Post on 18-Dec-2015
Marco Liserre liserre@ieee.org
Grid converter control
Grid converter control
Marco Liserre
liserre@poliba.it
Marco Liserre liserre@ieee.org
Grid converter control
A glance at the lecture content
• Introduction • Dc-voltage control• Power control• Islanding, microgrid, droop
control, grid supporting
Marco Liserre liserre@ieee.org
Grid converter control
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)
Marco Liserre liserre@ieee.org
Grid converter control
+
-dcV
1L 2L gLgii
cV
+
-
+
-V
+
-gV
POWER CONTROL
CURRENT CONTROL
VOLTAGE CONTROL
DC VOLTAGE CONTROL
GRID MANAGEMENT
dcV icV gV
+
-
Another major difference is that the grid converter could be requested to operate on the grid side as:
a controlled current source
a controller voltage source
Introduction
with the LCL-filter both the options
can be integrated within a multiloop
structure
Marco Liserre liserre@ieee.org
Grid converter control
Dc voltage control In the grid connected converter a change of the produced power causes
transient 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 discharge processes
Marco Liserre liserre@ieee.org
Grid converter control
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 )
2s
oo
P n Tv
C v
Voltage error as a result of power change
Marco Liserre liserre@ieee.org
Grid converter control
Linear control 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
Marco Liserre liserre@ieee.org
Grid converter control
1 1
ˆd 3ˆ ˆ ˆˆ ˆ ˆ ˆd 2dc dc
dc dc dc dc o o d d d d q q q qV v
V v C V v I i E e I i E e I it
Dc current [A]
ˆ 3ˆ 2 1dc o
od
v R
R Csi
1
ˆˆ 1dc o
oo
v R
R Csi
ˆ 3ˆ 1dc
d o
v
e R Cs
constant power case
plant
generator disturbance
grid disturbance
Linear control: small signal analysis
Marco Liserre liserre@ieee.org
Grid converter control
Voltage-oriented control The Voltage Oriented Control (VOC) of the grid converter is based on
the use of a dq-frame rotating at speed and oriented such as the d-axis is aligned on the grid voltage vector
The reference current d-component i*d is controlled to perform the active power regulation while the reference current q-component i*q is controlled to obtain reactive power regulation
Similar results can be achieved in a stationary -frame
i
i
qi di
i
Marco Liserre liserre@ieee.org
Grid converter control
ip
KK
s
dcv
dcV
P
Q
+ -
di
qi
dcV controller
PLLgv
gv
gv
fgV
je
gdv
gqv
*v
abc
je
i
i
di
qi
+-
di
di
gdv
+-
qi Current
controller
Currentcontroller
gqv
je
v
v
ip
KK
s
ip
KK
s
L
L
i αβ
abc
αβ
αβ
abc
2 2
1 gd gq
gq gdgd gq
v v
v vv v
gdv gqv
X
+ -
• active and reactive
power feed-forward
control
• Vdc control acts on
the power reference
Synchronous frame VOC: PQ open loop control
Marco Liserre liserre@ieee.org
Grid converter control
• active and reactive
power PI-based control
• Vdc control acts on id*
Synchronous frame VOC: PQ closed loop control
ip
KK
s
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
gv
fgV
je
gdv
gqv
*v
abc
je
i
i
di
qi
+-
di
di
gdv
+-
qi Current
controller
Currentcontroller
gqv
je
v
v
ip
KK
s
ip
KK
s
ip
KK
s
ip
KK
s
L
L
i αβ
abc
αβ
αβ
abc
gdv gqv
Marco Liserre liserre@ieee.org
Grid converter control
• PLL may be avoided but it is used for
making the control freq. adaptive
Stationary frame VOC: PQ open loop control
ip
K sK
s
2 2
i
i
i
i
i
+-
i
+-
i Current
controller
Currentcontroller
v
v
ip
K sK
s
2 2
abc
αβ *v
αβ
abc
dcV
P
Q
+ -
dcV controller
ip
KK
s
2 2
1 g g
g gg g
v v
v vv v
gv gv
X
+ -
dcv
PLLgv
gv
gv
f ,
• active and reactive
power feed-forward
control
• Vdc control acts on the
power reference
Marco Liserre liserre@ieee.org
Grid converter control
• PLL is still indispensable
for reference generation
Stationary frame VOC: PQ closed loop control
ip
K sK
s
2 2
θ
sin
cos
dcv
dcV
P
Q
P
Q+-
+-
+ -
i
i
I
Q controller
P controller
dcV controller
PQ calculation
+ -
i
i
i
+-
i
+-
i Current
controller
Currentcontroller
v
v
ip
K sK
s
2 2
ip
KK
s
ip
KK
s
ip
KK
s
abc
αβ *v
αβ
abc
g g
g g
P v i v i
Q v i v i
i
i
gv gv
PLLgv
gv
gv
f ,
• active and reactive
power PI-based control
• Vdc control acts on I
Marco Liserre liserre@ieee.org
Grid converter control
Microgrid operation with controlled storage
G+-
+-
+-
G
FLYWHEELVOLTAGE CONTROL
STORAGE CONTROL
VOLTAGE CONTROL
CURRENT CONTROL
WT
MICRO-GRID MANEGEMENT
*CV *
dcV *dc,ESV*
dcI
dcidcV i
cV dc,ESV
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
Marco Liserre liserre@ieee.org
Grid converter control
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 BA
V V VP
Z Z
2
sin sinA A BA
V V VQ
Z Z
cos A Ad A B
A
RP XQV V V
V
sin A Aq B
A
XP RQV V
V
A
A B
XP
V V A
A BA
XQV V
V
Marco Liserre liserre@ieee.org
Grid converter control
Droop control The angle δ 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
Marco Liserre liserre@ieee.org
Grid converter control
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 forming
Marco Liserre liserre@ieee.org
Grid converter control
Improving grid power quality: voltage dips
Vload
Ic
IloadIg
E
CURRENT CONTROLLEDgrid-feeding component adjusting reactive power according to grid
voltage variations
Vload
Vc
Iload
Ig
E
VOLTAGE CONTROLLEDgrid-forminng component
controlling its output voltage in order to stabilize load voltage
Voltage dip compensation by means of reactive power injection
Marco Liserre liserre@ieee.org
Grid converter control
Improving grid power quality: voltage dips
Iload
Ic’
E Ig
PIRepetitive
control
Ic’
+
- -
+
Iref
Vc’
grid
Vref
Vpeak
mpptd+ + MPPTalgorithm
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)
Marco Liserre liserre@ieee.org
Grid converter control
Conclusions
• AC Power control is performed through voltage and/or current 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 and harmonics)
Marco Liserre liserre@ieee.org
Grid converter control
Bibliography1. 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. Cárdenas, R. Peña, M. Pérez, J. Clare, G. Asher, and F. Vargas, “Vector Control of Front-End Converters for Variable-Speed Wind–Diesel 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. García de Vicuña, 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.
Marco Liserre liserre@ieee.org
Grid converter control
Bibliography9. 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 ISIE’00, Vol. 2, pp. 453-458, 2000.
13. R. A. Mastromauro, M. Liserre, A. Dell’Aquila, 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. 1707–1719, Nov/Dec. 2005.
Marco Liserre liserre@ieee.org
Grid converter control
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 Systems – in 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