Universal operation of small and medium size renewable

Universal operation of small and medium size renewable energy systems

Prof. Marco Liserre, PhD, IEEE fellow

Head of the Chair of Power Electronics

Christian-Albrechts-Universität zu Kiel

Kaiserstr. 2 D-24143 Kiel Germany

[email protected]

mailto:[email protected]

Introduction

Decentralized control of the grid converter: from

“multifunctional” to “universal” converter

Voltage and current control alternatives

Harmonic rejection

Transition among different operation modes

Universal Operation of Wind Turbine Systems without

Storage

Outline

Marco Liserre [email protected]

Source: IET, Aalborg University

Power Flow

Information Flow

Generators

TransmissionNetwork

DistributionNetwork

Customers

Power Flow

Information Flow

Generators

TransmissionNetwork

DistributionNetwork

Customers

Generators

TransmissionNetwork

DistributionNetwork

Customers


Only central power plants

Scenario: smart grid and renewables

Until 2000

Power Systems in 2012

Source: IET, Aalborg University

Power Flow

Information Flow

Generators

TransmissionNetwork

DistributionNetwork

Customers

Distributed Generation

Green Power

Power Flow

Information Flow

Generators

TransmissionNetwork

DistributionNetwork

Customers

Generators

TransmissionNetwork

DistributionNetwork

Customers

Distributed GenerationDistributed Generation

Green Power


Scenario: smart grid and renewables

Distributed generation based on renewable energies is changing the face of power system

Ancillary services are the first tangible effect !

Power converters for photovoltaic systems • High efficiency (new topologies and new devices) • Transformer-less topologies and Central inverters • Extended lifetime • Reactive power injection (ancillary services)

Inverter market share Vincotech patent


• Reliability • 10-20 MW wind turbines (power converter topologies and generators) • Paralleling of power converters or MV solutions ?

Power converters for wind systems

Gearbox

Converter

module 1

Converter

module 2

Converter

module 3

Converter

module 4

Converter

module 5

Converter

module 6

LV/MV

Transformer

Generator


Best renewable source for integration in residential buildings

Single-stage transformerless achieves high efficiency

Interaction with the grid (anti-islanding, reactive power

injection, ancillary services)

Small power (< 5 kW) PVS


Vdc

LCL

Filter

FilterDC/AC

Converter

Input power

sourcetransformer & utility

grid

local load

microgrid

PV

Panels

String

Vpv

Ipv

e

PWM

Anti-Islanding

Protections

i

Grid

Synchronization

MPPT Vdc

Control

AC Current

Control

AC Voltage

control for

ancillary functions

Best choice immediately outside residential areas for low impact

on the landscape

High penetration in stand-alone also in combination with other

DER

Power limitation issues, weak grid connection

Medium power (< 200 kW) WTS


Decentralized control of the grid converter: from “multifunctional” to “universal”

converter

The grid converter can supply power to the main grid and/or to local loads even

organized in a micro-grid

dcV

1L i

cV

+

-

+

-V

CC VC

icV

cV*

+

-

The ac capacitor voltage is

controlled though the ac

converter current

The current controlled

converter operates as a

current source to

charge/discharge the

capacitor

Introduction


Introduction The grid converter can operate as grid-feeding or grid-forming device

Main control tasks

manage the dc-link voltage (if there is not a dc/dc converter in charge of it)

inject ac power (active/reactive)

A third option is the operation as grid-supporting device (voltage, frequency, power

quality)

AC

PO

WE

R

CO

NT

RO

L

GRID

SUPPORTING

GRID

FORMING

DC VOLTAGE

CONTROL

GRID

FEEDING

PO

WE

R

TH

EO

RY

stationary

frame ab

natural

frame abc

rotating

frame dq

AC CURRENT

CONTROL

AC VOLTAGE

CONTROL


Ac voltage control

When it is needed to control the ac voltage because the system should operate

in stand-alone mode, in a microgrid, or there are requirements on the voltage

quality a multiloop control can be adopted

dcV

1L i

cV

+

-

+

-V

CC VC

icV

cV*

+

-

The ac capacitor voltage

is controlled though the

ac converter current

The current controlled

converter operates as a

current source to

charge/discharge the

capacitor


Results: load support in case of a voltage sag of 0.15 p.u.

