Patent Publication Number: US-2004048143-A1

Title: Method, apparatus and computer program product for managing a rechargeable battery

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to rechargeable batteries, and more particularly relates to improving the performance of rechargeable batteries, including Lithium Ion (“LiON”), Nickel Cadmium (“NiCd”), and Nickel Metal Anhydride (“NiMH”) based batteries.  
       [0003] 2. Related Art  
       [0004] A battery coverts chemical energy within its material constituents into electrical energy in the process of discharging. A rechargeable battery is ideally returned to its original charged state (or substantially close to it) by passing an electrical current in the opposite direction to that of the discharge. Presently well-known rechargeable battery technologies include LiON, NiCd, and NiMH.  
       [0005] A battery typically includes one or more cells, which are often collectively described as a pack of cells or a set of cells. The set of cells are conductively coupled to form a power source. Each of the rechargeable cells provides a nominal fixed voltage, e.g., 1.2V for NiCd, and NiMH cells. Depending on the load requirements, individual cells included in the set maybe arranged in series to generate a higher voltage, or in some cases the cells may be arranged in parallel to provide a higher current. Use of rechargeable battery cells to power portable electronic devices such as cellular phones, laptop computers and personal digital assistants is well known.  
       [0006] A “memory effect” is a well known limitation of rechargeable battery cells, especially NiCd and NiMH cells. According to this effect, a cell retains the characteristic of a previous charge/discharge cycle. To avoid the memory effect, it is a common practice to fully discharge a battery before recharging it. However, for many applications it may be impractical to take a battery out of service for recharging or even to fully discharge the battery before recharging. Therefore, a need exists to improve the organization of battery cells to permit selectively discharging or recharging. In particular, it would be desirable to reduce the impact of memory effect on the operation of rechargeable battery cells and thereby improve cell life.  
       SUMMARY  
       [0007] The foregoing need is addressed by the present invention. According to one form of the invention, a battery includes a first rechargeable battery cell having a number of replaceable sub-cells. The battery also includes sensors for measuring certain conditions of the sub-cells, including voltages, currents and temperatures, and an output switching device coupled to the sub-cells. The output switching device is operable, responsive to a first control signal, to selectively switch on a conductive path to a load from selected ones of the sub-cells. The battery also includes an input switching device coupled to the sub-cells. The input switching device is operable, responsive to a second control signal, to selectively switch on a conductive path to a source from selected ones of the sub-cells. Logic circuitry of the battery is coupled to the sensors and the input and output switching devices and is operable to automatically generate the control signals, responsive to the measured conditions, for switching a selected at least one of the sub-cells to supply the load and a selected at least one to recharge from the source.  
       [0008] Advantages and objectives of the invention, as well as other aspects and forms of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 illustrates a block diagram of a battery, according to an embodiment of the invention.  
     [0010]FIG. 2 illustrates aspects of cell organization for the battery of FIG. 1, according to an embodiment of the invention.  
     [0011]FIG. 3 illustrates details of one of the discrete cells of FIG. 2, according to an embodiment of the invention.  
     [0012]FIG. 4 illustrates details for one of the functional cells of FIGS. 1 and 2, according to an embodiment.  
     [0013]FIG. 5 illustrates details for the control block of FIG. 1, according to an embodiment of the invention.  
     [0014]FIG. 6 illustrates an embodiment of a battery with only a single functional cell, according to an embodiment of the invention.  
     [0015]FIG. 7 illustrates a flow chart for aspects of the functioning of a rechargeable-cell, smart battery, according to an embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0016] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings illustrating embodiments in which the invention may be practiced. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.  
     [0017]FIG. 1 illustrates a block diagram of a battery  100 , according to an embodiment of the invention. The battery  100  has three rechargeable cells  110 ,  120  and  130 , referred to herein as “functional cells.” (In other embodiments, the battery  100  has more or less than three functional cells.) In one embodiment, each cell  110 , etc. has the capacity to provide rated power to a load (not shown). In another embodiment, each cell  110 , etc. only has capacity to provide a portion of the rated power to the load, in which case a set of the cells, e.g, two of the cells, such as cells  110  and  120 , are required to provide rated power to the load.  
