MXPA97008374A - Method to diagnose the condition of a bate - Google Patents

Abstract

The present invention relates to a method for diagnosing the relative general condition of a rechargeable electrochemical module that undergoes periods of discharge interposed with periods of charge, wherein said periods of discharge reduce the net module charge and said periods of charge increase the load net module, comprising the steps of: subsequent to the download periods, providing the depth of the download module to provide the download module rate to calculate a numerical value (merit figure) as a predetermined function of the module depth of discharge and the discharge rate where said numerical value provides a direct indication of the relative general condition of the module

Description

METHOD FOR DIAGNOSING THE CONDITION OF A BATTERY TECHNICAL FIELD The present invention relates to the monitoring of batteries and more particularly to determining the condition or relative life of a battery with respect to operational and environmental exposures.

BACKGROUND OF THE INVENTION In applications employing secondary electrocrumal energy storage devices such as a battery pack including a plurality of individual battery modules, it is particularly desirable to provide a simple and reliable indication of the condition of the individual battery modules. Such information can be used for example to cut an incipient failure of battery modules which are indicated as being in a poor condition due to normal degradation or other factors that contribute to premature degradation.

Multiple battery modules in a string in series provide a challenge to control recharge and discharge, and diagnosis. Common strategies assume identical battery module capacities, temperatures and charging phases, but variations in the historical origin of the manufacturing process will introduce some variants among any set of battery modules. This problem is particularly significant where there is a large number of battery modules in a battery pack.

It is commonly observed that battery modules under normal service will still diverge from their original state. This occurs because the lower capacity battery modules will discharge more deeply than their counterpart battery modules in the rope. Assuming the most widely used general type of battery module, aqueous-acid lead, deeper discharge results in a higher sulfation, which promotes gassing during recharging and the subsequent advanced aging in those battery modules. The pattern continues until the weaker battery modules fail prematurely. This scenario does not consider the additional problems of pack rework, where unmatched battery modules are replaced, or packet temperature gradients leading to significant capacity variations.

During the last phases of discharge, the slope of the voltage-time curve becomes highly negative. However, if a battery module is weaker than the rest on a string, the voltage for the battery module will drop faster, and well before the pack average. The rate of change of voltage with respect to time (dV / dt) for a single drum module event will be the same for single drum modules as it is on larger strings, but the ratio of signal to noise for a rope will be depressed proportionally to the number of battery modules in the rope. This leads to difficulties in discriminating the discharge end of a battery module of significantly lower capacity than the normal battery module noise, and the discharge will be allowed to continue well beyond the optimum life capacity of the battery module. In a series package, the battery module will still be inverted, where the counter-part battery modules drive a charge reaction on the opposite electrodes. The loss of capacity may be enough to make the package subsequently useless.

Module unbalances can also cause problems during loading. The load is normally based on the average voltage, so charging a string containing a low capacity battery module will result in a battery module being driven at undesirably high voltages. This will lead to high gassing rates, which is a precursor to premature battery module failure. The recognition of the low capacity battery modules will be ensured if the voltages are monitored over a cell level; however, practical considerations preclude such extensive data acquisition. A common commitment is to monitor the discharges on the individual battery modules.

A secondary battery applications module that will benefit from a simple and reliable indication of the condition of the individual battery module are electric vehicle applications. The electric vehicle applications may present the most challenging environment to provide an accurate and simple indication of the condition of the battery module due to the widely variable conditions to which the vehicle is very likely to be exposed, including extreme environmental temperatures, currents dynamic discharge, relatively deep discharges, frequent recharges, and incomplete charging cycles. Electric vehicles conventionally employ a series cord of individual battery modules in which the least capable or weakest battery module is generally considered to be the determining factor in the advisability of obtaining a battery pack service. In such applications, it is commonly desirable to indicate to a vehicle operator the appropriateness of obtaining a timely service from the battery pack based on the less than adequate condition of one or more individual battery modules.

Known methods for determining the need for a battery pack service are generally unable to predict the impending failure and rely predominantly on the replacement history of the battery module, and / or the regular service programs based on time or miles traveled. Such a methodology is filled with a substantial possibility of misdiagnosis and unnecessary or incomplete battery module replacements.