Grid voltage E (top): voltage dip of 0.15 p.u., load voltage Vload (middle ), grid current Ig (bottom)

J. C. Vasquez, R. A. Mastromauro, J. M. Guerrero, M. Liserre, Voltage Support Provided by a Droop-Controlled Multifunctional

Inverter, IEEE Transactions on Industrial Electronics, vol.56, no.11, pp. 4510-4519, Nov. 2009.

R. A. Mastromauro, M. Liserre, T. Kerekes, A. Dell'Aquila, “A Single-Phase Voltage Controlled Grid Connected Photovoltaic System

with Power Quality Conditioner Functionality”, IEEE Transactions on Industrial Electronics, vol.56, no.11, pp. 4436-4444, Nov. 2009.


Voltage support provided by the DPGS at load level

The reactive power injection by grid-connected systems can enhance the voltage profile

The goal is to reduce the active power supplied by the low-voltage feeder, injecting reactive

power to support the voltage amplitude decreasing the current and as a consequence the losses

AC DC

PQ-inverter control

Optimal Reactive Power Control Dynamic

Load-Flow Reduced Network Model

QPV (t)

Distribution Network

MV/LV

PTR (t) VTR(t) θTR(t)

PPV (t) QPV (t) VPV(t) θPV(t) NON-OPTIMIZED

CONDITION

(PV INVERTER OFF)

OPTIMIZED CONDITION

(PV INVERTER ON)

TRANSFORME

R SUBSTATION PCC

TRANSFORMER

SUBSTATION PCC

F [HZ] 50 50 50 50

V1 [V] 229 228 230 229

V2 [V] 228 226 228 228

V3 [V] 228 230 228 231

I1 [A] 52.5 1.1 33 3.2

I2 [A] 52 1.1 36.5 2.2

I3 [A] 44 1.1 36.5 0.9

PTOT [W] 19950 730 20200 380

QTOT[VAR] 26550 0 8050 16500

cosφ 0.66 1 0.93 0.02


Voltage support provided by the DPGS at EPS area

The minor losses in the line obtained through reactive power injection should be bigger than the

additional losses in the inverter due to reactive power injection

Inverter losses

Substation

1

10

2

9

7

6

8

3

11

12

13

4

15

14

5

It can be proven using load flow analysis that only when the line is loaded and not for all the point of connection of the PV-system the minor line losses are bigger than the inverter losses

Voltage support provided by the DPGS at EPS area

A. Cagnano, E. De Tuglie, M. Liserre, R. A. Mastromauro, “Online Optimal Reactive Power Control Strategy of PV Inverters” IEEE

Transactions on Industrial Electronics, 2011.


Universal inverter


PMSG

chopR

DCu

DCC

Machine-side

converter

Grid-side

converterS

i

Power

filter

1i 2

i

Machine-side

control

Grid-side

controlUnidirectional

Communication

Link

PCCe

State

Load

UWT1

STS

l 1Z liZ

UWTi UWTN

lNZ

Grid

gZ

PCCe

Circuit

BreakerG

e

State manager

PCCe

State

Unidirectional

Communication

Link

DG

units

State

ISLe

Droop control

2

2

1cos cos sin sin

1cos sin sin cos

P EV E EVZ

Q EV E EVZ

Hypotesis:

1) purely inductive impedance

EVP

X

EQ V E

X

2

sin

cos

EVP

X

EV EQ

X X

2) small

Aim: to allow different sources, in a microgrid, sharing the load without a centralized

control and without communication


Droop control


GP

max

min

0

WTP

ZoneZone

EMEMa Eb Mcf f f

Generous Selfish2

GaP

GbP

GcP

1

GaP

GbP

GcP

Active and reactive power sharing can be tuned for each individual DER

deciding if the contribution should be more or less generous

dtPPnPPm pp )()( ***

dtQQnQQmVV qq )()( ***

PI Controller

)(1

)( *** PPs

nPPm pp a

)(1

)( *** QQs

nQQmVV qq a

Fractional PI Controller

In order to obtain low steady-state error and fast dynamic response without coupling between P and Q, it

can be demonstrated that active and reactive power regulation can be performed by PI controllers. It

results:

Droop control


Power Decoupling

To obtain Pc and Qc it is sufficient to know the ratio R/X.

sin cos

cos sin

arctan( )

