Circuit device

Abstract

To provide a circuit device having excellent reliability under various operation conditions.SOLUTION: Two battery packs 11, 12 connected in parallel form a current circulation circuit through a first secondary coil 52 and a second secondary coil 53 of a step-down transformer 5. The two secondary coils circulate secondary AC current only to the current circulation circuit, by supplying primary AC current to a primary coil 51 of the step-down transformer. The current circulation circuit includes contactors 41, 42 connected to the battery packs in series. A battery consists of multiple cells connected in series. The secondary coil of the step-down transformer is connected to the battery in series. Positive pulse voltages and negative pulse voltages are alternately applied to the primary coil of the step-down transformer. When the positive pulse voltage is applied and when the negative pulse is applied, the cell voltage is detected. Impedance of each cell, in particular its internal resistance, is detected based on the difference of those two cell voltages.SELECTED DRAWING: Figure 7

Description

Reference to Related Art

[0001] This application claims the priority of PCT / JP2023 / 04873 filed on February 14, 2023. All of its contents are incorporated by reference.

Technical Field

[0002] The present invention relates to a technique for improving the reliability of a circuit device. In particular, the present invention relates to a technique for improving the reliability of a DC power supply.

Background Art

[0003] The DC power supply of an electric vehicle including a battery supplies power to a traction motor through a motor drive circuit. When this DC power supply including a battery has a problem, serious accidents often occur in the electric vehicle. Therefore, this DC power supply needs to have excellent reliability.

[0004] Generally, in order to ensure the safety of the battery, the DC power supply of an electric vehicle has a power contactor for disconnecting the battery. However, when the mechanical contact of the contactor is opened, the inductance of the circuit forms an arc on the mechanical contact of the contactor. The traction motor of an electric vehicle uses a large amount of power. Therefore, the extinction of this arc is not easy.

[0005] Furthermore, it is known that electric vehicle batteries have various problems in cold weather. Therefore, it is important to heat the electric vehicle battery in cold weather. An AC heating technique that supplies an alternating current to the primary coil of a transformer is known. This transformer has a secondary coil connected in series with the battery. According to this AC heating technique, the battery can be heated quickly.

[0006] However, the battery of an electric vehicle is formed by connecting a large number of cells in series. The internal resistance of each cell varies depending on factors such as temperature and SOC. Therefore, even when a constant alternating current is supplied to the battery by AC heating technology, the temperature rise of each cell changes due to the variation in the internal resistance of each cell. For example, it is not easy to sufficiently heat a cell with an abnormally low internal resistance using this AC heating technology. For this reason, it is desired to detect the internal resistance of each cell in advance.

[0007] Furthermore, this AC heating technology requires a transformer connected in series with the battery. As a result, the arc generated at the contact becomes more serious due to the inductance of this transformer.

[0008] Furthermore, since the battery of an electric vehicle is large, the power cable connecting the battery and the motor drive circuit becomes long. Therefore, the arc generated at the contact becomes more serious due to the inductance of this power cable. In the prior art, a bypass circuit consisting of a capacitor and a resistor connected in series is known. This bypass circuit, called a surge killer, bypasses the surge current when the parallel-connected contacts are opened. However, this resistor reduces the surge current flowing into the capacitor.

[0009] The DC power supplies disclosed in Patent Documents 1 and 2 reduce the voltage difference between two batteries by charging only one of the two batteries connected in parallel. Each battery is connected in series with each contact.

[0010] Patent Document 3 held by the applicant of the present application discloses an alternating current supply circuit that supplies an alternating current to a battery. This alternating current supply circuit proposes a step-down transformer that supplies an alternating current to the battery in order to improve the charge and discharge performance of the battery in a low-temperature environment.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

[0012] An object of the present invention is to provide a circuit device having excellent reliability under various operating conditions. Preferably, this circuit device is constituted by a DC power supply of an electric vehicle. Preferably, the electric vehicle of the present invention includes, in addition to a ground vehicle having a traction motor, a ship, a submarine, an airplane, a drone, etc. having a motor for generating a driving force.

[0013] In a first aspect of the present invention, a current circulation circuit is formed by two secondary coils of a step-down transformer connected in series and two battery packs. Each secondary voltage induced in the two secondary coils circulates a secondary current in this current circulation circuit. The two battery packs connected in parallel supply a load current to an electrical load. One secondary coil is connected in series with one battery pack. The other secondary coil is connected in series with the other battery pack. Each secondary voltage induced in the two secondary coils has the same direction within this current circulation circuit.

[0014] When one of the two battery packs is discharged, the other is charged. In other words, the battery power discharged from one battery pack by the circulating current is temporarily stored by the other battery pack. Therefore, the oscillator connected to the primary coil of the step-down transformer only needs to supply the primary coil with power corresponding to the AC power loss due to the internal resistance of the two battery packs.

[0015] Preferably, the two secondary coils of the step-down transformer have the same number of turns as each other. The first secondary coil supplies a first secondary current to the electrical load. The second secondary coil supplies a second secondary current to the electrical load. These two secondary currents have equal amplitudes and opposite current directions. Eventually, the two secondary coils do not supply secondary current to the electrical load connected to the two battery packs. As a result, the secondary currents of the two secondary coils only circulate through the two battery packs.

[0016] In a first preferred embodiment, the controller has a battery heating mode for heating the low-temperature battery pack by the circulating current. This battery heating mode can be implemented together with the discharging operation or charging operation of the battery.

