CN103033759B - An Intelligent Judgment Method for Battery Thermal Runaway - Google Patents

Abstract

The invention relates to an intelligent judging method for thermal runaway of a storage battery, which belongs to the field of control. Its intelligent judging method includes the following steps: record a little battery voltage and current value every second; record a little battery voltage and current every minute; I _{storage charge} ≥ 0.01C10? If yes, proceed to the next step, otherwise return to the first step; |Un-Un-1|>1V? Yes, return to the first step, otherwise proceed to the next step; judge the upward trend of the current in the previous period, if it is an upward trend, execute the next step, otherwise Return to step 1; issue a thermal runaway alarm. It summarizes the phenomena that people have observed in the past, compiles a diagnostic program and integrates the current and voltage signals collected by the battery monitor to make intelligent judgments, draw appropriate conclusions and issue alarms.

Description

An Intelligent Judgment Method for Battery Thermal Runaway

technical field

The invention belongs to the field of control, in particular to a method for monitoring the running state of a storage battery.

Background technique

The importance of valve-regulated batteries in the operation of DC systems is well known, and the safe operation of DC systems depends on the reliability of batteries. The most serious consequence that the battery is prone to occur during operation is thermal runaway failure of the battery, which causes the battery to catch fire and burn, and the DC system loses power.

Several major fires in the DC power supply system were caused by thermal runaway of the battery.

The practice of operation proves that it is reasonable to make this provision. We can see from the analysis of the faulty battery that the lagging capacity of individual batteries during operation cannot explain the working condition of the entire battery group. However, if more than two batteries have insufficient capacity, Generally, it is symbolic. For example, the general dehydration of the battery causes insufficient capacity of the battery, the aging of the bus plate of the battery causes some plates to fail to work, and the overall life of the battery is reduced. No matter what the reason is, the reliability of the battery will be greatly reduced. , its function is to discharge reliably in the case of power loss, instead of cyclic charging and discharging, it can use the discharge limit of the battery, so even if 80% of the capacity can be stored, it is not safe for the DC system. .

On the other hand, because the battery is in the state of floating charge most of the time during operation, the floating charge current of the battery is very small, and the actual statistics in operation prove that it is less than 1mA/Ah. For a 300Ah battery, the floating current will not be greater than 0.3A. A grim reality faced by batteries in operation is that it is often reported that thermal runaway of batteries causes failure, explosion, and fire of the entire battery group. The final result is not only battery damage but also DC system paralysis, although the probability of such incidents is very low. But the consequences are serious. Conventional battery discharge tests cannot detect thermal runaway. At present, there are no other effective technical means to prevent it. We can only strengthen the monitoring of battery current based on experience and find that the battery current increases innocently. Just be vigilant. From the only battery thermal runaway event we encountered in operation practice, the performance of battery thermal runaway is that the battery current rises sharply under normal floating charge voltage operating conditions, and the float charge current of a 300Ah battery reaches about 20A when thermal runaway occurs. , when the normal floating charging voltage of the charger is dropped from 240V to 220V immediately, the battery current is reduced to below 1A, that is, the voltage drops by 10% to maintain a close to normal floating charging current, and the battery current remains unchanged. The battery terminal voltage is around 2V. We can also think that the internal electromotive force of the battery has dropped from 2.23V to 2V, and the battery with an electromotive force of 2V is charged at a normal floating charge voltage of 2.23V. The charging current depends entirely on the internal resistance of the battery. Usually, the capacity of a lead-acid battery The larger the internal resistance, the smaller the internal resistance. Therefore, once the battery is thermally runaway, the thermal runaway current generated by the battery with a large capacity will be greater, and the heat generated will be greater. Similarly, the capacity of the charger equipped with a battery with a large capacity is also large, resulting in a large number of batteries. Therefore, the consequences of thermal runaway of batteries larger than 300Ah are often fires and combustion. For chargers, no manufacturer has intelligently identified the charging current of the battery; what is the charging current caused by the capacity drop caused by battery discharge? What is the high-current charging that occurs when the battery capacity is full and under the condition of floating charge. If it is charging that occurs in the latter case, the monitor takes a series of measures to prevent the storage battery that is about to enter thermal runaway. The battery manufacturer’s technical instructions do not mention the conditions for thermal runaway. It only mentions that the voltage of the floating charge terminal of the battery is corrected at different temperatures, and the terminal voltage drops by 3mV every time the temperature rises. There is no emphasis on deviation from this relationship. What is the consequence? Judging from the actual measured voltage, the voltage provided by the manufacturer refers to the average value. The actual discrete value of the battery cell voltage during operation is much greater than this, and the actual work of 3mV temperature compensation is of little significance. I have observed and compared the charging current of the sealed valve-controlled battery after the regular equalization charge under the condition of floating charge and the charging current of the battery under the floating charge state, and found that the difference between the two currents is not large. This result shows that the charging voltage of the battery is normal. If it is higher than the floating charge voltage, as long as it is not greater than the maximum value of the equalizing charge voltage allowed by the manufacturer, it will not cause thermal runaway, which has other reasons.

