  This paper presents some recent trends in the research of grid-interactive
inverters. Particularly, this paper focuses on stability, ancillary services,
operation, and security of single and multiple inverters in the modern power
grid. A grid-interactive inverter performs as a controllable interface between
the distributed energy sources and the power grid. High-penetration of
inverters in a power distribution system can create some technical challenges
on the power quality, as well as voltage and frequency control of the system.
In particular, a weak grid can lead to voltage oscillation and consequently
instability. Moreover, the power grid is moving toward becoming a
cyber-physical system in which smart inverters can exchange information for
power marketing and economic dispatching. This puts the inverters at the risk
of insecure operations. Hence, security enhancement has become another primary
concern. Finally, the grid-interactive inverters are operated proportional
power-sharing while operating together with many inverters. Recent research on
coordinated operations is also discussed in this paper.