[0017] In a second preferred embodiment, the first battery pack is connected in series with the first contactor, and the second battery pack is connected in series with the second contactor. Thereby, only one of the two battery packs can be operated. Further, the controller has a mode for detecting an abnormality of each battery pack. For example, according to this mode, it is determined whether the internal resistance of each cell is within an allowable range. When the internal resistance of one cell is outside the allowable range, this one cell is determined to be an abnormal cell. Next, the contactor connected in series with the battery pack including this abnormal cell is opened. Thereby, when one battery pack includes an abnormal cell, the remaining one battery pack can drive the electrical load.

[0018] Eventually, by disconnecting the battery pack including the cell having an abnormal internal resistance from the DC power supply, the safety of the DC power supply including the battery pack is improved. Further, when only one of the battery packs has an abnormal cell, the other battery pack can be operated.

[0019] In a third preferred embodiment and a second aspect of the present invention, a step-down transformer is used to implement a cell resistance detection mode. According to this cell resistance detection mode, a positive pulse voltage and a negative pulse voltage are alternately applied to the primary coil in order to detect the impedance, particularly preferably the internal resistance, of each cell. As a result, the internal resistance of each cell can be constantly detected. This cell resistance detection mode can also detect the impedance of the cell instead of the internal resistance of the cell. This cell resistance detection mode can be realized by a circuit that is essentially common to the battery heating mode described above. This simplifies the DC power supply.

[0020] In this cell resistance detection mode, the positive pulse voltage and the negative pulse voltage are alternately applied to the primary coil of the step-down transformer. As a result, during the positive pulse period in which the positive pulse voltage is applied to the primary coil, the secondary coil supplies a positive secondary circulating current to each cell of the battery pack. Similarly, during the negative pulse period in which the negative pulse voltage is applied to the primary coil, the secondary coil supplies a negative secondary circulating current to each cell of the battery pack. The voltage of each cell of the battery pack is preferably detected by a battery management system (BMS).

[0021] This battery management system (BMS) detects the cell voltage during the positive pulse period and the negative pulse period that are temporally close to each other. As a result, a voltage difference, which is the difference between the cell voltage during the positive pulse period and the cell voltage during the negative pulse period, can be detected. Furthermore, based on this voltage difference and the current flowing through the battery pack, the internal resistance of each cell can be detected. As a result, the internal resistance of each cell can be constantly and accurately monitored.

[0022] In a third preferred embodiment, a contact protection mode for protecting a contact connected in series with a battery pack is implemented. According to this contact protection mode, a pulse voltage is applied to the primary coil immediately before the contact is turned off. The secondary voltage induced in the secondary coil supplies a secondary current. The direction of this secondary current is opposite to the direction of the surge current flowing through the contact. Thereby, in the transient period when the contact is opened, the arc generated at the contact of the contact can be reduced.

[0023] This contact protection mode can also be adopted in a DC power supply having two battery packs connected in parallel, as well as in a DC power supply having only one battery pack. Further, this contact protection mode is realized by a circuit essentially common to the cell resistance detection mode and / or the battery heating mode described above. Thereby, the circuit configuration of the DC power supply is simplified.

[0024] In a fourth preferred embodiment and a third aspect of the present invention, the contact is connected in parallel with a bypass circuit including a capacitor and a diode connected in series. This diode permits the charging of the capacitor by the surge current of the contact when the contact is opened. Therefore, this diode bypasses the surge current of the contact generated when the contact is turned off.

[0025] Furthermore, this diode prevents the capacitor from discharging through the contact when the contact is closed next. The charge accumulated in the capacitor is gradually discharged through the leakage resistance of the diode when the contact is opened. It is also possible to connect a high-resistance element for capacitor discharge in parallel with the diode. As a result, the spark generated when the contact of the contact is opened can be reduced well. The contact can also conduct an alternating current instead of a direct current.

[0026] In a fifth preferred embodiment, the motor drive circuit is disposed behind or in front of two battery packs arranged on the left and right of the electric vehicle. These two battery packs connected in parallel supply DC power to the motor drive circuit through three cables. Each of the two battery packs has a first electrode terminal and a second electrode terminal. The first electrode terminal is disposed near the motor drive circuit, and the second electrode terminal is disposed far from the motor drive circuit. The two first electrode terminals are connected to the motor drive circuit through a first cable and a second cable, and the two second electrode terminals are connected to the motor drive circuit through a third cable. The third cable extends into the space between the two battery packs.

[0027] As a result, the following effects can be achieved. First, the two battery packs are connected to the motor drive circuit through substantially equal cable impedances. Second, the length of the cables can be shortened. Third, since each cable is disposed between the two battery packs, the safety of the cables is improved.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

[0029] First Embodiment A preferred embodiment of the present invention applied to a DC power supply of a battery electric vehicle (BEV) will be described with reference to the drawings. However, the circuit device of the present invention can be further applied to other electric circuits such as a stationary DC power supply.

[0030] FIG. 1 is a schematic plan view showing a DC power supply 1 fixed to a bottom plate portion 100 of a battery electric vehicle (BEV). The DC power supply 1 includes a first battery pack 11, a second battery pack 12, cables 141-143, and a contact box 3. The first battery pack 11 is disposed on the left side of the bottom plate portion 100, and the second battery pack 12 is disposed on the right side of the bottom plate portion 100.

[0031] The first battery pack 11 is composed of four battery modules 111 - 114 arranged in order in the longitudinal direction of the vehicle. The second battery pack 12 is composed of four battery modules 121 - 124 arranged in order in the longitudinal direction of the vehicle. Each battery module has a pair of electrode terminals. One of each pair of electrode terminals is arranged on the left end face of each battery module, and the other is arranged on the right end face of each battery module. However, most of the electrode terminals of each battery module are omitted in FIG. 1.

