Patent Publication Number: US-2022219542-A1

Title: Method and system for detecting contactor weld

Description:
TECHNICAL FIELD 
     The present disclosure relates to a system for detecting a contactor weld for an electrified vehicle. 
     BACKGROUND 
     Electric vehicles are propelled by electric energy stored in vehicle batteries via switches and contactors. Contactor welding may occur when a large electric current flows through the contactor causing the contactor to remain at a closed position. 
     SUMMARY 
     A vehicle includes a traction battery, an electric machine, and a pair of contactors electrically between the traction battery and electric machine. The vehicle also includes a controller that sequentially generates a first command to open one of the contactors and a second command to open the other of the contactors. The controller further inhibits a next start of the vehicle based on voltage or current sensed before and after the first command is generated indicating that a first resistance between a bus electrically connected with the electric machine and a chassis of the vehicle increases after the first command is generated, and a duration of continuous reduction in voltage across the other of the contactors following the second command exceeds a predetermined threshold. 
     A method includes generating a first command to open a first contactor and a second command to open a second contactor, and inhibiting a next start of a vehicle responsive to voltage or current sensed before and after the generating the first command indicating that a first resistance between an electrical bus and a chassis of the vehicle does not increase after the first command is generated, and a second resistance between the electrical bus and chassis increases after the second command is generated. 
     A power system includes a battery and a controller. The controller inhibits charge of the battery according to voltage or current values sensed before and after contactors electrically connected to the battery are commanded to open and indicating that a leakage resistance associated with one of the contactors increases after the one of contactors is commanded to open, and a duration of a continuous voltage drop across another of the contactors after the another of the contactors is commanded to open exceeds a threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example block topology of an electrified vehicle illustrating drivetrain and energy storage components; 
         FIG. 2  illustrates an example diagram of a system controller and a battery electric control module; 
         FIG. 3  illustrates an example circuit diagram of a contactor weld detecting circuit; 
         FIG. 4  illustrates an example flow diagram of a process for contactor weld detection; and 
         FIG. 5  illustrates an example waveform diagram of RC dynamics of a contractor weld detection process. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     The present disclosure, among other things, proposes a system and method for detecting contactor welds for an electrified vehicle. 
       FIG. 1  illustrates a plug-in hybrid-electric vehicle (PHEV). A plug-in hybrid-electric vehicle  12  may comprise one or more electric machines (electric motors)  14  mechanically coupled to a hybrid transmission  16 . The electric machines  14  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  16  is mechanically coupled to an engine  18 . The hybrid transmission  16  is also mechanically coupled to a drive shaft  20  that is mechanically coupled to the wheels  22 . The electric machines  14  may provide propulsion and deceleration capability when the engine  18  is turned on or off. The electric machines  14  may also act as generators and may provide fuel economy benefits by recovering energy that would be lost as heat in the friction braking system. The electric machines  14  may also reduce vehicle emissions by allowing the engine  18  to operate at more efficient speeds and allowing the hybrid-electric vehicle  12  to be operated in electric mode with the engine  18  off under certain conditions. 
     A traction battery or battery pack  24  stores energy that may be used by the electric machines  14 . A vehicle battery pack  24  may provide a high voltage DC output. The traction battery  24  may be electrically coupled to one or more battery electric control modules (BECM)  25 . The BECM  25  may be provided with one or more processors and software applications configured to monitor and control various operations of the traction battery  24 . The traction battery  24  may be further electrically coupled to one or more power electronics modules  26 . The power electronics module  26  may also be referred to as a power inverter. One or more contactors  27  may isolate the traction battery  24  and the BECM  25  from other components when opened and couple the traction battery  24  and the BECM  25  to other components when closed. The power electronics module  26  may also be electrically coupled to the electric machines  14  and provide the ability to bi-directionally transfer energy between the traction battery  24  and the electric machines  14 . For example, a traction battery  24  may provide a DC voltage while the electric machines  14  may operate using a three-phase AC current. The power electronics module  26  may convert the DC voltage to a three-phase AC current for use by the electric machines  14 . In a regenerative mode, the power electronics module  26  may convert the three-phase AC current from the electric machines  14  acting as generators to the DC voltage compatible with the traction battery  24 . The description herein is equally applicable to a pure electric vehicle. For a pure electric vehicle, the hybrid transmission  16  may be a gear box connected to the electric machine  14  and the engine  18  may not be present. 
