WO2009041180A1

WO2009041180A1 - Protection device for assembled battery and assembled battery system containing the same

Info

Publication number: WO2009041180A1
Application number: PCT/JP2008/064556
Authority: WO
Inventors: Daisuke Kurose; Tetsuro Itakura; Yoshinao Tatebayashi; Nobuo Shibuya
Original assignee: Kabushiki Kaisha Toshiba
Priority date: 2007-09-26
Filing date: 2008-08-07
Publication date: 2009-04-02
Also published as: JP2009081949A

Abstract

A protection device for an assembled battery includes a plurality of capacitors (Cl, C2), a plurality of first switches (Ss) connected between battery cells(Bl, B2) of the assembled battery and the capacitors (Cl, C2) so as to sample voltages of the battery cells and hold the voltages in the capacitors (Cl, C2), a plurality of second switches (SA) to connect in parallel at least two capacitors (Cl, C2) of the plurality of the capacitors, and a controller (101) which controls the first switches (Ss) and the second switches (SA).

Description

D E S C R I P T I O N

PROTECTION DEVICE FOR ASSEMBLED BATTERY AND ASSEMBLED BATTERY SYSTEM CONTAINING THE SAME

Technical Field

The present invention relates to a protection device for an assembled battery having a function of correcting the dispersion of a voltage among battery cells and an assembled battery system containing the same .

Background Art

In recent years, an electric vehicle and a hybrid vehicle have been attracting public attention in viewpoints of reduction of environmental load. A vehicle mounted battery which determines the traveling performance of the electric vehicle and the hybrid vehicle is demanded to have a high voltage of more than several tens volts to enable the motor to be driven. For the reason, as the vehicle mounted battery, an assembled battery in which a plurality of battery cells each having a voltage of about 2V are connected in series is used.

For the assembled battery, dispersion among the battery cells is problematic. Although the same current flows in each battery cell because the battery cells are connected in series, the voltages are different if the capacitance is dispersed. If the voltages of the battery cells are different, there is a battery cell whose voltage reaches an upper limit voltage and other battery cell whose voltage drops to a lower limit voltage when it is discharged. Because the battery cell whose voltage reaches the upper limit voltage is in an over-charged state and the battery cell whose voltage reaches the lower limit voltage is in an over-discharged state, deterioration of battery performance is induced. To prevent the over-charge and over-discharge of the battery cell, the dispersion of voltage among the battery cells needs to be corrected.

To correct the dispersion of the cell voltage, JP- A 2007-006552 (KOKAI) has indicated voltage dispersion correcting circuit for equalizing the voltage of each battery cell using a detection result of a flying capacitor type voltage detection circuit for detecting the voltage of the battery cell. More specifically, JP-A 2007-006552 (KOKAI) includes a charge moving control circuit for controlling movement of charges between the battery cell and the capacitor circuit individually. The charge movement control circuit moves charges from a battery cell having a relatively high voltage to a capacitor circuit based on the voltage condition of each battery cell detected from the flying capacitor type voltage detection circuit and after that, moves the charges of the capacitor to a battery cell having a relatively low voltage. The dispersion of voltage of each battery cell is corrected by such a charge moving operation.

In the voltage dispersion correcting circuit described in JP-A 2007-006552 (KOKAI), the cell voltage dispersion correcting operation needs to be carried out following a detection result of the voltage of the battery cell by the flying capacitor type voltage detection circuit. According to JP-A 2007-006552 (KOKAI), an analog-to-digital converter (ADC) is used in the battery cell voltage detection circuit as estimated from a paragraph 0033 thereof.

Although the voltage detection circuit using the ADC is capable of detecting the voltage at a higher precision than the voltage detection circuit using a voltage comparator, power consumption of the ADC is large. Because the voltage detection circuit is always set to ON in order to correct the voltage dispersion of the battery cell, JP-A 2007-006552 has such a problem that the power consumption of the voltage dispersion correcting circuit is large.

Disclosure of Invention

An object of the present invention is to provide a protection device for an assembled battery having a function of correcting voltage dispersion with low power consumption, and an assembled battery system containing the protection device.

According to one aspect of the present invention, there is provided a protection device for an assembled battery comprising: a plurality of capacitors arranged corresponding to battery cells of the assembled battery; a plurality of first switches connected between the battery cells and the capacitors so as to sample voltages of the battery cells and hold the voltages in the capacitors; a plurality of second switches to connect in parallel at least two capacitors of the plurality of the capacitors; and a controller which controls the first switches and the second switches .

