LCL Filter Based Grid-Connected Photovoltaic
System with Battery Energy Storage
Anil Lamichhane
Dept.Electrical engineering
Shanghai Jiao Tong University
Shanghai, China
anillamichhane@sjtu.edu.cn
Lidan Zhou
Dept.Electrical engineering
Shanghai Jiao Tong University
Shanghai, China
zhoulidan@sjtu.edu.cn
Abstract— Grid-connected photovoltaic (PV) system has
gained momentum at an exponential rate in recent years.
Intermittent nature of PV system causing demand and generation
mismatch in power is one major issue. Additionally, the quality of
power supplied to the load and surplus power injected into the grid
along with better dynamic performance are other two main issues
of the grid-connected PV system. To address the problem of
intermittency and dynamic performance we use battery energy
storage (BES). Similarly, three-level neutral point clamped (NPC)
inverter with LCL filter is used for better current and voltage
waveforms to ensure the better-injected power quality. In this
paper, PV array, boost converter, maximum power point tracking
(MPPT) control, bidirectional converter, three-level NPC
inverter, and their associated control system is designed and
simulated in MATLAB/Simulink. The simulation results shows
the injected current has 0.68% THD, faster system response, and
generated power matches the load demand.
Keywords— Battery Energy Storage, Bidirectional converter,
LCL filter, MPPT, Photovoltaic System, three-level NPC
I. INTRODUCTION
Global energy consumption has increased with rapid
industrialization, economic development, and increased
population. The International Energy Agency estimates the
worldwide energy demand would be 17.715 Mtoe by 2050
which is 21.1% higher as compared to the energy demand of
2017[1]. Energy giant economies like China, United States,
European Union, India, Russia, and Japan still relies on fossil
fuels as the primary source of energy generation. However, the
exploitation of fossil fuels to meet the increasing energy demand
pose the threat of climate change and environmental pollution
due to the emission of greenhouse gases. Therefore, renewable
energy sources, which are clean, green and sustainable, are
gaining more attention from the past few decades.
Among the various sources of renewable energy such as PV,
wind, biomass, hydropower, biofuels, and geothermal; PV
generation has gained momentum because of climate policies
and dramatic fall in the price of solar over recent years.
This work was supported by Shanghai Natural Science Foundation (SNSF)
under grant 18ZR1418400.
Gang Yao
Dept.Electrical engineering
Shanghai Jiao Tong University
Shanghai, China
yaogangth@sjtu.edu.cn
Muhammad Luqman
Dept. Electrical engineering
Shanghai Jiao Tong University
Shanghai, China
luqman@sjtu.edu.cn
PV systems are mainly installed in two modes; one is
standalone, and another is grid-connected mode. In gridconnected mode, power flows back-and-forth to and from the
grid depending on the PV generation and load demand at a time
[2].
BES system combined with the PV-grid stores energy during
the peak sun-hours and supplies power to the load during the
event of peak load, and power cuts from the grid. Bidirectional
buck-boost converter carries out charging and discharging of
BES. Inconsistent weather, and non-uniform solar insolation are
responsible for the lower energy efficiency of the PV array.
MPPT system enables the dynamic adjustment of PV array
output voltage for power optimization. MPPT system controls
the output of the boost converter to provide constant dc link
voltage.
In this paper, Sunpower SPR-305-WHT-U PV module is
used to generate 7.6 KW power from 5*5 PV array. The boost
converter is designed to step up the variable PV voltage to
constant dc link voltage. Variable step size incremental
conductance method of MPPT is implemented to track
maximum power from PV array. Bidirectional dc-dc buck-boost
converter acts as the interface between the dc link and BES
system. Three phase three-level NPC inverter with third-order
LCL filter is used for better waveforms of output current and
voltage. Ac grid is modeled to be an ideal generator of 50 Hz,
380 Volts RMS. Either PV system or BES or Ac grid supplies
the local load depending on the system condition. The proposed
topology of the entire system and its control is modeled and
simulated in MATLAB/SIMULINK software. Simulation
results verify the validity and efficacy of design and modeling
procedure, for the proposed topology and its control.
II. SYSTEM TOPOLOGY DESCRIPTION AND DESIGN
A. PV Array
PV array from MATLAB Simulink library consisting five
series connected modules per string with five parallel string is
used. This array can generate total 7.6KW at full irradiance of
1000W/m2. The single diode model of PV cell is as shown in
Fig .1 Proposed topology of LCL filter based grid-connected PV system with battery energy storage
Fig. 2. Equation (1) gives the voltage-current characteristics of
the PV cell:
 q (V pv  Rs I pv )  V pv  Rs I pv
I pv  I ph  I s [exp 
 1 
(1)
nkT
Rsh


