The Ovation™ Microgrid Control System operates as a unified control architecture that continuously monitors system conditions and coordinates control actions across distributed energy resources, loads, and electrical infrastructure. Building on Ovation’s integrated control platform, microgrid operation is organized around three tightly connected elements: standard control functions that provide core system visibility and stability, embedded energy management that evaluates operating objectives and constraints, and integrated electrical control that manages power flow and system transitions. Together, these elements enable the Ovation Microgrid Control System to respond dynamically to changing conditions while maintaining reliable microgrid operation.
Standard Integrated Control Functions
Data Acquisition
Ovation I/O modules acquire data every second or 100 milliseconds to support control applications or information capture requirements. Dedicated Ovation sequence-of-event modules provide 1/8 millisecond event time tag resolution. The control system also obtains information, typically at 1-5 second intervals, using communication data link protocols such as IEC 61850, Modbus, IEC 60870-5-104, OPC, and DNP3.
The collected data can be transmitted across the Ovation network for use in operator workstations, control panels and process historians.
Process Graphics
Every Ovation system is delivered with project-specific graphics, such as single-line diagrams, that display real-time microgrid status. Control parameters entered into the graphic automatically manage microgrid processes. Critical analog values such as bus voltages, frequency, power flow, temperatures, inverter statuses, switch and breaker positions are also displayed.
Alarm Management
The Ovation control system includes an integrated intelligent alarm management system that prioritizes microgrid alarms to quickly isolate and address problems.
The Ovation alarm management system focuses the operator on important microgrid situations that deviate from normal operation. Abnormal conditions, such as points out of range (high or low electrical bus voltage or frequency), digital state changes (opening the grid breaker or automatic transfer switch operation) and drop time-outs are alarmed on Ovation operator workstations. Alarms displayed on the operator workstations are also sent to an alarm printer and the Ovation Process Historian which creates a chronological record of all process alarms and subsequent operator actions.
Data Archiving
The Ovation Process Historian provides mass storage and retrieval of process data, alarms, sequence-of-event records and operator inputs to the Ovation system. Data continuously acquired by the Ovation system is archived in the historian for retrieval and analysis. Data retention of the process historian is limited only by its disk space, which may be augmented by tape drives or a DVD drive.
Report Generation
The Ovation Process Historian includes a reporting system that presents relevant historical data in various formats. Predefined templates can be used for common reporting tasks. Custom report capabilities are available for more complex data analyses. Reports can be generated automatically on an hourly, shift, daily, monthly or yearly basis.
Energy Management for Coordinated Microgrid Control
Protection from High Macrogrid Demand Charges
A microgrid may have a “point of common coupling” connection to the distribution utility (or macrogrid) and a rate structure/contract that stipulates the maximum quantity of energy (MW h) that is allowed to be consumed in a given demand period. If this limit is exceeded, the microgrid manager may incur permanently higher demand charges.
Because the consumption demand is measured in energy (MW h) and not power (MW), the Ovation system predicts energy consumption at the end of the time period. Anticipated errors are estimated by measuring the present rate of power consumption and extrapolating to the end of the demand period. If the predicted value exceeds the maximum demand limit, the Ovation system automatically trims load or increases generation from generation resources or energy storage to limit the energy consumed from the macrogrid. It also generates an alarm to alert the operator to take corrective action.
Management of Energy Flow and Voltage Regulation at the Point of Common Coupling
Macrogrid operators view microgrids as distributed energy resources whose energy consumption or supply rate and its effect on system voltage must be tightly controlled. While microgrid operators can sell and deliver energy through the macrogrid, they can also provide critical voltage support not only to the microgrid itself but to the macrogrid as well.
The Ovation system manages the energy flow and voltage regulation at the “point of common coupling” at predetermined setpoints, which are consistently reached through high-speed responses to demand changes or equipment availability. Microgrid control goals often entail maximizing generation by renewable energy resources and minimizing electricity purchase costs. When a microgrid generates more power than demanded by its internal load, the Ovation system controls the flow of energy-to-energy storage resources, the macrogrid or both, as determined by the operator.
In situations where a microgrid cannot generate enough power to satisfy its internal loads, the Ovation system can disconnect (or shed) non-essential loads to minimize the need to draw power from the macrogrid if it is economically beneficial. Similarly, the Ovation system will shed microgrid loads if a weather or other emergency event disrupts macrogrid operation such that the microgrid cannot draw needed power. It will do so in order from least to most essential, preserving its ability to operate autonomously and self-supply the most essential loads for as long as possible.
Optimization of Energy Production, Storage and Purchase
Microgrids are comprised of any number of energy supply, energy storage and adjustable load (energy consumption) resources. They also have the ability to buy energy from or sell energy to macrogrid-connected suppliers and customers. Distributed energy resources may use various fuels, each with different costs and environmental impacts.
Microgrid performance objectives are often focused on minimizing the cost of energy, minimizing total environmental impact or a combination of the two. Emerson’s integrated Ovation advanced power applications use state-of-the-art optimization technology to assist microgrid operators in meeting their performance goals. The applications determine the best control setpoints to optimize distributed energy resource management.
