Microgrid system and controller thereof

Abstract

According to the micro-grid system and the controller thereof provided by the invention, when a to-be-removed power value exceeding the power margin of an energy storage system appears in the micro-grid system, the controller removes loads in the removable loads according to the priority of the cost performance and the power, the response time value and the importance of the removable loads; the sum of the power of the cut-off load is greater than or equal to the to-be-cut-off power value. In the application, on the basis of sorting each removable load by only considering the importance of the load traditionally, when the cost performance of each removable load is determined, the response time value index is introduced to represent the time cost of removal, and the matching degree index of the power of the load and the to-be-removed power value is also introduced. The cost performance of each load capable of being cut off is determined according to the three indexes, and the load can be cut off according to the priority of the cost performance, so that the accuracy and timeliness of load cutting off can be improved.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and to a microgrid system and its controller. Background Technology

[0002] Currently, the safe and stable operation of microgrid systems heavily relies on the rapid and precise regulation of controllers to maintain real-time power balance. However, sudden drops in the output power of distributed generation sources, surges in load demand, and limited output power of energy storage systems can all lead to power deficits within the microgrid, causing a frequency drop in the AC bus voltage. When the frequency of the AC bus voltage drops significantly and the power imbalance exceeds the regulation capacity of the power sources and energy storage, it is necessary to disconnect loads from the microgrid to prevent further collapse of the AC bus voltage and maintain stable operation. Therefore, disconnecting loads in a microgrid is the last line of defense for maintaining stable operation when power deficits occur.

[0003] With the increasing penetration of renewable energy and the growing electrification of power systems, microgrid systems are exhibiting problems such as insufficient grid support, small system size, and large fluctuations in power load, making it more difficult to maintain power balance within the microgrid system. Therefore, how to quickly and accurately disconnect loads when the frequency of AC bus voltage in a microgrid system experiences a significant drop is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application provides a microgrid system and its controller to improve the timeliness and accuracy of load shedding in a microgrid system.

[0005] Firstly, this application provides a controller for a microgrid system. The microgrid system includes an AC bus, an energy storage system, a power supply system, and loads. The energy storage system, power supply system, and loads are each connected to the AC bus. Among the multiple loads, those loads that are configured by the user to accept the controller's control adjustments and the on / off state of the AC bus are called switchable loads. The controller is used to: when a power value exceeding the power margin of the energy storage system appears in the microgrid system, based on the power, response time, and importance of the switchable loads, prioritize the switchable loads according to cost-effectiveness, so that the sum of the power of the switchable loads is greater than or equal to the power value to be switched; wherein, the cost-effectiveness is determined by the matching degree between the power of the switchable loads and the power value to be switched, the response time, and the importance.

[0006] In this application, based on the traditional method of ranking loads by only considering their importance, a response time index is introduced to represent the time cost of rescission when determining the cost-effectiveness of each load. A matching index between the load's power and the power to be rescinded is also introduced. The cost-effectiveness of each load is determined according to the above three indices, and the loads to be rescinded are ranked according to the priority of cost-effectiveness. This can improve the accuracy and timeliness of load rescission.

[0007] In this application, to improve the accuracy of load shedding, the controller dynamically calculates the cost-effectiveness of each shedding load based on the power value to be shedding each time (the power value to be shedding is less than or equal to the power value to be shedding in the microgrid system). Specifically, after calculating the cost-effectiveness of each shedding load and selecting the load with the highest cost-effectiveness as the required shedding load, if the total power of the selected load is less than the power value to be shedding, it means that another load needs to be selected from the shedding loads. In this case, the controller can update the power value to be shedding used in the next calculation of the cost-effectiveness of each shedding load, that is, update the power value to be shedding to the power value after removing the total power of the selected loads. This allows the selection of the required shedding load to be more accurate and closer to the power value to be shedding, ensuring that the total power of the multiple selected required shedding loads is closer to the power value to be shedding in the microgrid system.

[0008] In some embodiments of this application, in order to quickly select the required load to be cut off from the available loads, the controller can adopt a multi-stage decision-making mechanism to quickly select the required load to be cut off. For example, the controller can adopt a two-stage screening mechanism to quickly select the required load to be cut off. Specifically, the controller can determine a first cut-off power value based on the power value to be cut off. The first cut-off power value needs to cover a set proportion of the power value to be cut off, that is, the first cut-off power value is M% of the power value to be cut off, where M is greater than 0 and less than 100. The controller first performs an initial screening based on the first cut-off power value, i.e., coarse screening (referred to as coarse screening), and then performs a second screening based on the second cut-off power value, i.e., fine screening (referred to as fine screening). The second cut-off power value is the power value to be cut off minus the total power of the loads selected after coarse screening. Specifically, the controller determines the cost-effectiveness of each available load based on the matching degree between the power of the available load and the first cut-off power value, the response time value, and the importance. Among the available loads, the controller selects the first load according to the priority of cost-effectiveness, so that the sum of the power values ​​of the first loads is greater than or equal to the first cut-off power value. Subsequently, the controller updates the weighting coefficients for matching degree, response time value, and importance in determining the cost-effectiveness of each cut-off load. Based on the updated weighting coefficients, the controller re-determines the cost-effectiveness of each cut-off load according to the matching degree, response time value, and importance of the power of the cut-off load with the second cut-off power value. Among the cut-off loads, the second load is selected according to the priority of the updated cost-effectiveness, so that the sum of the power values ​​of the second loads is greater than or equal to the second cut-off power value.

