ratios

Stator Pieces Fixed Outer Rotor Fixed

22/6 3.67/1 4.67/1Outer-rotor-fixed operation yields a gear ratio of ns/pi

Stator-fixed operation yields a ge tio of (n p )/p

22/6 3.67/1 4.67/1

34/6 5.67/1 6.67/1

35/6 5.83/1 6.83/1

31/5 6 2/1 7 2/1gear ratio of (ns-pi)/pi

Gear ratios span from 3.67/1 to 13/113 different models given by

31/5 6.2/1 7.2/1

34/5 6.8/1 7.8/1

22/4 5.5/1 6.5/1

28/4 7/1 8/113 different models, given by the ratio of outer pole pairs to inner pole pairs, are used to simulate 26 different gear ratios

28/4 7/1 8/1

29/4 7.25/1 8.25/1

30/4 7.5/1 8.5/1

31/4 7 75/1 8 75/131/4 7.75/1 8.75/1

20/2 10/1 11/1

21/2 10.5/1 11.5/1

24/2 12/1 13/1


24/2 12/1 13/1

Results

Fixing the outer permanent magnet ring provides a full gear ratio increase over fixed-stator operation

po/piPercent Torque Ripple of Inner Rotor

Stator Fixed Outer Rotor Fixed

22/6 13 92 14 41Percent torque ripple was not detrimental in this change

22/6 13.92 14.41

34/6 10.58 10.93

35/6 1.94 3.01

31/5 3 44 3 5531/5 3.44 3.55

34/5 3.57 3.85

22/4 14.12 13.75

28/4 156.10 155.23

29/4 3.70 3.57

30/4 11.14 17.06

31/4 4.42 3.37

20/2 73.38 72.39

21/2 15.13 15.53


24/2 64.23 64.10

Electromagnetic Gear


High Frequency AC/AC Convertersg q y

Introduction

Types of AC/AC Converter:

Indirect AC/ AC ConverterIndirect AC/ AC Convertero DC Link AC/AC Converterso AC Link AC/AC Converters

Direct AC/AC Converter


DC Link AC/AC Converter

This type of converter is composed of two back-to-back voltage or current source converters connected via a DC link capacitor or reactor

Two power conversion stages (AC/DC + DC/AC)Rectifier and inverter systems DC t i th d li kDC energy storage in the dc-link

Most ASD in the current market



Diode Rectifier based Inverter (Diode Rectifier+ DC Link+PWM-VSI)

Problems:• High voltage and current stress over device• High dv/dt• Acoustic noise• Highly polluted by harmonics• DC link capacitors are bulky and are usually electrolytic



Back-to-Back Converter (PWM-VSR+DC Link+ PWM-VSI)

• Sinusoidal input/output currentsp / p• Bi-directional power flow• Large DC link capacitor & input inductors required for operation

• Large size and volume• Limited lifetime & limited high temperature operation

The harmonics problem is solved, but other problems still exist here.


p , p

30


Six step current fed converter

• Requires a relatively large reactor• Dynamic response is slowerDynamic response is slower


Direct Conversion

Matrix Converter

Problems:Problems:• Output/input voltage ratio limitation• No input/output Isolation


Our Proposed High Frequency AC Link Converter

Novel soft switching ac link converterHigh frequency ac linkIn ac ac case it uses 12 Bi directional SwitchesIn ac-ac case, it uses 12 Bi-directional SwitchesLink is formed by an inductor-capacitor pair (low reactive ratings)Switches are turned on at zero voltageSwitch turn offs are capacitance bufferedLow switching lossesVery compacty p

Advanced Electric Machines & Power Electronics (EMPE) Lab33

Comparing our proposed inverter with some of the existing inverters

Our proposed Kaco Blueplanet 1501 xi Fronius IG inverter series IGp pinverter

pGrid-Tie Inverter 15

http://www ecodirect com/Kacohttp://www.energymatters.com.au/images/fr

Referencehttp://www.ecodirect.com/Kaco-

Blueplanet-1501xi-p/kaco-blueplanet-1501xi.htm

onius/Energy%20Matters%20Fronius%20IG%20inverter%20series%20IG%2015%20-

IG%2060.pdf

Power rating 1.5 kW 1.5 kW 1.5 kW

PriceLess than

$1000$1,429.95 $3,074.00

$1000

Weight 13 lb. (6 kg) 30.8 lbs (14 kg) 19.84 lb (9 kg)

Efficiency 97% 94% 94.2 %


Principle of Operation

Link inductor charged using inputs

Charged link discharged to outputsCharged link discharged to outputs

The Inductor Current



Three input phases and one link to charge

Link charging is split into two Close to unity or desired PF at input

Link discharging is split into two intervals as wellLink discharging is split into two intervals as well.