     [0018] Battery  100  has control circuitry  180 , which includes a control block  135 , charge block  145  and output current switching device  170  interconnected as shown. Charge block  145  receives a voltage input  101  from an external source (not shown) and generates a recharge voltage  115  from the input  101 . For example, charge block  145  may be supplied by an AC source which charge block  135  converts to a DC output voltage, recharge voltage  115 . Recharge voltage  115  is coupled to the functional cells  110 , etc. for charging or recharging the cells. That is, in a charge mode of operation the charge  115  signal is applied to a selected cell  110 ,  120  or  130 , as will be described further herein below.  
     [0019]FIG. 2 shows additional aspects of cell organization for the battery  100  of FIG. 1, according to an embodiment of the invention. The battery  100  has  3  functional cells  110 ,  120  and  130  and control electronics  180 . The three functional cells  110 ,  120  and  130  in this embodiment each have three sub-cells, referred to also as “discrete” cells. That is, functional cell  110  includes discrete cells  201 - 203 , functional cell  120  includes discrete cells  204 - 206 , and functional cell  130  includes discrete cells  207 - 209 . (In other embodiments, the cells  110 , etc. have more or less than three discrete cells.) For the previously mentioned voltage in  101  and voltage out  102 , respective pairs of terminals are provided as shown to connect a power supply and to connect rated power to the load.  
     [0020] For interface  103 , the control electronics  180  provides interface pins as shown to communicate with an external device (not shown), such as a cellular phone, laptop computer or personal digital assistant. The control electronics  180  may support well known communication standards such as Universal Serial Bus (“USB”) and SM Bus. A block diagram herein, FIG. 5, illustrates further details of control electronics  180 , according to one embodiment.  
     [0021]FIG. 3 illustrates more details of the discrete cell  201  of FIG. 2, according to an embodiment of the invention. The details shown for cell  201  are typical for all the discrete cells  201 - 209  shown in FIG. 2. Sub-cell  201 , i.e., discrete cell  201 , includes a set of six rechargeable sub-sub-cells  310 - 360  connected in series, so that for this arrangement, with a nominal 1.2V potential for each sub-sub-cell  310 - 360 , the voltage of the overall discrete cell  201  is 6V. In other embodiments the sub-sub-cells are connected in parallel or in a series-parallel combination according to the needed voltage or current capacity of the cell  201 .  
     [0022] As shown, discrete cell  201  has sensors  302  and  304  for sensing current and battery temperature of the cell  201  and generating sensor signals  371  and  372 . The measurements for the discrete cell  201  properties such as voltage, current and temperature maybe collected at time intervals defined by predetermined parameters. Signals  371  and  372  and voltage  370  at the terminals of the cell  201  are sent along with other similar signals for discrete cells  202  and  203  (FIG. 2) to control block  135  (FIG. 1). In FIG. 1 the set of all these signals is shown as “sensors”  125 .  
     [0023] The discrete cells such as discrete cell  201  are the smallest modular unit for which sensor measurement is available and are the smallest replaceable units for maintenance or servicing A failure in any of sub-sub-cell  310 , etc. affects the availability of its entire discrete cell  201 . In the illustrated embodiment, a single temperature sensor  372  is shared among six rechargeable sub-sub-cells  310 - 360  rather than having a dedicated temperature sensor for each sub-sub-cell because this is generally more economical. It should be understood, however, that in other embodiments additional sensors are included.  
     [0024] Referring again to FIG. 1, sensors as shown in FIG. 3 are associated with the respective functional cells  110 , etc. and their respective discrete cells (FIG. 2). These sensors generate sensor signals  125 ,  126  and  127  indicating battery temperatures of the respective discrete cells of the functional cells  110 ,  120  and  130  and current at the respective terminals of the discrete cells. Likewise, the voltages of the discrete cells are also sent to the control block  135  among signals  125 ,  126  and  127 . Control block  135  also receives the charge  115  signal from charge block  145  and sends and receives interface signals  103  to an external device (not shown).  
