Electric vehicle

Abstract

To provide an electric vehicle that is configured to decrease frequencies of a carrier signal at a place where a calorific value of a switching element may increase to suppress the calorific value of the switching element.SOLUTION: An electric vehicle disclosed in the specification comprises a motor for running, an inverter and a controller. The inverter has a switching element, and generates AC power that is supplied to the motor by operating the switching element. The controller generates a PWM signal for driving the switching element using a carrier signal. The controller stores map data in which a predetermined range on a map is associated with frequencies of the carrier signal. When a temperature of the switching element is over a predetermined threshold temperature, the controller sets frequencies corresponding to a current position of the electric vehicle to the frequencies of the carrier signal, with reference to the map data.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an electric vehicle equipped with a motor for driving. [Background technology]

[0002] An electric vehicle includes a traction motor and an inverter that supplies AC power to the motor. The inverter converts DC power into AC power by turning on and off multiple switching elements. The switching elements are driven by a PWM signal. As is well known, the PWM signal is generated from a target current (or target voltage) for each phase of the motor and a carrier signal. The carrier signal is a triangular wave (or square wave) with a predetermined frequency. It is known that lowering the frequency of the carrier signal reduces losses in the switching elements and reduces the amount of heat generated by the switching elements (see, for example, Patent Document 1). On the other hand, lowering the frequency of the carrier signal increases current ripple, resulting in increased noise and vibration. Increasing the frequency of the carrier signal reduces noise and vibration but increases the amount of heat generated by the switching elements. In other words, there is a trade-off between noise and vibration and the amount of heat generated by the switching elements. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-307908 Summary of the Invention [Problem to be solved by the invention]

[0004] The present specification provides an electric vehicle that can suppress the amount of heat generated by switching elements by lowering the frequency of a carrier signal in places where the amount of heat generated by switching elements is likely to be high. [Means for solving the problem]

[0005] The electric vehicle disclosed in this specification includes a traction motor, an inverter, and a controller. The inverter has a switching element that generates AC power to be supplied to the motor by operating the switching element. The controller generates a PWM signal for driving the switching element using a carrier signal. The controller stores map data that associates predetermined areas on a map with the frequency of the carrier signal. When the temperature of the switching element exceeds a predetermined threshold temperature, the controller refers to the map data and sets the frequency of the carrier signal to a frequency corresponding to the current position of the electric vehicle. For example, in the map data, a frequency corresponding to an area within a circuit is set lower than a frequency for an area excluding the circuit.

[0006] For example, at a circuit, there is a high probability that the vehicle will be traveling at high speeds for long periods of time, which makes it extremely likely that the amount of heat generated by the switching elements will increase. The electric vehicle disclosed in this specification lowers the frequency of the carrier signal when the electric vehicle is located in an area where high-speed traveling is expected. This process reduces the amount of heat generated by the switching elements.

[0007] Details and further improvements of the technology disclosed in this specification are described in the following "Description of Embodiments of the Invention." [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram of an electric vehicle according to an embodiment; [Figure 2] 1 is an example of map data. [Figure 3] FIG. 10 is a flowchart of a carrier frequency determination process. DETAILED DESCRIPTION OF THE INVENTION

[0009] An electric vehicle 2 according to an embodiment will be described with reference to the drawings. FIG. 1 shows a block diagram of the electric vehicle 2. The electric vehicle 2 includes a battery 3, an inverter 10, a motor 20, a cooler 30, and a controller 40. The electric vehicle 2 runs on the motor 20. The inverter 10 converts DC power from the battery 3 into AC power for driving the motor 20. The motor 20 is driven by the AC power output from the inverter 10. The output shaft of the motor 20 is connected to wheels 22 via axles 21. The controller 40 determines a target output of the motor 20 according to the vehicle speed and accelerator opening, and controls the inverter 10 so that the output of the motor 20 follows the target output. The dotted arrows in FIG. 1 represent signal lines.

[0010] The inverter 10 will now be described. The inverter 10 includes six switching elements 11a-11f. For ease of explanation, "switching element" will be abbreviated to "SW element" below. The six SW elements 11a-11f are connected in series, two by two. The three series-connected bodies are connected in parallel to the battery 3. The SW elements 11a, 11c, and 11e on the positive side of the battery 3 may be referred to as upper SW elements, and the SW elements 11b, 11d, and 11f on the negative side may be referred to as lower SW elements. When the controller 40 alternately turns on and off the upper and lower SW elements, AC power is output from the midpoint of the series-connected body.

[0011] The inverter 10 is provided with a current sensor 12 that measures the output current, and the motor 20 is provided with a rotation speed sensor 23 that measures the rotation speed. The measurement data of the current sensor 12 and the rotation speed sensor 23 are sent to the controller 40.

