JP6640169B2 - Secondary battery state detection device and secondary battery state detection method - Google Patents

Description

  The present invention relates to a secondary battery state detection device and a secondary battery state detection method.

  Various vehicles such as an electric vehicle (EV) and a hybrid vehicle (HEV) are equipped with a secondary battery such as a lithium ion rechargeable battery or a nickel hydride rechargeable battery as a power source of an electric motor. In EVs and HEVs, dozens to hundreds of the above secondary batteries are connected in series, and the voltage between both ends of each secondary battery is detected. The voltage at both ends of the secondary battery is an important detection value in determining whether the battery is fully charged or overdischarged. For this reason, there has been a problem that if a failure occurs in the detection circuit and even one of the plurality of secondary batteries cannot be detected, all charging and discharging must be stopped.

  As a method of calculating an internal resistance which is an index indicating the degree of deterioration of a secondary battery, for example, a method described in Patent Document 1 has been proposed. In the secondary battery state detection device described in Patent Document 1, the respective battery voltages in the discharge state and the discharge stop state are held by a capacitor, and a difference voltage between the battery voltages held by a differential amplifier circuit is obtained. To obtain the internal resistance (= the state of the secondary battery). However, in the conventional secondary battery state detection device, it is not possible to obtain the voltage between both ends of the secondary battery instead of when the detection circuit fails.

JP 2014-219311 A

  The present invention has been made in view of the above background, and a secondary battery capable of detecting a voltage across the secondary battery using a differential amplifier circuit for detecting a state of the secondary battery. An object of the present invention is to provide a state detection device and a secondary battery state detection method.

  A secondary battery state detection device according to an aspect of the present invention includes a capacitor that holds a voltage between both ends of the secondary battery in a first state, a voltage between both ends of the secondary battery that is held by the capacitor, and a second state. A differential amplifier circuit to which the voltage between both ends of the secondary battery is input, and a voltage difference between the terminal voltages of the secondary battery in the first state and the second state output from the differential amplifier circuit. And a state detection unit for detecting a battery state of the secondary battery by using the input to the differential amplifier circuit in the first state and the second state. And a switching unit that switches between the voltage across the secondary battery and the reference voltage, based on the difference voltage between the voltage across the secondary battery and the reference voltage output from the differential amplifier circuit. Detects the voltage across the secondary battery A first voltage detection unit that, characterized by comprising a.

  The reference voltage may be a constant voltage output from a constant voltage source.

  The first voltage detection unit adjusts a constant voltage output from the constant voltage source so that the difference voltage falls within a predetermined range, and controls both ends of the secondary battery based on the adjusted difference voltage. The voltage may be detected.

  A plurality of the secondary batteries are provided, and a second voltage detection unit that detects a voltage between both ends of the plurality of the secondary batteries, and a failure detection that seeks a secondary battery that cannot be detected due to a failure of the second voltage detection unit. And the reference voltage may be a voltage between both ends of the secondary battery detected by the second voltage detection unit.

  When there are a plurality of rechargeable batteries capable of detecting a voltage between both ends by the second voltage detection unit, the first voltage detection unit determines a voltage between both ends of the rechargeable battery that is within a predetermined range. It may be a voltage.

  A battery state detection method according to an aspect of the present invention includes the steps of: holding a voltage between both ends of a secondary battery in a first state in a capacitor; and holding a voltage between both ends of the secondary battery held by the capacitor and a second state. Inputting the voltage between both ends of the secondary battery to a differential amplifier circuit, based on a difference voltage between the voltage between both ends of the secondary battery in the first state and the second state output from the differential amplifier circuit. Detecting the state of the battery by using the input to the differential amplifier circuit, the voltage across the secondary battery in the first state and the second state, A step of switching between a voltage across the secondary battery and a reference voltage, and a voltage across the secondary battery based on a voltage difference between the voltage across the secondary battery and the reference voltage output from the differential amplifier circuit. Detecting And wherein the door

  According to the above aspect, the voltage across the secondary battery can be detected using the differential amplifier circuit for detecting the state of the secondary battery.

