Balancing device for a battery module

Abstract

The balancing device (10) for a battery module (12) has a semiconductor switch (16) for each of the battery cells (14) of the battery module (12), a temperature sensor (18) for each semiconductor switch (16) and a control logic (20). Each semiconductor switch (16) can be connected to the associated battery cell (14) and is configured such that it can be switched on and off by a control signal provided by the control logic (20) for the semiconductor switch (16) in question in order to reduce an imbalance between charge states of the battery cells (14) of the battery module (12). Each temperature sensor (18) is designed to detect a first temperature signal (Temp1), which is representative of a temperature of the associated semiconductor switch (16). The control logic (20) is designed to control a switch position of the semiconductor switch (16) of a battery cell (14) to be balanced depending on a balancing request signal and the first temperature signal (Temp1).

Description

[0001] Description

[0002] Balancing device for a battery module

[0003] The invention relates to a balancing device for a battery module and a battery device.

[0004] In order to increase the maximum usable total energy of a battery module comprising multiple battery cells, the battery module can be symmetrical. A battery module is typically considered symmetrical when the charge level of all battery cells is identical at the time of a complete cycling cycle. During symmetry, the charge levels of the individual battery cells are equalized using a corresponding symmetry device. This is achieved, for example, by passive discharging, in which individual battery cells are discharged using a respective resistor connected in parallel to a respective energy storage cell, or by active charge transfer, in which charge is added to or removed from selected individual battery cells.

[0005] In today's battery management systems, which utilize passive balancing, the passive balancing current is limited to a specific value by external resistors. Balancing is controlled by dedicated battery management ICs. Due to the high power dissipation at the external resistors on the circuit board, these external resistors and the dedicated battery management ICs become very hot, so extensive mechanical measures using thermal underfill material must be implemented to minimize the temperature increase of the external resistors as much as possible. This requires significant thermal simulation effort and leads to limitations on the permissible balancing currents.

[0006] To solve this problem, initial approaches to limiting the balancing current based on pulse-width modulation already exist. In this case, the respective balancing current flowing through the resistor is pulse-width modulated. However, limiting the current increases the time required for balancing the respective battery cell. The object of the present invention is to create a balancing device that enables faster and / or more flexible and / or more reliable balancing of battery cells in a battery module.

[0007] The problem is solved by the features of the independent patent claims. Advantageous developments of the invention are characterized in the subclaims.

[0008] According to a first aspect, the above-mentioned object is achieved by a balancing device for a battery module. The battery module comprises a plurality of battery cells connected in series. The battery module can be a purely logical unit comprising several battery cells or a physical unit comprising several battery cells and separated from other battery modules, for example, by a separate housing and / or a common circuitry of the battery cells.

[0009] The symmetry device comprises a semiconductor switch for each of the battery cells of the battery module, a temperature sensor for each semiconductor switch, and control logic.

[0010] In this case, the respective semiconductor switch can be connected to the associated battery cell in such a way that it is connected in parallel with the associated battery cell. The respective semiconductor switch has a control terminal for receiving a control signal provided by the control logic for the semiconductor switch for controlling a switch position of the semiconductor switch.

[0011] The semiconductor switch comprises, for example, a switching transistor and a driver stage. The switching transistor comprises, for example, a field-effect transistor (FET). The switching transistor has an internal resistance, in particular a parasitic internal resistance, which limits the compensating current flowing through the switching transistor.

[0012] The respective temperature sensor is designed to detect a first temperature signal that is representative of a temperature of the associated semiconductor switch and to forward the first temperature signal to the control logic.

[0013] The control logic is configured to receive a symmetry request signal for a respective battery cell to be balanced from a control unit, for example, a battery management controller. Furthermore, the control logic is configured to control a switch position of the semiconductor switch of the battery cell to be balanced depending on the symmetry request signal and the first temperature signal.

[0014] The control logic can be formed by a hardware and / or software module.

[0015] The balancing of the battery cells is preferably done without external resistors. The balancing current that discharges the battery cells is diverted via the transistors.

