Electric vehicle and diagnostic method for electric vehicle

Abstract

The present invention is an electric vehicle, comprising: a motor for driving; an inverter for supplying AC current to the motor; three current sensors for measuring the current of each phase of the three-phase AC current output by the inverter; and a controller for controlling the motor through the inverter. The controller is configured to set the d-axis voltage command value to zero and the q-axis voltage command value to non-zero to control the motor when one of the current sensors cannot be used, and at the same time determine the current sensor that cannot be used.

Description

Technical Field

[0001] The technology disclosed in this specification relates to an electric vehicle having a motor for driving and a diagnostic method for the electric vehicle. In particular, it relates to an electric vehicle having three current sensors for measuring three-phase alternating current supplied to the motor, and to a technology for preventing the motor from generating useless torque when determining that a current sensor cannot be used. The "electric vehicle" in this specification includes a hybrid vehicle and a fuel cell vehicle having both a motor and an engine. Background Art

[0002] An electric vehicle has a three-phase AC motor as a driving motor and an inverter that converts power from a DC power source into a three-phase AC. Hereinafter, for simplicity of description, the three-phase AC motor is simply referred to as a motor.

[0003] Current feedback is essential for accurately controlling the motor used for driving. The sum of the three-phase AC is always zero, so if the current of two of the three phases can be measured, three-phase current feedback can be achieved. However, in order to detect the failure of the current sensor, ordinary electric vehicles have three current sensors that can measure all three-phase AC currents.

[0004] In the motor control device (control device for the motor of an electric vehicle) disclosed in Japanese Patent Laid-Open No. 2018-113734, a technology for identifying a faulty current sensor and continuing three-phase feedback control using the remaining two normal current sensors is disclosed. The technology for discovering a faulty current sensor is exemplified in Japanese Patent Laid-Open No. 2004-96933. Summary of the invention

[0005] In order to determine the current sensor that cannot be used, it is necessary to flow current through each phase and obtain the measurement value of each current sensor. In the case of an abnormality in the current sensor (or the signal line and / or the power line) during driving, when the current flows unplanned to determine the current sensor that cannot be used, it may cause the motor to output useless torque. The torque that the driver does not expect will cause discomfort to the driver. This specification provides a technology that prevents the motor from generating useless torque when one of the three current sensors used for current feedback cannot be used and the unusable current sensor is determined.

[0006] Even if the current sensor itself does not fail, if the signal line connecting the current sensor to the controller or the power line supplying power to the current sensor is disconnected, the current sensor cannot be used. In the following, the expression "failed current sensor" is replaced with the expression "unusable current sensor" in a broader sense.

[0007] The first mode of electric vehicle disclosed in this specification comprises: a motor for driving; an inverter for supplying alternating current to the motor; three current sensors for measuring the current of each phase of the three-phase alternating current output by the inverter; a controller for controlling the motor through the inverter, wherein the controller is configured to set the d-axis voltage command value to zero and the q-axis voltage command value to non-zero to control the motor when one of the current sensors cannot be used, and at the same time determine the current sensor that cannot be used. By setting the d-axis voltage command value to zero and the q-axis voltage command value to non-zero, current flows through the motor, but the motor does not generate torque. When the angular velocity of the motor is higher than the specified lower limit angular velocity, it is easy to achieve a state in which current flows through the motor but the motor does not generate torque by this method. The reason is explained in the embodiment.

[0008] In the above method, the controller is configured to control the motor in such a way that, when the angular velocity of the motor is lower than the specified lower angular velocity limit and one of the current sensors cannot be used, the d-axis voltage command value is set to zero and the q-axis voltage command value is set to non-zero, and the d-axis current becomes a positive value. Even if the torque generated by the motor is not strictly zero, the generated torque can be reduced. The reason is explained in the embodiment.

[0009] In the above aspect, the controller is configured to set the q-axis voltage command value to a value obtained by adding a product of the angular velocity of the motor and the strength of the magnetic field of the rotor of the motor to a constant greater than a predetermined positive lower limit constant.

