7/14/2019 Liserre Lecture 8
1/23
Grid converter control
Marco Liserre [email protected]
Grid converter control
Marco Liserre
7/14/2019 Liserre Lecture 8
2/23
Grid converter control
Marco Liserre [email protected]
A glance at the lecture content
Introduction
Dc-voltage control Power control
Islanding, microgrid, droop
control, grid supporting
7/14/2019 Liserre Lecture 8
3/23
Grid converter control
Marco Liserre [email protected]
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, powerquality)
ACPOWER
CONTROL
GRID
SUPPORTING
GRID
FORMING
DC VOLTAGE
CONTROL
GRID
FEEDING
POWER
THE
ORY
stationary
frameab
natural
frame abc
rotating
frame dq
AC CURRENT
CONTROL
AC VOLTAGE
CONTROL
7/14/2019 Liserre Lecture 8
4/23
Grid converter control
Marco Liserre [email protected]
+
-dcV
1L 2L gL
gii
cV
+
-
+
-V
+
-
gV
POWER CONTROL
CURRENT
CONTROL
VOLTAGE
CONTROL
DC VOLTAGE
CONTROL
GRID
MANAGEMENT
dcVi
cV gV
+
-
Another major difference is that the grid converter could be requested to operate onthe grid side as:
a controlled current source
a controller voltage source
Introduction
with the LCL-filter
both the options
can be integrated
within a multiloopstructure
7/14/2019 Liserre Lecture 8
5/23
Grid converter control
Marco Liserre [email protected]
Dc voltage control
In the grid connected converter a change of the produced power causestransient conditions hence charge or discharge processes of the dc capacitor
The increase of the produced power results in voltage overshoot while its
decrease results in voltage undershoot
So, from the point of view of the dc voltage control, power changes result in
voltage variations that should be compensated by charge or dischargeprocesses
dcV
1L i
cV
+
-
+
-V
+
-
2L gLgi
cV
+
-
gV
+
-
produced power
7/14/2019 Liserre Lecture 8
6/23
Grid converter control
Marco Liserre [email protected]
Dc voltage control
The dc voltage control is achieved through the control of the power exchanged by
the converter with the grid or through the control of a dc/dc converter
In the first case the decrease or increase of the dc voltage level is obtained
injecting more or less power to the grid respect to that one produced by the
WTS
In the second case the grid converter does not play a role in the
management of the dc-link
*
(3 )
2
so
o
P n Tv
C v
Voltage error as a result
of power change
7/14/2019 Liserre Lecture 8
7/23
Grid converter control
Marco Liserre [email protected]
Linear control
dcV
1L i
cV
+
-
+
-
V
CC
i
+
-
2L gL
gi
cV
+
-
gV
+
-
VCi*
synch
*
dcV
The control of the dc voltage through the ac current can result in the identification of
two loops, an outer dc voltage loop and an internal current loop
The internal loop is designed to achieve short settling times
On the other hand, the outer loop main goals are optimum regulation and stability
thus the voltage loop could be designed to be some what slower
Therefore, the internal and the external loops can be considered decoupled
7/14/2019 Liserre Lecture 8
8/23
Grid converter control
Marco Liserre [email protected]
dcV
TOTL
i+
-
V+
- E
oio1i +
-
1 1d 3
d 2
dc dcdc dc dc dc o o d d d d q q q q
V vV v C V v I i E e I i E e I i
t
Dccurrent
[A]
3
2 1
dc o
od
v R
R Csi
1
1
dc o
oo
v R
R Csi
3
1
dc
d o
v
e R Cs
constant power case
plant
generator disturbance
grid disturbance
Linear control: small signal analysis
7/14/2019 Liserre Lecture 8
9/23
Grid converter control
Marco Liserre [email protected]
Voltage-oriented control
The Voltage Oriented Control (VOC) of the grid converter is based onthe use of a dq-frame rotating at w speed and oriented such as the d-axis is aligned on the grid voltage vector
The reference current d-
