Electric vehicle

Abstract

To provide an electric vehicle that can warm a battery of a stopped electric vehicle by making use of heat generated by a specific switching element of an inverter while preventing the switching element from overheating.SOLUTION: An electric vehicle disclosed by the present specification includes a running motor, an inverter, a heat medium circulation system and a controller. The inverter is connected between a battery and the motor, and converts a direct current power of the battery into AC power and supplies it to the motor. The heat medium circulation system sends a heat medium that has passed through the inverter to the battery. The controller controls the inverter so that a q-axis current flowing to the motor is zero and a d-axis current alternately repeats a positive value and a negative value when a rotation speed of the motor is zero and a temperature of the battery is lower than a prescribed lower temperature threshold value. When the q-axis current is zero, the motor does not generate a torque. By alternately switching the d-axis current between a positive value and a negative value, an electric current is not concentrated in a specific switching element.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to an electric vehicle equipped with a motor for running, an inverter, and a battery. The electric vehicle in this specification may include a hybrid vehicle equipped with an engine together with a motor for running. [Background technology]

[0002] The efficiency of a battery decreases when the temperature is low. Therefore, Patent Document 1 discloses a technology in which a current is passed through a motor for driving so that the loss is increased, and the heat generated by the loss is used to warm the battery. Specifically, a current is passed through the motor so that the reluctance torque of the motor becomes a negative value. Patent Document 2 also discloses a technology in which a refrigerant is warmed by heat generated by motor loss. In the technology of Patent Document 2, the d-axis current command value Id* and the q-axis current command value Iq* are changed so that the d-axis current value Id moves in the direction of increasing along a constant torque curve in a dq coordinate system. This increases the loss of the motor and increases the amount of heat generated. In both of the technologies of Patent Documents 1 and 2, the amount of heat generated by the motor is increased by devising a current command to be passed through the motor while driving. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-110021 A [Patent Document 2] Patent Publication No. 2021-141747 Summary of the Invention [Problem to be solved by the invention]

[0004] There are cases where it is desirable to warm up the battery even when the electric vehicle is stopped. For example, this is the case when charging the battery when its temperature is low. Or, in cold regions, it is the case when warming up the battery at a time determined by a timer setting before using the electric vehicle. In this specification, warming up the battery is sometimes referred to as battery warming.

[0005] When an electric vehicle is stopped, the battery warm-up cannot rotate the motor. In this case, it is possible to continue to pass a constant current through a specific switching element of the inverter to heat the switching element, and use that heat to warm the heat medium sent to the battery. However, this can cause the specific switching element to overheat. This specification provides a technology that prevents the specific switching element of the inverter from overheating, while utilizing the heat generated by the switching element to warm the battery of a stopped electric vehicle. [Means for solving the problem]

[0006] The electric vehicle disclosed in this specification includes a motor for driving, an inverter, a heat medium circulating device, and a controller. The inverter is connected between the battery and the motor, and converts the DC power of the battery into AC power and supplies it to the motor. The heat medium circulating device sends the heat medium that has passed through the inverter to the battery. When the rotation speed of the motor is zero and the temperature of the battery is lower than a predetermined low temperature threshold, the controller controls the inverter so that the q-axis current flowing through the motor is zero and the d-axis current alternates between positive and negative values. If the q-axis current is zero, the motor does not generate torque. In other words, the zero rotation speed state of the motor is maintained. In addition, a current command value in which the d-axis current is a positive value lengthens the on-time of the upper switching element of a specified phase. A current flows through the upper switching element of a specified phase for a long time, and the temperature of the upper switching element rises. When the d-axis current is switched from a positive value to a negative value, the off-off of the upper switching element and the lower switching element is reversed, and the on-time of the lower switching element is lengthened. The temperature rise of the upper switching element stops, and the temperature of the lower switching element rises. In the above description, the "upper switching element" and the "lower switching element" may be reversed. The heat medium sent to the battery is heated by the amount of heat generated by the upper switching element or the amount of heat generated by the lower switching element. The heated heat medium warms the battery. According to the technology disclosed in this specification, the battery can be heated without rotating the motor and while preventing overheating of the inverter switching elements.

[0007] Details and further improvements of the technology disclosed in this specification are described in the following "Forms for Carrying Out the Invention". [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram of an electric vehicle according to an embodiment. [Diagram 2] 4 is a diagram showing the relationship between a voltage command value (maximum voltage), a carrier signal, and a PWM signal. [Diagram 3] 4 is a diagram showing the relationship between a voltage command value (minimum voltage), a carrier signal, and a PWM signal. [Figure 4] 4 is a flowchart of a battery warm-up process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 drive system of the electric vehicle 2. The electric vehicle 2 includes a battery 20, an inverter 10, a motor 30 for driving, a heat medium circulating device 40, and a controller 50. Although not shown in the figure, the output shaft of the motor 30 is connected to the wheels via a gear set. The motor 30 is a three-phase AC motor.

