WO2022254392A1

WO2022254392A1 - Method of determining the state of safety (sos) of a rechargeable battery

Info

Publication number: WO2022254392A1
Application number: PCT/IB2022/055189
Authority: WO
Inventors: Alessandro RICCIO; Valerio PALACINO; Salma NASR
Original assignee: Iveco S.P.A.
Priority date: 2021-06-03
Filing date: 2022-06-03
Publication date: 2022-12-08
Also published as: IT202100014435A1; KR20240017360A; EP4348280A1; CN117460965A

Abstract

Method of determining the state of safety of a rechargeable battery comprising the following steps: measuring (block 100) a group of different k variables (V1(t), V2(t),.. Vk(t)) that are used for characterizing the state of safety of said battery; determining k variable variations (h(x)) each one calculated as the mean value ([V1(t2)-V1(t1)]/(t2-t1), [V2(t2)-V2(t1)]/(t2-t1), … [Vk(t2)-Vk(t1)]/(t2-t1)) of the derivative of the respective variable over a predefined time interval (t2, t1); calculating for each variable variation (h(x)) the numerical value of a respective safety function representing the State of Safety (SOS) of the battery; calculating (block 130) a single value of a total safety function (f(x)); checking if the calculated value of the total safety function falls within a safety range and identifying accordingly a safe state (160) of the battery; if the total safety function falls outside of the safety range identifying an unsafe state of the battery (150).

Description

METHOD OF DETERMINING THE STATE OF SAFETY (SOS) OF A

RECHARGEABLE BATTERY

Cross-Reference to Related Applications

This patent application claims priority of Italian Patent Application No. 102021000014435 filed on June 3, 2021, the entire disclosure of which is incorporated herein by reference.

Technical Field of the Invention

The present invention relates to a method of determining the state of safety (SOS) of a rechargeable battery.

State of the Art

As it is known, electric vehicles are powered by rechargeable batteries, for instance lithium ion batteries, interconnected in cells to increase energy density. Batteries, especially lithium ion batteries, are sometimes prone to malfunctioning that may be rather dangerous when elevated energy densities are obtained. In fact, even if Lithium-ion technology is safe but with millions of consumers using batteries, failures may happen.

For sake of example, in 2006, a one-in-200,000 breakdown triggered a recall of almost six million lithium-ion packs. The maker of the lithium-ion cells in question, points out that on rare occasion microscopic metal particles may come into contact with other parts of the battery cell, leading to a short circuit within the cell. Short circuit may case overheating of the battery that may catch fire producing potentially dangerous gases.

There is therefore a need of providing a method that may determine the state of safety (SOS) of a rechargeable battery in a satisfactory manner by providing a numerical value clearly indicating the level of safety.

Know prior art method are qualitative in nature but do not provide a numerical quantification of the safety of the battery. For instance CN110696624A discloses a safety monitoring and early warning method comprising the steps of monitoring the environment temperature in a battery box for battery energy storage, and determining the safety state level of the battery box based on the environment temperature; if the environment temperature is smaller than a first pre-set temperature value, determining that the safety state level is a first-level state; if the environment temperature is equal to or greater than a first pre-set temperature value and less than a second pre-set temperature value, determining that the safety state level is a secondary state, and blocking a heat production chemical reaction of a defective battery in the battery box; if the environment temperature is equal to or greater than the second pre-set temperature value, determining that the safety state level is the pre- set dangerous state level according to the parameter values measured by the multiple sensors arranged in the battery box, so that the safety state of the battery is divided into multiple levels according to the environment temperature and other parameter values, and a manager can take corresponding measures for eliminating the dangerous state according to the safety state level

CN106842043A provides a test method for safety grade evaluation of a lithium ion battery. The test method comprises three of the following six types of test methods: short circuit, overcharging, over discharging, heating, extruding, and needling.

However, the need is continuously felt to improve existing methods for determining the state of safety of a battery.

An aim of the present invention is to satisfy the above mentioned needs.

Subject and Summary of the Invention

The above scope is obtained by the present invention as it relates to a method of determining the state of safety of a rechargeable battery as claimed in the appended set of claims.

Brief Description of the Drawings

For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example, with reference to the attached drawings wherein:

• Figure 1 is a schematic representation of a battery whose state is determined by the method of the present invention; and · Figure 2 is a flow chart describing the steps of the method of the present invention.

• Figure 3 shows the safety function of the present invention along with safe, warning and unsafe ranges

Detailed Description of Preferred Embodiments of the Invention In figure 1, numeral 1 indicates a battery (or a number of batteries) that are designed to supply power to an electric appliance 3 such as an inverter providing power supply to one (or more) electric motors M of an electric vehicle (not shown). An electronic unit 4 is connected through a can network

5 with a Battery Management system that is configured to monitor different variables of the battery 1 that shall be defined in the following.

