Control method of hybrid energy storage system, hybrid energy storage system and equipment

Abstract

The invention provides a control method of a hybrid energy storage system, the hybrid energy storage system and equipment, and relates to the technical field of electric power. According to the scheme, the operation mode (off-grid or grid-connected) of the hybrid energy storage system is accurately identified, and the power supply role is intelligently and dynamically allocated according to the control strategy corresponding to the current operation mode, so that efficient operation and optimal management of the system are realized, and the purpose of supplying power to the local load in the grid-connected or off-grid operation mode is achieved. In an off-grid mode, the high-rate charge-discharge advantage of the sodium-ion battery can be fully played, the power requirement is quickly responded, and stable power supply of the system is ensured; in the grid-connected mode, the charging and discharging power of the two energy storage units can be flexibly adjusted by combining the characteristics of the power grid, the interaction of the power grid is optimized, and the overall performance of the system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric power, in particular to a control method of a hybrid energy storage system, a hybrid energy storage system and equipment. BACKGROUND

[0002] Among many energy storage technologies, lithium ion battery energy storage systems are widely used due to their high energy density, long cycle life and relatively mature technology. However, in cold regions or low temperature environments, the performance of lithium ion batteries will decrease significantly. Low temperature will slow down the electrochemical reaction rate inside the battery and reduce the ion diffusion capacity, thereby limiting the capacity of the battery, reducing the discharge voltage, and affecting the charging efficiency. This limits the application of lithium ion battery energy storage systems in cold regions. If there is no external power supply and the lithium ion battery energy storage system cannot work, the local load cannot be powered. SUMMARY

[0003] The purpose of the embodiments of the present application is to provide a control method of a hybrid energy storage system, a hybrid energy storage system and equipment, to improve the problem that the local load cannot be powered in the case that there is no external power supply and the lithium ion battery energy storage system cannot work in the prior art.

[0004] In a first aspect, the embodiments of the present application provide a control method of a hybrid energy storage system, applied to an energy control unit in the hybrid energy storage system, the hybrid energy storage system further comprising a sodium ion energy storage unit and a lithium ion energy storage unit, and the method comprises: determining a current operation mode of the hybrid energy storage system, wherein the operation mode comprises an off-grid operation mode and a grid-connected operation mode, the off-grid operation mode refers to that the hybrid energy storage system is not connected to an external power grid, and the grid-connected operation mode refers to that the hybrid energy storage system is connected to the external power grid; adopting a control strategy corresponding to the current operation mode to dynamically allocate power supply roles of the sodium ion energy storage unit and the lithium ion energy storage unit.

[0005] In the above implementation process, by accurately identifying the operation mode (off-grid or grid-connected) of the hybrid energy storage system, and intelligently dynamically allocating the power supply roles according to the control strategy corresponding to the current operation mode, efficient operation and optimized management of the system are realized, and the purpose of supplying power to the local load in the grid-connected or off-grid operation mode is achieved. In the off-grid mode, the high-rate charge and discharge advantage of the sodium ion battery can be fully utilized to quickly respond to the power demand and ensure stable power supply of the system; in the grid-connected mode, the charge and discharge power of the two energy storage units can be flexibly adjusted in combination with the characteristics of the power grid to optimize the power grid interaction and improve the overall performance of the system.

[0006] Optionally, the current operation mode is an off-grid operation mode, and the control strategy corresponding to the current operation mode is adopted to dynamically allocate the power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit, including: In a case where it is detected that the ambient temperature is higher than a first set temperature, the sodium-ion energy storage unit and the lithium-ion energy storage unit are controlled to supply power to the local load; In a case where it is detected that the ambient temperature is lower than or equal to the first set temperature, the sodium-ion energy storage unit is controlled to supply power to the local load, and the sodium-ion energy storage unit is controlled to supply power to the heating device of the lithium-ion energy storage unit.

[0007] In the above implementation process, in the off-grid operation mode, the power supply roles of the sodium-ion and lithium-ion energy storage units are dynamically adjusted according to the ambient temperature, the differences in chemical properties of the two are ingeniously utilized, and precise and efficient energy management is achieved. When the ambient temperature is higher than the first set temperature, the sodium-ion and lithium-ion energy storage units cooperatively supply power to the local load, fully exert their respective advantages, and ensure stable and reliable power supply. When the ambient temperature is lower than or equal to the first set temperature, the sodium-ion energy storage unit not only supplies power to the local load, but also supplies power to the heating device of the lithium-ion energy storage unit, effectively solving the problem of limited performance of lithium-ion batteries in low-temperature environments, ensuring normal operation of the system in cold conditions, and significantly improving the adaptability and reliability of the hybrid energy storage system in the off-grid state.

[0008] Optionally, in the case where it is detected that the ambient temperature is lower than or equal to the first set temperature, the sodium-ion energy storage unit is controlled to supply power to the local load, and the sodium-ion energy storage unit is controlled to supply power to the heating device of the lithium-ion energy storage unit, including: In a case where it is detected that the ambient temperature is lower than or equal to the first set temperature, a discharge instruction is sent to the sodium-ion energy storage unit, and an instruction to suspend power supply to the local load is sent to the lithium-ion energy storage unit; The discharge instruction is used to instruct the sodium-ion energy storage unit to supply power to the heating device of the lithium-ion energy storage unit and the local load, and the instruction to suspend power supply to the local load is used to instruct the lithium-ion energy storage unit to suspend discharging. The lithium-ion energy storage unit is configured to supply power to the local load after the temperature of the lithium-ion energy storage unit reaches a second set temperature through the operation of the heating device, and the second set temperature is greater than the first set temperature.

[0009] In the implementation process described above, when the off-grid operation and the environmental temperature is lower than or equal to the first set temperature, the sodium-ion energy storage unit is controlled to supply power to the local load and the heating element of the lithium-ion energy storage unit, while the power supply of the lithium-ion energy storage unit to the local load is suspended, thereby ingeniously solving the problem of limited performance of lithium-ion batteries at low temperatures. After the temperature of the lithium-ion energy storage unit rises to the second set temperature, the power supply of the lithium-ion energy storage unit to the local load is restored. This process not only effectively prolongs the service life of the lithium-ion energy storage unit in a low-temperature environment, but also ensures the stability and reliability of the hybrid energy storage system under extreme conditions, and significantly improves the adaptability of the system to environmental changes.

[0010] Optionally, the current operation mode is a grid-connected operation mode, and the control strategy corresponding to the current operation mode is adopted to dynamically allocate the power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit, including: acquiring a working state parameter of the external power grid; determining whether the hybrid energy storage system needs to supply power to the external power grid according to the working state parameter; if so, controlling the charge and discharge power of the sodium-ion energy storage unit and the lithium-ion energy storage unit according to a set adaptive power control strategy.

[0011] In the implementation process described above, in the grid-connected operation mode, the working state parameter of the external power grid is acquired to accurately determine whether the hybrid energy storage system needs to supply power to the external power grid. If so, the charge and discharge power of the sodium-ion and lithium-ion energy storage units is dynamically adjusted according to the set adaptive power control strategy. This intelligent control method based on real-time grid state fully utilizes the chemical characteristics of the two types of energy storage units, improves the flexibility and response speed of the system, optimizes the power balance of the grid, and enhances the stability of the grid.

[0012] Optionally, the control of the charge and discharge power of the sodium-ion energy storage unit and the lithium-ion energy storage unit according to the set adaptive power control strategy includes: acquiring historical power data of the hybrid energy storage system; predicting the charge and discharge power situation of the hybrid energy storage system in a set time period according to the historical power data; determining a charge and discharge power strategy of the hybrid energy storage system according to the charge and discharge power situation, the remaining capacity of the lithium-ion energy storage unit, and the remaining capacity of the sodium-ion energy storage unit; adjusting the charge and discharge power of the lithium-ion energy storage unit and the sodium-ion energy storage unit according to the charge and discharge power strategy.

[0013] In the implementation process, the historical power data of the hybrid energy storage system is obtained and analyzed, and the remaining power of the sodium-ion and lithium-ion energy storage units is combined to dynamically formulate the charging and discharging power strategy, thereby achieving precise adjustment of the charging and discharging power of the two energy storage units. This data-driven adaptive control method can effectively optimize the energy management of the hybrid energy storage system and improve the operation efficiency and flexibility of the system.

[0014] Optionally, the adaptive power control strategy comprises: if the power change rate of the hybrid energy storage system is detected to exceed a set change rate, the sodium-ion energy storage unit is controlled to increase the discharging power and the lithium-ion energy storage unit is controlled to reduce the discharging power; and / or, if the state of charge of the sodium-ion energy storage unit is detected to be within a set range, the sodium-ion energy storage unit is controlled to increase the discharging power and the lithium-ion energy storage unit is controlled to reduce the discharging power; and / or, if the state of charge of the lithium-ion energy storage unit is detected to be lower than a set state of charge, the sodium-ion energy storage unit is controlled to increase the discharging power and the lithium-ion energy storage unit is controlled to reduce the discharging power.

