Tutorial April 2016- - PSIM Software · - 7 - 3 Phase grid connected PV inverter Tutorial V2.0 –...
Transcript of Tutorial April 2016- - PSIM Software · - 7 - 3 Phase grid connected PV inverter Tutorial V2.0 –...
3 Phase grid connected PV inverter
Tutorial –April 2016-
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Based on a work at www.powersmartcontrol.com
SmartCtrl© 2009-2016 by Carlos III University of Madrid. GSEP Power Electronics Systems Group
The software SmartCtrl© described in this manual is furnished under a license agreement. The software may be used or
copied only under the terms of the license agreement.
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Table of Contents
1. Introduction ............................................................................................. 3
2. AC Analysis in PSIM .................................................................................. 5
3. Import transfer function to SmartCtrl ................................................... 6
4. Control loop design with SmartCtrl ........................................................ 8
4.1. Select the sensor type: ............................................................................... 8
4.2. Select the regulator type: .......................................................................... 9
5. Closed loop performance ...................................................................... 13
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1. Introduction
This tutorial is intended to guide you, step by step, to design the inner control loop
in dq axis of a three phase grid connected PV inverter from its imported frequency
response. In this tutorial have not been included the outer control loop and the
MPPT.
There are a lot of possibilities to design the control loop of the aforementioned
system. One of them is the conventional control using axis decoupling by means of
feedforward loops as shown in the next figure.
PI
PI a
b
c
d
q
PWM Modulator
P*
Q*
Id*
Iq*
+
+
-
-
id
iq
a
b
c
d
q
223
2
qd
qd
dvv
vqvpi
223
2
qd
dq
qvv
vqvpi
VrsL
1GV+
-
dd
L
di
VrsL
1GV
+
-
qd qi
L
+REFdi _
ˆ
+
-
REFqi _ˆ
d
scK
dsc iK ˆ
-
dRi
scK
1
GV
L
scK
1
GV
L
+
+q
qRi
scK
qsc iK ˆ
+-
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Due to the axis decoupling, the conventional control scheme requires an
implementation with a high computational cost mainly for low cost applications.
For these applications (low cost µP, PIC, DSP or small FPGA) a simplified control
strategy is proposed and shown in the next figure. As it can be seen in this figure, a
direct PI control (without feedforward loops for axis decoupling) has been
proposed.
The plant (grey colored area) can be rewritten as it is shown in the next figure. The
obtained transfer functions can be classified as follows:
Mutual transfer functions:
d
q
q
d
d
I
d
I
ˆ
ˆ and
ˆ
ˆ
Self transfer functions
d
d
q
q
d
I
d
I
ˆ
ˆ and ,
ˆ
ˆ
Taking into account the symmetry of the balanced three phase inverter, two
identical PI controllers must be tuned. In order to design this PI compensator, two
different possibilities can be selected; it can be considered as converter plant the
mutual transfer function or the self one.
Due to the higher bandwidth and stable (together enough phase margin and
stable operation) is preferable to use the self transfer function.
PI
PI
+
+
-
-
22
·
···5.0
LrsL
rsLVDC
++
dI*
dIdd
22·
··5.0
LrsL
LVDC
*
qI
22
·
···5.0
LrsL
rsLVDC
qd
+-
22·
··5.0
LrsL
LVDC
qI
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The first step will be validate the theoretical self and mutual transfer functions by
means of a PSIM AC analysis of the three phase grid connected inverter.
2. AC Analysis in PSIM
The frequency response of the plant is obtained from the averaged model form of
the three phase inverter in dq axis by means of the PSIM AC analysis tool. In the
next figure the aforementioned converter is shown.
The obtained frequency response is included below:
AC sweepcontrol
AC source
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Before proceeding with the control loop design, the Bode diagram in the next
figure seeks to compare the frequency response obtained with PSIM (green trace)
and the aforementioned theoretical model (red trace).
Once the frequency response has been obtained, it must be imported to SmartCtrl.
