ABSTRACT:
In the transformerless photovoltaic (PV) system, the
common mode ground leakage current may appear due to the galvanic connection
between the PV array and the ground, which causes the safety issues and reduces
the efficiency. To solve this problem, a novel inverter topology with switched capacitors
is proposed in this paper. By connecting one pole of the PV cell directly to
the neutral line of the grid, the common mode current is eliminated. Meanwhile,
the switched capacitor technology is applied to increase the DC voltage
utilization rate. Furthermore, a modified unipolar sinusoidal pulse width modulation
(SPWM) strategy is proposed to reduce the pulsating current caused by the
charging and discharging operations of the switched capacitors. Also, several
optimization principles are put forward to further reduce the pulsating current
to improve the efficiency and reliability. Finally, the proposed topology and
modulation strategy are verified with simulation and a 250W experimental
prototype.
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig 1. Proposed
topology.
EXPECTED SIMULATION RESULTS:
Fig 2. Simulated Waveforms
Of Output Current And Current Stress On S3
With Different
Ratio Of C1/(C1+C2).
Fig 3. Experimental
Waveforms Of Igrid And Vgrid.
Fig 4. Current And
Voltage Stress On S3.
(a) C1/(C1+C2)=0.33
(C1 = 470μf, C2 = 940μf), Vbus = 400V
(b) C1/(C1+C2)
=0.67 (C1 = 940μf, C2 = 470μf), Vbus = 400V
(C) C1/(C1+C2) =0.33 (C1
= 470μf, C2 = 940μf), Vbus = 380V
Fig 5. Current Stress
On S3 Under Different Conditions.
CONCLUSION:
A
novel transformerless inverter topology with the switched capacitors is
proposed for the grid connected PV power generation system. Only five power
switches are required in the proposed PV inverter topology. The common mode
current is eliminated perfectly. The DC input voltage required is the same as
the full bridge inverter. A modified unipolar SPWM strategy is proposed for the
topology, enabling it to output three voltage levels. It is also guaranteed
that C2 is charged every switching cycle under this SPWM strategy, so
that the current pulse on the power devices caused by the switched capacitors
is reduced. Furthermore, based on the quantitative analysis of the devices’
current stress, the principles for optimizing the capacitances of the switched
capacitors C1 and C2 are given. The simulation and experimental
results are provided to verify the theoretical analysis.
REFERENCES:
[1]
Gonzalez R, Gubia E, Lopez J, Marroyo L, “Transformerless Single- Phase
Multilevel-Based Photovoltaic Inverter,” IEEE Transactions on HIndustrial
Electronics, Hvol. 55, Hno. 7, Hpp. 2694-2702, 2008.
[2]
Lopez O, Freijedo F.D, Yepes A.G, Fernandez-Comesaa P, Malvar J, Teodorescu R,
Doval-Gandoy J, “Eliminating Ground Current in a Transformerless Photovoltaic
Application,” IEEE Transactions on Energy conversion, vol. 25, no. 1,
pp. 140-147, 2010.
[3]
Araujo S.V, Zacharias P, Sahan B, “Novel Grid-Connected Non- Isolated
Converters for Photovoltaic Systems with Grounded Generator,” in HPower
Electronics Specialists Conference, H2008, pp. 58-65.
[4]
Lopez O, Teodorescu R, Doval-Gandoy J, “HMultilevel transformerless topologies
for single-phase grid-connected converters,” in IEEE Industrial Electronics,
IECON 2006-32nd Annual Conference on Digital Object Identifier, 2006, pp.
5191-5196.