[0012] The cooler 30 cools the SW elements 11a-11f and the motor 20. The cooler 30 includes a cooling water circulation path 31 that passes through the inverter 10, an oil cooler 34, and a radiator 33. The cooling water is circulated through the cooling water circulation path 31 by a water pump 32. The circulating cooling water cools the SW elements 11a-11f in the inverter 10. The inverter 10 includes a temperature sensor 13 that measures the temperature of the cooling water. Measurement data from the temperature sensor 13 is sent to the controller 40. The controller 40 uses the measurement data from the temperature sensor 13 as an estimate of the temperature of the SW elements.

[0013] The cooler 30 also includes an oil circulation path 35 that passes through an oil cooler 34 and the motor 20. Oil is circulated through the oil circulation path 35 by an oil pump 36. The motor 20 is cooled by the circulating oil.

[0014] The process by which the controller 40 controls the inverter 10 (switching elements 11a-11f) will be described. The controller 40 includes a target output calculation unit 41, a current command value calculation unit 42, a PWM driver 43, a frequency determination unit 44, a carrier signal generation unit 45, and a database 46. The target output calculation unit 41 acquires measurement data of the accelerator opening from an accelerator opening sensor 52 and acquires measurement data of the rotation speed of the motor 20 from the rotation speed sensor 23. The target output calculation unit 41 calculates the vehicle speed from the measurement data of the rotation speed sensor 23. The target output calculation unit 41 determines the target output of the motor 20 based on the vehicle speed and the accelerator opening. The current command value calculation unit 42 converts the target output into target values ​​(current target values) of the three-phase output current of the inverter 10. Furthermore, the current command value calculation unit 42 obtains the current output current of the inverter 10 from the measurement value of the current sensor 12. The current command value calculation unit 42 determines the current command value so as to reduce the difference between the current target value and the current output current.

[0015] The PWM driver 43 generates a PWM signal for driving each SW element so that the output current of the inverter 10 follows the current command value. The PWM driver 43 converts the target current value into a voltage command value and generates a PWM signal with a desired duty ratio by superimposing the voltage command value on a carrier signal. Here, the carrier signal is a triangular wave signal (or a square wave signal) with a predetermined frequency. The PWM driver 43 generates a PWM signal for each SW element. The generated PWM signal is supplied to each SW element 11a-11f. In this way, the controller 40 controls the inverter 10 (SW elements 11a-11f) so that the output of the motor 20 follows the target output.

[0016] Hereinafter, the frequency of the triangular wave (or square wave) of the carrier signal will be referred to as the carrier frequency. The carrier signal is generated by a carrier signal generation unit 45. The carrier signal generation unit 45 obtains the carrier frequency from a frequency determination unit 44. The frequency determination unit 44 obtains data on the current location of the electric vehicle 2 from a GPS sensor 51. The frequency determination unit 44 also reads map data stored in a database 46. The map data is data that associates a predetermined range on a map with a carrier frequency.

[0017] An example of map data is shown in Figure 2. The leftmost column of the table in Figure 2 (the "Map Range" column) would normally show the map range as a series of points represented by east longitude and north latitude, but to facilitate understanding, Figure 2 uses the notations "Range 1," "Range 2," and "Other than the above." "Range Characteristics" indicates the type of location / facility the range in the leftmost column is. The rightmost column lists the carrier frequency associated with each range. Carrier frequency F1 is associated with ranges other than range 1 and range 2. Below, carrier frequency F1 may also be referred to as reference frequency F1. Range 1, which is a racing circuit, is associated with frequency F2, which is smaller than reference frequency F1. Range 2, which has a slow-down restriction, is associated with frequency F3, which is larger than reference frequency F1.

[0018] Returning to FIG. 1, the frequency determination process will be further described. The frequency determination unit 44 obtains measurement data from the temperature sensor 13. As described above, the measurement data from the temperature sensor 13 is used as an estimate of the temperature of the SW element. For ease of explanation, the measurement data from the temperature sensor 13 will be referred to as the SW element temperature below. If the SW element temperature exceeds a predetermined threshold temperature, the frequency determination unit 44 refers to the map data and identifies a carrier frequency associated with the range to which the current location obtained from the GPS sensor 51 belongs. The identified carrier frequency is sent to the carrier signal generation unit 45, which generates a triangular wave (or rectangular wave) carrier signal of the identified carrier frequency, as described above.

[0019] The reference frequency F1 is also set as the initial value of the carrier frequency. In other words, the frequency determination unit 44 determines the reference frequency F1 as the carrier frequency when the SW element temperature does not exceed the temperature threshold value and when the current location of the electric vehicle 2 is unknown.