[0010] In the above aspect, the controller is configured to determine that a certain current sensor cannot be used when the sum of the measurement values ​​of the three current sensors is not zero.

[0011] In the above-mentioned manner, the controller is configured to infer the third estimated value of the phase current of the third current sensor in the current sensor according to the first measured value of the first current sensor and the second measured value of the second current sensor in the current sensor. The inference can also be based on Kirchhoff's law. The controller is configured to determine that the first current sensor and the second current sensor are normal when the sum of the squares of the first measured value, the second measured value, and the third estimated value is equal to 3 / 2 of the square of the input current input to the inverter. The controller is configured to determine that one of the first current sensor and the second current sensor cannot be used when the sum of the squares of the first measured value, the second measured value, and the third estimated value is different from 3 / 2 of the square of the input current input to the inverter. By performing such a comparison on the measured values ​​of the current sensors of the u-phase and the v-phase and the measured values ​​of the current sensors of the u-phase and the w-phase, the current sensor that cannot be used can be determined.

[0012] The second diagnostic method disclosed in the present specification is a diagnostic method for an electric vehicle, wherein the electric vehicle comprises: a motor for driving; an inverter for supplying alternating current to the motor; three current sensors for measuring the current of each phase of the three-phase alternating current output by the inverter; and a controller for controlling the motor through the inverter, and when one of the current sensors cannot be used, the d-axis voltage command value is set to zero, and the q-axis voltage command value is set to non-zero to control the motor, and at the same time the current sensor that cannot be used is determined.

[0013] The controller is configured to, after being able to determine that the current sensor cannot be used, infer the current of the phase corresponding to the current sensor that cannot be used based on the measurement values ​​of the two current sensors that can be used, and restart the current feedback control. During the period when the current sensor that cannot be used is determined, the electric vehicle travels only by inertia, but after the current sensor that cannot be used is determined, the electric vehicle can output a torque corresponding to the accelerator opening. During the period when the current sensor that cannot be used is determined, the motor does not generate a torque that the driver does not expect, and does not cause discomfort to the driver.

[0014] Details and further improvements of the technology disclosed in this specification are described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like numerals denote like elements.

[0016] Figure 1 It is a block diagram of a driving system of an electric vehicle according to an embodiment.

[0017] Figure 2 is a flow chart of the motor control performed by the controller.

[0018] Figure 3 is a block diagram of the motor control performed by the controller.

[0019] Figure 4 This is a graph showing the relationship between the electrical phase angle of the current with respect to the q-axis and the output torque of the motor. DETAILED DESCRIPTION

[0020] An electric car 2 according to an embodiment will be described with reference to the drawings. Figure 1 A block diagram showing a drive system of an electric vehicle 2. The electric vehicle 2 includes a power source 3, an inverter 5, a motor 6 for driving, and a controller 20. The power source 3 is a lithium-ion battery capable of outputting power with a voltage of 100 volts or more. The motor 6 is a three-phase AC motor. The output power (DC power) of the power source 3 is converted into AC power by the inverter 5 and supplied to the motor 6. A capacitor 4 for suppressing pulsation of current (voltage) is connected between the power source 3 and the inverter 5.

[0021] The electric car 2 includes a voltage sensor 11 for measuring the voltage of the power source 3 and a current sensor 12 for measuring the output current of the power source 3. The measured values ​​of the voltage sensor 11 and the current sensor 12 are sent to a controller 20 described later.

[0022] The inverter 5 includes six switching elements 5a-5f. Two of the six switching elements 5a-5f are connected in series. Three groups are connected in series in parallel. Diodes are connected in reverse parallel to each switching element 5a-5f. The controller 20 controls the motor 6 through the inverter 5. In addition, a voltage converter can also be connected between the power supply 3 and the inverter 5.

