Inverter control device and program

Abstract

To provide an inverter control device capable of avoiding an inverter and a rotary electric machine from being in a state of overheating while suppressing the torque reduction of the rotary electric machine or maintaining the torque.SOLUTION: The inverter control device is applied to a control system including a rotary electric machine and an inverter. The rotary electric machine has a stator winding. The inverter is electrically connected to the stator winding and has upper and lower arm switches. The inverter control device includes a switching control unit and a temperature acquiring unit. The switching control unit executes switching control of the inverter while providing a dead time, which is a period during which both of the upper and lower arm switches are in an off state. The temperature acquiring unit acquires a motor temperature Tmgd. The switching control unit, when executing switching control while applying a weakened field current to the stator winding, and when it is determined that the acquired motor temperature Tmgd exceeds a temperature threshold value TAH, reduces the actual dead time by shortening a target dead time value DT* and reduces the weakened field current.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an inverter control device and a program. [Background technology]

[0002] 2. Description of the Related Art Conventionally, as described in Patent Document 1, for example, there is known an inverter control device that is applied to a control system including a rotating electric machine having a stator winding and an inverter electrically connected to the stator winding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 3-198601 Summary of the Invention [Problem to be solved by the invention]

[0004] In a high-speed rotation region of a rotating electric machine, a field-weakening control may be performed in which a field-weakening current is passed through a stator winding. In this case, the magnitude of a current vector passed through the stator winding to generate a predetermined torque in the rotating electric machine is larger than when the field-weakening control is not performed. Therefore, when the field-weakening control is performed, the amount of heat generated by the inverter and the rotating electric machine is larger than when the field-weakening control is not performed, and at least one of the inverter and the rotating electric machine may become overheated.

[0005] In order to prevent at least one of the inverter and the rotating electric machine from overheating, it is possible to reduce the command torque of the rotating electric machine. However, in this case, there is a concern that the rotating electric machine may not be able to continue to be driven appropriately.

[0006] A main object of the present invention is to provide an inverter control device and a program that can prevent the inverter and the rotating electric machine from becoming overheated while suppressing a torque decrease in the rotating electric machine or maintaining the torque. [Means for solving the problem]

[0007] The present invention relates to an inverter control device applied to a control system including a rotating electric machine having a stator winding, and an inverter electrically connected to the stator winding and having upper and lower arm switches, the inverter control device comprising: a switch control unit that executes switching control of the inverter while providing a dead time, which is a period during which both the upper and lower arm switches are in an off state; and a temperature acquisition unit that acquires the temperature of at least one of the inverter and the rotating electric machine, wherein when the switching control is executed while a field-weakening current is passed through the stator winding, the switch control unit shortens the actual dead time and reduces the field-weakening current when it determines that the acquired temperature exceeds a temperature threshold value.

[0008] According to the present invention, when a switching control is performed while a field-weakening current is flowing through the stator winding, if it is determined that the temperature acquired by the temperature acquisition unit exceeds the temperature threshold value, the actual dead time is shortened, thereby increasing the voltage utilization rate of the inverter.

[0009] A higher voltage utilization rate provides a torque margin for the rotating electric machine. Therefore, in the present invention, the field weakening current is reduced. This reduces the magnitude of the current vector flowing through the stator winding, suppresses the amount of heat generated by the inverter and the rotating electric machine, and prevents the inverter and the rotating electric machine from overheating. At this time, the torque reduction caused by the reduction in the field weakening current can be suppressed by improving the voltage utilization rate, and the torque reduction caused by the reduction in the field weakening current can be compensated for by improving the voltage utilization rate.

[0010] According to the present invention as described above, it is possible to prevent the inverter and the rotating electric machine from becoming overheated while suppressing a torque decrease in the rotating electric machine or maintaining the torque. [Brief description of the drawings]

[0011] [Figure 1] 1 is an overall configuration diagram of a control system according to a first embodiment. [Diagram 2] FIG. 4 is a functional block diagram of torque control executed by the control device. [Diagram 3] 5 is a diagram showing changes in a command voltage and a carrier signal in switching control. FIG. [Figure 4] 4 is a time chart showing changes in the voltage between the terminals of each switch. [Diagram 5] 4 is a flowchart showing a procedure for overheat protection control. [Figure 6] 4 is a timing chart showing changes in current flowing through each switch and voltage between terminals. [Figure 7] FIG. 11 is a diagram showing a method for setting a dead time target value. [Figure 8] FIG. 4 is a diagram showing a method for setting a field-weakening current. [Figure 9] FIG. 13 is a diagram showing an example of a case where overheat protection control is performed. [Figure 10] 10 is a flowchart showing a procedure of overheat protection control according to a second embodiment. [Figure 11] 4 is a timing chart showing changes in current flowing through each switch and voltage between terminals. [Figure 12] FIG. 11 is a diagram showing a method for setting a dead time target value. [Figure 13] FIG. 11 is a configuration diagram of a control device according to a third embodiment. [Figure 14] 4 is a flowchart showing a procedure for overheat protection control. [Figure 15] FIG. 13 is a diagram showing a method for setting the discharge rate of a gate charge. [Figure 16] FIG. 11 is a diagram showing a method for setting a dead time target value. [Figure 17] 10 is a flowchart showing a procedure of overheat protection control according to a fourth embodiment. [Figure 18] 4 is a timing chart showing changes in current flowing through each switch and voltage between terminals. [Figure 19] 4 is a timing chart showing changes in current flowing through each switch and voltage between terminals. [Figure 20] FIG. 13 is a diagram showing a method for setting the discharge rate of a gate charge. [Figure 21] 13 is a flowchart showing a procedure of overheat protection control according to a fifth embodiment. [Figure 22] 4 is a timing chart showing changes in current flowing through each switch and voltage between terminals. [Figure 23] FIG. 13 is a diagram showing a method for setting the discharge rate of a gate charge. [Figure 24] 13 is a flowchart showing a procedure of overheat protection control according to a sixth embodiment. [Diagram 25] FIG. 13 is a diagram showing a method for setting the gate charge rate. [Figure 26] 13 is a flowchart showing a procedure of overheat protection control according to the seventh embodiment. [Figure 27] FIG. 13 is a diagram showing a method for setting the gate charge rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a control device according to the present invention will now be described with reference to the drawings. In this embodiment, a control system including a control device is mounted on a vehicle such as an electric vehicle.

[0013] As shown in Fig. 1, a vehicle 10 includes a rotating electric machine 20. The rotating electric machine 20 is a three-phase synchronous machine, and includes star-connected stator windings 21 for each phase. The stator windings 21 for each phase are arranged at an electrical angle of 120°. The rotating electric machine 20 of this embodiment is a permanent magnet synchronous machine having a rotor 22 equipped with permanent magnets as field poles.

[0014] The rotating electric machine 20 is an in-vehicle main engine, and its rotor 22 is capable of transmitting power to the drive wheels 11 of the vehicle 10. Torque generated by the rotating electric machine 20 functioning as an electric motor is transmitted from the rotor 22 to the drive wheels 11. This causes the drive wheels 11 to rotate. The rotating electric machine 20 may be an in-wheel motor integrally provided on the wheels of the vehicle 10, or a so-called on-board motor provided on the body of the vehicle 10.

[0015] The vehicle 10 includes an inverter 30, a capacitor 31, and a storage battery 12 that is a DC power source. The inverter 30 includes three phases of series-connected upper arm switches SWH and lower arm switches SWL. In this embodiment, each switch SWH, SWL is a voltage-controlled semiconductor switching element, specifically an IGBT. Therefore, the high potential side terminal of each switch SWH, SWL is a collector, and the low potential side terminal is an emitter. Freewheel diodes DH, DL are connected in inverse parallel to each switch SWH, SWL.