     In addition to providing energy for propulsion, the traction battery  24  may provide energy for other vehicle electrical systems. A vehicle may include a DC/DC converter module  28  that converts the high voltage DC output of the traction battery  24  to a low voltage DC supply that is compatible with other low-voltage vehicle loads. An output of the DC/DC converter module  28  may be electrically coupled to an auxiliary battery  30  (e.g., 12V battery). 
     The vehicle  12  may be battery electric vehicle (BEV) or a plug-in hybrid electric vehicle (PHEV) in which the traction battery  24  may be recharged by an external power source  36 . The external power source  36  may be a connection to an electrical outlet. The external power source  36  may be an electrical power distribution network or grid as provided by an electric utility company. The external power source  36  may be electrically coupled to electric vehicle supply equipment (EVSE)  38 . The EVSE  38  may provide circuitry and controls to regulate and manage the transfer of energy between the power source  36  and the vehicle  12 . The external power source  36  may provide DC or AC electric power to the EVSE  38 . The EVSE  38  may have a charge connector  40  for plugging into a charge port  34  of the vehicle  12 . The charge port  34  may be any type of port configured to transfer power from the EVSE  38  to the vehicle  12 . The charge port  34  may be electrically coupled to a charger or on-board power conversion module  32 . The power conversion module  32  may condition the power supplied from the EVSE  38  to provide the proper voltage and current levels to the traction battery  24 . The power conversion module  32  may interface with the EVSE  38  to coordinate the delivery of power to the vehicle  12 . The EVSE connector  40  may have pins that mate with corresponding recesses of the charge port  34 . Alternatively, various components described as being electrically coupled may transfer power using a wireless inductive coupling. 
     One or more wheel brakes  44  may be provided for decelerating the vehicle  12  and preventing motion of the vehicle  12 . The wheel brakes  44  may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes  44  may be a part of a brake system  46 . The brake system  46  may include other components to operate the wheel brakes  44 . For simplicity, the figure depicts a single connection between the brake system  46  and one of the wheel brakes  44 . A connection between the brake system  46  and the other wheel brakes  44  is implied. The brake system  46  may include a controller to monitor and coordinate the brake system  46 . The brake system  46  may monitor the brake components and control the wheel brakes  44  for vehicle deceleration. The brake system  46  may respond to driver commands and may also operate autonomously to implement features such as stability control. The controller of the brake system  46  may implement a method of applying a requested brake force when requested by another controller or sub-function. 
     One or more electrical loads  46  may be coupled to the high-voltage bus. The electrical loads  46  may have an associated controller that operates and controls the electrical loads  46  when appropriate. Examples of electrical loads  46  may be a heating module, an air-conditioning module or the like. 
     The various components discussed may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors. A system controller  50  may be present to coordinate the operation of the various components. 
     Referring to  FIG. 2 , an example diagram for a battery control system including the system controller  50  and the BECM  25  is illustrated. The system controller  50  may include one or more processors  102  configured to perform instructions, commands, and other routines in support of the processes described herein. For instance, the system controller  50  may be configured to execute instructions of vehicle applications  104  to provide features such as navigation, satellite radio decoding, and vehicle power management. Such instructions and other data may be maintained in a non-volatile manner using a variety of types of computer-readable storage medium  106 . The computer-readable medium  106  (also referred to as a processor-readable medium or storage) includes any non-transitory medium (e.g., tangible medium) that participates in providing instructions or other data that may be read by the processor  102  of the system controller  50 . Computer-executable instructions may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java, C, C++, C#, Objective C, Fortran, Pascal, Java Script, Python, Perl, and PL/SQL. 
