pi current controller for grid connected vsi in dpgs applications dpgs ...
Transcript of pi current controller for grid connected vsi in dpgs applications dpgs ...
PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONS
Buletinul AGIR nr. 3/2012 iunie-august 1
PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSDPGS APPLICATIONSDPGS APPLICATIONSDPGS APPLICATIONS
Lecturer Eng. Ana Luminita BAROTE, PhD1, Prof. Eng. Corneliu MARINESCU, PhD
1
1University „Transilvania” from Braşov
REZUMAT. REZUMAT. REZUMAT. REZUMAT. In aceasta lucrare se prezinta In aceasta lucrare se prezinta In aceasta lucrare se prezinta In aceasta lucrare se prezinta un studiu asupra un studiu asupra un studiu asupra un studiu asupra controlulcontrolulcontrolulcontroluluiuiuiui de de de de curent cu regulatore PI implementat in curent cu regulatore PI implementat in curent cu regulatore PI implementat in curent cu regulatore PI implementat in sistemul de referinta rotativ sistemul de referinta rotativ sistemul de referinta rotativ sistemul de referinta rotativ dqdqdqdq pentru convertoare de retea pentru convertoare de retea pentru convertoare de retea pentru convertoare de retea utilizate utilizate utilizate utilizate in aplicatii cu sisteme distribuite de generare. in aplicatii cu sisteme distribuite de generare. in aplicatii cu sisteme distribuite de generare. in aplicatii cu sisteme distribuite de generare. PrincipalePrincipalePrincipalePrincipalele obiective ale lucrariile obiective ale lucrariile obiective ale lucrariile obiective ale lucrarii suntsuntsuntsunt implementarea controlimplementarea controlimplementarea controlimplementarea controlului de curentului de curentului de curentului de curent in convertorul de in convertorul de in convertorul de in convertorul de rererereteateateatea si si si si compensarecompensarecompensarecompensareaaaa armonicelor de ordin armonicelor de ordin armonicelor de ordin armonicelor de ordin inferior.inferior.inferior.inferior. Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura analizata analizata analizata analizata aaaa fost simulata in fost simulata in fost simulata in fost simulata in SimulinkSimulinkSimulinkSimulink apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si control in timp real dSPACE. control in timp real dSPACE. control in timp real dSPACE. control in timp real dSPACE. Cuvinte cheie: Cuvinte cheie: Cuvinte cheie: Cuvinte cheie: convertor de retea, regulator de curent, compensator armonic, calitatea energiei.
ABSTRACT. ABSTRACT. ABSTRACT. ABSTRACT. This papThis papThis papThis paper deals with the design and implementation of PI current control method in the er deals with the design and implementation of PI current control method in the er deals with the design and implementation of PI current control method in the er deals with the design and implementation of PI current control method in the dqdqdqdq synchronous synchronous synchronous synchronous rotating reference frame for grid side converterrotating reference frame for grid side converterrotating reference frame for grid side converterrotating reference frame for grid side converter usedusedusedused in in in in DPGSDPGSDPGSDPGS applications. The goals of this paper are to implement a applications. The goals of this paper are to implement a applications. The goals of this paper are to implement a applications. The goals of this paper are to implement a current current current current control technique for the grid sidcontrol technique for the grid sidcontrol technique for the grid sidcontrol technique for the grid side e e e VSI andVSI andVSI andVSI and a compensation method a compensation method a compensation method a compensation method for lowfor lowfor lowfor low----order harmonicsorder harmonicsorder harmonicsorder harmonics. . . . A comparative A comparative A comparative A comparative study in terms of current harmonic distortion between study in terms of current harmonic distortion between study in terms of current harmonic distortion between study in terms of current harmonic distortion between two different valuestwo different valuestwo different valuestwo different values of PI of PI of PI of PI proportional gain proportional gain proportional gain proportional gain running in steady running in steady running in steady running in steady state condition is made. state condition is made. state condition is made. state condition is made. The analyzed structureThe analyzed structureThe analyzed structureThe analyzed structure was swas swas swas simulated with Simulated with Simulated with Simulated with Simulink softwareimulink softwareimulink softwareimulink software then then then then implemented and tested in implemented and tested in implemented and tested in implemented and tested in laboratory using a dSPACE setup.laboratory using a dSPACE setup.laboratory using a dSPACE setup.laboratory using a dSPACE setup. Keywords:Keywords:Keywords:Keywords: grid converter, current controller, harmonic compensator, power quality.
