A constant power charge-discharge control method for all-vanadium redox flow battery based on MPC-SP

Abstract

This invention discloses a constant power charge-discharge control method for vanadium redox flow batteries based on MPC-SP, applied to an energy storage control system consisting of an MPC-SP controller, a PCS, and the vanadium redox flow battery. Based on a preset SOC range, the controller dynamically and precisely adjusts the power output to the battery, increasing the power in stages as the actual SOC value of the battery increases. Simultaneously, the controller constantly monitors the battery terminal voltage Ud; when Ud reaches a voltage limit, it switches to constant voltage mode, effectively preventing battery damage due to excessive voltage. This state-based dynamic power management is far safer, more flexible, and more intelligent than traditional fixed constant power control. This invention reduces the rate of current change during the charge-discharge process of the vanadium redox flow battery, extending battery life while ensuring safety.

Description

Technical Field

[0001] This invention relates to the field of battery charge and discharge control technology, and in particular to a constant power charge and discharge control method for an all-vanadium redox flow battery based on MPC-SP. Background Technology

[0002] A vanadium redox flow battery (VRFB) is an emerging chemical energy storage device. It mainly consists of a stack, positive and negative electrode reservoirs, a circulation pump, and a control system. The stack is composed of multiple individual cells connected in series, and each individual cell includes electrodes, flow guides, graphite felt electrodes, graphite conductive plates, and an ion-exchange membrane. The positive electrode electrolyte consists of a solution of pentavalent and tetravalent vanadium ions, while the negative electrode electrolyte consists of a solution of trivalent and divalent vanadium ions. The circulation pump, as the power core of the system, is responsible for driving the electrolyte circulation within the system. The control system is crucial for the precise management and protection of the battery's charging and discharging processes.

[0003] Compared to traditional electrochemical batteries, vanadium redox flow batteries exhibit numerous advantages: flexible system design, long lifespan, safety and reliability, and environmental friendliness, making them particularly suitable for constructing large-capacity energy storage systems. However, during the charging and discharging process of vanadium redox flow batteries, the battery current and voltage fluctuate with changes in load, which can lead to unstable charging and discharging power. The rationality of battery charging and discharging management directly affects its performance, lifespan, and the overall system efficiency. Therefore, effectively controlling the battery's charging and discharging power becomes a crucial issue.

[0004] Traditional constant-power charging maintains a constant power input to the battery stack throughout the entire charging process. Initially, due to the lower battery voltage, the current is relatively high; as the battery voltage gradually increases, the charging current gradually decreases to maintain a constant power input. This charging method can quickly replenish battery energy and is suitable for scenarios requiring rapid charging. However, constant-power charging also has some limitations. In the initial stages of charging, due to the high power and low battery terminal voltage, the charging and discharging current can suddenly increase in a short period. In the later stages of charging, maintaining a high power input may cause the terminal voltage to exceed the limit. Furthermore, excessively high power input can cause the battery's internal temperature to rise, affecting battery life and performance. Therefore, in practical applications, it is necessary to reasonably control the charging power according to the battery's condition and system requirements to avoid adverse effects on the battery.

[0005] During constant-power charging of a vanadium redox flow battery (VRB), the battery's terminal voltage is low in the initial stage. To maintain a constant power, the current may increase rapidly in the early stages of charging. This sudden current change can have various adverse effects on the operation and lifespan of the VRB. The following discussion addresses these issues from three aspects: operational stability, battery lifespan, and electrolyte stability.

[0006] 1. Affects operational stability

[0007] In the initial stages of charging, the sudden increase in current causes a rapid acceleration of the electrochemical reaction rate inside the battery, resulting in uneven reactions on the electrode surface. Some areas react too vigorously, while others react relatively slowly, leading to an uneven potential distribution within the battery. This unevenness can cause battery voltage fluctuations, reduce charging efficiency, and may even trigger localized overheating.

[0008] 2. Affects battery life

[0009] High current density can cause severe polarization on the electrode material surface, accelerating corrosion and dissolution. For positive electrode materials, high current may lead to excessive oxidation of vanadium ions, generating unstable oxides that easily decompose during subsequent charge and discharge processes, reducing the activity of the electrode material. For negative electrode materials, sudden current changes may trigger hydrogen evolution reaction. The evolved hydrogen gas adheres to the electrode surface, hindering the normal progress of electrochemical reactions, and also causes expansion and contraction of the electrode material, accelerating electrode aging. Furthermore, sudden current changes can lead to increased internal battery temperature, which accelerates electrolyte decomposition and electrode material degradation, further shortening battery life.

