Electric vehicle and control method for an electric vehicle

Abstract

Electric vehicle (100), with: a motor (20) for locomotion, a transmission (22) connected to the motor (20), a battery (2), an inverter (13) configured to convert DC power output by the battery into AC power for driving the motor, a capacitor (7) connected between a positive electrode (13a) of DC input terminals of the converter (13) and a negative electrode (13b) of the DC input terminals of the converter (13), and a control element (9) configured to control the motor (20) by switching between a square wave control and a PWM control according to an operating point determined by a rotational speed of the motor (20) and an output torque of the motor (20), and to control a gear stage of the transmission (22), wherein the control element (9) is arranged to: in a range of operating points in which the motor (20) is PWM-controlled, within a first operating point range (C) defined by the rotational speed being between a first rotational speed (N1) and a second rotational speed (N2) and the output torque being a predetermined first torque (Ta) or more, setting a carrier frequency (fc) of the PWM control close to a resonance frequency or an integer multiple of the resonance frequency of an LC circuit including the capacitor (7), and setting another carrier frequency (fa, fb, fd, fe, ff, fg) outside the first operating point range (C), to assign a range of operating points in which the rotational speed is equal to or greater than a third rotational speed greater than the second rotational speed (N2) and the output torque is within a predetermined second torque (TL(N)) or more, to the square wave control, to control the motor (20) by means of the PWM control, and to change a gear stage when the operating point belongs to the first operating point range (C), and to control the motor (20) by means of the square wave control, and to change the gear stage when the rotational speed is close to the resonance frequency or the integer multiple of the resonance frequency.

Description

Background of the invention 1. Field of the invention

[0001] A technology disclosed in this specification relates to an electric vehicle including a motor for propulsion and a transmission, and a capacitor connected between a positive electrode and a negative electrode of an inverter that supplies AC power to the motor, and a control method for the electric vehicle. The "electric vehicle" of this specification includes a hybrid vehicle equipped with both a motor and an engine, and a fuel cell vehicle. 2. Description of the related art

[0002] An electric vehicle includes an inverter that converts electric power from a DC power source into AC power suitable for driving a motor for locomotion. In some cases, a smoothing capacitor is connected between a positive electrode and a negative electrode of DC input terminals of the inverter. It is known that LC resonance is likely to occur when the rotation speed of the motor is within a certain range in the case where the capacitor is connected between the DC power source and the inverter (for example, Japanese Patent Application Publication No. 2016-5368 (JP 2016-5368 A) and Japanese Patent Application Publication No. 2012-175769 (JP 2012-175769 A)). LC resonance increases current ripple and increases loss.Here, inductance causing the LC resonance may be a parasitic inductance of a power transmission path between the power source and the inverter, or may be an inductance of a coil included in a boost converter in the case where the boost converter is connected between the power source and the inverter.

[0003] JP 2016-5368 A discloses a technology for suppressing LC resonance by changing a pulse pattern for driving the inverter. An electric vehicle disclosed in JP 2012-175769 A includes a motor for propulsion and a transmission. In the technology disclosed in JP 2012-175769 A, the gear ratio of the transmission is determined such that the rotational speed of the motor does not fall into a rotational speed zone where LC resonance is induced.

[0004] A vehicle and a control method thereof are known from JP 2013-258825 A. Accordingly, to prevent resonance generation in an on-board boost converter that cannot implement boost control in a vehicle including a motor and the boost converter, a control device sets a target torque of the motor using a power mode map when the motor is operating in a resonance-avoidance range outside a resonance range in which resonance can be induced by an LC circuit formed in one arm. The control device enables control of the motor in a resonance range for the specified time in a traveling situation that results in a power shortage.Further, the control device sets the target torque of the engine using an eco mode map instead of the power mode map when the acceleration α in the vehicle longitudinal direction has exceeded a predetermined value α0. Summary of the invention

[0005] With the technology disclosed in JP 2012-175769 A, a specific rotational speed zone of the engine cannot be used at all. Therefore, the technology is inefficient. The technology of avoiding LC resonance by adjusting the gear ratio has room for improvement.

