JP2009290984A - Charge/discharge controller for vehicle battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control charge/discharge of a battery on the basis of a detection result by accurately detecting a voltage abnormality of a unit cell with a simple structure in a charge/discharge controller for a vehicle battery. <P>SOLUTION: A current IB of a battery, a voltage VB of a battery pack, and a temperature TB of a representative unit cell in the battery pack are detected (a step S101). Each voltage difference ΔVmax, ΔVmin between unit cells in the battery pack is estimated on the basis of a map stored in a controller 40 (a step S102). The maximum voltage Vmax and the minimum voltage Vmin of the unit cell in the battery pack are calculated on the basis of each voltage difference ΔVmax, ΔVmin and the voltage VB (a step S103). When the maximum voltage Vmax exceeds an upper limit value Vupper (a step S104) or when the minimum voltage Vmin is less than a lower limit value Vlower (a step S106), charge/discharge of the battery is controlled (steps S105, S107). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charging / discharging control device for a vehicle battery that includes a plurality of assembled batteries configured by connecting a plurality of single cells in series, and further configured by connecting these assembled batteries in series.

  A battery is used as a power source that supplies power to an electric motor that drives the vehicle. This battery includes a plurality of assembled batteries configured by connecting a plurality of single cells in series, and is configured by further connecting these assembled batteries in series. With this configuration, the battery secures a high voltage required by the electric motor and supplies electric power to the electric motor.

  Such a battery is vulnerable to overcharge and overdischarge, and if it is not used within the specified voltage range, the material inside the battery will be decomposed and the capacity will be significantly reduced, or it will become abnormally hot and unusable. There is a fear. Thus, a technique is known in which the upper limit value and the lower limit value of the voltage are clearly defined so that the battery does not become overcharged and overdischarged, and the voltage is controlled so that the voltage falls within those ranges.

  In Patent Document 1 below, a voltage detector is attached to each unit cell (single cell), and it is detected that the unit cell is in an abnormal voltage state, that is, overcharge and overdischarge, and based on the detection result. Thus, there is described a technique for controlling charging and discharging to be limited.

JP 2002-101565 A

  In Patent Document 1, since the voltage of the unit cell is detected by the voltage detector corresponding to each unit cell, it is possible to grasp the voltage abnormality for each unit cell. However, if a voltage detector is attached to each cell, the system becomes complicated and the cost increases.

  On the other hand, in order to simplify the system, a method of detecting a voltage for each assembled battery by attaching a voltage detector for each assembled battery instead of attaching a voltage detector for each single battery is conceivable. In this method, the average voltage of the cells constituting the assembled battery can be calculated from the voltage of the assembled battery. However, it is not possible to detect voltages in which variations occur in the individual cells in the assembled battery. Therefore, the voltage abnormality of the unit cell cannot be detected accurately, and as a result, there is a problem that the battery deteriorates and breaks down.

  An object of the present invention is to provide a vehicle battery charging / discharging control device capable of accurately detecting voltage abnormality of a single cell with a simple structure and controlling the charging / discharging of the battery based on the detection result. It is in.

  The present invention has a plurality of assembled batteries configured by connecting a plurality of single cells in series, and in a vehicle battery charge / discharge control device configured by further connecting these assembled batteries in series. Current detection means for detecting current, voltage detection means for detecting the voltage of the assembled battery, temperature detection means for detecting the temperature of a representative unit cell in the assembled battery, detected temperature, detected current, and in the assembled battery Voltage difference estimating means for estimating the voltage difference between the single cells in the assembled battery based on the temperature difference generated between the single cells of the battery, and the single cell in the assembled battery based on the estimated voltage difference and the detected voltage It has a voltage calculation means for calculating the maximum voltage and the minimum voltage, and a control means for controlling charge / discharge of the battery based on the calculation result of the voltage calculation means.

  Further, the control means can perform control so as to prohibit charging of the battery when the maximum voltage calculated by the voltage calculation means exceeds the upper limit value.

  Further, the control means can perform control so as to prohibit the discharge of the battery when the minimum voltage calculated by the voltage means is less than the lower limit value.