FIG. 1 is a circuit diagram illustrating a secondary battery state detection device according to a first embodiment of the present invention. 2 is a flowchart showing a detection procedure of a voltage between both ends of μCOM constituting the secondary battery state detection device of FIG. 1. It is a circuit diagram showing a secondary battery state detecting device of the present invention in a 2nd embodiment. 4 is a flowchart showing a detection procedure of a voltage between both ends of μCOM constituting the secondary battery state detection device of FIG. 3.

(1st Embodiment)
Hereinafter, the secondary battery state detection device according to the first embodiment will be described with reference to FIG. The secondary battery state detection device 1 of the present embodiment is mounted on an electric vehicle, for example, and detects the states of a plurality of secondary batteries Ce1 to Ce3 included in the battery pack 2 shown in FIG. Things. The secondary batteries Ce1 to Ce3 are connected in series with each other.

  As shown in FIG. 1, the secondary battery state detection device 1 of the first embodiment includes a first capacitor C1 and a second capacitor C2, a reference voltage source 8, a changeover switch SW1 and a switch unit 12, It includes a discharge unit 13, a voltage detection unit 14, an A / D converter 15, a differential amplifier circuit 16, an A / D converter 17, a CVS 18, and a microcomputer (hereinafter, μCOM) 19. I have.

  The first capacitor C1 and the second capacitor C2 are capacitors for holding bipolar voltages of the secondary batteries Ce1 to Ce3 in two states (for example, a charged state and a discharged state). Further, the first capacitor C1 and the second capacitor C2 are capacitors for holding the bipolar voltages of the secondary batteries Ce1 to Ce3 and the reference voltage Vref, respectively. The first capacitor C1 and the second capacitor C2 are connected to one of a plurality of secondary batteries Ce1 to Ce3 and a reference voltage source 8 selected by a switch unit 12 described later.

  The first capacitor C1 has a single-pole plate connected to a + input, which is one of two inputs of a differential amplifier circuit 16 described later. The second capacitor C2 has a single-pole plate connected to the-input, which is the other of the two inputs of the differential amplifier circuit 16 described later.

  The reference voltage source 8 is composed of, for example, a constant voltage source, and outputs a reference voltage Vref. In the present embodiment, a known constant voltage source that can adjust the reference voltage Vref (= constant voltage) is used as the reference voltage source 8.

  The changeover switch SW1 includes a switch that switches the connection of the terminal c between the terminal a and the terminal b. The terminal a is connected to the one plate of the first capacitor C1 and the positive input of the differential amplifier circuit 16, and the terminal b is connected to the single plate of the second capacitor C2 and the negative input of the differential amplifier circuit 16. Have been. The terminal c is connected to an e + terminal of a changeover switch SW + described later. The changeover switch SW1 is a switch that selects one of the first capacitor C1 and the second capacitor C2 and connects it to the e + terminal of the changeover switch SW +.

  The switch unit 12 includes two changeover switches SW + and SW−. The changeover switch SW + includes a switch that switches the e + terminal among the a +, b +, c +, and d + terminals. The terminals a + to c + are respectively connected to the positive electrodes of the secondary batteries Ce1 to Ce3. The d + terminal is connected to the positive electrode of the reference voltage source 8. The changeover switch SW + connects one positive electrode selected from the plurality of secondary batteries Ce1 to Ce3 and the reference voltage source 8 to one plate of the capacitors C1 and C2 selected by the changeover switch SW1.

  The changeover switch SW- is configured by a switch that switches an e- terminal among a-, b-, c-, and d- terminals. The terminals a- to c- are respectively connected to the negative electrodes of the secondary batteries Ce1 to Ce3. The d- terminal is connected to the negative electrode of the reference voltage source 8. The changeover switch SW- connects one negative electrode selected from the plurality of secondary batteries Ce1 to Ce3 and the reference voltage source 8 to the other electrode plates of the capacitors C1 and C2.

