Segmentation constant current charging design method for electric vehicle battery

　　Author ：Iflowpower – Portable Power Station Supplier

In order to achieve fast charging, it does not affect the battery life. The key is to make the fast charging process adaptive, that is, automatically adjust the size of the charging current based on the actual state of the battery, so that it always maintains a critical value of the chargeable current. nearby.

To this end, on the basis of battery fast charging, this paper tries to study the segmented constant current charger, in order to achieve intelligent fast charging and equalization charging of dynamic lithium batteries. 1 Battery fast charging segment constant current control 1.1 Selection of fast charging method Increase charging current, increased active substances recovered within units of battery plates, while charging time can be shortened, but excessive charging current damage battery.

Battery acceptable charging current is limited, and will decrease in exponential law as charging time. During the battery charging process, the charging current curve will cause the battery electrolyte in the index function curve (overcharge), and vice versa, it cannot effectively shorten the charging time. The idealized battery fast charging process is that the charging current is always maintained at the limit value of the battery charging acceptance current, that is, the charging current curve and the charging of the battery can receive the current curve.

This article selects easy segmentation constant current charging method, the key is to determine the appropriate stage constant current charging termination judgment criteria, constant current charging segment and each stage constant current charging current value. 1.2 Segmentation constant current charging control method To achieve automatic control of segment constant current charging, stage constant current charging termination judgment parameters can select charging time, battery temperature and battery voltage, etc.

A large number of survey analysis and battery charging test results show that single parameter control methods are difficult to achieve ideal segment constant current charge control. The charging time parameter control method is simple, but the battery model is different, the charging start state is different, the required charging time is different, if the charging time is used to control the end of the constant current charging during the charging time, it is easy to cause the battery overcharge or extend charging time. The advantage of the temperature parameter control method is that the battery temperature is too high, but due to the effect of the environment and sensor response time delay, if only the battery temperature parameters are used as the stage constant current charging termination judgment standard, it is easy to cause overcharging of the battery.

Voltage parameter control is considered to be a preferred stage constant current charging termination control method, but it is also apparent, such as: unrecognizable recharge voltage abnormality due to battery polar plate vulcanization and abnormal temperature in battery charging process Lift, thus causing the battery charging time to extend or damage the battery. In order to ensure that the actual charging state of the battery can be detected in various cases, the more desirable step-shaped charging current curve is achieved, and 3 parameters of charging time, battery temperature and termination voltage are combined as the basis for constant current charging. The control process is shown in Figure 1.

After the end of the segmentation constant current charging, the regulation of the pressure is charged for a period of time, to ensure that the battery can be completely sufficient. The specific control strategy of 3 control parameters is as follows. Time Parameter Control: According to the battery capacity and charging current, the time of a certain period of constant current charging is set in advance.

When the charging time reaches the set value, the constant current charging is ended by the press, and the charging current is reduced. Small, enter the next period of constant current charging. Temperature parameter control: Set a certain period of constant current charging to the battery temperature at the time of receiving current limit, control the charging device according to the battery temperature detected by the temperature sensor.

When the external ambient temperature is low, the maximum temperature of the set battery is higher, and the control temperature rise method is taken. When the temperature rise of the battery reaches the set value, the thermostat stops charging the charging device until the temperature falls to the appropriate value. Automatically enter the next stage constant current charging.

Voltage parameter control: The absolute voltage of the battery can reflect the charging of the battery. Set a certain period of constant current charge to meet or approach the charge acceptable current limit value. When the voltage reaches the set value, the charging device automatically ends this stage Flow charging, enter the next stage.

1.3 Segmentation constant current charging test study According to the capacity of the battery, T (N), I (N) and U (N), perform charging test, according to T (N), I (N), i (n) during charging Adjust and U (N), then carry out the next charging test. Each time the initial state of the battery is completely discharged, the charging time, charging efficiency, and battery temperature rise, etc.

are analyzed, the shortest charging process is shorter, and the battery temperature rise is relatively small. The control parameters of each stage and the incoming amount are shown in Table 1 and Table 2, the segmented constant current charging current curve is shown in FIG. By analyzing the test results, it can be concluded that the gradient of the constant flow value I (N) of each segment should be appropriately reduced.

Comparison of the temperature rise of the battery and the constant current constant state of each sector discovered that the time used for sufficient electricity, 5 segments of constant current charging time, while 4-segment constant current charging time Time to short in constant current charging. Therefore, appropriately reduce the reduction gradient of the constant flow value of each segment (the number of segments added) can make the actual charging current curve closer to the charging acceptance current curve. [Page] (2) Set the use of each constant flow section T (N) is not large.

