Abstract:
A vehicle includes an electronic control unit configured to perform control of an inverter by switching a plurality of controls including: first PWM control of generating a first PWM signal of a plurality of switching elements by comparison of voltage commands of respective phases based on a torque command of a motor with a carrier voltage and switching the plurality of switching elements; and second PWM control of generating a second PWM signal of the plurality of switching elements based on a modulation factor of a voltage and a voltage phase based on the torque command and the number of pulses in a predetermined period of an electrical angle of the motor and switching the plurality of switching elements. The electronic control unit is configured to limit execution of the second PWM control when an abnormality occurs in at least one of the current sensor or the voltage sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Japanese Patent Application No. 2016-091163 filed on Apr. 28, 2016, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND 
     1. Technical Field 
       [0002]    The disclosure relates to a vehicle and more particularly to a vehicle including a motor, an inverter, and a battery. 
       2. Description of Related Art 
       [0003]    As such a type of vehicle, a vehicle which includes an electric motor and a power conversion device having an inverter circuit that drives the electric motor by switching a plurality of switching elements and in which pulse signals of the plurality of switching elements are generated based on the number of pulses in one electrical period of the electric motor and a modulation factor of a voltage and a voltage phase based on a torque command of the electric motor to switch the plurality of switching elements has been proposed (for example, see Japanese Patent Application Publication No. 2013-162660 (JP 2013-162660 A). In such a vehicle, loss reduction in a drive system including the power conversion device and the electric motor as a whole is achieved by generating pulse signals to minimize power loss of the power conversion device and the electric motor based on the number of pulses, the modulation factor, and the voltage phase. 
       SUMMARY 
       [0004]    However, in the technique of generating pulse signals and outputting the pulse signals to the power conversion device in the above-mentioned vehicle, a period in which the pulse signals are generated is longer and responsiveness (trackability of an operating point when a target operating point changes) of the electric motor is lower in comparison with a technique of generating pulse signals by comparison of voltage commands of respective phases of the electric motor with a carrier voltage and outputting the pulse signals to the power conversion device. Accordingly, when an abnormality occurs in a voltage sensor or a current sensor, an overcurrent or an overvoltage is likely to occur in the inverter. 
         [0005]    The disclosure provides a vehicle that can prevent an overcurrent or an overvoltage from occurring in an inverter. 
         [0006]    A vehicle according to a first aspect of the disclosure includes a motor configured to drive the vehicle, an inverter configured to drive the motor by switching a plurality of switching elements, a battery configured to exchange power with the motor via the inverter, a current sensor configured to detect a current which is applied to the motor, a voltage sensor configured to detect a voltage of power which is supplied to the inverter, and an electronic control unit. The electronic control unit is configured to perform a control of the inverter by switching a plurality of controls including: i) first PWM control of generating a first PWM signal of the plurality of switching elements by comparison of voltage commands of respective phases based on a torque command of the motor with a carrier voltage and switching the plurality of switching elements; and ii) second PWM control of generating a second PWM signal of the plurality of switching elements based on a modulation factor of a voltage and a voltage phase based on the torque command and the number of pulses in a predetermined period of an electrical angle of the motor and switching the plurality of switching elements. The electronic control unit is configured to limit execution of the second PWM control when an abnormality occurs in at least one of the current sensor or the voltage sensor. 