     [0025] Note that herein, as is common in the art, the use of terms such as “signal” or “input” or “output” does not always explicitly distinguish between structure and function. One of ordinary skill in the art will understand from context that the terminology may indicate either structure or function or both. That is, for example, the term “signal” may refer in a general sense to the function of conveying logical information, or to a voltage, current, etc. that is generated to convey the information, or to a structure, such as a terminal or conductor for transmitting such a voltage or current.  
     [0026] Control block  135  has logic circuitry (not shown in FIG. 1) that determines operating status of each of the cells  110 ,  120  and  130  and their sub-cells responsive to the received signals  103 ,  115  and  125 - 127  and responsive to predetermined parameters to which the measured operating conditions are compared. Based on the status, the control block  135  logic circuitry generates and sends control signals  105 - 108  to the functional cells  110 , etc. and the output current switching device (“CSD”)  170  for controlling operation of the battery  100 . This includes selecting which of the cells  110 , etc. and discrete cells  201 , etc. supply voltage out  102  to an external load (not shown). That is, a cell such as cell  110  is selected to supply voltage out  102  by turning on a conductive path in the CSD  170  between the cell  110  and the load responsive to the control signal  108 .  
     [0027] The output current switching device  170  includes interconnections (not shown) for the functional cells. As previously mentioned, in one embodiment current must be combined from more than one cell  110 ,  120  or  130  to provide rated power to the load. In such a case, the control  108  signal causes the CSD  170  to select more than one of the cells  110 ,  120  and  130  to provide power. In one embodiment, the CSD  170  switches all the cells  110 , etc. in parallel to the load, and the functional cells  110 ,  120  and  130  thus operate to provide rated power for three times as long as would a single one of the cells  110 , etc.  
     [0028] In one aspect of an embodiment, the cells  110 , etc. and their sub-cells  201 , etc. are initialized. During initialization, and later during recharging, cells and sub-cells are fully charged prior to changing operational status to “on-line.” The control block  135  logic circuitry determines whether the charge cycle for a cell or sub-cell is complete so that the cell or sub-cell is eligible to be placed on-line based on whether the sensor signals  125 ,  126  and  127  indicate a cell or sub-cell&#39;s voltage, current and temperature measurements have achieved an acceptable, predetermined range within a certain charging time interval, according to the predetermined parameters.  
     [0029] Once a sufficient number of the cells and sub-cells are initialized or recharged, the control block  135  logic circuitry may selectively place one or more of the cells and one or more of the sub-cells therein in-service to provide rated power to the load. Once placed in service, the selected cell(s) and sub-cell(s) provide power until a predefined event occurs, as defined by the predetermined parameters. One such predefined event is when a cell or subcell&#39;s voltage drops below a specified threshold value. Another is when a specified maximum allowable on-line time period expires for the cell or sub-cell. On detection of such an event, the cell or sub-cell is switched out of service, and another one of the cells is switched in service to supply the load. Preferably this is done without interrupting current output to the load. The cell or sub-cell that was switched out of service may be placed in a “charge” mode for recharging, or may be placed in “maintenance” mode for being replaced, according to which the cell or sub-cell is isolated from the load and the recharging source. At the same time one or more other cell or sub-cell of the battery  100  continue to provide rated power to the load.  
     [0030] The control block  135  logic uses various techniques to determine the health or the operational status of the cells based on comparing the predetermined parameters to the information included in the signals  125 ,  126  and  127  representing cell voltage, current and temperature. Details will be described further herein below. In summary, however, the techniques include the following. In one aspect, the logic circuitry of control block  135  determines fitness for operation of a selected cell by measuring a difference between voltages of a cell before and after charging the cell for a specified charging interval. If the difference in voltage exceeds a certain predetermined threshold then the selected battery cell needs to be placed out-of-service, i.e., isolated from the load. According to another aspect, the logic circuitry determines completion of the recharge cycle based on measuring a difference between temperatures of a cell before and after charging the cell for a specified charging interval. If the difference exceeds a certain predetermined threshold then the selected battery cell needs to be placed out-of-service.  