According to another aspect of the present invention, there is provided a protection device for an assembled battery comprising: a plurality of capacitors arranged corresponding to battery cells of the assembled battery; an analog-to-digital converter which converts a voltage held in the capacitors to a digital signal so as to detect the voltages of the battery cells; a plurality of first switches connected between the battery cells and the capacitors so as to sample voltages of the battery cells and hold the voltages in the capacitors; a plurality of second switches to connect in parallel at least two capacitors of the plurality of the capacitors; and a plurality of third switches for transmitting the hold voltage to the analog-to-digital converter, a controller which controls the first switches, the second switches and third switches.

Further, according to another aspect of the present invention, there is provided an assembled battery system comprising: an assembled battery having a plurality of battery cells connected in series; the protection device.

Brief Description of Drawings

FIG. 1 is a block diagram showing schematically a protection device for an assembled battery according to an embodiment of the present invention and an assembled battery system;

FIG. 2 is a circuit diagram showing a protection unit according to a first embodiment;

FIG. 3 is a flowchart showing the procedure in the first embodiment;

FIG. 4 is a flowchart showing a modified procedure in the first embodiment;

FIG. 5 is a circuit diagram showing part of the protection unit according to a third embodiment; FIG. 6 is a timing chart showing an operation of a switch in a second embodiment; and

FIG. 7 is a flowchart showing the procedure in the second embodiment.

Best Mode for Carrying Out the Invention Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the protection device for the assembled battery according to an embodiment of the present invention is applied to an assembled battery 1 constituted of a plurality of battery modules 2A to 2D connected in series, each having a plurality of cell batteries 3-nm (n = 1 to 4, m = 1 to 5 in the example of FIG. 1) connected in series. As the cell battery 3-nm, a secondary battery, for example, a lithium ion battery is used. An end of the assembled battery 1 is connected to an external connecting terminal 7 and the other end thereof is connected to an external terminal 8 through a control unit 6.

The protection device 4 includes a control unit 6 common to protection units 5A to 5D connected to the battery modules 2A to 2D and the battery modules 2A to 2D. Although the protection device 4 may be sometimes incorporated in a different casing from for the assembled battery 1, it may be sometimes incorporated in a casing 9 together with the assembled battery 1 and used as an assembled battery system (called a battery pack) 10 together with the assembled battery 1.

FIG. 2 shows one of the protection units 5A to 5D. When the voltage of each cell (hereinafter referred to as cell voltage) of the battery modules 2A to 2D reaches a charge prohibiting voltage at the time of charging, basically the protection units 5A to 5D execute charge prohibiting operation and when the cell voltage reaches a discharge prohibiting voltage at the time of discharge, execute a discharge prohibiting operation as its basic function. However, description of such a basic function is omitted here.

Although in FIG. 2, two battery cells Bl and B2 are represented as the cell battery contained in the battery module corresponding to a protection unit, actually, a plurality of the cell batteries exist as described above.

According to this embodiment, the protection device corrects the dispersion of the cell voltage with low power consumption. Hereinafter, various embodiments of the protection units of FIG. 1 will be described in detail.

(First embodiment) An end of a switch S₃ for sampling the voltage (cell voltage) of the battery cells Bl and B2 (hereinafter referred to as sampling switch) is connected to both ends of the battery cells Bl and B2 as shown in FIG. 2 and the other end of the switch S₃ is connected to both ends of capacitors Cl and C2 corresponding to the cell batteries Bl and B2. A switch (hereinafter referred to as averaging switch) S^ is connected to the capacitors Cl and C2. That is, the averaging switch S^ is connected between one ends of an upper side of the same Figure of the capacitors Cl and C2 and between the other ends of a lower side. When the averaging switch S^ is turned on, the capacitors Cl and C2 are connected in parallel so that the voltages of Cl and C2 are averaged.

A microcontroller 100 achieved by the MPU includes a controller 101 for controlling the sampling switches S₃ and the averaging switch S^ and a communication portion 102. Although the communication portion 102 is provided to communicate with other protection unit and the control unit 6, detailed description of the communication portion 102 is omitted. Next, an averaging operation of the cell voltage in the protection unit of FIG. 2 will be described with reference to a flowchart of FIG. 3.

First, all the switches S₃ and S^ are turned off

(step SlOl). After that, the sampling switch Sg is turned on (step S102) . When the sampling switch Ss is turned on, the cell voltages of the battery cells Bl and B2 are sampled and sampled voltages are held by the capacitors Cl and C2.

Next, the averaging switch S^ is turned on (step S103) . When the averaging switch S& is turned on, the voltages of the capacitors Cl and C2 are averaged and consequently, the voltages of the battery cells Bl and

B2 are averaged. After step S103, whether or not the averaging operation is continued is determined in step S104 and if it is continued, the procedure is returned to step SlOl, in which the above-described operations are repeated. Assume that the capacitances of the battery cells Bl and B2 are Cg]_ and Cg2 ^and the capacitances of the sampling capacitors Cl and C2 are C. Further, assume that the averaged voltages of the battery cells Bl and B2 are Va and then that the voltage of Bl is Va + ΔV and the voltage of B2 is Va - ΔV while they are different from each other. That is, the voltage of the battery cell Bl is dispersed in a higher direction while the voltage of the battery cell B2 is dispersed in a lower direction.