         [0007]    In the vehicle according to the aspect, the control of the inverter is performed by switching the plurality of controls including the first PWM control and the second PWM control. The first PWM control is control of generating a first PWM signal by comparison of the voltage commands of respective phases based on the torque command of the motor with the carrier voltage and switching the plurality of switching elements of the inverter. The second PWM control is control of generating a second PWM signal based on a modulation factor of a voltage and a voltage phase based on the torque command of the motor and the number of pulses in a predetermined period of an electrical angle of the motor and switching the plurality of switching elements of the inverter. When an abnormality occurs in at least one of a current sensor detecting a current applied to the motor or a voltage sensor detecting a voltage of power supplied to the inverter, execution of the second PWM control is limited. In the second PWM control, a period in which the pulse signals are generated is longer and responsiveness of the electric motor is lower in comparison with the first PWM control. Accordingly, when an abnormality occurs in the voltage sensor or the current sensor, an overcurrent or an overvoltage is likely to occur in the inverter. As a result, it is possible to prevent an overcurrent or an overvoltage from occurring in the inverter by limiting execution of the second PWM control when an abnormality occurs in the voltage sensor or the current sensor. Here, the “limiting of execution of the second PWM control” includes reduction of an execution range of the second PWM control or prohibition of the second PWM control. 
         [0008]    The vehicle according to the aspect may further include: a boost converter configured to boost a voltage of power from the battery and to supply the boosted voltage to the inverter; a second current sensor configured to detect a current flowing in the boost converter; and a second voltage sensor configured to detect a voltage of power supplied to the boost converter. The electronic control unit may be configured to limit execution of the second PWM control when an abnormality occurs in at least one of the second current sensor or the second voltage sensor. According to the aspect, it is possible to prevent an overcurrent or an overvoltage from occurring in the inverter in the vehicle according to the aspect including a boost converter. Here, the “limiting of execution of the second PWM control” may include an operation stop of the boost converter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0010]      FIG. 1  is a diagram schematically illustrating a configuration of an electric vehicle according to an embodiment of the disclosure; 
           [0011]      FIG. 2  is a diagram illustrating an example of a relationship between a target operating point of a motor and areas of first and second PWM controls;  FIG. 3  is a flowchart illustrating an example of a second PWM control permission determining routine which is performed by an electronic control unit according to the embodiment; and 
           [0012]      FIG. 4  is a diagram illustrating a configuration of a hybrid vehicle according to a modified example. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0013]    Hereinafter, an embodiment of the disclosure will be described with reference to an example. 
         [0014]      FIG. 1  is a diagram schematically illustrating a configuration of an electric vehicle  20  according to an embodiment of the disclosure. The electric vehicle  20  according to the embodiment includes a motor  32 , an inverter  34 , a battery  36 , a boost converter  40 , and an electronic control unit  50  as illustrated in the drawing. 
         [0015]    The motor  32  is constituted by a synchronous generator-motor and includes a rotor in which a permanent magnet is embedded and a stator on which a three-phase coil is wound. The rotor of the motor  32  is connected to a drive shaft  26  which is connected to driving wheels  22   a  and  22   b  via a differential gear  24 . 
         [0016]    The inverter  34  is connected to the motor  32  and is also connected to the boost converter  40  via a high-voltage power line  42 . The inverter  34  includes six transistors T 11  to T 16  and six diodes D 11  to D 16 . The transistors T 11  to T 16  are arranged as pairs of two transistors to serve as a source side and a sink side with respect to a positive bus bar and a negative bus bar of the high-voltage power line  42 . The six diodes D 11  to D 16  are connected in reverse parallel to the transistors T 11  to T 16 , respectively. The three-phase coil (a U phase, a V phase, and a W phase) of the motor  32  is connected to junction points between the transistors constituting the pairs of the transistors T 11  to T 16 . Accordingly, when a voltage is applied to the inverter  34 , a rotating magnetic field is formed in the three-phase coil and the motor  32  is rotationally driven by causing the electronic control unit  50  to adjust a ratio of ON-time of each pair of transistors T 11  to T 16 . Hereinafter, the transistors T 11  to T 13  may be referred to as an “upper arm” and the transistors T 14  to T 16  may be referred to as a “lower arm.” A smoothing capacitor  46  is connected to the positive bus bar and the negative bus bar of the high-voltage power line  42 . 
         [0017]    The battery  36  is constituted by, for example, a lithium ion secondary battery or a nickel hydrogen secondary battery and is connected to the boost converter  40  via a low-voltage power line  44 . A smoothing capacitor  48  is connected to a positive bus bar and a negative bus bar of the low-voltage power line  44 . 
