CN106887864A - A kind of electrokinetic cell balance control method and respective battery management system - Google Patents

Abstract

The invention discloses a method for equalizing the power battery of an electric vehicle, which comprises the steps of: judging whether the battery packs of the electric vehicle need equalization processing when the electric vehicle is in a charging state or a discharging state; Each battery cell that needs to be balanced; read the balance time of each battery cell that needs to be balanced from the memory that stores the balance time of each battery cell, and The body is equalized with the corresponding equalization time. The invention also discloses a corresponding battery management system. The implementation of the invention can effectively reduce the hardware cost, reduce the heat dissipation risk of the hardware circuit, and improve the battery life.

Description

A power battery balancing control method and corresponding battery management system

technical field

The invention belongs to the field of passive equalization of power batteries of electric vehicles, and in particular relates to a power battery equalization control method and a corresponding battery management system.

Background technique

Electric vehicle power batteries usually consist of multiple single cells connected in series. Due to the inconsistency of the capacity, internal resistance and self-discharge rate of the single battery, the voltage of the single cell is inconsistent. In actual use, the capacity that the power battery can actually release is determined by the single battery with the worst performance. When the capacity of the single battery is exhausted, the power battery circuit must be cut off to protect the entire power battery; the charging process is also Similarly, when one of the single cells is fully charged and reaches the predetermined charging protection point (such as 4.2V), the power battery circuit must be cut off to protect the entire power battery. During the use of the power battery of an electric vehicle, the imbalance of the single battery is an important factor affecting the work of the battery pack, so it is very necessary to balance the battery pack.

In the prior art, there are mainly two types of methods for balancing batteries: active balancing and passive balancing. Using hardware circuits and related software control methods, the single battery can be discharged or recharged, which is called active balancing; the single battery can only be discharged, which is called passive balancing.

At present, the passive equalization control method usually adopts the power-on equalization method or the charging equalization method:

Among them, the power-on equalization method refers to reading the voltage of each single battery when the electric vehicle is powered on, and judging whether to balance the battery according to the static OCV relationship. Balanced operation.

The charging equalization method refers to reading the voltage of each single battery when the electric vehicle is charging. When the highest single battery voltage reaches the preset judgment point, according to the dynamic charging SOC-V curve relationship, it is judged whether to balance the battery pack. , if the balance condition is met, the battery pack will be balanced during the process of charging until the voltage of the single battery reaches the charging protection point.

However, these two existing passive equalization methods have different deficiencies. Among them, the power-on equalization method must read the accurate static cell voltage value to determine the cell capacity difference according to the static OCV relationship curve. So as to determine the equalization time. Due to the phenomenon of battery voltage drop, in order to obtain accurate static single voltage value, the vehicle must stand for a long enough time after stopping. The current vehicles basically do not have the function of timing when the vehicle is parked and turned off. In order to obtain the stationary time of the vehicle, an additional timing hardware module must be added, which increases the hardware cost.

In the charge equalization method, under the charging conditions, the time for the battery cell voltage to charge from the judgment point to the voltage protection point is relatively short. In order to achieve the equalization effect, the equalization current must be increased, which will increase the cost of hardware and the heat dissipation of the hardware circuit.

Contents of the invention

The technical problem to be solved by the present invention is to provide a power battery balancing control method and a corresponding battery management system, which can realize small current balancing, reduce hardware balancing costs and heat dissipation risks.

In order to solve the above technical problems, an embodiment of the present invention provides a power battery balancing control method for electric vehicles, including the following steps:

When the electric vehicle is in the state of charging or discharging, it is judged whether the battery pack needs to be balanced;

When equalization processing is required, determine each battery cell that needs equalization processing in all battery packs;

The equalization time of each battery cell that needs to be balanced is read from a memory that stores the equalization time of each battery cell, and the equalization process is performed on each battery cell with a corresponding equalization time.