[0023] The electric car 2 also has three current sensors 7 (7u, 7v, 7w). The current sensor 7 measures the three-phase AC flowing between the inverter 5 and the motor 6. The current sensor 7u measures the u-phase current. Similarly, the current sensor 7v (7w) measures the v-phase current (w-phase current). The measured values ​​of the current sensor 7 are also input to the controller 20.

[0024] The controller 20 includes a central processing unit 21 (CPU 21) and a memory 22. The memory 22 stores various data in addition to the programs executed by the CPU 21. The data stored in the memory 22 includes, for example, a map (or relational expression) for deriving a command value from a target torque of the motor 6.

[0025] The controller 20 is connected to the instrument panel 31. The controller 20 causes the instrument panel 31 to display the vehicle speed and the current state of the electric vehicle 2. When an abnormality occurs in the current sensor 7, the controller 20 causes the warning light of the instrument panel 31 to flash.

[0026] The controller 20 obtains the vehicle speed from the vehicle speed sensor 13. In addition, the controller 20 obtains the accelerator opening from the acceleration sensor 14. The motor 6 has an angle sensor 8. The controller 20 obtains the electrical angle and angular velocity of the motor 6 based on the measurement data of the angle sensor 8.

[0027] The controller 20 calculates the target torque of the motor 6 based on the measured values ​​of the vehicle speed sensor 13 and the acceleration sensor 14, and controls the inverter 5 (motor 6) in such a way that the output torque of the motor 6 follows the target torque. The controller 20 determines the current command value for the inverter 5 based on the target torque. The controller 20 determines the current command values ​​for the three phases respectively. The controller 20 implements feedback control using the measured values ​​of the current sensor 7 in such a way that the output current (three-phase AC) of the inverter 5 follows the corresponding current command values ​​respectively.

[0028] The current sensor 7 is further described. According to Kirchhoff's law, the sum of three-phase alternating current is always zero. Therefore, if two of the three-phase currents can be measured, the current of the remaining phase can be inferred. However, in order to cope with the failure of the current sensor 7, the electric vehicle 2 has a current sensor on each of the three phases, which can measure the current of all phases.

[0029] The controller 20 adds the measured values ​​of the three current sensors 7u, 7v, and 7w, and when the sum is not zero, determines that one of the three current sensors 7 is unusable. In addition, "the current sensor is unusable" means that, in addition to the current sensor failure, it also includes the disconnection of the signal line of the current sensor or the disconnection of the power supply line.

[0030] When the controller 20 determines that one of the three current sensors 7 is unusable, it identifies the unusable current sensor and estimates the current of the remaining phases based on the measured values ​​of the two normal current sensors. The controller 20 continues the current feedback control using the measured values ​​of the two normal current sensors and the current estimated value. While the unusable current sensor is identified, the controller 20 controls the inverter 5 in such a way that the motor 6 does not output torque in order to avoid causing discomfort to the driver.

[0031] Figure 2 The flowchart is a diagram showing the motor control executed by the controller 20. The controller 20 repeats the motor control in a fixed cycle. Figure 2First, the controller 20 checks the three current sensors 7 (step S2). As mentioned above, the controller 20 adds the measured values ​​of the three current sensors 7, and when the sum is not zero, it determines that a current sensor cannot be used. When the controller 20 determines that all the current sensors 7 can be used, it controls the motor 6 (inverter 5) through normal control (step S3: No, step S4). The specific processing of the normal control will be described later.

[0032] When the controller 20 determines that one of the current sensors 7 cannot be used, it flashes the warning light of the instrument panel 31 (step S3: yes, step S5). Then, the controller 20 starts zero torque control instead of normal control (step S6). Zero torque control means controlling the inverter 5 regardless of the accelerator opening so that the motor 6 does not output torque. The details of zero torque control will be described later.

[0033] While executing the zero torque control, the controller 20 determines the current sensor that cannot be used (step S7). When it is determined that the current sensor cannot be used, the controller 20 ends the zero torque control (step S8) and transfers to the avoidance travel control. The avoidance travel control refers to suppressing the upper limit output of the motor 6 while performing current feedback control using two current sensors that can be used. In the avoidance travel control, the controller 20 controls the instrument panel 31 to flash a warning light indicating that an abnormality has occurred in the travel control system, and displays a message strongly recommending that the vehicle be taken to a repair center as soon as possible.

