Abstract:
An integrated battery monitoring device includes a pair of input leads for coupling across the terminals of a battery cell to be monitored and a sensor for sensing a desired battery cell parameter. A self-contained power supply has the voltage across the battery cell terminals as an input thereto, the self-contained power supply being configured for providing power to the sensor. A pair of output leads communicates data generated by the sensor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present disclosure relates generally to battery monitoring systems and, more particularly, to an integrated battery monitoring device and system having distributed, self-powered sensors.  
           [0002]    Conventional battery installations commonly utilize a plurality of series connected battery cells in order to generate operating voltages higher than the nominal 1-3 volts typically present in an individual battery cell. In certain applications, a sufficient number of cells can be connected to achieve voltages as high as 400 volts (V) or more. Collectively, these multiple, series connected battery cells are referred to as a battery string. As a battery string is being charged, the individual cells could react differently to the charging current. In particular, it is desired that a given cell not be overcharged since this could damage the cell and perhaps even the entire battery.  
           [0003]    Accordingly, battery monitoring systems are sometimes used to periodically monitor the condition of the battery string by measuring the voltage, resistance, and temperature of the battery string and the individual cells This type of battery monitor system generally works in tandem with a battery charging system by providing battery information to the charging system, in order to maintain a proper state of charge and to regulate the voltage in the battery string. Alarms in the battery monitor system may be enabled or annunciated whenever a measured battery parameter exceeds a specified value so as to alert an owner/operator that the battery system is outside its designed operating range. In addition, a monitoring/charging system may also be used to periodically partially discharge or charge the battery string and/or individual battery cells by selectively coupling a test load or voltage source across the battery string or individual cells.  
           [0004]    However, conventional battery monitoring systems tend to be “wiring intensive” in that each measurement point (e.g., a voltage or temperature sensor device for a given cell) generally requires at least two signal leads and two power leads for each parameter measured. In addition, if the system is provided with the capability of switching in a load for discharging a given battery cell, the amount of wiring is further increased. This is especially the case for battery strings having hundreds of individual cells. Furthermore, since the common mode voltage of an individual battery cell can be on the order of hundreds of volts with respect to ground, some form of voltage isolation is needed between the measuring device and the system controller. This in turn results in the use of a local, isolated power source associated with the measuring device. Thus, it is desirable to be able to implement a battery monitoring system that is less wiring intensive and that utilizes fewer components, thereby increasing simplicity and reducing costs.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0005]    The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by an integrated battery monitoring device. In an exemplary embodiment, the device includes a pair of input leads for coupling across the terminals of a battery cell to be monitored and a sensor for sensing a desired battery cell parameter. A self-contained power supply has the voltage across the battery cell terminals as an input thereto, the self-contained power supply being configured for providing power to the sensor. A pair of output leads communicates data generated by the sensor.  
           [0006]    In another aspect, a battery monitoring system includes a central controller and a plurality of integrated battery monitoring devices. Each of the integrated battery monitoring devices has a pair of input leads coupled across the terminals of a corresponding battery cell included within a battery string. A communication bus is included between the central controller and the plurality of integrated battery monitoring devices, wherein each of the integrated battery monitoring devices includes a sensor for sensing a desired battery cell parameter, and a self-contained power supply therein having the voltage across the battery cell terminals as an input thereto. The self-contained power supply is configured for providing power to the sensor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0008]    [0008]FIG. 1 is a schematic diagram of an existing voltage transducer used in conjunction with an individual battery cell included within a battery string;  
         [0009]    [0009]FIG. 2 is a schematic diagram of a battery monitoring system employing transducers of the general type depicted in FIG. 1;  
         [0010]    [0010]FIG. 3 is a schematic diagram of integrated voltage and temperature sensing device featuring programmable load capability, in accordance with an embodiment of the invention; and  
         [0011]    [0011]FIG. 4 is a schematic diagram of a novel battery monitoring system implementing a plurality of sensing devices as shown in FIG. 3, in accordance with a further embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Disclosed herein is an integrated measurement and control module that connects directly to the terminals of a battery cell or jar and is used in conjunction with a central controller and monitoring system to maintain and diagnose the condition of a string of battery cells. The measurement and control module is self-powered, and contains its own serial communications interface for use with a central control system. The integration of several discrete measurement and control functions into a simple, self-powered modular component will reduce installation time over conventional battery monitor instrumentation systems, as well as decrease wiring and parts requirements.  
         [0013]    Referring initially to FIG. 1, there is shown a schematic diagram of an existing voltage transducer  100  used in conjunction with an individual battery cell  102  included within a battery string. A differential amplifier  104  is coupled to the terminals of the cell  102  and provides an output voltage signal to an isolated analog-analog converter  106  included within the transducer  100 . In turn, an output of the converter  106  is sent to an analog to digital converter included within a central control system (not shown in FIG. 1) via a first pair of leads  108 . As indicated previously, an isolated power supply  110  within the transducer  100  is used to provide voltage isolation between the measured cell voltage and the system controller. The isolated power supply  110  is fed from a local power supply (not shown in FIG. 1) through a second pair of leads  112 .  
