Energy management state machine for microgrid

Abstract

The embodiment of the invention relates to an energy management state machine for a microgrid. A method of monitoring a microgrid includes receiving a plurality of inputs, determining an output based on the plurality of inputs using a state machine, and outputting a control signal based on the output. The plurality of inputs includes a microgrid-side voltage measurement and a microgrid-side frequency measurement. The control signal is configured to control operation of the microgrid at a point of common coupling between the microgrid and the utility grid.

Description

Technical Field

[0001] The present disclosure relates to a method for supervising a microgrid and a supervision algorithm for a microgrid. Background Art

[0002] State machines are used as behavioral models that produce outputs based on the current state and given inputs. State machines are widely used as the basis for various control and supervision algorithms due to their role in organizing process flows and defining outputs based on multiple states of the system. However, traditional state machines are based on a very general view that is conceived as controllers of the system rather than selectors of operating conditions. Furthermore, the boundaries of traditional state machines are often not well defined.

[0003] In an electrical grid, particularly in a microgrid and / or low voltage microgrid, a control system must be implemented to control the production and / or distribution of power from multiple sources of different types. Microgrid monitoring and analysis can be performed by a processor-based control system that is configured to deliver power based on a schedule or based on a regional control module. However, the individual devices that make up a microgrid have different compliance standards and requirements, which may result in reduced compliance of the microgrid as a whole or certain devices within the microgrid.

[0004] Therefore, there is a need for improved methods for supervising microgrids to improve the compliance of microgrids and microgrid equipment and to ensure that compliance standards are met. Summary of the invention

[0005] A method for monitoring a microgrid includes receiving a plurality of inputs, determining an output based on the plurality of inputs using a state machine, and outputting a control signal based on the output. The plurality of inputs include a microgrid-side voltage measurement and a microgrid-side frequency measurement. The control signal is configured to control operation of the microgrid at a common coupling point between the microgrid and a utility grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The subject matter of the present disclosure is described in more detail below based on exemplary drawings. All features described and / or illustrated herein may be used alone or in combination in various combinations. The features and advantages of various implementations will become apparent by reading the following detailed description with reference to the accompanying drawings, which illustrate the following.

[0007] Figure 1 illustrates an energy management state machine flow chart 100 for microgrid supervision according to one embodiment; and

[0008] Figure 2A and Figure 2B A flow chart of energy management state machine operation for 3-level priority function determination according to one embodiment is illustrated. DETAILED DESCRIPTION

[0009] Aspects of the present disclosure provide an energy management state machine that includes a selector function. The selector function performs mode selection at the microgrid level to drive the microgrid under specific operating conditions. The selection process in the state machine has three priority levels that can be determined. The three-level priority determination is based on a determination function that sequentially identifies the operating conditions of the microgrid and uses logic to decide which of a plurality of functions should be selected for implementing microgrid operations. The energy management state machine determines the operating conditions of the microgrid through a combination of measurements and algorithm-based logic.

[0010] Embodiments of the present disclosure provide a method for customizing priority function preferences based on the selection of grid code compliance standards. Embodiments of the present disclosure also provide a method for clustering key microgrid measurements for grid-connected use cases by classifying these grid-connected use cases into various priority levels. A state machine that enables these methods is also provided. Advantageously, the state machine is simple and can be customized based on user preferences and various inputs from the microgrid and the larger grid to which the microgrid is connected or to be connected. The state machine is also scalable to accommodate microgrids of different sizes with different numbers of connected devices. The described state machine is also more flexible than traditional solutions, allowing a single state machine to be used across different microgrids and ensuring that all microgrid devices comply with user-selected compliance standards or predetermined compliance standards.

[0011] In one embodiment, a method is provided for tracking and analyzing current operating conditions of a microgrid through various measurements both inside and outside the microgrid from the perspective of a point of common coupling (PCC).

[0012] In one embodiment, a selector algorithm is provided for making intelligent decisions through 3-level prioritization to perform microgrid operation mode selection.

[0013] In one embodiment, a framework is provided for implementing an algorithm for clustering critical microgrid measurements for grid-connected use cases by classifying the grid-connected use cases into various priority levels.

