A soc equalization method for an energy storage system, medium and device

Abstract

The application discloses a SOC balancing method of an energy storage system, a medium and equipment; the method comprises the following steps: determining the required power of each phase of the energy storage system and calculating the total required power of the battery; obtaining the state information of each battery pack, combining the total required power of the battery to distribute the battery power instruction for realizing SOC balancing, and then determining the total inverter power of each inverter; according to the deviation of the required power of each phase and the average required power of three phases, the total inverter power of each inverter is redistributed to obtain the expected power instruction of each phase; the expected power instruction is adjusted based on the charge and discharge capacity constraint of each phase and the imbalance capacity constraint between phases to generate the final power instruction to control the operation of each inverter. The medium and equipment are used to implement the above method. The application has the beneficial effects that the application can realize the state of charge balancing between different battery packs while the three-phase power output of the energy storage system is not equal, and the system operation stability is improved.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a SOC balancing method, medium and equipment for an energy storage system. Background Technology

[0002] In existing technologies, the SOC balancing strategy for photovoltaic-storage hybrid inverters or energy storage inverters mainly involves determining the required output power of the system batteries based on the system's energy requirements, and then allocating the power of each battery according to information such as SOC and voltage. However, there is no description of how the battery power is allocated to the inverter side power. It can be assumed that the batteries and photovoltaics (if any) naturally obtain the inverter side power based on energy conservation, without involving the redistribution of the inverter side power of the unit itself.

[0003] Without inverter-side power redistribution strategies, existing SOC balancing strategies are only applicable to systems that do not require inverter-side power redistribution, such as single-phase energy storage systems, three-phase three-wire energy storage systems, and three-phase four-wire energy storage systems with balanced three-phase power output, or other split-phase systems. In other words, existing SOC balancing strategies are not applicable to three-phase energy storage systems that require unbalanced three-phase power output. Summary of the Invention

[0004] One objective of this application is to provide a SOC balancing method for energy storage systems that can address at least one of the deficiencies in the aforementioned background technology.

[0005] Another object of this application is to provide a computer-readable storage medium capable of implementing a SOC balancing method for an energy storage system that addresses at least one of the deficiencies in the aforementioned background art.

[0006] Another object of this application is to provide an electronic device capable of implementing a SOC balancing method for an energy storage system that addresses at least one of the deficiencies in the aforementioned background art.

[0007] To achieve at least one of the above objectives, one aspect of this application provides a SOC balancing method for an energy storage system, the energy storage system including at least one inverter and multiple battery packs; the method includes the following steps: determining the power demand of each phase in the energy storage system according to the operating mode and energy management strategy of the energy storage system, and calculating the total battery power demand of the energy storage system based on the obtained power demand; acquiring the state information of each battery pack in the energy storage system, and, in conjunction with the obtained total battery power demand, allocating a battery power command for achieving SOC balancing between battery packs to each battery pack, and determining the total inverter power required by each inverter; redistributing the total inverter power of each inverter according to the deviation between the power demand of each phase and the average power demand of the three phases, to obtain the expected power command for each inverter; adjusting the expected power command based on the charging and discharging capacity constraints of each phase and the inter-phase imbalance capacity constraints, to obtain the final power command for each inverter, used to control the operation of each inverter.

[0008] Preferably, the battery pack status information includes real-time SOC, capacity, and voltage. When the total battery power demand indicates that the battery pack needs to discharge, the power allocation coefficient of each battery pack is calculated based on the difference between the real-time SOC of each battery pack and the set discharge target equalization value, combined with the capacity and voltage. When the total battery power demand indicates that the battery pack needs to charge, the power allocation coefficient of each battery pack is calculated based on the difference between the set charging target equalization value and the real-time SOC of each battery pack, combined with the capacity and voltage. The ratio of the power allocation coefficient of each battery pack to the sum of the power allocation coefficients of all battery packs is used as a weight and multiplied by the total battery power demand to obtain the battery power command required by each battery pack.

[0009] Preferably, when allocating battery power commands, if the battery power command corresponding to a battery pack exceeds its rated power limit, the battery power command of that battery pack is limited to the rated power, and the excess portion is redistributed to battery packs that have not reached their rated power limit.

[0010] Preferably, in a three-phase energy storage system, the calculation expression for the expected power command corresponding to L of the i-th inverter is as follows: ; ; In the formula, This represents the desired power command corresponding to L for the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter. This represents the sum of the three-phase power demand of the energy storage system, and N represents the number of inverters in the energy storage system.

[0011] Preferably, in a three-phase energy storage system, the calculation expression for the expected power command corresponding to L of the i-th inverter is as follows: ; ; In the formula, This represents the desired power command corresponding to L for the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter. This represents the sum of the three-phase power demand of the energy storage system. This represents the power capability of the L-phase of the i-th inverter. This represents the sum of the power capabilities of all L-phase inverters.