     The system controller  50  may be provided with various features allowing the vehicle occupants/users to interface with the system controller  50 . For example, the system controller  50  may receive input from human-machine interface (HMI) controls  106  configured to provide for occupant interaction with the vehicle  12 . As an example, the system controller  50  may interface with one or more buttons (not shown) or other HMI controls configured to invoke functions on the system controller  50  (e.g., steering wheel audio buttons, a push-to-talk button, instrument panel controls, etc.). The system controller  50  may also drive or otherwise communicate with one or more displays  108  configured to provide visual output to vehicle occupants by way of a video controller  110 . In some cases, the display  108  may be a touch screen further configured to receive user touch input via the video controller  110 , while in other cases the display  108  may be a display only, without touch input capabilities. The system controller  50  may also drive or otherwise communicate with one or more speakers  112  configured to provide audio output to vehicle occupants by way of an audio controller  114 . 
     The system controller  50  may be further provided with a wireless transceiver  116  configured to communicate with a remote server  118  via a communication network  120 . The wireless transceiver  116  may be configured to support a variety of communication protocols including but not limited to Wi-Fi, Bluetooth, radio-frequency identification (RFID), near-field communication (NFC), Zigbee, ultra-wide band (UWB), cellular or the like. The system controller  50  may be configured to receive commands from the remote server  118  operated by a vehicle manufacturer or an associated party to perform various operations to the vehicle  12 . For instance, the system controller  50  may receive a command to perform a battery contactor weld test from the server  118  via the wireless transceiver  116 . In response, the system controller  50  may proceed with the test by transferring the command to the BECM  25  via an in-vehicle network  122 . Responsive to the conclusion of the weld test, the system controller  50  may obtain the test result from the BECM  25  and transmit the result to the remote server  118  via the wireless transceiver  116 . The in-vehicle network  122  connecting the system controller  50  and the BECM  25  may include, but not be limited to, one or more of a CAN, an ethernet network, or a media oriented system transport (MOST). 
     The BECM  25  may include a processor  124  configured to perform instructions, commands, and other routines in support of the processes described herein. For instance, the BECM  25  may be configured to execute instructions of battery application  126  to provide features such as charging, discharging, contactor weld test or the like. Such instructions and other data may be maintained in a non-volatile manner using a variety of types of computer-readable storage medium  128 . Data log (e.g. test results) may be maintained in the storage  128  as a part of battery data  130 . 
     Referring to  FIG. 3 , an example circuit diagram of a battery contactor weld detection circuit  200  of one embodiment of the present disclosure is illustrated. With continuing reference to  FIGS. 1 and 2 , the BECM  25  may be connected to a positive high-voltage (HV) bus/rail  202   a  and negative HV bus/rail  202   b . A plurality of high-voltage (HV) battery cells  204  may be connected in series between the positive and negative HV buses  202   a  and  202   b . It is noted that although the battery cells  204  are connected in series in the present example, other configurations may be used. The plurality of battery cells  204  may be connected in parallel, in series, and/or in the combination thereof. The circuit  200  may further include a ground line  206  to which the chassis of the vehicle  12  is connected. As discussed above, one or more contactors  27  may be connected between the vehicle  12  and the battery  24 . In the present example, a positive main contactor MC+  27   a  may be disposed on the positive HV bus  202   a  and a negative main contactor MC−  27   b  may be disposed on the negative HV bus  202   b , and the main contactors  27   a  and  27   b  may divide the circuit  200  into a vehicle side circuit  208  and a battery side circuit  210 . A precharge circuit  212  may be disposed on either or both of the positive and negative HV buses  202   a  and  202   b . In the present example, as illustrated in  FIG. 3 , the precharge circuit  212  may be disposed on the positive HV bus  202   a  connected in parallel with the positive main contactor  27   a . The precharge circuit  212  may include a precharge resistor  214  and a precharge contactor  216  connected in series. 
     The main contactors  27  and the precharge contactors  216  may be of various types. As an example, the contactors may be of a magnetic contactor type influenced by a low power/low voltage (LV) circuit (not shown) controlled by the BECM  25 . The contactor may be spring loaded. In an inactive condition, the spring may apply a tension between a contactor core (not shown) and a contactor coil (not shown) urging the contactor to open so the electricity cannot flow through. The core and coil may be referred to as the first and second terminal of the contactor. Responsive to the low power circuit being activated by the BECM  25 , electricity flows through the magnetic contactor. The electromagnet may generate a magnetic field overwhelming the spring tension so that the core contacts the coil so that the contactor is closed. To open the contactor, the BECM  25  may deactivate the low power circuit such that the magnetic field disappears and spring tension may urge the terminals to separate which opens the contactor. An electrical arc may be created during the closing process between contactor terminals as they move closer to each other. The high temperature of electrical arc may cause contactor terminals to melt and weld together. In this case, the spring tension may be unable to separate the contactor terminals which may cause unintended connection between the battery  24  and the vehicle  12 . While the main contactors  27   a  and  27   b  may have a higher chance to experience contactor welds, the precharge contactor  216  may be less likely to encounter such an issue because of a reduced current due to the precharge resistor  214 . For instance, the precharge resistor  214  may have a value of hundreds of ohms. 
     As illustrated in  FIG. 3 , a variety of capacitors and resistors may be connected between the HV buses  202  and the ground/chassis on both the vehicle side circuit  208  and the battery side circuit  210 . The capacitors and resistors may in the present example may represent lumped capacitance and resistance caused by parasitic effects and/or circuit components shown or not shown on each respective part of the circuit  200 . For instance, a positive battery capacitor C Batt+   218  may be connected between the positive HV bus  202   a  and the ground  206  on the battery side circuit  210 . A negative battery capacitor C Batt−   220  may be connected between the negative HV bus  202   b  and the ground  206  on the battery side circuit  210 . A positive vehicle capacitor C Veh+   222  may be connected between the positive HV bus  202   a  and ground the  206  on the vehicle side circuit  208 . A negative vehicle capacitor C Veh−   224  may be connected between the negative HV bus  202   b  and the ground  206  on the vehicle side circuit  210 . A positive battery resistor R Batt+   226  may be connected between the positive HV bus  202   a  and the ground  206  on the battery side circuit  210 . A negative battery resistor R Batt−   228  may be connected between the negative HV bus  202   b  and the ground  206  on the battery side circuit  210 . A positive vehicle resistor R Veh+   230  may be connected between the positive HV bus  202   a  and the ground  206  on the vehicle side circuit  208 . A negative vehicle resistor R Veh−   232  may be connected between the negative HV bus  202   b  and the ground  206  on the vehicle side circuit  210 . The lumped resistors/resistance described herein may also be referred to as leakage resistors/resistance. The lumped capacitor introduced above may be caused by parasitic capacitance on each of the battery and vehicle sides. Additionally or alternatively, one or more extra capacitors may be added to the circuit (e.g. on the vehicle side) to satisfy the specific design need. The lumped capacitors/capacitance may also be referred to as Y capacitors/capacitance. The value of each lumped capacitors may vary depending on design need. However, it may be generally recognized that the lumped capacitor on the battery side circuit  210  is much smaller than the lumped capacitor on the vehicle side circuit  208 . As an example, the total lumped capacitance on the battery side maybe less than 100 nF whereas the lumped capacitance on the vehicle side may be more than 1000 nF. Due to the significant difference in the capacitance values, the contactor weld detection may be made using the characteristics of the circuit based on RC dynamics of the circuit  200  (to be discussed in detail below). 
     Referring to  FIG. 4 , an example flow diagram of a process  300  for a contactor weld detection process is illustrated. In the present example, the process  300  may be performed after the vehicle  12  is being used. Both the main contactors  27  are closed and the precharge contactor  216  is open in the vehicle normal operating condition. With continuing reference to  FIGS. 1-3 , responsive to a key-off action after a user uses the vehicle  12  at operation  302 , at operation  304 , the BECM  25  starts the contactor weld detection by first measuring a positive leakage resistance between the positive HV bus  202   a  and ground  206  while both the main contactors  27  are still closed. As illustrated with reference to  FIG. 3 , a value of the leakage resistance between the positive HV bus  202   a  and ground  206  may be calculated using the following equation as the positive battery resistor R Batt+   226  and the positive vehicle resistor R Veh+   230  are connected in parallel. 
     
       
         
           
             
               R 
               
                 
                   leak 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   _ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   closed 
                 
                 + 
               
             
             = 
             
               
                 
                   R 
                   
                     Batt 
                     + 
                   
                 
                 × 
                 
                   R 
                   
                     
                       V 
                       ⁢ 
                       e 
                       ⁢ 
                       h 
                     
                     + 
                   
                 
               
               
                 
                   R 
                   
                     Batt 
                     + 
                   
                 
                 + 
                 
                   R 
                   
                     
                       V 
                       ⁢ 
                       e 
                       ⁢ 
                       h 
                     
                     + 
                   
                 
               
             
           
         
       
     
     Next, the BECM  25  commands to open the positive main contactor MC+  27   a  and measures the positive leakage resistance again. At operation  306 , the BECM  25  compares the leakage resistances measured before and after the positive main contactor MC+  27   a  has been commanded to open to determine if there is a significant change in the resistance value. If the positive main contactor MC+  27   a  is in a normal operating status and open, the vehicle side leakage resistance R Veh+   230  should be disconnected from the BECM  25  and therefore the new positive leakage resistance R leak_open+  should be substantially equal to the positive battery resistance R Batt+   226 . In general, the new leakage resistance R leak_open+  measured when the positive main contactor MC+  27   a  is open should be significantly greater than the previously measured resistance R leak_closed+ . If the BECM  25  determines that is the case, indicating the positive main contactor MC+  27   a  is operating normally, the process proceeds to operation  308 . Otherwise, the process proceeds to operation  318 . It is noted there are various methods to determine the increase in the leakage resistance before and after the main contactor  27   a  opens. For instance, the BECM  25  may directly compare the two values to determine if the later measured value is greater than the earlier measured value. Alternatively, magnitude threshold may be applied to the comparison process to prevent false readings due to the system glitches. The magnitude threshold may be a fixed threshold (e.g. 10-30 kΩ) and the BECM  25  may only determine the significant increase if the later measured resistance value is greater than the earlier measured value by at least the magnitude threshold (i.e. R leak_open+ &gt;R leak_closed+ +R threshold ). Alternatively, a dynamic magnitude threshold may be applied. The dynamical magnitude threshold may be a percentage of the earlier measured capacitance value. As an example, the BECM  25  may only determine the significant increase responsive to the later measured value is greater than the earlier measured value by more than 30% (i.e. 30% being the threshold). 
     At operation  308 , the BECM  25  further determines if the negative main contactor MC−  27   b  is welded by analyzing the RC dynamics of the circuit  200 . In the present example, a time constant parameter τ characterizing a circuit signal response to stabilization is used to make the RC dynamics determination. One or more leakage detection signals may be directly or indirectly measured from the HV buses  202  through a leakage detection circuit (isolation detection circuit, not shown) responsive to a test/trigger command. Depending on the specific configuration of the testing circuit, the leakage detection signals may vary signification. However, the signals may generally resemble a similar characteristic of a stabilization process. Referring to  FIG. 5 , a leakage detection signal waveform diagram  400  is illustrated. While the waveform from 0 to 9 seconds in time illustrates the leakage detection signals when the main contactors  27  are closed, the waveform from 100 to 109 seconds illustrates the leakage detection signals when the main contactors  27  are open. The waveform  402  may represent the leakage on the positive HV bus  202   a  influenced by the status of the positive main contactor MC+  27   a , and the waveform  404  may represent the leakage on the negative HV bus  202   b  influenced by the status of the negative main contactor MC−  27   b . Taking the waveform  404   a  for instance, the negative leakage detection signal lasts 4 seconds from 5 to 9 s when the negative main contactor MC−  27   b  is closed. The magnitude of the signal  404   a  starts high and gradually reaches a stable status at around 8 s. The stabilization process between 5 and 8 s may be referred to as a time constant parameter represented by τ. The time constant parameter τ may be calculated using the equation below: 
       τ= R×C  
 
     As discussed above with reference to  FIG. 3 , since the lumped capacitance C Veh  on the vehicle side circuit  208  is significantly greater than the lumped capacitance C Batt  on the battery side circuit  210  (at least 10 times more), the value of the time constant τ will heavily depend on whether the vehicle side circuit  208  is connected to the main circuit  200 . Taking the waveform  404  for instance, the time constant τ (i.e. 4 s) as illustrated in the waveform  404   a  when the negative main contactor MC−  27   b  is closed connecting the negative vehicle capacitor C Veh−  to the circuit  200  is significantly greater than the time constant τ (i.e. 0.2 s) as illustrated in the waveform  404   b  when the negative main contactor MC−  27   b  is open separating the negative vehicle capacitor C Veh−  from the circuit  200 . Due to the significant difference in the time constant as calculated, a threshold (e.g. 1 s) may be used to determine the status of the main contactors. 
     Returning to  FIG. 4 , at operation  310 , the BECM  25  determines if the time constant τ as calculated is less than the predetermined time threshold. If the answer is a yes, indicating the negative main contactor MC−  27   b  is open, the process proceeds to operation  312  to proceeds with the normal key-off procedure. Otherwise, if the answer for operation  310  is a no, the process proceeds to operation  314  to flag the possible welding of the negative main contactor MC−  27   b . Since the positive main contactor MC+  27   a  has already been determined to be open at operation  306 , the BECM  25  may only flag the fault for the negative main contactor MC−  27   b  at operation  314 . At operation  316 , the BECM  25  may store the fault condition as detected and report the condition to the system controller  50  for further processing. The system controller  50  may output a message via the HMI controls  106  to notify the condition to the vehicle user. Additionally or alternatively, the system controller  50  may report the condition to the remote server  118  via the wireless transceiver  116 . The BECM  25  may be further configured to inhibit the vehicle  12  from starting and/or the battery  24  being charged/discharged responsive to one of the main contactors being welded. 
     Returning to operation  306 , if the BECM  25  fails to detect a significant increase in the positive leakage resistance, the process proceeds to operation  318  to further determine the status of the negative main contactor MC−  27   b  by measuring the leakage resistance between the negative HV bus  202   b  and the ground  206  before and after commanding to open the negative main contactor MC−  27   b  and determining if there is a significant increase in the leakage resistance as measured. The negative leakage resistance detection procedures at operation  318  and  320  are substantially similar to the procedures in operation  304  and  306 . If the BECM  25  determines a significant increase in the negative leakage resistance before and after opening the negative main contactor MC−  27   b , the process proceeds to operation  322  to flag a possible welding of the positive main contactor MC+  27   a . Otherwise the process proceeds to operation  324  to flag both the main contactors  27  are possibly welded. 
     It should be noted that the process  300  as discussed above is merely introduced as an example of the present disclosure and the detailed process, operations and steps may vary depending on the specific design need. For instance, the process  300  may be altered to start with the negative main contactor detection first under substantially the same principle. The process at operation  308  and  310  may be referred to as a quick contactor weld detection process applicable to both the positive and negative main terminals. The quick contactor detection process may be independently performed responsive to a key-in input indicative of a user intent to start to use the vehicle  12 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. The word “increases” as used in the claims, for example, may refer to increases of at least 15%, 20%, etc. of the previous value. The phrase “does not change,” for example, may also refer to values that are within 5%, 10%, etc. of each other. Percentage values for particular applications can be obtained via testing, simulation, etc. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.