Wherein, when the electric vehicle is in a charging state or a discharging state, the step of judging whether its battery pack needs to be balanced further includes:

When the electric vehicle is in the charging state, when the current voltage of all battery packs does not reach the battery cell protection voltage, and when the equalization time corresponding to any battery cell in the battery pack is greater than zero, it is determined that the battery pack needs to be balanced ;

When the electric vehicle is in a discharging state, when the equalization time corresponding to any battery cell in the battery pack is greater than zero, it is determined that the battery pack needs to be balanced.

Among them, further include steps:

When the electric vehicle is in the charging state, when the current voltage of any battery pack reaches the protection voltage of the battery cell, the equalization time of each battery cell in the battery pack is re-determined, and each battery cell The equalization time is stored in the rewritable memory;

Wherein, the step of re-determining the equalization time of each battery cell of the battery pack includes:

judging whether the maximum voltage difference of each battery cell in the battery pack is greater than a predetermined voltage difference threshold;

If the judgment result is no, update the equalization time of each battery cell in the battery pack to zero, and store it in the rewritable memory;

If the judgment result is yes, record the current voltage value of each battery cell of each battery pack, and calculate the difference with the lowest voltage value therein, to obtain the voltage difference between each battery cell and the lowest voltage value; Re-determine the equalization time corresponding to each battery cell according to the voltage difference of each battery cell; store the equalization time of each battery cell into a rewritable memory.

Wherein, according to the voltage difference of each battery cell, the step of re-determining the equalization time corresponding to each battery cell is specifically:

The capacity difference corresponding to the voltage difference of each battery cell is obtained according to the dynamic charging SOC-V curve of the battery cell, and the equalization time is obtained by calculating according to the capacity difference and a predetermined equalization current value.

Wherein, reading the equalization time of each battery cell that needs equalization processing from the memory that stores the equalization time of each battery cell, and performing equalization for each battery cell with a corresponding equalization time The steps of equalization processing further include:

Read out the equalization time of each battery cell from the erasable memory;

Judging whether the equalization time is zero, if the judgment result is no, start battery equalization for the corresponding battery cell;

Decrementally update the equalization time of each battery cell at regular intervals, and replace the corresponding equalization time of the battery cell in the rewritable memory with the latest updated equalization time;

Repeat the above steps, if it is judged that the equalization time of a certain battery cell is zero, stop performing battery equalization on the corresponding battery cell.

Correspondingly, another aspect of the embodiments of the present invention also provides a battery management system, which includes:

a battery pack comprising a plurality of battery cells;

a plurality of battery management units, each of which corresponds to a battery cell, and is used to collect battery parameters of each of the battery cells; and

Rewritable memory for storing the equalization time of each battery cell;

a battery control unit, connected to the plurality of battery management units, configured to collect battery parameters of the battery cells, and generate a balancing control command for the battery cells according to the battery parameters,

Wherein, the battery electronic control unit generates a balancing control instruction according to the aforementioned battery balancing method, and the battery management unit balances the battery cells according to the balancing control command.

Implementing the embodiment of the present invention has the following beneficial effects:

The electric vehicle power battery balance control method provided by the embodiment of the present invention can use the two time periods when the battery cell voltage does not reach the battery protection and discharge when charging to perform balance. Since electric vehicles need to be charged almost every day, during charging It is necessary to judge whether the equalization operation is needed, so that the number of times to enter the equalization judgment is relatively large, and the battery can be balanced in time;

At the same time, judging whether equalization operation is required during charging does not need to consider the battery rest time; and because the charging current is controllable, according to the dynamic charging SOC-V curve of the battery cell, the equalization time can be obtained more accurately;

In addition, equalization is performed before charging reaches the battery protection point voltage and during discharge. Through long equalization time, small current (equalization current = capacity difference / equalization time) equalization function can be realized, which effectively reduces hardware costs and reduces heat dissipation of hardware circuits. Risk, and small current balance has a certain protective effect on battery life.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings on the premise of not paying creative efforts.

