International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
Design of HERIC Configuration Based Grid
Connected Single Phase Transformer less
Photovoltaic Inverter
Payal Somani
Divyesh J. Vaghela
M.Tech. student-electrical engineering department
Institute of technology-Nirma University
Ahmedabad, India
13meep11@nirmauni.ac.in
Electrical engineering department
Institute of technology-Nirma University
Ahmedabad, India
divyesh.vaghela@nirmauni.ac.in
Abstract— In a grid connected photovoltaic system, the main
aim is to design an efficient solar inverter with higher efficiency
and which also controls the power that the inverter injects into
the grid. The effectiveness of the general PV system anticipate on
the productivity by which the direct current of the solar module
is changed over into alternating current. The fundamental
requirement to interface the solar module to the grid with
increased productivity includes: Low THD of current injected to
the grid, maximum power point, and high power factor. In this
paper, a two stage topology without galvanic isolation is been
carried out for a single phase grid connected photovoltaic
inverter. The output from the PV panel is given to the DC/DC
boost converter, maximum power point tracking (MPPT) control
technique is being used to control the gate pulse of the IGBT of
boost converter. The boosted output is fed to the highly efficient
and reliable inverter concept (HERIC) inverter in order to
convert DC into AC with higher efficiency.
Keywords— DC/DC boost converter, Maximum power point
tracking (MPPT), HERIC Inverter.
I. INTRODUCTION
Now a days energy demands are increasing at a rapid rate
which has led to high utilization of fossil fuels, with negative
environment results like global warming, acid rain, depletion
of ozone layer etc. In order to conquer the negative effect of
fossil fuels the renewable energy sources discover a wide
application. Presently, renewable energy sources are the
attractive source of energy because of increased fuel
utilization, exhausting fossil fuels and their effect on
environment issues [1]. Solar energy is one of the most
attractive source of renewable energy. Thus the photovoltaic
solar energy comes up to be the most attractive distinct option
to supplement the generation of electricity due to numerous
advantages. Subsequently the photovoltaic inverter are turning
to an interesting topic for researchers. These inverters converts
the direct current (DC) supplied by the solar panels into
alternating current (AC) and feeds it into the utility grid.
According to the German DIN VDE 0126-1-1 standard [2],
there is a limitation for the common mode current (i.e. leakage
current) in the grid connected photovoltaic system. Hence the
line transformers are being used in order to provide electrical
insulation between the grid and the solar panel and also to
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
conquer the leakage current. But due to the plenty of
disadvantages such as weight, size, cost, and efficiency it finds
a low application now a days. High frequency dc-dc
transformers are also being used so as to provide galvanic
isolation but the efficiency of photovoltaic grid connected
system is still unsatisfactory. Thus to improve the efficiency,
transformerless grid connected photovoltaic inverters with low
leakage current finds a wide application.
The half-bridge inverters have topological favourable
circumstances which make up the issues like injection of dc
current into the grid and leakage current [2]. Since dc voltage
is not fully utilized in case of half-bridge inverter
consequently it finds less application. The full-bridge inverter
with bipolar SPWM technique can take care the issues of
leakage current, but the efficiency of these inverter is less
because of magnetic inductor losses and high switching losses.
The most widely used technique to diminish the leakage
current is to isolate the solar cell with the utility grid which
could be possible by structuring a new freewheeling path.
In this paper HERIC configuration based transformer less
single-phase PV topology is being analysed using MATLAB
2014(a). The main idea is to increase the productivity and
diminish the leakage current. A prototype of single phase grid
connected PV system is develop to verify the results.
II. SINGLE-PHASE TRANSFORMER LESS PV CONVERTERS
DERIVED FROM BRIDGE TOPOLOGY
The PV inverters, efficiently converts the DC source
generated from the PV panels to alternating source (AC). In
this section three power converter topologies are discussed.