[0010] A battery 20 is connected to a DC end of the inverter 10, and a motor 30 is connected to an AC end of the inverter 10. The inverter 10 converts the DC power of the battery 20 into AC power for driving the motor 30.

[0011] The circuit structure of the inverter 10 will be described. The inverter 10 includes six switching elements 11a, 11b, 11c, 11d, 11e, and 11f. The switching elements 11a and 11b are connected in series, and the switching elements 11c and 11d (11e and 11f) are also connected in series. The three sets of series-connected bodies are connected in parallel between the positive and negative poles of the DC terminal of the inverter 10. The midpoints of the three sets of series-connected bodies are connected to the AC terminal of the inverter 10. The switching elements 11a, 11c, and 11e on the positive pole side of the DC terminal are called upper arm switching elements, and the switching elements 11b, 11d, and 11f on the negative pole side of the DC terminal are called lower arm switching elements. When referring to any of the six switching elements 11a, 11b, 11c, 11d, 11e, and 11f without distinction, or when referring to the six switching elements collectively, they are referred to as switching elements 11. The switching element 11 is a semiconductor element for power conversion called a power transistor. Specifically, the switching element 11 is, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0012] A diode 12 is connected in inverse parallel to each switching element 11. In addition, each switching element 11 is accompanied by a temperature sensor 13.

[0013] The six switching elements 11 are controlled by a controller 50. The controller 50 determines a target output of the motor 30 based on the vehicle speed and accelerator opening, and drives the switching elements 11 so as to realize the target output. The switching elements 11 are driven by a PWM signal applied to their gates. The PWM signal is a binary pulse signal having a high potential and a low potential. When the PWM signal applied to the gate is at a high potential, the switching element 11 is turned on. That is, the drain electrode and source electrode (collector electrode and emitter electrode) of the switching element are conductive. When the PWM signal applied to the gate is at a low potential, the switching element 11 is turned off. That is, the drain electrode and source electrode (collector electrode and emitter electrode) of the switching element are disconnected.

[0014] The controller 50 supplies an inverted signal of the PWM signal supplied to the upper arm switching element 11a (11c, 11e) to the lower arm switching element 11b (11d, 11f). When a PWM signal with an appropriate duty ratio and its inverted signal are supplied to the upper arm switching element and the lower arm switching element, respectively, an AC current is output from the midpoint of the series connection.

[0015] The heat medium circulating device 40 cools the battery 20 and the inverter 10 (switching element 11) to prevent them from overheating. In addition, the heat medium circulating device 40 warms the battery 20 when the temperature of the battery 20 is too low.

[0016] The heat medium circulating device 40 includes a circulation path 41, a pump 42, and a heat medium cooler 43. A liquid heat medium is sealed in the circulation path 41. The pump 42 circulates the heat medium through the heat medium cooler 43, the inverter 10, and the battery 20 in that order. The heat medium cooler 43 cools the heat medium flowing through the circulation path 41. The heat medium cooler 43 may be, for example, a radiator or a chiller.

[0017] When the temperature of the inverter 10 (switching element 11) or the battery 20 is high, the controller 50 circulates the heat medium while operating the heat medium cooler 43. Then, the heat medium cooled by the heat medium cooler 43 flows to the inverter 10 and the battery 20. That is, the heat medium circulating device 40 cools the inverter 10 (switching element 11) and the battery 20.

[0018] If the temperature of the battery 20 is too low, the efficiency decreases. Therefore, when the battery 20 is at a low temperature, the controller 50 stops the heat medium cooler 43 and circulates the heat medium while driving the inverter 10. Then, the heat medium warmed by the heat of the inverter 10 (switching element 11) is sent to the battery 20. That is, the battery 20 is warmed. When the heat medium cooler 43 is a radiator, a shutter is provided to block the blowing of air to the radiator. When the controller 50 closes the shutter, the heat medium is no longer cooled by the radiator. That is, the heat medium cooler 43 stops its function.

[0019] The battery 20 is provided with a temperature sensor 23, and the controller 50 acquires the measurement value of the temperature sensor 23 to monitor the temperature of the battery 20. In addition, each switching element 11 is also provided with a temperature sensor 13, and the controller 50 acquires the measurement value of the temperature sensor 13 to monitor the temperature of each switching element 11.

[0020] The electric vehicle 2 includes a charging inlet 21. The battery 20 of the electric vehicle 2 can be charged by connecting an external power source to the charging inlet 21.

