power converters and control of renewable energy systems

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S:\bj_jn\shw\ICPE2004\slides_all.ppt www.iet.aau.dk

Power Converters and Controlof Renewable Energy Systems

by

Professor Frede BlaabjergAalborg University

Institute of Energy [email protected]

http://www.iet.aau.dk

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Outline

1. Short introduction to Aalborg University2. Development in Energy Technology3. Distributed power sources4. Single-phase PV-inverters5. Control of single-phase PV6. Control of three-phase inverters7. Converter topologies for wind turbines8. Control of wind turbines9. Summary

Power Converters and Controlof Renewable Energy Systems

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13000 students 150mill € 2500 employed 1600 VIP 900 TAP

Aalborg University

Faculty of Engineering and ScienceFinn Kjaersdam

20 Faculty Members10 Research Assistants10 Guest Researchers15 Ph.D. students 2 External professors12 TAP

Institute of Energy TechnologyJohn K. Pedersen

4000 Students 800 VIP 340 TAP

Institute of Electronic SystemsFlemming B. Frederiksen

PowerSystems

PowerElectronicSystems

ElectricalMachines

FluidPower

Systems

FluidMechanics

andCombustion

ThermalEnergy

Systems

Aalborg Universityand

Institute of Energy Technology

• Founded 1974

• Project-oriented and problem-based

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Energy Technology

POWER STATION

SOLAR CELLS

WIND TURBINE

MOTOR

PUMP

ROBOTICS

REFRIGERATOR

TELEVISION

LIGHT

TRANSFORMER

TRANSFORMER

INDUSTRY

=

POWER SUPPLYac dc

TRANSFORMER

COMPEN-SATOR

FACTS

FUELCELLS

FUEL

COMMUNICATION

COMBUSTIONENGINE

SOLARENERGY

TRANSPORT

3 3 3 1-3

3

DCAC

~

Energy System

POWER STATION

SOLAR CELLS

WIND TURBINE

MOTOR

PUMP

ROBOTICS

REFRIGERATOR

TELEVISION

LIGHT

TRANSFORMER

TRANSFORMER

INDUSTRY

=

POWER SUPPLYac dc

TRANSFORMER

COMPEN-SATOR

FACTS

FUELCELLS

FUEL

COMMUNICATION

COMBUSTIONENGINE

SOLARENERGY

TRANSPORT

3 3 3 1-3

3

DCAC

~

DCAC

DCAC

• Only full Energy Institute in Denmark

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Organisation

Strateticcooperation:• EMSD• EDS• CEES• NEED• FACE• WEST• DFV

Lab. Facilities:• Power electronics Systems• Drive Systems Tests• Hydraulic• Power systems• High Voltage• DSpace• Laser Systems• Fuel Cell Systems• Proto Type FacilitiesF

uel

cell

s

Inte

gra

ted

en

erg

y s

yst

em

s

Th

erm

al d

esi

gn

of

ele

c.

de

vic

e

Ind

ust

rial

dri

ve s

yst

em

s

Tra

ctio

n a

nd

au

tom

oti

ve

Po

wer

con

vert

ers

Ad

van

ced

Co

mb

ust

ion

an

d

Mu

ltip

hase

Pro

cess

es

Act

uato

rs a

nd

Mo

tio

n

Co

ntr

ol

••

20 VIP

15 PhD

10 Guest Researchers

10 Research Assistansts

12 TAPInstitute of Energy Technology

Power Systems

Thermal Energysystems

ElectricalMachines

Fluid PowerSystems

PowerElectronicSystems

Fluid Mechanics and

Combustion

Research Programme

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Key Competence

Power Electronic Systems

• Power Electronic Components

• AC/DC – DC/AC Converters

Topologies

• DC/DC Converter Topologies

• AC/AC Converter Topologies

• PFC and Active Filters

• PWM and Resonans Control

• Random Modulation

• Modelling and simulation

• Optimized Design

• FACTS – Converters for Power Systems

• Electrical Drive Systems

• DSP /:-controllers

• Test of Components and Systems

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Collaboration Partners - Industry

