Heat management circuit for battery

Abstract

This heat management circuit maintains a battery within a suitable temperature range. A PTC circuit composed of a number of PTC thermistors connected in series is disposed in contact with a battery module. The PTC circuit has both an abnormal high-temperature cell detection function for detecting an abnormal high-temperature cell, and a cell heating function for heating a low-temperature cell. The PTC thermistors are each composed of a polymer PTC element and are formed on a resin tape sequentially along the longitudinal direction of the resin tape. Each polymer PTC element includes a thin-film heat-sensitive resistance portion and a pair of thin-film electrode portions sandwiching the heat-sensitive resistance portion. The thin-film electrode portions also serve as a wiring conductor for connecting two adjacent polymer PTC elements. A number of battery modules are connected in parallel through module separation switches. A module separation switch connected in series with a defective battery module including an abnormal high-temperature cell separates the defective battery module.

Description

Battery Thermal Management Circuit

[0001] The present invention relates to a thermal management circuit for a battery.

[0002] Lithium-ion batteries used in electric propulsion devices such as electric vehicles consist of multiple cells connected in series and parallel. However, these batteries must be used within a narrow temperature range. Increased internal resistance in cold environments and cell temperature rise due to internal short circuits pose serious problems that must be addressed. The range of electric vehicles is significantly reduced due to the power consumption required for battery heating. Furthermore, the flight range of aviation electric propulsion devices is significantly reduced due to the weight of battery heating devices. Furthermore, thermal runaway of internally shorted cells poses a risk of battery fire. Therefore, early detection of abnormally high-temperature cells is desirable. However, it is not practical to detect the temperature of all cells in an electric vehicle, which has a very large number of cells.

[0003] Patent Document 1 proposes heating a low-temperature battery by passing current through a PTC element attached to the battery's periphery. This PTC element maintains a constant battery temperature due to its resistance-increasing characteristics. However, when PTC elements are placed on a large number of cells in an EV, the circuit cost increases significantly.

[0004] Patent Document 2 proposes detecting a specific temperature rise in any cell of a battery pack using multiple PTC thermistors connected in series. Each of the multiple PTC thermistors is adjacent to each individual cell of the battery. However, this technology has the drawback of reducing the sensitivity of detecting internal short-circuited cells.

[0005] Patent Document 3 proposes a passive self-balancing circuit using a PTC thermistor. This passive cell balancing circuit has a PTC thermistor connected in series with a discharge switch. However, since a high-voltage battery has many cells connected in series, Patent Document 3 requires an increase in circuit cost.

[0006] Patent Document 4 proposes a polymer PTC element in which nickel alloy particles are mixed into a thermoplastic crystalline polymer. When the temperature of the PTC element exceeds a predetermined trip temperature, the electrical resistance of the PTC element increases rapidly due to changes in the shape and crystallinity of the polymer.

[0007] Patent Document 5 proposes a polymer PTC element in which conductive particles are bonded to the surface of thermoplastic resin particles with a binder resin. Patent Document 6 proposes a sheet heating element that uses a polymer resin containing conductive carbon.

[0008] Patent Document 7 proposes a battery cell with a built-in PTC element. This PTC element is made of a binder resin with conductive particles mixed in. However, this PTC element connected in series with the cell increases the internal resistance of the cell, making it difficult to quickly charge the battery pack.

[0009] Japanese Patent Publication No. 1997-219279 Korean Patent Publication No. 2020-98978 Japanese Patent Publication No. 2022-108412 Japanese Patent No. 4734593 Japanese Patent No. 7595284 WO2005 / 002280 Japanese Patent No. 3586195

[0010] The present invention aims to provide a thermal management circuit for a battery that can prevent the battery from deviating from a suitable temperature range. The present invention is preferably applied to batteries installed in electric propulsion devices such as electric vehicles, electric motorcycles, and drones.

[0011] A first aspect of the present invention is described. This first aspect has a PTC circuit for detecting abnormally high temperatures in a battery module. The battery module includes multiple cells connected in series. The PTC circuit includes multiple PTC thermistors connected in series. This PTC circuit can be called a main PTC circuit. The PTC circuit outputs an alarm voltage for determining whether the battery module includes an abnormally high temperature cell. The PTC circuit also supplies a cell heating current to the PTC circuit for warming the battery module when the battery module is cold. In other words, a hot cell determination voltage is applied to the PTC circuit in a hot cell detection mode, and a cell heating voltage is applied to the PTC circuit in a battery heating mode.

[0012] The cell heating voltage is set higher than the high-temperature cell determination voltage. The cell heating voltage can be adjusted according to the battery temperature. Furthermore, the temperature of the PTC thermistor to which the cell heating voltage is applied is lower than the trip temperature of the PTC thermistor. This makes it possible to implement two types of thermal management operations using a simple circuit.

