Diagnostic method for electric propulsion system with reconfigurable battery system

An electric propulsion system for a mobile platform includes a battery system connected to positive and negative bus rails, an accessory load having a rotary electric machine, a traction power inverter module (“TPIM”), and an accessory load, switches configured to transition the battery modules to a series-connected (“S-connected”) configuration during a direct current fast-charging (“DCFC”) operation of the battery system, and a controller. When battery modules of the battery system are connected in series during a direct current fast-charging (“DCFC”) operation, the controller executes a diagnostic method to determine bus rail voltages on the positive and negative bus rails and a mid-bus voltage, identifies a diagnosed electrical condition of the electric propulsion system by comparing the voltages to expected values or ranges, and executes a control action in response to the diagnosed electrical condition.

INTRODUCTION

The present disclosure relates to a diagnostic method for use with an electric powertrain configured for energizing propulsion functions aboard a vehicle or other rechargeable mobile platform. Electric powertrains often include at least one polyphase/alternating current (“AC”) rotary electric machine constructed from a wound stator and a magnetic rotor. The stator windings are connected to an AC-side of a power inverter, with a direct current (“DC”)-side of the power inverter in turn connected to a DC voltage bus. When the electric machine functions as a traction motor, switching control of the ON/OFF states of individual semiconductor switches of the power inverter generates an AC output voltage at a level suitable for energizing the stator windings. The sequentially-energized stator windings produce a rotating magnetic field, which ultimately interacts with a rotor field to produce machine rotation and motor output torque.

The above-noted DC voltage bus is electrically connected to a voltage source, which is typically embodied as a multi-cell high-voltage battery system. Voltage ratings of batteries used for energizing the propulsion functions of motor vehicles and other mobile platforms continue to increase, with the increased pack voltages ultimately extending electric driving ranges and improving overall drive performance. Battery charging infrastructure and associated charging methodologies likewise continue to evolve.

For instance, some emerging DC fast-charging (“DCFC”) stations are capable of providing charging voltages of 800-1000V or more, while older “legacy” DCFC stations may be capable of providing lower charging voltages, for instance 400-500V. In order to accommodate a wider range of charging voltages, some battery systems utilize multiple battery modules. The individual battery modules may be selectively connected in parallel during propulsion operations and in series during high-voltage charging operations, with the series connection enabling utilization of higher charging voltages.

SUMMARY

Described herein are an electric propulsion system for a mobile platform and a method for diagnosing electrical conditions of the electric propulsion system. The electric propulsion system includes a battery system, a traction power inverter module (“TPIM”), and an electric machine. The battery system, which is connected to positive and negative voltage bus rails, has multiple battery modules, a switching control circuit, and a controller. The controller is configured to execute instructions embodying a method for detecting and isolating a diagnosed electrical condition from among multiple possible electrical conditions, some of which may be indicative of electrical fault conditions and others of which may be considered to be normal or expected conditions.

Each battery module has a corresponding module voltage. The battery system as a whole has a total voltage referred to herein as the battery voltage. The switching control circuit selectively establishes either a series-connected (“S-connected”) configuration of the battery modules in which the battery voltage is a multiple of the module voltage, or a parallel-connected (“P-connected”) configuration in which the battery voltage equals the module voltage. When operating in the P-connected configuration, the module voltages are essentially equal for the various battery modules, as will be appreciated by those of ordinary skill in the art, with the number of battery modules used in a given construction of the battery system determining the voltage multiple for the S-connected configuration.

A direct current fast-charging (“DCFC”) station provides a fast-charging voltage that may equal or greatly exceed the module voltage. In order to accommodate different possible charging voltages from a given encountered DCFC station, the switching control circuit is controlled upon connection to the DCFC station to select between the S-connected and P-connected configurations. The controller may select the appropriate configuration based on various mode selection factors, such as but not limited to the available maximum charging voltage from the DCFC station, temperatures and states of charge of the battery modules or the constituent battery cells thereof, and/or other factors. In this manner, the battery system is able to flexibly utilize higher or lower DCFC voltages.

As recognized herein, the act of switching to the S-connected configuration from the P-connected configuration may at times result in certain electrical conditions. Some electrical conditions are fault conditions. Others are normal or expected conditions. The construction of the individual switches forming the switching control circuit may be responsible for some of the electrical conditions, e.g., possible faults in the hardware embodying relays or contactors, or solid-state/high-energy semiconductor switches such as IGBTs or MOSFETs. The controller is therefore configured to execute the present method in order to help identify and isolate fault and no-fault electrical conditions in the electric propulsion system, for instance an electrical short of a positive or negative bus rail to chassis-ground, a motor winding fault, and other electrical fault or no-fault conditions as described herein.