The initial voltages Vl(O) and V2(0) of the battery cells Bl and B2 are Vl(O) = Va + ΔV and V2(0) = Va - ΔV, based on the above premise. Therefore, charges accumulated in the capacitors Cl and C2 by sampling are C(Va + ΔV) and C(Va - ΔV) .

Next, if the voltages are averaged by connecting the capacitors Cl and C2 in parallel with the averaging switch S^, the charges accumulated in the capacitors Cl and C2 are both CVa. After that, the sampling switch Ss is turned on so as to sample the voltages of the battery cells Bl and B2 again. According to the law of conservation of charge, the voltages Vl(I), V2(l) of the battery cells Bl and B2 when sampled again are as follows .

Vl(I) = V₃ + -^Sl— ΔV C_B1 + C :D

V2(l) = V₃ - C_B2 ΔV (2) C_B2 +C In the battery cell Bl in which the voltage dispersion is generated in the higher direction, the voltage dispersion ΔV x CBI/(CBI + C) is decreased by CΔV/(CB;I_ + C) from the initial ΔV as indicated in the equation (1). Thus, in the Bl, discharge is performed to the capacitor Cl, thereby the voltage being dropped. On the other hand, in the battery cell B2 in which the voltage dispersion is generated in the lower direction, the voltage dispersion ΔV x Cg]_/ (Cβi + C) is increased by CΔV/ (C_B2 + C) from the initial ΔV x Cg2 (Cβ2 + C) as indicated in the equation (2) . As a result, charging is carried out from the capacitor C2, so that the voltage is raised.

If the averaging operation of the cell voltage by on/off of the averaging switch S^ is repeated N times, the voltages Vl(N) and V2 (N) of the battery cells Bl and B2 are as follows.

Vl(N) = V_a + -^l— ΛV (3)

In the equations (3), (4), C_Bi/(C_Bi + C) and Cβ2/ (Cβ2 + C) is less than 1. Thus, if the averaging operation is continued (N becomes sufficiently large) , finally, the second item of the right side of the equations (3), (4) turns to zero, so that the voltage of the battery cells Bl and B2 is settled down to the average voltage Va. For example, if the voltage dispersion ΔV from the average voltage Va of the battery cell Bl is required to be 1/10, the quantity of necessary averaging operations (number of on/off of the averaging switch S^) M is as follows.

M = log_^^ (6) c_B1+c More specifically, assuming that the ratio between the capacitance Cg_]_ of the battery cell Bl and the capacitance C of the capacitors Cl and C2 is 10000:1, M of the equation (6) is 23,000. Although a case which the dispersion of the cell voltage is set to 1/10 is considered in this example, actually, N is selected so that the voltage dispersion is reduced to a demanded value .

According to this embodiment, the result of voltage detection of the battery cell by the voltage detection circuit using the ADC is not required unlike JP-A 2007-006552 (KOKAI), the dispersion of the cell voltage can be corrected by only on/off of the averaging switch S&. That is, the voltage dispersion can be corrected not accompanied by power consumption by the voltage detection circuit using the ADC.

Further, because the battery cell executes charging as well as discharging at the time of correction of the voltage dispersion, the service life of the battery is prolonged, which is an advantage of the present invention.

In FIG. 3, after the sampling switch Sg is turned on in step S102, the procedure proceeds to step S103, in which the averaging switch S_j^ is turned on. As other example, after step S102, the sampling switch S_s may be turned off and the procedure may be moved to step S103, in which the averaging switch S^ is turned on, as shown in FIG. 4. (Second embodiment)

According to the second embodiment shown in FIG. 5, the quantity of devices is reduced by sharing at least part of elements of the flying capacitor type voltage detection circuit and the voltage dispersion correcting circuit in the protection device. Hereinafter, various embodiments of the protection device of FIG. 2 will be described in detail.

In FIG. 5, the capacitors Cl and C2 for averaging the cell voltage described previously serve as a flying capacitor in the flying capacitor type voltage detection circuit. The microcontroller 100 includes an analog-to-digital converter (ADC) 103. Transmission switches Sl, S2 for transmitting a hold voltage of the capacitors Cl and C2 are placed between both ends of the capacitors Cl and C2 and the ADC 103. The cell voltages, that is, the voltages of the battery cells Bl and B2 are sampled and held in the capacitors Cl and C2 and transmitted to the ADC 103 by the transmission switches Sl, S2 and quantized to detect the cell voltages . Next, an operation of this embodiment will be described using a time chart of FIG. 6 indicating the operation timing of the switch and a flowchart of FIG. 7.