[0016] In each phase, a first end of the stator winding 21 is connected to the emitter of the upper arm switch SWH and the collector of the lower arm switch SWL. Second ends of the stator windings 21 of each phase are connected to each other at a neutral point. In this embodiment, the stator windings 21 of each phase are set to have the same number of turns.

[0017] The collectors of the upper arm switches SWH of each phase and the positive terminal of the storage battery 12 are connected by a positive bus bar Lp. The emitters of the lower arm switches SWL of each phase and the negative terminal of the storage battery 12 are connected by a negative bus bar Ln. The positive bus bar Lp and the negative bus bar Ln are connected by a capacitor 31. The capacitor 31 may be built in the inverter 30 or may be provided outside the inverter 30.

[0018] The storage battery 12 is, for example, a battery pack, and the terminal voltage of the storage battery 12 is, for example, several hundred V. The storage battery 12 is, for example, a secondary battery such as a lithium ion battery or a nickel-metal hydride battery.

[0019] The vehicle 10 includes a current sensor 32, a voltage sensor 33, a rotation angle sensor 34, a motor temperature sensor 35, an inverter temperature sensor 36, and a control device 37. The current sensor 32 detects currents flowing through the stator windings 21 of at least two of the phases. The voltage sensor 33 detects the terminal voltage of the capacitor 31 as a power supply voltage Vdc. The rotation angle sensor 34 is, for example, a resolver, and detects the rotation angle (specifically, the electrical angle) of the rotor 22. The motor temperature sensor 35 is, for example, a thermistor, and detects the temperature of the rotating electric machine 20 (for example, the temperature of the stator windings 21) as the motor temperature Tmgd. The inverter temperature sensor 36 is, for example, a thermistor or a temperature-sensitive diode, and detects the temperature of the inverter 30 (for example, the temperature of the upper and lower arm switches SWH, SWL) as the inverter temperature Tinvd. The detection values ​​of the sensors 32 to 36 are input to the control device 37.

[0020] The control device 37 is mainly composed of a microcomputer 37a, and the microcomputer 37a has a CPU. The functions provided by the microcomputer 37a can be provided by software recorded in a substantial memory device and a computer that executes the software, by software alone, by hardware alone, or by a combination of these. For example, when the microcomputer 37a is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a large number of logic circuits, or by an analog circuit. For example, the microcomputer 37a executes a program stored in a non-transitory tangible storage medium as a storage unit provided in the microcomputer 37a. The program includes, for example, a program for a process shown in FIG. 5. By executing the program, a method corresponding to the program is executed. The storage unit is, for example, a non-volatile memory. The program stored in the storage unit can be updated, for example, via a network such as the Internet.

[0021] The control device 37 receives the command torque Trq*. The control device 37 performs switching control of the switches SWH and SWL constituting the inverter 30 so as to control the torque of the rotating electric machine 20 to the received command torque Trq*. In each phase, the upper arm switch SWH and the lower arm switch SWL are alternately turned on with a dead time therebetween.

[0022] Next, the torque control of the rotating electric machine 20 executed by the control device 37 will be described with reference to Fig. 2. In the example shown in Fig. 2, current feedback control is performed as the torque control. Note that, instead of the current feedback control, torque feedback control may be performed.

[0023] The command current setting unit 40 sets the d-axis and q-axis command currents Id* and Iq* based on the command torque Trq* and the rotation speed Nm of the rotor 22. The d-axis and q-axis command currents Id* and Iq* may be calculated, for example, by minimum current maximum torque control (MTPA). The command current setting unit 40 may set the d-axis and q-axis command currents Id* and Iq* based on map information or formula information in which the command torque Trq* and the rotation speed Nm of the rotor 22 are associated with the d-axis and q-axis command currents Id* and Iq*. The rotation speed Nm of the rotor 22 may be calculated, for example, based on the detection value of the rotation angle sensor 34.

[0024] The two-phase conversion unit 41 converts the U-, V-, and W-phase currents in the three-phase fixed coordinate system into a d-axis current Idr and a q-axis current Iqr in a two-phase rotating coordinate system (dq coordinate system) based on the detection value of the current sensor 32 and the electrical angle θe detected by the rotation angle sensor 34.

[0025] The d-axis deviation calculation unit 42 calculates the d-axis current deviation ΔId by subtracting the d-axis current Idr from the d-axis command current Id*. The q-axis deviation calculation unit 43 calculates the q-axis current deviation ΔIq by subtracting the q-axis current Iqr from the q-axis command current Iq*.

[0026] The d-axis command voltage calculation unit 44 calculates a d-axis command voltage Vd as a manipulated variable for feedback-controlling the d-axis current Idr to the d-axis command current Id* based on the d-axis current deviation ΔId. The q-axis command voltage calculation unit 45 calculates a q-axis command voltage Vq as a manipulated variable for feedback-controlling the q-axis current Iqr to the q-axis command current Iq* based on the q-axis current deviation ΔIq. The feedback control used by the d-axis command voltage calculation unit 44 and the q-axis command voltage calculation unit 45 may be, for example, proportional-integral control.

[0027] The three-phase conversion unit 46 converts the d- and q-axis command voltages Vd, Vq in the two-phase rotating coordinate system into U-, V- and W-phase command voltages VU*, VV*, and VW* in the three-phase fixed coordinate system based on the d- and q-axis command voltages Vd, Vq and the electrical angle θe output from the d- and q-axis command voltage calculation units 44, 45. In this embodiment, the U-, V- and W-phase command voltages VU*, VV*, and VW* have sinusoidal waveforms with phases shifted by 120° in electrical angle.

[0028] The signal generating unit 47 generates drive signals GUH, GUL for the U-phase upper and lower arm switches SWH, SWL, drive signals GVH, GVL for the V-phase upper and lower arm switches SWH, SWL, and drive signals GWH, GWL for the W-phase upper and lower arm switches SWH, SWL by three-phase modulation based on the U-, V-, and W-phase command voltages VU*, VV*, VW* and the power supply voltage Vdc.

[0029] The signal generating unit 47 outputs the generated U-phase upper and lower arm drive signals GUH, GUL to the gates of the U-phase upper and lower arm switches SWH, SWL, outputs the generated V-phase upper and lower arm drive signals GVH, GVL to the gates of the V-phase upper and lower arm switches SWH, SWL, and outputs the generated W-phase upper and lower arm drive signals GWH, GWL to the gates of the W-phase upper and lower arm switches SWH, SWL. Thus, sine wave PWM control is performed as switching control of the inverter 30. Note that the carrier signal Sig in this embodiment is a triangular wave signal with equal rising and falling speeds.

[0030] 3 and 4 are diagrams showing an example of the execution mode of the sine wave PWM control, taking the U phase as an example. In Fig. 3, (a) shows the transitions of the U phase normalized command voltage VUS and carrier signal Sig over a period of 180 electrical degrees, and (b) shows the transition of the U phase PWM signal GU* over a period of 180 electrical degrees. In Fig. 4, (a) shows the transition of the U phase PWM signal GU*, (b) shows the transition of the inverted signal, (c) and (d) show the transitions of the upper and lower arm drive signals GUH and GUL of the U phase upper and lower arm switches SWH and SWL, and (e) and (f) show the transitions of the inter-terminal voltages VceH and VceL applied between the collector-emitter of each switch SWH and SWL of the U phase.

[0031] The signal generating unit 47 calculates the U-phase normalized command voltage VUS by dividing the U-phase command voltage VU* by half the power supply voltage Vdc. As shown in Fig. 3, the signal generating unit 47 calculates the U-phase PWM signal GU* based on a comparison of the magnitude between the U-phase normalized command voltage VUS and the carrier signal Sig.

