1

The Roles of Power Electronics in

Renewable Energy Deployment

Eduard Muljadi National Renewable

Energy Laboratory

Panel Presentation

IEEE-PES-ISGT 2014

Washington, DC

February 19-22, 2013

Credit: NREL – pix library

Outline

• Introduction

• Renewable energy resources

• Grid integration

• Power electronics control

• Environment

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Introduction

• Applications mW or MW level Isolated or grid connected

• Variability of the source Temporal (seconds, hour, day, week, season) Spatial (continental, local, plant)

• Large area coverage – Diversity (resource and electrical characteristics)

• Operation Normal/abnormal Balanced/unbalanced

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4

PV Plant (5~50 MW)

Rooftop PV

(1~30 kW)

Mobile 9-kW PV System

Bechler Meadows Ranger Station

Yellowstone National Park

Introduction

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Corp

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23816

Credit: Dennis Schroeder / NREL / 22192.JPG

Credit DOE / FEMP /27638

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California Region

Spring Peaking Summer Peaking

Pea

k

S

hif

t 24-Hour Wind Resource

24-Hour Solar Resource

Wind Resource – Midwest Wind Resource – West Coast

Low Output

8 a.m. – 14 p.m.

High Output

8 a.m. – 12 p.m.

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Offshore Wind Resource

U.S. Wind Resource

Solar Resource

Resources

7

Synchronous Generator (left) vs.

Wound Rotor Induction Generator (right)

What will happen if there is a sudden

disturbance in the transmission

network? To power AC-DC-AC power

converter to operate WTG in

variable speed

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Generator Sgen 4,000-W (Siemens)

1,300 to 2,235 MVA

Wind Turbine

Generator

1-6 MW

Conventional Power Plant vs. Renewable Energy Power Plant

Plant Diversity

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Type 1 Wind Turbine Generator (1% Slip)

Type 3 Wind Turbine Generator ( + 30% Slip) Type 4 Wind Turbine Generator (Full Conversion)

(100% Slip)

Type 2 Wind Turbine Generator (10% Slip)

Examples of Renewable Energy Resources

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Credit: David Hicks / NREL / 18557

Credit: Bill Timmerman/ 08989

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Credit: Dennis Schroeder / NREL / 27806

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Reference: Li, Y.; Yu, Y. H. (2012).

Synthesis of Numerical Methods for

Modeling Wave Energy Converter-Point

Absorbers: Preprint. 36 pp.; NREL Report

No. JA-5000-52115.

Grid Integration

• Interconnection

• Operation

• Standards – Grid codes

• Ancillary services (inertial response, frequency and governor response, reserves)

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15

Transmission to

other utilities

115kV and higher

Power plantUtility Scale Wind Farms (above 10 MW)

Small Wind Farm (less

than 10 MW)

26-115 kV

Single Large Wind

Turbine

Small Wind Turbine

Subtransmission

CustomersDistribution

Customers

Distribution Customers

4-35 kV 120-480 V

Step-up

transformer

Step-up

transformerStep-down

transformer

Step-down

transformer

Step-down

transformer

Distributed Interconnections per

IEEE-1547 Wind Farm Interconnections

Interconnection

Credit: NREL’s TGIG presentation archive.

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Base

Generators Adjustable

Generators

(Conventional

Gen., RE)

Variable

Generators

(RE)

Reserves

Storage

Base

Loads

Adjustable

Loads Variable

Loads Power Losses

Real Power

Freq UP

Freq Down

Line

Capacitance Switched

Capacitors Synchronous

Generators/

Condensers

Static

Compensation

Line

Inductance

Inductive

Load

Induction

Motors/Generators

Reactive Power

Voltage UP

Voltage Down

Real and Reactive Power Balance (To Keep Frequency and Voltage Constant)

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Voltage Ride Through

0

0.2

0.4

0.6

0.8

1

1.2

1.4

-1 0 1 2 3 4

Time (sec)

Vo

lta

ge

(p

.u.)

661

661A

LVRT-WECC Prop.

HVRT-WECC Prop.

Fault Ride-Through Capability

• Wind power plants should be able to stay on-

line under transient faults/disturbances.