Fig. 1 is a schematic diagram of the main flow of an electric vehicle power battery balancing control method provided by the present invention;

Fig. 2 is a more detailed flow diagram of an embodiment of step S10 in Fig. 1;

Fig. 3 is a schematic diagram of the SOC-V curve used for calculating the equalization time in an electric vehicle power battery equalization control method provided by the present invention;

Fig. 4 is a more detailed flow diagram of an embodiment of step S14 in Fig. 1;

Fig. 5 is a more detailed schematic flow chart of an electric vehicle power battery balancing control method provided by the present invention when the electric vehicle is in a charging state;

Fig. 6 is a more detailed schematic flow chart of an electric vehicle power battery balancing control method provided by the present invention applied when the electric vehicle is in a discharging state;

Fig. 7 is a schematic circuit topology diagram of an embodiment of a battery management system provided by the present invention;

FIG. 8 is a schematic structural diagram of an embodiment of an equalization circuit adopted in the battery management unit of FIG. 7 .

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

As shown in Figure 1, it is a schematic diagram of the main flow of a method for balancing control of electric vehicle power batteries provided by the present invention; in this embodiment, the method includes the following steps:

Step S10, when the electric vehicle is in the charging state or discharging state, and when the equalization time corresponding to any battery cell in the battery pack is greater than zero, determine whether the battery pack needs to be equalized; specifically, when the electric vehicle is in In the charging state, when the current voltage of all battery packs does not reach the battery cell protection point voltage (for example, 4.2V), read the corresponding equalization time, when the equalization time of any battery cell in the battery pack is greater than zero, it is determined that the battery pack needs to be equalized;

When the electric vehicle is in a discharging state, when the equalization time corresponding to any battery cell in the battery pack is greater than zero, it is determined that the battery pack needs to be balanced.

Step S12, when balancing processing is required, determine the battery cells that need to be balanced in all battery packs; specifically, read each battery cell according to the memory that stores the balancing time of each battery cell The equalization time corresponding to each battery cell, when the equalization time of any battery cell in the battery pack is greater than zero, it is determined that the battery cell corresponding to the equalization time needs to be equalized;

Step S14, reading the equalization time of each battery cell that needs equalization processing from the memory that stores the equalization time of each battery cell, and equalizing each battery cell with the corresponding equalization time deal with.

Please refer to Figure 2, which is a more detailed flow diagram of an embodiment of step S10 in Figure 1, specifically, it is a step further included in step S10: when the electric vehicle is in the charging state, when any battery When the current voltage of the battery pack reaches the protection voltage of the battery cell, re-determine the equalization time of each battery cell in the battery pack, and store the equalization time of each battery cell into the rewritable memory;

Wherein, the step of re-determining the equalization time of each battery cell of the battery pack includes:

Step S20, judging whether the maximum voltage difference of each battery cell in the battery pack is greater than a predetermined voltage difference threshold (such as 50mv);

Step S21, if the judgment result is no, update the equalization time of each battery cell in the battery pack to zero, and store it in the rewritable memory;

Step S22, if the judgment result is yes, then record the current voltage value of each battery cell in each battery pack, and calculate the difference with the lowest voltage value among them, to obtain the voltage between each battery cell and the lowest voltage value difference; according to the voltage difference of each battery cell, re-determine the equalization time corresponding to each battery cell; store the equalization time of each battery cell into a rewritable memory;

Wherein, according to the voltage difference of each battery cell, the step of re-determining the equalization time corresponding to each battery cell is specifically: obtaining the voltage difference of each battery cell according to the dynamic charging SOC-V curve of the battery cell The capacity difference corresponding to the value is calculated according to the capacity difference and a predetermined equalization current value to obtain the equalization time. An example is used for illustration below. As shown in FIG. 3 , a dynamic charging SOC-V curve is shown, which is obtained after testing at an ambient temperature of 25 degrees Celsius and charging with a charging current of 1C. In this embodiment, when the current voltage of one of the battery packs reaches the battery cell protection point voltage (for example, 4.2V), the current voltage value of one of the battery cells is 4.1V, and it is assumed that the current battery cell is the lowest The voltage value of the battery is 3.6V, so the difference between the two is 0.5V. According to the dynamic charging SOC-V curve, it can be known that the corresponding capacity difference is about 65%. Calculate the capacity difference and the balance current (such as dividing ), the equalization time of the battery cell can be obtained, and the equalization time of other battery cells can be obtained by the same method.

