Current distribution regulation and control voltage balance SOC optimization method

Abstract

The invention discloses a current distribution regulation and control voltage balance SOC optimization method, and the method comprises the specific steps: determining the type of a balance strategy according to the SOC difference between battery modules; according to the determined equalization strategy, the total cluster current of the system is distributed to each module according to SOC, and module reference current is generated and calculated; and finally, converting the module reference current into a bus voltage reference instruction, and controlling each module to track a voltage target to realize current distribution. According to the current distribution regulation and control voltage balance SOC optimization method provided by the invention, the target current is calculated, and then the current reference is converted into the bus voltage reference, so that the dynamic response speed and stability of the DC bus voltage are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of power control methods, specifically relating to a current distribution regulation, voltage balancing, and SOC optimization method. Background Technology

[0002] With the rapid development of renewable energy and the advancement of power electronics technology, energy storage systems are playing an increasingly important role in power systems. Energy storage systems can not only mitigate the volatility of renewable energy generation but also provide ancillary services such as frequency regulation, voltage regulation, and backup power, thereby improving the stability and economy of the power grid. In energy storage systems, the stable control of the DC bus voltage is one of the core issues, directly affecting the system's efficiency, safety, and dynamic response capabilities.

[0003] In energy storage systems, the stable control of DC bus voltage faces the following challenges: (1) Multi-source coordination problem: Energy storage systems are usually operated in combination with various energy sources such as photovoltaic, wind power, and supercapacitors. Different energy sources have different dynamic response speeds, and how to coordinate control becomes a challenge. (2) Impact of load change: When the grid load changes suddenly or the output of new energy sources changes abruptly, the DC bus voltage may fluctuate violently, requiring the control system to have rapid adjustment capabilities. (3) Battery management limitations: The charging and discharging rate of the battery is affected by factors such as SOC (state of charge) and temperature, and its constraints need to be considered in voltage control. (4) System efficiency optimization: Traditional PID control may be difficult to balance dynamic response and steady-state accuracy, requiring a more reliable control strategy. Summary of the Invention

[0004] The purpose of this invention is to provide a current distribution regulation voltage equalization SOC optimization method. By calculating the target current and then converting the current reference into a bus voltage reference, the dynamic response speed and stability of the DC bus voltage are improved.

[0005] The technical solution adopted in this invention is a current distribution regulation voltage equalization SOC optimization method. The specific steps are as follows: determine the equalization strategy type according to the SOC difference between each battery module; and according to the determined equalization strategy, distribute the total cluster current of the system to each module according to SOC, generate and calculate the module reference current; finally, convert the module reference current into a bus voltage reference command to control each module to track the voltage target and achieve current distribution.

[0006] The invention is further characterized in that, The upper and lower limits of bus voltage must meet the following requirements: (1) In the formula, Vbus_LimitU represents the upper limit of normal bus voltage, Vbus_LimitL represents the lower limit of normal bus voltage, Vbus_Total represents the set total bus voltage reference, and Nm represents the number of battery modules.

[0007] Equilibrium strategies include extreme equilibrium and fine-tuning equilibrium.

[0008] Assume that the minimum SOC module has the maximum charging current and the maximum SOC module has the minimum charging current during charging; assume that the minimum SOC module has the minimum discharging current and the maximum SOC module has the maximum discharging current during discharging; when the current has a sign, it is uniformly represented as the minimum SOC module current and the maximum SOC module current; the maximum allowable current Imax and minimum current Imin are limited by cluster current, voltage ratio, and upper limit of battery current, specifically: (2) (3) In the formula, max(,) represents the maximum value of the two input quantities, and min(,) represents the minimum value of the two input quantities; Vbatt_isocmax represents the module voltage corresponding to the maximum SOC module, and Vbatt_isocmin represents the module voltage corresponding to the minimum SOC module; Icls represents cluster current sampling, and Ibatt_Limit represents battery current limiting.

[0009] When the SOC difference between each battery module exceeds the set SOC difference threshold, extreme equalization is selected; when the SOC difference between each module does not exceed the set SOC difference threshold, fine-tuning equalization is selected.

