Method for operating a battery pack and battery pack

Abstract

The present invention relates to a method for operating a battery pack (10) having a plurality of battery cells (2) connected in series, a plurality of operable switches (4, 6), and a management system (30), wherein the switches (4, 6) are used to activate and deactivate the battery cells (2) during charging or discharging operation of the battery pack (10), and wherein the management system (30) is used to monitor the battery cells (2) and to operate the switches (4, 6). The invention also relates to a battery pack (10) configured to perform the method according to the invention.

Description

Technical Field

[0001] The present invention relates to a method for operating a battery pack having a plurality of battery cells connected in series, a plurality of controllable switches, and a management system, wherein the switches are used to activate and deactivate the battery cells during charging or discharging operation of the battery pack, and wherein the management system is used to monitor the battery cells and to control the switches.

[0002] Furthermore, the present invention relates to a battery pack configured to perform the method according to the present invention. Background Technology

[0003] In battery packs used in motor vehicles, multiple battery cells are connected in series to achieve higher voltage levels. This is necessary to reach the power levels of tens to hundreds of kilowatts required in motor vehicles, as the maximum possible current is limited by impedance losses. Therefore, the maximum achievable power is limited not only by the voltage level of the battery pack but also by the maximum possible current.

[0004] For example, in a 48V system, the voltage level is chosen such that it is always kept below the 60V threshold for high-voltage vehicle electrical grids. Therefore, its power is inherently limited to tens of kilowatts. The efficiency of the 48V system can be improved by using semiconductor technology capable of conducting high currents. To this end, two switches are installed for each battery cell, more specifically, one switch is connected in series with the battery cell and the other in parallel. Therefore, from a system perspective, each battery cell connected in series can be activated or bridged. Thus, the pack voltage of the battery pack can be adjusted in stages.

[0005] This allows for more battery cells to be connected in series in a 48V system than in other cases, without exceeding the 60V threshold during operation. If the voltage rises during regeneration or charging operation, the individual battery cells are deactivated to adhere to the stated voltage threshold. During enhanced or discharging operation, additional battery cells are activated to maintain the system voltage at a high level, thereby enabling higher power output.

[0006] Document CN 105226744 A discloses a method for active single-unit balancing systems.

[0007] A method and circuit for adaptive charging of a battery are known from the document US 2011 / 0285356 A1. Summary of the Invention

[0008] A method for operating a battery pack is proposed herein. The battery pack includes a plurality of battery cells connected in series and a plurality of controllable switches for activating and deactivating the battery cells during charging or discharging operation of the battery pack. Furthermore, the battery pack includes a management system for monitoring the battery cells and for controlling the switches.

[0009] "A battery cell connected in series" means that the battery cell can be multiple battery cells connected in parallel in a branch connected in series.

[0010] The battery pack's controllable switches are, in particular, semiconductor switches, such as MOSFETs or IGBTs.

[0011] For example, a first switch and a second switch can be assigned to each battery cell. Here, the first switch is connected in series with the battery cell to which it belongs, while the second switch is connected in parallel with a series circuit constructed by the first switch and the battery cell to which it belongs.

[0012] Each battery cell can be equipped with a first switch and a second switch. Alternatively, the controllable switches can be aggregated into a switch unit for operation via a management system.

[0013] When performing the method, the upper voltage limit value and the lower voltage limit value of the battery pack are first determined. Furthermore, the maximum charging current and the maximum discharging current of the battery pack are determined, which may depend on other parameters, such as temperature or state of charge. Additionally, the upper voltage limit value and the lower voltage limit value of each individual battery cell are determined.

[0014] Furthermore, the maximum desired state-of-charge deviation among the individual battery cells is determined. Since the total power of the battery pack is limited by the weakest battery cell, uniform aging of the battery cells is also desirable.

[0015] The maximum expected charge throughput deviation between the individual battery cells is also determined. Since the aging of the battery cells is closely related to the charge throughput, a charge throughput evenly distributed across the battery cells is also desirable. Here, "charge throughput" refers to the amount of charge accumulated during charging operation.

[0016] Preferably, the parameters to be determined mentioned above are dynamically predetermined during the charging or discharging operation of the battery pack. Therefore, for example, the pack temperature or aging condition of the battery pack can also be taken into account.