[0015] In the implementation process, the adaptive power control strategy is set to dynamically adjust the charging and discharging power of the sodium-ion and lithium-ion energy storage units according to the power change rate of the hybrid energy storage system, the state of charge (SOC) of the sodium-ion energy storage unit, and the SOC of the lithium-ion energy storage unit. This intelligent control method can effectively respond to rapid changes in system power, optimize power distribution, and ensure stable operation of the system under different operating conditions.

[0016] Optionally, the current operating mode of the hybrid energy storage system is determined by: detecting the voltage of a grid connection point where the hybrid energy storage system is connected to an external power grid; determining the connection state of the external power grid and the hybrid energy storage system according to the voltage; determining the current operating mode of the hybrid energy storage system according to the connection state.

[0017] In the implementation process, the voltage of the grid connection point where the hybrid energy storage system is connected to the external power grid is detected to accurately determine the connection state of the external power grid and the hybrid energy storage system, and then determine the current operating mode of the system. This voltage monitoring-based mode recognition method can quickly and accurately identify the grid-connected or off-grid state, ensuring timely switching of control strategies under different operating modes.

[0018] Optionally, the determining the connection state of the external power grid and the hybrid energy storage system according to the voltage comprises: When the voltage is less than a first set threshold or greater than a second set threshold, it is determined that the connection state of the external power grid and the hybrid energy storage system is disconnected, wherein the first set threshold is less than the second set threshold.

[0019] In the above implementation process, the judgment method based on the double thresholds can effectively avoid misjudgment caused by normal fluctuations of the power grid voltage, and improve the accuracy and reliability of the judgment.

[0020] Optionally, the voltage comprises a plurality of voltages sampled continuously. By using a plurality of voltage data sampled continuously to determine the connection state of the external power grid and the hybrid energy storage system, compared with single sampling, the actual change of the grid point voltage can be more comprehensively and accurately reflected. Continuous sampling can effectively avoid misjudgment caused by instantaneous voltage fluctuations or sampling errors, and improve the stability and reliability of the judgment.

[0021] In a second aspect, the embodiments of the present application provide a hybrid energy storage system, comprising: an energy control unit, a sodium-ion energy storage unit and a lithium-ion energy storage unit, the energy control unit is connected with the sodium-ion energy storage unit and the lithium-ion energy storage unit respectively, and the sodium-ion energy storage unit and the lithium-ion energy storage unit are connected; The energy control unit is configured to determine a current operation mode of the hybrid energy storage system, wherein the operation mode comprises an off-grid operation mode and a grid-connected operation mode, the off-grid operation mode refers to that the hybrid energy storage system is not connected with an external power grid, and the grid-connected operation mode refers to that the hybrid energy storage system is connected with the external power grid; and a control strategy corresponding to the current operation mode is adopted to dynamically allocate power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit.

[0022] Optionally, the sodium-ion energy storage unit comprises a plurality of battery clusters, each battery cluster is formed by a plurality of battery packs connected in series, and each battery pack is connected with an energy storage converter.

[0023] Optionally, the sodium-ion energy storage unit is a polyanion sodium-ion battery.

[0024] In a third aspect, the embodiments of the present application provide an electronic device comprising a processor and a memory, wherein the memory stores computer readable instructions, and when the computer readable instructions are executed by the processor, the steps in the method provided in the first aspect are executed.

[0025] In a fourth aspect, an embodiment of the present application provides a computer readable storage medium, having stored thereon a computer program, which, when executed by a processor, causes the processor to perform the steps of the method according to the first aspect.

[0026] In a fifth aspect, an embodiment of the present application provides a computer program product, comprising computer program instructions, which, when read and executed by a processor, perform the steps of the method according to the first aspect.

[0027] Other features and advantages of the present application will be further described in the following description, and in part will become apparent to those skilled in the art from the following description, or can be learned by practice of the application as set forth in the claims and appended description. The purposes and other advantages of the present application can be realized and attained by the structure particularly pointed out in the written description and claims hereof. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0029] Figure 1 A structural block diagram of a hybrid energy storage system is provided for the embodiments of the present application; Figure 2 A structural schematic diagram of an energy storage unit is provided for the embodiments of the present application; Figure 3 A flowchart of a control method of a hybrid energy storage system is provided for the embodiments of the present application; Figure 4 A structural block diagram of a control device of a hybrid energy storage system is provided for the embodiments of the present application; Figure 5 A structural schematic diagram of an electronic device for executing a control method of a hybrid energy storage system is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0030] The technical solutions of the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application.

[0031] It should be noted that the terms "system" and "network" in the embodiments of the present application can be used interchangeably. "Multiple" means two or more, and therefore, "multiple" in the embodiments of the present application can also be understood as "at least two". The association relationship of the associated objects is described, which means that there can be three kinds of relationships, for example, A and / or B can represent the following three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / ", if not specially stated, generally represents an "or" relationship between the associated objects before and after it.

[0032] It should also be noted that all the actions of obtaining signals, information or data in this application are carried out in accordance with the corresponding data protection regulations and policies of the country where the device is located, and with the authorization given by the owner of the corresponding device.

[0033] The embodiments of the present application provide a control method of a hybrid energy storage system, which accurately identifies the operation mode (off-grid or grid-connected) of the hybrid energy storage system, intelligently dynamically allocates the power supply role according to the control strategy corresponding to the current operation mode, realizes efficient operation and optimized management of the system, and achieves the purpose of supplying power to local loads in both grid-connected and off-grid operation modes. In the off-grid mode, the high-rate charge and discharge advantage of sodium ion batteries can be fully utilized to quickly respond to power demand and ensure stable power supply of the system; in the grid-connected mode, the charge and discharge power of the two energy storage units can be flexibly adjusted in combination with the characteristics of the power grid to optimize power grid interaction and improve the overall performance of the system.

[0034] In order to facilitate the understanding of the implementation process of the control method provided by the present scheme, the hybrid energy storage system of the present scheme will be introduced first, as shown in Figure 1 The hybrid energy storage system 10 includes an energy control unit (EMS) 11, a sodium ion energy storage unit 12 and a lithium ion energy storage unit 13. The energy control unit 11 is connected with the sodium ion energy storage unit 12 and the lithium ion energy storage unit 13 respectively, and the sodium ion energy storage unit 12 and the lithium ion energy storage unit 13 are connected.

[0035] In some embodiments, the power station can include multiple hybrid energy storage systems, and the power station is used to supply power to local loads. If the local load is deployed with an external power grid, it can also be powered by the external power grid.

[0036] In actual deployment, the sodium ion energy storage unit 12 and the lithium ion energy storage unit 13 can be understood as battery containers, i.e. sodium ion battery containers and lithium ion battery containers. The sodium ion energy storage unit 12 adopts sodium ion batteries, including multiple battery packs, each battery pack contains multiple battery cells, the battery cells form a battery pack through a specific electrical connection method, and the battery packs form a battery cluster through series connection. These battery clusters together form a sodium ion energy storage unit.

[0037] Sodium-ion batteries have good low-temperature performance, rate performance and long cycle life. In the hybrid energy storage system 10, they can mainly be used to bear high-frequency fluctuation loads and deep charge-discharge tasks. For example, in the power grid frequency modulation scenario, they can quickly respond to power changes, provide high-power output, and maintain good performance in low-temperature environments to ensure stable operation of the system.

[0038] According to the power and energy requirements of the system, multiple sodium-ion battery containers, i.e., multiple sodium-ion energy storage units 12, can be configured. The capacity of each container can be determined according to actual requirements, and is usually in the range of tens of kilowatts to hundreds of kilowatt-hours. Multiple containers in parallel can achieve large-capacity energy storage.

[0039] Similarly, the lithium-ion energy storage unit 13 also includes multiple battery clusters, which are formed by battery packs in series. Lithium-ion batteries have relatively low costs and stable quality, and in the hybrid energy storage system, they mainly bear stable low-frequency power output. It is suitable for tasks that require a long duration and relatively slow power changes, such as providing stable power output in daily energy support for the power grid.

[0040] Similarly, according to the overall design and requirements of the system, multiple lithium-ion battery containers can be configured, and the capacity of each container can also be determined according to actual requirements. Generally, the capacity of each container can be matched with that of the sodium-ion battery container to achieve the best performance of the system.

[0041] Considering the cost, the sodium-ion energy storage unit 12 in the present scheme is mainly used to power the lithium-ion energy storage unit 13 in low-temperature environments, so only one sodium-ion battery container can be deployed, while multiple lithium-ion battery containers can be deployed.

[0042] The energy control unit 11, as the control core of the hybrid energy storage system 10, is mainly responsible for the overall energy management and control strategy of the system, such as real-time monitoring of the operating state of the entire energy storage system, including the working parameters of the sodium-ion energy storage unit 12 and the lithium-ion energy storage unit 13, as well as the frequency, voltage, load and other information of the external power grid. According to these information and the power requirements of the system, the corresponding control instructions are generated and sent to the sodium-ion energy storage unit 12 and the lithium-ion energy storage unit 13.