     [0031] Also, the control block  135  logic circuitry is operable to detect failures and correct a memory effect, which tends to avoid cell reversals and increase cell life. Logic circuitry of the battery determines that a memory effect is present in one of the cells responsive to the cell or sub-cell repeatedly recharging to less than a full charge. To correct the memory effect the control circuitry gives priority to selecting the cell or sub-cell to supply the load and deplete its charge. This includes possibly even repeatedly preferentially selecting the cell or sub-cell each time after it recharges rather than switching other ones of the cells or sub-cells into service. Failure detection includes detecting a false recharge, insufficient discharge, sub-cell reversal or repeated memory effect. In detecting false recharge, the measured values indicate a cell or sub-cell charges to a predetermined voltage level during charging but then discharges too quickly once placed in service. In detecting insufficient discharge, the measured values indicate a cell or sub-cell does not discharge to a sufficiently low voltage during service. In detecting sub-cell reversal, the measured values indicate at least one of the sub-subcells  310 , etc. (FIG. 3) reverses polarity, such as by indicating a sudden drop in the voltage level of the sub cell. It should be appreciated that an important feature of the present invention is the capabilityto measure operating conditions over time, accumulate this data, compute rates and compare the data or computations to predetermined or externally supplied criteria.  
     [0032] In another aspect, the control block  135  logic circuitry is operable to compute a trickle charge, that is, to regulate and measure a current to a cell or sub-cell for a predetermined time interval within a predetermined voltage range.  
     [0033] Referring now to FIG. 4, more details are illustrated for the functional cell  110  of FIGS. 1 and 2, according to an embodiment. (It should be understood that functional cell  110  is typical of all three functional cells  110 ,  120  and  130 .) Functional cell  110  includes discrete cells  201 ,  202  and  203 , as previously shown in FIG. 2. Functional cell  110  also includes a voltage selector switch (“VSS”)  410 , a current selector switch (ISS“)  415 , a temperature selector switch (“TSS”)  420  which receive control signals  105  from and send sensor signals  125  to control electronics  180  (FIG. 1). The cell  110  also includes input cell current switching devices (“CSD&#39;s”)  401 ,  402 ,  403 , and output CSD  405 . (Note that a number of CSD&#39;s such as input CSD&#39;s  401 - 403  may be a single “device.”) Output terminals of the discrete cells  201 ,  202  and  203  are all coupled to the VSS  410  and the CSD  405 . (In FIG. 4, the output  370  is explicitly labeled for cell  201 .) The output CSD  405  receives a V SUP CTL signal from among signals  105 . The V SUP signal selects which ones of the cells  201 ,  202  and  203  supply the output voltage  102  from the functional cell  110  to control electronics  180  (FIG. 1).  
     [0034] The VSS  410  provides a mechanism to reduce the number of voltage inputs to the control electronics  180  (FIG. 1). More importantly, VSS  180  is operable to isolate the cells  201 - 203  so that the voltage of a cell  201 ,  202  or  203  can be measured independently of other voltages. VSS  410  is controlled by one of the control signals  105 , V SENSE CTL, which selects a voltage from one of the cells  201 , etc. to be asserted as V SENSE OUT, one of the sensor signals  125 .  
     [0035] Also, the terminals of each of the discrete cells  201 ,  202  and  203  are coupled to respective ones of the input CSD&#39;s  401 - 403  which are in turn. The CSD&#39;s  401 - 403  are all coupled to the recharge voltage supply  115  from charge block  145  (FIG. 1). The control signals  105  include V RCHG CTL signals coupled to the respective CSD&#39;s  401 - 403  to turn on a selected one of the CSD&#39;s  401 - 403  for conducting the recharge voltage  115  to recharge the selected cell  201 ,  202  or  203 .  
