Analysis and Control of a Photovoltaic System: Application to a High-Penetration Case Study

This paper explores a two-stage, multistring photovoltaic system connected by a common dc bus to a centralized inverter, interfaced with a utility grid. The centralized inverter is controlled via a decoupled current control method and interfaced to the utility grid through a distribution transformer. Inverter control is completely independent of maximum power point control of the boost converter, used to step up the photovoltaic (PV) array voltage. Modeling and stability analysis of the photovoltaic system interfaced with the IEEE 14 bus grid system via a double circuit transmission line are presented. A control strategy is developed to overcome instability problems associated with the series compensated transmission connecting the photovoltaic system to the grid. Studies are also conducted that explore the transient response of the photovoltaic system following a three-phase and single-line to ground fault on the transmission line. Additionally, participation factor analysis is applied to a small signal model of the entire system to identify the parameters that have the most influence on the system stability. The developed models and analysis are validated through detailed simulation studies. The results obtained from this paper reveal the importance of conducting system level analysis when characterizing grid-connected PV systems.