[0010] When extreme balance is selected, ignoring losses, the power balance between the battery side and the bus side is achieved, specifically as follows: (4) Where IRef_i represents the current reference of the i-th module, Vbatt_i represents the battery voltage sampling of the i-th module, ∑ i IRef_i·Vbatt_i represents the sum of the battery-side power of each module, and Vbus_Total·Icls represents the bus-side power; all variables are signed, and the current is positive in the discharge direction; Assuming the charging current of each battery module is calculated based on Imin during charging, it is expressed as: (5) In the formula, SOCi represents the SOC of the i-th module. This represents the minimum SOC among all modules, where k is a coefficient. Combining equations (4) and (5), we can obtain: (6) Therefore, it can be calculated that... : (7) Substituting equation (7) into equation (5) yields the current reference value for each module, and the calculated battery-side current reference value IRef_imax corresponding to the module with the highest SOC is observed.

[0011] If IRef_imax ≤ Imax, then no recalculation is performed; otherwise, recalculation is performed based on Imax, as shown below: (8) Combining (4) and (8) (9) The conclusion is : (10) Substituting equation (10) into equation (8) yields the current reference values ​​for each module. After obtaining the current references, these are converted into the bus voltage references VbusRef_i for each module: (11) To eliminate the difference between the sum of bus voltage references Vref_Total and the total bus voltage reference Vbus_Total, it is expressed as: (12) The corrected bus voltage reference Vref_i for each module is expressed as: (13).

[0012] When fine-tuning balancing is selected, the bus voltage is approximately proportional to the battery current, expressed as: (14) (15) In the formula, Vbus_avg represents the average value of the bus-side voltage of each module, and SOC_avg represents the average value of the SOC of each module. When entering the fine-tuning equalization mode, the proportional coefficient kP is calculated once, and kP is not updated in subsequent calculations until the next re-entry into the fine-tuning equalization mode. kP is expressed as: (16) In the formula, SOCmax represents the maximum value of SOC in each module; (17) In the formula, ΔVbusRefi represents the bus voltage reference value that needs to be adjusted for each module. The bus voltage reference for each module is the average bus voltage reference value plus the bus voltage reference value that needs to be adjusted, i.e.: (18) Thus making Balanced battery module SOC.

[0013] Compared with the prior art, the beneficial effects of the present invention are: (1) The current distribution regulation and voltage equalization SOC optimization method provided by the present invention converts the battery-side current reference of different battery modules into the bus-side voltage reference. Under the condition that the SOC differs regardless of whether the system power changes or not, it realizes the equalization control of SOC and the voltage control of the bus side, thereby improving the dynamic response speed and stability of the DC bus voltage. The current allocated to each battery module varies with the magnitude of SOC. When the current has a direction (discharge is positive), the module with a larger SOC is allocated a larger reference current. By converting the reference current into the module bus voltage reference, the battery-side current can be controlled by controlling the module bus-side voltage. Finally, the battery-side current and bus-side voltage of the battery modules can be controlled simultaneously, that is, the power of different battery modules can be controlled, thereby improving the operating efficiency and reliability of the system. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the current distribution regulation and voltage equalization SOC optimization method of the present invention; Figure 2 This is a schematic diagram of the signal flow of the battery energy storage system in an embodiment of the present invention.

[0015] Example 1 This invention provides a current distribution regulation and voltage equalization SOC optimization method, such as... Figure 1-2 As shown, firstly, based on the SOC of each battery module, the balancing strategy type is determined, and it is determined whether to use extreme balancing or fine-tuning balancing for each module. When the SOC difference between each battery module exceeds the set SOC difference threshold, extreme balancing is selected; when the SOC difference between each module does not exceed the set SOC difference threshold, fine-tuning balancing is selected.

[0016] Example 2 Based on Example 1, it should be noted that SOC (State of Charge) refers to the state of charge, which is the ratio of the amount of charge that the battery can extract from the cell at a specific point in time to the total capacity of the battery, reflecting the remaining state of charge of the battery.

[0017] Based on the determined equalization strategy, the total cluster current of the system is distributed to each module according to the state of charge (SOC), and the module reference current is generated and calculated. Finally, the module reference current is converted into the bus voltage reference, and each module is controlled to track the voltage target to achieve current distribution.