Contents of the invention

The technical problem to be solved by the present invention is to provide an intelligent judgment method for battery thermal runaway, which summarizes the phenomena observed by people in the past, compiles a diagnostic program and integrates the current and voltage signals collected by the battery monitor for intelligent judgment. Draw appropriate conclusions and alerts.

The technical solution of the present invention is to provide an intelligent judgment method for battery thermal runaway, which is characterized in that the intelligent judgment method includes the following steps:

1-1. Record a little bit of battery voltage and current every second;

1-2. Record the battery voltage and current value every minute;

1-3, I _{storage charge} ≥ 0.01C ₁₀ ? If yes, proceed to the next step, otherwise return to the first step;

1-4,｜Un-Un-1｜＞1V? Yes, return to the first step, otherwise go to the next step;

1-5. Judging the upward trend of the current in the previous period, if it is an upward trend, execute the next step, otherwise return to the first step;

1-6. A thermal runaway alarm is issued.

Wherein, the battery voltage value and current value are second average values.

The steps 1-3 are used to monitor whether the battery charging current exceeds the limit. .

Steps 1-4 are used to determine whether the current overrun is caused by equal charging or unstable voltage.

Compared with the prior art, the present invention has the advantages of summarizing the phenomena observed by people in the past, compiling a diagnostic program and combining the current and voltage signals collected by the battery monitor for intelligent judgment, drawing appropriate conclusions and Make an alarm.

Description of drawings

Fig. 1 is a schematic block diagram of a method for intelligently judging thermal runaway of a storage battery according to the present invention;

Figure 2 is an oscillogram of the DC power supply operation process controlled by the monitor.

Detailed ways

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

Among Fig. 1, intelligent judgment method of the present invention comprises the following steps:

1-1. Record a little bit of battery voltage and current every second;

1-2. Record the battery voltage and current value every minute;

1-3, I storage charge ≥ 0.01C10? If yes, proceed to the next step, otherwise return to the first step;

1-4,｜Un-Un-1｜＞1V? Yes, return to the first step, otherwise go to the next step;

1-5. Judging the upward trend of the current in the previous period, if it is an upward trend, execute the next step, otherwise return to the first step;

1-6. A thermal runaway alarm is issued.

Wherein, the battery voltage value and current value are second average values.

The steps 1-3 are used to monitor whether the battery charging current exceeds the limit. .

Steps 1-4 are used to determine whether the current overrun is caused by equal charging or unstable voltage.

The specific process and steps are described in detail as follows:

Judging the upward trend of current in the previous period

1. Historical data record of battery current

One average per minute. (Note: Since the battery current fluctuates within a certain range in normal state, it is not a constant value, so only one average value per minute can be taken)

Calculate the average value (10 point data) every 10 minutes, and then make a judgment. If the data per minute is within ±0.2A of the 10-minute average value, the battery float current is represented by an average value, and data compression is performed. The data format is: time period + value.

Calculate the average value (60 data) every 60 minutes, and then make a judgment. If the data per minute is within ±0.2A of the 60-minute average value, the battery float current is represented by an average value, and data compression is performed. The data format is: time period + value. If the data is out of tolerance, the historical current of the battery is recorded at a point of 10 minutes.

If the battery current exceeds 0.002C10, it will be recorded as an event, with one data recorded per second, and then averaged once per minute. As long as the current value fluctuation is less than ±0.2A, it will enter one point per minute record.

Judging the upward trend of current in the previous period

It is judged that the number of times recorded by the battery every 60 minutes is more than the number of times recorded once every 10 minutes within a month.