         [0014]    A separate temperature transducer/sensor could also be constructed from the device of FIG. 1 by simply reconfiguring the differential amplifier to measure a thermocouple junction or the resistance of a resistance temperature detector (RTD) type device.  
         [0015]    If used as part of an integrated battery monitoring system for individually monitoring each cell, the transducers of the type in FIG. 1 would contribute to an overly complicated wiring scheme, as is shown in the system of FIG. 2. In the example illustrated, the system  200  includes both a series of voltage transducers  202  and a series of temperature transducers  204  associated with each of a series of battery cells  206 . As can also be seen, the central controller  208  (including an analog/digital data acquisition system) includes a pair of signal leads coupled thereto from each individual transducer. Although there are only five cells illustrated in the exemplary system, it will be appreciated that a system having many more cells (e.g., a hundred or more) will result in a significantly large number of leads used in the system.  
         [0016]    In addition to the signal leads, each transducer also features a pair of power leads in communication with local power supply  210 . As also described previously, the system  200  also provides a selectively switchable load  212  localized at each of the cells  206  for selective discharge of a given cell. Because this switching is controlled at the central controller, a multiwire control cable  214  is used to route switching leads from the controller to the individual loads  212 . Again, such a system configuration is very wiring intensive and is often custom designed for each particular application, typically including multiple subcomponents.  
         [0017]    Therefore, in accordance with an embodiment of the invention there is disclosed an integrated vehicle battery monitoring device and system having distributed, self-powered sensors. The system is based upon the utilization of a single integrated, multifunction sensing device that is powered from the actual battery cell it is sensing. The sensing device is capable of measuring both the cell temperature and battery terminal voltage, as well as communicating the sensed data via an isolated serial communication interface to a central controller. The device further includes a programmable, switchable load to discharge the battery cell, the functioning of which is controlled through a central controller. Among other aspects, the sensing device is also is configured with a unique address though the central controller when the unit is installed to the battery cell.  
         [0018]    Referring now to FIG. 3, there is shown a schematic diagram of one possible embodiment of the integrated voltage and temperature sensing and monitoring device  300  (hereinafter referred to as an integrated “monitoring device” or “device”). A voltage boost and switching power supply  302  converts the voltage provided by the battery cell  304  from a nominal voltage (e.g., 1.5 V) to a voltage or voltages (e.g., +5 volts) suitable for use by the sensing amplifiers, A/D converter, serial controller and other components internally powered by device  300 . More specifically, a battery terminal voltage monitor  306  (e.g., a differential amplifier) has an input thereof coupled to the battery cell voltage and provides a scaled output coupled to an A/D converter  308 .  
         [0019]    In addition to performing a voltage sensing function, device  300  further includes a temperature sensing device  310  which may be implemented by differential amplifier configured to measure a thermocouple junction, or the resistance of a resistance temperature detector (RTD) device thermally connected to a battery terminal post through a low impedance path. The temperature sensing device  310  provides a scaled thermal output for digital conversion by A/D converter  308 .  
         [0020]    An additional connection to earth ground is provided with the device  300  and is monitored by a ground voltage sensor  312 . The current flowing from the negative terminal of the battery cell  304  to earth ground is converted to a voltage through a pair of grounding resistors  314 ,  316  serving as a voltage divider, and an amplifier  318 . The output of amplifier is sampled by the A/D converter  302  such that the voltage/ground current is ultimately communicated to a central controller (not shown in FIG. 3) thereby determining whether a ground fault exists within the battery string. By summing up and determining the currents that do not equal zero (in accordance with Kirchoff&#39;s Current Law), an indication of a ground fault may be generated. The magnitude of the current summation may be compared to a threshold value for signaling purposes.  
         [0021]    A programmable load  320  provides a programmable resistance that is selectively used to discharge the battery cell  304 , and communicates with a universal asynchronous receiver-transmitter (UART) and serial controller  322  through a control bus  324 . The UART/serial controller  322  in turn communicates with the central controller (again, not shown in FIG. 3) via a serial interface  326 . The UART/serial controller  322  is capable of controlling the operation of both the A/D converter  308  and the programmable load  320 , including reading the output of the A/D converter  308  and transmitting voltage and temperature data to the central controller. In addition, the UART/serial controller  322  receives serial voltage commands generated by the central controller and converts those commands to a suitable reference that the programmable load  320  uses in regulating the voltage of the battery terminal. As described in further detail hereinafter, the integrated sensing device  300  may also include a pushbutton type switch  328  for manual address programming of the particular sensing device module.  