The battery system is selectively connectable to an electrical load, such as an accessory load such as an auxiliary power module (“APM”), a compressor, the TPIM, etc. Multiple battery modules of the battery system have a module voltage, with the battery system also including a switching control circuit having switches each with a corresponding ON/OFF state. The switching control circuit is configured, via operation of the switches, to connect the battery modules in parallel to provide a first battery voltage equal to the module voltage. The parallel configuration is established during propulsion of the mobile platform via the rotary electric machine. A series configuration is selectively established via the switches to provide a second battery voltage at a multiple of the module voltage, which occurs during a charging operation of the battery.

In response to the battery modules being connected in series, the controller determines first (positive) and second (negative) bus rail voltages on the positive and negative bus rails, respectively, and a mid-bus voltage between the positive and negative rails, and then identifies a diagnosed electrical condition from among a plurality of possible electrical conditions using the first and second bus rail voltages and the mid-bus voltage. The controller thereafter executes a suitable control action in response to the diagnosed electrical condition. For instance, the control action may include recording a diagnostic code in memory of the controller that is indicative of the diagnosed electrical condition

Voltage sensors respectively connected to the bus rails and a mid-bus rail located therebetween may be used to measure the first (positive) and second (negative) bus rail voltages and a mid-bus voltage. The possible electrical conditions may include a short-to-ground condition of the positive or negative bus rail, and/or a short-to-ground condition of the mid-bus rail when the accessory load is connected to the bus. The possible electrical conditions may also include no-fault conditions in which the controller detects an expected voltage shift between the positive and negative bus rails when the electrical load is connected during the fast-charging operation.

Additionally, the possible electrical fault conditions may include a motor winding fault of the rotary electric machine. For instance, the controller may detect the motor winding fault by detecting a predetermined voltage oscillation at a predetermined switching frequency of each of the first (positive) and second (negative) bus rail voltages and the mid-bus voltage.

The controller may include a lookup table populated with expected values for the positive and negative bus rail voltages and the mid-bus voltage. In such an embodiment, the controller may identify and isolate the possible electrical conditions by comparing the various voltages to expected voltages stored in the lookup table.

A mobile platform is also disclosed herein that, according to an exemplary embodiment, includes road wheels connected to a platform body, an electrical load including a rotary electric machine configured to power the road wheels and thereby propel the mobile platform, and the above-noted battery system, voltage sensors, switching control circuit, and controller.

Additionally, a diagnostic method is disclosed for use with the above-noted electric propulsion system. In a particular embodiment of the method, in response to a transition from the P-connected configuration to the S-connected configuration prior to the charging of the battery system, the controller determines positive and negative bus rail voltages on the positive and negative bus rails, respectively, as the above-noted first and second bus rail voltages, and also determines the mid-bus voltage. The method includes identifying an electrical condition of the electric propulsion system, as a diagnosed condition, from among a plurality of possible electrical conditions using the bus rail voltages and the mid-bus voltage, including referencing a lookup table populated with expected values for the voltages. The method further includes executing a control action in response to the diagnosed electrical condition, including recording a diagnostic code in memory of the controller that is indicative of the diagnosed electrical condition.

The above summary is not intended to represent every embodiment or aspect of the present disclosure. Rather, the foregoing summary exemplifies certain novel aspects and features as set forth herein. The above noted and other features and advantages of the present disclosure will be readily apparent from the following detailed description of representative embodiments and modes for carrying out the present disclosure when taken in connection with the accompanying drawings and the appended claims.

The present disclosure is susceptible to modifications and alternative forms, with representative embodiments shown by way of example in the drawings and described in detail below. Inventive aspects of this disclosure are not limited to the particular forms disclosed. Rather, the present disclosure is intended to cover modifications, equivalents, combinations, and alternatives falling within the scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to the same or like components in the several Figures, a mobile platform20is depicted inFIG. 1that includes a body200and an electric propulsion system10, with the electric propulsion system10including a battery system11. In the depicted representative embodiment, the electric propulsion system10powers propulsion functions of the mobile platform20, with “exemplary” as used herein meaning a non-limiting example configuration illustrating certain aspects of the present teachings, i.e., not necessarily advantageous or preferred over other possible implementations. The mobile platform20is shown undergoing a direct current fast-charging (“DCFC”) operation in which the battery system11is electrically connected to an off-board DCFC station30, e.g., via a vehicle charging port200C that is internally connected to a DC charge coupler (not shown) using a length of high-voltage charging cable30C. Although not shown inFIG. 1, the end connection of the charging cable30C may be an SAE J1772 or other suitable charging plug or connector.