[0009] In some embodiments of this application, during the fine screening process, i.e., when determining the cost-effectiveness of each cut-off load used to select the second load, the controller can increase the weighting coefficient of the matching degree and decrease the weighting coefficient of the response time value or the weighting coefficient of importance. That is, increasing the weighting of the matching degree with the second cut-off power value during the fine screening process focuses on selecting the second load with a high power matching degree. This helps to reduce the gap between the total power of the selected first and second loads and the power value to be cut off, so that after the load is cut off, the frequency of the AC bus voltage of the microgrid system can be closer to the frequency before a significant frequency drop. Furthermore, while increasing the weighting coefficient of the power matching degree, only the weighting coefficient of the response time value can be decreased, or only the weighting coefficient of importance can be decreased, or both the weighting coefficients of the response time value and importance can be decreased simultaneously. The reduction ratios can be the same or different, and are not limited here.

[0010] In some embodiments of this application, in order to accurately cut off loads whose total power value is closer to the power value to be cut off, so that the frequency of the AC bus voltage of the microgrid system can be closer to the frequency before the significant frequency drop after the load is cut off, after the coarse screening and fine screening processes, a rollback optimization stage can be entered. The controller calculates the sum of the power of the selected first load and second load. If the sum of the power of the first load and the second load is equal to the power value to be cut off, the first load and the second load are directly cut off. If the sum of the power of the first load and the second load is greater than the power value to be cut off, the controller can screen from the first load and the second load to see if there is a redundant load, i.e., a third load, that causes over-cutting of power. If there is a third load, the third load is removed from the first load and the second load so that the sum of the power of the first load and the second load after the removal of the third load is greater than or equal to the power value to be cut off. Finally, the first load and the second load after the removal of the third load are cut off.

[0011] In this application, the controller employs a multi-stage decision-making mechanism. In the coarse screening stage, it quickly selects the first load with high cost-effectiveness; in the fine screening stage, it focuses on selecting the second load with high power matching; and in the backoff optimization stage, it eliminates the third load that may have generated power redundancy in the first two stages. Finally, it determines the loads to be disconnected. The decision-making mechanism emphasizes different aspects in each screening stage, ultimately achieving rapid and accurate load disconnection. This ensures that after load disconnection, the frequency of the microgrid system's AC bus voltage is closer to the frequency before a significant frequency drop.

[0012] In some embodiments of this application, to improve the accuracy of selecting the first load during the coarse screening process, after selecting the first load with the highest cost-effectiveness each time, the controller can iterate the cost-effectiveness of each cut-off load until the total power value of the selected first loads is greater than or equal to the first cut-off power value. Specifically, the controller determines the cost-effectiveness of each cut-off load based on the matching degree between the power of the cut-off load and the first cut-off power value, the response time value, and the importance. After selecting the first load with the highest cost-effectiveness, if the power value of the selected first load is less than the first cut-off power value, it means that a first load still needs to be selected from the cut-off loads. In this case, the controller can update the power value to be cut off used when calculating the cost-effectiveness of each cut-off load next time, that is, update the power value to be cut off to the third cut-off power value. The third cut-off power value is the power value after dividing the power value of the selected first load from the first cut-off power value. Based on the matching degree between the power of the cut-off load and the third cut-off power value, the response time value, and the importance, the cost-effectiveness of each cut-off load after removing the first load is re-determined, and the first load with the highest cost-effectiveness is selected. The above process is repeated until the sum of the power values ​​of the selected first loads is greater than or equal to the first cut-off power value. Before each cost-effectiveness calculation, the power value to be cut off is updated so that the power value to be cut off can be more accurately obtained when selecting the first load each time, ensuring that the total power of the multiple first loads selected in the end is closer to the first cut-off power value.

[0013] In some embodiments of this application, to improve the accuracy of selecting the second load during the screening process, after selecting the second load with the highest cost-effectiveness each time, the controller can iterate the cost-effectiveness of each cut-off load until the total power value of the selected second loads is greater than or equal to the second cut-off power value. Specifically, the controller determines the cost-effectiveness of each cut-off load based on the matching degree between the power of the cut-off load and the second cut-off power value, the response time value, and the importance. After selecting the second load with the highest cost-effectiveness, if the power value of the selected second load is less than the second cut-off power value, it means that a second load still needs to be selected from the cut-off loads. In this case, the controller can update the power value to be cut off used when calculating the cost-effectiveness of each cut-off load next time, that is, update the power value to be cut off to the fourth cut-off power value. The fourth cut-off power value is the power value after subtracting the power value of the selected second load from the second cut-off power value. Based on the matching degree between the power of the cut-off load and the fourth cut-off power value, the response time value, and the importance, the cost-effectiveness of each cut-off load after removing the second load is re-determined, and the second load with the highest cost-effectiveness is selected. The above process is repeated until the sum of the power values ​​of the selected second loads is greater than or equal to the second cut-off power value. Before each cost-effectiveness calculation, the power value to be cut off is updated so that the power value to be cut off can be more accurately obtained when selecting a second load each time, ensuring that the total power of the multiple second loads selected in the end is closer to the second cut-off power value.

[0014] In some embodiments of this application, the AC bus can be connected to the power grid via a switch, and the controller can periodically detect the power at the grid connection point and the switch status of the grid connection point in the microgrid system. When the controller detects that the switch at the grid connection point is open, i.e., a grid connection switch action occurs, it indicates that the microgrid system cannot transfer power to the power grid, which may cause a power imbalance in the microgrid system, requiring calculation of whether a power deficit has occurred in the microgrid system. In specific implementation, whether a power deficit has occurred can be determined based on whether the power at the grid connection point in the previous detection cycle exceeds the power margin of the energy storage system. When the switch at the grid connection point is open and the power at the grid connection point in the previous detection cycle is greater than the power margin of the energy storage system, it indicates that a power deficit has occurred in the microgrid system. In this case, the difference between the power at the grid connection point obtained in the previous detection cycle and the power margin of the energy storage system is used as the power to be cut off.