Danfoss Drives A/SDanfoss A/S

Grundfos A/S

Axel Åkerman A/S

Elfor

Nesa A/S

VestasWind Systems A/S

Logimatic A/S

Mita-Teknik a/s

Cooper Bussmann

DEFU

B&O

APC

ABB Motors

Migatronic

ThrigeElectric

Electrolux

Sauer Danfoss

Eltra

Nordex

Bonus Energy

PowerLynx

E2

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Basic Structure

10

9

8

7

6

5

4

3

2

1

Master Specialisation

Fundamental

Education

Basic Year

B.Sc.Thesis

Intro semester

The study each semester is based on a combination of courses and team based problem-oriented project work

Problem-based and project-oriented learning

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Implementation of problem-oriented andproject-organised education


Project solving

Literature Lectures Groupstudies

Experiments/Fieldwork/Tutorials

Problemanalysis

Problemsolving Report

PrototypingSimulation

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Distribution between courses and project work (one semester, 30 ETCS)

INT

RO

DU

CT

ION

solvingAnalysis Report

100%

75%

50%

25%

0%5 weeks 10 15 weeks

1. period 2. period 3. period 4. periodStart End

COURSES

Problem

EVALUATION(project/courses)

100%

75%

50%

25%

0%5 10 weeks

1. 2. 3. 4. Start

1 day

20 weeks

• 50% project work

• 25% project-oriented courses

• 25% basic courses

• Full week time table


6

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• Project proposal

• Group room

• Computer / Internet

• Laboratory

• Supervisor

What do the students need


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• Project themes during a complete study in power electronics anddrives

• Every semester one report

Design Oriented Analysis ofElectrical Machines andPower Electronic Systems

M.Sc. Project

Dynamics in electricalMachines and Power Systems

Dynamics

Controlin PowerElectronic Systems

ControlElectroni Systems

Design of ElectronicSystemsSystems

DesignSystem Design

Micro computersMicro-

Analogue andDigital Electronics

Analogue

Models RealityModels Reality

Reality and ModelsReality and Models

Power Control inElectrical Systems

B.Sc. Project

1. semester

2. semester

3. semester

4. semester

5. semester

6. semester

7. semester

8. semester

9. semester

10. semester

Power

Curriculum at Aalborg University

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Curriculum at Aalborg University

Offered courses and project time in the main areasof the power electronics and drives curriculum

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2. Development in Energy Technology

• Early developers shift around $15,000 per capita ($1997 PPP) as less energy-intensive services dominate economic growth

• Signs of saturation beyond $25,000

• Later developers require less energy

Per capita primary energy consumption grows with income in a similar pattern across countries and time

Source: Energy Needs, Choices and Possibilities – Scenarios to 2050 (Shell International 2001)

PPP = Purchasing Power Parity

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1970 1980 1990 2000 2010 20200

1,000

2,000

3,000

4,000

5,000

Commercial

Residential

Industrial

History Projections

Annual Electricity Sales by Sector, 1970-2020 (billion kWh)

WorldWide 13.000 22.500

US ~27% ~22%


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- Energy comsumption increases· More people (born, longer life-time etc.)· More equipment· Higher living standard· More production

- Global Energy Market becomes deregulated(electrical power, natural gas, etc.)

- Oil Prize rises

- New power sources interesting- More efficient use of the existing sources

· From production to end user· Power balance extremely important· New energy storage devices

