Not Applicable.
The present disclosure relates generally to power grids and, in particular, to systems and methods for managing microgrids. More particularly, to systems and methods for improving local control of generation and consumption assets of microgrids.
Microgrids are providing a growing percentage of the electric power consumed by electronic devices located on and away from microgrid locations. As more microgrids are connected with the bulk electric system (BES), the complications of microgrid control for both operators of the BES and of microgrids become more evident.
Although the concept of a microgrid has been known within the electrical utility industry for many years as a small scale electricity system, recent advances in material sciences and information technology, among others, have facilitated improved techniques and methodologies making microgrid installations more reliable, practical, and attractive for an increasing segment of electrical loads. The benefits of microgid installations are also well known in the industry. Generation sources within a typical microgrid are frequently from renewable resources and suffer less distribution system loss traveling much shorter distance from source to load. Microgrids also allow more user control over electricity consumption and creation, allowing increased security and reliability for some microgrid users as well as independence from traditional utilizes.
As interest and availability of microgrids increase, so too does their impact on the BES. While the typical microgrid covers a smaller area with a small number of power generation sources and loads, such as a single office building load serviced by generation from a small number of wind turbines, photovoltaics and traditional generation sources, the size varies greatly and can include any number of generation and load assets. Many such microgrids are connected to and, to some degree, dependent upon connection with the bulk electrical system for reliability, creating a “back-and-forth,” transactional relationship with local utilities and energy markets.
Many microgrids utilize some form of a master controller to facilitate data acquisition and perform monitoring and supervisory control over the operation of a microgrid during all microgrid operating modes (grid-connected, islanded, and transition between the two). In the current state of the art, master controllers have monitored the prevailing operating conditions of a microgrid and initiated pre-programmed, remedial actions if the system is not operating within acceptable limits (e.g. voltage and frequency violations). Microgrid master controllers have been designed with functionality to dispatch local resources to minimize the overall cost of meeting microgrid load by balancing generation and load reactively or in near-real time in order to reduce the purchase of electricity supply from the BES.
The size and complexity of microgrid installations utilizing many generation sources to fulfill demand within the microgrid, in whole or part, creates challenges for both the microgrid operator as well as any utilities that would like to anticipate demand from one or multiple microgrid installations as well as economically utilize any excess generation.
Historically, the ability to forecast demand within a microgrid and effectively balance generation to meet predicted, local load demands has been inaccurate and unreliable. Some microgrids have relied primarily on producing additional generation to ensure reliability. Without methods for accurately forecasting demand within a local system, excess generation created by such a microgrid must be stored or reintroduced to the BES. This too has caused additional issues for utilities that must identify load entering the BES and find methods to economically utilize that additional generation in a manner which does not violate strict reliability regulations. Moreover, such generation can be expensive to both purchase and utilize for utilities, while syncing excess generation for distribution to the BES can be difficult and unreliable for microgrid system operators as well.
Further, the ability to optimize microgrid activities has been hindered by the lack of a reliable valuation of dispatchable load. Without this valuation, microgrid managers do not have a clear conception of the true cost of the “generation” (by means of load shedding) employed to provide the microgrid's demanded load. Thus, unseen costs associated with shedding dispatchable load counteract the economic benefits of shedding that load in lieu of increasing generation or purchasing electricity from the BES. This decreases the usefulness of microgrid optimization activities, as these unseen costs may outweigh the apparent financial benefit of load shedding in certain situations.
In general, this disclosure is directed toward systems and methods for optimizing the communications, calculations, commands, and design of microgrids and the assets and coordinating devices installed therein.
Using the systems and methods described in this disclosure, microgrids can be developed and managed in a way that (1) simulates and tests the functions of a microgrid and microgrid coordinator, (2) increases accuracy of load forecasting both when connected to and isolated from the BES, (3) detects and clears faults during over-current protection both when connected to and isolated from the BES, (4) prevents variable generation resources from seizing during low-voltage situations, (5) optimizes the sourcing of microgrid electricity, (6) prevents false data from impacting microgrid operation, and (7) accurately calculates the cost of dispatchable load.
In one embodiment of the invention, at least one intelligent microgrid-coordinator device is installed on the microgrid premises. This microgrid coordinator contains the software necessary to keep a record of all load-consuming assets and load-generation resources on the microgrid. This microgrid coordinator may be used to categorize load-consuming assets into multiple types in order to increase the accuracy of load forecasting. Further, the value of dispatchable load is determined when planning involvement in DR events and microgrid optimization. Information on load-generation resources may be stored on the microgrid coordinator and used in optimization functions to determine the optimal percentage of load to be delivered from microgrid load-generation resources as opposed to from the BES. Variable load-generation resources are equipped with protection hardware to prevent them from ceasing to operate during low-voltage situations, increasing the safety of the microgrid and its connection to the BES. In order to protect from over-current faults when connected to and isolated from the BES, the microgrid coordinator is able to detect and clear faults at both BES fault-current levels and microgrid fault-current levels, and isolates the faulting portion of the microgrid accordingly. The microgrid coordinator may be used to aggregate all communications to and from the microgrid, and authenticates all communications from external sources. In this way, no false data is able to affect microgrid functions. In this embodiment, this combination of sophisticated components cannot be safely tested in the actual operating environment. Thus, the system includes a test simulator to simulate the microgrid and microgrid coordinator such that all functions may be safely tested before operating-environment execution.
