Abstract:
A method for controlling a traction power inverter module (TPIM) in a vehicle includes determining a commanded output torque of the motor using a controller. The method further includes controlling the TPIM and motor using a discontinuous pulse width modulated (DPWM) signal when the commanded output torque is less than a calibrated torque threshold. A continuous pulse width modulated (CPWM) signal is used when the commanded output torque is greater than the threshold. The method may include determining a direction of a change in the commanded output torque, and controlling the TPIM, via the controller, using the DPWM signal only when the commanded output torque drops below a predetermined hysteresis level. A vehicle includes a traction motor producing a motor torque for propelling the vehicle, an ESS, a TPIM, and a controller configured as noted above.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/410,089, filed Nov. 4, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to the control of a traction power inverter module of the type used aboard a vehicle. 
       BACKGROUND 
       [0003]    Certain vehicles can operate in one or more electric vehicle (EV) modes. In an EV mode, a high-voltage electric traction motor can be used as a prime mover. For example, an extended range electric vehicle (EREV) can be propelled by a fraction motor over a limited distance solely using battery power. Beyond a threshold range, a small internal combustion engine powers a generator to extend the effective EV range. A battery electric vehicle (BEV) operates exclusively in an EV mode, while a hybrid electric vehicle (HEV) selectively uses either or both of an internal combustion engine and a fraction motor(s) during different operating modes. 
         [0004]    An electric drive system of the type used for establishing an EV mode typically includes a traction power inverter module (TPIM). The traction motors used for propelling the vehicle in an EV mode are typically configured as multi-phase AC induction or permanent magnet machines, while the battery module from which the traction motor draws electrical power is a high-voltage DC storage device. Reliable AC-to-DC and DC-to-AC power conversion is thus necessary. Various semiconductor switches or solid state devices within the TPIM are controlled to achieve the required power conversion. However, conventional control methods may be less than optimal under certain vehicle operating conditions and loads. 
       SUMMARY 
       [0005]    Accordingly, a method is disclosed for controlling an electric traction motor of a vehicle using a controller and a traction power inverter module (TPIM). The controller selects and transmits a selected pulse width modulation (PWM) signal to the TPIM. The selected PWM signal as used herein is one of a continuous pulse width modulation (CPWM) signal and a discontinuous pulse width modulation (DPWM) signal. 
         [0006]    In one embodiment, selection of the PWM signal depends on a commanded output torque of the traction motor. The controller may automatically select the CPWM signal when the commanded output torque exceeds a calibrated threshold. Likewise, the DPWM signal may be selected when the commanded output torque is less than the calibrated threshold. A hysteresis band may be established with respect to the calibrated threshold in order to modify the calibrated threshold, e.g., based on the direction of a change in the commanded output torque, as will be explained in detail below. 
         [0007]    In particular, a method is disclosed for controlling a traction power inverter module (TPIM) in a vehicle having the TPIM and a traction motor. The method includes comparing a commanded output torque of the traction motor to a calibrated threshold using a controller. The method further includes automatically selecting a discontinuous pulse width modulated (DPWM) signal when the commanded output torque is less than the calibrated threshold, and automatically selecting a continuous pulse width modulated (CPWM) signal when the commanded output torque is greater than the calibrated threshold. The selected signal is transmitted from the TPIM to the traction motor to thereby control an operation of the fraction motor. 
         [0008]    A vehicle is also disclosed which includes a fraction motor, an energy storage system (ESS), a TPIM, and a controller. The controller determines a commanded output torque of the traction motor, and controls the TPIM and the traction motor using a selected PWM signal. A DPWM signal is selected when the commanded output torque is less than a calibrated torque threshold, and a CPWM signal is selected when the commanded output torque is greater than the calibrated torque threshold. 