Therefore

⇒ Power Electronics Technology one important enabling technology

General Trends

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POWER STATIONMOTOR

PUMP

ROBOTICS

REFRIGERATOR

TELEVISION

LIGHT

TRANSFORMER

INDUSTRY

=

POWER SUPPLYac dc

TRANSFORMER

3 3 3 1-3

~

Classical Power System

POWER STATIONMOTOR

PUMP

ROBOTICS

REFRIGERATOR

TELEVISION

LIGHT

TRANSFORMER

INDUSTRY

=

POWER SUPPLYac dc

TRANSFORMER

THERMALHEAT 3 3 3 1-3

~

POWER STATIONPOWER STATION

POWER STATIONPOWER STATION

3

3

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POWER STATION

SOLAR CELLS

WIND TURBINE

MOTOR

PUMP

ROBOTICS

REFRIGERATOR

TELEVISION

LIGHT

TRANSFORMER

TRANSFORMER

INDUSTRY

=

POWER SUPPLYac dc

TRANSFORMER

COMPEN-SATOR

FACTS

FUELCELLS

FUEL

COMBUSTIONENGINE

SOLARENERGY

3 3 3 1- 3

3

DCAC

~

Future Power System

POWER STATION

SOLAR CELLS

WIND TURBINE

MOTOR

PUMP

ROBOTICS

REFRIGERATOR

TELEVISION

LIGHT

TRANSFORMER

TRANSFORMER

INDUSTRY

=

POWER SUPPLYac dc

TRANSFORMER

COMPEN-SATOR

FACTS

FUELCELLS

FUEL

COMBUSTIONENGINE

SOLARENERGY

3 3 3 1- 3

3

DCAC

~

DCAC

DCAC

WIND TURBINEWIND TURBINE

TRANSFORMER

33Demands• Stability• Frequency control• Voltage control• Optimized control• ProtectionFocus in this

presentation

Focus in thispresentation

10

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2. Development in Energy TechnologyDevice development

Silicon carbide FETs

MOSFETs

Insulated-gatebipolar transistors

MOS-gated thyristors

Silicon

Bipolar transistors

1950 r6 0 r70 r80 r90 2000 2004 2010Year

Trench

Coolmos

IGCT

Diode

GTO

• Power devices are still being improved

• Both low-power and high-power devices

(S. Bernet, Berlin)

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0

50

100

150

200

1968

1983

1988

1993

1998

Year

Rel

ativ

e un

it

Components

Functions

0

20

40

60

80

100

120

1968

1988

1998

Year

%

Size (volume)

Weight

System level development

Adjustable Speed Drives (industrial )

• More integration• Lower volume• Higher power density• Lower cost

11

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Wind:

Problems to be solved

p(t) variable p(t) fixedp(t) variable

Energy storage?

Short-term solution - Long-term solution

Power Station

3. Distributed Power Sources

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Wind

Angle of attack:

Trailing edge

wind

Leading edge

Lift force

Drag force

Pitching moment

αα

β

β

φ

Pitch angle:

pCvRP 322

1ρπ=

v

R Ω⋅=λ

12

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Wind power conversion:

Power conversion &power control

Wind powerPower converter

(optional)

Power conversion &power control

Power conversionPower transmission Power transmission

Supply grid

Consumer

Rotor Gearbox (optional) Generator

Electrical Power

Key technology

Wind:

• Electromechanical Energy Conversion• Many configurations exist

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0

250000

500000

750000

1000000

1250000

2000 2005 2010 2015 2020 2025 2030

Year

MW

WF 10, 1999

BTM, 1999

EWEA, rev, 2000

EU, WP, 1997

IEA, 1998

Installed capacity: 2002 32 GW

Windforce 10: 2010 180 GW2020 1200 GW

2

2,5

3

3,5

4

4,5

5

2000 2005 2010 2015 2020Year

USD cent/kWh

Prediction of wind energy (associations)


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22

19891985 1992 1993 1996

∅ 15 m

∅ 30 m

∅ 46 m

∅ 37 m 600 kW

500 kW

300 kW

50 kW

∅ 46 m

∅ 112 m

4.500 kW

1.500 kW

∅ 70 m

200x

Growth of WTG‘s

Track recordin Denmark Development


Bigger and more efficient !

