Inverter device for electric vehicles

Abstract

Provided is an electric vehicle inverter device which makes it possible to sufficiently protect a switching element if an electric motor is in a locked state. The electric vehicle inverter device: is mounted in an electric vehicle comprising an electric motor that generates motive power for traveling; and drives the electric motor. The inverter device comprises: a multilevel inverter circuit that has a plurality of switching elements; a controller that controls the plurality of switching elements; and a temperature sensor that detects the temperature of each of the plurality of switching elements. Further, the multilevel inverter circuit has, as combinations for driving the switching elements, a plurality of combinations capable of outputting phase currents in the same phase and in the same direction. If torque is output from the electric motor and the electric motor is in a locked state in which the electric motor cannot rotate, the controller switches the combination of the switching elements for driving from among the plurality of combinations on the basis of the output of the temperature sensor.

Description

Technical Field

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[0001] The present invention relates to an inverter device for an electric vehicle.

Background Art

[0002] Patent Document 1 describes a vehicle equipped with an inverter capable of outputting power from a high-potential wiring, a medium-potential wiring, and a low-potential wiring. When the motor is locked, the operation of the inverter is alternately switched to a medium-potential operation, a high-potential operation, and a low-potential operation to protect the switching elements of the inverter.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=E35]]Between a plurality of switching elements constituting an inverter, there may already be variations in the amount of heat generation or temperature at the timing when the motor starts to lock. Also, the characteristics of the plurality of switching elements may be different. Therefore, even if the above protection method is adopted as it is, it may be difficult to sufficiently protect the plurality of driven switching elements.

[0005] An object of the present invention is to provide an inverter device for an electric vehicle that can more sufficiently protect switching elements when an electric motor is in a locked state.

Means for Solving the Problems

[0006] <1> One aspect of the present invention inverter device is It should be noted that there is a misspelling in the original text where "o000018" should probably be "0000018". This has been left as is in the translation as per the instructions.An inverter device for an electric vehicle, which is mounted on an electric motor that generates power for propulsion and drives the electric motor, Includes a first switching element and a second switching element A multilevel inverter circuit having multiple switching elements, A controller that controls the plurality of switching elements, A temperature sensor that detects the temperature of each of the plurality of switching elements, Equipped with, The multilevel inverter circuit has multiple combinations that are capable of outputting phase currents in the same phase and direction as combinations for driving the switching elements. The plurality of combinations include a first combination that drives the first switching element but does not drive the second switching element, and a second combination that does not drive the first switching element but drives the second switching element. When torque is output from the electric motor and the electric motor enters a locked state where it cannot rotate, the controller, based on the output of the temperature sensor, The first combination and the second combination are configured such that the temperature gradient of the element with the larger temperature margin is greater than the temperature gradient of the element with the smaller temperature margin. Switch. <2> Another embodiment of the present invention is an inverter device, An inverter device for an electric vehicle, which is mounted on an electric motor that generates power for propulsion and drives the electric motor, A multilevel inverter circuit having a plurality of switching elements, including a first switching element and a second switching element, A controller that controls the plurality of switching elements, A temperature sensor that detects the temperature of each of the plurality of switching elements, Equipped with, The multilevel inverter circuit has multiple combinations that are capable of outputting phase currents in the same phase and direction as combinations for driving the switching elements. The plurality of combinations include a first combination that drives the first switching element but does not drive the second switching element, and a second combination that does not drive the first switching element but drives the second switching element. When torque is output from the electric motor and the electric motor enters a locked state where it cannot rotate, the controller switches between the first combination and the second combination based on the output of the temperature sensor, at a rate that balances the temperature gradient of the first switching element and the temperature gradient of the second switching element, provided that the temperature margin of the first switching element and the temperature margin of the second switching element are in equilibrium. [Effects of the Invention]

[0007] According to the present invention, when an electric motor becomes locked, the combination of switching elements to be driven is switched based on the output of the temperature sensor, thereby providing better protection for the switching elements. [Brief explanation of the drawing]

[0008] [Figure 1] A block diagram showing an electric vehicle equipped with an inverter device, which is an embodiment of the present invention. [Figure 2]It is a diagram showing the multilevel inverter circuit of FIG. 1. [Figure 3] It is a data chart showing an example of a characteristic map of switching elements included in the controller. [Figure 4] It is a time chart showing an output example of the multilevel inverter circuit. <着 [Figure 5] It is a time chart showing a driving example of the switching element in the output example of FIG. 4. [Figure 6] It is a time chart showing an example of the temperature change of the switching element in the driving example of FIG. 5. [Figure 7] It is a flowchart showing an example of the inverter control process in the locked state. <00着00091> [Figure 8] It is a flowchart showing an example of the characteristic map learning process. [Figure 9] It is a diagram showing the multilevel inverter circuit of other embodiments.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 着

[0010] (Embodiment 1) FIG. 1 is a block diagram showing an electric vehicle equipped with an inverter device which is an embodiment of the present invention. FIG. 2 is a diagram showing the multilevel inverter circuit of FIG. 1.

