Reliability prediction method for large-capacity energy storage system based on three states

Abstract

The present application relates to a kind of based on three-state large-capacity energy storage system reliability prediction method, comprising the following steps: (1) according to short circuit, open circuit, three states of success, the reliability of energy storage system under two ways of series and parallel is analyzed;(2) with two monomers X i , X' i Parallel is analyzed, and reliability is analyzed;(3) it is assumed that fault does not occur simultaneously, at most only one fault point, and failure rate is equal;(4) obtain the reliability calculation formula of series system of n branch monomers;(5) obtain the maximum value setting formula of reliability;(6) obtain the reliability calculation formula of three-state system under two typical connection modes of m×n branch monomers;(7) introduce reliability average to further compare;The present application utilizes reliability mathematical analysis, formula derivation and the supporting hardware circuit, details the reliability prediction method of energy storage system, can provide strong basis for the design and research and development of energy storage system, and then greatly improve research and development efficiency and system reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to a three-state-based reliability prediction method for large-capacity energy storage systems. BACKGROUND

[0002] With the continuous rise in crude oil prices, people's environmental protection awareness is constantly enhanced, and the good driving experience of new energy electric vehicles makes more and more people purchase and use electric vehicles.

[0003] The battery is a core component on the electric vehicle, providing a constant supply of electric energy for the vehicle. Common batteries on the market include: lithium iron phosphate batteries, ternary lithium batteries, lead-acid batteries, super capacitors, etc.; but the voltage of the above-mentioned battery monomers is relatively low, and they cannot directly provide energy for electric vehicles.

[0004] Usually, a large number of battery monomers are connected in series and parallel to increase the voltage and capacity of the entire battery pack. For example, the Tesla Model-sp85D electric vehicle battery pack consists of a total of 7104 18650 lithium batteries. Due to the influence of production process, packaging, environmental temperature and other parameters, the parameters of each battery monomer are not consistent. If any battery fails, it will cause instability of the entire system; the common faults are mainly short circuit and open circuit, and the occurrence rates of the above two cases are not consistent.

[0005] In engineering applications, the most concerned function relationship between the number of series and parallel monomers and the system reliability and the maximum value setting, therefore, how to quickly and conveniently calculate the reliability value is of great significance for electric vehicle design, research and development or other large-capacity energy storage application fields.

[0006] For example, the Chinese invention patent with patent number CN201510662050.0 and the name of "Reliability judgment method for large-capacity energy storage equipment" discloses a reliability judgment method for large-capacity energy storage equipment; this method is only used for equipment that has been running, and through real-time monitoring of the voltage, current, power and other parameters of the running equipment, and through calculation, it is judged whether the system is in a stable running state, but this method cannot predict the reliability of the energy storage system that has not yet been running. SUMMARY

[0007] In view of the above status of the prior art, the technical problem to be solved by the present application is to provide a three-state-based reliability prediction method for large-capacity energy storage systems, which can accurately and effectively predict the reliability of the energy storage system that has not yet been running, provide a strong basis for the design and research and development of the energy storage system, and greatly improve the research and development efficiency and system reliability.

[0008] The application solves the above technical problems by adopting the technical scheme of a three-state-based reliability prediction method for a large-capacity energy storage system, characterized by comprising the following steps:

[0009] (1) According to the three states of short circuit, open circuit and success, the reliability of the energy storage system in series and parallel modes is analyzed, and the three states are recorded as follows:

[0010] X i is the connection success of unit i;

[0011] is the open circuit of unit i;

[0012] is the short circuit of unit i;

[0013] The probabilities thereof are as follows:

[0014] P(X i )=p i (1);

[0015]

[0016] and satisfy formula (4)

[0017] p i +q io +q is =1 (4);

[0018] (2) Taking two monomers X i and X i in parallel as an example to analyze the reliability, the formula for the reliability of two monomers in parallel is obtained:

[0019]

[0020] (3) Assuming that the faults do not occur at the same time, and at most only one fault point occurs, and the failure rates are equal, then:

[0021]

[0022] The formula (1), (2), (3) is brought into the above formula (6) and simplified to obtain:

[0023]

[0024] (4) The formula is further extended to the n-branch monomer parallel subsystem, and the reliability formula thereof is:

[0025]

[0026] By analogy with the above derivation process, the reliability calculation formula of the n-branch monomer series system can be obtained:

[0027]

[0028] (5) In the three-state energy storage system, due to the existence of short-circuit fault, the reliability of a large number of parallel single bodies cannot be improved, but the overall reliability of the system is decreased; therefore, partial derivatives are solved on both sides of formula (8), and After rearrangement and simplification, the reliability maximum setting formula is obtained:

[0029]

[0030] (6) The reliability calculation under the series or parallel mode is divided into two steps: firstly, the submodule reliability value is calculated; secondly, the overall system reliability value is calculated on the basis of the submodule; through the above process, the reliability calculation formula of the three-state system under the two typical connection modes of m*n single bodies is obtained:

[0031]

[0032] (7) The reliability average value is introduced to further compare and obtain the calculation formula (13).

[0033]

[0034] Preferably, in the step (6), the reliability of the two typical connection modes is respectively , q o , q s The circuit breaking probability and the short-circuit probability of each single body are respectively.

[0035] Preferably, in the step (7), the reliability average value is The minimum value and the maximum value of the reliability are respectively min , R max .

[0036] Compared with the prior art, the advantages of the present application are that: the present application utilizes the reliability mathematical analysis, formula derivation and the matching hardware circuit, and details the reliability prediction method of the energy storage system; in the engineering practice, as long as the corresponding connection mode is selected according to the actual situation, then the reliability prediction value under the connection mode can be obtained by substituting the related parameters, and the value is accurate and effective, which can provide a strong basis for the design and research and development of the energy storage system, and then greatly improve the research and development efficiency and the system reliability. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is the wiring diagram under the series mode of the present application;

[0038] Figure 2 It is the wiring diagram under the parallel mode of the present application;

[0039] Figure 3 A prediction graph for the maximum reliability of the three-state system of formula (8) of the present application;

[0040] Figure 4 A function relationship graph between the number of monomers m, n and reliability in series of the present application;

[0041] Figure 5 A function relationship graph between the number of monomers m, n and reliability in parallel of the present application;

[0042] Figure 6 A comparison graph of the average reliability in series and parallel of the present application;

[0043] Figure 7 A system connection block diagram when the present application works;

[0044] Figure 8 A wiring diagram of the control module of the present application;

[0045] Figure 9 A wiring diagram of the display output module of the present application;

[0046] Figure 10 A wiring diagram of the input module of the present application;

[0047] Figure 11 A system software flowchart of the present application. DETAILED DESCRIPTION

[0048] Unless otherwise defined, technical terms or scientific terms used in the present application shall have the usual meaning understood by a person with ordinary skill in the art to which the present application belongs. The terms "first", "second" and similar words used in the present application do not represent any order, number or importance, but are only used to distinguish different components. The terms "include" or "contain" and similar words mean that the elements or objects before the word cover the elements or objects listed after the word and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "up", "down", "left", "right" and the like are only used to represent relative positional relationships, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0049] In order to keep the following description of the embodiments of the present application clear and concise, the present application omits the detailed description of known functions and known components.

[0050] A three-state-based large-capacity energy storage system reliability prediction method, comprising the following steps:

[0051] (1) Figures 1-2 As shown in the figure, based on the three states of short circuit, open circuit and success, the reliability of the energy storage system in series and parallel modes is analyzed, and the three states are recorded as:

[0052] X i The connection is successful for unit i;

[0053] Connect a disconnect circuit for unit i;

[0054] Connect a short circuit to unit i.