[0015] In some embodiments of this application, the energy storage system and power supply system in the microgrid system can be directly or indirectly connected to the AC bus via switches. For ease of description, the energy storage system and power supply system directly or indirectly connected to the AC bus via switches are referred to as the first device, i.e., the source-storage device. The controller can periodically detect the switch status between the first device and the AC bus in the microgrid system. When the controller detects that the switch between the first device and the AC bus is open, i.e., a first device tripping event occurs, it indicates that the first device cannot output power to the AC bus, which may cause a power imbalance in the microgrid system, requiring calculation of whether a power deficit has occurred in the microgrid system. When the switch between the first device and the AC bus is open and the output power of the first device in the previous detection cycle is greater than the power margin of the energy storage system, it indicates that a power deficit has occurred in the microgrid system. The difference between the output power of the first device obtained in the previous detection cycle and the power margin of the energy storage system is then used as the power to be cut off.

[0016] In some embodiments of this application, the controller can periodically detect the voltage frequency of the AC bus in the microgrid system. When the controller detects that the absolute value of the deviation between the current AC bus voltage frequency and the voltage frequency of the previous detection cycle is greater than a preset threshold, it indicates that a frequency over-limit event has occurred in the microgrid system, which will lead to a power deficit in the microgrid system. The difference between the product of the absolute value of the deviation and the equivalent droop coefficient of the energy storage system and the power margin of the energy storage system is then used as the power to be cut off. In this application, the preset threshold can be determined based on the ratio of the power margin of the energy storage system to the frequency regulation coefficient, i.e., the equivalent droop coefficient, of the energy storage system.

[0017] In some embodiments of this application, the grid-connected switch operation, the first device tripping event, and the frequency over-limit event described above can all be used as conditions for determining whether the microgrid system meets the requirements for load shedding. The grid-connected switch operation, the first device tripping event, and the frequency over-limit event are periodically identified. When any of these events meets the conditions, it is considered that the microgrid system has a power value exceeding the power margin of the energy storage system that needs to be shedding. Furthermore, the detection period for each event can be consistent; for example, the controller checks the grid-connected switch status, the first device's switching status, and the AC bus frequency every 50ms. Alternatively, the controller can set corresponding detection periods for different events, decoupling the detection periods of each event.

[0018] In other embodiments of this application, some of the events described above, such as grid connection switch operation, first equipment tripping event, and frequency over-limit event, can also be used as conditions for determining whether the microgrid system meets the requirements for load shedding.

[0019] In this application, when the conditions for load shedding are detected, a load shedding flag or alarm can be triggered on the remote interface, and the power value to be shedding can be displayed on the remote interface.

[0020] Secondly, this application provides a microgrid system, comprising: a controller, an AC bus, an energy storage system, a power supply system, and loads as provided in the first aspect of this application; wherein the energy storage system, the power supply system, and the loads are respectively connected to the AC bus. The controller is used to control the connection status of the energy storage system, the power supply system, and the loads to the AC bus. Furthermore, the controller has the capability to acquire the switching status of the grid connection point, the power of the grid connection point, the output power of the important equipment (i.e., the first equipment), the switching status of the first equipment connected to the AC bus, the frequency of the AC bus voltage, and the remaining output power (also known as power margin) that all energy storage systems in the microgrid system can provide, i.e., energy storage backup capacity information. The controller has the capability to issue disconnection commands to disconnectable loads in the microgrid system, causing the disconnected loads to leave the microgrid system, so that the microgrid system can maintain stable operation even when the frequency of the AC bus voltage in the microgrid system drops significantly. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the architecture of a microgrid system;

[0022] Figure 2 A schematic diagram illustrating the process of load shedding by the controller in a microgrid system provided in an embodiment of this application;

[0023] Figure 3 A schematic diagram showing the change in AC bus voltage frequency when the output power of the power source is dated to 300KW in a microgrid system.

[0024] Figure 4 A schematic diagram showing the change in AC bus voltage frequency when the output power of the power source is dated to 470 kW in a microgrid system.

[0025] Figure 5 A schematic diagram illustrating the sequence of load shedding for a microgrid system. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "at least one" refers to one or more, where "multiple" refers to two or more. Therefore, in the embodiments of this invention, "multiple" can also be understood as "at least two". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are only used for distinguishing the descriptive purpose and should not be construed as indicating or implying relative importance or order.

[0027] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components, such as A and B being connected. Alternatively, A can be directly connected to C, and C can be directly connected to B, with A and B connected through C. In some scenarios, "connection" can also be understood as coupling, such as electromagnetic coupling between two inductors. In short, the connection between A and B enables the transmission of electrical energy between A and B.

[0028] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0029] Reference Figure 1 This application provides a microgrid system including: an AC bus, an energy storage system (ESS), a power supply system (PV), a load module (LOAD), and a controller. Figure 1(Not shown in the image). The energy storage system, power supply system, and loads are connected to the AC bus. Loads among the multiple loads that are configured by the user to accept the controller's control and the AC bus's on / off state are called switchable loads. This application does not limit the microgrid system topology and can apply to AC microgrid systems with single-bus, chain, or ring topologies. The controller can be a microgrid central controller (MGCC) or a coordination controller, among other controllers. The controller controls the connection status of the energy storage system, power supply system, and loads to the AC bus. Furthermore, the controller has the ability to acquire the switching status of the grid connection point, the power of the grid connection point, the output power of the important equipment (i.e., the first equipment), the switching status of the first equipment connected to the AC bus, the frequency of the AC bus voltage, and the remaining output power (also known as power margin) available from all energy storage systems in the microgrid system. The controller has the ability to issue disconnection commands to switchable loads in the microgrid system, causing the disconnected loads to leave the microgrid system, thus maintaining the stable operation of the microgrid system even when the frequency of the AC bus voltage drops significantly.

