JP6648709B2 - Battery module controller - Google Patents

Description

  The present invention relates to a control device for a battery module to which a plurality of unit cells are connected.

  A battery module as a power supply is mounted on a hybrid vehicle or an electric vehicle using a rotating electric machine as a driving source. The battery module includes a plurality of single cells (single cells). These cells are connected in series or in parallel.

  In each unit cell of the battery module, the SOC (Charge Ratio, State Of Charge) varies during the charging / discharging process due to a variation in constituent materials, a variation in temperature, and the like. At this time, from the viewpoint of preventing over-discharge, the discharge limit is based on the minimum SOC among the plurality of cells, and the remaining cells reach the discharge limit with a margin. From the viewpoint of preventing overcharging, the charging limit is determined based on the maximum SOC among the plurality of cells, and the charging process is completed before the remaining cells are fully charged. That is, it is difficult to sufficiently exhibit the charge / discharge capability of the battery module due to the variation in the SOC.

  Therefore, for example, in Patent Literature 1, an equalization process for equalizing the variation in the SOC of each unit cell is executed. It is difficult to directly measure the SOC of a cell, and the SOC is conventionally calculated indirectly. For example, the SOC is calculated based on the current integration and the open circuit voltage (OCV, Open Circuit Voltage). For the latter, it is known that there is a correspondence between the open circuit voltage and the SOC, and the SOC is calculated (estimated) by measuring the open circuit voltage of the cell. In the equalization process, the open circuit voltage between the cells is equalized.

JP-A-2005-186339

  By the way, the correspondence between the open circuit voltage and the SOC may not be uniquely determined (one-to-one correspondence) depending on the constituent material of the unit cell. For example, FIG. 4 shows an OCV curve of a unit cell. The horizontal axis shows SOC, and the vertical axis shows OCV. FIG. 4 shows two types of OCV curves. One is an OCV curve (charging curve) obtained by repeatedly executing an OCV measurement for charging the battery from a completely discharged state to a predetermined SOC and then measuring the OCV after a pause for a predetermined time. The other is an OCV curve (discharge curve) obtained by repeatedly performing an OCV measurement for measuring the OCV after discharging from a fully charged state to a predetermined SOC and then suspending for a predetermined time. As shown in these OCV curves, the unit cell has a hysteresis characteristic in which an open circuit voltage corresponding to a predetermined SOC changes according to a charge / discharge history. For example, there are a region where the change (hysteresis width) of the open circuit voltage is relatively large and a region where it is relatively small as surrounded by a broken line in FIG.

  In such a case, the accuracy of the equalization processing may be reduced. For example, in FIG. 5, when the OCV of the unit cell 1 is OCV_1 and the OCV of the unit cell 2 is OCV_2, the SOCs of both the unit cells become SOC_A. The process of adjusting the circuit voltages is performed, and the SOC difference is widened. In view of the above, the present invention provides a battery module control device capable of more accurately uniforming the SOC of a single cell having a hysteresis characteristic in which an open circuit voltage for a predetermined SOC changes according to a charge / discharge history. The purpose is to provide.

  The present invention relates to a control device for a battery module to which a plurality of unit cells are connected. The plurality of cells have an open circuit voltage with respect to a predetermined SOC that changes in accordance with a charging / discharging history, and have a first SOC region where the change is relatively large and a second SOC region where the change is relatively small. The control device includes a voltage detection circuit, an equalization circuit, and an equalization determination unit. The voltage detection circuit detects the voltage of each cell. The equalization circuit performs an equalization process for equalizing the voltages of the individual cells detected by the voltage detection circuit. The equalization determination unit, after a predetermined relaxation time has elapsed after the plurality of cells have been charged and discharged, of the voltage of each of the plurality of cells detected by the voltage detection circuit, the maximum voltage and the minimum voltage Is greater than or equal to a predetermined threshold value, and if any of the voltages of the plurality of cells is within the voltage range corresponding to the second SOC region, the equalization circuit is permitted to perform the equalization processing. .

  According to the present invention, aiming at a time when the OCV of all the cells is included in the voltage range corresponding to the second SOC region where the change in the open circuit voltage with respect to the predetermined SOC is relatively small (the hysteresis width is small) Permits execution of equalization processing. By doing so, the SOC can be more accurately uniformed than before.

It is a circuit diagram including a control device of a battery module concerning this embodiment. FIG. 3 is a diagram illustrating a first SOC region and a second SOC region with respect to an OCV curve of a unit cell. It is a flowchart which illustrates an equalization execution determination flow. It is a figure which illustrates the OCV curve of a cell. It is a figure which illustrates the OCV curve of a cell, and is a figure explaining the hysteresis characteristic according to charge / discharge history.