[0017] Next, the group current of the battery pack, the group voltage of the battery pack, the state of charge deviation of the corresponding individual battery cells, and the charge throughput deviation of the corresponding individual battery cells are determined.

[0018] Next, check the parameters identified above. Check whether the group current is less than a predetermined threshold, whether the group voltage is within the upper and lower group voltage limits, whether the state-of-charge deviation of the corresponding battery cell is below the maximum expected state-of-charge deviation, and whether the charge throughput deviation of the corresponding battery cell is below the maximum expected charge throughput deviation.

[0019] Here, the upper and lower voltage thresholds have absolute priority; that is, switching must be performed to adhere to this absolute priority. Therefore, the objective of adhering to the voltage group within the upper and lower voltage thresholds determines how many battery cells are active in a given time step. Another objective, adhering to the corresponding battery cell's state-of-charge deviation and charge throughput deviation within the determined or pre-given thresholds, determines which battery cells are active in that time step.

[0020] If all the above conditions are met, the switching process is not performed. That is, the activation mode used for the previous time step of the battery pack remains active.

[0021] Here, the method can also amplify the dynamic relaxation of conditions to reduce the number of switching processes. For example, the number of past switching processes can be converted into a factor, which is limited to at least 1 and a maximum value, using an exponentially weighted moving average filter. This factor is then multiplied by threshold values ​​for state of charge deviation and charge throughput deviation to reduce the number of switching processes.

[0022] If one of the parameters checked mentioned above does not meet the corresponding preconditions, then a new activation mode for the battery pack is identified.

[0023] To this end, the deviation of the state of charge (SOC) of the corresponding individual battery cells from the average value is first standardized. Here, the SOC deviation is converted into charge units, such as ampere-hours or ampere-seconds, so that this parameter exists in the next step in the same unit as the charge throughput deviation and without distortion caused by units.

[0024] The standardized state-of-charge deviation of the corresponding battery cell is given by the following formula:

[0025] .

[0026] Here, i is a natural number. It is the standardized state-of-charge deviation of the i-th battery cell. It is the identified state-of-charge deviation of the i-th battery cell, and It is the capacitance of the i-th battery cell.

[0027] The standardized state-of-charge deviation and the identified charge throughput deviation of the corresponding battery cells are then shown in the first coordinate system. Here, the charge throughput deviation of the battery cells is plotted on the first axis of the first coordinate system, while the standardized state-of-charge deviation of the battery cells is plotted on the second axis of the first coordinate system.

[0028] Here, a motion vector is formed for each battery cell.

[0029] The motion vector of an active battery cell during charging is given by the following formula, where "active battery cell" refers to a battery cell that is activated or switched to an active state:

[0030] .

[0031] Here, i is a natural number. It is the motion vector of the i-th battery cell that should be switched to the active state during charging operation. It is the average capacitance of the individual cells in the battery pack. Let be the capacitance of the i-th battery cell, n be a natural number and the total number of battery cells in the battery pack, and c be a binary vector representing the active (c... j =1) or inactive (c j =0) Battery cell, j is a natural number. Here, "inactive battery cell" refers to a battery cell that has been deactivated or bridged.

[0032] With the help of and The motion vector of the active battery cell during charging operation is obtained:

[0033] .

[0034] Therefore, for z≠n and z≠0, the motion vector In the first coordinate system, it points in the direction of 45°.

[0035] It goes without saying that not all battery cells are deactivated simultaneously. If all battery cells are active, then no coordinate system transformation is performed, because the battery cells do not move relative to each other.

[0036] The motion vector of an inactive battery cell during charging operation is given by the following formula:

[0037] .

[0038] Here, It is the motion vector of the i-th battery cell during charging operation, and the i-th battery cell should be inactive.

[0039] With the help of and The motion vectors of inactive battery cells during charging operation are obtained:

[0040] .

[0041] Therefore, for z≠n and z≠0, the motion vector In the first coordinate system, it points in the direction of -45°.

[0042] During the discharge operation of the battery pack, the charge throughput deviation of the corresponding battery cell is zero. The state-of-charge deviation of the corresponding battery cell during discharge operation corresponds to the state-of-charge deviation of the corresponding battery cell during charging operation, but with the opposite sign.

[0043] The motion vector of a single active battery cell during discharge operation is approximately given by the following formula:

[0044] .