  The voltage detection unit 14 is a circuit that detects a bipolar voltage of the battery pack 2. The A / D converter 15 converts the bipolar voltage of the battery pack 2 detected by the voltage detector 14 into a digital value and supplies the digital value to the μCOM 19.

  The charging / discharging unit 13 is connected to both poles of the battery pack 2 and can supply a predetermined charging current Ic and a predetermined discharging current Id when charging and discharging the secondary batteries Ce1 to Ce3 constituting the battery pack 2. It is provided in. The charging / discharging unit 13 is connected to a μCOM 19 described later, and in accordance with a control signal from the μCOM 19, charges the secondary batteries Ce1 to Ce3 by flowing a charging current Ic, and charges the secondary batteries Ce1 to Ce3 with a discharging current Id. To discharge.

  The differential amplifier circuit 16 is a well-known differential amplifier circuit that outputs a difference voltage between a + input and a − input. The A / D converter 17 converts the difference voltage Vm output from the differential amplifier circuit 16 into a digital value and supplies the digital value to the μCOM 19.

  The CVS 18 as a second voltage detection unit is configured by a detection circuit that detects the voltage between both ends of the secondary batteries Ce1 to Ce3, and sequentially outputs the detection results to the μCOM 19.

  The μCOM 19 is composed of a microcomputer having a well-known CPU, ROM, RAM and the like. The μCOM 19 functions as a state detection unit, and performs on / off control of the changeover switch SW1 and the switch unit 12 and controls the charge / discharge unit 13 to execute an internal resistance detection process for detecting the internal resistance of the secondary batteries Ce1 to Ce3. I do.

  In the internal resistance detection process, in the first state, the μCOM 19 connects the e + terminal of the changeover switch SW + to the a + terminal, connects the e− terminal of the changeover switch SW− to the a− terminal, and sets the c of the changeover switch SW1 to c. Connect the terminal to terminal a. As a result, the μCOM 19 causes the first capacitor C1 to hold the voltage between both ends of the secondary battery Ce1 in the first state. Thereafter, in the second state, the μCOM 19 connects the terminal c of the switch SW1 to the terminal b. As a result, the μCOM 19 causes the second capacitor C2 to hold the voltage between both ends of the secondary battery Ce1 in the second state. Then, the voltage across the secondary battery Ce1 in the first state and the second state is input to the positive input and the negative input to the differential amplifier circuit 16.

  Here, the first state and the second state indicate states in which currents flowing through the secondary batteries Ce1 to Ce3 are different. In the present embodiment, a state where the charging current Ic is flowing is defined as a first state, and a state where the discharging current Id is flowing is defined as a second state. The μCOM 19 controls the charge / discharge unit 13 based on the detection value from the voltage detection unit 14 to supply the charge current Ic and the discharge current Id to the secondary batteries Ce1 to Ce3.

Further, in the internal resistance detection processing, the μCOM 19 detects the internal resistance of the secondary battery Ce1 by taking in the difference voltage Vm, and detects the state of the secondary battery Ce1. More specifically, in the present embodiment, the voltage Vc1 across the secondary battery Ce1 in a charged state is represented by the following equation (1).
Vc1 = Ve1 + r1 × Ic (1)
Ve1: electromotive force of the secondary battery Ce1, r1: internal resistance of the secondary battery Ce1

On the other hand, the voltage Vd1 across the secondary battery Ce1 in the discharged state is represented by the following equation (2).
Vd1 = Ve1-r1 × Id (2)

  Therefore, the difference voltage Vm output from the differential amplifier circuit 16 has a value corresponding to Vc1−Vd1 = r1 × (Ic + Id), and if the charging current Ic and the discharging current Id are known in advance, the difference voltage Vm The resistance r1 can be obtained. The internal resistances r2 and r3 of the secondary batteries Ce2 and Ce3 can be obtained in the same manner.

  Further, the μCOM 19 controls the on / off of the changeover switch SW1 and the switch unit 12 to perform a voltage detection process for detecting the voltage across the secondary batteries Ce1 to Ce3. The process of detecting the voltage between both ends may be performed when a failure of the CVS 18 is detected. Further, it may be performed to perform a failure diagnosis of the CVS 18.

