Patent Publication Number: US-11381186-B2

Title: Motor drive device, electric oil pump, and method for detecting failure of motor drive device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is the U.S. national stage of application No. PCT/JP2019/031058, filed on Aug. 7, 2019, and priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Patent Application No. 2018-149094, filed on Aug. 8, 2018. 
     FIELD OF THE INVENTION 
     The present invention relates to a motor drive device, an electric oil pump, and a method for detecting a failure of a motor drive device. 
     BACKGROUND 
     In recent years, automobiles having an automatic driving function, electric automobiles, and the like are growing popular. In such vehicles, so-called electrification is progressing, and motors, electric pumps, and the like are used instead of hydraulic mechanisms. 
     An electric pump is mounted on a vehicle such as an automobile, and is used, for example, to circulate a refrigerant used for cooling an engine, a drive motor, or the like. An electric pump or the like may be required to have a redundant function for allowing a vehicle to travel even if it fails due to some factor. When a failure occurs, it is conceivable to detect the failure, disconnect the relevant part, and replace the function of the failed part with another element. 
     However, failure detection requires various sensors, which may lead to complicated structure and an increase in cost. 
     SUMMARY 
     A motor drive device according to an exemplary embodiment of the present invention includes a motor having a rotor and a stator, an inverter electrically connected to the motor, and a control device for controlling the inverter, wherein the control device includes: an impedance observer that estimates at least an amount of variation in impedance of the motor on the basis of a voltage command value, a current command value, and an actual current flowing between the inverter and the motor; a comparator that calculates the difference between the current command value and the actual current flowing between the inverter and the motor; and a failure detection unit that outputs a failure flag when the amount of variation in impedance exceeds or falls below a predetermined threshold, or when the difference calculated by the comparator exceeds or falls below a predetermined threshold. 
     A method for detecting a failure of a motor drive device according to an exemplary embodiment of the present invention includes: estimating, on the basis of a voltage command value, a current command value, and an actual current flowing between an inverter and a motor, at least an amount of variation in impedance of the motor by an impedance observer; calculating a difference between the current command value and the actual current flowing between the inverter and the motor by a comparator; and outputting, by a failure detection unit, a failure flag when the amount of variation in impedance exceeds or falls below a predetermined threshold, or when the difference calculated by the comparator exceeds or falls below a predetermined threshold. 
     The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a control device according to the present embodiment; 
         FIG. 2  is a block diagram showing a configuration of a failure detection system using a difference in current in the present embodiment; 
         FIG. 3  is a block diagram showing a failure detection system using a difference in impedance in the present embodiment; and 
         FIG. 4  is a block diagram showing a configuration of a control system according to a modification of the present embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Motor control according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Note that the scope of the present invention is not limited to the embodiment described below, but includes any modification thereof within the scope of the technical idea of the present invention. 
       FIG. 1  is an example of a block diagram showing the configuration of a control device  1 . The control device  1  according to the embodiment of the present invention shown in  FIG. 1  includes an inverter  10 , a torque-current command converter  20 , a three-phase current-voltage command converter  30 , an impedance observer  40 , a difference device  50 , and a failure detection unit  60 . The torque-current command converter  20 , the three-phase current-voltage command converter  30 , the impedance observer  40 , the difference device  50 , and the failure detection unit  60  are installed in a microcomputer  100  as a motor control device. Further, the microcomputer  100  outputs a signal for controlling the inverter  10  and controls the drive of a motor  200  on the basis of the signal. 