[0014] In one embodiment, a framework is provided for allowing selection of custom priority function preferences based on selection of grid code compliance criteria.

[0015] In one embodiment, an energy management state machine acts as a selector that handles grid support functions that comply with industry standards such as the Institute of Electrical and Electronics Engineers (IEEE) 1547 or the Italian Electricity Commission (CEI) 0-16. The energy management state machine can perform various grid-connected energy management functions, such as rule-based active power (P) and reactive power (Q) set point distribution, regulation curves that comply with IEEE 1547, and ride-through functions. The energy management state machine takes into account user preferences, distribution system operator (DSO) set points, utility maintenance and outage information, and measurement and communication error scenarios to describe microgrid operating conditions. Based on the operating conditions inferred from various inputs, the state machine can determine how the microgrid operates at the current time and in the future.

[0016] Embodiments of the present invention enable all devices within a microgrid to comply with one or more compliance standards. Specifically, since all devices within a microgrid are slave devices under a supervision scheme implemented by an embodiment of the disclosed state machine, all microgrid devices comply with the standards imposed by the state machine. Embodiments of the present invention also provide an aggregate supervision algorithm that reduces or eliminates the need for separate individual compliance-based control of devices in a microgrid. For example, traditional solutions require that each battery in a microgrid be individually controlled to ensure compliance, which may result in a longer control process compared to the embodiments of the present disclosure that aggregate data to more quickly achieve compliance of all batteries within a microgrid. Embodiments of the present disclosure also improve the reliability of the power grid through this aggregate compliance approach.

[0017] Figure 1 An energy management state machine flow chart 100 showing how a state machine is updated and used for microgrid supervision according to an embodiment of the present invention is illustrated. Input 102 is used to provide input to an energy management state machine 104, and a query 106 is implemented to determine whether a point of common coupling (PCC) breaker is closed. If it is determined that the PCC breaker is not closed, an islanded state machine 108 can be implemented, wherein the supervised microgrid is disconnected from the main utility line, but remains powered on to continue to supply power to the local loads of the microgrid. Otherwise, if the PCC breaker is not closed, a supervision algorithm is started 110.

[0018] Input 102 includes various types of inputs from the microgrid and the larger grid to which the microgrid is connected. Microgrid inputs may include microgrid measurements such as voltage, frequency, PCC active power, PCC reactive power, microgrid load information, and other similar inputs. In some embodiments, input 102 also includes one or more other measurements and / or information types, such as battery or device operating status, battery state of charge (SOC), user preferences, expected load and supply schedule, expected power outage information or schedule, measured or manually entered grid anomalies, microgrid health indicators, and error handling data. Input 102 from the larger grid to which the microgrid is connected may include one or more of the following: grid health indicators from static transfer switches (STS), maintenance signals, expected power outage signals from utility facilities or equipment, and / or DSO set point commands from grid operators. The energy management state machine 104 may determine whether the microgrid is in normal grid operation 112 or abnormal grid operation 124 based on the input 102 it receives.

[0019] If the energy management state machine 104 determines that the microgrid is in normal grid operation 112 based on the input 102 and other signals received by it, the state machine will establish PCC P and Q set points for load / source management 116. The PQ set points enter the inverter and change the output of the battery of the microgrid. In some embodiments, the load / source management in which the load of the microgrid is balanced is completed using a regulation curve for grid support 114, which can be stored as part of the state machine or accessed via the state machine. During normal grid operation 112, the state machine can also determine the frequency and / or voltage crossing threshold 120 for load / source management 116. The frequency and / or voltage crossing threshold 120 can be based on the standards specified in IEEE 1547, CEI 0-16, or other regulatory and / or privately established standards. The frequency / voltage crossing threshold 120 can also be used to switch the trip mechanism, thereby establishing a physical island 122 to separate the microgrid from the main utility line. Regardless of whether load / source management is implemented and / or physical islands 122 are established, the impact on the microgrid 118 is measured and then directed back to the energy management state machine 104. In some embodiments, measurements from the microgrid 118 are sent to the input 102 so that parameters or values ​​of the input 102 can be updated and then sent to the energy management state machine 104. In some embodiments, measurements from the grid are continuously sent directly to the energy management state machine 104 as updates.