[0020] The carrier frequency determination process will be explained again with reference to the flowchart in Fig. 3. The controller 40 (frequency determination unit 44) compares the SW element temperature (measurement data of the temperature sensor 13) with a threshold temperature (step S12). If the SW element temperature does not exceed the threshold temperature, the controller 40 sets the reference frequency F1 as the carrier frequency (step S12: NO, S19).

[0021] When the temperature of the SW element exceeds the threshold temperature, the controller 40 acquires the current position of the electric vehicle 2 from the GPS sensor 51 (step S13). The controller 40 collates the acquired current position with the map data (step S14). When the current position is within the range 1 (circuit field) in FIG. 2, the controller 40 sets F2 (<F1) as the carrier frequency (step S15: YES, S16). Also, when the current position is within the range 2 (slowdown limit range) in FIG. 2, the controller 40 sets F3 (>F1) as the carrier frequency (step S15: NO, S17: YES, S18). When the current position is not inside either range 1 or range 2, the controller 40 sets the reference frequency F1 as the carrier frequency (step S15: NO, S17: NO, S19).

[0022] The carrier frequency is determined by any one of steps S16, S18, and S19. The controller 40 generates a carrier signal at the determined frequency and uses that carrier signal to generate a PWM signal. The controller 40 supplies the PWM signal to the SW elements 11a - 11f (step S20).

[0023] Thus, the controller 40 generates a PWM signal with a carrier signal of a frequency corresponding to the current position of the electric vehicle 2 and drives the SW elements 11a - 11f with the generated PWM signal.

[0024] The advantages of the above carrier frequency determination process will be explained. As is well known, the carrier frequency determines the operating frequency of the SW element. Lowering the carrier frequency suppresses the loss of the SW element and the amount of heat generated by the SW element. On the other hand, when the carrier frequency is lowered, the current ripple becomes larger, and the noise and vibration become larger. Conversely, when the carrier frequency is increased, the noise and vibration become smaller, but the amount of heat generated by the SW element becomes larger. That is, there is a trade - off relationship between the noise and vibration and the amount of heat generated by the SW element.

[0025] The threshold temperature is set to a value slightly lower than the upper limit of the appropriate temperature range for the SW elements. In the map data, carrier frequency F2 corresponding to the circuit (range 1) is set lower than carrier frequency F1 for the range excluding the circuit. Because there is a high probability of high-speed driving for long periods of time on a circuit, there is an extremely high possibility that the SW elements will generate a large amount of heat. When driving on a circuit, vibration and noise are not a problem, but the large amount of heat generated can damage the SW elements. Alternatively, if electric vehicle 2 stops after high-speed driving, it is expected that the temperature of the SW elements will not drop easily because they will not be exposed to the wind from the road. Electric vehicle 2 can prevent overheating of the SW elements by lowering the carrier frequency on a circuit.

[0026] In the map data, a carrier frequency F3 corresponding to a slow-travel restriction range (range 2), such as a factory site, is set higher than a carrier frequency F1 for a range excluding the slow-travel restriction range. Increasing the carrier frequency increases the amount of heat generated by the SW elements, but reduces the current ripple of the SW elements. In the slow-travel restriction range, the target output of the motor is not high, so the amount of heat generated by the SW elements is likely not a problem. On the other hand, reducing the current ripple of the SW elements reduces noise and vibration. In the electric vehicle 2 of the embodiment, noise and vibration of the electric vehicle 2 can be reduced in the slow-travel restriction range.

[0027] The following points should be noted regarding the technology described in the embodiment: The map data in Fig. 2 is an example, and the correspondence between ranges and frequencies is not limited to that shown in Fig. 2.

[0028] The term "electric vehicle" disclosed in this specification includes hybrid vehicles that have an engine together with a motor for running, and vehicles equipped with fuel cells.

[0029] Although specific examples of the present 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 claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful. [Explanation of symbols]

[0030] 2: Electric vehicle 3: Battery 10: Inverter 11a-11f: Switching element 12: Current sensor 13: Temperature sensor 20: Motor 21: Axle 22: Wheel 23: Rotation speed sensor 30: Cooler 31: Cooling water circuit 32: Water pump 33: Radiator 34: Oil cooler 35: Oil circuit 36: Oil pump 40: Controller 41: Target output calculation unit 42: Current command value calculation unit 43: PWM driver 44: Frequency determination unit 45: Carrier signal generation unit 46: Database 51: GPS sensor 52: Accelerator opening sensor

Claims

[Claim 1] An electric vehicle, A driving motor; an inverter having a switching element and generating AC power to be supplied to the motor by operation of the switching element; a controller that generates a PWM signal for driving the switching element using a carrier signal; and the controller comprises: map data that associates a predetermined range on a map with the frequency of the carrier signal; When the temperature of the switching element exceeds a predetermined threshold temperature, the map data is referenced and the frequency corresponding to the current position of the electric vehicle is set as the frequency of the carrier signal. Electric car.

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