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Modeling and simulation Chapter | 5 127

5.3.1 The OpenDSS
The software came in 1997 still under the name of DSS—Distribution
System Simulator. In 2004 the DSS was acquired by EPRI solutions, and in
2008, it is released with open-source license, named OpenDSS [14].
The OpenDSS software is a power flow simulation algorithm that per-
forms the most varied analyses related to the planning of the electric distri-
bution system and the quality of the energy. Also, the software performs
analyses to meet the demands of future electric grids with DG. Quasi-static
solution modes allow the execution of sequential simulations over time, and
thus system analysis can be performed at any time of the day [15]. The main
modes of software simulation are
instantaneous power flow (snapshot),
daily power flow (daily mode),
annual power flow (yearly mode),
harmonic analysis,
dynamic analysis,
fault study, and
Monte Carlo fault study.
After being released in 2008 as open-source software, OpenDSS has
become widely used around the world. One of the features that make it popu-
lar is the offered package of interfaces for simulation. The program was
launched with a Component Object Model (COM) interface, and recently,
the “Direct DLL” interface was released so that users could access program
features on platforms incompatible with the COM interface [16].
The COM interface can be controlled by software such as Python,
MATLAB, and MS Office tools, with an emphasis on Visual Basic for
Applications. OpenDSS has recently come up with a version to run parallel
computing on modern multicore computers. This version is called OpenDSS-
PM (parallel machine) and is also freely available [16,17].

5.3.2 Power flow in OpenDSS: the current injection method
OpenDSS has been using two power flow algorithms. The standard method,
described as Normal method or current injection method, and the Newton
method, which should not be confused with the Newton Raphson method
[14]. The current injection method is an iterative method based on the theo-
rems of The ´venin and Norton and the concept of the nodal admittance
matrix.
Admittance matrix (Y) is assembled through the primitive nodal admit-
tance matrix method. Such matrix represents the admittance matrix of a sin-
gle element, and the various primitive matrices are specifically allocated in