  FIG. 1 illustrates a control device 14 of the battery module 12 according to the present embodiment. The battery module 12 and its control device 14 are mounted on, for example, a hybrid vehicle or an electric vehicle that uses a rotating electric machine as a drive source.

  The battery module 12 is connected to a plurality of unit cells 10 (unit cells). In the example shown in FIG. 1, n unit cells 10_1, 10_2,..., 10_n are connected in series. The cell 10 is formed of a secondary battery such as a lithium ion battery or a nickel hydride battery.

  The cells 10_1 to 10_n have a hysteresis characteristic in which an open circuit voltage (OCV) for a predetermined SOC changes according to a charge / discharge history. For example, the cell 10 has a negative electrode material to which Si or a SiO-based compound is added. For example, several percent of SiO is added to graphite, which is a main material of the negative electrode. At this time, as shown in FIG. 2, a hysteresis characteristic is remarkably exhibited in the relationship between the SOC and the OCV as compared with a single cell containing no SiO.

  As described above, as the OCV curve in FIG. 2, an OCV curve (charging curve) obtained by repeatedly executing the OCV measurement for charging the battery from a completely discharged state to a predetermined SOC, and then measuring the OCV after pausing for a predetermined period of time. ) And an OCV curve (discharge curve) obtained by repeatedly executing an OCV measurement for measuring the OCV after discharging from a fully charged state to a predetermined SOC and then suspending for a predetermined time. For example, according to the charging / discharging history of the cell 10, the OCV curve takes a locus included between the charge curve and the discharge curve.

  The hysteresis characteristic of the OCV of the unit cell 10 changes according to the SOC. For example, as shown in FIG. 2, the unit cell 10 has an SOC region (first SOC region) having a relatively large hysteresis width and an SOC region (second SOC region) having a relatively small hysteresis width. As will be described later, the equalization process is performed with the aim of the second SOC region having a relatively small hysteresis width.

  Returning to FIG. 1, the control device 14 includes a circuit unit 16 and a calculation unit 18. The circuit section 16 includes an equalizing circuit 20 and a voltage detecting circuit 22. The voltage detection circuit 22 and the equalization circuit 20 are partially common in circuit, and include a multiplexer 24, a voltage sensor 26, a sequencer 28, and an interface 30. The multiplexer 24, the voltage sensor 26, the sequencer 28, and the interface 30 may be mounted on one computer.

  Regarding the voltage detection circuit 22, wiring is drawn out from each of the nodes N_1 to N_n + 1 at the positive and negative ends of each of the unit cells 10_1 to 10_n. The wiring drawn from the node N_k between the negative electrode of one cell 10_k-1 (k = 2 to n) and the positive electrode of the other cell 10_k is connected to one negative electrode wiring LN_k-1 and the other positive electrode wiring LP_k. It is branched and connected to each channel CH (k-1) N, CHkP of the multiplexer 24.

  In the battery module 12, the wiring drawn from the node N_1 at the positive electrode end of the unit cell 10_1 closest to the positive electrode is connected to the channel CH1P of the multiplexer 24 as the positive wiring LP_1 without branching. Similarly, in the battery module 12, the wiring drawn from the node N_n + 1 at the negative electrode end of the cell 10_n closest to the negative electrode is connected to the channel CHnN of the multiplexer 24 as the negative wiring LN_n without branching.

  Further, wirings LP_0 and LN_0 for measuring the voltage of the entire battery module 12 are provided. The wiring LP_0 is drawn out from the node N_0P at the positive terminal of the unit cell 10_1 and connected to the channel CH0P of the multiplexer 24. The wiring LN_0 is drawn out from the node N_0N at the negative terminal of the unit cell 10_n and connected to the channel CH0N of the multiplexer 24.

  A smoothing capacitor Ck is connected between the positive electrode wiring LP_k and the negative electrode wiring LN_k. Further, a resistor RkP is provided on the positive electrode wiring LP_k, and a resistor RkN is provided on the negative electrode wiring LN_k. As will be described later, the resistors RkP and RkN double as a resistor for detecting the voltage of the unit cell 10_k and a discharge resistor for equalizing discharge.

  The equalizing circuit 20 shares a circuit with the voltage detecting circuit 22, and includes a positive wiring LP_k and a negative wiring LN_k, a resistance RkN and a resistance RkP, and switches SW1 to SWn. The switches SWk (k = 1 to n) are provided between the positive wiring LP_k and the negative wiring LN_k. The switch SWk is connected to the arithmetic unit 18 by a signal line (not shown), and its on / off switching control is possible.