[0032] The signal generating unit 47 generates an inverted signal by inverting the logic of the U-phase PWM signal GU*. The signal generating unit 47 generates upper and lower arm drive signals GUH and GUL for the U-phase upper and lower arm switches SWH and SWL by performing processing to separate the timings of logical inversion of the U-phase PWM signal GU* and the inverted signal by the dead time target value DT*. The dead time target value DT* is a period during which both the upper and lower arm drive signals GUH and GUL for the U-phase upper and lower arm switches SWH and SWL are turned off.

[0033] The signal generating unit 47 outputs the generated upper and lower arm drive signals GUH, GUL for the U-phase upper and lower arm switches SWH, SWL to the gates of the U-phase upper and lower arm switches SWH, SWL. As a result, the U-phase upper and lower arm switches SWH, SWL are turned on or off with the actual dead time DTr therebetween.

[0034] In detail, each switch SWH, SWL of the U phase is switched from the on state to the off state with a turn-off period toff sandwiched therebetween, and is switched from the off state to the on state with a turn-on period ton sandwiched therebetween. Here, in this embodiment, the on state of each switch SWH, SWL is a state in which the gate voltage of each switch SWH, SWL is equal to or higher than the threshold voltage Vth, and the off state of each switch SWH, SWL is a state in which the gate voltage of the switch is less than the threshold voltage Vth.

[0035] The on state of each switch SWH, SWL may be a state in which a current starts to flow through each switch SWH, SWL, or a state in which the inter-terminal voltages VceH, VceL of each switch SWH, SWL start to drop. The off state of each switch SWH, SWL may be a state in which the current flowing through each switch SWH, SWL is zero, or a state in which the inter-terminal voltages VceH, VceL of each switch SWH, SWL are the power supply voltage Vdc.

[0036] The turn-on period ton is the period from when the drive signals GUH, GUL of the switches SWH, SWL are switched to an ON command until the gate voltage of each switch SWH, SWL rises to the threshold voltage Vth. The turn-off period toff is the period from when the drive signals GUH, GUL of the switches SWH, SWL are switched to an OFF command until the gate voltage of each switch SWH, SWL falls to below the threshold voltage Vth. Note that Fig. 4 shows how the inter-terminal voltages VceH, VceL of the switches SWH, SWL change with the change in gate voltage.

[0037] In this case, the actual dead time DTr is the dead time target value DT* minus the turn-off period toff plus the turn-on period ton (DTr=DT*-toff+ton).

[0038] In this embodiment, when a field-weakening current is flowing through the stator winding 21, the control device 37 executes overheat protection control to reduce the field-weakening current while shortening the actual dead time DTr in order to prevent the inverter 30 and the rotating electric machine 20 from becoming overheated.

[0039] Next, the overheat protection control executed by the control device 37 will be described with reference to Fig. 5. The overheat protection control shown in Fig. 5 is executed repeatedly at a predetermined control period, for example.

[0040] In step S10, it is determined whether or not the field weakening control for causing a field weakening current to flow through the stator windings 21 is being executed.

[0041] If it is determined in step S10 that the field-weakening control is being executed, the process proceeds to step S11, where the motor temperature Tmgd detected by the motor temperature sensor 35 is acquired. The process of step S11 corresponds to the "temperature acquisition unit."

[0042] In step S12, it is determined whether the motor temperature Tmgd has exceeded a temperature threshold value TAH (for example, 140° C.).

[0043] If it is determined in step S12 that the motor temperature Tmgd is equal to or lower than the temperature threshold value TAH, the process proceeds to step S13, where the dead time target value DT* is set to an initial dead time target value.

[0044] In step S14, the d-axis command current Id* is set to an initial command current based on the command torque Trq* and the rotation speed Nm of the rotor 22. The initial command current is the d-axis command current Id* when the dead time target value DT* is the initial dead time target value.

[0045] On the other hand, if it is determined in step S12 that the motor temperature Tmgd exceeds the temperature threshold value TAH, there is a risk of the rotating electric machine 20 becoming overheated, so the process proceeds to step S15. In step S15, the magnitude of the current vector to the stator winding 21 is acquired. The magnitude of the current vector may be calculated based on the detection value of the current sensor 32 and the electrical angle. In this embodiment, the process of step S15 corresponds to the "current acquisition unit."

[0046] In step S16, the dead time target value DT* is made shorter than the initial dead time target value. In this embodiment, the smaller the magnitude of the current vector is, the shorter the dead time target value DT* is.

[0047] Here, the relationship between the magnitude of the current vector to the stator winding 21 and the turn-off period toff will be described. For example, the magnitude of the current vector may become small due to a low command torque Trq*. In this case, the smaller the magnitude of the current vector to the stator winding 21, the smaller the current Isw flowing through each switch SWH, SWL.

[0048] 6, (a) shows the transition of the current Isw flowing through one of the switches SWH, SWL that is turned off, and (b) shows the transition of the inter-terminal voltage Vce of the switch that is turned off. The second current Isw2 shown by the dashed line is smaller than the first current Isw1 shown by the solid line due to the smaller magnitude of the current vector to the stator winding 21. The first inter-terminal voltage Vce1 is the inter-terminal voltage when the first current Isw1 flows, and the second inter-terminal voltage Vce2 is the inter-terminal voltage when the second current Isw2 flows.

[0049] 6, when the switches SWH, SWL are turned off, the period required for the second current Isw2 to fall to 0 is shorter than the period required for the first current Isw1 to fall to 0. Therefore, the turn-off period toff when the second current Isw2 flows is shorter than the turn-off period toff when the first current Isw1 flows. In other words, the smaller the magnitude of the current vector to the stator winding 21, the shorter the turn-off period toff of the switch that is turned off of the switches SWH, SWL.

[0050] In order to realize an actual dead time DTr in which the switches SWH, SWL are not short-circuited, the smaller the current Isw flowing through each switch SWH, SWL, the shorter the turn-off period toff, and the shorter the turn-off period toff, the shorter the dead time target value DT* can be set. Therefore, in this embodiment, as shown in FIG. 7, the smaller the magnitude of the current vector to the stator winding 21, the shorter the dead time target value DT* is. This also shortens the actual dead time DTr. The dead time target value DT* may be set by map information or formula information in which the dead time target value DT* and the current vector to the stator winding 21 are associated with each other.

[0051] Returning to the explanation of Fig. 5, in step S17, the d-axis command current Id* is set so that the field weakening current is reduced compared to the initial command current. In detail, as shown in Fig. 8, the d-axis command current Id* is set so that the field weakening current is reduced as the dead time target value DT* is shorter.

[0052] The voltage utilization rate of the inverter 30 increases due to the shortening of the actual dead time DTr. The higher the voltage utilization rate, the more margin there is in the torque of the rotating electric machine 20. In this case, the field weakening current can be reduced. Therefore, in the command current setting unit 40, the d-axis command current Id* is set so that the field weakening current decreases as the dead time target value DT* becomes shorter. The map information or formula information relating the d-axis command current Id* and the dead time target value DT* may be created for each operating condition determined by the torque and rotation speed Nm of the rotating electric machine 20, taking into consideration the expected reduction in the field weakening current due to the improvement in the voltage utilization rate caused by the shortening of the actual dead time DTr. In this embodiment, steps S12, S16, and S17 correspond to the "switch control unit".

[0053] Fig. 9 shows an example of a case where overheat protection control is performed. Fig. 9(a) shows an operating region of an operating point determined from the rotation speed Nm and torque Trq of the rotating electric machine 20. Fig. 9(b) shows a transition of a current vector when the rotation speed Nm increases while the torque Trq of the rotating electric machine 20 is maintained at a predetermined torque Trqc. In Fig. 9, the solid line shows a case where the dead time target value DT* is set to the initial dead time target value, and the dashed line shows a case where the dead time target value DT* is shortened from the initial dead time target value.