[0006] A first aspect of the invention is an electric vehicle. The electric vehicle comprises: a motor for propulsion, a transmission connected to the motor, a battery, an inverter configured to convert DC power output by the battery into AC power for driving the motor, a capacitor connected between a positive electrode of DC input terminals of the inverter and a negative electrode of the DC input terminals of the inverter, and a control element configured to control the motor by switching between square wave control and PWM control according to an operating point determined by a rotational speed of the motor and an output torque of the motor, and to control a gear stage of the transmission, wherein the control element is configured to, in a range of operating points in which the motor is PWM-controlled,within a first operating point range defined by the rotational speed being between a first rotational speed and a second rotational speed and the output torque being a predetermined first torque or more, to set a carrier frequency of the PWM controller close to a resonance frequency or an integer multiple of the resonance frequency of an LC circuit including the capacitor, and to set another carrier frequency outside the first operating point range, to assign a range of operating points in which the rotational speed is equal to or greater than a third rotational speed greater than the second rotational speed and the output torque is within a predetermined second torque or more to the square wave control, to control the motor by means of the PWM controller, and to change a gear stage,When the operating point belongs to the first operating point range, control the motor using square wave control, and change the gear ratio when the rotation speed is close to the resonance frequency or an integer multiple of the resonance frequency. When the motor output is low, gear shifting is not performed to avoid LC resonance, thus allowing the motor to be used effectively.

[0007] In the electric vehicle, the control element may be configured to control the motor by means of the PWM control and execute a downshift control of downshifting the gear stage of the transmission when the operating point belongs to the first operating point range, and to control the motor by means of the rectangular wave control and execute a downshift control of downshifting the gear stage of the transmission when the rotation speed is close to the resonance frequency or the integer multiple of the resonance frequency.

[0008] A second aspect of the invention is a control method for an electric vehicle. The electric vehicle comprises: a motor for propulsion, a transmission connected to the motor, a battery, an inverter configured to convert DC power output from the battery into AC power for driving the motor, a capacitor connected between a positive electrode of DC input terminals of the inverter and a negative electrode of the DC input terminals of the inverter, and a control element. The control method includes controlling, by means of the control element, the motor by switching between a square wave control and a PWM control according to an operating point determined by a rotational speed of the motor and an output torque of the motor, and controlling, by means of the control element, a gear stage of the transmission, and setting, by means of the control element,in a range of operating points in which the motor is PWM-controlled, within a first operating point range defined by the rotational speed being between a first rotational speed and a second rotational speed and the output torque being a predetermined first torque or more, a carrier frequency of the PWM control being close to a resonance frequency or an integer multiple of the resonance frequency of an LC circuit including the capacitor, and setting, by means of the control element, another carrier frequency outside the first operating point range, assigning, by means of the control element, a range of operating points in which the rotational speed is equal to or greater than a third rotational speed greater than the second rotational speed and the output torque is within a predetermined second torque or more,to the square wave control, controlling, by means of the control element, the motor using the PWM control, and changing, by means of the control element, a gear stage when the operating point belongs to the first operating point range; and controlling, by means of the control element, the motor using the square wave control, and changing, by means of the control element, the gear stage when the rotational speed is close to the resonance frequency or an integer multiple of the resonance frequency. When the output of the motor is low, gear shifting is not performed to avoid LC resonance, and therefore, it is possible to use the motor effectively. Short description of the drawings

[0009] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which like reference numerals designate like elements, and wherein: Fig. 1 is a block diagram of an electric power system of an electric vehicle in one embodiment, Fig. 2 is a TN diagram of a motor, and Fig. 3 is a flowchart of a gear shift to avoid resonance. Detailed description of implementation examples

[0010] An electric vehicle 100 in one embodiment will be described with reference to the drawings. Fig. Figure 1 shows a block diagram of an electric power system of the electric vehicle 100. The electric vehicle 100 in the exemplary embodiment moves by means of a motor 20. The motor 20 is a three-phase AC motor. In addition to the motor 20 for movement, the electric vehicle 100 includes a battery 2, a DC converter 12, an inverter 13, a smoothing capacitor 7, a transmission 22, and a control element 9.