[0034] It takes only a short time to determine that the current sensor cannot be used. Compared with outputting a torque that the driver does not expect in a short time, implementing zero torque control will cause less discomfort to the driver.

[0035] Figure 3 A block diagram showing motor control performed by the controller 20 . Figure 3 This is a diagram for easily understanding the motor control program, schematically showing the motor control. For example, the switch 211 indicates switching between normal control and zero torque control, but in fact, when the controller 20 switches from the program for normal control to the program for zero torque control, the normal control stops. In addition, Figure 3 The solid rectangles represent program modules.

[0036] The controller 20 includes a target torque module 201, a command voltage and current module 202, a subtractor 203, a feedback control module 204, an adder 205, an inverse dq conversion module 206, a PWM signal module 207, a current check module 208, a dq conversion module 209, a zero torque control module 210, and a switch 211. As described above, each module is implemented by the CPU 21 executing a program stored in the memory 22 of the controller 20.

[0037] The vehicle speed Vel measured by the vehicle speed sensor 13 and the accelerator opening Acc measured by the acceleration sensor 14 are input to the target torque module 201. The target torque module 201 determines the target torque Trc of the motor 6 based on the vehicle speed Vel and the accelerator opening Acc. A mapping (or a relational expression) that specifies the relationship between the vehicle speed Vel, the accelerator opening Acc, and the target torque Trc is stored in the memory 22 of the controller 20. The target torque module 201 refers to the mapping or uses the relational expression to determine the target torque Trc based on the measured vehicle speed Vel and the accelerator opening Acc.

[0038] The target torque Trc is sent to the command voltage and current module 202. The command voltage and current module determines the d-axis feedforward voltage Vdff, the q-axis feedforward voltage Vqff, the d-axis current command value Idc, and the q-axis current command value Iqc according to the target torque Trc. The d-axis feedforward voltage Vdff and the q-axis feedforward voltage Vqff are command voltages for making the output torque of the motor 6 quickly approach the target torque Trc. The d-axis current command value Idc and the q-axis current command value Iqc are used for feedback control of the current of the motor 6 obtained from the current sensor 7. The feedback control will be described later.

[0039] The electrical angle Ae of the motor 6 is also used for conversion to the d-axis feedforward voltage Vdff, the q-axis feedforward voltage Vqff, the d-axis current command value Idc, and the q-axis current command value Iqc according to the target torque Trc. The electrical angle Ae is obtained from the angle sensor 8 mounted on the motor 6. The relationship between the target torque Trc and the d-axis feedforward voltage Vdff, etc. is specified by a mapping (or a relational expression) that includes the electrical angle Ae in the parameter. The mapping (or relational expression) is also pre-stored in the memory 22. The command voltage and current module refers to the mapping (or relational expression) and determines the d-axis feedforward voltage Vdff, etc. according to the target torque Trc.

[0040] The d-axis current command value Idc (q-axis current command value Iqc) is sent to the subtractor 203. In the subtractor 203, the difference between the d-axis current command value Idc (q-axis current command value Iqc) and the actual d-axis current Idr (q-axis current Iqr) obtained from the measurement value of the current sensor 7 is calculated. This difference is used for feedback control.

[0041] The measured values ​​Ius, Ivs, and Iws of the three current sensors 7 (7u, 7v, and 7w) are input to the current inspection module 208. In the current inspection module, the measured values ​​Ius, Ivs, and Iws of the three current sensors 7 are added to obtain the total. When the total is zero, the current inspection module 208 determines that all current sensors can be used. At this time, the current inspection module 208 outputs the currents Iur, Ivr, and Iwr of each of the three phases. The currents Iur, Ivr, and Iwr correspond to the outputs of the current sensors 7u, 7v, and 7w, respectively. Alternatively, one of the three currents Iur, Ivr, and Iwr may be a value inferred from the remaining two. According to Kirchhoff's law, for example, the u-phase current Iur can be obtained using the formula "Iur = -(Ivr + Iwr)".

