Series all-vanadium redox flow battery system modeling method based on resistance inconsistency

Abstract

The invention discloses a series all-vanadium redox flow battery system modeling method based on resistance inconsistency. The method comprises the following steps: step 1, establishing an equivalent loss operation circuit model and a Thevenin equivalent circuit of a series all-vanadium redox flow battery system; establishing an internal resistance inconsistency evaluation index based on the average equivalent internal resistance and the equivalent internal resistance of the all-vanadium redox flow battery; and step 2, based on the Thevenin equivalent circuit of the series all-vanadium redox flow battery system, obtaining parameter relationships in the series all-vanadium redox flow battery system, and establishing an internal resistance inconsistency evaluation model in the parameter relationships based on the internal resistance inconsistency evaluation indexes, thereby completing modeling. The method provided by the invention can provide powerful support for practical application of the all-vanadium redox flow battery.

Description

Technical Field

[0001] The invention relates to the field of all-vanadium liquid flow battery system modeling methods, in particular to a series all-vanadium liquid flow battery system modeling method based on resistance inconsistency. Background Art

[0002] Global energy demand has increased rapidly with the advancement of industrialization. The large-scale use of traditional energy has promoted the booming economy, but it has also caused serious environmental pollution and resource shortages. Countries around the world have incorporated new energy into their sustainable development strategies and have successively formulated relevant policies and measures to promote the development and utilization of new energy. Compared with traditional battery energy storage technology, all-vanadium liquid flow batteries have many advantages: First, they have a large power capacity and energy storage capacity, which can meet the energy storage needs of various scales. Secondly, all-vanadium liquid flow batteries have a long service life and can work continuously and stably for nearly 20,000 cycles, making them more economical and stable.

[0003] Large-capacity vanadium flow battery energy storage system (VRBS) plays a key role in the energy field. It is usually composed of multiple vanadium flow batteries (VRB modules) connected in series to meet the power and voltage requirements of the system. Due to differences in the manufacturing process, imbalance in the charging and discharging process, changes in the self-discharge rate, and different heat dissipation conditions, the consistency between the VRB modules may be reduced. The inconsistency between the VRB modules will reduce the overall performance of the VRBS, and even cause safety hazards in severe cases. Therefore, it is urgent to build a model for the VRBS and study and analyze its inconsistency problems to provide a theoretical reference for the safe and efficient operation of the VRBS.

[0004] Among the existing modeling methods for series-connected all-vanadium flow battery systems, the equivalent model method is based on the battery pack model of the equivalent circuit model. Its analysis basis is that the parameter differences between the monomers are small, which is not suitable for the modeling of battery packs with obvious inconsistencies. The iteration rule proposes a modeling method for series / parallel battery modules based on the iteration method, but the iteration is based on the constant current discharge process and is not suitable for describing the performance of batteries under complex working conditions. Summary of the invention

[0005] The present invention provides a series-connected all-vanadium liquid flow battery system modeling method based on resistance inconsistency, so as to solve the problem that the series-connected all-vanadium liquid flow battery system modeling method in the prior art does not consider the internal resistance inconsistency.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The modeling method of a series all-vanadium liquid flow battery system based on resistance inconsistency includes the following steps:

[0008] Step 1: Establish an equivalent loss calculation circuit model of a series-type all-vanadium liquid flow battery system, and simplify it to obtain the Thevenin equivalent circuit of the series-type all-vanadium liquid flow battery system;

[0009] Furthermore, an internal resistance inconsistency evaluation index is established based on the average equivalent internal resistance of each all-vanadium flow battery in the series-connected all-vanadium flow battery system and the equivalent internal resistance of each all-vanadium flow battery;

[0010] Step 2: Based on the Thevenin equivalent circuit of the series-type all-vanadium liquid flow battery system established in step 1, the relationship between the parameters in the series-type all-vanadium liquid flow battery system is obtained, and an internal resistance inconsistency evaluation model is established in the parameter relationship based on the internal resistance inconsistency evaluation index obtained in step 1, thereby completing the modeling.

[0011] Furthermore, in the Thevenin equivalent circuit of the series-connected all-vanadium liquid flow battery system obtained in step 1, the total terminal voltage of the series-connected all-vanadium liquid flow battery system is the sum of the terminal voltages of each all-vanadium liquid flow battery, and the total equivalent impedance of the series-connected all-vanadium liquid flow battery system is the sum of the equivalent impedances of each all-vanadium liquid flow battery.

