JP2011061955A - Device for adjusting capacity of battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacity adjustment device of a battery pack, capable of expanding a usable range of the battery pack. <P>SOLUTION: The capacity adjustment device includes a voltage detection means 24 which detects voltages of unit cells of the battery pack 21 connected with a plurality of unit cells 211 constituting a secondary battery, a deterioration degree detection means 24 which detects the degree of the deterioration of capacities of the unit cells on the basis of the voltage detected by the voltage detection means, a capacity adjustment means 247 which adjusts the battery capacities of the unit cells by performing the discharge processing of the unit cells, and a control means 24 which limits the discharge processing of the unit cells which should be adjusted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an assembled battery capacity adjustment device.

  In an assembled battery formed by connecting a plurality of single cells (cells), all the single cells have a predetermined voltage or a predetermined state of charge by appropriately controlling discharge of a capacity adjusting discharge circuit provided in each single cell. There is known a capacity adjustment device that equalizes variation in battery capacity so as to achieve (SOC, State of Charge) (Patent Document 1).

JP 2000-83327 A

  However, since the conventional capacity adjustment device is a capacity adjustment method that equalizes the voltage or SOC, the capacity is equalized immediately after the adjustment, but the subsequent voltage change due to individual differences in the degree of capacity deterioration of the unit cell. Tend to be different.

  As a result, there is a risk that variations occur immediately and overcharge or overdischarge occurs. Therefore, it has been necessary to limit the usable range of the assembled battery in order to prevent such overcharge or overdischarge.

The problem to be solved by the present invention is to provide an assembled battery capacity adjusting device capable of expanding the usable range of the assembled battery.

In the present invention, when adjusting the battery capacity of the unit cell by executing the discharge process of the unit cell, the problem is solved by limiting the discharge process according to the capacity deterioration degree or the full charge capacity of the unit cell to be adjusted. Resolve.

  According to the present invention, since the discharge process is limited according to the capacity deterioration degree or the full charge capacity of the unit cell to be adjusted, the unit battery having a large capacity deterioration degree or a small full charge capacity, that is, a large voltage drop degree. On the other hand, the discharge process is limited. As a result, since the time until reaching the lower limit voltage due to subsequent use becomes longer, the usable range of the assembled battery can be expanded.

1 is a block diagram showing a hybrid vehicle to which an embodiment of the invention is applied. FIG. 2 is a block diagram showing details around a battery 21 in FIG. 1. It is an electric circuit diagram which shows an example of the capacity | capacitance adjustment circuit of the battery 21 of FIG. 3 is a flowchart showing a control procedure of the battery controller 24 of FIG. 1. It is a graph which shows an example of the acquisition method of the open circuit voltage of the battery of step S1 and S4 of FIG. It is a graph which shows an example of the method of calculating SOC from the open circuit voltage of the battery of step S2 and S5 of FIG. It is a graph which shows an example of the capacity | capacitance adjustment method of step S11-S15 of FIG. 5 is a graph (part 1) illustrating an example of a capacity adjustment method in steps S11 to S15 in FIG. 5 is a graph (part 2) illustrating an example of a capacity adjustment method in steps S11 to S15 in FIG. It is a graph (comparative example) which shows an example of the capacity | capacitance adjustment method of step S11-S15 of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a power transmission system (powertrain) of a hybrid vehicle to which an embodiment of the present invention is applied. Internal combustion engine 1, motors 2 and 3, clutch 4, continuously variable transmission 5, speed reducer 6, a differential device 7 and a drive wheel 8. The output shaft of the motor 3, the output shaft of the internal combustion engine 1, and the input shaft of the clutch 4 are connected to each other, and the output shaft of the clutch 4, the output shaft of the motor 2, and the input shaft of the continuously variable transmission 5 are connected to each other. Has been.

In the hybrid vehicle of this example, the internal combustion engine 1 and the motor 2 become the propulsion source of the vehicle when the clutch 4 is engaged, while only the motor 2 becomes the propulsion source of the vehicle when the clutch 4 is released. The driving force of the internal combustion engine 1 and / or the motor 2 is transmitted to the drive wheels 8 via the continuously variable transmission 5, the speed reduction device 6 and the differential device 7.