[0011] The battery 2 is, for example, a lithium-ion battery, and the output voltage of the battery 2 is, for example, 200 V. The drive power of the motor 20 is, for example, 200 V to 600 V. The drive power of the motor 20 is sometimes higher than the output power of the battery 2, and for this, the electric vehicle 100 includes a DC converter 12. The DC converter 12 has both a step-up function for stepping up a voltage applied to the low-voltage terminals 12a, 12b and then outputting the voltage to the high-voltage terminals 12c, 12d, and a step-down function for stepping down a voltage applied to the high-voltage terminals 12c, 12d and then outputting the voltage to the low-voltage terminals 12a, 12b. That is, the DC converter 12 is a bidirectional DC-DC converter.

[0012] The DC converter includes a filter capacitor 3, a coil 4, power transistors 6a, 6b, and two diodes. The diodes are connected in reverse parallel to the power transistors 6a, 6b, respectively. The two power transistors 6a, 6b are connected in series between the high-voltage terminals 12c, 12d. One end of the coil 4 is connected to the positive electrode 12a of the low-voltage terminals. The other end of the coil 4 is connected to a midpoint between the two power transistors 6a, 6b, which are connected in series. The filter capacitor 3 is connected between the positive electrode 12a and the negative electrode 12b of the low-voltage terminals. The negative electrode 12b of the low-voltage terminals and the negative electrode 12d of the high-voltage terminals are directly connected to each other.

[0013] The power transistor 6a on the positive electrode side relates to a step-down operation, and the power transistor 6b on the negative electrode side relates to a step-up operation. When complementary drive signals are supplied to the power transistor 6a on the positive electrode side and the power transistor 6b on the negative electrode side, switching between the step-up operation and the step-down operation is passively performed depending on the balance between a voltage applied to the low-voltage terminals 12a, 12b and a voltage applied to the high-voltage terminals 12c, 12d. This function is suitable for an electric vehicle in which the motor 20 generates electricity when a driver depresses a brake pedal. That is, the motor 20 outputs torque when the driver depresses an accelerator pedal and generates regenerative electric power when the driver depresses the brake pedal.The DC converter 12 must perform switching between the boost function and the step-down function depending on the driver's random pedal input. Since switching between the boost mode and the step-down mode is performed passively, the DC converter 12 has the advantage that switching control dependent on the driver's pedal input is not necessary. The regenerative electric power is used to charge the battery 2.

[0014] DC input terminals 13a, 13b of the inverter 13 are connected to the high-voltage terminals 12c, 12d of the DC converter 12. The inverter 13 includes six power transistors 8a to 8f and six diodes. The six power transistors 8a to 8f comprise three pairs of series-connected power transistors. The three pairs of series-connected power transistors are connected in parallel between the positive electrode 13a and the negative electrode 13b of the DC input terminal. The six diodes are connected in inverse parallel to the six power transistors 8a to 8f, respectively. Alternating currents are output from the respective midpoints of the three pairs of series-connected power transistors. Three-phase alternating currents are output from the midpoints of the three pairs of series-connected power transistors.

[0015] The smoothing capacitor 7 is connected in parallel between the DC converter 12 and the inverter 13. In other words, the smoothing capacitor 7 is connected between the positive electrode 13a and the negative electrode 13b of the DC input terminal of the inverter 13. The smoothing capacitor 7 is provided to suppress pulsation of electric current flowing between the DC converter 12 and the inverter 13.

[0016] The power transistors 6a, 6b of the DC converter 12 and the power transistors 8a to 8f of the inverter 13 are controlled by the controller 9. The controller 9 decides a target output of the motor 20 based on the current rotation speed of the motor 20, the current accelerator operation amount, and the like. The target output of the motor 20 is converted into a target voltage of the DC converter 12 and a target frequency of the inverter 13. The controller 9 drives the power transistors 6a, 6b of the DC converter 12 to realize the target voltage and drives the power transistors 8a to 8f of the inverter 13 to realize the target frequency. A rotation speed sensor 21 is attached to the motor 20, and the rotation speed of the motor 20, which is measured by the rotation speed sensor 21, is sent to the control element 9. In Fig. 1, dashed arrows indicate signal lines. The control element 9 performs feedback control of the motor 20 (the inverter 13) based on measured data from the rotational speed sensor 21 and measured data from a current sensor (not shown) for measuring an electric current supplied to the motor 20.