[0043] In the present scheme, the energy control unit 11 can be used to determine the current operation mode of the hybrid energy storage system, and then adopt the control strategy corresponding to the current operation mode to dynamically allocate the power supply roles of the sodium-ion energy storage unit 12 and the lithium-ion energy storage unit 13. Among them, the operation mode can include an off-grid operation mode and a grid-connected operation mode, and the off-grid operation mode refers to that the hybrid energy storage system is not connected to the external power grid, and the grid-connected operation mode refers to that the hybrid energy storage system is connected to the external power grid. The detailed implementation process of the process is introduced in the subsequent method embodiment, and will not be described in detail here.

[0044] Based on the above embodiment, as shown in Figure 2 The sodium-ion energy storage unit 12 includes a plurality of battery clusters, each battery cluster is formed by a plurality of battery packs connected in series, and each battery pack is connected with a power conditioning system (PCS).

[0045] That is, for the sodium-ion energy storage unit 12, a battery pack level medium voltage direct hanging PCS is used, and the PCS is used to convert the direct current of the battery into alternating current or convert the alternating current into direct current, so as to realize the exchange of electric energy between the battery and the power grid.

[0046] Figure 2 Among them, each battery pack (1P48S) of the sodium-ion energy storage unit is connected with a medium voltage direct hanging PCS, adopts a three-level active neutral point clamped (ANPC) topology, and the power device is a SiC MOSFET. The 150V direct current is directly converted into 150V alternating current; the 150V alternating voltage of a plurality of battery packs is cascaded to 690V alternating current and connected to the grid. The PCS has a network forming type capability, and can provide a 3 times rated current of 10 seconds within 20ms through a virtual synchronous machine (SVG) algorithm, and can support the voltage and frequency of the power grid in the case of failure.

[0047] With the operation of the hybrid energy storage system 10, it is inevitable that a certain battery pack needs to be repaired and replaced, which will lead to the mixed use of new and old batteries in a battery cluster. Since the charge and discharge characteristics of new and old batteries are inconsistent, overcharging and overdischarging problems may occur. Based on this, in the present scheme, each battery pack of the sodium-ion energy storage unit is connected with a PCS, so that the differences between the battery packs can be isolated through the PCS, the mixed use of new and old batteries can be realized, and the available capacity and energy conversion efficiency of the entire station can be improved.

[0048] In the specific connection, one battery pack is connected with one PCS, the PCS is connected with the next battery pack, and the battery clusters are formed in series, and each battery cluster can be connected with a total control PCS. In this way, each PCS has independent control capability for the battery pack connected thereto, and can accurately regulate the power according to the characteristics of each battery pack.

[0049] For the lithium-ion energy storage unit 13, the deployment of the PCS can also be similar to that of the sodium-ion energy storage unit 12, and one battery pack can be connected to one PCS. Of course, in order to save costs, one battery cluster or one lithium-ion battery container can be connected to one PCS in the lithium-ion energy storage unit 13. In this case, the PCS is directly connected to the battery container and the power grid, and the power conversion and control are realized through the high-frequency switching action of the power electronic device. The battery can be operated in the appropriate state according to the charging and discharging power of the battery under the instruction condition of the system.

[0050] If one battery pack is connected to one PCS in the sodium-ion energy storage unit 12 or the lithium-ion energy storage unit 13, the problem of inconsistent electrochemical characteristics of the battery packs in one energy storage unit still exists. In order to solve this problem, active balancing between battery packs can be realized.

[0051] Active balancing between battery packs: Each battery pack can be equipped with a power monitoring module for collecting power data and transmitting it to the battery management system. The battery management system can calculate the power difference between each battery pack according to the preset time interval. If the difference exceeds the set threshold (such as 5%), an equalization strategy is developed according to the power difference, such as sending control instructions to the PCS of each battery pack, and the PCS performs charging and discharging operations to reduce the difference.

[0052] Alternatively, the power of each battery pack can also be dynamically balanced through bidirectional DC / AC energy routing between PCSs.

[0053] For the inconsistency of the battery cells in one battery pack, passive balancing within the battery pack can be used to solve the problem.

[0054] Passive balancing within the battery pack: In each battery pack, each battery cell is connected to a voltage monitoring module, which collects voltage data in real time and transmits it to the battery management unit. The battery management unit identifies the battery cells whose voltage exceeds the set threshold, closes the corresponding equalization resistor circuit, and makes the battery cell current flow through the resistor to discharge. When the voltage of the battery cell drops to within the set threshold, the battery management unit disconnects the circuit and stops balancing. In this way, the battery management unit can passively balance the battery cells in the battery pack with a current of 200 mA, maintaining a voltage difference of ≤20 mV.

[0055] For the sodium-ion energy storage unit 12 and the lithium-ion energy storage unit 13, one battery pack can include 52 battery cells or 104 battery cells, one battery cluster can include 5 battery packs or 8 battery packs, and the like, so that the voltage of one battery cluster is 1000 volts DC or 1500 volts DC, if the battery cluster is connected to the DC side of the PCS, it can be converted to 690 volts AC through the PCS, and can be boosted to 10KV through a transformer, connected to a 10KV bus, and transmitted to the local load or external power grid through the bus.

[0056] On the basis of the above embodiment, the sodium-ion energy storage unit 12 is a polyanion sodium-ion battery. The polyanion sodium-ion battery has good low-temperature performance and can discharge more than 90% of the electric quantity at minus 30℃. It also has good rate performance and supports 4P power, so as to quickly respond to the frequency support and voltage support of the power grid. The polyanion sodium-ion battery has a cycle life of more than 12000 times. Since the power station needs to frequently charge and discharge the battery when performing primary frequency modulation in the power grid, the polyanion sodium-ion battery can be used to respond to frequency modulation, so as to ensure the life of the lithium-ion energy storage unit 12.

[0057] The lithium-ion energy storage unit 13 can be a lithium iron phosphate energy storage unit.

[0058] In combination with the structure of the above-mentioned hybrid energy storage system, please refer to Figure 3 , Figure 3 A flowchart of a control method of a hybrid energy storage system provided in the embodiments of the present application is provided. The method is applied to an energy control unit in the hybrid energy storage system and includes the following steps: Step S110: Determine the current operation mode of the hybrid energy storage system.

[0059] The operation mode includes an off-grid operation mode and a grid-connected operation mode. The off-grid operation mode means that the hybrid energy storage system is not connected to the external power grid, and the grid-connected operation mode means that the hybrid energy storage system is connected to the external power grid.

[0060] The energy control unit can monitor the connection state of the hybrid energy storage system and the external power grid in real time through a power grid connection detection device (such as a voltage transformer, a synchronous detection device, etc.) installed in the system, so as to determine whether the current operation mode is the off-grid operation mode or the grid-connected operation mode.

[0061] The off-grid operation mode can have two understandings. One is that the hybrid energy storage system is not connected to the external power grid, such as in some mountainous areas or islands, and the power station is not connected to the external power grid. At this time, the local load can be powered by the hybrid energy storage system and the solar device. The other is that the hybrid energy storage system is originally connected to the external power grid and is powered by the external power grid, but when the external power grid fails, the connection with the hybrid energy storage system is disconnected. In these two cases, the hybrid energy storage system can be understood as not being connected to the external power grid. Here, the connection of the hybrid energy storage system to the external power grid can be understood as the connection of the power station to the external power grid.

[0062] Therefore, the energy control unit can detect the connection state of the external power grid and the hybrid energy storage system. When it is detected that the connection state is connected, it is determined that the current operation mode is the grid-connected operation mode. When it is detected that the connection state is not connected, it is determined that the current operation mode is the off-grid operation mode.

[0063] Step S120: Adopting the control strategy corresponding to the current operation mode, dynamically allocating the power supply roles of the sodium ion energy storage unit and the lithium ion energy storage unit.

[0064] In different operation modes, considering the differences in chemical properties of the two energy storage units, the corresponding control strategy is determined to control the power supply of the two energy storage units.

[0065] For example, sodium ion batteries have good rate performance and low-temperature performance, and are suitable for bearing high-frequency fluctuation loads and deep charge-discharge tasks. In the grid-connected operation mode, they can be mainly used for rapid changes in active power and short-term peak power demand. Sodium ion batteries can maintain good performance in low-temperature environments, so they are more suitable for bearing the main power supply task in low-temperature conditions. Therefore, whether in the grid-connected operation mode or the off-grid operation mode, the sodium ion energy storage unit can be used as the main power supply source in low-temperature environments.

[0066] Lithium ion batteries have relatively low cost and stable quality, and are suitable for bearing stable low-frequency power output. They are more suitable for bearing energy supply tasks with relatively long duration and slow power changes. The performance of lithium ion batteries in high-temperature environments is relatively good, but their performance in low-temperature environments will be greatly affected.

[0067] Specifically, for example, in the off-grid operation mode, the energy control unit first starts the sodium ion energy storage unit to supply power, and uses its quantitative rate performance and low-temperature performance to provide initial power supply for the local load.

