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CN-115173511-B - Power battery equalization method and device

CN115173511BCN 115173511 BCN115173511 BCN 115173511BCN-115173511-B

Abstract

The invention belongs to the technical field of battery systems, and particularly relates to a power battery balancing method and device, which are used for solving the problems that when the battery capacity is relatively large and inconsistent, the terminal voltage of a battery with low capacity in a battery pack is possibly higher than that of other batteries during or after charging, and the service life of the battery is influenced easily due to overcharge. The invention adopts a two-stage balancing strategy, the balancing is divided into two stages, different strategies are adopted in different stages, the battery with low chargeable capacity of the monomer is discharged, and the balancing target is that all the batteries reach the full state at the same time. The invention completes the equalization of the battery, and keeps the voltage deviation of the lithium ion battery or the battery pack within the expected range, thereby ensuring that each single battery keeps the same state during normal use so as to avoid the occurrence of overcharge and overdischarge. The invention eliminates various inconsistencies generated by the batteries after being grouped and in the using process, and reduces the influence caused by the inconsistencies of the batteries.

Inventors

  • HE YUNFEI
  • HAI BIN
  • HU ZHANGFEI
  • LU FAYAN

Assignees

  • 奇瑞汽车股份有限公司

Dates

Publication Date
20260508
Application Date
20220704

Claims (8)

  1. 1.A power battery equalization method is characterized by comprising the following steps of, Discharging the battery with higher single battery SOC through the first-stage equalization to enable the SOCs of all the individual batteries to be consistent; Discharging the battery with low chargeable capacity of the single battery through the second stage of equalization, so that the chargeable capacities of all the individual batteries are kept consistent, and the equalization target is that all the batteries reach a full state at the same time; The first stage of equalization includes determining a maximum cell voltage MaxCellVolt and a minimum cell voltage MinCellVolt and calculating a voltage difference DeltaCellVolt = MaxCellVolt-MinCellVolt; After the voltage difference DeltaCellVolt is larger than the set first target voltage difference TARGETDELTAV1 and the phenomenon lasts for more than the set time Wait seconds, the first stage of equalization is performed; Detecting the difference value between the voltage of each single battery and the minimum voltage, and when the difference value is larger than a set second target voltage difference TARGETDELTAV, starting a detected single battery balancing instruction, or closing the detected single battery balancing instruction; BalCmd = ((CellVoltages-MinCellVolt) > TARGETDELTAV 2), where BalCmd is boolean; when BalCmd of all the single batteries are zero, setting a balance completion flag flgBalCompl to 1 to complete the balance of the first stage; The second-stage equalization comprises the steps that if the state is a static state, the first-stage equalization is closed, and the state of judging whether equalization is started or not is returned to the beginning; if the state of charge is the state of charge, the second stage of equalization is entered, and in the second stage, the battery voltage difference is already smaller than TARGETDELTAV < 2 >; The current is stable in the charging process, the information of the temperature and the voltage of the single battery terminal is added, the SOC of the single battery can be estimated according to the lookup table of the voltage of the dynamic current terminal, the SOC of the single battery is obtained according to the charging current curve calibrated offline, the chargeable capacity of the current single battery is calculated according to the SOC, and the discharging balance is carried out on the battery with smaller chargeable capacity.
  2. 2. A power cell equalization method as defined in claim 1, wherein, The battery equalization is divided into a battery standing state or a charging state, wherein the battery is only subjected to first-stage equalization when standing still, and the battery is sequentially subjected to first-stage equalization and second-stage equalization when in the charging state.
  3. 3. A power cell equalization method as defined in claim 1, wherein, In the static state or the charging state of the batteries, the maximum voltage difference and time between the batteries are used as the initial conditions of the first-stage equalization in the first-stage equalization, and the discharge equalization is carried out on the batteries with overlarge single voltage differences in the first-stage equalization so as to achieve the consistency of the SOC; in the charging state, the equalization in the second stage takes the chargeable capacity and the average chargeable difference value as equalization starting conditions, the single battery SOC is estimated by utilizing the single battery voltage and the battery pack SOC, the single chargeable capacity is calculated, and the predicted value is dynamically adjusted according to the repeated iterative process so as to achieve the consistency of the chargeable capacity.
  4. 4. A power cell equalization method as defined in claim 1, wherein, The battery SOC may be calculated according to a current integration method, an open circuit voltage method, a Kalman filtering method, or a neural network method.
  5. 5. A power battery balancing device is characterized by comprising, The first-stage equalization unit discharges the battery with higher monomer SOC to make the SOC of all individual batteries consistent; The second-stage balancing unit is used for keeping the chargeable capacity of all the individual batteries consistent by discharging the battery with low chargeable capacity of the single battery, so that the balancing target is that all the batteries reach a full state at the same time; The first stage equalization unit includes determining a maximum cell voltage MaxCellVolt and a minimum cell voltage MinCellVolt, and calculating a voltage difference DeltaCellVolt = MaxCellVolt-MinCellVolt; After the voltage difference DeltaCellVolt is larger than the set first target voltage difference TARGETDELTAV1 and the phenomenon lasts for more than the set time Wait seconds, the first stage of equalization is performed; Detecting the difference value between the voltage of each single battery and the minimum voltage, and when the difference value is larger than a set second target voltage difference TARGETDELTAV, starting a detected single battery balancing instruction, or closing the detected single battery balancing instruction; BalCmd = ((CellVoltages-MinCellVolt) > TARGETDELTAV 2), where BalCmd is boolean; when BalCmd of all the single batteries are zero, setting a balance completion flag flgBalCompl to 1 to complete the balance of the first stage; the second-stage equalization unit comprises a state that if the state is a static state, the first-stage equalization is closed and returns to a state of initially judging whether equalization is started or not; if the state of charge is the state of charge, the second stage of equalization is entered, and in the second stage, the battery voltage difference is already smaller than TARGETDELTAV < 2 >; The current is stable in the charging process, the information of the temperature and the voltage of the single battery terminal is added, the SOC of the single battery can be estimated according to the lookup table of the voltage of the dynamic current terminal, the SOC of the single battery is obtained according to the charging current curve calibrated offline, the chargeable capacity of the current single battery is calculated according to the SOC, and the discharging balance is carried out on the battery with smaller chargeable capacity.
  6. 6. The power cell equalization apparatus of claim 5, wherein, The battery equalization is divided into a battery standing state or a charging state, wherein the battery standing state only comprises a first-stage equalization unit, and the charging state comprises a first-stage equalization unit and a second-stage equalization unit.
  7. 7. The power cell equalization apparatus of claim 5, wherein, The first stage equalization unit takes the maximum voltage difference and time between the batteries as first stage equalization starting conditions in a static state or a charging state of the batteries, and performs discharge equalization on the batteries with overlarge single voltage differences at the stage so as to achieve consistent SOC; and the second-stage equalization unit is used for estimating the SOC of the single battery and calculating the chargeable capacity of the single battery by using the single voltage and the SOC of the battery pack in a charging state and taking the chargeable capacity and the average chargeable difference value as equalization starting conditions, and dynamically adjusting the pre-estimated value according to a plurality of iterative processes so as to achieve the consistency of the chargeable capacity.
  8. 8. The power cell equalization apparatus of claim 5, wherein, The battery SOC may be calculated according to a current integration method, an open circuit voltage method, a Kalman filtering method, or a neural network method.

