IT202100014435A1 - METHOD FOR DETERMINING THE SAFETY STATUS (SOS) OF A RECHARGEABLE BATTERY - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

?METHOD TO DETERMINE THE SAFETY STATUS (SOS) OF A RECHARGEABLE BATTERY?

TECHNICAL FIELD

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

BACKGROUND OF THE INVENTION

As ? known, electric vehicles are powered by rechargeable batteries, such as lithium-ion batteries, connected together in cells to increase the density? of energy. Batteries, especially Li-ion batteries, are sometimes prone to malfunctions which can be quite dangerous when you get high density batteries. of high energy. In fact, even if the lithium-ion technology ? safe with millions of consumers using batteries, failure can occur.

For example, in 2006, one failure in 200,000 resulted in a recall of nearly six million lithium-ion packs. The manufacturer of the Li-ion cells in question points out that on rare occasions microscopic metal particles can come into contact with other parts of the battery cell, leading to a short circuit within the cell. The short circuit can cause the battery to overheat, which can? catch fire, producing potentially dangerous gases.

Therefore, there ? the need to provide a method that can satisfactorily determine the safety status (SOS) of a rechargeable battery, providing a numerical value that clearly indicates the safety level.

Known prior art methods are qualitative in nature, but do not provide a numerical quantification of battery safety.

For example, CN110696624A describes a safety monitoring and early warning method comprising the steps of monitoring the ambient temperature in a battery compartment for accumulating battery energy and determining the safety status level of the battery compartment based on the ambient temperature ; if the ambient temperature ? lower than a first preset temperature value, determine that the safety status level ? a first-level status; if the ambient temperature ? equal to or greater than a first preset temperature value and less than a second preset temperature value, determine that the safety state level is ? a secondary state and block a heat producing chemical reaction of a defective battery in the battery compartment; if the ambient temperature ? equal to or greater than the second preset temperature value, determine that the safety status level is ? the pre-set dangerous state level according to the parameter values measured by the multiple sensors arranged in the battery compartment, so that the safe state of the battery is divided into multiple levels according to the ambient temperature and other parameter values, and a manager can take corresponding measures to clear the dangerous state according to the safe state level.

CN106842043A provides test method for quality assessment? safety of a lithium-ion battery. The test method includes three of the following six types of test methods: short circuit, overload, over discharge, heating, extrusion and needle piercing.

However, there is a constant need to improve existing methods for determining the safety status of a battery.

An objective of the present invention ? to meet the aforementioned needs.

SUMMARY OF THE INVENTION

The aforementioned object is achieved thanks to the present invention, since this relates to a method for determining the safety status 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, ? described a preferred embodiment, by way of non-limiting example, with reference to the attached drawings, in which:

? figure 1 ? a schematic representation of a battery, whose state ? determined by the method of the present invention; And

? figure 2 ? a flowchart describing the steps of the method of the present invention.

? Figure 3 shows the safety function of the present invention together with the safe, warning and unsafe ranges.

DETAILED DESCRIPTION OF THE INVENTION

In Figure 1, the number 1 indicates a battery (or several batteries) that ? designed to supply electricity to an electrical appliance 3 such as an inverter which supplies electricity to one or more? electric motors M of an electric vehicle (not shown).

A unit electronics 4 ? connected through a Can 5 network to a battery management system that ? configured to monitor various variables of battery 1 which will be defined below.

The method for determining the safety status (SOS) of a rechargeable battery ? described with reference to the flow chart in Figure 2.

The method includes the following steps.

Measure (block 100) a set of k different variables (V1(t), V2(t), .. Vk(t)) which are used to characterize the safe state of battery 1.

Examples of measured variables V1(t), V2(t),... Vk(t) which belong to the group are one or more? of the following:

? Internal resistance in direct current (DCIR), whose unit? of measure? l?Ohm. The internal direct current resistance (DCIR) represents the resistance of the current flowing through battery 1. The value of DCIR is not ? fixed and varies based on many factors, such as battery materials, electrolyte concentration, temperature and depth? dump.

