A 5-level High Efficiency Low Cost Hybrid Neutral Point Clamped Transformerless Inverter for Grid Connected Photovoltaic Application


With the increase in the level of solar energy combination into the power grid, there occur a need for highly efficient multilevel transformerless grid connected inverter which is able to inject more power into the grid. In this paper, a novel 5-level Hybrid Neutral Point Clamped transformerless  inverter topology is proposed which has no important ground leakage current.

The proposed inverter is consider in detail and its switching design to generate multilevel output is discussed. The proposed inverter is compared with some popular transformerless inverter topologies. Simulations and experiments results confirm the service and good performance of the proposed inverter.



Fig. 1. Proposed hybrid neutral point clamped inverter


Fig. 2. Inverter operation at UPF

Fig. 3. Inverter operation at 300 lag PF

Fig. 4. Inverter output for increase of modulation index from 0.45 to 0.95

Fig. 5. Inverter output for decrease of modulation index from 0.95 to 0.45

Fig. 6. Dynamic performance of inverter for increase of load

Fig. 7. Dynamic performance of inverter for decrease of load

Fig. 8. Inverter operation with chopper balancing circuit activated

Fig. 9. Inverter operation with chopper balancing circuit deactivated


 A 5-level Hybrid neutral point clamped transformerless PV grid connected inverter is presented in this paper. The main characteristics of proposed transformerless inverter are:

1) Lower stress on the grid conform inductor, thereby reducing the filtering cost and size as compared to conventional 3-level inverters like H5 and HERIC  inverter.

2) Lower cost as compared to 5L-DCMLI as the proposed inverter want less no of clamping diodes.

3) Higher power handling capacity as compared to conventional 3-level inverters.

4) Higher efficiency as compared to 5L-DCMLI and H5 inverter.

5) No common mode leakage current as the proposed inverter belongs to the family of half bridge inverters.

6) The proposed inverter is capable of trade reactive power with the grid.

Therefore, with excellent performance in eliminating the CM current, multilevel output voltage and high efficiency, the proposed inverter provides an lively alternative to the conventional transformerless grid-connected PV inverters.

Moreover, due to its perfection over the 5L-DCMLI in terms of efficiency and cost parameters, the consistency of the proposed inverter is not limited to grid connected PV inverters and it can find its way for all the applications where currently 5L-DCMLI are employed.


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[3] E. Gubia, P. Sanchis, A. Ursua, J. Lopez, and L. Marroyo, “Ground currents in single phase transformerless photovoltaic systems”, Progress in Photovoltaics: Research and Applications, vol. 15, no. 7, pp. 629650, 2007.

[4] H. Xiao and S. Xie, “Leakage current analytical model and application in single-phase transformerless photovoltaic grid-connected inverter”, IEEE Transactions on Electromagnetic Compatibility, vol. 52, DOI 10.1109/TEMC.2010.2064169, no. 4, pp. 902913, Nov. 2010.

[5] S. Busquets-Monge, J. Rocabert, P. Rodriguez, S. Alepuz and J. Bordonau, “Multilevel Diode-Clamped Converter for Photovoltaic Generators With Independent Voltage Control of Each Solar Array”, in IEEE Transactions on Industrial Electronics, vol. 55, no. 7, pp. 2713-2723, July 2008. Doi: 10.1109/TIE.2008.924011

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