Reduction of high frequency zero sequence harmonics in parallel connected PV-inverters

High power photovoltaic plants are usually constituted of the connection of different photovoltaic subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless photovoltaic configurations characaterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and to the presence of undesirable parasitic earth capacitances is considered and a solution, which consists on the synchronisation of PWM triangular carrier is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.