A. Full-Bridge topology
Full Bridge topology is the most widely used technique for
grid connected single phase photovoltaic inverter. As
indicated in Fig. 1 it is develop by four transistor and through
LCL filter it is connected to the grid. These topology is
normally used in commercial purpose along with low
frequency transformers. However due to lower efficiency and
higher cost it is fascinating to study its application to
transformerless inverters. There are two types of modulation
schemes which are basically used for this inverter: 1) unipolar
modulation scheme and 2) bipolar modulation scheme. In
transformer less topologies.
The most well-known modulation scheme used is unipolar
PWM, because it has various advantages over bipolar PWM
scheme (for example, better efficiency, lower current ripple at
higher frequency etc). However these scheme is less suitable
for full bridge transformerless inverter since it requires high
frequency common mode voltage of amplitude Vdc/2, so as to
minimize the leakage current that appears due to the
photovoltaic panel’s parasitic capacitance.
C. High Efficient and Reliable Inverter Concept (HERIC)
The topology HERIC commercialized by Sunways,
integrates the advantages of the unipolar PWM modulation
with high efficiency and diminish leakage. These technique is
derived from the full-Bridge converter where AC bypass leg
has been added by means of back-to-back IGBTs connected in
parallel to bridge. These additional switches operate at the grid
frequency.
Fig, 3 shows the HERIC inverter where Cin is the DC-link
capacitor, L1 and L2 are filter inductance at grid side and C is
the filter capacitor. These additional switches has the two
major function: isolating the photovoltaic panel from the grid,
and preventing the reactive power exchange between the filter
inductors and capacitors during the zero voltage state, thus
increasing efficiency [8].
Fig. 1. A Single Phase Full-Bridge topology
In order to overcome the above problem of leakage current
bipolar PWM modulation technique is used for full-bridge
photovoltaic inverters. These modulation technique removes
high frequency components of the common mode voltage
applied to the panels [8], consequently the common mode
voltage has the low frequency components of the first
harmonic only which results in reduced leakage current. So in
order to limit peak value of leakage current, a good
synchronization is needed between the gate signals applied to
the bridge transistor. Thus these topology is not considered to
be the great distinct option for transformer less photovoltaic
inverter.
B. Half-Bridge topology
Fig. 3. Highly Efficient and Reliable Inverter Concept (HERIC)
topology
The converter operates as shown in table 1. During
positive half cycle T1 and T4 operates whereas T6 remains
connected in order to obtain active and zero vectors. When T1
and T4 are ON, current flows through the path PV – T1 – L1 –
grid – L2 – T4 and thus active vector is obtained, whereas
when T1 and T4 are OFF, the current freewheels through T6
and D5 and thus zero vector occurs. On the other hand during
negative half cycle T6 remains OFF and T5 remains
connected, whereas T3 and T2 operates. Active vector is
obtained when T3 and T2 are ON and the current flows
through the path PV – T3 – L2 – grid – L1 – T2, and the zero
vector is obtained when T3 and T2 are OFF and the current
freewheels through T5 and D6.
The main drawback of HERIC inverter is the high number of
switches, which leads to higher complexity and switching
losses as compared to conventional full-bridge inverter.
Table I. Conduction States for HERIC Inverter
Fig. 2. A Single Phase Half-Bridge topology
As indicated in Fig. 2 it is develop by two transistors and a
capacitor divider circuit is connected to the PV side. The
connection between the midpoint of the grid neutral and
capacitor divider circuit ensures constant common mode
voltage, hence intercepting the leakage current through the
parasitic capacitance of the PV module [8]. Although the
topology is simple and less expensive as compared to the full
bridge, it is rarely due to the drawbacks such as highly
distorted output current, output waveform has only two levels
and increased voltage stress, which are difficult to solve Thus
power transistors with higher blocking capacities are required,
which increases the switching losses.