     In the present embodiment, the motor drive device includes the motor  200  and the control device  1 . The motor  200  has a stator and a rotor that can rotate relative to the stator. The motor drive device according to the present embodiment is used, for example, in an electric oil pump. Note that the motor drive device may be used for applications other than the electric oil pump. 
     An angle sensor  210  is attached to the motor  200 . The angle sensor  210  detects the rotation angle of the rotor. The angle sensor  210  may be, for example, a combination of a magnetoresistive element and a sensor magnet, or a Hall element (including a Hall IC). Note that the angle sensor may detect the rotation speed of the rotor instead of the rotation angle of the rotor. 
     The inverter  10  has a plurality of switching elements. The inverter  10  is electrically connected to the stator. In the inverter  10  in the present embodiment, a metal-oxide semiconductor field-effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), or the like is used, for example, as the switching element (field effect transistor (FET)). In the present embodiment, the motor  200  is a three-phase motor. Therefore, the inverter  10  in the present embodiment has six FETs. 
     A current sensor  220  is further connected to the inverter  10 . In the present embodiment, one or more shunt resistors are used as the current sensor  220 . In the present embodiment, a current is detected from one shunt resistor. Note that, as the current sensor  220 , a so-called three-shunt resistor may be used, or a sensor other than the shunt resistor may be used. 
     A torque command value T* is given to the control device  1  as an input. The torque command value T* is obtained such that a torque detected by the torque sensor  230  is treated with a filter (not shown), and then, input as an assist torque. 
     The input torque command value T* is input to the torque-current command converter  20 . The torque-current command converter  20  performs a process of integrating a torque constant as a gain for the torque command value T*, and converts the torque command value into three-phase current command values I a *, I b *, and I c *. 
     The current command value I* is output from the torque-current command converter  20  and input to the three-phase current-voltage command converter  30  as a signal. The three-phase current-voltage command converter  30  converts the current command value I* into a predetermined voltage command value V* by inverse conversion of the voltage equation. The voltage command value V* is output from the three-phase current-voltage command converter  30 , converted to duty, and then input to the inverter  10  as a control signal. Further, the voltage command value V* is output from the three-phase current-voltage command converter  30  and also input to the impedance observer  40  as a signal. 
     The inverter  10  generates an ON/OFF control signal (PWM control) for each switching element in a predetermined switching pattern on the basis of the voltage command value V*, and applies a predetermined voltage and current to the motor  200 . 
     An actual current I given from the inverter  10  to the motor  200  is detected by the abovementioned current sensor  220  for each of the three phases (U phase, V phase, W phase). The detected three-phase actual currents I a , I b , and I c  are input to the impedance observer  40  as signals. 
     The impedance observer  40  can estimate an amount of variation ΔR in impedance in the motor drive device for each phase on the basis of the actual current I and the voltage command value V*. Here, the impedance observer  40  is, for example, a disturbance observer based on an inverse model of the control model of the motor in the present embodiment. However, the impedance observer  40  may be an observer other than the disturbance observer. Further, the impedance observer  40  can calculate an actual voltage V (actual three-phase voltage) by the following Equation 1 on the basis of the actual current I. 
     