  According to the charging / discharging control device for a vehicle battery of the present invention, it is possible to accurately detect a voltage abnormality of the single cell with a simple structure, and to control charging / discharging of the battery based on the detection result.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a charge / discharge control device for a vehicle battery according to the present invention will be described with reference to the drawings. In the embodiment according to the present invention, a hybrid vehicle is taken as an example of a vehicle that travels by the output of an electric motor, and a charge / discharge control device for a battery mounted on the hybrid vehicle will be described.

  First, the structure of the hybrid vehicle 10 which mounts the charging / discharging control apparatus of the vehicle battery in this embodiment is demonstrated using FIG. The hybrid vehicle 10 includes an internal combustion engine (hereinafter referred to as an engine) 12 as a prime mover, a first electric motor (hereinafter referred to as a first MG) 14, and a second electric motor (hereinafter referred to as a second MG) 16. Have A power distribution and integration mechanism 18 that distributes and integrates these powers is connected to the prime movers 12, 14, and 16. Drive wheels 22 are connected to the power distribution and integration mechanism 18 via a speed reduction mechanism 20. The powers of the prime movers 12, 14, 16 are integrated by the power distribution and integration mechanism 18, and then transmitted to the drive wheels 22 via the speed reduction mechanism 20, so that the hybrid vehicle 10 travels.

  The hybrid vehicle 10 can travel in various modes by controlling the output of the engine 12 and the first and second MGs 14 and 16. For example, various modes such as traveling with either the engine 12 or the second MG 16, traveling in cooperation with the engine 12 and the second MG 16, and generating power with the first MG 14 using a part of the output of the engine 12. Can be run. Furthermore, at the time of deceleration, regenerative power generation can be performed by the second MG 16 by the kinetic energy of the hybrid vehicle 10 input from the drive wheels 22.

  The first and second MGs 14 and 16 are synchronous motors that function as generators and function as electric motors. The first and second MGs 14 and 16 are connected to the battery 30 via the first and second inverters 24 and 26. The battery 30 is configured by a chargeable / dischargeable secondary battery, such as a nickel hydride secondary battery or a lithium ion secondary battery. The electric power stored in the battery 30 is converted from a direct current into a three-phase alternating current by the first and second inverters 24 and 26, and then supplied to the first and second MGs 14 and 16, and these MGs 14 and 16 are supplied. To drive. In addition, the power generated by the first and second MGs 14 and 16 during regeneration is converted from a three-phase alternating current to a direct current by the first and second inverters 24 and 26 and then sent to the battery 30 for storage. . Thus, the first and second MGs 14 and 16 can function as an electric motor and a generator.

  The hybrid vehicle 10 includes an electronic control unit (ECU) 40 that performs control based on the state of the vehicle and the driver's request. The electronic control unit 40 is configured as a microprocessor centered on a CPU. In addition to the CPU, a ROM (not shown) that stores a processing program, and a RAM (not shown) that temporarily stores data. Is provided. The electronic control device 40 is a device corresponding to the charge / discharge control device according to the present invention, and will be simply referred to as a control device 40 hereinafter.

  The control device 40 is connected to the engine 12, the first and second MGs 14 and 16, the first and second inverters 24 and 26, and the battery 30. The engine 12 is provided with a sensor for detecting the operating state of the engine 12, for example, a rotation speed sensor (not shown), and a signal is input from the sensor to the control device 40. The first and second MGs 14 and 16 are provided with sensors for detecting the operation state of the MGs 14 and 16, for example, rotation speed sensors (not shown), and signals are input from the sensors to the control device 40. The The battery 30 is provided with various sensors that detect the state of the battery 30. Various sensors will be described later with reference to FIG. Signals are input to the control device 40 from various sensors.

  The control device 40 determines the state of the vehicle based on the signal described above. Then, the control device 40 determines the driving force of the prime mover by combining the vehicle state and the driver's request, and outputs a control signal to the engine 12 and the first and second inverters 24 and 26. Thereby, the output distribution of the engine 12 and the first and second MGs 14 and 16 is optimally controlled. Note that the driver's request is determined based on signals sent from input means operated by the driver, such as an ignition switch, an accelerator pedal, a brake pedal, and a shift lever.

