Grid power cooperative control method of hybrid energy storage system based on emergency working condition

Abstract

The application belongs to the technical field of hybrid energy storage collaborative control, and specifically discloses a hybrid energy storage system power grid power collaborative control method based on emergency working conditions. By dividing the response process into a first frequency modulation stage, a second frequency modulation stage and a third frequency modulation stage when the power grid power enters an emergency working condition, and setting a dominant energy storage type according to the characteristics of each stage, the adaptive coupling of the energy storage type advantage and the response stage is realized, which helps to improve the regulation and control efficiency. At the same time, by obtaining the state of charge, geographical position and available power of all energy storage units of different energy storage types, an energy storage unit feature set is constructed. Thus, the dominant unit and the following unit are selected from the energy storage unit feature set according to the dominant energy storage type of each stage, an adaptive coordination mechanism within the same type of energy storage cluster in each stage can be established, the optimal allocation of the power instruction in the cluster is realized, and the overall cycle life of the energy storage system is effectively prolonged.

Description

Technical Field

[0001] This invention belongs to the field of hybrid energy storage collaborative control technology, and specifically discloses a method for grid power collaborative control of hybrid energy storage systems based on emergency operating conditions. Background Technology

[0002] When generator sets fail and trip or the output of new energy sources drops sharply during grid operation, it can lead to an instantaneous power shortage on the generation side, which in turn causes a sharp drop in grid frequency. Under such emergency conditions, hybrid energy storage systems that integrate flywheels, batteries and molten salts become a solution for grid power support due to the complementarity of the media. Given that different energy storage media have different characteristics, it is necessary to fully release the differentiated advantages of various energy storage media through coordinated control when supporting grid power.

[0003] Various hybrid energy storage coordinated control schemes have been proposed in the prior art. For example, Chinese Patent Publication No. CN121216513A discloses a primary and secondary frequency regulation coordinated control system for hybrid energy storage coupled with wind turbine generators. This system obtains the grid frequency deviation and frequency change rate through a state sensing module and synthesizes the total power demand including inertial response, primary frequency regulation, and secondary frequency regulation. It adopts a dynamic weight allocation strategy based on S-shaped nonlinear function to generate dynamic adjustment weights and decouple the total power demand into reference power commands for power-type energy storage and energy-type energy storage.

[0004] Although the above schemes have achieved a smooth transition and energy relay between different types of energy storage to a certain extent, they still have the following shortcomings: First, the above schemes enable power-type and energy-type energy storage to participate in parallel at all times, and only adjust the output ratio through dynamic weighting. However, the grid frequency drop process caused by actual grid faults has obvious phased characteristics. The requirements for energy storage response speed and sustainability vary at different stages. The unified parallel weighted control strategy cannot accurately match the most suitable energy storage medium as the dominant one for a specific stage, resulting in a decrease in regulation efficiency.

[0005] Second, existing solutions mainly focus on macroscopic power allocation for energy storage types, ignoring the fact that in actual engineering, the same type of energy storage often consists of multiple geographically dispersed independent units with different states of charge connected in parallel. Due to the lack of a unit coordination mechanism within the type, existing technologies are prone to overloading some units while leaving others idle when executing power commands, thus limiting the overall output capacity of the cluster. Summary of the Invention

[0006] To solve the above-mentioned technical problems, or at least partially solve them, the present invention provides a method for coordinated grid power control of a hybrid energy storage system based on emergency operating conditions.

[0007] The objective of this invention can be achieved through the following technical solution: a grid power coordinated control method for a hybrid energy storage system based on emergency operating conditions, comprising: determining to enter an emergency operating condition when the detected grid frequency is lower than the lower limit of the normal range.

[0008] Obtain the state of charge, geographical location, and available power of all flywheel, battery, and molten salt energy storage units to construct a feature set of energy storage units.

[0009] The emergency response process is divided into three stages: the first frequency regulation stage, the second frequency regulation stage, and the third frequency regulation stage. Each stage is dominated by flywheel energy storage, battery energy storage, and molten salt thermal energy storage, respectively.

[0010] In each stage, dominant and follower units are selected from the energy storage unit feature set according to the dominant energy storage type of that stage, and reserve units are pre-selected for subsequent stages.

[0011] The system controls the coordinated output power of the leading and following units in the current stage, and determines whether other types of energy storage need to intervene based on the real-time status. When intervention is required, the system selects the appropriate unit to intervene and output power.