     [0036] The ISS  415  provides a mechanism to reduce the number of current inputs to the control electronics  180  (FIG. 1). ISS  410  is controlled by one of the control signals  105 , I SENSE CTL, which selects a current from one of the cells  201 , etc. to be asserted as I SENSE OUT, another one of the sensor signals  125 . Likewise, the TSS  420  provides a mechanism to reduce the number of temperature inputs to the control electronics  180  (FIG. 1). TSS  420  is controlled by one of the control signals  105 , T SENSE CTL, which selects a current from one of the cells  201 , etc. to be asserted as T SENSE OUT, another one of the sensor signals  125 .  
     [0037] Referring now to FIG. 5, more details are illustrated for control block  135  of FIG. 1, according to an embodiment of the invention. In the illustrated embodiment, the control block  135  includes logic circuitry  575  and temperature, current and voltage quantizer/switch devices  540 ,  545  and  550 . Analog sensor signals  125 - 127  output from the functional cells  110 - 130  (FIG. 1) and the recharge voltage signal  115  from charge block  145  (FIG. 1) are received by the respective devices  540 ,  545  and  550 . The signals  125 - 127  are selected responsive to T SEL, I SEL and V SEL from the logic circuitry  575 , and the selected signals are converted by the devices  540 , etc. to digital signals T SENSE, I SENSE, and V SENSE, which are output to the logic circuitry  575 .  
     [0038] In the embodiment, the logic circuitry  575  includes a processor  510  operable to execute program instructions in response to the sensor signals  125 ,  126  and  127 . The logic circuitry  575  also includes a communications controller  580  coupled to the processor  510  operable to communicate with the processor  510  and to communicate via interface  103  to external devices (not shown) using a standard protocol such as Ethernet, I2C, etc. This interface  103  is useful for receiving new program instructions and data specifying new operating parameters. The logic circuitry  575  also includes a persistent memory  590  coupled to the processor  510 . The persistent memory  590  is used to store instructions (also known as a “software program”), predefined parameters specifying operating objectives, identifiers for the cells and sub-cells and measurements from the sensor signals providing a historical record of actual operating conditions. In one embodiment the historical record includes measured values for cell and sub-cell voltages versus time for several charge and discharge cycles, cell temperatures versus time for a predefined time interval, and voltages and corresponding timestamp values for a discharge low point and recharge high point. The record and identifiers may be transferred to an external device via the interface  103 . In various embodiments the one or more software programs are implemented in various ways, including procedure-based techniques, component-based techniques, and/or object-oriented techniques, among others. Specific examples include XML, C, C++, Java and Microsoft Foundation Classes (MFC).  
     [0039] Referring now to FIG. 6, a simpler embodiment of the battery  100  is illustrated which has only a single functional cell  110 . The functional cell  110  that is illustrated in FIG. 6 is identical to the functional cells  110  illustrated in FIG. 4. However, the control circuitry  180  is somewhat simpler than its counterpart illustrated in FIGS. 1 and 5. Specifically, since there is only one functional cell  110  in this embodiment, there is no need for the CSD  170  of FIG. 1 to select functional cells for supplying the output voltage  102 . Instead, CSD  405  selects which ones of the sub-cells, i.e., discrete cells  201 ,  202  or  203 , supply the output voltage  102 . Likewise, there is no need for the quantizing devices  540 ,  545 , and  550  to select among functional cells sensors. So in this embodiment the quantizing devices do not perform a selecting function and accordingly do not receive control signals for selecting.  
     [0040] Referring to FIG. 7, a flow chart for aspects of the functioning of rechargeable-cell, smart battery  100  is shown, according to an embodiment of the invention. It should be understood that the events described herein are not limited so as to be necessarily performed in the sequence in which they are set out. The logic circuitry includes a processor operable to execute program instructions in response to the sensor signals and a memory coupled to the processor. The logic circuitry also includes a communications controller coupled to the processor operable to communicate with the processor and to interface with an external device. In block  710  the controller receives program instructions and data specifying new operating parameters from the external device.  
