Advanced Controller Utilizing Natural Gas Engines for Microgrid Systems with Integrated Storage
Available for Licensing
US Utility Patent: US 10683815
US Utility Patent Pending: US 2020/0263615
At A Glance
Researchers at Colorado State University have developed an advanced multivariable robust controller for a microgrid system utilizing an integrated natural gas engine and storage device (e.g., battery). The storage device is used to supply transient power during net load variations, and the control system manages both the engine and storage systems, and their interaction, as to ensure:
- The net load is reliably delivered despite significant transient variations
- The engine speed (and microgrid frequency) deviation is minimal
- The battery State-of-Charge (SOC) is kept close to 50%
- The engine Air-Fuel-Ratio (AFR) is tightly controlled eliminating knock and misfire, while minimizing emissions.
The net effect of the advanced control and integrated storage is a natural gas engine based microgrid that can operate in situations requiring significant transient performance. These situations are numerous, and they are currently served by diesel-based systems, rather than cheaper, cleaner, abundant natural gas, because the performance capabilities listed in 1-4 are not possible with current technologies using natural gas engines under these operating conditions.
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The controller within a microgrid is essentially a power management system and it should keep the balance between power generation and consumption in order to minimize the frequency deviation that results from load fluctuation and variability in renewable energy sources. When there is excess power in a grid, the grid frequency tends to increase. This applies to both utility grids and microgrids. On the other hand, the grid frequency decreases if the generated power within a grid cannot fulfill the load demands. If the utility grid frequency deviation exceeds the allowed limits, breakers will open and cause blackouts. The same principle applies to microgrids. Hence, it is critical to maintain a constant engine speed regardless of system disturbances, variations, and uncertainties.
In summary, the technology here develops:
- Advanced multivariable robust control strategies for natural gas engines, delivering performance under both steady state and transient operation.
- Advanced multivariable robust control strategies for systems comprising disparate assets, e.g., a large slow actuator combined with a small fast actuator.
- A microgrid system comprising an integrated natural gas engine-based generator and an energy storage (e.g., battery) system. This integrated system is intended to afford both steady state and transient operating capabilities.
- Advanced multivariable robust control strategies for this integrated microgrid system.
In this setting, the storage device is used to supply transient power during net load variations. As such it is being utilized as a power, rather than energy, device. By this we mean that it is not intended to continuously supply large amounts of energy to the system, rather it is intended to supply short bursts of power. This means that an array of (relatively cheap) storage technologies, (e.g., battery, supercapacitor, flywheel) may be appropriate for various instantiations of the technology.
In this setting the controller is crucial. In particular our advanced multivariable robust control system manages both the engine and storage systems, and their interaction, so as to ensure:
- The net load is reliably delivered despite significant transient variations. This net load variation could arise from variation in user loads in the microgrid, or from variation in power output from renewable power assets (e.g., wind, solar) being utilized by the microgrid.
- The engine speed deviation is minimal. This ensures stability of the microgrid by regulating the microgrid frequency at its desired level (usually 60Hz) and keeping it within the desired operating limits. Without this tight speed/frequency control, transients could result in sufficient frequency departure to cause breakers to trip and thus disable the microgrid.
- The battery State-of-Charge (SOC) (or similar metric for other storage technologies) is kept close to 50%, despite the variable power flowing in/out of the battery/storage. This means that deep energy discharge is not required, and hence a variety of cheap storage options may be viable for this integrated system.
- The engine Air-Fuel-Ratio (AFR) is tightly controlled. This means that the engine is kept running at its optimal operating point, eliminating any knock or misfire. At the same time this is desirable from the viewpoint of minimizing emissions. Note that current control approaches to natural gas engines typically do not even attempt to control AFR during transient events because the control system cannot deliver adequate performance during this circumstance.
The net effect of the advanced control and integrated storage is a natural gas engine based microgrid that can operate in situations requiring significant transient performance (e.g., due to net load variation because of varying user loads or use of renewables such as wind and solar). These situations are numerous, and include mining sites, fracking operations, oil & gas industry operations, and other small scale microgrids where natural gas engines are desirable but transient performance is required. Note that these types of microgrids are currently served by diesel-based systems, rather than cheaper, cleaner, abundant natural gas, because the performance capabilities listed in 1-4 are not possible with current technologies using natural gas engines under these operating conditions.
Finally, note that a variety of different storage technologies are viable for this technology, and also a number of currently available control hardware/software platforms could be adapted to implement the controller. As such the innovation is not limited to a narrow set instantiations of the technology, but rather it could be implemented in several different forms. In each case it can enable new application areas for natural gas engines, facilitating their use in areas where it would be desirable to use natural gas (rather than diesel) because of cost, emissions etc., but it is not possible with current technologies.
- Facilitates the use of natural gas engines requiring significant transient performance
- Displaces diesel fuel for cheaper, cleaner natural gas
- Delivers enhanced performance
- Tighter speed/frequency regulation and
- Exceptional control of Air-Fuel-Ratio (AFR) which drives emissions
- Deep energy discharge is not required (cheaper storage options are viable)
- Microgrids utilizing natural gas engines
- Natural gas engine manufacture
- Mining sites
- Fracking operations
- Oil & gas industry operations
- Other small scale microgrids
Han, Yi. “Microgrid Optimization, Modelling and Control.” Mountain Scholar, 2014, mountainscholar.org/bitstream/handle/10217/88434/Han_colostate_0053A_12725.pdf?sequence=1&isAllowed=y.
Last updated: September 2020