Abstract:
A method of processing a resolver fault in a motor generator unit (MGU) includes receiving a position signal from a resolver describing a measured angular position of a rotor of the MGU, determining the presence of the resolver fault using the position signal, and calculating or extrapolating an estimated rotor position when the resolver fault is determined. A predetermined resolver fault state may be determined using a measured duration of the resolver fault, and the MGU may be controlled using the estimated rotor position for at least a portion of the duration of the resolver fault. A motor control circuit is operable for processing the resolver fault using the above method, and may automatically vary a torque output or a pulse-width modulation (PWM) of the MGU depending on the duration of the resolver fault.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates a method and a motor control circuit adapted for processing a motor/generator unit (MGU) resolver fault. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a high-voltage propelled vehicle such as a hybrid-electric vehicle (HEV) or an electric vehicle (EV), an onboard energy storage system (ESS) provides a source of at least a portion of the necessary propulsive power. An internal combustion engine may be shut off or selectively powered down when the vehicle is idling in order to conserve fuel. Energy may be captured during a regenerative braking event in order to recharge the ESS, and thereby further optimize fuel economy. The ESS may be configured as a bank of battery cells that collectively store a relatively high voltage, e.g., 300 volts or higher. This voltage is transmitted to one or more high-voltage devices, including one or more motor/generator units (MGU), via a high-voltage bus and a power inverter module (PIM). 
         [0003]    To ensure optimal performance of the various electrical systems aboard the HEV or EV, an electronic control unit or controller may be used to perform various electrical measurements and/or onboard diagnostics. One such component is a resolver. This device may be configured as absolute angle transducer, and may be used to monitor the changing angular position and rotational speed of a rotor portion of the MGU. Motor torque may be controlled using the rotor position and other feedback signals. Certain conventional vehicle control systems may utilize simple switch-debouncing procedures of the type known in the art, which may in turn cause the vehicle to shut down during a resolver fault in an attempt at preventing undesirable generation of motor torque during the duration of the resolver fault. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, a method is provided herein that allows a controller of an MGU, e.g., an MGU used for propelling an HEV or EV, a sufficient amount of time to “ride out” an intermittent resolver fault without necessarily shutting the vehicle down, thus providing a relatively smooth transition from a resolver fault state to a normal operating state. The method may be embodied in algorithmic form and automatically executed via the controller during a detected resolver fault. Motor position, required motor torque capacity, and fault recovery logic may be determined by the controller in a manner consistent with the detected fault. 
         [0005]    Using the algorithm of the invention, the controller may detect the resolver fault, e.g., by checking discrete fault inputs or control output signals from a 12-bit resolver decoder chip or other decoder chip of the type known in the art. When the controller sees a particular resolver fault, such as one of four resolver fault states as set forth below in one particular embodiment, a rotor position signal transmitted by the resolver is temporarily disregarded, and a different estimated value is instead calculated or extrapolated from a last known valid position and motor speed. The last known valid speed may then be used as the present speed, and the resolver fault state may be automatically changed to a cautionary state. 