component i*d is controlled toperform the active powerregulation while the referencecurrent q-component i*q iscontrolled to obtain reactive
power regulation Similar results can be
achieved in a stationary ab-frame
ia
ib
qi di
b
d
qi
a
7/14/2019 Liserre Lecture 8
10/23
Grid converter control
Marco Liserre [email protected]
ip KK
s
dcv
dcV
P
Q
+-
di
qi
dcV controller
PLLgv
gv a
gv b
fgV
je
gdv
gqv
*v
abc
je
ia
ib
di
qi
+-
di
di
gdv
+-
qi Current
controller
Currentcontroller
gqv
je
va
vb
i
p
KK
s
i
p
KK
s
L
L
i
abc
abc
2 2
1 gd gq
gq gdgd gq
v v
v vv v
gdv gqv
X
+-
active and reactive
power feed-forwardcontrol
Vdc control acts on
the power reference
Synchronous frame VOC: PQ open loop control
qi di
d
q
i
7/14/2019 Liserre Lecture 8
11/23
Grid converter control
Marco Liserre [email protected]
active and reactive
power PI-based control
Vdc control acts on id*
Synchronous frame VOC: PQ closed loop control
qi di
d
q
i
i
pKKs
gd d gq q
gq d gd q
P v i v i
Q v i v i
dcv
dcV
P
Q
di
qi
P
Q
+-
+-
+-
di
qi
Q controller
P controller
dcV controller
PQ controller
+-
PLLgv
gv a
gv b
fg
V
je
gdv
gqv
*v
abc
je
ia
ib
di
qi
+-
di
di
gdv
+-
qi Current
controller
Currentcontroller
gqv
je
va
vb
i
p
KK
s
i
p
KK
s
i
p
KK
s
i
p
KK
s
L
L
i
abc
abc
gdv
gqv
7/14/2019 Liserre Lecture 8
12/23
Grid converter control
Marco Liserre [email protected]
PLL may be avoided but it is used for
making the control freq. adaptive
Stationary frame VOC: PQ open loop control
ia
ib
b
i
a
i
p
K sK
s
2 2w
ia
ib
i
ia
ib
+-
ia
+-
ib Current
controller
Currentcontroller
va
vb
i
p
K sK
s
2 2w
abc
*v
abc
dcV
P
Q
+-
dcV controller
i
p
KK
s
2 2
1 g g
g gg g
v v
v vv v
a b
b aa b
gv a gv b
X
+-
dcv
PLLgv
gv a
gv b
f ,w
active and reactive
power feed-forwardcontrol
Vdc control acts on the
power reference
7/14/2019 Liserre Lecture 8
13/23
Grid converter control
Marco Liserre [email protected]
PLL is still indispensable
for reference generation
Stationary frame VOC: PQ closed loop control
ia
ib
b
i
a
i
p
K sK
s
2 2w
sin
cos
dcv
dcV
P
Q
P
Q
+-
+-
+-
ia
ib
I
Q controller
P controller
dcV controller
PQ calculation
+-
i
ia
ib
+-
ia
+-
ib Current
controller
Currentcontroller
va
vb
i
p
K sK
s
2 2w
i
p
KK
s
i
p
KK
s
i
p
KK
s
abc
*v
abc
w
a a b b
b a a b
g g
g g
P v i v i
Q v i v i
iaib
gv a gv b
PLLgv
gv a
gv b
f ,w
active and reactive
power PI-based control
Vdc control acts on I
7/14/2019 Liserre Lecture 8
14/23
Grid converter control
Marco Liserre [email protected]
Microgrid operation with controlled storage
G+
-
+
-
+
-
G
FLYWHEELVOLTAGE
CONTROLSTORAGECONTROL
VOLTAGE
CONTROL
CURRENT
CONTROL
WT
MICRO-GRID MANEGEMENT
*CV
*
dcV *dc,ESV*dcI
dci dcV i cV dc,ESV
w
ENERGY STORAGE
load
Multiloop control for microgrid operation with WT system
The management of the dc voltage is in charge of the controlled storage
unit ESS
A flyweel is used
7/14/2019 Liserre Lecture 8
15/23
Grid converter control
Marco Liserre [email protected]
Droop control
Using short-line model and complex phasors, the analysis below is valid for
both single-phase and balanced three-phase systems.
At the section A
For a mainly inductive line
I
VA
Z
Vd
VBI
VB0
VA
Vq
RIXI
BA
cos cosA A BAV V V
PZ Z
2
sin sinA A B
A
V V VQ
Z Z
cosA A
d A BA
RP XQV V V
V
sin A A
q BA
XP RQV V
V
A
A B
XP
V V AA B
A
XQV V
V
7/14/2019 Liserre Lecture 8
16/23
Grid converter control
Marco Liserre [email protected]
Droop control The angle can be controlled regulating the active power P whereas the inverter
voltage VA is controllable through the reactive power Q. Control of the frequency dynamically controls the power angle and, thus, the real
power flow.
Thus by adjusting P and Q independently, frequency and amplitude of the grid
voltage are determined
However, low voltage distribution lines have a mainly resistive nature.
