Lectre-13 Wind Energy System Configurations-02

7 - 02009 IEEE PES Wind Plant Collector System Design Working Group

Characteristics of Wind Turbine Generators for

Wind Power Plants

IEEE PES General Meeting 2009Calgary, Alberta

Mitch Bradt, P.E.University of Wisconsin-Madison


Machine Types Mechanical Energy Conversion Basic Electro-mechanical Machines

Wound Rotor Synchronous Generator Induction Generator (Wound and Squirrel Cage) Permanent Magnet Synch Generator

Types of Turbines Based on Speed Control 1: Fixed Speed 2: Limited Variable Speed 3: Variable Speed with Partial Scale PE Converters

This is the so-called Doubly-Fed Generator

4: Variable Speed with Full Scale PE Converters 5: Variable speed with Mechanical Transmission


Generating Lift


and then Torque

R

Rotational Speed

Tip Speed R


Real Power Coefficients It turns out that energy is lost due:

Finite number of Blades Wake Rotation Airfoil Drag

Tip Speed Ratio

WindVR


Basic 3 Machine Types

If

N

S

a-

a+

b-

c+b+

c-

Wound Rotor Synchronous:

a-

a+

b-

c+b+

c- N

S

a-

a+

b+

b-

c+

c-

Permanent Magnet Synch. Induction

Characteristic Wound Rotor SM PM Synch Mach. InductionRotor Speed (Elec.): Synchronous with Variable: SlipRotor Field Excitation: Variable Field Current Fixed Variable by InductionPower Range: kW-GW W-kW W-MWVARs: Source or Sink VARs0 SinkEfficiency: High-Very High High-Very High Low-Medium

Cost: High Med Low

r


Basic Synchronous Machines

If

N

S

a-

a+

b-

c+b+

c-

Sinusoidally Distributed Balanced 3 Stator Windings

StatorWindings

(Distributed)Rotor

Winding(Distributed)

Wound Rotor

The Rotor Field Winding is Energized with DC Current If.

(2-PoleMachinesDepicted)

The Field Bf Rotates Synchronously with the Rotor at speed

Induces Sinewave Voltages in Stator Windings

Bf Van0

Vcn-240

Vbn-120

a

b

c

n


Smooth Rotor Sync. Machine

If

N

S

a-

a+

b-

c+b+

c-

+

-jXM

jXlr jXlsRr Rs

fI

DC Field Looks like a Current Source with f = 2:Per-Phase

Circuit Model:

fs

ff IN

NI

f

ff R

VI

fI Aligned with Rotor

aI

aV

+

-

jXS Rs

E

One Reactance Model:

lsMS XXX

aI

aV+

-

+

-

jXM jXls Rs

Mf XIjE

Convert Field to Voltage-Source:

E

Mf LIE Proportional to Speed

XS

aI

aV+

-

Bf


StableUnstable

P1.5

1.0

0.5

a

a

VE

Stability Limit

Stable Unstable

Synch Machine: Power-Angle Curves

aV

sa XIj

aI

E

Generating, Lagging Current

0P0Q

0 0

Generating, Leading Current

Sinking VARs Sourcing VARs

Over-Excited

aV sa XIj

aI E

0P0Q

00

Under-Excited

P3M 3 EVaXssin

Where:E, EMF of fieldVa, terminal voltageXs, synchronous reactance, vector angle between Va & E


Wound Rotor Synchronous MachineP-Q Capability (D-curve)

Reactive capability curve (D-curve)

Continuous reactive power output capability is limited by:

armature current limit AB (stator overheating)

field current limit BC (rotor overheating)

end turn heating limit CD


Basic Induction Machines

Sinusoidally Distributed Balanced 3 Stator Windings Rotor Speed is Generally Non-Synchronous:

Rotor Can turn Faster (Generator) or Slower (Motor) than Input Frequency

Wound Rotors: Rotor Windings brought out through Slip Rings: Allowing Speed/Torque Control

Squirrel-Cage Rotors: Rotor Windings are simple Shorted Bars cast into Rotor Laminations Low-Cost, Rugged Commercial / Industrial Work-Horse FIRST WINDTURBINES

Wound Rotor Squirrel-Cage Rotor

a-

a+

b+

b-

c+

c-

r

rs Slip:


Induction Generator Model

-

++

-mV

Rs jLls jLlr rI

jM sRr

sI

sV

Power:

sRIP rrag

23sPRIP agrrlossr 2, 3

SSout VIP 3Air-Gap Power

[W]

[W]

PagPout

-

++

-mV

Rs jLls jLlr rI

jM

)1( ss

Rr sI

sV

PagPout

Rr)1( s

sVr

rV+-

+ -

Converted Power

Power from an External

Rotor SourceRotor Loss

Vr = 0 if no external source of Power to

the Rotor


Induction Machine Torque-Speed

-2

-1.5

-1

-0.5

0

0.5

1

1.5

1 -0.5 0 0.5 1 1.5 2

Rated Voltage V1 & Frequency f

SynchronousSpeed

Rated Torque/Speed

Motoring

Generating

Braking


Permanent Magnet Sync. Machine

a-

a+

b-

c+b+

c- N

S

Advantages of PM Sync. Machines: No Field Winding Very Low Reactance Very Linear: Long Air-Gap Compact and Efficient

PermanentMagnet

Bf

Br

ml

Bm

HmDemagnetization

ResidualFlux Density

HBB rrm 0

Hc0

r 1 (Air)

Typical PMB-H Curve:

ag

+

-jXM

jXlr jXlsRr Rs

fI

PM Rotor Looks like a Current Source with f = 2:Per-Phase

Circuit Model:

fI Aligned with Rotor

aI

aV

mrmf lBKI

All Other Characteristics Like Wound Rotor Machine with Constant If


Recall thatthe energy capture (vis-a-vis Cp) is dependent

upon the Tip Speed Ratio

...as Wind Speed(Vwind) changes, it is desirable toallow to changeas well.

WindVR


Type 1 Wind Turbine

Fixed Speed -- limited control of slip (2-3%) and Real PowerConsumes VARs

GearBox IG

CollectorFeeder

The rotor blades may be pitch-regulated to control power

Soft Starter Cap Bank


Real and Reactive Power


Type 2 Wind TurbineVariable Speed -- More control of slip (up to 10%)

Consumes VARs

Variable Rotor ResistanceVia slip rings with wound rotor IGPlaced on rotor as with OptiSlip

GearBox IG

CollectorFeeder

Soft Starter Cap Bank


Real and Reactive Power with Rext


Type 3 Wind TurbineVariable Speed -- More control of slip (up to 50%)

Can control VARsPartial Scale Converters Required (~30% of Machine)

GearBox

CollectorFeederIG

IGPstator

Protor

Pnet

Operation Below Synchronous Speed

IGPstator

Protor

Pnet

Operation Above Synchronous Speed


Type 4 Wind Turbine

Variable Speed -- Wide control of slip (up to 100%)Can control VARs

Full Scale Converters Required (>100% of Machine)

Machines excitation can be controlled by machine side converterCan use any type of machine! Field Wound SG, PM-SG or even IG

GearBox

IG/SG

CollectorFeeder

An opportunity to eliminate the gearbox existsSince Wild AC from generator can be conditioned to 60Hz grid


Type 5 Wind Turbine


Voltage Control

Types 1 & 2: control limited to Power Factor Corrections Caps

Type 3: Rotor-side converter controls d-axis current on rotor to control voltage

Type 4: Grid-side converter supplies reactive power to control voltage

Type 5: Automatic Voltage Regulator, typical of Synchronous machines


Reactive Power Capabilities

Types 1 & 2: Caps may be set to hold a fixed PF

Types 3 & 4: typical range is 0.95 (cap) to 0.9 (ind)

Type 5: similar to conventional Sync. Machine

NOTE: Types 3, 4, 5, may be able to provide VAR support even while not producing Watts Types 3 & 4: in a fashion similar to a STATCOM Type 5: in a fashion similar to a Sync. Condenser


Thank You!

Are there any Questions?

Mitch Bradt, [email protected]

Documents

Lectre-13 Wind Energy System Configurations-02