[0018] The following calculations assume that the upper and lower limits of the bus voltage must be met: (1) In the formula, Vbus_LimitU represents the upper limit of normal bus voltage, Vbus_LimitL represents the lower limit of normal bus voltage, Vbus_Total represents the set total bus voltage reference, and Nm represents the number of battery modules.

[0019] Example 3 Based on Example 2, the design maximizes the charging current of the module with the minimum SOC and minimizes the charging current of the module with the maximum SOC; conversely, it minimizes the discharging current of the module with the minimum SOC and maximizes the discharging current of the module with the maximum SOC. When the current values ​​are signed, they are uniformly represented as minimum SOC module current and maximum SOC module current. The maximum and minimum allowable currents Imax and Imin are limited by cluster current, voltage ratio, and battery current limit, specifically: (2) (3) In the formula, max(,) represents the maximum value of the two input quantities, and min(,) represents the minimum value of the two input quantities; Vbatt_isocmax represents the module voltage corresponding to the maximum SOC module, and Vbatt_isocmin represents the module voltage corresponding to the minimum SOC module; Icls represents cluster current sampling, and Ibatt_Limit represents battery current limit, which is a positive value.

[0020] Example 4 Based on Example 3, when extreme equalization is selected, losses are ignored, and the power balance between the battery side and the bus side is achieved, specifically: (4) Where IRef_i represents the current reference of the i-th module, Vbatt_i represents the battery voltage sampling of the i-th module, ∑ i IRef_i·Vbatt_i represents the sum of the battery-side power of each module, and Vbus_Total·Icls represents the bus-side power; all variables are signed, and the current is positive in the discharge direction.

[0021] Assuming the charging current of each battery module is calculated based on Imin during charging, it is expressed as: (5) In the formula, SOCi represents the SOC of the i-th module. This represents the minimum SOC among all modules, where k is a coefficient. Combining equations (4) and (5), we can obtain: (6) Therefore, it can be calculated that... : (7) Substituting equation (7) into equation (5) yields the current reference value for each module, and the calculated battery-side current reference value IRef_imax corresponding to the module with the highest SOC is observed.

[0022] Example 5 Based on Example 4, when IRef_imax ≤ Imax, no recalculation is performed; otherwise, recalculation is performed based on Imax, as shown below: (8) Combining (4) and (8) (9) The conclusion is : (10) Substituting equation (10) into equation (8) yields the current reference values ​​for each module. After obtaining the current references, these are converted into the bus voltage references VbusRef_i for each module: (11) To eliminate the difference between the sum of bus voltage references Vref_Total and the total bus voltage reference Vbus_Total, it is expressed as: (12) The corrected bus voltage reference Vref_i for each module is expressed as: (13).

[0023] Example 6 Based on Example 5, when fine-tuning equalization is selected, the bus voltage is approximately proportional to the battery current, as expressed as: (14) (15) In the formula, Vbus_avg represents the average value of the bus-side voltage of each module, and SOC_avg represents the average value of the SOC of each module. When entering the fine-tuning equalization mode, the proportional coefficient kP is calculated once, and kP is not updated in subsequent calculations until the next re-entry into the fine-tuning equalization mode. kP is expressed as: (16) In the formula, SOCmax represents the maximum value of SOC in each module; (17) In the formula, ΔVbusRefi represents the bus voltage reference value that needs to be adjusted for each module. The bus voltage reference for each module is the average bus voltage reference value plus the bus voltage reference value that needs to be adjusted, i.e.: (18) Thus making Balanced battery module SOC.

[0024] In summary, traditional PID bus voltage control directly uses feedback to achieve closed-loop control of the bus voltage. When the total bus power changes or remains constant, to achieve real-time power distribution changes among battery modules, the module bus voltage and battery current need to follow the power changes without controlling the current. This invention, while considering the battery SOC difference, first calculates the target current and then converts the current reference to a bus voltage reference, effectively controlling both the current and bus voltage simultaneously, significantly improving the stability and regulation capability of the energy storage system.

Claims

1. A current distribution regulation and voltage equalization SOC optimization method, characterized in that, The specific steps are as follows: determine the balancing strategy type based on the SOC differences between each battery module; Based on the determined balancing strategy, the total cluster current of the system is distributed to each module according to the state of charge (SOC), and the module reference current is generated and calculated. Finally, the module reference current is converted into the bus voltage reference, and each module is controlled to track the voltage target to achieve current distribution.

