JP5491935B2 - Secondary battery discharge control device - Google Patents

Description

  The present invention relates to a discharge control device for a secondary battery, and more particularly to control of a discharge current.

  An electric vehicle such as an electric vehicle or a hybrid vehicle that obtains a vehicle driving force by an electric motor is equipped with a secondary battery, and the electric motor is driven by electric power stored in the secondary battery. Such an electric vehicle has a function of braking by regenerative braking, that is, by causing the motor to function as a generator during vehicle braking and converting the kinetic energy of the vehicle into electric energy. The converted electric energy is returned to the secondary battery and reused when acceleration is performed.

  When a secondary battery is overdischarged or overcharged, the battery performance is deteriorated. Therefore, it is necessary to grasp the state of charge (SOC: State of Charge) of the secondary battery and control the charge / discharge.

  By the way, depending on the manufacturing process and the subsequent use state, the battery performance varies for each battery block, and the charge state of each battery block constituting the secondary battery may vary. When charging / discharging of each battery block is repeated for a secondary battery configured by connecting such battery blocks in series, the battery block with a small capacity becomes overdischarged or overcharged, and the charge state between the battery blocks The dispersion of Therefore, in order to prevent overdischarge or overcharge, the range of capacity that can be used as a battery block is narrowed, and the lifetime of the secondary battery is apparently reduced.

  Therefore, conventionally, in order to suppress and equalize the capacity variation between the battery blocks constituting the secondary battery, a discharge circuit is provided in each battery block, the voltage of each battery block is measured, and Techniques for operating a discharge circuit to discharge the battery block have been proposed.

  For example, in Patent Document 1, a high voltage secondary battery side and a low voltage microcomputer side are insulated using a photocoupler in which a light emitting diode and a light receiving diode are mutually insulated, and a serial parallel register is used. A configuration is disclosed in which serial data is transmitted from a microcomputer and a control command is transmitted in parallel to a discharge circuit provided in each battery block constituting the secondary battery to control the discharge circuit.

  In Patent Document 2, when the voltage of each battery block constituting the secondary battery is measured, the variation in electromotive force between the battery blocks is periodically calculated from the measured voltage, and the variation exceeds the reference value Discloses a configuration for discharging a battery block having the highest electromotive force.

JP 2005-333717 A JP 2008-178186 A

  When discharging a battery block in a discharge circuit, there are constant current discharge, constant power discharge, and constant resistance discharge as discharge methods. Among them, the constant power discharge method is a relatively short time for the battery block. The voltage can be reduced to a specified voltage. In the constant power discharge method, control is performed such that the discharge current is gradually increased as the terminal voltage of the battery block decreases so that the discharge power becomes constant.

  However, in the conventional constant power discharge method, the discharge current is determined in advance regardless of the environmental temperature at the time of discharge of the discharge circuit because it is within the set value range in consideration of the capability and characteristic variation of the discharge circuit. For this reason, there has been a problem that the discharge current is not necessarily the optimum value. If the discharge current is not optimized, the time required to discharge the battery block to a specified voltage will increase. The problem that the discharge current is not optimized is the discharge that is performed as a pre-treatment for battery disassembly when the secondary battery is recycled, or the measurement of the SOC in order to estimate the deterioration and remaining life of the battery. It also occurs in the discharge.

  An object of the present invention is to provide an apparatus capable of optimizing the discharge current and shortening the discharge time when discharging the battery block in order to equalize the capacity of the battery block constituting the secondary battery.

The present invention relates to a discharge control device for a secondary battery that discharges each battery block constituting a secondary battery, a discharge circuit connected to each battery block, and a temperature detection that detects a temperature of the discharge circuit. And a control circuit for controlling the discharge current in the discharge circuit in accordance with the detected temperature and the slope of the voltage change of the battery block over time .

In one embodiment of the present invention, the discharge circuit is provided for each battery block,
A battery block to be discharged is selected from the battery blocks, and the discharge is performed for each battery block.

  In another embodiment of the present invention, the battery blocks constituting the secondary battery are discharged together.

  In another embodiment of the present invention, the temperature detecting means is provided for each discharge circuit, and the control circuit is configured to detect the temperature detected by the discharge circuit provided in the selected battery block. The discharge current is controlled accordingly.

  In another embodiment of the present invention, the control circuit controls a discharge current according to a difference between an allowable maximum temperature of the discharge circuit and the detected temperature.

  According to the present invention, when discharging the battery block in order to equalize the capacity of the battery block constituting the secondary battery, the discharge current can be optimized to reduce the discharge time in consideration of the temperature of the discharge circuit.