         [0006]    According to one embodiment, the four resolver faults may include: a short-duration fault (SD Fault), a medium-duration fault (MD Fault), a long-duration fault (LD Fault), and a repeated medium-duration fault (RMD Fault). As used herein, the term “SD Fault” refers to a resolver fault that occurs when the duration of the resolver fault is shorter than a calibrated threshold, i.e., an initial coast period. During such an initial coast period, the PIM operates normally or without any degradation or change in performance. An MD Fault occurs when the duration of the resolver fault is longer than the initial coast period but shorter than a calibrated maximum allowable resolver retry period. The LD Fault occurs when the duration of the resolver fault is longer than the calibrated resolver retry period. The RMD Fault occurs when the duration of a series of resolver faults is greater than the initial coast period and shorter than the calibrated resolver retry period. 
         [0007]    In particular, a method of processing a resolver fault for a motor generator unit (MGU), such as but not limited to those typically used for propelling an HEV or EV as described above, includes receiving a rotor position signal from a resolver describing a measured position of a rotor of the MGU, detecting the resolver fault, and calculating or extrapolating a position of the rotor when the resolver fault is detected. A predetermined resolver fault state may be selected or determined using the duration of the resolver fault. A controller controls an operation of the MGU, e.g., a torque output and/or pulse width modulation (PWM) process, using the estimated position, i.e., the calculated or extrapolated rotor position, over at least a portion of the resolver fault state. 
         [0008]    A controller is also provided for a motor/generator unit (MGU) having a resolver adapted for monitoring the position of the rotor. The controller is adapted for detecting a resolver fault using a signal from the resolver, extrapolating a position of the rotor when the resolver fault is detected, selecting a resolver fault state based on a duration of the resolver fault, and controlling the output of the MGU using the extrapolated rotor position for at least a portion of the duration of the selected resolver fault state. Output of the MGU may be controlled by automatically varying a PWM operation thereof based on the duration of the resolver fault, or by at least temporarily reducing torque output of the MGU when the duration is greater than a first threshold duration and less than a second threshold duration. Torque output may be reduced to zero when the duration is greater than the second threshold duration. 
         [0009]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of a vehicle having a resolver and a motor controller; 
           [0011]      FIG. 2  is a graph describing a first resolver fault condition executable using the controller shown in  FIG. 1 ; 
           [0012]      FIG. 3  is a graph describing a second resolver fault condition executable using the controller shown in  FIG. 1 ; 
           [0013]      FIG. 4  is a graph describing a third resolver fault condition executable using the controller shown in  FIG. 1 ; 
           [0014]      FIG. 5  is a graph describing a fourth resolver fault condition executable using the controller shown in  FIG. 1 ; and 
           [0015]      FIG. 6  is a flow chart describing an algorithm for executing the method of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures,  FIG. 1  shows a vehicle  10  having a motor control circuit  11 , although the circuit may be used separately from the vehicle without departing from the intended inventive scope. Circuit  11  includes a controller  12  having an algorithm  100  adapted for executing the method of the present invention during a predetermined resolver fault condition, as will be described below with reference to  FIGS. 2-6 . The vehicle  10  includes a transmission  14  having at least one high-voltage electric motor/generator unit (MGU)  16  and at least one gear set (GS)  17 . 
         [0017]    The controller  12  may be configured as a digital computer generally including a CPU, and has sufficient memory for executing its required functions, such as read only memory (ROM), random access memory (RAM), electrically-programmable read only memory (EPROM), etc. The controller  12  may include a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and input/output (I/O) circuitry and devices, as well as appropriate signal conditioning and buffering circuitry. Any algorithms resident in the controller  12  or accessible thereby, including the algorithm  100  described below with reference to  FIG. 6 , or any other required control algorithms, may be stored in ROM and automatically executed by the controller  12  to provide the required control functionality. 