[0068] Of course, in the off-grid mode, if the state of charge (SOC) of the sodium-ion energy storage unit decreases to a certain threshold, the energy control unit can start the lithium-ion energy storage unit according to the power demand of the local load and the state of the lithium-ion energy storage unit. The power distribution algorithm is used to reasonably distribute the output power of the sodium-ion energy storage unit and the lithium-ion energy storage unit, for example, high-frequency fluctuating loads are allocated to the sodium-ion energy storage unit, and low-frequency stable loads are allocated to the lithium-ion energy storage unit.

[0069] The energy control unit can monitor the SOC and output power of the two energy storage units in real time, dynamically adjust the power distribution ratio according to the preset control strategy, and ensure the stable operation of the system and the service life of the battery.

[0070] In the grid-connected mode, the external power grid mainly supplies power to the local load, and the external power grid can charge the sodium-ion energy storage unit and the lithium-ion energy storage unit, so that the two energy storage units store electric energy. Of course, the energy control unit can monitor the power demand of the external power grid and the power balance inside the system in real time, adjust the charge and discharge power of the sodium-ion energy storage unit and the lithium-ion energy storage unit according to the dispatching instructions of the power grid and the operating state of the system. When the power demand of the power grid increases, the sodium-ion energy storage unit can be preferentially used to respond quickly to increase the discharge power, and the lithium-ion energy storage unit can appropriately increase the discharge power or reduce the charge power according to the power grid demand and its own state. When the power demand of the power grid decreases, the sodium-ion energy storage unit is preferentially used to reduce the discharge power or increase the charge power, and the lithium-ion energy storage unit adjusts the charge power according to its own state and the power grid demand.

[0071] When switching between operating modes, such as switching from the grid-connected mode to the off-grid mode, the energy control unit can gradually increase the output power of the sodium-ion energy storage unit to gradually take over all the load power. When switching from the off-grid mode to the grid-connected mode, the energy control unit first adjusts the output power of the sodium-ion energy storage unit to synchronize it with the power of the external power grid, then gradually reduces the output power of the sodium-ion energy storage unit to transfer the load power to the external power grid, and at the same time, adjusts the charge and discharge power of the lithium-ion energy storage unit according to the power grid demand.

[0072] In the above implementation process, by accurately identifying the operating mode (off-grid or grid-connected) of the hybrid energy storage system, and intelligently dynamically allocating the power supply role according to the control strategy corresponding to the current operating mode, efficient operation and optimal management of the system are achieved, and the purpose of supplying power to the local load in both grid-connected and off-grid operating modes is achieved. In the off-grid mode, the high-rate charge and discharge advantage of sodium-ion batteries can be fully utilized to quickly respond to power demand and ensure stable power supply of the system; in the grid-connected mode, the charge and discharge power of the two energy storage units can be flexibly adjusted in combination with the characteristics of the power grid to optimize power grid interaction and improve the overall performance of the system.

[0073] On the basis of the above-mentioned embodiments, when the current operation mode is the off-grid operation mode, the energy control unit can also detect the ambient temperature, and in the case where it is detected that the ambient temperature is higher than a first set temperature, control the sodium-ion energy storage unit and the lithium-ion energy storage unit to supply power to the local load. In the case where it is detected that the ambient temperature is lower than or equal to the first set temperature, control the sodium-ion energy storage unit to supply power to the local load, and control the sodium-ion energy storage unit to supply power to the heating element of the lithium-ion energy storage unit.

[0074] In the installation environment of the hybrid energy storage system, a high-precision ambient temperature sensor can be reasonably arranged to collect the ambient temperature, and the ambient temperature sensor is connected to the energy control unit and can transmit the collected ambient temperature to the energy control unit.

[0075] A temperature data collection module can be arranged in the energy control unit, which can read the data of the ambient temperature sensor at a set time interval. The energy control unit can preprocess the collected temperature data, including filtering to remove noise, calibrating data deviation, etc., to improve the accuracy of temperature monitoring.

[0076] The first set temperature, such as 0℃, can be configured in the energy control unit in advance according to the performance characteristics of the lithium-ion battery and the system operation requirements. This first set temperature is the critical point for distinguishing whether the lithium-ion battery needs to be heated. When the temperature is lower than the first set temperature, the lithium-ion battery cannot be discharged, and the sodium-ion energy storage unit needs to supply power to the heating element of the lithium-ion energy storage unit to make the temperature of the lithium-ion energy storage unit reach a set temperature or above, so that the lithium-ion energy storage unit can work normally.

[0077] The energy control unit can compare the ambient temperature and the first set temperature in real time. When the ambient temperature is higher than the first set temperature, it is judged as normal temperature condition, and at this time, the mode of controlling the sodium-ion energy storage unit and the lithium-ion energy storage unit to supply power to the local load together is triggered.

[0078] When the ambient temperature is lower than or equal to the first set temperature, it is judged as low-temperature condition, and the mode of controlling the sodium-ion energy storage unit to supply power alone and heat the lithium-ion energy storage unit is triggered. For example, the energy control unit controls the sodium-ion energy storage unit to supply power to the local load alone, and at the same time, part of the power is allocated to the sodium-ion energy storage unit to supply power to the heating element of the lithium-ion energy storage unit.

[0079] The energy control unit can determine the size of the heating power according to the heating demand of the lithium-ion energy storage unit and the available power of the sodium-ion energy storage unit. For example, the output power of the sodium-ion energy storage unit is controlled by the PCS, part of which is used to meet the power demand of the local load, and the other part is used to heat the lithium-ion energy storage unit through the heating element (such as the heating film or heating wire installed in the lithium-ion battery container, air conditioner, etc.).

[0080] It can be understood that if the ambient temperature is lower than or equal to the first set temperature in the grid-connected operation mode, at this time if the lithium ion energy storage unit cannot work due to low temperature, the heating element of the lithium ion energy storage unit can be powered by the external power grid. Of course, the heating element of the lithium ion energy storage unit can also be powered by the sodium ion energy storage unit.

[0081] In the above implementation process, in the off-grid operation mode, the supply roles of the sodium ion and lithium ion energy storage units are dynamically adjusted according to the ambient temperature, and the differences in chemical properties of the two are ingeniously utilized to achieve precise and efficient energy management. When the ambient temperature is higher than the first set temperature, the sodium ion and lithium ion energy storage units cooperate to supply power to the local load, fully exerting their respective advantages to ensure stable and reliable power supply. When the ambient temperature is lower than or equal to the first set temperature, the sodium ion energy storage unit not only supplies power to the local load, but also supplies power to the heating element of the lithium ion energy storage unit, effectively solving the problem of limited performance of lithium ion batteries in low temperature environments, ensuring normal operation of the system in cold conditions, and significantly improving the adaptability and reliability of the hybrid energy storage system in off-grid state.

[0082] On the basis of the above embodiment, the energy control unit sends a discharge instruction to the sodium ion energy storage unit and a instruction to suspend power supply to the local load to the lithium ion energy storage unit when detecting that the ambient temperature is lower than or equal to the first set temperature. The discharge instruction is used to instruct the sodium ion energy storage unit to supply power to the heating element of the lithium ion energy storage unit and the local load, and the instruction to suspend power supply to the local load is used to instruct the lithium ion energy storage unit to suspend discharging. The lithium ion energy storage unit supplies power to the local load after the temperature of the lithium ion energy storage unit reaches the second set temperature by working through the heating element, and the second set temperature is greater than the first set temperature.

[0083] The energy control unit triggers the corresponding control process when detecting that the ambient temperature is lower than or equal to the first set temperature, such as sending a discharge instruction to the sodium ion energy storage unit and a instruction to suspend power supply to the local load to the lithium ion energy storage unit. When the ambient temperature is lower than or equal to the first set temperature, the lithium ion energy storage unit itself may not be able to discharge, so it cannot make its heating element work. The reason why the instruction to suspend power supply to the local load is sent to the lithium ion energy storage unit is that after the temperature of the lithium ion energy storage unit is greater than the first set temperature, it is prevented from discharging to supply power to the local load, which may cause unstable power.

[0084] After receiving the discharge instruction, the sodium ion energy storage unit continues to discharge, that is, supplies power to the local load and the lithium ion energy storage unit at the same time, such as connecting the power supply circuit of the sodium ion energy storage unit to the lithium ion energy storage unit, and supplying power to the heating element of the lithium ion energy storage unit through the power supply circuit.

[0085] When the lithium-ion energy storage unit receives an instruction to suspend power supply to the local load, it can suspend the discharging process, such as disconnecting the power supply connection with the local load. The alternating current output by the sodium-ion energy storage unit provides power for the heating element of the lithium-ion energy storage unit.

[0086] A temperature sensor is installed in the lithium-ion energy storage unit to detect the temperature of the lithium-ion energy storage unit. After the heating element starts to work, the temperature of the lithium-ion energy storage unit gradually rises.