[0030] The controller provided in this application embodiment is specifically used to: when a power value to be cut off exceeds the power margin of the energy storage system in a microgrid system, cut off loads in the cut-off loads according to the power, response time value and importance of the cut-off loads, so that the sum of the power of the cut-off loads is greater than or equal to the power value to be cut off; wherein, the cost-effectiveness is determined by the matching degree between the power of the cut-off loads and the power value to be cut off, the response time value and the importance.

[0031] In this application, based on the traditional method of ranking loads by only considering their importance, a response time index is introduced to represent the time cost of rescission when determining the cost-effectiveness of each load. A matching index between the load's power and the power to be rescinded is also introduced. The cost-effectiveness of each load is determined according to the above three indices, and the loads to be rescinded are ranked according to the priority of cost-effectiveness. This can improve the accuracy and timeliness of load rescission.

[0032] In practical implementation, the controller can calculate the cost-effectiveness of each shuntable load according to the following formula:

[0033] V i =ω p M p (P i ,P re )+ω c M c (W i )+ω t M t (Ti )

[0034] Among them, V i For the cost-effectiveness of the i-th removable load, P i For the power of the i-th switchable load, W i For the importance of the i-th removable load, T i Let P be the response time value of the i-th detachable load. re The power value for preparing for resection. M p ω is an evaluation function for the matching degree between the power of the load that can be cut off and the power value to be cut off. p M is the weighting coefficient for the matching degree. c ω is the evaluation function for the importance of removable load. c M is the weighting coefficient for importance. t ω is the evaluation function for the shearable load response time. t This is the weighting coefficient for response time.

[0035] Specifically, the evaluation function M evaluates the degree of matching between the power of the load that can be cut off and the power value to be cut off. p It can be set as a piecewise dynamic matching function, which encourages the priority selection of switchable loads with power close to the power to be cut off, that is, the power P of the i-th switchable load. i The closer to the power value P to be cut re The higher the matching score of the i-th reversible power, the better. The evaluation function M for the importance of reversible load... c An exponential function model can be used to encourage the priority removal of ordinary removable loads; that is, the higher the importance of the i-th removable load, the lower its importance score. The evaluation function for the removable load response time is M. t A hyperbolic model can be used to encourage the priority selection of removable loads with low response time costs. That is, the longer the response time of the i-th removable load, the lower the response time score of the i-th removable load. Furthermore, additional penalty evaluations can be imposed on removable loads whose response time exceeds twice the time threshold.

[0036] In this application, to improve the accuracy of load shedding, the controller dynamically calculates the cost-effectiveness of each shedding load based on the power value to be shedding each time (the power value to be shedding is less than or equal to the power value to be shedding in the microgrid system). Specifically, after the controller calculates the cost-effectiveness of each shedding load according to the above formula and selects the load with the highest cost-effectiveness as the required shedding load, if the total power of the selected loads is less than the power value to be shedding, it means that a load needs to be selected from the shedding loads as the required shedding load. In this case, the controller can update the power value P to be shedding used in the next calculation of the cost-effectiveness of each shedding load. re The power value P that is about to be removedre The updated power value is the power value after removing the total power of the selected loads. This allows for a more precise approximation of the power value to be cut off each time a load to be selected is chosen, ensuring that the total power of the finally selected loads to be cut off is closer to the power value to be cut off in the microgrid system. For ease of understanding, an example is given: For instance, if the power value to be cut off in the microgrid system exceeds the power margin of the energy storage system by 10 kW, the power value to be cut off is P... re Calculate the cost-effectiveness of each cut-off load for a 10kW load, and select load 1 with the highest cost-effectiveness. If the power of load 1 is 6kW, which is less than the cut-off power value of 10kW, then it is necessary to continue selecting loads from the cut-off loads and set the power value P to be cut off. re Updated to 10KW - 6KW = 4KW, based on the power value P to be cut. re Recalculate the cost-effectiveness of each load that can be cut off for 4KW, and select load 3 with the highest cost-effectiveness. If the power of load 3 is 4KW, and the sum of the power of load 1 and load 3 is equal to the power to be cut off, which is 10KW, then load 1 and load 3 are cut off.

[0037] In some embodiments of this application, in order to quickly select the required load to be cut off from the available loads, the controller can adopt a multi-stage decision-making mechanism to quickly select the required load to be cut off. For example, the controller can adopt a two-stage screening mechanism to quickly select the required load to be cut off. Specifically, the controller can determine a first cut-off power value based on the power value to be cut off. The first cut-off power value needs to cover a set percentage of the power value to be cut off, that is, the first cut-off power value is M% of the power value to be cut off, where M is greater than 0 and less than 100. In order to achieve rapid screening of cost-effective loads, the set percentage of the first cut-off power value can be set to be greater than 70%. The controller first performs an initial screening based on the first cut-off power value, i.e., coarse screening (referred to as coarse screening), and then performs a second screening based on the second cut-off power value, i.e., fine screening (referred to as fine screening). The second cut-off power value is the power value to be cut off minus the total power of the loads selected after coarse screening. Specifically, the controller determines the cost-effectiveness of each available load based on the matching degree between the power of the available load and the first cut-off power value, the response time value, and the importance. Among the available loads, the controller selects the first load according to the priority of cost-effectiveness, so that the sum of the power values ​​of the first loads is greater than or equal to the first cut-off power value. Subsequently, the controller updates the weighting coefficient ω of the matching degree used to determine the cost-effectiveness of each shelvable load. p The weighting coefficient ω of the response time value t And the weighting coefficient ω of importance cBased on the updated weighting coefficients, and considering the matching degree between the power of the available loads and the second cut-off power value, response time, and importance, the cost-effectiveness of each available load is re-determined. Among the available loads, the second load is selected according to the updated cost-effectiveness priority, ensuring that the sum of the power values ​​of the second loads is greater than or equal to the second cut-off power value. For ease of understanding, an example is given: For instance, if the power to be cut off in a microgrid system exceeds the power margin of the energy storage system by 100 kW, the first cut-off power value is 70% of the power to be cut off, i.e., 70 kW. In the coarse screening process, the power value P to be cut off is... re Calculate the cost-effectiveness of each shuntable load for 70kW and select the first load with the highest cost-effectiveness. If the power of the first load (70kW) equals the power to be shunted (70kW), a fine screening process is performed. The second shunting power value is set to 30kW, which is the power value to be shunted (100kW) minus the power value of the first load (70kW). Furthermore, the weighting coefficients used to determine the cost-effectiveness, including the matching degree, response time, and importance, are updated according to the power value P to be shunted. re Recalculate the cost-effectiveness of each removable load for 30KW, select the second load with the highest cost-effectiveness, and if the power of the second load is 30KW, which is equal to the second removable power value of 30KW, the fine screening process is completed.