The sequence and the pairs calculated so as to minimize the partial resonance times while meeting the desired harmonic levels


Principle of OperationMode 1 Mode 2


Principle of OperationMode 3 Mode 4ode 3 Mode 4


Principle of OperationMode 5 Mode 6Mode 6


Principle of OperationMode 7 Mode 8



M d 9 16 h d 1 8 h h li k i d


Modes 9-16 are the same as modes 1-8, except that the link current is reversed


1st

Power Cycle



2nd

PowerPower Cycle


Applications of the proposed Inverter

Our proposed converter can be used as :

AC‐AC, AC‐DC, DC‐AC, DC‐DC

And the most important applications are:AC drives

S lSolar Inverter

Wind Turbine Inverter

Battery‐Utility Interface


Simulation Results

AC-AC (15 kW)

Li k 10 kHLink frequency

10 kHz

Peak Link current

110 A

Link Inductance

140 µH

Link Capacitance

0.2 µF


Simulation Results


Simulation Results

DC-AC: Solar Converter


Simulation Results


Simulation Results

Power Reversal

DC/AC We have achieved DC/AC power reversal time of less than 1 ms.

AC/DC


AC/DC

50

Simulation Results

Input Filtered current Input Voltage


Simulation Results

Output Filtered current Output Voltagep g


Actual Converter


Actual Converter results

Low power results


Actual Converter results

Link voltage and Link Current


Conclusion

The proposed converter is a soft switched high frequency AC link converterThe efficiency is high (around 98%)It is very compactIt is very compactSwitching losses are very small due to the design and control methodThe size of the converter is very compactIt can even be used for power reversal application, and simulations have shown 1ms power reversal time.


Flywheel Energy Storage System Fundamentals

Charging Mode of the Flywheel Power in Input electronics Motor Flywheel (stored)

TRp

LriAvA

TAp TBp TCp TSp TTp

uA iRuR

rA

uB

uC

vB

vC

iB

iCTCTBT T TS T

PMSMuS

uT

iS

iT

vRS

vST

C

Flywheel

Line-Side Converter Machin-Side Converter

Cr

TCnTBnTAn TRn TSn TTnT


Discharging Mode of the FlywheelPower out Output electronics Generator Flywheel

57

Comparison of High Speed and Low Speed 2 MW Machines

Height 73” (1.85 m)

Conventional 2MW Machines

Height 73” (1.85 m)

Conventional 2MW Machines

73”(1.85m)

hi h

Weight 11,310 lbs. (5130 kg)

Power Density 0.39 kW/kg (326 kW/m3)

Length 90” (2.28 m)

Weight 11,310 lbs. (5130 kg)


Length 90” (2.28 m)

high

28” Height 28” (0 71 m)

Calnetix 2MW High Speed Machines

Height 28” (0 71 m)

Calnetix 2MW High Speed Machines28

(0.71m) high Weight 1650 lbs. (748 kg)


Length 53” (1.34 m)

Height 28 (0.71 m)

Weight 1650 lbs. (748 kg)


Length 53” (1.34 m)

Height 28 (0.71 m)


Limiting Geometric Design Considerations

Stored Energy Moment of inertia of the flywheel• Radius

212

E Jω=

• Mass

• Height (length) of the flywheel

The square of the rotational velocity of the flywheel

2

2r mhJ =

Limiting Geometric Design ConsiderationsTip speed ( ) due to the strength of the materialstV r ω=p p ( ) g• Steel constructions: 220 to 240 m/s

• Composite structures: more than 1000 m/s

Rotor dynamic behaviors• The various rotor critical (resonant) speeds

• The ability of the flywheel assembly to avoid or traverse them without failure

Advanced Electric Machines & Power Electronics (EMPE) Lab 599/1/2009

High Speed Flywheel

High Speed FlywheelOperate above 10,000 rpm up to 100,000 rpmA flywheel with a low mass but a highA flywheel with a low mass but a high limit for the mechanical tensionThe flywheel has a compound construction with a strength 5 times higher than steelhigher than steelThe mass moment of inertia, weights and dimensions are relatively smallThe rotor runs in a vacuum and is supported by magnetic bearingssupported by magnetic bearingsThe magnetic bearing requires a second set of bearings for emergencyThe output frequency of the synchronous generator is in the kHzsynchronous generator is in the kHz rangeDue to thermal reasons the rotor has no windingsA drawback is the high price of the


A drawback is the high price of the system

An Example of Flywheel Energy Storage System (source: VYCON)

Non‐contact fully levitated rotorSecondary Mechanical Bearings for back‐up only

High CycleFull Cycle every 15 minutes

DSP Controlled

140 kW for 15 Seconds

1. Flywheel 4. Flywheel Controller

2. GUI 5. Power Stack


3. Master Controller 6. Vacuum Pump

Experimental Set up


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