[0032] Each battery module is connected by six busbars 131 - 136. Busbar 131 connects the negative electrode terminal of battery module 111 and the positive electrode terminal of battery module 112. Busbar 132 connects the negative electrode terminal of battery module 112 and the positive electrode terminal of battery module 113. Busbar 133 connects the negative electrode terminal of battery module 113 and the positive electrode terminal of battery module 114.

[0033] Busbar 134 connects the negative electrode terminal of battery module 121 and the positive electrode terminal of battery module 122. Busbar 135 connects the negative electrode terminal of battery module 122 and the positive electrode terminal of battery module 123. Busbar 136 connects the negative electrode terminal of battery module 123 and the positive electrode terminal of battery module 124.

[0034] The first battery pack 11 has a positive electrode terminal 11P and a negative electrode terminal 11N. The positive electrode terminal 11P is the positive electrode terminal of battery module 111, and the negative electrode terminal 11N is the negative electrode terminal of battery module 114. Similarly, the second battery pack 12 has a positive electrode terminal 12P and a negative electrode terminal 12N. The positive electrode terminal 12P is the positive electrode terminal of battery module 121, and the negative electrode terminal 12N is the negative electrode terminal of battery module 124.

[0035] The contact box 3 of the DC power supply 1 is arranged behind the two battery packs 11 and 12. The contact box 3 fixed to the front end face of the motor drive circuit 2 supplies the DC power of the battery packs 11 and 12 to the motor drive circuit 2. The motor drive circuit 2 includes a three-phase inverter that applies a three-phase AC voltage to a traction motor (not shown).

[0036] The positive terminal 11P of the first battery pack 11 and the positive terminal 12P of the second battery pack 12 are connected to the contact box 3 through a common cable 143. The negative terminal 11N of the first battery pack 11 is connected to the contact box 3 through a cable 142. The negative terminal 12N of the second battery pack 12 is connected to the contact box 3 through a cable 141. The three cables 141 - 143 extend in the front - rear direction between the two battery packs 11 and 12.

[0037] Thereby, even when another vehicle collides with the side of this electric vehicle, the safety of the cables 141 - 143 can be improved. Furthermore, since the two battery packs 11 and 12 use a common cable 143, the variation in the current flowing through the two battery packs 11 and 12 can be reduced. Furthermore, the two symmetrically arranged cables 141 and 142 can have substantially equal electrical resistance values. For this reason, the variation in the current flowing through the two battery packs 11 and 12 is reduced.

[0038] Figure 2 shows the DC power supply 1 composed of the battery circuit 10 and the contact box 3. The battery circuit 10 includes a first battery management system (first BMS) 110 that monitors the first battery pack 11 and a second battery management system (second BMS) 120 that monitors the second battery pack 12. The first BMS 110 detects the current of the first battery pack 11 and the cell voltage of each cell of the first battery pack 11. Similarly, the second BMS 120 detects the current of the second battery pack 12 and the cell voltage of each cell of the second battery pack 12.

[0039] In FIG. 2, the first BMS 110 detects the module voltages of battery modules 111-114. Similarly, the second BMS 120 detects the module voltages of battery modules 121-124. Therefore, in FIG. 2, battery modules 111-114 and battery modules 121-124 each consist of one cell. This simplifies the explanation.

[0040] The contact box 3 houses a high-side circuit 31, a low-side circuit 32, a step-down transformer 5, and a controller 7. The contact box 3 has a high-side terminal 9H and a low-side terminal 9L for supplying DC power to the motor drive circuit 2.

[0041] The high-side terminal 9H is connected to the cable 143 through the high-side circuit 31. The high-side circuit 31 has a common contact 43, a pre-charge contact 44, a low-resistance element 45, a capacitor 81C, and a diode 81D. The common contact 43 connects the cable 143 and the high-side terminal 9H. The serially connected pre-charge contact 44 and low-resistance element 45 form a pre-charge circuit connected in parallel with the common contact 43.

[0042] As is well known, before the common contact 43 is turned on, the pre-charge contact 44 is turned on in advance. Thereby, a smoothing capacitor (not shown) connected to the high-side terminal 9H and the low-side terminal 9L is slowly charged through the low-resistance element 45. This smoothing capacitor reduces the switching noise voltage generated from the motor drive circuit 2.

[0043] Furthermore, the serially connected capacitor 81C and diode 81D form a bypass circuit connected in parallel with the common contact 43. This bypass circuit suppresses the contact spark generated when the common contact 43 is turned off. The operation of this bypass circuit will be described later.

[0044] The low-side terminal 9L is connected to the cables 141 and 142 through the low-side circuit 32. The low-side circuit 32 has the contacts 41 and 42, and the secondary coils 52 and 53. The low-side terminal 9L is connected to the cable 141 through the contact 41. Further, the low-side terminal 9L is connected to the cable 142 through the contact 42.

[0045] The step-down transformer 5 has the primary coil 51 wound around the magnetic core 50, and the two secondary coils 52 and 53. The secondary coil 52 is connected in series with the contact 42, and the secondary coil 53 is connected in series with the contact 41. In this embodiment, the number of turns of the secondary coils 52 and 53 is one turn, and the number of turns of the primary coil 51 is 100 turns. The number of turns of the primary coil 51 can be appropriately selected. The oscillator 6 applies a primary AC voltage to the primary coil 51. For example, the oscillator 6 consists of an H-bridge circuit composed of four MOSFETs.

[0046] The controller 7 controls the operations of the contacts 41 - 44 and the oscillator 6 based on the internal resistance values of each cell calculated by the first BMS 110 and the second BMS 120.

[0047] The switching control of the two battery packs will be described with reference to FIG. 3. The common contact 43 is turned on before the start of this battery pack switching. First, it is determined whether the battery pack 11 is normal (S100). In this embodiment, it is determined whether all cells of the battery pack 11 have an internal resistance value within a predetermined allowable range. If the internal resistance value of at least one cell of the battery pack 11 is outside this allowable range, the contact 42 is cut off (S102). Thereby, the motor drive circuit 2 is operated only by the battery pack 12.

[0048] Next, it is determined whether the battery pack 12 is normal (S104). In this embodiment, it is determined whether all cells of the battery pack 12 have an internal resistance value within a predetermined allowable range. If the internal resistance value of at least one cell of the battery pack 12 is outside this allowable range, the contactor 41 is opened (S106). As a result, the motor drive circuit 2 is operated only by the battery pack 11. Next, if the internal resistance values of all cells included in the battery packs 11 and 12 are within this allowable range, the two contactors 41 and 42 are closed (S108). As a result, the losses of the battery packs 11 and 12 can be reduced. Furthermore, it is possible to prevent the SOC difference between the battery packs 11 and 12 from expanding.

[0049] Ultimately, the DC power supply 1 has two battery packs 11 and 12 connected in parallel. The DC power supply 1 further has two contactors 41 and 42 connected in series separately from these two battery packs 11 and 12. Therefore, it is possible to select either parallel operation or individual operation of the two battery packs 11 and 12.

[0050] For example, a case where another vehicle collides with the left side of an electric vehicle is described with reference to FIG. 1. The first battery pack 11 is housed in the left side portion of this electric vehicle. In this case, the first battery pack 11 may be damaged, but the functions of the second battery pack 12 and the cables 141-143 may be maintained. The first battery pack 11 that has received a mechanical impact may have some cells with abnormal internal resistance values. Therefore, by opening the contactor 42, a fire in the first battery pack 11 can be prevented, and the traction motor can be driven by the second battery pack 12.

[0051] Conversely, in a case where another vehicle collides with the right side of the electric vehicle, a fire in the second battery pack 12 can be prevented by opening the contactor 41. Furthermore, the first battery pack 11 can drive the traction motor.

[0052] In this embodiment, the two contactors 41 and 42 divide the current supplied to the traction motor. As a result, the arc currents of the contactors 41 and 42 are significantly reduced respectively. For example, the arc energy of the contactor 41 in the emergency cut-off of the contactor 41 becomes approximately 1 / 4 because the current of the contactor 41 is about halved. Further, when only the contactor 41 is opened, the inductance of the traction motor increases the discharge current of the battery pack 11. As a result, the arc energy generated by the opening of the contactor 41 is further reduced.

[0053] Ultimately, when the two battery packs 11 and 12 connected in parallel supply current to the inductive load in parallel, the spark generated by the opening of either contactor is significantly reduced. However, when the contactor 41 is opened, only the current of the battery pack 12 flows through the inductances of the cable 141 and the secondary coil 53. As a result, these inductances increase the arc energy of the contactor 41. Similarly, when the contactor 42 is opened, only the current of the battery pack 11 flows through the inductances of the cable 142 and the secondary coil 52. As a result, these inductances increase the arc energy of the contactor 42.

[0054] Next, the supply of alternating current to the battery packs 11 and 12 by the step-down transformer 5 will be described with reference to FIGS. 4 and 5. This supply of alternating current is typically carried out in a cold environment, but it can also be carried out to improve the electrical characteristics of the battery pack. The oscillator 6 applies an alternating voltage VT1 to the primary coil 51. The frequency of the alternating voltage VT1 is, for example, 10 kHz. When the frequency is high, the step-down transformer 5 becomes compact. The alternating voltage VT1 consists of a positive pulse voltage and a negative pulse voltage that are alternately repeated. When the alternating voltage VT1 is applied to the primary coil 51, a secondary voltage VT2 is induced in each of the secondary coils 52 and 53. The directions of the two secondary voltages VT2 are the same.

[0055] The battery pack 11 has an open-circuit voltage VB and an internal resistance r10. The battery pack 12 has an open-circuit voltage VB and an internal resistance r20. The open-circuit voltages of the two battery packs 11 and 12 are not exactly the same. However, for the sake of simplicity, it is assumed that they are equal to each other. The two secondary voltages VT2 circulate a secondary current IC through a current circulation circuit composed of the two battery packs 11 and 12. The two battery packs 11 and 12 supply a load current IL to the motor drive circuit 2 through the connection point 54 of the two secondary coils 52 and 53. The current component supplied to the motor drive circuit 2 by the secondary coil 52 has the same amplitude and the opposite direction as the current component supplied to the motor drive circuit 2 by the secondary coil 53.

[0056] Figure 4 shows the current flow during the period when a positive pulse voltage is applied. The secondary voltage VT2 of the secondary coil 52 reduces the current component supplied to the motor drive circuit 2 by the battery pack 11. Conversely, the secondary voltage VT2 of the secondary coil 53 increases the current component supplied to the motor drive circuit 2 by the battery pack 12. Eventually, the load current IL is not affected by the two secondary coils 52 and 53.

[0057] Figure 5 shows the current flow during the period when a negative pulse voltage is applied. The secondary voltage VT2 of the secondary coil 52 increases the current component supplied to the motor drive circuit 2 by the battery pack 11. Conversely, the secondary voltage VT2 of the secondary coil 53 reduces the current component supplied to the motor drive circuit 2 by the battery pack 12. Eventually, the load current IL is not affected by the two secondary coils 52.

[0058] Ultimately, when the secondary coil 52 connected in series with the battery pack 11 has the same number of turns as the secondary coil 53 connected in series with the battery pack 12, the alternating current IC can circulate only through the battery packs 11 and 12. Thereby, during the period when the battery packs 11 and 12 discharge to the motor drive circuit 2, the alternating current circulation through the battery packs 11 and 12 can be realized. Similarly, during the period when the battery packs 11 and 12 are charged, the alternating current circulation through the battery packs 11 and 12 can be realized.