[0038] In some embodiments of this application, during the fine screening process, i.e., when determining the cost-effectiveness of each cut-off load used to select the second load, the controller may increase the weighting coefficient ω of the matching degree. p And reduce the weighting coefficient ω of the response time value t Or the weighting coefficient ω of importance c This involves increasing the weighting of the matching degree with the second power cut-off value during the fine screening process, focusing on selecting the second load with a high power matching degree. This helps reduce the gap between the total power of the selected first and second loads and the power value to be cut off, allowing the frequency of the microgrid system's AC bus voltage to be closer to the frequency before a significant frequency drop after the load is cut off. Furthermore, increasing the weighting coefficient ω of the power matching degree... p At the same time, the weighting coefficient ω of the response time value can be reduced only. t Or, simply reduce the weighting coefficient ω of importance. c Alternatively, simultaneously reduce the weighting coefficient ω of the response time value. t And the weighting coefficient ω of importance c Furthermore, the reduction ratios of the two can be the same or different, and this is not limited here. For ease of understanding, an example is given: For instance, in the coarse screening process, the weighting coefficient ω for calculating the power matching degree of cost-effectiveness... p The weighting coefficient ω for the response time value is 0.4. t And the weighting coefficient ω of importance cThe values ​​are 0.3 respectively; during the fine screening process, the weighting coefficient ω of the power matching degree can be adjusted. p Adjusted to 0.6, the weighting coefficient ω of the response time value t And the weighting coefficient ω of importance c They were adjusted to 0.2 respectively.

[0039] In some embodiments of this application, in order to accurately cut off loads whose total power value is closer to the power value to be cut off, so that the frequency of the AC bus voltage of the microgrid system can be closer to the frequency before the significant frequency drop after the load is cut off, after the coarse screening and fine screening processes, a backoff optimization stage can be entered. The controller calculates the sum of the power of the selected first load and second load. If the sum of the power of the first load and the second load is equal to the power value to be cut off, the first load and the second load are directly cut off. If the sum of the power of the first load and the second load is greater than the power value to be cut off, the controller can screen the first load and the second load to see if there is a redundant load, i.e., a third load, that causes over-cutting of power. If a third load exists, the third load is removed from the first load and the second load so that the sum of the power of the first load and the second load after the removal of the third load is greater than or equal to the power value to be cut off. Finally, the first load and the second load after the removal of the third load are cut off. For ease of understanding, an example is given: For example, when the power value to be cut off in the microgrid system exceeds the power margin of the energy storage system by 100KW, the first power cut-off value is 70% of the power value to be cut off, i.e., 70KW. After coarse and fine screening processes, the total power of the first and second loads is 130KW, of which the power of the third load is 30KW. After removing the third load, the sum of the power of the first and second loads is 100KW, which is equal to the power value to be removed.

[0040] In this application, the controller employs a multi-stage decision-making mechanism. In the coarse screening stage, it quickly selects the first load with high cost-effectiveness; in the fine screening stage, it focuses on selecting the second load with high power matching; and in the backoff optimization stage, it eliminates the third load that may have generated power redundancy in the first two stages. Finally, it determines the loads to be disconnected. The decision-making mechanism emphasizes different aspects in each screening stage, ultimately achieving rapid and accurate load disconnection. This ensures that after load disconnection, the frequency of the microgrid system's AC bus voltage is closer to the frequency before a significant frequency drop.

[0041] In some embodiments of this application, to improve the accuracy of selecting the first load during the coarse screening process, after selecting the first load with the highest cost-effectiveness each time, the controller can iterate the cost-effectiveness of each cut-off load until the total power value of the selected first loads is greater than or equal to the first cut-off power value. Specifically, the controller determines the cost-effectiveness of each cut-off load based on the matching degree between the power of the cut-off load and the first cut-off power value, the response time value, and the importance. After selecting the first load with the highest cost-effectiveness, if the power value of the selected first load is less than the first cut-off power value, it indicates that a first load still needs to be selected from the cut-off loads. In this case, the controller can update the power value P to be cut off used in the next calculation of the cost-effectiveness of each cut-off load. re The power value P that is about to be removed re The power is updated to the third cutoff power value, which is the power value after subtracting the power value of the selected first load from the first cutoff power value. Based on the matching degree between the power of the cutoff loads and the third cutoff power value, the response time, and importance, the cost-effectiveness of each cutoff load after removing the first load is re-determined, and the first load with the highest cost-effectiveness is selected. This process is repeated until the sum of the power values ​​of the selected first loads is greater than or equal to the first cutoff power value. Before each cost-effectiveness calculation, the power value to be cut off is updated so that the power value to be cut off is more accurately approximated each time the first load is selected, ensuring that the total power of the finally selected first loads is closer to the first cutoff power value. For ease of understanding, an example is given: For instance, if the power value to be cut off in a microgrid system exceeds the power margin of the energy storage system by 100kW, the first cutoff power value is 70% of the power value to be cut off, i.e., 70kW. In the coarse screening process, according to the power value to be cut off P... re Calculate the cost-effectiveness of each load that can be cut off for a 70kW load, and select the first load with the highest cost-effectiveness. If the power of the first load is 40kW, which is less than the power value P to be cut off. re If the load is 70kW, then the first load needs to be selected from the available loads, and the power value P to be cut off should be set. re Updated to 70KW - 40KW = 30KW, based on the power value P to be cut off. re Recalculate the cost-effectiveness of each removable load for 30KW, and select the first load with the highest cost-effectiveness. If the power of the selected first load is 30KW, the sum of the power of the two selected first loads is equal to the first removable power value of 70KW, and the coarse screening process is completed.

