Microgrid Economic
Dispatch Engine
TM
Automate generation dispatch to
maximize microgrid benefits
• Integrate renewable energy sources with traditional generation
sources.
• Optimize distributed energy resource (DER) dispatch to improve
your return on investment (ROI), extend the operational duration,
and meet control objectives.
• Incorporate security and hardened reliability for control of
microgrids with critical loads.
• Account for maintenance factors associated with the minimum
runtime, number of starts, number of cycles, and efficiency curves.
• Add dynamic or static system inputs, such as energy and fuel
prices, the weather, and the desired operation mode.
Overview
The SEL Microgrid Economic Dispatch Engine unlocks the ability for microgrid
owners and operators to control microgrids from an economic viewpoint.
Cost factor data from DERs and energy storage systems is integrated into the
dispatch engine to reduce the total operation cost, improve ROI, and meet
control objectives.
The dispatch engine is built into the SEL Real-Time Automation Controller
(RTAC), which is a secure, reliable, high-performance platform. The RTAC
includes intuitive software to simplify integration with SEL relays for monitoring
and control of inverter interfaces, generators, governors, breakers, and more.
The dispatch engine forecasts the microgrid load profile and determines the
optimal generation dispatch, accounting for operational constraints, such as
fuel costs, the weather, the state of charge mode, and energy import/export
costs. You can link the engine dispatch schedule directly to DER set points or
a powerMAX® automatic generation control (AGC) system, or you can visually
present the schedule to operators for manual control.
In permanently islanded or grid-connected microgrids, the dispatch engine
accounts for multivariable cost functions, integrates large numbers of
generation assets, incorporates intelligent battery charging strategies, and
constantly updates forecasts based on real-time data. The engine provides
individually optimized dispatch for solar, wind, battery, and traditional
generation assets to account for the variance of availability and costs.
The RTAC platform offers scalable solutions for microgrids of all sizes.
Architecture
A typical SEL Microgrid Economic Dispatch Engine system involves an RTAC
with the dispatch engine as the centralized generation dispatch optimizer that
interfaces with SEL relays that protect and control a microgrid. Using load
measurements from relays at the point of common coupling (PCC), DER, and
feeders saves costs by eliminating unnecessary hardware. A communications
network provides reliable monitoring and control of the microgrid. The
geographic limitations and critical nature of the microgrid impact which
network design is optimal. Industrial and military users might find that fiberoptic Ethernet cable provides the best performance, security, and reliability,
whereas remote microgrid operators might find secure wireless networking to
be most economical.
Each DER is monitored and controlled by an SEL relay with a large touchscreen
for local control and monitoring. The SEL relay provides the necessary
protection for each generator or energy storage unit and allows the
optimization RTAC to retrieve metering information and send commands for
economic optimization.
The system architecture is scalable for any size of microgrid. SEL offers several
RTAC platform options that support the dispatch engine. Operators of large,
mission-critical microgrids that require precise, reliable power quality for
critical loads that cannot black out should consider adding the dispatch engine
to SEL’s powerMAX solution.
SEL Microgrid Economic
Dispatch Engine RTAC
SEL-3555
DNP3
Protection
Governor and
Exciter Dispatch
PCC
H/W
SEL-751
Reconnection
Inverter Dispatch
Load Shedding
Load Sharing
Short- and OpenCircuit Protection
Voltage and
Frequency
Regulation
IEEE Compliance
Power and Power
Factor (PF) Control
SEL-751
SEL-751
SEL-751
IEC 61850
GOOSE
Add economic optimization with the dispatch engine to
microgrids controlled by SEL protective relays.
Features
350
Cost factors are microgrid operation considerations
that influence the engine optimization. To calculate
the optimal unit commitment, the dispatch engine
must know the price per unit of energy for each gridconnected DER and utility. The optimization process
also considers the mechanical and maintenance costs
associated with operation.