? Difference between minimum and maximum temperature of the battery 1, the unit? of measure? ?C. Average temperature of the battery 1, the unit? of measure? ?C.

? Open circuit voltage OCV or VOC, the unit? of measure? Volt. The open circuit voltage? the difference of electric potential between two terminals of the battery 1 when disconnected from? appliance 3 which ? powered by battery.

? SOH health status of battery 1 which ? represented by a percentage %. The health status SOH represents the working condition of a battery compared to its ideal working condition (100%).

? State of charge SOC of battery 1 which ? represented by a percentage %. (0% = fully discharged; 100% = fully charged).

? Insulation resistance measured in Ohm: the insulation resistance? the parallel equivalent resistance of the insulation resistances of the positive and negative terminals with respect to the earth reference.

? Variation of battery temperature with respect to time measured in degrees/min.

Block 100 also supplies the measured variables V1(t), V2(t), .. Vk(t) sampled in the times (t2 and t1) and calculates the k variations of variables h(x) as the mean value (or average ) of the derivative of the k<th >variable in the time interval [t2, t1] (i.e. difference quotients), the k variations of variables h(x) are calculated as [V1(t2)- V1(t1)]/ (t2-t1), [V2(t2)- V2(t1)]/(t2-t1), ? [Vk(t2)-Vk(t1)]/(t2-t1). Sampling times can be, for example, a few milliseconds.

Can the changes in variables h(x) be computed by using a rolling average time window to compute each variable value over a longer period of time? long. The derivative can be calculated between mean values of different windows (tm-tm-1).

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

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

Where

? h(x) represents the variation of variables;

? m ? a setting parameter that allows you to control the speed? of decrease of the safety function, m pu? be set to 1; that is, m represents the steepness of the safety function curve f(x). A greater value of m makes the curve more? steep, thus providing fewer values of the safety function f(x). This parameter? also a function of the health of the battery pack e

? d represents the target value of the variation of variables h(x) that ? depending on the state of health of the battery.

Figure 3 shows how the safety function f(x) depends on the parameters m and d. In the same figure, the safe, warning, and unsafe ranges are shown.

Indeed, when the variation of variables h(x) corresponds to the target value d, the safety function ? 1.

As the difference between the target value d and the measured variable variation h(x) increases, the safety function f(x) decreases considerably 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 example, the ideal value d of the change in temperature with time ? 0.8 degrees/min for a new battery pack and as the battery becomes heavier old, the best variation of the temperature with time will increase? at 1.5 degrees/min. So, d pu? vary between 0.8 and 1.5 depending on the health of the battery.

Therefore, in the above f(x) safety function, the calibration parameters d and m could be set appropriately according to the health status of the battery pack.

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

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

Different ways can be considered to calculate the single value of a total safety function, preferably selecting from the calculated safety functions the worst one, i.e. the lowest value. Alternative ways to calculate the single value of a total safety function include determining the weighted average of the calculated values or determining a product of the calculated values.

Block 130? followed by block 140 which checks whether the calculated value of the total safety function falls within a safety interval.

In the event that the calculated total safety function falls within the safety interval, block 140 ? followed by block 150 which identifies a safe state of the battery. Safe state? stored and is also notified to a user of battery 1. The method then returns to the starting point ?start? for continuous monitoring of battery pack health.

If the verification of block 140 ? negative, ie the total safety function falls outside the safety interval, block 140 ? followed by block 160 which identifies an unsafe state of the battery. Unsafe state? memorized and ? also notified to a battery user. Automatic actions such as breaking the connection between battery 1 and appliance 3 powered by battery 1 can also be performed. Similar to the previous case, the method then returns to the initial starting point for continuous monitoring of the health of the battery pack.

As highlighted above, block 120 verifies whether the values of the calculated safety functions f(x) fall within the respective safety intervals of Fig. 3.