  Next, a schematic configuration of the battery 30 will be described with reference to FIG. The battery 30 has a plurality of assembled batteries 34 formed by connecting a plurality of single cells 32 in series, and these assembled batteries 34 are further connected in series. That is, the battery 30 has all the unit cells 32 included in the assembled battery 34 connected in series connected in series. By connecting all the cells 32 in series, the battery 30 secures the high voltage required by the first and second MGs 14 and 16.

  The battery 30 is provided with various sensors that detect the state of the battery 30. The various sensors are a voltage detector 50, a temperature detector 52, and a current detector 54. The voltage detector 50 is a sensor that detects the terminal voltage of the assembled battery 34 and is provided corresponding to each assembled battery 34. The temperature detector 52 is a sensor that detects the temperature of the representative unit cell 32 in the assembled battery 34, and is provided corresponding to each assembled battery 34. The current detector 54 is a sensor that detects the current of the battery 30 and is provided in a circuit in the battery 30.

  The charge / discharge characteristics of a general battery will be described with reference to FIGS. FIG. 3 is a diagram showing a state of the time change of the voltage of the single cell during discharge. FIG. 4 is a diagram showing the relationship between the internal resistance of the cell and the temperature of the cell. In these figures, discharge is taken as an example of charging / discharging of the battery and the characteristics thereof will be described, but the charging characteristics are also the same.

  In FIG. 3, the time change of the plurality of single cells at the time of discharging is represented by a curve indicated by reference numeral 60. Note that the number of single cells is, for example, four. In a section in which the elapsed time from the start of discharge is short, the voltage of each unit cell decreases with substantially the same tendency. That is, the voltage difference between the single cells is extremely small. On the other hand, when the elapsed time from the start of discharge becomes longer than a section where the discharge time is short, a difference between the voltages tends to occur due to a difference in temperature of each unit cell. As a result, as shown in FIG. 3, the four unit cells are separated as indicated by the curves 60 a to 60 d, and the voltage decreases respectively. Here, as shown in FIG. 3, the voltage drop of the curve indicated by reference numeral 60a is the slowest, followed by the curve indicated by reference numeral 60b, and then the curve indicated by reference numeral 60c. You can see the most remarkable. A curve obtained by averaging the voltages of these single cells is indicated by a broken line 62. After a certain period of time (the right end of the curve), even if the curve 62, which is the average voltage of each unit cell, is in the range equal to or higher than the lower limit value of the voltage, the curve 60d is lower than the lower limit value of the voltage. Therefore, it can be seen that even when the average voltage of the plurality of single cells is compared with the lower limit value and the average voltage is equal to or higher than the lower limit value, the voltages of some of the single cells become lower than the lower limit value. In the case of charging, on the contrary, if the elapsed time from the start of charging is long, even if the average voltage is equal to or lower than the upper limit value by comparing the average voltage and the upper limit value of the plurality of single cells, The voltage of some cells exceeds the upper limit.

  Thus, when charging / discharging a several cell continuously for a long time, a difference will arise in the voltage of each cell normally by the difference of the temperature etc. of a cell. Therefore, even if the average voltage of the plurality of single cells constituting the assembled battery is calculated from the terminal voltage of the assembled battery and the charge / discharge control is performed so that the average voltage is within the range of the upper and lower limit values, some of the single cells May exceed the upper limit value or less than the lower limit value.

  In general, the internal resistance of a single cell depends on the temperature of the single cell. That is, when the current flowing through the cell is constant, the voltage of the cell depends on the temperature of the cell. FIG. 4 is a diagram showing the internal resistance and temperature of the unit cell during discharge. The dashed curve indicates the characteristics of the internal resistance of the unit cell when the discharge time is relatively short. From this curve, it can be seen that the internal resistance is small when the temperature of the unit cell is high, and the internal resistance increases as the temperature of the unit cell decreases. The solid line curve shows the characteristics of the internal resistance of the unit cell when the discharge time is longer than that of the broken line curve. Similarly to the dashed curve, this curve also shows that when the cell temperature is high, the internal resistance is small, and as the cell temperature decreases, the internal resistance increases. Also, the solid curve tends to have a higher internal resistance as the temperature of the unit cell becomes lower than the dashed curve. In other words, when the discharge time is long, the internal resistance of the unit cell tends to depend on temperature. This characteristic is the same at the time of charging. The longer the charging time, the greater the tendency of the internal resistance of the unit cell depending on the temperature.