         [0018]    The boost converter  40  is connected to the high-voltage power line  42  and the low-voltage power line  44 . The boost converter  40  includes two transistors T 31  and T 32 , two diodes D 31  and D 32 , and a reactor L. The transistor T 31  is connected to the positive bus bar of the high-voltage power line  42 . The transistor T 32  is connected to the transistor T 31  and the negative bus bars of the high-voltage power line  42  and the low-voltage power line  44 . The two diodes D 31  and D 32  are connected in reverse parallel to the transistors T 31  and T 32 , respectively. The reactor L is connected to a junction point between the transistors T 31  and T 32  and the positive bus bar of the low-voltage power line  44 . By causing the electronic control unit  50  to adjust a ratio of ON-time of the transistors T 31  and T 32 , the boost converter  40  supplies power of the low-voltage power line  44  to the high-voltage power line  42  with step-up of a voltage or supplies power of the high-voltage power line  42  to the low-voltage power line  44  with step-down of a voltage. 
         [0019]    The electronic control unit  50  is constituted as a microprocessor including a CPU  52 , and includes a ROM  54  storing a processing program, a RAM  56  temporarily storing data, and an input and output port in addition to the CPU  52 . 
         [0020]    Signals from various sensors are input to the electronic control unit  50  via the input port. Examples of the signals input to the electronic control unit  50  include a rotational position Om from a rotational position sensor  32   a  (for example, a resolver) that detects a rotational position of the rotor of the motor  32  and phase currents Iu and Iv from current sensors  32   u  and  32   v  that detect currents flowing in the phases of the motor  32 . Examples of the input signals further include a voltage VB from a voltage sensor  36   a  connected between terminals of the battery  36 , a current IB from a current sensor  36   b  connected to an output terminal of the battery  36  and a reactor current IL from a current sensor  37   b  connected to a reactor L. Examples of the input signals further include a voltage VH of the capacitor  46  (the high-voltage power line  42 ) from a voltage sensor  46   a  connected between terminals of the capacitor  46  and a voltage VL of the capacitor  48  (the low-voltage power line  44 ) from a voltage sensor  48   a  connected between terminals of the capacitor  48 . Examples of the input signals further include an ignition signal from an ignition switch  60 , a shift position SP from a shift position sensor  62  that detects an operation position of a shift lever  61 , an accelerator opening Acc from an accelerator pedal position sensor  64  that detects a degree of stepping on an accelerator pedal  63 , and a brake pedal position BP from a brake pedal position sensor  66  that detects a degree of stepping on a brake pedal  65 . Examples of the input signals further include a vehicle speed VS from a vehicle speed sensor  68 . 
         [0021]    Various control signals are output from the electronic control unit  50  via the output port. Examples of the signal output from the electronic control unit  50  include switching control signals to the transistors T 11  to T 16  of the inverter  34  and switching control signals to the transistors T 31  and T 32  of the boost converter  40 . 
         [0022]    The electronic control unit  50  computes an electrical angle θe and a rotation speed Nm of the motor  32  based on the rotational position θm of the rotor of the motor  32  from the rotational position sensor  32   a.  The electronic control unit  50  computes a state of charge (SOC) of the battery  36  based on an integrated value of the current IB of the battery  36  from the current sensor  36   b.  Here, the SOC is a ratio of power capacity dischargeable from the battery  36  to the total capacity of the battery  36 . 
         [0023]    In the electric vehicle  20  according to the embodiment having the above-mentioned configuration, the electronic control unit  50  performs the following travel control. In the travel control, a required torque Td* required for a drive shaft  26  is set based on the accelerator opening Acc and the vehicle speed VS, the set required torque Td* is set as a torque command Tm* of the motor  32 , and switching control of the transistors T 11  to T 16  of the inverter  34  is performed to drive the motor  32  in accordance with the torque command Tm*. A target voltage VH* of the high-voltage power line  42  is set to drive the motor  32  in accordance with the torque command Tm* and switching control of the transistors T 31  and T 32  of the boost converter  40  is performed such that the voltage VH of the high-voltage power line  42  reaches the target voltage VH*. 