• The voltage should tolerate 0 p.u. for 15 ms

(9 cycles).

• Wind power plants should be able to regulate

the power factor between 0.95 leading/lagging.

• Wind power plants should have a SCADA

system to allow remote access and monitoring.

Voltage vs. Maximum Clearing

Time as Described in IEEE 1547

Adaptable to

Regional Code

Power Electronics Control

• Generator level

• Plant level

• Transmission level

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19

Ma

xim

ize

En

erg

y C

ap

ture

Load Control

Gearbox Preservation

Po

wer

Qu

ality

Re

al a

nd

Re

ac

tive

Po

wer

Co

ntr

ol

Short/Long-Term DC

Distributed Storage

Provide Active Damping to

Power System Network

At the

Generator Level

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Ma

xim

ize

En

erg

y C

ap

ture

Po

wer

Qu

ality

Re

al a

nd

Re

ac

tive

Po

wer

Co

ntr

ol

Short/Long-Term DC

Distributed Storage

Provide Active Damping to

Power System Network

At the

Generator Level

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•Many (hundreds) of wind turbines (1 MW to 5 MW each)

•Prime mover: Wind (wind turbine) – Renewable (free, natural, pollution free)

•Controllability: Curtailment

•Predictability: Wind variability based on wind forecasting, influenced more by nature (wind) than humans, based on maximizing energy production (unscheduled operation).

•Located at wind resource; may be far from the load center.

•Generator: Four different types (fixed speed, variable slip, variable speed, full converter) – Non-synchronous generation

•Types 3 and 4: Variable speed with flux-oriented controller (FOC) via power converter. Rotor does not have to rotate synchronously.

At the Plant Level

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A

B

C+

RPMARPMC

A

B

C+

RPMARPMC

5 10 15 20 250

1 106

2 106

Max Cp

8 m/s

9.2 m/s

10.8 m/s

12 m/s pitch=0 deg

12 m/s pitch=4.75 deg

Power vs RPM for different wind speeds

RPM (low speed shaft)

Pow

er

(W) 1 .5 10

6

11 21

A

B

C

D

D’

P

5 10 15 20 250

1 106

2 106

Max Cp

8 m/s

9.2 m/s

10.8 m/s

12 m/s pitch=0 deg

12 m/s pitch=4.75 deg

Power vs RPM for different wind speeds

RPM (low speed shaft)

Pow

er

(W) 1 .5 10

6

11 21

A

B

C

D

D’

P

Trated limit

Type 1 & 2

Type 3 & 4

At the Plant Level

Inertial Response from a Wind Turbine

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(Load

Center)

Wind Power

Generator

Other

Generators

VAR

Compensation

to Help

Regulate

Voltage

Storage

VR d, V

P, Q

d, V

Wind

At the

Transmission Level

Variability

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Thermal Limit

(Thin Wire)

Stability Limit

(High Impedance,

Long Distance,

Weak Grid)

Wind Power

Generator

Wind Power

Generator

Storage

Storage (Load Center)

FACTS

At the

Transmission Level

Transmission Constraints

Environment

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26 G

oo

gle

Ma

p o

f a

win

d p

ow

er

pla

nt,

Te

ha

ch

ap

i, C

A

Credit: Stephen Drouilhet / 05626

Reference: McNiff, B. (2002). Wind Turbine Lightning Protection Project:

1999-2001. 100 pp.; NREL Report No. SR-500-31115.

Reference: NREL Software Aids Offshore Wind Turbine Designs (Fact

Sheet). Innovation Impact: Wind, NREL (National Renewable Energy

Laboratory). (2013). 1 pg.; NREL Report No. FS-6A42-60377.

Conclusions

• Cost reduction in the past 20 years • Many and diverse opportunities for Power Electronics

Generation, transmission, and distribution

• Know the limitations Thermal, magnetic, electric (voltage, current) etc.

• Know the applications Environment: Ocean, land-based, isolated, clusters Opportunities to work in parallel (PV – Wind – CSP)

• Leverage existing and future technologies Other industries (drives, transportation, ship building) Modern technologies (smart control, wireless, condition monitoring,

cyber physical and security, synchrophasor, market driven)

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The information contained in this presentation is subject to a government license.