C

C

X R

P P P PZ ZT

Q Q Q R X Q

Z Z

X R

sinC

EVP

Z

2cosC

EV EQ

Z

If the line it is not purely inductive


Universal Power control


Tra

nsfo

rma

ntio

n

ma

trix

TD

ST z

z 1

F z

F z

Pfk

PVk

V

GQ

GQ

GQ

GFQ

GFP

GP

GP

GP

GP

GQ

d

C

d

CV

V

S

S

z 1

T zDfk

ST z

z 1IVk

S

PCC

PCCE

S

S

S

S

PCCE

ST z

z 1PCC

S

PCC

(A)

(B)

(C)

(D)

baseV

base

PLANT

Voltage and current control alternatives


1

f fR sL

1

fsC

2 2

1

R sL2i

e

2i

Cv

Cv1i Ciu

Cv

1i

Ci

ZOHController

PLANT

The voltage control regulates the voltage across the capacitor to implement the droop characteristic

As it is disposed in cascade with the droop control, its response time must be small enough to neglect their coupling

Analysis of most suitable voltage technique involves:

• Single-loop vs. Multi-loop

• Inductor current vs. capacitor current feedback

• Grid-connected and stand-alone operation modes

• LC-resonance damping, time response, perturbation and switching noise rejection, discrete time domain, harmonic rejection, etc

Introduction

Single-loop: P + Resonant and virtual impedance

e

*Cv

Cv

Cv-1z

*u

VZ z2i

PLANTP

RES

Voltage Controller

Less sensors.

Trade-off between performance and stability.

Virtual impedance loop, only activated when grid-connected to cancel the most representative current harmonics.

C5

L5

C7

L7

C13

L13i2

2

5,7,11,13 1

n

V Zv

n n n

L sZ z ZOH k

L C s


Double-loop: P + Resonant and P

Outer controller (PR) achieves steady-state voltage error while the inner one (P) is added to improve perturbation rejection and LC resonance damping (not in discrete-time domain).

P value trade-off between stability and high dynamics.

Not tracking performance but perturbation rejection differences are encountered when using ic or i1.

Small kp values achieve good resonance damping, high ki values fast dynamics.

;

101

102

103

-100

-50

0

50

100

i1

iC

Magnitude (

db

)

Bode Diagram

e

*Cv

Cv

Cv

-1z*u

PLANTP

RES

1Ci or i

* * 1Ci or iP

Voltage Controller Current Controller


Double-loop: Two P + Resonant

Extra PR:

Sinusoidal current waveforms assured and higher gain at 50 Hz.

Extra computational effort and control complexity (one root more) leading to loss of stability

;

e

*Cv

Cv

Cv

-1z*u

PLANTP

RESP

RES

1Ci or i

* * 1Ci or i

Voltage Controller Current Controller

101

102

103

-200

-100

0

100

200

i1

iC

Mag

nitu

de (

db

)

Bode Diagram

ic provides better switching attenuation and i1 a wider peak at 50 Hz good for frequency drifts


Comparison ;


101

102

103

-5

-2.5

0

2.5

5

Frequency (Hz)

Magnitude of the Sensitivity Transfer Function S(Z) (db)

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

1 5 10 50 100-30

-20

-10

0

10

20

Frequency (Hz)

a) |Z0| (db)

1 5 10 50 100

-300

-200

-100

0

Frequency (Hz)

b) Angle of Z0 (º deg)

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

0 0.2 0.4 0.6 0.8 1

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Imag

inar

y ax

is

Real axis

24kW

24kW

6kW

6kW

24kW

24kW

6kW6kW

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

d1

d2

d3

d4

d5

Re[L(z)]

Im[L

(z)]

SL

PR+P iC

PR+P i1

PR+PR iC

PR+PR i1

Grid-connected

Island mode

;

Grid voltage profile and main parameters

Comparison in terms of settling times and power quality

Microgrid

Grid-connected


Simulation Results

;

Single-loop with virtual impedance


Simulation Results

;

Multi-loop: P + Resonant and P

ic i1


Simulation Results

;

Multi-loop: two P + Resonant

ic i1


Simulation Results

Harmonic rejection

Universal Harmonic Rejection

*

11

2 23

( )

2( )

2

ref Ci H Ci

i

H

i i iodd

v v Z s i

K sZ s

s K s

In grid-connected: harmonic-free current into the grid

Current harmonics compensation loop

Voltage harmonics compensation loop


In island operation mode the aim of the control is to supply

the loads with sinusoidal voltage in spite of non-linear or

unbalanced loads

The proposed control strategy allows to modify the inner

loops control structure when the islanding is detected, in

particular the resonant compensators can be applied in the

voltage control loop without changing the voltage reference

Simulation Results

Harmonic compensation strategy in grid-connected operation mode


Simulation Results Harmonic compensation strategy in island operation mode


Experimental Results


Experimental Results Current harmonic compensation

The current presents a low distortion, since the

THD is reduced from 6% to 2% .


