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CN-113540583-B - Method for operating a battery pack and battery pack

CN113540583BCN 113540583 BCN113540583 BCN 113540583BCN-113540583-B

Abstract

The invention relates to a method for operating a battery pack (10) having a plurality of battery cells (2) connected in series to one another, a plurality of controllable switches (4, 6), and a control system (30), wherein the switches (4, 6) are used for activating and deactivating the battery cells (2) during a charging or discharging operation of the battery pack (10), and wherein the control system (30) is used for monitoring the battery cells (2) and for controlling the switches (4, 6). The invention also relates to a battery pack (10) arranged for performing the method according to the invention.

Inventors

  • M. Clende
  • J. SCHNEIDER
  • L. shandler
  • O. keus

Assignees

  • 罗伯特·博世有限公司

Dates

Publication Date
20260505
Application Date
20210415
Priority Date
20200415

Claims (9)

  1. 1. A method for operating a battery pack (10) having a plurality of battery cells (2) connected to one another in series, a plurality of controllable switches (4, 6) and a management system (30), wherein the controllable switches (4, 6) are used for activating and deactivating the battery cells (2) during a charging or discharging operation of the battery pack (10), and wherein the management system (30) is used for monitoring the battery cells (2) and for controlling the switches (4, 6), The method comprises the following steps: a) Determining an upper set voltage limit value of the battery (10) and a lower set voltage limit value of the battery (10), a maximum charging current of the battery (10) and a discharging current of the battery (10), an upper cell voltage limit value of the battery cells (2) and a lower cell voltage limit value of the battery cells (2), a maximum desired state of charge deviation between the battery cells (2) and a maximum desired charge throughput deviation between the battery cells (2); b) Ascertaining a pack current (IP) of the battery pack (10), a pack voltage (UP) of the battery pack (10), a state of charge deviation of the respective battery cell (2) and a charge throughput deviation of the respective battery cell (2); c) Checking whether a numerical group current (IP) is less than a predetermined threshold value, whether the group voltage (UP) is within the upper and lower group voltage limits, whether a charge state deviation of the respective cell (2) is below a maximum desired charge state deviation and whether a charge throughput deviation of the respective cell (2) is below a maximum desired charge throughput deviation; d) Normalizing the state of charge deviation of the respective battery cell (2) if one of the parameters checked in step c) does not meet the respective precondition, wherein if all the parameters checked in step c) meet the respective precondition, no switching process is performed; e) -showing in a first coordinate system (40) a normalized state of charge deviation of the respective battery cell (2) and a ascertained throughput deviation of the respective battery cell (2), wherein the normalized state of charge deviation of the battery cell (2) is plotted on a first coordinate axis (41) of the first coordinate system (40), whereas the throughput deviation of the battery cell (2) is plotted on a second coordinate axis (42) of the first coordinate system (40), and a motion vector is formed for each battery cell (2); f) Converting motion vectors of the respective battery cells (2) into a second coordinate system (50), wherein a discharge coordinate axis (51) of the second coordinate system (50) represents a first direction of motion of the battery cells (2) in the second coordinate system (50) during a discharge operation of the battery pack (10), and a charge coordinate axis (52) of the second coordinate system (50) represents a second direction of motion of the battery cells (2) in the second coordinate system (50) during a charge operation of the battery pack (10); g) An activation mode for activating or deactivating the battery cells (2) during a charging or discharging operation of the battery pack (10) is ascertained.
  2. 2. Method according to claim 1, characterized in that the parameters to be determined in step a) are dynamically predefined during the charging or discharging operation of the battery (10).
  3. 3. Method according to claim 1 or 2, characterized in that step g) comprises the following sub-steps in a discharging operation of the battery (10): ga) classifying the battery cells (2) along a discharge coordinate axis (51) of the second coordinate system (50); gb) ascertaining a number l of active battery cells (2) for adhering to the upper set of voltage limits, wherein l is a natural number; gc) ascertaining an activation mode for the battery pack (10); gd) applying said activation mode.
  4. 4. Method according to claim 1 or 2, characterized in that step g) comprises the following sub-steps in the charging operation of the battery (10): ge) classifying the battery cells (2) along a charging coordinate axis (52) of the second coordinate system (50); gf) ascertaining a first number m of active battery cells (2) for adhering to the upper set of voltage limits, wherein m is a natural number; gg) a first current limit value for the first number m of active battery cells (2), Ascertaining a second current limit value for a second number m+1 of active cells (2), Ascertaining a third current limit value for a third number m-1 of active battery cells (2); gh) ascertaining a maximum power by means of the ascertained first, second and third current limit values; gi) selecting one number of active battery cells (2) from the first, second and third numbers m, m+1, m-1 of active battery cells (2) for said maximum power; gj) ascertaining an activation mode for the battery pack (10); gk) to use the activation mode.
  5. 5. A battery pack (10) arranged for performing the method according to any of claims 1 to 4.
  6. 6. The battery (10) according to claim 5, characterized in that a first switch (4) and a second switch (6) are assigned to each of the battery cells (2), wherein the first switch (4) is connected in series with the associated battery cell (2), wherein the second switch (6) is connected in parallel with a series circuit configured by the first switch (4) and the associated battery cell (2).
  7. 7. The battery (10) according to claim 5 or 6, characterized in that the battery (10) comprises a sensor for measuring a group current (IP) flowing through the battery (10).
  8. 8. The battery pack (10) according to claim 5 or 6, characterized in that the battery pack (10) comprises a sensor for measuring the cell voltage (UZ) applied to the individual cells (2) of the battery pack (10) and for measuring the pack voltage (UP) applied to the battery pack (10).
  9. 9. A vehicle established for performing the method according to any one of claims 1 to 4 and/or comprising the battery pack (10) according to any one of claims 5 to 8.