It is a block diagram of the discharge device of embodiment. It is a processing flowchart of an embodiment. It is a graph which shows the time change of the voltage of a battery block, and an electric current. It is a graph which shows the time change and area | region of the voltage of a battery block. It is a processing flowchart of other embodiments.

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

  FIG. 1 shows a configuration block diagram of a discharge device (or capacity equalization device) in the present embodiment. The discharge device includes a microcomputer 110, photocouplers PD, PR and PC in which light emitting diodes and light receiving diodes are insulated from each other, a control unit 100, and discharge circuits D1 to Dn provided for the respective battery blocks B1 to Bn. And a secondary battery 10. The control unit 100 includes a level conversion circuit 130 and a serial input / parallel output register 120.

  The secondary battery 10 is an assembled battery configured by connecting n battery blocks B1 to Bn in series. Each of the battery blocks B1 to Bn is configured by further connecting a plurality of single cells (cells) in series. The single battery is composed of, for example, a nickel metal hydride battery.

  The discharge circuit Dn is provided in the battery block Bn and includes a discharge resistor Rn and an npn transistor Qn connected in series with each other. One end of discharge resistor Rn is connected to the positive terminal of battery block Bn, and the other end is connected to the collector terminal of npn transistor Qn. The emitter terminal of npn transistor Qn is connected to the negative terminal of battery block Bn. When the transistor Qn is turned on by the control signal Cn supplied to the base terminal of the npn transistor Qn, a current flows through the discharge resistor Rn, and the battery block Bn is discharged. The discharge current of the battery block Bn is controlled by the control signal Cn. The same applies to the other discharge devices D1, D2,.

  A temperature sensor 12 is provided at a predetermined portion of the discharge circuits D1 to Dn, and the temperature of the discharge circuits D1 to Dn is detected and supplied to the microcomputer 110. The temperature sensor 12 is provided in each of the discharge circuits D1 to Dn, and may detect the temperature of each of the discharge circuits D1 to Dn. Only one temperature sensor 12 may be provided to detect the representative temperature of the discharge circuits D1 to Dn. May be. Alternatively, a plurality of temperature sensors 12 may be provided, and the average value of these may be detected as the representative temperature of the discharge circuits D1 to Dn. In the figure, a case where only one temperature sensor 12 is provided is shown.

  The serial input / parallel output register 120 includes a data input terminal DATA, a reset terminal RST, a clock input terminal CLK, and the same number of parallel output terminals Y1 to Yn as the battery blocks B1 to Bn, and serial data from the microcomputer 110 is input thereto. The The serial input / parallel output register 120 outputs each data bit of the serial data from the parallel output terminals Y1 to Yn at a timing when a predetermined number of bits of data are taken. Of the parallel output terminals Y1 to Yn, only the output terminal corresponding to the battery block to be discharged is switched to the high level, and the remaining output terminals are set to the low level.

  The level conversion circuit 130 receives signals from the parallel output terminals Y1 to Yn of the serial input / parallel output register 120, and controls signals C1 to C1 to turn on and off the npn transistors Q1 to Qn constituting the discharge circuits D1 to Dn. Convert to Cn and output. Each output terminal of level conversion circuit 130 is connected to the base terminals of npn transistors Q1-Qn.

  The microcomputer 110 receives each voltage (terminal voltage) of the battery blocks B1 to Bn measured by a voltage measurement circuit (not shown), and selects a battery block having a high voltage. Then, serial data for discharging the battery block having a high voltage is generated and output to the control unit 100 as an optical signal. When creating serial data, the temperature of the discharge circuits D1-Dn detected by the temperature sensor 12 is taken into consideration. The serial data output from the microcomputer 110 is supplied to the serial input / parallel output register 120 of the control unit 100 via the photocoupler PD. The photocouplers PR and PC are for transmitting a reset signal and a clock signal from the microcomputer 110, respectively. The microcomputer 110 is electrically insulated from the high voltage secondary battery 10 by a photocoupler.

  In such a configuration, the microcomputer 110 determines whether or not to operate the discharge circuits D1 to Dn, and the serial data from the microcomputer 110 is discharged via the photocoupler PD and the control unit 100 according to the determination result. Supply to D1 to Dn. The discharge circuits D1 to Dn discharge the battery blocks B1 to Bn constituting the secondary battery 10 individually according to a command from the microcomputer 110, and equalize the capacities of the battery blocks B1 to Bn. The microcomputer 110 discharges the battery blocks B1 to Bn by the constant power discharge method, but shortens the discharge time by optimizing the discharge current according to the temperature of the discharge circuits D1 to Dn. In other words, the discharge current is conventionally set within a preset range, but in the present embodiment, the discharge is performed at the maximum discharge current in a temperature range that can be allowed by the discharge circuits D1 to Dn based on the temperature of the discharge circuits D1 to Dn. To control.

