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

Abstract

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 VSCbased 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.

Online Assessment of Transient Stability of Grid Connected PV Generator With DC Link Voltage and Reactive Power Control

“…In the existing literature, there are works reported on transient stability assessment criterion for grid connected VSCs equipped with power synchronization control and droop control [3], [4], [6], [8], [12], [13]. However, transient stability assessment of V dc and Q control based PV generation is reported only in [14]. The transient stability criterion presented in [14] is chosen for comparison because the methods presented in [3], [4], [6], [8], [12], [13] are not applicable for V dc and Q control based PV generator.…”

“…The virtual power angle of VSC is investigated in [13] to carry out the transient stability analysis of droop control based VSC. The transient stability of grid connected PV generator with dc link control is analyzed in [14] by investigating the PV control loops. The stability analysis of IIDGs with induction machine loads is presented in [15] through eigen-value analysis.…”

“…However, there is limited literature on transient stability analysis of dc link voltage (V dc ) and reactive power (Q) control based PV. • The transient stability analysis of V dc and Q control based PV is presented in [14]. Literature [14] requires computation of the area under the two nonlinear functions to assess the PV generator stability.…”

“…• The transient stability analysis of V dc and Q control based PV is presented in [14]. Literature [14] requires computation of the area under the two nonlinear functions to assess the PV generator stability. Even though the transient stability assessment method presented in [14] gives a comprehensive insight on ac side dynamics, this approach is computationally heavy and will be difficult to implement online.…”

“…Analyzing transient stability of PV based on dc side dynamics is not explored in the existing literature. • The stability criterion proposed in this paper can assess the transient stability of grid connected PV from dc link voltage dynamics alone unlike [5], [7], [14] which require dynamics of multiple ac side quantities. So, the proposed criterion has computational advantage over the methods proposed in [5], [7], [14].…”