Three phase Single Stage Photovoltaic Inverter with

Prévia do material em texto

Three-phase Single Stage Photovoltaic Inverter with 
Active Filtering Capabilities 
Victor Mifiambres-Marcos, Enrique Romero-Cadaval, Miguel Angel Guerrero-Martinez and 
Maria Isabel Milanes-Montero 
Power Electrical and Electronic Systems (PE&ES), Escuela de Ingenierfas Industriales, Universidad de Extremadura, 
Avda. Elvas sin, 06006, Badajoz, Badajoz, 
Email: vrninmar@unex.es.eromero@unex.es.mguerrero@peandes.unex.es.rnilanes@unex.es. 
Telephone: +34924289300/678 7, Fax: +34924289601 
Abstract-This paper presents a study about the power in­
jection of grid connected photovoltaic plants when there are 
non-linear loads connected to the point of common coupling. 
The smartgrid scenario suggests that the photovoltaic energy 
should take care not only about the active power, but also 
about the reactive power. The study compares the last years 
criteria of injecting the maximum active power, with the expected 
tendency of providing reactive power in an active filter way for 
avoiding currents harmonics in the grid. The topology used is 
a traditional three-phase inverter controlled by a power balance 
technique through a synchronous hysteresis band. First of all, 
a power injection system that do not care about the loads 
connected into the grid is developed, then the loads are taken 
into account to improve the grid operation by supplying them. 
Both configurations are implemented in a prototype to compare 
the results via experimental tests. 
Index Terms-Photovoltaic systems, Smart grids, Power har­
monic filters, Power quality, Power conversion, Inverters, Current 
control, Solar energy. 
I. INTRODUCTION 
The photovoltaic generation systems (PVGS) have increased 
a lot over the last years [1], and they usually inject the power 
into the grid with unitary power factor, that is, injecting a 
sinusoidal current in phase with the voltage of the distribution 
electrical network. However, the smartgrids introduced a new 
vision for the energy supplied by the distributed generation, 
including photovoltaics. The compensation of the grid with 
reactive power is already accepted for transient states, and it 
is expected to be for the steady state. In this way, the PVGS 
should inject the energy into the grid and also act as an active 
power filter. 
There are several configurations for connecting the pho­
tovoltaic (PV ) panels [2]-[4]. The centralized configuration 
with multiple PV panels connected into arrays reduces the 
quantity of inverters, which are high powered, avoids the boost 
stage of the PV, but the MPPT is also centralized, blocking 
diodes are needed and its reliability depends on big inverters. 
The string configuration with multiple PV panels connected in 
series to a single stage inverter avoids the blocking diodes and 
a high voltage can be achieved increasing the efficiency. The 
multi-string configuration with multiple PV panels connected 
in series to a single stage DC/DC converter and then into a 
unique inverter combining the centralized and the string for 
a higher efficiency. The AC modules put the converter into 
the PV panel providing a plug and play characteristic with a 
individually computed MPPT but the need of a sharp boost 
stage limits the efficiency. And also, the module configuration 
where the DC/DC converters connected to the strings share its 
output with several inverters improves the efficiency in every 
point of irradiation [4]. These characteristics involve that for 
higher power photovoltaic plants the centralized configuration 
is the most extended [5]. 
Also, there are lots of topologies for the power injection 
system (PIS) [2], [6]. The tendencies basically are the single 
stage topologies with or without galvanic isolation, and the 
multi-stage topologies with galvanic isolation (on the high 
or on the low frequency side) or without it. The single 
stage topology with galvanic isolation is the best suitable for 
centralized configurations to improve the efficiency and avoid 
leakage currents [5], [7]. 
