Wind Generation Challenges & New Technologieshome.engineering.iastate.edu/~jdm/wesep594/WindOverviewPitch_2015Mar4.pdfof GE Wind Turbine-Generators for Grid Studies,” version 4.5,

Wind Generation Challenges & New Technologies

Matthew Richwine March 4, 2015

Proprietary Information: This document contains GE proprietary information and may not be used or disclosed to others, except with the written permission of the General Electric Co.

2 Wind Overview

3/4/2015

Agenda

• Introduction

• Grid Integration Challenges

• “New” Technologies

• Conclusions

Introduction


4 Wind Overview

3/4/2015

Matt Richwine

Education

BS, Electrical & Computer Engineering, Cornell University, 2008

MEng, Systems Engineering, Cornell University, 2009

Work Experience

GE Energy Consulting, 2013 – Present

• Leading sub-synchronous resonance and torsional interaction studies

• Analyzing renewable generation integration on existing island systems

• Testing and modeling thermal and renewable plants for grid code compliance

GE Wind Generator & Electrical Systems Engineer, 2009 – 2013

• Specified, developed, and validated a new DFIG for a new electrical system

• Introduced a thermal control strategy for wind generators to optimize output


5 Wind Overview

3/4/2015

Growth of the Industry

Source: AWEA, 1Q 2014 [1]

Wind Integration Challenges


7 GE Title or job number

3/5/2015

As renewable energy increases, it will:

• Have a greater impact on the grid;

• Displace other generation;

• Become essential to grid reliability; and

• Need to be more predictable during disturbances

• Transmission reinforcement

• Forecasting

• Operational flexibility

Looking Ahead

Renewable energy must be a good citizen on the grid


8 Wind Overview

3/4/2015

• Wind power forecasting to improve unit commitment

• Refine up reserve requirements based on wind power forecast

• Increase thermal unit ramp rate capability

• Advanced wind turbine technologies to support the grid when it is stressed

Strategies to Improve Integration

Predictable response to frequency events Coordinated response to voltage events


Frequency Response


10 Wind Overview

3/4/2015

Sustained Wind Power Drops Planning for Challenging System Events

Largest hourly wind power drop, three large baseload units on outage, largest wind power forecasting error, rapid sub-hourly solar variability.

Sustained drops in wind power could consume the available up reserve on the system and/or challenge the systems ramp rate capability

Active Power Control Stability Model

Trip

Signal

1

1+ sTp

Pmech Wind

Power

Model

Wind

Speed

Blade

Pitch

Torque Control

X

Anti-windup onPower Limits

Under

Speed

Trip

(glimv)

ref err

Pitch Control

Kpp+ Kip/s

(glimt )rotor

1

1+ sTpc

+

K pc+ K

ic/ s

+

min& d /dt

min

max

& d /dt max

+

+

To

getwg

cmd

Pwmin& d /dt minP

Pwmax

& d /dtmaxP

Anti-windup onPitch Limits

Anti-windup onPitch Limits

Kptrq + Kitrq

/ s

s4s2

s1s0

s3

Pelec

Rotor

Model

s5

1

From

getwg(pelec)

Pdbr

From

ewtgfc(elimt)

+ +

Active Power

Control

(optional)

Auxiliary

Signal

(psig)

WTG Terminal

Bus Frequency

fbus

pstl

Pord

To extwge

or ewtgfc

(vsig)

sTw

1 + sTw

s10

PsetAPC

Power Response

Rate Limit

pinp

plim

perr

wsho

+

+

+

+

+

Pitch

Compensation

s6 s9

1 + 60s

dpwi +

- 0.75P2elec

+ 1.59Pelec

+ 0.63

WindINERTIA

Control

(optional)

Pmin

Pmax

1.

01

apcflg

Clark, N.W. Miller, J. J. Sanchez-Gasca, “Modeling

of GE Wind Turbine-Generators for Grid Studies,”

version 4.5, April 16, 2010. Available from GE

Energy.

Frequency

Response

Curve

1

1+sTpav

fbu

s

To gewtg

Trip Signal

(glimt)

pavl

Wind

Power

Model

Pmin

Pmax

Release

Pmax

if fflg set

Active Power Control

(optional)

fflg

pavf

psetpstl

+

+

1.

If (fbus < fb)

OR (fbus > fc)

0

apcflg

1

1

WTG Terminal

Bus Frequency

Wind

Speed

(glimv)

1.