[0021] As mentioned above, the efficiency of the battery 20 decreases if its temperature is too low. For example, when charging with an external power source, if the temperature of the battery 20 is low, the charging efficiency decreases. Alternatively, if the electric vehicle 2 starts to run when the battery 20 is in a low-temperature state, the battery 20 will be used at a low efficiency. Therefore, the controller 50 can warm the battery 20 with a heat medium while the electric vehicle 2 is stopped (i.e., while the motor 30 is stopped from rotating).

[0022] As described above, it is necessary to drive the inverter 10 in order to warm the battery 20. When driving the inverter 10 while the electric vehicle 2 is stopped, the controller 50 devise a PWM signal to be given to the switching element 11 so that a current flows through the motor 30 but the motor 30 does not output torque (so that the motor 30 does not rotate).

[0023] The output torque Trq of the motor 30 is given by the following (Equation 1).

number

[0024] In (Equation 1), the symbol Pn represents the number of magnetic poles of the rotor. The symbols Id and Iq represent the d-axis current and the q-axis current flowing through the motor 30, respectively. The symbols Ld and Lq represent the d-axis inductance and the q-axis inductance of the rotor of the motor 30, respectively. According to (Equation 1), when the q-axis current Iq is zero and the d-axis current Id is non-zero, a current flows through the motor 30 (i.e., the switching element 11), but the motor 30 does not generate torque. That is, the rotation speed of the motor 30 remains zero. When the battery 20 is warmed up while the vehicle is stopped, the controller 50 controls the inverter 10 so that the q-axis current Iq is zero and the d-axis current Id is non-zero. Then, while the rotation of the motor 30 is stopped, a current flows through the switching element 11, and the switching element 11 generates heat. At the same time, the controller 50 drives the pump 42 (the heat medium cooler 43 is stopped) to circulate the heat medium between the inverter 10 and the battery 20. The battery 20 is heated by the heat medium heated by the switching element 11 .

[0025] However, if a constant d-axis current continues to flow, the load on a particular switching element 11 increases, and there is a risk of that switching element 11 overheating. Therefore, the controller 50 controls the inverter 10 (switching elements 11) so that the q-axis current Iq flowing through the motor 30 is zero and the d-axis current Id alternates between positive and negative values. This alleviates current concentration on the particular switching element 11, and prevents the switching element 11 from overheating.

[0026] An example of a PWM signal to be applied to the switching element 11 will be described. The controller 50 controls the inverter 10 so that the q-axis current Iq is zero and the d-axis current Id is the current Imax. The controller 50 converts the current command value (q-axis current command value Iq=0, d-axis current command value Id=Imax) into a voltage command value. The controller 50 compares the voltage command value with a carrier signal (triangular wave signal) to generate a PWM signal. The relationship between the current command values ​​Id, Iq and the voltage command values ​​Vd, Vq when the motor 30 is stopped (when the motor rotation is zero) is expressed by the following (Equation 2). In (Equation 2), the symbol R means the electrical resistance of the stator coil of the motor 30.

[0027]

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[0028] Assume that the q-axis current command value Iq is zero, and the d-axis current command value is a constant value, for example, Imax. When the d-axis and q-axis voltage command values ​​in (Equation 2) are converted into three-phase (U, V, W) voltage command values, for example, the U-phase voltage command value becomes the maximum voltage Vmax. The controller 50 compares the voltage command value with the carrier signal, and generates a PWM signal in which the section where the voltage command value > the carrier signal is at a HIGH potential and the section where the voltage command value < the carrier signal is at a LOW potential (FIG. 2). The PWM signal provided to the upper arm switching element 11a of the U phase at this time is as shown in FIG. 2(b). Note that the symbol "SW element" in FIG. 2 (and FIG. 3) means "switching element." The time of the HIGH potential of the PWM signal provided to the upper arm switching element 11a becomes longer. That is, the time during which current flows through the upper arm switching element 11a becomes longer. The amount of heat generated by the upper arm switching element 11a increases.

[0029] When the PWM signal to the U-phase upper arm switching element 11a is at a low potential, that is, while the upper arm switching element 11a is off, a current flows through the diode 12 associated with the U-phase lower arm switching element 11b.

[0030] The d-axis current command value Id is switched from a positive current command value Imax to a negative current command value (-Imax). The U-phase voltage command value becomes the minimum voltage value Vmin (FIG. 3). The PWM signal applied to the upper arm switching element 11a of the U-phase at this time is as shown in FIG. 3(b). The time period during which the PWM signal applied to the upper arm switching element 11a is at a LOW potential becomes longer. As described above, the signal obtained by inverting the PWM signal for the upper arm switching element becomes the PWM signal for the lower arm switching element (FIG. 3(c)). Therefore, at this time, the time period during which the PWM signal applied to the lower arm switching element 11b is at a HIGH potential becomes longer. That is, the time period during which a current flows through the lower arm switching element 11b becomes longer. The amount of heat generated by the lower arm switching element 11b increases. Conversely, the time period during which a current flows through the upper arm switching element 11a becomes shorter, and the amount of heat generated by the upper arm switching element 11a is suppressed. Overheating of the upper arm switching element 11a is prevented. During a period in which the PWM signal applied to the lower arm switching element 11b is at a low potential, a current flows through the diode 12 associated with the upper arm switching element 11a.

