Decentralized Generation In Microgrids

Juan Carlos Vásquez Quintero
Advisor: Josep María Guerrero Zapata
Ph.D. Thesis Dissertation
2009

Ph.D. on Automatics, Robotics and Vision

I. Motivation: Introduction to Microgrids
II. Thesis objectives
III. Decentralized control: P/Q droop method
IV. Droop control method applied to voltage sag mitigation
V. Operation modes of a microgrid
Grid-connected operation mode
 Islanded operation mode
Transitions between grid connected and islanded modes
VI. Hierarchical control of microgrids
 Primary control:
- P/Q droop. Modeling and control
- Virtual Impedance: hot swap operation (smooth connection)
 Secondary control:
- f/V Restoration (island) and Synchronization (island to grid
connected mode)
Tertiary control:
- P/Q flow control at the PCC
VII. Conclusions and publications
VIII. Future work

Ph.D. Thesis dissertation Page 2

connected mode)
VII. Conclusions
VIII. Future work


Distributed Generation (DG) Paradigm and Smart grids
Nowadays problem:
 Energy crisis & climate change.
 Kyoto’s protocol: reduction of CO2 emission.

Raise of renewable energy:
 Photovoltaic.
 Wind.
 Hydrogen.
 Micro-turbines.

Small energy storage systems:
 Uninterruptible Power Sources (UPSs).
 Flywheels.
 Super capacitors.
 Compressed air devices.
 Mini-hydraulics.


So, what is a Microgrid?
Small energy storage
Renewable energy sources
systems
PV Wind turbine
Grid panel system UPS

PCC
Inverters

Common
... . AC bus
Intelligent
Bypass
Power Distribution Switch
Network (IBS) Distributed loads


Microgrids are required in the next electrical grid

mgrids…
Avoid transmission power losses
Improve the system efficiency
Increase the reliability


connected mode)
VII. Conclusions
VIII. Future work


Control of single DG units according to Microgrid requirements:

 Modeling of the DG unit
 Use appropriate control variables to control P and Q
 Derive decentralized controllers (droops)
 Propose control strategies for grid connected and islanded
operation
 Grid-connected mode:
 Accuracy of the P and Q injected
 Voltage sags and harmonics ride through
 Large grid impedance variation
 Islanded mode:
 Voltage stability
 Harmonic current sharing
 Hot-swap operation


Hierarchical control of microgrids

 Primary control – Inside the DG units
 Droop functions – Virtual inertias
 Harmonic current sharing
 Hot-swap operation
 Secondary control – Inside the microgrid
 Frequency and amplitude restoration
 Synchronization loops
 Tertiary control – Outside the microgrid
 P and Q power flow at the PCC


(IET department, AAU,
Denmark)


connected mode)
VII. Conclusions
VIII. Future work


The circulating current concept

i1 Critical AC
DC link
bus

io  i1  i2 Distributed
critical
i2 loads
DC link


The circulating current concept

E 1f1 Z o1
rL1 L1 L2 rL2 Z o2 E 2f2
V 0o
i1 i2
ZL
DG 1 DG #2
S 1=P 1+jQ 1 S 2=P 2+jQ 2

Circulating power analysis S L = P L +jQ

S S1  S2 consequently… P P  P2
1 Q Q1  Q2

Assuming L1  (Zo1  Z L1 ), L2  (Zo 2  Z L 2 )

And total output impedance is manly inductive

X T  ( L1  L2 )


 P/Q expressions

being E1 E2 EE
P  sin f  1 2 f
XT XT sin f  f
E  E1  E2
Q 
V
E cos f 1
f  f1  f2 XT

Circulating currents:

E1 E2 E
i p  f iQ 
VX T XT

Assuming inductive output impedance, the active and reactive powers
or currents can be controlled by adjusting the phase and the
amplitude of the output voltage.