     [0041] In block  715  sensors of the battery measure certain conditions of the sub-cells, including voltages, currents and temperatures. The battery includes logic circuitry coupled to the sensors. In block  720 D selected control signals are automatically asserted and de-asserted by the logic circuitry responsive to the measured conditions for the sub-cells.  
     [0042] In block  720  the logic circuitry makes adjustments to the battery. This includes numerous features previously described. Some of these are set out explicitly in FIG. 7 as blocks  720 A through  720 F, described further herein below.  
     [0043] In block  725  the controller sends at least part of the historical record to the external device. In block  730  the following are stored in the memory. i) instructions, ii) predefined parameters specifying operating objectives, and iii) measurements from the sensor signals.  
     [0044] Referring now to blocks  720 A through  720 F perviously mentioned, in block  720 A the logic circuitry determines whether a charge cycle for a sub-cell is complete responsive to the sensor signals for the sub-cell indicating the sub-cell&#39;s voltage, current and temperature measurements are in a predetermined range within a certain time interval.  
     [0045] In block  720 B one or more of the sub-cells is selected by the control block logic circuitry to supply the load. In some instances this is responsive to detecting that a sub-cell has repeatedly recharged to less than a certain voltage level.  
     [0046] In block  720 C at least one of the sub-cells selected to supply the load is selected to stop supplying the load upon occurrence of a predetermined event. The events which trigger this include one or more of the following: i) the selected sub-cell&#39;s voltage drops below a specified threshold value, and ii) a specified maximum allowable on-line time period expires for the selected sub-cell.  
     [0047] In block  720 E one or more conductive paths are selectively switched on and off by one or more output switching devices coupled to the sub-cells. This conductively couples a selected set of one or more of the sub-cells to a load and de-couples others. The output switching device or devices switch on and off the selected path or paths responsive to which control signals are asserted and de-asserted. That is, responsive to detecting an event described in connection with block  720 B for a sub-cell, the sub-cell is switched out of service and another one of the sub-cells is switched to supply the load such that current to the load is maintained without interruption.  
     [0048] In block  720 F one or more other conductive paths are selectively switched on and off by respective input switching devices coupled to the sub-cells. This conductively couples and a selected set of one or more of the sub-cells to a recharging source and de-couples others. The input switching device or devices switch on and off the selected path or paths to the recharge source responsive to another set of the control signals asserted and de-asserted by the logic circuitry. That is, a sub-cell switched out of service is switched to one of the following modes: a charge mode in which the sub-cell is conductively coupled to the recharging source so that the sub-cell may be recharged, or a maintenance mode in which the sub-cell is isolated from the source and the supply so that the sub-cell may be replaced.  
     [0049] The description of the present embodiment has been presented for purposes of illustration, but is not intended to be exhaustive or to limit the invention to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. To reiterate, the embodiments were chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention. Various other embodiments having various modifications may be suited to a particular use contemplated, but maybe within the scope of the present invention. Those of ordinary skill in the art will appreciate that the hardware and methods illustrated herein may vary depending on the implementation. For example, it should be understood that while the control block logic circuitry has been described as a processor-based implementation, it would be within the spirit and scope of the invention to encompass an embodiment using a discrete logic based implementation. Also, the control block of the described embodiment maybe a cellular telephone or a personal digital assistant capable of communicating with other computers and/or telephones. Other devices, such multiple processors and memory devices and the like, may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention.  
     [0050] In this embodiment, point-to-point connections for each of the signals are illustrated. However, other embodiments use a bus, e.g., a SM bus to transfer the signals between the functional cells  510 ,  520  and  530  and the processor  510 .  
     [0051] Additionally, it is important to note that while the present invention has been described in the context of having a processor and memory, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed as computer readable medium of instructions in a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such a floppy disc, a hard disk drive, a RAM, and CD-ROMs and transmission-type media such as digital and analog communications links.  
     [0052] To reiterate, many additional aspects, modifications and variations are also contemplated and are intended to be encompassed within the scope of the following claims. Moreover, it should be understood that in the following claims actions are not necessarily performed in the particular sequence in which they are set out.