         [0022]    In the embodiment depicted in FIG. 3, voltage isolation is provided between the central controller and the integrated monitoring device  300  through a pair of optically coupled isolators  330 ,  332 , one for data transmission from the UART/serial controller  322  and one for data receiving. Other forms of voltage isolation, however, could also be used, such as isolation transformers. Finally, FIG. 3 also illustrates the use of buffers in conjunction with each of the optically coupled isolators  330 ,  332 . A transmit buffer  334  and a receive buffer  336  thus provide scaled voltage signals between the central controller and the optically coupled isolators  330 ,  332 . The buffers and the optoelectronics on the central controller side of the isolation are powered by a power supply (Vserial) that provides half wave rectification (through diode  338  and capacitor  339 ) of the received serial bit stream. In other words, the single pair of conductors  340  transmits both data and isolated power to the monitoring device  300 . As such, the transmitter in the central controller will therefore supply sufficient transmitter power so as to be able to run each monitoring device  300  connected thereto. In order to minimize the number of communication wires used, a half duplex serial protocol is implemented. It will be appreciated that a full duplex scheme could alternatively be used to increase communication bandwidth; however, the addition of a third conductor would increase the total number of communication wires used.  
         [0023]    The advantages of the integrated monitoring device  300  described above are further appreciated when illustrated in the context of a battery monitoring system  400 , shown in FIG. 4. As can be seen, a central controller  402  includes an analog/digital (A/D) data acquisition system for communication with each of a plurality of individual integrated monitoring devices  300  associated with a battery cell  304 . For purposes of simplicity, the system  400  is shown in conjunction with a five-cell battery string  404 , but it should be appreciated that several hundred cells and associated devices  300  could be used in a practical application of system  400 . It will immediately be noted from the diagram that the number of wires used to connect the central controller  402 , the monitoring devices  300  and the battery cells  304  is drastically reduced as compared with the system of FIG. 2. Particularly, each integrated monitoring device  300  receives a pair of conductors coupled to the terminal of each cell  304  and a pair of conductors in communication with a communications bus  406  connected to the central controller  402 .  
         [0024]    Communications Protocol  
         [0025]    In operation of battery monitoring system  400 , a master/slave protocol between the central controller  402  and the individual integrated monitoring devices  300  may be utilized, wherein the central controller serves as the master. The individual slave devices  300  will not initiate any communication unless requested by the central controller  402  to broadcast its data. Rather, the central controller  402  polls each of the devices  300  in the battery string  404  one at a time when the central controller  402  requires specific data from a particular device  300 . Alternatively, the central controller  402  can also send broadcast messages to all devices  300  simultaneously whenever a common command is used, such as a set time or the beginning of a data acquisition sequence. The monitoring devices  300  are each programmed with a unique address that is used in communications with the central controller  402 . Thus, the central controller  402  transmits a specific device address and an associated command over the two-wire channel. The monitoring device that corresponds to the transmitted address will then implement the command as requested by the central controller  402 , thereafter transmitting its status or information back to the central controller  402 . The central controller  402  is programmed to sequentially send out commands one at a time to all of the connected monitoring devices  300 .  
         [0026]    A further advantage of system  400  and monitoring devices  300  is the modular capability thereof with respect to a self-configurating addressing mode. In a “normal” operating mode, the unique address of a given monitoring device  300  is selected by the central controller  402  while the device  300  is powered up and remains in communication with the central controller  402 . In addition, however, software in the central controller system  402  enables a user to place the system in an “addressing” mode. The addressing mode could be used, for example, during the replacement of a particular sensing device  300  or during initial installation of each sensing device  300  in the battery monitoring system. The user supplies information to the controller  402  by designating the physical location of the monitoring device  300  in the battery string. Thereafter, the controller repeatedly transmits a special “receive address” command over the communication communications bus  406 . The user then presses the pushbutton switch  328  (FIG. 3) located on the monitoring device  300  to accept the receive address command form the central controller  402 , and causing the device address in its own internal memory location. The process is then repeated as needed until all monitoring device addresses have been programmed. In the event given monitoring device  300  requires replacement or repair, a new device would be installed on the battery terminal post and the program address sequence described would be repeated for the replaced monitoring device only.  
         [0027]    Heretofore, the instrumentation of every battery cell in a battery string has been impractical to implement for large battery installations. Since the temperature in a battery string can vary greatly from cell to cell, the battery life and capacity can be extended if the individual cell voltages of the battery are controlled as a function of the battery cell temperature. When the battery is in a standby mode (i.e., a “float charge mode”), the central controller  402  will sequentially issue voltage reference commands to each monitoring device  300 . The specific reference command for a given device  300  is a function of the battery cell type and temperature of the cell. This technique can achieve precise voltage control over each individual cell during the charging cycle. Because batteries in a float mode are typically charged with a small charging current, the power rating of the programmable load is relatively low due to the product of the low charging current and small cell voltage. Thus, this low power requirement allows the programmable load function to be integrated into a relatively small area within the monitoring device  300 .  
         [0028]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.