[0042] The currents Iur, Ivr, and Iwr of each of the three phases are input to the dq conversion module 209. The dq conversion module 209 converts the three-phase currents Iur, Ivr, and Iwr into d-axis current Idr and q-axis current Iqr using the electrical angle Ae of the motor 6. The conversion from the three-phase current to the d-axis and q-axis currents is well known, so the description is omitted.

[0043] As described above, in the subtractor 203, the difference between the d-axis current command value Idc and the d-axis current Idr and the difference between the q-axis current command value Iqc and the q-axis current Iqr are calculated. The obtained difference is input to the feedback control module 204. The feedback control module 204 determines the d-axis feedback voltage Vdfb and the q-axis feedback voltage Vqfb in such a way that the difference between the d-axis current command value Idc and the d-axis current Idr and the difference between the q-axis current command value Iqc and the q-axis current Iqr become smaller. The feedback control module 204 determines the d-axis feedback voltage Vdfb and the q-axis feedback voltage Vqfb according to a control rule such as P control, PI control or PID control.

[0044] The d-axis feedback voltage Vdfb (q-axis feedback voltage Vqfb) and the d-axis feedforward voltage Vdff (q-axis feedforward voltage Vqff) are added in the adder 205. As a result of the addition, the d-axis voltage command value Vdc and the q-axis voltage command value Vqc are obtained. The d-axis voltage command value Vdc and the q-axis voltage command value Vqc are converted into voltage command values ​​Vuc, Vvc, and Vwc of each of the three phases in the inverse dq conversion module 206. This conversion also refers to the electrical angle Ae.

[0045] The voltage command values ​​Vuc, Vvc, and Vwc of each phase are compared with the carrier signal in the PWM signal module 207 and converted into the switching elements ( Figure 1The output of the PWM signal module 207, i.e., the PWM signal, is sent to the upper arm switching elements 5a, 5c, and 5e of the inverter 5. The lower arm switching element (e.g., the switching element 5b) is supplied with a complementary signal to the PWM signal of the upper arm switching element 5a.

[0046] The above is the normal control. When all three current sensors 7 are usable, the d-axis and q-axis feedforward voltages Vdff and Vqff are determined according to the target torque Trc, and the output torque of the motor 6 quickly approaches the target torque Trc by controlling the inverter 5 according to these values. In addition, by performing feedback control corresponding to the difference between the d-axis current command value Idc (and the q-axis current command value Iqc) obtained according to the target torque Trc and the d-axis current Idr (and the q-axis current Iqr) obtained from the motor 6, the output torque of the motor 6 accurately follows the target torque Trc.

[0047] In addition, when the controller 20 adopts advance angle control, in the inverse dq conversion module 206, the d-axis voltage command value Vdc and the q-axis voltage V command value Vqc are converted into voltage command values ​​Vuc, Vvc, and Vwc of each of the three phases according to the angle obtained by adding the specified advance angle to the electrical angle Ae.

[0048] When the sum of the measured values ​​Ius, Ivs, and Iws of the three current sensors 7u, 7v, and 7w in the current check module 208 is not zero, the current check module 208 determines that one of the current sensors 7u, 7v, and 7w cannot be used. In this case, the current check module 208 controls the switch 211 to switch the input end of the inverse dq conversion module 206 from the adder 205 to the zero torque control module 210. The zero torque control module 210 outputs the d-axis voltage command value Vdc and the q-axis voltage command value Vqc in a manner that current flows through the motor 6 but no torque is output. That is, when one of the current sensors 7u, 7v, and 7w cannot be used, the controller 20 stops the normal control and transfers to the zero torque control.

[0049] The zero torque control module 210 expresses the d-axis voltage command value Vdc and the q-axis voltage command value Vqc as shown in the following (Equation 1).

