Lithium ion battery pack active equalization method based on inductance and capacitance

Abstract

The invention belongs to the technical field of battery equalization, and particularly relates to a lithium ion battery pack active equalization method based on inductors and capacitors. The defect that an existing equalization method is long in equalization time can be overcome, active equalization of the lithium ion battery pack based on inductance and capacitance is provided, equalization can be carried out in the pack at the same time through a series lithium ion battery pack double-layer equalization method, and the equalization speed can be effectively increased. Comprising the steps that S1, a series battery pack is divided into n battery modules, and each battery module comprises three single batteries; s2, each battery module is connected with a bottom-layer equalizer and is connected with a top-layer equalizer through a relay switch; s3, when the single batteries in the single battery module need to be equalized, executing internal equalization by using the corresponding bottom-layer equalizer; and when energy among the plurality of battery modules needs to be balanced, balancing among the modules is executed by using a top-layer equalizer.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery balancing, and in particular relates to an active balancing method for a lithium-ion battery pack based on inductance and capacitance. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles due to their high energy density, low self-discharge rate and long cycle life. However, due to the limited capacity and low voltage of single lithium-ion batteries, series-parallel battery packs are often used in practical applications to meet the capacity and power requirements of electric vehicles. However, due to the limitations of existing design and manufacturing processes, there are inconsistencies in parameters such as capacity and internal resistance between the individual cells in the battery pack, and these differences tend to amplify over time, resulting in reduced energy utilization of the battery pack, shortened service life, and even safety issues. In order to improve the inconsistency problem of the battery pack, an effective balancing method must be introduced.

[0003] Battery balancing technology can be divided into two types according to its working mode: passive balancing and active balancing. Passive balancing uses a simple and cost-effective method to release the excess energy in the higher capacity battery in the form of heat energy through resistance, so as to achieve energy balancing between batteries. The advantages of this method are simple control, low cost and high reliability; however, it also has obvious limitations, namely low balancing efficiency and slow process. In contrast, active balancing uses components such as capacitors, inductors, transformers or converters as energy transmission media to redistribute the energy of each battery cell to achieve the purpose of balancing. This technical solution not only improves the efficiency of energy balancing, but also speeds up the balancing speed, solving the shortcomings of passive balancing in efficiency and speed. In summary, although passive balancing provides a simple and economical option, active balancing is undoubtedly a better choice when pursuing an efficient and fast battery management system. Summary of the invention

[0004] The present invention aims at the defects of the prior art and provides an active equalization method for lithium-ion battery packs based on inductors and capacitors. It can overcome the disadvantage of the existing equalization method that the equalization time is long, provide active equalization of lithium-ion battery packs based on inductors and capacitors, and use a double-layer equalization method of series-connected lithium-ion battery packs, so that equalization can be performed simultaneously within the group, which can effectively speed up the equalization speed.

[0005] To achieve the above object, the present invention adopts the following technical solution, an active equalization method for a lithium-ion battery pack based on inductance and capacitance, comprising the steps of:

[0006] S1, dividing the series-connected battery group into n battery modules, each battery module containing 3 single cells;

[0007] S2, each battery module is connected to a bottom balancer and connected to the top balancer through a relay switch;

[0008] S3. When the cells in a single battery module need to be balanced, the corresponding bottom-level balancer is first used to perform internal balancing; when the energy between multiple battery modules needs to be balanced, the top-level balancer is then used to perform inter-module balancing.

[0009] Furthermore, in S1, the series battery pack is composed of m single cells connected in series, which are divided into n battery modules, each battery module is composed of 3 single cells, and the battery module is marked as M. i Each single cell in the series battery pack is marked as B i-j , i is the i-th battery module, j is the j-th battery in the battery module; each battery module M i The corresponding underlying equalizer C i Each bottom-level equalizer is connected to the top-level equalizer through a relay switch; the MOS tubes connected to the single battery are marked as S i-1 , S i-2 , …, S i-8 , the relay in the bottom equalizer is marked as Q i MOS tubes connected to the battery module are marked as S1, S2, ..., S8 in sequence, and the relay switch in the top-level equalizer is marked as Q i-1 , Q i-2 The balanced topology includes 8n+8 MOS tubes, 3n relay switches, 8n diodes, and n inductors L i , LC series circuit; the LC series circuit includes an inductor L and a capacitor C connected in series.