Description

Power battery equalization method and device Technical Field The invention relates to the technical field of battery systems, in particular to a power battery equalization method and device. Background In order to meet the power and voltage requirements of the electric automobile, the battery pack of the electric automobile needs a plurality of single batteries to be used in series-parallel connection. When the single battery leaves the factory, the parameters such as the capacity, the internal resistance and the like of the battery of the same model of the same batch of factory cannot be completely consistent due to the technical problems and the non-uniformity of materials. The inconsistency of the above battery parameters is further exacerbated by the effects of temperature, ventilation conditions, and self-discharge levels of the individual batteries in the battery pack during loading. Thereby causing a decrease in the capacity of the battery pack and reducing the service life of the battery pack. In the prior art, in order to reduce the influence caused by inconsistent battery packs, improve the performance of the battery packs, prolong the service lives of the battery packs, ensure the use safety and reliability of the batteries, and generally, the battery packs need to be managed in a balanced way. The current common equalization strategy adopts the cell terminal voltage as a reference constraint, and equalization is carried out when the difference value of the cell terminal voltages in the battery pack reaches a certain threshold value, and the equalization is finished when the difference value has no obvious difference. However, when the battery with low capacity in the battery pack is charged or after being charged, the terminal voltage may be higher than that of other batteries, and this method without considering the capacity of the battery will cause a further increase in the current chargeable capacity gap of the battery after the battery capacity is relatively inconsistent. In summary, when the capacities of the batteries in the prior art are not consistent, the terminal voltage of the battery with low capacity in the battery pack may be higher than that of other batteries during or after charging, and overcharge is easy to occur, which affects the service life of the battery. Disclosure of Invention The invention provides a power battery balancing method and a device, aiming at solving the problems that when the battery capacity is relatively large and inconsistent, the terminal voltage of a battery with low capacity in a battery pack is possibly higher than that of other batteries during or after charging, and the service life of the battery is influenced easily due to overcharge. The invention adopts a two-stage balancing strategy, the balancing is divided into two stages, and different strategies are adopted in different stages. Discharging the battery with low chargeable capacity, and balancing the battery to reach full state. A power battery equalization method includes, a step of, Discharging the battery with higher single battery SOC through the first-stage equalization to enable the SOCs of all the individual batteries to be consistent; And discharging the battery with low chargeable capacity of the single battery through the second stage of equalization, so that the chargeable capacities of all the individual batteries are kept consistent, and the equalization target is that all the batteries reach the full state at the same time. Furthermore, the battery equalization is divided into a battery standing state or a charging state, wherein the battery standing state is only subjected to first-stage equalization, and the charging state is sequentially subjected to first-stage equalization and second-stage equalization. Further, in the state of battery rest or charge, the first stage of equalization takes the maximum voltage difference and time between batteries as the initial conditions of the first stage of equalization, and the stage of discharge equalization is carried out on batteries with overlarge single voltage differences so as to achieve the consistency of SOC; in the charging state, the equalization in the second stage takes the chargeable capacity and the average chargeable difference value as equalization starting conditions, the single battery SOC is estimated by utilizing the single battery voltage and the battery pack SOC, the single chargeable capacity is calculated, and the predicted value is dynamically adjusted according to the repeated iterative process so as to achieve the consistency of the chargeable capacity. Further, the first stage of equalization includes determining a maximum cell voltage MaxCellVolt and a minimum cell voltage MinCellVolt and calculating a voltage difference DeltaCellVolt = MaxCellVolt-MinCellVolt; After the voltage difference DeltaCellVolt is larger than the set first target voltage difference TARGETDELTAV1 and the phenomenon lasts for more