l14 – generationl14 – generation eien20 design of electrical machines, iea, 2016 5 avo r design...

L14 – Generation

EIEN20 Design of Electrical Machines, IEA, 2016 1

Industrial Electrical Engineering and AutomationLund University, Sweden

L14: Power Generation

Power conversion in large scale

Avo R Design of Electrical Machines 2

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TOPOLOGY Select machine type

EMSM, PMSM, RSM or in combination

A number of predefined constructions

Electromagnet

Permanent magnet

Reluctance magnet


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Objectives for today

• Electric power generation– Primary mover – wind power– Generator types – SCIG, DFIG, … via GB vs DD– and Development – variable speed drive with maximum power

tracking, light construction, super conductor, …

• Electrical machines with high specific torque (Nm/kg)– Transversal flux machines


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Motivation

• Cost vs Efficiency of systems driven by electrical machines

– Reliability, less complex– Induction machines (IM) use (still?) 90% of all the power used

by machines– Electrically magnetised synchronous machines (EMSM) provide

most of the electrical power

• Construction of electrical machines– Least expensive, lowest maintenance

• Control of electrical machines– Reliability, easy and cheap to control

L14 – Generation



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Electricity from wind

• Primary power is related to wind speed vw3 cube, turbine capture

πrb2 area and design (pitch angle θ, tip speed ratio λ)

• Blade tip speed vb is limited and independent of turbine radius or blade length rb

• Rotation speed ω is inversely proportional to the radius rb

32,21

wbpair vrCP

2/33nb

b

nbn PrvPrPT


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Power conversion coefficient

• Energy conversion ratio of mechanical rotatingenergy of the turbine to the total kinetic energy available from the wind

• Energy extraction by slowing down the wind

• Theoretical maximum 59.3% known as Betz limit


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Cost of energy

• The levelized cost of electricity (LCOE) is the net present value of the unit-cost of electricity over the lifetime of a generating asset

• The capital expenditure (CAPEX) is the cost of developing or providing non-consumable parts for the product or system

• The operational expense (OPEX) is an ongoing cost for running the product/system

L14 – Generation



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Turbine manufacturers and concepts• Constant Speed (CS) ~1.5MW

(3x) GB + IM with 2 speeds or extended slip

• Double fed IM (DFIG) ~1.5MW 1/4Pn converter gives 0.6-1.1 times speed range

– Grid-fault ride-through enabled by gear and full converter (GFC)

– Brushless – maintenance

• Direct drives (DD): EMSM, PMSM & combined

– Large less & efficient machines vs reduced parts and increased reliability


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Nacelle <2013

CS NEG m

icon

DD Ene

rcon E-

66

DD Sway Turbine

GFC Winwind


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Specification examples <2008


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Top head weight

L14 – Generation



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nDevelopment directions

• Reliability – gear-less, brushless

– BDFIG double fed stator windings

• Alternative gear box– Magnetic gears

• Lighter construction – semi core-less

– Large diameter light construction

• Increased power density –super conducting


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Magnetic power transmission by magnetic gear

• Two rotors with differing numbers of permanent magnet poles

• An intermediate ring with stationary magnetic pole-pieces

• The pole-pieces modulatethe magnetic fields to link the rotors' movement

• PMSM + magnetic gearing integration

• High specific torque!


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Superconductor

• Resistance drops off at materials critical transition temperature

• Critical (maximum) current and magnetic field under which material remains superconducting

• Practical superconductor wires: HTS cooled by liquid N2

• Machine design where Bg >> Bsat

temperature

resi

stan

ce Non-super-conductor

~1e+6~1e+6~1e+6~1e+6~1e+6

Jc,A/cm2

1109239189

c,°KSuperconductor Hc, TNbTi 11-12

Nb3Sn 25-29MgB2 15-20YBCO >100

Bi-2223 >100 Industrial Electrical Engineering and AutomationLund University, Sweden

Small scale wind power generators

Topology selection and design experience

L14 – Generation



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0 5 10 15 20 25 30 35 40 45 500

5

10

15

20

25

30

35

40

45

50

100

100

100

200

200

200

300

300

300

400

400

400

500

500

500

600

600 700

700

800

800

900

900

1000

1000

torque of RF machine, TemRF [Nm]

radi

us, r

[cm

]

length, l [cm]0 5 10 15 20 25 30 35 40 45 50

100

100

10 0

200

200

200

300

300

300

400

400

400

500

500

500

600

600

600

700

700 800

800

900

900

1000

1000

torque of AF machine, TemAF [Nm]

length, l [cm]

• Radial flux machine

• Axial flux machine

• Selected value of magnetic shear stress

– σ=5000 N/m2

– Coreless machines

lr

h

h r

l lrT EFem

22

33

332

5.05.032

1322

lrlr

rrrdrrTo

io

r

rAFem

o

i

Torque capability


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Low speed & high power

• Based on the previous torque capability map the power capability at50 rpm is expressed

• By estimating the thickness for the machine h=10 cm and average density of 7kg/dm3 the weightis expressed

0 5 10 15 20 25 30 35 40 45 500

5

10

15

20

25

30

35

40

45

50

1

1

1

2

2

2

3

3

3

4

4

5

5

6

6

7

7

power of RF machine, PemRF [kW]

radi

us, r

[cm

]

length, l [cm]0 5 10 15 20 25 30 35 40 45 50

1

1

1

2

2

2

3

3

3

4

4

4

5

5

6

6

7

7

power of AF machine, PemAF [kW]

length, l [cm]