  Thus, the internal resistance of the unit cell tends to depend on the temperature of the unit cell when the charge / discharge time is long. A plurality of unit cells constituting the assembled battery may cause a temperature difference between the unit cells due to their arrangement or the like. Then, when the charge / discharge time is long and a temperature difference occurs between the single cells, a difference occurs in the internal resistance between the single cells. As a result, as shown in FIG. 3, a difference occurs in the voltage of each unit cell.

  Next, the voltage characteristics of the unit cell for each temperature during discharging will be described with reference to FIGS. FIG. 5 shows a case where the current value is, for example, 6.5A, and FIG. 6 shows a case where the current value is, for example, 13A. The plurality of curves shown in FIGS. 5 and 6 are different in cell temperature. That is, the curve of reference numeral 64a is −15 ° C., reference numeral 64b is −20 ° C., reference numeral 64c is −25 ° C., reference numeral 64d is −30 ° C., and reference numeral 64e is −35 ° C. In the present embodiment, as an example, a case will be described in which the variation in the temperature of the cells between the assembled batteries is 5 ° C., that is, the temperature difference between the cells is 5 ° C. However, the present invention is not limited to this, and a temperature difference between single cells greater than or less than 5 ° C. can be adopted as a design value.

  As shown in FIGS. 5 and 6, it can be seen that the voltage drop is more remarkable in the unit cell having a lower temperature than the unit cell having a higher temperature. Here, when the temperature difference between the single cells in the assembled battery is set to 5 ° C., for example, the single cell at the time when the voltage of the single cell 5 ° C. lower than the certain cell reaches the lower limit value and the single cell 5 ° C. lower than that. Let the voltage difference of the battery be ΔV. This voltage difference ΔV greatly depends on the temperature and current of the unit cell. A summary of the results is shown in FIG.

  In the case of charging, although not shown in the figure, it can be seen that, contrary to FIGS. 5 and 6, the unit cell having a higher temperature has a higher voltage rise than the unit cell having a lower temperature. Further, when the temperature difference between the single cells in the assembled battery is, for example, 5 ° C., a single cell at the time when the voltage of the single cell 5 ° C. higher than a certain single cell reaches the upper limit value and a single cell 5 ° C. higher than that Is a voltage difference ΔV. This voltage difference ΔV greatly depends on the temperature and current of the unit cell. A summary of the results is shown in FIG.

  7 and 8 are maps obtained by experimentally determining the voltage difference ΔV between the single cells from the temperature TB and the current IB of the single cells when the temperature difference between the single cells in the assembled battery is 5 ° C. FIG. 7 is a map in which the voltage difference ΔVmin between the single cells at the time of discharging is obtained from the temperature TB and the current IB of the single cells. FIG. 8 shows the voltage difference ΔVmax between the single cells at the time of charging. It is the map calculated | required from temperature TB and electric current IB. These maps are used in estimating the voltage differences ΔVmax and ΔVmin between the single cells from the temperature TB and the current IB of the single cells in the control operation of the control device 40 described later.

  Next, the control operation of the control device 40 that controls the charging / discharging of the battery 30 based on the voltage of the unit cell 32 according to the embodiment of the present invention will be described with reference to the flowchart of FIG.

  First, the control device 40 includes the voltage VB between the terminals of the assembled battery 34 detected by the voltage detector 50, the temperature TB of the representative cell 32 in the assembled battery 34 detected by the temperature detector 50, and current detection. The current IB of the battery 30 detected by the device 54 is input (step S101).

  Next, voltage differences ΔVmax and ΔVmin between the single cells 30 are estimated from the map from the temperature TB and the current IB (step S102). The voltage differences ΔVmax and ΔVmin indicate variations from the average voltage value between the single cells 30. At the time of charging, the voltage difference ΔVmax is estimated from the map ΔVmax * map, and at the time of discharging, the voltage difference ΔVmin is estimated from the map ΔVmin * map. The map is shown in FIGS. 7 and 8, for example, and is stored in advance in the ROM of the control device 40. Further, the map assumes that the temperature difference generated between the single cells in the assembled battery is 5 ° C., but a map having a temperature difference higher or lower than this temperature difference can also be used.