If any of the calculated values of the safety functions fall within the respective warning range of Fig. 3 , block 120 ? followed by block 170 which increases by one?unit? (+1) a counter that accumulates the number of violations of the safety function, a timer is started at the same time, then said timer is started from the moment when ? a first accumulated violation was detected.

Once the counter value reaches a limit value (C_limit) and the timer ? within a predetermined time limit (T_warning), (block 180 following block 170), a warning state is set for the battery (block 190) in another way, if the timer ? out of the time limit T_warning and the counter ? lower than the limit value (C_limit), the counter and the timer are reset to zero (block 200). In both cases, the method returns to its starting point.

In the light of the foregoing, the advantages of the method for determining the safety status of a rechargeable battery according to the invention are evident.

Thanks to the proposed method, ? It is possible to anticipate an unsafe condition of the battery before a major failure occurs, using the data related to the sensors already? existing on vehicle batteries.

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

Claims (1)

CLAIMS 1.- Method for determining the safety status of a rechargeable battery, comprising the following steps: measuring (block 100) a group of k different variables (V1(t), V2(t), .. Vk(t)) which they are used to characterize the safety status of said battery; determine k changes of variables (h(x)) each calculated as 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 in a predefined time interval (t2, t1); calculate for each variable variation (h(x)) the numerical value of a respective safety function which represents the Safety State (SOS) of the battery; calculating (block 130) a single value of a total safety function (f(x)); check if the calculated value of the full safety function is within a safe range and consequently identify a safe state (160) of the battery; if the full safety function falls outside the safety range, identify an unsafe battery state (150). 2.- Method as defined in claim 1, in which a group of k different variables comprises two or more? of the following variables: ? Direct current internal resistance (DCIR) which represents the resistance of the current flowing through the battery or the difference between the minimum temperature and the maximum temperature of the battery; ? Average battery temperature; ? Open circuit voltage (OCV or VOC) which represents the difference in electric potential between two battery terminals when disconnected from any circuit powered by the battery; ? Battery temperature variation versus time; ? State of health (SOH) of the battery calculated as the condition of a battery compared to its ideal condition (100%); ? State of charge (SOC) of the battery, represented by a percentage; ? Insulation resistance calculated as the equivalent parallel resistance of the insulation resistances of the positive and negative terminals with respect to the earth reference. 3.- Method as defined in claim 1 or 2 in which said safety function (f(x)) ? the following: Where ? h(x) represents the variation of variables; ? m ? a setting parameter that allows you to control the speed? of decrease of the safety function (f(x)); ? d represents the target value of the change of variables (h(x)) which depends on the state of health of the battery. 4.- A method as defined in claim 3 when dependent on claim 2, where the target value (d) of the variation of variables associated with the variation of the battery temperature with respect to time? between 0.8 degrees/min and 1.5 degrees/min. 5.- Method as defined in any of the preceding claims, wherein, if any calculated value of the safety functions falls within the respective warning interval, a counter is incremented and a timer is started, said counter counting whenever any value calculated safety functions are within the respective warning range; the method further comprises the steps of identify a warning state (190) once the counter value reaches a limit value (C_limit) and that the timer ? within a predefined time limit (T_warning); And reset the counter and the timer once ? said period of time has elapsed ((T_warning)) (200). 6.- Method as defined in any one of the preceding claims, wherein the step of calculating (block 130) a single value of a total safety function comprises the step of selecting among the calculated safety functions the worst one having the lower value of all or the step of determining a 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.- A method as defined in any of the preceding claims, including notifying a user when it is determined that the battery is in an unsafe state. 8.- Method as defined in any one of the preceding claims, comprising interrupting the connection between said battery (1) and an appliance (3) powered by said battery (1) when it is determined that said battery (1) is ? in an unsafe state. The method as defined in claim 5, comprising notifying a user when the battery is identified to be in the warning state.