The motors 2 and 3 are AC motors such as a three-phase synchronous motor or a three-phase induction motor. The motor 3 is mainly used for starting and power generation of the internal combustion engine, and the motor 2 is mainly used for propulsion and braking of the vehicle.

  The motors 2 and 3 are not limited to AC motors, and DC motors can also be used. Further, when the clutch 4 is engaged, the motor 3 can be used for propulsion and braking of the vehicle, and the motor 2 can be used for starting the internal combustion engine 1 and generating power.

The clutch 4 is a powder clutch, and the transmission torque can be adjusted because the transmission torque is substantially proportional to the excitation current. The continuously variable transmission 5 is a continuously variable transmission such as a belt type or a toroidal type, and the gear ratio can be adjusted steplessly.

The motors 2 and 3 are driven by inverters 22 and 23, respectively. When a DC motor is used for the motors 2 and 3, a DC / DC converter is used instead of the inverters 22 and 23. The inverters 22 and 23 are connected to a battery 21 that is a secondary battery via a common DC link 25, and the DC charging power of the battery 21 is converted into AC power and supplied to the motors 2 and 3. , 3 is converted into DC power to charge the battery 21.

  Since the inverters 22 and 23 are connected to each other via the DC link 25, the electric power generated by the motor during the regenerative operation is directly supplied to the motors 2 and 3 during the power running operation without going through the battery 21. can do.

The battery 21 is a lithium ion battery. The battery 21 may be another type of battery such as a nickel metal hydride battery or a lead battery.

The controller 9 includes a microcomputer, its peripheral components, various actuators, and the like. The rotation speed and output torque of the internal combustion engine 1, the transmission torque of the clutch 4, the rotation speed and output torque of the motors 2 and 3, and the continuously variable transmission 5 The transmission ratio, the SOC of the battery 21, etc. are comprehensively controlled via the engine controller 11, the transmission controller 51 and the battery controller 24.

FIG. 2 is a block diagram showing details around the battery 21 of FIG. As shown in FIG. 2, a battery controller 24 is connected to the battery 21. The battery controller 24 includes a current sensor 241 that detects a current flowing through the battery 21 and a total voltage sensor that detects a total voltage of the battery 21. 242, a temperature sensor 243 that detects the temperature of the battery 21, and a communication line 244 that connects to a cell controller (not shown) of the assembled battery that constitutes the battery 21 are connected.

FIG. 3 is an electric circuit diagram showing an example of a capacity adjustment circuit of the assembled battery constituting the battery 21 of FIGS. 1 and 2. The battery 21 which is an assembled battery is formed by connecting a plurality of single cells 211 which are secondary batteries in series and / or in parallel, and this figure shows an example in which a plurality of single cells 211 are connected in series. These are represented by single cells 211a, 211b. The hybrid vehicle system shown in FIG. 1 is collectively referred to as a battery 21, but when referring to the entire battery 21, it is referred to as an assembled battery 21, and when referring to individual batteries constituting the assembled battery, it is referred to as a single battery 211. , To distinguish between the two.

One end of a pair of voltage detection lines 245 is connected to both terminals of each unit cell 211, and the other end is connected to an AD conversion port of the battery controller 24 (or cell controller), for example. Is detected.

Between the pair of voltage detection lines 245, a switching element 246 such as a transistor and a resistor 247 for adjusting the capacity by consuming the electric power of the unit cell 211 are connected. When the battery controller 24 determines that it is necessary to adjust the variation in the capacity of each unit cell 211, a switching ON / OFF signal is input from the battery controller 24 to the switching element 246 (base of the transistor) for a predetermined time. The electric power of the cell 211 to be adjusted is discharged by the resistor 247.

  Next, the capacity adjustment method of this example will be described.

  FIG. 4 is a flowchart showing a control procedure executed by the battery controller 24 of FIG.