[0013] In a preferred embodiment, each PTC thermistor comprises a polymer PTC element formed on a common flexible and electrically insulating resin tape. This polymer PTC element has a heat-sensitive resistor whose electrical resistance changes with temperature and a pair of conductor electrodes facing each other across the heat-sensitive resistor. The polymer PTC elements connected in series on the resin tape are arranged in order along the length of the resin tape. The electrodes of one polymer PTC element extend along the length of the resin tape and are connected to the electrodes of the adjacent polymer PTC element. This allows for the fabrication of multiple PTC thermistors and the wiring of each PTC thermistor to be achieved through a simple manufacturing process.

[0014] In a preferred embodiment, the PTC circuit comprises an upper arm and a lower arm connected in series, each of which comprises a plurality of PTC thermistors connected in series. Furthermore, a window comparator to which the output signal voltage of the PTC circuit output from the connection point between the upper arm and the lower arm is applied operates as a high-temperature cell detection circuit for detecting high-temperature cells. This allows for highly accurate high-temperature cell detection.

[0015] A second aspect of the present invention will now be described. This second aspect includes a PTC circuit having multiple PTC thermistors connected in series. Each PTC thermistor, thermally coupled to multiple cells of a battery module, is formed of a polymer PTC element formed in order along the longitudinal direction of a common flexible and electrically insulating resin tape. Each polymer PTC element has a pair of thin-film electrode portions facing each other across a thin-film thermal resistor portion. The thin-film electrode portions also serve as wiring conductors for connecting two adjacent polymer PTC elements in series. This allows the PTC circuit to be manufactured using a simple manufacturing process.

[0016] A third aspect of the present invention is described. This third aspect has a PTC circuit having multiple PTC thermistors connected in series. Each PTC thermistor, which detects abnormally high cell temperatures, is thermally coupled to multiple cells of a battery module. The multiple battery modules that make up the battery pack are connected in parallel through different module isolation switches.

[0017] When a battery module includes a high-temperature cell, the module isolation switch isolates the battery module including the high-temperature cell from the battery pack, thereby preventing the cell temperature from rising due to an internal short circuit.

[0018] In a preferred embodiment, operation of the module isolation switch is avoided during fast charging of the battery module, thereby avoiding erroneous isolation of the battery module during fast charging, because the temperature of normal cells sometimes becomes high during fast charging.

[0019] In a preferred embodiment, when the number of cells in each battery module is N (N is an integer equal to or greater than 3), each battery module has (N-1) cell connection points. A cell connection point refers to a connection point between two adjacent cells. Cell connection points in each battery module having approximately the same potential are called same-order connection points. The same-order connection points in each battery module are connected to the same input terminal of the battery management system through different PTC thermistors.

[0020] A battery module including an internal short-circuited cell is called an internal short-circuited module. As the voltage of the internal short-circuited cell gradually decreases, the voltage of the internal short-circuited module gradually decreases. As a result, the battery modules other than the internal short-circuited module supply charging current to the internal short-circuited module through their respective PTC thermistors connected to the input terminals of the battery management system. This charging current increases the heat generation of the internal short-circuited cell.

[0021] When an internal short circuit occurs in a module, some of the PTC thermistors connected to the input terminals of the battery management system become highly resistant, and as a result, the charging current is reduced by these highly resistant PTC thermistors.

[0022] In a preferred embodiment, the polymer PTC elements constituting the PTC thermistors are formed on a common resin tape that is flexible and electrically insulating, thereby enabling the formation of each PTC thermistor connected to the input terminal of the battery management system through a simple process.

[0023] In a preferred embodiment, the battery modules are connected in parallel to one another through an even number of secondary coils of the step-down transformer. Furthermore, one half of the even number of secondary coils has a winding direction opposite to that of the other half. As a result, by supplying a primary AC current to the primary coil of the step-down transformer, a secondary current circulating in each battery module can be induced, thereby efficiently heating the battery modules.

[0024] A fourth aspect of the present invention is described. According to this fourth aspect, to heat cold battery modules, AC current is supplied from secondary coils of a step-down transformer to the battery modules. Each battery module supplies a load current to an electrical load through a different secondary coil. The secondary coils form a heating circuit for heating the battery modules.

[0025] One half of the even number of secondary coils supplies a first AC current to one half of the even number of battery modules. The other half of the even number of secondary coils supplies a second AC current to the other half of the even number of battery modules. These two AC currents have essentially equal amplitudes and opposite phases. According to this fourth aspect, the AC current circulates within each battery module and does not flow to an electrical load. According to this fourth aspect, the AC power consumed by circuit elements other than the battery modules can be reduced.

[0026] Preferably, each secondary coil has an equal number of turns. Furthermore, one half of the secondary coil and the other half are wound in opposite directions around the magnetic core. This allows the secondary AC current of the step-down transformer to circulate through each battery module but not to be supplied to the electrical load.

[0027] The following sentence adequately expresses this fourth aspect: A battery thermal management circuit comprising a heating circuit including a step-down transformer supplying secondary alternating currents to battery modules, the step-down transformer having an even number of secondary coils separately connected in series with an even number of battery modules, one half of the secondary coils supplying a first alternating current to one half of the battery modules, and the other half of the secondary coils supplying a second alternating current to the other half of the battery modules, the two alternating currents having essentially equal amplitudes and opposite phases to each other.

[0028] FIG. 1 is a circuit diagram showing a power supply circuit of an EV battery pack. FIG. 2 is a circuit diagram showing a PTC circuit. FIG. 3 is a flowchart showing the battery heating operation and high-temperature cell detection operation of the PTC circuit. FIG. 4 is a side view showing a tape-shaped PTC circuit adjacent to a side surface of each cell of a battery module. FIG. 5 is an enlarged plan view of the tape-shaped PTC circuit. FIG. 6 is a cross-sectional view of the tape-shaped PTC circuit shown in FIG. 5. FIG. 7 is an enlarged plan view showing another example of a tape-shaped PTC circuit. FIG. 8 is a cross-sectional view of the tape-shaped PTC circuit shown in FIG. 7. FIG. 9 is a schematic diagram showing a tape-shaped PTC circuit that meanders between each cell of a battery module. FIG. 10 is a plan view showing an example of a tape-shaped sub-PTC circuit. FIG. 11 is a circuit diagram showing a modified version of the power supply circuit shown in FIG. 1. FIG. 12 is a schematic diagram showing the step-down transformer shown in FIG. 11. FIG. 13 is a schematic diagram showing a modified version of the step-down transformer.

[0029] An example of the battery temperature management technology of the present invention will be described with reference to Fig. 1. Fig. 1 is a block circuit diagram showing a power supply circuit for a pure electric vehicle (BEV). This EV power supply circuit, which supplies power to an inverter (not shown) for driving a traction motor, includes a battery pack 100, a main PTC circuit 500, a PTC power supply circuit 600, a fuse circuit 700, a sub PTC circuit 800, and a battery management system 900.

[0030] Battery pack 100 consists of four battery modules 1-4 connected in parallel. Battery module 1 consists of four battery cells 11-14 connected in series, battery module 2 consists of four battery cells 21-24 connected in series, battery module 3 consists of four battery cells 31-34 connected in series, and battery module 4 consists of four battery cells 41-44 connected in series. These battery cells can be simply referred to as cells.

[0031] The main PTC circuit 500 consists of four PTC circuits 51-54. PTC circuit 51 is arranged adjacent to battery module 1, PTC circuit 52 is arranged adjacent to battery module 2, PTC circuit 53 is arranged adjacent to battery module 3, and PTC circuit 54 is arranged adjacent to battery module 4. Each of the PTC circuits 51-54 includes four PTC (positive temperature coefficient) thermistors connected in series. Each PTC thermistor in one PTC circuit is adjacent to four cells of an adjacent battery module. One end of each PTC circuit is connected to the PTC power supply circuit 600, and the other end is grounded.

[0032] The fuse circuit 700 includes four electrically controlled fuses 71-74. The electrically controlled fuses 71-74 are disposed adjacent to the electrically controlled fuses 75-78. When a current is supplied to the electrically controlled fuse 75, the electrically controlled fuse 71 is interrupted. When a current is supplied to the electrically controlled fuse 76, the electrically controlled fuse 76 is interrupted. When a current is supplied to the electrically controlled fuse 77, the electrically controlled fuse 77 is interrupted. When a current is supplied to the electrically controlled fuse 78, the electrically controlled fuse 78 is interrupted. Other types of switches, such as relays, can be employed in place of the electrically controlled fuses 71-74.

[0033] Battery pack 100 is divided into four cell groups. A first potential cell group consisting of cells 11, 21, 31, and 41 has the highest potential. A second potential cell group consisting of cells 12, 22, 32, and 42 has the second highest potential. Similarly, a third potential cell group consisting of cells 13, 23, 33, and 43 has the third highest potential. A fourth potential cell group consisting of cells 14, 24, 34, and 44 has the lowest potential.

[0034] The positive terminal of cell 11 is connected to the high potential output terminal VH through an electrically controlled fuse 71, and the positive terminal of cell 12 is connected to the high potential output terminal VH through an electrically controlled fuse 72. Similarly, the positive terminal of cell 13 is connected to the high potential output terminal VH through an electrically controlled fuse 73, and the positive terminal of cell 14 is connected to the high potential output terminal VH through an electrically controlled fuse 74.

[0035] The negative terminals of cells 14, 24, 34, and 44 having the lowest potential are connected to the low potential output terminal VL. An electrical load (not shown) is connected to the high potential output terminal VH and the low potential output terminal VL. The PTC power supply circuit 600 applies a predetermined DC voltage VX to the PTC circuits 51-54. The PTC power supply circuit 600 applies one of two DC voltage values ​​to the PTC circuits 51-54.

[0036] The sub-PTC circuit 800 includes three PTC thermistor sets 81-83. Each of the PTC thermistor sets 81-83 consists of four PTC thermistors 85-88. One end of each of the four PTC thermistors 85-88 is connected to one of the input terminals 92-94 of the battery management system 900. The other end of each of the four PTC thermistors 85-88 is connected to one of the four battery modules 1-4.

[0037] Each of the PTC thermistors 85-88 of the PTC thermistor set 81 individually connects the negative electrode of any one of cells 11, 21, 31, and 41 to an input terminal 92. In other words, the PTC thermistor set 81 is connected to the input terminal 92 through a first potential cell group. Similarly, each of the PTC thermistors 85-88 of the PTC thermistor set 82 individually connects the negative electrode of any one of cells 12, 22, 32, and 42 to an input terminal 93. In other words, the PTC thermistor set 82 is connected to the input terminal 93 through a second potential cell group. Similarly, each of the PTC thermistors 85-88 of the PTC thermistor set 83 individually connects the negative electrode of any one of cells 13, 23, 33, and 43 to an input terminal 94. In other words, the PTC thermistor set 84 is connected to the input terminal 94 through a third potential cell group.

[0038] The battery management system 900 has input terminals 91-95. The input terminal 91 is connected to the high-potential output terminal VH, and the input terminal 95 is connected to the low-potential output terminal VL. The battery management system 900 includes MOS transistors 96-99 for passive self-balancing. The input terminals 91 and 92 are connected by a transistor 96. The input terminals 92 and 93 are connected by a transistor 97. The input terminals 93 and 94 are connected by a transistor 98. The input terminals 94 and 95 are connected by a transistor 99. The battery management system 900 has a built-in cell voltage detection function that detects the voltage difference between two adjacent input terminals.

[0039] During normal operation, the electrical resistance of the PTC thermistors 85-88 is sufficiently low so that the four cells in each potential group have the same potential. Therefore, the battery management system 900 detects the voltage of each potential cell group and controls the charging and discharging operations of the battery pack 100 based on this detection result. As is well known, when the voltage of a specific potential cell group is higher than a predetermined voltage value, one of the specific switches 96-99 is turned on. This allows a passive self-balancing operation to be performed to discharge the potential cell group with an excessive cell voltage.

[0040] In this passive cell balancing operation, the PTC thermistors 85-88 can act as current limiting resistors to limit the passive cell balancing currents flowing through the switches 96-99.

[0041] The details of the PTC circuit 51 will be described in detail with reference to Fig. 2. The PTC circuits 52-54 have essentially the same circuit configuration as the PTC circuit 51. However, the battery module 1 shown in Fig. 2 is made up of eight cells 11-18 connected in series. Therefore, the PTC circuit 51 is made up of eight PTC thermistors 511-518 connected in series.

[0042] PTC thermistor 511 is in contact with cell 11, and PTC thermistor 512 is in contact with cell 12. PTC thermistor 513 is in contact with cell 13, and PTC thermistor 514 is in contact with cell 14. PTC thermistor 515 is in contact with cell 15, and PTC thermistor 516 is in contact with cell 16. PTC thermistor 517 is in contact with cell 17, and PTC thermistor 518 is in contact with cell 18.

[0043] The series-connected PTC thermistors 511-514 are referred to as the upper arm 51a, and the series-connected PTC thermistors 515-518 are referred to as the lower arm 51b. The PTC power supply circuit 600 applies a predetermined DC voltage VX to the series-connected upper arm 51a and lower arm 51b. As a result, the connection point between the upper arm 51a and the lower arm 51b outputs a signal voltage VS. Furthermore, the PTC power supply circuit 600 applies the predetermined DC voltage VX to a reference voltage generation circuit 601.

[0044] This reference voltage generating circuit 601 consists of resistors R1, R2, and R3 connected in series. As a result, the junction of resistors R1 and R2 outputs a high-side reference voltage Vr1, and the junction of resistors R2 and R3 outputs a low-side reference voltage Vr2. The window comparator 601, to which the voltages VS, Vr1, and Vr2 are applied, outputs an output signal S1 to a controller 604. This controller 604 controls the current supplied to an electrical resistance element 75 adjacent to the electrically controlled fuse 71.

[0045] The window comparator 601 includes a high-side comparator 602 and a low-side comparator 603. The high-side comparator 602 compares the signal voltage VS with a high-side reference voltage Vr1, and the low-side comparator 603 compares the signal voltage VS with a low-side reference voltage Vr2. In Fig. 2, the high-side reference voltage Vr1 is set to 60% of the DC voltage VX, and the low-side reference voltage Vr2 is set to 40% of the DC voltage VX.

[0046] When signal voltage VS is lower than high-side reference voltage Vr1 and higher than low-side reference voltage Vr2, window comparator 601 outputs a high level to controller 604. When signal voltage VS is higher than high-side reference voltage Vr1, window comparator 601 outputs a low level to controller 604. When signal voltage VS is lower than low-side reference voltage Vr2, window comparator 601 outputs a low level to controller 604. As is well known, window comparator 601 applies a high level voltage S1 to controller 604 only when signal voltage VS is between high-side reference voltage Vr1 and low-side reference voltage Vr2. Similarly, the other three window comparators (not shown), to which the voltages of PTC circuits 52-54 are applied, also apply signal voltages S2-S4 to controller 604.

