PERFORMANCE ANALYSIS OF GRID INTERACTIVE SOLAR PHOTOVOLTAIC INVERTER

Abstract

Solar Photovoltaic (PV) system is a simple, reliable and environment friendly technology. These days the grid interactive PV system demands the inverter which is highly efficient, compact in size, lighter and economical. The PV inverters present in the market use either low frequency or high-frequency transformers. But the problem with low or the line frequency transformers is that they are bulkier and needs lots of space for their installations whereas with high-frequency transformer is that they involve many power stages which makes it complex and makes the system less efficient. To sort out this problem of solar PV system, the transformer less inverter configuration is adopted which makes the system highly efficient, cheaper and easier to install. Unluckily, with the transformerless inverter configuration safety issues become the main concern as in this configuration a galvanic connection between the grid and the PV array exists which is hazardous for the people working there. Because of this galvanic connection, the leakage current finds its way between PV array and the ground through the parasitic capacitors in the grid interactive PV inverter. The leakage current generated due to common mode voltage increases the current distortion, the system losses, and electromagnetic interference. The leakage current flows through the metallic body of PV module causes personal safety problems. In this work, single phase grid interactive solar PV inverter is analyzed with three modulation strategies. These modulation strategies are unipolar, bipolar and hybrid. The performances are analyzed in terms of leakage current, CMV, efficiency, power losses, and total harmonic distortion (THD) at various irradiance levels. It has been found that the basic full bridge (H4) PV inverter topology is not suitable for grid-connected transformerless applications with unipolar and hybrid modulation strategies. They are generating high leakage current and inject grid current with high THD. However, these issues can be mitigated by using bipolar modulation strategy, as it generates constant CMV. But it has more power losses and large inductor size. Therefore, in order to reduce the leakage current PV inverter and control strategy should generate constant CMV. Moreover, inverter should exhibits high efficiency and able to inject reactive power into the utility grid. To bridge the gap, a common mode voltage clamped H5 topology with improved control strategy is proposed which can reduce the leakage current and have reactive power injection capability. The proposed inverter generates constant common mode voltage and it avoids the need of common mode filter. The iv performance analysis of the proposed topology is done on Matlab/Simulink and the simulation results are validated experimentally.