T1
T2
T3
T4
T5
T6
Vout
ON
OFF
OFF
ON
OFF
ON
Vin
OFF
OFF
OFF
OFF
OFF
ON
0
OFF
ON
ON
OFF
ON
OFF
-Vin
OFF
OFF
OFF
OFF
ON
OFF
0
III. MAXIMUM POWER POINT TRACKING
MPPT algorithms are necessary because PV arrays have a
nonlinear V-I characteristic with a unique point where the
power produced is maximum. This point basically depends
upon the two factors that is irradiance and temperature of the
panel [10]. Both these factors changes according to climatic
condition and also depends upon the seasons in a year.
Furthermore, irradiation can change rapidly due to changing
Weather conditions such as clouds. Thus it is very important
to track the MPP accurately during different atmospheric
condition in order to obtain maximum power. In the recent
years many MPPT algorithms have been published. They
differ in many features such as complexity, cost or efficiency,
sensors required. However, it is worthless to use a more
expensive and complicated method if the same results are
obtained from the simpler and less expensive one. This is the
reason why some of the proposed techniques are not used.
A. Incremental Conductance
The Incremental Conductance (IC) method is used in order
to overcome the drawbacks of the PO algorithm when
subjected to fast changing environmental conditions. With the
help of voltage and current measurements, the conductance
I/V and incremental conductance dI/dV are determined so that
the decision can be made to increase or decrease the operating
voltage according to the operating point on the left or the right
of the MPP respectively.
The working principle of the IC method relies on the fact
that the slope of the PV panel power curve is negative on the
right of the MPP, zero at the MPP and positive on the left of
the MPP as follows:
dP/dV > 0 Left of MPP (V<VMPP)
dP/dV = 0 at MPP (V=VMPP)
dP/dV < 0 Right of MPP (V>VMPP)
According to the IC algorithm given in Figure, the current and
voltage are measured at previous and current states, then a test
is conducted to assess on one side if the difference in voltage
and current is equal to zero respectively, and on the other side
if the variation of voltage is equal to zero and the balancing
condition dI/dV +I/V = 0 at MPP is obtained. If so, no changes
take place in the operations process. If not, the IC method acts
to increase or decrease the voltage according to the difference
in current or the condition dI/dV + I/V is superior or inferior at
zero respectively.
Fig. 5. Output Voltage of HERIC Inverter
Fig. 6. Output Current of HERIC Inverter
A. Complete Model Simulation With and Without MPPT
The simulation of complete PV system is being carried out
without MPPT using MATLAB/Simulink. The simulation
model includes PV panel followed by DC-DC boost converter
and HERIC inverter. From the simulation results it has been
noticed that the inverter output without MPPT is much
distorted as compared to the output of inverter with MPPT.
IV. SIMULATION RESULTS
The simulation of HERIC inverter is being carried out
using MATLAB/Simulink. The simulation consist of a DC
source followed by modified H-bridge and an output filter.
Simulation results are carried out at a load of 5kW. Figure 4
indicates simulation of Heric Inverter.
Fig. 7. Output Voltage at variable irradiance without MPPT
Fig. 4. Simulation of HERIC Inverter
Fig. 8. Output Current at variable irradiance without MPPT
Fig. 9 Output Voltage of PV System with MPPT
Fig. 14. FFT Analysis of Output Current without filter
Fig. 10. Output Current of PV System with MPPT
V. HARDWARE RESULTS
A prototype of HERIC inverter is being made and is tested
for different load.
Fig. 15. FFT Analysis of Output Current with filter
Fig. 11. Gating Signals for Bridge Inverter
Fig. 16. Output Voltage with RL load without filter
Fig. 12. Gating Signals for AC coupling Switch
Fig. 17. Output Voltage with RL load with filter
Fig. 13. Output Voltage with R load without filter
A single phase transformerless grid connected inverter
with six power switches is being analyzed. The operation
mode of the topology is analyzed through simulation and is
being verified by a prototype. In this paper, a two stage
topology without galvanic isolation is been carried out for a
grid connected single phase photovoltaic inverter. The output
from the solar panel is fed to DC/DC boost converter in order
to obtain constant boosted voltage, maximum power point
tracking (MPPT) control technique is being used to control the
gate pulse of the IGBT of boost converter. These constant
boosted output is fed to the highly efficient and reliable
VI. CONCLUSION
inverter concept (HERIC) inverter in order to convert DC into
AC with higher efficiency.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
Ming Xu, Li Zhang, Yan Xing, Lanlan Feng 2012, “A Novel H6-Type
Transformerless Inverter for Grid Connected Photovoltaic Application”
7th IEEE conference on Industrial Electronics and Applications.