[0016] The described balancing device has the advantage that thermal management and thermal protection can be relocated to a semiconductor chip for battery management, which includes the semiconductor switches. Virtually unlimited compensating currents can flow. The control logic is designed to limit the compensating current by appropriately controlling the semiconductor switch, taking into account, in particular, the local temperature rise of the integrated semiconductor switches, in particular the switching transistors. Advantageously, the respective integrated temperature control with the temperature sensor and the control logic in the semiconductor chip can react much faster and protect the components integrated in the semiconductor chip much better than temperature control with an external temperature sensor.External resistors for balancing are not required, as temperature control is performed so quickly that the integrated semiconductor is effectively protected from damage. The currents permitted for balancing are preferably limited only by the internal resistance of the integrated transistors, especially field-effect transistors.

[0017] In at least one advantageous embodiment according to the first aspect, the control logic controls the switch position of the semiconductor switch of the battery cell to be symmetrized, for which the symmetry request signal signals symmetrization, depending on the first temperature signal such that, if a value of the first temperature signal falls below a predetermined lower threshold value, the control logic controls the semiconductor switch such that it assumes a closed state, and if the value of the first temperature signal exceeds a predetermined upper threshold value, the control logic controls the semiconductor switch such that it assumes an open state.

[0018] The control logic is thus designed to limit the compensating current through variable pulse-width modulation of the semiconductor switch, taking particular account of the local temperature rise of the integrated semiconductor switches, especially the switching transistors. During a compensating phase, short but high current pulses flow if thermally permissible. The measured temperature has a direct influence on the switching on and off of the semiconductor switches.

[0019] In at least one advantageous embodiment according to the first aspect, the temperature sensor comprises an integrated diode structure arranged on the semiconductor switch. The diode structure can be formed, for example, by a diode or a transistor. In particular, the diode structure can be arranged on a switching transistor of the semiconductor switch. Since the silicon can heat up very quickly locally due to the internal resistance of the switching transistor, the diode structure is preferably arranged on the active transistor area of ​​the switching transistor.

[0020] In at least one advantageous embodiment according to the first aspect, the diode structure has a pn junction. This enables easy measurement of the temperature of the semiconductor switch.

[0021] In at least one advantageous embodiment according to the first aspect, the balancing device is integrated on a semiconductor chip. Furthermore, the control logic is configured to receive a second temperature signal, representative of an average chip temperature of the semiconductor chip, from the control unit and to control the switch position of the semiconductor switch of the battery cell to be balanced depending on the second temperature signal.

[0022] The control logic thus controls the switch position depending on the first temperature signal, the second temperature signal, and the symmetry request signal. If the value of the first temperature signal exceeds the upper threshold, i.e., a maximum permissible local temperature of the semiconductor switch is exceeded, the affected semiconductor switch is opened, and the compensation phase or symmetry phase for this semiconductor switch is stopped until the semiconductor switch is back within a safe thermal range, i.e., the temperature of the semiconductor switch has dropped sufficiently that the temperature of the semiconductor switch is a sufficient distance from the maximum permissible local temperature of the semiconductor switch.If an upper limit for the average chip temperature is exceeded, all compensation processes are stopped and thus all semiconductor switches are put into an open state until the average chip temperature has dropped again until it is a sufficient distance from the upper limit.

[0023] The compensating current pulses can therefore flow as long as the local temperature and the average temperature on the semiconductor chip are each within the safe range.

[0024] According to a second aspect, the aforementioned object is achieved by a battery device. The battery device comprises one or more battery modules. Furthermore, the battery device comprises a balancing device according to the first aspect for the battery module(s) or for at least some of the battery modules. The battery module(s) has(have) a plurality of battery cells connected in series.

[0025] Advantageous embodiments according to the first aspect are also valid for the second aspect.

[0026] Embodiments of the invention are explained in more detail below with reference to the schematic drawings.

[0027] They show:

[0028] Figure 1 : a simplified (partial) block diagram of a battery device with a balancing device and

[0029] Figure 2: an example of a balancing current from a battery cell.

[0030] In the figures, like reference numerals are used for elements with essentially the same function; however, these elements need not be identical in all details. The description of the subject matter specified here is not limited to the individual specific embodiments. Features of different embodiments may be combined with one another—where technically feasible—to form further embodiments. For example, variations or modifications described with regard to one of the embodiments may also be applicable to other embodiments, unless otherwise stated.

[0031] Figure 1 shows a simplified (partial) block diagram of a battery device 1 with a balancing device 10.