[0047] Next, the thermal runaway prevention operation of this embodiment will be described below. Generally, battery thermal runaway begins when an internal short circuit occurs in one cell of the battery pack 100. When an internal short circuit occurs in a cell 12, the open circuit voltage of this cell 12 is shorted through an internal short circuit resistance RS formed in the cell 12. As a result, the power energy of the cell 12 is consumed, and the temperature of the cell 12 gradually rises.

[0048] Next, the high-temperature monitoring operation of the battery module 1 will be described with reference to FIG. 2. The battery module 1 consists of a high-side module 1H and a low-side module 1L. The high-side module 1H adjacent to the upper arm 51a consists of cells 11-14. The low-side module 1L adjacent to the lower arm 51b consists of cells 15-18. When all cells 11-18 of the battery module 1 have temperatures within the normal temperature range, the PTC thermistors 511-518 each have a low resistance. Therefore, the signal voltage VS is approximately half the power supply voltage VX, and the high-temperature monitoring signal S1 output by the window comparator 601 to the controller 604 becomes high level.

[0049] Next, when any one of cells 11-14 in high-side module 1H becomes hot, the PTC thermistor adjacent to the short-circuited cell has a high resistance. An internally shorted cell is a cell with a high temperature. As a result, signal voltage VS becomes lower than low-side reference voltage Vr2, and window comparator 601 outputs a low-level voltage. Similarly, when any one of cells 15-18 in low-side module 1L becomes hot due to an internal short, the PTC thermistor adjacent to this short-circuited cell has a high resistance. As a result, signal voltage VS becomes higher than high-side reference voltage Vr1, and window comparator 601 outputs a low-level voltage.

[0050] Consequently, when the battery module 1 includes an abnormally high temperature cell, the window comparator 601 outputs a low-level high temperature monitoring signal S1 to the controller 604. When the low-level high temperature monitoring signal S1 is input, the controller 604 supplies current to the electrical resistance element 75. As a result, the heated electrical resistance element 75 cuts off the adjacent electrically controlled fuse 71. Similarly, the controller 604 controls the electrically controlled fuses 72-74.

[0051] However, during the period when the battery modules 1-4 are being fast charged, the signal voltage VS of the PTC circuits 51-54 may become high even though the battery modules 1-4 do not contain any internal short-circuited cells, which may result in the fuse circuit 700 being activated. Therefore, it is preferable to prohibit current supply to the electrical resistance elements 75-78 when the battery pack 100 is being fast charged.

[0052] Next, the circuit operation for suppressing the rate of increase of the internal short-circuit current in the internal short-circuited cell will be described. In FIG. 1 , the battery pack 100 essentially comprises four battery modules 1-4 connected in parallel. When an internal short-circuit occurs in a cell 12, the stored charge and open-circuit voltage of the cell 12 gradually decrease. As a result, the voltage of the battery module 1 becomes lower than the voltages of the other battery modules 2-4. Therefore, the battery modules 2-4 charge the battery module 1 through the fuse 71. This means that the charge loss of the cell 12 is suppressed despite the discharge caused by the internal short-circuit in the cell 12. In other words, the battery modules 2-4 discharge through the internal short-circuit resistance of the cell 12. Eventually, the charge of all the battery modules 1-4 is discharged through the internal short-circuited cell 12, causing the internal short-circuited cell 12 to become hot.

[0053] However, according to this embodiment shown in FIG. 1 , the battery pack 100 is divided into four battery modules 1-4. Therefore, when battery module 1 includes an internal short-circuit cell 12, fuse 71 is blown. As a result, the internal short-circuit current supplied from battery modules 2-4 to the internal short-circuit cell 12 of battery module 1 becomes zero. Ultimately, the total amount of power consumption of the internal short-circuit cells 12 is significantly reduced, thereby suppressing thermal runaway of the internal short-circuit cells 12.

[0054] Next, the operation of the sub-PTC circuit 800 will be described when an internal short circuit occurs in a cell 12. The internally shorted cell 12 of the battery module 1 is connected in parallel with the other cells of the battery modules 2-4 through the PTC thermistors 85-88 of the sub-PTC circuit 800. Therefore, when the voltage of the internally shorted cell 12 drops, the battery modules 2-4 charge the internally shorted cell 12 through the PTC thermistor sets 81-83 of the sub-PTC circuit 800. However, the PTC thermistor sets 81-83 are heated. As a result, the internal short-circuit current supplied from the battery module 2-4 to the internally shorted cell 12 is effectively limited by the PTC thermistor sets 81-83.

[0055] For example, the battery module 2-4 supplies current to the internally shorted cell 12 through the PTC thermistor set 81. This current flows from the PTC thermistors 86-88 through the PTC thermistor 85 to the internally shorted cell 12. Therefore, this current in the PTC thermistor 85 is the sum of the currents of the PTC thermistors 86-88. As a result, the high-temperature PTC thermistor 85 has a high resistance. Eventually, the PTC thermistor 85 almost completely cuts off the current supply from the battery module 2-4 to the internally shorted cell 12.

