Transient Stability of Vdc - Q Control-Based PV Generator With Voltage Support Connected to Grid Modelled as Synchronous Machine

The increasing penetration of PhotoVoltaic (PV) generation has a significant impact on the transient stability of power systems. Power electronics interface, control strategies and lack of inherent rotational element are the main factors that distinguish PV generation from conventional synchronous machine-based generation. In addition, the time constants of the PV control loops and Phase Locked Loop (PLL) are of the same order unlike the synchronous generators. The conventional equal area criterion based stability analysis is not applicable for PV generators with DC-link voltage and reactive power control. The transient stability analysis of power system with PV generation is not well explored in the literature. This paper proposes a criterion to assess the transient stability of a grid connected VSC-based PV generator with DC-link voltage and reactive power control. The PV generator is equipped with Low Voltage Ride Through (LVRT) capability, voltage and frequency support functionalities. The grid is modelled as a Synchronous Machine (SM) with finite inertia. The transient stability is assessed considering the dc link capacitor, outer and inner PV controls, PLL and grid dynamics. The proposed criterion is derived using two nonlinear functions and the Voltage Support (VS) signal of PV generator. The proposed criterion is applicable to all types of short-circuit faults with/without fault resistance. The criterion is validated through time-domain simulations. The Critical Clearing Time (CCT) calculated using the proposed criterion matches with the CCT obtained from time-domain simulations.