[0012] Preferably, in a three-phase energy storage system, for the i-th inverter, the corresponding phase charging and discharging capacity constraints are as follows: ; The corresponding phase imbalance capacity constraint is: ; In the formula, This represents the lower limit of the charging power corresponding to L for the i-th inverter. L represents the upper limit of the discharge power corresponding to the i-th inverter. This represents the maximum phase-to-phase unbalanced power corresponding to the i-th inverter. This represents the desired power command corresponding to L for the i-th inverter. This represents the demand correction amount for the L phase of the i-th inverter.

[0013] Preferably, in a three-phase energy storage system, the three phases of the energy storage system are ordered according to the magnitude of their corresponding power requirements, namely, the first phase, the second phase, and the third phase. The final power command allocation for the first, second, and third phases corresponding to any inverter includes the following process: applying its own charging and discharging capability constraint to the expected power command corresponding to the first phase to obtain the corresponding final power command; allocating the expected power command corresponding to the second phase according to the final power command of the first phase, and applying the phase imbalance capability constraint with the first phase, as well as its own charging and discharging capability constraint, to obtain the final power command corresponding to the second phase; and executing the final power command allocation for the third phase according to the allocation results of the first and second phases, and applying its own charging and discharging capability constraint.

[0014] Preferably, when the energy storage system includes multiple inverters, a preset number of inverters and corresponding battery packs are considered as a subsystem, resulting in multiple subsystems. First, the final power command for each phase of each subsystem is obtained through the SOC balancing method. Then, the SOC balancing method is executed again for each subsystem to obtain the final power command for each phase of each inverter in the subsystem.

[0015] Another aspect of this application provides a computer-readable storage medium storing a computer program; when the computer program is executed by a processor, it implements the above-described SOC balancing method for an energy storage system.

[0016] Another aspect of this application provides an electronic device including a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program to implement the above-described SOC balancing method for an energy storage system.

[0017] Compared with the prior art, the beneficial effects of this application are as follows: (1) This application can simultaneously achieve the state of charge balance between different battery packs when the output three-phase power of the energy storage system is not equal, thereby avoiding long-term overcharging or over-discharging of some batteries due to the power difference between phases and improving the system's operational stability.

[0018] (2) This application adopts a two-level architecture of first performing battery-side SOC equalization allocation and then performing inverter-side three-phase power secondary allocation, which decouples the battery equalization algorithm from the inverter's three-phase output power, ensuring that the battery pack SOC tends to be consistent and accurately meeting the system's unbalanced demand for three-phase active power.

[0019] (3) When generating the final power command for each phase, automatically verify and meet the charging and discharging limit power of each phase of each inverter and the maximum allowable unbalanced power between phases to avoid operating beyond the hardware capacity and improve system safety and reliability.

[0020] (4) This application does not rely on a specific energy management strategy and can be seamlessly adapted to various operating conditions such as photovoltaic priority self-use, peak-valley arbitrage, demand management, grid-connected / off-grid operation, and is compatible with the access of different renewable energy power generation units such as photovoltaic, wind power, and hydropower. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the working steps of this application; Detailed Implementation

[0022] The present application will now be further described in conjunction with specific embodiments. It should be noted that, in the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0023] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of this application.

[0024] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0025] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0027] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0028] It is important to understand that the SOC equalization method of this application is applicable not only to three-phase systems that require unbalanced power output, but also to other split-phase systems that require unbalanced output. Of course, it is also applicable to all energy storage systems that do not require unbalanced power output, such as single-phase systems, three-phase systems, and other split-phase systems. For ease of understanding, the technical solution of this application will be described in detail below using a three-phase energy storage system requiring unbalanced power output as an example.

[0029] One aspect of this application provides a SOC balancing method for an energy storage system, the energy storage system including at least one inverter and multiple battery packs; such as Figure 1 As shown, one preferred embodiment includes the following steps: S100: Based on the operating mode and energy management strategy of the energy storage system, determine the required power of each phase in the energy storage system, and calculate the total battery required power of the energy storage system based on the obtained required power.

[0030] It should be understood that existing SOC (State of Charge) equalization methods typically assume three-phase power balance (or are only applicable to single-phase systems), and cannot directly handle scenarios where the three-phase power demands are inconsistent. If the demands of each phase are directly aggregated into a total power without distinguishing between them, the inverter output will not accurately match the actual demands of each phase. During operation, the loads on each phase of an energy storage system may be severely unbalanced (e.g., a large number of single-phase loads concentrated in phase A), and renewable energy sources may also have single-phase connections (such as single-phase photovoltaic inverters). In this case, the power demands of each phase differ significantly, and they must be calculated separately to obtain an accurate total battery demand.

[0031] S200: Obtain the status information of each battery pack in the energy storage system, combine it with the obtained total battery power demand, allocate battery power commands to each battery pack to achieve SOC balance between the packs, and determine the total inverter power required by each inverter.

