Electric vehicle

Abstract

To reduce a difference between a degree of temperature rise of an RC-IGBT of a phase through which a positive current of an inverter flows and a degree of temperature rise of the RC-IGBT of a phase through which a negative current flows when a motor reaches a locking state.SOLUTION: In an electric vehicle comprising a motor, an inverter configured with six reverse-conductive IGBTs, and a controller for controlling the inverter, the controller corrects a target electric angle so that a current flowing through a transistor of a reverse-conductive IGBT is reduced, and a current flowing through a diode of the reverse-conductive IGBT is enlarged when detecting a locking state of the motor.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an electric vehicle, and more particularly to an electric vehicle equipped with an electric motor driven by three-phase AC and an inverter configured with six reverse-conducting IGBTs. [Background technology]

[0002] A conventional electric vehicle of this type has been proposed that, when it is determined that the motor is locked (a state in which current flows through the motor but the rotation of the motor is stopped, and the driving force is on, the brake is off, and the vehicle is stopped), it reduces the torque command value of the motor by a predetermined value, and then controls the inverter so that the torque command value is reduced at a variable rate in which the torque reduction rate becomes smaller over time (see, for example, Patent Document 1). In this electric vehicle, the above control suppresses the temperature rise of the inverter switching elements that occurs when the torque is reduced when it is determined that the motor is locked. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-076536 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned electric vehicle, if the inverter is configured using six reverse conducting insulated gate bipolar transistors (RC-IGBTs), in a locked state, current flows through the transistor of the RC-IGBT in the phase through which a positive current flows (for example, the W phase), and current flows through the diode of the RC-IGBT in the phase through which a negative current flows (for example, the V phase). In this case, the degree of temperature rise per unit time of the transistor differs from that of the diode, so after a certain time has elapsed since the locked state was reached, the temperature of the RC-IGBT in the phase through which a positive current flows will differ from the temperature of the RC-IGBT in the phase through which a negative current flows. This makes it necessary to impose drive restrictions based on the temperature of the phase whose temperature rises first, shortening the time until the drive restrictions can be imposed.

[0005] The main purpose of the electric vehicle disclosed herein is to reduce the difference in the degree of temperature rise of the RC-IGBT in the phase through which positive current flows in the inverter and the degree of temperature rise of the RC-IGBT in the phase through which negative current flows when the electric motor reaches a locked state. [Means for solving the problem]

[0006] The electric vehicle of the present disclosure employs the following measures to achieve the above-mentioned main object.

[0007] The electric vehicle of the present disclosure includes: a power storage device; an electric motor capable of generating electricity driven by three-phase AC; an inverter configured with six reverse conducting IGBTs, which converts DC power from the power storage device into three-phase AC power and supplies the three-phase AC power to the electric motor; a control device that controls the inverter; An electric vehicle comprising: When the control device detects a locked state of the motor, the control device corrects the target electrical angle so that a current flowing through a transistor of the reverse conducting IGBT decreases and a current flowing through a diode of the reverse conducting IGBT increases. It is characterized by:

[0008] When a control device for an electric vehicle disclosed herein detects a locked state of the electric motor (a state in which current flows through the electric motor but the rotation of the electric motor is stopped, and the driving force is on, the brake is off, and the vehicle is stopped), the control device corrects a target electrical angle so that the current flowing through the transistor of a reverse conductive insulated gate bipolar transistor (RC-IGBT) decreases and the current flowing through the diode of the RC-IGBT increases. Generally, in an RC-IGBT, when the same current flows through the transistor and the diode, the temperature rise of the transistor is greater than that of the diode. Therefore, by correcting the target electrical angle so that the current flowing through the transistor of the RC-IGBT in the phase through which a positive current flows decreases and the current flowing through the diode of the RC-IGBT in the phase through which a negative current flows increases (as a negative value), the difference between the degree of temperature rise of the RC-IGBT in the phase through which a positive current flows and the degree of temperature rise of the RC-IGBT in the phase through which a negative current flows can be reduced. To decrease the current flowing through the RC-IGBT transistor and increase the current flowing through the RC-IGBT diode, the target electrical angle can be corrected to be offset toward the retard side. The offset amount depends on the hardware, but it can be adjusted so that the temperature of the RC-IGBT in the phase through which a positive current flows and the temperature of the RC-IGBT in the phase through which a negative current flows are the same after a certain time (for example, 1, 2, or 3 seconds) has passed since the locked state was reached. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing an outline of the configuration of an electric vehicle 20 according to an embodiment of the present disclosure. [Figure 2] 4 is a flowchart showing an example of a process performed by an electronic control unit 50 during locking according to the embodiment. [Figure 3]3 is an explanatory diagram showing an example of time-dependent changes in current flowing through three phases of a motor 32 and element temperatures of an inverter 34. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, a mode (embodiment) for carrying out the present disclosure will be described. Fig. 1 is a diagram showing an outline of the configuration of an electric vehicle 20 according to an embodiment of the present disclosure. As shown in the figure, the electric vehicle 20 according to the embodiment includes a motor 32 for driving, an inverter 34, a battery 36, and an electronic control unit 50.

[0011] The motor 32 is configured as a three-phase AC motor and includes a rotor with a permanent magnet embedded in the rotor core and a stator with a three-phase coil wound around the stator core. The rotor of the motor 32 is connected to a drive shaft 26 that is connected to the drive wheels 22 a, 22 b via a differential gear 24.

[0012] The inverter 34 is used to drive the motor 32. The inverter 34 is connected to the battery 36 via a power line 38 and is composed of six reverse conductive insulated gate bipolar transistors (RC-IGBTs), each of which is an IGBT (insulated gate bipolar transistor) and a freewheel diode integrated on a single chip. The inverter 34 has six switching elements, i.e., transistors T11 to T16, and six diodes D11 to D16 connected in parallel to the six transistors T11 to T16, respectively. The transistors T11 to T16 are arranged in pairs, two at a time, on the source and sink sides of the positive and negative lines of the power line 38. The junctions of the two transistors in each pair are connected to the coils of the corresponding phases (U, V, and W) of the motor 32. Therefore, when a voltage is applied to the inverter 34, the electronic control unit 50 adjusts the proportion of the on time of the paired transistors T11 to T16, thereby forming a rotating magnetic field in the three-phase coil and driving the motor 32 to rotate.

[0013] The battery 36 is configured as a lithium ion secondary battery or a nickel-metal hydride secondary battery, and is connected to the inverter 34 via a power line 38. A smoothing capacitor 39 is attached to the power line 38.

[0014] The electronic control unit 50 is configured as a microcomputer having a CPU, ROM, RAM, flash memory, and input / output ports. The electronic control unit 50 receives inputs of the rotational position θm of the rotor of the motor 32 from a rotational position sensor 32a, the U-phase and V-phase currents Iu and Iv of the motor 32 from current sensors 32u and 32v, the voltage Vb of the battery 36 from a voltage sensor 36a, the current Ib of the battery 36 from a current sensor 36b, the temperature Tb of the battery 36 from a temperature sensor 36c, and the voltage VL of the power line 38 (capacitor 39) from a voltage sensor 39a. The electronic control unit 50 also receives inputs of a start signal from a start switch 60, a shift position SP indicating the operating position of the shift lever 61 from a shift position sensor 62, an accelerator opening Acc indicating the depression amount of the accelerator pedal 63 from an accelerator pedal sensor 64, a brake pedal position BP indicating the depression amount of the brake pedal 65 from a brake pedal sensor 66, and a vehicle speed V from a vehicle speed sensor 67.

[0015] The electronic control unit 50 outputs control signals to the transistors T11 to T16 of the inverter 34. The electronic control unit 50 calculates the electrical angle θe and rotation speed Nm of the motor 32 based on the rotational position θm, and estimates the output torque Tm of the motor 32 based on the phase currents Iu, Iv and the electrical angle θe. The output torque Tm is estimated, for example, by assuming that the sum of the currents of each phase of the motor 32 is zero, performing a coordinate transformation (three-phase to two-phase transformation) on the U-phase and V-phase phase currents Iu, Iv to d-axis and q-axis currents Id, Iq using the electrical angle θe of the motor 32, and then applying the d-axis and q-axis currents Id, Iq to a predetermined relationship between the currents Id, Iq and the output torque Tm to derive the output torque Tm.

[0016] In the electric vehicle 20 of this embodiment, the electronic control unit 50 sets the required traveling torque Td* required for traveling (required of the drive shaft 26) as the torque command Tm* for the motor 32, and controls the transistors T11 to T16 of the inverter 34 so that the motor 32 is driven by the torque command Tm*. Here, the required traveling torque Td* is set based on the accelerator pedal position Acc and the vehicle speed V. The inverter 34 is controlled, for example, by pulse width modulation (PWM) control.

[0017] In PWM control, first, the sum of the currents of the phases of the motor 32 is set to zero, and coordinate conversion (3-phase to 2-phase conversion) is performed on the U-phase and V-phase currents Iu and Iv to d-axis and q-axis currents Id and Iq using the electrical angle θe of the motor 32. Next, d-axis and q-axis current commands Id* and Iq* are set based on the torque command Tm*, and d-axis and q-axis voltage commands Vd* and Vq* are calculated so that the differences between the d-axis and q-axis current commands Id* and Iq* and the currents Id and Iq are canceled out. Then, using the electrical angle θe of the motor 32, the d-axis and q-axis voltage commands Vd* and Vq* are coordinate-converted (2-phase to 3-phase conversion) into voltage commands Vu*, Vv*, and Vw* for each phase, and PWM signals for the transistors T11 to T16 are generated by comparing these voltage commands Vu*, Vv*, and Vw with the carrier voltage, thereby controlling the switching of the transistors T11 to T16.

[0018] Next, the operation of the electric vehicle 20 of this embodiment, particularly the operation when the motor 32 is locked, will be described. The locked state of the motor 32 refers to a state in which current flows through the motor 32 but rotation of the motor 32 is stopped. This state refers to a state in which the driving force is on but the brake is off, such as when the vehicle is stopped because it is unable to overcome a curb or the like due to insufficient driving force, or when the vehicle is stopped because it is unable to climb an uphill slope. Figure 2 is a flowchart showing an example of a process executed by the electronic control unit 50 of this embodiment when the vehicle is locked. This process is repeated while the system is running.

[0019] When the locked state process is executed, the electronic control unit 50 first determines whether the motor 32 is in a locked state (step S100). As described above, whether the motor 32 is in a locked state can be determined by determining whether the vehicle is stopped with the driving force on and the brake off. If it is determined that the motor 32 is not in a locked state, the electronic control unit 50 determines that this process is unnecessary and ends the process.