At the same time, when the equalization time of each battery cell is stored in a rewritable memory, the verification information can be written at the same time.

As shown in Figure 4, it is a more detailed flow diagram of an embodiment of step S14 in Figure 1; the step S14 further includes:

Step S30, read out the equalization time of each battery cell from the erasable memory;

Step S32, judging whether the equalization time is zero, if the judging result is no, start the battery equalization for the corresponding battery cell;

Step S34, regularly perform decremental update processing on the equalization time of each battery cell (for example, update once every 3 seconds, that is, subtract 3 seconds from the current equalization time to obtain the latest equalization time), and update the latest The equalization time replaces the corresponding equalization time of the battery cells in the erasable memory;

Step S36 , repeating the above steps, if it is determined that the equalization time of a certain battery cell is zero, stop performing battery equalization on the corresponding battery cell.

In order to facilitate the understanding of the working principle of the present invention, a more detailed flow diagram of the present invention applied to an electric vehicle in a charging state is shown in FIG. 5 ;

In Fig. 5, when the car enters the charging process, it is first judged in step S51 whether the voltage of any battery cell has reached the charging protection point voltage (for example, 4.2V); if the judgment result is yes, then enter step S52; Otherwise, enter step S56;

In step S52, it is judged whether the highest and lowest voltages of the battery cells in the battery pack are in the normal range, and the voltage acquisition line is not disconnected, if the judgment result is no, then in step S54, stop the equalization process; if it is judged If the result is yes, then enter step S59;

In step S59, it is judged whether the maximum voltage difference of each battery cell in the battery pack is greater than a predetermined voltage difference threshold (such as 50mv), wherein specifically the predetermined voltage difference threshold can be set as required;

If the judgment result is no, in step S60, the equalization time of each battery cell in the battery pack is updated to zero, and stored in a rewritable memory (such as EEPROM), and then go to step S57;

If the judgment result is yes, then in step S53, record the current voltage value of each battery cell of all battery packs, and calculate the difference with the lowest voltage, and obtain the latest equalization time of each battery cell through conversion;

In step S55, record the latest equalization time of each battery cell in the rewritable memory mentioned in step S60, and write the verification information;

In step S56, it is judged whether the equalization time of each battery cell is 0, if the result of the judgment is yes, then in step S57, stop equalizing the corresponding battery cell, that is, give the slave who controls the battery cell The board sends an equalization stop command; if the judgment result is no, proceed to step S58;

In step S58, it is judged whether the equalization condition is currently met, for example, whether the current battery temperature is within a predetermined range, if not, then in step S57, stop equalizing the corresponding battery cell; if yes, in step S59, Equalize the corresponding battery cell, that is, send an equalization start command to the slave board that controls the battery cell, and at the same time update the equalization time corresponding to the battery cell regularly, and write the latest equalization time into the available corresponding location in the flash memory.

FIG. 6 shows a more detailed flow diagram of the present invention applied to electric vehicles in a discharge state;

In Figure 6, when the car enters the discharge process, first read the information in the erasable memory (EEPROM) in step S61, such as position information, verification information, etc.;

In step S62, the verification information is judged to determine whether the verification information is normal;

If the judgment result in step S62 is yes, then in step S64, read the equalization time corresponding to each battery cell in the battery pack; if the judgment result in step S62 is no, then stop the equalization process in step S63;

In step S65, it is judged whether the equalization time of each battery cell is 0, if the judgment result is yes, then in step S66, stop equalizing the corresponding battery cell, that is, give the slaves who control the battery cell The board sends an equalization stop command; if the judgment result is negative, proceed to step S67;

In step S67, it is judged whether the equalization condition is currently met, for example, whether the current battery temperature is within a predetermined range, if not, then in step S66, stop equalizing the corresponding battery cell; To perform equalization, that is, to send an equalization start command to the slave board controlling the battery cell, and at the same time regularly update the equalization time corresponding to the battery cell, and write the latest equalization time into the erasable Write to the corresponding location of the memory, and write the verification information at the same time.