The topology used in this paper consists on a traditional 
three-phase inverter that injects the power from the PV cells 
into the grid. The control technique not only has to inject the 
active power, but it also has to track the maximum power 
point (MPPT) from the PV array and inject with synchroniza­
tion with the voltage grid. Actually, there are several MPPT 
methods [8 ], [9], perturb and observe, incremental conduc­
tance, neural networks, fuzzy controllers, but in this work the 
direct method of the derivative of the power with respect to 
the voltage has been applied [8 ], [10]. The synchronization 
methods are a lot too [11], [12], but the highlight is the phase 
locked loop (PLL), so in this work a modified three-phase 
PLL or synchronous reference frame PLL (SRF-PLL) called 
auto-adjustable synchronous reference frame (ASRF) has been 
implemented [13]. 
In this work, the current injection is carried out by solving 
the MPPT and by controlling the synchronization with the 
positive sequence fundamental component voltage grid. The 
technique has been implemented in a grid-connected three­
phase two level inverter prototype controlled through a syn­
chronous current hysteresis band (SHB) with a non-linear load 
connected at the point of common coupling (PCC) under two 
scenarios. The first one ignores the non-linear load providing 
a sinusoidal PIS current, but a distorted grid current, and the 
second one improves the grid operation by supplying it and 
maintaining a sinusoidal current in the distribution network as 
978-1-4673-2421-2/12/$31.00 ©2012 IEEE 5253 
an active filter does. In this way, the PIS not only supply the 
non-linear load, but also injects the rest of the power into the 
grid. Several works has been developed with this philosophy, 
but most of them are only validated through simulation results 
[10], [14]-[ 18 ]. 
II. TOPOLOGY 
Fig. 1 shows the scheme of the studied topology. The PVGS 
is connected to the PCC, with nodes a, band c, through the 
PIS by means of the inductor L and a transformer to enable 
galvanic isolation. The transformation ratio, m, is considered 
as 1: l. The electric grid and a non-linear load composed by 
a non-controlled rectifier an a resistance are connected to the 
PCC. 
A. Control technique 
Firstly, The MPPT algorithm assures the extraction of the 
maximum power of the PVGS, giving the PVGS reference 
current, iPV,rej, to achieve. Then the power balance technique 
could be applied by ignoring the non linear loads (INL) or 
supplying the non-linear loads (SNL). 
1) Injection ignoring non-linear loads (INL): Usually, the 
non-linear loads connected to the PCC are not taken into 
account when injecting the current of the PVGSs. The control 
technique is based on the power balance between the PVGS 
and the grid and, assuming a positive sequence fundamental 
component injected current, one has: 
PPV = Ps + PL = 3VS,LNIT,1 COscp + PL) (1) 
where Ppv is the PVGS power, Ps is the grid power, 
VS,LN is the RMS value of the line to neutral grid voltage, 
Ir,l is the RMS value of the positive sequence fundamental 
component of the inverter current and PL are the losses of 
the system. This implies that the grid has to supply the non­
linear load disturbing the grid currents, while the PVGS injects 
pure sinusoidal currents in phase with the positive sequence 
fundamental component of the voltage grid to obtain the unity 
power factor, that is, maximizing the active power. Solving (1) 
with these criteria one has: 
VpvlPV,rej = 3Vs,LNIr,1,rej + PL) (2) 
where Vpv is the PVGS voltage and IT,l,rej the RMS value of 
the positive sequence fundamental component of the inverter 
current. In this way, one can calculate the reference current 
for the PIS: 
I 
_ VpvlPV,rej - PL 
T,l,rej -
3V S,LN 
(3) 
and knowing that thelosses are unknown, this term could be 
compensated in the closed loop controller. 
2) Injection supplying non-linear loads (SNL): Other pos­
sibility is to take advantage of the distributed generation to 
supply the non-linear loads connected at the PCC in order to 
maintain the grid current without disturbances. This time, the 
current injected by the inverter must supply the non-linear load 
connected at the PCC, but at the same time, it must inject a 
grid current in phase with the positive sequence fundamental 
component of the grid voltage to achieve the maximum power 
factor at the grid. As the grid reference current must be 
sinusoidal, the power balance gives: 
I -
VpvlPV,rej - PL - PNL 
S,l,rej -
3V 
) 
S,LN 
(4) 
where IS,l,rej is the sinusoidal reference for the current grid 
and PNL is the power dissipated by the non-linear load. 