  In step S1, an open circuit voltage for each cell 211 is acquired. The open circuit voltage referred to here is a) an open circuit voltage Ea obtained by actual measurement when the battery 21 is in a no-load state, and b) an IV characteristic obtained from a current value and a voltage value sampled during charge / discharge. Ec = (total voltage) + (current value) × (temperature and deterioration correction) based on extrapolation, that is, open circuit voltage Eb estimated by power calculation, or c) current value and total voltage value actually measured during charging / discharging Any of the open circuit voltage Ec estimated by the internal resistance) can be adopted.

  Since the open circuit voltage Ea is measured when there is no load, it can be measured at the time of no load when starting the automobile (before turning on the high power system) or when the key is turned off. On the other hand, since the open circuit voltages Eb and Ec can be measured even when there is no load, the open circuit voltages are acquired by appropriately selecting them.

  As an example, the procedure for obtaining the open circuit voltage Eb will be described. The open circuit voltage Eb captures a change in the current of the cell 211 when the vehicle is running, and samples a plurality of current values I and voltage values V as shown in FIG. The circle X in the figure is the measured sampling point, and the characteristic straight line L (= R · I + Eb) is obtained by performing a linear regression operation on the IV data sampling data in the IV coordinates. The intersection of the characteristic line L and the vertical axis (voltage axis) is the open circuit voltage Eb. Note that the slope R of the characteristic line L is the internal resistance of the unit cell 211 according to Ohm's law.

  In step S <b> 2, the SOC for each unit cell 211 is calculated with reference to the open-circuit voltage-SOC map of the unit cell set in the memory area of the battery controller 24. FIG. 6 is a graph showing the correlation between the open circuit voltage of the unit cell 211 and the SOC, and the relationship is unchanged even if the temperature and capacity degradation degree of the unit cell 211 change. Therefore, the SOC is calculated from the open-circuit voltage E acquired in step S1 with reference to the open-circuit voltage-SOC map shown in FIG. 5 set in the battery controller 24.

  Steps S1 and S2 are executed for all the unit cells 211a, 211b,.

  In step S3, based on the SOC of each unit cell 211 calculated in step S2, it is determined whether there is a unit cell 211 that requires capacity adjustment. If there is a unit cell 211 that requires capacity adjustment, Proceeding to step 4, if there is no unit cell 211 that requires capacity adjustment, the process is terminated without executing steps S4 to S15.

  Regarding the necessity of capacity adjustment determined in step S3, for example, the average value of the SOC of each unit cell 211 is obtained, and if there is a unit cell whose difference from this average value is a predetermined value or more, the capacity adjustment is performed. If the difference between the minimum SOC and the maximum SOC of each unit cell 211 varies beyond a predetermined value, the capacity can be adjusted, or other similar criteria can be used.

  In step S4, the open voltage of the battery 21, that is, the entire assembled battery is acquired. Any of the open-circuit voltages Ea, Eb, and Ec described in step S1 can be used as the open-circuit voltage here. For example, as shown in FIG. 5, the open voltage Eb of the entire assembled battery can be obtained by extrapolating the IV characteristics obtained from the current value and voltage value sampled during charging and discharging.

  In step S5, the SOC of the entire assembled battery is calculated with reference to the open voltage-SOC map of the assembled battery set in the memory area of the battery controller 24. In this calculation as well, the SOC can be calculated by referring to a preset map as shown in FIG.

In step S6, the capacity deterioration degree of the entire assembled battery is calculated. The degree of capacity deterioration here is a characteristic value indicating the degree of deterioration of the current capacity with respect to the initial capacity C _{0 of the} battery, and is a capacity deterioration rate indicating the ratio of capacity deterioration or a capacity maintenance ratio indicating the ratio of remaining capacity. It means to include both. That is, the capacity deterioration rate β (%) and the capacity maintenance rate γ (%) of the assembled battery are expressed as follows: the initial capacity of the assembled battery is C ₀ , the current battery capacity is C, and the temperature correction coefficient with respect to the reference temperature is α.
[Formula 1]
β = 100− (αC / C ₀ ) × 100
[Formula 2]
γ = 100−β = (αC / C ₀ ) × 100
It is represented by