The battery system11, the internal structure and reconfigurable series-parallel switching control of which is described in detail below with reference toFIGS. 2A and 2B, may be used as part of the mobile platform20ofFIG. 1or as within other rechargeable electrical systems, such as but not limited to mobile power plants, robots, conveyor or transport platforms, etc. For vehicular applications, non-motor vehicles including aircraft, marine vessels, and rail vehicles may enjoy similar benefits. For illustrative consistency, the mobile platform20will be described hereinafter as an exemplary application benefitting from the present teachings to vehicular applications in general or motor vehicle applications in particular.

The mobile platform20in the illustrated embodiment includes front and rear road wheels14F and14R, respectively. The road wheels14F and14R are connected to separate front and rear drive axles14AF and14AR, respectively. In an all-wheel drive (“AWD”) embodiment, the drive axles14AF and14AR may be individually powered by separate rotary electric machines (not shown) each functioning as traction motors via corresponding traction power inverter module25or125, which are depicted schematically inFIGS. 3 and 5as described below.

The mobile platform20may be variously embodied as a plug-in electric vehicle having the battery system11, e.g., a multi-cell lithium ion, zinc-air, nickel-metal hydride, or lead acid battery system11, that can be selectively recharged via a charging voltage (“VCH”) from the off-board DCFC station30. When the mobile platform20is in operation, switching control of the battery system11is performed by a controller50, via control signals (arrow CCO), to ultimately energize a rotary electric machine28(seeFIGS. 3 and 5) to generate and deliver motor torque to the road wheels14F and/or14R, and to thereby propel the mobile platform20and/or to perform other useful work. Thus, the battery system11and the controller50together form the battery system11, with other possible components such as thermal management/cooling and power electronic hardware omitted for illustrative clarity.

The controller50ofFIG. 1includes a processor (P) and memory (M), with the memory (M) including application-suitable amounts of tangible, non-transitory memory, e.g., read only memory, whether optical, magnetic, flash, or otherwise. The controller50also includes application-sufficient amounts of random-access memory, electrically-erasable programmable read only memory, and the like, as well as a high-speed clock, analog-to-digital and digital-to-analog circuitry, and input/output circuitry and devices, as well as appropriate signal conditioning and buffer circuitry. The controller50is programmed to execute instructions100embodying a fault detection and isolation method, with the controller50receiving input signals (arrow CCI) indicative of a drive-requested or autonomously-requested charging mode of the battery system11and, in response, outputting the control signals (arrow CCO).

Some of the input signals (arrow CCI) may be determined during a charging operation as part of ongoing communication between the controller50and the DCFC station30, as will be appreciated by those of ordinary skill in the art. Such communication occurs upon connection of the mobile platform20to the DCFC station30, such as when the DCFC station30communicates its maximum charging voltage (VCH) to the controller50. In a drive/propulsion mode, an operator-requested or autonomously-determined propulsion request may cause the controller50to establish a parallel-connected (“P-connected”) configuration of the battery system11. During certain DCFC operations, the controller50may selectively reconfigure the battery system11to a series-connected (“S-connected”) configuration to take advantage of the charging voltage VCH, as will now be described with reference toFIGS. 2A and 2B.

Referring toFIG. 2A, in a simplified embodiment the battery system11may be constructed from as few as two battery modules12A and12B. Additional battery modules may be used in other embodiments, with the two battery modules12A and12B used hereinafter solely for illustrative consistency and simplicity. The battery modules12A and12B are depicted in a P-connected configuration, with each battery module12A and12B having a battery module voltage VBas noted above, with the battery voltage VBATbeing equal to the battery module voltage VB.