1. INTRODUCTION
The energy demand has increased in the last years as
a result of the industrial development, and is predicted
to continue increasing, by at least 50 % in the next 10
years. This has focused more research attention on
Distributed Power Generation Sources (DPGS), a
promising alternative to satisfy the ever-growing need
for electricity, like wind turbines, photovoltaic systems,
etc. and the parameters of their connection to the grid,
[1], [2]. The increase interest in renewable energy
production together with higher and higher demand
from the energy distribution companies (TSO),
regarding grid energy injection and grid support in case
of a failure raises new challenges in terms of control for
renewable energy sources (RES) systems [3]. A general
block diagram of a DPGS is shown in Fig. 1.
Fig. 1. DPGS block diagram.
The main objectives investigated in this paper are
the control part of the power converter connected to the
grid by means of a passive filter and a harmonic
compensation technique. In the literature, different
power converter topologies are used to interface DPGS
with the utility network, [4]-[7].
In this work, the investigation is limited to the
control of three phase pulse width modulated (PWM)
voltage source inverter (VSI), the most used power
electronic interface for RES [8].
In order to apply to a broad range of DPGS, the
input power sources are not considered, the inverter
being powered by a DC power source.
Current control technique for the grid inverter is
modeled, simulated and implemented in laboratory
using dSpace setup, followed by a comparative analysis
between the obtained results.
A synchronous rotating dq frame PI current
controller was chosen to control the VSI. This method
is analyzed and implemented in the paper. A description
of dq-PI current controller advantages and
disadvantages is presented in [9], [10].
As a tradeoff between a good noise rejection and
good dynamics for the analyzed structure, the PI
integrator gain was set to Ki=1000 [11] and for the size
of the proportional gain Kp, which determines the
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bandwidth and stability phase margin [11]-[13], were
chosen two different values (Kp=10 and Kp=20).
A comparative study between these two values will
be presented in the simulation and experimental results
session.
By adding a Harmonic Compensator (HC) to the
current controller, a good harmonics rejection is
obtained in both analyzed cases.
A PLL is used also in this strategy in order to detect
the grid phase angle θ and grid frequency.
The paper is organized as follows: in Section II the
grid connected system configuration with the control
methods, Section III describes the simulation and
experimental results while conclusions are provided in
Section IV.
2. SYSTEM CONFIGURATION AND CONTROL
The analyzed system configuration of the grid
connected inverter is presented in Fig. 1. The input
power sources are considered a DC power supply, a
VSI with PI current controller + HC and a
synchronization technique, a LCL filter, a transformer
and a utility grid.
The structure of the grid side converter based on PI
current controllers in dq frame control involving cross
coupling and feed forward of the grid voltages as
depicted in Fig. 2. By using the Park transformations,
the three phase currents and voltages from abc frame
are transformed in dq frame currents and voltages.
The iq current component determines reactive power
while id decide the active power flow. Thus the active
and reactive power can be controlled independently.
Employment of PI controllers for current regulation
as Fig. 2 illustrates, cross-coupling terms and grid
voltage feed-forward may be necessary in order to
obtain best results [14].
dI
*
dI
abcI
θ
0*=qI
qI
Lω
Lω
*
dV
dV
qV qHCV
dHCV
*
qV
dqPdqI
*
abcV
×÷
dcV
*P *Q
Fig. 2. The dq current control based on PI controller with HC.
The input of the current controller is the error
between the measured and reference grid current. The
current controller output is the reference grid voltage,
which divided by the DC source voltage gives the duty
cycle for the inverter.
A HC is applied in synchronous reference frames,
where the currents being regulated are dc quantities,
which eliminates the steady-state error, in order to
obtain an improved power quality in the analyzed
configuration.
As can be seen in Fig. 3, two controllers should be
implemented in two frames rotating at -5ω and +7ω.
Two transformation modules are necessary to transfer
the αβ stationary quadrature system into dq
synchronous rotating frame and vice versa. Noticeable
is in this case the complexity of the control algorithm,
compared with the structure implemented in stationary
reference frame, [11], [15].
As the most important harmonics in the current
spectrum are the 5th and 7th, in this paper HC is
designed to compensate these two selected harmonics.
