Active/reactive power control of PV grid-tied NPC inverter using 3-D space vector modulation in abc coordinate

Flexible active and reactive power injection to the grid is one of the requirements of medium-scale PV power plants (PVPP). Due to the high penetration of installed distributed generation (DG) units to the power system, the flexible active/reactive power control capability is necessary for medium-scale PVPPs in order to maintain the power quality and reliability of the power system. A three-dimensional space vector modulation (3-D SVM) in abc coordinate with combination of proportional-resonant (PR) controller is proposed for 4-wire NPC grid-connected inverter of the multi-string PVPP. The implementation of 3-D SVM in stationary coordinate (αβ coordinate) for 4-wire multilevel inverters requires high computational complexity. However, in the proposed 3-D SVM which is implemented in abc coordinate, the computational complexity is decreased and flexible balanced/unbalanced active/reactive power injection capability is achieved. The performance of the proposed controller is investigated on the three-level neutral-point-clamped (NPC) inverter of a 10 kW grid-connected multi-string PVPP, which is considered as the state of the art for medium-scale PVPPs. Various operation conditions like partial shading of PV strings and balanced/unbalanced grid faults are implemented.