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Photo-voltaic

iSC

iPV

id uPV

IPV

PPV

pMPP

UPVuO C

iSC

(uMPP, iMPP)

Efficiencymaximum 20 %

14

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PV – Installed capacity

Japan and German leading countries(Source: www.iea-pvps.org)

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PV – Price development

• Price is decreasing

15

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Fuel-cell

• PEM• Solid Oxide• Molten Carbonate• Phosphoric Acid

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Fuel-cell

Characteristic (ideally and non-ideally)Steady progress but no long track-recordMany potential applications (micro-power to power-station)

16

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4. Single-phase PV-inverters

PVArray

PV Inverter& Filter Grid

Controlreference

Basic control

• Maximize power from the PV array/Sun• Interconnect to the grid

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Central inverter String inverter Module integratedinverter

PV - configurations

• Power level dependent• Prize dependent

17

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PVInverters

with DC-DCconverter

without DC-DCconverter

with isolation

without isolation

on the LF side

on the HF side

with isolation

without isolation

Characteristics of topologies

• Galvanic isolation necessary some places• LF/HF transformer (cost-volume issue)• Without boost / with boost of voltage

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DC

ACGridPV

Array

DC

DC

DC

ACGridPV

Array

DC

AC

AC

DC

PV inverter with HF transformer in the dc -dc converter

• Isolated push-pull boost converter

• PWM VSI

18

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DC

DC

DC

ACGridPV

Array

• Boost converter

• Full-bridge inverter (PWM VSI)

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DC

ACGridPV

Array

• Full -bridge inverter (PWM VSI)• Grid-side transformer• Volume high

19

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DC

ACGrid

PVArray

• PWM IGBT inverters (VSI) • Multilevel inverter

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5. Control of single-phase PV

ug

SYSTEM CONTROL

Qref P ref

Structure

• Maximum Power Point Tracking (MPPT)• Anti – Islanding detection• Low current THD• Active part in grid control

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Duty-cycle control

•Simpel (no current sensor)

•Difficult to protect converter

Compensator Pulse-widthmodulator

Converter

Sensor gain

vref

vFC(t)

iload

(t)

d(t)+

-

vDC

(t)Errorsignal

Controlsignal

Referenceinput

CompensatorComparator and

controller

Converter

Sensor gain

vref

vFC

(t)

iload

(t)

d(t)+

-

v DC(t)

Errorsignal

Controlsignal

Referenceinput

iswitch (t)

iswitch (t)iswitch_ref(t)

Current control

•Extra current sensor

•Better dynamics and protection

DC-DC converter

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The current loop with PR controller and HC

ii*

ii

GPI(s)

Gd(s)

Gf(s) ii ui

*

ug

ii*

ii

Gc(s)

Gh(s)

Gd(s)

Gf(s) ii ui

*

The current loop with PI controller

( ) IPI P

KG s Ks

= + 2 2( )c P Io

sG s K Ks ω

= ++

( )223,5,7

( )h Ihh o

sG s Ks hω=

=+

∑

• Proportional Resonant (PR) controller uses GI for integration• No grid voltage feed-forward is required when using PR• Additional GIs used for selective harmonic compensation (HC)

Dc-ac converter – current-controlled H-bridge with LCL filter

( )( )

2 2

2 2

( ) 1( )

( )L Ci

fi i res

s zi sG s

u s L s s ω

+= =

+

12LC g fz L C

− =

( ) 22 i g L C

resi

L L z

Lω

+ ⋅=

21

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2 2( )GI I

o

sG s K

s ω=

+

• Double integrator • Infinite gain at resonance frequency ωo

• High attenuation outside ωo

• Notch filter à selective harmonic compensation• Zero stationary error• High disturbance rejection

0

5 0

1 0 0

1 5 0

2 0 0

2 5 0

3 0 0

Mag

nitu

de (

dB)

102

103

-90

-45

0

4 5

9 0

Pha

se (d

eg)

Ki=10Ki=1Ki=100

Ki=10Ki=1Ki=100

Bode Diagram

Frequency ( rad/sec)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

time [sec]

GI response

inout

Generalized integrators (GI)

42

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Disturbance rejection (current error ratio disturbance) of the P R+HC, PR and P

-150

-100

-50

0

-540

-450

-360

-270

PR+HCPIP

( )* 0

( )( )( ) 1 ( ) ( ) ( ) ( )

i

f

g c c d fi

G ssu s G s G s G s G sε

=

=+ + ⋅ ⋅

• PR exhibit higher attenuation (125 dB) than PI (8 dB)• PI rejection capability at 5th and 7th harmonic is comparable with

that one of a simple proportional controller, the integral action being irrelevant.