[0010] 3. Affects electrolyte stability

[0011] In VRB (Vibration Reduction Battery), the electrolyte is the energy storage medium, and its stability directly affects the battery's operating efficiency and lifespan. Sudden current changes accelerate the redox reaction of vanadium ions in the electrolyte, potentially leading to irreversible polymerization or precipitation of some vanadium ions, reducing the electrolyte's conductivity and stability. For example, at high temperatures, pentavalent vanadium ions easily transform into vanadium pentoxide precipitate, affecting the battery's reliability and thermal management performance. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a constant power charge-discharge control method for vanadium redox flow batteries based on MPC-SP. MPC stands for Multi-Parameter Coupling, and SP stands for Staged Power. This invention can reduce the rate of current change during the charge-discharge process of vanadium redox flow batteries, extend battery life, and ensure safety.

[0013] This invention is achieved through the following technical solution:

[0014] A constant power charge-discharge control method for vanadium redox flow batteries based on MPC-SP is applied to an energy storage control system consisting of an MPC-SP controller, a PCS, and a vanadium redox flow battery. The method specifically includes the following steps:

[0015] S1, Set power setpoint P ref The set power setpoint P ref Input to the MPC-SP controller;

[0016] S2: Obtain the external terminal voltage of the vanadium redox flow battery. U d Charging and discharging current I d The SOC and the open-circuit voltage OCV of the single-cell vanadium redox flow battery are input to the MPC-SP controller.

[0017] S3: MPC-SP controller determines the power setpoint. P ref Is it greater than 0? P ref >0 If yes, proceed to step S4; otherwise, jump to step S5.

[0018] S4: The vanadium redox flow battery is in discharge mode. Based on the data obtained in step S2, the discharge termination condition is set. If the discharge termination condition is met, the discharge stops; otherwise, the output reference power is calculated according to formula (1). Proceed to step S6;

[0019] (1)

[0020] in, K c1 ~ K c4 To reduce the power factor, SOC HH , SOC max , SOC H , SOC L , SOC LL , SOC min These represent the ultra-high state of charge, maximum permissible state of charge, high state of charge, low state of charge, extremely low state of charge, and minimum permissible state of charge, respectively. SOC max >SOCHH >SOC H >SOC L >SOC LL >SOC min ;

[0021] S5: The vanadium redox flow battery is in charging mode. Based on the data obtained in step S2, the charging end condition is set. If the charging end condition is met, charging is stopped, and the output reference power is calculated according to formula (2). Proceed to step S6; (2)

[0022] in K c1 ~ K c4 The power reduction factor;

[0023] S6: The MPC-SP controller will output the reference power. Send to PCS;

[0024] S7: If >0 Then the vanadium redox flow battery begins constant power discharge, and vice versa, it begins constant power charging.

[0025] S8: PCS calculates the real-time power P of the vanadium redox flow battery.

[0026] S9: The reference power received by the PCS The power deviation is obtained by comparing it with the calculated actual power value P.

[0027] S10: The PCS achieves constant power charging and discharging of the vanadium redox flow battery through power deviation and closed-loop control algorithms, i.e. .

[0028] The external terminal voltage U d Open-circuit voltage (OCV) and charge / discharge current of a single vanadium redox flow battery. I d The data were obtained from the vanadium redox flow battery using voltage transformers and current transformers, respectively.

[0029] The SOC mentioned above is calculated using the ampere-hour integration method, and the calculation formula is as follows:

[0030] ,

[0031] in, SOC 0 represents the initial state of charge of the vanadium redox flow battery. CN This is the rated capacity of the all-vanadium redox flow battery. η The charge / discharge efficiency of the vanadium redox flow battery.

[0032] The power reduction factor K c1 ~ K c4 The value ranges from (0, 1).

[0033] The discharge termination condition mentioned in step S4 is: SOC≤SOC min or U d ≤U dmin or OCV≤OCV min or ;

[0034] in, SOC min It is the minimum permissible state of charge. U dmin This is the minimum voltage limit for the battery terminals. OCV min It is the minimum open-circuit voltage limit. I dmin It is the minimum allowable value for battery charging and discharging current.