[0012] Furthermore, in step 1, the internal resistance inconsistency evaluation index established is as shown in the following formula:

[0013]

[0014] in: represents the average equivalent internal resistance of each vanadium redox flow battery in the series-connected vanadium redox flow battery system, Z eqi represents the equivalent internal resistance of the i-th all-vanadium liquid flow battery, and Z eqi There are the following relations:

[0015]

[0016] Wherein, m is the total number of all-vanadium liquid flow batteries in the series-connected all-vanadium liquid flow battery system.

[0017] Furthermore, in step 2, the internal resistance inconsistency evaluation model established is as shown below:

[0018]

[0019] Where: Z eqs (s) = transfer function representing the total impedance of the system; s represents the complex frequency variable in the transfer function; k 2i represents the impedance proportional coefficient of the ith battery stack; a represents the potential constant; b represents the impedance constant.

[0020] The method of the present invention can provide strong support for the practical application of all-vanadium liquid flow batteries by optimizing performance, improving efficiency, extending life, and enhancing system reliability. Compared with the prior art, the advantages of the present invention are:

[0021] 1. Improve performance prediction and optimization capabilities: Inconsistency modeling can help us more accurately predict the performance of all-vanadium liquid flow batteries under different working conditions. This is crucial for the design of battery management systems (BMS), which can monitor and adjust the working status of the battery in real time, thereby optimizing the performance of the overall system.

[0022] 2. Extend battery life: Inconsistent battery performance under different working conditions may cause some battery cells to decay prematurely. Through inconsistency modeling, personalized maintenance strategies can be adopted for different battery cells to avoid overcharging and discharging, reduce battery cell losses, and extend the overall service life of the battery pack.

[0023] 3. Improve the energy density and efficiency of the system: By establishing an accurate inconsistency model, the efficiency loss of the system under different operating conditions can be effectively evaluated and optimized. This helps to improve the overall efficiency of the all-vanadium liquid flow battery and maximize the energy storage and release capabilities.

[0024] 4. Improve system reliability: Through inconsistency modeling, potential failure points of different single cells can be discovered, and timely diagnosis and optimization adjustments can be made, thereby improving the long-term stability and reliability of the battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 4 is a circuit diagram of equivalent loss calculation of a single VRB in an embodiment of the present invention.

[0026] Figure 2 is a Thevenin equivalent circuit diagram of a single VRB in an embodiment of the present invention.

[0027] Figure 3 It is an equivalent loss calculation circuit diagram of a series-type all-vanadium liquid flow battery system in an embodiment of the present invention.

[0028] Figure 4 4 is a Thevenin equivalent circuit diagram of a series-connected all-vanadium liquid flow battery system in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0030] This embodiment discloses a modeling method for a series-type all-vanadium liquid flow battery system based on resistance inconsistency, comprising the following steps:

[0031] Step 1: Establish a circuit model and internal resistance inconsistency evaluation index.

[0032] In this embodiment, an equivalent loss calculation circuit model of a series-connected all-vanadium liquid flow battery system is first established, and then simplified to obtain a Thevenin equivalent circuit of the series-connected all-vanadium liquid flow battery system.

[0033] Specifically, for a single all-vanadium liquid flow battery (hereinafter referred to as VRB), an equivalent loss calculation circuit model of a single VRB is established as follows: Figure 1 shown. Figure 1 Medium: U d (s) represents the terminal voltage, I d (s) represents the charge and discharge current, I f (s) is the bypass current, R f (s) is the bypass resistor, Ip(s) is the pump loss current, Ic(s) is the capacitor current, Ce(s) is the electrode capacitance, Uc(s) is the capacitor voltage, Us(s) is the stack voltage, Is(s) is the stack current, R rea Represents the internal resistance of the reaction, R res is the ohm resistance, s represents the complex frequency variable in the transfer function. Through the algorithm, the VRB is analyzed in detail, which can better understand the equivalent loss characteristics of the VRB and provide a reference for the design and optimization of the system.

[0034] Set the initial condition U c (0) = 0, Uc represents the capacitor voltage, and Figure 1 The equivalent loss calculation circuit model of VRB shown in FIG. 1 is simplified to obtain the Thevenin equivalent circuit corresponding to VRB. The specific circuit is as follows: Figure 2 shown. Figure 2 Medium: U d (s) represents the terminal voltage, I eq (s) represents the pump loss current, E eq (s) represents the equivalent electromotive force, Z eq (s) is the equivalent impedance.