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Grid voltage and current with PI controller.

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-25

-20

-15

-10

-5

0

5

10

15

20

25

time[sec]

Ig (exp) [5A/div]Ug (exp) [100/div]

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-25

-20

-15

-10

-5

0

5

10

15

20

25

time[sec]


0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-25

-20

-15

-10

-5

0

5

10

15

20

25

time[sec]


Grid voltage and current with PR controller.

Grid voltage and current with PR + HC controller.

THD = 12% THD=8% THD=5%

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The measured grid current harmonic spectrum for PI, PR and PR+HC control strategies and the limits for IEEE 929

5 0 1 5 0 2 5 0 350 4 5 0 5 5 0 6500

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Cur

rent

har

mon

ic [A

]

F r equency [Hz ]

P I - [% ]THD=12 .665P + R E S - [ % ] T H D = 8 . 1 6 5 5P + R E S + H C - [ % ] T H D = 5 . 4 0 2 8I E E E 9 2 9 - [ % ] T H D = 5

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Grid impedance measurement embedded on the inverter control using harmonic injection

Anti-islanding – Grid impedance measurement

Grid impedance measurement using external device

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Goals

-Developing a measurement technique for estimating the grid impedance value.

-Embedding the technique into an existing single-phase Photo-Voltaic inverter.

-Testing the method against the ENS requirements.

ENS Requirements (Mains monitoring unit with allocated Switching Devices)

-Detection of the grid impedance change of more then 0.5 Ω.

-Isolation of the PV-inverter from the grid within 5 s .

-Existence of two independent monitoring-units for redundancy.

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Gri

d co

nnec

tion

Control

75 Hz injection

PWM

Impedance estimation

Inverter DC-DC converter dc-link

Software development and download

PV cells

DSP board

Trip

ping

&

Pr

otec

tions

Voltage

Current

LCD Display

System diagram of the PV-inverter with implementation of the grid impedance estimation.

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Principle of Operation-The PV-inverter injects a harmonic disturbance

-The duration of the disturbance is limited to several fundamental periods

-The grid response is recorded by the same sensors used for the c ontrol

loop

-By knowing the voltage and the current, the grid impedance value is

derived as:

where: Rg and Lg denote the resistive and inductive part of the grid,

ω h and ϕh represent the frequency and the phase angle of the injected harmonic,

N is the number of samples per fundamental period,

v(n) is the input signal (voltage or current) at the n sample,

Λh is the complex vector of the hth harmonic, having the real and the imaginary parts λhrand λh i

)()()(

hIhVhZ =

ghg LjRhZ ⋅⋅+= ω)( hihrh

N

n

N

n

h

j

Nnh

nvjN

nhnv

λλ

ππ

⋅+=Λ

⋅⋅

⋅⋅−

⋅⋅

⋅=Λ ∑∑−

=

−

=

1

0

1

0

2sin)(

2cos)(

25

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HarmonicInjection

Grid

Anti-aliasing Sample&Hold A / D Windowing Pre-processing DFT

Post-processing

Anti-aliasing Sample&Hold A / D Windowing Pre-processing DFT

Voltage Signal

Current Signal

U Z = —

I

ImpedanceTripping

&Display

Internal Logic

Harmonic Current

Harmonic Voltage

Principle of harmonic detection and calculation of the grid impedance .


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Non-continuous injection of the harmonic into the grid.

Final settings used in the PV implementation.


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Measured response detecting a 0.5 Ω resistive increase of impedance.

Experimental setup for testinga grid impedance change.