Here, the battery capacity C of the current assembled battery is the integrated value ΔAh of the discharge current from the open circuit voltage E1 and SOC1 at the start of discharge shown in FIG. 6 to the open circuit voltage E2 and SOC2 at the end of discharge.
[Formula 3]
C = 100 × ΔAh / (SOC1−SOC2) = 100 × ΔAh / ΔSOC
It can be expressed as

In the above formula 1, the temperature correction coefficient α and the initial capacity C _{0 of the} assembled battery are known. In Equation 3, ΔAh is measured as a time integral value of the current value detected by the current sensor 241 shown in FIG. 2, and ΔSOC is calculated from the open circuit voltage E1 at the start of discharge and the open circuit voltage E2 at the end of discharge. Can do.

  Thereby, the capacity deterioration rate β or the capacity maintenance rate γ of the assembled battery can be calculated.

In step S7, the internal resistance increase rate of the assembled battery is calculated. The internal resistance R can be calculated as the slope of the primary regression line L when the open circuit voltage E of the assembled battery is acquired in step S4, and the internal resistance increase rate is R / R _{0 when the} initial internal resistance is R _0. Can be calculated.

In step S8, ΔSOC = SOC−SOC _min is calculated from the SOC of the assembled battery calculated in step 5 to a preset lower limit SOC _min of the assembled battery SOC. Here, the case where there is a vehicle requirement condition for the lower limit value of the SOC of the assembled battery is shown, but depending on the system, ΔSOC up to an arbitrary SOC that becomes a management point of vehicle performance may be calculated instead of the lower limit value of the SOC. Good. Further, the same determination may be made not only on the discharge side but also on the charge side, that is, the upper limit SOC _max of the SOC.

The calculated ΔSOC is multiplied by the assembled battery capacity deterioration rate β (or assembled battery capacity maintenance rate γ) obtained in step 6 by the assembled battery initial capacity C ₀ and used up to the lower limit of discharge. The battery capacity to be calculated is calculated in units of Ah, for example. In the following description, the calculation is performed in units of Ah, but may be performed in units of Wh.

  In step S9, the capacity deterioration rate β ′ (or capacity maintenance rate γ ′) of the cell 211 that requires the capacity adjustment determined in step S3 is calculated. If there are a plurality of cells that require capacity adjustment in step S3, a capacity deterioration rate β ′ (or capacity maintenance rate γ ′) is calculated for each cell 211. In addition, when there are a plurality of unit cells 211 whose capacity needs to be adjusted, the following steps S10 to S15 are executed for each unit cell 211.

  The calculation of the capacity deterioration rate β ′ or the capacity maintenance rate γ ′ for the single battery 211 is the same as the calculation of the capacity deterioration rate β or the capacity maintenance rate γ of the assembled battery 21 in step S6 described above. It can be obtained by Equations 1 to 3 for 211.

In step S10, the rate of increase in internal resistance of the target cell 211 that requires capacity adjustment is calculated. As for the internal resistance increase rate, as with the calculation of the internal resistance increase rate of the assembled battery 21 in step S7 described above, the internal resistance R is a linear regression line when the open circuit voltage E of the cell 211 is acquired in step S1. The internal resistance increase rate can be calculated as R / R _{0 when the} initial internal resistance is R ₀ .

  In step S11, the battery capacity (Ah) of the assembled battery 21 calculated in step 8 is subtracted from the battery capacity (Ah) of the single battery that requires capacity adjustment. Thereby, the battery capacity (Ah) of the unit cell 211 at the SOC lower limit value of the assembled battery 21 is obtained.

In step S12, the battery capacity (Ah) for each cell 211 at the SOC lower limit value of the assembled battery 21 obtained in step S11, and the capacity maintenance rate γ ′ for each cell 211 obtained in step S9 (or 100−capacity). The deterioration rate β ′) is multiplied by the initial capacity C ₀ of the single battery 211 to calculate the SOC of the single battery 211 at the SOC lower limit value of the assembled battery 21.