[0050] [Formula 1]

[0051] Vdc=0,Vqc=Ce+W×PHI

[0052] Here, symbol W represents the angular velocity of the motor 6. Symbol Ce represents a positive constant. Constant Ce is greater than a predetermined positive lower limit constant Cmin. Symbol PHI represents the intensity of the magnetic field of the magnet of the rotor of the motor 6.

[0053] By controlling the motor 6 (inverter 5) according to the voltage command value of (Equation 1), the motor 6 rotates by inertia while not outputting torque. The motor 6 does not generate torque, but since the q-axis voltage command value Vqc is non-zero, current flows from the inverter 5 to the motor 6. The current flows through the motor 6, so the current sensor 7 outputs a certain measurement value. The current check module 208 determines that the current sensor cannot be used based on the measurement value of the current sensor 7.

[0054] First, the case where a current flows through the motor 6 but the motor 6 does not generate torque by adopting the voltage command value of (Formula 1) is described. The following relationships (Formula 2) and (Formula 3) are known between the d-axis voltage Vd, the q-axis voltage Vq and the d-axis current Id, the q-axis current Iq.

[0055] [Formula 2]

[0056] Vd=R×Id-W×Lq×Iq

[0057] [Formula 3]

[0058] Vq=R×Iq+W×Ld×Id+W×PHI

[0059] In (Formula 2) and (Formula 3), symbol R represents the resistance of the coil of the stator of the motor 6. Symbol W represents the angular velocity of the rotor of the motor 6. Symbols Ld and Lq represent the inductance of the d-axis and q-axis of the rotor. Symbol PHI represents the strength of the magnetic field of the permanent magnet of the rotor.

[0060] During the running of the electric vehicle 2, the angular velocity W is a positive value. If the angular velocity W is large, in other words, if the resistance R<<angular velocity W, the second term on the right side of (Equation 2) is significantly larger than the first term on the right side, and the first term on the right side can be ignored. In this case, when the d-axis voltage command value Vdc is set to zero to control the motor 6, the q-axis current Iq becomes zero.

[0061] On the other hand, the output torque Trq of the motor 6 is expressed by the following equation (Equation 4).

[0062] [Formula 4]

[0063] Trq=Pn×PHI×Iq+(Ld-Lq)×Id×Iq

[0064] In (Formula 4), the symbol Pn represents the number of magnetic poles of the rotor. The other symbols are as described above.

[0065] As can be seen from (Equation 4), if the q-axis current Iq is zero, the output torque Trq of the motor 6 also becomes zero. When the d-axis voltage command value is set to zero and the q-axis voltage command value is set to non-zero to control the motor 6 (inverter 5), a state in which current flows through the motor 6 but no torque is output can be achieved.

[0066] In the above description, the premise is that the resistance R is sufficiently smaller than the angular velocity W. This condition corresponds to the case where the angular velocity W of the motor 6 is greater than a predetermined lower limit angular velocity Wmin. The lower limit angular velocity Wmin is predetermined based on the performance of the motor 6 .

[0067] When the angular velocity W is less than the lower limit angular velocity Wmin, the d-axis voltage command value Vdc is set to zero, and the q-axis voltage command value is selected so that the d-axis current Id becomes a positive value. In this way, although the current flows through the motor 6, the output torque Trq can be suppressed to a small value. The reason is described below.

[0068] The angle between the q-axis in the dq space and the rotating magnetic field (magnetic field generated by the stator) is called the electrical phase angle Be. The strength of the magnetic field generated by the stator is proportional to the total current flowing through the stator. The symbol Ia represents the total current flowing through the stator. The output torque Trq of the motor 6 can be expressed by (Equation 5) using the electrical phase angle Be and the total current Ia. In addition, the motor 6 is an interior permanent magnet synchronous motor (IPMSM).