         [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 traction power inverter module (TPIM) and a controller as disclosed herein; 
           [0011]      FIG. 2  is a schematic illustration of a TPIM which is usable with the example vehicle shown in  FIG. 1 ; 
           [0012]      FIG. 3  is a torque versus speed plot describing commanded output torque of a traction motor  12  on the vertical axis and motor output speed on the horizontal axis; and 
           [0013]      FIG. 4  is a flow chart describing a method for selecting between PWM signals during the control of a TPIM of the type shown in  FIG. 2 . 
       
    
    
     DESCRIPTION 
       [0014]    Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, and beginning with  FIG. 1 , a vehicle  10  includes a controller  40 . The controller  40  is configured to execute a method  100 , which may be embodied as a set of process instructions recorded on a tangible/non-transitory memory device  42 . 
         [0015]    Using the present method  100 , the controller  40  automatically selects between a continuous pulse width modulation (CPWM) signal and a discontinuous pulse width modulation (DPWM) signal depending on the commanded output torque of an electric traction motor  12 . The selected signal is then used to control a traction power inverter module (TPIM)  24 , i.e., a DC-to-AC and AC-to-DC power inverter, such as the example described below with reference to  FIG. 2 . While one traction motor  12  is shown in  FIG. 1  for simplicity, other vehicle embodiments may include a plurality of such fraction motors, with the control of each being as set forth below. 
         [0016]    As applied in the field of electric motor control, PWM techniques deliver pulsed energy to a target system, e.g., the TPIM  24  of  FIG. 1 , via a rectangular pulse wave. The pulse wave has a pulse width that is automatically modulated by a controller, e.g., the present controller  40 , thus resulting in a particular variation of an average value of the pulse waveform. By modulating the pulse width using the controller  40 , energy flow is precisely regulated to the fraction motor  12  through the TPIM  24 . By switching voltage to the TPIM  24  or other load with an appropriate duty cycle, the output approximates a desired output voltage. Therefore, PWM techniques can be used as an efficient means of motor control aboard the vehicle  10 . 
         [0017]    In particular, the controller  40  shown in  FIG. 1  is configured to determine the presently commanded motor output torque of the traction motor  12 , and to automatically select between a CPWM and a DPWM mode via PWM signal (arrow  11 ) depending on the motor output torque. Other commands, such as a commanded motor speed, may be used, either alone or in conjunction with the commanded motor torque. 
         [0018]    In a DPWM signal switching does not occur near the peaks of a sinusoidal phase current signal. In a CPWM signal, e.g., a Space Vector PWM signal or another suitable CPWM signal, switching occurs continuously, including at the peaks of the sinusoidal phase current signal. The two PWM modes therefore have relative advantages and drawbacks. 
         [0019]    Therefore, at high duty cycles, e.g., at light-to-medium electrical loads, the controller  40  automatically selects the DPWM mode. This provides lower switching losses and increases system efficiency. At such light-to-medium electrical loads, motor-induced noise, vibration, and harshness (NVH) is typically minimal. At higher loads/lower duty cycles, the controller  40  automatically selects the CPWM mode to optimize driveline NVH performance. Efficiency is thus sacrificed to some extent at lower duty cycles in order to reduce NVH where it would otherwise be the most noticeable to a driver of the vehicle  10 . However, the overall drive cycle impact is expected to be minimal due to the low duty cycle. 
         [0020]    Still referring to  FIG. 1 , the vehicle  10  may be configured in the embodiment shown in  FIG. 1  as an extended-range electric vehicle (EREV). Other possible embodiments include a battery electric vehicle (BEV) and a hybrid electric vehicle (HEV). Regardless of the embodiment, the vehicle  10  includes at least one traction motor  12 , which can be used to propel the vehicle in an electric-only (EV) operating mode. Each traction motor  12  powers a motor output shaft  16 , which is connected to an input member (not shown) of a transmission  14 . The transmission  14  may include as many gear sets, clutches, brakes, and interconnecting members as are needed to produce a desired set of speed ratios. An output member  20  of the transmission  14  ultimately powers a set of drive wheels  22 . 
