With the increase in the level of solar energy integration into the power grid, there arises 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 inherent ground leakage current. The proposed inverter is analyzed in detail and its switching pattern to generate multilevel output is discussed. The proposed inverter is compared with some popular transformerless inverter topologies. Simulations and experiments results confirm the feasibility and good performance of the proposed inverter.
Fig. 1. Proposed hybrid neutral point clamped inverter
EXPECTED SIMULATION RESULTS:
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 interfacing 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 requires less no of clamping diodes.
3) Higher power handling capability 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 exchanging 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 exciting alternative to the conventional transformerless grid-connected PV inverters. Moreover, due to its superiority over the 5L-DCMLI in terms of efficiency and cost parameters, the pertinence 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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