Oscilloscope Synchronization


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6. Control of three-phase inverters

- More high distributed power applications

- Common issues as an active filter inverter· grid interaction· need to minimise switching ripple impact

⇒ The control of a distributed inverter has an advantage compared to an active filter (easier dc-link control) but has also to deal with grid interaction which may be more complex comparedto motor interaction

- Common issues with ASD· Less responsibility on the dc-voltage control· Manage the parallel connection of several units

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6. Control of three-phase invertersL-filter grid connection LCL-filter grid connection

( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )

1 12

1 12

dq d d d o

qd q q q o

di ti t Ri t e t p t v t

dt Ldi t

i t Ri t e t p t v tdt L

ω

ω

− = − − +

+ = − − +

1

1 1

11 11 1

1 1

2 2

22 2

2 2

2

2 2

10 0 0

10 0 0

1 10 0 0

1 10 0 0

10 0 0

10 0 0

f f

f f

d d

q q

C d C df f

C q C q

f fd d

q q

RL L

Ri iL Li i

v vC Cdv vdt

C Ci iRi i

L LR

L L

ω

ω

ω

ω

ω

ω

− −

− − − − = − − − − − −

1

1

2

2

1 0 000 0

1 0 000 0

0 0 10

0 00 0 1

00 0

d d

q q

L

e vLe v

L

L

− − + +

In a dq-frame rotating at the line frequency

F r e q u e n c y ( H z )

1 0 2 1 0 3 1 0 4- 1 0 0

- 8 0

- 6 0

- 4 0

- 2 0

0

2 0F r o m : I n p u t P o i n t T o : O u t p u t P o i n t

F r e q u e n c y ( H z )

Mag

nitu

de (

dB)

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Cascade control

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Current control in a rotating frame

The current control can be performed

on the grid current or on the

converter current

The voltage used for the dq-frame orientation could be measured after a dominant reactance

d

q

β

α

)(te

)(ti

qi di

ω

0( )

0

ip

PI dqi

p

KKsD s

KKs

+ =

+

56

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Grid voltage Harmonic compensators

( )223,5,7 0

( )R ihh

sG s k

s hαβ

ω=

=+ ⋅

∑

2 20

2 20

0

( )0

ip

PRi

p

K sK

sD s

K sK

s

αβω

ω

+ + = +

+

Current control in a stationary frame

the harmonics to be compensated should be within the bandwidth of the current controller otherwise stability problems may arise

In both the cases (stationary and rotating) the stability using an LCL-filter should be verified

( )( )

2 2

2 22

( ) 1( )

( )LC

res

s zi sG s

v s L s s ω

+= =

+

29

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To stabilize the current loop against LCL-filter resonance:

- passive damping (resistor -> losses)

- active damping:

- multi-loop (use of more sensors)

- notch filter in cascade to the main controller

2 2

2 2( ) oAD

o

z zG z

z p −

= −

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Direct power control

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Results (grid voltage background distortion)

Effect of the grid voltage background distortion on the currents

Use of harmonic compensators

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Results (LCL-filter resonance)

Use of active

damping

No active

damping

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Other issues:

- reduction of the number of sensors:

- voltage sensorless (DPC, VOC with PLL as an observer)

- current sensorless (overcurrent protection ?)

- non-ideal conditions:

- measurement of the grid voltage after a dominant reactance

- grid unbalance

- EMC issues:

- differential mode: IEC limitation only for < 2 kHz > 150 kHz

- common mode: use of extra filter or modify LCL-filter

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7. Converter topologies for wind turbines

Basic topology for wind turbine

• Fixed speed with capacitor bank

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Mechan ica l Ene rgy Sou rceVar iab le Speed

D i r e c t G e a r b o x

Mult ipolar Synch ronous& Nove l Mach ines

Conven t iona lSynchronous Mach ines

Induct ion Mach ines

Wound Ro to r( f ie ld contro l )