  In step S13, the load voltage of the cell 211 when discharging according to the vehicle request in this state is calculated. In calculating the load voltage, the load voltage is estimated from the discharge load, the initial internal resistance, and the internal resistance increase rate (step S10).

  In step S14, based on the load voltage calculated in step S13, it is determined whether or not the target single cell 211 that requires capacity adjustment reaches the discharge lower limit voltage of the single cell 211. In addition, this discharge lower limit voltage can also be set to SOC = 0%, and can also be set to the value below it or more.

  When it is determined in step S14 that there is no unit cell 211 that reaches the discharge lower limit voltage, the process proceeds to step S15 to perform capacity adjustment. However, when there is a unit cell that reaches the discharge lower limit voltage, the unit cell 211 is reached. In this case, the routine is terminated without adjusting the capacity to prevent overdischarge.

  In step S15, the SOC of the unit cell 211 that requires capacity adjustment and does not overdischarge even when the capacity adjustment is executed is adjusted. The SOC adjustment amount at this time is the battery capacity at which the target cell 211 for capacity adjustment does not reach the lower limit voltage even when discharging according to the vehicle request is performed in the state of the SOC lower limit value of the assembled battery 21. It is assumed that the SOC adjustment amount is appropriately set as the adjustment amount.

  The concept of the above capacity adjustment will be described with reference to FIGS. 7 and 8A to 8C.

  FIG. 7 is a graph showing the relationship of the SOC with respect to the battery capacity, and shows a case where the capacity deterioration rates β and β ′ of the assembled battery 21 average A and the cell B are different. That is, it is assumed that the capacity deterioration rate β ′ of the cell B is larger (the degree of deterioration is larger) than the capacity deterioration rate β as the assembled battery average A. Therefore, as shown in the figure, the usable range (Ah) of the unit cell B becomes narrower than the usable range (Ah) as the assembled battery average.

  It is assumed that the SOC of the assembled battery A and the single battery B at a certain point is in the state shown in FIG. 8A and the capacity adjustment of the single battery B is required.

  Here, in the conventional capacity adjustment method, when adjusting the capacity of the state of charge SOC-B of the cell B as shown in FIG. 8A, the target SOC is set to the state of charge SOC of the battery pack A as shown in FIG. 8C, for example. -A is set, and the discharge process is executed until the SOC-B of the battery B becomes SOC-A.

  However, since the capacity deterioration rate β ′ of the battery B is larger than the capacity deterioration rate β of the battery pack average A, the range (battery capacity) until the battery B reaches the SOC lower limit SOCmin by the subsequent discharge is the battery pack. It is smaller than that of average A. That is, as shown in FIG. 8C, when there is a maximum load request for the battery pack average A, the cell B falls below the lower limit SOCmin and is overdischarged. In other words, in order to prevent overdischarge, the assembled battery cannot meet the load demand from the vehicle.

  On the other hand, in the capacity adjustment of this example, depending on the capacity deterioration rate β ′ (corresponding to the slope of the characteristic line in FIG. 8A) of the unit cell B whose capacity is to be adjusted, as shown in FIG. The discharge process is not performed and the discharge process is limited to the middle as shown in FIG. 8B. That is, the state of charge SOC-B is limited to SOC-B1, and SOC-B1 and SOC-A are not set to zero.

  For example, as shown in FIG. 8B, this limit amount can be a value that returns so as to match the range in which the assembled battery average A can correspond to the subsequent vehicle request, or a value greater than that.

  In the above-described embodiment, the capacity adjustment amount is limited according to the capacity deterioration rate β ′ of the cell 211 to be capacity-adjusted or the capacity maintenance rate γ ′ that is interpolated with the capacity deterioration rate. β ′ and the capacity maintenance rate γ ′ are correlated with the fully charged capacity of the unit cell 211, that is, the battery capacity (Ah) when the SOC is 100%. Therefore, instead of the capacity deterioration rate β ′ and the capacity maintenance rate γ ′, the capacity adjustment amount may be limited according to the fully charged battery capacity of the unit cell 211.