         [0021]    The traction motor  12  may be configured as a multi-phase AC induction or permanent magnet electric machine, and rated for approximately 60 VAC to 300 VAC depending on the design. The TPIM  24  is electrically connected to the traction motor  12  using a high-voltage AC bus  26 , e.g., a conductive bus bar, interconnect member, or cable. The TPIM  24  converts DC power to AC power and vice versa as needed using a plurality of semiconductor switches  50  (see  FIG. 2 ), for example an insulated gate bipolar transistor (IGBT) or a field-effect transistor (FET), e.g., a metal oxide semiconductor FET (MOSFET), in order to provide the required power flow aboard the vehicle  10 . The TPIM  24  is electrically connected to an energy storage system (ESS)  28 , such as a multi-cell rechargeable battery module, using a high-voltage DC bus  30 . The traction motor  12  therefore is able to alternately supply and draw power to and from the ESS  28  as needed depending on the current powertrain operating mode. 
         [0022]    When the vehicle  10  is configured as an EREV, the ESS  28  may be selectively energized by an electric generator  32 . When the generator  32  is operating, electrical energy (arrow  34 ) is supplied to the ESS  28  and/or directly to the traction motor  12  to extend the effective EV operating range of the vehicle  10 . The generator  32  may be selectively turned on and off as needed by the controller  40 , or by other suitable control module such as a transmission control processor depending on the state of charge of the ESS  28 . 
         [0023]    The controller  40  may be configured as a motor control processor, a hybrid/transmission control processor, and/or other digital computer having a microprocessor or central processing unit, read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high speed clock, analog-to-digital (A/D) and digital-to-analog (D/A) circuitry, and input/output circuitry and devices (I/O), as well as appropriate signal conditioning and buffer circuitry. Any algorithms resident in the controller  40  or accessible thereby, including any instruction required for executing the present method  100  as described below with reference to  FIG. 4 , may be stored in non-transitory/tangible memory  42 , e.g., flash memory, a magnetic disc, an optical disc, etc., and automatically executed by the controller  40  to provide the respective functionality. 
         [0024]    Referring to  FIG. 2 , the TPIM  24  is in communication with the controller  40  of  FIG. 1 . The TPIM  24  may include a network of semiconductor switches  50  having a first input coupled to a voltage source, e.g., the ESS  28 , and an output coupled to the traction motor  12 . Although a single voltage source is shown, a distributed DC link with two series sources may also be used. Three pairs of series semiconductor switches  50  correspond to the three current phases of the traction motor  12 . Phase currents (arrows  13 ,  15 , and  17 ) are thus delivered from the TPIM  24  to various phase windings  25 ,  27 , and  29  of the traction motor  12 . 
         [0025]    Each of the pairs of semiconductor switches  50  of  FIG. 2  comprises a first semiconductor switch  51  and a second semiconductor switch  53 . Each switch  51  is electrically connected to a positive electrode of the ESS  28 . Each second switch  53  is electrically connected to a negative electrode of the ESS  28 , and to the respective first switch for that particular switch pair. 
         [0026]    During operation, torque from the traction motor  12  is delivered to the drive wheels  22  of  FIG. 1 . In order to power the traction motor  12 , DC power is provided from the ESS  28  to the TPIM  24 , which converts the DC power into suitable AC power. The conversion of DC power to AC power occurs within the TPIM  24 , and is performed by repeatedly switching the semiconductor switches  50  within the TPIM using the controller  40  of  FIG. 1 . 
         [0027]    Generally, the controller  40  of  FIG. 1  produces the PWM signals (arrow  11 ) for controlling the switching action of the TPIM  24 . The TPIM  24  then converts the PWM signals to a modulated voltage waveform suitable for operating the traction motor  12 . In a typical application with a three-phase AC current motor, three separate PWM signals are generated, one each for a respective pair of the semiconductor switches  50  shown in  FIG. 2 . 
