Synchronous PWM control of triple transformer-connected inverters for photovoltaic system

This paper presents results of research of modulation processes in power conversion system with triple voltage source inverters, supplied by photovoltaic (PV) strings, and connected to a four-winding transformer. The transformer has in this case specific connections between the secondary windings and inverters, allowing providing of multilevel voltages at secondary windings of the transformer. Specialized space-vector-based strategy of pulsewidth modulation (PWM) has been used for control of inverters, insuring quarter-wave symmetry of winding voltages for any modulation indices and switching frequency of inverters. Analysis and comparison of harmonic composition of winding voltages and output voltages of inverters has been done. The validity of the analyzed processes has been verified by simulations: three basic variants of the scheme of modulation have been applied for control of inverters.