Introduction to Microgrids - esci-ksp.orgesci-ksp.org/wp/wp-content/uploads/2012/05/Day2_8...Microgrids.pdf · Microgrid operation Islanded operation Voltage and frequency management

臺灣 2011年8月24~25日

18-Aug-11 1

APEC 2011Advanced Control Architectures for

Intelligent Microgrids

Josep M. Guerrero, Prof.

Institute of Energy Technology, Aalborg University

[email protected]

Outline

1 Microgrids systems

2 Control of VSIs for microgrids

3 Droop control and virtual impedance concept

4 Hierarchical control of microgrids

5 Power quality in microgrids

6 DC microgrids

Centralized vs Distribuited Power Systems

General advantages of the DPS:

• Redundancy

• Modularity

• Fault tolerance

• Efficiency

• Reliability

• Easy maintenance

• Smaller size

• Lower design cost

Microgrid operation

Microgrid operation modes:• Grid connected

• Islanded

Typical structure of a flexible microgrid

. . . .

PV

panel system

PCC

UPS

Common

AC bus

Distributed loads

Intelligent

Bypass

Switch

(IBS)

Wind turbine

Inverters

Renewableenergy sources

Utility Grid

18-Aug-11 4

Microgrid operation modes• Operation modes and transfers of the flexible microgrid and STS

grid status supervisory

• Virtual inertias are often implemented through control loops known as droop method.

• Intelligent microgrids are required to integrate DG, DS, and dispersed loads into the future smart grid.

• Microgrids should be able to operate autonomously but also interact with the main grid.

• CSI units are normally used for PV or WT systems that require maximum power point tracker algorithms.

• VSI units are used for storage energy systems to support the voltage and frequency of the microgrid in island mode.

Microgrid operation

18-Aug-11 5

Microgrid operation

18-Aug-11 6

Islanded / Grid-connected operation• Operation modes and transfers of the flexible microgrid and

Static Transfer Switch (STS)

From grid-connected an islanded modes, it is necessary a smooth transition.For both modes, the converters could work as voltage sources!

STS = OFF

STS = ON

Grid

Connected

E= Vg

w=wg

E= V*

w=w*

P= P* ; Q=Q*

Import/export

P/Q

Islanding

Operation

Synchronization

Current/Voltage

Source

Voltage

Source

Microgrid operation

Islanded operation• Preplanned islanded operation: If any events in the main grid are

presented, such as long-time voltage dips or general faults, among others, islanded operation must be started.

• Nonplanned islanded operation: If there is a blackout due to a disconnection of the main grid, the microgrid should be able to detect this fact by using proper algorithms.

18-Aug-11 7

Microgrid operation

Islanded operation• Voltage and frequency management: The system acts like a

voltage source, controlling power flow through voltage and frequency control loops adjusted and regulated as reference within acceptable limits.

• Supply and demand balancing: In grid-connected mode, the frequency of the DG units is fixed by the grid. Changing the setting frequency, new active power set points that will change the power angle between the main grid and the microgrid can be obtained.

• Power quality: The power quality can be established in two levels. The first is reactive power compensation and harmonic current sharing inside the microgrid, and the second level is the reactive power and harmonic compensation at the PCC; thus, the microgridcan support the power quality of the main grid.

18-Aug-11 8

Microgrid Configurations

• AC-DC Hybrid MicrogridHierarchy of loads

Source: SMA

18-Aug-11 9

Microgrid Configurations

Connection interface (CI)

18-Aug-11 10

11

Inner control loops

To Load/grid

VSI control strategy

av

bv

cv

lbi

lci

bC cC

Ccv

Cbv

Cav

PWM

abc

laiaL

bL

cL

obL

ocL

aC

n

li Cv

Current P + Resonant Controller

abc

Voltage P + Resonant Controller

refv

Inner Loops

obi

Three Phase

Reference

Generator

oci

oaioaL

dcv

abc

*i

pVk

2 22iV

c os

k s

s w w

pIk

22

5,7,11... 2 o

niHh

h c h

k s

s s ww=

2 22iI

c os

k s

s w w

22

5,7,11... 2 o

nvHh

h c h

k s

s s ww=

abc

x

Power stage and control of a 3 phase VSI with LCL filter

1 1/ 2 1/ 22 / 3· ·

0 3 / 2 3 / 2

a

b

c

vv

vv

v

=

Alpha-beta transformation

12

Block diagram of the closed-loop VSI.