[0069] [Formula 5]

[0070]

[0071] The first term on the right side of (Equation 5) corresponds to the magnetic torque, and the second term on the right side corresponds to the reluctance torque. Figure 4 The relationship between the electrical phase angle Be and the output torque Trq of the motor 6 is shown in FIG. Figure 4 It can be seen that when the electrical phase angle Be is near -90 degrees, the torque Trq of the motor is close to zero and is flat. That is, by keeping the electrical phase angle Be near -90 degrees, the torque of the motor can be suppressed near zero even if the electrical phase angle Be changes. The relationship (Equation 6) is known between the electrical phase angle Be, the total current Ia, the d-axis current Id, and the q-axis current Iq.

[0072] [Formula 6]

[0073] Id=-Ia×sin(Be), Iq=Ia×cos(Be)

[0074] When the electrical phase angle Be is near -90 degrees, the q-axis current Iq is near zero and the d-axis current Id becomes a positive value. In other words, if the q-axis current can be kept near zero and the d-axis current Id can be kept at a positive value, the electrical phase angle Be can be kept near -90 degrees and the output torque of the motor can be kept near zero.

[0075] When the angular velocity W of the motor 6 is lower than the predetermined lower limit angular velocity Wmin and one of the current sensors 7 cannot be used, the controller 20 sets the d-axis voltage command value Vdc to zero and sets the q-axis voltage command value to non-zero, and further controls the motor 6 in such a manner that the d-axis current Id becomes a positive value. By controlling the motor 6 in this manner, although the current flows through the motor 6, the output torque can be suppressed to be small.

[0076] Since the q-axis voltage Vq is expressed by (Formula 3), when the angular velocity W is smaller than the lower limit angular velocity Wmin, the controller 20 sets the d-axis voltage command value Vdc to zero and sets the q-axis voltage command value Vqc by the following (Formula 7).

[0077] [Formula 7]

[0078] Vqc=W×Ld×Id+W×PHI=Ce+W×PHI

[0079] Symbol Ce is a constant with a positive value greater than the specified lower limit constant Cmin. (Formula 7) is the same as (Formula 1) shown previously. By describing the q-axis voltage command value Vqc in (Formula 1), the d-axis current Id can be kept as a positive value, and as a result, the current can flow through the motor 6 while suppressing the output torque to zero or small.

[0080] The controller 20 determines a current sensor that cannot be used while performing zero torque control. One example of a method of finding a current sensor that cannot be used is as follows.

[0081] The following relationship (Formula 8) is known between the currents Iu, Iv, and Iw of each of the three phases and the total current Ia flowing through the stator.

[0082] [Formula 8]

[0083]

[0084] The u-phase current Iu is obtained by Iu=-(Iv+Iw). Therefore, when the u-phase current Iu of (Equation 8) is expressed by the v-phase current Iv and the w-phase current Iw, (Equation 9) is obtained.

[0085] [Formula 9]

[0086]

[0087] The same formula as (Formula 9) can be obtained by representing the v-phase current Iv with the u-phase current Iu and the w-phase current Iw. The same formula can be obtained by representing the w-phase current Iw with the u-phase current Iu and the v-phase current Iv. In addition, the total current Ia flowing through the stator is equal to the input current of the inverter 5. The input current of the inverter 5 can be measured by the current sensor 12. The controller 20 infers the current of the remaining phase based on the measurement values ​​of any two current sensors 7. When the sum of the squares of the three-phase currents obtained based on the measurement values ​​of the two current sensors 7 is equal to 3 / 2 of the square of the input current Ia input to the inverter 5, the controller 20 determines that the two current sensors 7 can be used. On the other hand, when the sum of the squares of the three-phase currents obtained based on the measurement values ​​of the two current sensors 7 is different from 3 / 2 of the square of the input current Ia, the controller 20 determines that one of the two current sensors 7 cannot be used.

[0088] By using (Equation 9) and two equivalent formulas, the controller 20 can determine the current sensor that cannot be used.

[0089] After being able to identify the unusable current sensor, the controller 20 estimates the current of the phase corresponding to the unusable current sensor based on the measurement values ​​of the two usable current sensors and restarts the current feedback control.