In an illustrative and non-limiting embodiment, the battery module voltage VBmay be in the range of about 400-500V and the charging voltage VCHfrom the DCFC station30ofFIG. 1may either be in the same range, or the charging voltage VCHmay be higher, for instance 800-1000V, with other battery and charging voltage levels also being usable within the scope of the disclosure. Thus, the P-connected configuration ofFIG. 2Ahas a battery voltage VBATthat is the potential difference between positive and negative DC bus rails17+and17−, and that is equal to the battery module voltage VB. In the S-connected configuration ofFIG. 2B, the battery voltage VBATis a multiple of the battery module voltage VB, with the multiple being the number of S-connected battery modules used in the construction of the battery system11.

In the exemplary circuit topology ofFIGS. 2A and 2B, which uses two battery modules12A and12B for illustrative simplicity, a switching control circuit15is constructed from multiple switches, e.g., switches S1, S2, and S3, with more than three switches possibly used in other embodiments. The switches S1, S2, and S3may be configured as electromechanical and/or electromagnetic switches such as relays or contactors, or as solid-state semiconductor switches such as MOSFETs, IGBTs, etc. For illustrative simplicity, therefore, the individual switches S1, S2, and S3are depicted as binary switches having an ON/conducting state when in a closed position and an OFF/non-conducting state when in an open position.

Switch S1is connected between the negative (−) terminal of battery module12A and the negative DC bus rail17−, while switch S2is connected between the positive (+) terminal of battery module12B and a positive DC bus rail17+. Switch S3in turn is disposed between the battery modules12A and12B. Specifically, one side (A) of switch S3is connected between switch S1and the negative (−) terminal of battery module12A, with an opposing side (B) of the switch S3being connected between the positive (+) terminal of battery module12B and switch S2.

When switch S3is opened and switches S1and S2are closed, which is the case depicted inFIG. 2A, the battery modules12A and12B are connected in electrical parallel. Likewise, when switch S3is closed and switches S1and S2are opened, as shown inFIG. 2B, the battery modules12A and12B are connected in electrical series. Therefore, the battery voltage VBATincreases inFIG. 2Brelative to its level inFIG. 2A, and thus the battery system11is able to utilize a higher charging voltage relative to the configuration ofFIG. 2A. The ON/OFF state of switch S3remains opposite to the ON/OFF state of switches S1and S2regardless of whether the battery modules12A and12B are in a P-connected or an S-connected configuration.

Referring briefly toFIG. 3, the electric propulsion system10may include the battery system (“BHV”)11, TPIM25, electric machine (“ME”)28, and a gearbox or transmission (“T”)18. A DC-DC converter or auxiliary power module (“APM”)42may be connected to the positive and negative bus rails17+and17−and configured to reduce the battery voltage level to levels suitable for charging an auxiliary battery (“BAUX”)11A. e.g., 12-15V. Another TPIM125and electric machine128may be used in some embodiments, with torque (arrow TM) from the electric machines28and/or128directed to the front and/or rear road wheels14F and14R depending on the operating mode. Thus, an electrical load placed on the battery system11is collectively referred to herein as an accessory load40, with certain diagnostic conditions depending on whether or not the accessory load40is connected to the voltage bus during charging of the battery system11as set forth below.

Referring toFIG. 4, the battery system11is electrically connected to the DCFC station30and the accessory load (“LD”)40, such as but not limited to the APM42ofFIG. 3, the electric machine(s)28and/or128, the TPIMs25and/or125, an air conditioning control module, etc. The electrical circuit described herein may include the DCFC station30, the battery system11, and the accessory load40. Isolation resistors in the DCFC station30are represented as R7and R8. Likewise, at the accessory load40shown at far right inFIG. 4, the capacitors are represented by C5and C6and the isolation resistors are represented as R5and R6, with a nominal accessory (“ACC”)40A shown schematically. The battery system11includes a cell stack13C, with isolation resistors R1and R2, and capacitors C1and C2for battery module12A and its associated power electronics, and with isolation resistors R3and R4and capacitors C3and C4for battery module12B and its associated power electronics.

Within the battery system11during a DC fast-charging process, a mid-bus node Nmis present at a midpoint of the DC voltage bus, i.e., at mid-bus rail located between the positive and negative bus rails17+and17−, as will be appreciated by those of ordinary skill in the art. A mid-bus voltage Vmis present at the mid-bus node Nm. The positive DC bus rail17+has a sensor node N1with a corresponding first (positive) bus rail voltage V1, with sensor node N1possibly including a voltage sensor operable for measuring and reporting the first (positive) bus rail voltage V1to the controller50. Likewise, a second (negative) bus rail voltage V2is present on the negative DC bus rail17−at a sensor node N2, with the total voltage capability of the battery system11being the potential between sensor nodes N1and N2.