If it is more, it means that the battery current measurement is stable, and the current rising trend is selected as the rising trend of the average value recorded in 60 minutes in 1, 2, 3, 4, 5, 10, 20, and 30 days (to exclude event records, and use For the recorded value after the event is recorded, if the charging current out-of-tolerance occurs 25 days before the event is recorded, the recorded data of the previous 30th day cannot be taken). The specific judgment method is: the latter data minus the previous data to determine whether it is positive or negative. If the positive is greater than the negative, it means that the current is rising during this period of time and a "thermal runaway alarm" is reported.

If it is less than that, it means that the current measurement is unstable or there are many events, judge the time from the last event to the occurrence of "battery charging current over limit", calculate the current average value by ten equal divisions, and then judge; subtract the previous data from the latter data to judge positive burden. If the positive is greater than the negative, it means that the current is rising during this period of time and a "thermal runaway alarm" will be reported.

Judging the rising trend of the battery current within 6 months, the recorded data after the event, calculating the monthly average value, and judging the rising trend, the method is the same as before.

Definition of event record: event record refers to the three processes of discharging, charging, and equalizing charge in the process of battery float charging, and the entire time period of the event should end when the battery current is less than 0.001C10. The time period of the battery thermal runaway judgment process should not include the event, otherwise the data of the event will interfere with the judgment and cause misjudgment.

The importance of valve-regulated batteries in the operation of DC systems is well known. The safe operation of DC systems depends on the reliability of batteries. For battery performance, people can only verify and judge whether the life of batteries has reached the end by conducting battery discharge tests. For this reason, the national standard stipulates that under the condition of full-capacity discharge, if the capacity of two batteries in the whole set of batteries is lower than 80% and the standard is still not reached after equal charging, the set of batteries is considered to be at the end of its life and should be replaced. Operation practice proves that it is reasonable to make this provision. We can see from the analysis of the faulty battery that the lagging capacity of individual batteries during operation cannot explain the working conditions of the entire battery group. However, if more than two batteries have insufficient capacity, generally It is symbolic. For example, the general dehydration of the battery causes insufficient capacity of the battery, the aging of the bus plate of the battery causes some plates to fail to work, and the overall life of the battery is reduced. No matter what the reason is, the reliability of the battery will be greatly reduced. , its function is to discharge reliably in the case of power loss, instead of cyclic charging and discharging, it can use the discharge limit of the battery, so even if 80% of the capacity can be stored, it is not safe for the DC system. .

On the other hand, because the battery is in the state of floating charge most of the time during operation, the floating charge current of the battery is very small, and the actual statistics in operation prove that it is less than 1mA/Ah. For a 300Ah battery, the floating current will not be greater than 0.3A. A grim reality faced by batteries in operation is that it is often reported that thermal runaway of batteries causes failure, explosion, and fire of the entire battery group. The final result is not only battery damage but also DC system paralysis, although the probability of such incidents is very low. But the consequences are serious. Conventional battery discharge tests cannot detect thermal runaway. At present, there are no other effective technical means to prevent it. We can only strengthen the monitoring of battery current based on experience and find that the battery current increases innocently. Just be vigilant. From the only battery thermal runaway event we encountered in operation practice, the performance of battery thermal runaway is that the battery current rises sharply under normal floating charge voltage operating conditions, and the float charge current of a 300Ah battery reaches about 20A when thermal runaway occurs. , when the normal floating charging voltage of the charger is dropped from 240V to 220V immediately, the battery current is reduced to below 1A, that is, the voltage drops by 10% to maintain a close to normal floating charging current, and the battery current remains unchanged. The battery terminal voltage is around 2V. We can also think that the internal electromotive force of the battery has dropped from 2.23V to 2V, and the battery with an electromotive force of 2V is charged at a normal floating charge voltage of 2.23V. The charging current depends entirely on the internal resistance of the battery. Usually, the capacity of a lead-acid battery The larger the internal resistance, the smaller the internal resistance. Therefore, once the battery is thermally runaway, the thermal runaway current generated by the battery with a large capacity will be greater, and the heat generated will be greater. Similarly, the capacity of the charger equipped with a battery with a large capacity is also large, resulting in a large number of batteries. Therefore, the consequences of thermal runaway of batteries larger than 300Ah are often fires and combustion. For chargers, no manufacturer has intelligently identified the charging current of the battery; what is the charging current caused by the capacity drop caused by battery discharge? What is the high-current charging that occurs when the battery capacity is full and under the condition of floating charge. If it is charging that occurs in the latter case, the monitor takes a series of measures to prevent the storage battery that is about to enter thermal runaway. The battery manufacturer’s technical instructions do not mention the conditions for thermal runaway. It only mentions that the voltage of the floating charge terminal of the battery is corrected at different temperatures, and the terminal voltage drops by 3mV every time the temperature rises. There is no emphasis on deviation from this relationship. What is the consequence? Judging from the actual measured voltage, the voltage provided by the manufacturer refers to the average value. The actual discrete value of the battery cell voltage during operation is much greater than this, and the actual work of 3mV temperature compensation is of little significance. I have observed and compared the charging current of the sealed valve-controlled battery after the regular equalization charge under the condition of floating charge and the charging current of the battery under the floating charge state, and found that the difference between the two currents is not large. This result shows that the charging voltage of the battery is normal. If it is higher than the floating charge voltage, as long as it is not greater than the maximum value of the equalizing charge voltage allowed by the manufacturer, it will not cause thermal runaway, which has other reasons.