[0020] If it is determined in step S100 that the motor 32 is locked, a reference target phase angle θb* is calculated (step S110), and a phase angle offset value θof is calculated (step S120). The reference target phase angle θb* can be calculated based on the accelerator pedal position Acc, which reflects the driver's torque demand. The phase angle offset value θof can be adjusted so that, after a certain time, the temperature of the element in the phase through which a positive current flows and the temperature of the element in the phase through which a negative current flows are approximately the same. FIG. 3 is an explanatory diagram showing an example of the time changes in the current flowing through the three phases of the motor 32 and the element temperature. In the figure, the thick solid line indicates the w-phase, the thick dashed line indicates the v-phase, and the thick dashed-dotted line indicates the u-phase. Focusing on the period from time T2 to time T3, the element temperature of the w-phase through which a positive current flows increases relatively rapidly in response to the rising current between time T1 and time T2. Meanwhile, the element temperature of the v-phase, through which a negative current flows, of the three phases of the motor 32 rises between time T1 and time T2 in response to the rising edge of the negative current, but remains lower than that of the w-phase. In the w-phase, through which a positive current flows, current flows through an on-state transistor, while in the v-phase, through which a negative current flows, current flows through a diode. Because the degree of temperature rise when the same current flows is greater in a transistor than in a diode, in an RC-IGBT in which the transistor and diode are integrated into a single chip, the element temperature of the w-phase becomes higher than that of the v-phase. In this embodiment, the phase angle offset value θof is calculated so that the current in the phase through which a positive current flows decreases and the current in the phase through which a negative current flows increases, so that the element temperatures of the phase through which a positive current flows and the phase through which a negative current flows become substantially the same after a certain time (e.g., 1 second, 2 seconds, or 3 seconds) from the locked state. Specifically, in the example of FIG. 3, when a locked state is determined at time T2, the phase is shifted toward the retard side until the w-phase element temperature and the v-phase element temperature become substantially constant at time T3. This value is determined in advance by experimentation, machine learning, or the like, and stored in ROM as the phase angle offset value θof. The phase angle offset value θof is then read out instead of being calculated.

[0021] Once the phase angle offset value θof is calculated in this way, the target phase angle θ* is adjusted (step S130), and this process ends. The target phase angle θ* can be adjusted by reflecting the phase angle offset value θof in the reference target phase angle θb* (θ* = θb* + θof).

[0022] In the electric vehicle 20 according to the embodiment described above, when the motor 32 reaches a locked state, the target phase angle θ* is set using a phase angle offset value θof that reduces the current in the phase through which a positive current flows and increases the current in the phase through which a negative current flows among the three phases of the motor 32. This makes it possible to make the element temperature of the phase through which a positive current flows and the element temperature of the phase through which a negative current flows substantially the same after a certain time (e.g., 1 second, 2 seconds, or 3 seconds) has passed since the motor 32 reached a locked state. In other words, it is possible to reduce the difference in the degree of temperature rise of the RC-IGBT in the phase through which a positive current flows and the phase through which a negative current flows of the inverter 34 when the motor 32 reaches a locked state.

[0023] The correspondence between the main elements of the embodiment and the main elements of the invention described in the "Means for Solving the Problem" section will be explained below. In the embodiment, the battery 36 corresponds to the "electricity storage device," the motor 32 corresponds to the "electric motor," the inverter 34 corresponds to the "inverter," and the electronic control unit 50 corresponds to the "control device."

[0024] The correspondence between the main elements of the embodiments and the main elements of the invention described in the "Means for Solving the Problem" section does not limit the elements of the invention described in the "Means for Solving the Problem" section, since the embodiments are examples for specifically explaining the mode for implementing the invention described in the "Means for Solving the Problem" section. In other words, the interpretation of the invention described in the "Means for Solving the Problem" section should be based on the description in that section, and the embodiments are merely specific examples of the invention described in the "Means for Solving the Problem" section.

[0025] The above describes the forms for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and it goes without saying that the present disclosure can be implemented in various forms within the scope that does not deviate from the gist of the present disclosure. [Industrial Applicability]

[0026] The present disclosure is applicable to the electric vehicle manufacturing industry and the like. [Explanation of symbols]

[0027] 20 electric vehicle, 22a,22b drive wheels, 32 motor, 32u,32v current sensor, 34 inverter, 36 battery, 36c temperature sensor, 50 electronic control unit.

Claims

[Claim 1] a power storage device; an electric motor capable of generating electricity driven by three-phase AC; an inverter including six reverse conducting IGBTs that converts DC power from the power storage device into three-phase AC power and supplies the three-phase AC power to the electric motor; a control device that controls the inverter; An electric vehicle comprising: When the control device detects a locked state of the electric motor, the control device corrects the target electrical angle so that a current flowing through a transistor of the reverse conducting IGBT decreases and a current flowing through a diode of the reverse conducting IGBT increases. An electric vehicle characterized by:

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