[0087] The second set temperature is related to whether the lithium-ion energy storage unit can work stably. For example, if the lithium-ion energy storage unit can discharge stably above 10°C, the second set temperature can be 10°C.

[0088] When the temperature of the lithium-ion energy storage unit rises to the second set temperature, the energy control unit determines that the lithium-ion energy storage unit has met the conditions for resuming power supply, and then sends an instruction to the lithium-ion energy storage unit to resume power supply. After receiving the instruction, the lithium-ion energy storage unit restarts the discharging process and supplies power to the local load together with the sodium-ion energy storage unit.

[0089] In the case where the lithium-ion energy storage unit and the sodium-ion energy storage unit supply power to the local load together, the energy control unit can dynamically adjust the output power of the sodium-ion energy storage unit and the lithium-ion energy storage unit to ensure stable operation of the system and balance of power supply and demand.

[0090] In the off-grid operation mode, the two energy storage units can be charged by the solar device, and in the grid-connected operation mode, the two energy storage units can be powered by the external power grid.

[0091] In some embodiments, power adjustment can be based on the state of the battery. The energy control unit can adjust the power according to the difference in SOC of the two energy storage units. If the SOC of the sodium-ion energy storage unit is higher and the SOC of the lithium-ion energy storage unit is lower, the discharging power of the lithium-ion energy storage unit can be appropriately increased and the discharging power of the sodium-ion energy storage unit can be reduced, so that the SOCs of the two energy storage units gradually tend to balance. Conversely, the same applies.

[0092] In some embodiments, dynamic adjustment can be based on power optimization. For example, the energy control unit can use an optimization algorithm (such as a particle swarm optimization algorithm, a genetic algorithm, etc.) to optimize the power output of the two energy storage units in real time. The optimization objectives include minimizing the capacity decay of the batteries, maximizing the energy utilization rate of the system, minimizing the operating cost of the system, etc. For example, through the particle swarm optimization algorithm, the best power output combination of the sodium-ion energy storage unit and the lithium-ion energy storage unit is found under the constraint conditions of meeting the power demand of the local load and the stability of the system, so as to achieve the above optimization objectives.

[0093] In some embodiments, frequency stability control can be used. The energy control unit adjusts the power output according to the frequency change of the system. When the frequency rises, the charging power of the lithium ion energy storage unit is increased or the discharging power of the sodium ion energy storage unit is reduced to absorb the excess power, and when the frequency drops, the discharging power of the sodium ion energy storage unit is increased or the charging power of the lithium ion energy storage unit is reduced to provide more power output, thereby maintaining the stability of the system frequency.

[0094] The energy control unit generates control instructions for each energy storage unit according to the dynamic power adjustment strategy, including the size of the power output, the charging and discharging state, etc. These control instructions are sent to the total control PCS of the energy storage unit, which can adjust the charging and discharging power of the energy storage unit. After the PCS receives the control instructions, the charging and discharging current and voltage of the energy storage unit are quickly adjusted through the high-frequency switching action of the internal power electronic device, thereby realizing accurate control of the power output.

[0095] The energy control unit can compare the system state after power adjustment with the expected target. If it is found that there is a deviation between the actual state and the target state, such as unbalanced power distribution or unstable system voltage, the energy control unit will make a new power adjustment decision based on the feedback information, generate new control instructions, and execute the power adjustment process again.

[0096] This process is repeated in a closed loop to ensure that the system is always in an optimal operating state, dynamically adjusts the output power of the two energy storage units, and ensures stable operation and power supply-demand balance of the system.

[0097] In the above implementation process, when operating in off-grid mode and the ambient temperature is less than or equal to the first set temperature, the sodium ion energy storage unit is controlled to supply power to the local load and the heating element of the lithium ion energy storage unit, while the lithium ion energy storage unit is suspended from supplying power to the local load, thereby ingeniously solving the problem of limited performance of lithium ion batteries at low temperatures. After the temperature of the lithium ion energy storage unit rises to the second set temperature, the supply of power to the local load is restored. This process not only effectively prolongs the service life of the lithium ion energy storage unit in a low-temperature environment, but also ensures the stability and reliability of the hybrid energy storage system under extreme conditions, and significantly improves the adaptability of the system to environmental changes.

[0098] In some embodiments, when the current operating mode is the grid-connected mode, the energy control unit can obtain the working state parameters of the external power grid, determine whether the hybrid energy storage system needs to supply power to the external power grid according to the working state parameters, and if so, control the charging and discharging power of the sodium ion energy storage unit and the lithium ion energy storage unit according to the set adaptive power control strategy.

[0099] In the grid-connected operation mode, the external power grid is connected with the local load, and the local load is powered by the external power grid. Under normal circumstances, the sodium-ion energy storage unit and the lithium-ion energy storage unit are in a suspended discharge state and are in a charging state, and the external power grid charges the sodium-ion energy storage unit and the lithium-ion energy storage unit.

[0100] A power grid parameter detection device is installed at the connection point of the hybrid energy storage system and the external power grid, including a voltage transformer, a current transformer, a frequency meter, and a power analyzer, etc., for real-time monitoring of the working state parameters of the external power grid, such as voltage, current, frequency, power, etc. These power grid parameter detection devices can be connected with the energy control unit, so that the energy control unit can obtain the working state parameters of the external power grid.

[0101] The energy control unit can perform real-time analysis on the collected working state parameters of the external power grid, for example, according to the voltage deviation, frequency deviation, power gap, etc. parameters, to determine whether the power supply quality of the external power grid meets the requirements. For example, set the grid abnormal threshold, such as voltage deviation exceeding the set voltage range, frequency deviation exceeding the set frequency range, and / or power gap exceeding the set proportion, etc. When the working state parameters of the external power grid exceed these thresholds, it is determined that the hybrid energy storage system needs to supply power to the external power grid. Conversely, the hybrid energy storage system does not need to supply power. Alternatively, the collected working state parameters of the external power grid can be input into a pre-trained neural network model to predict whether the external power grid needs the hybrid energy storage system to supply power based on these working state parameters.

[0102] Among them, the set adaptive power control strategy can be pre-configured according to the power supply demand of the external power grid. For example, when the grid frequency drops, the discharge power of the sodium-ion energy storage unit and the lithium-ion energy storage unit can be increased, and when the grid frequency rises, the charging power of the sodium-ion energy storage unit and the lithium-ion energy storage unit can be increased.

[0103] At the same time, considering the characteristics of the sodium-ion energy storage unit and the lithium-ion energy storage unit, the charge and discharge power of the two energy storage units is reasonably allocated, for example, the high-frequency fluctuation load is allocated to the sodium-ion energy storage unit, and the low-frequency stable load is allocated to the lithium-ion energy storage unit.

[0104] In some embodiments, the adaptive power control strategy here can refer to the power adjustment based on the battery state, the dynamic adjustment strategy based on power optimization, or the frequency stability control strategy mentioned in the above embodiments, and the energy control unit can control the charge and discharge power of the two energy storage units according to the corresponding strategy.

[0105] It can be understood that in the grid-connected mode, the local load is also connected to the external power grid, and the hybrid energy storage system and the local load are connected to the same transformer. When the hybrid energy storage system supplies power to the external power grid, the output voltage of the hybrid energy storage system is slightly higher than the voltage of the external power grid, so the hybrid energy storage system supplies power to the local load at this time. Of course, if the hybrid energy storage system does not need to supply power to the external power grid, the local load is supplied by the external power grid, and at this time the hybrid energy storage system can take power from the external power grid to charge.

[0106] In the above implementation process, in the grid-connected operation mode, the working state parameters of the external power grid are obtained to accurately determine whether the hybrid energy storage system needs to supply power to the external power grid. If so, the charging and discharging power of the sodium ion and lithium ion energy storage units is dynamically adjusted according to the set adaptive power control strategy. This intelligent control method based on real-time power grid state fully utilizes the chemical characteristics of the two types of energy storage units, improves the flexibility and response speed of the system, optimizes the power balance of the power grid, and enhances the stability of the power grid.

[0107] On the basis of the above embodiment, in the manner of controlling the charging and discharging power of the two energy storage units according to the set adaptive power control strategy, the historical power data of the hybrid energy storage system can be obtained, and the charging and discharging power of the hybrid energy storage system in a set time period can be predicted according to the historical power data. Then, according to the charging and discharging power and the remaining capacity of the lithium ion energy storage unit and the remaining capacity of the sodium ion energy storage unit, the charging and discharging power strategy of the hybrid energy storage system in a future time period is determined, and then the charging and discharging power of the lithium ion energy storage unit and the sodium ion energy storage unit is adjusted according to the charging and discharging power strategy.

[0108] The historical power data of the hybrid energy storage system can be stored in an external storage or in a storage unit of the hybrid energy storage system. The historical power data can include the charging and discharging power of the sodium ion energy storage unit and the lithium ion energy storage unit, the total power of the system, the power exchanged with the power grid, etc. The data collection time range should be long enough to cover different operating conditions and seasonal changes.

[0109] In order to facilitate subsequent analysis and modeling, the historical power data can be arranged in time sequence to form time series data and normalized.