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       
                         ( 
                         
                           
                             R 
                             th 
                           
                           + 
                           
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               R 
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                             L 
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                               d 
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                       ⁢ 
                       I 
                     
                     - 
                     EMF 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
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     In Equation 1, R th  is an impedance of the motor, ΔR th  is an impedance error of the motor, and L is an inductance. EMF is a back electromotive force. 
     The amount of variation ΔR th  in impedance for each phase is fed back to the three-phase current-voltage command converter  30 . The three-phase current-voltage command converter  30  outputs voltage command values V a *, V b *, and V c * for each phase using the following Equation 2 on the basis of the fed-back amount of variation ΔR th  in impedance for each phase, the current command value I*, and the actual voltage V. 
     
       
         
           
             
               
                 
                   
                     
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     ΔR tha , ΔR thb , and ΔR thc  shown in Equation 2 include an amount of variation in impedance due to temperature and an amount of variation due to failure. Meanwhile, in electric oil pumps, the temperature of oil, which is a refrigerant, is often measured. In that case, the measured oil temperature is the same as the motor coil temperature and the drive circuit temperature because of temperature equilibration. Therefore, it is desirable that values obtained by eliminating an amount of variation in impedance due to temperature using the measured oil temperature are used as ΔR tha , ΔR thb , and ΔR thc . 
     The actual current I detected by the current sensor  220  and the current command value I* output from the torque-current command converter  20  are input to the difference device  50 . The difference device  50  calculates a difference ΔI between the actual current I and the current command value I*. 
     The difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance are input to the failure detection unit  60  as signals. The failure detection unit  60  can determine failures (failure in duty, failure in the shunt resistor, failure in the FET of the inverter, failure in the angle sensor, failure in the motor structure, etc.) on the basis of the difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance. 
     For example, a failure in duty, a failure in the shunt resistor, and a failure in the FET of the inverter can be determined using the amount of variation ΔR in impedance and the difference ΔI between the actual current I and the current command value I*. Regarding the failure in duty, the failure is determined by cumulatively adding the difference ΔI between the actual current I and the current command value I*. Further, the failure in the angle sensor can be determined on the basis of the difference ΔI between the actual current I and the current command value I*. A failure due to variation in impedance in the motor drive device can be determined on the basis of the amount of variation ΔR in impedance. 
     Furthermore, since the failure occurs independently for each electrical and electronic component, the ΔR generated due to the failure changes only in one of the ΔR tha , ΔR thb , and ΔR thc . Therefore, one phase showing a variation having a predetermined amount or more is extracted by majority vote, whereby the accuracy of failure detection can be improved. 
     Note that the failure detection unit  60  may determine the failure using not only the difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance but also an output value of the angle sensor  210 . 
     Further, in the present embodiment, the output of the torque-current command converter  20  and the output of the three-phase current-voltage command converter  30  are fed forward to the impedance observer  40 , the difference device  50 , and the like, respectively. That is, the torque-current command converter  20  and the three-phase current-voltage command converter  30  constitute a feedforward control system. 
     Next, a logic of failure detection using the difference ΔI between the actual current I and the current command value I* in the failure detection unit  60  will be described.  FIG. 2  is a block diagram showing a configuration of a failure detection system using the difference ΔI between the actual current I and the current command value I*. First, three-phase two-axis conversion is performed for the actual current I and the current command value I* on the basis of the rotation angle (electric angle) of the rotor detected by the angle sensor  210 . The two axes herein are so-called d-q synchronous coordinate systems. The magnetic flux (N pole) direction of a permanent magnet of the rotor is defined as a d-axis, and the direction 90 degrees forward from the d-axis in the positive direction at an angle θ is defined as a q-axis. The angle θ herein means what is represented by an electric angle. 
     As described above, the actual current I is detected by the current sensor  220  or the like. The detected actual current I is subjected to three-phase two-axis conversion on the basis of the rotation angle (electric angle) of the rotor detected by the angle sensor  210 . 
     The value of actual current I CNV  and the current command value I CNV * which have been subjected to three-phase two-axis conversion are compared, and a failure is determined on the basis of the comparison result. When it is determined that there is a failure, the failure detection unit  60  outputs a failure flag  70  (signal). For example, the failure detection unit  60  calculates the difference ΔI between the value of the actual current I and the current command value I* which have been subjected to three-phase two-axis conversion for each of the d-axis and the q-axis. Subsequently, the difference value ΔI T  which is a target value of ΔI and the actual difference value ΔI A  are obtained for each of the d-axis and the q-axis. Then, the difference between ΔI T  and ΔI A  of each axis is added. When the added value with the above method exceeds (or falls below) a predetermined threshold, it is determined that a failure occurs. The control device  1  stops the drive of the motor  200 , for example, on the basis of the failure flag  70  output from the failure detection unit  60 . 