0*
5=dI
0*
5=qI
αI
βI
θ θ
θ5je
θ5je
−
ω5−
0*
7=dI
0*
7=qI
θ θ
θ7je
− θ7je
ω7+
αV
βV
αV
βV
αI
βI
s
Ki5
s
K i7
s
Ki5
s
Ki7
Fig. 3. The HC diagram for PI controller.
In order to synchronize the injected grid current with
the grid voltage, a PLL block is used. A Dual Second
Order Generalized Integrator – DSOGI are employed in
the Quadrature-Signals Generator (QSG) to obtain two
couples of orthogonal and cleaned signals. Practically
the grid disturbances are filtered before entering in the
PLL scheme [11], [16]. Block diagram of a DSOGI-
PLL is presented in Fig. 4.
abcV
αV
βV
'
αV
'
αqV+
βV
'
βqV
+
αV+
qV
+
dV
ffω
'ω
'ω
'+θ
'+θ∫
Fig. 4. Block diagram of the three-phase DSOGI-PLL.
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The output of the PI controller in addition with the
feed forward frequency ωff is modulated and gives the
phase angle (θ). The grid phase angle obtained during
experiments with the voltages (+
αV ,+
βV ) are represented
in Fig. 5.
0 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]
SO
GI-
PLL
Valpha+ Theta PLL Vbeta+
Fig. 5. Grid phase angle.
The active and reactive powers flowing from an
inverter to a grid can be described and expressed as in
Fig. 6. The used P/Q droop control method [17], [18]
has the ability to change the active and reactive power
reference according with the system requirements.
Therefore, in the studied configuration, the reference
active power values are set at P*=500; 1000; 1500;
2000 W and Q*=0 var. It is mentioned that, the nominal
power of the grid side inverter is 2.2 kVA.
Fig. 6. P/Q droop functions in studied configuration.
3. SIMULATION AND EXPERIMENTAL RESULTS
The proposed system has been modeled and
simulated using the Matlab/Simulink environment.
Fig. 7 shows the block diagram. The simulation
results will be used and verified during the practical
implementation.
The experimental results are obtained on a
laboratory test bench in the Green Laboratory at
Aalborg University of Denmark. The current control
method of the grid side inverter have been implemented
in dSPACE platform and tested for evaluating their
performance. The setup block diagram is presented in
Fig. 8 and consists in a three-phase inverter with the
rated power of 2.2 kVA , 2 series connected DC power
supplies (3 kW, 330 V), LCL filter (see Table I), LEM
boxes for measurement of Vdc, Iabc and Vabc, three-phase
transformer (5 kVA) and a dSPACE system. The
parameters of the system are presented in Table I.
The LCL filter implemented is composed by three
reactors with resistance RI and inductance LI on the
converter side and three capacitors CF; a further branch
of the filter, represented as three reactors with
resistance RG and inductance LG, comes from taking in
account the impedance of the transformer adopted for
connection to the grid and the grid impedance. Effect of
the filter is the reduction of high frequency current
ripple injected by the inverter [19].
The control system was developed in
Matlab/Simulink and then automatically processed and
run by the DS1103 PPC card. A Graphical User
Interface (GUI) (see Fig. 9) has been build using the
Control Desk software in order to allow a real time
control and evaluation of the system.
The GUI can be used to control inputs like: start/stop
of the system; active and reactive power reference and
current control methods. Also, it can be used to view
different outputs like: measured three phase grid
currents and voltages; measured DC voltage; measured
active and reactive power; phase angle provided by the
PLL, etc.
As well, different experimental cases can be tested,
like a step or stairs in the active power reference to
confirm the good implementation of the analyzed
current control method.
Table 1
Details of the hardware setup
Parameter Value
Grid voltage (line-line rms) 380 V
Grid frequency 50 Hz
Inverter-side inductance mHLI 9.6=
Inverter-side resistance Ω= 1.0IR
Grid side inductance (Transformer
inductance)
mHLG 2=
Grid side resistance Ω= 4.1GR
Filter capacitance FCF µ7.4=
Switching frequency kHzf s 10=
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Vdc=650 V
g
A
B
C
+
-
A
B
C
A
B
C
Ri, Li
Vabc
Iinv
Iout
Vdc
w_sync
Duty Cycles
Pl Current Control
Vabc
Iabc
A
B
C
a
b
c
IabcA
B
C
a
b
c
Vabc
Iabc
A
B
C
a
b
c
Grid Currents
N
A
B
C
650
Vg
Vmg
w_sync
A
B
C
A
B
C
Rg, Lg
A B C
A B C
Fig. 7. Simulink block diagram.
