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Transcript of FPGA based Transformer less grid connected inverter … · converter for Photo voltaic applications...
@IJMTER-2015, All rights Reserved 242
FPGA based Transformer less grid connected inverter using boost
converter for Photo voltaic applications
1M.Subashini,
2S.Divyaprasanna,
3V.Chithirai selvi,
4K.Devasena
1,2,3,4Assistant Professor, Department of Electrical and Electronics Engineering,
Shanmuganathan Engineering College, Arasampatti, Pudukkottai, India.
Abstract— This project proposes a novel transformer less grid connected power converter with
negative grounding for a photovoltaic generation system. The negative terminal of the solar cell
array can be directly connected to the ground in the proposed grid-connected power converter to
avoid the transparent conducting oxide corrosion that occurs in some types of thin-film solar cell
array. The proposed grid-connected power converter consists of a dc–dc power converter and a dc–
ac inverter. The salient features of the proposed power converter are that some power electronic
switches are simultaneously used in both the dc–dc power converter and dc–ac inverter, and only two
power electronic switches operate at high switching frequency at the same time (one is in the dc–dc
power converter and the other is in the dc–ac inverter). The leakage current of the photovoltaic
generation system is reduced because the negative terminal of the solar cell array is connected
directly to the ground. Finally, a prototype was developed to verify the performance of the proposed
grid-connected power converter. The experimental results show that the performance of the proposed
grid-connected power converter is as expected.
Keywords- Boost converter, FPGA, solar panel, dc link voltage control, voltage source inverter
I. INTRODUCTION
The salient features of the reduction of the transformer and proposed power converter are
only two power electronic switches of the power converter are operated at high switching frequency
simultaneously (one is a dc–dc power converter and the other is a dc–ac inverter), and the negative
terminal of the solar cell array is directly connected to the ground to solve the problems of TCO
corrosion and leakage current for some types of thin-film solar cell array. The experimental results
show that the proposed grid-connected power converter can trace the maximum power point of the
solar cell array, convert solar power to a high quality ac power to inject into the utility, and reduce
the leakage current of the solar cell array. Using an isolation transformer in the grid-connected
inverter can solve the problem of the leakage current caused by the earth parasitic capacitance in
solar modules. There are two types of grid-connected inverter with an isolation transformer.
a) Line frequency transformer
b) High-frequency transformer.
The solar modules can be grounded directly and there is no current path for leakage current
because the line frequency transformer is isolated. This system supplies no dc current to the grid and
has the advantage of a simple control circuit. However, the line frequency transformer’s
disadvantages are large volume, high weight, and high cost. The wide use of fossil fuels has resulted
in the emission of greenhouse gases and the cost of fossil-fuel energy has become higher and higher.
Climate change, caused by these greenhouse gases, has seriously damaged the environment. Because
of the problems associated with climate change, interest in renewable energy sources, such as solar
power and wind power, has increased Many materials can be used to manufacture solar cells, but
polycrystalline Si and mono crystalline Si is the most widely used. A thin-film solar cell can generate
power under conditions of low irradiation. Therefore, the thin-film solar cell has the potential to
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 243
generate electrical power for a longer time than a crystalline Si solar cell. Since the thin-film cell can
be easily combined with glass, plastic, and metal, it can be incorporated in green architecture. The
use of thin-film solar cells has increased steadily and this trend is set to continue in the future.
In general, an earth parasitic capacitance will be generated between solar modules and their
ground. This parasitic capacitance is about 50–150 nF/kW for a glass-faced solar cell array.
However, this capacitance is increased to 1 μF/kW if the thin-film solar cell array is used. Serious
leakage current occurs if a high-frequency pulsating voltage is applied between the thin-film solar
modules and the ground. Corrosion damage in thin-film modules, caused by a so-called transparent
conductive oxide (TCO) corrosion of cadmium telluride (Cd-Te) or amorphous silicon (A-Si), is
observed if the voltage of the negative terminal of a solar module is lower than that of the ground.
The damage to the electrical conductivity of the inside of the glass cover cannot be repaired and
causes substantial power loss. Consequently, the life of thin-film solar modules is shortened.
However, TCO corrosion can be prevented by the negative grounding of solar modules.
II. TRANSFORMERLESS GRID CONNECTED INVERTER
By overcoming the disadvantages of existing with transformer power converter and reduction
in cost simultaneously is a very challenging task. Removing the transformer, removing the negative
current & avoiding the leakage current of the converter modification are considered in this project. In
below we discuss briefly the proposed project.
The proposed Novel Transformer less Grid-Connected Power Converter are show in figure.5,
it’s consist of Solar Cell, DC – DC power converter, DC –AC inverter and load. D.C voltage is
generated from the Solar panel. It will be given to DC – DC power converter. Boost converter is one
of the SMPS topologies. SMPS circuit consists of the power circuit and the control circuit. The
power stage performs the basic power conversion from the input voltage to the output voltage and
includes switches and the output filter. Then output of the dc to dc converter is given to Inverter then
output of the sine wave connected grid as we as load, FPGA is programmed to generate PWM.