[0012] When a decline in the state of charge of the dominant unit is detected at the current stage, which requires triggering a change of dominance, a new dominant unit is selected from the same type of energy storage unit.

[0013] The process continues through each stage until the power grid frequency returns to normal, at which point the emergency condition is lifted.

[0014] Combining all the above technical solutions, the positive effects of this invention are as follows: 1. By dividing the response process of the power grid emergency condition into a first frequency regulation stage, a second frequency regulation stage, and a third frequency regulation stage, and setting the dominant energy storage type according to the characteristics of each stage, this invention achieves adaptive matching between the advantages of energy storage types and the response stage, significantly improving the hierarchical response capability to power grid frequency disturbances. To a certain extent, it avoids the ineffective occupation of high-cost power resources and the delay in the intervention of energy resources, which helps to improve the regulation efficiency.

[0015] 2. This invention constructs a feature set of energy storage units by acquiring the state of charge, geographical location, and available power of all energy storage units of different energy storage types. Thus, at each stage, the dominant energy storage type of that stage is selected from the feature set of energy storage units to select the leading and following units. This enables the establishment of an adaptive coordination mechanism within the energy storage cluster of the same type within each stage, achieving optimal allocation of power commands within the cluster. This avoids the unbalanced phenomenon of some units being idle while others are overworked, effectively improving the overall output capacity of the energy storage system.

[0016] 3. When the present invention uses the dominant unit and follower unit of the dominant energy storage type to provide power support at each stage, it selects the adaptation unit of other energy storage types to intervene in the power output according to the real-time status to provide incremental support. The instantaneous filling of cross-types eliminates the power support blind spot to a certain extent and ensures the continuity and sufficiency of power support in emergency conditions. Attached Figure Description

[0017] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0018] Figure 1 This is a diagram illustrating the implementation steps of the method of the present invention.

[0019] Figure 2 This is a flowchart illustrating the process of selecting dominant and follower units from the energy storage unit feature set at each stage of the present invention, based on the dominant energy storage type at that stage.

[0020] Figure 3 This is a flowchart illustrating the implementation of controlling the coordinated output power of the leading unit and the following unit in the current stage in this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See Figure 1 As shown, the present invention proposes a grid power coordinated control method for hybrid energy storage systems based on emergency conditions, including: S1, when the detected grid frequency is lower than the lower limit of the normal range, it is determined to enter an emergency condition.

[0023] In power grid operation, when sudden disturbances occur, such as the failure and tripping of large-capacity generator units or a precipitous drop in the output of new energy clusters, the instantaneous output power on the generation side will decrease sharply, resulting in a severe shortage of active power in the system. This will lead to an abnormal state in which the power grid frequency drops sharply and exceeds the lower limit of the normal range. The normal range of the power grid frequency can be defined according to national standards. If such emergency conditions are not quickly intervened, the continuous drop in frequency can easily lead to large-scale disconnection of generator units from the grid, ultimately causing the power grid frequency to collapse.

[0024] In responding to grid emergencies, it is often necessary to utilize other energy storage media to support grid power. Commonly used energy storage media include flywheels, batteries, and molten salt thermal energy storage. However, each energy storage medium has different characteristics. Flywheel energy storage is a physical energy storage technology based on the kinetic energy storage of a high-speed rotating body, featuring high response speed and extremely high power density, but relatively low energy density and short continuous discharge time. Battery energy storage is an electrochemical energy storage technology that combines high power density with medium energy density. Molten salt thermal energy storage is an energy storage technology based on thermal energy storage and thermodynamic cycle power generation, featuring ultra-high energy density and long-term continuous discharge capability, but relatively slow response speed. Relying solely on a single type of energy storage medium for power support often fails to simultaneously meet the dual requirements of extremely fast response and long-term continuous discharge. Therefore, hybrid energy storage systems integrating these three technologies can achieve effective grid power support through performance complementarity.

[0025] S2. Obtain the state of charge, geographical location, and available power of all flywheels, batteries, and molten salt energy storage units, and construct a feature set of energy storage units.

[0026] When using hybrid energy storage systems to support grid power, it's important to consider that energy storage media of the same type are not single aggregates, but rather complex clusters composed of multiple geographically dispersed and heterogeneously operating independent units connected in parallel. If macroscopic averaging control is used, ignoring individual differences between units, it can easily lead to problems such as uneven load distribution within the cluster. Therefore, this step is used to collect the state of charge, geographical location information, and available power of all energy storage units.

