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A Transformerless Grid Connected Photovoltaic Inverter with Switched Capacitors

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.

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A Transformerless Grid Connected Photovoltaic Inverter with Switched Capacitors

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  1. ELECTRICAL PROJECTS USI ELECTRICAL PROJECTS USING MATLAB/SIMULINK NG MATLAB/SIMULINK Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 A Transformerless Grid Connected Photovoltaic Inverter with Switched Capacitors 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 For Simulation Results of the project Contact Us Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245

  2. ELECTRICAL PROJECTS USI ELECTRICAL PROJECTS USING MATLAB/SIMULINK NG MATLAB/SIMULINK Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 CIRCUIT DIAGRAM: Fig 1. Proposed topology. EXPECTED SIMULATION RESULTS: For Simulation Results of the project Contact Us Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245

  3. ELECTRICAL PROJECTS USI ELECTRICAL PROJECTS USING MATLAB/SIMULINK NG MATLAB/SIMULINK Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 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. For Simulation Results of the project Contact Us Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245

  4. ELECTRICAL PROJECTS USI ELECTRICAL PROJECTS USING MATLAB/SIMULINK NG MATLAB/SIMULINK Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 Fig 4. Current And Voltage Stress On S3. (a)C1/(C1+C2)=0.33 (C1 = 470μf, C2 = 940μf), Vbus = 400V For Simulation Results of the project Contact Us Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245

  5. ELECTRICAL PROJECTS USI ELECTRICAL PROJECTS USING MATLAB/SIMULINK NG MATLAB/SIMULINK Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 (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. For Simulation Results of the project Contact Us Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245

  6. ELECTRICAL PROJECTS USI ELECTRICAL PROJECTS USING MATLAB/SIMULINK NG MATLAB/SIMULINK Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245 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 aTransformerless 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. For Simulation Results of the project Contact Us Gmail:asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in 0-9347143789/9949240245

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