Conventional droop method

o1 Frequency droop
o o2 
 m *
 P    *  mP
’ m’ 
’ Emax = 5%
P’
max=2%
P Pmax P
P1 P’1 P’2 P2
Output Z=jX Z=R(q=0o)
Impedance (inductiveq=90o) Amplitude droop
Active P
EV
sin f 
EV
f EV cos f  V 2 E
P E*
power X X R E  E *  nQ
Reactive EV cos f  V 2 V EV
Q  (E V ) Q  sin f E
power X X R
Frequency droop   *  mP   *  mQ
Amplitude droop E  E*  nQ E  E*  nP Qmax Q

Controller:    *  mP
E  E *  nQ

System Dynamics: ˆ ˆ ˆ ˆ
s 3f  As 2f  Bsf  Cf  0
c
A   2 X  nV cos  
X

B  c c X  ncV cos   mVE cos  
X
c  1 
C mVE  X cos   nV  
X X
 

Depends on m, n, X, c System transient can not be modified


Conventional droop method: Static restrictions

1) Static trade-off: F/V regulation and P/Q power sharing.
2) Limited transient response. System dynamic is
determined by m, n and strongly determined by X.
3) Unbalancing on line impedance when P/Q is shared.
4) Synchronization problems in relation with the utility
main (F and f deviation).
5) Line impedance dependence (islanded mode).

Static trade-off: F/V regulation


Proposed strategy: Adaptive droop method
Q* Droop functions
ipcc Q  Qc 
LPF Gq (s) 
P/Q E*

90º Decoupling *
v pcc P* Transformation E

ipcc LPF
P Pc G p ( s) f Vref *
E sin(t  f )
Power Calculation
Zg qg Impedance estimation
algorithm

f  Gp (s)Z g (P  P*)sinq g  Q  Q*  cosq g 

 
 G p ( s) 
mi  mp s  md s 2
s
E  E*  Gq (s)Z g (P  P*)cosq g  Q  Q*  sinq g  n n s

 
 Gq (s)  i p
s


Power flow modeling
 EVg cos f  Vg 2  EVg VSI Vpcc Grid
P  cosq g  sin f sinq g E
 Zg  Zg
 
 EVg cos f  Vg 2  EVg i pcc
Q  sinq g  sin f cosq g Ef Zo Zg Vg 0º
 Zg  Zg
 

P/Q Decoupling transformation

Pc  Z g  (P sinq g  Q cosq g ) 2000

Qc  Z g  (P cosq g  Q sinq g ) Active Power
Reactive Power
1500

P[W] & Q[VAr]
1000

Pc  EVg sinf
Qc  EVg cosf Vg 2  Vg  E Vg 
500

Pc is mainly dependent on the phase f, and 0

Qc depends on the voltage difference 2 4 6 8 10
between the VSI and the grid (E – Vg). Time[s]


System dynamics  
1
 P* sin q g  Q* cosq g 
  tan  



 P* cosq g  Q* sin q g  Vg 2 Z
g  



Vg 2 cosq g  P*Z g
E
Vg  cosq g cos   sin q g sin  

Characteristic equation
a4 s 4  a3 s3  a2 s 2  a1s  a0  0

a4  T 2  2Tmd Vg Ecos
a3  4T  4md n pVg 2 E  2Vg cos  2md E  Tn p  Tm p E 
a2  2Vg cos Tmi E  Tni  2n p  2m p   4Vg 2 E  m p n p  md ni   4
a1  4Vcos  ni  mi E   4V 2 E  mi n p  m p ni 
a0  4ni mi EV 2


Validating the obtained model
-3
x 10
10

8

6
Phase [rd]

4

2

Model
Real
0

-2
0 0.2 0.4 0.6 0.8 1
Time [s]

System and model dynamic response


Root Locus
System stability 30

20

3
10

Imaginary Axis
b) 1 2
0

-10
4

-20

-30
-100 -80 -60 -40 -20 0
Real Axis

Root Locus
1

0.8

a) 0.6

0.4

Figure Parameter

Imaginary Axis
0.2 4
1
2 3
0

a) 0.00005<mp <0.0001 c) -0.2

-0.4

b) 1e-6<md <4e-5 -0.6

-0.8

c) 0.0004<np <0.01 -1
-350 -300 -250 -200 -150 -100 -50 0
Real Axis


 Line impedance sensitivity

1600 1600

1400 1400

1200 1200

1000 1000

800 800

600 600

400 400

200 R=1 200 R=1
R=2 R=2
0 0
R=3 R=3
-200 -200
0 0.5 1 1.5 2 0 0.5 1 1.5 2

(a) (b)
Start up of P for different line impedances, (a) with and (b) without the
estimation algorithm of Zg.