As the non-linear load consumption is unknown, it could 
be considered together with the system losses for the closed 
loop compensator. The power dissipated by the non-linear 
load involves three different operation modes with the SNL 
configuration: 
• Ppv > PN L, the total of the non-linear load power is 
supplied by the inverter, and the rest is injected into the 
grid with a unity power factor sinusoidal waveform. 
• Ppv = PN L, no injection into the grid. According to 
Fig 1 this happens when: 
(1.35V3Vs LN) 2 
PPV = PN L = R ' 
(5) 
• PPV < PN L the non-linear load is supplied by both the 
inverter and the grid but the waveform demanded from 
the grid will be sinusoidal. 
Both (3) and (4) could be treated as the same expressions, 
and the current magnitude, IT,l,rej or IS,l,rej, selects the con­
figuration of the control technique, INL or SNL, respectively. 
Adding the phase term, and considering PN L as losses, one 
has the next equation: 
[ ia,rej 1 
ib,rej 
ic,rej 
v'2Vpv IPV,rej - PL 
3VS,LN 
[ UP,a 1 
Up,b 
Up,b 
(6) 
where ia,rej, ib,rej and ic,rej are the sinusoidal reference cur­
rents and uP,a, Up,b and uP,c are unitary sinusoidal waveforms 
that synchronize with the line-to-neutral voltages, in order to 
provide unity power factor at the inverter output with INL or 
at the grid with SNL. 
B. Modulation technique 
The modulation technique developed for the inverter is a 
synchronous hysteresis band that tries to deliver the sinusoidal 
reference current mentioned above as a current controller. The 
way to do this is to measure the inverter currents for INL 
control, or the grid currents for SNL control, ia, ib and ic in 
general, and compare each one with its sinusoidal reference: 
(7) 
where ierror,a, ierror,b and ierror,c are the current errors of 
each phase, k is a numeric index and Ts is the sample period 
5254 
-_._._._._._._._._._._._------------------------------------------------------Cl .. ·u r--;,----_.fYL�CiT:::.a�.:..!_I==��===I .m.m�.�.S:.mm, is.a • . a i i i ! .. ! PVGS IT,b. b : � VS.ab Electric 
Grid tl 
.. 
tJ iT,e • c i is.e • i VS.bc ��j-t===:�===r1 .. � .. � .. ·� .. ·1· � .. � .. � .. ·� .. �·· -���-j , .................................... 
·
pis.................................. !iNL.a !iNL.b !iNL.c __ n_ 
Non-I;near load [
�
]
 
Figure L Studied topology. 
of the algorithm. The switching signals for each switch in the 
inverter are calculated with the next comparison: 
C. 
st = s� = { � 
s+ = s- = { c c 
s+ = s- = { c c 
Passive elements 
0 
1 
0 
1 
if 
if 
if 
if 
if 
if 
ierror,a < 0 
ierror,a 2: 0 
ierror,b < 0 
ierror,b 2: 0 
ierror,c < 0 
ierror,c 2: 0 
(8) 
The inductor of the inverter output can be calculated in 
order of the maximum ripple allowed for the injected current. 
Looking at the topology in Fig. 1, this ripple happens when the 
difference between the line-to-neutral voltage of the inverter 
output and the line-to-neutral voltage of the grid. Using the 
expression that defines the response of an inductor one has a 
criteria to select the inductance: 
L = (�V
pv - V'2"vS,LN) Ts , (9) 
c 
where Ts is the sample period and c is the maximum current 
ripple. 
III. PIS CONTROL SCHEME 
Fig. 2 shows the control scheme developed for the PIS. 