[0020] If the energy management state machine 104 determines that the microgrid is in abnormal grid operation 124 based on the input 102 and other signals it receives, an abnormal performance category analysis 126 may be implemented, where compliance with various threshold voltage and / or frequency values ​​may be evaluated. In one embodiment, the category analysis 126 may be tailored for a Category II design under IEEE 1547. In some embodiments, the category analysis 126 may be tailored for a Category I or III design under IEEE 1547 or another category or set of thresholds under CEI 0-16 or another standard. If the category analysis 126 indicates that the trip mechanism should be actuated, an unplanned island sequence 128 may be initiated, resulting in the establishment of a physical island 122 when the trip mechanism is tripped. The changes implemented in the microgrid 118 are then measured and forwarded to the energy management state machine 104.

[0021] In one embodiment, the regulation curves for grid support 114 are compliant with IEEE 1547 or CEI 0-16 in terms of voltage, power, power factor, frequency, and reactive power related curves. In one embodiment, frequency / voltage ride-through threshold 120 is configured to provide IEEE 1547 or CEI 0-16 compliance during faults and grid dynamic events by performing voltage / frequency ride-through operations. In one embodiment, load / source management 116 is configured to enable power scheduling between microgrid devices based on tracked reference PCC active power and reactive power.

[0022] It should be easy to understand. Figure 1 The illustrated and described embodiments may be implemented in an iterative manner to provide real-time or near real-time measurements to the energy management state machine 104 so that when an input 102 or a measurement from a microgrid 118 requires intervention, such intervention can be performed immediately. Such intervention may include, for example, establishing a physical island 122 via tripping a trip mechanism to prevent damage to the microgrid, its components, and / or the main utility line. In some embodiments, the foregoing method may be implemented iteratively with a preset delay or with a delay that is dynamically adjusted by the energy management state machine 104 based on the input 102 and whether more frequent or time-sensitive monitoring and / or intervention is required based on the conditions observed via the input 102. This may enable the energy management state machine to operate more efficiently and economically for applications that do not require real-time monitoring or when safety requirements allow for delayed intervention.

[0023] Figure 2AThe first part of an energy management state machine operation flow chart 200 for 3-level priority function determination is illustrated. The operation flow includes an input 202, which is used by an energy management state machine 204 to determine a microgrid function assignment. The microgrid function assignment causes the energy management state machine 204 to output one or more signals 206, 208, 210, 212 for controlling the operation of the microgrid and / or the devices within the microgrid. The input 202 can be updated based on grid-side measurement updates and microgrid-side measurement updates via an update signal 214. In some embodiments, the update signal 214 may include a MODBUS signal. In other embodiments, the update signal 214 may take the form of a different serial data communication protocol.

[0024] Figure 2B The second part of the energy management state machine operation flow chart 200 is illustrated. The set point update signal 206 can be output by the energy management state machine to establish the operating set point for various devices in the microgrid 250. For example, in the illustrated embodiment, the set point update signal 206 can establish the operating set point for the battery energy storage system, the uninterruptible power supply (UPS), the diesel generator, or the photovoltaic cell. It should be easily understood that in the context of the present disclosure, different types and quantities of devices can be included in the microgrid 250, and these devices are controlled via the set point update signal 206. The trip signal 208 can be output by the energy management state machine to determine whether the circuit breaker should be tripped at the PCC to make the microgrid island. In some embodiments, the trip signal 208 can be configured to trip the circuit breaker that disconnects only a part of the microgrid or only disconnects a number of all available devices of the microgrid. A first reduction decision signal 210 can be output to provide load reduction between devices in the microgrid 250. For example, the first reduction decision signal 210 can be used to provide load reduction between multiple electric vehicle charging stations. A second curtailment decision signal 212 may also be provided for load shedding in a second category or subset of devices in the microgrid 250. For example, the second curtailment decision signal 212 may be used to provide load shedding for one or more buildings or facilities within the microgrid.