[0090] The specific examples of the present invention are described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various deformations and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exert the usefulness of the technology alone or through various combinations, and are not limited to the combinations recorded in the claims at the time of application. In addition, the technology illustrated in this specification or the drawings can achieve multiple purposes at the same time, and achieving one of the purposes itself has a technically beneficial effect.

Claims

1. An electric vehicle, characterized in that: have: A motor, which is used for driving; an inverter that supplies alternating current to the motor; Three current sensors, which measure the current of each phase of the three-phase alternating current output by the inverter; a controller for controlling the motor through the inverter, The controller is configured to: When one of the current sensors cannot be used in a state where the angular velocity of the motor is greater than a predetermined lower limit angular velocity, the motor is controlled by setting the d-axis voltage command value to zero and the q-axis voltage command value to non-zero in such a manner that the electrical phase angle between the q-axis in the dq space and the rotating magnetic field of the motor becomes -90 degrees, and at the same time, determining the current sensor that cannot be used, When the angular velocity of the motor is lower than the lower limit angular velocity and one of the current sensors cannot be used, the motor is controlled in such a way that the electrical phase angle is maintained near -90 degrees, the d-axis voltage command value is set to zero, and the q-axis voltage command value is set to non-zero, and the d-axis current becomes a positive value, and at the same time, the current sensor that cannot be used is determined.

2. The electric vehicle according to claim 1, characterized in that: The controller is configured to determine that a certain current sensor cannot be used when a sum of measurement values ​​of the three current sensors is not zero.

3. The electric vehicle according to claim 1 or 2, characterized in that: The controller is configured to, inferring a third estimated value of a phase current of a third current sensor among the current sensors based on a first measured value of a first current sensor and a second measured value of a second current sensor among the current sensors, When the sum of the squares of the first measured value, the second measured value, and the third estimated value is equal to 3 / 2 of the square of the input current to the inverter, it is determined that the first current sensor and the second current sensor are usable. When the sum of the squares of the first measured value, the second measured value, and the third estimated value is different from 3 / 2 of the square of the input current, it is determined that one of the first current sensor and the second current sensor cannot be used.

4. A diagnostic method for an electric vehicle, the electric vehicle comprising: A motor, which is used for driving; an inverter that supplies alternating current to the motor; Three current sensors, which measure the current of each phase of the three-phase alternating current output by the inverter; a controller for controlling the motor through the inverter, The electric vehicle diagnostic method is characterized in that: When one of the current sensors cannot be used in a state where the angular velocity of the motor is greater than a predetermined lower limit angular velocity, the motor is controlled by setting the d-axis voltage command value to zero and the q-axis voltage command value to non-zero in such a manner that the electrical phase angle between the q-axis in the dq space and the rotating magnetic field of the motor becomes -90 degrees, and at the same time, determining the current sensor that cannot be used, When one of the current sensors cannot be used when the angular velocity of the motor is less than the lower limit angular velocity, the motor is controlled in such a way that the electrical phase angle is maintained near -90 degrees, the d-axis voltage command value is set to zero, the q-axis voltage command value is set to non-zero, and the d-axis current becomes a positive value, and at the same time, the current sensor that cannot be used is determined.

5. The diagnostic method according to claim 4, characterized in that: When the sum of the measured values ​​of the three current sensors is not zero, it is determined that one of the current sensors cannot be used.

6. The diagnostic method according to claim 4 or 5, characterized in that: inferring a third estimated value of a phase current of a third current sensor among the current sensors based on a first measured value of a first current sensor and a second measured value of a second current sensor among the current sensors, When the sum of the squares of the first measured value, the second measured value, and the third estimated value is equal to 3 / 2 of the square of the input current to the inverter, it is determined that the first current sensor and the second current sensor are usable. When the sum of the squares of the first measured value, the second measured value, and the third estimated value is different from 3 / 2 of the square of the input current, it is determined that one of the first current sensor and the second current sensor cannot be used.

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