From left to right one has the measurements, the injected 
currents ia, ib and ic with iT for INL or is for SNL, the 
line-to-neutral grid voltages VS,an, VS,bn and VS,cn, the voltage 
of the PV array, v pv, which can be equaled to the DC bus 
voltage, and the PV current i pv. The MPPT block calculate 
the PV reference current iPV,rej to reach the MPP. The 
Reference Current Generation block (RCG) provides a sinu­
soidal reference current to be injected with unity power factor. 
Finally, the switching signals generation block (SSG) solves 
the synchronous hysteresis band to generate the switching 
signals. 
A. Maximum power point tracking 
The scheme of the MPPT is shown in Fig. 3. It solves the 
derivative dPpv /dVpv in every sample period and take it to 
zero through a PI controller for the feedback loop control in 
ia ira iS,a 
ib = iTb or iSb 
ie irc is.c 
VS,(fn 
VS,bn 
VS,CII 
MPPT 
�� Maximum 
�� Power Point 
Tracking 
VS.an 
VS.bn 
VS.CIJ 
b 
� 
ipv 
iT -> Ignoring Non-linear loads (INL) 
is -> Supplying Non-linear loads (SNL) 
ia 
ib 
� 
la,ref 
ReG ib.rej 
Reference 
� 
Current 
Generation 
SSG 
Switching 
signals 
generation 
+ -
Sa'Sa 
+ -
Sb ,Sb 
+ -
Sc ,sc 
Figure 2. PIS Control Scheme. 
Low 
Pass 
Filter 
Figure 3. Maximum power point tracking scheme. 
order to reach the MPP of the PV array [ lO]. A low pass filter 
is implemented to delete the higher frequencies. The output 
of the PI is the reference PV array current, iPV,rej. 
B. Reference current generation 
The scheme of the RCG is shown in Fig. 4. A PLL called 
ASRF [13] is used to synchronize with the positive sequence 
fundamental component of the grid voltage. It calculates the 
sinusoidal unitary waveforms to create the reference current 
phase in order to reach the unity power factor at the inverter 
output (INL) or at the grid (SNL) (6). Below, the reference 
injected current magnitude is obtained by solving the power 
balance (6). A PI for controlling the error between ipv and 
iPV,rej is added in order to compensate the losses of the 
system, including the power demanded by the non-linear load 
in the SNL configuration. After all, the reference injected 
current, irej is obtained. 
5255 
VS.all 
VS.bn 
VS.CII 
ASRF UP,a Up,b 
Auto- UP.c 
Adjustable 
Synchronous 
Reference 
Frame 
VS,RMS 
Figure 4. Reference current generation scheme, 
ia,refi ib,refi ie,ref s; ,s; ,s; 
Figure 5. Switching signal generation scheme. 
C. Switching signal generation 
The scheme of the SSG is shown in Fig, 5, It basically 
calculates the error between the measured injected currents 
and their references obtained in the RCG. Then the switching 
signals are generated by a simple comparison (8), 
IV. EXPECTED BEHAV IOR 
Fig, 6 shows the expected behavior of the system defined 
in Fig, 1 at the PCC when the SNL configuration is selected. 
On the one side one has the phase-to-phase voltages and the 
rectifier currents, which are variables that are expected to be 
always the same, and on the other side one has the inverter 
output currents and the grid currents, which will change in 
order to the PVGS generation. 
Fig. 6(c) and Fig. 6(e) show the expected response of these 
magnitudes when Ppv > PNL, and Fig. 6(d) and Fig. 6(f) 
when Ppv < PNL. The first case involves an inverter currents 
that supply the rectifier and inject energy into the grid, while 
in the second case the rectifier is supplied by the inverter and 
the grid. In both cases the grid currents maintain sinusoidal 
waveforms thanksto the active and reactive power the inverter 
manages. It is obvious that with the INL configuration, the grid 
currents and the inverter output currents change their roles 
between themselves. 
V. EXPERIMENTAL SETUP 
The system and the proposed control techniques have been 
analyzed through experimental tests. The equipment to carry 
out the analysis is shown in Fig. 7. It has been implemented 
in a 1:2.7 scale. The summary is the next: 
• HP 6035A system power supply, to simulate the PV array 
with 420 V. 