As annotated inFIG. 4, three current variables are assumed in the analysis of an electrical circuit corresponding to the battery system11, where current I1flows into sensor node N1, current I3flows out of sensor node N2, and current (arrow I2) flows out of mid-bus node Nm, with the indicated variables being used as set forth herein to diagnose and isolate certain electrical conditions, some of which may be fault conditions and others of which may be no-fault or fault-free/expected results. Boxes [3], [4], and [6] inFIG. 4representing the locations of different potential faults.

Referring briefly toFIG. 5, the accessory load40may be alternatively embodied as an accessory load140when the TPIM25and electric machine28are connected to the battery system11. For illustrative simplicity, one phase leg of the TPIM25is depicted inFIG. 5, withFIG. 5likewise depicting a corresponding stator winding WSof the electric machine28. As will be appreciated by those of ordinary skill in the art, the TPIM25includes multiple semiconductor switches having ON/OFF states controlled via pulse-width modulation (“PWM”), pulse-density modulation (“PDM”), or other suitable switching control techniques. The opening/closing operation of two such switches SA1and SA2is represented by double-headed arrows AA. For instance, the switches SA1and SA2may be commanded by the controller50ofFIG. 1or another electronic control device to toggle at a calibrated switching frequency, e.g., 10-20 kHz or another value depending on the application. When the electric machine28is connected as shown, another possible electrical fault condition may occur at the location indicated by box [5].

The battery system11may be analyzed mathematically as follows:

Referring to table60ofFIG. 6A, from the above equations the expected/reference values for V1, V2, and Vmcan be obtained as noted above. Diagnostic ranges corresponding to each variable V1, V2, and Vm, are proposed considering possible HV bus ripples, component variance, etc., with each range having a low (“L”) and high (“H”) limit, may be related for an exemplary set of six diagnostic (“DIAG”) results 1, 2, 3, 4, 5, and 6. For instance, for the first diagnostic case or result (1), the subscript “11L” in abbreviation “V11L” refers to first diagnostic case (1), the first (positive) bus rail voltage (V1), and the low (“L”) limit. Similarly, the subscript “12H” in abbreviation “V12H” refers to first diagnostic case (1), the second (negative) bus rail voltage (V2), and the high (“H”) limit, with “Vm”, “VmL”, and “VmH” respectively referring to the mid-bus voltage and its low and high limits. Note that battery voltage will vary during operation depending on load and other conditions. To account for this, a lookup table may be populated with adjusted threshold ranges derived from expected values for the above-noted bus rail and mid-bus voltages. For instance, the expected values may be adjusted by multiplying by a factor to account for battery voltage variance during operation depending on load and other conditions. For example, the positive bus voltage V1is multiplied by (V1−Vm)/(V1r−Vmr), the negative bus voltage V2is multiplied by (V2−Vm)/(V2r−Vmr), while the mid-bus voltage is multiplied by (V1−Vm)/(V1r−Vmr) if Vmis positive, and by (V2−Vm)/(V2r−Vmr) if Vmis negative.

Table160ofFIG. 6Bis a non-limiting example scenario in which the battery module voltages (VB) are 400V and the battery voltage (VBAT) is 800V, and using example values of the capacitors and resistors in the DCFC station30and electric propulsion system10, the low and high values in each range, for each of the diagnostic cases, may be calculated by subtracting or adding a threshold value (“Vthd”), and thus the values in the lookup table may be ranges as opposed to fixed discrete values. Likewise, the listed ranges and values inFIG. 6Bare illustrative of one possible implementation of the present teachings.

Diagnostic conditions (1) and (2) ofFIGS. 6A and 6Bare normal or expected conditions during an exemplary DCFC operation, i.e., fault-free, with the accessory load40or140being off/not energized or on/energized, respectively. When the accessory load40or140is energized, the accessory load40or140is powered at less than the DCFC voltage, e.g., at 400V as used below with a DCFC voltage of 800V inFIG. 6B. Conditions 1 and 2 therefore depict a voltage shift that should occur when turning on the accessory load40or140, in this example shifting the first bus rail voltage V1on the positive rail17+ofFIGS. 4 and 5by an expected amount. The second bus rail voltage V2on the negative rail17−thus likewise shifts by the expected amount. Thus, implementations of the present method100may include using lookup tables populated with the first and second bus rail voltages V1and V2, and the mid-bus voltage Vm, with ranges and values that are relevant to the particular voltages used in the battery system11.