[0011] The electric vehicle 1 in FIG. 1 includes drive wheels 2, an electric motor 11 that outputs driving power to the drive wheels 2, a battery 13 that supplies power to the electric motor 11, and an inverter device 20 that drives the electric motor 11. The inverter device 20 includes a multilevel inverter circuit 21 that converts power between the electric motor 11 and the battery 13, and a controller 22 that controls a plurality of switching elements Q1 to Q12 of the multilevel inverter circuit 21.

[0012] When an acceleration operation is performed using the driving control unit (not shown), the controller 22 drives the multi-level inverter circuit 21 at a timing corresponding to the requested torque, thereby powering the electric motor 11. Powering the electric motor 11 sends positive torque to the drive wheels 2, accelerating the electric vehicle 1. When a deceleration operation is performed using the driving control unit (not shown), the controller 22 drives the multi-level inverter circuit 21 at a timing corresponding to the requested torque, thereby regenerating the electric motor 11. Regenerative operation sends negative torque to the drive wheels 2, decelerating the electric vehicle 1. The requested torque is the output torque required for the electric motor 11, calculated based on the acceleration or deceleration operation.

[0013] If, while driving, the electric vehicle 1 encounters a step and is unable to overcome it, a positive torque may be output to the electric motor 11 and the drive wheels 2, while the electric motor 11 and the drive wheels 2 become unable to rotate. This state of the electric motor 11 is called the locked state. In the locked state, the inability to rotate includes not only the state in which the rotor of the electric motor 11 is almost stopped, but also the state in which the rotor alternates between forward and reverse rotation within a range that does not reach a 90° rotation.

[0014] The multilevel inverter circuit 21 is a circuit that provides three phase outputs, u-phase, v-phase, and w-phase, to, for example, a three-phase electric motor 11. The multilevel inverter circuit 21 has three potential points: a high-side potential point P1, a low-side potential point P0, and an intermediate potential point P2 of the battery 13. The multilevel inverter circuit 21 can generate a voltage between any two of these potential points as the output of one phase. With this configuration, the multilevel inverter circuit 21 can switch the magnitude of its output (e.g., output voltage) between multiple magnitudes.

[0015] More specifically, the multilevel inverter circuit 21 comprises a high-side potential point P1 and a low-side potential point P0 to which a DC voltage is supplied, and two capacitors C1 and C2 that generate an intermediate potential point P2 from the DC voltage. Furthermore, the multilevel inverter circuit 21 comprises three-phase output lines (u-phase, v-phase, and w-phase) L1 to L3, and a plurality of switching elements Q1 to Q12 that can switch between connecting and disconnecting each potential point. The plurality of switching elements Q1 to Q12 include switching elements Q1 to Q3 provided between the high-side potential point P1 and the three-phase output lines L1 to L3, respectively, and switching elements Q4 to Q6 provided between the low-side potential point P0 and the three-phase output lines L1 to L3, respectively. Furthermore, the multiple switching elements Q1 to Q12 include forward-flow switching elements Q7 to Q9, which are provided between the intermediate potential point P2 and the three-phase output lines L1 to L3, respectively, and reverse-flow switching elements Q10 to Q12, which are provided between the intermediate potential point P2 and the three-phase output lines L1 to L3, respectively. Rectifier elements D7 to D9, which interrupt the reverse current, are connected in series to the forward-flow switching elements Q7 to Q9. Rectifier elements D10 to D12, which interrupt the forward current, are connected in series to the reverse-flow switching elements Q10 to Q12.