         [0018]    The vehicle  10  includes a high-voltage energy storage system (ESS)  18 , e.g., a lithium ion battery module or other suitable high-voltage device that has the ability to selectively store and dispense electrical power as needed, and an internal combustion engine (E)  20  having an output member  21  that serves as or is connected to an input member to the transmission  14 . A final drive assembly (not shown) may be operatively connected to an output member  22  of the transmission  14  and drive wheels  24  for propulsion of the vehicle  10 . Other power sources may be used to propel the vehicle  10  within the intended scope of the invention, such as a fuel cell (not shown). The vehicle  10  may be propelled at times exclusively using the ESS  18  and the MGU  16 . 
         [0019]    In the hybrid vehicle embodiment of  FIG. 1 , the ESS  18  is electrically-connected to the MGU  16  via a high-voltage DC bus  26  and a DC- to-AC pulse-width modulating (PWM) power inverter module or PIM  28 . As will be understood by those of ordinary skill in the art, a PIM such as the PIM  28  is configured to receive motor control commands and control inverter states to provide motor drive or regeneration functionality. When operating as an electric motor, the MGU  16  may draw electrical energy from the ESS  18 , and likewise may generate electrical energy to the ESS  18  for storage therewithin when operating as a generator. According to one embodiment, the MGU  16  may be configured as a three-phase alternating current (AC) high-voltage motor, such as a permanent magnet synchronous motor of the type known in the art. 
         [0020]    Still referring to  FIG. 1 , the MGU  16  includes a rotor  19  having a determinable angular rotor position (arrow P R ). A resolver (R)  27  having a decoder chip  23  is electrically connected to the rotor  19 , and is adapted for continuously monitoring and/or measuring the rotor position (P R ), and for communicating this value, along with the speed of the rotor, to the controller  12  for use by algorithm  100 . The controller  12  executes one or more motor control responses in response to a detected resolver fault condition using values of a set of control input signals, including but not necessarily limited to the measured rotor position (P R ). 
         [0021]    The algorithm  100  is automatically executed during a predetermined resolver fault condition, which according to one embodiment may include each of: a short-duration fault (SD Fault), a medium-duration fault (MD Fault), a long-duration fault (LD Fault), and a repeated medium-duration fault (RMD Fault), as shown in  FIGS. 2-5 , respectively. The SD Fault occurs when the duration of the fault is shorter than an initial coast period, i.e., a period over which rotor speed remains substantially unchanged to the mechanical time constant, while the MD Fault occurs when the duration of the fault is longer than the initial coast period but shorter than a calibrated resolver retry period. Likewise, the LD Fault occurs when the duration of the fault is longer than the calibrated resolver retry period, while the RMD Fault occurs when the duration of the fault is greater than the initial coast period and less than a calibrated retry period. 
         [0022]    Referring to  FIG. 2 , the first resolver fault condition, i.e., the SD Fault, may be depicted via a graph  30 . Algorithm  100  of  FIG. 6  as described below is executed when a duration (T F ) of a detected resolver fault  32  in a fault trace  34 , i.e., the time measured between points  33  and  35 , is shorter than a calibrated initial coast period (T 1 ). For example, if the duration of resolver fault  32  is 5 ms and the calibrated initial coast period (T 1 ) is 20 ms, a fault state trace  36  may switch from “good” to “caution” at point  33 , and a fault counter trace  38  may begin to ramp up at point  33  at a calibrated rate. The resolver fault  32  terminates at point  35 , and thereafter the fault state trace  36  may automatically switch from “caution” to “good”. Fault counter trace  38  may then ramp down at the same or a different calibrated rate depending on the desired functionality. 
         [0023]    By changing the calibrated rate of the fault counter the time to transition from a “caution” state to a “good” state may be modified as needed to optimize performance. If a resolver fault is detected after the calibrated initial coast period (T 1 ), the controller  12  will follow the sequence shown in  FIG. 3 , i.e., the MD Fault. The graph  30  also shows a motor state trace  40 , a pulse-width modulation (PWM) trace  50  describing the status of the PIM  28 , a torque capacity trace  60  describing the output status of the MGU  16 , and a rotor angle or position validity trace  70 . 
         [0024]    For the SD Fault condition of  FIG. 2 , the motor state trace  40  describes the uninterrupted operation of the MGU  16  at 100% of its torque capacity, as indicated by trace  60 . The validity of any measurements using the resolver  27  is affirmed in trace  70 , and PWM continues via the PIM  28  per normal calibrated PWM functionality. At point  33 , the controller  12  extrapolates the rotor position using the last known position/speed. After point  35  the controller  12  again utilizes the rotor position values transmitted by the resolver  27 . 
         [0025]    Referring to  FIG. 3 , the medium-duration or MD Fault may be depicted via graph  130 . Graph  130  depicts the “resolver retry” functionality of algorithm  100  when a duration (T F ) of a resolver fault  32  in trace  34 , i.e., the time measured between points  33  and  35 , is longer than a calibrated initial coast period (T 1 ) but shorter than a resolver retry period (T 2 ). Fault state trace  36  may automatically switch from a “good” state to a “caution” state at point  33 , and then remain in the caution state through the initial coast period, i.e., until T 1 , and remaining in a variant of the cautionary state, “down 4 retry, until a time corresponding to point  35 A of trace  34 . Recovery begins at point  35 A, continuing for a calibrated recovery period (T 3 ). The torque ramp-up period commences at T 3 , and concludes at T 4 . Fault counter trace  38  may ramp up at a calibrated rate beginning at point  33 , with the ramp terminating after the initial coast period (T 1 ). At point  35 , i.e., when the resolver fault  32  initially terminates, the fault state trace  36  may continue to indicate a cautionary state (labeled “Down 4 Retry” in  FIG. 3 ). During a retry diagnostic period (T sd  to T 2 ) another resolver fault  32 A may be automatically initiated with respective start and stop points  33 A,  35 A. Ramp down of the fault counter trace  38  may begin at point  35 A, again at a calibrated rate. 
         [0026]    When the resolver fault  32  sustains longer than the initial coast period (T 1 ) as shown in  FIG. 3 , the controller  12  of  FIG. 1  may be presented with two choices: (1) if calibration is set to a first value, e.g., a value of 1, the controller  12  may change the fault state from “caution” to “retry”, and the controller will then execute diagnostics that will shut down the PIM  28  and launch the retry process. If calibration is set to a second value, e.g., 0, the controller  12  will instead go to the LF Fault mode shown in  FIG. 4 . When calibration is set to the first value, the PIM  28  is shut down, and available motor torque (trace  60 ) is reduced to a threshold minimum value. After the PIM  28  has been shut down, the controller  12  waits through the minimum shutdown period (T 1  to T sd ), and then checks the resolver fault during the retry period (T sd  to T 2 ). 
         [0027]    For induction motors, the minimum shutdown period (T 1  to T sd ) should be calibrated for the current of MGU  16 , i.e., its stator current and its rotor current, to decay to a threshold minimal value. When the MGU  16  is configured an induction motor, the stator current will be zero as soon as the PIM  28  is turned off, but the rotor current (i rotor ) will decay as a function of the rotor time constant (T r ), per the function: 
         [0000]    
       