[0035] The charging termination condition mentioned in step 5 is: SOC≥SOC max or U d ≥U dmax or OCV≥OCV max or ;

[0036] in, SOC max It is the maximum permissible state of charge. U dmax This is the maximum voltage limit of the battery terminals. OCV max This is the maximum open-circuit voltage limit. I dmax This is the maximum allowable value for battery charging and discharging current.

[0037] The advantages of this invention are: (1) This invention uses a power controller, which processes the power setpoint of the constant power charging and discharging of the battery to obtain a stepped power value. Specifically, based on the preset SOC range division, the controller dynamically and accurately adjusts the power output to the battery. As the actual SOC value of the battery increases, the power is increased in stages. At the same time, the controller constantly monitors the battery terminal voltage Ud. When Ud reaches the voltage limit, it switches to constant voltage mode to effectively prevent the battery from being damaged due to excessive voltage. This state-based dynamic power management is far safer, more flexible and intelligent than the traditional fixed constant power control.

[0038] (2) In the initial stage of battery operation, the terminal voltage is low due to the low concentration of active materials in the electrodes. This invention starts with a low power value and gradually increases the power output in stages and in a controlled manner as the battery voltage increases. This "gradual" approach greatly avoids the drastic disturbance of electrochemical reactions on the electrode surface caused by sudden current changes, reduces the probability of side reactions (such as hydrogen evolution), protects the electrode structure, and thus significantly improves the charge and discharge efficiency of the battery in the initial stage. This step-by-step segmented control method can also reduce the concentration polarization phenomenon caused by changes in electrolyte concentration at the end of the charge and discharge phase, further improving energy utilization.

[0039] (3) Because the power output of this invention changes smoothly and regularly in a stepwise manner, the battery always operates within a relatively stable and predictable state range. This allows researchers to more accurately capture and record key performance parameters such as voltage, current, and temperature of the battery at different SOC levels and power grades, enabling in-depth analysis of battery performance, fault diagnosis, life prediction, and subsequent system optimization, thus making it more beneficial for scientific research. Attached Figure Description

[0040] Figure 1 The variation curves of the charge / discharge power of the all-vanadium redox flow battery and the conventional constant power charge / discharge power are set for this invention.

[0041] Figure 2 A block diagram illustrating the control method for the charge and discharge power of a vanadium redox flow battery. Detailed Implementation

[0042] like Figure 1 , 2 As shown, a constant power charge-discharge control method for a vanadium redox flow battery based on MPC-SP is applied to an energy storage control system consisting of an MPC-SP controller, a PCS, and a vanadium redox flow battery. The method specifically includes the following steps:

[0043] S1, Set power setpoint P ref The set power setpoint Pref Input to the MPC-SP controller;

[0044] S2: Obtain the external terminal voltage of the vanadium redox flow battery. U d Charging and discharging current I d The SOC and the open-circuit voltage OCV of the single-cell vanadium redox flow battery are input to the MPC-SP controller.

[0045] The external terminal voltage U d Open-circuit voltage (OCV) and charge / discharge current of a single vanadium redox flow battery. I d The data were obtained from the vanadium redox flow battery using voltage transformers and current transformers, respectively.

[0046] The SOC mentioned above is calculated using the ampere-hour integration method, and the calculation formula is as follows:

[0047] ,

[0048] in, SOC 0 represents the initial state of charge of the vanadium redox flow battery. C N This is the rated capacity of the all-vanadium redox flow battery. η The charge / discharge efficiency of the vanadium redox flow battery.

[0049] S3: MPC-SP controller determines the power setpoint. P ref Is it greater than 0? P ref >0 If yes, proceed to step S4; otherwise, jump to step S5.

[0050] S4: The vanadium redox flow battery is in discharge mode. Based on the data obtained in step S2, the discharge termination condition is set. If the discharge termination condition is met, the discharge stops; otherwise, the output reference power is calculated according to formula (1). Proceed to step S6;

[0051] (1)

[0052] in, K c1 ~ K c4 The power reduction factor, the power reduction factor K c1 ~ K c4 The value ranges from (0, 1). SOC HH , SOC max , SOC H , SOC L , SOC LL , SOC min These represent the ultra-high state of charge, maximum permissible state of charge, high state of charge, low state of charge, extremely low state of charge, and minimum permissible state of charge, respectively. SOC max >SOC HH >SOC H >SOC L >SOC LL > SOC min ;

[0053] S5: The vanadium redox flow battery is in charging mode. Based on the data obtained in step S2, the charging end condition is set. If the charging end condition is met, charging is stopped, and the output reference power is calculated according to formula (2). Proceed to step S6; (2)

[0054] in K c1 ~ K c4 The power reduction factor; the power reduction factor K c1 ~ K c4 The value ranges from (0, 1).