Conditions 3-5 ofFIGS. 6A and 6Bdescribe various possible “fault” conditions, with other fault conditions being possible within the scope of the disclosure. In a particular embodiment, conditions 3, 4, and 6, which are respectively labeled inFIG. 4as boxes [3], [4], and [6], correspond to negative bus, positive bus, and mid-bus short-to-body or short-to-chassis/ground conditions, respectively. Such short conditions are characterized by zero voltage (“0V”) at one of the three sensor nodes N1, N2, or Nm. Condition 5 is depicted numerically as box [5] inFIG. 5and represents a motor winding short fault, with a corresponding voltage oscillation pattern at each nodes N1, N2, and Nm for the first bus rail voltage V1at sensor node N1and for the second bus rail voltage V2at sensor node N2. As with the values of the first and second bus rail voltages V1and V2, the oscillation frequency and range is application-specific and depends on the particular configuration of the DCFC station30, the battery system11ofFIGS. 4 and 5, and the identity of the accessory loads40or140.

Condition 6 describes an abnormal condition where the mid-bus voltage Vmis expected to be non-zero value but becomes zero due to a fault when the accessory load40or140is connected to the voltage bus.

Such a result may be indicative of a mid-bus rail short-to-ground condition. In response to a transition from the P-connected configuration ofFIG. 2Ato the S-connected configuration ofFIG. 2Bprior to DC fast-charging of the battery system11, the controller50determines the positive and negative bus rail voltages (V1and V2) on the positive and negative bus rails, respectively, and the mid-bus voltage Vm. The method100proceeds by identifying an electrical condition of the electric propulsion system10, as a diagnosed condition, from among a plurality of possible electrical diagnostic conditions (1)-(6) using the first and second bus rail voltages (V1and V2) and mid-bus voltage Vm, including referencing a lookup table such as tables60or160populated with expected values for voltages V1, V2, and Vm. The method100also includes executing a control action in response to the diagnosed electrical condition, including recording a diagnostic code in memory (M) of the controller50that is indicative of the diagnosed electrical condition.

In executing the method100, the controller50may progress through a logic flow by comparing the voltages V1, V2, and Vmto corresponding ranges as set forth above, and then selecting a corresponding one of the diagnostic results. The control action taken by the controller50may be expected to vary with the result, with “normal” or “expected” results not necessarily requiring a particular action, or possibly resulting in the recording of a diagnostic code indicative of the result, while fault modes may trigger a particular action including recording a failing diagnostic code and possibly other hardware-related protection and/or recovery actions.

The possible electrical diagnostic conditions may include a short-to-ground condition of the positive bus rail when the first (positive) bus rail voltage V1is 0 volts, a short-to-ground condition of the negative bus rail when the second (negative) bus rail voltage V2is 0 volts, a short-to-ground condition of the mid-bus rail when the mid-bus voltage Vmis 0 volts, and a no-fault condition in which the controller50detects an expected voltage shift between the positive and negative bus rails when the electrical load is connected to the battery system. The conditions could also include a motor winding fault of the rotary electric machine, with the controller50configured to detect the motor winding fault by detecting a voltage oscillation of the bus rail voltages V1and V2and the mid-bus voltage Vmat a predetermined switching frequency.

Referring toFIG. 7, an example embodiment of the method100commences with block B102, with the controller50calculating expected values V1r, V2r, and Vmrfor the first (positive) and second (negative) bus rail voltages V1and V2and the mid-bus voltage Vm, respectively, e.g., using the above-noted mathematical approach. Such values may be stored in a lookup table, or the expected values may be calculated in real-time, e.g., using an equivalent circuit model. Block102also includes measuring or reading the first (positive), second (negative), and mid-bus voltages V1, V2, and Vmat nodes N1, N2, and Nm, respectively. The method100proceeds to block B103once the expected values have been calculated and the voltage readings have been received and temporarily recorded.

At block B103, the controller50compares each of the voltage readings from block B103for the first and second bus rail voltages (V1and V2) and the mid-bus voltage (Vm) to the expected values denoted by subscript “r”, with the expected values being ranges having corresponding low and high thresholds for the first diagnostic condition, i.e., a normal or expected values when the accessory load40or140is disconnected from the voltage bus during charging. The method100proceeds to block B104when the values fall within their assigned ranges and the accessory load40or140is not disconnected from the voltage bus. Otherwise, the method100proceeds to block B105.