[0032] It should be understood that when multiple battery packs are used in parallel, due to differences in initial SOC, aging rates, and temperature, allocating power to them at the same rate can lead to prolonged over-discharge of battery packs with high SOC and prolonged over-charging of battery packs with low SOC, accelerating battery degradation and potentially causing safety accidents. Since differences between battery packs are unavoidable, this step involves dynamically adjusting the charge and discharge power commands of each battery pack to gradually reduce the SOC gap and achieve charge and discharge balance. Simultaneously, the power commands allocated to each battery pack must meet the total power demand of the battery.

[0033] S300: Based on the deviation between the power demand of each phase of the energy storage system and the average power demand of the three phases, the total inverter power of each inverter is redistributed to obtain the expected power command for each inverter.

[0034] It's important to understand that if the total power of each inverter is simply distributed equally within itself (i.e., each of the three phases occupies 1 / 3), the total three-phase power of all inverters will be equal, failing to meet the system's requirement for balanced power demand across phases. Conversely, if the total power is directly distributed according to the phase demand ratio, some inverters may exceed their phase capacity, and a single inverter's total power demand may not meet the SOC (State of Charge) balance requirement. Therefore, when allocating demand, the system-level imbalance demand needs to be distributed to each inverter, taking into account the inverter's own total power. This step, through a secondary allocation architecture, ensures that the total power of each phase at the system level equals the demand while also making the three-phase power within a single inverter as balanced as possible.

[0035] S400: Based on the charging and discharging capacity constraints of each phase and the inter-phase imbalance capacity constraints, the desired power command is adjusted to obtain the final power command for each phase, which is used to control the operation of each inverter.

[0036] It should be understood that the expected power command calculated in step S300 is an ideal value, which may violate the inverter's hardware safety limits or grid connection standards (such as IEEE 1547 requirements for current imbalance). If not restricted, it may lead to equipment damage, protection activation, or grid connection failure. Therefore, hardware constraints are set in this step to ensure that the final power command of each phase of the inverter approaches the expected value as closely as possible while satisfying all hardware constraints.

[0037] Understandably, this application can simultaneously achieve state-of-charge (SOC) balancing among different battery packs when the three-phase output power of the energy storage system is unequal, avoiding long-term overcharging or over-discharging of some batteries due to phase power differences, thus improving system operational stability. This application employs a two-stage architecture: first, battery-side SOC balancing allocation, and then secondary allocation of three-phase power on the inverter side. This decouples the battery balancing algorithm from the inverter's three-phase output power, ensuring both consistent battery pack SOC and precise fulfillment of the system's unbalanced three-phase active power requirements. When generating the final power command for each phase, it automatically verifies and satisfies the charging and discharging limits of each inverter phase and the maximum permissible phase imbalance power, preventing operation beyond hardware capabilities and improving system safety and reliability. This application does not rely on specific energy management strategies and can seamlessly adapt to various operating conditions such as photovoltaic-priority self-consumption, peak-valley arbitrage, demand management, and grid-connected / off-grid operation. It is also compatible with the access of different renewable energy generation units such as photovoltaic, wind, and hydropower.

[0038] It is important to understand that in step S100, the energy storage system operates in two modes: grid-connected and off-grid. During grid-connected operation, the demand power is generated by the energy management strategy based on electricity prices, load, and power generation forecasts. During off-grid operation, the demand power is determined by the actual power consumed by the load. Taking a photovoltaic-storage system as an example, the energy management strategy includes photovoltaic priority self-consumption, peak-valley arbitrage, and demand management. For photovoltaic priority self-consumption, the load prioritizes consuming photovoltaic power, with surplus electricity used to charge the battery bank or feed it into the grid; when insufficient, the battery bank discharges to supplement the demand. For peak-valley arbitrage, power is absorbed from the grid during off-peak hours to charge the battery bank, and during peak hours, the battery bank discharges to supply the load or feed it back into the grid. For energy management, the maximum power that the load can draw from the grid is limited, with any excess power supplemented by the battery bank discharging.

[0039] In a specific embodiment, when executing step S100, in a three-phase energy storage system that requires unbalanced power output, phases A, B, and C each need to have their required power set independently, as follows: , , If the power demand is positive, it means that the phase requires power output from the inverter; if the power demand is negative, it means that the phase requires power absorption from the inverter. The total battery power demand of an energy storage system is typically obtained by subtracting the total real-time power generation of renewable energy from the sum of the three-phase power demands. We can assume the total real-time power generation of renewable energy is... The formula for calculating the total battery power demand P is: .

[0040] Understandably, this step calculates the power demand of each phase separately and aggregates it into the total battery demand, providing an accurate target value for subsequent decoupled SOC balancing and three-phase imbalance control. This ensures the accuracy of system-level power balance and avoids control errors caused by ignoring phase differences.

[0041] It's important to understand that if the calculated total battery power demand P is positive, it means the energy storage system needs to discharge the battery pack overall; if the calculated total battery power demand P is negative, it means the energy storage system needs to charge the battery pack overall. The real-time total power generation of renewable energy can be photovoltaic power, wind power, or hydropower. For ease of understanding, the following will use a photovoltaic-energy storage system as an example to describe this step in detail.