[0055] S6: The MPC-SP controller will output the reference power. Send to PCS;

[0056] S7: If >0 Then the vanadium redox flow battery begins constant power discharge, and vice versa, it begins constant power charging.

[0057] S8: PCS calculates the real-time power P of the vanadium redox flow battery.

[0058] S9: The reference power received by the PCS The power deviation is obtained by comparing it with the calculated actual power value P.

[0059] S10: The PCS achieves constant power charging and discharging of the vanadium redox flow battery through power deviation and closed-loop control algorithms, i.e. .

[0060] The discharge termination condition mentioned in step S4 is: SOC≤SOC min or U d ≤U dmin or OCV≤OCV min or ;

[0061] in, SOC min It is the minimum permissible state of charge. U dmin This is the minimum voltage limit for the battery terminals. OCV min It is the minimum open-circuit voltage limit. I dmin It is the minimum allowable value for battery charging and discharging current.

[0062] The charging termination condition mentioned in step 5 is: SOC≥SOC max or U d ≥U dmax or OCV≥OCV max or ;

[0063] in, SOC max It is the maximum permissible state of charge. U dmax This is the maximum voltage limit of the battery terminals. OCV max This is the maximum open-circuit voltage limit. I dmax This is the maximum allowable value for battery charging and discharging current.

[0064] Set the power setpoint and input it into the MPC-SP controller. This power setpoint is the system's desired charging and discharging power.

[0065] The external terminal voltage, charge / discharge current, state of charge (SOC), and open-circuit voltage of a single vanadium redox flow battery are acquired and input into the MPC-SP controller. These parameters are important indicators of the battery's current state and are used for subsequent control decisions.

[0066] MPC-SP controller determines the power setpoint. P Is ref greater than 0? If P If ref>0, then enter the discharge mode (step S4); otherwise, enter the charging mode (step S5).

[0067] Discharge mode: If the discharge termination condition is met (such as current reaching the upper limit, voltage falling below the lower limit, SOC reaching the lower limit, or OCV falling below the lower limit), then the discharge stops; otherwise, the output reference power is calculated according to formula (1).

[0068] Charging mode: If the charging end conditions are met (such as the current reaching the lower limit, the voltage exceeding the upper limit, the SOC reaching the upper limit, or the OCV exceeding the upper limit), then charging is stopped; otherwise, the output reference power is calculated according to formula (2).

[0069] The MPC-SP controller sends the output reference power to the PCS (Power Conversion System).

[0070] Depending on the sign of the reference power, the vanadium redox flow battery begins constant power discharge or constant power charging.

[0071] PCS calculates the real-time power of the vanadium redox flow battery.

[0072] The PCS compares the received reference power with the actual power to obtain the power deviation.

[0073] PCS adjusts the charging and discharging power through power deviation and closed-loop control algorithms (such as PID control) to achieve constant power charging and discharging of vanadium redox flow batteries.

[0074] Precise control:

[0075] This invention achieves constant power charging and discharging by accurately calculating the reference power using an MPC-SP controller. This control method is more accurate and stable than traditional open-loop control or simple closed-loop control.

[0076] Dynamic adaptability:

[0077] The MPC-SP controller can monitor the battery status in real time and adjust the control strategy according to dynamic changes in the battery (such as changes in SOC, voltage, etc.). This dynamic adaptability enables the system to maintain good performance under different operating conditions, such as stable operation when the battery is aging or environmental conditions change.

[0078] Security:

[0079] By setting termination conditions for discharge and charge, problems such as overcharging, over-discharging, overcurrent, and overvoltage of the battery can be effectively avoided, thereby extending battery life and improving system safety. For example, when the current reaches the upper limit or the voltage falls below the lower limit, the system will automatically stop discharging or charging.

[0080] High-efficiency energy management:

[0081] The MPC-SP controller optimizes power distribution, ensuring that the vanadium redox flow battery maintains high energy conversion efficiency throughout the charging and discharging process. This not only improves the overall performance of the energy storage system but also reduces energy loss and enhances the system's economics.