[0025] Input 202 includes grid-side input and microgrid input. Grid-side input may include, for example, maintenance data, expected outage data, grid health indicator, and DSO set point. Microgrid input may include, for example, user preferences, microgrid-side measurements, and error handling data (such as data identifying error-affecting devices and disabling set points). Microgrid-side measurements may include, for example, PCC voltage, frequency, distributed electrical resource (DER) output, battery SOC, and load information. Different inputs 202 are used as a basis for determining different priority levels within energy management state machine 204. For example, microgrid-side measurements may be used to make a first priority function determination or a so-called "level A" priority function determination. Maintenance data, expected outage information, grid health indicator, and / or DSO set point may be used to make a second priority function determination or a so-called "level B" priority function determination. User preferences and / or error handling data may be used to make a third priority function determination or a so-called "level C" priority function determination.

[0026] Examples of user preferences include: selecting a particular regulation curve; a particular active power (Pset) or reactive power (Qset) or a combination of both to be tracked by the microgrid; and providing dynamic voltage support as part of a voltage ride-through implementation while the microgrid voltage is in a normal operating region. Regulation curves may include, for example, VQ, PF, VP, and other similar curves representing relationships between microgrid attributes. Providing dynamic voltage support may include: supplying reactive power from the microgrid.

[0027] Even though the user can set certain preferences as described above, the operating mode of the microgrid depends on the results of the priority determination described in the present disclosure. For example, because the DSO command has a higher priority than the user preference during the normal operating mode of the microgrid, the DSO command will be used to operate the microgrid in normal mode rather than during the user preference. Therefore, regardless of whether the user continues to provide user preferences, when the priority determination reaches a decision to have the microgrid operate in the user-preferred operating mode, the microgrid will operate only based on the user preferences selected by the user. In another example, the user can select a user preference for the microgrid to send specific active power (Pset) and reactive power (Qset) to the larger grid as part of a load / source management operation for set point tracking. In this case, if the grid is in normal operating conditions and there is no command from the DSO to operate in a specific mode, the priority determination of the energy management state machine will make operational decisions based on the user preferences. Reference FIG. 2A to FIG. 2B and Tables 1-3, the present disclosure includes additional details regarding determining operating conditions and the role of user preferences.

[0028] In the illustrated embodiment, the Level A priority is used to determine whether the microgrid is in normal operation or abnormal operation and whether a tripping operation should be implemented. Therefore, for the Level A priority function, the energy management state machine may have three states: state (0) indicates abnormal microgrid operation, state (1) indicates normal microgrid operation, and state (2) indicates a tripping operation. The Level A priority function determines the highest priority level signal of the energy management state machine. The output of the Level A priority function and the resulting operating state of the microgrid are determined according to Table 1, where voltage and frequency are received as inputs to the state machine, and the output value of the Level A priority function has a value of (0), (1) or (2), where the output value (0) indicates a ride through, (1) indicates an unplanned island, and (2) indicates that an action should be implemented based on a DSO command or one or more user preferences.

[0029]

[0030] Table 1

[0031] Therefore, possible outcomes of the Level A priority function are as follows: ride-through when the microgrid voltage or frequency is in an abnormal operating state; unplanned islanding if the voltage or frequency enters the trip region under the relevant compliance criteria; and execution of an action dependent on a DSO command or one or more user preferences.

[0032] Level B priority is used to collect information based on signals from the main utility (e.g., the larger grid to which the microgrid is connected or intended to be connected) and DSO signals after determining the operating condition of the microgrid based on the level A priority function. The information collected in level B may include, for example, information about maintenance, expected power outages by the utility, grid health status received from the STS of the microgrid (if applicable), and / or DSO commands for the microgrid (such as set point tracking or a specific operating mode (e.g., by following the regulation curve of voltage reactive power, voltage active power, or other similar regulation curves)). The output of the level A priority function is used by the level B priority function. Therefore, the level B priority function receives values ​​(0), (1), (3) from the level A priority function. The level B priority function also receives problem condition values ​​and DSO condition values. The problem condition values ​​(identified as "(no maintenance, no power outage, and microgrid healthy)" in Table 2) include: (0), indicating a grid-side problem; and (1), indicating no problem. The DSO condition values ​​include: (1) indicating a PQ setpoint, and (2) indicating no PQ setpoint. The output of the Level B priority function is determined according to Table 2. The output of the Level B priority function has a value of (0), (1), (2), or (3), where the output value (0) indicates a crossing, (1) indicates an unplanned island, (2) indicates a DSO command, and (3) indicates an action dependent on one or more user preferences.