Fig. 8. Experimental setup.
Fig. 9. Control Desk GUI.
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In order to validate proper system operation, the
following simulations and experiments were carried
out:
Case 1: PI controller parameters (Kp=10,
Ki=1000, Ki5,7=150) without and with HC;
Case 2: PI controller parameters (Kp=20,
Ki=1000, Ki5,7=150) without and with HC.
A. Case 1: PI controller parameters (Kp=10, Ki=1000, Ki5,7=150) without and with HC
Measurements were performed at four different
reference values of active power (starting with 500 W
to 2000 W), without and with HC and the reactive
power reference sets to 0. Is analyzed how the control
parameters are varying in function of the input power
variation and can be seen that the id and iq (Fig. 10) / P
and Q (Fig. 11) measured signals are tracking very well
their references.
0 0.005 0.01 0.015 0.02 0.025 0.03-2
-1
0
1
2
3
4
5
6
Time [s]
Id,
Iq m
ea
su
red
an
d r
efe
ren
ce
[A
]
iq-meas iq-ref id-ref id-meas
Fig. 10. Id and Iq reference and measured currents.
0 0.005 0.01 0.015 0.02 0.025 0.03-1000
-500
0
500
1000
1500
2000
2500
3000
Time [s]
P&
Q
Pref Qref Qmeas Pmeas
Fig. 11. P and Q reference and measured powers.
In Fig. 12 is shown the injected current to the grid
for phase A (IA) in the case of control with PI controller
without HC in both, simulation (Fig. 12a) and
experimental (Fig. 12b) cases.
Total harmonic distortion (THD) is an important
index widely used to describe power quality issues in
transmission and distribution systems.
0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent P
hase
with P
I contr
olle
r w
ithout
HC
[A
]
500 W
1000 W
1500 W
2000 W
THD
Simulation Results
PI without HCKi=1000;Kp=10.
(a)
0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent P
hase
with P
I contr
olle
r w
ithout H
C [A
]
500 W
1000 W
1500 W
2000 W
THD
Experimental Results
(b)
PI without HCKi=1000;Kp=10.
Fig. 12. Grid current phase (IA) in the case of PI controller without
HC: a) Simulation results; b) Experimental results.
The THD of grid current with the 5th and 7
th
harmonics were presented numerically using the control
desk graphical interface (see Fig. 9). But for the graphic
representation of the harmonic spectrum for both cases,
measured grid currents have been implemented in
Matlab and with the discrete powergui, the FFT
analysis was made for each active power value.
The THD spectrum of the grid currents in the
simulation and experimental cases was analyzed
starting at 0.888 s and 0.08 s for 1 cycle in all analyzed
cases. By using a Kp=10 gain for PI controller without
HC, the results can be seen in Fig. 13.
(a)
PI controller without HC, Ki=1000, Kp=10.
0
5
10
15
20
25
30
TH
D C
urr
en
ts [
%]
Simulation 28,37 21,95 16,63 12,34
Experiment 28,59 22,14 16,75 12,35
500 W 1000 W 1500 W 2000 W
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(b)
0 2 4 6 8 10 12 14 16 18 200
2
4
6
8
10
Harmonic order
Mag (
% o
f F
undam
enta
l)
SimulationExperiment
P=2000 WQ=0 var
Fig. 13. THD representation of the grid current in the Case 1 in
both simulation and experimental cases for: (a) different values of
active power; (b) P=2000 W (harmonics spectrum).
It can be seen that the used current control method
provides a THD that is higher than the limit imposed by
the standard IEEE 1547.1 [20], therefore, the power
quality delivered to the network must be improved by
using the HC technique in order to keep the THD below
the requested 5 %.
After HC implementation, the THD level decreases
and a good power quality is obtained. The results
obtained for grid currents with harmonics level at
different reference values of active power are presented
in Fig. 14 and Fig. 15.
0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent P
hase
with P
I C
ontr
olle
r +H
C [A
]
500 W
1000 W
1500 W
2000 W
(a)
Simulation Results
PI with HCKi=1000;Kp=10.
THD
0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent P
hase
with P
I contr
olle
r + H
C [A
]
500 W
1000 W
1500 W
2000 W
(b)
Experimental Results
THDPI with HC Ki=1000;Kp=10.