     Failure detection of the angle sensor  210  will be described as an example of failure detection using the difference ΔI in current between the actual current I and the current command value I*. 
     When the angle sensor  210  fails, control including the feedforward control described above is performed on the basis of the rotor position information output from the failed angle sensor  210 . In this case, there is a difference in current value between the actual current I when there is no failure and an actual current I B  when there is a failure. The difference ΔI is calculated for each of the d-axis and q-axis on the basis of the actual current I and the current command value I*. The difference value ΔI T  which is a target value of ΔI and the actual difference value ΔI A  are obtained for each of the d-axis and q-axis, and when a value obtained by adding the difference between ΔI T  and ΔI A  of each axis exceeds (or falls below) a predetermined threshold, it is determined that a failure occurs in the angle sensor, and a failure flag is output. 
     As shown in  FIG. 4 , a detection margin m may be added to the current command value I CNV * (indicated current) that has been subjected to three-phase two-axis conversion, the actual current I CNV  that has been subjected to three-phase two-axis conversion and the current command value added with the detection margin m (I CNV *+m) may be compared, and a failure of the angle sensor may be determined on the basis of the comparison result. The threshold can be made variable by using the detection margin m. 
     The difference value ΔI T , which is a target value of ΔI, and the actual difference value ΔI A  vary depending on the magnitude of the disturbance factor. The detection margin is used to vary a failure determination threshold in order to prevent false detection or detection failure due to changes in disturbance factors. Disturbance factors include power supply voltage, motor rotation speed, target torque, motor winding temperature, etc. 
     Next, a logic of failure detection using ΔR in the failure detection unit  60  will be described. 
     The impedance observer  40  calculates the difference between the three-phase voltage command values V a *, V b *, and V c * and the actual three-phase voltages V a , V b , and V c . The amount of variation ΔR in impedance is obtained by dividing the voltage difference ΔV by the current command value I* in Equation 2 on the basis of the differences between the three-phase voltage command values V a *, V b *, and V c * and the actual three-phase voltages V a , V b , and V c , and the three-phase current command values I a *, I b *, and I c *. 
     The calculated amount of variation ΔR in impedance is compared to a predetermined threshold, and a failure determination is performed on the basis of the comparison result. The failure detection unit  60  outputs the failure flag  70  (signal) when it is determined that a failure has occurred. 
     Impedance failure will be described as an example of failure determination using the amount of variation ΔR in impedance. 
     The stator includes a plurality of coils. Examples of impedance failures include disconnection of windings constituting the coil and deformation of a bus bar connected to the coil. 
     When such an impedance failure occurs, a difference between an impedance when there is no failure and an impedance when there is a failure, that is, an amount of variation ΔR in impedance, occurs. When the amount of variation ΔR in impedance exceeds (or falls below) a predetermined threshold, the failure detection unit  60  determines that a failure has occurred in the impedance, and outputs the failure flag  70 . 
     In the abovementioned failure determination, only one of the difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance is used. However, a failure of the motor drive device may be determined using both the difference ΔI in current between the actual current I and the current command value I* and the amount of variation ΔR in impedance. 
     For example, in a case where: there is an abnormality in the duty that is a control signal of the inverter  10 ; the current sensor has a failure; or the switching element (FET, etc.) of the inverter  10  has a failure, the actual current I, the actual voltage V, and the impedance R vary, compared to the case where there are no failures, and therefore, the difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance both vary. 
     Therefore, when the difference ΔI between the actual current I and the current command value I* exceeds (or falls below) the predetermined threshold, and when the amount of variation ΔR in impedance exceeds (or falls below) the predetermined threshold, at least one of the cases where there is an abnormality in the duty that is the control signal of the inverter  10 , the current sensor  220  has a failure, and the switching element (FET, etc.) of the inverter  10  has a failure occurs. That is, the failure detection unit  60  can determine these failures on the basis of both the current difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance, and output the failure flag. 
     In other words, the failure detection unit  60  can determine an abnormality in the duty, a failure in the current sensor, a failure in the switching element, a failure in the angle sensor, and a failure in impedance on the basis of at least one of the current difference ΔI between the actual current I and the current command value I* and the amount of variation ΔR in impedance. 
     The embodiment described above relates to motor control. However, the present invention may be used for electric power steering, electric pumps, other actuators, etc. that use the motor. 
     The features described in the present specification can be combined as appropriate as long as they are inconsistent with each other. 
     Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     While preferred embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.