[0016] The multiple switching elements Q1 to Q12 are not particularly limited, but are power semiconductor switches such as IGBTs (Insulated Gate Bipolar Transistors). The multiple switching elements Q1 to Q12 may have different characteristics (i.e., different sizes, different specifications, etc.) from, for example, switching elements Q1 to Q6 and switching elements Q7 to Q12. Furthermore, the multiple switching elements Q1 to Q12 may include elements with a rated temperature of a first temperature (e.g., 150°C) and elements with a rated temperature of a second temperature different from the first temperature (e.g., 200°C). For example, if a Si (silicon) semiconductor element is used, the rated temperature will be the first temperature, and if a SiC (silicon carbide) semiconductor element is used, the rated temperature will be the second temperature. Other semiconductor materials may be used as the multiple switching elements Q1 to Q12, or elements of other semiconductor materials may be included.

[0017] The multilevel inverter circuit 21 is equipped with temperature sensors H1 to H12 that measure the temperature of each of the multiple switching elements Q1 to Q12. Each of the temperature sensors H1 to H12 is configured to detect the temperature of each switching element Q1 to Q12 based on the forward voltage of a temperature-sensing diode connected to the wiring of the multilevel inverter circuit 21. However, the temperature sensors H1 to H12 can be configured in any way as long as they can detect the temperature of each switching element Q1 to Q12. The detection results from the temperature sensors H1 to H12 are sent to the controller 22.

[0018] The multilevel inverter circuit 21 has multiple combinations for driving the switching elements Q1 to Q12, each capable of outputting a phase current in the same phase and direction. For example, the above combinations capable of outputting a forward u-phase current in the u-phase include the combination of switching elements Q1 and Q5, the combination of switching elements Q1 and Q11, and the combination of switching elements Q7 and Q5. Similarly, there are multiple combinations for each of the above combinations capable of outputting a reverse u-phase current, a forward and reverse v-phase current, and a forward and reverse w-phase current, respectively. "Driving" a switching element means turning it on (i.e., turning the switch off to enable current flow).

[0019] The multilevel inverter circuit 21 is driven by the controller 22, which selects and drives one of the multiple switching elements Q1 to Q12 according to the rotation angle and rotation speed of the electric motor 11. This drive enables either traction operation, which generates torque in the electric motor 11, or regenerative operation, which generates negative torque in the electric motor 11. The driving method for the switching elements Q1 to Q12 is not particularly limited, but the PWM (Pulse Width Modulation) method is applied.

[0020] Figure 3 is a data chart showing an example of a characteristic map of the switching elements in the controller. The controller 22 has a characteristic map M1 in the storage medium 22a, which stores characteristic data related to the temperature of each switching element Q1 to Q12. The characteristic data includes multiple types of parameters representing heat generation characteristics, multiple types of parameters representing cooling capacity, and thermal specification data.

[0021] Parameters representing heat generation characteristics are parameters that show the relationship between specific driving conditions and the amount of heat generated. These parameters include, for example, parameters showing the relationship between the current of a switching element and the amount of heat generated, parameters showing the relationship between the continuous driving time of a switching element and a correction value for the amount of heat generated, and parameters showing the relationship between the driving duty cycle of a switching element and a correction value for the amount of heat generated. The controller 22 can calculate the amount of heat generated by each switching element Q1 to Q12 using the driving conditions of each switching element Q1 to Q12 and the above parameters for each switching element Q1 to Q12. Parameters representing cooling capacity are parameters that show the relationship between specific conditions and the cooling capacity. These parameters include, for example, parameters showing the relationship between ambient temperature and cooling capacity, parameters showing the relationship between the temperature of other adjacent switching elements and a correction value for cooling capacity, and parameters showing the relationship between the temperature of the switching element itself and a correction value for cooling capacity. The controller 22 can calculate the cooling capacity of each switching element Q1 to Q12 from the above conditions. Thermal specification data includes thermal capacity and rated temperature.

[0022] The controller 22 can calculate the heat generation and cooling amount of each switching element Q1 to Q12 using the driving conditions of the multilevel inverter circuit 21, the ambient temperature, the temperatures of the switching elements Q1 to Q12, and the characteristic data of the characteristic map M1. From these, the controller 22 calculates the temperature gradient and temperature margin change of each switching element Q1 to Q12. It can be estimated. The driving conditions of the multilevel inverter circuit 21 described above include conditions that allow the driving conditions of each switching element Q1 to Q12 to be estimated, such as the output power, the rotational speed and rotational angle of the electric motor 11, and the driving pattern of each switching element Q1 to Q12. The "temperature gradient" described above means the amount of temperature rise per unit time. The "temperature margin" described above means the difference between the rated temperature and the current temperature at each switching element Q1 to Q12 (temperature margin = rated temperature - current temperature).