  The equalizing circuit 20 illustrated in FIG. 1 is a so-called passive balancing type (equalizing discharge type) circuit. When the switch SWk is closed, a loop circuit including the cell 10_k, the resistor RkP, the switch SWk, and the resistor RkN is formed. . The voltage of the cell 10_k is reduced by the power of the cell 10_k being consumed (discarded) by the resistors RkP and RkN. For example, the unit cell 10_k having the minimum SOC is set as a target (target cell), and the switches SW1 to SWk-1, and SWk + 1 to SWn are turned on (connected state) for the other unit cells 10_1 to 10_k-1, 10_k + 1 to 10_n. . This causes the cells 10_1 to 10_k-1, 10_k + 1 to 10_n to perform equalized discharge, and the OCV of the cell 10_k as a target cell is replaced by the OCV of all the other cells 10_1 to 10_k-1, 10_k + 1 to 10_n. Align.

  The sequencer 28 is composed of, for example, a programmable logic controller (PLC). The sequencer 28 receives a voltage value detection command for a predetermined single cell 10 — k via the interface 30 and outputs a channel command corresponding to the command to the multiplexer 24. For example, when receiving a voltage value detection command for the cell 10 — k, the channel command for selecting the channels CHkP and CHkN is output to the multiplexer 24. By the channel switching by the multiplexer 24, the voltage sensor 26 detects the voltage between the channels CHkP and CHkN. The detected voltage value is transmitted to the calculation unit 18 via the interface 30. In this manner, the voltage detection circuit 22 can detect the voltages VB_1 to VB_n of the respective cells 10_1 to 10_n. When detecting the voltage of the entire battery module 12, the channels CH0P and CH0N are selected.

  The calculation unit 18 is configured by, for example, a computer, and includes a CPU and a storage unit. The calculation unit 18 may be, for example, a vehicle-mounted battery ECU (electronic control unit). When the CPU executes the equalization program and the equalization execution determination program stored in the storage unit of the arithmetic unit 18, the arithmetic unit 18 includes the first voltage comparison unit 32, the second voltage comparison unit 34, and the relaxation determination unit 36. , An equalization determination unit 38 and an equalization processing control unit 40.

<Equalization execution determination flow>
FIG. 3 illustrates an equalization execution determination flow performed by the arithmetic unit 18. This flow is executed a plurality of times at predetermined time intervals, for example, after the ignition-off point at which the vehicle system is stopped. First, the relaxation determination unit 36 determines whether or not the cells 10_1 to 10_n are in a relaxation state (S10).

  The relaxed state refers to a state in which a state in which no current flows after charging and discharging of the unit cell 10 continues and polarization is eliminated. At this time, the terminal voltage of the cell 10 is measured as an open circuit voltage (OCV).

  For example, the relaxation determination unit 36 includes a timer (not shown). The relaxation determination unit 36 measures a period of time during which no current is supplied (a period of no load) from the time when the charging and discharging of the cell 10 is completed, and when a predetermined relaxation time has elapsed, the cells 10_1 to 10_n are in the relaxed state. Is determined.

  The point in time when the charging and discharging of the cell 10 is completed includes, for example, a point in time when a system main relay (not shown) connecting the battery module 12 and the load is shut off. If the vehicle is a plug-in type vehicle that can be externally charged, as an example of the time when the charging and discharging of the single battery 10 is completed, a charge relay (shown in FIG. Z) was interrupted.

  In step S10, when it is determined that the cell 10 is not in the voltage relaxation state, the present flow ends. When it is determined that the cell 10 is in the voltage relaxation state, the arithmetic unit 18 outputs a command to the voltage detection circuit 22 to detect the voltages VB_1 to VB_n of all the cells 10_1 to 10_n (S12). . The voltages VB_1 to VB_n detected by the voltage detection circuit 22 are sent to the first voltage comparison unit 32 and the second voltage comparison unit 34.

  In addition, even when the system main relay is shut off, a minute current may flow from the battery module 12 as a so-called dark current. In such a case, the calculation unit 18 may calculate the IR loss corresponding to the dark current, and reflect (voltage correction) on the voltage detected by the voltage detection circuit 22. The corrected voltage value is transmitted to the first voltage comparison unit 32 and the second voltage comparison unit 34.

  The first voltage comparison unit 32 determines whether or not the voltages VB_1 to VB_n fall within a range from a lower threshold Vth0 to an upper threshold Vth1, which is a voltage region corresponding to the second SOC region, as shown in FIG. (S14). If any of the voltages VB_1 to VB_n is not included in the above range, this flow ends.

