CN105811028A - A SOC state estimation method for lithium-ion battery system - Google Patents

Abstract

The invention provides a SOC state estimation method of a lithium ion battery system, which comprises the steps of selecting battery monomers of different anode materials to be connected in parallel to obtain a battery module with the capacity consistent with that of the battery system, and then connecting in series according to the high-voltage requirement of the battery system to obtain the battery system; in the charging and discharging process of the battery system, the battery management system BMS obtains the real-time open-circuit voltage OCV of a certain battery module obtained by connecting a plurality of battery monomers of which the open-circuit voltages OCV and the state of charge SOC are in a linear relation in parallel, and then obtains the real-time state of charge SOC of the battery module according to a pre-written SOC-OCV curve of the battery monomers, and the real-time state of charge SOC is used as the real-time state of charge SOC of the battery system. The SOC-OCV curve of the single battery with the linear relation between the open-circuit voltage OCV and the SOC is utilized to accurately calibrate the SOC state of the battery system, so that an accurate value can be provided for estimating the residual electric quantity of the battery system.

Description

A SOC state estimation method for lithium-ion battery system

technical field

The invention relates to the technical field of battery system SOC calibration, in particular to a method for estimating the SOC state of a lithium-ion battery system.

Background technique

Since the invention, development and commercialization of lithium-ion secondary batteries by Sony Corporation of Japan in 1991, lithium-ion batteries have developed rapidly, their application scope has been expanding, and their market share has been increasing, especially with the advent of the energy crisis and the increasing environmental pressure. , Lithium-ion batteries are used as a power source in electric vehicles, which further expands the market demand for lithium-ion batteries.

At present, the cathode material of batteries in the domestic market is mostly lithium iron phosphate. Due to the inherent characteristics of lithium iron phosphate materials, the open circuit voltage OCV of lithium iron phosphate batteries is relatively close to the state of charge SOC, and it is difficult to establish a one-to-one correspondence, as shown in Figure 1. Therefore, when the battery management system BMS manages the lithium iron phosphate battery system, it is very easy for the SOC state to jump. The main reason is that in the SOC state of 30% to 70%, the OCV changes little. Therefore, it is difficult to accurately predict the SOC state of the lithium iron phosphate battery system no matter whether the ampere-hour integration method or the open circuit voltage method is used.

Contents of the invention

The object of the present invention is to provide a method for estimating the SOC state of a lithium-ion battery system, which accurately calibrates the SOC state of the battery system by using the SOC-OCV curve of the battery cell in which the open circuit voltage OCV and the state of charge SOC are linearly related.

Technical scheme of the present invention is:

A kind of SOC state estimation method of lithium ion battery system, comprises the following steps:

(1) Select two or more battery cells with different positive electrode materials, among which, the open circuit voltage OCV of at least one battery cell has a linear relationship with the state of charge SOC;

(2) For each type of battery cell selected, according to the capacity of the battery system, several battery cells of this type are connected in parallel to obtain a battery module consistent with the capacity of the battery system;

(3) Determine the quantity of each battery module according to the high voltage requirements of the battery system;

(4) Adjust the SOC state of each battery module to the same level, and then connect each battery module in series to obtain a battery system;

(5) Write the SOC-OCV curve of the battery cell whose open circuit voltage OCV has a linear relationship with the state of charge SOC into the battery management system BMS;

(6) During the charging and discharging process of the battery system, the battery management system BMS obtains the real-time open circuit voltage OCV of a battery module obtained by parallel connection of several battery cells whose open circuit voltage OCV and state of charge SOC have a linear relationship, and then according to The pre-written SOC-OCV curve of the battery cell is used to obtain the real-time SOC of the battery module, which is used as the real-time SOC of the battery system.

In the method for estimating the SOC state of a lithium-ion battery system, in step (1), at least one battery cell is a battery cell made of a positive electrode material including a ternary material.

In the method for estimating the SOC state of the lithium-ion battery system, in step (4), the SOC state of each battery module is adjusted to a state where both are fully charged at the same time or are all discharged at the same time.