[0027] Among them, the state of charge reflects the proportion of the energy storage unit's current remaining energy to its rated capacity, characterizing energy sustainability; the geographical location reflects the electrical distance of the energy storage unit relative to the grid frequency disturbance point, characterizing the spatiotemporal response timeliness of power injection; and the available power reflects the upper limit of the maximum charging / discharging power that the energy storage unit can safely provide, which can be used as a constraint boundary for power allocation commands, so as to select the optimal, closest, and most capable matching unit as the power support object for the corresponding energy storage type in emergency conditions.

[0028] Specifically, S2 contains the following: read the state of charge data corresponding to the current rotational speed from the flywheel control system of each flywheel energy storage unit.

[0029] Read the state of charge data corresponding to the current remaining capacity from the battery management system of each battery energy storage unit.

[0030] Read the current state of charge data corresponding to the current thermal storage capacity from the thermal energy storage management system of each molten salt thermal storage unit.

[0031] The maximum allowable output power is read in real time from the power conversion system of each energy storage unit as the available power data.

[0032] The geographical location of each energy storage unit is determined in real time using positioning equipment.

[0033] The collected state of charge, available power, and geographical location are associated and stored according to the energy storage type of each energy storage unit to generate a feature set of energy storage units.

[0034] S3. The emergency response process is divided into three stages: the first frequency regulation stage, the second frequency regulation stage, and the third frequency regulation stage. Each stage is dominated by flywheel energy storage, battery energy storage, and molten salt thermal energy storage, respectively.

[0035] Considering that when the power grid enters an emergency operating condition, the frequency drop trajectory caused by the actual fault is not a linear or homogeneous single process, but rather exhibits a multi-stage dynamic evolution characteristic, with different power support requirements at each stage, if no stage division is made and a fixed energy storage type ratio or uniform parallel weighted control is used throughout the process, it will lead to timing performance mismatch problems.

[0036] Therefore, this invention divides the dynamic process of grid frequency drop into three frequency regulation stages and implements a stage-led control strategy to achieve time matching between the physical characteristics of the energy storage medium and the power support requirements of the grid.

[0037] In a preferred embodiment of the present invention, the stages are divided as follows: S31. After the emergency condition is triggered, the power grid frequency will undergo a nonlinear transient process of evolving from a steady state to a sharp drop. The rate of change of the power grid frequency is calculated in real time by differentiation. When the rate of change of the power grid frequency first exceeds the preset impact threshold, it indicates that the power grid has suffered a sudden high-power disturbance, and the frequency drop enters a stage of violent acceleration. This moment is recorded as the starting point of the first frequency regulation stage. When the rate of change of the power grid frequency falls from the peak to below the impact threshold, it indicates that the maximum acceleration process of the frequency drop has ended, and the dynamics of the power grid frequency change from violent deterioration to a slow change state. This moment is recorded as the end point of the first frequency regulation stage.

[0038] S32. Take the end time of the first frequency regulation stage as the starting point of the second frequency regulation stage, monitor the recovery process of the power grid frequency in real time, and when the frequency reaches the frequency recovery boundary point for the first time (usually set to a safe value slightly lower than the lower limit of the normal range, such as 49.5Hz), it means that the frequency has gotten rid of the risk of a sharp drop, but has not yet fully recovered to the normal range. Take this moment as the end of the second frequency regulation stage.

[0039] S33. Take the end time of the second frequency regulation stage as the starting point of the third frequency regulation stage, monitor the relative position of the grid frequency and the lower limit of the normal range in real time, and when the grid frequency reaches the lower limit of the normal range for the first time, it indicates that the active power supply and demand of the grid has been rebalanced and the frequency has returned to the normal range. Record this moment as the end of the third frequency regulation stage.

[0040] S34. Using the start and end points of each stage as time boundaries, the continuous emergency response process is divided into the first frequency modulation stage, the second frequency modulation stage, and the third frequency modulation stage.

[0041] In the above embodiments, the impact threshold characterizes the safe criticality of the power grid frequency change rate, representing the maximum frequency change rate that the power grid can withstand under normal operating conditions. Specifically, it can be set according to the limit provisions of national standards, such as 0.5 Hz / s.

[0042] After dividing the phases, since the power support requirements of each phase are different, this invention fully matches the energy storage medium with corresponding performance advantages as the dominant energy storage type according to the phase requirements, thereby achieving the optimal time-series configuration of hybrid energy storage to support the power grid, effectively avoiding resource mismatch under single energy storage or fixed ratio control.