         [0024]    Control of the inverter  34  will be described below. In the embodiment, as the control of the inverter  34 , any one of sinusoidal pulse width modulation (PWM) control, overmodulation PWM control, and rectangular wave control is performed. The sinusoidal PWM control is control of controlling the inverter  34  to apply (supply) a pseudo three-phase 
         [0025]    AC voltage to the motor  32 , the overmodulation PWM control is control of controlling the inverter  34  to apply an overmodulation voltage to the motor  32 , and the rectangular wave control is control of controlling the inverter  34  to apply a rectangular wave voltage to the motor  32 . When the sinusoidal PWM control is performed and a pulse width modulation voltage based on a sinusoidal wave voltage is used as the pseudo three-phase AC voltage, a modulation factor Rm has a value ranging from 0 to about 0.61. When a pulse width modulation voltage based on a superimposed voltage acquired by superimposing 3n-th (for example, third) harmonic voltages on the sinusoidal wave voltage is used as the pseudo three-phase AC voltage, the modulation factor Rm has a value ranging from 0 to about 0.71. The modulation factor Rm is a ratio of an effective value of an output voltage of the inverter  34  (a voltage applied to the motor  32 ) to an input voltage (the voltage VH of the high-voltage power line  42 ). In the embodiment, in order to enlarge the range of the modulation factor 
         [0026]    Rm in which the sinusoidal PWM control can be performed, it is assumed that the pulse width modulation voltage based on the superimposed voltage is used as the pseudo three-phase AC voltages. When the rectangular wave control is performed, the modulation factor Rm has a value of about 0.78. In the embodiment, in consideration thereof, it is assumed that any one of the sinusoidal PWM control, the overmodulation PWM control, and the rectangular wave control is performed based on the modulation factor Rm. The sinusoidal PWM control will be described below. Neither overmodulation control nor rectangular wave control is essential to the disclosure and thus detailed description thereof will not be made. 
         [0027]    In the embodiment, first PWM control or second PWM control is performed as the sinusoidal PWM control. The first PWM control is control of generating a first PWM signal of the transistors T 11  to T 16  to switch the transistors T 11  to T 16  by comparing voltage commands Vu*, Vv*, and Vw* of the phases of the motor  32  with a carrier voltage (a triangular wave voltage). The second PWM control is control of generating a second PWM signal of the transistors T 11  to T 16  based on the modulation factor Rm of a voltage, a voltage phase θp, and the number of pulses Np in a predetermined period (for example, half a period or one period of an electrical angle θe of the motor  32 ) to switch the transistors T 11  to T 16 . It is assumed that the first PWM signal is generated at an interval Δt1 corresponding to half a period or one period of the carrier voltage (a triangular wave voltage with a frequency of 3 kHz to 5 kHz) when the first PWM control is performed, and the second PWM signal is generated at an interval Δt2 longer than the interval Δt1 when the second PWM control is performed. 
         [0028]    When the first PWM control is performed, the generation period of the PWM signal can be set to be shorter than when the second PWM control is performed, and thus the responsiveness (adherence to an operating point when a target operating point changes) of the motor  32  can be improved. When the second PWM control is performed, it is possible to reduce a core loss of the motor  32  or to reduce harmonic component by generating the second PWM signal to reduce (for example, to minimize) the core loss of the motor  32  or generating the second PWM signal to reduce (for example, to minimize) harmonic component of a voltage or a current (particularly, low-order harmonic component such as rotational sixth harmonic component and rotational twelfth harmonic component of the motor  32 ), in comparison with the case in which the first PWM control is performed. 