Fig. 14. Grid phase current (IA) in the case of PI controller with
HC: a) Simulation results; b) Experimental results.
As it can be seen in Fig. 13a, at P*=2000 W, the PI
control technique without compensation provides a
THD of 12.35 % (experiment results) and after HC
implementation, the THD level decreases to 3.9 %
(Fig. 15a) and a good power quality is obtained.
(a)
PI controller with HC, Ki=1000, Kp=10.
0
2
4
6
8
10
12
14
TH
D C
urr
en
ts [
%]
Simulation 12,73 6,95 4,77 3,81
Experiment 12,93 7,07 4,97 3,9
500 W 1000 W 1500 W 2000 W
(b)
0 2 4 6 8 10 12 14 16 18 200
1
2
3
Harmonic order
Mag (
% o
f F
undam
enta
l)
Simulation
ExperimentP=2000 WQ=0 var
Fig. 15. THD representation of the grid current in the Case 1 in
both simulation and experimental cases for: (a) different values of
active power; (b) P=2000 W (harmonics spectrum).
In order to check if the unity power factor is
achieved in Fig. 16, the A phase of the grid voltage
(VA/50) is plotted together with the A phase of the grid
current for the same case presented before. It can be
noticed that the grid current and voltage are in phase,
for the reactive power value fixed to 0.
0 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]
Va&
Ia
Va
Ia
(a)
0 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]
Va&
Ia
Va
Ia
(b)
Fig. 16. Experimental results for voltage and current phase at
Kp=10, Ki=1000 in the case of: a) PI without HC; b) PI with HC.
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B. Case 2: PI controller parameters (Kp=20,
Ki=1000, Ki5,7=150) without and with HC
In the second case, simulation and experimental
conditions remain the same as in the first case, except
the proportional gain of the PI controller, which was set
to Kp=20. For comparative analysis, the simulations and
measurements were performed for the same values of
active power, without and with HC. The grid phase
current in the case of PI controller without HC is
presented in Fig. 17.
0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent
Phase
with P
I contr
olle
r w
ithout
HC
[A
]
500 W
1000 W
1500 W
2000 W
(a)
PI without HCKi=1000;Kp=20.
Simulation Results
THD
0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent
Phase
with P
I contr
olle
r w
ithout
HC
[A
]
500 W
1000 W
1500 W
2000 W
(b)
Experimental Results
PI without HCKi=1000;Kp=20.
THD
Fig. 17. Grid phase current (IA) in the case of PI controller without
HC: a) Simulation results; b) Experimental results.
It can be seen that the value of grid current is
changed with the increasing the active power, starting
from approx. 1 A at 500 W until circa 4 A at 2000 W.
As can be seen in Fig. 18a, grid currents THD
decreases with proximity of the rated power of the VSI.
A detailed harmonic order representation for 2000 W is
presented in Fig. 18b.
(a)
PI controller without HC, Ki=1000, Kp=20.
0
5
10
15
20
25
TH
D C
urr
en
ts [
%]
Simulation 22,26 15,48 9,23 8,09
Experiment 22,34 15,49 9,33 8,16
500 W 1000 W 1500 W 2000 W
(b)
0 2 4 6 8 10 12 14 16 18 200
2
4
6
8
Harmonic order
Ma
g (
% o
f F
un
da
me
nta
l)
Simulation
ExperimentP=2000 WQ=0 var
Fig. 18. THD representation of the grid current in the Case 2
(without HC) in both simulation and experimental cases for: (a)
different values of active power; (b) P=2000 W (harmonics level).
0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent
Phase
with P
I contr
olle
r+H
C [
A]
500 W
1000 W
1500 W
2000 W
(a)
THDPI with HCKi=1000;Kp=20.
Simulation Results
0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5
-4
-3
-2
-1
0
1
2
3
4
5
Time [s]
Grid C
urr
ent
Phase
with P
I contr
olle
r +
HC
[A
]
500 W
1000 W
1500 W
2000 W
(b)
THD
Experimental Results
PI with HCKi=1000;Kp=20.
Fig. 19. Grid phase current (IA) in the case of PI controller with HC
(Ki=1000, Kp=20): a) Simulation results; b) Experimental results.
As can be seen in Fig. 18, the THD level is lower
than the values of Fig. 13, without HC implementation,
which means that in this case, increasing the PI
proportionl gain leads to decrease THD.