[0043] The specific matching is as follows: In the first frequency regulation phase, due to the large fluctuations in grid frequency, extremely fast response speed and extremely high power density are required to provide virtual inertia support. Flywheels have high response speed and extremely high power density, and can release huge kinetic energy instantaneously in the first few seconds of frequency drop, providing strong virtual inertia support and effectively supporting the frequency drop rate. However, limited by its low energy density, flywheels cannot maintain output for a long time; if they are forcibly used to dominate the subsequent phases, they will be forced to withdraw due to rapid depletion of kinetic energy, which can easily trigger a second frequency drop. Therefore, flywheels are suitable as the dominant energy storage type in this phase.

[0044] In the second frequency regulation phase, the frequency change slows down but remains at a dangerously low level. Continuous high-power injection is needed to quickly pull the frequency back to the normal range. Battery storage, with its high power and energy density, can seamlessly take over after the flywheel disengages, providing stable power thrust to help the frequency quickly recover from its low point to near normal. However, the total life-cycle cost of batteries is high, and long-term, high-capacity support is less economical. Allowing them to continue dominating this phase would result in excessive system capacity redundancy and accelerated equipment aging. Therefore, battery storage is suitable as the dominant energy storage type in this phase.

[0045] In the third frequency regulation stage, the frequency has returned to near the normal range, but the system's active power deficit has not been fully filled. It requires ultra-high energy density and long-term continuous discharge capability to support the power. Molten salt thermal storage has ultra-high energy density and long-term continuous discharge capability. Although the response is relatively slow, the frequency no longer fluctuates drastically in this stage, and the requirement for response speed is not high. Molten salt is suitable as the dominant energy storage type to provide long-term power support and ensure that the frequency remains stable in the normal range for a long time.

[0046] S4. In each stage, select the dominant and follower units from the energy storage unit feature set according to the dominant energy storage type of that stage, and pre-select reserve units for subsequent stages.

[0047] After completing the matching of the dominant energy storage type, given that similar energy storage typically consists of multiple heterogeneous units, it is necessary to select suitable units from this type of cluster to execute power commands. However, a single energy storage unit is limited by its rated power capacity and operational reliability. If only a single unit is selected, it is highly susceptible to grid disconnection due to overload or single-point failure, leading to support interruption. Therefore, this invention adopts a dominant plus follower configuration mode, that is, selecting a unit with optimal state as the dominant unit to establish the control benchmark, and dynamically matching several follower units for power distribution.

[0048] See Figure 2 As shown, in one possible implementation of the present invention, the selection of the dominant unit and the follower unit is carried out as follows: at each stage, all energy storage units of the same type are selected from the energy storage unit feature set according to the dominant energy storage type of that stage.

[0049] From all selected energy storage units of the same type, those with a state of charge below a preset participation threshold are eliminated. This ensures that units with sufficient energy reserves are included in the effective candidate pool, guaranteeing that the subsequently selected leading and following units can reliably participate in frequency regulation throughout the process, avoiding their withdrawal due to energy depletion. The participation threshold represents the minimum energy redundancy boundary that an energy storage unit can safely undertake frequency regulation tasks under emergency conditions. Specifically, it can be based on the minimum safe operating charge limit specified by the manufacturer of the corresponding energy storage type.

[0050] The remaining energy storage units of the same type were arranged according to their state of charge from high to low and their geographical location from the grid frequency disturbance point from near to far, resulting in the optimal ranking of state of charge and electrical distance.

[0051] The ranking number of each energy storage unit is extracted from the optimal ranking results of state of charge and electrical distance, and then summed to obtain the comprehensive optimal ranking value.

[0052] The energy storage unit with the lowest comprehensive optimization ranking value is selected as the dominant unit for the current stage.

[0053] The shortest electrical distance means the smallest transmission path impedance and the lowest power response delay, which can maximize local support efficiency and reduce line loss. Through the above comprehensive ranking and comparison, it can be ensured that the selected dominant unit has both high response timeliness and high energy continuity.

[0054] After excluding the selected dominant units, the remaining energy storage units of the same type are sorted from high to low according to their state of charge, and several units at the top of the sort, such as two, are selected as the follower units for the current stage.

[0055] Considering the short timing transition window between stages, in order to avoid support gaps caused by the handover of leadership in subsequent stages, this invention also introduces a pre-selected reserve unit for the subsequent stage during the current stage, ensuring that the new leading unit can seamlessly switch in at the moment the leadership handover command is triggered, thereby ensuring the continuity of power support.