[0110] In some embodiments, a model suitable for time series prediction can be used to predict the charging and discharging power of the hybrid energy storage system, such as a long short-term memory network based on machine learning, a BP neural network model, and a recurrent neural network model such as a gated recurrent unit. These models can be obtained by training a large amount of data in advance.

[0111] The trained prediction model is applied to historical power data to predict the charging and discharging power of the hybrid energy storage system in a set time period, and the charging and discharging power condition is obtained. The charging and discharging power condition can include the charging and discharging power value at each time point and the corresponding confidence interval.

[0112] In the manner of predicting the charging and discharging power strategy of the hybrid energy storage system in the future time period according to the charging and discharging power condition and the remaining power of the lithium ion energy storage unit and the remaining power of the sodium ion energy storage unit, the predicted charging and discharging power condition can represent the trend of the charging and discharging power demand in the future time period, such as the size and direction of the power (charging or discharging), so that the SOC change of each energy storage unit in the future time period can be calculated according to the remaining power of the lithium ion energy storage unit (i.e. SOC), the remaining power of the sodium ion energy storage unit (SOC) and the predicted charging and discharging power. Then, the charging and discharging power of each energy storage unit can be dynamically adjusted based on the predicted SOC change and the charging and discharging characteristics of the battery.

[0113] For example, if the current SOC of the lithium ion energy storage unit is 40%, and it is predicted that a continuous discharging power of 5kW is required in the next 1 hour, according to the capacity and discharging efficiency of the battery, it is estimated that the SOC after 1 hour will be reduced to 30%. If the predicted SOC is lower than the lower limit of the safety range, the discharging power is reduced or the charging power is increased in advance; if the predicted SOC is too high, the discharging power is appropriately increased or the charging power is reduced, so that the SOC is ensured to be within a reasonable range.

[0114] When determining the charging and discharging power strategy, under the premise of meeting the system power demand, the high-rate charging and discharging characteristics of the sodium ion battery can be considered to develop a higher discharging power strategy to bear the rapid power change and high-frequency fluctuation part in the system, while ensuring that its SOC changes within a reasonable range to avoid over-discharge. For the lithium ion energy storage unit, in combination with its SOC and the characteristics of being sensitive to deep charging and discharging, a relatively stable charging and discharging power strategy is developed to mainly bear the low-frequency stable power output of the system. When the predicted charging and discharging power demand is low, the charging power is appropriately increased to recover the SOC; when the predicted power demand is high, the discharging power is reasonably allocated according to the SOC and the health state of the lithium ion energy storage unit to avoid deep discharge.

[0115] The setting of the set time period in the above can be determined according to the operation characteristics of the hybrid energy storage system and the demand of the power grid, such as one day, which is a long time period and is suitable for power analysis and planning for a long time. The set time period can also be short, such as 1 hour, which is suitable for more accurate short-term power prediction and real-time control. The length of the predicted charging and discharging power strategy of the hybrid system can be the future time period, which can be the same as the set time period or different, such as greater than the set time period or less than the set time period.

[0116] In some embodiments, after obtaining the historical power data, wavelet decomposition can be performed on the historical power data. For example, the historical power data is taken as an input signal, and wavelet decomposition is performed using a selected wavelet function and decomposition scale. Through wavelet transform, the original power signal is decomposed into sub-band signals of different frequency bands. For example, in the case of decomposition into three scales, three detail coefficients (d1, d2, d3) of different frequency bands and one approximation coefficient (a3) of low frequency are obtained, wherein d1 corresponds to the highest frequency band, mainly containing noise and rapid fluctuation components in the signal; d2 and d3 correspond to the medium frequency band, reflecting the slower fluctuations of the power; and a3 represents the low-frequency trend term of the power signal.

[0117] The input data of the prediction model includes the characteristic values of the sub-band signals after wavelet decomposition, historical power values, time stamps, and other information. Here, the charging and discharging power situation within one day or within one hour can be predicted. Of course, the charging and discharging power situation within different time lengths, such as one day and one hour, can also be predicted respectively.

[0118] In some embodiments, historical power data can be obtained every time period (such as one hour), and the charging and discharging power situation is predicted in a rolling manner, so that the charging and discharging power of the two energy storage units can be adjusted in real time according to the actual power demand.

[0119] In the above implementation process, by obtaining the historical power data of the hybrid energy storage system and performing prediction analysis, and combining the remaining power of the sodium-ion and lithium-ion energy storage units, a dynamic charging and discharging power strategy is formulated, and precise adjustment of the charging and discharging power of the two energy storage units is realized. This data-driven adaptive control method can effectively optimize the energy management of the hybrid energy storage system and improve the operating efficiency and flexibility of the system.

[0120] On the basis of the above embodiments, in the manner of controlling the charging and discharging power of the two energy storage units according to the set adaptive power control strategy, the following strategies can also be formulated: (1) If it is detected that the power change rate of the hybrid energy storage system exceeds the set change rate, the sodium-ion energy storage unit is controlled to increase the discharging power and the lithium-ion energy storage unit is controlled to reduce the discharging power.

[0121] In this manner, the energy control unit can collect the total power output value of the hybrid energy storage system in real time and calculate the power change rate within a time period. A power change rate threshold, i.e., a set change rate, is set. If the power change rate exceeds the set change rate, it indicates that the system power demand may have changed sharply, such as sudden increase or decrease of power grid load or power fluctuation caused by fault, and at this time the charging and discharging power of the energy storage units needs to be adjusted to stabilize the system.

[0122] Sodium-ion batteries have high rate discharge capability and can quickly respond to power changes, increasing their discharge power to quickly fill the system power gap and reduce the power change rate. Lithium-ion batteries are relatively poor at quickly changing power, so reducing their discharge power can prevent them from being damaged by excessive power changes, and more power adjustment tasks can be assigned to sodium-ion batteries.

[0123] (2) If the SOC of the sodium-ion energy storage unit is detected to be within the set range, control the sodium-ion energy storage unit to increase the discharge power and control the lithium-ion energy storage unit to reduce the discharge power.

[0124] In this way, the energy control unit can obtain the current SOC of the sodium-ion energy storage unit in real time, determine whether it is within the set range, and set the set range based on the performance of the sodium-ion battery. For example, within the set range, the sodium-ion battery has optimal performance and can better balance the depth of discharge and battery life.

[0125] Therefore, when the SOC of the sodium-ion energy storage unit is within the set range, it indicates that it has sufficient remaining capacity to undertake more discharge tasks and can fully utilize its performance. By transferring part of the discharge demand to the sodium-ion battery, the discharge pressure on the lithium-ion battery is reduced, the life of the lithium-ion battery is prolonged, and the system power distribution is optimized.

[0126] (3) If the SOC of the lithium-ion energy storage unit is detected to be lower than the set state of charge, control the sodium-ion energy storage unit to increase the discharge power and control the lithium-ion energy storage unit to reduce the discharge power.

[0127] In this way, the energy control unit can obtain the current SOC of the lithium-ion energy storage unit in real time, and if the SOC is lower than the set state of charge, it indicates that the battery is in a low capacity state and that continued deep discharge may damage the battery performance and life. Therefore, the sodium-ion battery can be allowed to undertake more discharge tasks to give the lithium-ion battery time to recover its capacity. Reducing the discharge of the lithium-ion battery can prevent it from being damaged by deep discharge and ensure stable operation of the system.

[0128] The above strategy can take effect as long as any one of the conditions is met. The specific amount of increase and decrease in discharge power can be adjusted according to actual conditions, and the specific amount of adjustment each time can be relatively small. If the adjustment still does not meet the requirements, further adjustment is continued, which can achieve stepwise adjustment and avoid the problem of excessive one-time adjustment leading to suboptimal power distribution of the two energy storage units.

[0129] In the above implementation process, through the set adaptive power control strategy, the charge and discharge power of the sodium-ion and lithium-ion energy storage units is dynamically adjusted based on the power change rate of the hybrid energy storage system, the state of charge (SOC) of the sodium-ion energy storage unit, and the SOC of the lithium-ion energy storage unit. This intelligent control method can effectively respond to rapid changes in system power, optimize power distribution, and ensure stable operation of the system under different operating conditions.

[0130] It should be noted that the adaptive power control strategy in the grid-connected operation mode is also applicable to the control strategy when the sodium-ion energy storage unit and the lithium-ion energy storage unit jointly supply power to the local load in the off-grid operation mode, that is, in the off-grid operation mode, if the lithium-ion energy storage unit can continue to supply power to the local load after being warmed up, the adaptive control strategy can be used to control the charge and discharge power of the two energy storage units.

[0131] On the basis of the above embodiment, in the manner in which the energy control unit determines the current operation mode of the hybrid energy storage system, the voltage of the grid connection point at which the hybrid energy storage system is connected to the external power grid can be detected, and then the connection state of the external power grid and the hybrid energy storage system can be determined according to the voltage, and the current operation mode of the hybrid energy storage system can be determined according to the connection state.

