Critical Clearing Time Calculation using Energy Functions for VSC based Grid Connected PV Generators with PQ Control

The present study proposes a method to calculate Critical Clearing Time (CCT) for Photovoltaic (PV) Generators using energy functions. The Voltage Source Converter (VSC) based grid connected two stage PV generator with Active and Reactive power (PQ) control is considered for the study. The proposed method is developed based on the fault trajectory of the system during the most severe fault on the system. Two energy functions are identified based on the feedback control strategy of PV generator. One energy function corresponds to the P control loop and the other energy function corresponds to the Q control loop. A criterion is proposed using the energy functions to determine the stability of system after fault clearance. The proposed method for CCT calculation is validated using time-domain simulations. The impact of control parameters and DC link capacitance on CCT is also investigated. The proposed method of CCT calculation requires lesser computations than calculating CCT through time-domain simulations.