[0056] Specifically, the process of pre-selecting reserve units for subsequent stages includes: during the execution of the current stage, selecting all energy storage units that meet the dominant energy storage type from the energy storage unit feature set according to the dominant energy storage type of the next stage.

[0057] Units that are currently in operation and whose state of charge is below the participation threshold will be removed from the selected energy storage units.

[0058] The remaining candidate cells are sorted from highest to lowest charge state, and at least two cells with the highest charge state are selected as reserve cells for the next stage.

[0059] A hot standby command is sent to all reserve units via the communication network, putting them into standby mode and uploading status data in real time, but they do not participate in power output for the time being.

[0060] When entering the next stage, the optimal cell is selected from the reserve cell set based on the dual criteria of having the highest state of charge and being closest to the disturbance point, and the remaining reserve cells are automatically converted into follower cells.

[0061] S5. Control the power output of the leading and following units in the current stage, and determine whether other types of energy storage need to be intervened based on the real-time status. When intervention is required, select the appropriate unit to intervene and output power.

[0062] Because a dominant-follower configuration mode is adopted in each stage, a collaborative output mechanism between the dominant unit and the follower unit needs to be established when executing power command allocation.

[0063] See Figure 3 As shown, in one optional implementation, the coordinated output power of the leading unit and the following unit in the current stage is controlled as follows: S51, the leading unit is controlled to operate in voltage source mode, where voltage source mode means that the leading unit simulates the external characteristics of a synchronous generator through a power electronic converter, autonomously establishes voltage and frequency, and has self-synchronization capability. Since the deviation of the grid frequency from the normal range is dynamic, in voltage source mode, the output power value of the leading unit can be adjusted in real time according to the degree of deviation of the grid frequency from the normal range. Specifically, when the frequency deviation is large, the power injection is automatically increased; when the deviation decreases, the power injection is reduced, which enables the leading unit to adaptively match the real-time active power deficit of the grid and assume the leading role.

[0064] S52. Obtain the current total power deficit of the power grid in real time, subtract the current actual output power of the leading unit from the total power deficit, and calculate the remaining power demand that needs to be shared by the following units.

[0065] S53. Allocate the remaining power demand to all follower units according to the proportion of their current available power to the total available power of all follower units, and issue power commands synchronously. The follower units usually operate in current source mode. In this mode, they do not have the ability to autonomously sense the grid frequency and only strictly respond to the power allocation value issued by the master unit, which reflects master-slave cooperation.

[0066] S54. Monitor the state of charge of all following units in real time. When the state of charge of any unit drops to the participation threshold, temporarily remove the unit from the allocation list and redistribute its original power share according to the available power ratio of the remaining following units.

[0067] S55. When the state of charge of a removed cell subsequently recovers to above the participation threshold, it is reinstated into the allocation list, and the allocation ratio of each cell is recalculated.

[0068] In the current stage of coordinated control of similar energy storage based on a dominant and follower approach, due to the inherent limitations of the physical characteristics of a single energy storage medium, such as the limited energy capacity of a flywheel, the limited rate capability of a battery, and the limited response rate of molten salt, when faced with situations such as high power surges or long-term power shortages, relying solely on the current dominant type of energy storage cluster may result in situations such as saturation of available power, rapid depletion of state of charge, or insufficient response bandwidth, making it impossible to independently fill the real-time power gap.

[0069] To address the aforementioned issues, this invention introduces dynamic intervention across different energy storage types. By leveraging the differentiated advantages of heterogeneous energy storage, it provides power support when the dominant energy storage capacity is insufficient, ensuring sufficient power support for the power grid under emergency conditions.

[0070] The following detailed explanation of the dynamic intervention criteria and selection strategy for cross-type energy storage is based on specific embodiments: (1) In the first frequency regulation stage, the state of charge of all flywheel follower units and the rate of change of grid frequency are monitored in real time. When the state of charge of all flywheel follower units is lower than the participation threshold and the rate of change of grid frequency continues to exceed the impact threshold (e.g., the duration exceeds 100ms), it indicates that the flywheel cluster has lost its continuous support capability and the grid is suffering from a continuous high power shortage impact, rather than a short-term fluctuation. At this time, it is determined to trigger battery intervention because although the flywheel has the advantage of high response, it is limited by low energy density and will quickly exhaust its kinetic energy under continuous high power impact. If battery energy storage with high energy density and fast response speed is not introduced in time, the grid will face a power support gap.