[0054] When the dead time target value DT* is set to the initial dead time target value, the first boundary b1 divides the operating region into a first low speed region Rs1 and a first high speed region Rh1. The first low speed region Rs1 is a region where the rotation speed Nm is lower than the first boundary b1. The first high speed region Rh1 is a region where the rotation speed Nm is equal to or higher than the first boundary b1. On the other hand, when the dead time target value DT* is shortened below the initial dead time target value, the second boundary b2 divides the operating region into a second low speed region Rs2 and a second high speed region Rh2. The second low speed region Rs2 is a region where the rotation speed Nm is lower than the second boundary b2. The second high speed region Rh2 is a region where the rotation speed Nm is equal to or higher than the second boundary b2.

[0055] In the first low-speed region Rs1 and the second low-speed region Rs2, the magnitude of the current vector is substantially constant. On the other hand, in the first high-speed region Rh1 and the second high-speed region Rh2, the magnitude of the current vector increases as the rotation speed Nm increases due to an increase in the field-weakening current.

[0056] When the dead time target value DT* is made shorter than the initial dead time target value by the process of step S16, the rotation speed Nm at which the magnitude of the current vector starts to increase becomes higher than when the dead time target value DT* is set to the initial dead time target value. In this case, the process of step S17 can be performed to reduce the field weakening current to be less than the initial command current, thereby reducing the magnitude of the current vector.

[0057] According to the present embodiment described above in detail, the following effects can be obtained.

[0058] When the motor temperature Tmgd is determined to exceed the temperature threshold value TAH while the switching control is being performed while a field-weakening current is flowing through the stator winding 21, the actual dead time DTr is shortened by shortening the dead time target value DT*. This increases the voltage utilization rate of the inverter 30.

[0059] A higher voltage utilization rate provides more torque for the rotating electric machine 20. Therefore, in the present invention, the field-weakening current is reduced. This reduces the magnitude of the current vector flowing through the stator winding 21, suppresses the amount of heat generated by the inverter 30 and the rotating electric machine 20, and prevents the inverter 30 and the rotating electric machine 20 from overheating. At this time, the torque reduction caused by the reduction in the field-weakening current can be suppressed by improving the voltage utilization rate, and the torque reduction caused by the reduction in the field-weakening current can be compensated for by improving the voltage utilization rate.

[0060] According to the present embodiment described above, it is possible to prevent the inverter 30 and the rotating electric machine 20 from becoming overheated while suppressing a decrease in the torque of the rotating electric machine 20 or maintaining the torque.

[0061] When it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the dead time target value DT* is shortened from the initial dead time target value as the magnitude of the current vector to the stator winding 21 decreases. This makes it possible to appropriately shorten the actual dead time DTr in response to the change in the magnitude of the current vector.

[0062] The shorter the dead time target value DT*, the more the field weakening current is reduced. In other words, the field weakening current is reduced while taking into consideration the expected reduction in the field weakening current due to the improvement in the voltage utilization rate caused by the shortening of the actual dead time DTr. This allows for appropriate overheat protection.

[0063] <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, the process when it is determined that the motor temperature Tmgd has exceeded the temperature threshold value TAH is changed. Specifically, instead of the dead time target value DT* being shortened as the magnitude of the current vector to the stator winding 21 is smaller, the dead time target value DT* is shortened as the inter-terminal voltage Vce applied between the collector-emitter of each switch SWH, SWL is lower.

[0064] The overheat protection control executed by the control device 37 will be described with reference to Fig. 10. The overheat protection control shown in Fig. 10 is executed repeatedly at a predetermined control period, for example. For convenience, the same processes as those shown in Fig. 5 are denoted by the same reference numerals in Fig. 10.

[0065] If the determination in step S12 is affirmative, the process proceeds to step S18. In step S18, the power supply voltage Vdc is acquired. As the power supply voltage Vdc, the detection value of the voltage sensor 33 may be used. Then, the process proceeds to step S19. In this embodiment, the process in step S18 corresponds to the "voltage acquisition unit."

[0066] In step S19, the dead time target value DT* is made shorter than the initial dead time target value. In this embodiment, the lower the power supply voltage Vdc is, the shorter the dead time target value DT* is in the command current setting unit 40. Note that in this embodiment, the process of step S19 corresponds to a "switch control unit."

[0067] Here, the relationship between the power supply voltage Vdc and the dead time target value DT* will be described. For example, the power supply voltage Vdc may become low due to a low output voltage of the storage battery 12. In this case, the lower the power supply voltage Vdc, the lower the inter-terminal voltage Vce of each switch SWH, SWL in the off state.

[0068] FIG. 11 is a diagram showing the transition of the current Isw flowing through one of the switches SWH and SWL that is turned off, and the inter-terminal voltage Vce. FIGS. 11(a) and 11(b) correspond to FIGS. 6(a) and 6(b). The second power supply voltage Vdc2 is a voltage lower than the first power supply voltage Vdc1. The third inter-terminal voltage Vce3 shown by a solid line is the inter-terminal voltage of the switch that is turned off under the first power supply voltage Vdc1. The third current Isw3 is a current flowing through the switch that is turned off in response to the third inter-terminal voltage Vce3. The fourth inter-terminal voltage Vce4 shown by a dashed line is the inter-terminal voltage of the switch that is turned off under the second power supply voltage Vdc2. The fourth current Isw4 is a current flowing through the switch that is turned off in response to the fourth inter-terminal voltage Vce4.

[0069] When the switches are switched to the off state, the time required for the voltage Vce4 between the fourth terminals to rise to the second power supply voltage Vdc2 is shorter than the time required for the voltage Vce3 between the third terminals to rise to the first power supply voltage Vdc1. Therefore, when each switch SWH, SWL is switched to the off state, the turn-off period toff when the switch is switched to the off state under the second power supply voltage Vdc2 is shorter than the turn-off period toff when the switch is switched to the off state under the first power supply voltage Vdc1. In other words, the lower the power supply voltage Vdc is, the shorter the turn-off period toff of the switch becomes.

[0070] Therefore, in this embodiment, focusing on the relationship that the lower the power supply voltage Vdc, the shorter the turn-off period toff, the controller 37 shortens the dead time target value DT* as shown in Fig. 12, the lower the power supply voltage Vdc. This makes it possible to appropriately shorten the actual dead time DTr in response to the change in the power supply voltage Vdc.

[0071] <Third embodiment> The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the smaller the magnitude of the current vector, the shorter the dead time target value DT* is, and in addition, the smaller the magnitude of the current vector, the higher the discharge rate of the gate charge is.

[0072] As shown in Fig. 13, the control device 37 has a drive circuit 50 and a speed change unit 51. The drive circuit 50 switches each switch SWH, SWL from one of an on state and an off state to the other based on each drive signal GUH-GWL input from the microcomputer 37a. Note that, since the configurations related to the upper and lower arm switches SWH, SWL of the control device 37 are basically the same, for convenience, Fig. 13 shows the configuration related to the lower arm switch SWL of the W phase.

[0073] The speed change unit 51 includes a constant voltage power supply 52, a charging path 53, a charging switch 54, and a charging resistor 55. The constant voltage power supply 52 is connected to the gate of the lower arm switch SWL via the charging path 53. The charging path 53 is provided with the charging switch 54 and the charging resistor 55.

[0074] The speed change unit 51 includes a discharge path 56, a discharge switch 57, and a discharge resistor 58. The emitter of the lower arm switch SWL is connected to the lower arm switch SWL via the discharge path 56. The discharge path 56 is provided with the discharge switch 57 and the discharge resistor 58.