The beneficial effects of the present invention are:

It can be seen from the above technical solution that the present invention utilizes the SOC-OCV curve of the battery cell in which the open circuit voltage OCV and the state of charge SOC have a linear relationship to accurately calibrate the SOC state of the battery system, thereby providing accurate estimation of the remaining power of the battery system. value.

Description of drawings

Figure 1 is the SOC-OCV curve diagram of a lithium iron phosphate battery cell;

Fig. 2 is a SOC-OCV curve diagram of a ternary material battery cell.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Since the ternary material battery (the positive electrode material is NCM or NCA or the positive electrode material is doped with other elements based on these two) has a one-to-one correspondence between the SOC and the OCV state, as shown in Figure 2. Therefore, this feature of the ternary material battery can be used to calibrate the SOC state of the battery system.

The present invention will be described below by taking a battery system formed by a lithium iron phosphate battery cell and a ternary material battery cell as an example. Of course, in addition to the battery cells made of ternary materials, other battery cells that have a linear relationship between the open circuit voltage OCV and the state of charge SOC can also be selected.

A kind of SOC state estimation method of lithium ion battery system, comprises the following steps:

S1. Select a lithium iron phosphate battery cell and a ternary material battery cell. The open circuit voltage OCV of the ternary material battery cell has a linear relationship with the state of charge SOC.

S2. According to the capacity of the battery system to be formed, connect several lithium iron phosphate batteries in parallel to obtain a lithium iron phosphate battery module consistent with the capacity of the battery system. Similarly, take several ternary material battery cells in parallel to obtain the battery system. Ternary material battery modules with consistent capacity.

S3. Determine the quantity of lithium iron phosphate battery modules and ternary material battery modules according to the high voltage requirements of the battery system to be formed.

S4. Adjust the SOC state of each lithium iron phosphate battery module and ternary material battery module to the same level, such as fully charged at the same time or discharged at the same time or adjusted to other SOC states, and then each lithium iron phosphate battery module and ternary material battery module The element material battery modules are connected in series to obtain a battery system.

S5. Write the SOC-OCV curve of the ternary material battery cell into the battery management system BMS. The SOC-OCV curve of the ternary material battery cell is obtained through testing, including the SOC-OCV curve of the charging process and the discharge process. SOC-OCV curve.

S6. During the charging and discharging process of the battery system, the battery management system BMS obtains the real-time open circuit voltage OCV of a ternary material battery module, and then obtains the OCV of the ternary material battery module according to the pre-written SOC-OCV curve The real-time state-of-charge SOC of the element material battery module is used as the real-time state-of-charge SOC of the battery system.

The above-mentioned embodiments are only descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, those skilled in the art may make various modifications to the technical solutions of the present invention. and improvements, all should fall within the scope of protection determined by the claims of the present invention.

Claims (3)

1. the SOC method for estimating state of a lithium-ion battery systems, it is characterised in that comprise the following steps:

(1) choosing and have the two or more battery cells of different positive electrode, wherein, the open-circuit voltage OCV of a kind of battery cell is linear with state-of-charge SOC；

(2) for the every kind of battery cell chosen, according to the capacity of battery system, take several this kind of battery cell parallel connection and obtain the battery module consistent with the capacity of battery system；

(3) according to the high voltage demands of battery system, the quantity of every kind of battery module is determined；

(4) the SOC state of each battery module is adjusted to same level, then the series connection of each battery module is obtained battery system；

(5) the SOC-OCV curve of battery cell linear with state-of-charge SOC for open-circuit voltage OCV is written in battery management system BMS；

(6) in the charge and discharge process of battery system, battery management system BMS obtains by the real-time open-circuit voltage OCV of the battery cell that several open-circuit voltages OCV is linear with state-of-charge SOC certain battery module obtained in parallel, SOC-OCV curve further according to this kind of battery cell being previously written, obtain the real-time state-of-charge SOC of this battery module, as the real-time state-of-charge SOC of battery system.

The SOC method for estimating state of lithium-ion battery systems the most according to claim 1, it is characterised in that in step (1), a kind of battery cell is the battery cell being made up of the positive electrode including ternary material.

The SOC method for estimating state of lithium-ion battery systems the most according to claim 1, it is characterised in that in step (4), is adjusted to the SOC state of each battery module be filled with electricity simultaneously or be all vented the state of electricity simultaneously.