The method of determining the state of safety (SOS) of a rechargeable battery is described with reference to the flow chart of figure 2.

The method comprises the following steps.

Measuring (block 100) a group of different k variables Vi(t), V2(t), .. V_k(t) that are used for characterizing the state of safety of the battery 1. Examples of measured variables Vi(t), V2(t),... V_k(t) belonging to the group are one or more of the following:

• Direct current internal resistance (DCIR) whose measuring unit is Ohm. Direct current internal resistance (DCIR) represents the resistance of current flowing through the battery 1. The value of DCIR is not fixed, and varies depending on multiple factors, such as battery materials, electrolyte concentration, temperature, and depth of discharge.

• Difference between minimum and maximum temperature of the battery 1, the measuring unit is °C. Average battery 1 temperature, the measuring unit is °C.

• Open circuit voltage OCV or VOC, the measuring unit is

Volt. Open-circuit voltage is the difference of electrical potential between two terminals of the battery 1 when disconnected from appliance 3 that is supplied by the battery.

• State of health SOH of the battery 1 that is represented by a percentage %. The state of health SOH represents the working condition of a battery compared to its ideal working condition (100%).

• State of charge SOC of the battery 1 that is represented by a percentage %. (0% = empty; 100% = full).

• Insulation resistance measured in Ohm: The insulation resistance is the parallel equivalent resistance of the insulation resistances of the positive and negative terminals with respect to the ground reference .

• Variation of the temperature of the battery with respect to time measured in degree/min Block 100 also provides the measured variables Vi(t), V2(t), .. V_k(t) sampled in times (t2 and ti) and calculates the k variable variations h(x) as the mean (or average) value of the derivative of the k^th variable over the time interval [t2, 11] (i.e. difference quotients) the k variable variations h(x) are calculated as [Vi(t2)^~ Vi(ti)]/(t2-ti), [V₂(t2)- v₂ (ti)]/(t2-ti), ... [V_k (12)^— Vk(ti)]/(t2-ti). Sampling times may be, for instance, few milliseconds.

Variable variations h(x) may be calculated by using a moving average time window to calculate every variable value over a longer period of time. Derivative may be calculated between average values of different windows (t_m-t_m-i)·

The method further comprises (block 110) calculating - for each k variable variation h(x) - the numerical value of a respective safety function f (x) representing the State of Safety (SOS) of the battery.

An example of a possible safety function f (x) is the following:

Where • h(x) represents the variable variation;

• m is a setting parameter that allows to control the rate of the decrease of the safety function, m may be set to 1; namely mrepresents the steepness of the safety function f (x) curve. A greater value of m makes the curve steeper and hence giving less values of the safety function f (x). This parameter is also a function of the state of health of the battery pack and

• d represents a target value of the variable variation h(x) that is function of the state of health of the battery.

Figure 3 shows how the safety function f (x) depends on the parameter m and d. In the same figure, the safe, warning and unsafe ranges are shown. In fact, when the variable variation h(x) corresponds to the target value d, the safety function is 1.

With the increase of difference between the target value d and the measured variable variation h(x) the safety function f(x) decreases significantly, and even more when m increases. In other words, the value of the safety function varies between 0, completely unsafe, and 1, completely safe.

For instance, the ideal value d of the variation of the temperature with time is 0.8 degree/min for a new battery pack and, as the battery gets older, the best variation of the temperature with time will increase to 1.5 degree/min. Thus, d may vary between 0.8 and 1.5 based on the state of the health of the battery.

Hence, in the above safety function f (x), the calibration parameters d and m may be set appropriately in accordance to the health of the battery pack.

Block 110 is followed by both block 120 and block 130.

Block 130 calculates a single value of a total safety function taking into the contribution of the already calculated (in block 110) k values of the respective safety functions corresponding to k different variables.

Different ways of calculating the single value of a total safety function may be taken into considerations, preferably by selecting from the calculated safety functions the worst one, i.e. the smallest value. Alternative ways of calculating the single value of a total safety function comprise determining weighted average of the calculated values or determining a product of the calculated values.

Block 130 is followed by block 140 that checks if the calculated value of the total safety function falls within a safety range.

In case the calculated total safety function falls within the safety range, block 140 is followed by the block 150 that identifies a safe state of the battery. The safe state is memorized and is also notified to a user of the battery 1. The method then returns to the initial point "start" for continuous monitoring the health of the battery pack.

If the check of block 140 is negative, namely the total safety function falls outside of the safety range, the block 140 is followed by the block 160 that identifies an unsafe state of the battery. The unsafe state is memorized and is also notified to a user of the battery. Automatic actions may also be performed such as interrupting connection between battery 1 and appliance 3 supplied by the battery 1. Similar to the previous case, the method then returns to the initial point start for continuous monitoring the health of the battery pack.

As above outlined, block 120 checks if the values of the calculated safety functions f(x) fall within respective safety ranges of Fig. 3.

If any calculated value of the safety functions falls inside the respective warning range of Fig.3, block 120 is followed by the block 170 that increments of one unit (+1) a counter that accumulates the number of violations of the safety function, at the same moment a timer is started, thus said timer is started from the time in which a first accumulated violation has been detected.

Once the value of the counter reaches a limit value (C_limit) and the timer is within a predetermined time limit (T_warning), (block 180 following block 170), a warning state for the battery is set (block 190) otherwise, if the timer is outside the time limit T_warning and the counter is less than the limit value (C_limit), counter and timer are reset (block 200). In both the cases the method returns to the initial point start.

In view of the foregoing, the advantages of the method of determining the state of safety of a rechargeable battery according to the invention are apparent.

Thanks to the proposed method, it is possible to anticipate an unsafe condition of the battery before a major fault takes place, by using data related to sensors already existing on the vehicle batteries

It is clear that modifications can be made to the described method of determining the state of safety of a rechargeable battery which do not extend beyond the scope of protection defined by the claims.

Claims

1.- Method of determining the state of safety of a rechargeable battery comprising the following steps: measuring (block 100) a group of different k variables (Vi(t), V2(t), .. V_k (t)) that are used for characterizing the state of safety of said battery; determining k variable variations (h (x)) each one calculated as the mean value ([Vi(t2)-Vi(tp ]/(t2-ti), [V2(t2)^~

V₂ (ti)]/(t2-ti), ... [V_k (t2)-V_k (ti)]/(t2-ti)) of the derivative of the respective variable over a predefined time interval (t, ti); calculating for each variable variation (h (x)) the numerical value of a respective safety function representing the State of Safety (SOS) of the battery; calculating (block 130) a single value of a total safety function {f (x)); checking if the calculated value of the total safety function falls within a safety range and identifying accordingly a safe state (160) of the battery; if the total safety function falls outside of the safety range identifying an unsafe state of the battery (150).

2.- Method as defined in claim 1 wherein a group of different k variables comprise two or more of the following variables:

• Direct current internal resistance (DCIR) representing the resistance of current flowing through the battery or the difference between the minimum and the maximum temperature of the battery;

• Average battery temperature;

• Open circuit voltage (OCV or VOC) representing the difference of the electrical potential between two terminals of the battery when disconnected from any circuit that is supplied by the battery;

• Variation of the temperature of the battery with respect to time;

• State of health (SOH) of the battery calculated as the condition of a battery compared to its ideal conditions (100%);

• State of charge (SOC) of the battery that is represented by a percentage;

• Insulation resistance calculated as the parallel equivalent resistance of the insulation resistances of the positive and negative terminals with respect to the ground reference.

3.- Method as defined in claim 1 or 2 wherein said safety function (f (x)) is the following:

where

• h(x) represents the variable variation; • m is a setting parameter that allows to control the decrease rate of the safety function {f (x));

• d represents the target value of the variable variation (h(x)) that depends on the state of health of the battery.

4.- Method as defined in claim 3 when depending on claim

2 where the target value (d) of the variable variation associated to the variation of the temperature of the battery with respect to time is between 0.8 degree/min and 1.5 degree/min.

5. Method as defined in any of the preceding claims, wherein, if any calculated value of the safety functions falls inside the respective warning range, a counter is incremented and a timer is started, said counter counting each time any calculated value of the safety functions falls inside the respective warning range; the method further comprises the steps of identifying a warning (190) state once the value of the counter reaches a limit value (C_limit) and the timer is within a predefined time limit (T_warning); and resetting the counter and the timer once said period of time ((T_warning)) is elapsed (200).

6. Method as defined in any of the preceding claims, wherein, the step of calculating (block 130) a single value of a total safety function comprises the step of selecting from the calculated safety functions the worst one having the smallest value or the step of determining weighted average of the calculated values of the safety functions or the step of determining a product of the calculated values of the safety functions.

7. Method as defined in any of the preceding claims, including the notification to a user when the battery is determined to be in the unsafe state.

8. Method as defined in any of the preceding claims, including the interruption of the connection between said battery (1) and an appliance (3) supplied by said battery (1) when said battery (1) is determined to be in the unsafe state.

9. Method as defined in claim 5, including the notification to a user when the battery is identified to be in the warning state.