1.  Field of the Invention
The present invention relates to a battery control device for controlling charging and discharging operations with respect to battery packs including alkaline storage batteries and mounted on, for example, devices driven by battery packs, such as electric vehicles including automated guided vehicles. 
2.  Description of the Related Art
Conventionally, as a low-pollution vehicle designed for the purpose of solving environmental problems and energy problems, an electric vehicle such as a HEV (hybrid electric vehicle) and a PEV (pure electric vehicle) has received a great deal of attention.  The electric vehicle has a battery pack, which includes alkaline storage batteries, mounted therein, and the electric power of the battery pack drives an electric motor so as to run the electric vehicle. 
The electric vehicle includes an inverter for controlling motor drive and a battery control device for obtaining an output state of the battery pack and controlling charging and discharging operations with respect to the battery pack according to the output state of the battery pack, so as to stably supply the electric power to the electric motor via the inverter. 
Such a conventional battery control device measures voltage and current output by the battery pack so as to calculate a remaining capacity SOC (State Of Charge; a value representing how much electric power remains in the battery pack) of the battery pack based on the measurement results.  For example, the conventional battery control device controls the charge and discharge operations with respect to the battery pack so as to keep the remaining capacity SOC of the battery pack within a prescribed range.  When the remaining capacity SOC falls below the prescribed range, the conventional battery control device performs a charging operation on the battery pack while inhibiting a discharging operation. 
The battery pack as described herein includes a plurality of serially-connected battery blocks.  In the casewhere the conventional battery control device charges the battery pack so as to keep the remaining capacity SOC of the battery pack within a prescribed range, when the plurality of battery blocks are uneven in remaining capacity SOC some battery blocks are forced to be overcharged.  Alternatively, in some cases, the conventional battery control device periodically overcharges the entire battery pack so as to realize evenness in state of charge between the plurality of battery blocks. 
However, in the conventional battery control device, when a minute crack and/or a minute pinhole are/is made in a single alkaline storage battery included in the battery pack through long-time use, such a minute crack and/or a minute pinhole cannot be easily detected.  When an alkaline storage battery is overcharged, water in an electrolyte contained in a unit-battery case of the single alkaline storage battery is electrolyzed, so that hydrogen and oxygen gasses are generated.  Further, when the hydrogen gas is emitted through the minute crack and/or the minute pinhole to the outside of the single alkaline storage battery, the amount of the emitted hydrogen gas is small and the hydrogen gas is diffused due to cooling air from a battery cooling fan, thereby making it difficult to detect the minute crack and/or the minute pinhole in a unit battery. 
Furthermore, when the unit battery is left with the minute crack and/or the minute pinhole, battery deterioration is accelerated, thereby significantly reducing the reliability of the battery pack.  Examples of the battery deterioration include a rise in internal resistance due to loss in moisture content of the electrolyte or due to carbon dioxide absorbed into the electrolyte, a decrease in remaining capacity SOC due to hydrogen emitted from the unit-battery case (in the case where nickel-metal hydride batteries are used in place of the alkaline storage batteries), erosion of a negative electrode, etc. 
According to one aspect of the present invention, there is provided a battery control device for controlling input to and output from a battery pack, in which the battery pack includes a plurality of serially-connected battery blocks each including a plurality of serially-connected unit batteries, and the device includes: an internal resistance measurement section for each battery block; and a first malfunctioning battery detection section for detecting the unit battery as a leakage malfunctioning battery based on an internal resistance variation measured for each battery block during a prescribed time interval of a charging operation, wherein detection information about the leakage malfunctioning battery is reflected in the control of charging and discharging operations. 
According to this structure, the first malfunctioning battery detection section detects a unit battery detection section detects a unit battery as a leakage malfunctioning battery based on internal resistance variation and detection information about the leakage malfunctioning battery is reflected in the control of the charge and discharge operations.  Therefore, a battery block which includes a unit battery having a minute crack and/or a minute pinhole can be detected early enough, thereby preventing the reliability of a battery pack from being reduced. 
In one embodiment of the invention, the first malfunctioning battery detection section determines that the unit battery is a leakage malfunctioning battery when a difference in internal resistance variation between the unit battery and a normal battery is greater than a constant obtained based on battery characteristics, and the internal resistance variation is an internal resistance difference, or a difference in internal resistance derivative value, measured during a prescribed time period. 
According to this structure, a leakage malfunctioning battery can be precisely and readily detected. 
According to another aspect of the present invention, there is provided a battery control device for controlling input to and output from a battery pack, in which the battery pack includes a plurality of serially-connected battery blocks each including a plurality of serially-connected unit batteries, and the device includes: a battery voltage measurement section for each battery block; and a second malfunctioning battery detection section for detecting the unit battery as a leakage malfunctioning battery based on a battery voltage variation measured for each battery block during a prescribed time interval of an overcharging operation, wherein detection information about the leakage malfunctioning battery is reflected in the control of charging and discharging operations. 
