Page 162 - Decision Making Applications in Modern Power Systems

126 Decision Making Applications in Modern Power Systems

Regarding purpose or functionalities, smart inverters can be divided into
five categories as follows:

Monitoring and scheduling: functions that allow the operator to adjust
and collect information from the inverter, including the connect and dis-
connect function.
Frequency support: functions that provide frequency support for the grid,
such as the Frequency/Watt function.
Real-power support: functions that provide support for active power to
the grid, such as dynamic real-power support.
Power factor support: functions that act by adjusting the reactive power,
such as the fixed PF function.
Voltage support: functions that support the voltage to the grid, such as
the dynamic Volt/Watt function.

5.2.3 Final considerations
Changes in the distribution system require more detailed engineering about
the impacts that may arise; insertion of generation into distribution changes
the concept of the unidirectional power flow and exposes customers and dis-
tributors to new challenges. Understanding and dealing with new problems
will be critical to the future of distribution systems.

5.3 Modeling and simulation using OpenDSS
The changes in the distribution grid with the insertion of DG systems bring
several technical challenges as presented in the previous topic. Also, the
modeling of these new systems has become more complex, requiring sophis-
ticated analyses and reliable algorithms for a true description of grid
behavior.
According to [13], the distribution system analysis programs have
evolved from simple voltage drop calculators of balanced loads to sophisti-
cated systems with graphical interactions that allow one to know and quan-
tify grid parameters. The best known methods, such as Gauss Seidel and
Newton Raphson, may not show convergence in many distribution system
analyses due to high R=X ratio and the radial structure of distribution grids.
In addition, as the distribution grid has a strong tendency to be unbalanced
among phases, such methods are not advised to work with positive sequence
models only.
Thus this topic is intended to analyze the three-phase current injection
method, based on the decomposition of the nodal admittance matrix that
composes the OpenDSS software. A brief historical presentation of the soft-
ware, PV systems, storage, and load models of an active distribution grid is
presented.