[0056] The basic operation of the controller 604 will be described with reference to the flowchart shown in FIG. 3. First, the battery management system 900 determines whether the temperature of the battery pack 100 is below freezing. Based on this determination, the controller 604 determines whether a battery heating operation should be initiated (S100). If the temperature of the battery pack 100 is below freezing, the battery heating operation is performed (S102). In this battery heating operation, the power supply voltage VX applied from the PTC power supply circuit 600 to the four PTC circuits 51-54 is shifted to a high-level voltage value.

[0057] For example, this high-level voltage VX is 100 V. On the other hand, the power supply voltage VX used to detect abnormally high-temperature cells in battery modules 1-4 is 10 V. Therefore, the battery heating current flowing through the PTC circuits 51-54 is approximately 10 times the high-temperature cell detection current. Due to this increase in the power supply voltage VX, the ohmic loss of the PTC circuits 51-54 during battery heating is approximately 100 times greater than during abnormally high-temperature cell monitoring operation. This allows the PTC circuits 51-54 to sufficiently heat adjacent battery cells.

[0058] However, it is important that the PTC thermistors in the PTC circuits 51-54 do not jump to a high resistance value when a battery heating current flows through the PTC circuits 51-54. Next, the controller 604 determines whether the temperature of the battery pack 100 is higher than 0°C (S104). If the determination is Yes, the power supply voltage VX is shifted to a low level (S106). This allows the PTC circuits 51-54 to return to monitoring the abnormally high temperature cells in the battery modules 1-4.

[0059] Next, it is determined whether the battery pack 100 includes an abnormally high temperature cell (S108). If the battery pack 100 includes an abnormally high temperature cell, the fuse connected in series with the battery module including the abnormally high temperature cell is cut off (S110). Next, an alarm signal is output indicating the occurrence of an abnormally high temperature cell that may lead to a thermal runaway accident due to, for example, an internal short circuit (S112). Furthermore, when the occurrence of an abnormally high temperature cell is detected, the battery pack 100 is strongly cooled.

[0060] An example of a PTC circuit 51 will be described with reference to FIG. 4. In FIG. 4, cells 11-18 of a battery module 1 are arranged side by side. A tape-shaped PTC circuit 51 is in close contact with each side surface of the cylindrical cells 11-18 arranged in a row. The PTC thermistors 511-518 shown in FIG. 2 are dispersed and arranged at predetermined intervals within the tape-shaped PTC circuit 51. As a result, the PTC thermistor 511 is in close contact with cell 11, and the PTC thermistor 512 is in close contact with cell 12. The PTC thermistor 513 is in close contact with cell 13, and the PTC thermistor 514 is in close contact with cell 14. The PTC thermistor 515 is in close contact with cell 15, and the PTC thermistor 516 is in close contact with cell 16. The PTC thermistor 517 is in close contact with cell 17, and the PTC thermistor 518 is in close contact with cell 18.

[0061] 5 is a partially enlarged plan view of the PTC circuit 51. PTC layers 551-554 and conductor films 561-565 are disposed on the insulating tape 50. The conductor films 561, 563, and 565 are disposed at one widthwise end of the insulating tape 50, and the conductor films 562 and 564 are disposed at the other widthwise end of the insulating tape 50. One end of the PTC layer 551 is bonded to the conductor film 561, and the other end of the PTC layer 551 is bonded to the conductor film 562. As a result, the PTC layer 551 forms the PTC thermistor 511, and the conductor films 561 and 562 form electrodes of the PTC thermistor 511. Furthermore, the conductor films 561 and 562, which extend in the longitudinal direction of the insulating tape 50, also serve as wiring conductors connecting the PTC thermistors.

[0062] Similarly, one end of PTC layer 552 is bonded to conductor film 563, and the other end of PTC layer 552 is bonded to conductor film 562. Similarly, one end of PTC layer 553 is bonded to conductor film 563, and the other end of PTC layer 553 is bonded to conductor film 564. Similarly, one end of PTC layer 554 is bonded to conductor film 565, and the other end of PTC layer 554 is bonded to conductor film 564. In this manner, PTC thermistors 512-514 are formed. Each arrow in FIG. 5 indicates the direction of current flow within PTC circuit 51.

[0063] A cross-sectional view of a tape-shaped PTC circuit 51 will be described with reference to FIG. 6 . A PTC layer 551 is formed on an insulating tape 50 made of a highly flexible polycarbonate film. Furthermore, conductor films 561 and 562 made of copper foil are formed on both ends of the PTC layer 551. An insulating tape 500 made of a polycarbonate film is formed on the PTC layer 551 and the conductor films 561 and 562. Furthermore, the insulating tape 50 is covered with a protective tape 501 made of copper foil, and the insulating tape 500 is covered with a protective tape 502 made of copper foil. A polyimide film with excellent thermal conductivity can be used in place of the protective tapes 501 and 502.