According to this structure, the second malfunctioning battery detection section detects a unit battery as a leakage malfunctioning battery based on battery voltage variation and detection information about the leakage malfunctioning battery is reflected in the control of the charge and discharge operations.  Therefore, a battery block which includes a unit battery having a minute crack and/or a minute pinhole can be detected early enough, thereby preventing the reliability of a battery pack from being reduced. 
In one embodiment of the invention, the second malfunctioning battery detection section determines that the unit battery is a leakage malfunctioning battery when a difference in voltage variation between the unit battery and a normal battery is greater than a constant obtained based on battery characteristics, and the voltage variation is a voltage difference, or a difference in voltage derivative value, measured during a prescribed time period. 
According to this structure, a leakage malfunctioning battery can be precisely and readily detected. 
In one embodiment of the invention, the battery control device further includes a third malfunctioning battery detection section for detecting the unit battery as a leakage malfunctioning battery based on a battery temperature variation measured for each battery block during a prescribed time interval of the overcharging operation. 
According to this structure, a unit battery is detected as a leakage malfunctioning battery based on both a battery internal resistance or battery voltage characteristic and a battery temperature characteristic, and therefore the leakage malfunctioning battery can be precisely detected.  The detection of a leakage malfunctioning battery can be based only on the battery temperature characteristic.  However, in such a case, it is necessary to provide a temperature sensor for each of a plurality of battery blocks.  A battery voltage is measured for each battery block so as to be used in remaining capacity calculation, and therefore the battery voltage characteristic for use in the present invention can be readily obtained.  Thus, it is desirable to detect the leakage malfunctioning battery based only on the battery internal resistance characteristic or the battery voltage characteristic, since the number of elements used in the battery controller can be reduced. 
In one embodiment of the invention, the third malfunctioning battery detection section determines that the unit battery is a leakage malfunctioning battery when a difference in temperature variation between the unit battery and a normal battery is greater than a constant obtained based on battery characteristics, and the temperature variation is a temperature difference, or a difference in temperature derivative value, measured during a prescribed time period. 
According to this structure, a leakage malfunctioning battery can be precisely and readily detected. 
In one embodiment of the invention, the battery control device further includes a fourth malfunctioning battery detection section for detecting an internal resistance rise malfunctioning battery based on an internal resistance variation measured for each battery block during a prescribed time interval by measuring an internal resistance for each battery block during charging and discharging operations before or after detecting the leakage malfunctioning battery. 
According to this structure, the abnormal battery detection section can detect abnormal batteries based on an open-circuit voltage difference measured during a prescribed time period so asto distinguish between the abnormal batteries and the other normal batteries, and therefore it is possible to readily detect a minor short-circuit malfunctioning battery, an internal resistance rise malfunctioning battery and a leakage malfunctioning battery. 
In one embodiment of the invention, the battery control device further includes a fifth malfunctioning battery detection section for detecting a minor short-circuit malfunctioning battery based on reduction in battery voltage corresponding to a voltage of a single battery cell for each battery block during a charging operation before or after detecting the internal resistance rise malfunctioning battery. 
According to this structure, a leakage malfunctioning battery can be precisely and readily detected. 
In one embodiment of the invention, the battery control device further includes an abnormal battery detection section for detecting abnormal batteries based on a difference in open-circuit voltage measured during a prescribed time period before detecting at least any one of a minor short-circuit malfunctioning battery, an internal resistance rise malfunctioning battery and a leakage malfunctioning battery. 
According to this structure, a unit battery having a minute crack and/or a minute pinhole is detected so as not to overcharge a battery block which includes the unit battery having a minute crack and/or a minute pinhole, and therefore water electrolysis is kept from occurring in that unit battery, thereby preventing the generation of hydrogen. 
In one embodiment of the invention, the abnormal battery detection section determines that the unit battery is an abnormal battery when a difference in open-circuit voltage variation between the unit battery and a normal battery is greater than a constant obtained based on battery characteristics. 
According to this structure, by providing, as an alarm, detection information about a unit battery as a malfunctioning battery by means display or sound immediately after the leakage malfunctioning battery is detected, a battery block which includes the unit battery having a minute crack and/or a minute pinhole can be detected early enough.  By replacing the detected leakage malfunctioning battery with a normal battery, the reliability of the battery pack can be prevented from being reduced.  Moreover, the detection information about the unit battery as a leakage malfunctioning battery can be stored in a storage section (internal memory) such that an informing section can obtain the detection information from the internal memory during a maintenance operation.  By replacing the leakage malfunctioning battery with a normal battery in the maintenance operation, it is possible to ensure that the reliability of the battery pack is prevented from being reduced. 
In one embodiment of the invention, the battery control device further includes an overcharge prohibition section for prohibiting a battery block including the unit battery as a leakage malfunctioning battery being overcharged during a charging operation. 
In one embodiment of the invention, the battery control device further includes a storage section for storing detection information about the unit battery as a leakage malfunctioning battery such that an informing section can provide the detection information as an alarm. 
Thus, the invention described herein makes possible the advantages of providing a battery control device for detecting a battery block, which includes a unit battery having a minute crack and/or a minute pinhole, early enough, so as to prevent the reliability of a battery pack from being reduced. 
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.