[0010] Furthermore, in S2, the bottom balancer: single cell B i-1 , B i-2 , B i-3 The positive electrode and the MOS tube S in series i-2j Connected to the diode, the B i-1 , B i-2 ,Bi -3 The negative electrode and the MOS tube S in series i-2j+1 Connected to diode; battery B i-1 The positive electrode is connected in series with the MOS tube S i-1 Connected to diode, battery B i-3 The negative electrode is connected in series with the MOS tube S i-8 Connected to diode; switch Q i and inductor L i The left side of the positive end of the series circuit is connected to the MOS tube S in series i-2j+1 And diode, MOS tube S in series i-1Connected to diode; relay switch Q i and inductor L i The left side of the negative end of the series circuit is connected to the MOS tube S in series i-2j And diode, MOS tube S in series i-8 Connected to diode;

[0011] Relay switch Q in the bottom equalizer i and inductor L i The positive end of the series circuit is connected to the relay switch Q in the top equalizer. i-1 The left side is connected; the relay switch Q in the bottom equalizer i and inductor L i The right side of the negative end of the series circuit is connected to the top equalizer relay switch Q i-2 connected to the left side.

[0012] Furthermore, in S2, the top equalizer: the LC series circuit and the MOS tube form a bridge circuit, the left side of the top of the inductor L is connected to the MOS tubes S1 and S2, and the right side of the top of the inductor L is connected to the MOS tubes S5 and S6; the left side of the bottom of the capacitor C is connected to the MOS tubes S7 and S8, and the right side of the bottom of the capacitor C is connected to the MOS tubes S3 and S4;

[0013] Relay switch Q i-1 and Q i-2 Connected to the bridge circuit; when i is an odd number, the relay switch Q i-1 Connected to the left side of the bridge circuit, relay switch Q i-2 Connected to the right side of the bridge circuit; when i is an even number, the relay switch Q i-1 Connected to the right side of the bridge circuit, the relay switch Q i-2 Connect to the left side of the bridge circuit.

[0014] (That is: the relay switch Q in the bottom equalizer i and inductor L i The series circuit is connected to the top equalizer relay switch Q i-1 and Q i-2 connected to form an energy transfer path. )

[0015] Furthermore, during the balancing process of S3:

[0016] S3.1. For each sampling period, determine the state of charge (SOC) of the single battery. ij , calculate the average state of charge of the battery module and the average state of charge of the battery pack

[0017] S3.2, setting the bottom equalizer opening threshold α1 and the top equalizer opening threshold α2;

[0018] S3.3, when SOC ij and When the absolute value difference of is greater than α1, the bottom-level equalizer is started; when n bottom-level equalizers stop working, and and When the absolute value difference of is greater than α2, the top equalizer is started.

[0019] Furthermore, in S3.3, during the bottom-level balancing period: according to Divide the batteries in each battery module into high-energy batteries and low-energy batteries;

[0020] Discharge and balance high-energy batteries, and charge and balance low-energy batteries. When there are multiple high-energy batteries, if they are adjacent, select multiple high-energy batteries (more than 2) for discharge and balance. If they are not adjacent, select SOC ij The largest high-energy battery is used for discharge balancing; when there are multiple low-energy batteries (greater than 2), if they are adjacent, multiple low-energy batteries are selected for charge balancing; if they are not adjacent, SOC ij The smallest low energy cells are charge balanced.

[0021] Furthermore, in S3.3, during top-level balancing:

[0022] choose The largest high-energy battery modules are discharged and balanced;

[0023] choose The smallest low-energy battery modules are charged equally.

[0024] Compared with the prior art, the present invention has beneficial effects.

[0025] The present invention is a novel double-layer balancing method suitable for series-connected battery packs. The first characteristic is that the balancing process of each bottom-layer equalizer is independent, with multiple energy transfer paths and flexible energy transfer methods. The second characteristic is that, under the premise of ensuring the safe operation of the circuit, the number of single cells can be changed by simply adding or reducing the corresponding MOS tubes, which is easy to expand. The third characteristic is that it has good performance in terms of balancing speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. The protection scope of the present invention is not limited to the following description.

[0027] Figure 1 It is a balanced topology diagram of a specific embodiment.

[0028] Figure 2 It is an active balancing method to control the strategy process Figure 1 .

[0029] Figure 3 It is an active balancing method to control the strategy process Figure 2 .