[0042] In some embodiments of this application, to improve the accuracy of selecting the second load during the screening process, after selecting the second load with the highest cost-effectiveness each time, the controller can iterate the cost-effectiveness of each cut-off load until the total power value of the selected second loads is greater than or equal to the second cut-off power value. Specifically, the controller determines the cost-effectiveness of each cut-off load based on the matching degree between the power of the cut-off load and the second cut-off power value, the response time value, and the importance. After selecting the second load with the highest cost-effectiveness, if the power value of the selected second load is less than the second cut-off power value, it indicates that a second load still needs to be selected from the cut-off loads. In this case, the controller can update the power value P to be cut off used in the next calculation of the cost-effectiveness of each cut-off load. re The power value P that is about to be removed re The power value is updated to the fourth cutoff power value, which is the power value after subtracting the power value of the selected second load from the second cutoff power value. Based on the matching degree between the power of the cutoff loads and the fourth cutoff power value, the response time, and importance, the cost-effectiveness of each cutoff load after removing the second load is re-determined, and the second load with the highest cost-effectiveness is selected. This process is repeated until the sum of the power values ​​of the selected second loads is greater than or equal to the second cutoff power value. Before each cost-effectiveness calculation, the power value to be cut off is updated so that the power value to be cut off is more accurately approximated each time a second load is selected, ensuring that the total power of the finally selected multiple second loads is closer to the second cutoff power value. For ease of understanding, an example is given: For instance, if the power value to be cut off in a microgrid system exceeds the power margin of the energy storage system by 100 kW, the first cutoff power value is 70% of the power value to be cut off, i.e., 70 kW. After the coarse screening process, the second cutoff power value is determined to be 30 kW. In the fine screening process, the power value to be cut off is P... re Calculate the cost-effectiveness of each load that can be cut off for a 30kW load, and select the second load with the highest cost-effectiveness. If the power of the second load is 20kW, which is less than the power value P to be cut off. re If the load is 30kW, then a second load needs to be selected from the available loads, and the power value P to be cut off should be set. re Updated to 30KW - 20KW = 10KW, based on the power value P to be cut off. re Recalculate the cost-effectiveness of each removable load for 10KW, and select the second load with the highest cost-effectiveness. If the power of the selected second load is 10KW, the sum of the power of the two selected second loads is equal to the second removable power value of 30KW, and the fine screening process is completed.

[0043] In some embodiments of this application, the AC bus can be connected to the power grid via a switch, and the controller can periodically detect the power at the grid connection point and the switch status of the grid connection point in the microgrid system. When the controller detects that the switch at the grid connection point is open, i.e., a grid connection switch action occurs, it indicates that the microgrid system cannot transfer power to the power grid, which may cause a power imbalance in the microgrid system, requiring calculation of whether a power deficit has occurred in the microgrid system. In specific implementation, the power P at the grid connection point in the previous detection cycle can be used as a reference. pcc_last Does it exceed the power margin P of the energy storage system? ES_lim2 To determine if a power deficit has occurred. The power P at the grid connection point is calculated when the switch at the grid connection point is open and in the previous detection cycle. pcc_last Greater than the power margin P of the energy storage system ES_lim2 If this indicates a power deficit in the microgrid system, the power P at the grid connection point obtained in the previous detection cycle will be used. pcc_last With the power margin P of the energy storage system ES_lim2 The difference is taken as the power value P to be removed. cut That is, P cut =P pcc_last -P ES_lim2 .

[0044] In some embodiments of this application, the energy storage system and power supply system in the microgrid system can be directly or indirectly connected to the AC bus via switches. For ease of description, the energy storage system and power supply system directly or indirectly connected to the AC bus via switches are referred to as the first device, i.e., the source-storage device. The controller can periodically detect the switch status between the first device and the AC bus in the microgrid system. When the controller detects that the switch between the first device and the AC bus is open, i.e., a first device tripping event occurs, it indicates that the first device cannot output power to the AC bus, which may cause a power imbalance in the microgrid system, requiring calculation of whether a power deficit has occurred in the microgrid system. The first device tripping event occurs when the switch between the first device and the AC bus is open and the first device's output power P in the previous detection cycle... i Greater than the power margin P of the energy storage system ES_lim2 If this indicates a power deficit in the microgrid system, the output power P of the first device obtained in the previous detection cycle will be used. i With the power margin P of the energy storage system ES_lim2 The difference is taken as the power value P to be removed. cut That is, P cut =P i -P ES_lim2 .

[0045] In some embodiments of this application, the controller can periodically detect the voltage frequency of the AC bus in the microgrid system. The controller will detect when the absolute value of the deviation between the current AC bus voltage frequency and the voltage frequency of the previous detection cycle is greater than a preset threshold Δf. max When a frequency over-limit event occurs in the microgrid system, it indicates that a power deficit will occur in the microgrid system. Therefore, the absolute value of the deviation Δf is compared with the equivalent droop coefficient k of the energy storage system. f The product of the energy storage system and the power margin P ES_lim2 The difference is taken as the power value P to be removed. cut That is, P cut =k f Δf-P ES_lim2 In this application, a preset threshold Δf is used. max Based on the power margin P of the energy storage system ES_lim2 The frequency regulation coefficient of the energy storage system, i.e., the equivalent droop coefficient k f The ratio is determined, i.e., Δf max =P ES_lim2 / k f .