         [0029]    In the embodiment, it is assumed that an area in which an effect of execution of second PWM control can be expected to a certain extent is determined as a second PWM control area and an area in which the effect cannot be expected to the certain extent is determined as a first PWM control area to improve responsiveness of a motor  32 , based on an experiment result or an analysis result of performing the first PWM control and the second PWM control on target operating points of the motor  32 .  FIG. 2  is a diagram illustrating an example of a relationship between the target operating points of the motor  32  and the first PWM control area and the second PWM control area. In the example illustrated in  FIG. 2 , an area (Area  1 ) in which a rotation speed Nm of the motor 32 ranges from 1000 rpm to 3500 rpm, and either a torque command Tm* thereof is equal to or greater than 10 Nm or the torque command Tm* ranges from −100 Nm to −10 Nm, an area (Area  2 ) in which the rotation speed Nm of the motor  32  ranges from 3500 rpm to 6000 rpm, and either the torque command Tm* ranges from 10 Nm to 150 Nm or the torque command Tm* ranges from −100 Nm to −10 Nm, an area (Area  3 ) in which the rotation speed Nm of the motor  32  ranges from 3500 rpm to 6000 rpm, and either the torque command Tm* is equal to or greater than 150 Nm, an area (Area  4 ) in which the rotation speed Nm of the motor  32  ranges from 6000 rpm to 9000 rpm, and either the torque command Tm* ranges from 10 Nm to 100 Nm or the torque command Tm* ranges from −50 Nm to −10 Nm, and an area (Area  5 ) in which the rotation speed Nm of the motor  32  ranges from 6000 rpm to 9000 rpm, and either the torque command Tm* ranges from 100 Nm to 150 Nm or the torque command Tm* ranges from −100 Nm to −50 Nm are set as the second PWM control area. An area other than the second PWM control area is set as the first PWM control area. Here, the areas have different numbers of pulses in the second PWM control area. 
         [0030]    An operation of an electric vehicle  20  according to the embodiment having the above-mentioned configuration, particularly, an operation when an abnormality occurs in current sensors  32   u  and  32   v  detecting phase currents Iu and Iv flowing in the motor  32  or a voltage sensor  46   a  detecting a voltage VH of a high-voltage power line  42 , will be described below.  FIG. 3  is a flowchart illustrating an example of a second PWM control permission determining routine which is performed by an electronic control unit  50  according to the embodiment. This routine is repeatedly performed. 
         [0031]    When the second PWM control permission determining routine is performed, the electronic control unit  50  first determines whether an abnormality occurs in any of the current sensors  32   u  and  32   v  detecting phase currents Iu and Iv flowing in the motor  32  and the voltage sensor  46   a  detecting a voltage VH of a high-voltage power line  42  (Step S 100 ). This determination can be performed, for example, by storing a determination result of whether an abnormality (malfunction) occurs in a sensor through an abnormality determining routine which is not illustrated in a predetermined area of a RAM  56  for each sensor and checking whether an abnormality occurs in each sensor in the predetermined area of the RAM  56 . 
         [0032]    When no abnormality occurs in any of the current sensors  32   u  and  32   v  and the voltage sensor  46   a,  the second PWM control is permitted (Step S 110 ) and the routine ends. In this case, the first PWM control and the second PWM control are switched and performed based on the areas illustrated in  FIG. 2 . 
         [0033]    On the other hand, when an abnormality occurs in any of the current sensors  32   u  and  32   v  and the voltage sensor  46   a,  execution of the second PWM control is prohibited (Step S 120 ) and the routine ends. In this case, when the second PWM control is executed, execution of the second PWM control can be switched to execution of the first PWM control. As described above, in the second PWM control, a period in which pulse signals are generated is longer and the responsiveness of the motor  32  is lower. Accordingly, when an abnormality occurs in any one of the current sensors  32   u  and  32   v  and the voltage sensor  46   a,  an overcurrent or an overvoltage is likely to occur in the inverter  34 . However, it is possible to improve the responsiveness of the motor  32  and to prevent an overcurrent or an overvoltage from occurring in the inverter  34  by prohibiting execution of the second PWM control and executing the first PWM control. 