1 to 6, the electric vehicle power battery balance control method provided by the embodiment of the present invention can use the two time periods when the battery cell voltage does not reach the battery protection during charging and when discharging to perform equalization. Cars need to be charged almost every day. When charging, it is judged whether equalization operation is required, so that the number of times to enter the equalization judgment is relatively large, and the battery can be balanced in time;

At the same time, judging whether equalization operation is required during charging does not need to consider the battery rest time; and because the charging current is controllable, according to the dynamic charging SOC-V curve of the battery cell, the equalization time can be obtained more accurately;

In addition, equalization is performed before charging reaches the battery protection point voltage and during discharge. Through long equalization time, small current (equalization current = capacity difference / equalization time) equalization function can be realized, which effectively reduces hardware costs and reduces heat dissipation of hardware circuits. Risk, and small current balance has a certain protective effect on battery life.

As shown in FIG. 7 , it shows a schematic circuit topology diagram of an embodiment of a battery management system provided by the present invention; as shown in FIG. 7 , the battery management system of the embodiment of the present invention includes a control board 1, from the board 2 and the plurality of battery packs 3 . Wherein, each battery pack includes a plurality of battery cells 30, and the collection slave board 2 includes a plurality of battery management units 20, and each battery management unit 20 corresponds to a battery cell 30, and is used to collect each Battery parameters of the battery cell, such as battery voltage, temperature, etc. The control board 1 is connected to multiple acquisition slave boards 2 through the CAN bus, and the control board 1 includes a battery electronic control unit 10 and a rewritable storage unit 12 . The rewritable memory 12 is used to store the equalization time of each battery cell; the battery electronic control unit 10 is used to collect the battery parameters of the battery cells 30 from the battery management unit 20 in the board, and generate battery cells according to the battery parameters A body balance control instruction, including calculating and obtaining the equalization time of each battery cell, and controlling the battery management unit 20 to start or stop the equalization process for the corresponding battery cell; wherein, the balance control instruction may include a balance stop command and a balance start Order. For the specific generation of the equalization control command for the battery cell, and the process of controlling the equalization of the battery cell on or off, please refer to the introduction to FIGS. 1 to 6 above.

FIG. 8 is a schematic structural diagram of an embodiment of an equalization circuit adopted in the battery management unit of FIG. 7 . Wherein, the circuit for performing equalization includes a MOS switch tube 200 and a balance resistor R1; the on-off of the MOS switch tube can be controlled by the balance control command, when the balance control command is a balance start command, the MOS switch tube 200 is connected, and the balance resistance There is a battery passing through R1, which can realize the balancing effect on the battery cells 30; when the balancing control command is a balancing stop command, the MOS switch tube 200 is disconnected, and no battery passes through the balancing resistor R1, which can realize the balancing effect on the battery cells 30. Stop equalization.

Implementing the embodiment of the present invention has the following beneficial effects:

The electric vehicle power battery balance control method provided by the embodiment of the present invention can use the two time periods when the battery cell voltage does not reach the battery protection and discharge when charging to perform balance. Since electric vehicles need to be charged almost every day, during charging It is necessary to judge whether the equalization operation is needed, so that the number of times to enter the equalization judgment is relatively large, and the battery can be balanced in time;

At the same time, judging whether equalization operation is required during charging does not need to consider the battery rest time; and because the charging current is controllable, according to the dynamic charging SOC-V curve of the battery cell, the equalization time can be obtained more accurately;

In addition, equalization is performed before charging reaches the battery protection point voltage and during discharge. Through long equalization time, small current (equalization current = capacity difference / equalization time) equalization function can be realized, which effectively reduces hardware costs and reduces heat dissipation of hardware circuits. Risk, and small current balance has a certain protective effect on battery life.