[0046] In some embodiments of this application, the grid-connected switch operation, the first device tripping event, and the frequency over-limit event described above can all be used as conditions for determining whether the microgrid system meets the requirements for load shedding. The grid-connected switch operation, the first device tripping event, and the frequency over-limit event are periodically identified. When any of these events meets the conditions, it is considered that the microgrid system has a power value exceeding the power margin of the energy storage system that needs to be shedding. Furthermore, the detection period for each event can be consistent; for example, the controller checks the grid-connected switch status, the first device's switching status, and the AC bus frequency every 50ms. Alternatively, the controller can set corresponding detection periods for different events, decoupling the detection periods of each event.

[0047] In other embodiments of this application, some of the events described above, such as grid connection switch operation, first equipment tripping event, and frequency over-limit event, can also be used as conditions for determining whether the microgrid system meets the requirements for load shedding.

[0048] In this application, when the conditions for load shedding are detected, a load shedding flag or alarm can be triggered on the remote interface, and the power value to be shedding can be displayed on the remote interface.

[0049] Reference Figure 2 The specific process by which the controller of the microgrid system provided in this application performs multi-stage intelligent load shedding includes the following steps:

[0050] S101 Periodically detect parameters such as power and switch status at the grid connection point, output power and switch status of the first device, voltage and frequency of the AC bus, and power margin of the energy storage system.

[0051] S102. Determine whether the microgrid system meets the conditions for load shedding.

[0052] Specifically, the power P of the grid connection point can be determined by the switch being open at the grid connection point and in the previous detection cycle. pcc_last Greater than the power margin P of the energy storage system ES_lim2 When this occurs, it indicates that the microgrid system has a power deficit, confirming that the conditions for load shedding are met, and the power P at the grid connection point obtained in the previous detection cycle is used as the reference. pcc_last With the power margin P of the energy storage system ES_lim2 The difference is taken as the power value P to be removed. cut That is, P cut =P pcc_last -P ES_lim2 .

[0053] Specifically, the switch between the first device and the AC bus can be disconnected, and the output power P of the first device in the previous detection cycle can be... i Greater than the power margin P of the energy storage system ES_lim2 When this occurs, it indicates that the microgrid system has a power deficit, confirming that the conditions for load shedding are met, and the output power P of the first device obtained in the previous detection cycle is used as the reference. i With the power margin P of the energy storage system ES_lim2 The difference is taken as the power value P to be removed. cut That is, P cut =P i -P ES_lim2 .

[0054] Specifically, this can be achieved when the absolute value of the deviation between the voltage frequency and the rated frequency of the AC bus exceeds a preset threshold Δf. max This indicates that a frequency over-limit event has occurred in the microgrid system, which will lead to a power deficit in the microgrid system. It determines that the conditions for load shedding are met, and compares the absolute value of the deviation Δf with the equivalent droop coefficient k of the energy storage system. f The product of the energy storage system and the power margin P ES_lim2 The difference is taken as the power value P to be removed. cut That is, P cut =k f Δf-P ES_lim2 .

[0055] S103. Based on the matching degree between the power of the load that can be cut off and the first cut-off power value, the response time value, and the importance, dynamically calculate the cost-effectiveness of each load that can be cut off, quickly screen the first load with high cost-effectiveness, and iterate the cost-effectiveness of each load that can be cut off based on the first cut-off power value remaining after removing the power of the screened first load, until the sum of the power values ​​of the screened first loads is greater than or equal to the first cut-off power value.

[0056] S104. Update the weight coefficients of matching degree, response time value and importance in the cost-effectiveness calculation.

[0057] S105. Based on the matching degree between the power of the switchable load and the second cut-off power value, the response time value and the importance, dynamically calculate the cost-effectiveness of each switchable load, quickly screen the second load with high cost-effectiveness, and iterate the cost-effectiveness of each switchable load based on the second cut-off power value remaining after removing the power of the screened second load, until the sum of the power values ​​of the screened second loads is greater than or equal to the second cut-off power value.

[0058] S106. Check whether the total power value of the first and second loads selected by cumulative screening is equal to the power value to be cut off. If yes, proceed to step S107; if no, proceed to step S108.

[0059] S107, Directly remove the first and second loads.

[0060] S108. Screen from the first load and the second load to see if there is a third load that would cause power over-cutting. If yes, proceed to step S109; otherwise, proceed to step S107.

[0061] S109. Remove the third load from the first load and the second load, and disconnect the first load and the second load after the removal of the third load.

[0062] Reference Figure 3 and Figure 4In a microgrid system, with power output derating of 300kW and 470kW respectively, the multi-stage intelligent load shedding method provided in this application is used. The changes in AC bus voltage frequency are compared with those achieved using existing load shedding methods and without load shedding. Existing technology 1 shedding loads based on a frequency threshold and through multiple rounds of load reduction, while existing technology 2 uses a static priority ranking method based on load importance to shedding loads. The comparison shows that the multi-stage intelligent load shedding method provided in this application can effectively suppress AC bus voltage frequency drops and quickly maintain the stability of the microgrid system, i.e., the time T0 required to maintain voltage frequency stability is the shortest, and the system response speed is faster. Furthermore, the multi-stage intelligent load shedding method provided in this application allows for more precise load shedding, enabling the AC bus voltage frequency of the microgrid system to be closer to the frequency before a significant frequency drop after load shedding.

[0063] Reference Figure 5 In a microgrid system, when the power output derating is 300kW and 470kW respectively, the multi-stage intelligent load shedding method provided in this application is used for operation, compared with the prior art 2 which uses a static priority ranking method based on load importance for load shedding. The comparison shows that prior art 2 selects loads for shedding in a fixed order. For example, when the power derating is 300kW, the order of load shedding is load 5 → load 4 → load 3, and when the power derating is 470kW, load 2 is added to the load shedding list. However, in the multi-stage intelligent load shedding method provided in this application, the first and second loads selected do not have a fixed order.