[0045] Here, It is the motion vector of the i-th battery cell during discharge operation, and the i-th battery cell should be switched to the active state.

[0046] Therefore, for z≠n and z≠0, the motion vector In the first coordinate system, it points in the direction of -90°.

[0047] The motion vector of an inactive battery cell during discharge operation is approximately given by the following formula:

[0048] .

[0049] Here, It is the motion vector of the i-th battery cell during discharge operation, and the i-th battery cell should be inactive.

[0050] Therefore, for z≠n and z≠0, the motion vector In the first coordinate system, it points in the direction of 90°.

[0051] The motion vectors of the corresponding battery cells are then transformed into a second coordinate system. This second coordinate system has a discharge axis and a charging axis. The discharge axis of the second coordinate system represents the first direction of motion of the battery cell during the discharge operation of the battery pack, while the charging axis of the second coordinate system represents the second direction of motion of the battery cell during the charging operation of the battery pack.

[0052] One possible transformation matrix is ​​given approximately by the following formula:

[0053] .

[0054] Subsequently, during the charging or discharging operation of the battery pack, the activation mode for activating or deactivating the battery cell is determined by means of the motion vector of the corresponding battery cell.

[0055] Preferably, when identifying the activation mode for activating or deactivating individual cells during the discharge operation of the battery pack, the individual cells are first classified along the first coordinate axis of the second coordinate system, preferably in ascending order.

[0056] Then, the number l active battery cells are identified to comply with the upper group voltage limit value. Here, l is a natural number. In terms of ascending classification, this refers to the first l battery cells in the classified vector, and thus the first time the upper group voltage limit value is exceeded for the l+1 active battery cells.

[0057] Next, the activation mode used for the battery pack was determined.

[0058] Then, the activation mode is applied.

[0059] Preferably, when identifying the activation mode for activating or deactivating individual battery cells during the charging operation of the battery pack, the individual battery cells are first classified along the charging coordinate axis of the second coordinate system, preferably in ascending order.

[0060] Then, the first m active battery cells are identified to comply with the upper voltage limit value. Here, m is a natural number. In terms of ascending classification, this refers to the first m battery cells in the classified vector, and thus the first time the upper voltage limit value is exceeded for the m+1 active battery cells.

[0061] The first current limit value for the battery cells used in the activity of the first number m is then determined. Here, a feasible solution due to the individual performance of the battery cells is to either connect an additional battery cell and reduce the current for this purpose, thereby complying with all operating limits, or to deactivate another battery cell, thereby increasing the current accordingly, thus achieving higher power.

[0062] Therefore, the second current limit value for the battery cells used for the second number of m+1 activities and the third current limit value for the battery cells used for the third number of m-1 activities are determined simultaneously or thereafter. If m equals the total number n of battery cells connected in series in the battery pack, then the calculation step for the second current limit value of the battery cells used for the second number of m+1 activities is cancelled. Here, the current and voltage limit values ​​of the battery cells and the group voltage limit value of the battery pack are taken into account.

[0063] The maximum power was then determined using the identified first, second, and third current limits.

[0064] Subsequently, a number of active battery cells are selected from the first number m, the second number m+1, and the third number m-1 for the maximum power.

[0065] Next, the activation mode used for the battery pack was determined.

[0066] Then apply the activation mode.

[0067] Furthermore, a battery pack is proposed, which is configured to perform the method according to the invention.

[0068] Preferably, each battery cell is equipped with a first switch and a second switch. Here, the first switch is connected in series with its corresponding battery cell, while the second switch is connected in parallel with a series circuit constructed by the first switch and its corresponding battery cell.

[0069] Preferably, each battery cell is equipped with a first switch and a second switch. Here, the first switch is connected in series with the battery cell to which it belongs, while the second switch is connected in parallel with a series circuit constructed by the first switch and the battery cell to which it belongs.

[0070] Preferably, the battery pack includes a sensor for measuring the pack current flowing through it. In this case, the individual cell current flowing through each battery cell can be determined by means of an activation mode. Alternatively, the battery pack may include sensors for measuring both individual cell current and the pack current.

[0071] Preferably, the battery pack includes a sensor for measuring the individual cell voltage applied to each cell of the battery pack and for measuring the pack voltage applied to the battery pack.