[0042] In a specific example, the energy storage system operates in a "grid-connected, peak-valley arbitrage" mode. During peak electricity prices, the energy storage system needs to discharge power to the grid to generate revenue. Based on the energy management strategy, the power demand of phase A of the energy storage system is calculated to be +30kW, phase B +20kW, and phase C +10kW; simultaneously, the total real-time photovoltaic power generation is 15kW. Therefore, the total battery power demand P = 30 + 20 + 10 - 15 = 45kW, indicating that the energy storage system needs to discharge 45kW from the battery pack.

[0043] In a specific embodiment, when executing step S200, the battery pack's status information includes real-time SOC, capacity, and voltage. When the total battery power demand is positive, meaning the battery pack needs to discharge, the power allocation coefficient for each battery pack is calculated based on the difference between the real-time SOC of each battery pack and the set discharge target equalization value, combined with capacity and voltage. When the total battery power demand is negative, meaning the battery pack needs to charge, the power allocation coefficient for each battery pack is calculated based on the difference between the set charging target equalization value and the real-time SOC of each battery pack, combined with capacity and voltage. The ratio of each battery pack's power allocation coefficient to the sum of all power allocation coefficients is used as a weight and multiplied by the total battery power demand to obtain the battery power command required by each battery pack.

[0044] For ease of understanding, the following will take the i-th battery pack as an example and describe the battery power command P corresponding to that battery pack. i The specific calculation process is described in detail through expressions.

[0045] .

[0046] In the formula, P represents the total power demand of the battery. Let M represent the power allocation coefficient corresponding to the i-th battery pack, and M represent the total number of battery packs.

[0047] Wherein, when the i-th battery pack needs to discharge, its corresponding power allocation coefficient is... The calculation expression is: .

[0048] In the formula, This represents the real-time SOC value of the i-th battery pack. This represents the set discharge target equalization value. The specific value can be adjusted according to energy demand. For example, it can be 0.2, which means that the battery pack stops discharging when the SOC value reaches 20%. This represents the capacity of the i-th battery pack. This represents the voltage of the i-th battery pack.

[0049] When the i-th battery pack needs charging, its corresponding power allocation coefficient The calculation expression is: .

[0050] In the formula, This represents the set charging target equalization value. The specific value can be adjusted according to energy demand. For example, it can be 0.9, which means that charging will stop when the battery pack reaches 90% SOC.

[0051] Understandably, based on the above expression, a battery pack with a higher real-time SOC value can handle more power demand during discharge; conversely, a battery pack with a lower real-time SOC value can handle more power demand during charging. This adaptively reduces the SOC difference between battery packs without human intervention; the charging and discharging directions are symmetrical, and the algorithm is simple and reliable.

[0052] It should be understood that, based on the above expression, the SOC of all battery packs can linearly change to the same equilibrium value. When pursuing rapid equilibrium, the calculation expression for the power distribution coefficient can be modified so that during discharge, the highest SOC drops to the second highest SOC, then together drops to the third highest SOC, and so on, until the SOC of all battery packs drops to the same equilibrium value; during charging, the lowest SOC rises to the second lowest SOC, then together rises to the third lowest SOC, and so on, until the SOC of all battery packs rises to the same equilibrium value.

[0053] It is important to note that when allocating battery power commands to each battery pack, it is necessary to set allocation power boundaries based on the rated power, voltage, and current limits of each battery pack. These boundaries restrict the allocated power for each battery pack, and any unallocated power is distributed to other battery packs that have not yet reached their limits. In other words, if the battery power command for a battery pack exceeds its rated power limit, the battery power command for that battery pack is limited to its rated power, and the excess is redistributed to battery packs that have not yet reached their rated power limits. This process is repeated until all power is allocated and no power remains.

[0054] To make it easier to understand, the following will take the discharge of a battery pack as an example to describe in detail the specific process of obtaining battery power commands.

[0055] In a specific example, assume the total battery power demand P = 60kW; the number of battery packs M = 3, labeled as battery pack #1, battery pack #2, and battery pack #3. Specifically, battery pack #1 has a real-time SOC of 90%, capacity Q = 100Ah, and voltage U = 400V; battery pack #2 has a real-time SOC of 70%, capacity Q = 100Ah, and voltage U = 400V; and battery pack #3 has a real-time SOC of 50%, capacity Q = 100Ah, and voltage U = 400V.

[0056] Setting the target equalization value for discharge to 0.2, the power allocation coefficient for battery pack #1 is 28000, for battery pack #2 it is 20000, and for battery pack #3 it is 12000. Substituting these values ​​into the calculation expression for the battery power command, we can calculate that the battery power command allocated to battery pack #1 is 28kW, to battery pack #2 it is 20kW, and to battery pack #3 it is 12kW.

[0057] In this embodiment, after calculating the battery power command, the total inverter power corresponding to each inverter can be calculated in real time based on the battery power command allocated to the battery pack connected to that inverter, real-time power generation data, and the current energy management strategy. Specifically, for the i-th inverter, its corresponding total inverter power is... The calculation expression is as follows: .