  In the voltage detection processing, the μCOM 19 first controls the charge / discharge unit 13 to stop charging and discharging. It is not essential to stop the charge / discharge current, that is, set the charge / discharge current to zero. It is sufficient that the charge / discharge current is such that the voltage drop occurring in the internal resistances r1 to r3 can be tolerated, and may not be 0. Thereafter, the μCOM 19 connects the e + terminal of the changeover switch SW + to the a + terminal, connects the e− terminal of the changeover switch SW− to the a− terminal, and connects the c terminal of the changeover switch SW1 to the a terminal. As a result, the μCOM 19 causes the first capacitor C1 to hold the voltage between both ends of the secondary battery Ce1.

  Thereafter, the μCOM 19 connects the e + terminal of the changeover switch SW + to the d + terminal, connects the e− terminal of the changeover switch SW− to the d− terminal, and connects the c terminal of the changeover switch SW1 to the b terminal. As a result, the μCOM 19 causes the second capacitor C2 to hold the reference voltage Vref. Then, the voltage between both ends of the secondary battery Ce1 and the reference voltage Vref are input to the positive input and the negative input to the differential amplifier circuit 16.

Further, the μCOM 19 detects the voltage across the secondary battery Ce1 by taking in the difference voltage Vm at this time. More specifically, the difference voltage Vm at this time is expressed by the following equation (3).
Vm = (Vc1−Vref) × Av (3)
Av: gain of the differential amplifier circuit 16

  Therefore, since the gain Av and the reference voltage Vref are known, the μCOM 19 can obtain the voltage Vc1 across the secondary battery Ce1 from the difference voltage Vm. Similarly, the voltages Vc2 and Vc3 at both ends of the secondary batteries Ce2 and Ce3 can be obtained.

  Next, the details of the procedure for detecting the voltage between both ends of the secondary battery state detection device 1 described above will be described with reference to the flowchart of FIG. First, the μCOM 19 connects both ends of the secondary battery Cen and the first capacitor C1 (Step S1).

  Thereafter, the μCOM 19 waits for a predetermined time such that the voltage across the first capacitor C1 becomes equal to the voltage Vcn across the rechargeable battery Cen (n is set to 1 as an initial value), and then the μCOM 19 and the reference voltage source 8 and the second voltage The capacitor C2 is connected (Step S2). Thus, the voltage Vcn across the secondary battery Cen and the reference voltage Vref are input to the differential amplifier circuit 16 at the + input and the − input.

  Next, the μCOM 19 takes in the difference voltage Vm of the differential amplifier circuit 16 and determines whether or not the difference voltage is greater than the first threshold value Vthmax (step S3). If the difference voltage Vm> the first threshold value Vthmax (Y in step S3), the μCOM 19 may have a possibility that the output voltage of the A / D converter 17 is saturated because the both-ends voltage Vcn is too large as compared with the reference voltage Vref. If there is, the reference voltage Vref is increased by a predetermined amount (step S8), and the process returns to step S1.

  On the other hand, if the difference voltage Vm is equal to or smaller than the first threshold value Vthmax (N in step S3), the μCOM 19 determines whether the difference voltage Vm is lower than the second threshold value Vthmin (step S4). If the difference voltage Vm <the second threshold value Vthmin (Y in step S4), the μCOM 19 determines that the voltage Vcn is too small compared to the reference voltage Vref and the accuracy is not good, and lowers the reference voltage Vref by a predetermined amount. Later (step S9), the process returns to step S1 again.

  If the second threshold Vthmin ≦ the difference voltage Vm ≦ the first threshold Vthmax (N in step S3 and N in step S4), the μCOM 19 calculates the both-ends voltage Vcn from the difference voltage Vm (step S5). Thereafter, the μCOM 19 increments n (step S6), and determines whether n = 3 (step S7). If n is not 3 (N in step S7), the μCOM 19 determines that the voltages Vc1 to Vc3 are not detected for all the secondary batteries Ce1 to Ce3 constituting the assembled battery 2, and returns to step S1 again. .