[0072] A vehicle is also proposed, which is configured to perform the method according to the invention and / or include a battery pack according to the invention.

[0073] This invention proposes a rule-based method that can be implemented effectively.

[0074] The battery pack's group voltage limit is maintained as high as possible using the method according to the invention, so as to minimize current and thus losses and aging effects. If individual battery cells should not be active, it is preferable to deactivate such cells, thereby simultaneously reducing the state-of-charge deviation and charge throughput deviation of all battery cells in the battery pack.

[0075] This significantly improves the efficiency of batteries in a 48V vehicle electrical network. Furthermore, it eliminates the need for circuitry for balancing inactive or active cells, a process required in conventional battery packs to equalize the state of charge of series-connected battery cells. In high-voltage battery systems, this invention can be used to limit the voltage range of the vehicle electrical network, thereby improving the cost and efficiency of electric drive components.

[0076] Furthermore, the method according to the invention can be performed with different initial values ​​for the state of charge and capacitance of individual battery cells. Additionally, if necessary, other parameters such as cell temperature can be extended by adding additional dimensions to the coordinate system. Attached Figure Description

[0077] Embodiments of the invention will be explained in detail with the aid of the accompanying drawings and the following description. Wherein are shown:

[0078] Figure 1 The first flowchart of the method during the discharge operation of the battery pack is shown.

[0079] Figure 2 A second flowchart of the method during the charging operation of the battery pack is shown.

[0080] Figure 3 A schematic diagram of the first and second coordinate systems is shown, and

[0081] Figure 4 A schematic diagram of a battery pack set up to perform the method is shown. Detailed Implementation

[0082] In the following description of embodiments of the invention, the same or similar elements are designated by the same reference numerals, and in some cases these elements are not described repeatedly. The accompanying drawings are merely schematic illustrations of the subject matter of the invention.

[0083] Figure 1 A first flowchart 100 of the method according to the invention is shown during the discharge operation of the battery pack 10 (see [link]). Figure 4 ).

[0084] Here, in the first step 101, the upper voltage limit value and the lower voltage limit value of the battery pack 10 are determined. Furthermore, the maximum charging current and the maximum discharging current of the battery pack 10 are determined. Additionally, the upper voltage limit value of the individual battery cell 2 is determined (see...). Figure 4 ) and the lower single-cell voltage limit value of the battery cell 2.

[0085] Furthermore, in the first step 101, the maximum expected state of charge deviation between the battery cells 2 and the maximum expected charge throughput deviation between the battery cells 2 are determined. Here, charge throughput is understood as the amount of charge accumulated during charging operation.

[0086] Preferably, the parameters to be determined mentioned above are given in advance dynamically. Thus, for example, the group temperature or aging state of the battery pack 10 can also be taken into account.

[0087] In the second step 102, the group current IP, the group voltage UP, the state of charge deviation of the corresponding battery cell 2, and the charge throughput deviation of the corresponding battery cell 2 are determined. The state of charge deviation and the charge throughput deviation of the corresponding battery cell 2 can be determined, for example, by determining the individual current IZ of the corresponding battery cell 2.

[0088] In step 103, the parameters identified above are checked. The group current IP is checked to see if it is less than a predetermined threshold, if the group voltage UP is within the upper and lower group voltage limits, if the state of charge deviation of the corresponding battery cell 2 is below the maximum expected state of charge deviation, and if the charge throughput deviation of the corresponding battery cell 2 is below the maximum expected charge throughput deviation.

[0089] Here, the upper and lower voltage thresholds have absolute priority; that is, the upper and lower voltage thresholds must be switched to comply with this priority. Therefore, within the upper and lower voltage thresholds, the objective of maintaining the group voltage UP is determined by how many battery cells 2 are active in a given time step. Here, another objective, within the determined or pre-given thresholds, is to maintain the corresponding state of charge deviation and charge throughput deviation of the battery cells 2, thus determining which battery cells 2 are active in the given time step.

[0090] If all the mentioned conditions are met, the switching process is not performed. That is, the activation mode for the previous time step of the battery pack 10 remains active.

[0091] Here, the method can also amplify the dynamic relaxation of the conditions in order to reduce the number of switching processes.

[0092] If one of the parameters checked mentioned above does not meet the corresponding preconditions, a new activation mode for the battery pack 10 is identified.