VSI Local Bypass Z
L load g
Vg Block diagram scheme of the
C proposed method
v pcc Grid
Voltage and Grid parameters Ident.
d q
current Algorithm (Estimated
Driver and Monitoring Transf Values)
ipcc SOGI-FLL g Vg Zg qg
PWM
generator
*

Sine * E* P
f PC P/Q

P
Current Voltage Vref generator Droop
QC Decoupling

Loop Loop E sin(  t  f ) E Q
control Transf * 
Q
Inner loops

PWM inverter L =713m H Local Bypass Transformer
load 5kVA
VDC
400V  C  2.2m F Z Grid


L =713m H 10mH
Hardware ic E Vg ig
Setup dSPACE


Power Calculation Zg qg
QC
i pcc Q   
LPF
Gq ( s)
  
Q 0
*
E *
ES
90º GS
v pcc P/Q (Freezing) E
Decoupling
f
*
PC
Vref
i pcc LPF
P G p ( s)

  E sin(  t  f )

P* fS

LPF PI (s) fS VG ( rms ) LPF PI (s) ES
VG GS VC ( rms ) GS
Phase Synchronization Amplitude Restoration

Block diagram of the whole proposed controller using the
synchronization control loops


Synchroniz. Process
(grid and VSI voltages)

Synchroniz. Error
signal

Island Grid connected mode Island

P/Q load step during
grid transitions


Active power transient
response for Q*=0
(P: Blue, Q:black)

Active power transient
during a P* step.

Reactive power transient
during a Q* step (absorbing)


Conclusions
 A novel control for VSIs with the capability of flexibly operating grid-
connected and islanded mode based on adaptive droop control strategy was
proposed.

 Active and reactive power can be decoupled from the grid impedance in
order to injected the desired power to the grid.

 Enhancement of the classic droop control method.

 A novel control for injecting the desired active and reactive power
independently into the grid for large range of impedance grid values was
presented. This control is based on a parameters estimation provided by an
identification algorithm.


connected mode)
VII. Conclusions
VIII. Future work


Shunt DG inverter Control objectives:
i. Enhances the stability and the dynamic
QG response by damping the system.
ii. Provides all the active power given by the PV
V 0º source, and extracted in the previous stage
by the maximum power point tracker (MPPT).
LG  iii. Supports the reactive power required by the
grid when voltage sag is presented
RL into the grid.
E

IC
E
f
IG Vg 0º
IC  IG  I L
I Gd I C '
IG '  IGd  jIGq I Gq
IL ' E
Ef  V 0º IC
IG  f
jX I Gq Vg ' 0º
Equivalent circuit of the power stage

It can be observed that during a
Q – E relationship
voltage sag, the amount of reactive E
current needed to maintain the load
voltage at the desired value is
V E E V
inversely proportional to the grid V E
impedance.
Q
Q0 Q0

Inductance value

Maximum P delivered by the VSI (f=90o)
Large inductance will help in mitigating
EV
X voltage sags.
Pmax


System modeling and Control design
f  Gp (s)  PC  PC*  sin q   QG  QG  cosq 

*

E  E*  Gq (s)  PC  PC  cos q  QG  QG  sin q 

* *


s5  a4 s 4  a3 s3  a2 s 2  a1s  a0  0
a4  4o Z
a3  V o cos  (n p  Em p )  2o (1  2 2 ) Z
2 2

a2  2V o  cos  n p  Em p   o VE cos mi  4o Z
2 2 3

V
a1  V o cos  (n p  Em p )  VEo (2 cosmi 
4 3
o n p m p )  o4 Z
Z
V mi  m p s
a0  VEo mi (cos  n p )
4
G p ( s) 
Z s
Gq (s)  n p