[0075] When the input drive signal GWL is an ON command, the drive circuit 50 performs a charging process to supply a charging current to the gate of the lower arm switch SWL. In the charging process, the output voltage of the constant voltage power supply 52 is applied to the gate of the lower arm switch SWL via the charging resistor 55. According to the charging process, the gate voltage of the lower arm switch SWL rises to a threshold voltage Vth or higher, and the lower arm switch SWL is switched to the ON state. Therefore, the voltage VceL between the terminals of the lower arm switch SWL drops from the power supply voltage Vdc to 0.

[0076] When the input drive signal GWL is an OFF command, the drive circuit 50 performs a discharge process to discharge charge from the gate of the lower arm switch SWL. In the discharge process, the gate charge of the lower arm switch SWL is discharged from the gate via the discharge resistor 58. According to the discharge process, the gate voltage of the lower arm switch SWL drops to less than the threshold voltage Vth, and the switch SWL is switched to the OFF state. Therefore, the voltage VceL between the terminals of the lower arm switch SWL rises from 0 to the power supply voltage Vdc.

[0077] The drive circuit 50 increases the discharge speed of the gate charge in the discharge process by controlling the speed change unit 51. In this embodiment, the discharge resistor 58 is a variable resistor that changes its resistance value based on a signal from the drive circuit 50. The drive circuit 50 increases the discharge speed of the gate charge by reducing the resistance value of the discharge resistor 58. This shortens the turn-off period toff of each switch SWH, SWL.

[0078] The overheat protection control executed by the control device 37 will be described with reference to Fig. 14. The overheat protection control shown in Fig. 14 is executed repeatedly at a predetermined control period, for example. In Fig. 14, the same processes as those shown in Fig. 5 are denoted by the same reference numerals for convenience.

[0079] If it is determined in step S12 that the motor temperature Tmgd is equal to or lower than the temperature threshold value TAH, the process proceeds to step S20, where the discharge rate of the gate charge is set to the initial discharge rate, and then the process proceeds to step S13.

[0080] If it is determined in step S12 that the motor temperature Tmgd exceeds the temperature threshold value TAH, the process proceeds to step S21. In step S21, the magnitude of the current vector to the stator winding 21 is acquired. Then, the process proceeds to step S22. Note that in this embodiment, the process of step S21 corresponds to a "current acquisition unit."

[0081] In step S22, the discharge rate of the gate charge is increased above the initial discharge rate. Specifically, as shown in Fig. 15, the smaller the magnitude of the current vector to the stator winding 21, the higher the discharge rate of the gate charge is set by the control device 37. In other words, in this embodiment, the smaller the magnitude of the current vector, the smaller the resistance value of the discharge resistor 58 is set by the control device 37.

[0082] If the discharge rate of the gate charge is increased, the surge voltage Vs generated in one of the switches SWH and SWL that is turned off increases. In this case, the terminal voltage Vce of each switch SWH and SWL may exceed the allowable voltage Vmax, which may reduce the reliability of each switch SWH and SWL. The allowable voltage Vmax is the upper limit of the range that the terminal voltage Vce of each switch SWH and SWL may take.

[0083] Therefore, in this embodiment, the control device 37 reduces the resistance value of the discharge resistor 58 within a range in which the terminal voltage Vce of each switch SWH, SWL does not exceed the allowable voltage Vmax. For example, the control device 37 increases the discharge speed of the gate charge in consideration of the relationship between the surge voltage Vs generated in each switch SWH, SWL and the magnitude of the current vector to the stator winding 21. In detail, an off-surge voltage is generated when each switch SWH, SWL is switched to the off state. The off-surge voltage becomes higher as the magnitude of the current vector to the stator winding 21 increases. In this case, the smaller the magnitude of the current vector to the stator winding 21, the less likely it is that the terminal voltage Vce of each switch SWH, SWL will exceed the allowable voltage Vmax. Therefore, as described above, the control device 37 increases the discharge speed of the gate charge as the magnitude of the current vector to the stator winding 21 decreases.

[0084] Returning to the explanation of FIG. 14, in step S23, the dead time target value DT* is made shorter than the initial dead time target value. In this embodiment, similar to the explanation of FIG. 7 above, the smaller the magnitude of the current vector to the stator winding 21, the shorter the dead time target value DT* is. Furthermore, focusing on the relationship that the higher the discharge rate of the gate charge, the shorter the turn-off period toff, the higher the discharge rate of the gate charge, as shown in FIG. 16, the shorter the dead time target value DT* is. Note that in this embodiment, the processes of steps S22 and S23 correspond to a "switch control unit."

[0085] According to this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the discharge rate of the gate charge is increased to be higher than the initial discharge rate, thereby further shortening the turn-off period toff. This allows the dead time target value DT* to be further shortened. As a result, the actual dead time DTr can be suitably shortened.

[0086] Within the range where the inter-terminal voltage Vce of each switch SWH, SWL does not exceed the allowable voltage Vmax, the smaller the magnitude of the current vector to the stator winding 21, the higher the discharge rate of the gate charge is. This makes it possible to shorten the turn-off period toff while ensuring the reliability of each switch SWH, SWL.

[0087] <Fourth embodiment> The fourth embodiment will be described below with reference to the drawings, focusing on the differences from the second embodiment. In this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the lower the power supply voltage Vdc, the shorter the dead time target value DT* is, and in addition, the lower the power supply voltage Vdc, the faster the discharge speed of the gate charge of each switch SWH, SWL is.

[0088] The overheat protection control executed by the control device 37 will be described with reference to Fig. 17. The overheat protection control shown in Fig. 17 is executed repeatedly at a predetermined control period, for example. For convenience, the same processes as those shown in Fig. 10 are denoted by the same reference numerals in Fig. 17.

[0089] If it is determined in step S12 that the motor temperature Tmgd is equal to or lower than the temperature threshold value TAH, the process proceeds to step S24, where the discharge rate of the gate charge is set to the initial discharge rate, and then the process proceeds to step S13.

[0090] If it is determined in step S12 that the motor temperature Tmgd exceeds the temperature threshold value TAH, the process proceeds to step S25. In step S25, the power supply voltage Vdc is acquired. Then, the process proceeds to step S26. In this embodiment, the process of step S25 corresponds to the "voltage acquisition unit".

[0091] In step S26, the discharge rate of the gate charge is made higher than the initial discharge rate. In this embodiment, the resistance value of the discharge resistor 58 is made smaller as the power supply voltage Vdc becomes lower.

[0092] Here, the relationship between the power supply voltage Vdc and the discharge rate of the gate charge will be described. As described in the second embodiment, the lower the power supply voltage Vdc, the lower the inter-terminal voltage Vce of each of the switches SWH, SWL in the off state.

[0093] 18 and 19 are diagrams showing the transition of the current Isw flowing through one of the switches SWH and SWL that is turned off and the inter-terminal voltage Vce when the resistance value of the discharge resistor 58 is reduced. The second power supply voltage Vdc2 is a voltage lower than the first power supply voltage Vdc1. It is assumed that the resistance value of the discharge resistor 58 is the same in FIGS. 18 and 19.

[0094] When the resistance value of the discharge resistor 58 is reduced, the discharge speed of the gate charge increases. As a result, the turn-off period toff of the switch SWH, SWL that is turned off is shortened, while the surge voltage Vs generated when the switch SWH, SWL is switched to the off state increases. In this case, the inter-terminal voltage Vce temporarily becomes higher than the power supply voltage Vdc.