[0023] Note that the characteristic data stored in the characteristic map M1 is not limited to the example above. For example, the characteristic data may be map data or parameters of a calculation formula that can calculate estimated values ​​of the temperature gradient of each switching element Q1 to Q12 by inputting general driving conditions and general environmental conditions (ambient temperature, etc.).

[0024] Multiple switching elements Q1 to Q12 do not have uniform specifications (size, semiconductor type, etc.). There are differences in the cooling structures of the multiple switching elements Q1 to Q12 (for example, the distance between each element and the corresponding cooling fin, the cooling capacity of each cooling fin, etc.). Therefore, the temperature characteristics of the multiple switching elements Q1 to Q12 include variations.

[0025] The controller 22 may monitor the driving conditions and environmental conditions and temperature of the multiple switching elements Q1 to Q12 during normal operation of the electric vehicle 1, and perform a learning process to update the characteristic data of the characteristic map M1 based on the results of the monitoring. This learning process allows the characteristic map M1 to reflect changes in the temperature characteristics of each switching element Q1 to Q12, even if these changes occur due to the aging of the multilevel inverter circuit 21 and its cooling device.

[0026] <Example of driving a switching element> Figure 4 is a time chart showing an example of the output of a multilevel inverter circuit. Figure 5 is a time chart showing an example of the driving of switching elements in the output example of Figure 4. Figure 6 is a time chart showing an example of the temperature change of switching elements in the driving example of Figure 5. Figure 5 shows the output of the u-phase and an example of the driving of four switching elements Q1, Q5, Q7, and Q11. The chart lines for the switching elements represent the ON state when high levels and the OFF state when low levels. Figure 6 shows the change in temperature margin of two switching elements Q5 and Q7 that generate heat in the output of the u-phase.

[0027] As shown in Figure 4, during the period T1 in which the electric motor 11 is operating, the multilevel inverter circuit 21 outputs a three-phase current corresponding to the rotor's rotation angle and rotation speed. Focusing on the switching elements Q1, Q5, Q7, and Q11 related to the u-phase output during period T1, the controller 22 performs the following control. That is, as shown in the period T1 in Figure 5, during the positive current output period, the controller 22 alternately switches between driving the switching elements Q7 and Q11 (timing t11, t13, etc.) and driving the switching elements Q1 and Q11 (timing t12, t14, etc.). Also, during the negative current output period, the controller 22 alternately switches between driving the switching elements Q7 and Q5 (timing t15, t17, etc.) and driving the switching elements Q7 and Q11 (timing t16, t18, etc.). The controller 22 switches the above driving of the switching elements Q1, Q5, Q7, and Q11 using the pulse width of the PWM control.

[0028] When the electric motor 11 stops, the output of the multilevel inverter circuit 21 also stops, as shown in period T2 of Figure 4. Then, at timing t31, when the system is locked, a nearly constant three-phase current output from the multilevel inverter circuit 21 continues according to the rotor's rotation angle, as shown in period T3 of Figure 4. In the example in Figure 4, the system is locked at a rotation angle where a forward current Iu1 flows through the u-phase coil, a reverse current Iv1 flows through the v-phase coil, and the current in the w-phase coil is zero.

[0029] When the controller 22 enters a locked state at timing t31, it drives the switching elements Q1, Q5, Q7, and Q11 so that the output currents for period T3 in Figure 4 (output current Iu1 for the u phase, output current Iv1 = -Iu1 for the v phase) are generated, as shown in period T3 in Figure 5. Here, switching element Q1 is referred to as the first switching element Q1, and switching element Q7 is referred to as the second switching element Q7.

[0030] The above output currents Iu1 and Iv1 can be generated by a first combination of switching elements in which the first switching element Q1 is driven and the second switching element Q7 is not driven (the combination of "Q1, Q5" and the combination of "Q1, Q11"). Furthermore, the above output currents Iu1 and Iv1 can be generated by a second combination of switching elements in which the first switching element Q1 is not driven and the second switching element Q7 is driven (the combination of "Q7, Q5"). The combination of switching elements Q1 and Q5 can continuously supply output currents Iu1 and Iv1 by pulse driving of that combination alone. The combination of switching elements Q1 and Q11 and the combination of switching elements Q7 and Q5 can continuously supply output currents Iu1 and Iv1 by alternately performing pulse driving of these combinations.