[0033]

[0034] Table 2

[0035] Thus, possible outcomes of the Level A priority function include, for example, ride-through when the microgrid voltage or frequency is in an abnormal operating state; unplanned islanding if the voltage or frequency enters the trip region under the relevant compliance criteria; higher priority of the DSO command for tracking the PQ setpoint under normal operating conditions; and following the regulation curve.

[0036] The Level C priority is determined by a final priority function that depends on one or more user preferences regarding the operating mode of the microgrid and the status of all measurable devices in the microgrid. Therefore, the Level C priority function also helps the energy management state machine select the appropriate mode under normal operating conditions of the microgrid by considering special scenarios on the devices local to the microgrid (such as, for example, device failures, overloads, tracking problems, etc.). Scenario detection is implemented by another module referred to herein as the error detection and handling module. The analysis provided by the error detection and handling module is used to make device-specific operating mode selections regarding PCC power scheduling, and a status indication is issued as an output to notify the end users of the microgrid of the selection.

[0037] The Level C priority function receives the output of the Level B priority function. The Level C priority function also receives user preferences, where a value (1) indicates a regulation profile, a value (2) indicates load / source management, and a value (3) indicates ride through dynamic voltage (DynV) support. The Level C priority function also receives error detection values ​​(identified in Table 3 as "(No PVerr & No BESSerr & No DGerr & No Loaderr)"), where a value (0) indicates a sensor error and a value (1) indicates no sensor error. The output of the Level C priority function is based on

[0038] Table 3 is used to determine.

[0039]

[0040]

[0041] Table 3

[0042] The level C priority function determination is the last stage of the energy management state machine. The result function of level C is selected as the operating state of the microgrid. Based on the operating state selection, the microgrid follows the Figure 1 The appropriate section of the algorithm.

[0043] Possible results of the Level C priority function include: ride-through when either the microgrid voltage or frequency is in an abnormal operating state; initiating an unplanned island if the voltage or frequency enters a trip zone based on compliance criteria; giving higher priority to DSO commands for tracking PQ set points under normal operating conditions; following the regulation curve; selecting a user preference for operating the microgrid in ride-through mode; tracking the regulation curve; and / or using load / source management to track the PQ set point to determine the energy management state machine selection for the microgrid operating state.

[0044] It should be readily appreciated that, although specific values ​​of the inputs and outputs of the energy management state machine and its various priority functions have been described above, these specific values ​​may be replaced with different values ​​without departing from the spirit of the present disclosure.

[0045] The state machines described herein can be implemented by a controller configured to control the operation of a microgrid. For example, in one embodiment, the state machine can be implemented in a controller that directly controls the microgrid and is implemented at a PCC. In some embodiments, the controller can control the operation of the microgrid from a remote location. For example, microgrid measurement updates can be sent to a cloud-based control system that is configured to send control signals to the microgrid, thereby enabling computing and control hardware (e.g., one or more processors and controllers) to be located off-site.

[0046] In the context of describing the present invention (especially in the context of the following claims), the use of the terms "a" and "an", "the" and "at least one" and similar references are to be interpreted as covering the singular and the plural, unless otherwise indicated herein or clearly contradicted by the context. The use of the term "at least one" followed by a list of one or more items (e.g., "at least one of A and B") is to be interpreted as meaning one item selected from the listed items (A or B) or any combination of two or more items (A and B) in the listed items, unless otherwise indicated herein or clearly contradicted by the context. The terms "comprising", "having", "including" and "containing" are to be interpreted as open terms (i.e., meaning "including but not limited to"), unless otherwise indicated herein. References to ranges of values ​​herein are intended only as a shorthand method of individually referencing each individual value falling within the range, and each individual value is incorporated into the specification as if it were individually referenced herein. All methods described herein may be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by the context. The use of any and all examples or exemplary language (e.g., "such as") provided herein is intended merely to better illuminate the invention and does not limit the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0047] Preferred embodiments of the present invention are described herein, including the best mode known to the inventor for implementing the present invention. Variations of these preferred embodiments may become apparent to those of ordinary skill in the art after reading the foregoing description. The inventor expects that the skilled person may adopt such variations as appropriate, and the inventor hopes that the present invention can be practiced in a manner different from the manner specifically described herein. Therefore, the present invention includes all modifications and equivalents to the subject matter recited in the appended claims as permitted by applicable law. Moreover, unless otherwise indicated herein or clearly contradictory to the context, any combination of the elements described above in all possible variations thereof is encompassed in the present invention.