And the highest voltage Vmax and the lowest voltage Vmin of the cell 32 in the assembled battery 34 are calculated (step S103). The maximum voltage Vmax is calculated during charging, and the minimum voltage Vmin is calculated during discharging. The maximum voltage Vmax is calculated by the following formula.
Vmax = VB / N + ΔVmax (Formula 1)
On the other hand, the minimum voltage Vmin is calculated by the following equation.
Vmin = VB / N−ΔVmin (Expression 2)
Here, N is the number of unit cells 32 constituting one assembled battery 34.

  Next, the maximum voltage Vmax calculated in step S103 is compared with the set upper limit value Vupper (step S104), and if the maximum voltage Vmax exceeds the upper limit value Vupper, control is performed to prohibit charging (step S105). ). On the other hand, if the maximum voltage Vmax is equal to or lower than the upper limit value Vupper, the current state is maintained and the process proceeds to step S106. By this operation, it is possible to control such that the voltage of any single battery 30 does not exceed the upper limit value and the lower limit value.

  Then, the lowest voltage Vmin calculated in step S103 is compared with the set lower limit value Vlower (step S106), and if the lowest voltage Vmin is less than the lower limit value Vlower, control is performed to inhibit discharge (step S107). . On the other hand, when the minimum voltage Vmin is equal to or higher than the lower limit value Vlower, the current state is maintained and the operation ends.

  According to the present embodiment, the maximum voltage Vmax and the minimum voltage Vmin of the unit cell 32 are calculated only by detecting the terminal voltage VB of the assembled battery 34 constituting the unit cell 32 without detecting the voltage for each unit cell 32. Therefore, the voltage detection system can have a simple structure. Further, by determining the upper and lower limit ranges based on the calculated maximum voltage Vmax and the minimum voltage Vmin, it is possible to accurately detect the voltage abnormality of the unit cell 32, and based on this detection result, the charge of the battery 30 is charged. Discharge can be controlled appropriately.

It is a figure showing the composition of the hybrid vehicle concerning this embodiment. It is a figure which shows the structure of the battery which concerns on this embodiment. It is a figure which shows the mode of the time change of the voltage of the cell at the time of discharge. It is a figure which shows the relationship between the internal resistance of a cell, and the temperature of a cell. It is a figure which shows the voltage characteristic of the cell for every temperature when an electric current value is 6.5A. It is a figure which shows the voltage characteristic of the cell for every temperature when an electric current value is 13A. It is a map which estimates voltage difference (DELTA) Vmin between the single cells at the time of discharge. It is a map which estimates voltage difference (DELTA) Vmax between the single cells at the time of charge. It is a flowchart which shows an example of control operation of a control apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Hybrid vehicle, 30 battery, 32 cell, 34 assembled battery, 40 control apparatus, 50 voltage detector, 52 temperature detector, 54 current detector.

Claims (3)

In a charging / discharging control device for a vehicle battery having a plurality of assembled batteries configured by connecting a plurality of single cells in series, and further connecting these assembled batteries in series,
Current detection means for detecting the current of the battery;
Voltage detection means for detecting the voltage of the assembled battery;
Temperature detecting means for detecting the temperature of a representative unit cell in the assembled battery;
Voltage difference estimation means for estimating a voltage difference between the single cells in the assembled battery based on the detected temperature, the detected current, and the temperature difference generated between the single cells in the assembled battery;
Voltage calculating means for calculating the highest voltage and the lowest voltage of the cells in the assembled battery based on the estimated voltage difference and the detected voltage;
Control means for controlling charge / discharge of the battery based on the calculation result of the voltage calculation means;
A vehicle battery charge / discharge control device comprising: In the vehicle battery charge / discharge control device according to claim 1,
The vehicle battery charging / discharging control apparatus, wherein the control means performs control so as to prohibit charging of the battery when the maximum voltage calculated by the voltage calculating means exceeds an upper limit value. In the vehicle battery charge / discharge control device according to claim 1 or 2,
The vehicle battery charge / discharge control apparatus according to claim 1, wherein the control means controls the battery discharge to be prohibited when the minimum voltage calculated by the voltage means is less than a lower limit value.

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