ece356 -- 20150910 -- bradt

ECE 356 September 10, 2015 Mitch Bradt, PE Electric Power Processing for Alterna6ve Energy Systems, Slide 1

Wind Turbine Generators: The Basics

ECE 356—Electric Power Processing for Alternative Energy Systems


U.S. Wind Energy Poten;al

Copyright © 2008 3TIER, Inc. All Rights Reserved. For permission to reproduce or distribute: [email protected]


U.S. Wind Project Installa;ons Source: American Wind Energy Association U.S. Wind Industry Annual Market Report –

2014 Fourth Quarter


WTG: The Basics -‐-‐ Outline

Wind Turbine Generator Technology:

The Mechanical Side Wind Turbine Generator Technology:

The Electrical Side


Wind Turbine Generator Technology: The Mechanical Side


LiC and Drag: Aerodynamic Forces

Wind attack point!

lift!

Pressure!

Vacuum!The air moving along the upper!surface of the blade travels faster !than air on the lower surface !

Reduced lift!Flow on upper and lower surface equal ⇒ no lift!

Wind attack point!

Reduced lift , Stall !Wind attack point!

drag!


The wind turbine seen from above:!


The wind turbine seen from above:!

View of the tip profile, the largest profile, the blade twist and blade root (circle)!

The wind direction will vary!

with the wind speed! variation!

!The wind force resulting from the rotor tip speed !!

The tip speed is specific for each WTG type and normally near 60 m/s!

Wind direction!

On the next slides !we will look at the blade tip position!

ROTOR PLANE!


Angle of AIack, alpha

CL

Wind speed12 m/s

60 m/s

Increased power

As wind speed increases, the rotor turning power becomes greater and the generator produces more electricity

The blade section will see the resulting wind direction only and it will create a lifting force (CL)

CL can be split into a rotor thrust force and a power direction

Blade tip speed 60 m/s

Wind speed 8 m/s Resulting wind direction

CL Rotor thrust Power


Wind !speed !16 m/s!

Tip speed 60 m/s! !The stall-mode is developed gradually throughout the blade!

Aerodynamic - Wind influence on the blade!

!!! !!

!The higher wind, the more stall!

!!

!!

Stall rotor- fixed position!

At high wind speed the lift force is lost due to stall!

CL!

Changing the Wind Speed Changes Wind Direction Relative to the Rotor Blade


Aerodynamic - Variable speed !

!!

Blade tip speed 80 m/s!

Wind speed 16 m/s!

CL!

Power!

Blade tip speed 70 m/s!

Wind speed 16 m/s!

CL!

Power!


Pitch regulation and blade position!

q  The normal stop position is +90° !

m/s!

kW!

Wind!

l  To control the rotor acceleration, the blades have variable blade position in order to carry out a smooth grid cut-in!

l  Pitch turbines achieve variable speed compared to the fixed speed rotor of stall wind turbines!

•  Up to 7-8 m/s winds,! the pitch is set to 0°!


Genera;ng LiC …


…and then Torque

R

Rotational Speed ω Tip Speed ω⋅R


Betz’s Elemental Momentum Theory

q  Given that and

2

21 vmE ⋅= Avm ⋅⋅= ρ

ρ — air density

v — air speed

A— swept area of blades

q  Then.. AvEPWind ⋅⋅== 3

21ρ

q  We can state that the Power a turbine can extract is:

!"

#$%

& ⋅⋅⋅= AvCP PTurbine3

21ρ

q  Betz showed through conservation of momentum that the maximum Power Coefficient (CP) happens when the downstream speed is slowed to 1/3 of the incident speed

593.02716

, ==BetzPC


Real Power Coefficients

q  It turns out that energy is lost due: •  Finite number of Blades •  Wake Rotation •  Airfoil Drag

Tip Speed Ratio

WindVR⋅=ωλ


Wind Turbine Generator Technology: The Electrical Side


Power Systems


AC Systems •  Power system voltages and currents are AC, and have the form

where in N. America.

•  Instantaneous power

•  Manipulating where

Real component

Imaginary component


Instantaneous Power V and I in phase I lags V by 30 deg

P=0.5, Q=0.0 P=0.433, Q=0.25


Apparent (complex) Power l  Using phasors to find P and Q.

–  Apparent power: Volt-Amps “VA” –  Power factor: = P/S =

Active power Watts

Reactive power Volt-Amps Reactive “VARs”

(where * means complex conjugate)


Ac;ve (real) and Reac;ve (imaginary) Power l  Active power – frequency.

–  System frequency is governed (approximately) by

§  System frequency, §  Total mechanical power, §  Total electrical power,

–  If exceeds , the power system will slow down. –  If exceeds , the power system will speed up. –  Governors on generators regulate system frequency by controlling the

mechanical power. l  Reactive power – voltage.

–  Not as simple as frequency dynamics. –  General principle:

§  Injecting reactive power into the system raises (local) voltages. §  Absorbing reactive power from the system lowers (local) voltages.

§  Total system inertia, §  Total system damping,


Basic 3φ Machine Types

If

N

S

a-

a+

b-

c+ b+

c-

ω

Wound Rotor Synchronous:

a-

a+

b-

c+ b+

c- N

S

a-

a+

b+

b-

c+

c-

Permanent Magnet Synch. Induction

ω

Characteristic Wound Rotor Synch Perm Magnet Synch Induction Rotor Speed (Elec.): Synchronous with ω Asynchronous (slip) Rotor Field Excitation: Varies-—field winding Fixed—PM Varies by Induction Power Range: kW-GW W-kW W-MW Reactive Power: Source or Sink ≅0 Sink Conventionally used: Almost all Generation “new kid on the block” Most Industrial Motors Used in WTG: Some, not many Increasing in WTG First turbines

Only type 4 Types 1, 2, 3


Basic Synchronous Machines

If

N

S

A-

A+

B-

C+ B+

C-

ω

q  Sinusoidally Distributed Balanced 3φ Stator Windings

Stator Windings (Distributed)

Rotor Winding (Distributed)

Wound Rotor

l  The Rotor Field Winding is Energized with DC Current If.

(2-Pole Machines Depicted)

l  The Field Bf Rotates Synchronously with the Rotor at speed ω:

–  Induces Sinewave Voltages in Stator Windings

Bf


Basic Induc;on Machines

q  Sinusoidally Distributed Balanced 3φ Stator Windings

q  Rotor Speed is Generally Non-Synchronous: Rotor Can turn Faster (Generator) …

… or Slower (Motor) than Input Frequency

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

q  “Squirrel-Cage” Rotors: •  Rotor Windings are simple Shorted Bars cast into Rotor Laminations

•  Low-Cost, Rugged è Commercial / Industrial Work-Horse FIRST WINDTURBINES

Wound Rotor Squirrel-Cage Rotor

a-

a+

b+

b-

c+

c-

ωr

ωωω rs −

=Slip:


Type 1 Wind Turbine

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

Gear Box IG Collector

Feeder

The rotor blades may be pitch-regulated to control power

Soft Starter Cap Bank

Examples: Vestas V-82, Mitsubishi MWT-1000 ** becoming less common


Real and Reac;ve Power


Type 2 Wind Turbine

Variable Speed -- More control of slip (up to 10%) Consumes VARs

Variable Rotor Resistance • Via slip rings with wound rotor IG • Placed on rotor as with OptiSlip®

Gear Box IG Collector

Feeder

Soft Starter Cap Bank

Examples: Vestas V-47, Suzlon S-64/88 no longer common—stepping stone to Type 3…


Real and Reac;ve Power with Rext


Type 3 Wind Turbine Variable Speed -- More control of slip (up to 50%) Can control VARs Partial Scale Converters Required (~30% of Machine)

Gear Box

Collector Feeder IG

IG Pstator

Protor

Pnet

Operation Below Synchronous Speed

IG Pstator

Protor

Pnet

Operation Above Synchronous Speed

Ex: GE 1.5, Acciona 1500, Vestas V90, Gamesa G80 ** State of the Art

REPower 5M (126 m dia.) Commissioned offshore. 5MW Output Based on Doubly Fed type machine


Type 4 Wind Turbine

Variable Speed -- Wide control of slip (up to 100%) Can control VARs Full Scale Converters Required (>100% of Machine)

Machine’s excitation can be controlled by machine side converter ⇒Can use any type of machine! Field Wound SG, PM-SG or even IG

Gear Box

IG/ SG

Collector Feeder

An opportunity to eliminate the gearbox exists Since “Wild AC” from generator can be conditioned to 60Hz grid

Ex: GE 2.5, Siemens 2.3, Clipper 2.5, Enercon E112 ** State of the Art


Areva Wind

Direct-Drive��PM Wind Turbines

q  S;sldjfl;asjdf

l  Many alternative wind turbine and PM machine configurations

l  Machine ratings up to 8 MW

ABB

GE The Switch


Size of Modern Wind Generators

Manwell Fig 1.15


Factors Driving Recent Growth of Wind Power

• Fiber composites for constructing low cost blades.

• Improved operation and maintenance leading to increased availability.

• Economy of scale.

• Application of power electronics to allow variable blade speed and enhance efficiency and energy output.

• Decreasing cost of power electronics.

• Accumulated field experience improving the capacity factor (% of rated kWhr attained on annual basis)

(in addition to financial subsidies)


Thank You!

q  Are there any Questions?

Mitch Bradt, PE [email protected]

ece356 -- 20150910 -- bradt

Documents