0 5 10 15 20 25 30 35 40 45 500

5

10

15

20

25

30

35

40

45

50

100

100

100

200

200

200

300

300 400

400

500

500

weight of RF machine, MemRF [kg]

radi

us, r

[cm

]

length, l [cm]0 5 10 15 20 25 30 35 40 45 50

100

100

100

200

200

200

300

300

300

400

400

500

500

weight of AF machine, MemAF [kg]

length, l [cm]


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Axial Flux PMG

Villavind

• Winding layouts, core-less and light-core machine• Characteristics with passive resistive load


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n Green medium power household supply– Direct drive HMWG for

axial wind turbines– Challenge: low speed &

”low cost” application

Series EM excitation– Self power-up

Taking advantage of– Open slots– High fill coils – distributed concentrated

windings

HMSM for Wind power application

Parameter Unit ValueActive length mm 100Stator inner diameter mm 400Rotor outer diameter mm 600Nominal speed rpm 50Current density A/mm2 10

L14 – Generation



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Scope of the study

32-pole 33-coil 8-pm HMSMOptimize coupling vscogging– Arrange poles (Np),– stator teeth & coils (Nc),– # of magnets and location

4 different cases are analyzed– Machine parameters– Torque and cogging

Pattern Flux ratio ValueNp-Nc-Nm Ψpm/Ψhm[Vs] Phm/Pmax[W]

32-33-8 0.95 / 3.26 736 / 135032-30-8 0.65 / 3.05 736 / 122028-27-4 0.43 / 2.66 525 / 114026-24-2 0.25 / 2.40 490 / 1040


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Outcomes

0 50 100 1500

10

20

30

40

50

60

extracted and total electric power, P [W]

volta

ge, U

[V]

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8current, I [A]

32-33-832-30-828-27-426-24-2

0 200 400 600 800 1000 1200 1400 1600 18000

20

40

60

80

100

120

140

160

180

200

extracted and total electric power, P [W]

volta

ge, U

[V]

0 1 2 3 4 5 6 7current, I [A]

32-33-832-30-828-27-426-24-2

Generator characteristics– Derived from machine

parameters @ 50 rpm– PM excitation above– HM excitation below

Unattractive solution– Limited power

generation capability at the speed range of interest

– 3kW minus 0.7kW for excitation @ 100 rpm


Magnetic circuit

Materials, forming, flux-linking…


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Material engineering

• Permanent magnets– High energy NdFeB magnets Br=1.45T, Hc=1.1MAm– Max working temperature of NdFeB > 200oC – Price between 10$/kg and 25$/kg

• Soft Magnetic Powder Composites– SomaloyTM500 12.5W/kg @ 1T & 0.1kHz, 1.54T @ 10kA/m– Accucore 6W/kg @ 1T & 0.1kHz, 1.72T @ 10kA/m

• High saturation ferromagnetic alloys – Hiperco50 44W/kg @ 2T & 0.4kHz

• Amorphous Ferromagnetic alloys– Metglass® 0.125W/kg @ 1T & 0.05kHz,

L14 – Generation



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0 1000 2000 3000 4000 5000 6000 70001

2

3

4

5

6

7

8

9

relative magnetic permeability, []

spec

ific

loss

, p [W

/kg]

M235-35AM250-35AM270-35AM300-35A

M330-35A

M700-35A

M250-50AM270-50AM290-50AM310-50AM330-50AM350-50A

M400-50A

M470-50AM530-50A

M600-50A

M700-50A

M800-50A

M940-50A

M530-50HP M310-65AM330-65A

M350-65A

M400-65AM470-65A

M530-65A

M600-65A

M700-65A

M800-65A

M1000-65A

M600-65HP

M600-100A

M700-100A

M800-100A

M1000-100A

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

relative magnetic permeability, []

flux

dens

ity, B

[T]

M235-35AM250-35AM270-35AM300-35AM330-35A

M700-35A

M250-50AM270-50AM290-50AM310-50AM330-50A

M350-50AM400-50AM470-50AM530-50A

M600-50A

M700-50AM800-50AM940-50A

M530-50HP

M310-65AM330-65A

M350-65A

M400-65A

M470-65A

M530-65AM600-65AM700-65A

M800-65A

M1000-65A

M600-65HP

M600-100AM700-100A

M800-100A

M1000-100A


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From material to construction


Direct torque machines

Choices among TFM


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High power density machines: TFM

• The torque of an a.c. machine is proportional to the magnetic (air gap flux density Bg) and electric (stator line current density A) loadings.

• Attractiveness TFM: T=f(Np), the line current density A of a TFM increases with the number of poles. High frequency of armature current and flux increases the power density.

• Care with TFM: the power factor which is inherently low and to the cogging torque which is inherently high.

L14 – Generation



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nComparison TFM

Harris, 1997Avo R Design of Electrical Machines 30

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Transverse M

• Blissenbach & Hennebergerfrom Aachen (2001)

• Pn=30.5kW, n=650rpm, Tn=450Nm, In=73A, U=220V

• Rg=295mm, L=115mm, M=29kg

• T/M=15.5Nm/kg, cos(φ)=0.62• FW used for loss reduction


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Transverse M

• Dickinson, Jack & Mecrowfrom Newcastle (2002)

• Tn=25.6Nm, In=7.3A, • Ro=188.4mm, M=2.8kg• T/M=9.3Nm/kg, cos(φ)=0.62• Thermal design: pooting of the

coil 0.1W/mK→0.63W/mK• Optimization target: cost

efficient solution


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Transverse M

Simple high-fill coils, magnetic core as simple and manufacturable as possible

l14 – generationl14 – generation eien20 design of electrical machines, iea, 2016 5 avo r design...

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