Description

Method for operating a battery pack and battery pack Technical Field The invention relates to a method for operating a battery pack having a plurality of battery cells connected in series to one another, a plurality of controllable switches and a control system, wherein the switches are used for activating and deactivating the battery cells during a charging or discharging operation of the battery pack, and wherein the control system is used for monitoring the battery cells and for controlling the switches. The invention further relates to a battery pack which is designed to carry out the method according to the invention. Background In a battery pack for a motor vehicle, a plurality of battery cells are connected in series in order to achieve a higher voltage level. This is necessary in order to achieve the power levels of tens to hundreds of kw necessary in a motor vehicle, since the maximum possible current is limited by the impedance losses. The maximum achievable power is therefore limited not only by the voltage level (Spannungslage) of the battery but also by the maximum possible current. For example, in the case of the system of 48V, the voltage level is selected such that it remains below the 60V limit value for the high-voltage on-board system. Therefore, its power is inherently limited to tens of kilowatts. The efficiency capability of the 48V system can be improved through the use of semiconductor technology that can conduct high currents. For this purpose, two switches are provided for each cell and one switch is connected in series with the cell and the other switch is connected in parallel with the cell. Thus, from a system perspective, each series-connected cell can be activated or bridged. Thus, the stack voltage (Packspannung) of the stack can be adjusted in stages. This allows more cells to be connected in series than would otherwise be the case in a 48V system, without exceeding the 60V-limit value in operation. If the voltage increases during regeneration or during charging operation, the individual cells are deactivated in order to comply with the voltage limit value. In the boost operation or the discharge operation, an additional battery cell is activated so as to maintain the system voltage at a high level, thereby enabling higher power. Document CN 105226744A discloses a method for an active monomer balancing system. A method and a circuit for adaptively charging a battery are known from the document US 2011/0285356 A1. Disclosure of Invention A method for operating a battery is presented. The battery pack comprises a plurality of battery cells connected in series with one another and a plurality of controllable switches for activating and deactivating the battery cells during a charging or discharging operation of the battery pack. Furthermore, the battery pack comprises a management system for monitoring the battery cells and for actuating the switches. By "battery cells connected in series with each other" is meant that the battery cells can be a plurality of battery cells connected in parallel in branches connected in series. The controllable switches of the battery are in particular semiconductor switches, such as for example MOSFETs or IGBTs. For example, a first switch and a second switch can be assigned to each battery cell. The first switch is connected in series with the associated battery cell, while the second switch is connected in parallel with a series circuit formed by the first switch and the associated battery cell. The battery cell can be provided with a first switch and a second switch, respectively. It is also conceivable that the controllable switches are integrated into a switching unit for actuation by the management system. In performing the method, an upper set voltage limit value of the battery pack and a lower set voltage limit value of the battery pack are first determined. Furthermore, a maximum charge current of the battery and a maximum discharge current of the battery are determined, which may depend on other variables, such as, for example, temperature or state of charge. In addition, an upper cell voltage limit value of the battery cell and a lower cell voltage limit value of the battery cell are determined. Furthermore, a maximum desired state of charge deviation between the battery cells is determined. Since the total power of the battery is limited by the weakest cell, an even distribution of the cells is equally desirable for aging. A maximum desired charge throughput offset between the cells is also determined. Since the aging of the cells is closely related to the throughput of charge, a uniform distribution of the throughput of charge to the cells is also desirable. Here, "charge throughput" refers to the amount of charge accumulated in the charging operation. The above-mentioned parameters to be determined are preferably dynamically predefined during the charging or discharging operation of the battery. Thus, for example, the stack tempera