[0095] As shown in FIG. 18, when a surge voltage Vs occurs and a voltage higher than the first power supply voltage Vdc1 occurs, the inter-terminal voltage Vce of one of the switches SWH, SWL that is turned off exceeds the allowable voltage Vmax.

[0096] 19, if the second power supply voltage Vdc2 is sufficiently low, the inter-terminal voltage Vce of the switch SWH, SWL that is turned off does not exceed the allowable voltage Vmax even if the surge voltage Vs occurs. In other words, the lower the power supply voltage Vdc is, the less likely it is that the inter-terminal voltage Vce will exceed the allowable voltage Vmax even if the discharge rate of the gate charge is increased.

[0097] Therefore, in this embodiment, focusing on the relationship that the lower the power supply voltage Vdc, the less likely the inter-terminal voltage Vce is to exceed the allowable voltage Vmax even if the discharge rate of the gate charge is increased, the controller 37 increases the discharge rate of the gate charge as the power supply voltage Vdc is lower, as shown in Fig. 20. In this embodiment, the controller 37 decreases the resistance value of the discharge resistor 58 as the power supply voltage Vdc is lower.

[0098] In step S27, the dead time target value DT* is made shorter than the initial dead time target value. In this embodiment, as described above in FIG. 12, the lower the power supply voltage Vdc, the shorter the dead time target value DT*. Furthermore, as described above in FIG. 16, the higher the discharge rate of the gate charge, the shorter the dead time target value DT*. In this embodiment, the processes of steps S26 and S27 correspond to a "switch control unit."

[0099] According to this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the discharge rate of the gate charge is increased to be higher than the initial discharge rate, so that the turn-off period toff is further shortened. This allows the dead time target value DT* to be further shortened. As a result, the actual dead time DTr can be suitably shortened.

[0100] The lower the power supply voltage Vdc, the higher the discharge rate of the gate charge is, thereby making it possible to shorten the turn-off period toff while ensuring the reliability of each of the switches SWH and SWL.

[0101] <Fifth embodiment> Hereinafter, the fifth embodiment will be described with reference to the drawings, focusing on the differences from the fourth embodiment. In this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the discharge speed of the gate charge of each switch SWH, SWL is increased as the element temperature of each switch SWH, SWL is increased, instead of the discharge speed of the gate charge of each switch SWH, SWL being increased as the power supply voltage Vdc is decreased.

[0102] The overheat protection control executed by the control device 37 will be described with reference to Fig. 21. The overheat protection control shown in Fig. 21 is executed repeatedly at a predetermined control period, for example. In Fig. 21, the same processes as those shown in Fig. 17 are denoted by the same reference numerals for convenience.

[0103] If it is determined in step S12 that the motor temperature Tmgd has exceeded the temperature threshold value TAH, the process proceeds to step S28. In step S28, the element temperature of each switch SWH, SWL is acquired. As the element temperature of each switch SWH, SWL, the element temperature calculated based on the detection value of the inverter temperature sensor 36 may be acquired. Then, the process proceeds to step S29. In this embodiment, the process of step S28 corresponds to the "temperature acquisition unit".

[0104] In step S29, the discharge rate of the gate charge is made higher than the initial discharge rate. In this embodiment, the resistance value of the discharge resistor 58 is made smaller as the element temperatures of the switches SWH and SWL increase.

[0105] Here, the relationship between the element temperature of each switch SWH, SWL and the discharge rate of the gate charge will be described. The IGBT constituting each switch SWH, SWL has a characteristic that the allowable voltage Vmax increases as the element temperature increases.

[0106] Fig. 22 shows the transition of the current Isw flowing through one of the switches SWH, SWL that is turned off, and the inter-terminal voltage Vce when the gate resistance of the discharge resistor 58 is reduced. Fig. 22 also shows the first permissible voltage Vmax1 at the first element temperature, and the second permissible voltage Vmax2 at a second element temperature that is higher than the first element temperature. The second permissible voltage Vmax2 is higher than the first permissible voltage Vmax1 due to the rise in element temperature.

[0107] At the first element temperature, the resistance value of discharge resistor 58 is reduced, thereby increasing surge voltage Vs, and therefore terminal voltage Vce exceeds first allowable voltage Vmax1. On the other hand, at the second element temperature, even if surge voltage Vs increases due to the resistance value of discharge resistor 58 being reduced, terminal voltage Vce does not exceed second allowable voltage Vmax2. In other words, the higher the element temperature, the higher the allowable voltage Vmax becomes, and therefore, even if the discharge rate of the gate charge is increased, terminal voltage Vce is less likely to exceed allowable voltage Vmax.

[0108] Therefore, in this embodiment, as shown in FIG. 23, the control device 37 increases the discharge rate of the gate charge as the element temperature increases.

[0109] Returning to the explanation of Fig. 21, in step S30, the dead time target value DT* is made shorter than the initial dead time target value. In this embodiment, as explained above in Fig. 16, the higher the discharge rate of the gate charge, the shorter the dead time target value DT* is. In this embodiment, the processes of steps S29 and S30 correspond to a "switch control unit."

[0110] According to this embodiment, the higher the element temperature is, the faster the gate charge is discharged, thereby making it possible to shorten the actual dead time DTr while ensuring the reliability of each of the switches SWH and SWL.

[0111] Sixth Embodiment Hereinafter, the sixth embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the dead time target value DT* is not shortened, but the charging rate of the gate charge is increased.

[0112] The drive circuit 50 controls the speed change unit 51 to increase the charging speed of the gate charge in the charging process. In this embodiment, the charging resistor 55 is a variable resistor that changes its resistance value based on a signal from the drive circuit 50. The drive circuit 50 increases the charging speed of the gate charge by decreasing the resistance value of the charging resistor 55. This shortens the turn-on period ton of each switch SWH, SWL.

[0113] The overheat protection control executed by the control device 37 will be described with reference to Fig. 24. The overheat protection control shown in Fig. 24 is executed repeatedly at a predetermined control period, for example. In Fig. 24, the same processes as those shown in Fig. 5 are denoted by the same reference numerals for convenience.

[0114] If it is determined in step S12 that the motor temperature Tmgd is equal to or lower than the temperature threshold value TAH, the process proceeds to step S31, where the charging rate of the gate charge is set to the initial charging rate, and then the process proceeds to step S14.

[0115] If it is determined in step S12 that the motor temperature Tmgd exceeds the temperature threshold value TAH, the process proceeds to step S32 after the process of step S15. In step S32, the charging rate of the gate charge is increased above the initial charging rate. In detail, as shown by the solid line in FIG. 25, the controller 37 increases the charging rate of the gate charge as the magnitude of the current vector to the stator winding 21 increases. In other words, in this embodiment, the controller 37 decreases the resistance value of the charging resistor 55 as the magnitude of the current vector to the stator winding 21 increases. In this embodiment, the process of step S32 corresponds to a "switch control unit."

[0116] When the gate charge charging rate is increased, the surge voltage Vs generated in each switch SWH, SWL increases. In this case, the terminal voltage Vce of each switch SWH, SWL exceeds the allowable voltage Vmax, which may reduce the reliability of each switch SWH, SWL.

[0117] Therefore, in this embodiment, the control device 37 reduces the resistance value of the charging resistor 55 within a range in which the terminal voltage Vce of each switch SWH, SWL does not exceed the allowable voltage Vmax. For example, the control device 37 increases the charging speed of the gate charge in consideration of the relationship between the surge voltage Vs generated in each switch SWH, SWL and the magnitude of the current vector. In detail, an on-surge voltage is generated when each switch SWH, SWL is switched to the on state. In this embodiment, the freewheel diodes DH, DL have a characteristic that the smaller the magnitude of the current vector, the shorter the reverse recovery time. Therefore, the smaller the magnitude of the current vector, the higher the on-surge voltage. In this case, the larger the magnitude of the current vector to the stator winding 21, the more difficult it is for the terminal voltage Vce of each switch SWH, SWL to exceed the allowable voltage Vmax. Therefore, as described above, the control device 37 increases the charging speed of the gate charge as the magnitude of the current vector to the stator winding 21 increases.