Switching pulse given to the MOSFET it is generated from PWM Controller. The PWM pulses are
given to input of Optocoupler. Optocoupler is used to isolate between Control circuit and driver
circuit.
III. PROPOSED CONTROL STRATEGY FOR BLDCM
Fig. 1 shows the circuit configuration of the proposed photovoltaic generation system. As can
be seen, the grid-connected power converter is transformer less, and its negative terminal is
connected directly to the ground. Both the problems of TCO corrosion and leakage current in Cd-Te
or A-Si thin-film solar cell array can be avoided. The proposed transformer less grid-connected
power converter is composed of a dc–dc power converter and a dc–ac inverter. The dc–dc power
converter is a boost converter. The dc–dc power converter consists of three dc capacitors C1, C2, and
C3, an inductor L1, two diodes D1 and D2, and four power electronic switches G1, G2, G3, and G5.
The dc–dc power converter converts the dc voltage of the solar cell array to a stabilized dc voltage.
The dc–ac inverter consists of two dc capacitors C2 and C3, an AC inductor Lf, and four power
electronic switches G4, G5, G6, and G7. The dc–ac inverter further converts the output dc voltage of
the dc–dc power converter into ac power and injects into the grid. As seen in Fig. 1, the power
electronic switch G5 controls both the dc–dc power converter and the dc–ac inverter. Fig.3 wave
forms are shows the timing sequence for power electronic switches of the proposed power converter
for positive half cycle. This is the timing sequence for power electronic switches during the positive
half-cycle of the utility voltage. During the positive half cycle of the utility voltage, the dc–dc power
converter changes are noted.
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 244
NEGATIVE HALF CYCLE
Fig.2 wave forms are shows the timing sequence for power electronic switches of the
proposed power converter for negative half cycle. For the negative half-cycle of the utility voltage,
the dc–dc power converter charges the capacitor C2, so the duty cycle of G1 controls the voltage of
capacitor C2. (Du 2 = ton2/T2) Capacitor C3 supplies power to the dc–ac inverter, and G4 of the dc–
ac inverter is switched at high frequency to control the output current.
Figure 1. Circuit configuration of the proposed transformer less power converter for photovoltaic generation system
Figure 2. Timing sequence for power electronic switches of the proposed power converter. (a) Positive half-cycle. G2,
G3, G4, G5, and G7are
Low frequency, G1 and G6 are high frequency
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 245
Figure 3. Timing sequence for power electronic switches of the proposed power converter for Negative half-cycle G2,
G3, G5, G6 and G7 are low frequency and G1, G4 are high frequency
MODES OF OPERATIONS
The operation of power electronic switches during the each half-cycle of the utility voltage
can also be divided into three time intervals. The current paths during these time intervals of the each
half-cycle of the utility voltage are shown in below modes of operations.
MODE - I OPERATION [T01, T02]
Figure 4. Current path under time duration [t01, t02]
The current path during this time interval is shown in Fig.4 G1 of the dc–dc power converter
is switched on to energize the inductor L1. Because G3 and G5 are both ON, a diode D2 is series
connected to G3 to prevent C3 from short circuit. In the dc–ac inverter, G6 is switched ON and the
output voltage Vo is +Vdc2. The output current of the dc–ac inverter is supplied from C2.
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 246
MODE - II OPERATION [T02, T03]
Figure 5. Current path under time duration [t02, t03]
The current path during this time interval is shown in Fig.5. In the dc–dc power converter, G1
and G2 are switched OFF. G3 and G5 are still ON. The energy stored in the inductor L1 is de-
energized via the path D2, G3 and the flying diode of G5 to charge the capacitor C3. G6 of the dc–ac
inverter is still ON, and the output voltage Vo is still +Vdc2. The filter inductor of the dc–ac inverter
is energized from C2.
MODE - III OPERATION [T03, T04]
The current path during this time interval is shown in below Fig.6 In the dc–dc power
converter, the energy stored in the inductor L1 is still de-energized via the path D2, G3 and the flying
diode of G5 to charge the capacitor C3. G6 of the dc–ac inverter is switched OFF, and the output
current is flowing through G5 and the flying diode of G7 to form a loop. Therefore, the voltage Vo is
0, and the filter inductor of the dc–ac inverter is de-energized.
Figure 6. Current path under time duration [t03, t04]
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 247
MODE - IV OPERATION [T11, T12]
Figure 7. Current path under time duration [t11, t12]
The current path during this time interval is shown in Fig.7. G1 of the dc–dc power converter
is switched on to energize the inductor L1. Because G4 and G7 are both ON, a capacitor C3 is series
connected to G4 to prevent G7 from short circuit. In the dc–ac inverter, G4 is switched ON and the
output voltage Vo is +Vdc3. The output current of the dc–ac inverter is supplied from C3.