[0093] Therefore, in step 104, the deviation of the state of charge of the corresponding battery cell 2 from the average value is standardized. Here, the state of charge deviation is converted into charge units, such as ampere-hours or ampere-seconds, so that this parameter exists in the next step in the same unit as the charge throughput deviation and without distortion caused by units.

[0094] In step 5, 105, in the first coordinate system 40 (see...) Figure 3 The diagram shows the standardized state-of-charge deviation of the corresponding battery cell 2 and the identified charge throughput deviation of the corresponding battery cell 2. Here, on the first coordinate axis 41 of the first coordinate system 40 (see...) Figure 3 The charge throughput deviation of battery cell 2 is plotted on the first coordinate system 40, while on the second coordinate axis 42 (see...) Figure 3 The standardized state of charge deviation of battery cell 2 is then plotted on the top.

[0095] Here, a motion vector is formed for each battery cell 2.

[0096] In step 6, 106, the motion vector of the corresponding battery cell 2 is transformed to the second coordinate system 50 (see...). Figure 3 In this context, the second coordinate system 50 has a discharge coordinate axis 51 (see...). Figure 3 The second coordinate system 50 has a discharge coordinate axis 51, which represents the first direction of movement of the battery cell 2 in the second coordinate system 50 during the discharge operation of the battery pack 10, and a charging coordinate axis 52 (see [reference]). Figure 3 In the charging operation of battery pack 10, the second direction of movement of battery cell 2 is represented in the second coordinate system 50.

[0097] In step 107, it is checked that the battery pack 10 is in discharge operation.

[0098] Subsequently, the activation mode is determined based on the motion vector of the corresponding battery cell 2, so as to activate or deactivate the battery cell 2 during the discharge operation of the battery pack 10.

[0099] Here, in the eighth step 108, the battery cells 2 are classified along the discharge coordinate axis 51 of the second coordinate system 50.

[0100] In step 109, the number of active battery cells 2, i.e., l, is identified to comply with the upper group voltage limit value. Here, l is a natural number.

[0101] Subsequently, in step 110, the activation mode for the battery pack 10 is determined.

[0102] In step 111, the activation mode is applied.

[0103] Figure 2 A second flowchart 200 of the charging operation of the battery pack 10 according to the method of the present invention is shown.

[0104] Here, the first six steps 201 to 206 correspond to the first six steps 101 to 106, which were previously... Figure 1 The implementation methods are described.

[0105] Here, in the first step 201, the upper voltage limit value and the lower voltage limit value of the battery pack 10 are determined. Furthermore, the maximum charging current and the maximum discharging current of the battery pack 10 are determined. Additionally, the upper voltage limit value and the lower voltage limit value of the individual battery cell 2 are determined.

[0106] Furthermore, in the first step 201, the maximum expected state of charge deviation between the battery cells 2 and the maximum expected charge throughput deviation between the battery cells 2 are determined. Here, charge throughput is understood as the amount of charge accumulated during charging operation.

[0107] Preferably, the parameters to be determined mentioned above are given in advance dynamically. Thus, for example, the group temperature or aging state of the battery pack 10 can also be taken into account.

[0108] In the second step 202, the group current IP, the group voltage UP, the state of charge deviation of the corresponding battery cell 2, and the charge throughput deviation of the corresponding battery cell 2 are determined. The state of charge deviation and the charge throughput deviation of the corresponding battery cell 2 can be determined, for example, by determining the individual current IZ of the corresponding battery cell 2.

[0109] In the third step 203, the parameters identified above are checked. This includes checking whether the group current IP is less than a predetermined threshold, whether the group voltage UP is within the upper and lower group voltage limits, whether the state-of-charge deviation of the corresponding battery cell 2 is below the maximum expected state-of-charge deviation, and whether the charge throughput deviation of the corresponding battery cell 2 is below the maximum expected charge throughput deviation.

[0110] If all the above conditions are met, the switching process is not performed. That is, the activation mode for the previous time step of the battery pack 10 remains active.

[0111] If one of the parameters checked mentioned above does not meet the corresponding preconditions, a new activation mode for the battery pack 10 is identified.