E *a (1  a )  Qmax X
V = a*E* (being a as the voltage sag percentage)
np 
Qmax E *a


System stability
a) b)

c)

Figure Parameter
a) 20e-6<mp <1e-3
b) 2e-6<mi <1.8m
c) 8.5mH<LG <5000mH


Control diagram
PL , QL
PG , QG  LG
P , QC IL
Vg 0º IG C

Load
VC IC
 
Inner Repetitive  PI
loop  Control I ref control

VC Vref VC
QG PC
P
IG Q Droop Outer P/Q
Control P * calculation IC
calculation Q*  0 ( MPPT ) control loop
Q'
IG QG  
Gq ( s)
LPF  
90º QG  0
*
V*
VC P/Q V
Decoupling *
Vref Vref
PC 
P'  f
IC LPF G p ( s)
V sin(t  f ) 
 
Power PC * f*
LPF
Calculation

Set-up and simulation results
P/Q transient responses by the PV
inverter in presence of a voltage sag of
0.15 p.u when Pc*=500W

Current waveforms in case of a voltage
sag of 0.15 p.u (inverter current ic , grid
current Ig and load current Iload)


Simulation results
Grid voltage waveform in presence
of 1st, 3rd, 5th 7th and 9th voltage
harmonics.

P/Q transient responses and step
changes provided by the PV inverter


(detail) Inverter output voltage,
active and reactive power transient
responses under a nonlinear load

(detail) Current waveforms in case of
a nonlinear load. Vg (upper), Inverter
current (middle), grid current


Laboratory set-up

(Electrical Engineering department, Polytechnic of Bari, Italy)


Experimental results

Waveform of the grid voltage and the
grid current during the sag.

Case of a voltage sag of 0.15 p.u (voltage
controlled with droop control) grid voltage,
load voltage and grid current.

Voltage waveform during the sag. Grid voltage
and current (upper). Grid voltage, capacitor
voltage and load voltage (lower)


Conclusions

 A detailed analysis has shown that the novel adaptive droop control strategy
has superior behavior in comparison with the existing droop control methods,
ensuring efficient control of frequency and voltage even in presence of voltage sags

 The converter provides fast dynamic response and active power to local loads
by injecting reactive power into the grid providing voltage support at fundamental
frequency.

Using the basis of the droop characteristic, a new control strategy was proposed,
providing all the desired active power given by the PV source.

The validity of the proposed control showed ride-through capability to the system,
even if a voltage sag is presented in the grid.

PhD Thesis dissertation Page 43

connected mode)
VII. Conclusions
VIII. Future work


PV Wind turbine
panel system UPS

PCC
Inverters

Common
AC bus
. . .
Static
Transfer switch Distributed loads Micro-grid
(IBS)
Typical structure of inverter microgrid based on renewable energy resources

Synchronization
Islanded mode Grid -connected
Operation mode restoration
Grid failure Islanded mode Grid -connected
IBS disconnection Operation mode


Primary control: droop Control (P/Q Sharing,
softstart).
Secondary Control: Synchronization and Tertiary
Restoration (Set-points assignation to the DGs ). Control
Tertiary Control : Power Import/export
from/to the grid. Secondary Control

Primary Control

Bypass off
E= V*
P= P* ; Q=Q*
Import/export
*
P/Q
Grid Islanding
Connected Operation

E= Vg
Bypass on g


Primary control: Droop Control (P/Q Sharing, softstart).
The inverters are programmed to act as generators by including virtual inertias
through the droop method.
Grid-connected mode: Microgrid is connected to the grid through an IBS. In this
case, all DG units must be programmed with the same droop function

Normally, P∗ should coincide with the nominal active power of each inverter, and
Q∗ = 0.