2 2

1( ) ( )

( ) ( ) 1 ( ) ( ) 1

v i PWMc ref o

v i PWM v i PWM

G s G s G CsV V iLCs Cs G s G s G LCs Cs G s G s G

=

1

sL

abcv

PWMG oi

li

ci1

sC

PWM inverter L-C Filter P + Resonant Controllers

cvref

v

dcv

( )vG s ( )iG s

*i

22 2 2

5,7,11

( )v pV

o

rV hV

ho

G s kk sk s

s s hw w=

=

22 2 25,7,11

( )i pI

o

hIrI

ho

G s kk sk s

s s hw w=

=

1

1 1.5PWM

s

GT

=

Inner control loops

Voltage tracking Output impedance

Voltage control loop Current control loop

Computation delay

13

Bode diagram of the tracking voltage transfer function Gv(s)

Inner control loops

Objective: closed-loop band pass filter characteristics with 0dB, 0º

P+R

P+R+H

14

Inner contro loops

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-400

-200

0

200

400

Time [s]

Vo

lta

ge

[V

]

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-10

-5

0

5

10

Time [s]

Inv

ert

er

Ou

tpu

t C

urr

en

t [I

]

Results

abc-Voltages

abc-Currents

Control of parallel converters

Master-slave control

• Voltage source: grid forming units

• Current source: MPPT units. WT and PV

In this system is not necessary current sharing!

dcv av

bv

cv

Lbi

Lci

aCbC cC

n

Ccv

Cbv

Cav

abc

Li Cv

SVM

Voltage ResonantController

Current Resonant Controller

abc

Lai

cL

bL

aLoaL

obL

ocL

2oaL

2obL

2ocL

obi

oci

oai

dcv

2av

2bv

2cv

2aC 2bC 2cC

n

2Cbv

2Cav2L bi

2L ci

2L ai 2aL

2bL

2cL

2Ccv

2obi

2oci

2oai

Load

SVM

abc

Three Phase Reference

Generator

abc

abc


MPPTMPPT

Energy Storage System PV/WT

18-Aug-11 15

Control of parallel converters

Woo-Cheol Lee “A Master and Slave Control Strategy for Parallel Operation of Three-Phase UPS Systems with Different Ratings”

. . . Load

VoltageSource

(Master)

Current ControlledSources (Slave)

Im IoIsnIs2Is1

Master-slave control

18-Aug-11 16

Droop control for AC MGs

Droop control of AC systems

sinVE

PX

=Active power Reactive power

mP= *www*

P

w

w

Pmax

Frequency droop

*E E nQ= E*

Q

E

Qmax

Amplitude droop

E 11 E 22V0o

DG Inverter 1 Load

112

DG Inverter 2

1X 2X

1i 2i

18-Aug-11 17


P. Kundur

• Synchronous generator

Equation of motion:

Inertia constant:

m e

dJ T T

dt

w=

stored energy E

H srating power P

= = with 21

2E Jw=

rw1

2Hs

Tm

eT

aT

eT

rw

aT

Tm

s

H

Laplace Operator

Mechanical torque (pu)

Electrical torque(pu)

Accelerating torque (pu)

Inertia constant (MW-Sec/MVA)

Rotor speed deviation (pu)

Inertias in power systems

18-Aug-11 18


• Synchronous generator transient response

oP

P

POWER

FREQUENCY

f60 zH

TIME - SECONDS

Inertias in power system

There is a dynamic and a static droop. The static droop coeficient is P/f.

18-Aug-11 19

Virtual synchronous generators

• Inverters that mimic synchronous converters

• Kawamura’s approach (2005)

High Reliability and High Performance Parallel-Connected UPS System with Independent ControlEduardo Kazuhide Sato

18-Aug-11 20

Virtual synchronous generators

European Project VSYNC: http://www.vsync.eu

Inertias means not only load-dependent frequency (droops),but also local storage energy system.

18-Aug-11 21



• Trade-off power sharing / amplitude - frequency regulation

Phase droops are not feasible since the initial phase of each inverter is different!