[0017] In Fig. 1, the control element 9 is expressed by a single rectangle. The control element 9 can realize the function in cooperation with a storage device in which programs are stored and a plurality of central processing units.

[0018] An output shaft of the engine 20 is connected to the transmission 22. An output shaft of the transmission 22 is connected to drive wheels 23 via an axle and a differential gear. The transmission 22 can be a stepped transmission or a continuously variable transmission (CVT). The transmission 22 is also controlled by the control element 9.

[0019] As in Fig. As shown in Figure 1, the battery 2, the filter capacitor 3, the coil 4, and the smoothing capacitor 7 are constantly connected. The filter capacitor 3, the smoothing capacitor 7, and the coil 4 form an LC circuit, and LC resonance occurs in some cases. The LC resonance increases a ripple current generated by the power transistors 6a, 6b, 8a to 8f and increases power loss. Therefore, it is desirable to suppress the LC resonance. An algorithm for suppressing the LC resonance is implemented in the control element 9. A process for suppressing the LC resonance is described below.

[0020] To drive the inverter 13, the control element 9 uses PWM control and square wave control while performing switching between PWM control and square wave control. In PWM control, it is necessary to generate a carrier wave. The control element 9 uses one of several carrier frequencies depending on a predetermined condition. Since PWM control and square wave control are well-known for inverters, detailed descriptions are omitted.

[0021] Fig. Figure 2 shows a TN diagram of the motor 20. The TN diagram is a graph in which the abscissa axis indicates the rotation speed of the motor 20, and the ordinate axis indicates the output torque of the motor 20. The TN diagram shows the condition of switching between PWM control and square wave control and the condition of switching the carrier frequencies.

[0022] The control element 9 performs the PWM control in a range where the rotation speed of the motor 20 is less than a rotation number N3. The control element 9 performs the switching to the rectangular wave control in a range (a range (H) in Fig. 2), where the rotation speed is greater than the rotation speed N3 and where the output torque is high. To facilitate understanding, the area (H) where the square wave control is executed is shown in gray.

[0023] The range in which PWM control is performed is divided into seven ranges depending on the rotation speed and the output torque, and a different carrier frequency is used for each range. In a range (A) where the rotation speed is less than a rotation speed N1 and where the output torque is higher than a torque Ta, the carrier frequency is set to a frequency fa. In a range (B) where the rotation speed is less than the rotation speed N1 and where the output torque is less than the torque Ta, the carrier frequency is set to a frequency fb. In a range (C) where the rotation speed is between the rotation speed N1 and a rotation speed N2 and where the output torque is greater than the torque Ta, the carrier frequency is set to a frequency fc.In a range (D) where the rotation speed is between the rotation speed N1 and the rotation speed N2 and where the output torque is less than the torque Ta, the carrier frequency is set to a frequency fd. In a range (E) where the rotation speed is between the rotation speed N2 and the rotation speed N3 and where the output torque is higher than the torque Ta, the carrier frequency is set to a frequency fe. In a range (F) where the rotation speed is between the rotation speed N2 and the rotation speed N3 and where the output torque is less than the torque Ta, the carrier frequency is set to a frequency ff. In a range (G) where the rotation speed is greater than the rotation speed N3 and where the output torque is less than a torque TL(N), the carrier frequency is set to a frequency fg.The "torque TL(N)" shows that the output torque of the motor 20 is expressed as a function in which the output torque of the motor 20 changes depending on the rotation speed N of the motor 20. A solid line TL(N) in . Fig. Figure 2 shows a relationship between output torque and rotation speed. The carrier wave is not used in the area (H) where square wave control is performed.

[0024] The LC resonance occurs when the resonance frequency of the LC circuit in Fig. 1 (or an integer multiple of the resonant frequency) is close to one of the ripple frequencies of the power transistors 6a, 6b, 8a to 8f. In this specification, the "resonant frequency" means the "resonant frequency or an integer multiple of the resonant frequency."

[0025] In PWM control, the ripple frequency is equal to the carrier frequency, and in square wave control, the ripple frequency is equal to the rotation frequency of the motor 20. Therefore, when a carrier frequency close to the LC resonance frequency is almost selected, the controller 9 performs gear shifting of the transmission 22 and changes the rotation speed and output torque of the motor 20 to a range where a different carrier frequency is used.