[0064] Another example of the PTC circuit 51 will be described with reference to Figures 7 and 8. Conductor films 561 and 563 are formed on the lower insulating tape 501. Furthermore, a tape-shaped PTC layer 59 is formed on the conductive films 561 and 563. Conductor films 562 and 564 are formed on the PTC layer 59. Furthermore, the upper insulating tape 502 covers the conductive films 562 and 564. The conductive films 561 and 562 sandwich the PTC layer 59 in the thickness direction. The conductive films 562 and 563 sandwich the PTC layer 59 in the thickness direction. The conductive films 563 and 564 sandwich the PTC layer 59 in the thickness direction.

[0065] The conductor film 561, the PTC layer 59, and the conductor film 562 form one PTC thermistor. The conductor film 562, the PTC layer 59, and the conductor film 563 form another PTC thermistor. The conductor film 563, the PTC layer 59, and the conductor film 564 form yet another PTC thermistor. In conclusion, the conductor film 562 extending in the longitudinal direction of the insulating tapes 501 and 502 also serves as a wiring conductor for connecting two adjacent PTC thermistors. Similarly, the other conductor films also serve as wiring conductors for connecting two adjacent PTC thermistors.

[0066] Another example of the PTC circuit 51 will be described with reference to Fig. 9. Fig. 9 shows the cells 12-15 of the battery module 1. The flat cylindrical cells 12-15 are arranged close to each other. Furthermore, tape-like PTC circuits 51 are arranged in a serpentine pattern in the narrow gaps between the cells 12-15 and are in close contact with the side surfaces of the cells 12-15.

[0067] PTC thermistor set 81, which is part of tape-shaped PTC sub-circuit 800, will be described with reference to FIG. 10 . PTC layers 850-880 and conductor films 580-584 are formed on insulating tape 80. Conductor films 580-584 are made of linear copper foil. PTC layer 850, disposed between conductor films 580 and 581, forms PTC thermistor 85. PTC layer 860, disposed between conductor films 580 and 582, forms PTC thermistor 86. PTC layer 870, disposed between conductor films 580 and 583, forms PTC thermistor 87. PTC layer 880, disposed between conductor films 580 and 584, forms PTC thermistor 88.

[0068] 10 , conductor film 580 is connected to input terminal 92 of battery management system 900. Conductive film 581 is connected to the negative electrode of cell 11, and conductor film 582 is connected to the negative electrode of cell 21. Similarly, conductor film 583 is connected to the negative electrode of cell 31, and conductor film 584 is connected to the negative electrode of cell 41. This makes it possible to realize a sub-PTC circuit 800 with a simple structure.

[0069] Polymer PTC elements used as PTC thermistors can be manufactured based on the conventional techniques described in many publicly known documents, including the above-mentioned Patent Documents 4 to 6. The electrical properties of the polymer PTC element, such as the resistance value and trip temperature, can be appropriately changed by adjusting the shape of the polymer PTC element, the types of raw materials, and the compounding ratios of the materials.

[0070] Another example of the battery temperature management technique of the present invention will be described with reference to FIG. 11. FIG. 11 is a block circuit diagram showing a power supply circuit for a pure electric vehicle (BEV). This power supply circuit is the same as the power supply circuit shown in FIG. 1 except for a step-down transformer circuit 1000. Therefore, the following description will mainly focus on the step-down transformer circuit 1000.

[0071] This step-down transformer circuit 1000 comprises a step-down transformer 1001 and an oscillator 1002. The step-down transformer 1001 comprises a primary coil 1003 and four secondary coils 1004-1007 wound around a magnetic core 1010 that form a closed magnetic circuit.

[0072] Secondary coil 1004 is connected in series with fuse 71, and secondary coil 1005 is connected in series with fuse 72. Secondary coil 1006 is connected in series with fuse 73, and secondary coil 1007 is connected in series with fuse 74. When oscillator 1002 applies a primary AC voltage to primary coil 1003, each of secondary coils 1005-1007 applies a low secondary voltage to battery modules 1-4, respectively.

[0073] The direction of the secondary voltage induced in each secondary coil 1004-1007 is indicated by an arrow in Fig. 11. The secondary voltages in secondary coils 1004 and 1006 are induced in the opposite direction compared to the secondary voltages in secondary coils 1005 and 1007. In other words, the first secondary AC voltage induced in secondary coils 1004 and 1006 is opposite in direction to the second secondary AC voltage induced in secondary coils 1005 and 1007. Therefore, the pair of battery modules 1 and 3 and the pair of battery modules 2 and 4 form a circulation circuit in which a secondary AC current circulates.

[0074] A first load current flowing through battery modules 1 and 3 generates a first DC magnetic flux in magnetic core 1010. Similarly, a second load current flowing through battery modules 2 and 4 generates a second DC magnetic flux in magnetic core 1010. When the first and second load currents are equal to each other, the sum of the first and second DC magnetic fluxes is zero. FIG. 12 shows an example of step-down transformer 1001, and FIG. 13 shows a modified example of step-down transformer 1001. According to this embodiment, battery modules 1-4 can be heated by PTC circuits 51-54 and / or step-down transformer circuit 1000.