[0071] All battery energy storage units are screened from the feature set of energy storage units, and the battery energy storage unit with the highest state of charge is selected as the intervention unit. This is to avoid the new intervention unit from frequently starting and stopping due to insufficient power. The intervention output is in the current source mode because the flywheel still has the dominant power at this time. The battery, as an incremental supplement, only needs to respond to the power command to inject power and quickly fill the power vacuum left by the flywheel cluster.

[0072] (2) In the second frequency regulation stage, since the dominant battery cell undertakes the task of providing the main power support, the discharge rate is usually the highest. When the rate of decrease of the state of charge of the dominant battery cell exceeds the rate limit (e.g., 1.5% / s, corresponding to the high rate discharge state) and the duration exceeds the preset duration (e.g., 30s), it indicates that the power shortage of the grid has a long-term continuous characteristic. The current battery cluster is operating at the limit rate to maintain the frequency recovery. If no intervention is made, the battery will exhaust the available energy in a very short time, resulting in a sudden interruption of the support capacity. Since the flywheel energy density is extremely low, it cannot provide long-term energy support. At this time, it is determined that the molten salt intervention is triggered.

[0073] All molten salt thermal energy storage units were screened from the energy storage unit feature set, and the molten salt thermal energy storage unit with the highest available power was selected to intervene in the output in current source mode.

[0074] (3) In the second frequency regulation stage, although the fluctuation of the grid frequency has become smooth, the grid may still experience transient disturbances due to the random fluctuation of the load. Such disturbances are characterized by large rate of change and short duration. When the grid frequency change rate instantaneously exceeds the impact threshold, it is difficult to achieve rapid smoothing if only relying on the relatively slow-responding battery, which may lead to secondary oscillation of the frequency. Since the flywheel has a high response speed, it is determined to trigger the flywheel intervention at this time.

[0075] The flywheel unit with the fastest response speed and a state of charge higher than the participation threshold is selected from the energy storage unit feature set to output power instantaneously in voltage source mode. This is because in voltage source mode, the flywheel can adjust its output autonomously and instantly according to the local frequency measurement value without waiting for the upper layer to allocate instructions, thereby eliminating communication delay, realizing rapid smoothing, and exiting after the grid frequency change rate recovers to below the impact threshold.

[0076] (4) In the third frequency regulation stage, the dominant energy storage type has been switched to molten salt thermal energy storage. Since molten salt power generation is based on thermal cycle and has control lag, it is easy to cause regulation overshoot or low frequency oscillation when dealing with rapid random fluctuations in grid load. When the output power of the dominant molten salt unit and the grid frequency show continuous excessive fluctuations, for example, a fixed time window for evaluating the fluctuation is set as the monitoring period, such as 100ms. When the rate of change of power and frequency exceeds the fluctuation limit for three consecutive monitoring periods (which can be set according to the grid stability standard), it indicates that continuous excessive fluctuations have occurred synchronously. At this time, the slow response characteristics of the molten salt system have mismatched with the current dynamic demand of the grid, forming a negative damping effect. It is necessary to introduce an external energy storage unit with fast response capability to offset the lag effect of molten salt.

[0077] Since the periodic characteristics of grid frequency fluctuations directly determine the required control bandwidth, and different energy storage media have significantly different response bandwidths, it is necessary to perform matching intervention based on the fluctuation period to achieve the optimal smoothing effect. Specifically, zero-crossing detection or fast Fourier transform can be used to perform spectral analysis on grid frequency data to obtain the period of the dominant fluctuation component. If the fluctuation period is less than the preset period threshold, it indicates that the fluctuation period is short and changes extremely rapidly. Such fluctuations require high response speed, and in this case, the flywheel unit with the fastest response is selected for intervention. If the fluctuation period is greater than or equal to the preset period threshold, it indicates that the fluctuation period is longer. Such fluctuations have relatively lower requirements for response speed, but higher requirements for continuous energy throughput. In this case, the battery unit with the highest state of charge is selected for intervention. The period threshold is a dividing value used to distinguish between high and low grid frequency fluctuations, such as 2 seconds.

[0078] S6. When the current stage detects a decrease in the state of charge of the dominant unit that requires a change of dominance, a new dominant unit shall be selected from the same type of energy storage units.

