Neutral point clamped transformerless grid connected inverter having voltage buck-boost capability for solar photovoltaic systems

This study proposes a neutral point clamped grid-connected transformerless inverter for solar photovoltaic (PV) systems. This inverter has the capability to function in buck-boost mode. Thus the PV voltage level can be chosen to be of lesser value as compared to that of the existing buck type of inverters. This leads to increment in yield of power when PV modules are required to operate under mismatched conditions owing to possibility of more parallel connection of PV modules. Furthermore, buck-boost nature of the proposed inverter also facilitates operation under considerable variation in PV array voltage caused by wide changes in meteorological conditions. The other advantages of the inverter include: (a) elimination of concerns pertaining to the leakage current issues in transformerless grid-connected solar PV systems, (b) elimination of grid current sensor requirement, (c) elimination of shoot-through fault etc. The operating principle of the developed inverter supported by relevant analysis is presented. Control strategy devised for the inverter is provided. Results of detailed simulation studies carried out on MATLAB/Simulink platform are presented to ascertain viability of the proposed scheme. Exhaustive experimental validation has been carried out by utilizing a scaled down laboratory prototype of the proposed inverter.