Fig.2 Equivalent circuit of PV cell
where I ph is photocurrent; I s is diode saturation current; q is
an electronic charge; T is temperature (K); n is P-N junction
ideality factor; Rs , and Rsh are intrinsic series resistances of PV
cell.
B. Boost Converter and MPPT
Boost converter with MPPT control is responsible for
regulation of PV output voltage for tracking the maximum
power point to generate maximum possible energy from the PV
system. Fig. 1 shows the circuit configuration of boost converter
connected to PV array. The different topologies of boost
converter for PV system are discussed in [3]. The boost
converter is designed to boost the variable PV output voltage to
a constant 700 Volt. Boost converter component parameters are
designed based on the equation given by [4].
iL 
V pv
DTs
2L
V
v  dc DTS
2 RCdc
(2)
where iL is considered to be 5% of the output current is
inductor current ripple, v is considered to be 1% of the output
dc voltage is dc link voltage ripple, D is duty cycle, and
1
is switching period.
Ts 
fs
MPPT algorithm provides the control signal for the proper
gating of the boost converter. In this paper; we implement the
variable step incremental conductance (IC) MPPT. Fig.3 shows
the flowchart of the implemented MPPT algorithm.
C. Bidirectional DC-DC Converter with BES
The bidirectional dc-dc converter is responsible for the
charging and discharging operation of the BES unit. Various
topology and configuration on the bidirectional dc-dc converter
for the PV system can be found in [6]-[7]. In this paper, a generic
battery model of MATLAB/Simulink is used. Fig. 1 shows the
typical configuration of the bidirectional converter used in this
paper. To charge the BES when PV output is high, bidirectional
converter is operated as buck converter applying the gating
signal to switch S1 .In case of low power from PV system or
power cut off from grid, bidirectional converter is operated as
boost converter applying a gating signal to switch S 2 , thus
discharging the battery and supplying energy to the load.
Bidirectional converter component parameters are designed
based on equation in [8], which are presented below:
Boost mode of operation:
CH 
D
RH f s  VH / VH 
D 1  D  RH
(4)
2
Lb,min 
(3)
Buck mode of operation:
2 fs
(5)
Lb,min 
1  D  RL
impedance, thus lower the current ripple across the grid current
(6)
2 fs
Where, RH and RL are the equivalent load resistance at boost
and buck side, CH is the capacitance value at the boost side
Lb,min is the minimum value of inductance and f s
is the
Fig. 5 Block diagram of LCL filter model
Start
[11]. The proper sizing of the LCL filter ensures high-quality
grid-current. LCL filter parameters are calculated with [12]
Sample V(k), I(k)
Converter side inductor:
dI=I(k)-I(k-1), dV=V(k)-V(k-1)
dP=V(k)*I(k)-V(k-1)*I(k-1)
Step=N*abs(dP/dV)
No
Yes
D(k)=D(k-1)
dV=0
dI/dV=-I/V
Yes D(k)=D(k-1)
No
dI/dV>-I/V
dI>0
Yes
No
No
D(k)=D(k-1)
+ Step
Yes
dI=0
No
Yes
Lf 
D(k)=D(k-1)
- Step
D(k)=D(k-1)
- Step
D(k)=D(k-1)
+ Step
Vdc
4 f sw imax
where imax is the converter side maximum ripple current.
Filter capacitance:
I ac
(8)
Cbase 
2 f acVac
where Cbase is the rated capacitance.
The maximum value of capacitance is limited by:
C f  5%Cbase
(9)
Grid side inductor:
Lg  rL f
Update V(k-1)=V(k),I(k-1)=I(k)
switching frequency.
D. Three Level NPC Inverter
PV system and BES produces the electricity in DC form,
which requires conversion into suitable AC form for supplying
power to the load, and to the grid. Inverter does DC to AC power
conversion. Different topology and configuration of an inverter
for grid-connected PV system are maintioned detail in [9].
Reference [10] uses two-level NPC for hybrid PV/battery
system. In this paper, we consider three phase three level NPC
V
because it provides three output voltage levels,  dc , 0 and
2
Vdc
which results in better sinusoidal waveform and lower