[0031] The controller 22 switches between the first combination and the second combination of switching elements based on the outputs of temperature sensors H1 and H7. More specifically, the controller 22 switches between the first combination and the second combination at an appropriate rate based on the temperature margin between the first switching element Q1 and the second switching element Q7.

[0032] When the system enters a locked state, at the initial timing t31, variations may occur in the temperature margins of multiple switching elements Q1 due to the previous driving of the electric motor 11. In the case of Figure 6, at the initial timing t31 of the locked state, the temperature margin of the second switching element Q7 is greater than that of the first switching element Q1.

[0033] In a situation where there is a difference in temperature margin, the controller 22 switches the combination of switching elements to be driven at a rate such that the temperature gradient of the element with the larger temperature margin is greater than the temperature gradient of the element with the smaller temperature margin (see period T3a). In the example in Figure 5, the controller 22 selects a combination such that the driving rate of the first switching element Q1, which has a smaller temperature margin, is the lowest. That is, the driving rate of the combination of switching elements Q1 and Q5 is set to zero, and the driving rate of alternating driving of switching elements Q1 and Q11 and switching elements Q7 and Q5 is set to 100%. With this driving, the first switching element Q1 and the second switching element Q7 are driven at the same rate. However, due to the characteristic of the smaller element size of the second switching element Q7, the temperature gradient of the first switching element Q1 becomes gentler than the temperature gradient of the second switching element Q7 (see period T3a in Figure 6).

[0034] Note that the controller 22 does not need to be set to the lowest possible drive ratio for the first switching element Q1 within the above temperature margin. The controller 22 may set the drive ratio of the first switching element Q1 to a slightly higher value than the lowest possible value, as long as the temperature gradient of the first switching element Q1 is gentler than the temperature gradient of the second switching element Q7.

[0035] Then, as the above-described drive continues during period T3a, the temperature margins of the first switching element Q1 and the second switching element Q7 are balanced at the end timing t32. "Temperature margin balance" means that the difference between the two temperature margins is less than 5°C.

[0036] Once the temperature margins are balanced, the controller 22 then calculates the drive ratio that balances the temperature gradient of the first switching element Q1 and the temperature gradient of the second switching element Q7, based on the characteristic map M1. Then, as shown in period T3b in Figure 5, pulse driving of switching elements Q1 and Q5, and alternating driving of switching elements Q1, Q11 and switching elements Q7 and Q5 are performed to generate the output current Iu1, so that the said drive ratio is achieved. The above statement that "the temperature gradients are balanced" means that the difference in temperature gradients is within 15% of the larger temperature gradient, more preferably within 5%. As this driving continues during period T3b, as shown in Figure 6, the temperature margins of the first switching element Q1 and the second switching element Q7 both decrease while remaining in equilibrium.

[0037] Here, we show the control of the comparative example. The dashed line in Figure 6 shows the change in the temperature margin of switching elements Q1 and Q7 when the control of the comparative example is performed. Let's assume that, as the control of the comparative example, the pulse drive ratio of switching elements Q1 and Q5 is set to 100% from the start of the locked state t31. In such a case, the drive ratio of the first switching element Q1 becomes higher than the drive ratio of the second switching element Q7. Therefore, as shown in the comparative example line in Figure 6, the temperature margin of the second switching element Q7 remains large, while the temperature margin of the first switching element Q1 suddenly decreases, and the temperature margin of the first switching element Q1 reaches zero prematurely.

[0038] However, according to the control of this embodiment, as shown in Figure 6, the time until the temperature margin between the first switching element Q1 and the second switching element Q7 reaches zero can be made significantly longer compared to the control of the comparative example. Therefore, there is a higher possibility that the electric motor 11 can be avoided before the temperature margin between the first switching element Q1 and the second switching element Q7 reaches zero, thereby providing sufficient protection for the switching elements Q1 and Q7.

[0039] Switching elements Q1 and Q5, connected to the high-side potential point P1 and the low-side potential point P0, respectively, often have similar temperature characteristics. Similarly, switching elements Q7 and Q11, connected to the intermediate potential point P2, often have similar temperature characteristics. Therefore, by performing the switching control shown in Figure 6, the temperature margins of switching elements Q5 and Q11 change in the same way as the temperature margins of switching elements Q1 and Q7. Consequently, the time it takes for the temperature margins of switching elements Q5 and Q11 to reach zero also becomes longer, providing sufficient protection for all switching elements Q1, Q5, Q7, and Q11 that are driven in the locked state.

[0040] Furthermore, there may be cases where the temperature characteristics vary more among multiple switching elements Q1 to Q12. In addition, there may be four or more combinations of switching elements that, when driven, can output a locked current. In these cases, the controller 22 can select any two switching elements whose drive ratio can be changed as the first and second switching elements that control the drive ratio. If there are multiple sets of such two switching elements, multiple sets of first and second switching elements may be selected. The controller 22 then calculates what drive ratio should be used for the selected first and second switching elements to bring the temperature gradient closer to equilibrium, and drives the switching elements at the calculated drive ratio. With this control, as in the examples in Figures 4 to 6, the time during which the temperature margin of the switching elements driven in the locked state is zero can be extended, thereby ensuring sufficient protection for each switching element.

[0041] Alternatively, the controller 22 can determine the output phase with the largest current value among the three-phase outputs, depending on the rotational position of the locked rotor. When the output phase with the largest current value is determined to be a single phase, it can be estimated that the switching element among the multiple switching elements Q1 to Q12 that carries the current for that output phase will experience the fastest decrease in temperature margin. Therefore, in such cases, the controller 22 may select the two switching elements whose temperature margins are estimated to decrease the fastest as the first and second switching elements that control the drive ratio. However, the controller 22 selects a combination in which the first switching element is driven and the second switching element is not driven, and a combination in which the second switching element is driven and the first switching element is not driven, in order to generate the required output current for each phase. With this type of control, as described above, the time during which the temperature margin of the switching element driven in the locked state becomes zero can be extended, thereby ensuring sufficient protection for each switching element.

[0042] Furthermore, in the above embodiment, after the temperature margins of the first switching element Q1 and the second switching element Q7 were balanced, the controller 22 calculated a drive ratio based on the characteristic map M1 that would decrease the temperature margins while maintaining balance. However, the controller 22 does not need to calculate the drive ratio based on the characteristic map M1. That is, the controller 22 can start driving at a certain drive ratio, and once the temperature margins begin to widen, it can perform control to change the drive ratio so that both temperature margins change in the opposite direction to the widening. This type of control can also achieve control that decreases the temperature margins while maintaining balance.

[0043] Note that the driving patterns of switching elements Q1 to Q12 described with reference to Figure 5 are merely examples, and various other patterns may be applied as driving patterns for switching elements Q1 to Q12 in normal and locked states.

[0044] <Inverter control processing in locked state> Next, we will explain a specific example of the processing performed by the controller 22 that controls the multi-level inverter circuit 21 described above, with reference to a flowchart. Figure 7 is a flowchart showing an example of inverter control processing in the locked state.

[0045] In this process, first, the controller 22 determines whether a locked state has occurred based on the requested torque and the rotational position data of the rotor of the electric motor 11 (step S1). If the result is NO, the process returns to step S1 and the determination process of step S1 is repeated. On the other hand, if the result is YES, the controller 22 proceeds to the next step S2.

[0046] When the process proceeds to step S2, the controller 22 determines the output phase with the maximum current value among the three-phase outputs based on the rotor's rotational position data (step S2). Furthermore, the controller 22 extracts multiple combinations of switching elements Q1 to Q12 that can generate the current of the output phase determined in step S2 by pulse driving or alternating driving (step S3). In addition, the controller 22 sets the first and second switching elements to be compared in terms of temperature margin (step S4).

[0047] Next, the controller 22 calculates, by referring to the characteristic map M1, what ratio (i.e., driving ratio) of driving the multiple combinations extracted in step S3 should be performed so that the temperature gradient of the first switching element and the temperature gradient of the second switching element are in equilibrium (step S5).

[0048] Subsequently, the controller 22 determines whether the temperature margins of the two switching elements are balanced (step S6). If the answer is NO, the controller 22 sets the drive ratio for each of the multiple combinations extracted in step S3 so that the drive ratio of the switching element with the smaller temperature margin is minimized (step S7). On the other hand, if the result of step S6 is YES, the controller 22 sets the drive ratio for each of the multiple combinations extracted in step S3 as the drive ratio calculated in step S5 (step S8).

[0049] Once the drive ratio is set in steps S7 and S8, the controller 22 drives the switching element at the set drive ratio (step S9). The controller 22 then determines whether the lock state has been released (step S10). If it is NO, it returns to step S6 and repeats the process from step S6. If it is YES, the controller 22 terminates the inverter control process in the locked state and returns to the inverter control process in normal mode.