[0026] Fig. Fig. 3 shows a flowchart of a gear shift process executed by the control element 9 to avoid the LC resonance. In the embodiment, it is assumed that a carrier frequency near the LC resonance frequency corresponds to the region (C) in the TN diagram of the Fig. 2, and carrier frequencies very different from the resonance frequency are assigned to the other regions (A), (B), (D) to (G). Region (C) is a region in which the rotation speed of the motor 20 is between the rotation number N1 and the rotation number N2 and in which the output torque is greater than Ta.

[0027] Furthermore, a rotation number between the rotation number N4 and the rotation number N5 is assumed to be a rotation number close to the resonance frequency in the region (H), which is the rectangular wave control range. In fact, a rotation number Ns between the rotation number N4 and the rotation number N5 coincides with the resonance frequency, and LC resonance significantly occurs in a region containing the rotation number Ns (a region between the rotation number N4 and the rotation number N5).

[0028] The control element 9 periodically performs the process of Fig. 3. The control element 9 obtains the current rotation speed and the current output torque of the engine 20 and determines whether a first condition is met (step S2). The first condition is a condition that the current rotation speed of the engine 20 is within a range from the rotation speed N1 to the rotation speed N2 and the current output torque is equal to or greater than Ta. If the first condition is met, LC resonance occurs. Therefore, if the first condition is met, the control element 9 sends a gear shift command to the transmission 22 (step S2: YES, S4). Specifically, the control element 9 commands a downshift to the transmission 22. That is, the control element 9 downshifts the gear stage by one. By downshifting, the gear ratio of the transmission 22 increases.Then, in order to match the vehicle speed and the output torque before gear shifting, the rotation speed of the motor 20 increases and the output torque decreases.

[0029] Hereinafter, the rotation speed and output torque of the motor 20 during travel is referred to as a running state of the motor 20. In the TN diagram of the Fig. 2, a driving state of the engine 20 is expressed as a point. For example, it is assumed that the engine speed (vehicle speed) as the driving state gradually changes from a point P1 to Fig. 2. The driving state moves from point P1 to a point P2 in Fig. 2. Point P2 is on the boundary between area (A) and area (C). When the driving condition enters area (C), the determination is YES in step S2 of the Fig. 3, so that the control element 9 commands a downshift to the transmission 22. By downshifting the transmission 22, the rotational speed of the engine 22 increases rapidly, and the output torque decreases rapidly, so that the driving state moves directly from point P2 to a point P3. Point P3 is located in the region (D). In the region (D), LC resonance does not occur because the carrier frequency fd is very different from the LC resonance frequency. That is, LC resonance is avoided.

[0030] The controller 9 acquires the current rotation speed and the current output torque of the motor 20 and determines whether a second condition is satisfied (step S3). The second condition is a condition that the current rotation speed of the motor 20 is in a range from the rotation speed N4 to the rotation speed N5 in the area (H) where the square wave control is executed. The square wave control is executed in the case where the rotation speed is greater than the rotation speed N3 and the output torque of the motor 20 is equal to or greater than the torque TL(N). Accordingly, the second condition can be expressed as a condition that the current rotation speed of the motor 20 is in a range from the rotation speed N4 to the rotation speed N5 and the current output torque is equal to or greater than the torque TL(N).As described above, the torque TL(N) expresses a relationship in which the output torque TL changes depending on the rotation speed N of the engine 20. When the second condition is met, the controller 9 sends the gearshift command to the transmission 22 (step S3: YES, S4). Specifically, the controller 9 commands the downshift to the transmission 22. That is, the controller 9 shifts the gear stage down by one. By means of the downshift, the gear ratio of the transmission 22 increases. Then, in order to coordinate with the vehicle speed and the output torque before the gearshift, the rotation speed of the engine 20 increases, and the output torque decreases.