  FIG. 2 shows a processing flowchart of the present embodiment. First, the microcomputer 110 determines whether or not to operate the discharge circuits D1 to Dn (S101). This determination is performed as follows, for example. That is, the voltage variation of each of the battery blocks B1 to Bn is calculated, the calculated voltage variation is compared with a predetermined threshold value, and when the calculated voltage variation exceeds the threshold value, the highest voltage is obtained. The battery block is selected as a battery block to be discharged. And it determines with operating the discharge circuit connected to the selected battery block. Of course, other methods, for example, an electromotive force for each battery block may be calculated and a determination may be made based on the electromotive force.

  Next, when it is determined that any one of the discharge circuits D1 to Dn is to be operated, the microcomputer 110 detects the temperature T of the discharge circuits D1 to Dn (S102), and the allowable maximum temperature Tmax in the discharge circuits D1 to Dn is determined. The detected temperature T is compared (S103). Then, according to the temperature comparison result, serial data is generated and supplied to the discharge circuits D1 to Dn to control the discharge current (S104). Specifically, the discharge current is increased as the difference (Tmax−T) between the maximum allowable temperature Tmax and the detected temperature T is larger. The microcomputer 110 stores the relationship between the difference between the allowable maximum temperature Tmax and the detected temperature T and the discharge current in advance in a memory as a map or table, and calculates the allowable maximum value by referring to the map or table. Serial data can be created by reading the discharge current corresponding to the difference between the temperature Tmax and the detected temperature T.

  For example, it is assumed that the voltage variation of the battery blocks B1 to Bn exceeds the threshold value, and the battery block B1 is the highest voltage. In this case, the microcomputer 110 determines to operate the discharge circuit B1 connected to the battery block B1 in order to discharge the battery block B1. Then, the temperature data T is detected, compared with the maximum allowable temperature Tmax, serial data is generated and supplied to the discharge circuits D1 to Dn so that the discharge current increases as the difference increases. A base current corresponding to the difference between the allowable maximum temperature Tmax and the detected temperature T is supplied to the base terminal of the npn transistor Q1 constituting the discharge circuit B1, thereby controlling the discharge current.

  In addition, when the temperature sensor 12 is installed for each of the discharge circuits D1 to Dn and the temperature is detected for each of the discharge circuits D1 to Dn, the discharge current is controlled using the temperature corresponding to the discharge circuit determined to be activated. Needless to say. For example, when operating the discharge circuit B1, the discharge current is controlled according to the temperature T1 of the discharge circuit B1. In this case, since the discharge current can be controlled in accordance with the temperature of the discharge circuit to be operated, more optimal discharge can be performed.

  In FIG. 3, the time change of the voltage current of the battery block of discharge object in this embodiment is shown. In the figure, the horizontal axis represents time t, the left vertical axis represents voltage V, and the right vertical axis represents current I. In the figure, symbol a represents a voltage change, and symbols b, c, and d represent current changes in the case of constant resistance discharge, constant current discharge, and constant power discharge, respectively. Further, the symbol e is a time change of the discharge current of the present embodiment, which is a time change when the temperature of the discharge circuit is taken into consideration. In the initial stage of discharge, the temperature of the discharge circuit is still sufficiently lower than the allowable maximum temperature Tmax, so that the discharge current also increases in comparison with the case of the conventional constant power discharge (symbol d). Thereafter, when the temperature of the discharge circuit rises along with the discharge and eventually reaches the vicinity of the maximum allowable temperature Tmax, the discharge current becomes almost the same as in the case of the conventional constant power discharge. As described above, according to the discharge method of the present embodiment, the discharge current can be increased particularly in the initial stage of the discharge, so that the discharge time can be shortened as compared with the conventional case.