2
THD as compared to two-level inverter topology. Other
significant advantages are low switching frequency and lower
IGBT modules can be used as the voltage stress is reduced to
half the dc voltage.
E. LCL Filter
Quality of power supplied to the local load and injected into
the grid respectively has become the primary concern in recent
years. To eliminate the switching harmonics generated from the
PWM, filters are necessary for the grid-connected PV system.
Since LCL filter has a capacitor branch, it can bypass higher
switching harmonics thus reducing the size of the inductor used.
It also provides better decoupling between the filter and the grid
(10)
where r usually is  1 .
Damping resistor:
Return
Fig. 3 Flowchart of variable step size INC MPPT method [5]
(7)
Rd 
2
Cf
L f Lg C f
L f  Lg
(11)
Where,  is damping ratio.
Fig. 4 LCL filter model
Equation (12) gives the mathematical model for the LCL filter
in Fig. 4.
vs  vc  is ( R f  sL f )

vc  vg  ig ( Rg  sLg )

1

(12)
vc  ic ( Rd  sC )
f

is  ic  ig

where R f and R g are the parasitic resistance of L f , and Lg .
From the block diagram in Fig.5 and from (12), after canceling
the intermediate variables is , ig , ic , vc and ignoring the
disturbance term vg , the transfer function from vs to ig can be
solved as (13)
ig ( s )

vs ( s )
A. Boost Converter Control
The reference output voltage generated based on the MPPT
algorithm is compared to the actual PV output voltage. The error
(e) is passed to the PI controller with k p and ki value 0.001
and 0.002 respectively. The output of this PI controller
1  s.Rd C f
s .L f Lg C f  s .(( R f  Rd ) L f )C f  s.(( L f  Lg )  ( R f Rd  Rg Rd  R f Rg )C f )  ( R f  Rg )
3
2
(13)
Now, we plot the bode diagram of LCL and L= L f  Lg filter (
C f  0 ), based on (13). From Fig. 6 we can observe that in
low-frequency range both LCL and L filters are nearly the
same, and in the high-frequency range, LCL filter has a much
larger slope of attenuation than L filter.
Fig.7 Boost converter control structure
compared with the triangular wave of 20 KHz that drives the
boost converter switch (S) with a gating signal (g) for boosting
the PV voltage as shown in Fig. 7.
Fig.8 Bidirectional dc-dc converter control structure
B. Bidirectional Dc-Dc Converter Control
The control system of bidirectional converter consists of two
loops, outer voltage control loop and inner current control loop
as shown in Fig. 8. The outer loop is responsible for maintaining
constant dc link voltage while the inner loop maintains the
charging/ discharging current of battery energy storage unit. The
PI controller parameters for outer control loop are k p 2 =1.8 and
ki 2 =37.6. Similarly, for the inner control loop, 39 and 410.25
are respective k p1 and ki1 values.
Fig.6 Bode diagram of LCL and L filter
III. SYSTEM CONTROLLERS
The overall system is designed based on the PI controllers
because of their simpler structure and ease of tuning. The
transfer function of the PI controller is given as:


K  s   k p s  ki / s
Where, k p proportional gain
(14)
C. Three Level NPC inverter Control
Since the current through capacitor branch is much smaller
compared to grid current and from Fig.6 LCL filter can be
usually approximated into an inductor ( L f  Lg ), by neglecting
the capacitor branch. Thus, the following equation becomes
valid for the circuit in Fig. 1
ki is an integral gain.
Fig. 9 NPC inverter control Structure
(16)
Fig.10 shows that system with BES has more stable dc bus
voltage as compared to the system without BES. Similarly, Fig.
11 shows that the system without BES is slower reaching the
steady state at nearly 0.1s while the system with BES reaches its
steady state at 0.05s. Fig. 12 shows that the THD of the injected
grid current is 0.68%.
Based on (16) the control loop for NPC inverter in synchronous
voltage oriented control (Synchronous VOC-control) [13]-[14]
in dq frame can be designed to decouple dq component and
eliminate grid disturbance as shown in Fig. 9.In Fig. 9 output
of the outer voltage control loop which is igd  controls the
B. Intermittency Due to Changing Solar Irradiance
PV array is set to operate on variable solar insolation; 1000
W/m2 from 0-1sec, 500 W/m2 from 1-2 sec and 300 W/m2 from
2-3sec. 3760-Watt load equivalent to the PV power generation
when insolation is 500 W/ m2 is connected for 3 seconds of
simulation.
active power flow from the PV system to grid. Since in this
paper, we do not consider reactive power flow igq  is set to
Fig. 13 (a)-(d) shows the different simulation waveform of
the PV array. For variable solar insolation, it can be seen from
Fig. 13 (b)-(d) MPPT is tracking the changes rapidly thus
allowing the maximum power generation from PV array.
d
ig ,abc  Rig ,abc  vg ,abc
dt
Applying Park Transformation of (15)
igd 
vsd 
0 1 igd   vgd 
d igd 
   L    R    .L 
  