The invention may take the form of a system for managing a microgrid, configured to:
The invention may also include a method to optimize microgrid operations by:
The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
While this invention may be embodied in many forms, there are specific embodiments of the invention described in detail herein. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.
For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated.
In general, this disclosure is directed toward systems and methods for managing microgrid operations. The disclosure proposes installing at least one intelligent microgrid coordinator on a microgrid site. This microgrid coordinator aggregates communications to and from the microgrid, and contains intelligent software capable of managing microgrid operations in more sophisticated a manner than has previously been applied in any single microgrid management solution.
Referring to
If communications are approved by Validation Software 106, they are sent by Microgrid Coordinator 104 to the corresponding assets in the microgrid by any communication protocol known in the art. Load Generating Devices 108, Load Storage Devices 110, and Load Consuming Devices 112 are examples of assets to which communications may be passed. These communications will typically be usage commands such as “turn on,” “turn off,” “ramp up,” “ramp down,” and “deliver load to,” among others. Microgrid Coordinator 104 may also accept communications from Load Generating Devices 108, Load Storage Devices 110, and Load Consuming Devices 112. These communications will typically be instantaneous asset properties, such as “amount of load being generated,” “amount of load stored,” “amount of load being consumed,” and various other status messages.
Load Generating Devices 108 may deliver generated load within Microgrid 100 to either Load Storage Devices 110 or Load Consuming Devices 112. Load Storage Devices 110 may deliver stored load to Load Consuming Devices 112. Microgrid 100 may transmit load to BES 114 as it is being generated by Load Generating Devices 108, from Load Storage Devices 110, or from Load-Consuming Devices 112 in the form of dispatched load.
Using the systems and methods of this application, the total load of the microgrid can be forecasted more accurately than standard BES forecasting methods would allow by using a grouping and averaging forecasting process. This process is shown in
Once assets are sorted into Load Type A and Load Type B, multiple estimation methods may be used to estimate the forecasted load for that particular asset on the microgrid. These estimation methods are shown here as Estimation Method A, Estimation Method B, and Estimation Method C, but in other embodiments a different number of estimation methods may be used. The particular methods of estimation used are not critical to the systems and methods, but the Box-Jenkins Method, Winters-Taylor Method, and Kalman Filter Load Model are examples of potential estimation methods that could be used in this process.
Once all methods have estimated the forecasted load for the corresponding load type, the estimate results for each method are analyzed to identify inaccuracies. Method results may be analyzed, for example, to determine whether the results from one method are above a certain number of standard deviations above or below the mean value of the results of all methods combined. Method results may also be analyzed to determine whether they are significantly different from a historical or otherwise expected value. The results from methods that are shown to be inaccurate are discarded, and the remaining results are averaged. As depicted here, Load Estimate Average 212 is composed of all results from Estimation Methods 206-210, whereas Load Estimate Average 214 is composed of only results from Estimation Methods 206-208; results from Estimation Method 210 were rejected. Load Estimate Average 212 and Load Estimate Average 214 are then summed to determine Total Load Estimate 216. This accurate load forecast is useful for many microgrid operations, including but not limited to determining the microgrid's availability to participate in demand response events or generation optimization for the microgrid.
The systems and methods of this application utilize a microgrid optimization process to ensure that the microgrid is obtaining its load in the most economically advantageous fashion while conforming to microgrid constraints. A microgrid optimization process calculates, for any amount of microgrid load, the percentage of electricity to acquire from multiple electricity resources in order to serve that load most economically.
In some embodiments, Resource Data 302 may incorporate a consideration of the opportunity cost of one or more potential resources. Including opportunity cost of resources enables the valuation of dispatchable load. The value of dispatchable load is beneficial when determining optimal microgrid function both in terms of responding to demand-response events and in terms of reducing the cost of operating the microgrid in general. There are several different components to consider when valuing dispatchable load. Efficiency cost, for example, includes factors such as the wear and tear that electrical equipment suffers when it is switched between one state and another over a long period of time. These costs may be negligible in residential and smaller commercial microgrids, but can add up in larger microgrids, especially those that participate in demand-response events quickly. Productivity cost, as opposed to efficiency cost, includes factors that tend to affect the microgrid owner's profit. For an owner of a microgrid running a commercial office building, for example, load may be dispatched by temporarily shutting down air conditioning units. As temperature in the office increases, employees in the office may get uncomfortable, causing their productivity to decrease. The effect that this productivity has on the microgrid owner's profits may greatly affect the valuation that dispatchable load.