Experimental Results

Voltage harmonic compensation


Transition among different operation modes

Three operation modes: Grid-Connected, Stand-Alone or Synchronization.

S=1: The system is synchronized (Synch=1)and there is not any islanding condition (AI=1).

S=2: A islanding conditions has been detected (AI=0) and circuit breaker 2 is disconnected, hence, Vpcc and Vpcc1 are not synchronized (Synch=0). Integrators of droop controller are disabled.

S=3: The islanding conditions is cleared (AI=1) but the system is not synchronized with the grid yet (Synch=0). wt and E and are the phase and amplitude of Vpcc1, but the output of PI_P and PI_Q are not supplied in this state. When the system is synchronized again, the output of the integral part are reset.

Universal droop control


f and V

measurements

Inject

Start

Island

AI=1

Inject

or

maxf f

maxV V

AIf f AIV V

islP islQ

No

No

No

Yes Yes

Yes

( )·

( )·

isl fP AI

isl VQ AI

P K f sign f f

Q K V sign V V

rated

rated

f f f

V V V

Anti-islanding method.

Active method based on the positive feedbacks of active and reactive power.

Synchronization system.

2 PLLs and 2 buffers that monitor amplitude and phase of Vpcc and Vpcc1.

When the phase and amplitude differences remain lower than certain thresholds, the synchronization is finished.

Universal droop control


Grid-connectedStand-

AloneGrid-Connected

Synchronization

0 5 10 15 20 25 30-15

-10

-5

0

5

10

Act

ive

(kW

) an

d R

eact

ive(

kVA

r)po

wer

tran

sfer

Time (s)

P

Q

Pload=10kW Qload=0VAr P*=10kW Q*=0Var

9.96 9.98 10 10.02 10.04 10.06-500

0

500

Volta

ges in

PC

C (

V)

a)

Vpcc

a

Vpcc1

a

9.96 9.98 10 10.02 10.04 10.06-0.5

0

0.5

1

1.5

Contr

ol s

ignals

d)Time(s)

AI

Synch

9.96 9.98 10 10.02 10.04 10.060

200

400

Am

plit

ude

of V

pcc1 (

V)

b)

9.96 9.98 10 10.02 10.04 10.0620

40

60

Fre

quency

of V

pcc1 (

Hz)

c)14.8 14.9 15 15.1 15.2 15.3 15.4

-500

0

500

Vol

tage

s in

PC

C(V

)

a)

Vpcc

a

Vpcc1

a

14.8 14.9 15 15.1 15.2 15.3 15.4-0.5

0

0.5

1

1.5

Con

trol

sig

nals

b)Time (s)

AI

Synch

Islanding detection

Re-synchronization.


Simulation Results

Pload=10kW Qload=2VAr P*=10kW Q*=0Var

1.9 1.95 2 2.05 2.1-400

-200

0

200

400

Volta

ges in

PC

C

Vpcca

Vpcc1a

1.9 1.95 2 2.05 2.1-0.5

0

0.5

1

1.5

Contr

ol s

ignals

Time (s)

AI

Synch

2.4 2.45 2.5 2.55 2.6 2.65 2.7 2.75 2.8-400

-200

0

200

400

Volta

ges in

PC

C

Vpcca

Vpcc1a

2.4 2.45 2.5 2.55 2.6 2.65 2.7 2.75 2.8-0.5

0

0.5

1

1.5

Contr

ol s

ignals

Time (s)

AI

Synch


Simulation Results

Pload=10kW Qload=-2VAr P*=10kW Q*=0Var

1.9 1.95 2 2.05 2.1-400

-200

0

200

400

Volta

ges in

PC

C

Vpcca

Vpcc1a

1.9 1.95 2 2.05 2.1-0.5

0

0.5

1

1.5

Contr

ol s

ignals

Time (s)

AI

Synch

2.4 2.5 2.6 2.7 2.8-400

-200

0

200

400

Volta

ges in

PC

C

Vpcca

Vpcc1a

2.4 2.5 2.6 2.7 2.8-0.5

0

0.5

1

1.5

Contr

ol s

ignals

Time (s)

AI

Synch


Simulation Results

Advanced control options: fractional PI

Fractional PI The generic fractional PI order system representation in the Laplace domain is given as

n

m

sasa

sbsbsb

sX

sYsG

n

m

aa

bbb

.....1

.....