SYNTHESIS OF THE INVENTION Therefore, it is an object of the present invention to simply and reliably determine the condition of each battery module in a battery pack.

It is an additional object to determine the condition of each battery module according to the variety of factors that affect the performance of such factors as cycle experience, depth of discharge, energy demands, memory effects, and low voltage excursions. .

Still another object of the present invention is to provide an indication of the conditions of the individual battery modules of a battery pack as a simply numerical quantity whose magnitude is generally indicative of the condition of the respective battery module.

These and other objects of the present invention are provided to monitor the module voltages, the packet current and the temperature of the battery pack. The monitored parameters are compensated for the temperature in the case of module voltages and filtered to alleviate the effects of the transient conditions. During the periods in which the battery pack is being discharged, this is during the periods of net reduction in the module load, the removed load is taken into account in a charge of the accumulator and the state of the load module is updated by an appropriate technique. The used package charge is considered with respect to a used charge accumulator which accounts for either the load inside and outside the package by accumulating the charge and discharge during the unloading periods and the loading period. The duration of the discharge periods is considered by a time accumulator. The module capacity is updated during the discharge periods in accordance with the updated status of the load and the accumulator used for charging. Preferably, the time accumulator and the charge accumulator are not replaced until the battery pack is fully charged.

The depth of the discharge module is calculated from the load outside the accumulator and the capacity of the module.

Similarly, the discharge rate of the module is calculated from the load outside the accumulator and the time accumulator. A predetermined function of the download module depth and the module download rate is used to return a numerical value which is indicative of the relative general condition of the module.

According to another aspect of the invention, the low battery module voltage events are determined for the individual modules when the module voltage falls below a predetermined current compensated threshold indicative of an irreversible module damage. A current account of such events is maintained and used as an additional factor to decrease the general condition of the module.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a computer-based controller for use in implementing the determination of the condition of the battery module according to the present invention.

Figure 2 is a flow chart depicting several example steps and routines performed by the computer-based controller of Figure 1 to carry out the present invention in an electric vehicle; Y Figure 3 is a flow chart representing several steps executed by the controller of Figure 1 to carry out the present invention in accordance with a preferred implementation.

DESCRIPTION OF THE PREFERRED MODALITY The preferred embodiment described as follows is with respect to an electric vehicle application. Other applications may similarly benefit from the present invention and include such applications as hybrid electric vehicles and battery power storage systems alone.

In accordance with the present exemplary embodiment and implementation in an electric vehicle, a battery pack for use in an electric vehicle includes a twelve (12) volt regulated regulated lead acid (VRLA) battery connected in series of twenty-six (26) to provide a 312 volt motive voltage source as measured across the ends of the array. The series arrangement of batteries is hereinafter referred to as the battery pack and each individual regulated regulated lead acid battery in the battery pack can henceforth be referred to interchangeably as the battery module, the module of batteries or the battery. All those previous references to this point in the description regarding the battery pack and the battery module should be given the similar meaning. An exemplary regulated 12 volt lead acid lead acid battery module for practicing the present invention is commercially available from General Motors Corporation, Delphi Automotive Systems, and may be identified as part number 19010704. The lead acid battery module Regulated ventilation has a typical capacity of 53 Ah. As determined at a discharge rate of 25A to 27 degrees Celsius and a maximum current range of 400A discharge to 250A recharge. The operating temperature of the identified battery module is from essentially 18 degrees Celsius to 55 degrees Celsius at discharge and from 5 degrees Celsius to 50 degrees Celsius at recharge. The current minimum compensated voltage is specified to essentially 10.5V per battery module.