Two possibilities:
1) Importing energy from the grid: the IBS must adjust P∗ by using low
bandwidth communications to absorb the nominal power from the grid in
the PCC.
2) Exporting energy to the gr. the IBS may enforce to inject the rest of the
power to the grid. Moreover, it must adjust the power references.id



This is done with small increments and decrements of P∗ as a function of the
measured grid power, by using a slow PI controller:

P*  k p ( Pg *  Pg )  ki  ( Pg *  Pg )dt  Pi*

where Pg and Pg∗ are the measured and the reference active powers of the grid,
respectively, and Pi∗ is the nominal power of the inverter i.

Similarly, reactive-power control law can be defined as

Q*  k ' p (Qg *  Qg )  k 'i  ( Pg *  Pg )dt  Qi*

where Qg and Qg∗ are the measured and the reference reactive powers of the
grid, respectively, and Q i ∗ is the nominal reactive power.



Islanded mode : When the grid is not present, the IBS disconnects the microgrid
from the main grid, starting the autonomous operation:

 Droop method is enough to guarantee proper power sharing between the
DG units.
 Energetic storage: Power sharing should take into account the batteries
charging level of each module.


Level of charge of the batteries
mmin
 * m
a
sist a 1
Batteries Batteries Fully charge
a  0.01 Empty
30% charged fully charged

P
30% Pmax Pmax Droop characteristic as a function
of the batteries charge level.


Primary control analysis :

 P  c V  cos   E sin   e 
    
 Q  s  c X  sin  E cos   f 
c V
e  (n  nd s ) cos   e  E sin   f 
s  c Rd
m  V  c
f     md  sin   e  E sin   f 
s  Rd ( s  c )
s3  As 2  Bs  C  0
c   V 
A 2 RD  nV cos   nd cV cos   mdVE  cos   nd c  
X   X 
c  V  V 
B  c  ncV cos   mVE cos   nd c  md cVE  cos   n  
X  X  X 
c  V
C  mVE  cos   n 
X  X



Stability for all battery charge conditions

Root locus plot in function of the batteries charge level
(arrows indicate decreasing value from 1 to 0.01).


Power scheme of the primary control
Virtual output impedance concept

Zo Vref  vo  io Zo (s)
*

t Inner loops
 Vref v
Voltage Current PWM +UPS

0.1
 loop loop Inverter
io
Zo (H)

0.05
ZO(s)
0
0.6
10
0.8 1 1.2 1.4 1.6 1.8 2
Virtual output impedance loop
P
Io1 (A)

0

-10 Voltage  P*
10
0.6 0.8 1 1.2 1.4 1.6 1.8 2
*
Vo Reference P/Q
Q* Calculation
E sin (t) E
Io2 (A)

0

Q
-10
0.6 0.8 1 1.2 1.4 1.6 1.8 2 P/Q control outer loops
time (s)


Secondary control: Restoration and synchronization

In order to restore the microgrid voltage to nominal values, the supervisor sends
proper signals by using low bandwidth communications. This control also can be
used to synchronize the microgrid with the main grid before they have to be
interconnected, facilitating the transition from islanded to grid-connected mode.

Grid
Freq. measurement

PLL
_
PI Primary
 *
control control Dg units
+
Supervisory control

Primary
control Dg units


Secondary control analysis :
c V
e  (n  nd s ) cos   e  E sin   f 
s  c Rd
m  V  c
f     md  sin   e  E sin   f 
s  Rd ( s  c )

m  ( P*  Pi* ) EV c
Pi 
X ( s  c )

