Operation and control of single phase micro-sources in a utility connected grid

Abstract

This paper proposes operation and control of converter based single phase distributed generators (DG) in a utility connected grid. A common utility practice is to distribute the household single-phase loads evenly between the three phases. The voltage unbalance between the phases remains within a reasonable limit. However the voltage unbalance can be severe if single-phase rooftop mounted PVs are distributed randomly between the households. Moreover, there can also be single-phase nonlinear loads present in the system. The cumulative effect of all these will cause power quality problem at the utility side. The problem can be macabre if three-phase active loads (e.g., induction motors) are connected to the utility feeder. To counteract this problem, we have proposed two different schemes. In this first scheme a distribution static compensator (DSTATCOM) is connected at the utility bus to improve the power quality. The DSTATCOM only supplies reactive power and no real power. In the second scheme, a larger three-phase converter controlled DG is placed that not only supplies the reactive power but also provides active power. The efficacies of the controllers have been validated through simulation for various operating conditions using PSCAD.