L a r g e P Econver te r

Pe rmanen tM a g n e t


C a g eR o t o r M / C


W o u n d R o t o r o rBrushless DF

Wound

Electr ical Energy SourceF ixed Frequency o r DC

R o t o r

Stator

Machinet ype

Transmiss ion

Wound Wound W o u n d

G r i dconnect ion

O u t p u t

S m a l l P Econver te r

Input

P o w e rconvers ion

Heat lossdump load

Variable speed

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ØLimited speed range (-20% to +20%, typically)ØSmall -scale power converter (Less power losses, price )ØComplete control of active Pref and reactive power Q ref

ØNeed for slip-ringsØNeed for gear

Gear

Doubly-fedinduction generator

Pitch

Grid

V

DC

AC

AC

DC

PrefQref

Doubly-fed induction generator - wounded rotor

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ØFull speed rangeØNo brushes on the generatorØComplete control of active og reactive powerØProven technologyØFull-scale power converterØNeed for a gear

Gear

Inductiongenerator

Pitch

GridDC

AC

AC

DC

Pref Qref

VI

Induction generator - Squirrel cage rotor

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ØFull speed rangeØPossible to avoid gear (multi -pole generator)ØComplete control of active and reactive powerØBrushless (reduced maintenance )ØNo power converter for field (higher efficiency)ØFull scale power converterØMulti -pole generator big and heavyØPermanent magnets needed

Synchronous generator - Permanent magnets

PM-synchronousGeneratorMulti-pole

Pitch

GridDC

AC

AC

DC

Pref Qref

IX

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• Doubly-fed induction generator system• Horns Reef, Denmark

160 MW Windfarm (in operation)

Group 1 out of 5

Grid

Group 5 out of 5

....................

Power station

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Why offshore?

Advantages:· Better wind resources· Low roughness· Many unexploited sites· No people around to be bothered· Possibility for large projects near

loadcenters· No physical limits for size and

weight = great future!

Disadvantages:· Installation and maintenance are

more complicated and expensive· More safety measures to be taken

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Why offshore?

Horns Reef: 80 turbines, V80-2.0 MW, 160 MW installed in total.Water depth: 7-13 m, waves 8 m, 560 x 560m btw. turbines, 20 sq km 600 GWh (expected) ~ 2% of Denmark’s annual electricity consumption

Distance to Blåvandshuk = 14 km

Distance to Esbjerg harbour = 40 km

Horns Reef

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• Two-speed windturbine system• Nysted, Denmark

160 MW Windfarm (in operation)

G r o u p 1

....................

Group4

G r o u p 5

....................

G r o u p 8

........................................

Power station

36

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8. Control of wind turbines

Doubly-fed generator system

DFIG control

Power controller Speed controller Wind turbine control

Rotor side converter controller Grid side

converter controller

Measurement grid point M

θ

AC DC AC DC

meas gen ω

PWM PWM

N T

ref conv grid P ,

ref conv grid Q ,

meas d c U

meas grid P

meas grid P

meas grid Q

meas a c I

ref dc U

ref rated grid P ,

cross - coupling Grid

operators control system

meas rotor I

DFIG control

Power controller Power controller Speed controller Speed controller Wind turbine control

Rotor side converter controller Rotor side converter controller Grid side

converter controller

Measurement grid point M

θ

AC DC AC DC

meas gen ω

PWM

N T

ref conv grid P ,

ref conv grid Q ,

meas d c U

meas grid P

meas grid P

meas grid Q m

a c I

ref dc U

ref rated grid P ,

cross - coupling Grid

operators control system

mea s rotor I

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8. Control of wind turbines

Multi-pole generator system

vDC

vDC

Generatorrectifier

Gridinverter Inductance

Gridcontrol

Powercontrol

PMG

Grid

refQrefP

vga, gb, gc

iga, gb, gc

v vi i

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9. Summary

• Renewable energy is on its move• Power electronics important enabling technology• Basic power conversion• Advanced control enters into the systems• Both internal and external control (system)• New control methods appear to improve performance• New methods are still necessary• Monitoring and advanced diagnosis will also be integrated

power converters and control of renewable energy systems

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