  On the other hand, if n = 3 (Y in step S7), the μCOM 19 determines that the both-end voltages Vc1 to Vc3 have been detected for all the secondary batteries Ce1 to Ce3 constituting the assembled battery 2, and ends the processing.

  According to the above-described first embodiment, the input to the differential amplifier circuit 16 is made by the changeover switch SW1 as the changeover unit and the switch unit 12 to the rechargeable batteries Ce1 to Ce3 in the first state and the second state. It is possible to switch between the voltage between both ends, the voltage between both ends of the secondary batteries Ce1 to Ce3, and the reference voltage Vref. The μCOM 19 detects the internal resistance (state) of the battery based on the difference voltage Vm between the voltages of the secondary batteries Ce1 to Ce3 in the first state and the second state output from the differential amplifier circuit 16. .

  Further, the μCOM 19 detects the voltage across the secondary batteries Ce1 to Ce3 based on the voltage across the secondary batteries Ce1 to Ce3 output from the differential amplifier circuit 16 and the difference voltage Vm between the reference voltage Vref. Thus, the voltage across the secondary batteries Ce1 to Ce3 can be detected using the differential amplifier circuit 16 for detecting the internal resistance of the secondary batteries Ce1 to Ce3. For this reason, even if the CVS 18 fails, the voltage between both ends of the secondary batteries Ce1 to Ce3 can be detected, so that it is not necessary to stop charging and discharging of the secondary batteries Ce1 to Ce3, and the vehicle can continue running.

  Further, by comparing the voltage between both ends of the secondary batteries Ce1 to Ce3 detected by the CVS 18 with the voltage between both ends of the secondary batteries Ce1 to Ce3 detected using the differential amplifier circuit 16, the CVS18 and the battery state detection are performed. Failure diagnosis of the device 1 can also be performed.

  Further, according to the above-described first embodiment, the reference voltage Vref is a constant voltage output from the constant voltage source. Thereby, the detection accuracy of the voltage between both ends of the secondary batteries Ce1 to Ce3 can be further improved to zero.

  Further, according to the above-described first embodiment, as shown in steps S3, S4, S9, and S10, the μCOM 19 determines that the difference voltage Vn is within a predetermined range (that is, equal to or less than the first threshold Vthmax and equal to or greater than the second threshold Vthmin). ), The reference voltage Vref output from the reference voltage source 8 is adjusted. The μCOM 19 detects the voltage between both ends of the secondary batteries Ce1 to Ce3 based on the adjusted difference voltage Vm. As a result, the output of the A / D converter 17 is suppressed from being saturated or, on the contrary, too small, and the detection accuracy of the voltage between both ends of the secondary batteries Ce1 to Ce3 can be further improved.

  According to the above-described first embodiment, the battery pack 2 includes the three secondary batteries Ce1 to Ce3, but the present invention is not limited to this. The number of the secondary batteries Ce1 to Ce3 is one, and there may be three or more.

  In the first embodiment described above, two capacitors C1 and C2 are provided, but the invention is not limited to this. A single capacitor may be used to hold the secondary batteries Ce1 to Ce3 in the first state, and the secondary batteries Ce1 to Ce3 in the second state may be directly input to the differential amplifier circuit 16. .

  Also, as the switching unit, one configured by the changeover switch SW1 and the switch unit 12 as described in the first embodiment is an example. The switching unit inputs the input to the differential amplifier circuit 16 with the voltage between both ends of the secondary batteries Ce1 to Ce3 in the first state and the second state, the voltage between both ends of the secondary batteries Ce1 to Ce3, and the reference voltage Vref. Any configuration can be used as long as it can be switched between.

  In the first embodiment described above, the μCOM 19 outputs the reference voltage from the reference voltage source Vref such that the difference voltage Vn falls within a predetermined range (that is, a range equal to or less than a first threshold value Vthmax and equal to or greater than a second threshold value Vthmin). Although the voltage Vref was adjusted, it is not limited to this. Adjustment of the reference voltage Vref is not essential.