The thermal runaway mechanism of the battery is still unclear to us, but the performance of thermal runaway has some regularity and mainly has the following external characteristics:

1. The normal floating charging current of the battery increases, for example, the normal floating charging current of a 300Ah battery is less than 0.3A, and the current increases to 20A when the thermal runaway occurs. At this time, the increased current cannot continue to be converted into chemical energy, which only causes the battery to generate a large amount of heat and gas. The generated heat causes the electromotive force of the battery itself to drop, further increasing the input current of the battery, forming a vicious circle.

2. The temperature of the battery body rises sharply, the shell softens under high temperature, and the pressure generated by a large amount of gas deforms the battery shell.

For the above changes, because the general operating personnel do not have experience in this field, it is difficult to judge that the battery has entered a state of thermal runaway at the initial stage. When the operating personnel on duty find out the situation and take measures, it is too late.

Therefore, it is imminent to develop a monitor that can monitor the working condition of the battery. The purpose of the development of the intelligent battery monitor is to summarize the phenomena that people have observed in the past, compile a diagnostic program and integrate the current and voltage signals collected by the battery monitor. Make intelligent judgments, draw appropriate conclusions and issue alarms.

The following are the main points of work for the judgment of this technical solution:

1. Set the capacity of the running battery, and the monitor will automatically set the maximum floating charge current of the battery. For example, the maximum float charge current of the battery automatically set for a 300Ah battery is 300mA (1mA per ampere hour).

2. Measure the charging current and charging voltage of the battery that is put into operation. If it is a new battery, the monitor will start to judge when the floating charging current of the battery is less than the maximum floating charging current. When the current enters a stable value state, it will automatically set the initial state of the battery , it is considered that the capacity of the battery is 100%, and based on this, the working state of the battery in the future is monitored. Carry out memory, and use this as a standard to monitor whether the battery current has an upward trend and exceeds the set value.

3. It can automatically distinguish the charging current after the battery is discharged, and will not misjudge the charging current as thermal runaway current.

4. If the experience is compiled into an expert diagnostic program through the computer, the monitoring ability of the equipment will be greatly improved.

When the battery is thermally out of control, the temperature rises, the current increases, the acid gas diffuses, and the shell is deformed. By monitoring the above phenomena, problems can be found in time.

In Figure 2, the relationship between battery current, voltage and state is given:

1. Battery charging process in the first area

This area is the charging process of the battery. The initial voltage of the battery is 88V. Obviously, if the charging voltage of 110V is directly added to such a low battery voltage, it will cause serious charging current overload and damage the battery. Charging is under the control of the monitor. The current limit is 0.1C10 to charge the battery with a constant current. In this case, the battery is 300AH, and the current limit is 30A. During this process, the battery voltage rises slowly. After a period of charging, the voltage of the battery rises to the equalized charging voltage (121V), and the charger maintains the equalized charging voltage. At this time, the charging current of the battery increases with the increase of capacity, and the terminal voltage of the battery gradually rises. The terminal voltage of the battery and the equalized charging voltage The difference gradually decreases, causing the battery current to gradually decrease. When it reaches a certain value, the equal charging timer is started, and the timer is over. The charging process ends and enters the second area.