[0118] According to this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the resistance value of the charging resistor 55 is decreased. This increases the charging speed of the gate charge, thereby shortening the turn-on period ton of each switch SWH, SWL. As a result, the actual dead time DTr can be shortened.

[0119] Within a range in which the inter-terminal voltage Vce of each switch SWH, SWL does not exceed the allowable voltage Vmax, the larger the magnitude of the current vector to the stator winding 21, the higher the charging speed of the gate charge is. This makes it possible to shorten the turn-on period ton of each switch SWH, SWL while ensuring the reliability of each switch SWH, SWL in accordance with changes in the magnitude of the current vector to the stator winding 21.

[0120] <Modification of the Sixth Embodiment> Instead of increasing the charging rate of the gate charge as the magnitude of the current vector to the stator winding 21 increases, the charging rate of the gate charge may be increased as the magnitude of the current vector to the stator winding 21 decreases, as shown by the dashed line in Fig. 25. In other words, in this embodiment, the control device 37 may decrease the resistance value of the charging resistor 55 as the magnitude of the current vector to the stator winding 21 decreases.

[0121] In this embodiment, the freewheel diodes DH, DL have a characteristic that the reverse recovery current increases as the magnitude of the current vector increases. Therefore, the on-surge voltage increases as the magnitude of the current vector increases. In this case, the smaller the magnitude of the current vector to the stator winding 21, the less likely it is that the inter-terminal voltage Vce of each switch SWH, SWL will exceed the allowable voltage Vmax. Therefore, as described above, the controller 37 increases the charging speed of the gate charge as the magnitude of the current vector to the stator winding 21 decreases.

[0122] Seventh embodiment The seventh embodiment will be described below with reference to the drawings, focusing on the differences from the second embodiment. In this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the dead time target value DT* is not shortened, but the charging rate of the gate charge is increased.

[0123] The overheat protection control executed by the control device 37 will be described with reference to Fig. 26. The overheat protection control shown in Fig. 26 is executed repeatedly at a predetermined control period, for example. In Fig. 26, the same processes as those shown in Fig. 10 are denoted by the same reference numerals for convenience.

[0124] If it is determined in step S12 that the motor temperature Tmgd is equal to or lower than the temperature threshold value TAH, the process proceeds to step S33, where the charging rate of the gate charge is set to the initial charging rate, and then the process proceeds to step S14.

[0125] If it is determined in step S12 that the motor temperature Tmgd exceeds the temperature threshold value TAH, the process proceeds to step S34 after the process of step S18. In step S34, the charging rate of the gate charge is made higher than the initial charging rate. In this embodiment, the process of step S34 corresponds to the "switch control unit."

[0126] 18 and 19, the lower the power supply voltage Vdc, the less likely it is that the inter-terminal voltage Vce will exceed the allowable voltage Vmax even if the charging rate of the gate charge is increased. Therefore, in this embodiment, the controller 37 increases the charging rate of the gate charge as the power supply voltage Vdc is lower, as shown in Fig. 27. In this embodiment, the lower the power supply voltage Vdc, the smaller the resistance value of the charging resistor 55 is.

[0127] According to this embodiment, when it is determined that the motor temperature Tmgd exceeds the temperature threshold value TAH, the lower the power supply voltage Vdc, the higher the charging speed of the gate charge is set. This makes it possible to shorten the turn-on period ton of each of the switches SWH, SWL while ensuring the reliability of each of the switches SWH, SWL in response to changes in the power supply voltage Vdc.

[0128] <Other embodiments> Each of the above embodiments may be modified as follows.

[0129] The temperatures of the rotating electric machine 20 and the inverter 30 used in the overheat protection control are not limited to values ​​detected by temperature sensors, and may be values ​​estimated by a temperature estimation unit included in the control device 37.

[0130] In the process of step S12, instead of determining whether the motor temperature Tmgd has exceeded the temperature threshold value TAH, it may be determined whether the inverter temperature Tinvd has exceeded the temperature threshold value of the inverter 30.

[0131] In the processes of steps S15 and S21, instead of obtaining the magnitude of the current vector to the stator winding 21, the effective value or current amplitude of the phase current flowing through the stator winding 21 may be obtained. In this case, in the process of step S16, the dead time target value DT* may be shortened as the effective value or current amplitude of the phase current flowing through the stator winding 21 becomes smaller. Also, in the process of step S22, the discharging speed of the gate charge may be increased as the effective value or current amplitude of the phase current flowing through the stator winding 21 becomes smaller, and in the process of step S32, the charging / discharging speed of the gate charge may be increased.

[0132] The speed change unit 51 may be configured to include a plurality of resistors with different resistance values ​​instead of the variable resistor discharge resistor 58. In this case, in the discharge process, the discharge speed of the gate charge may be increased by discharging the charge from the gate through a resistor with a small resistance value.

[0133] Instead of being configured to include the charging resistor 55, which is a variable resistor, the speed changer 51 may be configured to include a plurality of resistors with different resistance values. In this case, in the charging process, the charging speed of the gate charge may be increased by supplying a charging current to the gate via a resistor with a small resistance value.

[0134] The speed change unit 51 may increase the voltage setting value of the constant voltage power supply 52 instead of decreasing the resistance value of the charging resistor 55. This makes it possible to increase the charging current supplied to each switch SWH, SWL, and therefore the charging speed.

[0135] The moving body on which the control system is mounted is not limited to a vehicle, but may be, for example, a train, an airplane, or a ship. For example, if the moving body is an airplane, the rotating electric motor serves as the flight power source for the aircraft, and if the moving body is a ship, the rotating electric motor serves as the navigation power source for the ship. In addition, the control system is not limited to a system mounted on a moving body, but may be a stationary system.

[0136] The control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by the computer. [Explanation of symbols]

[0137] 10...vehicle, 20...rotating electric machine, 30...inverter, 37...control device

Claims

1. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches; In an inverter control device (37) applied to a control system including: a switch control unit that performs switching control of the inverter while providing a dead time, which is a period during which both of the upper and lower arm switches are in an off state; a temperature acquisition unit that acquires a temperature of at least one of the inverter and the rotating electric machine; Equipped with When the switch control unit determines that the acquired temperature exceeds a temperature threshold value while performing the switching control while flowing a field-weakening current through the stator winding, the switch control unit shortens the actual dead time, and reduces the field-weakening current as the actual dead time becomes shorter.

2. The switch control unit is generating drive signals for turning on and off the switches of the upper and lower arms while setting a dead time target value for turning off both of the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; 2 . The inverter control device according to claim 1 , wherein, when it is determined that the acquired temperature exceeds the temperature threshold value, the actual dead time is shortened by setting the dead time target value to a shorter value.

3. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches; In an inverter control device (37) applied to a control system including: a switch control unit that performs switching control of the inverter while providing a dead time, which is a period during which both of the upper and lower arm switches are in an off state; a temperature acquisition unit that acquires a temperature of at least one of the inverter and the rotating electric machine; a current acquisition unit that acquires a current flowing through the switch; Equipped with The switch control unit is generating drive signals for turning on and off the switches of the upper and lower arms while setting a dead time target value for turning off both of the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; an inverter control device which, when executing the switching control while flowing a field-weakening current through the stator winding, on condition that it is determined that the acquired temperature exceeds a temperature threshold, sets the dead-time target value shorter as the acquired current becomes smaller, thereby shortening the actual dead time and reducing the field-weakening current.