[0132] In a specific implementation, a voltage transformer can be installed at the grid connection point at which the hybrid energy storage system is connected to the external power grid, for measuring the voltage of the grid connection point. The voltage transformer is connected to the energy control unit, and can send the collected voltage to the energy control unit.

[0133] It should be noted that if the power station is not deployed with an external power grid, the voltage of the grid connection point cannot be detected at this time, and the current operation mode can be directly determined as the off-grid operation mode at this time.

[0134] Of course, if an external power grid is deployed, the voltage can be detected to determine whether the external power grid has failed, and if it has failed, the connection state indicates disconnection, and the current operation mode is determined as the off-grid operation mode at this time, and if it has not failed, the connection state indicates connection, and the current operation mode is determined as the grid-connected operation mode at this time.

[0135] In the above implementation process, the connection state of the external power grid and the hybrid energy storage system is accurately determined by detecting the voltage of the grid connection point at which the hybrid energy storage system is connected to the external power grid, and then the current operation mode of the system is determined. This voltage monitoring-based mode recognition method can quickly and accurately identify the grid-connected or off-grid state, and ensure that the control strategy is switched in time under different operation modes.

[0136] On the basis of the above embodiment, when determining the connection state, if the voltage is less than a first set threshold or greater than a second set threshold, it is determined that the connection state of the external power grid and the hybrid energy storage system is disconnected, wherein the first set threshold is less than the second set threshold.

[0137] The first set threshold and the second set threshold can be determined according to a rated voltage of the external power grid and an allowable deviation range. For example, the first set threshold is a lower limit of voltage, and the second set threshold is an upper limit of voltage. For example, the rated voltage of the power grid is 380V, and the allowable deviation is -10% to +10%, the first set threshold is 342V (380*0.9), and the second set threshold is 418V (380*1.1).

[0138] The energy control unit compares the collected voltage with the first set threshold and the second set threshold. If the voltage is less than the first set threshold or greater than the second set threshold, it is considered that the external power grid has a fault, and the connection state is disconnected. Otherwise, the connection state is normal.

[0139] When the connection state is disconnected, it is determined that the current operation mode is an off-grid operation mode. When the connection state is normal, it is determined that the current operation mode is a grid-connected operation mode.

[0140] Specifically, in the grid-connected operation mode, the voltage of the grid-connected point is collected in real time. If the voltage of the grid-connected point is abnormal due to a power grid fault, such as being less than the first set threshold or greater than the second set threshold, the energy control unit determines that the off-grid operation mode, and the hybrid energy storage system switches to the off-grid operation mode to supply power to the local load. After the fault is eliminated, the voltage of the grid-connected point returns to the normal range. After the energy control unit detects that the voltage is normal, the system is reconnected to the external power grid, and the grid-connected operation mode is restored.

[0141] In the above implementation process, the judgment method based on the double thresholds can effectively avoid misjudgment caused by normal fluctuations of the voltage of the power grid, and improve the accuracy and reliability of the judgment.

[0142] On the basis of the above embodiment, in order to avoid misjudgment, the collected voltage can include a plurality of voltages sampled continuously.

[0143] For example, the energy control unit stores the voltage collected by the voltage transformer in the buffer area according to the time sequence. The energy control unit can determine after each continuous plurality of voltages (such as 10 voltages) are obtained. (The buffer area stores 10 voltage values each time, and the newly collected voltage is stored in the buffer area in a way of covering the longest stored voltage.) If the plurality of voltages are all lower than the first set threshold or all higher than the second set threshold, it is considered that the connection state is disconnected, and the corresponding off-grid operation control process is triggered.

[0144] In some embodiments, the mean value of the plurality of voltages can also be calculated. If the mean value is lower than the first set threshold or higher than the second set threshold, it is considered that the connection state is disconnected, and the off-grid operation mode is entered.

[0145] In the implementation process, the connection state of the external power grid and the hybrid energy storage system is determined by using the plurality of voltage data sampled continuously, compared with single sampling, the actual change of the grid-connected point voltage can be more comprehensively and accurately reflected. The continuous sampling can effectively avoid misjudgment caused by instantaneous voltage fluctuation or sampling error, and improve the stability and reliability of the determination.

[0146] Please refer to Figure 4 , Figure 4 A structural block diagram of a control device 200 of a hybrid energy storage system is provided for the embodiments of the present application. The control device 200 of the hybrid energy storage system can be a module, a program segment or code on an electronic device (i.e. an energy control unit). It should be understood that the control device 200 of the hybrid energy storage system corresponds to the above-mentioned method embodiments, and can perform each step involved in the method embodiments. The specific functions of the control device 200 of the hybrid energy storage system can be referred to the description in the above, and the detailed description is appropriately omitted here to avoid repetition.

[0147] Optionally, the control device 200 of the hybrid energy storage system comprises: An operation mode determination module 210 is configured to determine a current operation mode of the hybrid energy storage system, wherein the operation mode comprises an off-grid operation mode and a grid-connected operation mode, the off-grid operation mode refers to that the hybrid energy storage system is not connected to an external power grid, and the grid-connected operation mode refers to that the hybrid energy storage system is connected to the external power grid. A control module 220 is configured to dynamically allocate power supply roles of the sodium ion energy storage unit and the lithium ion energy storage unit by using a control strategy corresponding to the current operation mode.

[0148] Optionally, the current operation mode is the off-grid operation mode, and the control module 220 is configured to control the sodium ion energy storage unit and the lithium ion energy storage unit to supply power to a local load when detecting that an ambient temperature is higher than a first set temperature; and control the sodium ion energy storage unit to supply power to the local load and control the sodium ion energy storage unit to supply power to a heating device of the lithium ion energy storage unit when detecting that the ambient temperature is lower than or equal to the first set temperature.

[0149] Optionally, the control module 220 is configured to send a discharging instruction to the sodium ion energy storage unit and send an instruction to suspend power supply to the local load to the lithium ion energy storage unit when detecting that the ambient temperature is lower than or equal to the first set temperature. The discharge instruction is used to instruct the sodium-ion energy storage unit to supply power to the heating element of the lithium-ion energy storage unit and the local load, the instruction for suspending power supply to the local load is used to instruct the lithium-ion energy storage unit to suspend discharging, and the lithium-ion energy storage unit is used to supply power to the local load after the temperature of the lithium-ion energy storage unit reaches a second set temperature through the working of the heating element, wherein the second set temperature is greater than the first set temperature.

[0150] Optionally, the current operation mode is a grid-connected operation mode, and the control module 220 is configured to acquire an operating state parameter of the external power grid, determine whether the hybrid energy storage system needs to supply power to the external power grid according to the operating state parameter, and control the charging and discharging power of the sodium-ion energy storage unit and the lithium-ion energy storage unit according to a set adaptive power control strategy if the hybrid energy storage system needs to supply power to the external power grid.

[0151] Optionally, the control module 220 is configured to acquire historical power data of the hybrid energy storage system, predict the charging and discharging power condition of the hybrid energy storage system in a set time period according to the historical power data, determine a charging and discharging power strategy of the hybrid energy storage system according to the charging and discharging power condition, the remaining electric quantity of the lithium-ion energy storage unit and the remaining electric quantity of the sodium-ion energy storage unit, and adjust the charging and discharging power of the lithium-ion energy storage unit and the sodium-ion energy storage unit according to the charging and discharging power strategy.

[0152] Optionally, the control module 220 is configured to control the sodium-ion energy storage unit to increase the discharging power and control the lithium-ion energy storage unit to reduce the discharging power if it is detected that the power variation rate of the hybrid energy storage system exceeds a set variation rate, and / or control the sodium-ion energy storage unit to increase the discharging power and control the lithium-ion energy storage unit to reduce the discharging power if it is detected that the state of charge of the sodium-ion energy storage unit is in a set range, and / or control the sodium-ion energy storage unit to increase the discharging power and control the lithium-ion energy storage unit to reduce the discharging power if it is detected that the state of charge of the lithium-ion energy storage unit is lower than a set state of charge.

[0153] Optionally, the operation mode determination module 210 is configured to detect the voltage of a grid-connected point at which the hybrid energy storage system is connected to the external power grid, determine the connection state of the external power grid and the hybrid energy storage system according to the voltage, and determine the current operation mode of the hybrid energy storage system according to the connection state.

[0154] Optionally, the operation mode determination module 210 is configured to determine that the connection state of the external power grid and the hybrid energy storage system is disconnected if the voltage is less than a first set threshold or greater than a second set threshold, wherein the first set threshold is less than the second set threshold.

[0155] Optionally, the voltage comprises a plurality of voltages sampled consecutively.

[0156] It should be noted that, for the convenience and brevity of description, the specific working process of the apparatus described above can refer to the corresponding process in the foregoing method embodiments, which will not be described here.