MODE - V OPERATION [T12, T13]
Figure 8. Current path under time duration [t12, t13]
The current path during this time interval is shown in Fig.8. In the dc–dc power converter, G1
is switched OFF. G4 and G7 are still ON. And the switch G2 is going to ON. The energy stored in
the inductor L1 is de-energized via the path D1, G2 and the charge the capacitor C3. G7 of the dc–ac
inverter is still ON, and the output voltage Vo is still +Vdc2. The filter inductor of the dc–ac inverter
is energized from C2.
MODE – VI OPERATION [T13, T14]
The current path during this time interval is shown in below Fig.9. In the dc–dc power
converter, the energy stored in the inductor L1 is still de-energized via the path D1, G2 and the flying
diode of G5 to charge the capacitor C3. G6 of the dc–ac inverter is switched OFF, and the output
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 248
current is flowing through G5 and the flying diode of G7 to form a loop. Therefore, the voltage Vo is
0, and the filter inductor of the dc–ac inverter is de-energized.
Figure 9. Current path under time duration [t13, t14]
IV. SIMULATION AND EXPERIMENTAL RESULTS
To verify the feasibility of the proposed strategy, simulations and experiments are carried out.
Figure 10. Boost converter based transformer less grid connected systems Simulink diagram
Figure 11. Boost converter based transformer less grid connected systems PWM generation Simulink diagram
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
@IJMTER-2015, All rights Reserved 249
Figure 12. Boost converter based transformer less grid connected systems output voltage
Figure 13. Boost converter based transformer less grid connected systems PWM pulses to the inverter
Figure 14. Boost converter based transformer less grid connected systems hardware view.
International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 02, Issue 11, [November – 2015] ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
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V. CONCLUSIONS
The implementation of transformer less grid connected power converter for photovoltaic
generation system was analyzed in this thesis. The electric circuit parameters of the power converter
were empirically derived using a series of measurements collected from experimental test. Using
these parameters the current, voltage was designed for the transformer less grid connected power
converter for photovoltaic generation system. The transformer less grid connected power converter
for photovoltaic generation system was modeled in Mat lab’s Simulink. With the simulated
performance of the power converter ability to arrive at a desired voltage and current, testing was
conducted in the lab using the various parameter of the power converter. The laboratory model of the
power converter constructed to collect data to the transformer less grid connected power converter
for photovoltaic generation system of an accurate manner.
REFERENCES
[1] U. Boeke and H. van der Broeck, “Transformer-less converter concept for a grid-connection of thin-film
photovoltaic modules,” in Proc. IEEE Ind. Appl. Soc. Annu. Meet, Oct. 5–9, 2008, pp. 1–8.
[2] Chen, W. Wang, C. Du, and C. Zhang, “Single-phase hybrid clamped three-level inverter based photovoltaic
generation system,” in Proc. IEEE Int. Symp. Power Electron. Distrib. Generation Syst., Jun. 16–18, 2010, pp. 635–
638.
[3] Kerekes, M. Liserre, R. Teodorescu, C. Klumpner, and M. Sumner, “Evaluation of three-phase transformer less
photovoltaic inverter topologies,” IEEE Trans. Power Electron., vol. 24, no. 9, pp. 2202–2211, Sep. 2009.
[4] S. V. Araujo, P. Zacharias, and B. Sahan, “Novel grid-connected non-isolated converters for photovoltaic systems
with grounded generator,” in Proc. IEEE Power Electron. Spec. Conf., Jun. 15–19, 2008, pp. 58–65.
[5] L. Ma, T. Kerekes, R. Teodorescu, X. Jin, D. Floricau, and M. Liserre, “The high efficiency transformer-less PV
inverter topologies derived from NPC topology,” in Proc. Eur. Conf. Power Electron. Appl., Sep. 8–10, 2009, pp.
1–10.
M.Subashini received the B.E. Degree in Electrical and Electronics Engineering from
GANADIPATHY TULSI'S Engineering College, Vellore, Anna University, Chennai, India
in 2007 and Post graduation in Power Electronics & Drives in Shanmuganathan
Engineering College, Pudukkottai under Anna University, Chennai, India in 2015. She is
currently working as assistant professor in Shanmuganathan Engineering College,
Pudukkottai.
S.Divyaprasanna received B.E degree in Electrical and Electronics Engineering from
Government College of Engineering, Bargur in 2003 and M.E degree in Power Electronics
and Drives from Government College of Engineering, Tirunelveli in 2010.She is currently
working as assistant professor in Shanmuganathan Engineering College, Pudukkottai.
V.Chithirai selvi was born in 1984. She finished her graduation in 2007 at Alagappa
Chettiyar College of Engineering and Technology, Karaikudi in the field of Electrical and
Electronics Engineering. She finished her master degree in the field of Power electronics
and drives in the year of 2015at Shanmuganathan engineering college, Arasampatti. Since
2011 she has been an assistant professor at Shanmuganathan Engineering College,
Pudukkottai.
K.Devasena received B.E degree in Electrical and Electronics Engineering from PSNA
college of Engineering and Tech and M.Tech degree in Power systems from PRIST
UNIVERSITY Thanjavur in 2013.Now She is currently working as assistant professor in
Shanmuganathan Engineering College, Pudukkottai.