[0035] Therefore, according to Figure 2 The Thevenin equivalent circuit of VRB is shown in FIG. 1 . The relationship between the parameters in the Thevenin equivalent circuit of VRB can be obtained as shown in formulas (1), (2), and (3):

[0036] U d (s) = E eq (s)+I eq (s)·Z eq (s) (1)

[0037] E eq (s)=K(s)·U s (s) (2)

[0038] Ieq (s)=I d (s)-I p (s) (3)

[0039] In formulas (1), (2), and (3): U d (s) is the terminal voltage, E eq (s) is the equivalent terminal voltage, I eq (s) is the equivalent current, Z eq (s) is the equivalent impedance, K(s) is the potential equivalent coefficient, U s (s) is the stack voltage, I d (s) is the charge and discharge current, I p (s) is the pump loss current, and there is formula (4):

[0040]

[0041] In formula (4): R f is the bypass resistor, R rea is the reaction internal resistance, R res is the ohmic resistance, C e represents the electrode capacitance, K(s) is the potential equivalent coefficient, and Z eq (s) is the equivalent impedance, k1 is the potential proportionality coefficient, k2 is the impedance proportionality coefficient, s represents the complex frequency variable in the transfer function, a is the potential constant, and b is the impedance constant.

[0042] Connect the equivalent loss calculation circuit models of each VRB in series electrically to obtain the following Figure 3 The equivalent loss calculation circuit model of the series-type all-vanadium liquid flow battery system (hereinafter referred to as the all-vanadium liquid flow battery system VRBS) is shown. Figure 3 Medium: I d Indicates the total terminal current, U d Indicates terminal voltage, I d1 is the terminal current of the i-th VRB, R fi is the bypass resistor of the i-th VRB, I pi represents the pump loss current of the i-th VRB, C ei represents the electrode capacitance of the i-th VRB, U si represents the stack voltage of the i-th VRB, R reai represents the reaction internal resistance of the i-th VRB, R resi is the ohmic resistance of the i-th VRB.

[0043] The equivalent loss calculation circuit model of the series VRBS is simplified, and the Thevenin equivalent circuit of the series VRBS is obtained as follows: Figure 4 As shown, Figure 4 Medium: I eq(s) represents the equivalent current of VRBS, U d (s) represents the equivalent terminal voltage of VRBS, E eqi (s) represents the equivalent electromotive force of the i-th VRB, Z eqi (s) represents the equivalent impedance of the i-th VRB. Figure 4 It can be seen that in the equivalent loss calculation circuit model of the series VRBS, the current flowing through different positions is the same, the total terminal voltage of the VRBS is the accumulation of the terminal voltages of each VRB, and the total equivalent impedance of the VRBS is the sum of the equivalent impedances of each VRB.

[0044] The dynamic characteristics of the series VRBS are more complex, and the various VRB modules involved will affect each other. To simplify the analysis process, this embodiment mainly considers the impact of the voltage, current, impedance and SOC of each VRB on the system, while other parameters are not considered for the time being. During the operation of the VRB, SOC, as a measure of the remaining capacity of the battery, cannot be measured directly, but can only be calculated through parameters such as the terminal voltage and terminal current of the battery. The calculation formula of SOC is as follows:

[0045]

[0046] In the formula, SOC0 represents the initial value of SOC, I d Represents the terminal current, U d Represents the terminal voltage, E N Indicates the capacity of VRB.

[0047] In this embodiment, the internal resistance of the battery is considered to be a key parameter for measuring the power performance and service life of the battery, and is particularly important for the performance evaluation of the all-vanadium liquid flow battery energy storage system. The change in internal resistance is affected by many factors, covering multi-dimensional factors such as the manufacturing process of the battery, the selection of raw materials, daily usage conditions, and environmental changes. Among them, the impact of temperature changes on internal resistance is particularly significant. The inconsistency of the internal resistance of the VRBS will cause inconsistencies in the terminal voltage and SOC change rate of each VRB module. At the same time, during the charging process, the VRB module with a high internal resistance will obtain a higher voltage, and thus will reach a full state before the VRB with a low internal resistance, further affecting the consistency of the charge and discharge capacity and the overall performance of the system. Therefore, according to the following Figure 4 The Thevenin equivalent circuit of the series-type VRBS shown in FIG. 1 is a diagram showing a series-type VRBS. In this embodiment, an internal resistance inconsistency evaluation index is established based on the average equivalent internal resistance of each all-vanadium liquid flow battery in the series-type all-vanadium liquid flow battery system and the equivalent internal resistance of each all-vanadium liquid flow battery, as shown in formula (6):

[0048]

[0049] In formula (6): Z Represents the evaluation index of internal resistance inconsistency, δZ The larger the value is, the higher the internal resistance inconsistency of VRBS is; m is the total number of all-vanadium liquid flow batteries in the series-connected all-vanadium liquid flow battery system; represents the average equivalent internal resistance of each vanadium liquid flow battery in the series-connected vanadium liquid flow battery system; Z eqi represents the equivalent internal resistance of the i-th all-vanadium liquid flow battery, and and Z eqi There are the following relations:

[0050]

[0051] Combining (6) and (7), we can get formula (8):

[0052]

[0053] In formula (8): Z eqi represents the equivalent internal resistance of the i-th all-vanadium liquid flow battery, represents the average equivalent internal resistance of each vanadium liquid flow battery in the series-connected vanadium liquid flow battery system, m is the total number of vanadium liquid flow batteries in the series-connected vanadium liquid flow battery system, and k 2i It represents the impedance proportionality coefficient of the ith battery stack, a is the potential constant, and b is the impedance constant

[0054] Step 2: Based on the Thevenin equivalent circuit of the series-connected all-vanadium liquid flow battery system established in step 1, the relationship between the parameters in the series-connected all-vanadium liquid flow battery system is obtained, including the terminal voltage U of VRBS. d (s), equivalent current I eq (s), the equivalent electromotive force E of the i-th VRB eqi (s), the equivalent internal resistance Z of the i-th all-vanadium liquid flow battery eqi And in the parameter relationship, based on the internal resistance inconsistency evaluation index obtained in step 1, an internal resistance inconsistency evaluation model is established, as shown in formula (9):

[0055]

[0056] In formula (9): U d (s) is the terminal voltage of VRBS, E esq represents the equivalent electromotive force of VRBS, I eq (s) is the equivalent current, Z eq (s) is the equivalent impedance of VRBS, E eqi (s) represents the equivalent electromotive force of the i-th VRB, m is the total number of vanadium liquid flow batteries in the series-connected vanadium liquid flow battery system, δ Z An evaluation index representing the inconsistency of internal resistance. represents the average equivalent internal resistance of each vanadium liquid flow battery in the series-connected vanadium liquid flow battery system, k 2i It represents the impedance proportional coefficient of the ith battery stack, a is the potential constant, and b is the impedance constant.

[0057] Thus, the series vanadium liquid flow battery system modeling based on resistance inconsistency is completed. The above model provides a theoretical basis for the analysis of the inconsistency problem of series VRBS.

[0058] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0059] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A modeling method for a series all-vanadium liquid flow battery system based on resistance inconsistency, characterized in that: The following steps are involved: Step 1: Establish an equivalent loss calculation circuit model of a series-type all-vanadium liquid flow battery system, and simplify it to obtain the Thevenin equivalent circuit of the series-type all-vanadium liquid flow battery system; Furthermore, an internal resistance inconsistency evaluation index is established based on the average equivalent internal resistance of each all-vanadium flow battery in the series-connected all-vanadium flow battery system and the equivalent internal resistance of each all-vanadium flow battery; Step 2: Based on the Thevenin equivalent circuit of the series-type all-vanadium liquid flow battery system established in step 1, the relationship between the parameters in the series-type all-vanadium liquid flow battery system is obtained, and an internal resistance inconsistency evaluation model is established in the parameter relationship based on the internal resistance inconsistency evaluation index obtained in step 1, thereby completing the modeling.

2. The method for modeling a series all-vanadium liquid flow battery system based on resistance inconsistency according to claim 1, characterized in that: In the Thevenin equivalent circuit of the series-connected all-vanadium liquid flow battery system obtained in step 1, the total terminal voltage of the series-connected all-vanadium liquid flow battery system is the sum of the terminal voltages of each all-vanadium liquid flow battery, and the total equivalent impedance of the series-connected all-vanadium liquid flow battery system is the sum of the equivalent impedances of each all-vanadium liquid flow battery.

3. The method for modeling a series all-vanadium liquid flow battery system based on resistance inconsistency according to claim 1, characterized in that: In step 1, the internal resistance inconsistency evaluation index established is as follows: in: represents the average equivalent internal resistance of each vanadium redox flow battery in the series-connected vanadium redox flow battery system, Z eqi represents the equivalent internal resistance of the i-th all-vanadium liquid flow battery, and Z eqi There are the following relations: Wherein, m is the total number of all-vanadium liquid flow batteries in the series-connected all-vanadium liquid flow battery system.

4. The method for modeling a series all-vanadium liquid flow battery system based on resistance inconsistency according to claim 1, characterized in that: In step 2, the internal resistance inconsistency evaluation model established is as follows: Where: Z eqs (s) = the total impedance of the system Transfer Function ; s represents the complex frequency variable in the transfer function; k 2i represents the impedance proportional coefficient of the ith battery stack; a represents the potential constant; b represents the impedance constant.

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