[0058] In the formula, This represents the sum of the battery power commands of all battery packs connected to the i-th inverter. This represents the real-time power generation of the generator unit connected to the i-th inverter. , , Let A, B, and C represent the required inverter power for the i-th inverter.

[0059] To facilitate understanding, the process of obtaining the total inverter power of the inverter will be described in detail, using the three battery packs mentioned above as examples.

[0060] In a specific example, assume the energy storage system includes two inverters, labeled Inverter #1 and Inverter #2; Inverter #1 is connected to battery packs #1 and #2, and Inverter #2 is connected to battery pack #3. If Inverter #1 is connected to a photovoltaic string, and the real-time power generation of the photovoltaic string is 20kW, and Inverter #2 is not connected to an external power generation unit, then the total inverter power of Inverter #1 is 68kW, and the total inverter power of Inverter #2 is 12kW.

[0061] In a specific embodiment, when executing step S300, based on the required power of each energy storage system obtained in step S100 and the total inverter power of each inverter obtained in step S200, there are multiple ways to calculate the expected power command corresponding to each inverter. For ease of understanding, two specific examples will be used to describe them in detail below.

[0062] In a specific example, for the L phases of the i-th inverter, where L = {A, B, C}, the calculation expression for the corresponding desired power command is as follows: ; .

[0063] In the formula, This represents the desired power command corresponding to phase L of the i-th inverter, which is equal to the inverter power required by phase L of the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter, i.e., the demand correction amount for phase L. This represents the sum of the three-phase power demand of the energy storage system, and N represents the number of inverters in the energy storage system.

[0064] As can be understood from the expression in this example, the calculation of the desired power command adopts an average distribution method; that is, the total inverter power of each inverter is first evenly distributed across the three phases, and then a secondary correction is made based on the system's unbalanced demand. Specifically, if the demand of phase A of the energy storage system is 30kW higher than the average of the three phases, then each inverter's phase A needs an additional (30 / N)kW. Therefore, the calculation of the desired power command in this example is more suitable for situations where the capabilities of each inverter in the energy storage system are not significantly different.

[0065] In another specific example, the expression for calculating the desired power command corresponding to L for the i-th inverter is as follows: .

[0066] In the formula, This represents the desired power command corresponding to phase L of the i-th inverter, which is equal to the inverter power required by phase L of the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter. This represents the sum of the three-phase power demand of the energy storage system. This represents the power capability of the L-phase of the i-th inverter. This represents the sum of the power capabilities of all L-phase inverters.

[0067] As can be understood from the expression in this example, the calculation of the desired power command uses a weighted allocation method. When the L-phase capability of a certain inverter is particularly large, its allocation deviation is also larger, thus making fuller use of hardware resources. Therefore, this example is more suitable for scenarios where the capabilities of each inverter in an energy storage system differ significantly. Through weighted allocation, inverters with higher power capabilities can undertake more imbalance correction.

[0068] To facilitate understanding, the following section will describe in detail the specific calculation process of the expected power command using the above average allocation method and weighted allocation method with specific parameters.

[0069] Specifically, assuming the power demand corresponding to energy storage system A is 30kW, the power demand corresponding to B is 20kW, and the power demand corresponding to C is 10kW; then the average three-phase power demand is 20kW; the deviation between phase A and the average three-phase power demand is +10kW, the deviation between phase B and the average three-phase power demand is 0kW, and the deviation between phase C and the average three-phase power demand is -10kW. The energy storage system includes two inverters, labeled Inverter #3 and Inverter #4; wherein, the total inverter power of Inverter #3 is 40kW, and the total inverter power of Inverter #4 is 20kW.

[0070] (1) According to the method of equal distribution.

[0071] For inverter #3: the three-phase average base value is 40 / 3≈13.33kW; the demand correction value for phase A is +10 / 2=+5kW, the demand correction value for phase B is 0kW, and the demand correction value for phase C is -5kW; then the expected power command corresponding to phase A is 13.33+5=18.33kW, the expected power command corresponding to phase B is 13.33kW, and the expected power command corresponding to phase C is 13.33-5=8.33kW.

[0072] For inverter #4: the three-phase average base value is 20 / 3≈6.67kW; the demand correction value for phase A is +5kW, the demand correction value for phase B is 0kW, and the demand correction value for phase C is -5kW; then the expected power command corresponding to phase A is 6.67+5=11.37kW, the expected power command corresponding to phase B is 6.67kW, and the expected power command corresponding to phase C is 6.67-5=1.67kW.

[0073] (2) A weighted allocation method is adopted.

[0074] Assume that the A-phase capacity of inverter #3 is 30kW and the A-phase capacity of inverter #4 is 10kW.

[0075] For inverter #3: the three-phase average base value is 40 / 3≈13.33kW; the demand correction value for phase A is +10×30 / (30+10)=+7.5kW, so the expected power command for phase A is 13.33+7.5=20.83kW.

[0076] For inverter #4: the three-phase average base value is 20 / 3≈6.67kW; the demand correction value for phase A is +10×10 / (30+10)=+2.5kW, so the expected power command for phase A is 6.67+2.5=9.17kW.