dt  igq 
vsq 
1 0   igq   vgq 
 igq 
Where, L  L f  Lg and R  R f  Rg .
vs,abc  L
(15)
zero.
IV. SIMULATION RESULTS
A. Power Quality and Dynamic Performance
PV array is set to operate on constant solar insolation of 1000
W/m2 and temperature is 298 K. The system is simulated
without BES and with BES for 4 seconds. The total generated
power from the PV system is injected to grid without connecting
any load in the system. Dc-link voltage at dc bus and injected
grid current at PCC are measured, without BES and with BES.
Fig. 14 (a)-(d) shows the different simulation waveforms of
BES unit. Since the connected load is less than PV generation
for 0-1 sec, the PV system charges the battery to store the extra
energy; SOC of battery increases. For 1-2 sec PV generation is
equal to load demand, BES remains ideal; SOC of the battery
will also remain ideal. For 2-3 sec PV generation is less than
load demand, BES discharges to supply power to load; SOC of
the battery decreases.
Fig. 15 shows the power flow to/from the grid. For 0-1 sec
PV generation is higher than load demand, part of this surplus
power charges the BES while sending remaining power to the
Fig.10 a) Dc link voltage without BES
a)
Solar insolation
b)
c)
PV voltage
d)
PV output power
b) Dc link voltage with BES
PV current
Fig. 13 Simulation waveforms of PV array
Fig. 11 a) Injected grid current without BES b) Injected grid current with
Fig. 12) FFT of injectedBES
grid current of Fig. 11 b)
a)
BES power
b) SOC of battery
grid. For 1-2 sec PV generation is precisely equal to load
demand; there is no flow of power to/from the grid. For 2-3 sec
load demand is higher than PV generation; deficit power is
supplied by BES and grid together causing the flow of power
from grid to load.
c) BES Voltage
d) BES Current
V. CONCLUSION
In this paper, LCL based grid-connected system with
battery energy storage is designed and simulated in
MATLAB/Simulink environment. Variable step IC method
used for tracking MPPT proves its accuracy and tracking speed
to be highly efficient. The proposed configuration of three-level
NPC with LCL filter allows current with very low THD to be
injected into the grid. BES system with grid-connected PV
system enhances the dynamic performance, maintains the dc
link voltage constant despite the change in solar irradiance, and
solves the problem of intermittency. Although the intermittency
problem is solved with BES, more detail analysis is required for
managing the charging and discharging states of BES that
ensures the economic feasibility of the studied topology.
Fig. 14 Simulation waveforms of BES unit
REFERENCES
[1]
Fig. 15 Simulation waveform of power flow to/from grid
Table 1. shows the parameters of the component used for the
simulation of considered topology.
S.N
1.
2.
TABLE 1. PARAMETERS
Parameters
Nominal Voltage
144 V
Rated Capacity
200 Ah
Initial SOC
60 %
Parameters of Boost Converter
Inductor, L
3.
4.
Values
Parameters of Battery Model
5 mH
Parameters of Bidirectional Converter
Inductor,
Lb
50 mH
Resistor,
Rb
0.35 Ohm
Parameters of LCL filter
Converter side inductance,
Parasitic resistance of
Lf
3.5 mH
Lf , Rf
0.05 Ohm
Lg
1.2 mH
Grid side Inductance,
Parasitic resistance of Lg , R g
0.02 Ohm
Filter Capacitance,
Cf
2.045 µF
Damping resistor,
Rd
3.99 Ohm
International Energy Agency (2018, Sept.). Key World Energy Statistics
2018 [Online]. Available: https://webstore.iea.org/key-world-energystatistics-2018
[2] Genesis Alvarez, Hadis Moradi, Mathew Smith, and Ali Zilouchian,
"Modeling a Grid-Connected PV/Battery Microgrid System with MPPT
controller." [Online]. Available: https://arxiv.org/abs/1710.00063
[3] Nor Hanisah Baharudin, Tunku Muhammad Nizar Tunku Mansur, Fairuz
Abdul Hamid, Rosnazri Ali, Muhammad Irwanto Misrun, "Topologies of
DC-DC Converters in Solar PV Applications," Indonesian Journal of
Electrical Engineering and Computer Science, vol. 8, no. 2, pp.368-374,
Nov. 2017
[4] Robert W. Erickson, and Dragan Maksimovic, “Principles of Steady-State
Converter Analysis,” in Fundamentals of Power Electronics, 2nd edition,
NJ, USA: Kluwer Academic Publisher, 2000, ch. 2, pp. 22-28
[5] Fangrui Liu, Shanxu Duan; Fei Liu, Bangyin Liu, and Yong Kang, “A
Variable Step Size INC MPPT Method for PV Systems,” IEEE Trans.
Industrial Electronics, vol.55, no. 7, July 2008
[6] Mahmoud Saleh, Yusef Esa, Yassine Mhandi, Werner Brandauer, and
Ahmed Mohamed, “Design and Implementation of CCNY DC microgrid
testbed,” in IEEE Industry Applications Society Annual Meeting,
Portland, OR, 2016, pp. 3-5
[7] Mirza Mursalin Iqbal, and Kafiul Islam, “Design and Simulation of A PV
System With Battery Storage Using Bidirectional DC-DC Converter
Using Matlab Simulink,” International Journal of Scientific &
Technology Research, vol. 6, July 2017
[8] Kuei-Hsiang Chao, Ming-Chang Tseng, Chun-Hao Huang, Yang-Guang
Liu, and Liang-Chiao Huang, “Design and Implementation of
Bidirectional DC-DC converter for Stand-Alone Photovoltaic Systems,
”International Journal of Computer, Consumer and Control, vol.2, no.3,
2013
[9] R. Mechouma, B.Azoui, and M. Chaabane, “Three-phase grid connected
inverter for photovoltaic systems, a review,” in 2012 First International
Conference on Renewable Energies and Vehicular Technology,
Hammamet, Tunisia
[10] Fei Ding, Peng Li, Bibin Huang, Fei Gao, Chengdi Ding, and Chengshan
Wang, “ Modeling and Simulation of Grid-connected Hybrid
Photovoltaic/Battery Distribution Generation System,” in 2010 China
International Conference on Electricity Distribution, Nanjing, China
[11] Xinbo Ruan, Xuehua Wang, Donghua Pan, Dongsheng Yang, Weiwei Li,
and Chenlei Bao, “Introduction,” in Control Techniques for LCL-Type
Grid-Connected Inverter, Science Press Beijing, Springer,2017, pp. 1-23
[12] A.E.W.H. Kahlane, L. Hassaine, and M. Kherchi, “LCL filter design for
grid connected systems,” in Revue des Energies Renouvelables SIENR,
2014
[13] Remus Teodorescu, Macro Liserre, and Pedro Rodriguez, “Grid
Converter Control for WTS,” in Grid Converters for Photovoltaic and
Wind Power Systems, 1st ed. , John Wiley and Sons, Ltd, 2011, ch.9, pp.
219-226
[14] George Alin Raducu, “Control of Grid Side Inverter in a B2B
Configuration for WT Applications,” M.S. thesis, Dept. Power
Electronics and Drives, Aalborg University, Denmark,2008