[0064] The microgrid system and controller provided in this application, when a power value exceeding the power margin of the energy storage system appears in the microgrid system, the controller prioritizes the loads that can be cut off based on their power, response time, and importance, according to cost-effectiveness, so that the sum of the power of the cut-off loads is greater than or equal to the power value to be cut off. In this application, building upon the traditional method of prioritizing loads based solely on their importance, a response time index is introduced to represent the time cost of cutting off loads when determining their cost-effectiveness. A matching index between the load's power and the power value to be cut off is also introduced. By determining the cost-effectiveness of each load according to these three indices and prioritizing them based on cost-effectiveness, the accuracy and timeliness of load cutting can be improved.

[0065] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A controller of a microgrid system, characterized by, The micro-grid system comprises an AC bus, an energy storage system, a power supply system and a load, and the energy storage system, the power supply system and the load are connected with the AC bus respectively; The controller is configured to: when the to-be-cut power value exceeding the power margin of the energy storage system occurs in the micro-grid system, according to the power, response time value and importance of the cuttable load in the load, cut the load in the cuttable load according to the priority of the cost performance ratio, so that the sum of the power of the cut load is greater than or equal to the to-be-cut power value; wherein the cost performance ratio is determined by the matching degree of the power of the cuttable load and the to-be-cut power value, the response time value and the importance.

2. The controller of claim 1, wherein, The controller is specifically configured to: determine the cost performance ratio of each cuttable load according to the matching degree of the power of the cuttable load and the first cut power value, the response time value and the importance, and select a first load in the cuttable load according to the priority of the cost performance ratio, so that the sum of the power values of the first load is greater than or equal to the first cut power value, and the first cut power value is less than the to-be-cut power value; update the weight coefficients for determining the matching degree, the response time value and the importance in the cost performance ratio of each cuttable load respectively, and re-determine the cost performance ratio of each cuttable load according to the matching degree of the power of the cuttable load and the second cut power value, the response time value and the importance according to the updated weight coefficients, and select a second load in the cuttable load according to the priority of the updated cost performance ratio, so that the sum of the power values of the second load is greater than or equal to the second cut power value; the second cut power value is the power value after the first cut power value is removed from the to-be-cut power value.

3. The controller of claim 2, wherein, The controller is further configured to: when determining the cost performance ratio of each cuttable load for selecting the second load, increase the weight coefficient of the matching degree, and decrease the weight coefficient of the response time value or the importance.

4. The controller of claim 2, wherein, The controller is specifically configured to: when the sum of the power of the first load and the second load is greater than the to-be-cut power value, remove a third load from the first load and the second load, so that the sum of the power of the first load and the second load after removing the third load is greater than or equal to the to-be-cut power value.

5. The controller of claim 2, wherein, The controller is specifically configured to: determine the cost performance ratio of each cuttable load according to the matching degree of the power of the cuttable load and the first cut power value, the response time value and the importance, and select the first load with the highest cost performance ratio; when the power value of the selected first load is less than the first cut power value, re-determine the cost performance ratio of each cuttable load after removing the first load according to the matching degree of the power of the cuttable load and the third cut power value, the response time value and the importance, and select the first load with the highest cost performance ratio, until the sum of the power values of the selected first load is greater than or equal to the first cut power value; wherein the third cut power value is the power value after the first cut power value is removed from the power value of the selected first load.

6. The controller of claim 2, wherein, The controller is specifically configured to: According to the matching degree, response time value and importance of the power of each of the removable loads and the second cut-off power value, the cost performance of each of the removable loads is determined, and the second load with the highest cost performance is selected; When the power value of the selected second load is less than the second cut-off power value, according to the matching degree, response time value and importance of the power of each of the removable loads and the fourth cut-off power value, the cost performance of each of the removable loads after the first load and the second load are removed is re-determined, and the second load with the highest cost performance is cut off until the sum of the power values of the selected first load and second load is greater than or equal to the to-be-cut-off power value; wherein the fourth cut-off power value is the power value after the power value of the selected second load is removed from the second cut-off power value.

7. The controller of any one of claims 1-6, wherein, The controller is further configured to: periodically detect the power of the point of common coupling and the switching state of the point of common coupling in the micro-grid system; when the switching of the point of common coupling is off and the power of the point of common coupling in the last detection cycle is greater than the power margin of the energy storage system, the difference between the power of the point of common coupling in the last detection cycle and the power margin of the energy storage system is taken as the to-be-cut-off power value.

8. The controller of any one of claims 1-6, wherein, The controller is further configured to: periodically detect the output power of the first device and the switching state between the first device and the AC bus in the micro-grid system; the first device includes the power supply system and the energy storage system; when the switching between the first device and the AC bus is off and the output power of the first device in the last detection cycle is greater than the power margin of the energy storage system, the difference between the output power of the first device in the last detection cycle and the power margin of the energy storage system is taken as the to-be-cut-off power value.

9. The controller of any one of claims 1-6, wherein, The controller is further configured to: periodically detect the voltage frequency of the AC bus in the micro-grid system; when the absolute value of the deviation between the voltage frequency of the AC bus at the current moment and the voltage frequency at the last detection cycle is greater than a preset threshold, the difference between the product of the absolute value of the deviation and the equivalent droop coefficient of the energy storage system and the power margin of the energy storage system is taken as the to-be-cut-off power value.

10. A microgrid system, characterized by, The micro-grid system comprises: the controller according to any one of claims 1-9, an AC bus, an energy storage system, a power supply system and a load; wherein the energy storage system, the power supply system and the load are connected with the AC bus respectively; The controller is configured to control the connection state of the energy storage system, the power supply system and the load with the AC bus respectively.

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