These productivity costs may be determined by different factors in different situations. For example, if load were dispatched in the above commercial office building by shutting off non-critical software-development servers at a software company, the effects on long-term profit caused by not developing software on those servers for the time period they are shut off would affect the valuation of dispatching the corresponding load. In industrial setting, dispatchable load may power large equipment that takes a long time to cycle on once it is shut off, so a short-term load-shedding event may have longer effects on productivity for those machines. Further, if those machines are involved in a manufacturing process that cannot be completed by the start of the load-shedding event and cannot be stopped without forfeiting the progress made by that point, the microgrid owner may suffer lost product. This may be common, for example, in processes that are required to be performed at a constant temperature, such as preparing food and smelting metals. In residential settings, such as a microgrid containing a large apartment, dormitory, or condominium complex or even a house running a microgrid, valuation of dispatchable load may include the negative effect shedding that load has on the comfort of residents, rather than on the profit of the microgrid owner.
Once Resource Data 302 has been obtained, Microgrid Coordinator 300 Formulates the Optimization Function 304 in the form of a minimization objective function. The optimization function at this point takes into account Resource Data 302 and the target load amount to be provided by the function. The particular minimization function used is not material to this application. Once the optimization function is formulated, Microgrid Controller 300 Applies Constraints 306 to the objective function. Potential constraints include, but are not limited to, (1) generator availability, (2) generator maximum and minimum limits, (3) generator ramping rates, (4) minimum generation limit produced by the heating/cooling requirements of Combined Heat and Power (CHP) generating units needs for the microgrid for the CHP portion of the generation, (5) dispatchable load limits, (6) storage device availability, and (7) reserve requirements.
These constraints are used to eliminate potential objective-function solutions that fall outside what is feasible, possible, permitted, or preferred. For example, microgrid generator availability and ramping properties would foreclose solutions that would require more generation by microgrid resources than those resources could provide or that would not respect the ramping rates of microgrid generation resources. Dispatchable load maximum limits would foreclose solutions that would require more target load to be provided by dispatching microgrid resources than microgrid owners would prefer.
Once Microgrid Coordinator 300 Applies Constraints 306, it proceeds to Minimize the Objective Function 308. The minimized solution of the objective function is the operating plan to procure the target load. With the solution, MicroGrid Coordinator 300 Formulates Optimization Commands 310 to be transmitted to all assets involved in the optimized operating plan. These optimization commands could take the form of a command to a microgrid generator to ramp up or down generation, to a load asset to reduce consumption as part of load dispatch, to a storage device to release electricity to load assets, or to cut off a generator's or storage device's feed to a load asset, forcing the asset to source electricity from a different generator, a different storage device, or from the BES. Once these commands are available, Microgrid Coordinator 300 Transmits Optimization Commands 312 to all involved assets.
In addition to the benefits of coordinating microgrid activities in an economically optimal way, the systems and methods herein protect the microgrid from certain risks associated with being attached to the BES. For example, when variable generation resources (such as solar panels and wind turbines) are exposed to low-voltage situations, inverters within the variable generation resources may cease to operate. The systems and methods of the present disclosure protect these resources from low-voltage situations by equipping those resources with a protective device that enables them to operate while exposed to low voltage.
A further embodiment of microgrid protection provided by the systems and methods involves high levels of current. When microgrid load assets are exposed to unexpectedly high levels of current, they can be damaged, destroyed, and cause risk to operators of those assets. The systems and methods of this disclosure include over-current protection to protect microgrid load and generation assets from overcurrent faults, whether those overcurrents originate while the microgrid is connected to the BES or from internally while the microgrid is islanded (when isolated from the BES). However, over-current situations while connected to the BES and over-current situations present in the local islanded microgrid have different properties and different solutions. Additionally, a microgrid with a diverse and/or geographically disparate design can require different over-current protection settings depending on internal state conditions in the microgrid. Over-current situations while connected to the BES will involve higher fault current levels than over-current situations present in the local islanded microgrid. Thus, the microgrid coordinator must dynamically re-classify fault current levels and settings on-the-fly, pending real-time evaluation of the current state of the microgrid. Further, faults may require the microgrid coordinator to isolate all or some of the microgrid from the BES, or isolate components or feeders internal within the microgrid until the fault is cleared.
Such an embodiment is illustrated in
The systems and methods of the present disclosure include testing on a specially developed microgrid simulator in order to ensure that the systems and methods are safe to be implemented in the operating environment. The test system may simulate the key touch points of the microgrid coordinator, such as simulating data acquisition, supervisory control, and the microgrid to grid connection. In
This application claims priority to U.S. Provisional patent application No. 61/954,359 filed Mar. 17, 2014, the entire content of which is hereby incorporated by reference.
Number | Date | Country | |
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61954359 | Mar 2014 | US |