[0077] In a specific embodiment, when executing step S400, there are constraints on the charging and discharging capabilities of each phase. That is, each phase of each inverter has its own hardware-determined power limit, including a lower limit for charging power and an upper limit for discharging power; the final power command must be between the two. There are also constraints on the phase imbalance capability. That is, due to limitations such as DC bus capacitor ripple, uneven heat dissipation, and shared current of switching transistors, the power difference between the three phases of the inverter cannot be too large.

[0078] For ease of understanding, taking the i-th inverter as an example, the corresponding phase charging and discharging capacity constraints are as follows: .

[0079] The corresponding phase imbalance capacity constraint is: .

[0080] In the formula, This represents the lower limit of the charging power corresponding to the i-th inverter, and the specific value range can be determined by those skilled in the art based on their actual needs. For example, it can be -0.5 to -0.3 times the rated power. L represents the upper limit of the discharge power corresponding to the i-th inverter. The specific value range can be determined by those skilled in the art based on their actual needs. For example, it can be 0.3 to 0.5 times the rated power. This represents the maximum phase-to-phase unbalanced power corresponding to the i-th inverter. The specific value range can be determined by those skilled in the art based on their actual needs. For example, it can be 0.2 to 0.6 times the total inverter power. This represents the desired power command corresponding to L for the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter.

[0081] To facilitate understanding, the formula corresponding to the phase-to-phase imbalance capacity constraint will be derived below, using the demand correction amount of phase A of the i-th inverter. For example, we have: .

[0082] Since the difference between the desired power commands of any two phases must be less than or equal to the maximum value of the interphase unbalanced power. Therefore: .

[0083] Similarly, the demand correction amounts for phases B and C can be derived. and All of these must satisfy the aforementioned phase imbalance capability constraints. Among them, , , These represent the desired power commands for phases A, B, and C of the i-th inverter, respectively.

[0084] It's important to understand that when allocating the final power command for each phase of the inverter, if the allocated expected power command exceeds any of the aforementioned constraints, a sorting iterative allocation algorithm is used for restriction and redistribution until all constraints are satisfied. That is, if the final power command allocated to a phase cannot meet the constraints, the final power command for that phase is assigned the constraint's limit value, and the unallocated values ​​are distributed to other inverters. For ease of understanding, a specific example will be provided below to describe in detail the process of allocating the final power command using the sorting iterative allocation algorithm.

[0085] In a specific example, the three phases of the energy storage system are ordered according to their corresponding power requirements, namely, phase 1 L1, phase 2 L2, and phase 3 L3. The allocation of the final power command for any i-th inverter corresponding to phases L1, L2, and L3 includes the following process: (1) Apply its own charging and discharging capability constraint to the expected power command corresponding to the first phase L1 to obtain the corresponding final power command.

[0086] Understandably, if the expected power command corresponding to the first phase L1 does not exceed its own charging and discharging limit, the expected power command will be used as the final power command; if the expected power command corresponding to the first phase L1 exceeds its own charging and discharging limit, the expected power command will be limited to the limit value, and the excess will be redistributed to other inverters that have not reached their limits.

[0087] (2) Allocate the expected power command corresponding to the second phase L2 according to the final power command of the first phase L1, and apply the phase imbalance capability constraint of the first phase L1 and the charging and discharging capability constraint of the second phase L2 to obtain the final power command corresponding to the second phase L2.

[0088] It is understandable that when allocating power to the second phase L2, adjustments are no longer made based on the desired power command, but rather a direct redistribution based on the final power command of the first phase L1. During allocation, in addition to satisfying its own charging and discharging capabilities, it must also meet the phase imbalance capability constraint with the first phase L1. The constraint on its own charging and discharging capabilities is the same as that on the first phase L1, and therefore will not be repeated here. The phase imbalance capability constraint with the first phase L1 must satisfy: .

[0089] .

[0090] .

[0091] In the formula, This represents the demand correction amount for the second phase L2 of the i-th inverter. This represents the demand correction amount for the first phase L1 of the i-th inverter. This represents the maximum phase-to-phase unbalanced power corresponding to the i-th inverter.

[0092] Understandably, the derivation process for the above-mentioned interphase imbalance capacity constraint conditions is as follows: .

[0093] Similarly, we have: ; .

[0094] in, and It can be further transformed into: .

[0095] .

[0096] (3) Based on the allocation results of the first phase L1 and the second phase L2, the third phase L3 is allocated the final power command and its own charging and discharging capacity is constrained.

[0097] It is understandable that, since the allocation results of the first phase L1 and the second phase L2 are known, the third phase L3 does not need to be allocated independently, but is automatically determined by the conservation of total power, that is: .

[0098] In the formula, This represents the required adjustment amount for the third phase L3 of the i-th inverter.