Claims

1. A method for monitoring a microgrid, comprising: Receive multiple inputs; determining an output based on the plurality of inputs using a state machine; as well as outputting a control signal based on the output, wherein the plurality of inputs include a microgrid-side voltage measurement and a microgrid-side frequency measurement; and Wherein the control signal is configured to control the operation of the microgrid at a point of common coupling between the microgrid and a utility grid.

2. The method of claim 1 , wherein using the state machine to determine the output based on the plurality of inputs further comprises: determining the output based on at least one first priority function and one second priority function, wherein the first priority function receives one or more of the plurality of inputs to determine a first priority function output, and The second priority function receives one or more of the plurality of inputs and the first priority function output to determine a second priority function output. 3 . The method of claim 2 , wherein the one or more inputs received by the first priority function include the microgrid-side voltage measurement and the microgrid-side frequency measurement.

4. The method of claim 3, wherein the first priority function output and the second priority function output are each one of: a voltage or frequency ride-through selection, an unplanned islanding signal, an action dependent on a distribution system operator command, and an action dependent on a user preference.

5. The method of claim 2, wherein the one or more inputs received by the second priority function include one or more of: maintenance status, expected outages, utility grid health indicators, and distribution system operator set points.

6. The method of claim 2, wherein using the state machine to determine the output based on the plurality of inputs further comprises: determining the output based on a third priority function, The third priority function receives one or more of the plurality of inputs and the second priority function output to determine a third priority function output. 7 . The method of claim 6 , wherein the one or more inputs received by the third priority function include one or more of: a user preference and an error handling signal.

8. The method of claim 6, wherein the third priority function output is one of: a voltage or frequency ride-through selection, an unplanned islanding signal, a regulation curve selection, an active power and reactive power set point disable signal, and a load or source management signal for managing a device of the microgrid.

9. The method according to claim 1, further comprising: Measure microgrid side operating parameters; updating the plurality of inputs based on the measured microgrid-side operating parameters; as well as iteratively repeating the steps of the method such that the state machine receives input that is iteratively updated based on the measured microgrid-side operating parameters, The operating parameters include voltage and frequency of the microgrid.

10. The method of claim 9, wherein the operating parameters further include one or more of: active power measured at the point of common coupling, reactive power measured at the point of common coupling, battery state of charge, and microgrid load information.

11. The method of claim 1, wherein the control signal is configured to operate the microgrid in compliance with the standards specified in the Institute of Electrical and Electronics Engineers IEEE 1547 or the Italian Electrical and Electronics Commission CEI 0-16.

12. The method of claim 11, wherein the control signal is configured to comply with IEEE 1547 or CEI 0-16 to operate the microgrid through voltage or through frequency.

13. The method of claim 11, wherein the control signal is configured to island the microgrid if the plurality of inputs include an abnormal voltage signal and an abnormal frequency signal from the microgrid.

14. A non-transitory computer readable medium having processor executable instructions stored thereon, wherein the processor executable instructions, when executed by one or more processors, facilitate execution of a method for monitoring a microgrid, the method comprising: Receive multiple inputs; determining an output based on the plurality of inputs using a state machine; as well as outputting a control signal based on the output, wherein the plurality of inputs include a microgrid-side voltage measurement and a microgrid-side frequency measurement; as well as Wherein the control signal is configured to control the operation of the microgrid at a point of common coupling between the microgrid and a utility grid.

15. A system comprising one or more processors, wherein the one or more processors are configured, alone or in combination, to provide implementation of a method comprising: Receive multiple inputs; determining an output based on the plurality of inputs using a state machine; as well as outputting a control signal based on the output, wherein the plurality of inputs include a microgrid-side voltage measurement and a microgrid-side frequency measurement; as well as Wherein the control signal is configured to control the operation of the microgrid at a point of common coupling between the microgrid and a utility grid.

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