)(

)(1

10

1

10

Where:

• b0, b1, ......, bm and a1, a2, ......, an are constant model parameters or model coefficients;

• β0<β1<…<βm and α1<α2< ..... <αn are the fractional powers or fractional orders

The main idea is to develop a functional operator PI, associated to an order α not restricted to

integer numbers, that generalizes the usual notions of integrals. The transfer function of a

fractional PI is given by

aasT

KsGi

P

11

Where:

• Kp is the proportional constant,

• Ti is the constant time integrator;

• α is the fractional PI order α

=1

<1

PI controller

Fractiponal PI controller


Tuning of the fractional PI in the droop control loop

Assuming a P/Q decoupling and modeling the low-pass filters with a first-order approximation, the

active and reactive power, given by one inverter, can be derived as:

fpfp

f

c

c PPs

nPPmX

EVPP

sP **

*1)(

)( a

fqfq

f

c

c QQs

nQQmX

EEVQQ

sQ **

*1))((

)( a


Tuning of the fractional PI in the droop control loop

ACTIVE POWER

(P)

REACTIVE

POWER (Q)

Fractional PI order (α) 1 < αp < 0.3; 1 <αq< 0.3

Proportional constant (Kp) 0.000009 0.009

Constant time integrator

(Ti) 20 200

Bode diagram of active power Bode diagram of reactive power


Simulation Results

Active power Reactive power

variation of

load

power request

by the load

power supply

by the inverter


Experimental results

Fractional PI controller PI controller

Where:

CH3: Converter current; CH1grid-voltage; CH4 inverter voltage output.

single inverter in

grid-connected

operation mode

two inverter in

grid-connected

operation mode


Universal Operation of Wind Turbine Systems without Storage


The kinetic storage of the UWT together with a suitable control strategy can be used to operate the UWT in island mode for a certain time without any additional storage

Statistical assessment of the power reliability improvement shall be done by means of SIER

Introduction

Wind

turbineRotor

DC-link

capacitors

Aerodynamic

losses

Mechanical

losses

Generator

and switching

losses

Switching and

filter losses

Injected

power

Generated

powerWind

Power

Kinetic stored

energy

MPPT LOSSES

LOADb )

)

P

a P P

WT MPPT

WTb

) P P

) P

a

WT LOAD LOSSESb )

a )

P ( P P )

0

a )Grid connec

b ) Is

te

d

d

lan

Chopper

losses

0 10 20 30 40 500

5

10

15

20

Power (kW)

Pro

bab

ilit

y (%

)

Generation

Load P1

=15 kW

Load P2

=20 kW

Load P3

=25 kW

Load P4

=30 kW

Load P5

=35 kW

Load P6

=40 kW


Depending on the steady-state operation mode the different curves for the generation control can be sketched

Calculation of SIER

0 5 10 15 20 250

0.2

0.4

0.6

0.8

1

Wind speed (m/s)

Per

uni

t va

lues

I IIIII

Power

CP

Torque

Rotor Speed

Pitch Angle

Depending on the load and on the island operation time different interruption times can be calculated

0 5 10 15 20 250

10

20

30

40

50

60

Time (s)

Pro

bab

ilit

y (%

)

tSD

@ P1

= 15 kW

tSD

@ P2

= 20 kW

tSD

@ P3

= 25 kW

tSD

@ P4

= 30 kW

tSD

@ P5

= 35 kW

tSD

@ P6

= 40 kW

tINT

@ T1

= 10 s

tINT

@ T2

= 2 min

tINT

@ T3

= 10 min

0

10

20

30

40

50

60

0 5 10 15 20 250

10

20

30

40

50

60

Time (s)