18-Aug-11 22

wo1

wo2

PP’1 P’2P1 P2

m

m’

P

P’w’

w

w

wo

w’

w’’

* mPw w=

2%maxw =



P

Q

GenerationP>0

StorageP<0

Capacitive loadQ > 0

Inductive loadQ < 0

18-Aug-11 23


• Study of P/Q flow in function of the output impedance

Generalized droop control

The R – V virtual resistance in a DC microgrid can be see as Q – V droop in an inductiveAC microgrid. The w – P droop is added to synchronize the system.

Z

E

VSI S P jQ=

0ºV

2

2

cos cos

sin sin

EVP

Z

EVQ

Z

V

Z

V

Z

=

=

By using the Park transformation, the droop method functions become

18-Aug-11 24

Virtual Impedance

• Droop control in AC

Objective: fix the output impedance

Virtual Impedance concept

oI

( )oZ s ( )DZ s

oV

( ) refG s v

ov

oi

P/Q

Calculation and droop

control

PWM +UPS

Inverter

Current

loop

Voltage

loop

ZD(s)

Reference generator

Programable output impedance

refv

Inner loops

E

w

*

ov

P/Q control loops

18-Aug-11 25

Virtual Impedance

p

D

EI

L

w

STTt

DfDoDfD eLLLL/**** )(

=

Initial PLL error

Output impedance

t

( )oZ tiZ

fZ

Z

E

VSI S P jQ=

0ºV

I

Soft-start operation

The virtual output impedance is a control variable.Increasing the output impedance can reduce the initial current peak at the connection

18-Aug-11 26

Virtual Impedance

Hot-swap capability

This capability allow us to connect DGs without stop the microgrid, formantainance reasons.

4 DG units microgrid

Virtual impedance

Output currentsBefore the connection, a PLL have to synchronize the DG with the MG.A the connection the virtual impedance is high to reduce the initial current peak.

18-Aug-11 27

Low voltage ride-though

Reactive power control of a grid-connected DG.

Low voltage ride-through

Trade-off during voltage dips: 1) voltage follower (Q=0) 2) stiff voltage source (Q high)

18-Aug-11 28

E

E*E

nomQQ

nomQ

*E E nQ=

Capacitive load Inductive loadLRE

GQ

GL

0ºgV




DG current

Grid current

Load current

Voltage dip

During the voltage grid, the converter injects reactive current (90º)

18-Aug-11 29




Active power remains constant (to the load). Reactive power is injected to mantain thevoltage inside the droop characteristic.

18-Aug-11 30

Hierarchical control

Hierarchical

Control

Principle

Enterprise Software Solution for Power Systems

Primary Control

TertiaryControl

Secondary Control BW

Import/export power

Restoration/Syncro.

Inner loops

(droop,softstart)

18-Aug-11 31


Droop control for three phase VSIs

** ( )P

rest syncG s P P

s

w w

=

P

QE

Three Phase

Reference Generator

()

c o c ov i v i

c o c ov i v i 1°LPF

Cv

oi

Power Calculation

*

*E

Droop Control

( )QG s

( )P sG 1°LPF

*

sec

* ( )QG Es QE E Q =

*P

*Q

Power loops

secw1 s

refv

18-Aug-11 32


Virtual impedance control for three phase VSIs

aC

oi oi

PWM

abc

C

Cv

vR vLw

vRvLw

refv Virtual Impedance loop

vv

Current P + Resonant Controller

Voltage P + Resonant Controller

oabci

Inner loops

L

labcioL

1VSI

V v o v o

V v o v o

V R i L i

V R i L i

w

w

=

=

2

1 ( ) ( ) ( ) ( )( )

( ) ( ) ( ) 1

v i PWM D

o o

v i PWM

G s G s G s Z sCsZ s L s

LCs Cs G s G s G s

=

( ) refG s voI

( )oZ s ( )DZ s

vV

( ) ( ) ( )out ref o ov s G s v Z s i=

18-Aug-11 33

Islanding microgrids• Grid-connected microgrids operate synchronized with the grid

• Islanded microgrids:

Frequency and amplitudes are load-dependent

• Secondary control can contribute to:

Frequency restoration

Amplitude regulation

Power quality (harmonics and unbalance compensation)

Energy management system can be used to:

• Load shedding

• Regulation of the generator’s consumption

Secondary Control

18-Aug-11 34

Secondary Control in Electric Power Systems

PowerController

Load

DG3

PowerController

Load

DG2 PowerController

Load

DG1

Grid

This area consists of DG’s with thedroop control. In island mode thefrequency can droop down!