[0099] After completing the allocation based on total power conservation, it is necessary to check whether the third phase L3 meets its own charging and discharging capacity constraints. If it does not, it indicates that the previous allocation results of the first phase L1 and the second phase L2 are infeasible and need to be adjusted back (usually the second phase L2 is adjusted first, and the first phase L1 is adjusted if necessary). However, in practice, because the priority order ensures that the power of the first phase L1 and the second phase L2 are within a reasonable range, and the total power is conserved, the third phase L3 usually will not exceed the limit. The expression for the charging and discharging capacity constraints of the third phase L3 is: .

[0100] In the formula, This represents the lower limit of the charging power corresponding to the third phase L3 of the i-th inverter. This represents the upper limit of the discharge power corresponding to the third phase L3 of the i-th inverter. This represents the total inverter power of the i-th inverter.

[0101] To facilitate understanding, the following detailed description of the final power command allocation process for the three phases of the inverter will be provided using a specific parameter example.

[0102] Specifically, assuming a certain inverter has a total inverter power of 30kW, and the charging and discharging capacity of each phase is: a maximum discharge capacity of 15kW, a minimum charge capacity of -10kW, and a maximum inter-phase imbalance power of 12kW. The demand correction for the first phase L1 is +8kW, for the second phase L2 it is +2kW, and for the third phase L3 it is -10kW. Therefore, the expected power command for the first phase L1 is 10 + 8 = 18kW, for the second phase L2 it is 10 + 2 = 12kW, and for the third phase L3 it is 10 - 10 = 0kW.

[0103] When allocating the final power command to the first phase L1, since the expected power command for the first phase L1 is greater than the discharge limit, the final power command for the first phase L1 is limited to the discharge limit, i.e., 15kW. The excess 3kW can be allocated to other inverters. Since the final power command for the first phase L1 is 15kW, the remaining 15kW of the total inverter power is allocated to the second phase L2 and the third phase L3. At this time, the demand correction for the first phase L1 is reduced from +8kW to +5kW.

[0104] When allocating the final power command to the second phase L2, we can set the adjusted demand correction as X, then the adjusted expected power command is 10 + X. Since the expected power command needs to meet its own charging and discharging capacity constraints, we have -10 ≤ 10 + X ≤ 15, so the range of X is -20 ≤ X ≤ 5. Simultaneously, we also need to ensure that the adjusted expected power command for the third phase L3 meets the charging and discharging capacity constraints, hence -10 ≤ 10 - 5 - X ≤ 15, so the range of X is -10 ≤ X ≤ 15. Taking the intersection of the ranges of X, we get -10 ≤ X ≤ 5.

[0105] For the constraint of phase imbalance capability: .

[0106] .

[0107] .

[0108] It can be calculated that: -7≤X≤2.

[0109] Assuming X is set to 2kW, the final power command for the second phase L2 is 12kW. Correspondingly, the final power command for the third phase L3 can be calculated as 3kW, meaning the adjusted demand correction for the third phase L3 is -7kW, which is greater than 6kW and does not meet the phase imbalance constraint. Therefore, the value of the demand correction X for the second phase L2 needs to be readjusted. Assuming X is readjusted to 1kW, the final power command for the second phase L2 is 11kW; correspondingly, the final power command for the third phase L3 can be calculated as 4kW, meaning the demand correction for the third phase L3 is now -6kW, which perfectly meets the phase imbalance constraint. Finally, the final power command for the first phase L1 of this inverter can be allocated as 15kW, the final power command for the second phase L2 as 11kW, and the final power command for the third phase L3 as 4kW.

[0110] In one specific embodiment, the SOC balancing method of this application continuously and cyclically executes steps S100 to S400 at preset time intervals, thereby achieving dynamic control of the energy storage system. The preset time interval can be set according to the system response speed and control accuracy requirements, for example, it can be set to hundreds of milliseconds to several seconds. Through continuous cyclic execution, the SOC balancing method of this application can dynamically adjust the power distribution strategy according to the real-time changes in the system operating state, ensuring that the dual objectives of SOC balancing and three-phase unbalanced power output can be achieved under different operating conditions.

[0111] In a specific embodiment, for large-scale energy storage systems, i.e., systems comprising a large number of inverters, a predetermined number of inverters and their corresponding battery packs can be considered as a single subsystem, resulting in multiple subsystems. Therefore, when the energy storage system performs State of Charge (SOC) balancing, the final power command for each phase of each subsystem is first obtained using the SOC balancing method. Then, the SOC balancing method is executed again for each subsystem to obtain the final power command for each phase of each inverter within that subsystem. This cascaded control architecture effectively manages large and complex energy storage systems, reduces the computational complexity of system-level control, and maintains control accuracy and flexibility within each subsystem.

[0112] In one specific embodiment, the SOC balancing method of this application can be deployed to a parallel system with a master-slave control architecture, a parallel system with a distributed control architecture, or a parallel system with tiered control. The controller executing the SOC balancing method of this application in the energy storage system can be implemented using an MCU, FPGA, DSP, or ARM chip.

[0113] Another aspect of this application provides a computer-readable storage medium, in a preferred embodiment of which a computer program is stored on the storage medium; when the computer program is executed by a processor, it implements the above-described SOC balancing method for the energy storage system.