[0031] In this way, when the d-axis current Id (d-axis current command value) alternates between positive and negative values, the time during which current alternates between the upper arm switching element and the lower arm switching element becomes longer. Therefore, a constant amount of heat is maintained throughout the inverter 10, but overheating of the switching element 11 is prevented.

[0032] A flowchart of the control for heating the battery 20 while the vehicle is stopped is shown in Fig. 4. The temperature raising control will be described with reference to Fig. 4. The process of Fig. 4 is performed prior to charging the battery 20 with an external power source. That is, the controller 50 starts the process of Fig. 4 when an external power source is connected to the battery 20.

[0033] 4 is started if the temperature of battery 20 is below the lower limit of the optimum temperature range when an external power source is connected to charging inlet 21. In FIG. 4, the symbol "SW element" also means "switching element."

[0034] The controller 50 drives the inverter 10 with the q-axis current Iq=zero and the d-axis current=current Imax as command values ​​(step S12). The inverter 10 continues to be driven with the above current command values ​​until the temperature of the switching element 11 exceeds a predetermined upper limit temperature (steps S13: NO, S15: NO). When the temperature of the switching element 11 exceeds the predetermined upper limit temperature, the controller 50 inverts the positive and negative of the value of the d-axis current Id (d-axis current command value) and continues to drive the inverter 10 (steps S13: YES, S14). At this time, the command value of the q-axis current Iq remains zero. As described above, when the command value of the d-axis current Id is inverted, the time during which a long current flows alternates between the upper arm switching element and the lower arm switching element. In this way, a constant amount of heat is maintained throughout the inverter 10, but overheating of the switching element 11 is prevented.

[0035] When the temperature of the battery 20 exceeds the lower limit of the optimum temperature range, the controller 50 stops the inverter 10 and ends the temperature increase process (steps S15: YES, S16).

[0036] The controller 50 of the electric vehicle 2 in the embodiment controls the inverter 10 so that the q-axis current flowing through the motor 30 is zero and the d-axis current alternates between positive and negative values ​​when the rotation speed of the motor 30 is zero and the temperature of the battery 20 is lower than a predetermined low temperature threshold. The electric vehicle 2 in the embodiment can warm up the battery 20 of the electric vehicle 2 while parked, by utilizing heat generated by a specific switching element 11 of the inverter 10, while preventing overheating of the switching element 11. The "lower limit of the optimum temperature range" in the embodiment corresponds to the "low temperature threshold." "Controlling the inverter 10 so that the q-axis current flowing through the motor 30 is zero and the d-axis current alternates between positive and negative values" may be rephrased as "controlling the inverter by setting the q-axis current command value to zero and alternately setting the d-axis current command value to positive and negative values."

[0037] Points to note regarding the technology described in the embodiment are described below. In the temperature rise process (FIG. 4) of the embodiment, when the temperature of the switching element exceeds the upper limit temperature, the positive and negative command values ​​of the d-axis current Id are reversed. Since the rate of temperature rise of the switching element and the current flowing through the switching element are known, the controller 50 may reverse the positive and negative command values ​​of the d-axis current Id at a fixed cycle, regardless of the temperature of the switching element.

[0038] Alternatively, since the temperature of the heat medium flowing through the inverter 10 is an indicator of the temperature of the switching element 11, the controller 50 may be configured to reverse the sign of the command value of the d-axis current Id when the temperature of the heat medium in the inverter 10 exceeds a predetermined temperature threshold.

[0039] Although specific examples of the present invention have been described above in detail, 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. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0040] 2: Electric vehicle 10: Inverter 11, 11a-11f: Switching element 12: Diode 13: Temperature sensor 20: Battery 21: Charging inlet 23: Temperature sensor 30: Motor 40: Heat medium circulating device 41: Circulation path 42: Pump 43: Heat medium cooler 50: Controller

Claims

[Claim 1] It is an electric vehicle, A driving motor; A battery; A power supply is connected between the battery and the motor, and converts DC power from the battery into AC power. and an inverter for converting the converted value into a value to be supplied to the motor; a heat medium circulating device that sends the heat medium that has passed through the inverter to the battery; a controller that controls the inverter so that, when the rotation speed of the motor is zero and the temperature of the battery is lower than a predetermined low temperature threshold, a q-axis current flowing through the motor is zero and a d-axis current alternately takes positive and negative values; An electric vehicle equipped with

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