[0082] Integration and scalability:

[0083] This invention can be easily integrated into existing energy storage systems and works in conjunction with devices such as PCS. Furthermore, the parameters of the MPC-SP controller can be adjusted and optimized according to different application scenarios, exhibiting excellent scalability.

[0084] This invention presents a constant power charge-discharge control method for vanadium redox flow batteries based on MPC-SP. Through precise model prediction and closed-loop control, it achieves efficient, safe, and accurate control of the charge-discharge process of vanadium redox flow batteries. This not only improves the performance and reliability of energy storage systems but also provides strong technical support for the widespread application of vanadium redox flow batteries in large-scale energy storage.

Claims

1. A constant power charge-discharge control method for an all-vanadium redox flow battery based on multi-parameter coupled MPC-stepped power SP, characterized in that: This technology is applied to an energy storage control system consisting of an MPC-SP controller, a PCS, and a vanadium redox flow battery, and specifically includes the following steps: S1, Set power setpoint The set power setpoint Input to the MPC-SP controller; S2: Obtain the external terminal voltage of the vanadium redox flow battery. Charging and discharging current The SOC and the open-circuit voltage OCV of the single-cell vanadium redox flow battery are input to the MPC-SP controller. S3: MPC-SP controller determines the power setpoint. Is it greater than 0? If yes, proceed to step S4; otherwise, jump to step S5. S4: The vanadium redox flow battery is in discharge mode. Based on the data obtained in step S2, the discharge termination condition is set. If the discharge termination condition is met, the discharge stops; otherwise, the output reference power is calculated according to formula (1). Proceed to step S6; (1) in, ~ To reduce the power factor, , , , , , These represent the ultra-high state of charge, maximum permissible state of charge, high state of charge, low state of charge, extremely low state of charge, and minimum permissible state of charge, respectively. ; S5: The vanadium redox flow battery is in charging mode. Based on the data obtained in step S2, the charging end condition is set. If the charging end condition is met, charging is stopped, and the output reference power is calculated according to formula (2). Proceed to step S6; (2) wherein cos φ is the power factor​ S6: The MPC-SP controller will output the reference power to the PCS; S7: If Then the vanadium redox flow battery begins constant power discharge, and vice versa, it begins constant power charging. S8: PCS calculates the real-time power P of the vanadium redox flow battery. S9: The reference power received by the PCS The power deviation is obtained by comparing it with the calculated actual power value P. S10: The PCS achieves constant power charging and discharging of the vanadium redox flow battery through power deviation and closed-loop control algorithms, i.e. .

2. The constant power charge-discharge control method for an all-vanadium redox flow battery based on multi-parameter coupled MPC-stepped power SP as described in claim 1, characterized in that: The external terminal voltage Open-circuit voltage (OCV) and charge / discharge current of a single vanadium redox flow battery. The data were obtained from the vanadium redox flow battery using voltage transformers and current transformers, respectively.

3. The constant power charge and discharge control method for a vanadium redox flow battery based on multi-parameter coupling (MPC) and step power (SP) according to claim 1, characterized in that: The SOC mentioned above is calculated using the ampere-hour integration method, and the calculation formula is as follows: in, This represents the initial state of charge of the vanadium redox flow battery. This is the rated capacity of the all-vanadium redox flow battery. The charge / discharge efficiency of the vanadium redox flow battery.

4. The constant power charge-discharge control method for an all-vanadium redox flow battery based on multi-parameter coupled MPC-stepped power SP as described in claim 1, characterized in that: The power factor is reduced The value range is between (0, 1).​ 5. The constant power charge and discharge control method of a vanadium redox flow battery based on multi-parameter coupling (MPC) - stepped power (SP) according to claim 1, characterized in that: The discharge termination condition mentioned in step S4 is: or or or ; in, It is the minimum permissible state of charge. This is the minimum voltage limit for the battery terminals. It is the minimum open-circuit voltage limit. It is the minimum allowable value for battery charging and discharging current.

6. The constant power charge-discharge control method for an all-vanadium redox flow battery based on multi-parameter coupled MPC-stepped power SP as described in claim 1, characterized in that: The charging termination condition mentioned in step 5 is: or or or ; in, It is the maximum permissible state of charge. This is the maximum voltage limit of the battery terminals. This is the maximum open-circuit voltage limit. This is the maximum allowable value for battery charging and discharging current.

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