The invention disclosed above is only a preferred embodiment of the present invention, which certainly cannot limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (8)

1. a kind of electric automobile power battery balance control method, it is characterised in that comprise the following steps：

When electric automobile is in charged state or discharge condition, judge whether its battery pack needs to carry out equilibrium treatment；

When needing to carry out equilibrium treatment, it is determined that needing to carry out each battery cell of equilibrium treatment in all battery packs；

The time for balance for needing to carry out each battery cell of equilibrium treatment is read from the memory of the time for balance of each battery cell that is stored with, and equilibrium treatment is carried out with corresponding time for balance to each battery cell.

2. electric automobile power battery balance control method as claimed in claim 1, it is characterised in that described when electric automobile is in charged state or discharge condition, judges whether its battery pack needs the step of carrying out equilibrium treatment to further include：

Electric automobile be in charged state when, when all battery packs current voltage be not up to battery cell protection voltage, and when in the battery pack the corresponding time for balance of any battery monomer be more than zero, it is determined that battery pack needs to carry out equilibrium treatment；

When electric automobile is in discharge condition, when the corresponding time for balance of any battery monomer is more than zero in the battery pack, it is determined that battery pack needs to carry out equilibrium treatment.

3. electric automobile power battery balance control method as claimed in claim 1, it is characterised in that further include step：

When electric automobile is in and fills state; when the current voltage of any battery group has reached the protection voltage of battery cell; the time for balance of each battery cell of battery pack is then redefined, and the time for balance of each battery cell is stored in scratch pad memory.

4. electric automobile power battery balance control method as claimed in claim 1, it is characterised in that include the step of the time for balance of each battery cell for redefining battery pack：

Judge the maximum voltage difference of each battery cell in battery pack whether more than a predetermined voltage difference threshold value；

If it is judged that being no, then the time for balance of each battery cell in the battery pack is updated to zero, and be stored in scratch pad memory；

If it is judged that be yes, then the current voltage value of each battery cell of each battery pack is recorded, and carry out with wherein minimum voltage value asking poor respectively, obtain the voltage difference between each battery cell and minimum voltage value；According to the voltage difference of each battery cell, the corresponding time for balance of each battery cell is redefined；The time for balance of each battery cell is stored in scratch pad memory.

5. electric automobile power battery balance control method as claimed in claim 4, it is characterised in that according to the voltage difference of each battery cell, is specially the step of redefine each battery cell corresponding time for balance：

The corresponding capacity difference of each battery cell voltage difference is obtained according to battery core dynamic charging SOC-V curves, is carried out calculating acquisition time for balance according to the capacity difference and predetermined euqalizing current value.

6. electric automobile power battery balance control method as claimed in claim 5, it is characterised in that further include the step that the time for balance of each battery cell is stored in scratch pad memory：

Check information is write in the scratch pad memory.

7. the electric automobile power battery balance control method as described in claim any one of 1-6, it is characterized in that, the step of reading the time for balance for needing to carry out each battery cell of equilibrium treatment in the memory of the time for balance from each battery cell that is stored with, and carry out equilibrium treatment with corresponding time for balance to each battery cell further includes：

From the scratch pad memory, the time for balance of each battery cell is read；

Judge whether the time for balance is zero, if it is judged that being no, then start to the battery balanced of respective battery monomer；

Timing carries out renewal treatment of successively decreasing to the time for balance of each battery cell, by renewal after newest time for balance replace the corresponding time for balance of battery cell described in the scratch pad memory；

Repeat the above steps, if the time for balance for determining a certain battery cell is zero, stop carrying out corresponding battery cell battery balanced.

8. a kind of battery management system, it is characterised in that including：

Battery pack, the battery pack includes multiple battery cells；

Multiple battery management units, each described battery management unit is corresponding with a battery cell respectively, the battery parameter for gathering each cell；And

Scratch pad memory, the time for balance for storing each battery cell；

Battery control unit, is connected with the multiple battery management unit, the battery parameter for collecting the battery cell, and the Balance route order of the cell is generated according to the battery parameter,

Wherein, according to the battery equalization method generation Balance route instruction as described in any one of claim 1 to 7, the battery management unit carries out equilibrium to the battery electric control unit according to the Balance route order to the battery cell.