[0157] Please refer to Figure 5 , Figure 5 A structural schematic diagram of an electronic device for performing a control method of a hybrid energy storage system according to an embodiment of the present application is shown in FIG. 3. The electronic device can be the energy control unit described above, and can include at least one processor 310, such as a CPU, at least one communication interface 320, at least one memory 330, and at least one communication bus 340. The communication bus 340 is used to realize the connection and communication between the components. The communication interface 320 of the device in the embodiment of the present application is used to communicate signaling or data with other node devices. The memory 330 can be a high-speed RAM memory, or a non-volatile memory, such as at least one disk memory. The memory 330 can also be at least one storage device located away from the aforementioned processor. The memory 330 stores computer readable instructions, and when the computer readable instructions are executed by the processor 310, the electronic device performs the method process described above.

[0158] It can be understood that Figure 5 The structure shown is only schematic, and the electronic device can include more or fewer components than those shown in Figure 5 , or have a different configuration from Figure 5 . Figure 5 The components shown in may be implemented in hardware, software, or a combination thereof.

[0159] The embodiment of the present application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to perform the method process performed by the electronic device in the method embodiment.

[0160] The embodiment of the present application discloses a computer program product, which includes a computer program stored on a non-transitory computer readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the method provided by each method embodiment described above, for example, including: determining a current operation mode of the hybrid energy storage system, wherein the operation mode comprises an off-grid operation mode and a grid-connected operation mode, the off-grid operation mode refers to that the hybrid energy storage system is not connected to an external power grid, and the grid-connected operation mode refers to that the hybrid energy storage system is connected to the external power grid; adopting a control strategy corresponding to the current operation mode to dynamically allocate power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit.

[0161] To sum up, the embodiment of the present application provides a control method of a hybrid energy storage system, a hybrid energy storage system and equipment, which accurately identifies the operation mode (off-grid or grid-connected) of the hybrid energy storage system, intelligently dynamically allocates power supply roles according to the control strategy corresponding to the current operation mode, realizes efficient operation and optimized management of the system, and achieves the purpose of supplying power for local loads in both grid-connected and off-grid operation modes. In the off-grid mode, the high-rate charge and discharge advantage of the sodium-ion battery can be fully utilized to quickly respond to power demand and ensure stable power supply of the system; in the grid-connected mode, the charge and discharge power of the two energy storage units can be flexibly adjusted in combination with the characteristics of the power grid to optimize power grid interaction and improve the overall performance of the system.

[0162] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other manners. The above-described device embodiments are only schematic. For example, the division of the units is only a logical function division. There can be another division manner for the actual implementation, for example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between the units can be indirect couplings or communication connections through some interfaces, devices or units, and can be electrical, mechanical or in other forms.

[0163] In addition, the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, i.e., can be located in one place, or can be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0164] Furthermore, each functional module in each embodiment of the present application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0165] In this document, the relationship terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations.

[0166] The above embodiments are only used to illustrate the present application, but not to limit the present application. The present application can be modified and changed by those skilled in the art without departing from the spirit and principle of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A control method for a hybrid energy storage system, characterized in that, An energy control unit applied in a hybrid energy storage system, the hybrid energy storage system further including a sodium-ion energy storage unit and a lithium-ion energy storage unit, the method comprising: The current operating mode of the hybrid energy storage system is determined, wherein the operating mode includes an off-grid operating mode and a grid-connected operating mode. The off-grid operating mode refers to the hybrid energy storage system not being connected to the external power grid, and the grid-connected operating mode refers to the hybrid energy storage system being connected to the external power grid. The power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit are dynamically allocated by adopting a control strategy corresponding to the current operating mode.

2. The method according to claim 1, characterized in that, The current operating mode is an off-grid operating mode. The adoption of a control strategy corresponding to the current operating mode to dynamically allocate the power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit includes: When the ambient temperature is detected to be higher than the first set temperature, the sodium ion energy storage unit and the lithium ion energy storage unit are controlled to supply power to the local load. When the ambient temperature is detected to be lower than or equal to the first set temperature, the sodium ion energy storage unit is controlled to supply power to the local load, and the sodium ion energy storage unit is controlled to supply power to the heating element of the lithium ion energy storage unit.

3. The method according to claim 2, characterized in that, The step of controlling the sodium-ion energy storage unit to supply power to the local load and controlling the sodium-ion energy storage unit to supply power to the heating element of the lithium-ion energy storage unit when the ambient temperature is detected to be lower than or equal to the first set temperature includes: If the ambient temperature is detected to be lower than or equal to the first set temperature, a discharge command is sent to the sodium ion energy storage unit, and a command to suspend power supply to the local load is sent to the lithium ion energy storage unit. The discharge command is used to instruct the sodium ion energy storage unit to supply power to the heating element of the lithium ion energy storage unit and the local load. The command to pause power supply to the local load is used to instruct the lithium ion energy storage unit to pause discharge. The lithium ion energy storage unit is used to supply power to the local load after the temperature of the lithium ion energy storage unit reaches a second set temperature through the operation of the heating element, wherein the second set temperature is greater than the first set temperature.

4. The method according to claim 1, characterized in that, The current operating mode is grid-connected operation mode. The step of adopting a control strategy corresponding to the current operating mode to dynamically allocate the power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit includes: Obtain the operating status parameters of the external power grid; Determine whether the hybrid energy storage system needs to supply power to the external power grid based on the operating status parameters; If necessary, the charging and discharging power of the sodium-ion energy storage unit and the lithium-ion energy storage unit shall be controlled according to the set adaptive power control strategy.

5. The method according to claim 4, characterized in that, The step of controlling the charging and discharging power of the sodium-ion energy storage unit and the lithium-ion energy storage unit according to the set adaptive power control strategy includes: Obtain historical power data of the hybrid energy storage system; Predict the charging and discharging power of the hybrid energy storage system within a set time period based on the historical power data. Based on the charging and discharging power status, the remaining power of the lithium-ion energy storage unit, and the remaining power of the sodium-ion energy storage unit, the charging and discharging power strategy of the hybrid energy storage system is determined. The charging and discharging power of the lithium-ion energy storage unit and the sodium-ion energy storage unit is adjusted according to the charging and discharging power strategy.

6. The method according to claim 4, characterized in that, The step of controlling the charging and discharging power of the sodium-ion energy storage unit and the lithium-ion energy storage unit according to the set adaptive power control strategy includes: If the power change rate of the hybrid energy storage system is detected to exceed the set change rate, the sodium ion energy storage unit is controlled to increase its discharge power and the lithium ion energy storage unit is controlled to decrease its discharge power. And / or, if the state of charge of the sodium ion energy storage unit is detected to be within a set range, the sodium ion energy storage unit is controlled to increase its discharge power and the lithium ion energy storage unit is controlled to decrease its discharge power. And / or, if the state of charge of the lithium-ion energy storage unit is detected to be lower than the set state of charge, the sodium-ion energy storage unit is controlled to increase its discharge power and the lithium-ion energy storage unit is controlled to decrease its discharge power.

7. The method according to any one of claims 1-6, characterized in that, Determining the current operating mode of the hybrid energy storage system includes: Detect the voltage at the grid connection point where the hybrid energy storage system is connected to the external power grid; The connection status between the external power grid and the hybrid energy storage system is determined based on the voltage. The current operating mode of the hybrid energy storage system is determined based on the connection status.

8. The method according to claim 7, characterized in that, Determining the connection status between the external power grid and the hybrid energy storage system based on the voltage includes: If the voltage is less than a first set threshold or greater than a second set threshold, the connection between the external power grid and the hybrid energy storage system is determined to be disconnected, wherein the first set threshold is less than the second set threshold.

9. The method according to claim 8, characterized in that, The voltage includes multiple voltages sampled continuously.

10. A hybrid energy storage system, characterized in that, The hybrid energy storage system includes: An energy control unit, a sodium-ion energy storage unit, and a lithium-ion energy storage unit are provided. The energy control unit is connected to the sodium-ion energy storage unit and the lithium-ion energy storage unit, respectively. The energy control unit is used to determine the current operating mode of the hybrid energy storage system, wherein the operating mode includes an off-grid operating mode and a grid-connected operating mode. The off-grid operating mode refers to the hybrid energy storage system not being connected to the external power grid, and the grid-connected operating mode refers to the hybrid energy storage system being connected to the external power grid. The control unit adopts a control strategy corresponding to the current operating mode to dynamically allocate the power supply roles of the sodium-ion energy storage unit and the lithium-ion energy storage unit.

11. The hybrid energy storage system according to claim 10, characterized in that, The sodium-ion energy storage unit includes multiple battery clusters, each battery cluster is formed by multiple battery packs connected in series, and each battery pack is connected to an energy storage converter.

12. The hybrid energy storage system according to claim 10, characterized in that, The sodium-ion energy storage unit is a polyanion sodium-ion battery.

13. An electronic device, characterized in that, It includes a processor and a memory, the memory storing computer-readable instructions that, when executed by the processor, perform the method as described in any one of claims 1-9.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it performs the method as described in any one of claims 1-9.

15. A computer program product, characterized in that, It includes computer program instructions, which, when read and executed by a processor, perform the method as described in any one of claims 1-9.

Images