300
250
200
Generator 1
150
100
Generator 2
50
0
0
• Fuel price
800
• Battery state of charge strategy
Natural Gas Usage (Nm3/hour)
900
• Generator operation region constraints
4,000
5,000
Diesel generator fuel consumption.
• Energy price
• Generator efficiency curves
3,000
Generator Active Power (kW)
The dispatch engine RTAC accepts cost factor
setting updates via manual entry or real-time data
links to information like market pricing for energy.
Optimization impact variables include the following:
• Generator transition cost
2,000
1,000
7
6
700
5
600
Natural Gas Consumption
500
4
Heat Contribution
400
3
300
2
200
1
100
0
0
0
500
1,000
1,500
2,000
2,500
3,000
3,500
Generator Active Power (kW)
Combined heat and power (CHP) natural gas
consumption and heat contribution curves.
4,000
Heat Contribution (MBTU/Ibm)
Cost Factor Management
400
Diesel Usage (gal/hour)
The SEL Microgrid Economic Dispatch Engine features
support both grid-connected and permanently islanded
microgrids. DERs are often operated in different
modes, such as isochronous (ISO), droop, and constant
power, to achieve operational goals. The dispatch
engine accounts for the various modes of operation
and cost factors of each DER and then determines the
most economical dispatch.
Diesel 1
–1,000
Diesel 3
–1,500
CHP 2
–2,000
–2,500
–3,000
–3,500
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
90
95
100
Time (minutes)
Optimized fuel consumption.
70
Islanded
Islanded
60
Energy Storage System (ESS) State of Charge (SOC)
Cost ($)
–500
ESS 2
ESS 1
50
40
SOC Resiliency Limit
SOC Resiliency Limit
30
20
10
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
Time (minutes)
Battery state of charge control when islanded and grid-connected with resiliency limits.
Load and Generation Forecasting
Each microgrid has a unique load profile that changes throughout the day,
seasons, and over time. The dispatch engine creates a demand load profile. Using
system measurements, the dispatch engine updates the forecast as conditions
change. If there is a significant offset between forecasted and actual demand,
the optimization engine reevaluates the dispatch solution to determine if
improvements are possible.
Forecasts are also helpful for generation scheduling. If the dispatch engine has
access to weather, solar, and wind data, it can provide a more accurate forecast.
By analyzing the load profile demand requirements for the entire day, the
generation scheduling can account for the required number of unit starts and
stops as well as for keeping generation units near the most efficient operating
point. Storage units, such as lithium-ion and redox flow batteries, allow the
dispatch engine to calculate the most cost-beneficial periods to charge and
discharge. The engine takes into account discharge and charge rates as well
as maintenance costs associated with the number of cycles operated.
Forecast
90
Load
80
PU %
70
60
50
Wind
Profile
40
30
Solar
Irradiance
20
10
0
12
Time of Day
Use the dynamic load and generation forecasting
to optimize source loading.
Dispatch Scheduling
Dispatch scheduling, often referred to as unit commitment, is the process of
determining the optimal set points for DERs across a forecast time period. The
dispatch engine uses the historical load, solar, and wind profiles to determine
which units can supply the required load or generate the maximum revenue
during each optimization interval. Optimization intervals (typically 10–60
minutes) define how often the engine updates generation set points throughout
the day.
With integrated renewable energy resources, the dispatch engine accounts for
the variability of generation by keeping enough traditional generation resources
running to support critical loads or by keeping the microgrid grid-connected.
The dispatch engine considers devices in maintenance mode to be out of
service and will use other resources to optimize the cost of operation. If utility
interconnection agreements limit or penalize import and export violations, the
engine will schedule DER dispatch set points to avoid penalties.
14,000
12,000
10,000
Import Limit
6,000
4,000
2,000
0
–2,000
–4,000
Export Limit
–6,000
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
Time (minutes)
Import and export control for utility interconnection agreement compliance.
There is no import/export value during islanded operation.
Utility
Power Dispatch
kW
8,000
Battery Energy
Storage System
CHP
Solar
14
Time of Day
Generation dispatch for lowest cost of operation
based on load forecast and renewable availability.
100
Microgrid Visualization
The dispatch engine can collect data from a variety of sources thanks
to the RTAC’s extensive protocol support, which provides flexibility for
system design and visualization. The RTAC gathers real-time information
from sources where available, and the system operator can assign
visibility of other parameters.
SEL microgrid solutions include an HMI for monitoring, control, and
diagnostics. With the dispatch engine, the HMI can show the cost of
operation for detailed historical analysis of estimated savings and offers
visibility of the future cost impact associated with adding new assets or
taking assets out of service for maintenance.
Applications
Potential dispatch engine applications for both grid-connected and
permanently-islanded microgrids include the following:
• Remote Communities—Reduce the dependency on fossil fuels through
the integration of renewable energy resources.
• Industrial Facilities—Optimize generation efficiency while maintaining
resiliency for critical loads.
• Commercial Buildings—Reduce the cost of ownership through
economic dispatch and demand reduction.
• Military Bases—Reliably and securely enhance the resiliency of
mission-critical facilities by eliminating dependency on utility sources
and reducing fuel consumption.
• School Campuses—Easily incorporate DERs across large campuses by
using secure wireless communications to coordinate resource dispatch
for demand reduction and disaster resiliency.
Combining the Dispatch Engine
With powerMAX
You can combine the SEL Microgrid Economic Dispatch Engine with powerMAX
AGC, which provides mission-critical power quality control for microgrids with a
dynamic topology of parallel generators. This combination offers precise, highspeed control of generators and the contingency event response. The dispatch
engine can automatically trigger a recalculation of the scheduled generation
dispatch if significant system events occur. Unplanned islanding, internal faults,
and large energy price changes often mean the planned energy unit commitment
is no longer optimal. In this case, the engine will regenerate the planned unit
commitment and update the AGC within seconds of the system event.
Many microgrids do not have a human operator. These systems can depend
on the dispatch engine to plan targeted set points. powerMAX AGC regulates
generator outputs around base set points to maintain the power interchange
at the utility tie within user-defined limits. The powerMAX AGC system can
dynamically recalculate control set points under all system bus configurations
and can respond to load-shedding events within a few milliseconds. The engine
optimizes the base set points used by the AGC system.
System Events
Cost Factors
Recalculation
Triggers
Fuel Price
Generator Transition
Cost
Generator Efficiency
Curves
Inputs
Dispatch Engine
Generator Operation
Region Constrains
Automatic Generation
Control Module
Dispatch
Generators
Feedback
Target Set
Points
Battery Charging
Strategy
Forecasts
Load Profile
Weather
Energy Price
The dispatch engine accounts for various factors and user inputs in order to optimize a microgrid’s generation.
Security
Value
The dispatch engine RTAC provides a secure access point
into your microgrid with the following features:
Regardless of your DER mix, the SEL
Microgrid Economic Dispatch Engine
will minimize costs while ensuring
your scheduling goals and other
operational constraints are satisfied.
You can maximize ROI for microgrids
that encompass even a small number
of generation assets.
• Unique login accounts and profiles to comply with rolebased user authentication requirements.
• Lightweight Directory Access Protocol (LDAP) central
authentication that works with your existing LDAP server.
• Intrusion detection/notification and access logging to
maintain system integrity.
• Secure engineering access via Secure Shell (SSH).
• SEL exe-GUARD® whitelist antivirus technology to protect
against malware and other cybersecurity threats.
• Industry-leading integration of security technologies by
mapping security tags into SCADA reports.
• No backdoor passwords.
• No Microsoft Windows operating system.
SEL Engineering Services
+1.509.332.1890 | esinfo@selinc.com | selinc.com
© 2019 by Schweitzer Engineering Laboratories, Inc.
PF00611 · 20191205