  As described above, according to the capacity adjustment of the assembled battery of this example, the discharge process is limited according to the capacity deterioration rate β ′, the capacity maintenance rate γ ′ or the full charge capacity of the cell 211 to be adjusted. The discharge process is restricted for the unit cell 211 having a large rate or a small capacity maintenance rate or a small full charge capacity, that is, a large degree of voltage drop, and a predetermined amount of battery capacity is secured.

  As a result, it takes a long time to reach the lower limit voltage due to subsequent use, and the usable range of the assembled battery 21 can be expanded.

  The battery controller 24 corresponds to voltage detection means, deterioration degree detection means, control means and load voltage calculation means of the present invention, and the switching element 246, resistor 247 and battery controller correspond to capacity adjustment means of the present invention. .

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2, 3 ... Motor 4 ... Clutch 5 ... Continuously variable transmission 6 ... Deceleration device 7 ... Differential gear 8 ... Drive wheel 9 ... Controller 21 ... Battery (assembled battery)
211 ... Single cells 22, 23 ... Inverter 24 ... Battery controller 241 ... Current sensor 242 ... Voltage sensor 243 ... Temperature sensor 244 ... Communication line 245 ... Voltage detection line 246 ... Switching element 247 ... Resistance

Claims (6)

Voltage detection means for detecting a voltage of the unit cell of a battery pack to which a plurality of unit cells which are secondary batteries are connected;
A deterioration degree detecting means for detecting a capacity deterioration degree of the unit cell based on the voltage detected by the voltage detecting means;
Capacity adjusting means for adjusting the battery capacity of the unit cell by executing discharge processing of the unit cell;
A battery pack capacity adjustment apparatus comprising: control means for restricting discharge processing of the unit cell to be adjusted according to the degree of capacity degradation of the unit cell detected by the deterioration degree detection unit. The capacity adjustment apparatus for an assembled battery according to claim 1,
The control means has a capacity of a single cell having a relatively large capacity deterioration degree with respect to a voltage or SOC after the capacity adjustment of the single battery having a relatively small capacity deterioration degree detected by the deterioration degree detecting means. A battery pack capacity adjustment device that limits discharge processing of a single battery having a relatively large capacity deterioration degree so that the adjusted voltage or SOC is increased by a predetermined amount. The capacity adjustment device for an assembled battery according to claim 2,
Load voltage calculation means for calculating a load voltage required from the load of the assembled battery is provided,
When the load voltage calculated by the load voltage calculating unit is requested, the control unit is configured to have a relatively small cell voltage or SOC that has a relatively low capacity deterioration degree and a single cell that has a relatively large capacity deterioration degree. The battery pack capacity adjustment apparatus sets the predetermined amount so that the time until the voltage or SOC reaches a predetermined lower limit coincides. Voltage detection means for detecting a voltage of the unit cell of a battery pack to which a plurality of unit cells which are secondary batteries are connected;
A full charge capacity detection means for detecting a battery capacity in a fully charged state of the unit cell based on the voltage detected by the voltage detection means;
Capacity adjusting means for adjusting the battery capacity of the unit cell by executing discharge processing of the unit cell;
A battery pack capacity adjustment apparatus comprising: control means for restricting discharge processing of the single cell to be adjusted according to the full charge capacity of the single battery detected by the full charge capacity detection means. The capacity adjustment device for an assembled battery according to claim 4,
The control means includes a single battery having a relatively large full charge capacity with respect to the voltage or SOC after the capacity adjustment of the single battery having a relatively small full charge capacity detected by the full charge capacity detecting means. A capacity adjustment device for a battery pack that limits discharge processing of a single battery having a relatively large full charge capacity so that a voltage or SOC after capacity adjustment is increased by a predetermined amount. In the capacity adjustment apparatus of the assembled battery according to claim 5,
Load voltage calculation means for calculating a load voltage required from the load of the assembled battery is provided,
When the load voltage calculated by the load voltage calculation means is requested, the control means is a single battery voltage or SOC that has a relatively small full charge capacity and a single battery that has a relatively large full charge capacity. The battery pack capacity adjustment apparatus sets the predetermined amount so that the time until the voltage or SOC reaches a predetermined lower limit coincides.

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