IEEE Power & Energy Magazine - March/April 2020 - 74

A set of rules developed from an off-line economic
evaluation by co-optimizing multiple use cases
could be used as a reasonable starting point.
rules developed from an off-line economic evaluation by cooptimizing multiple use cases could be used as a reasonable
starting point.
This project used a similar approach where the initial set
of rules was developed using the findings of economic evaluation. For instance, assigning priority to each use case is one
of the many options used for the coordination of multiple use
cases; the relative economic benefit of SSPC use cases was
used as a basis for the prioritization of multiple use cases for
value-based control. An optimal dispatch profile of the SSPC
ESS obtained from the economic evaluation provided useful
information on 1) the typical time and length of operation
of various use cases for maximizing benefits, 2) the change
in SoC during those time periods, and 3) the conditions that

cause use cases to switch from one to another. This information provided valuable insight while designing a rule-based
charge/discharge strategy.
Figure 5 is a conceptual diagram of the multiple use-case
coordination strategy implemented at SSPC. By default,
the controller operates within a main coordination loop
that maintains the SoC for the highest priority use case,
enables scheduled services, and makes transitions to a usecase control function with fulfillment of the conditions of
entry. Although operating within a use-case control loop,
the controller performs scheduled charge/discharge operations while monitoring for conditions to exit the loop (e.g.,
the schedule finished, the SoC limit violated, or a change of
priority ranking).

Implementation

try

]

[C E

UC1

]

[C E

* Maintain SoC for Top
Priority Service
* Enable Scheduled Services
* Check for Active Services
Main
Coordination
Loop
* Check for Priority Ranking
* Monitor SoC and Make
Transition to Main Loop
* Perform Scheduled
UCn
Charge/Discharge
UC2

figure 5. A rule-based coordination of multiple use cases. UC: use case; C ENT: conditions of entry; CEXT: conditions of exit.

SSPC Site
EMS
EMS
* Regulation MW Set Point
* Contingency Reserve
MW Set Point
* Arbitrage MW Set Point

* Availability
* SoC
* MW
* Mvar
* kV
Use Case
* Enabled, Ready, and Active
* Current Day Start, End, and Priority
* Next Day Start, End, and Priority

figure 6. The shared data point between EMS and SSPC ESSs.
74

ieee power & energy magazine

PGE has deployed a PLC-based
control system at SSPC, and control capability was expanded by
adding new routines to the existing PLC programs. Strategies
developed for the coordination of
multiple use cases and the control
of individual use cases were first
represented using flowcharts for
discussion, understanding, and
refinement and were subsequently
coded into the PLC.
Three status variables are used
for each use case: enabled, ready,
and active. A priority setting option
is developed for setting the priority
of each use case. For manual entry
mode, day-ahead schedules are
entered using hourly values for the
next 24 h.
Data points used to facilitate
communication between the utility's EMS and SSPC's ESS are
presented in Figure 6. For the
overall site, the availability, SoC,
MW and MVar outputs, and voltage are communicated to the
EMS. The status and schedu l ing variables are communicated fo r e a ch s e r v ic e. For
regulation, energy arbitrage, and
march/april 2020

IEEE Power & Energy Magazine - March/April 2020

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