  In the present embodiment, the discharge current is controlled according to the temperature of the discharge circuits D1 to Dn, but the discharge current may be controlled using another parameter in addition to the temperature of the discharge circuits D1 to Dn. FIG. 4 shows a typical voltage-time change at the time of discharging the battery blocks B1 to Bn. The voltages of the battery blocks B1 to Bn have a characteristic of decreasing relatively steeply at the initial stage of discharge, decreasing relatively gently thereafter, and then decreasing again relatively steeply. Therefore, as shown in FIG. 4, the voltage time change can be divided into three regions A, B, and C. Regions A and C are regions where the voltage decreases relatively steeply, and the discharge current increase ΔI is set relatively large in consideration of the sudden decrease in voltage when discharging at constant power. The region B is a region where the voltage decreases relatively gently, and the discharge current increase ΔI is also set relatively small in consideration of the gentle decrease of the voltage when performing constant power discharge. The microcomputer 110 acquires the voltage V of the battery blocks B1 to Bn in addition to the temperature T of the discharge circuits D1 to Dn, calculates the gradient dV / dt of the time change of the voltage V, and the battery block according to dV / dt It is identified which of the areas A to C shown in FIG. 4 B1 to Bn are located, and the increase in the discharge current is controlled according to the identified area.

  FIG. 5 shows a processing flowchart in this case. The processing from S201 to S203 is the same as the processing from S101 to S103 in FIG. Next, the microcomputer 110 detects the slope dV / dt of the time change of the voltage of the battery block to be discharged (S204). Then, according to the detected dV / dt, it is determined in which of the areas A to C shown in FIG. 4 the battery block is located (S205). When determining the region, the voltage of the battery block may be additionally used. For example, dV / dt is compared with a reference value, and if it is less than or equal to the reference value, it is determined that the region is B. Considering the voltage of the battery block, if the voltage is relatively high, it is determined as the region A, and if the voltage is relatively low, it is determined as the region C. The region can also be determined using a two-dimensional map or table of dV / dt and voltage V.

  After determining the area, the microcomputer 110 controls the discharge current according to the comparison result in S203 and the determination result in S205 (S206). Specifically, assuming that the increase in the discharge current is ΔI, the discharge current is controlled by ΔI = K1 · (Tmax−T) + K2 · (set value for each region). Here, K1 and K2 are coefficients, and the “set value for each area” is a constant set in advance for each of the areas A to C. (Set values of areas A and C)> (Set value of area B). Of course, instead of determining the region according to dV / dt, dV / dt can also be used directly. In this case, the above equation is ΔI = K1 · (Tmax−T) + K2 · dV / dt.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various change is possible.

  For example, in the present embodiment, a nickel metal hydride battery is illustrated as the secondary battery 10, but a lithium ion battery may be used.

  In the present embodiment, the discharge circuits D1 to Dn are discharge resistors and npn transistors. However, the present invention is not limited to this. The discharge resistors are variable resistors, and discharge is performed by controlling the resistance values of the variable resistors. The current may be controlled.

  In this embodiment, the discharge current is controlled according to the difference between the allowable maximum temperature Tmax and the detected temperature T. First, the allowable maximum temperature Tmax and the detected temperature T are compared in magnitude, and Tmax> T. The discharge current may be controlled according to the detected temperature T after confirming that there is. In short, the discharge current value may be dynamically changed according to the temperature of the discharge circuits D1 to Dn, that is, the operating temperature or the environmental temperature of the discharge circuits D1 to Dn.

  Moreover, in this embodiment, although discharge is performed for every battery block, you may discharge a some battery block collectively. In this case, the number of discharge circuits is not limited, and only one battery block may be provided or may be provided for each battery block. Further, the number of temperature sensors is not limited. For such a discharge that is collectively performed on a plurality of battery blocks, a discharge is performed as a pre-treatment for battery disassembly when the secondary battery is recycled, and SOC is measured in order to estimate battery deterioration and remaining life. It can be suitably used for the discharge performed at the time.

  10 secondary battery (assembled battery), 12 temperature sensor, 100 control unit, 110 microcomputer, D1-Dn discharge circuit.

Claims (5)

A secondary battery discharge control device that discharges each battery block constituting the secondary battery,
A discharge circuit connected to each battery block;
Temperature detecting means for detecting the temperature of the discharge circuit;
A control circuit that controls the discharge current in the discharge circuit according to the detected temperature and the slope of the voltage change of the battery block over time ;
A discharge control device for a secondary battery, comprising: The apparatus of claim 1.
The discharge circuit is provided for each battery block;
A secondary battery discharge control device, wherein a battery block to be discharged is selected from the battery blocks, and the discharge is performed for each battery block. The apparatus of claim 1.
A discharge control device for a secondary battery, wherein the battery blocks constituting the secondary battery are discharged together. The apparatus of claim 2.
The temperature detection means is provided for each of the discharge circuits,
The control circuit controls a discharge current according to the detected temperature of the discharge circuit provided in the selected battery block. In the apparatus in any one of Claims 1-4,
The control circuit controls a discharge current according to a difference between an allowable maximum temperature of the discharge circuit and the detected temperature.

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