  Note that the lower threshold Vth0 and the upper threshold Vth1 are set in advance by the calculation unit 18. For example, the lower limit threshold value Vth0 is an OCV corresponding to SOC = α% at which the difference between the discharge curve and the charge curve starts to widen. The upper threshold Vth1 is an OCV corresponding to the upper limit (max%) of the SOC usage range of the cell 10. That is, the second SOC region is a region of not less than α% and not more than max%.

  Further, the lower threshold Vth0 and the upper threshold Vth1 may be updated according to the battery state. For example, during traveling or during plug-in charging, the voltage, current, temperature, and the like of the battery module 12 may be obtained, the state of deterioration of the battery may be learned from the obtained measured values, and the threshold may be updated sequentially.

  Here, as shown in FIG. 2, even within the second SOC region, there is a slight difference in the voltage (OCV) corresponding to the SOC between the discharge curve and the charge curve. Therefore, in both the discharge curve and the charge curve, the lower limit threshold Vth0 and the upper limit threshold Vth1 are set within a range where the SOC does not fall below α% and does not exceed max%.

  For example, as shown in FIG. 2, in the OCV until the SOC reaches α%, the charge curve is slightly higher than the discharge curve. In other words, in the OCV where the SOC reaches α% in the charge curve, the OCV is sufficiently included in the second SOC region in the discharge curve. In such a case, the lower limit threshold Vth0 is set with the charging curve in mind. That is, the OCV when the SOC reaches α% in the charging curve is set to the lower threshold Vth0. Similarly, as for the upper limit threshold Vth1, the OCV at which the SOC becomes max% in the relatively lower curve of the discharge curve and the charge curve is set as the upper limit threshold Vth1.

  In step S14, when the voltages VB_1 to VB_n are included in the range from the lower threshold Vth0 to the upper threshold Vth1, the second voltage comparison unit 34 determines that the difference between the maximum voltage and the minimum voltage of the voltages VB_1 to VB_n is a predetermined value. It is determined whether the difference is equal to or larger than the threshold voltage difference (S16). If the difference between the maximum voltage and the minimum voltage is smaller than the predetermined threshold voltage difference, it is determined that the equalization processing is unnecessary, and this flow ends.

  In step S16, when the difference between the maximum voltage and the minimum voltage of the voltages VB_1 to VB_n is equal to or larger than the predetermined threshold voltage difference, the equalization determination unit 38 performs the equalization process on the equalization process control unit 40. Is permitted (S18). In response, the equalization circuit 20 performs the above-described equalization processing based on passive balancing under the control of the equalization processing control unit 40 (S20). During the equalization process, the voltages of the cells 10_1 to 10_n are appropriately detected by the voltage detection circuit 22. For example, when the voltages of all the cells 10_1 to 10_n become equal, the equalization processing ends.

  In the above-described embodiment, the relatively high SOC area is set as the equalization processing area. However, the present invention is not limited to this mode. For example, in a unit cell in which Si or lithium titanate (LTO) is mixed as a negative electrode, the hysteresis width is relatively widened in a relatively high SOC region. In such a case, the relatively low SOC area may be set as the equalization processing area (second SOC area).

  Reference Signs List 10 cell, 12 battery module, 14 control device, 16 circuit unit, 18 arithmetic unit, 20 equalization circuit, 22 voltage detection circuit, 24 multiplexer, 26 voltage sensor, 28 sequencer, 30 interface, 32 first voltage comparison unit, 34 second voltage comparison unit, 36 relaxation determination unit, 38 equalization determination unit, 40 equalization processing control unit.

Claims (1)

A control device for a battery module to which a plurality of cells are connected,
The plurality of cells have an open circuit voltage with respect to a predetermined SOC that changes according to a charge / discharge history, and has a first SOC region where the change is relatively large and a second SOC region where the change is relatively small,
The control device includes:
A voltage detection circuit for detecting a voltage of each of the unit cells,
An equalization circuit that performs an equalization process for equalizing the voltages of the respective cells detected by the voltage detection circuit,
After a predetermined relaxation time has elapsed after the plurality of cells have been charged and discharged, the difference between the maximum voltage and the minimum voltage among the voltages of the plurality of cells detected by the voltage detection circuit is different. When the voltage is equal to or higher than a predetermined threshold and any of the voltages of the plurality of cells is included in the voltage range corresponding to the second SOC region, the equalization circuit is permitted to perform the equalization processing. An equalization determination unit;
A control device for a battery module, comprising: