IEEE Power & Energy Magazine - March/April 2020 - 63

for future hardware-in-the-loop capability. However, test
systems and scenarios are typically stored in files and
may be specific to simulators. In the LTB, reduced-order
system models for the North American grid and various
scenarios, i.e., future high-renewable cases and a multiterminal HVdc overlay network, have been developed
and are shown in Figure 2.

Substation Simulators
This module simulates the sensors and automation
devices that reside in substations. This category acts as
the intermediate component between the simulated physical system and data-driven applications and is composed
of networked physical devices, including phasor measurement units (PMUs), remote telemetry units (RTUs), and
control automation devices. The PMU and RTU modules
receive raw simulation data from the simulator and output simulated measurement data with noise, errors, and
losses, which may be sampled from probability distributions. In the other direction, automation devices receive
control set points from the energy management system
(EMS) and control system and modify the model parameters in the simulator.

Energy Management System
This type of module integrates the control-room functions
for optimizing the grid energy dispatch. More broadly,
it may also include system control and data acquisition
(SCADA) system functions for monitoring and control.
Modules in the EMS/SCADA system include monitoring

AC Transmission
Line

functions (i.e., state estimation and visualization), scheduling functions (i.e., economic dispatch), and security
functions (i.e., contingency screening). EMS functions
receive data from the downstream substation simulators
and output results to control systems, automation devices,
or operators. The platform integrates standard routines
available in open-source packages as well as advanced
EMS functions, such as the two-stage state estimator (see
Rouhani et al. in the "For Further Reading" section). The
time resolutions for EMS functions range from seconds
to hours.

Control System
This category is a collection of advanced yet experimental
control algorithms that researchers want to test and verify,
based on models and/or measurement data. Different from
the conventional local feedback controls modeled in the simulator, the control system aims at leveraging time-stamped
high-resolution measurement and estimation data for widearea control. Control modules receive data directly from
data concentrators or EMS functions and output control signals to automated devices, which eventually act on the grid.
The time resolutions for control modules vary from seconds
to minutes.

Distributed Messaging Server and Clients
This includes a set of routines and application program interfaces (APIs) for distributed messaging between modules.
Between any two communicating modules, the one providing
input data to the other is called the upstream module, while

VSC-Based HVdc
Stations

Wind Farm
AC Load Bus

Synchronous
Generator

HVdc Line

figure 2. A future scenario of part of the reduced-order North American system with the continental HVdc overlay. Note
that not all ac transmission lines are visualized at the zoom level. VCS: voltage source converter.
march/april 2020

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IEEE Power & Energy Magazine - March/April 2020

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2020