18-Aug-11 35

Secondary Control in Electric Power Systems

Source: UCTE. A1 – Appendix 1: Load-Frequency Control and Performance

18-Aug-11 36

Secondary Control for Microgrids

Secondary control action

Primary control ensures P sharing by drooping the frequency

Secondary control:• Restore the nominal frequency• Cannot work localy, it needs to be centralized.

f

0f

refPscheduledP

)a

maxP

No secondary control

Primaryresponse

P

Permanentdrop in

frequencyPermanentincrease in generation

f

0f

refPscheduledP

)b

maxP

Using secondary control

Primaryresponse

P

Temporarydrop in

frequency Permanentincrease in generation

Secondaryresponse

18-Aug-11 37

Secondary Control for Microgrids

Secondary control Implementation

Low bandwidth

communications

Primary control

P/Q Droopcontrol

Secondary control

Frequency &Voltage

restoration loop

wMG

wMG

Gw(s)

EMG

E*MG

GE(s)

vref

ZD(s)

Virtual impedance

dE

dwM

i

c

r

o

g

r

i

d

wMG / EMG

measurements

+

+

_

_

ov

oi

Current

loop

Voltage

loop

Inner loops

PWM

+UPS

Inverter_

Primary control

P/Q Droopcontrol

vref

ZD(s)

Virtual impedance

ov

oi

Current

loop

Voltage

loop

Inner loops

PWM

+UPS

Inverter_

+

ws

Secondary control is located in the Microgrid Central Controller measure frequency and voltage. The output of the control is send through communications to adjust the referenceof the local primary controllers (droops).

18-Aug-11 38

Microgrid synchronization with the grid

Synchronization is not necessary to be fast. Slow (to avoid unstability problems) butwell accurate (allowing seamless transition to grid-connected mode).

18-Aug-11 39

Tertiary Control

Tertiary control for AC microgrids• Terciary control and synchronization control loops implementation

Secondary

control

Tertiary control

+_

+_

Microgrid

PIQ

PIP

90º

PI

LPF

*

MGE*

iE

*

iw

,g gP Q

PCCbypass

GQ

GP*

GP

GQ

*

GQ

maxw

minwmaxE

minE

grid connected

Island

Island

grid connected

.Synchron

loopFreezing

sw

P/Q

Grid

calculation

Distributed synchronization loop

In grid connected modeP and Q from the MG to

the grid can becontrolled by tertiary

control.

In islandedmode secondarycontrol fixes frequency and amplitude of the MG.

*

MGw

18-Aug-11 40

Tertiary Control

Tertiary control for AC microgrids

• Low voltage ride-trough of the Microgrid

Freezing or disconnecting the integral term of the E –Q tertiary control.

The Microgrid will work like a STATCOM

MicrogridQ

V

18-Aug-11 41

Microgrid example

Islanding detection

Islanding detection

Frequencydeviation

STS open (protection)Q integratorsdisconnected

Non-planningIslanding

18-Aug-11 42

Smart-Grids

Microgrids interconnectionStiff grid

Tertiary SGSecondary SG

Primary SG/Tertiary ClusterSecondary Cluster

Primary ClusterTertiary

Secondary

DG#1

DG#2

Primary

Primary

MG#1

PCC#1

DG#3

DG#4

PrimaryMG#2

PCC#2

Primary

Cluster I Cluster II

18-Aug-11 43

Power Quality in Microgrids

Advanced Active Filtering in a Single Phase High Frequency AC Microgrid - Sudipta Chakraborty

Microgrids

Fuel cell

PV

Battery

SourceBus

PWM PWM

UPQC Controller

UPQC

Non-linearLoad

Linear Load

Load bus

PWM PWM

UPLC Controller

UPLC

Utility

UtilityInvertersand Loads

UtilityConnection

Bus

1cV

V

IntermediateSupply Bus hfV

Loadi

1ci

1ci1cV

hfi

hfVhfi

Loadi

LoadV

CV

ci

cVci

VLi

*P*Q

sV

18-Aug-11 44

Droop control allows P and Q sharing, averaged over the fundamental frequency.