[0032] The battery device 1 has at least one battery module 12. The battery module 12 has a plurality of battery cells 14. In the exemplary embodiment shown in Figure 1, only two battery cells 14 and the corresponding components of the balancing device 10 are shown for reasons of simplification.

[0033] The balancing device 10 has a semiconductor switch 16 and a temperature sensor 18 for each of the battery cells 14. Furthermore, the balancing device 10 has a control logic 20. In the example shown in Figure 1, the control logic 20 comprises a logic circuit 24 for each semiconductor switch 16. The balancing device 10 is preferably integrated on a semiconductor chip.

[0034] The respective semiconductor switch 16 is connected to the associated battery cell 14. The semiconductor switch 16 comprises, for example, a switching transistor, in particular a field-effect transistor, which is controlled by a driver stage 22 of the semiconductor switch 16. An input of the driver stage 22 is connected, for example, to the associated logic circuit 24.

[0035] The respective semiconductor switch 16 is thus configured to receive a control signal from the control logic 20 and, depending on the control signal, to transfer the switching transistor into a conductive or closed state or into a blocking or open state. When the semiconductor switch 16 is closed, a current flows from the battery cell 14. This makes it possible to at least reduce an asymmetry between the charge states of the battery cells 14 of the battery module 12. The respective temperature sensor 18 is configured to detect a first temperature signal Tempi, which is representative of a temperature of the associated semiconductor switch 16, and to forward the first temperature signal Tempi to the control logic 20, in particular to the associated logic circuit 24.

[0036] The temperature sensor 18 comprises an integrated diode structure arranged on the semiconductor switch 16. Alternatively, the diode structure can be arranged adjacent, preferably in the immediate vicinity, to the switching transistor.

[0037] The diode structure, for example, features a pn junction. The voltage drop across a pn junction depends not only on the current but also on the temperature. This temperature dependence is due to the presence of thermally generated charge carriers in the semiconductor.

[0038] The logic circuit 24 of the control logic 20 is configured to receive a symmetry request signal Req_Sym for the associated battery cell 14, which is provided, for example, by a battery management controller (BMS controller). The BMS controller receives measurement data, for example, from a battery monitoring unit, which the BMS controller uses to determine a state of charge of the individual battery cells 14. If the state of charge of the battery cells 14 differ too much, the BMS controller can initiate discharging of the selected battery cells 14 by outputting a respective symmetry request signal Req_Sym to selected battery cells 14 that have a state of charge that is too high relative to other battery cells 14.

[0039] Furthermore, the logic circuit 24 is configured to receive the first temperature signal Tempi from the associated semiconductor switch 16 and, for example, a second temperature signal Temp2 from the BMS controller. The second temperature signal Temp2 is determined, for example, based on the first temperature sensor signals from the battery module 12, for example, by averaging. Alternatively or additionally, one or more additional temperature sensors can also be used.

[0040] The control logic 20 thus controls the switch position depending on the first temperature signal Tempi, the second temperature signal Temp2 and the symmetry request signal Req_Sym. A symmetry phase of the battery cell 14 is started and ended depending on the symmetry request signal Req_Sym. If during the symmetry phase the first temperature signal Tempi falls below the lower threshold and thus a maximum permissible local temperature of the semiconductor switch 16 is not exceeded, the semiconductor switch 16 associated with the battery cell 14 is closed. Preferably, the second temperature signal Temp2 is also taken into account. This means that the semiconductor switch 16 is only closed if the second temperature signal Temp2 does not exceed a predetermined upper average threshold. If the value of the first temperature signal Tempi exceeds the upper threshold, ieIf the temperature of the semiconductor switch 16 exceeds a maximum permissible local temperature, the affected semiconductor switch 16 is opened, and the compensation phase for this semiconductor switch 16 is stopped until the semiconductor switch 16 is again in a safe thermal range, where the first temperature signal Tempi falls below the lower threshold again and the temperature of the semiconductor switch 16 has thus dropped sufficiently that the temperature of the semiconductor switch 16 is sufficiently far from the upper threshold. This is repeated until the symmetry request signal Req_Sym signals that the symmetry phase is complete.If the upper average threshold value of the second temperature signal Temp2 is exceeded during the symmetry phase, and thus an upper limit value for the average chip temperature, all compensation processes are stopped and thus all semiconductor switches 16 are put into an open state until the average chip temperature has dropped again until it is a sufficient distance from the upper average threshold value.