Pi (ki  k p s)mEV c / N
 2
Pg *
Xs  c [ X  mEV (nk p  1)]s  NmEV c ki


Stability analysis:
Root Locus
1

0.8

0.6

0.4

0.2
4 5 Root-locus plot for
Imaginary Axis

0 a) 0.1 ≤ ki ≤ 0.8.
-0.2
b) 0.7 ≤ kp ≤ 0.8.
-0.4

-0.6

-0.8

-1 Root Locus
-80 -70 -60 -50 -40 -30 -20 -10 0
25
Real Axis
20
a) 15

10

5
4

Imaginary Axis
0

-5

-10
5
-15

-20

b) -25
-70 -60 -50 -40 -30
Real Axis
-20 -10 0


Power scheme of the secondary control

Io
Current
V*
dV control
Driver and
Frequency restoration
Voltage restoration loop
level PWM Inverter
level Voltage Generator
ref
Secondary Gwr(s)
control control
Inner
o loop
loops Vo
Vref Gvr(s)
Primary control (droop method)
vo
Voltage restoration Io
Current
level V*
dV control
Driver and
Low bandwidth loop
PWM Inverter
communications Voltage
Generator
Secondary control control
Inner
loop
loops Vo
Primary control (droop method)


Tertiary Control : Power Import/export from/to the grid
This energy production level controls the power flow between the
microgrid and the grid.
Power flow can be controlled by adjusting the frequency (changing the phase
in steady state) and amplitude of the voltage inside the microgrid by measuring
the P/Q through the static bypass switch. (Grid-connected mode).

  *  m(P  P*)
 PG and PG they can be compared with   *  mP  mP*
*

*
the desired PG and QG .

The control laws can be expressed as
following: *  
grid
d v  k pQ  Q  QG   kiQ   Q  QG  dt
*
G
*
G

d  k pP  P*  P   kiP   P*  P  dt
G G G G

P0 P0 P


Power scheme of the tertiary control

Bypass
Main AC grid

P,Q Microgrid
PLL RMS
P/Q
calculation
df
Q Emax _
_
Q* Vref ++
+
Gq Gse dv
Emin df Secondary
P _ max control
P* + fref +
Gp +
Gsw d
min
Tertiary control Synchronization loop



Inverter_I
500 P* Io1 Vload
P
Q* Vo1 PQ MAIN
P*
calculation Q
ILoad
P* Io2 Iload
pm_sense
Q* Vo2
50 1 RL
qm_sense
Q*
Inverter_II RLoad

Switch
IGrid
Grid connected
Inverter I , Inverter II and Operation
Vgrid ouput voltage P grid
Q grid P*

grid status
Validation
vgrid 2000 P Nominal Inv Q*
(Sg)
Vgrid Vg P Nominal Inv P* grid
V.sin (Wt) L2 Iogrid Pid_Pout
[Vload] VL Pid_Pin
1000
phi_g Q* grid
Terminator R+L
P*grid
1000e-6 model
Vgrid
Grid 0 PID
1000e-6 Status
default Q*grid I_Pgrid



4000

3000
UPS # 2
2000 disconnected
P(W)

P1
1000
P2
Pg
0
Grid connected Islanded
-1000
0 1 2 3 4 5 6 7 8 9
t(s)

4000 Active power transients between grid connected and islanded
modes for 2 DG units
3000

2000
PhD Thesis dissertation
(W)

Page 60


Hot-swap capability

Currents of the UPS#1, UPS#2, UPS#3 and UPS#4 in a) Soft-start
operation, and b) Disconnection scenario



Output current 1

Circulating current

Output current 2

X: 100ms/div, Y: 20 A/div



Non-linear loads

Waveforms of output voltage and load current sharing a nonlinear
load. (X-axis: 5 ms, Y -axis: 20 A/div).


From the analysis, system stability and power management control starting
from a single voltage source inverter to a number of interconnected DG
units forming flexible Microgrids:

A dynamic model design and a small signal analysis.
Control-oriented modeling based on active and reactive power analysis.
A control strategy in order to inject both the desired active and the
reactive power independently into the grid for large range of impedance
grid values.
 Control synthesis based on enhanced droop control technique capable of
decouple active and reactive power flows.
Voltage ride-through capability, by controlling the injection of reactive
power to solve grid voltage sags.


