Modelling, Control and Stability Analysis of Photovoltaic Systems in Power System Dynamic Studies

This thesis investigates the impact of: i) the low voltage ride-through and dynamic voltage support capability; ii) the active current recovery rate; iii) the local voltage control; and iv) the plant-level voltage control of large-scale photovoltaic systems on short-term voltage stability and fault-induced delayed voltage recovery as well as transient and frequency stability. The power system dynamic performance is analysed using state-of-the-art methods, such as phasor mode time-domain simulations and the calculation of the critical clearing time that determines the stability margin. Moreover, the recently developed Kullback-Leibler divergence measure is applied to assess the quality of the voltage recovery. Drawbacks of this metric are outlined and a novel metric, the so-called voltage recovery index, is defined that quantifies the delayed voltage recovery more systematically. The studies are performed with a generic photovoltaic system model and typical model parameters are used that were determined in collaboration with a manufacturer. The stability analysis is performed in DIgSILENT PowerFactory using: i) a one-load infinite-bus system; and ii) an IEEE multi-machine voltage stability test system, namely the Nordic test system. The results show that with the adequate control of photovoltaic systems, power system dynamic performance can be significantly improved.