It is not able to guarantee harmonic current sharing!

P

Q

CalculationVref

w

E

PWMInner loops

CL

vo

Inverter

DSP

iovo

A/D

PLL

Pow

er

calc

ula

tion


Harmonic current sharing

18-Aug-11 45


Harmonics current sharing• Control objective: Harmonic current sharing

proportional to the nominal DG power.

• Trade off: harmonic current sharing/voltage THD

Source: Y. E. Wu

18-Aug-11 46


Harmonics current sharing

• For Zline1 # Zline2, harmonic current sharing is not possible

• Harmonic virtual impedance can enhance sharing

Zh = Vh/Ih

• Trade off VTHD and harmonic current sharing.

E 11E 22

V0o

i2DG #1

112

i2

Zo2

DG #2

Zo1

LoadZ

1LineZ 2LineZ

1hI 2hI

18-Aug-11 47

Gp(s)

P&Qcalculation

P1

Q1

Gq(s)

VoltageReferenceE·sin(wt)

w

E

E*

Voltage Loop

vo*

Inverter

Inverter #i

+

_

w*+_

Current Loop + PWM

+_

Zo1

v

i

Virtual output impedance loop

BPFHarmonic current sharing loop


Selective harmonic selection: fundamental and each of the harmonics can have different output impedance.

Droop control

Virtual Output Impedance with harmonic current sharing loop

18-Aug-11 48


Frequency (rad/sec)

Ph

ase (

de

g);

Ma

gn

itu

de (

dB

)

Bode Diagrams

-80

-60

-40

-20

0

20

Virtual output impedance

-100

-50

0

50

100

150

200

1

3 5 7 9 11

103

10410

2

22 2

2)(

ii

ii

sks

sksH

w=


18-Aug-11 49



Parallel Control of the UPS Inverters With Frequency-dependent Droop SchemeS . J. Chiang and J. M. Chang

Whole frequency range

Fundamental

Harmonics

18-Aug-11 50


Droop method with virtual output impedance and selective harmonic

DSP implementation is appropriate for the multi-loop droop framework18-Aug-11 51

(a) Nonlinear load, Y: 2 A/div, X: 5 ms/div; (b) Resistive // nonlineal load, Y: 10 A/div, X: 5 ms/div.

(a) (b)


Droop method for resistive output impedance

18-Aug-11 52


Voltage harmonic reduction by using current harmonics injection

E 1111 Zo1

1LineZ

1hI

PCCV

VgZg

GRIDDG/MG

18-Aug-11 53


Decentralized voltage harmonic reduction in an islanded microgrid

dcv

av

bv

cv

lbi

lci

aC bC cC

n

Ccv

Cbv

Cav

abc

abc

i i v v oi oi

SVM



abc

Virtual Impedance

Loop

abc

lai

Bypass Switch

cL

bL

aLoaL

obL

ocL

gaL

gbL

gcL

*sync m Pww w =

w*

Frequency droop

P

*E E nQ= E*

Amplitude droop

P

abc

abc

abc

obi

oci

oai

P Q

1w

E

1w

Three phase

Reference GeneratorE sin (wt)