Referring now to Figure 1, there is illustrated a computer-based controller suitable for the implementation of the present invention involved in the computer instruction sets illustrated by the flow diagrams of Figures 2 and 3. The controller 300 comprises a conventional microprocessor-based computer 311 including central processing unit (CPU), read-only memory (ROM), random access memory (RAM), electrically programmable read-only memory (EPROM), non-volatile memory or keep alive (NVM) and the high-speed internal clock. The controller is activated by means of a voltage source without peripheral motor (V +) which is scaled and regulated by the controller 315. The controller is shown between placed with the battery pack 321 and is adapted to monitor the package quantities of battery such as the individual battery module voltages through lines 323 and the battery module voltage circuit 305, the battery pack current through the packet current circuit 301, the battery pack voltage through the battery pack voltage circuit 303, and the battery pack temperature through the packet temperature circuit 307. The 305 module voltage circuit provides multiple channel tester / voltmeter functions having an analog output for conversion to digital data by analog to digital converter 309. In operation, the voltages of the battery modules Individuals are examined and digitized, one at a time, and read within the appropriate temporary records of the random access memory. The packet stream and the packet voltage are similarly examined, converted, and read within the places of the temporary random access memory. The temperature of the battery pack comprises one or more inputs for example since the transistors strategically placed in the battery pack are analyzed, digitized and read within the temporary RAM locations. The interference input / output comprises discrete control signals provided for external interconnection with the vehicle systems, for example, a battery charger. The serial data link comprises a high speed data communication bus that communicates with other vehicle systems, for example a vehicle system controller. A preferred controller as described and illustrated is generally available from Delco Electronics Corporation, and is generally referred to as a battery pack monitor (BPM).

The read-only memory of controller 300 has a resident set of computer instructions for execution by the microprocessor for basic input and output functions including packet monitoring and voltage acquisition, temperature and current data. The electrically programmable read-only memory further contains sets of instructions for implementing specific control, data manipulation and communication functions including those associated with the implementation of the battery condition determination carried out in accordance with the present invention.

The specific sets of program instructions for execution by the controller of FIG. 1 in carrying out the diagnostic functions of the present invention are illustrated in FIGS. 2 and 3. In FIG. 2, the set of instructions represented by FIG. Flow chart is carried out at any time that the battery pack monitor is activated. In the case of the present example where the electric vehicle is concerned, the battery pack monitor is activated at any time when the vehicle is operable for reason such as when an operator places a key in a cylinder and operates the key to a running position. Similarly, the battery pack monitor is activated any time the vehicle is being recharged from a remote charging station, such activation being triggered by the proper interconnection of the vehicle with the remote charging station.

The present invention is carried out with respect to a plurality of individual battery modules and as such the standard matrix annotations can be used in the Figures and the text that follow. Where variables are shown on type face, printing and a matrix of appropriate dimension is represented. For example, the annotation representing a matrix of compensated temperature-compensated battery module voltages as described below is Vmod. In addition, according to the preferred implementation in an electric vehicle, three main control circuits are provided as will be described later. In general, however, only one control circuit is effective at the same time to carry out its particular functions. The direction of the control circuit may be provided by flags as described below. All control circuits share at least parts of the instruction and data acquisition sets set in block 203 of the flow chart and in at least parts of the load state determination instruction sets set in block 205 of the flow diagram. Other sets of instructions in both blocks 203 and 205 may be reserved for execution by one or the other of the various control circuits and then activated and therefore suspended for the other control circuits not active then. These various sets of instructions that are particular to certain control circuits will be definitively set forth and identified as appropriate.

Beginning with block 201, a series of program steps are carried out upon initial activation of the battery pack monitor 300. The series of program steps represented by the initialization block 201 are effective for putting the various registers, accounts , flags, timers and variables for use by the remaining repetitively executed instruction sets corresponding to blocks 203-225 for carrying out the present invention. The initialization block 201 is effective to read in data from predefined memory locations of a non-volatile memory corresponding to the history of the battery pack that can be updated during the driving and / or charging cycles in the following steps. In addition, the initialization block 201 represents program steps for recognizing service information that can be provided via the serial data link by a service technician and the conventional interconnect diagnostic tool. The service information will preferably contain positional information indicative of which battery modules, if any, were replaced during the most recent service carried out. If the battery pack is not changed with respect to the battery modules, the historical data stored in the non-volatile memory provide initial values via the diagnostic tool or interconnected. If the battery pack is changed with respect to one or more of the battery modules, the variables corresponding to the replaced battery modules are initialized with new battery module values. In this way, the battery pack monitor is always refreshed with the service information after the service is completed so that the characteristic differences in operation between the new replacement battery modules and the battery modules against part of the Battery pack are taken into account for a future execution of the remaining instruction set. The invention is therefore seen to accommodate new package or reconditioned package conditions, where all or some of the battery modules have been replaced. In these cases, the selected data must be extracted through the 1/0 port and replaced with the initial values.