[0059] The DC power supply 1 can select the parallel operation and the single operation of the two battery packs. The spark generated by the opening of the contact shortens the contact life. The spark energy is proportional to the series inductance of the circuit.

[0060] Therefore, the inductance of the secondary coil 52 or 53 enhances the spark of the contact 41 or 42. This problem is improved by the contact protection operation shown in FIGS. 6 and 7.

[0061] FIG. 6 shows the current flow during the transient period when the contact 42 is opened. The battery pack 11 supplies the current I1 to the motor drive circuit 2, and the battery pack 12 supplies the current I2 to the motor drive circuit 2. The oscillator 6 applies a positive pulse voltage VT1 to the primary coil 51 during this transient period. Thereby, the secondary coils 51 and 52 circulate a positive-direction circulating current ICP through the battery packs 11 and 12 and the contacts 41 and 42. As a result, the battery pack 11 is charged and the battery pack 12 is discharged.

[0062] Furthermore, the current flowing through the contact 42 during the period when the contact 42 is open is I1 - ICP. As a result, the life of the contact 42 is improved.

[0063] Figure 7 shows the current flow during the transient period when the contactor 41 is opened. The battery pack 11 supplies the current I1 to the motor drive circuit 2, and the battery pack 12 supplies the current I2 to the motor drive circuit 2. The oscillator 6 applies a negative pulse voltage VT1 to the primary coil 51 during this transient period. As a result, the secondary coils 51 and 52 circulate a negative-direction circulating current ICN through the battery packs 11 and 12 and the contactors 41 and 42. Consequently, the battery pack 11 is discharged and the battery pack 12 is charged. Further, the current flowing through the contactor 41 whose contacts are performing an opening operation becomes I2 - ICN. As a result, the life of the contactor 41 is improved.

[0064] The transient period during which the contactor 41 or 42 is open is short. Therefore, the oscillation power supplied to the step-down transformer 5 by the oscillator 6 is conserved.

[0065] However, the step-down transformer 5 does not have a secondary coil connected in series with the common contactor 43 shown in FIG. 2. For this reason, the arc of the common contactor 43 cannot be suppressed by the secondary pulse current of the step-down transformer 5. This problem can be solved by the bypass circuit 81 shown in FIG. 2.

[0066] This bypass circuit 81 connected in parallel with the common contactor 43 consists of a capacitor 81C and a diode 81D connected in series. The diode 81D bypasses the spark current of the common contactor 43.

[0067] Next, prevention of arcing in the common conductor 43 will be described. The battery packs 11 and 12 supply DC current to the traction motor through the motor drive circuit 2. When the common conductor 43 is opened, an arc is generated on the contacts of the common conductor 43. The inductance connected in series with the common conductor 43 supplies the arc energy. The motor drive circuit 2 is connected in parallel with a smoothing capacitor. Therefore, this smoothing capacitor absorbs the inductance energy of the traction motor. However, the cables 141 - 143 and the step - down transformer 5 connected in series with the battery packs 11 and 12 have an inductance that increases the arc of the common conductor 43. This problem is solved by a bypass circuit 81 connected in parallel with the common conductor 43.

[0068] This bypass circuit consists of a capacitor 81C and a diode 81D connected in series. When the common contactor 43 is open, a bypass current flows through the capacitor 81C and the diode 81D. As a result, the arc of the common contactor 43 is well eliminated.

[0069] When the common contactor 43 is closed, the charge accumulated in the capacitor 81C is short - circuited through the common contactor 43. However, this short - circuit is blocked by the diode 81D. The charge accumulated in the capacitor 81C is slowly discharged through the high reverse resistance value of the diode 81D during the period when the common contactor 43 is closed.

[0070] The DC power supply 1 shown in FIG. 2 opens the contactor 42 when one cell of the battery pack 11 is defective. Further, the DC power supply 1 opens the contactor 41 when one cell of the battery pack 12 is defective. Thereby, in most cases where a defective cell is detected, the operation of the electric vehicle can be continued.

[0071] Particularly important cell failures are internal short - circuits of the cell due to dendrite growth. Battery fires caused by thermal runaway of the cell sometimes occur due to this internal short - circuit. It is known that the internal resistance of the cell gradually decreases due to dendrite growth. Therefore, by monitoring the internal resistance of the cell, the occurrence of an internal short - circuit of the cell in the near future can be predicted. However, the detection of the internal resistance of the cell for finding an internal short - circuit of the cell essentially always needs to be carried out. This means that the internal resistance detection operation of each cell must be carried out even during the discharge or charge of the battery. However, the detection of the internal resistance of each cell during this discharge or charge is difficult due to fluctuations in the discharge current or charge current.

[0072] Figures 8 and 9 disclose a novel cell resistance detection operation using a compact step - down transformer 5. Figure 8 shows a part of a first battery management device (first BMS) 110 that detects the cell voltage of a battery pack 11. A second battery management device (second BMS) 120 that detects the cell voltage of a battery pack 12 is also essentially the same as the first BMS 110. In Figure 8, only four cells 11A - 11D of the battery pack 11 are shown. The first BMS 110 sequentially transmits the cell voltages V11 - V14 of the cells 11A - 11D to the controller 7.

