IEEE Power & Energy Magazine - July/August 2017 - 44

critical and noncritical loads, DERs, and other conventional
power sources. This platform is being extended to include
power hardware, including a PV inverter, battery-based storage, and an electric vehicle, at the National Renewable Energy
Laboratory (NREL) with support from the DOE's National
Laboratory Impact Initiative under the Microgrid Controller
Innovation Challenge. However, this approach does not provide insight into how a microgrid controller will perform for
the specific microgrid being designed.
Therefore, the third goal of the evaluation is that of sitespecific performance assessment and compliance. This goal
addresses the question of whether a specific microgrid controller is capable of managing a unique portfolio of microgrid assets
to meet utility interconnection and customer requirements.
All three goals of laboratory evaluations described herein
require testing in the context of an overall microgrid system. The microgrid controller will need to be customized for

the specific laboratory setup that will be used to model the
actual microgrid. Therefore, close cooperation between the
laboratory staff performing the evaluation and the microgrid
controller provider is required for successful evaluation.

Site-Specific Microgrid
Controller Evaluation

Several options are available for evaluating a site-specific
microgrid controller in a laboratory setting, as illustrated in Figure 2. The first approach [Figure 2(a)] shows pure simulation,
where all components are represented in simulation. While such
an approach may be used by microgrid controller developers in
the early stages of product development, the challenge here is
that the microgrid controller needs to be recreated with the simulation software used by the laboratory performing the evaluation. Therefore, a more popular option is controller-HIL (CHIL)
simulation, where the microgrid controller hardware is interfaced with a simulated microgrid
and assets [see Figure 2(b)]. A transient simulation, with a time step
Simulation
Simulation
in the range from tens to hundreds
of microseconds, is able to be performed using either a commercial
Electric Power
Electric Power
real-time simulator-available from
System
System
vendors such as Opal-RT, RealTime Digital Power System Simulation (RTDS), Typhoon, or SpeedDER
Generator
DER
Generator
goat-or a custom-built real-time
simulator. It is sometimes necessary
to simplify the electric power system
model with respect to the microgrid,
based on the capability or capacity
Microgrid Controller
of the real-time simulator. However,
Microgrid Controller
if properly developed, the reduced(a)
(b)
order model characteristics (e.g.,
short circuits or voltages) and perSimulation
formance will be similar to that of
the full model. A CHIL simulation
setup requires significant effort to
Electric Power
implement, especially regarding the
System
communication interface between
the microgrid controller hardware
and the simulation platform.
Adding a power-HIL (PHIL)
DER
Generator
simulation
to the CHIL simulation,
DER
Generator
as shown in Figure 2(c), allows for
the use of actual hardware, either
the exact model planned for the
microgrid site or a representative
model with similar characteristics.
Microgrid Controller
Microgrid Controller
Utilizing real hardware components
(c)
(d)
reduces modeling inaccuracies, espefigure 2. Options for laboratory evaluations of microgrid controller compliance with cially because proprietary controls of
various vendors embedded within the
site-specific requirements: (a) pure simulation, (b) CHIL, (c) CHIL and PHIL, and (d)
power hardware, such as PV inverters,
hardware only.

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july/august 2017

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