syncw

cv oi

dcv

2av

2bv

2cv

2aC 2bC 2cC

n

2Cbv

2Cav

2aL

2bL

2cL

2Ccv

PWM

abcInverter 2 Control System

abc abc

2li

abc

2Cv 2oi

Nonlinear

Load

PLL

2lai

2lbi

2lci

Power Calculation

HarmonicCompensation

2oai

2obi

2oci

D

Inverter 1 Control System

*

HCI

235uF84uH

100W

18-Aug-11 54


Decentralized voltage harmonic reduction in an islanded microgrid

Before Compensation After Compensation

THD% 5th % 7th % THD% 5th % 7th %

Voltage DG1 3.8 2.9 2.0 1.2 0.6 0.5

DG2 2.9 2.1 1.5 1.1 0.5 0.4

Load 5.3 4.2 2.8 3.2 2.3 2.0

Current DG1 58.6 53.7 22.9 87.6 75.2 44.1

DG2 45.8 41.5 18.8 44.5 38.1 22.5

Load 52.2 45.6 20.9 66.1 56.7 33.3

18-Aug-11 55


Secondary control for voltage harmonic distribution

in islanded microgrids

AC Bus

DG#1

5dq

DG#2

5dq

PLL dq

5w

*

5dqv

5th

Deadband

5th Harmonic

( )SHG s

Harmonic Controller

Secondary Control

7th HarmonicLow Bandwidth Communications

5w

5w

235uF

84uH

100W

Non Linear Load

5dqv

18-Aug-11 56

Harmonics in Microgrids

18-Aug-11 57

LPF

w

to other

DGs

bv

DG Local Controller

(Primary Level)

dcV

L

L

L

CC

DG Power Stage

Point of Common

Coupling (PCC)

abcoi

abcov

abcLi

C

5dq

HCR

Z

Z

Z

av

abcv

cv

LBCL

Gate Signals

Secondary Controller

1dq

v

5dq

v resE

LBCL

PLL

resw

aoi

boi

coi

aov

bov

cov

aLi

cLi

bLi

7dq

HCR

7dq

v

abcdq

abcdq

7

abcdq

5

LPF

LPF

Secondary control for voltage harmonic compensation in

islanded Microgrids


18-Aug-11 58

PR

Current

Controller

PR

Voltage

Controller

Three-phase Sinusoidal Reference Generator

abc

abc

abc

Virtual Impedance

Loop

abc

Powers Calculation

abc

P Q

Active Power Droop Controller

E

PWM

oi

ovLi

abcoiabcovabcLi

*v*i

Reactive Power Droop Controller

Gate Signals

reswresE

7

dqHCR

7

refv

5

dqHCR

5

dq

dq

Compensation Effort Controller

DG local controller (primary level)


Test system for secondary harmonic compensation

18-Aug-11 59

PCC

DG2

Linear

Load

2Z

DG1

2Z

2Z

1Z

1Z

1Z

Nonlinear

Load

Z Z Z


Secondary control for voltage harmonic compensation

18-Aug-11 60

(a) Before amplitude restoration and harmonic compensation

(b) After amplitude restoration (no harmonic compensation)

(c) After amplitude restoration and harmonic compensation

Unbalance in Microgrids

Voltage unbalance definition

,

,

rms

rms

C

C

vUF

v

=

rmsCv

,

rmsCv

,

Voltage unbalance factor (UF) is considered as the index of unbalance.

UF can be defined as follows:

where and are rms values of negative and positive

sequences of the DG output voltage.

18-Aug-11 61


Unbalance compensation for a grid-connected DG

abc

abc

i i v v oi oi

Voltage P+ResonantController

Current P+ResonantController

abc

Virtual Impedance

Loop

abc

Switch

abc

Three phase

Reference GeneratorE sin ()

RL

Positive and Negative Sequence Calculation

Control System

oi

Cv

Unbalance Compensation

P Q

dcV

oai

obi

oci

oaL

obL

obL

cCbCaC

av

bv

cv

aL

bL

cL

Lai

Lbi

Lci

CavCbv

CcvGRID

gaL

gbL

gcL

gaR

gbR

gcR

*UF

Cv

PI

UF

*

PWM

*E

Cv

ActivePower Controller

ReactivePower Controller

RMSCalculation

Power Calculation

, rmsC

v

, rmsC

v

18-Aug-11 62


Unbalance compensation for a grid-connected DG

DG output Voltage

18-Aug-11 63


Decentralized unbalance compensation for a microgrid

abc

abc

i i v v oi oi



abc

Virtual Impedance

Loop

abc Power Calculation

abc

Three phase

Reference Generator

syncw

nResistive Load

PLL

Positive and Negative Sequence

Calculation

Inverter 1

Control System

Inverter 2 Control Systemabc

cv

oi

oi

cv

C

Q

cv

Unbalance Comp.