  In the above-described first embodiment, the control of the charging / discharging unit 13 by the μCOM 19 causes the secondary batteries Ce1 to Ce3 to be in the first state (the state where the charging current Ic is flowing) and the second state (the state where the charging current Id is flowing). Is flowing), but is not limited to this. A change in the charge / discharge current accompanying the load drive of the vehicle may be used. That is, the first state may be set before the change of the charge / discharge current of the vehicle, and the second state may be set after the change.

(Second embodiment)
Next, a secondary battery state detection device 1 according to a second embodiment will be described with reference to FIG. In FIG. 3, portions that are the same as those of the secondary battery state detection device 1 of FIG. 1 already described in the first embodiment described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

  As shown in FIG. 3, the secondary battery state detection device 1 of the first embodiment includes a first capacitor C1 and a second capacitor C2, a changeover switch SW1, a switch unit 12, a charge / discharge unit 13, It includes a voltage detector 14, an A / D converter 15, a differential amplifier circuit 16, an A / D converter 17, a CVS 18, and a μCOM 19. In the second embodiment, no reference voltage source 8 is provided.

  The first and second capacitors C1 and C2 and the changeover switch SW1 are the same as those in the above-described first embodiment, and a detailed description thereof will be omitted. The switch unit 12 includes two changeover switches SW + and SW−. The changeover switch SW + includes a switch that switches the e + terminal among the a +, b +, and c + terminals. The terminals a + to c + are respectively connected to the positive electrodes of the secondary batteries Ce1 to Ce3. The changeover switch SW + connects one positive electrode selected from the plurality of secondary batteries Ce1 to Ce3 to one pole plate of the capacitors C1 and C2 selected by the changeover switch SW1.

  The changeover switch SW- is configured by a switch that switches an e- terminal among a-, b-, and c- terminals. The terminals a- to c- are respectively connected to the negative electrodes of the secondary batteries Ce1 to Ce3. The changeover switch SW- connects one negative electrode selected from the plurality of secondary batteries Ce1 to Ce3 to the other electrode plates of the capacitors C1 and C2.

  The CVS 18 includes a detection circuit that detects the voltage between both ends of the secondary batteries Ce1 to Ce3, and outputs the detection result to the μCOM 19. The CVS 18 may not be able to detect the voltages across all the secondary batteries Ce1 to Ce3 due to, for example, a failure of an internal switch. The CVS 18 includes, for example, a known disconnection detection circuit, and can obtain secondary batteries Ce1 to Ce3 that cannot be detected due to its own failure. Then, the CVS 18 supplies the result to the μCOM 19.

  The μCOM 19 performs a process of detecting the internal resistance and a process of detecting the voltage between both ends, as in the first embodiment. The process of detecting the internal resistance is the same as that of the first embodiment, and thus a detailed description is omitted here.

  In the detection processing of the both-ends voltage, the μCOM 19 inputs, instead of the reference voltage Vref, the voltages at both ends of the secondary batteries Ce1 to Ce3 whose both-ends have been detected by the CVS 18 to the differential amplifier circuit 16 as the reference voltage Vref. Now, a case will be described in which the voltage across the secondary battery Ce1 cannot be detected by the CVS 18 and the voltage across the secondary battery Ce2 can be detected. The μCOM 19 connects the e + terminal of the changeover switch SW + to the a + terminal, connects the e− terminal of the changeover switch SW− to the a− terminal, and connects the c terminal of the changeover switch SW1 to the a terminal. As a result, the μCOM 19 causes the first capacitor C1 to hold the voltage between both ends of the secondary battery Ce1.