[0041] Figure 2 shows an example of a single equalizing current pulse from a battery cell 14.

[0042] The on-time duration T_on of the semiconductor transistor depends on the measured temperature for the respective semiconductor transistor, i.e., the first temperature signal Temp_1. The maximum height l_Peak of the compensating current pulse depends on the internal resistance RDson of the switching transistor and the cell voltage Uz of the battery cell 14 being discharged. For this current l_Peak, l_Peak = Uzell / RDson applies.

[0043] The current rise and fall l_off depends on parasitic inductances in the supply lines. The current rise and fall can be slowed down if necessary by using inductive elements in the compensation path (e.g., due to limitations in the wiring harness or battery chemistry).

[0044] A balancing phase of one of the battery cells 14 preferably comprises a plurality of such balancing current pulses, whereby the time intervals between the balancing current pulses can vary. The turn-on times T_on can also vary in each case, since the chip ambient temperature of the semiconductor switch 16 can also change during the balancing phase.

[0045] Since the silicon heats up locally quite quickly due to the internal resistance of the switching transistor, the implemented temperature sensors monitor temperatures and allow equalization pulses only when they are thermally permissible. Since in most cases the battery cells 14 are only balanced during the charging and parking phases, the thermal influence on the sensitive temperature sensors 18 is generally tolerable.

[0046] List of reference symbols

[0047] 1 battery device

[0048] 10 Symmetry device

[0049] 12 Battery module

[0050] 14 battery cells

[0051] 16 semiconductor switches

[0052] 18 Temperature sensor

[0053] 20 Control logic

[0054] 22 driver stage

[0055] 24 logic circuit

[0056] Req_Sym symmetry request signal

[0057] Tempi first temperature signal

[0058] Temp2 second temperature signal

Claims

Patent claims 1 . Balancing device (10) for a battery module (12) having a plurality of battery cells (14) connected in series, wherein the balancing device comprises a semiconductor switch (16) for each of the battery cells (14) of the battery module (12), a temperature sensor (18) for each semiconductor switch (16) and a control logic (20), and wherein - the respective semiconductor switch (16) can be connected to the associated battery cell (14) in such a way that it is connected in parallel to the associated battery cell (14), - the respective semiconductor switch (16) has a control terminal for receiving a control signal provided by the control logic (20) for the semiconductor switch (16) for controlling a switch position of the semiconductor switch (16), - the respective temperature sensor (18) is designed to detect a first temperature signal (Tempi ) which is representative of a temperature of the associated semiconductor switch (16) and to forward the first temperature signal (Tempi ) to the control logic (20), and - the control logic (20) is designed to receive a symmetry request signal (Req_Sym) for a battery cell (14) to be symmetrized and to control a switch position of the semiconductor switch (16) of the battery cell (14) to be symmetrized depending on the symmetry request signal (Req_Sym) and the first temperature signal (Tempi).

2. Balancing device (10) according to claim 1, wherein the control logic (20) controls the switch position of the semiconductor switch (16) of the battery cell (14) to be balanced depending on the first temperature signal (Tempi ) such that when a value of the first temperature signal (Tempi ) falls below a predetermined lower threshold value, the control logic (20) controls the semiconductor switch such that it assumes a closed state, and when the value of the first temperature signal (Tempi ) exceeds a predetermined upper threshold value, the control logic (20) controls the semiconductor switch such that it assumes an open state.

3. Balancing device (10) according to claim 1 or 2, wherein the temperature sensor (18) comprises an integrated diode structure arranged on the semiconductor switch (16).

4. Balun (10) according to claim 3, wherein the diode structure has a pn junction.

5. Balancing device (10) according to one of the preceding claims, wherein the balancing device (10) is integrated on a semiconductor chip and the control logic (20) is designed to receive a second temperature signal (Temp2) which is representative of an average chip temperature of the semiconductor chip and to control the switch position of the semiconductor switch (16) of the battery cell (14) to be balanced depending on the second temperature signal (Temp2).

6. Battery device (1 ), comprising one or more battery modules (12) and for the or for at least some of the battery modules (12) a Balancing device (10) according to one of claims 1 to 5, wherein the battery module or the battery modules (12) have a plurality of battery cells (14) connected in series.

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