3. Import transfer function to SmartCtrl
1.1 Open your SmartCtrl Software.
1.2 Import the frequency analysis.
Press on button to select text file imported data (current mode control) or
select the corresponding option within the Data menu.
10 100 1 103
1 104
20
0
20
40
60
dBIDPsim1 Freci
MG Freci
Freci
10 100 1 103
1 104
300
200
100
0
100
FaseIDPsim1 Freci
FG Freci
Freci
(dB
)
Frecuency (Hz)
de
gre
es
Frecuency (Hz)
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Next, the .txt file containing the frequency response from the PSIM AC Analysis is
loaded. The corresponding window is shown below:
The loaded transfer function is automatically shown:
Complete the switching frequency data in the left lower corner of the window and
click OK to continue.
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4. Control loop design with SmartCtrl
4.1. Select the sensor type:
The current sensor specification window is automatically shown. It is necessary to
set the sensor gain and the bandwidth (pole frequency) of the Hall effect sensor.
Then, press OK.
Switching frequency
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4.2. Select the regulator type:
The PI regulator specification window is automatically shown.
For an equivalent analog implementation of the compensator, it is necessary to set
the modulator gain and the value of the resistance “R11”. In this case the
resistance value is not important because the PI regulator to be implemented in
PSIM is given by the values of the proportional gain and the time constant. Once
the desired values have been introduced press OK.
Sensor gain
Pole frequency
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Once all the control loop transfer functions have been defined, the crossover
frequency and the phase margin must be selected. Click on the "Set.." button and
the solutions map will be displayed.
Modulator gain
R11 value
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Now, select the crossover frequency and the phase margin of the loop just by
clicking within the white zone and click OK to continue. The selected pair (PM and
fcross) will provided stable operation. Optimization process could be carried out in
the main SmartCtrl window.
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Once the crossover frequency and the phase margin have been selected, the
solution map will be shown on the right side of the input data window. If, at any
time, the two aforementioned parameters need to be changed, just click on the
shown solution map. (See next figure)
Confirm the design. Now accept the selected configuration and confirm the design,
the program will automatically show the performance of the system in terms of
frequency response, etc...
The regulator components to be introduced into PSIM are the Kp and Kint values.
Regulator components
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5. Closed loop performance
In order to check the closed loop performance of the regulator calculated with
SmartCtrl, a closed loop simulation with PSIM has been carried out. Both the
simulation schematic circuit and the simulation results are included below.
vd*
vq*
abs
vd*
vq*abs
Id*
abs
Iq*
vq*
vd*
V
P_ref
VQ_ref
V
V
Id_ref
V
Iq_ref15k
300m
K
2/3
K
2/3
b
a
c
d
q
o
K
-1
wt
Vmod_a
Vmod_b
Vmod_c
165m
15k
P
5k
Id_fil
vd*
Iq_fil
K
1.5 V p_dq V q_dq
Id_fil
vq*
Iq_fil
K
1.5
vq* vd*
Id*
Iq*
Iq_fil
Id_fil
Power References Generation
Direct PI control
PI8.24078m1.89538m
PI
1.89538m8.24078m
PI components calculated by
SmartCtrl
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As it can be seen in the previous simulation results, the system has a good
performance (without the use of feedforward decoupling loops). Therefore, the
control loop design with the proposed method by means PSIM and SmartCtrl is
valid to connect a three phase PV inverter to the grid.
Note than more detailed power stages can also been controlled by means this
strategy (PSIM plus SmartCtrl). LCL filters, digital implementation with delay effects
and every other parasitic effect can be included in PSIM before the AC analysis to
obtain a plant transfer function as realistic as it will be required.
0.0
-50.00
-100.00
50.00
100.00
Ia_fil Ib_fil Ic_fil
0.0K
-10.00K
-20.00K
10.00K
20.00K
30.00K
p_dq P_ref
0.0K
-5.00K
5.00K
10.00K
15.00K
20.00K
q_dq Q_ref
0.0 0.10 0.20 0.30 0.40
Time (s)
0.0
-100.00
-200.00
100.00
200.00
Va Ia_fil
Active Power Step
Reactive Power Step