2. The current distribution regulation voltage equalization SOC optimization method according to claim 1, characterized in that, The upper and lower limits of bus voltage must meet the following requirements: （1） In the formula, Vbus_LimitU represents the upper limit of normal bus voltage, Vbus_LimitL represents the lower limit of normal bus voltage, Vbus_Total represents the set total bus voltage reference, and Nm represents the number of battery modules.

3. The current distribution regulation voltage equalization SOC optimization method according to claim 2, characterized in that, The equilibrium strategy types include extreme equilibrium and fine-tuning equilibrium.

4. The current distribution regulation voltage equalization SOC optimization method according to claim 3, characterized in that, Assume that the minimum SOC module has the maximum charging current and the maximum SOC module has the minimum charging current during charging; assume that the minimum SOC module has the minimum discharging current and the maximum SOC module has the maximum discharging current during discharging; when the current has a sign, it is uniformly represented as the minimum SOC module current and the maximum SOC module current; the maximum allowable current Imax and minimum current Imin are limited by cluster current, voltage ratio, and upper limit of battery current, specifically: （2） （3） In the formula, max(,) represents the maximum value of the two input quantities, and min(,) represents the minimum value of the two input quantities; Vbatt_isocmax represents the module voltage corresponding to the maximum SOC module, and Vbatt_isocmin represents the module voltage corresponding to the minimum SOC module; Icls represents cluster current sampling, and Ibatt_Limit represents battery current limiting.

5. The current distribution regulation voltage equalization SOC optimization method according to claim 4, characterized in that, When the SOC difference between each battery module exceeds the set SOC difference threshold, extreme equalization is selected; when the SOC difference between each module does not exceed the set SOC difference threshold, fine-tuning equalization is selected.

6. The current distribution regulation voltage equalization SOC optimization method according to claim 5, characterized in that, When extreme balance is selected, ignoring losses, the power balance between the battery side and the bus side is achieved, specifically as follows: （4） Where IRef_i represents the current reference of the i-th module, Vbatt_i represents the battery voltage sampling of the i-th module, ∑ i IRef_i·Vbatt_i represents the sum of the battery-side power of each module, and Vbus_Total·Icls represents the bus-side power; all variables are signed, and the current is positive in the discharge direction; Assuming the charging current of each battery module is calculated based on Imin during charging, it is expressed as: （5） In the formula, SOCi represents the SOC of the i-th module. This represents the minimum SOC among all modules, where k is a coefficient. Combining equations (4) and (5), we can obtain: （6） Therefore, it can be calculated that... : （7） Substituting equation (7) into equation (5) yields the current reference value for each module, and the calculated battery-side current reference value IRef_imax corresponding to the module with the highest SOC is observed.

7. The current distribution regulation voltage equalization SOC optimization method according to claim 6, characterized in that, If IRef_imax ≤ Imax, then no recalculation is performed; otherwise, recalculation is performed based on Imax, as shown below: （8） Combining (4) and (8) （9） The conclusion is : （10） Substituting equation (10) into equation (8) yields the current reference values ​​for each module. After obtaining the current references, these are converted into the bus voltage references VbusRef_i for each module: （11） （11） To eliminate the difference between the sum of bus voltage references Vref_Total and the total bus voltage reference Vbus_Total, it is expressed as: （12） The corrected bus voltage reference Vref_i for each module is expressed as: （13）。 8. The current distribution regulation voltage equalization SOC optimization method according to claim 4, characterized in that, When fine-tuning balancing is selected, the bus voltage is approximately proportional to the battery current, expressed as: （14） （15） In the formula, Vbus_avg represents the average value of the bus-side voltage of each module, and SOC_avg represents the average value of the SOC of each module. When entering the fine-tuning equalization mode, the proportional coefficient kP is calculated once, and kP is not updated in subsequent calculations until the next re-entry into the fine-tuning equalization mode. kP is expressed as: （16） In the formula, SOCmax represents the maximum value of SOC in each module; （17） In the formula, ΔVbusRefi represents the bus voltage reference value that needs to be adjusted for each module. The bus voltage reference for each module is the average bus voltage reference value plus the bus voltage reference value that needs to be adjusted, i.e.: （18） Thus making Balanced battery module SOC.

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