Control strategy of PV-fed, grid-interfaced, seven-level T-type MLI for distributed power generation

摘要

The major concern with renewable sources of energy, feeding the distributed power generation system, is the power quality, reliability and efficiency of the system. This study proposes a novel topology comprising single-phase, seven-level, grid-connected photovoltaic-fed (PV) inverters in parallel. An important expediency of connecting multilevel inverters (MLIs) in parallel is that the failure of any source or the MLI module itself will never stop the overall generation, leading to improved efficiency and reliability of the system. This study also incorporates a novel controller comprising of two DC and an AC controller that independently controls the DC-link voltage of PV system and AC-side voltage so as to inject a pure sinusoidal current at unity power factor into the grid. Also, the AC controller discussed here is self-synchronising, i.e. aloof of phase-locked loop. The power mismatch problem that basically arises due to partial shading conditions in PV system has also been discussed. The MATLAB/Simulink-based proposed two seven-level grid-connected inverters in parallel are modelled and simulation results are presented. An experimental prototype of the PV-fed grid-connected system comprising two seven-level inverters in parallel is developed and tested to validate the simulation results.