Moving to block 203, a set of instructions for reading within the battery module voltages V not conditioned from working memory locations, unconditioned package stream I and non-conditioned temperatures T. Ideally, non-conditioned temperatures T are measurements of temperature made at the battery module level such as by a plurality of insulated thermal resistors having a 1 to 1 correspondence with the package modules. However, such an arrangement is not generally practical so that a predetermined number of strategically placed thermal resistors are employed to generally represent the temperatures of certain groups of battery modules within a battery pack. The conditioning of the inputs is also achieved in the block labeled 203 and comprises averaging the individual temperature measurements T to produce an average packet temperature Tav. The un-conditioned battery module voltages are temperature compensated according to the difference between the conditioned package temperature T and the calibrated reference temperature, and the gain calibrated according to well-known compensation techniques. The individual temperature compensated battery module voltages are filtered such as by sliding a window filter that pushes the older respective voltage measurement out of a pre-dimensioned stack while adding the most recently acquired and battery module voltage. respective temperature compensated for it. Other filtering techniques that aim to reduce the transitory effects deleterios can be used similarly. The respective stack arrays are then averaged algebraically to arrive at the respective compensated temperature filtered battery module voltages V od. Similarly, the unconditioned packet stream is filtered by sliding a window filter and algebraically averaging to arrive at a filtered pack stream Iav. The states of the low battery module voltage flags, Vlo, are determined by the steps of block 203. The low voltage flags are set for the battery module voltages which exhibit an unbalanced current voltage under which is effectively indicative of an undesirable battery module condition. For example, in the exemplary embodiment where regulated-lead lead acid batteries are used, the discharge of a battery module at a compensated current voltage of less than essentially 10.5 volts significantly increases the possibility of irreversible conversion of the battery. Active battery material, from lead oxide, to lead sulfate due to the effects of isolation as is well known in the art. It would result in a fall in capacity proportional to the damage.

Preferably, a low voltage flag is placed for any battery module which exhibits a compensated current voltage essentially corresponding to an extreme depth of discharge, for example a depth of 80 percent discharge, as empirically determined for example as a voltage compensated battery module voltage function. Additionally, the instructions placed in block 203 are effective to determine the incremental time? T that elapsed since the previous execution of block 203.

Block 205 below represents the set of instructions for determining the state of charge of the battery module and the state of charge of the package. In accordance with a preferred method for determining the state of charge of the battery modules, an integration of hour-amp over the predetermined average packet current Iav is carried out. The used package charge, Qused, is defined according to the convention that the charge decreases with the unloading of the package and that the load increases during the loading of the package through external means or via regenerative braking of the vehicle.

Qused = Qused + Iav *? T (1) During only the drive circuit, as determined in the present example by a flag indicating that an external load source is connected, the load outside the battery pack, ie only discharge currents, also accumulates as Qout.

Qout = Qout - Iav *? T (2) When the value of Iav is less than a predetermined negative threshold representative of a pack discharge level experienced during the "idle" conditions of the vehicle to account for certain parasitic current withdrawals from the battery pack, a drive timer of cumulative cycle td? n is increased by incremental time? t. -drive = t -ádri? vte. +? t (3) The program steps of block 205 then proceed to calculate the state of charge of each battery module and the state of charge of the package in general.

The state of charge was calculated through a series of empirical formulas. An exemplary method for calculating the state of charge is described in U.S. Patent No. 5,578,915 issued on 26 November 1996 to Crouch, Jr., and others and assigned to the assignee of the present invention. Generally, a determination was made in relation to the magnitude of the average packet current Iav and a voltage threshold of the battery module Vmod as a function of the average packet current Iav. If Iav is outside the predetermined current limits, or if the battery module voltage Vmod exceeds a voltage threshold corresponding to a minimally discharged battery module, then the state of charge is calculated through time integration techniques. Conventional amps as shown below. This form of charge calculation status is the exclusive form used during the charging circuit regardless of current and voltage conditions.