Control each constant flow section of each constant flow section is easier to implement, however, since the battery is different or due to battery capacity attenuation due to battery capacity attenuation, the best constant current is optically reduced. Charging time also changed. The uncertainty of the battery is difficult to determine the optimal charging time.

The following phenomenon often occurs in the test: a certain constant current is charged to the set charging time, but the charging voltage is denoted by the termination voltage. At this time, this test has chosen to continue charging at the constant flow value until the charging voltage is reached Terminate the voltage; the charging time of a constant current charging setting has not yet, but the battery has been paid a lot (the electrolyte "boiling"), and the charging voltage is higher than the set termination voltage or battery temperature rises to the limited value, In this case, the charger will immediately stop the constant current charging and automatically transfer to the next stage. It can be seen that during the automatic control of the charging process, the use of charging time is not large.

(3) Battery temperature should not be separate as segmented constant current charge control parameters. In theory, when the battery charge is different when the charging is started, the battery temperature can be used as an automatic stop control parameter of each stage constant current charging. However, the error and hysteresis of the temperature sensor easily cause the battery overcharge, so it is not advisable to use the battery temperature separately as a segment constant current charging termination control parameter.

(4) Termination Voltage Parameters u (n) is poor in adaptability to abnormal conditions. Setting the termination voltage of different constant current values ​​to control parameters, can adaptive to the charge state of the battery and the charging of the battery during the battery use, and the control is relatively simple. However, when the performance of the battery changes abnormally, the original set termination voltage may be too high or too low, causing the battery overcharge or reducing the charging current and extending the entire charging time.

Further, in different constant current charging stages, the charge polarization of the battery is also different, and the charging voltage rise rate in the time of receiving current limits will also be significantly different, and it is necessary to accurately set various constant current charging. Termination of voltage is very difficult. 2 Intelligent Control of Battery Segmentation Control 2.

1 Segmentation Constant current charging intelligent control method According to the results and analysis of segmented constant current charging test, the segmentation constant current charge control method is adjusted as follows: (1) Adoption Capacity gradient method determination stage constant current charging termination standard. Through theoretical analysis and a large number of experimental studies, this paper believes that the use of capacity gradient parameters DU / DC as stage constant current charging termination judgment standard is appropriate. According to the constant current charging characteristic curve of this type, the charging stop capacity gradient parameter is determined.

During the charging process, the controller samples the charging voltage in the set frequency, calculates the capacity gradient value of I (N), and is charged with the setup The termination capacity gradient standard is compared, and according to the comparison result, it is determined whether or not to terminate the current stage constant current charging. (2) Reduce the reduction gradient of constant flow value of each segment. The first constant flow value I (1) of the type of battery is determined by test, and the current decrease in current decrease in stage constant current charging is reduced.

If the charging current is reduced, the time to reach the charging stop capacity gradient value is short (set a minimum charging time), the increase in current decline is appropriately increased. (3) Set the battery temperature to the charging security control parameters. Set the maximum temperature limit value of the battery, during the charging process, if the battery temperature reaches the limit, stop charging immediately.

When the battery temperature drops to normal temperature, the charging current is appropriately reduced until the constant current charging ends. 2.2 Segment constant current charging intelligent control circuit segmentation constant current charging intelligent control circuit is shown in Figure 3.

The circuit uses a CPU control to detect the charging battery and the charging ambient temperature, and the battery is charged, and the voltage and current of the battery during the sample charging process are controlled to control the segmented constant current charging process. 2.3 Intelligent segmentation constant current charging test research The charging test according to the adjusted segmentation constant current charging method, in order to facilitate comparison, using the same model of the charging test before the method adjustment, the initial state of the charging is identical.

The control parameters of the constant flow charge after the adjustment method and the charged charge are shown in Table 3, and the control parameters of the regulation stage thereof and the incoming amount of the charge are the same as the value in Table 2, and the segmentation after adjustment method The constant current charging current curve is shown in Figure 4. During the segmentation constant current charging test after the adjustment method, the battery does not have high temperature and stop charging, the charging time is shortened, and the charging efficiency is also improved, and the entire charging process is automatically performed according to the set procedure, Do not manually intervene, realize intelligent fast charging. 3 Conclusion The constant current charging termination standard parameters are determined using a capacity gradient method, reducing the gradient of the step constant current charging current, and supplemented by the battery temperature is too high, and the protection control of the charging can realize the intelligent fast charging control of the power lithium battery.

The test results show that this constant current charging control method can effectively shorten the charging time, improve charging efficiency, and extend battery life.