Improved Low Voltage Ride-through Capability of PV Connected to the Unbalanced Main Grid

Because of the commitment between the large-scale photovoltaic power plants and the main grid to cope with different low voltage conditions in the grid, Low Voltage Ride Through (LVRT) capability of such plants is necessary. Handling this situation is more challenging when the main grid is under unbalanced conditions.  In this paper, a new LVRT approach is proposed to reduce oscillations in this situation. To this end, the simultaneous positive, negative, and zero sequences control (PNZSC) method is proposed to provide a suitable reference current for eliminating oscillations of the active power, and similarly to reduce voltage oscillations of the DC side. The zero sequence control is achieved through proper inverter switching.Also, this method limits the inverter output current to the maximum rated value. A Dual Second Order Generalized Integrator - Frequency Locked Loop (DSOGI-FLL) is used for better synchronizing of the inverter to the grid, in asymmetric faults. Besides, an interleaved DC-DC converter and a Neutral Point Clamped (NPC) Inverter are used to reduce Total Harmonic Distortion (THD) and losses. The performance of the proposed approach is confirmed using simulation of different possible scenarios in MATLAB/Simulink environment.