• SEMIKRON solution for the 2-level inverter. 
• Ixys solution for the non-controlled rectifier. 
• LA 205-S. Hall effect current transducers to measure ipv 
and, iT,a, iT,b and iT,c (lNL), or is,a, is,b and is,c (SNL). 
• VS500B. Voltage sensors to measure VDc and, VS,an, 
VS,bn and VS,cn' 
10 
$ 
" o \ � il '" 
.§ '" 
0.02 003 0.04 
-100 0.01 0.02 003 0.04 
Time(s) Time(s) 
(a) (b) 
$ $ �� �� ,,-'" ,,-'" I\,. I\,. Q.."--Q.."--- 0 � '" 
� � -10 
'0 j is -200 0.01 0.02 0.03 0.04 
Time(s) 
(c) (d) 
$ $ 5 
�;i �;i "-"- v� v� '-'- "-"-- � � 
� 
� 
'0 � 
is � 
(e) (f) 
Figure 6. Ideal waveforms for the SNL configuration at the PCC: (a) phase­
to-phase grid voltages, (b) Rectifier currents, (c) grid currents with Ppv > 
PN L, (d) Inverter output currents with Ppv > PN L, (e) grid currents with 
Ppv < PN L and (f) Inverter output currents with Ppv < PN L· 
Figure 7. Experimental setup: (1) HP system power supply, (2) SEMIKRON 
2-level inverter, (3) Inductors, (4) Vishay non-controlled rectifier, (5) Sensors, 
(6) xPCTarget Target and (7) Oscilloscope. 
• Passive elements. L = 25 mH, and a resistor with 66 n. 
• Grid. 8 5 V and 50 Hz. 
• xPCTarget control platform. Rapid prototyping control 
platform supported by MATLAB/SIMULINK, a Host 
5256 
Ch1 200V 
Ch3 5.0A Q 
Ch1 200V 
Ch3 5.0A Q 
Ch2 5.0A Q 
Ch4 5.0A Q 
5.0A 
5.0A 
(a) 
(c) 
M 4.0ms 625kSk 1.6�s,pt 
A Ch3 f 1.3A 
M 4.0ms 625kSIs 1.6jJsJpt 
A Ch3 f 1.3A 
Ch1 200V 
Ch3 5.0A Q 
Ch1 200V 
Ch3 5.0A Q 
Ch2 5.0A Q 
Ch4 5.0A Q 
Ch2 5.0A 
Ch4 5.0A 
(b) 
(d) 
M 4.0ms 625kSk 1.6 �s,pt 
A Ch3 f 1.3A 
M 4.0ms 625kSk 16�s,pt 
A Ch3 f 1.3A 
Figure 8. Experimental results: (a) INL configuration, (b) SNL configuration with Ppv > PN L, (c) SNL configuration with Ppv = PN L and (d) SNL 
configuration with Ppv < PNL. 
Channels: (1) Phase-to-neutral grid voltage of the phase a, (2) Inverter current of the phase a, (3) Rectifier current of the phase a and (4) Grid current of the 
phase a. 
PC for programming the algorithm and a Target PC to 
execute it at 12.5 kHz. 
V I. EXPERIMENTAL ANALY SIS AND RESULT S 
The results are presented in Fig. 8 , with the phase-to-neutral 
grid voltage and the current waveforms of the phase a at the 
PCC. 
Fig. 8 (a) shows the experiment with the INL configuration 
while Fig. 8 (b, c, d) show the SNL configuration with different 
irradiances. One can see how the grid current is distorted while 
the inverter injection is sinusoidal with the INL technique. 
However, the SNL technique provides a distorted inverter 
current in order to maintain a sinusoidal waveform in the grid 
current. The sinchronization between the PCC voltage and the 
grid current presents a unitary power factor as it was expected. 