         [0034]    In the above-mentioned electric vehicle  20  according to the embodiment, when an abnormality occurs in any of the current sensors  32   u  and  32   v  detecting phase currents Iu and Iv flowing in the motor  32  and the voltage sensor  46   a  detecting the voltage VH of the high-voltage power line  42 , execution of the second PWM control is prohibited. Accordingly, it is possible to prevent an overcurrent or an overvoltage from occurring in the inverter  34 . 
         [0035]    In the electric vehicle  20  according to the embodiment, when an abnormality occurs in any of the current sensors  32   u  and  32   v  detecting phase currents Iu and Iv flowing in the motor  32  and the voltage sensor  46   a  detecting the voltage VH of the high-voltage power line  42 , execution of the second PWM control is prohibited, but execution of the second PWM control may be limited. For example, execution of the second PWM control in the area other than Area  1  in the second PWM control area illustrated in  FIG. 2  may be prohibited or execution of the second PWM control in a case other than the case in which the electric vehicle cruises and travels in the second PWM control area may be prohibited. In this case, when an abnormality occurs in one of the current sensors  32   u  and  32   v  and the second PWM control is executed, a phase current may be estimated from the detected value of a current sensor in which no abnormality occurs. When an abnormality occurs in the voltage sensor  46   a,  the boost converter  40  stops its operation and a voltage VL of a low-voltage power line  44  can be used as a voltage of power supplied to the inverter  34 . In the latter, prohibition of the boost converter  40  from being operated corresponds to the limiting of execution of the second PWM control. 
         [0036]    In the electric vehicle  20  according to the embodiment, when an abnormality occurs in any of the current sensors  32   u  and  32   v  detecting phase currents Iu and Iv flowing in the motor  32  and the voltage sensor  46   a  detecting the voltage VH of the high-voltage power line  42 , execution of the second PWM control is prohibited, but when an abnormality occurs in any one of a current sensor  37   b  detecting a reactor current IL flowing in a reactor L or a voltage sensor  48   a  detecting a voltage VL of a low-voltage power line  44 , execution of the second PWM control may be prohibited or execution of the second PWM control may be limited. 
         [0037]    In the electric vehicle  20  according to the embodiment, the boost converter  40  is disposed between the battery  36  and the inverter  34 , but the boost converter  40  may not be disposed. 
         [0038]    In the electric vehicle  20  according to the embodiment, a configuration including the motor  32 , the inverter  34 , and the battery  36  is employed. However, as illustrated in a hybrid vehicle  120  according to a modified example of  FIG. 4 , a configuration including an engine  122 , a planetary gear  124 , a motor  132 , and an inverter  134  in addition to the motor  32  and the inverter  34  may be employed. Here, the motor  132  is connected to a sun gear of the planetary gear  124 , the engine  122  is connected to a carrier thereof, and the drive shaft  26  and the motor  32  are connected to a ring gear thereof The inverter  134  is connected to the motor  132  and is also connected to the high-voltage power line  42 . 
         [0039]    In the embodiment, the motor  32  serves as the “motor,” the inverter  34  serves as the “inverter,” the battery  36  serves as the “battery,” the current sensors  32   u  and  32   v  serve as the “current sensor,” the voltage sensor  46   a  serves as the “voltage sensor,” and the electronic control unit  50  serves as the “control unit.” The current sensor  37   b  serves as the “second current sensor,” and the voltage sensor  48   a  serves as the “second voltage sensor.” 
         [0040]    While aspects of the disclosure have been described with reference to the embodiment, the embodiment is only a specific example of the disclosure. The disclosure is not limited to the embodiment, and can be modified in various forms without departing from the scope of the disclosure. 
         [0041]    The disclosure is applicable to the industry of manufacturing vehicles.