  Thereafter, the μCOM 19 connects the e + terminal of the changeover switch SW + to the b + terminal, connects the e− terminal of the changeover switch SW− to the b− terminal, and connects the c terminal of the changeover switch SW1 to the b terminal. Accordingly, the μCOM 19 causes the second capacitor C2 to hold the voltage between both ends of the secondary battery Ce2. Then, the voltage between both ends of the secondary battery Ce <b> 1 and the secondary battery Ce <b> 2 is input to the differential amplifier circuit 16 to the + input and the − input.

Further, the μCOM 19 detects the pressure across the secondary battery Ce1 by taking in the difference voltage Vm at this time. More specifically, the difference voltage Vm at this time is expressed by the following equation (4).
Vm = (Vc1−Vc2) × Av (4)
Av: gain of the differential amplifier circuit 16

  Therefore, since the gain Av and the voltage Vc2 between both ends are known, the μCOM 19 can obtain the voltage Vc1 between both ends of the secondary battery Ce1 from the difference voltage Vm.

  Next, the details of the procedure for detecting the voltage between both ends of the secondary battery state detection device 1 according to the second embodiment described above will be described with reference to the flowchart of FIG.

  The secondary batteries Ce1 to Ce3, for which the CVS 18 could not determine the voltage at both ends, are referred to as secondary batteries Cex, and the secondary batteries Ce1, to Ce3, for which the CVS 18 was able to determine the voltage at both ends, are referred to as secondary batteries Ceo. explain.

  Further, the μCOM 19 connects one of the secondary batteries Cex to the first capacitor C1, and causes the first capacitor C1 to hold the voltage between both ends of the secondary battery Cex (step S11). Thereafter, the μCOM 19 connects one of the secondary batteries Ceo to the second capacitor C2, and causes the second capacitor C2 to hold the voltage across the secondary battery Ceo (step S11). As a result, the differential amplifier circuit 16 receives the positive and negative voltages of the secondary battery Cex and the secondary battery Ceo, respectively.

  Next, the μCOM 19 takes in the difference voltage Vm of the differential amplifier circuit 16 and determines whether or not the difference voltage is within a predetermined range not less than the second threshold value Vthmin and not more than the first threshold value Vthmax (step S12). If the second threshold value Vthmin ≦ the difference voltage Vm ≦ the first threshold value Vthmax (Y in step S12), the μCOM 19 obtains the voltage across the secondary battery Cex from the difference voltage Vm (step S13).

  Next, if the μCOM 19 has determined the voltages at both ends of all the secondary batteries Cex (Y in step S14), the process ends. On the other hand, if the voltages at both ends have not been obtained for all the secondary batteries Cex (N in step S14), the μCOM 19 uses the secondary battery Cex that has not been obtained as the first capacitor C1 and the secondary battery Ceo as the second capacitor Ceo. After the connection to the capacitor C2 (step S15), the process returns to step S12.

  If the second threshold value Vthmin ≦ the difference voltage Vm ≦ the first threshold value Vthmax is not satisfied (N in step S12), the μCOM 19 determines whether or not all the secondary batteries Ceo have been switched (step S16). If the switching has not been performed (N in step S16), the μCOM 19 switches the secondary battery Ceo input to the differential amplifier circuit 16 (step S17), and then returns to step S12 again. Accordingly, if there are a plurality of secondary batteries Ceo, if the voltage across the secondary battery Ceo is too large or too small with respect to the secondary battery Cex, the secondary battery Ceo input to the differential amplifier circuit 16 is Can switch.

  On the other hand, if the switching has been performed (Y in step S16), the μCOM 19 determines whether the difference voltage Vm is larger than the first threshold value Vthmax (step S18). If it is larger (Y in step S18), the μCOM 19 determines that the voltage across the rechargeable battery Cex is higher than the voltage across all the rechargeable batteries Ceo and that some abnormality has occurred, After executing the process (step S19), the process ends.