SOC = SOCold + [(I *? T) / Qmodold] * 100 (4) Where SOC is the state of charge of the current battery module, SOCold is the state of charge of the most recent historical battery module, Qmodold is the most recent historical available capacity of a fully charged battery module. The incremental load term, Iav *? T, is divided by the most recent measurement of the available capacity of the full charge battery module to provide a fractionless fraction contribution to the total charge state. The expression of the state of charge in percentages from 0 to 100 percent repre- sents the multiplication of the fractional contribution without unit per 100 as shown. Conventional time-based integration corresponds essentially to nominally discharged battery modules, for example, above 80 percent charge state where the voltage is relatively inelastic with respect to capacity.

Only during the drive circuit, if Iav is within the current limits, the state of charge was determined from one of two mixed polynomial functions of packet current Iav and battery module voltage Vmod. Generally, the selection of one of the polynomial functions used in the calculation of the state of charge depends on the state of charge of the battery module as determined by empirically determined current voltage ratios appropriately. That is, a first function SOC = Al * Iav + Bl * Vmod + Cl * Iav * Vmod + Dl (5) it is used when the state of charge is essentially between a nominal discharge and a deep discharge, such as, for example, 80 percent and 20 percent load status and a second function SOC = A2 * Iav + B2 * Vmod + C2 * Iav * Vmod + D2 * Vmod2 + E (6) it is used when the state of charge is below the deep discharge (for example 20 percent charge state).

In the equations (5) and (6) given above representing a polynomial function to define the state of charge, the coefficients Al, Bl, Cl, DI, A2, B2, C2, D2 and E are all determined with multivariable regression techniques. commonly used while the general equation forms are applied to empirically collect Iav and Vmod and SOC data sets according to known calibration processes.

An important part of the instruction set comprises the load state determination block 203, the individual battery module capacities, Qmod, of the battery modules are updated based on the recently determined SOC load state and the packet load used , Qused as shown below.

Qmod = Oused (7) 1 - SOC 100 Where the denominator represents the fractional charge removed from the battery module based on the updated status of the previously calculated charge state provided. The update of the individual battery module * capacities, Qmod occurs only during the drive circuit when the effective capacity is known to depend largely on the discharge characteristics and will therefore account for the discharge conditions present.

Block 207 immediately determines the state of a flag connected to the load source. A relocate flag indicates that the load source is disconnected and that the drive circuit is active. The specific functions carried out during the drive circuit are represented by block 221 of the Figure. In the drive circuit, a voltage cover can be determined to detrimentally limit the high battery module voltages due to the limitation of the battery modules to accept regenerative braking currents. Other functions that affect discharge handling are also included in the drive circuit.

Block 209 determines the state of a full load flag. The full charge flag is not set until a loading sequence has been carried out completely as described below. A relocation flag directs control to the specific load circuit instruction set associated with block 223. Generally, the load circuit instruction set is effective for controlling the recharge of the battery pack according to a predetermined charging methodology . For example, a preferred recharging method comprises a series of staggered current level requests invoked in response to predetermined voltage caps. The full charge flag is set only when a predetermined minimum current is requested or the amount of charge exceeds a predetermined overload threshold. Therefore, an initial termination of a load, such as through operator intervention, will not result in a full load flag being placed and the execution of certain sets of instructions associated with achieving a full recharge. Other load circuit functions may include battery pack temperature checks to be used to modify load current requests for the purpose of thermal management.

Upon completion of the loading as determined by a full load flag placed in block 209, the instructions associated with blocks 211 and 215 are executed. Block 211 carries out an update to a low battery module voltage event counter, LOWBATT, in accordance with the state of the low battery module voltage flags, Vlo, as previously determined through the steps data acquisition and conditioning of block 203. LOWBATT is increased to account for the events of deeply discharged battery module which are known to cause irreversible battery damage and reduce the active material available in the battery module.

Block 215 immediately determines if equalization of the battery modules is required by the state of a required charge equalization flag. Generally, the required charge equalization flag is thus requested by an equalization charge based on certain historical considerations of the battery pack such as the total amp hours removed from the pack which can be provided in an appropriate accumulator, the differences in voltages of battery module in excess of a desired magnitude, and the service cycle history of the battery pack. In the equalization circuit instruction set in block 225, a predetermined equalization current is supplied to the battery pack to bring all battery modules to essentially the same level of charge as is known to be desirable in the art.