[0114] Another aspect of this application provides an electronic device, in one preferred embodiment of which includes a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program to implement the above-described SOC balancing method for an energy storage system.

[0115] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method for SOC balancing in an energy storage system, the energy storage system comprising at least one inverter and multiple battery packs; characterized in that, The method includes the following steps: Based on the operating mode and energy management strategy of the energy storage system, the required power of each phase in the energy storage system is determined, and the total battery required power of the energy storage system is calculated based on the obtained required power. The status information of each battery pack in the energy storage system is obtained, and combined with the total battery power demand, a battery power command is allocated to each battery pack to achieve SOC balance between the packs, and the total inverter power required by each inverter is determined. Based on the deviation between the power demand of each phase of the energy storage system and the average power demand of the three phases, the total inverter power of each inverter is redistributed to obtain the expected power command for each inverter. Based on the constraints of each phase's charging and discharging capacity and the inter-phase imbalance capacity, the desired power command is adjusted to obtain the final power command for each phase, which is used to control the operation of each inverter.

2. The SOC equalization method for an energy storage system as described in claim 1, characterized in that, Battery pack status information includes real-time SOC, capacity, and voltage; When the total battery demand indicates that the battery pack needs to be discharged, the power allocation coefficient of each battery pack is calculated based on the difference between the real-time SOC of each battery pack and the set discharge target equalization value, combined with the capacity and voltage. When the total battery demand indicates that the battery pack needs to be charged, the power allocation coefficient of each battery pack is calculated based on the difference between the set charging target equalization value and the real-time SOC of each battery pack, combined with the capacity and voltage. The ratio of the power allocation coefficient of each battery pack to the sum of the power allocation coefficients of all battery packs is used as a weight, and multiplied by the total battery power demand to obtain the battery power command required by each battery pack.

3. The SOC balancing method for an energy storage system as described in claim 1, characterized in that, When allocating battery power commands, if the battery power command corresponding to a battery pack exceeds its rated power limit, the battery power command of that battery pack will be limited to the rated power, and the excess portion will be redistributed to battery packs that have not reached their rated power limit.

4. The SOC balancing method for an energy storage system as described in claim 1, characterized in that, In a three-phase energy storage system, the calculation expression for the expected power command corresponding to L of the i-th inverter is as follows: ； ； In the formula, This represents the desired power command corresponding to L for the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter. This represents the sum of the three-phase power demand of the energy storage system, and N represents the number of inverters in the energy storage system.

5. The SOC equalization method for an energy storage system as described in claim 1, characterized in that, In a three-phase energy storage system, the calculation expression for the expected power command corresponding to L of the i-th inverter is as follows: ； ； In the formula, This represents the desired power command corresponding to L for the i-th inverter. L represents the power demand of the energy storage system. This represents the total inverter power of the i-th inverter. This represents the demand correction amount for phase L of the i-th inverter. This represents the sum of the three-phase power demand of the energy storage system. This represents the power capability of the L-phase of the i-th inverter. This represents the sum of the power capabilities of all L-phase inverters.

6. The SOC equalization method for an energy storage system as described in claim 4 or 5, characterized in that, For the i-th inverter, the corresponding phase charging and discharging capacity constraints are as follows: ； The corresponding phase imbalance capacity constraint is: ； In the formula, This represents the lower limit of the charging power corresponding to L for the i-th inverter. L represents the upper limit of the discharge power corresponding to the i-th inverter. This represents the maximum phase-to-phase unbalanced power corresponding to the i-th inverter. This represents the desired power command corresponding to L for the i-th inverter. This represents the demand correction amount for the L phase of the i-th inverter.

7. The SOC equalization method for an energy storage system as described in claim 1, characterized in that, In a three-phase energy storage system, the three phases of the system are ordered according to their corresponding power requirements, namely, the first phase, the second phase, and the third phase. The final power command allocation for the first, second, and third phases corresponding to any inverter includes the following process: Apply its own charging and discharging capability constraint to the first corresponding expected power command to obtain the corresponding final power command; The expected power command of the second phase is allocated according to the final power command of the first phase, and the phase imbalance capability constraint of the first phase and its own charging and discharging capability constraint are applied to obtain the final power command of the second phase. Based on the allocation results of the first and second phases, the final power command is allocated to the third phase, and its own charging and discharging capability constraints are imposed.

8. The SOC equalization method for an energy storage system as described in claim 1, characterized in that, When the energy storage system includes multiple inverters, a preset number of inverters and corresponding battery packs are treated as a subsystem, resulting in multiple subsystems. First, the final power command for each phase of each subsystem is obtained through the SOC balancing method. Then, the SOC balancing method is executed again for each subsystem to obtain the final power command for each phase of each inverter in the subsystem.

9. An electronic device, characterized in that, It includes a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program to implement the SOC balancing method of the energy storage system as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The storage medium stores a computer program; when the computer program is executed by a processor, it implements the SOC balancing method of the energy storage system as described in any one of claims 1-8.

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