1

1+sTfc

deadband

• 83 MW plant in Alberta

• Test is release of high frequency input

• Std GE WTG model (wndtge); parameters tuned for this plant

12

Field Test and Model of GE Wind Plant Frequency Response

WindINERTIA™: Inertial Response Option for GE Wind Turbine Generators

Nicholas Miller Kara Clark Robert Delmerico Mark Cardinal

GE Energy



3/5/2015

Why Inertial Response: System Needs • Increasing Dependence on Wind Power

– Large Grids with Significant Penetration of Wind Power

• Modern variable speed wind turbine-generators do not contribute to system inertia

• System inertia declines as wind generation displaces synchronous generators (which are de-committed)

• Result is deeper frequency excursions for system disturbances

• Increased risk of

– Under-frequency load shedding (UFLS)

– Cascading outages

Inertial response will increase system security and aid large scale integration of wind power



3/5/2015

Control Concept • Use controls to extract stored inertial energy

• Provide incremental energy contribution during the 1st 10 seconds of grid events;

– Allow time for governors and other controls to act

• Target incremental energy similar to that provided by a synchronous turbine-generator with inertia (H constant) of 3.5 pu-sec.

• Focus on functional behavior and grid response: do not try to exactly replicate synchronous machine behavior



3/5/2015

Constraints • Not possible to increase wind speed

• Slowing wind turbine reduces aerodynamic lift:

– Must avoid stall

• Must respect WTG component ratings:

– Mechanical loading

– Converter and generator electrical ratings

• Must respect other controls:

– Turbulence management

– Drive-train and tower loads management



3/5/2015

How does it work? Basic components of a GE Double-Fed Asynchronous Wind Turbine Generator:

Wind Turbine

f rotor P rotor

f net P stator

3 f AC Windings

Converter

P rotor F rotor

P conv F network

Electrical Power Delivered to Grid

Wound-Rotor Generator

Machine Terminals

Wind



3/5/2015

How does it work? Part 2

ema TTTdt

dJ

Electrical Torque, Te

Mechanical Torque, Tm

Basic machine equations for all rotating machines

base

2mo

VA

J

2

1H

baseVA

sec)-(Watt RotortheinStoredEnergyKineticH

Basic Notation:

J is the inertia of the entire

drive-train in physical units

H is the inertia

constant – it is scaled to

the size of the machine.

A typical synchronous

turbine-generator

has an H of about 3.5

MW-sec/MW.



3/5/2015


Electrical Torque, Te

Mechanical Torque, Tm

So what?

• In steady-state, torques must be balanced

• When electrical torque is greater than mechanical torque, the rotation slows extracting stored inertial energy from the rotating mass



3/5/2015

What’s Different?

Synchronous Generator

Wind Turbine*

Mechanical power

Governor Response / Fuel Flow Control

Pitch Control / Uncontrolled Wind Speed

Electrical Power Machine Angle (d-q Axis) / passive

Converter Control / active

Inertial Response

Inherent / Uncontrolled

By Control Action

* Variable speed, pitch controlled WTGs



3/5/2015


Wind

Electrical Torque is a function of: (1) Converter Control (2) Commands from Turbine Control

Mechanical Torque is a function of: (1) Wind Speed (2) Blade Pitch (3) Blade Speed ( ά Rotor Speed)

WindINERTIA uses controls to increase electric power during the initial stages of a significant

downward frequency event



3/5/2015

What happens during a grid event? 1. Disturbance (e.g. generator trip) initiates grid frequency decline

2. WindINERTIA detects significant frequency drop

3. Instructs WTG controls to increase electrical power

4. Additional electric power delivered to the grid

5. Rate and depth of grid frequency excursion improves

6. WTG slows as energy extracted from inertia; lift drops

7. Other grid controls, especially governors, engage to restore grid frequency towards nominal

8. WindINERTIA releases increased power instruction

9. WTG electric power drops, to allow recovery of rotational inertial energy and energy lost to temporarily reduced lift

10. Transient event ends with grid restored



3/5/2015

58.0

58.5

59.0

59.5

60.0

60.5

0 10 20 30

Time (Seconds)

Win

d P

lan

t P

OI

Bu

s F

req

ue

ncy

(H

z)

1000 MW Synchronous Machine

1000 MW Wind without WindINERTIA

1000 MW Wind with Simple WindINERTIA Model (Rated Wind Speed)

Reference Case

Without WindINERTIA frequency

excursion is ~4% worse

With WindINERTIA

frequency excursion is

~21% better

An Example: 14GW, mostly hydro system, for trip of a large generator

Minimum frequency is the critical performance concern for reliability



3/5/2015

58.0

58.5

59.0

59.5

60.0

60.5

0 10 20 30

Time (Seconds)

Win

d P

lan

t P

OI

Bu

s F

req

ue

ncy

(H

z)

1000 MW Synchronous Machine

1000 MW Wind without WindINERTIA

1000 MW Wind with Simple WindINERTIA (Wind Speed above Rated)

1000 MW Wind with Simple WindINERTIA Model (Rated Wind Speed)

With WindINERTIA

frequency excursion is

~21-23% better

An Example (continued) :

Range of possible recovery

characteristics

Performance is a function of wind and other conditions: not perfectly deterministic like synchronous machine inertial response



3/5/2015

• Not possible to drive grid frequency

• Controls driven with an external frequency signal – (very similar to frequency of previous example)