[0050] The above-described inverter control process in the locked state enables an example of control of the multilevel inverter circuit 21 as shown in Figures 4 to 6.

[0051] <Characteristic Map Learning Process> Next, we will explain the learning process for the characteristic map M1. Figure 8 is a flowchart showing an example of the characteristic map learning process performed by the controller 22. The characteristic map learning process can be started at any time, for example, during normal driving.

[0052] When the characteristic map learning process is started, the controller 22 monitors the drive pattern of the multilevel inverter circuit 21, the ambient temperature of the multilevel inverter circuit 21, and the temperatures of each switching element Q1 to Q12 for a predetermined period and collects this data (step S11). The drive pattern refers to, for example, the output current, the combination in which the multiple switching elements Q1 to Q12 are driven, and the duty cycle at which they are driven. Then, based on the data collected in step S11, the controller 22 calculates the correction values ​​for each parameter of the characteristic map M1 (step S12).

[0053] Next, the controller 22 determines whether the correction value is greater than or equal to a threshold (step S13). If it is NO, the characteristic map learning process is terminated. On the other hand, if the determination result in step S13 is YES, each parameter of the characteristic map M1 is corrected based on the correction value (step S14). Then, the controller 22 terminates the characteristic map learning process.

[0054] Through this learning process, even if changes occur in the temperature characteristics of multiple switching elements Q1 to Q12 due to aging of the multilevel inverter circuit 21 and its cooling device, these changes can be reflected in the characteristic map M1.

[0055] The inverter control processing program G1 and the characteristic map learning processing program G2 in the locked state described above are stored in a non-transient computer-readable medium 22a of the controller 22. The controller 22 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium described above may store the programs G1 and G2.

[0056] As described above, according to the inverter device 20 of this embodiment, in the multilevel inverter circuit 21, there are multiple combinations of switching elements Q1 to Q12 that can output phase currents in the same phase and direction. Among the multiple switching elements Q1 to Q12, there may be switching elements that already have a large temperature difference when the system is locked. Also, there may be large differences in the heat generation characteristics and cooling characteristics among the multiple switching elements Q1 to Q12. Therefore, if the multiple switching elements to be driven are driven equally, the temperature margin of one of the switching elements may reach zero first. However, according to the inverter device 20 of this embodiment, when the electric motor 11 is locked, the controller 22 switches the combination of switching elements Q1 to Q12 to be driven from among the above multiple combinations based on the output of the temperature sensors H1 to H12. Therefore, even if there are differences in temperature margin, heat generation characteristics and cooling characteristics when the system is locked, it is possible to switch the combination of switching elements Q1 to Q12 to be driven so that the temperature margin of the driving switching elements approaches a balanced state. Therefore, by extending the time during which the temperature margin of a switching element driven in the locked state becomes zero, sufficient protection of the switching element can be ensured.

[0057] Furthermore, according to the inverter device 20 of this embodiment, there are multiple combinations of switching elements that can output phase currents in the same phase and direction. Among these multiple combinations, there is a first combination that drives the first switching element (e.g., switching element Q1) but does not drive the second switching element (e.g., switching element Q7). Furthermore, among these multiple combinations, there is a second combination that does not drive the first switching element (e.g., switching element Q1) but drives the second switching element (e.g., switching element Q7). When a locked state occurs, the controller 22 switches between the first and second combinations at a rate such that the temperature gradient of the element with the larger temperature margin is greater than the temperature gradient of the element with the smaller temperature margin. By such control, the time during which the temperature margin of the first and second switching elements is zero can be extended, thereby ensuring sufficient protection of these switching elements.

[0058] Furthermore, according to the inverter device 20 of this embodiment, when the temperature margins of the first switching element (e.g., switching element Q1) and the second switching element (e.g., switching element Q7) are balanced in the locked state, the control is performed as follows. That is, in the above case, the controller 22 switches between the first combination and the second combination at a drive ratio that balances the temperature gradient of the first switching element and the temperature gradient of the second switching element. By such control, the heat-generating switching elements are distributed in an appropriate proportion, and the time during which the temperature margin of the switching elements driven in the locked state is zero can be extended. Therefore, sufficient protection of the driven switching elements can be achieved.