[0075] Fig. 12 is a schematic diagram showing the step-down transformer 1001 shown in Fig. 11. Half of the four secondary coils 1004-1007 are wound in the opposite direction to the other half. Fig. 13 is a schematic diagram showing another step-down transformer that can be employed in the step-down transformer circuit shown in Fig. 11. Two secondary coils 1004 and 1006 are wound in the opposite direction to each other.

[0076] A modification of the power supply circuit shown in Fig. 11 will be described. In Fig. 11, battery modules 1-4 supply a load current to an external load. This load current is the sum of four module load currents IL1-IL4. The module load current IL1 is supplied from battery module 1 to the external load through secondary coil 1004. The module load current IL2 is supplied from battery module 2 to the external load through secondary coil 1005. The module load current IL3 is supplied from battery module 3 to the external load through secondary coil 1006. The module load current IL4 is supplied from battery module 4 to the external load through secondary coil 1007.

[0077] The winding direction of secondary coils 1004 and 1006 is opposite to that of secondary coils 1005 and 1007. Therefore, the sum of the four module load currents IL1-IL4 (IL1+IL3-IL2-IL4) forms a residual load flux in magnetic core 1010. Each secondary voltage induced in secondary coils 1004-1007 is affected by this residual load flux. This problem can be solved by adding a compensation current to primary coil 1003 to cancel this residual load flux. For example, assume that primary coil 1003 has 100 turns and each secondary coil 1004-1007 has one turn. The compensation current supplied to primary coil 1003 is (-IL1-IL3+IL2+IL4) / 100.

Claims

1. A thermal management circuit for a battery comprising: a PTC circuit having a number of PTC thermistors connected in series and thermally coupled to a number of cells of a battery module; a high-temperature cell detection circuit that determines whether the battery module includes a high-temperature cell based on a signal voltage from the PTC circuit; and a controller that controls the current supplied to the PTC circuit, wherein the controller applies a high-temperature cell determination voltage to the PTC circuit for the determination, and the controller applies a cell heating voltage to the PTC circuit in a low-temperature environment, and the cell heating voltage is higher than the high-temperature cell determination voltage.

2. A battery thermal management circuit as described in claim 1, wherein each of the PTC thermistors is made of a polymer PTC element, and each of the polymer PTC elements is formed in order in the longitudinal direction of a common resin tape that is flexible and electrically insulating.

3. The thermal management circuit for a battery according to claim 2, wherein the PTC circuit has an upper arm portion and a lower arm portion connected in series, the upper arm portion and the lower arm portion each comprise a plurality of the PTC thermistors connected in series with each other, and the high-temperature cell detection circuit includes a window comparator that receives a signal voltage from a connection point between the upper arm portion and the lower arm portion.

4. A thermal management circuit for a battery comprising a PTC circuit having a number of PTC thermistors connected in series and thermally coupled to a number of cells of a battery module, wherein each of the PTC thermistors is made of a polymer PTC element, and each of the polymer PTC elements is formed in order in the longitudinal direction of a common resin tape that is flexible and electrically insulating, and each of the polymer PTC elements has a thin-film heat-sensitive resistor portion whose electrical resistance increases rapidly under specified high-temperature conditions, and a pair of thin-film electrode portions facing each other across the heat-sensitive resistor portion to supply current to the heat-sensitive resistor portion, and the thin-film electrode portions also serve as wiring conductors for connecting two adjacent polymer PTC elements in series.

5. A thermal management circuit for a battery comprising a PTC circuit having a number of PTC thermistors connected in series and thermally coupled to a number of cells of a battery module, a high-temperature cell detection circuit that determines whether the battery module includes a high-temperature cell based on a signal voltage from the PTC circuit, and a controller that controls the current supplied to the PTC circuit, wherein the plurality of battery modules are connected in parallel via module isolation switches for module isolation, and the controller shuts off the module isolation switch connected in series with the battery module including the high-temperature cell when the occurrence of the high-temperature cell is detected.

6. The battery thermal management circuit according to claim 5, wherein the controller stops turning off the module isolation switch during a period when the battery module is being fast charged.

7. A battery thermal management circuit as claimed in claim 5, wherein each of said battery modules has an equal number of cells, and each of said cell connection points of said battery modules is connected to the same input terminal of the battery management system through a different PTC thermistor.

8. A battery thermal management circuit according to claim 7, wherein each of said PTC thermistors is made of a polymer PTC element, and each of said polymer PTC elements is formed on a common resin tape having flexibility and electrical insulation properties.

9. A battery thermal management circuit as claimed in claim 5, wherein the battery modules are connected in parallel to one another through an even number of secondary coils of a step-down transformer, one half and the other half of the even number of secondary coils have winding directions opposite to each other, and the controller heats the battery modules by supplying a primary AC current to the primary coils of the step-down transformer when the temperature of the battery modules is low.

Images