At the end of the equalization charging circuit as indicated by a reset charge equalization flag, the instruction sets associated with the blocks 218 and 217 are executed. The instruction set of block 217 is detailed in the flow diagram of Figure 3 and returns an updated condition of the battery modules. After determining the condition of the battery modules in block 217, block 218 represents the execution of instructions to reset certain variables and flags. The low battery module voltage flags, Vlow is reset. The charge accumulators outside (Qout) and the used package charge (Qused) are also reset to zero.

Additionally, following the full load, the cumulative cycle drive timer t, ^ is reset to zero. At this point, after any necessary charge equalization, the state of charge, SOC is set to 100 indicating full capacity.

Block 219 next represents a wait in lieu of the operational state of the vehicle being loaded to be driven such as by verification of the connected flag of external load source. A flag set essentially results in a wait condition indicated by the return line 231. The disconnection of the load source results in a reset of the external load source flag and the return to block 203 for acquisition and conditioning data. according to the drive circuit.

Referring now to Figure 3, the specific instruction sets that represent the flow chart to determine the condition of the individual battery modules are set below. A "merit figure", hereinafter FOM, is defined herein as a simple numerical for each battery module, the value of which indicates the relative life condition of the respective battery module. In the present exemplary embodiment, the Merit Figure varies from 0 to 10 even when any desired scale may be used. A merit figure of a new battery module is set to 10 while a merit figure of a worn or minimally effective battery module is essentially zero. The routine is referred to by block 217 of the flow chart previously described in Figure 2.

First, block 301 recalls from memory the most recent historical values for the figure of merit. These values were calculated and stored during the completion of the most recent past of a load and stored in a non-volatile memory. Block 303 immediately moves the figure of historical merit inside the FOMold work registers.

The figure of merit is then calculated by a set of instructions represented by the calculation block 305 of the figure. According to a preferred calculation of the figure of merit, the following simplified expression was used: K, -Oout (1 + K) FOM = FOM? Ld-K, -é? 1 K3-Qmod-t? 4 dpve "Ks • LOWBATT (8) As can be seen by inspection, the preferred merit figure expression contains non-linear and linear terms. The non-linear term includes an exponential term that when it expands outward it exposes some of the critical features of the present invention as follows:?, - oout (1+?) | Oout \ __? _ I Oout I? 4 K3 - Qmod - t? 4 I = K2 \ Qmod / K3 \ t ?? vc í (9) drive where Oout j represents the depth of \ Qmod I most recent discharge cycle of discharge based on the adjusted battery module capacities, I Oout 'trive represents the most recent discharge cycle load removal rate, ¥ _, K3 and K represent coefficients which are used to weigh the individual contributions of the appropriate terms and are determined with commonly used multivariate regression techniques well known to those skilled in the art. The loss of capacity and therefore the degradation in the general condition of the battery module, result in accordance with known relationships to depth of discharge and rate of charge removal. As described above with respect to low voltage events, some irreversible material conversion may be associated with battery module discharge. All discharges have the tendency to irreversibly convert the active battery material thereby reducing the amount of active material available to react and thus reducing the capacity of the battery module. Extremely deep discharges, such as those associated with low voltage events, however, additionally exhibit isolation of other active material by restricting electrolyte access. Therefore, the depth of the discharge accounts for the effects of material conversion more than the restriction effects that are taken into account by the low battery module voltage event counter. The removal of charge has temporary and lasting effects on the capacity of the battery modules. Generally, it is understood that the capacity of a battery module at a high discharge rate is not as great as the capacity of the same battery module at a lower discharge rate. This is mainly understood to be due to the effects of surface sulfation and electrolyte diffusion time constants. The more initial coating of the active material at higher discharge rates leads to spillage of active material and therefore to premature loss of capacity. Therefore, the discharge rate term accounts for such accelerated degradation in the life of the battery module.

The calibration terms Kj-Ks are chosen so that the figure of merit reaches a minimum value substantially in accordance with a predetermined percentage of nominal battery module capacity. Generally, a battery module is considered to be at the end of its useful life when its capacity is reduced to 80 percent of its rated capacity.