  If not large (N in step S18), the μCOM 19 determines that the voltage across the rechargeable battery Cex is lower than all the rechargeable batteries Ceo, and determines whether step S21 described below has already been executed (step S20). ). If not executed (N in step S20), the μCOM 19 exchanges the first and second capacitors C1 and C2 (step S21). That is, in step S21, the μCOM 19 connects the secondary battery Cex and the second capacitor C2, and connects the secondary battery Ceo and the first capacitor C1. Thus, the voltage across the secondary battery Ceo is input to the positive input of the differential amplifier circuit 16, and the voltage across the secondary battery Cex is input to the negative input. Thereafter, the μCOM 19 returns to step S12, and switches the secondary battery Ceo connected to the + input until the second threshold value Vthmin ≦ the difference voltage Vm ≦ the first threshold value Vthmax.

  According to the above-described second embodiment, the voltage across the rechargeable battery Ceo detected by the CVS 18 is input as the reference voltage. Accordingly, it is not necessary to provide the reference voltage source 8 for outputting a reference voltage separately from the secondary batteries Ce1 to Ce3, and cost can be reduced.

  Further, according to the second embodiment described above, when there are a plurality of secondary batteries Ceo whose both ends can be detected by the CVS 18, the μCOM 19 sets the secondary battery Ceo as a reference voltage when the difference voltage Vm falls within a predetermined range. can do. Thereby, the detection accuracy of the voltage between both ends of the secondary batteries Ce1 to Ce3 can be further improved.

  According to the above-described embodiment, the secondary battery Ceo is switched when the difference voltage Vm is within the predetermined range. However, the present invention is not limited to this. Switching is not mandatory.

  Note that the present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the gist of the present invention.

Reference Signs List 1 battery state detection circuit 16 differential amplifier circuit 18 CVS (second voltage detection unit, failure detection unit)
19 μCOM (state detector, first voltage detector)
C1 First capacitor (capacitor)
Ce1 to Ce3 Secondary battery Vm Difference voltage

Claims (6)

A capacitor that holds the voltage across the secondary battery in the first state, and a differential that receives the voltage across the secondary battery held by the capacitor and the voltage across the secondary battery in the second state An amplifier circuit; and a state detector configured to detect a battery state of the secondary battery based on a voltage difference between voltages across the secondary battery in the first state and the second state output from the differential amplifier circuit. And a battery state detection device comprising:
A switching unit that switches an input to the differential amplifier circuit between a voltage across the secondary battery in the first state and the second state, and a voltage across the secondary battery and a reference voltage;
A first voltage detector that detects a voltage across the secondary battery based on a difference voltage between the voltage across the secondary battery and a reference voltage output from the differential amplifier circuit. Battery state detection device.   The battery state detection device according to claim 1, wherein the reference voltage is a constant voltage output from a constant voltage source.   The first voltage detection unit adjusts a constant voltage output from the constant voltage source so that the difference voltage falls within a predetermined range, and controls both ends of the secondary battery based on the adjusted difference voltage. The battery state detection device according to claim 2, wherein the voltage is detected. A plurality of the secondary batteries are provided,
A second voltage detection unit that detects a voltage between both ends of the plurality of secondary batteries,
A failure detection unit that seeks a secondary battery that cannot be detected due to a failure in the second voltage detection unit,
The battery state detection device according to claim 1, wherein the reference voltage is a voltage between both ends of the secondary battery detected by the second voltage detection unit.   When there are a plurality of rechargeable batteries capable of detecting a voltage between both ends by the second voltage detection unit, the first voltage detection unit determines a voltage between both ends of the rechargeable battery that is within a predetermined range. The battery state detection device according to claim 4, wherein the voltage is a voltage. A step of holding a voltage between both ends of the secondary battery in the first state in a capacitor, and a differential amplifier circuit for comparing the voltage between both ends of the secondary battery held by the capacitor and the both ends of the secondary battery in the second state. And detecting a battery state based on a voltage difference between voltages across the secondary battery in the first state and the second state output from the differential amplifier circuit. In the battery state detection method,
A step of switching an input to the differential amplifier circuit between a voltage across the secondary battery in the first state and the second state, and a voltage across the secondary battery and a reference voltage;
Detecting a voltage across the secondary battery based on a difference voltage between the voltage across the secondary battery and a reference voltage output from the differential amplifier circuit. .

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