Novel Three-Phase PLL with Per Phase Grid Angle Tracking Capability for Shunt-Connected Solar Microinverter

A shunt-connected solar microinverter can effectively mitigate the high starting current of induction motors and seamlessly redirect the energy source back to the power grid with grid synchronization. However, external disturbances in the power grid can influence the motor starting operation, and it becomes a predominant issue for grid-connected systems to act independently of these scenarios. The frequent grid faults, voltage sags, and swells can negatively affect the durability of the motor. This paper proposes a novel three-phase phase-locked loop (PLL) that can track the grid angle of each phase independently in faulty grid conditions. The existing DQ-PLL is modified with the proposed PLL structure for the microinverter application. This can help the line-connected IM system tackle the unbalanced grid scenario and run the induction motor efficiently with minimal impact from the grid faults.