JP7696465B2 - circuit device - Google Patents

Description

Related Art References

This application claims priority to PCT/JP2023/04873, filed February 14, 2023, the entire contents of which are incorporated by reference.

The present invention relates to a technology for improving the reliability of circuit devices. In particular, the present invention relates to a technology for improving the reliability of DC power supplies.

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

Generally, to ensure the safety of the battery, the DC power supply of an electric vehicle has a power contactor to disconnect the battery. However, when the mechanical contacts of the contactor are opened, the inductance of the circuit will form an arc on the mechanical contacts of the contactor. The traction motor of an electric vehicle uses large power. Therefore, it is not easy to extinguish this arc.

Furthermore, electric vehicle batteries are known to have various problems in cold weather. For this reason, it is important to heat electric vehicle batteries in cold weather. AC heating technology is known, in which an alternating current is supplied to the primary coil of a transformer. This transformer has a secondary coil connected in series with the battery. With this AC heating technology, the battery can be heated quickly.

However, electric vehicle batteries are formed by connecting many cells in series. The internal resistance of each cell varies depending on the temperature, SOC, etc. Therefore, even if a constant alternating current is supplied to the battery using AC heating technology, the temperature rise of each cell varies depending on the fluctuation of 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 desirable to detect the internal resistance of each cell in advance.

Furthermore, this AC heating technique requires a transformer in series with the battery. As a result, arcing across the contactor is more severe due to the inductance of this transformer.

Furthermore, because the battery of an electric vehicle is large, the power cable connecting the battery and the motor drive circuit is long. Therefore, arcing on the contactor becomes 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 contactor is opened. However, the resistor reduces the surge current flowing into the capacitor.

The DC power supplies disclosed in US Pat. Nos. 5,993,333 and 5,993,635 reduce the voltage difference between two batteries connected in parallel by charging only one of the two batteries. Each battery is connected in series with each contactor.

Patent document 3 owned by the present applicant discloses an AC current supply circuit that supplies AC current to a battery. This AC current supply circuit proposes a step-down transformer that supplies AC current to a battery in order to improve the charging and discharging performance of the battery in a low-temperature environment.

WO2013/042165 Japanese Patent 7071229 Japanese Patent 7301208

The object of the present invention is to provide a circuit arrangement having excellent reliability under various operating conditions. Preferably, the circuit arrangement is configured as a DC power supply for an electric vehicle. The electric vehicle of the present invention preferably includes a ground vehicle having a traction motor, as well as a ship, submarine, airplane, drone, etc. having a motor that generates propulsion force.

In a first aspect of the present invention, a current circulation circuit is formed by two secondary coils of a step-down transformer and two battery packs connected in series. Each secondary voltage induced in the two secondary coils circulates a secondary current in this current circulation circuit. 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 in this current circulation circuit.

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 in the other battery pack. Therefore, the oscillator connected to the primary coil of the step-down transformer only needs to supply to the primary coil power equivalent to the AC power loss due to the internal resistance of the two battery packs.

Preferably, the two secondary coils of the step-down transformer have equal numbers of turns. 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. As a result, the two secondary coils do not supply secondary currents to the electrical loads connected to the two battery packs. As a result, the secondary currents of the two secondary coils circulate only through the two battery packs.

In a first preferred embodiment, the controller has a battery heating mode for heating a cold battery pack by circulating current. This battery heating mode can be implemented in conjunction with a battery discharging or charging operation.

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. This allows only one of the two battery packs to be operated. Furthermore, the controller has a mode for detecting an abnormality in each battery pack. For example, this mode determines 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 the abnormal cell is opened. This allows an electric load to be driven by the remaining battery pack when one battery pack includes an abnormal cell.

As a result, by disconnecting the battery pack containing the cell with abnormal internal resistance from the DC power supply, the safety of the DC power supply including the battery pack is improved. Furthermore, when only one battery pack has an abnormal cell, the other battery pack can be operated.

In the third preferred embodiment and the second aspect of the present invention, the cell resistance detection mode is implemented by using a step-down transformer. According to this cell resistance detection mode, a positive pulse voltage and a negative pulse voltage are alternately applied to the primary coil to detect the impedance, particularly preferably the internal resistance, of each cell. This allows the internal resistance of each cell to 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 essentially common to the battery heating mode already described. This simplifies the DC power supply.