[0031] For example, it is assumed that the engine speed (vehicle speed) as the driving state of the engine 20 gradually changes from a point P4 in Fig. 2. When the running state enters the area (H) for square wave control, the control element 9 switches the control for the inverter 13 from PWM control to square wave control. If the rotation speed of the motor continues to increase, the running state moves to a point P5 in Fig. 2. Point P5 is located at a boundary where the second condition is satisfied. If the rotation number exceeds N4, the determination is YES in step S3 of the Fig. 3, so that the control element 9 commands the downshift to the transmission 22. By downshifting the transmission 22, the rotational speed of the engine 20 increases rapidly, and the output torque decreases rapidly, so that the driving state moves directly from point P5 to point P6. Point P6 is beyond a rotational speed range in which LC resonance occurs (a range from rotational speed N4 to rotational speed N5). Accordingly, LC resonance does not occur. That is, LC resonance is avoided.

[0032] If the determination NO is made in each of steps S2 and S3, the LC resonance is unlikely to occur. Therefore, the process of Fig. 3 without gear shifting to avoid resonance. The process of Fig. 3 is carried out periodically, thus avoiding LC resonance.

[0033] The electric vehicle 100 in the embodiment performs gear shifting when the rotation speed of the motor 20 is within a predetermined range and the output of the motor 20 is greater than the predetermined output threshold. The case where the rotation speed of the motor 20 is within a predetermined range and the output of the motor 20 is greater than a predetermined output threshold is a case where any of the ripple frequencies of the power transistors 6a, 6b, 8a to 8f is close to the resonance frequency of the LC circuit. The controller 6 avoids the LC resonance by controlling the transmission (gear stage) such that the ripple frequencies are not close to the resonance frequency of the LC circuit.In the case where the output torque is less than a predetermined torque threshold (the torque Ta or the torque TL(N) in the embodiment), the gear shift to avoid the LC resonance is not performed because the LC resonance is unlikely to occur.

[0034] Remarks regarding the technology described in the embodiment will be described. The control element 9 can display a plurality of TN maps similar to the TN map (the TN diagram showing the range in which the LC resonance can occur) shown in Fig. 2, and can switch the TN map depending on a condition. For example, the control element 9 can switch the TN map depending on the temperature of the DC converter 12 or the inverter 13. Alternatively, the control element 9 can perform switching among a plurality of TN maps that provide different drivability, such as a sport mode and an eco mode, depending on a driver switching operation. In each TN map, a unique range in which the LC resonance can occur is specified. In each TN map, the range in which the LC resonance can occur is specified by the rotation speed and the output torque of the motor 20. The control element 9 stores the TN maps in a mathematical formula format or a data array format.

[0035] In the exemplary embodiment, the command to the transmission to avoid LC resonance is the downshift command. The command to the transmission to avoid LC resonance can be an upshift command.

[0036] The rotation speed of the engine and the vehicle speed have a unique relationship with the gear ratio. Accordingly, it is noted that the "rotation speed of the engine" in the present specification can be replaced with the "vehicle speed." Each of the torque Ta and the torque TL(N) in the embodiment corresponds to an example of the output threshold. The output torque of the engine and the supplied electric current (supplied electric power) to the motor also have a unique relationship. Therefore, it is noted that the "output torque" in the embodiment can be replaced with the "electric current to be supplied to the engine" or the "electric power to be supplied to the motor."

[0037] The gearshift control in Fig. 3 is a control scheme to avoid LC resonance. Separate from the gear shift control in Fig.3, the control element 9 performs gear shift control to increase drivability.

[0038] The technology disclosed in the present specification can also be applied to a hybrid vehicle having both an engine and an engine for locomotion and to a fuel cell vehicle including a fuel cell as a power source.

[0039] Specific examples of the invention have been described in detail above. These are merely examples and do not limit the scope of the claims. The technology described in the scope of the claims includes various modifications and alterations of the specific examples described above. Technical elements described in the present specification or drawings have technical utility independently of or with various combinations. The invention is not limited to the combinations described in the claims at the time of application. Furthermore, the technology described in the present specification or drawings can serve a variety of purposes simultaneously and has technical utility simply by serving one of the purposes.