P Q

n

av2

bv2

cv2

dcvdcv

aL2

bL2

cL2

aLi 2

bLi 2

cLi 2

aCv 2

bCv 2cCv 2

aC2bC2cC2oaL2

obL2

ocL2

oai2

obi2

oci2

oai1

obi1

oci1

oaL1

obL1

ocL1

cC1bC1aC1

av1

bv1

cv1

aL1

bL1

cL1

aLi 1

bLi 1

cLi 1

aCv 1bCv 1

cCv 1


RectivePower Controller

E

PWM

PWM

w

18-Aug-11 64


Decentralized unbalance compensation for a microgrid

Voltage after and before compensation

Unsymmetrical line

18-Aug-11 65


Secondary control for unbalance compensation in

islanded Microgrids

bv

Three-phase Sinusoidal Reference

Generator

Lai oai

abc

abc

PR

Voltage

Controller

abc

Virtual Impedance

Loop

abc Power Calculation

abc

Positive Sequence Calculation

DGi Local Control System

oi

ov

PQ

dcV

obi

oci

L

L

L

Lbi

Lci

oav

obv

ocv


*E

PWM

*

oiov

Li

CC

DG Power Stage

Point of Common

Coupling (PCC)

abcoiabcovabcLi

refv

refi

C

PR

Current

Controller

iUCR

L

L

L

av

abcv

cv

Positive and Negative Sequence Calculation

v

v

VUF Calculation

VUF

*VUF

ReactivePower Controller

dq

iCSG nCSG

dq

Sec

on

da

ry C

on

tro

ller

Low Bandwidth

Communication LinknUCR

sI

P

kk

18-Aug-11 66


1L

DG2DG1

a

b

c

Unbalanced

Load

Switch

1L

1L

2L

2L

UBZ

Balanced

Load

BZ

PCC

2L

VUF at PCC and DGs terminal (CSG1=1,CSG2=1.25)

VUF at PCC and DGs terminal (CSG1=CSG2=1)

VUF at PCC and DGs terminal (DG1 communication link failure

at t=3.5sec)

18-Aug-11 67


(a)

(b)

(c)

(d)

(e)

(f)

Fig. 8. Three-phase voltage waveforms (a) PCC-before comp. (b) PCC-after comp.

(c) DG1-before comp. (d) DG1-after comp.

(e) DG2-before comp. (f) DG2-after comp.

Three-phase voltage waveforms

PCC

DG1

DG2

BEFORE COMPENSATION AFTER COMPENSATION

18-Aug-11 68


Conclusions

• Voltage harmonics in microgrids can be reduced by injecting current harmonic or adjusting harmonic voltage in the DG terminals

• Secondary control can be used to close the loop of the harmonic voltage compensation in the microgrid

• Tertiary control can be used to reduce the current harmonics injected by the microgrid to the grid

• A ponderated trade off between the secondary and tertiary controls have to be designed

• Unbalances in microgrids can be reduced by injecting a voltage negative sequence in the DG proportional to Q negative sequence

• Secondary control and tertiary control for unbalance compensation can be used for islanding and grid-connected microgrids.

• Reactive power have to be limited and ponderated for harmonics and unbalance compensation.

18-Aug-11 69

Distributed Energy Storage in Microgrids

18-Aug-11 70

PG1

PG2

PG3

PMG

PS1

PS2

Source: “Distribution Voltage Control forDC Microgrid with Fuzzy Control and Gain-Scheduling Control,” H. Kakigano et Al.

Distributed Energy Storage in Microgrids

18-Aug-11 71

SOC1 – SOC2 PS1, PS2

Adaptive droop control:

DC: V=V* - (k/SoC)Io

AC: w=w* - (k/SoC)P

Extended Kalman Fiters are used to obtain the SoC of the batteries.

References

[1] J. M. Guerrero, J. C. Vasquez, J. Matas, M. Castilla, etc, "Control strategy for flexible microgrid based on parallel line-interactive UPS systems," IEEE Trans. Industrial Electronics, Vol. 56, No. 3, pp. 726-736, 2009.

[2] J. M. Guerrero, J. Matas, etc, "Decentralized control for parallel operation of distributed generation inverters using resistive output impedance," IEEE Trans. Industrial Electronics, Vol. 54, No. 2, pp. 994-1004, 2007.

[3] Y. W. Li and C. Kao, "An accurate power control strategy for power-electronics-interfaced distributed generation units operating in a low-voltage multibus microgrid," IEEE Trans. Power Electronics, Vol. 24, No. 12, pp. 2977-2988, 2009.