Depending on the irradiance, the current of the grid is 
positive or negative, in order to the photovoltic power and the 
non-linear load demand. If the irradiance is high, the inverter 
could supply the non-linear load and at the same time inject 
the rest of the power into the grid. When the irradiance is low 
the non-linear load needs power from the grid to be supplied. 
The limit is on Fig. 8 (c), where the grid presents zero power. 
If the irradiance is very low, the voltage from the PVGS is 
not enough for the PIS to inject or to act as an active power 
filter. In this situation, the PIS could be disconnected from the 
PVGS to use it as an active power filter by boosting its DC 
bus with the grid voltage. In this way, the PIS could be used 
5257 
when there is no power from the PVGS to be extracted so the 
system increase its performance by a continuous working. 
The ripple of the voltage is due to the switching frequency 
of the inverter and the high impedance of the grid autotrans­
former. This effect does not affect the synchronization since 
the ASRF rejects the noise and the disturbances. The ripple 
in the grid currents and the inverter currents are due to the 
synchronous hysteresis band and the inverter output induc­
tance. The inductance value fixes the compromise between the 
switching ripple and the bandwidth, that is, higher inductances 
provides lower high frequency distortion but involves a slower 
response, so the high slopes of the rectifier currents will be 
tracked worse. Anyway, the current ripple could be improved 
by a LCL output filter. 
V II. CONCLUSION 
In this work a grid connected three-phase single stage in­
verter for injecting the power from a photovoltaic system with 
active filtering capabilities has been presented. The control 
system calculates the reference current to be injected attending 
at the power balance of the system and the unity power factor. 
The synchronous hysteresis band follows this reference to 
provide it at the output of the inverter, as it is usually done, 
or at the grid. In the first case, the grid current is distorted, 
because of the non-linear load, while in the second case it is 
not, as the inverter helps by supplying the non-linear loads 
connected at the PCC following the line drawn in smartgrids. 
The whole system has been implemented with a prototype, 
in order to validate the controlled topology and to compare 
different situations through experimental results. Different 
irradiance situations have been analyzed in the active filtering 
mode, as its quantity has an impact on the power injection. 
The grid current is always sinusoidal, but it can be positive 
or negative depending on the power injection and the power 
demanded by the non-linear load. 
ACKNOWLEDGMENT 
The authors would like to thank to the Spanish institutions 
"Ministerio de Economfa y Competitividad" and "Gobierno de 
Extremadura", and to the "FEDER Funds" for its support in 
this research. 
REFERENCES 
[1] V. Salas and E. Olias. "Overview of the Photovoltaic Technology Status 
and Perspective in Spain." Renewable and Sustainable Energy Reviews. 
vol. 13. pp. 1049-1057. 2009. 
[2] S. Nema, R. K. Nema, and G. Agnihotri, "Inverter Topologies and 
Control Structure in Photovoltaic applications: A Review," Journal of 
Renewable and Sustainable Energy, vol. 3, p. 012701, 2011. 
[3] J. M. Carrasco, L. G. Franquelo, J. T Bialasiewicz, E. Galvan, R. C. P. 
Guisado, M. A. M. Prats, J. I. Leon, and N. Moreno-Alfonso, "Power­
electronic systems for the grid integration of renewable energy sources: 
A survey," IEEE Transactions on Industrial Electronics, vol. 53, no. 4, 
pp. 1002-1016, 2006. 
[4] L. Zhang, K. Sun, Y. Xing, L. Feng, and H. Ge, "A modular grid­
connected photovoltaic generation system based on dc bus," Power 
Electronics, IEEE Transactions on, vol. 26, no. 2, pp. 523 -531, feb. 
201l. 
[5] V. Salas and E. Olias, "Overview of the state of technique for pv inverters 
used in low voltage grid-connected pv systems: Inverters above 10 kw," 
Renewable and Sustainable Energy Reviews, vol. 15, no. 2, pp. 1250 -
1257, 2011. 