[0073] Cell 11A has an open circuit voltage (OCV) V1 and an internal resistance (IR) r1. Cell 11B has an open circuit voltage V2 and an internal resistance r2. Cell 11C has an open circuit voltage V3 and an internal resistance r3. Cell 11D has an open circuit voltage V4 and an internal resistance r4. Cells 11A - 11D supply a load current IL to the motor drive circuit 2. Further, the secondary voltages induced in the secondary coils 52 and 53 circulate a circulating current IC through cells 11A - 11D. As a result, the internal resistances r1 - r4 of cells 11A - 11D each generate a voltage drop due to the load current IL and the circulating current IC. Therefore, the cell voltage V11 of cell 11A becomes V1 + r1(IL + IC), and the cell voltage V12 of cell 11B becomes V2 + r2(IL + IC). Similarly, the cell voltage V13 of cell 11C becomes V3 + r3(IL + IC), and the cell voltage V14 of cell 11D becomes V4 + r4(IL + IC).

[0074] The oscillator 6 alternately applies a positive pulse voltage and a negative pulse voltage to the primary coil 51 of the step - down transformer 5. The secondary coils 52 and 53 circulate a substantially constant - current positive pulse current ICP through the battery packs 11 and 12 during the positive pulse period when the positive pulse voltage is applied to the primary coil 51. Further, the secondary coils 52 and 53 circulate a substantially constant - current negative pulse current ICN through the battery packs 11 and 12 during the negative pulse period when the negative pulse voltage is applied to the primary coil 51. The integrated value of the positive pulse current ICP is equal to the integrated value of the negative pulse current ICN.

[0075] The cell voltages V11 - V14 are sequentially selected by the first BMS 110 during the positive pulse period, converted into digital signals by the A / D converter 60, and then sent to the controller 7. Similarly, the cell voltages V11 - V14 are sequentially selected by the first BMS 110 during the negative pulse period, converted into digital signals by the A / D converter 60, and then sent to the controller 7. As a result, eight cell voltages are transmitted to the controller 7.

[0076] The detection operation of the internal resistance r1 of cell 11A will be described. First, during the positive pulse period when the positive pulse current ICP flows through cell 11A, the cell voltage V11 is detected. This cell voltage V11 is called the positive cell voltage V11P. Next, during the negative pulse period when the negative pulse current ICN flows through cell 11A, the cell voltage V11 is detected. The cell voltage V11 is called the negative cell voltage V11N. It is assumed that the positive pulse current ICP and the negative pulse current ICN have the same amplitude. Furthermore, it is assumed that cell 11A has a constant open-circuit voltage V1 during the positive pulse period and the negative pulse period.

[0077] Next, the voltage difference ΔV between the two cell voltages V11P and V11N is detected. This voltage difference ΔV does not include the open-circuit voltage V1 of cell 11A. Furthermore, when the load current IL is constant, the voltage difference ΔV does not include the voltage drop (r1·IL) of the internal resistance r1 due to the load current IL. Therefore, the voltage difference ΔV becomes 2IC·r1, and the internal resistance r1 becomes ΔV / 2IC. Eventually, by using the AC circulating current supplied by the step-down transformer 5 to the battery pack 11, the internal resistance r1 can be detected without being affected by the load current IL and the open-circuit voltage V1 during the period when the battery pack 11 discharges to the motor drive circuit 2. The internal resistance of each of cells 11B - 11D is detected in the same way.

[0078] The circuit of the first battery management device (first BMS) 110 will be described with reference to FIG. 8. The positive electrode of cell 11A is connected to the signal line 71 through the switch S1. The positive electrode of cell 11B is connected to the signal line 72 through the switch S2. The positive electrode of cell 11C is connected to the signal line 71 through the switch S3. The positive electrode of cell 11D is connected to the signal line 72 through the switch S4. The negative electrode of cell 11D is connected to the signal line 71 through the switch S5. Each of the switches S1 - S5 consists of two MOSFETs connected in series in opposite directions. The two signal lines 71 and 72 are connected to the capacitor 70.

[0079] When switches S1 and S2 are turned on, the voltage of capacitor 70 becomes equal to the cell voltage V11 of cell 11A. When switches S2 and S3 are turned on, the voltage of capacitor 70 becomes equal to the cell voltage V12 of cell 11B. When switches S3 and S4 are turned on, the voltage of capacitor 70 becomes equal to the cell voltage V13 of cell 11C. When switches S4 and S5 are turned on, the voltage of capacitor 70 becomes equal to the cell voltage V14 of cell 11D. Each voltage of capacitor 70 is converted into a digital signal by A / D converter 60 by turning on two of the four switches S6 - S9, and then transmitted to controller 7. Switches S6 - S9 are composed of two MOSFETs connected in series in the reverse direction, similar to switches S1 - S4.

[0080] Figure 9 is a timing chart showing the switch operations of switches S1 - S9. In the first half and the second half of period T1, switches S1 and S2 are turned on, and the voltage of capacitor 70 becomes equal to cell voltage V11. Similarly, in the first half and the second half of period T2, switches S2 and S3 are turned on, and the voltage of capacitor 70 becomes equal to cell voltage V12. In the first half and the second half of period T3, switches S3 and S4 are turned on, and the voltage of capacitor 70 becomes equal to cell voltage V13. Similarly, in the first half and the second half of period T4, switches S4 and S5 are turned on, and the voltage of capacitor 70 becomes equal to cell voltage V14.

[0081] In the first half of period T1, switches S6 and S9 are turned on immediately after switches S1 and S2 are turned off. In the second half of period T1, switches S7 and S8 are turned on immediately after switches S1 and S2 are turned off. Similarly, in the first half of period T2, switches S6 and S9 are turned on immediately after switches S2 and S3 are turned off. In the second half of period T2, switches S7 and S8 are turned on immediately after switches S2 and S3 are turned off.