In this cell resistance detection mode, a positive pulse voltage and a negative pulse voltage are alternately applied to the primary coil of the step-down transformer. As a result, during the positive pulse period when 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 when 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).

This battery management system (BMS) detects the cell voltage during each positive pulse period and negative pulse period that are close to each other in time. This makes it possible to detect the voltage difference between the cell voltage during the positive pulse period and the cell voltage during the negative pulse period. Furthermore, based on this voltage difference and the current flowing through the battery pack, it is possible to detect the internal resistance of each cell. As a result, it is possible to constantly and accurately monitor the internal resistance of each cell.

In a third preferred embodiment, a contactor protection mode is implemented to protect a contactor connected in series with the battery pack. According to this contactor protection mode, a pulse voltage is applied to the primary coil just before the contactor is turned off. A secondary voltage is induced in the secondary coil to supply a secondary current, the direction of which is opposite to the direction of the surge current flowing through the contactor. This can reduce arcing at the contactor contacts during the transient period when the contactor is opened.

This contactor protection mode can be adopted not only in a DC power supply having two battery packs connected in parallel, but also in a DC power supply having only one battery pack. Furthermore, this contactor protection mode is realized by a circuit that is essentially common to the cell resistance detection mode and/or battery heating mode already described. This simplifies the circuit configuration of the DC power supply.

In a fourth preferred embodiment and the third aspect of the present invention, the contactor is connected in parallel with a bypass circuit including a series connected capacitor and diode. The diode allows the contactor surge current to charge the capacitor when the contactor is opened. The diode thus bypasses the contactor surge current that occurs when the contactor is turned off.

Furthermore, the diode stops the capacitor from discharging through the contactor when it is next closed. The charge stored in the capacitor is gradually discharged through the leakage resistance of the diode when the contactor is opened. It is also possible to connect a high resistance element for discharging the capacitor in parallel with the diode. As a result, sparks that occur when the contactor contacts are opened can be effectively reduced. The contactor can also carry alternating current instead of direct current.

In a fifth preferred embodiment, the motor drive circuit is disposed behind or in front of two battery packs disposed on the left and right sides 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 is extended into the space between the two battery packs.

This provides the following advantages: First, the two battery packs are connected to the motor drive circuit through cable impedances that are approximately equal. Second, the length of the cables can be shortened. Second, the safety of the cables is improved because each cable is disposed between two battery packs.

FIG. 1 is a schematic plan view showing the spatial arrangement of a DC power supply according to a first embodiment. FIG. 2 is a circuit diagram showing the DC power supply of FIG. FIG. 3 is a flowchart showing the connection switching of the battery pack. FIG. 4 is a schematic circuit diagram showing the positive component of the secondary current circulating in the AC current circulating circuit. FIG. 5 is a schematic circuit diagram showing the negative component of the secondary current circulating in the AC current circulating circuit. FIG. 6 is a schematic circuit diagram showing a secondary current for reducing arcing in the first contactor. FIG. 7 is a schematic circuit diagram showing a secondary current for reducing arcing in the second contactor. FIG. 8 is a schematic circuit diagram showing a circuit for detecting the internal resistance of each cell. FIG. 9 is a timing chart showing the operation of detecting the internal resistance of each cell in sequence. FIG. 10 is a flow chart illustrating various modes using a common step-down transformer. FIG. 11 is a schematic plan view showing the spatial arrangement of DC power supplies in a modified embodiment. FIG. 12 is a circuit diagram showing the DC power supply of FIG. FIG. 13 is a schematic plan view showing the spatial arrangement of the DC power supplies of the second embodiment. FIG. 14 is a circuit diagram showing the DC power supply of FIG. FIG. 15 is a circuit diagram showing a bypass circuit according to the third 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 arrangement of the present invention can also be applied to other electric circuits such as stationary DC power supplies.

Figure 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 has a first battery pack 11, a second battery pack 12, cables 141-143, and a contactor 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.

The first battery pack 11 consists of four battery modules 111-114 arranged in sequence in the fore-and-aft direction of the vehicle. The second battery pack 12 consists of four battery modules 121-124 arranged in sequence in the fore-and-aft direction of the vehicle. Each battery module has a pair of electrode terminals. One of each pair of electrode terminals is located on the left end surface of each battery module, and the other is located on the right end surface of each battery module. However, most of the electrode terminals of the battery modules are omitted from FIG. 1.

Each battery module is connected by six bus bars 131-136. Bus bar 131 connects the negative terminal of battery module 111 to the positive terminal of battery module 112. Bus bar 132 connects the negative terminal of battery module 112 to the positive terminal of battery module 113. Bus bar 133 connects the negative terminal of battery module 113 to the positive terminal of battery module 114.

Bus bar 134 connects the negative terminal of battery module 121 and the positive terminal of battery module 122. Bus bar 135 connects the negative terminal of battery module 122 and the positive terminal of battery module 123. Bus bar 136 connects the negative terminal of battery module 123 and the positive terminal of battery module 124.

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

The contactor box 3 of the DC power source 1 is disposed behind the two battery packs 11 and 12. The contactor box 3, which is fixed to the front end face of the motor drive circuit 2, supplies DC power from 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).

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 contactor box 3 via a common cable 143. The negative terminal 11N of the first battery pack 11 is connected to the contactor box 3 via a cable 142. The negative terminal 12N of the second battery pack 12 is connected to the contactor box 3 via a cable 141. The three cables 141-143 extend in the front-rear direction between the two battery packs 11 and 12.

This improves the safety of the cables 141-143 even when another vehicle collides into the side of the electric vehicle. 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 cables 141 and 142, which are arranged symmetrically with respect to each other, can have approximately equal electrical resistance values. Therefore, the variation in the current flowing through the two battery packs 11 and 12 is reduced.

Figure 2 shows a DC power source 1 consisting of a battery circuit 10 and a contactor 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.

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

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

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 contactor 43, a precharge contactor 44, a low resistance element 45, a capacitor 81C, and a diode 81D. The common contactor 43 connects the cable 143 to the high side terminal 9H. The precharge contactor 44 and the low resistance element 45, which are connected in series, form a precharge circuit connected in parallel with the common contactor 43.

As is well known, the precharge contactor 44 is turned on before the common contactor 43 is turned on. This causes the smoothing capacitor (not shown) connected to the high side terminal 9H and the low side terminal 9L to be slowly charged through the low resistance element 45. This smoothing capacitor reduces the switching noise voltage generated by the motor drive circuit 2.

Furthermore, the series-connected capacitor 81C and diode 81D form a bypass circuit connected in parallel with the common contactor 43. This bypass circuit prevents contact sparks that occur when the common contactor 43 is turned off. The operation of this bypass circuit will be described later.

The low-side terminal 9L is connected to cables 141 and 142 through the low-side circuit 32. The low-side circuit 32 has contactors 41 and 42 and secondary coils 52 and 53. The low-side terminal 9L is connected to cable 141 through the contactor 41. Furthermore, the low-side terminal 9L is connected to cable 142 through the contactor 42.

The step-down transformer 5 has a primary coil 51 and two secondary coils 52 and 53, each wound around a magnetic core 50. The secondary coil 52 is connected in series with the contactor 42, and the secondary coil 53 is connected in series with the contactor 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 selected appropriately. The oscillator 6 applies a primary AC voltage to the primary coil 51. For example, the oscillator 6 is composed of an H-bridge circuit consisting of four MOSFETs.

The controller 7 controls the operation of the contactors 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.

The switching control of the two battery packs will be described with reference to FIG. 3. The common contactor 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 the cells of the battery pack 11 have internal resistance values within a predetermined tolerance range. If the internal resistance value of at least one cell of the battery pack 11 is outside this tolerance range, the contactor 42 is cut off (S102). As a result, the motor drive circuit 2 is operated only by the battery pack 12.

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

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

For example, FIG. 1 illustrates a case where another vehicle collides with the left side of an electric vehicle. A first battery pack 11 is housed in the left portion of the 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. In the first battery pack 11 that has been subjected to a mechanical shock, some cells may have 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.

Conversely, in the 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.

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 each significantly reduced. For example, the arc energy of the contactor 41 in an emergency shutdown of the contactor 41 is approximately 1/4 because the current of the contactor 41 is approximately halved. Furthermore, 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 caused by the opening of the contactor 41 is further reduced.

As a result, when two parallel-connected battery packs 11 and 12 supply current in parallel to an inductive load, the sparks caused by the opening of either contactor are greatly reduced. However, when contactor 41 is opened, only the current of battery pack 12 flows through the inductances of cable 141 and secondary coil 53. As a result, these inductances increase the arc energy of contactor 41. Similarly, when contactor 42 is opened, only the current of battery pack 11 flows through the inductances of cable 142 and secondary coil 52. As a result, these inductances increase the arc energy of contactor 42.

Next, the supply of AC 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 AC current supply is typically performed in a cold environment, but can also be performed to improve the electrical characteristics of the battery pack. The oscillator 6 applies an AC voltage VT1 to the primary coil 51. The frequency of the AC voltage VT1 is, for example, 10 kHz. When the frequency is high, the step-down transformer 5 becomes compact. The AC voltage VT1 consists of a positive pulse voltage and a negative pulse voltage that are alternately repeated. When the AC 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.

Battery pack 11 has an open circuit voltage VB and an internal resistance r10. 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 actually different. 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 consisting 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 an equal amplitude and an opposite direction to the current component supplied to the motor drive circuit 2 by the secondary coil 53.

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

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 that the battery pack 11 supplies to the motor drive circuit 2. Conversely, the secondary voltage VT2 of the secondary coil 53 reduces the current component that the battery pack 12 supplies to the motor drive circuit 2. Ultimately, the load current IL is not affected by the two secondary coils 52.

After all, 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 AC current IC can circulate only through the battery packs 11 and 12. This allows AC current circulation through the battery packs 11 and 12 to be realized during the period when the battery packs 11 and 12 are discharging to the motor drive circuit 2. Similarly, AC current circulation through the battery packs 11 and 12 can be realized during the period when the battery packs 11 and 12 are charging.

The DC power supply 1 can select parallel operation of two battery packs or standalone operation. Sparks caused by opening of the contactor shorten the contact life. Spark energy is proportional to the series inductance of the circuit.

The inductance of the secondary coil 52 or 53 therefore increases the sparking of the contactor 41 or 42. This problem is remedied by the contactor protection operation shown in Figures 6 and 7.

Figure 6 shows the current flow during the transient period when the contactor 42 is open. The battery pack 11 supplies a current I1 to the motor drive circuit 2, and the battery pack 12 supplies a current I2 to the motor drive circuit 2. During this transient period, the oscillator 6 applies a positive pulse voltage VT1 to the primary coil 51. This causes the secondary coils 51 and 52 to circulate a positive circulating current ICP through the battery packs 11 and 12 and the contactors 41 and 42. As a result, the battery pack 11 is charged and the battery pack 12 is discharged.

Furthermore, the current flowing through the contactor 42 while the contactor 42 is open is I1-ICP. As a result, the life of the contactor 42 is improved.

Figure 7 shows the current flow during the transient period when the contactor 41 is open. The battery pack 11 supplies a current I1 to the motor drive circuit 2, and the battery pack 12 supplies a 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. This causes the secondary coils 51 and 52 to circulate a negative circulating current ICN through the battery packs 11 and 12 and the contactors 41 and 42. As a result, the battery pack 11 is discharged and the battery pack 12 is charged. Furthermore, the current flowing through the contactor 41, whose contacts are performing an opening operation, is I2-ICN. As a result, the life of the contactor 41 is improved.

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

However, the step-down transformer 5 does not have a secondary coil connected in series with the common contactor 43 shown in FIG. 2. Therefore, 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.

This bypass circuit 81, which is 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.

Next, the prevention of arcing of 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 occurs on the contact of the common conductor 43. An 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, the 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 arcing of the common conductor 43. This problem is solved by the bypass circuit 81 connected in parallel with the common conductor 43.

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

When the common contactor 43 is closed, the charge stored in the capacitor 81C is shorted through the common contactor 43. However, this short circuit is prevented by the diode 81D. The charge stored in the capacitor 81C is slowly discharged through the high reverse resistance of the diode 81D while the common contactor 43 is closed.

The DC power supply 1 shown in FIG. 2 opens contactor 42 if one cell of battery pack 11 is defective. In addition, the DC power supply 1 opens contactor 41 if one cell of battery pack 12 is defective. This allows the electric vehicle to continue operating in most cases where a defective cell is found.

A particularly important cell failure is an internal short circuit in the cell caused by dendrite growth. This internal short circuit sometimes causes battery fires due to thermal runaway in the cell. It is known that the internal resistance of a cell gradually decreases due to dendrite growth. Therefore, by monitoring the internal resistance of a cell, it is possible to predict the occurrence of an internal short circuit in the cell in the near future. However, detection of the internal resistance of a cell in order to detect an internal short circuit in a cell essentially needs to be performed at all times. This means that the operation of detecting the internal resistance of each cell must be performed even while the battery is being discharged or charged. However, detecting the internal resistance of each cell during this discharging or charging is difficult due to fluctuations in the discharging current or charging current.

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 unit (first BMS) 110 that detects the cell voltage of the battery pack 11. A second battery management unit (second BMS) 120 that detects the cell voltage of the battery pack 12 is 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 transmits the cell voltages V11-V14 of the cells 11A-11D in sequence to the controller 7.

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. Furthermore, the secondary voltage induced in the secondary coils 52 and 53 circulates a circulating current IC through cells 11A-11D. As a result, the internal resistances r1-r4 of cells 11A-11D generate voltage drops due to the load current IL and the circulating current IC, respectively. Therefore, the cell voltage V11 of cell 11A is V1+r1 (IL+IC), and the cell voltage V12 of cell 11B is V2+r2 (IL+IC). Similarly, the cell voltage V13 of cell 11C is V3 + r3 (IL + IC), and the cell voltage V14 of cell 11D is V4 + r4 (IL + IC).

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 positive pulse current ICP to the battery packs 11 and 12 during a positive pulse period when the positive pulse voltage is applied to the primary coil 51. Furthermore, the secondary coils 52 and 53 circulate a substantially constant negative pulse current ICN to the battery packs 11 and 12 during a negative pulse period when the negative pulse voltage is applied to the primary coil 51. The integral value of the positive pulse current ICP is equal to the integral value of the negative pulse current ICN.

The cell voltages V11-V14 are selected in sequence by the first BMS 110 during the positive pulse period, converted to a digital signal by the A/D converter 60, and then sent to the controller 7. Similarly, the cell voltages V11-V14 are selected in sequence by the first BMS 110 during the negative pulse period, converted to a digital signal by the A/D converter 60, and then sent to the controller 7. As a result, eight cell voltages are sent to the controller 7.

The operation of detecting the internal resistance r1 of cell 11A will be described. First, during the positive pulse period when a 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 a 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 equal amplitudes. It is further assumed that cell 11A has a constant open circuit voltage V1 during the positive pulse period and the negative pulse period.

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) across the internal resistance r1 due to the load current IL. Therefore, the voltage difference ΔV is 2IC·r1, and the internal resistance r1 is ΔV/2IC. In the end, by utilizing the AC circulating current supplied to the battery pack 11 by the step-down transformer 5, the internal resistance r1 can be detected without being affected by the load current IL or the open circuit voltage V1 during the period when the battery pack 11 is discharging to the motor drive circuit 2. The internal resistances of cells 11B-11D are also detected in the same manner.

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

When switches S1 and S2 are turned on, the voltage of capacitor 70 is equal to cell voltage V11 of cell 11A. When switches S2 and S3 are turned on, the voltage of capacitor 70 is equal to cell voltage V12 of cell 11B. When switches S3 and S4 are turned on, the voltage of capacitor 70 is equal to cell voltage V13 of cell 11C. When switches S4 and S5 are turned on, the voltage of capacitor 70 is equal to 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 four switches S6-S9, and then transmitted to controller 7. Switches S6-S9, like switches S1-S4, are composed of two MOSFETs connected in series in the opposite direction.

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

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.

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

As a result, each cell voltage is transmitted to the capacitor 70 in sequence under the control of the switches S1-S4. Furthermore, the voltage of the capacitor 70 is sent to the A/D converter 60 under the control of the switches S6-S9, which is implemented after the switches S1-S4 are turned off. The switches S6-S9 have the function of inverting the voltage direction of the capacitor 70. The positive pulse current ICP flows in the first half of the period T1-T4 of the circulating current IC, and the negative pulse current ICN flows in the second half of the period T1-T4 of the circulating current IC. Therefore, two types of cell voltages of one cell are detected every period T1-T4. For example, when the battery pack 11 consists of 100 cells connected in series with each other, it takes 100 periods to detect the internal resistance of all the cells.

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. Because the directions of the positive pulse current ICP and the negative pulse current ICN are opposite, the voltage difference ΔV can be increased.

Other electrical parameters of each cell can also be calculated based on the internal resistances r1-r4 of cells 11A-11D. For example, the deterioration of cells 11A-11D can be estimated based on the internal resistances r1-r4. Furthermore, the voltage drop of each internal resistance r1-r4 can be calculated from the internal resistance values r1-r4 of cells 11A-11D. The open circuit voltages V1-V4 of each cell 11A-11D can be calculated from these voltage drops and the cell voltages V11-V14.

An example of control by 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 temperature Tb of the battery packs 11 and 12 is lower than a predetermined threshold value Tth (S100). If the determination result is Yes, an AC heating subroutine (S102) is executed to supply AC current to the battery packs 11 and 12. If the determination result is No, this AC heating subroutine is not executed.

In this AC heating subroutine, the oscillator 6 supplies a primary AC current to the primary coil 51. This induces secondary voltages in the same direction 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 temperature of the battery packs 11 and 12 reaches a predetermined value, this AC heating subroutine is terminated.

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.

Next, it is determined whether all the internal resistance values detected from the battery pack 11 are within a predetermined tolerance range (S106), and if the determination result is No, the process proceeds to step S108. In step S108, a contactor protection subroutine is executed to protect the contactor 42. 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 approximately equal to the load current IL. As a result, the current flowing through the contactor 42 becomes approximately zero. Next, the contactor 42 is opened (S110). As a result, no arc is generated on the contactor 42.

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

In step S114, a contactor protection subroutine is executed to protect the contactor 41. According to this contactor protection subroutine, the oscillator 6 passes a secondary circulating current. This secondary circulating current reduces the current through the contactor 41. Preferably, this secondary circulating current is approximately equal to the load current IL. This causes the current through the contactor 41 to be approximately zero. Next, the contactor 41 is opened (S116). As a result, no arc is generated on the contactor 41.

If all the internal resistance values of the battery packs 11 and 12 are within a predetermined tolerance range, the contactors 41 and 42 are closed. This causes the battery packs 11 and 12 to supply the load current IL to the motor drive circuit 2.

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.

One modified embodiment is described with reference to FIG. 11. Battery pack 11 of DC power supply 1 consists of battery modules 111-114, and battery pack 12 consists of battery modules 121-124. Each battery module in FIG. 11 is arranged in the opposite direction compared to each battery module in FIG. 1. FIG. 12 shows DC power supply 1 of FIG. 11. Contactors 41 and 42 are arranged on the high side, and contactors 43 and 44 are arranged on the low side. Secondary coils 52 and 53 are arranged on the high side.

Second embodiment A 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 contactor box 3. Furthermore, the battery modules 121-124 shown in Fig. 13 are arranged in a reverse direction compared to the battery modules 121-124 shown in Fig. 1.

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

In FIG. 13, the battery module 124 with the highest potential and the battery module 114 with the lowest potential are close to the contactor box 3. As a result, the length of the cables 141 and 142 is minimized. Therefore, the reduced inductance of the cables 141-143 reduces arcing of the contactors 43 and 46 shown in FIG. 14.

Figure 14 is a circuit diagram showing the DC power supply 1 shown in Figure 13. 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 a cable 141, a contactor 46, and a 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 a cable 142 and a contactor 43. The motor drive circuit 2, which is made up of a three-phase inverter, is connected in parallel with the smoothing capacitor 20.

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

A 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, which 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.

In the end, 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, this circulating current can detect the internal resistance of each cell of the battery packs 11 and 12. Furthermore, by circulating the circulating current IC in the opposite direction to the load current IL just before the contactor 43 or 46 is opened, arcing of the contactor 43 or 46 can be suppressed. The bypass circuit 81 can also be connected in parallel with the contactor 43.

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 comprises a first bypass circuit 81 and a second bypass circuit 82. The first bypass circuit 81 comprises a capacitor 81C and a diode 81D connected in series. The second bypass circuit 82 comprises 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.

As a result, when the contactor 46 interrupts the current I1, the first bypass circuit 81 reduces the arcing of the contactor 46. Conversely, when the contactor 46 interrupts the current I2, the second bypass circuit 82 reduces the arcing of the contactor 46.

For example, in the first and second embodiments, the second bypass circuit 82 is active during the period when the motor drive circuit 2 regenerates current to the battery packs 11 and 12. Furthermore, this bidirectional bypass circuit is effective in protecting the AC contactors that cut off the AC current. To delay the charging of these capacitors, it is possible to connect a charging resistor in series with the diode. Furthermore, to accelerate the discharging of these capacitors, it is possible to connect a discharging resistor in parallel with the diode.

Claims (4)

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. 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. 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. 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: