Microgrid Economic Dispatch EngineTM

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.

OverviewThe 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.

PCCH/W

IEC 61850GOOSE

DNP3

SEL Microgrid Economic Dispatch Engine RTAC

SEL-751

SEL-751 SEL-751 SEL-751

SEL-3555

Add economic optimization with the dispatch engine to microgrids controlled by SEL protective relays.

Reconnection

Load Shedding

Short- and Open-Circuit Protection

IEEE Compliance

Power and Power Factor (PF) Control

Protection

Governor and Exciter Dispatch

Inverter Dispatch

Load Sharing

Voltage and Frequency Regulation

ArchitectureA 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 fiber-optic 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.

FeaturesThe 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.

Cost Factor ManagementCost 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 grid-connected DER and utility. The optimization process also considers the mechanical and maintenance costs associated with operation.

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:

• Energy price

• Fuel price

• Generator transition cost

• Generator efficiency curves

• Generator operation region constraints

• Battery state of charge strategy

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sel U

sage

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/hou

r)

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Combined heat and power (CHP) natural gas consumption and heat contribution curves.

Diesel generator fuel consumption.

Optimized fuel consumption.

Battery state of charge control when islanded and grid-connected with resiliency limits.

–500

–1,000

–1,500

–2,000

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–3,5005 2010 15 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

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Diesel 3

CHP 2

Cost

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Load and Generation ForecastingEach 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.

Use the dynamic load and generation forecasting to optimize source loading.

PU %

Time of Day

0

SolarIrradiance

WindProfile

Load

Forecast

12

10

20

30

40

50

60

90

80

70

Dispatch SchedulingDispatch 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.

Solar

CHP

Utility

Battery EnergyStorage System

Pow

er D

ispa

tch

Time of Day

14

10,000

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–6,000Export Limit

Import Limit

Time (minutes)

kW

5 2010 15 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Import and export control for utility interconnection agreement compliance. There is no import/export value during islanded operation.

Generation dispatch for lowest cost of operation based on load forecast and renewable availability.

Microgrid VisualizationThe 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.

ApplicationsPotential 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.

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, high-speed 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.

Combining the Dispatch Engine With powerMAX

Cost Factors

Fuel Price

Generator Transition Cost

Generator Efficiency Curves

Generator Operation Region Constrains

Battery Charging Strategy

Forecasts

Load Profile

Weather

Energy Price

System Events

Automatic Generation Control Module Generators

Dispatch

Recalculation Triggers

Target Set Points

Inputs Feedback

The dispatch engine accounts for various factors and user inputs in order to optimize a microgrid’s generation.

Dispatch Engine

SecurityThe dispatch engine RTAC provides a secure access point into your microgrid with the following features:

• Unique login accounts and profiles to comply with role-based 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.

ValueRegardless 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.

© 2019 by Schweitzer Engineering Laboratories, Inc. PF00611 · 20191205

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