[0030] Figure 4 It is an active balancing method to control the strategy process Figure 3 . DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and beneficial effects of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0032] like Figure 1 As shown in the specific embodiment: the active balancing method of lithium-ion battery pack based on inductance and capacitance is composed of m single cells connected in series, divided into n groups, each battery module is composed of 3 single cells; the balancing topology includes 8n+8 MOS tubes, 3n relay switches, 8n diodes, n inductors L i , LC series circuit; the LC series circuit includes an inductor L and a capacitor C connected in series;

[0033] Battery modules are marked with M i Each single cell in the series battery pack is marked as B i-j , i is the i-th battery module, j is the j-th battery in the battery module; each battery module M i The corresponding underlying equalizer C i Each bottom-level equalizer is connected to the top-level equalizer through a relay switch; the MOS tubes connected to the single battery are marked as S i-1 , S i-2 , …, S i-8 , the relay in the bottom equalizer is marked as Q i MOS tubes connected to the battery module are marked as S1, S2, ..., S8 in sequence, and the relay switch in the top-level equalizer is marked as Q i-1 , Q i-2 ;

[0034] In the bottom balancer, single cell B i-1 , B i-2 , B i-3 The positive electrode and the MOS tube S in series i-2j Connected to the diode, the B i-1 , B i-2 ,Bi -3 The negative electrode and the MOS tube S in seriesi-2j+1 Connected to diode; battery B i-1 The positive electrode is connected in series with the MOS tube S i-1 Connected to diode, battery B i-3 The negative electrode is connected in series with the MOS tube S i-8 Connected to diode; switch Q i and inductor L i The left side of the positive end of the series circuit is connected to the MOS tube S in series i-2j+1 And diode, MOS tube S in series i-1 Connected to diode; relay switch Q i and inductor L i The left side of the negative end of the series circuit is connected to the MOS tube S in series i-2j And diode, MOS tube S in series i-8 Connected to diode;

[0035] Relay switch Q in the bottom equalizer i and inductor L i The positive end of the series circuit is connected to the relay switch Q in the top equalizer. i-1 The left side is connected; the relay switch Q in the bottom equalizer i and inductor L i The right side of the negative end of the series circuit is connected to the top equalizer relay switch Q i-2 The left side is connected;

[0036] In the top-level equalizer, the LC series circuit and the MOS tube form a bridge circuit. The left side of the top of the inductor L is connected to the MOS tubes S1 and S2, and the right side of the top of the inductor L is connected to the MOS tubes S5 and S6; the left side of the bottom of the capacitor C is connected to the MOS tubes S7 and S8, and the right side of the bottom of the capacitor C is connected to the MOS tubes S3 and S4; the relay switch Q i-1 and Q i-2 Connected to the bridge circuit; when i is an odd number, the relay switch Q i-1 Connected to the left side of the bridge circuit, relay switch Q i-2 Connected to the right side of the bridge circuit; when i is an even number, the relay switch Q i-1 Connected to the right side of the bridge circuit, the relay switch Q i-2 Connect to the left side of the bridge circuit;

[0037] The relay switch Q i Control the corresponding underlying balancing controller C i Is it working? The relay switch Q i-1 , Q i-2 Control the corresponding battery module M i Perform top-level balancing;

[0038] The balancing method is: when the battery module needs to be balanced, the bottom balancer C i Achieve balancing between single cells in a battery module. The balancing process of each battery module is independent. When balancing between battery modules is required, the top-level balancer is used to achieve balancing between battery modules. Perform bottom-level balancing first, then top-level balancing.

[0039] like Figure 2-4 As shown, during the charging and discharging process of the series battery pack, the state of charge SOC of the single battery in the series battery pack is determined in each sampling cycle. ij , average state of charge of battery module Average state of charge of battery pack Set the equalization circuit battery module opening threshold to α1, and the battery module opening threshold to α2; The underlying equalizer starts working when and The top level equalizer starts working.

[0040] When SOC ij and When the absolute value difference between the two is greater than α1, the bottom equalizer starts to work; The batteries in each battery module are divided into high-energy batteries and low-energy batteries; high-energy batteries are selected for discharge balancing, and low-energy batteries are selected for charge balancing. When there are multiple high-energy batteries, if they are adjacent, multiple high-energy batteries are selected for discharge balancing. If they are not adjacent, SOC ij The largest high-energy battery is used for discharge balancing. If there are multiple low-energy batteries, if they are adjacent, multiple low-energy batteries are selected for charge balancing. If they are not adjacent, SOC ij The smallest low energy cells are charge balanced.

[0041] So back and forth to SOC i-j and SOC i When the absolute value of the difference between the two is less than or equal to α1, the bottom-level equalizer stops working.

[0042] When n underlying balancers stop working, and and When the absolute value difference between the two is greater than α2, the top equalizer starts to work; The largest high-energy battery module is discharged and balanced, and the The smallest low-energy battery modules are charged equally.

[0043] So back and forth and When the absolute value of the difference between the two is less than or equal to α2, the inter-group balancing circuit stops working.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, it should be understood by those skilled in the art that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. Therefore, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. An active equalization method for a lithium-ion battery pack based on inductance and capacitance, characterized in that: Includes steps: S1, dividing the series-connected battery group into n battery modules, each battery module containing 3 single cells; S2, each battery module is connected to a bottom balancer and connected to the top balancer through a relay switch; S3. When the cells in a single battery module need to be balanced, the corresponding bottom-level balancer is first used to perform internal balancing; when the energy between multiple battery modules needs to be balanced, the top-level balancer is then used to perform inter-module balancing.