[4] D. M. Vilathgamuwa, P. C. Loh and Y. W. Li, "Protection of microgrids during utility voltage sags," IEEE Trans. Industrial Electronics, Vol. 53, No. 5, pp. 1427-1436, 2006.

[5] F. Katiraei, M. R. Iravani and P. W. Lehn. "Micro-grid autonomous operation during and subsequent to islanding process," IEEE Trans. Power Delivery, Vol. 20, No. 1, pp. 248-257, 2005.

[6] H. Gaztanaga, I. Etxeberria-Otadui, S. Bacha and D. Roye, "Real-time analysis of the control structure and management functions of a hybrid microgrid system," in Proc. IECON Conf., 2006, pp. 5137-5142.

[7] C. Jin, P. C. Loh, P. Wang, Y. Mi, F. Blaabjerg, "Autonomous operation of hybrid AC-DC microgrids," in Proc. ICSET Conf., 2010.

[8] X. Liu, P, Wang and P. C. Loh, "A hybrid AC/DC microgrid and its coordination control," IEEE Trans. Smart Grid, to be published.

[9] X. Yu, A. M. Khambadkone, H. H. Wang, etc, "Control of parallel-connected power converters for low-voltage microgrid-Part I: A hybrid control architecture," IEEE Trans. Power Electronics, Vol. 25, No. 12, pp. 2962-2970, 2010.

[10] C. T. Lee, C. C. Chuang, C. C. Chu and P. T. Cheng, "Control strategies for distributed energy resources interface converters in the low voltage microgrid," in Proc. ECCE Conf., 2009, pp. 2022-2029.

18-Aug-11 72

Name Josep M. Guerrero (喬瑟輔) Photo

Title Full Professor

Postal

Address

Aalborg University, Institute of Energy

Technology, Pontoppidanstraede 101,

DK-9220 Aalborg East, Denmark

Telephone Tel:

Cell: +34652045551

Email [email protected]

Website www.et.aau.dk

Educational

Background

• 1993 ~ 1997. B.Sc Telecommunications Engineer (Technical University of Catalonia,

Barcelona)

• 1997 ~ 2000. M.Sc Electronic Engineer (Technical University of Catalonia, Barcelona)

• 2000 ~ 2003. PhD Power Electronics (Technical University of Catalonia, Barcelona)

Work

Experience

• Feb 1999 ~Aug 2004 Assistant professor (Technical University of Catalonia, Barcelona)

• Sept 2004 ~Aug 2008 Lecturer professor (Technical University of Catalonia, Barcelona)

• Sept 2008~Present Associate Professor (now part time) (Technical University of Catalonia,

Barcelona)

• July 2011~Present Full Professor (Aalborg University, Spain)

Autobiography

Josep M. Guerrero (S’01–M’04–SM’08) was born in Barcelona, Spain, in 1973. He received the B.S. degree

in telecommunications engineering, the M.S. degree in electronics engineering, and the Ph.D. degree in power

electronics from the Technical University of Catalonia, Barcelona, Spain, in 1997, 2000 and 2003, respectively.

He is part time Associate Professor with the Department of Automatic Control Systems and Computer

Engineering, Technical University of Catalonia, where he currently teaches courses on FPGAs and control of

renewable energy systems. From 2011 he is a Full Professor at the Institute of Energy Technology, Aalborg

Universiy, Denmark, and responsible of the Microgrid research program. He has been a visiting Professor at

Zhejiang University, China, and University of Cergy-Pontoise, France. His research interests include power

electronics converters for distributed generation and distributed energy storage systems, control and

management of microgrids and islanded minigrids, and photovoltaic and wind power plants control. He is an

associate editor of the IEEE Transactions on Industrial Electronics and IEEE Transactions on Power

Electronics. He currently chairs of Renewable Energy Systems Technical Committee of IEEE IES. He is an

elected IEEE IES Adcom member.

Documents

Introduction to Microgrids - esci-ksp.orgesci-ksp.org/wp/wp-content/uploads/2012/05/Day2_8...Microgrids.pdf · Microgrid operation Islanded operation Voltage and frequency management