[0079] Although units with higher state of charge are preferred as the initial leaders when selecting the leading units at each stage, in actual operation under emergency conditions, the energy consumption rate of the leading unit may far exceed expectations due to the random fluctuations of the grid power deficit and the aging characteristics of the leading unit itself. When the state of charge of the current leading unit drops to the participation threshold, it indicates that the unit has reached its continuous output limit. If it continues to forcibly lead, it will face the risk of shutdown. Therefore, this invention achieves the continuity of power support by switching the leadership of similar energy storage units.

[0080] Specifically, selecting a new dominant unit from the same type of energy storage units includes the following: when changing the dominant unit within the same phase, the current dominant unit, all currently operating follower units, and units with a state of charge below the participation threshold are removed from all energy storage units of the same dominant energy storage type as the dominant unit in this phase.

[0081] The remaining standby cells are sorted from highest to lowest charge state, and the cell ranked first is selected as the new dominant cell.

[0082] A dominance mode activation command is sent to the new dominance unit, controlling the original dominance unit to reduce its output power at a preset rate, while simultaneously controlling the new dominance unit to increase its output power at a synchronous rate. This ensures that during the handover process, the sum of the output power of the two units is equal to the dominance power required by the grid. At the same time, the original dominance unit is switched to standby or charging mode, while the original follower unit continues to maintain its current power output state.

[0083] It should be noted that geographical location is considered when initially selecting the dominant unit to ensure that the unit closest to the disturbance point is put into operation first. However, when this optimal unit needs to be replaced due to depletion, the grid state has changed from the initial state. In this case, the primary goal is to ensure the continuity of power support and avoid interruptions, and geographical location can be used as a secondary selection criterion.

[0084] S7. Execute each stage sequentially until the power grid frequency returns to the normal range and the emergency condition is lifted.

[0085] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0086] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0087] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0088] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0089] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for coordinated grid power control of a hybrid energy storage system based on emergency operating conditions, characterized in that, include: When the detected power grid frequency is below the lower limit of the normal range, it is determined that an emergency operating condition has been entered. Obtain the state of charge, geographical location, and available power of all flywheel, battery, and molten salt energy storage units, and construct a feature set of energy storage units; The emergency response process is divided into three stages: the first frequency regulation stage, the second frequency regulation stage, and the third frequency regulation stage. Each stage is dominated by flywheel energy storage, battery energy storage, and molten salt thermal energy storage, respectively. In each stage, dominant and follower units are selected from the energy storage unit feature set according to the dominant energy storage type of that stage, and reserve units are pre-selected for subsequent stages. Control the power output of the dominant and follower units in the current stage, and determine whether other types of energy storage need to be intervened based on the real-time status. When intervention is required, select the appropriate unit to intervene and output power. When a decrease in the state of charge of the dominant unit is detected at the current stage, which requires a change of dominance, a new dominant unit shall be selected from the same type of energy storage unit. Execute each stage sequentially until the power grid frequency returns to the normal range and the emergency condition is lifted; The first frequency modulation stage, the second frequency modulation stage, and the third frequency modulation stage are divided as follows: The rate of change of the power grid frequency is calculated in real time. When the rate of change of the power grid frequency first exceeds the preset impact threshold, the moment is recorded as the start of the first frequency regulation stage. When the rate of change of the power grid frequency falls from the peak to below the impact threshold, the moment is recorded as the end of the first frequency regulation stage. The end point of the first frequency regulation phase is taken as the starting point of the second frequency regulation phase. The recovery process of the power grid frequency is monitored in real time, and the moment when the frequency first reaches the frequency recovery boundary point is taken as the end point of the second frequency regulation phase. The end time of the second frequency regulation stage is taken as the starting time of the third frequency regulation stage. The relative position of the power grid frequency and the lower limit of the normal range is monitored in real time. When the power grid frequency reaches the lower limit of the normal range for the first time, the moment is recorded as the end time of the third frequency regulation stage. The process for selecting the dominant unit is as follows: At each stage, all energy storage units of the same type are selected from the energy storage unit feature set according to the dominant energy storage type of that stage, and then units with a state of charge lower than the preset participation threshold are eliminated. The remaining energy storage units of the same type are arranged according to their state of charge from high to low and their geographical location from the grid frequency disturbance point from near to far, so as to obtain the optimal ranking results of state of charge and electrical distance. The ranking number of each energy storage unit is extracted from the optimal ranking results of state of charge and electrical distance, and then summed to obtain the comprehensive optimal ranking value; The energy storage unit with the lowest comprehensive optimization ranking value is selected as the dominant unit for the current stage.

2. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 1, characterized in that: The feature set for constructing the energy storage unit includes the following: Read the state of charge data corresponding to the current speed from the flywheel control system of each flywheel energy storage unit; Read the state of charge data corresponding to the current remaining capacity from the battery management system of each battery energy storage unit; Read the current state of charge data corresponding to the current thermal storage capacity from the thermal energy storage management system of each molten salt thermal storage unit; The maximum allowable output power is read in real time from the power conversion system of each energy storage unit as the available power data; The geographical location of each energy storage unit is physically marked at its installation location using positioning equipment; The collected state of charge, available power, and geographical location are associated and stored according to the energy storage type of each energy storage unit to generate a feature set of energy storage units.

3. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 1, characterized in that: The following selection process is used for the following follower unit: After excluding the selected leading units, the remaining energy storage units of the same type are sorted from high to low according to their state of charge, and the top-ranked units are selected as the following units for the current stage.

4. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 1, characterized in that: The process for pre-selecting preliminary units for subsequent stages includes: During the current phase of execution, based on the dominant energy storage type for the next phase, all energy storage units that meet the energy storage type are selected from the energy storage unit feature set, and units that are already in operation in the current phase and whose state of charge is below the participation threshold are removed. The remaining elements are sorted from highest to lowest charge state, and at least two elements at the top of the sort are selected as reserve elements for the next stage.

5. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 1, characterized in that: The process for controlling the coordinated output power of the dominant and follower units in the current stage is as follows: The control unit operates in voltage source mode and adjusts the output power value of the control unit in real time according to the degree of deviation between the grid frequency and the normal range. The current total power deficit of the power grid is obtained in real time. The actual output power of the leading unit is subtracted from the total power deficit to calculate the remaining power demand that needs to be shared by the following units. Allocate the remaining power demand to all follower units according to the proportion of their current available power to the total available power of all follower units, and issue power commands synchronously. The charge state of all follower units is monitored in real time. When the charge state of any unit drops to the participation threshold, the unit is temporarily removed from the allocation list and its original power share is redistributed according to the available power ratio of the remaining follower units. When the removed cells regain a charge state above the participation threshold, they are reinstated to the allocation list, and the allocation ratio of each cell is recalculated.

6. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 5, characterized in that: The process of determining whether other types of energy storage are needed, and selecting an adapter unit to intervene in power output when intervention is needed, includes: In the first frequency regulation phase, when the state of charge of all flywheel follower units is below the participation threshold and the grid frequency change rate continues to exceed the impact threshold, it is determined that the battery intervention is triggered; the battery energy storage unit with the highest state of charge is selected to intervene and output in current source mode. In the second frequency regulation stage, when the rate of decrease in the state of charge of the dominant battery cell exceeds the rate limit and the duration exceeds the preset duration, it is determined that molten salt intervention is triggered; the molten salt thermal storage unit with the highest available power is selected to intervene and output in current source mode. In the second frequency regulation phase, when the grid frequency change rate instantaneously exceeds the impact threshold, it is determined that the flywheel intervention is triggered; the flywheel unit with the fastest response speed and a state of charge higher than the participation threshold is selected to output power instantaneously in voltage source mode, and exits after the grid frequency change rate recovers to below the impact threshold; In the third frequency regulation stage, when the output power of the dominant molten salt unit and the grid frequency show continuous excessive fluctuations, the type of intervention unit is determined according to the periodic characteristics of the grid frequency fluctuation. If the fluctuation period is less than the preset period threshold, the flywheel unit with the fastest response speed is selected for intervention. If the fluctuation period is greater than or equal to the preset period threshold, the battery unit with the highest state of charge is selected for intervention.

7. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 1, characterized in that: The selection of a new dominant unit from similar energy storage units includes the following: When changing the dominant unit within the same phase, remove the current dominant unit, all currently operating follower units, and units with a state of charge below the participation threshold from all energy storage units of the same dominant energy storage type as the current phase. The remaining standby cells are sorted from highest to lowest charge state, and the cell ranked first is selected as the new dominant cell.

8. The grid power coordinated control method for hybrid energy storage systems based on emergency operating conditions as described in claim 7, characterized in that: The selection of a new dominant unit from similar energy storage units also includes: A dominance mode activation command is sent to the new dominance unit to control it to gradually take over the power output share of the original dominance unit, while the original dominance unit is switched to standby or charging mode, and the original follower unit continues to maintain its current power output state.

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