M. Kaliamoorthy, V. Rajasekaran, I. Gerald Christopher Raj March
2014."Single-phase _fteen-level grid-connected inverter for photovoltaic
system with evolutionary programming based MPPT algorithm" Solar
Energy 105 (2014) 314329.
S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, ‘‘A review of single-phase
grid-connected inverters for photovoltaic modules,’’ IEEE Trans.
Industry Applications, vol. 41, no. 5, pp. 1292—1306.
R. Gonzalez, E. Gubia, and J. Lopez, and L. Marroyo, ‘‘Transformerless
single-phase multilevel-based photovoltaic inverter,’’ IEEE Trans.
Industrial Electronics, vol. 55, no.7, pp. 2694-2702, July 2008.
S. V. Araujo, P. Zachariasm, and R. Mallwitz, ‘‘Highly efficient
singlephase transformerless inverters for grid-connected photovoltaic
systems,’’ IEEE Trans on Industrial Electronics, vol. 57, no. 9, pp. 31183128.
H. F. Xiao, S. J. Xie, ‘‘Leakage current analytical model and application
in single-phase transformerless photovoltaic grid-connected inverter,’’
IEEE Trans. on Electromagnetic Compatibility, vol. 52, no. 4, pp. 902913, November 2010.
M. Calais, V.G. Agelidis, "Multilevel converters for Single-Phase Grid
Connected Photovoltaic Systems-An Overview", IEEE Symposium on
Industrial Electronics, ISlE 1998, Vol. 1.
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
Ivan Patrao, Emilio Figueres, Fran Gonzalez-Espin, Gabriel Garcera,
“Transformerless topologies for grid-connected single-phase
photovoltaic inverters” Renewable and Sustainable Energy Reviews 15
(2011) 3423-3431.
L. Huber, Y. Jang, and M. M. Jovanovic, “Performance evaluation of
bridgeless PFC boost rectifiers,” IEEE Trans. Power Electron., vol. 23,
no. 3, pp. 1381–1390, May 2008.
Cedrick Lupangu Nkashama, "Maximum Power Point Algorithm for
Photovoltaic Home Power Supply" April 201
R. Gonzalez, 1. Lopez, P. Sanchis, L. Marroyo; "Transformerless
Inverter for Single-Phase Photovoltaic Systems"; IEEE Transactions on
Power Electronics, Volume 22, Issue 2, March 2007 Page(s):693 – 697
T. Meynard and H. Foch, “Multi-level conversion: High voltage chopper
and voltage source inverters,” in Proc. 23rd Annu. IEEE Power Electron.
Spec. Conf., Jun.–Jul. 1992, pp. 397–403.
J. Yungtaek, M. M. Jovanovic, and D. L. Dillman, “Bridgeless PFC
boost rectifier with optimized magnetic utilization,” in Proc. IEEE
APEC, Feb. 2008, pp. 1017–1021.
T.kerekes, R. Teodorescu, C. Klumpner, M. Sumner, D. Floricau, R.
Rodriguez; “Evaluation of three-phase tranformerless photovoltaic
inverter topologies”, European conference on Power Electronics and
Application, 2-5 Sept. 2007; Page(s): 1-10.
T.kerekes, R. Teodorescu, U.Borup; “Tranformerless Photovoltaic
Inverters Connected to the Grid”, Applied Power Electronics
Conference, APEC 2007; 25th Feb. 2007-1st March. 2007 Page(s):
1733-1737.