Multifunctional control of single-phase transformerless PV inverter connected to a distribution network

Recently transformerless grid-tied photovoltaic (PV) inverters are getting popular in order to address several concerns; for example, poor efficiency, large size, and heavy weight compared to those with traditional inverter topologies. However, according to the several recently updated grid codes, the grid-tied PV inverter are required to provide full range of services such as maximum power injection, grid voltage regulation (VR), and fault ride through (FRT). In this paper, the performance of a transformerless PV system with a new droop based controller connected to the low voltage distribution system under different operating condition is investigated. In order to provide full-range of grid supporting services, three operation modes are proposed. A detail description of the transformerless PV inverter, droop based controller, and the control strategy are provided. The theoretical analysis is verified using nonlinear simulations in MATLAB/Simulink software environment. The results show that the presented system is capable of injecting maximum power when participate in the grid voltage regulation, and also can enhance fault ride through capability.