         [0028]    A variety of different types of DPWM and CPWM techniques can be used in the various embodiments. In general, CPWM is defined as a PWM technique where each phase leg of the TPIM  24  is switching continuously over the full 360° cycle of the modulated voltage waveform. Some non-limiting examples of suitable CPWM techniques include sine PWM, third harmonic injection PWM, and classical space vector PWM. Likewise, DPWM is defined herein as a PWM technique where each phase leg of the TPIM  24  is not switched over the full 360° cycle of the modulated waveform. For example, each phase leg of the TPIM  24  cannot be switched for four 30°, two 60°, or one 120° segment of the 360° cycle of the modulated voltage waveform. Some examples of suitable DPWM techniques include, but are not limited to, generalized DPWM (GDPWM), DPWM 0 , DPWM 1 , DPWM 2 , DPWM 3 , DPWMMIN, and DPWMMAX, as these terms are well understood in the art. 
         [0029]    Referring to  FIG. 3 , a torque/speed chart  65  plots commanded output torque of the traction motor  12  shown in  FIG. 1  on the vertical axis  60  and motor output speed on the horizontal axis  70 . The controller  40  of  FIG. 1  references a calibrated torque threshold (line  52 ). Above the calibrated torque threshold (line  52 ), i.e., shaded area  80 , the controller  40  automatically selects the CPWM mode to control the TPIM  24 . Below the calibrated torque threshold (line  52 ), i.e., area  90 , the controller  40  automatically selects the DPWM mode to control the TPIM  24 . 
         [0030]    The controller  40  may also apply a hysteresis band or zone  55 . The hysteresis zone  55  is defined by the calibrated torque threshold (line  52 ) and a calibrated hysteresis line  152 . When motor output torque is rising rapidly, the controller  40  may transition to CPWM when the commanded torque exceeds the torque threshold (line  52 ). However, when motor output torque is decreasing from above the torque threshold (line  52 ), the controller  40  may instead use the hysteresis line  152  as the level at which DPWM is selected. In one possible embodiment, the hysteresis line  152  may be set at approximately 90% of the level of the torque threshold (line  52 ), e.g., a torque threshold of 200 Nm and a hysteresis level of 180 Nm, although a larger or smaller hysteresis zone may also be used within the scope of the present invention. 
         [0031]    Referring to  FIG. 4 , one possible embodiment of the present method  100  is described with reference to the structure of  FIG. 1 . Beginning at step  102 , the controller  40  determines the commanded motor output torque of the traction motor  12 . Step  102  may include referencing the present transmission operating mode, and/or processing a driver&#39;s torque request such as an apply rate and/or travel of an accelerator pedal. Once the commanded motor output torque is known, the controller  40  proceeds to step  104 . 
         [0032]    At step  104 , the controller  40  compares the commanded motor output torque from step  102  to the calibrated torque threshold (line  52 ), or alternatively to the hysteresis line  152  if such an embodiment is used. If the commanded motor output torque exceeds the calibrated torque threshold (line  52 ), the controller  40  proceeds to step  106 . If the commanded motor output torque is less than the calibrated torque threshold (line  52 ), the controller  40  proceeds instead to step  108 . 
         [0033]    At step  106 , the controller  40  automatically executes a predetermined CPWM technique as explained above. Step  106  includes transmitting, from the controller  40 , the PWM signal (arrow  11 ) to the TPIM  24 , with the PWM signal in this instance being a CPWM signal. The controller  40  then repeats step  104  to determine if CPWM is still required. 
         [0034]    At step  108 , the controller  40  automatically executes a predetermined DPWM technique as explained above. Step  108  includes transmitting, from the controller  40 , the PWM signal (arrow  11 ) to the TPIM  24 , with the PWM signal in this instance being a DPWM signal. The controller  40  repeats step  104  to determine if DPWM is still required. Thus, the selection of a PWM strategy is dependent on the commanded motor output torque or, in other embodiments, another predetermined vehicle operating condition of the electric drive system. The present approach may provide a balance between low distortion, torque ripple, and high efficiency. 
         [0035]    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.