[0055] The probabilities are as follows:

[0056] P(X i )=p i (1)

[0057]

[0058] And satisfy formula (4)

[0059] p i +q io +q is =1 (4)

[0060] (2) With two monomers X i 、X i Taking parallel connection as an example, reliability analysis is carried out: the system can only operate reliably when the two cells are not disconnected at the same time and no cell is short-circuited. Therefore, the reliability of the two cells in parallel is:

[0061]

[0062] (3) The basic assumptions stipulate that failures do not occur simultaneously, there is at most one failure point, and the failure rates are equal, so:

[0063]

[0064] Substitute formula (1), (2), (3) into the above formula (6) and simplify to obtain:

[0065]

[0066] Derivation process:

[0067]

[0068] (4) Formula (7) is only for X i 、X i The reliability analysis of the two-unit parallel system can be further extended to the reliability of the subsystem with n units in parallel:

[0069]

[0070] The reliability calculation formula of n series monomer string system can be obtained by analogy with the above derivation process:

[0071]

[0072] Therefore, under the premise of only considering failure, large-capacity energy storage system can improve system reliability by increasing the number of parallel monomers.

[0073] (5) In the three-state energy storage system, due to the existence of short-circuit failure, a large number of parallel monomers cannot improve the reliability, but on the contrary, it makes the overall system reliability decline; Therefore, the function relationship between the number of parallel monomers and reliability and the maximum setting principle are most concerned in engineering applications, and the partial derivative of both sides of formula (8) is taken, and After rearrangement and simplification, the reliability maximum setting formula is obtained:

[0074]

[0075] Figure 3 is the solution of formula (8), and the equation is solved when n=2, 3, 4, 5, respectively. The maximum value curve of the reliability of the three-state system; The figure can clearly show that: when the short-circuit probability q s of the energy storage system is large, the fewer the number of parallel monomers, the higher the system reliability; On the contrary, when the short-circuit probability q o of the system is large, the fewer the number of series, the more stable the system.

[0076] (6) Formulas (8), (9) only give the reliability calculation formula of parallel and series subsystems, and Figure 1 , 2 The reliability calculation under the two connection modes can be divided into two steps: first, calculate the submodule reliability value; Second, calculate the overall system reliability value based on the submodule; Through the above process, the reliability calculation formula of the three-state system under the two typical connection modes of m×n monomers can be obtained:

[0077]

[0078] are the reliabilities under the two typical connection modes, respectively, q o and q s are the probabilities of short-circuit and short-circuit of each monomer, respectively.

[0079] Maxwell's MC-3000 supercapacitors were used as the research unit, with a rated voltage of 2.7V and a capacity of 3000F (this article does not consider the impact of dispersion on the entire energy storage system). A 48V module was formed by connecting 18 units in series and 10 units in parallel as an example. Given the probabilities of short circuits and open circuits (see the table in the appendix of "Reliability Engineering"), the reliability of the two typical connection methods was calculated.

[0080] Figure 4 、 Figure 5 The functional relationships between the number of monomers m and n and the reliability under the two connection modes are shown respectively; the specific graphs are drawn by Matlab, and the detailed parameter settings are shown in Table 1.

[0081] Table 1 Reliability parameters

[0082]

[0083] (7) Figure 4 、 Figure 5 It is difficult to clearly see which method is better, so the present invention introduces the average reliability value for further comparison; Figure 5 This is a comparison chart of the average reliability of the two connection methods. The calculation formula is shown in (13). is the average reliability, R min 、R max The minimum and maximum reliability values ​​respectively.

[0084]

[0085] from Figure 6 It can be clearly seen that the second connection method is still better than the first connection method in the three-state energy storage system.

[0086] Specific operation method:

[0087] like Figure 7 As shown, the input module inputs the parameters required by the system into the control module. After calculation, the control module sends the data to the display module. The user can directly see the predicted value of the reliability of the energy storage system through the display module. The power module supplies power to both the display module and the control module.

[0088] like Figure 8 As shown, the microcontroller XTAL1 and XTAL2 ports are connected in parallel with the crystal oscillator Y1 (11.0592M), and the two ends of the crystal oscillator are connected to the capacitors C1 (22p) and C2 (22p), and finally converge to the ground (GND).

[0089] The single-chip computer RST port is connected with the button switch (RST), the other end of the button switch is connected with the power supply VCC (+5V), a capacitor C4 (10uF) is connected in parallel with the button switch (RST), meanwhile, the negative pole pin of the capacitor is connected with a resistor R7 (10K), and the other end of the resistor R7 is connected with the ground (GND).

[0090] The single-chip computer EA / VPP port is connected with the power supply VCC (+5V), and the VSS port is connected with the ground (GND).