2. The long-term floating charging working state of the second area

As the charging voltage turns to the floating charging state, the voltage drop causes the battery voltage to be higher than the charger voltage and the bus voltage, and the battery discharges the bus load. After a few minutes, the battery voltage drops to be equal to the floating charging voltage. After a long period of time, the charger There is only a small float charge current for the battery to supplement the discharge of the internal resistance of the battery, and the float charge voltage remains stable for a long time to ensure the normal operation of the DC bus voltage. This process has to be maintained until 3 months (or 6 months) later, the monitor will charge the battery equally and enter the third area.

3. The equalization stage of the third area

Long-term floating charging will cause the dispersion of battery terminal voltage to increase, and the capacity of some batteries will decrease. Therefore, the battery should be adjusted in the equalization charging stage to ensure battery performance. The average charging voltage of the battery is higher than the floating charging voltage, and the battery current increases to make up for the loss of long-term floating charging. After a period of charging (usually 3 hours), the consistency of the battery terminal voltage becomes better, and some lagging capacity is compensated by charging. The monitoring command returns to the floating charge voltage, and enters a long-term floating charge state, which is the fourth area. Repeating this cycle, the monitor automatically maintains the battery until one day an accident causes an AC power outage, and the battery supplies power to the DC bus load and enters the fifth area.

4. Accident discharge stage in the fifth area

The AC power loss caused by grid failure and the like makes the battery enter the discharge state, and the voltage of the battery will gradually drop over time due to the discharge. Until the AC power supply is restored, the charger supplies power to the storage battery and the DC system again, and enters the sixth area. The working process of the sixth area is the same as that of the first area.

load short circuit

The picture is not drawn, but it is actually a sharp pulse. The whole process is very short, generally within 4~16mS, and the current amplitude is very large, about 10A~800A. The best sampling rate for recording this current is within 1mS.

Because the present invention summarizes the phenomena that people have observed in the past, compiles it into a diagnostic program and integrates the current and voltage signals collected by the storage battery monitor to make intelligent judgments, draw appropriate conclusions and issue alarms.

The invention can be widely used in the field of monitoring the running state of the accumulator.

Claims (1)

1. a storage battery thermal runway intelligent judgment, comprises some battery tension values of record per second and current value; Some battery tension values of every member record and current value; It is characterized in that described intelligent determination method comprises the following steps:

1-1, judge I _{store and fill}>=0.01C ₁₀carry out next step, otherwise return the first step;

1-2, judgement | Un-Un-1| > 1V? be return the first step, otherwise carry out next step;

1-3, sentence electric current ascendant trend the last period, ascendant trend in this way, performs next step, otherwise returns the first step;

1-4, send thermal runaway alarm;

Wherein said battery tension value and current value are mean value second;

Wherein said 1-1 step is for monitoring whether battery charging current transfinites;

Whether wherein said 1-2 step all fills or caused by spread of voltage for judging that electric current transfinites;

Wherein, described intelligent determination method carries out the mean value calculation of an accumulator floating charging flow valuve for every 10 minutes, then judges, as data per minute 10 minutes mean value ± 0.2A within, accumulator floating current represents with a mean value, carries out data compression;

Described intelligent determination method carries out the mean value calculation of an accumulator floating charging flow valuve for every 60 minutes, then judge, as data per minute 60 minutes mean value ± 0.2A within, accumulator floating current represents with a mean value, carries out data compression;

As accumulator floating current exceeds 0.002C ₁₀then as logout, record per second data, then per minute average once, as long as current value fluctuation be less than ± 0.2A within, just enter a some record per minute;

Intelligent determination method described in it passes judgment on the number of times that in month, accumulator 60 minutes records number of times once once recorded more than 10 minutes, if the number of times that 60 minutes records number of times once once recorded more than 10 minutes, then battery current Measurement sensibility is described, relatively electric current ascendant trend is chosen as mean value ascendant trend in 1,2,3,4,5,10,20,30 day of 60 minutes records, rear data is subtracted previous data positive and negative to differentiate; If be just greater than negative, then illustrating that electric current is rise in this period of time, report " thermal runaway alarm ";

If 60 minutes records number of times is once less than the number of times once recorded for 10 minutes, illustrates that current measurement is unstable or event is more, sentence last event apart from the time that " battery charging current transfinites " occurs, ask current average with ten deciles, then judge; Rear data are subtracted previous data positive and negative to differentiate; If be just greater than negative, then illustrating that electric current is rise in this period of time, report " thermal runaway alarm ".