[0112] Therefore, in step 204, the deviation of the state of charge of the corresponding battery cell 2 from the average value is standardized. Here, the state of charge deviation is converted into charge units, such as ampere-hours or ampere-seconds, so that this parameter exists in the next step in the same unit as the charge throughput deviation and without distortion caused by units.

[0113] In the fifth step 205, the standardized state of charge deviation of the corresponding battery cell 2 and the identified charge throughput deviation of the corresponding battery cell 2 are shown in the first coordinate system 40. Here, the charge throughput deviation of the battery cell 2 is plotted on the first coordinate axis 41 of the first coordinate system 40, while the standardized state of charge deviation of the battery cell 2 is plotted on the second coordinate axis 42 of the first coordinate system 40.

[0114] Here, a motion vector is formed for each battery cell 2.

[0115] In step 206, the motion vector of the corresponding battery cell 2 is transformed into the second coordinate system 50. Here, the second coordinate system 50 has a discharge coordinate axis 51 and a charging coordinate axis 52. The discharge coordinate axis 51 of the second coordinate system 50 represents the first direction of motion of the battery cell 2 during the discharge operation of the battery pack 10, while the charging coordinate axis 52 of the second coordinate system 50 represents the second direction of motion of the battery cell 2 during the charging operation of the battery pack 10.

[0116] In step 207, it is checked that the battery pack 10 is in charging operation.

[0117] Subsequently, the activation mode used to activate or deactivate the battery cell 2 during the charging operation of the battery pack 10 is determined based on the motion vector of the corresponding battery cell 2.

[0118] Here, in the eighth step 208, the battery cells 2 are classified along the charging coordinate axis 52 of the second coordinate system 50.

[0119] In step 209, the first number m active battery cells 2 are identified to comply with the upper group voltage limit values. Here, m is a natural number.

[0120] In step 210, the first current limit value of the battery cell 2 used for the activity of the first number m is determined. Here, a feasible solution due to the individual performance of the battery cell 2 is that if an additional battery cell 2 is turned on and the current is reduced for this purpose, thereby complying with all operating limit values, or if another battery cell 2 is deactivated, thereby enabling a corresponding increase in current, higher power can be obtained.

[0121] Therefore, in step 210, the second current limit value for the battery cells 2 used for the second number m+1 activities and the third current limit value for the battery cells 2 used for the third number m-1 activities are also determined. If m is equal to the total number n of the battery cells 2 connected in series in the battery pack 10, then the step of calculating the second current limit value for the battery cells 2 used for the second number m+1 activities is cancelled. Here, the current and voltage limit values ​​of the battery cells 2 and the group voltage limit value of the battery pack 10 are taken into account.

[0122] In step 111, the maximum power is determined based on the identified first, second, and third current limit values.

[0123] In the twelfth step 212, a number of active battery cells 2 are selected from the first number m, the second number m+1, and the third number m-1 for the maximum power.

[0124] The activation mode for the battery pack 10 is then determined in step 13, 213.

[0125] In step 214, the activation mode is applied.

[0126] Figure 3 A schematic diagram of the first coordinate system 40 and the second coordinate system 50 is shown.

[0127] The first coordinate system 40 has a first coordinate axis 41 and a second coordinate axis 42. Here, the first coordinate axis 41 and the second coordinate axis 42 of the first coordinate system 40 are perpendicular to each other. The charge throughput deviation is plotted on the first coordinate axis 41 of the first coordinate system 40. The normalized state of charge deviation is plotted on the second coordinate axis 42 of the first coordinate system 40.

[0128] Here, the standardized state of charge deviation of the corresponding battery cell 2 and the identified charge throughput deviation of the corresponding battery cell 2 are shown in the first coordinate system 40.

[0129] Subsequently, a motion vector is formed for each battery cell 2.

[0130] The motion vector of the corresponding battery cell 2 is transformed into the second coordinate system 50. Here, the second coordinate system 50 has a discharge coordinate axis 51 and a charging coordinate axis 52. The discharge coordinate axis 51 of the second coordinate system 50 represents the first motion direction of the battery cell 2 during the discharge operation of the battery pack 10, while the charging coordinate axis 52 of the second coordinate system 50 represents the second motion direction of the battery cell 2 during the charging operation of the battery pack 10.

[0131] As described above, the discharge coordinate axis 51 of the second coordinate system 50 is perpendicular to the first coordinate axis 41 of the first coordinate system 40, while the angle between the charging coordinate axis 52 of the second coordinate system 50 and the first coordinate axis 41 of the first coordinate system 40 is 45°.

[0132] like Figure 3 As shown, the battery cell 2 always moves along the discharge axis 51 and the charging axis 52 of the second coordinate system 50. During the discharge operation of the battery pack 10, the battery cell 2 moves along the first direction 61 when it is active and along the second direction 62 when it is inactive. During the charging operation of the battery pack 10, the battery cell 2 moves along the third direction 63 when it is active and along the fourth direction 64 when it is inactive.

[0133] exist Figure 3 The first battery cell 21 and the second battery cell 22 are also shown.

[0134] During the discharge operation of the battery pack 10, the first battery cell 21 is preferably inactive, and thus moves upward toward the charging coordinate axis 52 of the second coordinate system 50. The second battery cell 22 is preferably switched to an active state, and thus moves downward toward the charging coordinate axis 52 of the second coordinate system 50.

[0135] During the charging operation of the battery pack 10, the first battery cell 21 is preferably active and the second cell 22 is preferably inactive, so that it moves toward the discharge coordinate axis 51 of the second coordinate system 50.

[0136] The activation mode for the battery pack 10 is determined based on the motion vector of the corresponding battery cell 2.

[0137] Figure 4 A schematic diagram of a battery pack 10 configured to perform the method is shown, which is particularly configured for use in electric vehicles. The battery pack 10 includes a plurality of battery cells 2 connected in series with each other.

[0138] "Battery cells 2 connected in series with each other" means that they can be multiple battery cells 2 connected in parallel in a series-connected branch.

[0139] Each battery cell 2 of the battery pack 10 has a negative terminal and a positive terminal. Each battery cell 2 provides a cell voltage UZ, which is applied between the negative terminal and the positive terminal of the battery cell 2.

[0140] The battery pack 10 also includes a negative electrode 11 and a positive electrode 12. A pack voltage UP is applied between the negative electrode 11 and the positive electrode 12.

[0141] The battery pack 10 also includes multiple controllable switches 4 and 6 for activating and deactivating individual battery cells 2 during charging or discharging operation of the battery pack 10.

[0142] like Figure 4 As shown, each battery cell 2 is assigned a first switch 4 and a second switch 6. Here, the first switch 4 is connected in series with its corresponding battery cell 2, while the second switch 6 is connected in parallel with the series circuit constructed by the first switch 4 and the corresponding battery cell 2.

[0143] The battery pack 10 also includes a sensor (not shown) for measuring the pack current IP flowing through the battery pack 10. In this case, the individual cell current IZ flowing through each battery cell 2 of the battery pack 10 can be determined according to the activation mode.

[0144] The battery pack 10 also has sensors (not shown) for measuring the individual cell voltage UZ of each battery cell 2. Each battery cell 2 in the battery pack 10 is assigned a sensor for measuring the individual cell voltage UZ. Furthermore, the battery pack 10 has a sensor for measuring the group voltage UP between electrodes 11 and 12.

[0145] Alternatively, the battery pack 10 may include sensors for measuring the individual cell current IZ and for measuring the pack current IP. In this case, a sensor for measuring the individual cell current IZ of the individual cell 2 can be assigned to each individual cell 2 of the battery pack 10.

[0146] The battery pack 10 also includes a management system 30, which monitors individual battery cells 2 and controls switches 4 and 6. The management system 30 is connected to sensors (not shown). During operation of the battery pack 10, measurements detected by the sensors are transmitted to the management system 30.

[0147] The management system 30 is also connected to the corresponding switches 4 and 6. The management system 30 can individually control each of the switches 4 and 6.

[0148] This invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, many variations are possible within the scope of the claims and are well understood by those skilled in the art.

Claims

1. A method for operating a battery pack (10) having a plurality of battery cells (2) connected in series, a plurality of controllable switches (4, 6) and a management system (30), wherein the controllable switches (4, 6) are used to activate and deactivate the battery cells (2) during charging or discharging operation of the battery pack (10), and wherein the management system (30) is used to monitor the battery cells (2) and to control the switches (4, 6). The method includes the following steps: a) Determine the upper voltage limit value and the lower voltage limit value of the battery pack (10), the maximum charging current and the discharge current of the battery pack (10), the upper voltage limit value and the lower voltage limit value of the battery cell (2), the maximum expected state of charge deviation between the battery cells (2), and the maximum expected charge throughput deviation between the battery cells (2); b) Determine the group current (IP) of the battery pack (10), the group voltage (UP) of the battery pack (10), the state of charge deviation of the corresponding battery cell (2) and the charge throughput deviation of the corresponding battery cell (2); c) Check whether the group current (IP) is less than a predetermined threshold, whether the group voltage (UP) is within the upper group voltage limit and the lower group voltage limit, whether the state of charge deviation of the corresponding battery cell (2) is lower than the maximum expected state of charge deviation, and whether the charge throughput deviation of the corresponding battery cell (2) is lower than the maximum expected charge throughput deviation. d) If one of the parameters checked in step c) does not meet the corresponding precondition, the state of charge deviation of the corresponding battery cell (2) is standardized, wherein if all the parameters checked in step c) meet the corresponding precondition, the switching process is not performed. e) The standardized state of charge deviation and the identified charge throughput deviation of the corresponding battery cell (2) are shown in the first coordinate system (40), wherein the standardized state of charge deviation of the battery cell (2) is plotted on the first coordinate axis (41) of the first coordinate system (40), and the charge throughput deviation of the battery cell (2) is plotted on the second coordinate axis (42) of the first coordinate system (40), and a motion vector is formed for each battery cell (2); f) Transform the motion vector of the corresponding battery cell (2) into the second coordinate system (50), wherein the discharge coordinate axis (51) of the second coordinate system (50) represents the first motion direction of the battery cell (2) in the second coordinate system (50) during the discharge operation of the battery pack (10), and the charging coordinate axis (52) of the second coordinate system (50) represents the second motion direction of the battery cell (2) in the second coordinate system (50) during the charging operation of the battery pack (10); g) Identify the activation mode used to activate or deactivate the individual battery cells (2) during the charging or discharging operation of the battery pack (10).

2. The method according to claim 1, characterized in that, During the charging or discharging operation of the battery pack (10), parameters to be determined in step a) are dynamically pre-given.

3. The method according to claim 1 or 2, characterized in that, Step g) includes the following sub-steps during the discharge operation of the battery pack (10): The battery cells (2) are classified along the discharge coordinate axis (51) of the second coordinate system (50); gb) Identify the number l active battery cells (2) to comply with the above group voltage limit values, where l is a natural number; gc) Determine the activation mode used for the battery pack (10); gd) uses the activation mode described above.

4. The method according to claim 1 or 2, characterized in that, Step g) includes the following sub-steps in the charging operation of the battery pack (10): The battery cells (2) are classified along the charging coordinate axis (52) of the second coordinate system (50); gf) Identify the first number m active battery cells (2) to comply with the above group voltage limit values; where m is a natural number; gg) Determine the first current limit value for the battery cell (2) used for the activities of the first number m. Determine the second current limit value for the battery cell (2) used for the second number m+1 activities. Determine the third current limit value of the battery cell (2) used for the third number m-1 activity; The maximum power is determined by using the identified first, second, and third current limit values; gi) selects one number of active battery cells (2) from the first, second and third numbers m, m+1, m-1 for the maximum power. gj) Determine the activation mode used for the battery pack (10); gk) uses the activation mode described above.

5. A battery pack (10) configured to perform the method according to any one of claims 1 to 4.

6. The battery pack (10) according to claim 5, characterized in that, Each of the battery cells (2) is assigned a first switch (4) and a second switch (6), wherein the first switch (4) is connected in series with the battery cell (2) to which it belongs, and wherein the second switch (6) is connected in parallel with a series circuit constructed by the first switch (4) and the battery cell (2) to which it belongs.

7. The battery pack (10) according to claim 5 or 6, characterized in that, The battery pack (10) includes a sensor for measuring the pack current (IP) flowing through the battery pack (10).

8. The battery pack (10) according to claim 5 or 6, characterized in that, The battery pack (10) includes sensors for measuring the individual cell voltage (UZ) applied to each individual cell (2) of the battery pack (10) and for measuring the group voltage (UP) applied to the battery pack (10).

9. A vehicle configured to perform the method according to any one of claims 1 to 4 and / or include a battery pack (10) according to any one of claims 5 to 8.

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