[0040] An electric vehicle (100) comprises: a motor (20) for propulsion, a transmission (22) connected to the motor (20), a battery (2), an inverter (13) configured to convert DC power output from the battery into AC power for driving the motor, a capacitor (7) connected between a positive electrode (13a) of DC input terminals of the inverter (13) and a negative electrode (13b) of the DC input terminals of the inverter (13), and a control element (9) configured to change a gear stage of the transmission (22) when both a condition i) and a condition ii) are met. Condition i) is a condition that the rotational speed of the motor (20) is within a predetermined range. Condition ii) is a condition that the output of the motor (20) exceeds a predetermined output threshold.

Claims

[1] Electric vehicle (100), with: a motor (20) for locomotion, a transmission (22) connected to the motor (20), a battery (2), an inverter (13) configured to convert DC power output by the battery into AC power for driving the motor, a capacitor (7) connected between a positive electrode (13a) of DC input terminals of the converter (13) and a negative electrode (13b) of the DC input terminals of the converter (13), and a control element (9) configured to control the motor (20) by switching between a square wave control and a PWM control according to an operating point determined by a rotational speed of the motor (20) and an output torque of the motor (20), and to control a gear stage of the transmission (22), wherein the control element (9) is arranged to: in a range of operating points in which the motor (20) is PWM-controlled, within a first operating point range (C) defined by the rotational speed being between a first rotational speed (N1) and a second rotational speed (N2) and the output torque being a predetermined first torque (Ta) or more, setting a carrier frequency (fc) of the PWM control close to a resonance frequency or an integer multiple of the resonance frequency of an LC circuit including the capacitor (7), and setting another carrier frequency (fa, fb, fd, fe, ff, fg) outside the first operating point range (C), to assign a range of operating points in which the rotational speed is equal to or greater than a third rotational speed greater than the second rotational speed (N2) and the output torque is within a predetermined second torque (TL(N)) or more, to the square wave control, to control the motor (20) by means of the PWM control, and to change a gear stage when the operating point belongs to the first operating point range (C), and to control the motor (20) by means of the square wave control, and to change the gear stage when the rotational speed is close to the resonance frequency or the integer multiple of the resonance frequency. [2] Electric vehicle (100) according to claim 1, wherein the control is set up to to control the motor (20) by means of the PWM control, and to carry out a downshift control of a downshift of the gear stage of the transmission (22) when the operating point belongs to the first operating point range (C), and to control the motor (20) by means of the square wave control, and to execute a downshift control of downshifting the gear stage of the transmission (22) when the rotational speed is close to the resonance frequency or the integer multiple of the resonance frequency. [3] Control method for an electric vehicle (100), wherein the electric vehicle (100) comprises: a motor (20) for propulsion, a transmission (22) connected to the motor (20), a battery (2), an inverter (13) configured to convert a direct current power output by the battery into alternating current power for driving the motor, a capacitor (7) connected between a positive electrode (13a) of direct current input terminals of the inverter (13) and a negative electrode (13b) of the direct current input terminals of the inverter (13), and a control element (9), the tax procedure includes: controlling, by means of the control element (9), the motor (20) by switching between a square wave control and a PWM control according to an operating point determined by a rotational speed of the motor (20) and an output torque of the motor (20), and controlling, by means of the control element (9), a gear stage of the transmission (22), setting, by means of the control element (9), in a range of operating points in which the motor (20) is PWM-controlled, within a first operating point range (C), which is defined by the rotational speed being between a first rotational speed (N1) and a second rotational speed (N2) and the output torque being a predetermined first torque (Ta) or more, a carrier frequency (fc) of the PWM control close to a resonance frequency or an integer multiple of the resonance frequency of an LC circuit including the capacitor (7), and setting, by means of the control element (9), another carrier frequency (fa, fb, fd, fe, ff, fg) outside the first operating point range (C), assigning, by means of the control element (9), a range of operating points in which the rotational speed is equal to or greater than a third rotational speed greater than the second rotational speed (N2) and the output torque is within a predetermined second torque (TL(N)) or more, to the square wave control, controlling, by means of the control element (9), the motor (20) by means of the PWM control, and changing, by means of the control element (9), a gear stage when the operating point belongs to the first operating point range (C), and controlling, by means of the control element (9), the motor (20) by means of the square wave control, and changing, by means of the control element (9), the gear stage when the rotational speed is close to the resonance frequency or the integer multiple of the resonance frequency.

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