Block B104includes recording a diagnostic code indicative of the first diagnostic condition (“DIAG 1”), i.e., normal or expected conditions when the accessory load40or140is not running during charging. The method100resumes with block B102in a calibrated control loop such that method100executes in such a loop during the entirety of the charging operation.

Block B105, which is analogous to block B103, includes comparing the voltage measurements from block B102to threshold ranges indicative of a mid-bus short condition. That is, block B105may determine if the mid-bus voltage Vmis initially a non-zero value, similar to condition (2), but has transitioned to 0 volts when the accessory load40or140is connected to the voltage bus during charging. The controller50proceeds to block B106when the conditions of block B105are satisfied, and to block B107in the alternative.

At block B106, the controller50records a diagnostic code indicative of the sixth diagnostic condition (“DIAG 6”), i.e., a possible mid-bus rail short-to-ground condition that could occur when the accessory load40or140are on during a DCFC process. The method100resumes with block B102as noted above with respect to block B104.

Block B107includes comparing the bus rail measurements from block B102to the low/high threshold ranges for the second diagnostic condition, i.e., normal or expected conditions when the accessory load40or140is on or running during charging. The controller50proceeds to block B108when the conditions of block B107are satisfied, and to block B109in the alternative.

At block B108, the controller50records a diagnostic code indicative of the second diagnostic condition (“DIAG 2”), i.e., normal or expected conditions in which the accessory load40or140is running during charging. The method100resumes with block B102as noted above with respect to block B104.

Block B109includes comparing the voltage measurements for the first (positive) and second (negative) bus rails voltages V1and V2, and the mid-bus voltage Vm, to calibrated ranges for a short of the negative bus rail17−to the body200or other electrical ground ofFIG. 1, and then proceeding to block B110when the voltages fall within their corresponding expected ranges. The method100instead proceeds to block B113when the voltages are outside of the corresponding ranges for such a condition.

Block B110includes determining, via the controller50, whether the voltages V1, V2, and Vmoscillate (“OSC”) within a particular voltage range at a particular frequency. The method100proceeds to block B111when such oscillation is detected. Otherwise, the method100proceeds to block B112.

At block B111, the controller50records a diagnostic code indicative of the fifth diagnostic result (“DIAG 5”), i.e., a possible motor winding fault. The method100then resumes with block B102.

At block B112, the controller50records a diagnostic code indicative of the third diagnostic result (“DIAG 3”), i.e., a short of the negative bus rail17−to the body200or other electrical ground. The method100then resumes with block B102.

Block B113includes comparing the voltage measurements for the bus rail voltages V1, V2, and Vmto calibrated ranges for the fourth diagnostic condition, i.e., a possible short of the positive bus rail17+to the body200or other electrical ground. The method100proceeds to block B114when the voltages fall within their corresponding ranges for such a condition. The method100instead proceeds to block B115when the voltages are outside of the corresponding ranges.

Block B114includes recording a diagnostic code indicative of the fourth diagnostic result (“DIAG 4”). The method100then resumes with block B102.

Block B115includes recording a diagnostic code indicative of a no-fault or alternative fault condition (“NF/ALT”). Depending on the programming of the controller50, that is, block B115may be a no-fault condition or additional analysis may be performed with additional ranges corresponding to other possible fault modes. Therefore, the six indicated electrical conditions ofFIGS. 6A, 6B, and 7are not limiting, with more or fewer conditions possible used in other embodiments.

Use of the present method100may facilitate detection and isolation of electrical fault conditions in the electric propulsion system10ofFIG. 1in which an S-connected battery configuration is selectively enabled during charging to utilize higher charging voltages. As noted above, transitioning from a P-connected configuration to an S-connected configuration may increase the probability of experiencing certain electrical faults, such as but not limited to the fault conditions detailed inFIGS. 6A and 6B. These and other benefits may be readily envisioned by one of ordinary skill in the art in view of the foregoing disclosure.

While some of the best modes and other embodiments have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims. Those skilled in the art will recognize that modifications may be made to the disclosed embodiments without departing from the scope of the present disclosure. Moreover, the present concepts expressly include combinations and sub-combinations of the described elements and features. The detailed description and the drawings are supportive and descriptive of the present teachings, with the scope of the present teachings defined solely by the claims.