IEEE Power & Energy Magazine - July/August 2017 - 76

mine the improvement goals and the general strategy
for responding to each stakeholder need.
✔ Tabulate prioritized stakeholder requirements: A priority is developed given parameters such as an importance rating and a target value for each requirement.
✔ Tabulate prioritized technical solutions: Representing the output results from the entire evaluation, it is
utilized to derive the priorities assigned to technical
solutions by other components in the matrix. It also
measures technical performance achieved by competing solution providers. Last, it captures the degree of
difficulty involved in developing each solution.

Interrelationship
Between
HOWs and HOWs

Relationship Between
WHATs and HOWs

Prioritized
Stakeholder
Requirements

Stakeholder
Requirements
(WHATs)

Technical Solutions
(HOWs)

Architectural Design

Prioritized Technical
Solutions

figure 4. The house of quality for prioritizing technical solutions.

✔ List technical solutions: This is a list of how the re-

quirement will be met or exceeded by a process or a
technical solution.
✔ Develop a relationship matrix between whats and hows:
Using symbols or figures, assign a scale to represent the
relationship strength between these two (i.e., strong,
medium, or weak).
✔ Develop the interrelationship matrix between hows: To
identify where proposed solutions support or impede
each other. Assign interrelationship strengths among
all proposed solutions to create a correlation matrix between the hows versus hows (i.e., strong positive, positive, negative, and strong negative).
✔ Competitive assessment-In this quadrant, develop a
competitive evaluation of how the stakeholder requirements are met by competing project solutions (i.e.,
alternative microgrid developers). It will serve to deter-

With the reassurance that technical requirements have carefully been vetted and organized, the team begins the architectural design. There are two main layers to be designed:
✔ energy infrastructure layer
✔ communications and control layer.
Primary power components such as power transformers,
breakers, capacitor banks, inductor banks, feeders, distribution transformers, and reclosers are part of the energy
infrastructure layer. Closely coupled, a communications and
control layer is made up of primary, secondary, and tertiary
control layers.

Microgrid Control
Once integrated as a system, how does a microgrid platform
yield expected levels of safety and performance? Given
the technical solutions derived from the stakeholder requirement analysis process, we propose to use a hierarchy of
control layers well known in more traditional energy market
segments (i.e., central generation). This framework comprises three main layers of control: primary, secondary, and
tertiary. Each control layer is implemented to support different functions in the microgrid and can vary in its needs for
communication and speed. Table 2 lists the typical functions
and control components associated with each control layer.

table 2. Microgrid control hierarchy.

Control Level

Temporal
Requirement

Tertiary

Typical Functions

Control Components

Minutes

* Load forecasting
* Optimization for
dispatch
* Modeling

* Software

Secondary

Seconds

* SCADA
* Load control

* Premise microgrid controller
* Building automation system

Primary

Micro- to
milliseconds

* Energy storage inverter
* Switching logic
controller
* Protection
* Local DER control * Premise protection relays
* Inverter controller
* Generator governor

ieee power & energy magazine

Primary Control
This layer is conceptualized as
local control or internal control.
A main objective of primary control is to achieve equal power
sharing by balancing the generation among the microgrid DER
sources. In this layer, control of the
output voltage and phase angle at
each DER source is performed.
Droop control is the most common primary control method
adopted in microgrids due to its
fast response, reliance on local
measurement, and independence
of the use of communications
july/august 2017

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2017