         
           
             
               i 
               rotor 
             
             = 
             
               
                 i 
                 
                   rotor 
                   initial 
                 
               
                
               
                  
                 
                   - 
                   
                     t 
                     
                       T 
                       r 
                     
                   
                 
               
             
           
         
       
     
         [0000]    Therefore, for an induction motor the minimum shutdown period may be approximately three to four times that of the rotor time constant (T r ). 
         [0028]    In case of permanent magnet (PM) motors, the minimum shutdown period may be calibrated to avoid overshoot due to a three-phase short operation, which can be calibrated on when resolver signals are absent. Resolver fault recovery may be checked at all times during the interval of T 1  to T 2 . PWM may be prevented or delayed until the resolver state is good. In either case, i.e., PM or induction-type motors, the value of Tsd may be calibrated. 
         [0029]    During the retry diagnostics period (from T sd  to T 2 ), as soon as the resolver fault disappears at any point, e.g., at point  35 , the controller  12  may count downward via the counter (CNT 3 ) as shown by traces  37 ,  137 . The counter will reach zero at point  39  when no fault is present over the duration of the recovery period. If the counter reaches zero before the resolver retry period expires, the controller may change the fault state from “recovery” to “good”, e.g., at point  39 . The PIM  18  may then be turned on, as indicated by trace  50 . The initial torque capability at point  39  will be zero, and will recover linearly to 100% at point  61  during the torque ramp-back period. Rotor position is obtained from the resolver  27  after point  39 . 
         [0030]    Referring to  FIG. 4 , a long-duration of LD Fault is shown by graph  230 , with the LD Fault occurring when the duration of the fault is longer than the calibrated resolver retry period. The LD fault occurs if the counter (CNT 3 ) does not reach zero until the end of resolver retry period (T 2 ), i.e., at point  39 . The controller  12  may then change the resolver fault state (trace  36 ) to “fault” at point  39 , and may change the motor state from RUN to Fault at point  39  as indicated by trace  40 . The PIM  28  of  FIG. 1  responds according to the predefined fault action. Note that at point  71  the validity trace  70  is switched to “invalid” and the torque capacity is reduced to 0% as shown by trace  60 . PWM functionality ceases, as indicated by trace  50 . 
         [0031]    Referring to  FIG. 5 , the resolver retry functionality is shown with repeated medium-duration faults, i.e., the RMD Fault condition, via a graph  330 . Recovery may occur multiple times due to repeated medium-duration faults  32 . However, a maximum number (n) of faults in the recovery may be limited to a calibrated value. If the MD Fault occurs (n) times, the controller  12  of  FIG. 1  may change the fault state from “caution” to “fault” at point  41 . 
         [0032]    Referring to  FIG. 6  in conjunction with the vehicle  10  of  FIG. 1 , the algorithm  100  is shown in flow chart form commencing with step  102 . The controller  12  receives signals from the resolver  27  and detects or otherwise determines whether a resolver fault is present. The resolver  27  may include decoder chip  23  that transmits various signals to the controller  12 , e.g., a loss of signal (LOS), a degradation of signal (DOS), or a loss of tracking (LOT). As will be understood by those of ordinary skill in the art, an LOS may be detected when a resolver input falls below the specified threshold by comparing the monitor signal to a fixed minimum value. A DOS may be detected when a resolver input exceeds the specified threshold. A LOT may be detected when an internal error signal exceeds a threshold level, or when the input signal exceeds a maximum tracking rate. 
         [0033]    Upon detection of the resolver fault, the algorithm  100  proceeds to step  104  wherein a timer may be started and ramped at a calibrated rate. Once started, at step  106  the algorithm  100  switches the resolver fault state from “good” to “caution”, and then proceeds to step  108 . 
         [0034]    At step  108 , the algorithm  100  compares the resolver fault duration (T F ) to a first calibrated value, referred to hereinabove as the initial coast period as described above. The algorithm  100  proceeds to step  120  if the duration (T F ) is less than the first calibrated value/initial coast period, otherwise proceeding to step  110 . 
         [0035]    At step  110 , the algorithm  100  compares the duration (T F ) to a second calibrated value, i.e., a maximum allowable resolver retry period. If the duration (T F ) is longer than the second calibrated value/resolver retry period, the algorithm  100  proceeds to step  112 , otherwise it proceeds to step  114 . 
         [0036]    At step  112 , the algorithm  100  executes the Long Duration (LD) Fault processes detailed above. 
         [0037]    At step  114 , the algorithm  100  determines whether the number of resolver faults is greater than a calibrated threshold (n), as explained above. If so, the algorithm  100  proceeds to step  118 . Otherwise, the algorithm  100  proceeds to step  116 . 
         [0038]    At step  116 , the algorithm  100  executes the Medium Duration (MD) Fault process detailed above. 
         [0039]    At step  118 , the algorithm executes the Repeated Medium Duration or RMD Fault process described above. 
         [0040]    Using the algorithm  100  in conjunction with the vehicle  10  as set forth above, a robust strategy is provided for processing resolver faults without necessarily shutting down the vehicle. Execution of the algorithm  100  may enable a reduced chance of setting a resolver fault code, less frequent vehicle shut down events, and reduced warranty costs. 
         [0041]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.