[0082] In the first half of cycle T3, switches S6 and S9 are turned on immediately after switches S3 and S4 are turned off. In the second half of cycle T3, switches S7 and S8 are turned on immediately after switches S3 and S4 are turned off. Similarly, in the first half of cycle T4, switches S6 and S9 are turned on immediately after switches S4 and S5 are turned off. In the second half of cycle T4, switches S7 and S8 are turned on immediately after switches S4 and S5 are turned off.

[0083] Ultimately, each cell voltage is sequentially transmitted to capacitor 70 under the control of switches S1 - S4. Further, the voltage of capacitor 70 is sent to A / D converter 60 under the control of switches S6 - S9 which is carried out after switches S1 - S4 are turned off. Switches S6 - S9 have the function of inverting the voltage direction of capacitor 70. The positive pulse current ICP flows in the first half of cycles T1 - T4 of the circulating current IC, and the negative pulse current ICN flows in the second half of cycles T1 - T4 of the circulating current IC. Therefore, two types of cell voltages of one cell are detected for each of cycles T1 - T4. For example, when battery pack 11 consists of 100 cells connected in series with each other, detecting the internal resistance of all cells requires 100 cycles.

[0084] The internal resistance r of the cell is ΔV / (ICP + ICN). ΔV is the voltage difference between the cell voltage value during the period when the positive pulse current ICP flows through the battery pack and the cell voltage value during the period when the negative pulse current ICN flows through the battery pack. Since the directions of the positive pulse current ICP and the negative pulse current ICN are opposite, the voltage difference ΔV can be increased.

[0085] Based on the internal resistances r1 - r4 of cells 11A - 11D, other electrical parameters of each cell can also be calculated. For example, the degradation of cells 11A - 11D can be estimated based on the internal resistances r1 - r4. Further, the voltage drops of each of the internal resistances r1 - r4 can be calculated from the internal resistance values r1 - r4 of cells 11A - 11D. The open - circuit voltages V1 - V4 of each of cells 11A - 11D can be calculated from these voltage drops and the cell voltages V11 - V14.

[0086] A control example of the controller 7 will be described with reference to the flowchart shown in FIG. 10. The contactors 41 - 43 are closed. Next, it is determined whether the temperatures Tb of the battery packs 11 and 12 are lower than a predetermined threshold value Tth (S100). If the determination result is Yes, an AC heating subroutine (S102) for supplying an alternating current to the battery packs 11 and 12 is executed. If the determination result is No, this AC heating subroutine is not executed.

[0087] In this AC heating subroutine, the oscillator 6 supplies a primary AC current to the primary coil 51. As a result, a secondary voltage in the same direction is induced in the secondary coils 51 and 52, and a secondary circulating current is supplied to the battery packs 11 and 12. As a result, the battery packs 11 and 12 are heated. When the temperatures of the battery packs 11 and 12 reach a predetermined value, this AC heating subroutine is terminated.

[0088] Next, an internal resistance detection subroutine is executed (S104). In this internal resistance detection subroutine, a positive pulse current and a negative pulse current are alternately supplied to each cell in order to detect the internal resistance of each cell of the battery packs 11 and 12. As a result, the first BMS 110 detects the internal resistance value of the battery pack 11, and the second BMS 120 detects the internal resistance value of each cell of the battery pack 12.

[0089] Next, it is determined whether all the internal resistance values detected from the battery pack 11 are within a predetermined allowable range (S106). If the determination result is No, the process proceeds to step S108. In step S108, a contactor protection subroutine for protecting the contactor 42 is executed. According to this contactor protection subroutine, the oscillator 6 passes a secondary circulating current. This secondary circulating current reduces the current flowing through the contactor 42. Preferably, this secondary circulating current is substantially equal to the load current IL. As a result, the current flowing through the contactor 42 becomes almost zero. Next, the contactor 42 is opened (S110). As a result, no arc is generated on the contactor 42.

[0090] If all the internal resistance values of the battery pack 11 are within the allowable range, it is determined whether all the internal resistance values of the battery pack 12 are within the allowable range (S112). If the determination result is No, the process proceeds to step S114.

[0091] In step S114, a contact protection subroutine for protecting the contact 41 is executed. According to this contact protection subroutine, the oscillator 6 passes a secondary circulating current. This secondary circulating current reduces the current flowing through the contact 41. Preferably, this secondary circulating current is substantially equal to the load current IL. As a result, the current flowing through the contact 41 becomes almost zero. Next, the contact 41 is opened (S116). As a result, an arc does not occur on the contact 41.

[0092] If all the internal resistance values of the battery packs 11 and 12 are within a predetermined allowable range, the contacts 41 and 42 are closed. Thereby, the battery packs 11 and 12 supply the load current IL to the motor drive circuit 2.

[0093] In particular, it is important to determine whether the internal resistance r of each cell is higher than a predetermined minimum value. When the internal resistance r is lower than this minimum value, an internal short circuit of the cell is presumed.

[0094] One modification is described with reference to FIG. 11. The battery pack 11 of the DC power supply 1 is composed of battery modules 111-114, and the battery pack 12 is composed of battery modules 121-124. Each battery module in FIG. 11 is arranged in the reverse direction compared to each battery module in FIG. 1. FIG. 12 shows the DC power supply 1 in FIG. 11. The contacts 41 and 42 are arranged on the high side, and the contacts 43 and 44 are arranged on the low side. The secondary coils 52 and 53 are arranged on the high side.

[0095] Second Embodiment The second embodiment of the present invention will be described with reference to FIG. 13. In FIG. 13, the cable 143 is not connected to the contact box 3. Further, the battery modules 121-124 shown in FIG. 13 are arranged in the reverse direction compared to the battery modules 121-124 shown in FIG. 1.