[0059] Furthermore, according to the inverter device 20 of this embodiment, the controller 22 has a characteristic map M1, and uses the characteristic data of the characteristic map M1 to calculate the above-mentioned drive ratio and control the multilevel inverter circuit 21. Therefore, the controller 22 can efficiently control the temperature gradient of the driving switching elements. Thus, the time during which the temperature margin of the driving switching elements becomes zero in the locked state can be extended, and sufficient protection of the driving switching elements can be achieved.

[0060] Furthermore, when the controller 22 drives the multilevel inverter circuit 21 during periods other than the locked state, it performs a learning process to update the characteristic data of the characteristic map M1 based on the outputs of the temperature sensors H1 to H12. This process allows the characteristic map M1 to reflect changes in the heat generation characteristics of the multiple switching elements Q1 to Q12, as well as the cooling performance of the multilevel inverter circuit 21, even if these changes occur over time. Therefore, the calculation of the drive ratio using the characteristic data of the characteristic map M1 can be performed more accurately.

[0061] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, the specific configuration of the multilevel inverter circuit 21 is shown in Figure 2. However, the multilevel inverter circuit can be changed to various circuit configurations, such as applying a multilevel inverter circuit 21A with a different circuit configuration shown in Figure 9. Also, in the above embodiments, an example was shown where the electric vehicle 1 is an electric vehicle (EV), but the inverter device 20 of this embodiment may be installed in electric vehicles such as HEVs (Hybrid Electric Vehicles) and PHEVs (Plug-in Hybrid Electric Vehicles). Furthermore, details shown in the embodiments can be appropriately modified without departing from the spirit of the invention. [Industrial applicability]

[0062] This invention can be used in inverter devices for electric vehicles. [Explanation of symbols]

[0063] 1. Electric Vehicle 2 drive wheels 11 Electric motor 13 Batteries 20 Inverter device 21 Multilevel Inverter Circuit C1, C2 Capacitors D7~D12 Rectifier elements L1~L3 Output Lines P1 High-side potential point P2 Intermediate potential point P0 Low-side potential point Q1~Q12 Switching elements H1~H12 Temperature Sensor 22 controllers 22a Storage medium M1 Characteristic Map G1, G2 Program

Claims

1. An inverter device for an electric vehicle, which is mounted on an electric motor that generates power for propulsion and drives the electric motor, A multilevel inverter circuit having a plurality of switching elements, including a first switching element and a second switching element, A controller that controls the plurality of switching elements, A temperature sensor that detects the temperature of each of the plurality of switching elements, Equipped with, The multilevel inverter circuit has multiple combinations that are capable of outputting phase currents in the same phase and direction as combinations for driving the switching elements. The plurality of combinations include a first combination that drives the first switching element but does not drive the second switching element, and a second combination that does not drive the first switching element but drives the second switching element. The inverter device for an electric vehicle is characterized in that, when torque is output from the electric motor and the electric motor enters a locked state where it cannot rotate, the controller switches between the first combination and the second combination based on the output of the temperature sensor, such that the temperature gradient of the first switching element with a larger temperature margin is greater than the temperature gradient of the second switching element with a smaller temperature margin.

2. An inverter device for an electric vehicle, which is mounted on an electric motor that generates power for propulsion and drives the electric motor, A multilevel inverter circuit having a plurality of switching elements, including a first switching element and a second switching element, A controller that controls the plurality of switching elements, A temperature sensor that detects the temperature of each of the plurality of switching elements, Equipped with, The multilevel inverter circuit has multiple combinations that are capable of outputting phase currents in the same phase and direction as combinations for driving the switching elements. The plurality of combinations include a first combination that drives the first switching element but does not drive the second switching element, and a second combination that does not drive the first switching element but drives the second switching element. The controller is characterized in that, when torque is output from the electric motor and the electric motor enters a locked state where it cannot rotate, the controller switches between the first combination and the second combination based on the output of the temperature sensor, in a ratio that balances the temperature gradient of the first switching element and the temperature gradient of the second switching element, when the temperature margin of the first switching element and the temperature margin of the second switching element are in equilibrium.

3. The inverter device for an electric vehicle according to claim 1 or 2, wherein the controller has characteristic data representing the temperature gradient of the first switching element when the first switching element is driven by the first combination and the temperature gradient of the second switching element when the second switching element is driven by the second combination, and controls the multilevel inverter circuit in the locked state using the characteristic data.

4. The inverter device for an electric vehicle according to claim 3, characterized in that the controller performs a learning process to update the characteristic data based on the output of the temperature sensor when driving the multilevel inverter circuit during a period other than the locked state.

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