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After HC implementation, in Fig. 20 is observed that
the THD is within the limits imposed by the standard
[20] at P*= 2000 W for Kp = 20.
(a)
PI controller with HC, Ki=1000, Kp=20.
0
2
4
6
8
10
12
14
16
TH
D C
urr
en
ts [%
]
Simulation 14,31 8,72 5,8 4,61
Experiment 14,49 8,88 5,81 4,81
500 W 1000 W 1500 W 2000 W
(b)
0 2 4 6 8 10 12 14 16 18 200
1
2
3
Harmonic order
Mag (
% o
f F
undam
enta
l)
Simulation
ExperimentP=2000 WQ=0 var
Fig. 20. THD representation of the grid current in the Case 2 (with HC) in both simulation and experimental cases for: (a) different
values of active power; (b) P=2000 W (harmonics spectrum).
For a better visualization of data in the analyzed
cases, in Fig. 21 was made a comparative analysis
between them. Based on these results, it can be
concluded that PI controller with HC implemented in
dq synchronous rotating frame has the best performance
for Kp=10.
(a)
0
10
20
30
TH
D C
urr
en
ts [
%]
Kp=10 with HC 12,73 6,95 4,77 3,81
Kp=20 with HC 14,31 8,72 5,8 4,61
Kp=10 without HC 28,37 21,95 16,63 12,34
Kp=20 without HC 22,26 15,48 9,23 8,09
500 W 1000 W 1500 W 2000 W
(b)
0
10
20
30
TH
D C
urr
en
ts [
%]
Kp=10 with HC 12,93 7,07 4,97 3,9
Kp=20 with HC 14,49 8,88 5,81 4,81
Kp=10 without Hc 28,59 22,14 16,75 12,35
Kp=20 without HC 22,34 15,49 9,33 8,16
500 W 1000 W 1500 W 2000 W
Fig. 21. Comparative analysis between the two values of the
proportional gain of the PI controller, with and without HC:
(a) Simulation results; (b) Experimental results.
Small differences in the THD currents values
between simulation and experimental results (for both
studied cases) can be observed in Fig. 21. The
explanation for these is that in a real system the losses
are present that were not considered in simulations.
4. CONCLUSIONS
This paper presents a PI current control method
considering harmonics compensation for grid connected
converters in steady state conditions.
The configuration was modeled and simulated in
Simulink, implemented in a dSPACE platform and
tested with an experimental test setup.
The simulation results validated by the
experimental results show that the proposed control
method (PI current controller without/with HC and a
three-phase DSOGI-PLL) is effective for DPGS
applications.
A better energy quality delivered to the grid with
PI proportional gain set at Kp=10, comparing with
Kp=20 is obtained. However, if HC is not implemented,
the Kp = 20 case has a smaller THD.
ACKNOWLEDGMENT
This paper is supported by the Sectoral Operational
Programme Human Resources Development (SOP
HRD), financed from the European Social Fund and by
the Romanian Government under the project number
POSDRU/89/1.5/S/59323.
BIBLIOGRAPHY
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PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONS
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About the authors
Lecturer Eng. Luminita BAROTE, PhD
University “Transilvania” from Braşov
email: [email protected]
She received the Dipl. Ing. degree in Electrical Engineering and Computers Science from “Transilvania” University,
Brasov in 2005, Dipl. Master degree in 2007 and the Ph.D in 2009 in Electrical Engineering from the same university.
Currently, she is a researcher at the Department of Electrical Engineering, Faculty of Electrical Engineering and
Computers Science, Transilvania University of Brasov. Her current research interests are in the area of renewable energy
systems: small power wind turbine working in stand-alone system with storage devices (lead acid battery, vanadium redox
flow battery) and also current control techniques for the grid side converter in DPGS applications.
Prof. Eng. Corneliu MARINESCU, PhD.
University “Transilvania” from Braşov
email: [email protected]
He received the Dipl. Ing. degree in Electromechanics from Politehnic Institute, Brasov, in 1971, and the Ph. D. from the
Politehnica University Bucharest in 1991. Currently, he is full professor at the Department of Electrotechnics, Faculty of
Electrical Engineering and Computers Science, Transilvania University of Brasov. Also, he is head of POWERELMA
(Power Electronics and Electrical Machines) research laboratory in the same faculty mentioned above. His areas of
interests include power electronics applied to renewable energy sources. He is author or co-author of more than 100
journal/conference papers in his research fields.
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