2. The method according to claim 1, characterized in that In S1, the series battery pack is composed of m single cells connected in series, which are divided into n battery modules. Each battery module is composed of 3 single cells. The battery module is marked as M. i Each single cell in the series battery pack is marked as B i-j , i is the i-th battery module, j is the j-th battery in the battery module; Each battery module M i The corresponding underlying equalizer C i Each bottom-level equalizer is connected to the top-level equalizer through a relay switch; the MOS tubes connected to the single battery are marked as S i-1 , S i-2 , …, S i-8 , the relay in the bottom equalizer is marked as Q i MOS tubes connected to the battery module are marked as S1, S2, ..., S8 in sequence, and the relay switch in the top-level equalizer is marked as Q i-1 , Q i-2 The balanced topology includes 8n+8 MOS tubes, 3n relay switches, 8n diodes, and n inductors L i , LC series circuit; the LC series circuit includes an inductor L and a capacitor C connected in series.

3. The method according to claim 1, characterized in that In S2, the bottom balancer: single cell B i-1 , B i-2 , B i-3 The positive electrode and the MOS tube S in series i-2j Connected to the diode, the B i-1 , B i-2 ,Bi -3 The negative electrode and the MOS tube S in series i-2j+1 Connected to diode; battery B i-1 The positive electrode is connected in series with the MOS tube S i-1 Connected to the diode, battery B i-3 The negative electrode is connected in series with the MOS tube S i-8 Connected to diode; switch Q i and inductor L i The left side of the positive end of the series circuit is connected to the MOS tube S in series i-2j+1 And diode, MOS tube S in series i-1 Connected to diode; relay switch Q i and inductor L i The left side of the negative end of the series circuit is connected to the MOS tube S in series i-2j And diode, MOS tube S in series i-8 Connected to diode; Relay switch Q in the bottom equalizer i and inductor L i The positive end of the series circuit is connected to the relay switch Q in the top equalizer. i-1 The left side is connected; Relay switch Q in the bottom equalizer i and inductor L i The right side of the negative end of the series circuit is connected to the top equalizer relay switch Q i-2 connected to the left side.

4. The method according to claim 1, characterized in that: In S2, the top equalizer: the LC series circuit and the MOS tube form a bridge circuit, the left side of the top of the inductor L is connected to the MOS tubes S1 and S2, and the right side of the top of the inductor L is connected to the MOS tubes S5 and S6; the left side of the bottom of the capacitor C is connected to the MOS tubes S7 and S8, and the right side of the bottom of the capacitor C is connected to the MOS tubes S3 and S4; Relay switch Q i-1 and Q i-2 Connected to the bridge circuit; when i is an odd number, the relay switch Q i-1 Connected to the left side of the bridge circuit, relay switch Q i-2 Connected to the right side of the bridge circuit; when i is an even number, the relay switch Q i-1 Connected to the right side of the bridge circuit, the relay switch Q i-2 Connect to the left side of the bridge circuit.

5. The method according to any one of claims 1 to 4, characterized in that: During the balancing process of S3: S3.

1. For each sampling period, determine the state of charge (SOC) of the single battery. ij , calculate the average state of charge SOC of the battery module i and the average state of charge SOC of the battery pack; S3.2, setting the bottom equalizer opening threshold α1 and the top equalizer opening threshold α2; S3.3, when SOC ij and SOC i When the absolute value difference of is greater than α1, the bottom-level equalizer is started; when n bottom-level equalizers stop working and SOC i When the absolute value difference between α and SOC is greater than α2, the top-level equalizer is started.

6. The method according to claim 5, characterized in that In S3.3, during the bottom balancing period: according to SOC ij -SOC i ≥α1 divides the batteries in each battery module into high-energy batteries and low-energy batteries; Discharge and balance high-energy batteries, and charge and balance low-energy batteries. If there are multiple high-energy batteries, if they are adjacent, select multiple high-energy batteries for discharge balance. If they are not adjacent, select SOC ij The largest high-energy battery is used for discharge balancing; when there are multiple low-energy batteries, if they are adjacent, multiple low-energy batteries are selected for charge balancing; if they are not adjacent, SOC ij The smallest low energy cells are charge balanced.

7. The method according to claim 5, characterized in that In S3.3, during top-level equilibrium: Select SOC i The largest high-energy battery modules are discharged and balanced; Select SOC i The smallest low-energy battery modules are charged equally.

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