First, all the switches Ss, S^, Sl and S2 are turned off (step S201) . After that, the sampling switch S₃ is turned on (step S202) . When the sampling switch S₃ is turned on, the cell voltages of the battery cells Bl and B2 are sampled at the same time and after that, the sampling switch S₃ is turned off so as to hold the sampled voltage in the capacitors Cl and C2 (step S203) .

According to this embodiment, the voltage detection mode can be set by user as he or she desires. After step S203, whether or not voltage detection mode is selected is determined (step S204) and if the voltage detection mode is selected, the transmission switches Si (i = 1, 2) are turned on successively and the hold voltages of the capacitors Cl and C2 are transmitted to the ADC 103 and the hold voltages are quantized or converted to digital signals (step S205) . After that, the transmission switches Si (i = 1, 2) is turned off (step S206) . Next, if it is determined that the voltages of all the capacitors Cl and C2 are detected under voltage detection mode in step S207, the procedure proceeds to step S208, in which the averaging switch S^ is turned on, so that the voltages of the capacitors Cl and C2 are averaged, thereby the voltages of the battery cells Bl and B2 being averaged. After step S208, whether or not the averaging operation is continued is determined in step S209 and if it is continued, the procedure is returned to step S201, in which the above-described operation is repeated.

According to this embodiment, the voltage detection function and the cell voltage dispersion correcting function can be achieved only by adding the averaging switch S^ to the conventional flying capacitor type voltage detection circuit and changing the control sequence of the switch controller 101. Further, because in this embodiment, the cell voltage dispersion correcting operation is carried out regardless of whether or not the voltage detection is executed, the number of the averaging operation (on/off of averaging switch Ss) needs to be matched with the number of the voltage detection. For example, if it is desired to eliminate the dispersion correction quickly, the number of the averaging operation is set larger than that of the voltage detection.

As another embodiment, the averaging operation may be carried out only when the voltage is detected as required, by omitting the processing of step S204 of FIG. 7. In this case, the dispersion of the cell voltage is eliminated successively with repetition of the voltage detection.

Although in the first, second embodiments, the voltages are averaged by connecting the capacitors Cl and C2 connected to each of the two battery cells Bl and B2, if two or more battery cells are connected in series, it is permissible to connect two or more capacitors corresponding to each battery cell in parallel so as to average the voltages. In this case, plural capacitors may be divided to some groups and each group may be averaged. However, if all the capacitors are connected in parallel so as to average the voltages, the voltage dispersion among all the battery cells can be corrected at the same time.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

C L A I M S

1. A protection device for an assembled battery having a plurality of battery cells connected in series, comprising: a plurality of capacitors arranged corresponding to the battery cells; a plurality of first switches connected between the battery cells and the capacitors so as to sample voltages of the battery cells and hold the voltages in the capacitors; a plurality of second switches to connect in parallel at least two capacitors of the plurality of the capacitors; and a controller which controls the first switches and the second switches.

2. The protection device according to claim 1, wherein the controller is configured to repeat a series of control of (a) turning on the first switches in a predetermined period of time, (b) turning off the first switches and (c) turning on the second switches.

3. An assembled battery system comprising: a plurality of battery cells connected in series; and the protection device according to claim 1.

4. A protection device for an assembled battery having a plurality of battery cells connected in series, comprising: a plurality of capacitors arranged corresponding to the battery cells/ an analog-to-digital converter which converts a voltage held in the capacitors to a digital signal so as to detect the voltages of the battery cells; a plurality of first switches connected between the battery cells and the capacitors so as to sample voltages of the battery cells and hold the voltages in the capacitors; a plurality of second switches to connect in parallel at least two capacitors of the plurality of the capacitors; and a plurality of third switches for transmitting the hold voltage to the analog-to-digital converter, a controller which controls the first switches, the second switches and third switches.

5. The protection device according to claim 4, wherein the controller is configured to repeat a series of controls of (a) turning on the first switches, (b) turning off the first switches, (c) turning on the third switches, (d) turning off the third switches and (e) turning on the second switches.

6. The protection device according to claim 4, wherein the controller is configured to repeat a series of controls of, (a) turning on the first switches, (b) turning off the first switches, (c) determining whether or not voltage detection mode is set, (cl) if the voltage detection mode is set, (e) turning on the third switches, (f) turning off the third switches, (g) turning on the second switches and (c2) unless the voltage detection mode is set, (h) turning on the second switches .

7. The protection device according to claim 4, wherein the controller is configured to control the second switches and the third switches so that a number by which the capacitors are connected in parallel by the second switches per specified unit time is larger than a number by which the hold voltage is transmitted to the analog-to-digital converter by the third switches per the specified unit time.

8. An assembled battery system comprising: an assembled battery having a plurality of battery cells connected in series; and the protection device according to claim 4.