0 0pf f k P P 0 0qV V k Q Q
Q
V
V0
Q0 P
f
f0
P0
7/14/2019 Liserre Lecture 8
17/23
Grid converter control
Marco Liserre [email protected]
Droop control for grid supporting operation
The droop control is not only used in island application when it is needed
to a have a wireless load sharing but also in order to support the grid
In this case grid-feeding and grid-forming schemes can be modified
accordingly including droop control
grid feeding grid formingVSI
Modulator
dcv+
-
1L
v
i
CvC fC
*
v
+
-
Current
control
+
-
Voltage
control
*i
Power
calculation
Droop
control
*
cvsynch
P
Q
VSI
Modulator
dcv+
-
1L
v
i
CvC fC
*v
+
-
Current
control
+
-
*i
Inverse
droop
control
synch
7/14/2019 Liserre Lecture 8
18/23
Grid converter control
Marco Liserre [email protected]
Improving grid power quality: voltage dips
Vload
E
Iload
Ig
Ic
Vload
E
Iload
Ig
Ic
compensation of a voltage dip of 0.3 pu
Vload
E
Iload
Ic
Ig
VLg
VLg VLg
current-controlled converter in normal
conditionsvoltage-controlled converter in normal
conditions
Vload
Ic
IloadIg
E
CURRENT CONTROLLED
grid-feeding component adjusting
reactive power according to grid
voltage variations
Vload
Vc
IloadIg
E
VOLTAGE CONTROLLED
grid-forminng component
controlling its output voltage in
order to stabilize load voltage
Voltage dip compensation by means of reactive power injection
7/14/2019 Liserre Lecture 8
19/23
Grid converter control
Marco Liserre [email protected]
Improving grid power quality: voltage dips
Iload
Ic
EIg
PIRepetitive
control
Ic
+
- -
+
Iref
Vc
grid
Vref
Vpeak
mpptd+ + MPPT
algorithm
PV
Ipv
Upv
PLL
Vg
Also low power PV systems can be designed to improve the power
quality. They can provide grid voltage support and compensation of
harmonic distortion at the point of common coupling (PCC)
7/14/2019 Liserre Lecture 8
20/23
Grid converter control
Marco Liserre [email protected]
Conclusions
AC Power control is performed through voltage and/orcurrent control
Grid forming, grid feeding or grid supporting
Grid supporting: harmonics, reactive power, dips
Droop control for amplitude and frequency control
Voltage control can be used for supporting voltage (dips andharmonics)
7/14/2019 Liserre Lecture 8
21/23
Grid converter control
Marco Liserre [email protected]
Bibliography
1. F. Blaabjerg, R. Teodorescu, M. Liserre, A. V. Timbus, Overview of Control and Grid Synchronization for
Distributed Power Generation Systems IEEE Transactions on Industrial Electronics, Ottobre 2006, Vol. 53,No. 5, pagg. 1398-1408.
2. R. Crdenas, R. Pea, M. Prez, J. Clare, G. Asher, and F. Vargas, Vector Control of Front-End Converters
for Variable-Speed WindDiesel Systems IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL.
53, NO. 4, AUGUST 2006 1127.
3. K. De Brabandere, B. Bolsens, J. Van den Keybus, A. Woyte, J. Driesen and R. Belmans, A voltage and
frequency droop control method for parallel inverters Proc. of Pesc 2004, Aachen 2004
4. J. M. Guerrero, L. Garca de Vicua, J. Matas, M. Castilla, and J. Miret, A Wireless Controller to Enhance
Dynamic Performance of Parallel Inverters in Distributed Generation Systems IEEE TRANSACTIONS ON
POWER ELECTRONICS, VOL. 19, NO. 5, SEPTEMBER 2004, 1205-1213.
5. C. Klumpner, M. Liserre, F. Blaabjerg, Improved control of an active-front-end adjustable speed drive with a
small de-link capacitor under real grid conditions PESC 04, Vol. 2, 20-25 June 2004, pp. 1156 1162.
6. T. Ohnishi, Three phase PWM converter/inverter by means of instantaneous active and reactive power
control, Proc. of IECON 91, Vol. 2, 1991, pp. 819-824.
G id l
7/14/2019 Liserre Lecture 8
22/23
Grid converter control
Marco Liserre [email protected]
Bibliography
9. L. Malesani, L. Rossetto, P. Tenti and P. Tomasin, AC/DC/AC PWM converter with reduced energy storage in
the dc link, IEEE Transactions on Industry Applications, 1995, 287-292.
10. Poh Chiang Loh and Donald Grahame Holmes, Analysis of Multiloop Control Strategies for LC/CL/LCL-
Filtered Voltage-Source and Current-Source Inverters IEEE TRANSACTIONS ON INDUSTRY
APPLICATIONS, VOL. 41, NO. 2, MARCH/APRIL 2005, 644-654.
11. Jinn-Chang Wu; Hurng-Liahng Jou, "A new UPS scheme provides harmonic suppression and input power
factor correction," IEEE Transactions on Industrial Electronics, , vol.42, no.6, pp.629-635, Dec 1995
12. J.R. Espinoza, G. Joos, M. Perez, T.L.A Moran, Stability issues in three-phase PWM current/voltage source
rectifiers in the regeneration mode, Proc. of ISIE00, Vol. 2, pp. 453-458, 2000.
13. R. A. Mastromauro, M. Liserre, A. DellAquila, T. Kerekes, A Single-Phase Grid Connected Photovoltaic
System with Power Quality Conditioner Functionality, accepted for future publication on IEEE Transactions
on Industrial Electronics.
14. Y. W. Li, D. M. Vilathgamuwa and P. C. Loh, Micro-grid power quality enhancement using a three-phase four-
wire grid-interfacing compensator, IEEE Trans. Ind. Applicat., vol. 41, pp. 17071719, Nov/Dec. 2005.
G id t t l
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Grid converter control
Marco Liserre liserre@ieee org
Acknowledgment
Part of the material is or was included in the present and/or past editions
of the
Industrial/Ph.D. Course in Power Electronics for Renewable Energy
Systemsin theory and practice
Speakers: R. Teodorescu, P. Rodriguez, M. Liserre, J. M. Guerrero,
Place: Aalborg University, Denmark
The course is held twice (May and November) every year
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