Gas-liquid dynamic model-based accurate lithium-ion battery SOC estimation method

Patent metadata

Field	Value
Publication number	US-11300620-B2
Application number	US-201716626252-A
Country	US
Kind code	B2
Filing date	Dec 19, 2017
Priority date	Dec 14, 2017
Publication date	Apr 12, 2022
Grant date	Apr 12, 2022

Abstract

A gas-liquid dynamic model-based accurate lithium-ion battery SOC estimation method, the gas-liquid dynamic model being a cylindrical closed container, a pipe and a valve that can be opened or closed being mounted at the top of the container, a liquid having a volume of Vw being held in the cylindrical container, and the remaining volume, V, being the volume of a gas having a pressure of P. According to the accurate SOC estimation method, a model, different from conventional RC equivalent circuit model and electrochemical model, is established from the perspective of a gas-liquid coexistence system. The method comprises the following steps: setting up an ideal gas state equation, a gas continuous motion equation, a gas-liquid dissolution equilibrium equation, etc. according to a gas-liquid coexistence system model; deriving steady state and transient state recursion formula of the gas-liquid coexistence system according to the model equations; performing intermittent charging and discharging stationary test on a certain model of battery; and fitting the expression of the relation between SOC and open circuit voltage, and recognizing parameter values of the gas-liquid coexistence system model, so as to achieve online estimation of a battery SOC value. The recursion formula is simple, has self-convergence characteristics, and can accurately describe the nonlinear characteristics of the battery.

First claim

The invention claimed is:

1. A method for accurately estimating SOC of a lithium ion battery based on a gas-liquid dynamic model, characterized in that it comprises the following steps:
a constant current intermittent charging-resting experiment is performed on a lithium ion battery, and the formula of relationship between the open circuit voltage (OCV) and the SOC is fitted according to the measured data;
a variable current intermittent charging/discharging-resting experiment is performed on a lithium ion battery, the OCV corresponding to SOC data is used to identify the parameters of the gas-liquid dynamic model;
establishing a gas-liquid dynamic model: the physical prototype of the gas-liquid dynamic model is a cylindrical closed vessel which is a gas-liquid coexistence system, the pipe ( 3 ) and valve ( 4 ) are installed at the top of the vessel, there is V W volume of liquid ( 1 ) in the cylindrical vessel and the remaining volume V of the vessel is filled with the gas ( 2 ) whose pressure is P, the amount of substance is n and density is ρ; the resistance coefficient of whole pipeline ( 3 ) and valve ( 4 ) is μ, the external nozzle ( 5 ) gas pressure of the pipe ( 3 ) is P 0 ; when this gas-liquid coexistence system is in balance, the amount of gas moles dissolved in liquid is n j , the pressure change of the gas from the non-steady state to the steady state in this system is P S ;
deriving the SOC estimation model of charge and discharge: according to gas-liquid dynamics model,
the transient equation of gas-liquid model is deduced according to the steady-state equation of gas-liquid model in discharging; to verify the steady-state and transients equation of gas-liquid model have real roots and moreover, have only one positive real root in discharging; the transient equation of gas-liquid model is deduced according to the steady-state equation of gas-liquid model in charging; to verify the steady-state and transients equation of gas-liquid model have real roots and moreover, have only one positive real root in charging;
according to the variable current intermittent discharging-resting experiment data, the parameters of the steady and transient recursion formula are identified in gas-liquid coexistence system of the charging and discharging;
battery SOC is estimated by using charging/discharging model;
a variable current pulse charging/discharging-resting test on a lithium-ion battery is performed and the open circuit voltage and corresponding to SOC data are recorded;
to verify the SOC estimation model of charge and discharge: according to the variable current pulse charging/discharging-resting data, the accuracy of predicting the open circuit voltage is verified by the gas-liquid dynamic model;

the verified SOC estimation model of charge and discharge is used to realize the accurate estimation of SOC for lithium-ion battery.

2. According to claim 1 , a method for accurately estimating SOC of lithium ion battery, based on gas-liquid dynamic model, is characterized in that the following is the step of deriving a transient equation of a gas-liquid model in a discharge state according to a steady-state equation of a gas-liquid model:
the gas-liquid dynamic model is in steady state at time t 1 , at this moment, the gas pressure is P 1 , and the amount of gas substance is n 1 , and the amount of gas substance dissolved in the liquid is n j1 ; when the valve ( 4 ) of the vessel is opened and the length of time is Δt, the gas in the system is released outward, and the flow rate of gas is I, and the resistance coefficient of whole pipeline is μ, and the pressure of the external nozzle ( 5 ) is P 0 ; the valve ( 4 ) is closed at the time t 2 =t 1 +Δt, at which time the gas pressure is P 2 and the amount of the gas substance is n 2 ; after a period of time, the gas-liquid dynamic model reaches the steady state again, at this time, the gas pressure in the vessel is P*, and the amount of gas substance dissolved in liquid is n j2 , P S is a pressure which changes when gas in the vessel changes from non-steady state to steady state, The continuity equation of gas flow when the gas comes out of the vessel:
P 2 =P 0 +½ρ I 2 +½μρ I,

ρ: the gas density.

3. According to claim 2 , a method for accurately estimating SOC of lithium ion battery based on gas-liquid dynamic model is characterized in that
at time t 1 , the ideal gas state equation is
P 1 V=n 1 RT,
T: thermodynamic temperature
P 1 : gas pressure,
n 1 : the amount of gas substance,
V: gas volume,
R: thermodynamic constant;

solubility equation of gas gap filling:

n

j
⁢

⁢
1

=

P
1

⁢

φ
m

⁢

V
w

RT
+

b
m

⁢

P
1

,

φ m : effective clearance
b m : Van der Waals volume
V W : liquid volume
the continuity equation of gas flow:
P 2 =P 0 +½ρ I 2 +½μρ I,

ρ: the gas density
I: gas flow
μ: the resistance coefficient of whole pipeline

when the time is t 2 , ideal gas equation of state:
P 2 V=n 2 RT
after the system reaches the steady state again after t 2 , the ideal gas state equation:
P*V=n*RT;

solubility equation for gas gap filling:

n
j
*

=

P
*

⁢

φ
m

⁢

V
w

RT
+

b
m

⁢

P
*

the amount of gas substances is
n*=n 2 +n j1 −n* j .

4. According to claim 3 , a method for accurately estimating SOC of lithium ion battery based on gas-liquid dynamic model is characterized in that,
the changing pressure of gas during steady state, that is, the transient equation of gas-liquid model under discharging state:

⁢

Assignees

• Univ Jiangsu

Inventors

• Chen Biao
• Jiang Haobin
• Li Huanhuan
• Wang Yaping
• Zhao Qian

Classifications

• H01M10/486

  for measuring temperature · CPC title

• G01R31/007

  using microprocessors or computers · CPC title

• H01M2010/4271

  Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing · CPC title

• H01M10/0525

  Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries · CPC title

• G01R31/367 Primary

  Software therefor, e.g. for battery testing using modelling or look-up tables · CPC title