[0091] The single-chip computer P0.0-P0.7 ports are respectively connected with the DB1-DB7 of the display screen LCD12864.

[0092] The single-chip computer P1.0-P1.7 ports are respectively connected with the P10-P17 ports of the button switch in the input module.

[0093] The single-chip computer P3.0-P3.1 ports are respectively connected with the P30-P31 ports of the button switch in the input module.

[0094] The single-chip computer P3.4-P3.6 ports are respectively connected with the 4, 5, 6 ports of the display screen LCD12864.

[0095] As shown in the figure, the 1, 2 ports of the display screen LCD12864 are short-circuited and connected with the ground (GND). Figure 9

[0096] The 2, 19 ports of the display screen LCD12864 are short-circuited and connected with the ground (GND) through the capacitor C12 (0.1uF).

[0097] The 17 port of the display screen LCD12864 is respectively connected with the positive pole of the resistor R11 (4.7K) and the capacitor C15 (10uF), the other end of the resistor R11 is connected with the VCC (+5V), and the negative pole is connected with the ground (GND).

[0098] The 18 port of the display screen LCD12864 is connected with one end of the sliding resistor R14 (5K), the other end of the R14 is connected with the ground (GND), and the middle slice is connected with the 3 of the display screen LCD12864.

[0099] The 15 and 16 ports of the display screen LCD12864 are directly short-circuited and connected with the power supply VCC (+5V).

[0100] The input module is shown in the figure, which mainly uses a 4×6 button matrix to realize the control of different functions. The horizontal column output P10-P13 of the button matrix is respectively connected with the P1.0-1.7 ports of the single-chip computer, and the input module P140P17, P30-P31 is similar to the above connection, which will not be described here. Figure 10 ​​

[0101] The operation process of the prediction instrument is as shown in the following steps: Figure 11 Firstly, the connection mode of the energy storage system is selected, then the next step is entered, otherwise the input is re-entered, then the required parameter values are inputted, the result is directly displayed after being determined, otherwise the input is re-entered.

[0102] The present application utilizes reliability mathematical analysis, formula derivation and the matching hardware circuit, and details the reliability prediction method of the energy storage system. In engineering practice, as long as the corresponding connection mode is selected according to the actual situation, and the relevant parameters are substituted, the reliability prediction value under the connection mode can be obtained, and the value is accurate and effective, which can provide a strong basis for the design and research and development of the energy storage system, and thus greatly improve the research and development efficiency and the system reliability.

[0103] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for reliability prediction of large capacity energy storage system based on three states, characterized in that, The steps include the following: (1) According to the short circuit, open circuit, success three states, the reliability of energy storage system under series and parallel two ways is analyzed, and the three states are recorded as: X i Unit i is connected successfully; Connect a circuit breaker for unit i; connect a short circuit to the unit i; The probabilities are as follows: P(X i ) = p i (1) And meet formula (4) p i +q io +q is = 1 (4); (2) Two monomers X i , X i Parallel reliability analysis, get two monomers parallel reliability formula: (3) Assuming that the faults do not occur at the same time, and at most only one fault point, and the failure rate is equal, then: Bring formula (1), (2), (3) into the above formula (6) and simplify to get: (4) The formula is further extended to n single parallel subsystem, and the reliability formula is: Through the above derivation process, the reliability calculation formula of n single series system can be obtained: (5) In the three-state energy storage system, due to the existence of short-circuit fault, the reliability of a large number of parallel single bodies cannot be improved, but the overall reliability of the system is decreased; therefore, the partial derivatives of both sides of formula (8) are calculated, and The reliability maximum setting formula is obtained by sorting and simplifying: (6) The reliability calculation of series or parallel connection is divided into two steps: first, calculate the reliability value of the sub-module; Second, calculate the reliability value of the whole system based on the sub-module; Through the above process, the reliability calculation formula of three-state system under two typical connection modes of m×n single units is obtained: (7) The average value of reliability is introduced to further compare and obtain the calculation formula (13): The step (6) in the application q, q o q, q s are respectively the open circuit and short circuit probability of each monomer The step (7) in is the reliability average value, R min , R max respectively the reliability minimum value, maximum value.

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