Stochastic analysis of solar and wind hybrid rooftop generation systems and their impact on voltage behavior in low voltage distribution systems

Abstract

In recent years, with the expansion of residential distributed generation systems, advanced measurement infrastructures and distribution management systems, hybrid photovoltaic (PV) and wind turbine (WT) rooftop generation systems (hybrid systems) are flourishing. Since the output power of these systems highly depends on weather conditions that can change during a day, their increased level of penetration may have significant effects on residential low voltage distribution networks (residential networks).The objective of this paper is to study the effects of different penetration levels of these hybrid systems on daily voltage profile, voltage fluctuation and voltage imbalance of balanced and unbalanced residential networks during different seasons of a year. In order to model uncertainties of daily active and reactive power consumption by residential homes and also daily PV and WT system output power during different seasons with 1-min resolution, our study used the ARIMA simulator in the MATLAB R2013b software environment. The evaluations in this paper are focused on voltage behavior in a standard balanced and unbalanced three-phase four-wire low voltage residential network with the results providing valuable information and data for universities and industry working to advance the fast growth of these hybrid systems. Some key findings are as follows: (1) The increased penetration level of the hybrid system leads to decreased voltage violation of the acceptable limit. (2) Tap-changer operation prevents more voltage drop, and the system voltage drop exceeds acceptable limits for a few minutes. (3) In unbalanced conditions, the LV distribution transformer must be equipped with an automatic tap-changer. (4) Unique seasonal distribution functions of active and reactive power, solar and wind system power have been developed using 1-min system performance modeling.