• Performance a function of wind speed – (also, not possible to hold wind speed constant during tests)

• Since WTG must respect other controls – Turbulence & drivetrain and tower loads management

affect performance of individual WTGs at any particular instant

– Exact performance of single WTG for a single test is not too meaningful

– Aggregate behavior of interest to grid

Field Tests Approach and Constraints:

WindINERTIA validation tests: Multiple tests over varying wind conditions


Field Tests Results:

Test count:

8 m/s - 19 tests

10 m/s – 19 tests

14 m/s – 52 tests

0

300

600

900

1200

1500

1800

0 10 20 30 40 50 60 70 80

Time (Seconds)

Po

wer

(kW

)

8 m/s Avg Meas 10 m/s Avg Meas 14 m/s Avg Meas



3/5/2015

Summary & Conclusions • Need and demand for inertial response from WTGs has been

growing

• GE now offers a new, grid friendly feature to meet this need

• The feature has been field tested; a dynamic model has been created

• Fundamental physical differences in WTGs mean that inertial behavior is not identical to synchronous machines

• Future grid codes may require inertial response; they must recognize physical reality & constraints

WindINERTIATM - another aid to the continued successful large scale integration of wind power


Volt/VAR Coordination


Key components of plant systems

• Provide functions similar to conventional power plant

• Coordinated control of all WTG

• Integration with substation equipment

• 200+ systems in operation controlling 8000+ turbines

WindSCADA

• Utility grade SCADA system

• Integrated monitoring & control of WTG, substation

• Tools for O&M operations

• Robust remote and local access

• Industry accepted protocols for data transfer

WindCONTROL


30 Wind Overview

3/4/2015

Hierarchical Control Philosophy

Individual WTGs have fast, autonomous, self-protecting regulation of their terminal voltages

• Individual WTGs will always respond rapidly and correctly for grid voltage events

WindCONTROL provides plant-level controls to meet performance requirements (e.g., voltage regulation) at the point-of-interconnection (POI)

• Sends supervisory reactive power commands to individual WTGs to ‘trim up’ initial individual WTG response

• Coordinates other substation equipment (e.g., switched shunt capacitors)

• Interfaces with utility SCADA

• Accepts commands (e.g., voltage reference setpoint) from utility system operator

Voltage Regulation


31 Wind Overview

3/4/2015

WindCONTROL

QWTG

PWTG

QWTG

PWTG

QWTG

PWTG

QWTG

PWTG

QWTG

PWTG

QWTG

PWTG

QL

QC

HV Bus

LV Bus

Reactive Compensation

(if required)

PWP

QWP

Substation

Point of Interconnection

(POI)

Reactive

Power

Controller

LTC

Plant Level Control System

• Coordinated turbine and plant supervisory control structure

• Voltage, VAR, & PF control

• PF requirements primarily met by WTG reactive capability, but augmented by mechanically switched shunt devices if necessary

• Combined plant response eliminates need for SVC, STATCOM, or other expensive equipment

• Integrated with substation SCADA


“New” Technologies


33 Wind Overview

3/4/2015

Challenges of Scale

Mass outpaces power capacity as wind turbine size increases for a given technology

Wind Turbine Component Overview

Source: AWEA [1]

• Power increase is approximately quadratic (swept area)

• Mass increase is approximately cubic (material volume)


34 Wind Overview

3/4/2015

Steel Tube Tower Design

4 20+m tube tower sections

Transportation challenges due to weight and size (diameter & length)

Tower cost is a significant portion of turbine cost


35 Wind Overview

3/4/2015

Steel Tube Tower Limits

Imagine a 130+ meter tube tower… • For structural integrity, tube thickness

at the bottom must increase • Increased thickness increased weight

… run into shipping constraints • Shipping constraints for tube tower

sections to be shorter • More, thicker tower sections… cost

increases quickly • Shipping cost, assembly cost… not to

mention raw material cost


36 Wind Overview

3/4/2015

Enabler… Space Frame Tower

Weight savings: >25% for 96m tower height

100% on-site assembly

Shipping in standard containers

Large-diameter base increases stiffness


37 Wind Overview

3/4/2015

Tower Assembly

Economics hinges on efficient assembly

Sections built on ground, then stacked x8 (4 for tube) 96m towers

Key Components:

Structural fabric exterior with a tensioning system

Maintenance-free bolts – ~4000 fasteners on space frame tower


Conclusions



3/5/2015

• More capable, coordinated wind plants

• Improved forecasting

• Operational procedures (down-reserves)

• In creasing thermal unit flexibility (ramp rates)

• Driving cost effectiveness through technology

Elements of a Renewable Energy Era



3/5/2015

Thank You Questions?

© 2013 General Electric Company.

Wind Generation Challenges & New Technologieshome.engineering.iastate.edu/~jdm/wesep594/WindOverviewPitch_2015Mar4.pdfof GE Wind Turbine-Generators for Grid Studies,” version 4.5,

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