Performance Calculations
Emerson’s Global Performance Advisor is available to calculate the efficiencies of any gas and/or steam turbo-generators in the microgrid. The advisor allows operators to identify controllable losses, track equipment performance against design specifications, and quickly identify problematic process areas to reduce operating costs. This solution provides a complete set of boiler and turbine performance calculations (based on ASME Performance Test Codes) to match the specific plant equipment set.
Electrical Control for Secure Microgrid Operation
Breaker Control and Interfacing to IEDs
The Ovation system’s embedded breaker control logic allows an operator to issue OPEN and CLOSE commands from single-line diagrams displayed on operator workstations. Before an operation takes place, the logic checks to ensure that the breaker is in the proper state to perform that operation. If a command is issued and the status indicator does not reflect the new state (i.e. the breaker does not indicate that the operation was successful) within a certain amount of time, an alarm is generated.
The Ovation system continuously monitors macrogrid power quality. When a macrogrid problem is detected, Ovation can open the breaker at the point of common coupling within 50 microseconds. This action immediately islands the microgrid, protecting and preserving its ability to continue serving native load.
Ovation communicates with intelligent electronic devices (IEDs) using various protocols including:
- Modbus over RS485 serial link
- Modbus over TCP/IP
- DNP
- Profibus
- IEC 61850
- IEC 60870-5-104
Load Shedding
Load shedding is a critical microgrid control function. Ovation microgrid contingency analysis and load shedding applications automatically respond to electrical disturbances, such as loss of grid or loss of a power producer, to restore stable conditions.
If a power source such as a grid, generator or inter-connect breaker on a generation bus is lost (a contingency) the corresponding load in the amount originally supplied by that power source must be immediately shed. This ensures that the remaining power producers are not over-loaded and disturbance to the microgrid is minimized.
Failure to immediately reduce load to match available generation results in a blackout of the microgrid.
The Ovation platform’s load shedding application selects the feeders serving loads to be dropped from a list of available feeders. Feeders are selected in order from the least to the most critical. The logic also checks that the load-shed breaker is available (closed and has MW flow) for automatic tripping and connected to the importing bus, not to the exporting bus.
The list of breakers for each possible load-shed case is continuously updated and shared with the controllers. The Ovation system automatically and instantaneously sheds the selected breakers when a power source is lost.
Ovation graphics readily show microgrid operators the list of loads to shed in a contingency. At any time, the operator can adjust a load’s priority or temporarily remove it from the load shedding system to prevent it from being shed during a contingency Naturally, care must be taken not to remove too much load from the load shedding system, since this could cause a general blackout of the microgrid.
Ovation’s fast load shedding logic avoids generator overload and a possible blackout. Loads are shed when the power-source breaker is opened.
A microgrid disconnected from the macrogrid operates as an independent electrical island, where the island’s frequency must be maintained by the island’s own power producers. If the microgrid load exceeds generation, then the island frequency will relatively slowly fall below the nominal value of 60 Hz (50 Hz in many world areas).
When the island frequency goes below a minimum threshold value, the Ovation logic sheds enough low-priority loads to bring the frequency back to the nominal value. Lowering frequency typically happens over a long period of time and thus this is commonly referred to as “slow load shedding”.
Slow load-shedding may also be required if grid tie-line transformers approach an overload condition.
Supply/Demand Balancing (Frequency/Voltage Control)
Control techniques for balancing power supply with demand within the microgrid vary depending on the types of power generation, storage and load equipment inside the microgrid’s boundaries; whether the microgrid is connected to the macrogrid; and whether the microgrid’s load uses alternating current (AC), direct current (DC) or a hybrid of the two.
Macrogrid-connected systems always ensure that there is enough power available to supply the microgrid’s loads. In this case, Ovation controls the microgrid’s production, storage and use of energy and power, using macrogrid-supplied energy and power within limits defined by the goals of the microgrid. This includes use of reactive power in cases where there may be charges from the macrogrid operator for consumption or production of reactive power beyond some limit.
Islanded microgrids ensure a balanced supply with demand by adjusting setpoints on generators, inverters, transformers and controllable load elements, such as thermostats. Islanded loads are shed only when necessary to keep frequency, voltage and power factor throughout the microgrid at desired values.
In the special case of AC and hybrid power microgrids with rotating generators, frequency control is used to balance real power supply. Voltage is controlled using various reactive power elements such as generator excitation adjustments, transformer on-load tap-changers (OLTCs) and capacitor banks.
For microgrids that do not have rotating generators (AC, DC or hybrid), voltage and power factor (or reactive power) measurements taken throughout the microgrid are kept within desired ranges by adjusting setpoints on inverters, transformers and controllable load elements. Load shedding is also used in this scenario as a last resort.
In any case, Ovation microgrid control ensures the most reliable, economical and environmentally responsible operation possible.
Synchronization
Synchronization is the process of measuring and controlling the voltages, frequencies and phase angles of the systems on either side of a breaker. Synchronization ensures that differences between these parameters are within specified limits before closing the breaker. Failure to do so risks catastrophic failure of equipment in both systems. This is a critical function when connecting an islanded microgrid to a macrogrid to exchange energy.
Similarly, before opening the breakers, the current and power flow across the breakers must be below defined limits.
Ovation microgrid control includes both hardware and software checks for synchronization, along with an auto-synchronizer interface that synchronizes the microgrid with the macrogrid.
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