[0096] The cable 143 shown in FIG. 13 connects the positive terminal 11P of the battery module 111 and the negative terminal 12N of the battery module 121. The cable 141 connects the positive terminal 12P of the battery module 124 and the contact box 3. The cable 142 connects the negative terminal 11N of the battery module 114 and the contact box 3.

[0097] In FIG. 13, the battery module 124 with the highest potential and the battery module 114 with the lowest potential are close to the contact box 3. As a result, the lengths of the cables 141 and 142 are the shortest. Therefore, by reducing the inductance of the cables 141-143, the arcs of the contacts 43 and 46 shown in FIG. 14 are reduced.

[0098] FIG. 14 is a circuit diagram showing the DC power supply 1 shown in FIG. 13. The two battery packs 11 and 12 are connected in series. The positive terminal of the battery pack 12 is connected to the motor drive circuit 2 through the cable 141, the contact 46, and the secondary coil 54 of the step-down transformer 5. The negative terminal of the battery pack 11 is connected to the motor drive circuit 2 through the cable 142 and the contact 43. The motor drive circuit 2 composed of a three-phase inverter is connected in parallel with the smoothing capacitor 20.

[0099] The bypass circuit 31 composed of the capacitor 81C and the diode 81D connected in series is connected in parallel with the contactor 46. The contactor 46 and the bypass circuit 31 form the high-side circuit 31. The contactor 44 and the low-resistance element 45 connected in series form the precharge circuit. This precharge circuit connected in parallel with the contactor 43 forms the low-side circuit 32 together with the contactor 43.

[0100] The secondary voltage is induced in the secondary coil 53 by the primary current supplied from the oscillator 6 to the primary coil 51 of the step-down transformer 5. The battery packs 11 and 12, the contactor 46, the secondary coil 54, the smoothing capacitor 20, and the contactor 43 form a current circulation circuit in which the secondary circulating current IC circulates. The smoothing capacitor 20 that absorbs the high-frequency noise voltage of the three-phase inverter of the motor drive circuit 2 has a relatively high capacitance. Therefore, the smoothing capacitor 20 can absorb the charge charged or discharged from the battery packs 11 and 12 by the secondary circulating current IC.

[0101] Ultimately, the current circulation circuit of the second embodiment can achieve essentially the same effect as the current circulation circuit of the first embodiment. Therefore, this circulating current can heat the low-temperature battery pack 11 or 12. Furthermore, the internal resistance of each cell of the battery packs 11 and 12 can be detected by this circulating current. Moreover, immediately before the contactor 43 or 46 is opened, the arc of the contactor 43 or 46 can be suppressed by circulating the circulating current IC in the direction opposite to the load current IL. The bypass circuit 81 can also be connected in parallel with the contactor 43.

[0102] Third Embodiment A third embodiment of the present invention will be described with reference to FIG. 15. FIG. 15 shows a bidirectional bypass circuit 80 connected in parallel with the contactor 46. This bidirectional bypass circuit 80 consists of a first bypass circuit 81 and a second bypass circuit 82. The first bypass circuit 81 consists of a capacitor 81C and a diode 81D connected in series. The second bypass circuit 82 consists of a capacitor 82C and a diode 82D connected in series. The first bypass circuit 81 and the second bypass circuit 82 are each connected in parallel with the contactor 46. The current directions of the two diodes 81D and 82D are opposite to each other.

[0103] As a result, when the contactor 46 cuts off the current I1, the first bypass circuit 81 reduces the arc of the contactor 46. Conversely, when the contactor 46 cuts off the current I2, the second bypass circuit 82 reduces the arc of the contactor 46.

[0104] For example, in the first and second embodiments, during the period when the motor drive circuit 2 regenerates current to the battery packs 11 and 12, the second bypass circuit 82 becomes effective. Furthermore, this bidirectional bypass circuit is effective for protecting an AC contactor that cuts off an alternating current. In order to delay the charging of these capacitors, it is possible to connect a charging resistor in series with the diode. Furthermore, in order to accelerate the discharge of these capacitors, it is possible to connect a discharge resistor in parallel with the diode.

Claims

1. A circuit device including a first battery pack and a second battery pack connected in parallel to each other, The circuit arrangement further includes a step-down transformer driven by an oscillator controlled by the controller; the step-down transformer has a first secondary coil connected in series with the first battery pack and a second secondary coil connected in series with the second battery pack; the two secondary coils and the two battery packs form a current circulating circuit for circulating a secondary current of the step-down transformer; A circuit device, characterized in that the two secondary voltages induced in the two secondary coils have the same direction in the current circulation circuit.

2. 2. The circuit device according to claim 1, wherein the controller has a battery heating mode for heating the battery packs by circulating the secondary current through the current circulation circuit when the first battery pack and the second battery pack are at low temperatures.

3. the first battery pack is connected in series with a first contactor; the second battery pack is connected in series with a second contactor; The controller: detecting a state of the two battery packs; closing the two contactors when the two battery packs are not faulty; opening the second contactor when the second battery pack is faulty; and opening said first contactor when said first battery pack is defective.

4. Each of the two battery packs is composed of a number of cells connected in series; the controller has a cell resistance detection mode for detecting an internal resistance of each of the cells by alternately applying a positive pulse voltage and a negative pulse voltage to a primary coil of the step-down transformer; The cell resistance detection mode includes: detecting a positive cell voltage of each of the cells when the positive pulse voltage is applied to the primary coil; detecting a negative cell voltage of each of the cells when the negative pulse voltage is applied to the primary coil; calculating an internal resistance of each of the cells based on a voltage difference between the positive cell voltage and the negative cell voltage; 2. The circuit arrangement according to claim 1, further comprising:

Images