A Grid Connected Phase Shifted Full Bridge based PV Inverter with Off-grid Operation Capability

A three phase grid connected phase shifted full bridge (PSFB) based solar PV (SPV) inverter which can operate both in off-grid and on-grid mode is proposed in this paper. This inverter has a high-frequency isolated DC-DC stage through a PSFB which delivers substantial voltage gain and galvanic isolation via a High Frequency Transformer. The control strategy of its high frequency stage is simplified as compared to dual active bridge (DAB) based stage due to reduction in number of controlled switches. A suitable control strategy which can operate the PV array of the inverter at its maximum power point (MPP) during on-grid mode and non-maximum power point (NMPP) during the off-grid mode along with the transition in any of these modes. When the grid fails this inverter islands itself from the AC grid and goes to off-grid mode to deliver the local load connected at the point of common coupling. When the grid is present, the inverter runs in on-grid mode to inject a sinusoidal current to the grid at a unity power factor. A comprehensive explanation of the power stage configuration of the inverter, its operating principle and control strategy covering all the operating modes of it have been explained. A 30 kW PV system based on this inverter is implemented in the MATLAB-SIMULINK platform and extensive simulation studies have been performed on this model to verify the viability of the proposed scheme and its control strategy.