I. Overview of MAFRIT
The Multi-Area Frequency Response Integration Tool (MAFRIT) is primarily designed to enable research
on high to very high variable renewable energy (VRE) integration. Being an open source tool, researchers
in the broader power systems community can use, modify, and expand it to explore the impacts of very
high variable renewable energy integration on the reliability of power systems. MAFRIT has been
developed at NREL primarily to fill the gap between production cost simulation or scheduling tools and
traditional electromechanical transient simulation tools. Production cost simulation tools typically do not
consider ac power flow or dynamics of power systems that are needed to model power system frequency
response. Similarly, electromechanical dynamics simulations tools are not typically designed to simulate
long-term dynamics that are essential to capturing the AGC-timeframe dynamics that have a significant
impact on frequency response performance of power systems. The capability offered by MAFRIT to bridge
the gap between these two categories of tools has and will become increasingly important as VRE
integration increases in the grid and concerns arise regarding the impacts of reduced system inertia and
variability and uncertainty of power outputs of VREs on frequency response of power systems. Figure 1
shows how MAFRIT fills the gap between the two categories of tools.
Figure 1 – MAFRIT integrates Scheduling & Dynamics Simulations
Figure 2 shows the conceptual diagram of MAFRIT. As shown in the figure, MAFRIT has two distinct
modules. The first is the dynamic simulation module that simulates the electromechanical transients of
power systems by solving a set of differential algebraic equations (DAEs). The DAEs are solved using
sequential-implicit approach meaning that algebraic and differential equations are solved sequentially
with implicit integration methods used for solving the differential equations. Figure 3 shows the data flow