[6] F. Blaabjerg, F. lov, T Terekes, R. Teodorescu, and K. Ma, "Power 
electronics - key technology for renewable energy systems," in Power 
Electronics, Drive Systems and Technologies Conference (PEDSTC), 
20ll 2nd, feb. 2011, pp. 445 -466. 
[7] T-F. Wu, C.-H. Chang, L.-c. Lin, and c.-L. Kuo, "Power loss com­
parison of single- and two-stage grid-connected photovoltaic systems,"Energy Conversion, IEEE Transactions on, vol. 26, no. 2, pp. 707 -715, 
june 2011. 
[8] T Esram and P. Chapman, "Comparison of photovoltaic array maximum 
power point tracking techniques," Energy Conversion, IEEE Transac­
tions on, vol. 22, no. 2, pp. 439 -449, june 2007. 
[9] G. Petrone, G. Spagnuolo, R. Teodorescu, M. Veerachary, and M. ViteUi, 
"Reliability issues in photovoltaic power processing systems," Industrial 
Electronics, IEEE Transactions on, vol. 55, no. 7, pp. 2569 -2580, july 
2008. 
[l0] E. Romero-Cadaval, M.-I. Milanes-Montero, F. Barrero-Gonzalez, and 
E. Gonzalez-Romera, "Power injection system for photovoItaic genera­
tion plants with active filtering capability," in Compatibility and Power 
Electronics, 2009. CP E '09., may 2009, pp. 35 -42. 
[11] M. Boyra and J.-L. Thomas, "A review on synchronization methods for 
grid-connected three-phase vsc under unbalanced and distorted condi­
tions," in Power Electronics and Applications (EP E 2011), P roceedings 
of the 20ll-14th European Conference on, 30 2011-sept. 1 2011, pp. 1 
-10. 
[12] F. Freijedo, J. Doval-Gandoy, O. Lopez, C. Martinez-Penalver, A. Yepes, 
P. Fernandez-Comesana, J. Malvar, A. Nogueiras, J. Marcos, and 
A. Lago, "Grid-synchronization methods for power converters," in 
Industrial Electronics, 2009. 1ECON '09. 35th Annual Conference of 
IEEE, nov. 2009, pp. 522 -529. 
[l3] V. Minambres-Marcos, M. I. Milanes-Montero, B. M. Vinagre-Jara, 
and E. Romero-Cadaval, "Phase Locked Loop for Distorted Three­
Phase Systems Tested with a PI, a PID and a Fractional PI," Przeglad 
Elektrotechniczny Electrical Review, vol. 10, pp. 201-207, 2009. 
[14] S. Rajasekar and R. Gupta, "PhotovoItaic array based multilevel inverter 
for power conditioning," in Power and Energy Systems (ICPS), 20ll 
International Conference on, dec. 2011, pp. 1 -6. 
[15] A. Blorfan, P. Wira, D. Flieller, G. Sturtzer, and J. Merckle, "A 
three-phase hybrid active power filter with photovoltaic generation and 
hysteresis current control," in IECON 2011 - 37th Annual Conference 
on IEEE Industrial Electronics Society, nov. 2011, pp. 4316 -432l. 
[l6] H. Tumbelaka and M. Miyatake, "Simple integration of three-phase 
shunt active power filter and photovoltaic generation system with 
fibonacci-search-based mppt," in Industrial Electronics Applications 
(ISIEA), 2010 IEEE Symposium on, oct. 2010, pp. 94 -99. 
[17] H. Beltran, Z. Chen, E. Belenguer, N. Aparicio, S. Segui-Chilet, and 
F. Gimeno-Sales, "Photovoltaic inverters used as active filters for im­
provement of iv distribution networks," in Electric Utility Deregulation 
and Restructuring and Power Technologies, 2008. DRPT 2008. T hird 
International Conference on, april 2008, pp. 2749 -2756. 
[18] R. Patidar, S. Singh, and D. Khatod, "Single-phase single-stage grid­
interactive photovoltaic system with active filter functions," in Power 
and Energy Society General Meeting, 2010 IEEE, july 2010, pp. I -7. 
5258