As seen from the general preferred form of expression (8) for the merit figure calculation, the previously calculated FOMold is decreased by a non-linear term determined as a function of the effects of the most recent discharge cycle depth of downloads based on the adjusted battery module capacities, and the most recent discharge cycle load removal rate. It is noted that the cycle time taken into account in the accumulated time t ^^ is not reset, nor are the charge accumulators, unless a full recharge has been completed. Therefore, incomplete recharges between the drive circuits will account for the incomplete material conversion effects through the depth of the discharge term.

In the preferred implementation, the low battery module voltage event counter, LOWBATT, is weighted by Kj to provide a measure of the degradation of the battery module condition due to the low battery module voltage events proportional to the same. This linear term is therefore seen as decreasing the figure of merit in proportion to the number of irreversible low battery module voltage events encountered during the life of the battery module. The alternate implementation may vary with the low battery module voltage event counter where the proper operation based only on the depth of the discharge and the discharge rate terms.

Block 305 is followed by storage of the recently updated merit figure in a non-volatile memory.

Even though the invention has been described by way of certain preferred embodiments, such embodiments are intended to be taken by way of example and not limitation. It is anticipated that certain modifications, improvements and alternatives may be apparent to a person practicing with ordinary skill in the art and that such modifications, improvements and alternatives are intended to fall within the scope of the invention as defined in the appended claims.

Claims (6)

R E I V I ND I C A C I O N S

1. A method for diagnosing the relative general condition of a rechargeable electrochemical module that suffers periods of discharge interposed with periods of charge, wherein said periods of discharge reduce the net module load and said periods of charge increase the net module load, which comprises The steps of: subsequent to discharge periods; provide the depth of discharge module Oout I, Qmod provide the download module rate Oout \ ai /, and calculating a numerical value (figure of merit) as a predetermined function of the depth of the discharge module and of the discharge rate where said numerical value provides a direct indication of the relative general condition of the module.

2. The method for downloading the relative general condition of a rechargeable electrochemical module as claimed in clause 1 further characterized in that it comprises the step of: during periods of discharge, detect a predetermined module voltage condition (LOWBATT); wherein said predetermined function further includes detection of the module voltage condition.

3. The method for diagnosing the relative general condition of a rechargeable electrochemical module as claimed in clause 1 characterized in that the step of providing the discharge module depth comprises the steps of: provide the module capacity (Qmod); determine the load removed from the module (Qout) by means of accumulated discharges during the periods of discharge; calculate the depth of the discharge module as the proportion of said determined load removed from said module capacity Oout] \ Qmod I

4. The method for diagnosing the relative general condition of a rechargeable electrochemical module as claimed in clause 1 characterized in that the step of providing a discharge module rate comprises the steps of: determine the load removed from the module (Qout) by accumulating downloads during the download periods; determine the time elapsed during the discharge periods (tdrive); calculate the discharge module rate as the proportion of said determined load removed from said elapsed time | Oout -drive

5. The method for diagnosing the relative general condition of a rechargeable electrochemical module as claimed in clause 1 characterized in that the step of providing the module discharge depth comprises the steps of: provide the module capacity (Qmod); determine the load removed from the module (Qout) by accumulating the discharges during the multiple discharge periods characterized by interposed recharge periods that fail to fully recharge the module; Y calculate the depth of discharge of the module as the proportion of said determined load removed from said module I Oout \ Qmod capacity

6. The method for diagnosing the relative general condition of a rechargeable electrochemical module as claimed in clause 2 characterized in that the step of detecting a predetermined module voltage condition (LOWBATT) comprises detecting a module voltage below a threshold of default compensated current voltage. SUMMARY A method for diagnosing the general condition of a battery module in a series of such modules comprising battery pack monitors of voltage (V), current (I) and temperatures (T) of the modules and the battery pack . The accumulators account for various amounts of charge including the out charge (Qout) and the net charge used (Qused) for the battery pack as well as the duration of the discharge period (tdrive). The state of charge is provided by appropriate means and is used to update the module capabilities (Qmod). The various charge and time accumulators are used to derive discharge depth and discharge rate information by providing inputs to certain functions to determine simple numerical outputs indicative of the general condition of the modules.