Pro

bab

ilit

y (%

)

tSD

@ P1

= 15 kW

tSD

@ P2

= 20 kW

tSD

@ P3

= 25 kW

tSD

@ P4

= 30 kW

tSD

@ P5

= 35 kW

tSD

@ P6

= 40 kW

tINT

@ T1

= 10 s

tINT

@ T2

= 2 min

tINT

@ T3

= 10 min

0

10

20

30

40

50

60


UWT can be used to reduce the average interruption time

The reduction in the average interruption time obtained by means of the Universal Operation is quite remarkable, being at least 22.27 % and 60.5 % in the best case

Calculation of reduction of interruption time

'Tμ (s)

Average Load Consumption

P1μ P2μ P3μ P4μ P5μ P6μ

Ave

rag

e

Inte

rru

pti

on

Du

rati

on

T 1μ 3.95 4.64 5.26 5.69 6.19 6.52

T 2μ 62.50 71-02 78.32 83.37 87.82 91.59

T 3μ 321.83 364.82 401.08 427.83 446.63 466.39

Conclusions

Universal operation of power converters is needed in the future distribution

grids characterized by frequent disconnection and operation in island mode

Major challenges are in low voltage distribution lines because of not negligible

resistive nature and of similar time constants of different control loops

Many different options exist for the internal control loops (current and voltage)

and they have been reviewed also considering harmonic control

Fractional control can make easier to tune power controllers that should work

in very different operational modes (grid-connected and island)

Universal Operation without added storage is feasible and can lead to reduce

the interruption time


Publications Remus Teodorescu, Marco Liserre, Pedro Rodriguez “Grid Converters for Photovoltaic and Wind Power

Systems”, Wiley-IEEE, ISBN 8-0-470-05751-3, January 2011. 2nd reprint in 9 months. Translated in

Chinese 2012.

Mario Rizo, “Universal operation of small wind turbine systems”, University of Alcala de Henares, Spain,

2013.

M. Rizo, M. Liserre, E. Bueno, F. J. Rodríguez, F. Huerta, “Universal wind turbine working in grid-connected

and island operating modes”, Mathematics and Computers in Simulation, Elsevier, 2012.

M. Liserre, A. Nagliero, R. A. Mastromauro, N. A. Orlando, D. Ricchiuto, A. Altomare, M. Nitti, A. Dell’Aquila

“Universal operation of small and medium size Renewable Energy Systems” invited paper at PEIA 2011,

Doha, Qatar.

M. Rizo, M. Liserre, E. Bueno and F.J. Rodríguez “Universal wind turbine working grid-connected and

stand-alone”, Electrimacs 2011.

D. Ricchiuto, M. Liserre, R. Mastromauro, A. Dell’Aquila, A. Pigazo, “Fractional-Order Based Droop Control

Of An Universal Wind-Turbine System”, EPE 2011.

M. Rizo, E. Bueno, A. Dell’Aquila, M. Liserre, R. A. Mastromauro “Generalized Controller for Small Wind

Turbines Working Grid-Connected and Stand-Alone”, ICCEP 2011, Ischia.

A. Nagliero, R. A. Mastromauro, D. Ricchiuto, M. Liserre, M. Nitti, “Gain-scheduling-based Droop Control for

Universal Operation of Small Wind Turbine Systems”, ISIE 2011, Gdansk, Poland.

A. Nagliero, R. A. Mastromauro, D. Ricchiuto, M. Liserre, “Harmonic Control Strategy for Universal

Operation of Wind Turbine Systems” Powereng 2011, Malaga, Spain.

A. Nagliero, R. A. Mastromauro, V.G. Monopoli, M. Liserre, A. Dell’Aquila, “Analysis of a universal inverter

working in grid-connected, stand-alone and micro-grid” ISIE 2010, Bari.

A. Nagliero, A. Lecci, R. A. Mastromauro, M. Liserre, A. Dell'Aquila, "Particle Swarm Optimization of a

universal inverter," IECON 2010 - 36th Annual Conference on IEEE Industrial Electronics Society , vol., no.,

pp.199-204, 7-10 Nov. 2010


Acknowledgment The work has been developed in close cooperation with

and in particular with Prof. Emilio Bueno and PhD student Mario Rizo


GEISER:

Group of Electronics Engineering Applied

to Renewable Energy Systems Department of Electronics

Alcalá University (Spain)

http://geiser.depeca.uah.es/

http://geiser.depeca.uah.es/

Documents

Universal operation of small and medium size renewable