 Droop-controlled microgrids can be used in islanded mode.
 Improvements to the conventional droop method are required for
integrate inverter-based energy resources:
 Improvement of the transient response
 Virtual impedance: harmonic power sharing and hot-swapping
 Adaptive droop control laws
 The hierarchical control is required for a AC microgrid:
 Primary control is based on the droop method allowing the
connection of different AC sources without any
intercommunication.
 Secondary control avoids the voltage and frequency deviation
produced by the primary control. Only low bandwidth
communications are needed to perform this control level. A
synchronization loop can be add in this level to transfer from
islanding to grid connected modes.
 Tertiary control allows to import/export active and reactive power
to the grid.


Journal Publications
Control Strategy for Flexible Microgrid Based on Parallel Line-Interactive UPS
Systems. Guerrero, J.M.; Vasquez, J.C.; Matas, J.; Castilla, M.; de Vicuna, L.G.
Industrial Electronics, IEEE Transactions on, Volume 56, Issue 3, March 2009
Page(s):726 – 736.

Voltage Support Provided by a Droop-Controlled Multifunctional Inverter
Vasquez, J.C.; Mastromauro, R.A.; Guerrero, J.M.; Liserre, M. Industrial electronics,
IEEE Transactions on , Volume 56, Issue 11, Nov. 2009 Page(s):4510 – 4519

Adaptive Droop Control Applied to Voltage-Source Inverters Operating in Grid-
Connected and Islanded Modes. Vasquez, J.C.; Guerrero, J.M.; Luna, A.; Rodriguez,
P.; Teodorescu, R. Industrial Electronics, IEEE Transactions on Volume 56, Issue 10,
Oct. 2009 Page(s):4088 – 4096

Book chapters

Josep M. Guerrero and Juan. C. Vasquez, Uninterruptible Power Supplies, The
Industrial Electronics Handbook, Second edition, Irwin, J. David (ed.).


Conference Publications

Adaptive Droop Control Applied to Distributed Generation Inverters Connected to the Grid, J.
C. Vasquez, J. M. Guerrero, E. Gregorio, P. Rodriguez, R. Teodorescu and F.Blaabjerg, IEEE
International Symposium on Industrial Electronics (ISIE’08). Pages 2420-2425. Jun. 30, 2008.

Droop Control of a Multifunctional PV Inverter. R. A.Mastromauro,M. Liserre, A. dell’Aquila,
J.M. Guerrero and J. C. Vasquez, IEEE International Symposium on Industrial Electronics
(ISIE’08), pages 2396-2400. Jun. 30, 2008.

Ride-Through Improvement of Wind-Turbines Via Feedback Linearization, J.Matas, P.
Rodriguez, J.M. Guerrero, J. C. Vasquez, In IEEE International Symposium on Industrial
Electronics (ISIE’08), Pages 2377-2382, Jun. 30, 2008.

Parallel Operation of Uninterruptible Power Supply Systems in Microgrids, J. M. Guerrero, J.
C. Vasquez, J. Matas, J. L. Sosa and L. Garcia de Vicuña, 12th European Conference on Power
Electronics and Applications (EPE’07), sept.2007.Page(s): 1-9.

Hierarchical control of droop-controlled DC and AC microgrids−a general approach towards
standardization, J. M. Guerrero, J. C. Vasquez and R. Teodorescu, “,” in Proc. IEEE IECON,
2009, pp. 4341-4346.


Control and power management of DC coupling microgrids.

Addresses an open field for new renewable energy power-management control
strategies. (Power quality, electrical power quality, reliability and flexible
operation in Microgrids). Hierarchical control.

Integrated energy storage systems.

 Capabilities and limitations of each storage technology. The final goal is to
develop and integrate energy storage systems specifically designed and optimized
for grid-tied PV applications.

Improving the hierarchical control strategy.

DPS applications such as telecom voltage networks.
Hard power quality standards, demand new control strategies imposed for
energy management of Microgrids, based on intelligent/adaptive algorithms.
Enhancing of tertiary control for harmonics injection to the grid (power quality)
Active filters functionalities.


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Decentralized Generation In Microgrids

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