4. The switch control unit is When the drive signal for the off operation is generated, a discharge process is performed to discharge electric charge from the gates of the switches of the upper and lower arms, thereby turning off the switches of the upper and lower arms; 4. The inverter control device according to claim 3, wherein, when it is determined that the acquired temperature exceeds the temperature threshold, the smaller the acquired current is, the higher the discharge rate of the charge in the discharge process is set, and the higher the discharge rate of the charge is, the shorter the dead time target value is set.

5. A voltage acquisition unit that acquires a power supply voltage of the inverter, 4. The inverter control device according to claim 2, wherein, when it is determined that the acquired temperature exceeds the temperature threshold value, the switch control unit sets the dead time target value to be shorter as the acquired power supply voltage is lower.

6. The switch control unit is When the drive signal for the off operation is generated, a discharge process is performed to discharge electric charge from the gates of the switches of the upper and lower arms, thereby turning off the switches of the upper and lower arms; 6. The inverter control device according to claim 5, wherein, when it is determined that the acquired temperature exceeds the temperature threshold, the lower the acquired power supply voltage, the higher the discharge rate of the charge in the discharge process is set, and the higher the discharge rate of the charge, the shorter the dead time target value is set.

7. The upper and lower arm switches have a characteristic that the higher the temperature of the switch, the higher the allowable value of the voltage applied to the switch; The temperature acquisition unit acquires a temperature of the switch, The switch control unit is When the drive signal for the off operation is generated, a discharge process is performed to discharge electric charge from the gates of the switches of the upper and lower arms, thereby turning off the switches of the upper and lower arms; 4. The inverter control device according to claim 2 or 3, wherein, when it is determined that the acquired temperature of at least one of the inverter and the rotating electric machine exceeds the temperature threshold, the higher the acquired temperature of the switch, the higher the discharge rate of the charge in the discharge process is set, and the higher the discharge rate of the charge, the shorter the dead time target value is set.

8. The switch control unit is generating drive signals for turning on and off the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; When the drive signal for an ON operation is generated, a charging process is performed to charge the gates of the switches of the upper and lower arms, thereby turning on the switches of the upper and lower arms; 2. The inverter control device according to claim 1, wherein when it is determined that the acquired temperature exceeds the temperature threshold, a process for increasing a charging rate of the electric charge in the charging process is performed, thereby shortening the actual dead time.

9. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches and diodes connected in anti-parallel to the switches; In an inverter control device (37) applied to a control system including: a switch control unit that performs switching control of the inverter while providing a dead time, which is a period during which both of the upper and lower arm switches are in an off state; a temperature acquisition unit that acquires a temperature of at least one of the inverter and the rotating electric machine; a current acquisition unit that acquires a current vector flowing through the stator winding; Equipped with The diode has a characteristic that the smaller the magnitude of the current vector flowing through the stator winding, the shorter the reverse recovery time becomes, The switch control unit is generating drive signals for turning on and off the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; When the drive signal for an ON operation is generated, a charging process is performed to charge the gates of the switches of the upper and lower arms, thereby turning on the switches of the upper and lower arms; an inverter control device which, when performing the switching control while flowing a field-weakening current through the stator winding, when it is determined that the acquired temperature exceeds a temperature threshold, performs a process of increasing a charging rate of the electric charge in the charging process as the magnitude of the acquired current vector increases, thereby shortening the actual dead time and reducing the field-weakening current.

10. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches and diodes connected in anti-parallel to the switches; In an inverter control device (37) applied to a control system including: a switch control unit that performs switching control of the inverter while providing a dead time, which is a period during which both of the upper and lower arm switches are in an off state; a temperature acquisition unit that acquires a temperature of at least one of the inverter and the rotating electric machine; a current acquisition unit that acquires a current vector flowing through the stator winding; Equipped with The diode has a characteristic that a reverse recovery current increases as the magnitude of the current vector flowing through the stator winding increases, The switch control unit is generating drive signals for turning on and off the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; When the drive signal for an ON operation is generated, a charging process is performed to charge the gates of the switches of the upper and lower arms, thereby turning on the switches of the upper and lower arms; an inverter control device which, when performing the switching control while flowing a field-weakening current through the stator winding, when it is determined that the acquired temperature exceeds a temperature threshold, performs a process of increasing a charging rate of the electric charge in the charging process as the magnitude of the acquired current vector becomes smaller, thereby shortening the actual dead time and reducing the field-weakening current.

11. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches; A computer (37a); A program applied to a control system comprising: The computer includes: a process of performing switching control of the inverter while providing a dead time during which both of the upper and lower arm switches are in an off state; acquiring a temperature of at least one of the inverter and the rotating electric machine; a process of shortening an actual dead time and decreasing the field weakening current as the actual dead time becomes shorter when it is determined that the acquired temperature exceeds a temperature threshold value in a case where the switching control is being performed while a field weakening current is flowing through the stator winding; A program to execute.

12. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches; A computer (37a); A program applied to a control system comprising: The computer includes: a process of performing switching control of the inverter while providing a dead time during which both of the upper and lower arm switches are in an off state; acquiring a temperature of at least one of the inverter and the rotating electric machine; obtaining a current through the switch; a process of generating drive signals for turning on and off the switches of the upper and lower arms while setting a dead time target value for turning off both of the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; a process of shortening an actual dead time and reducing the field-weakening current by setting the dead time target value shorter as the acquired current is smaller, on condition that the acquired temperature is determined to exceed a temperature threshold value, when the switching control is being performed while a field-weakening current is flowing through the stator winding; A program to execute.

13. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches and diodes connected in anti-parallel to the switches; A computer (37a); A program applied to a control system comprising: The diode has a characteristic that the smaller the magnitude of the current vector flowing through the stator winding, the shorter the reverse recovery time becomes, The computer includes: a process of performing switching control of the inverter while providing a dead time during which both of the upper and lower arm switches are in an off state; acquiring a temperature of at least one of the inverter and the rotating electric machine; A process of acquiring a current vector flowing through the stator winding; A process of generating drive signals for turning on and off the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; a process of turning on the switches of the upper and lower arms by performing a charging process of charging the gates of the switches of the upper and lower arms when the drive signal for turning on the switches is generated; a process of shortening the actual dead time and reducing the field-weakening current by performing a process of increasing a charging rate of the electric charge in the charging process as the magnitude of the acquired current vector increases when the switching control is being performed while a field-weakening current is flowing through the stator winding and it is determined that the acquired temperature exceeds a temperature threshold value; A program to execute.

14. A rotating electric machine (20) having a stator winding (21); an inverter (30) electrically connected to the stator winding and having upper and lower arm switches and diodes connected in anti-parallel to the switches; A computer (37a); A program applied to a control system comprising: The diode has a characteristic that a reverse recovery current increases as the magnitude of the current vector flowing through the stator winding increases, The computer includes: a process of performing switching control of the inverter while providing a dead time during which both of the upper and lower arm switches are in an off state; acquiring a temperature of at least one of the inverter and the rotating electric machine; A process of acquiring a current vector flowing through the stator winding; A process of generating drive signals for turning on and off the switches of the upper and lower arms, and executing the switching control based on the generated drive signals; a process of turning on the switches of the upper and lower arms by performing a charging process of charging the gates of the switches of the upper and lower arms when the drive signal for turning on the switches is generated; a process of shortening the actual dead time and reducing the field-weakening current by performing a process of increasing a charging rate of the electric charge in the charging process as the magnitude of the acquired current vector decreases when the switching control is being performed while a field-weakening current is flowing through the stator winding and it is determined that the acquired temperature exceeds a temperature threshold value; A program to execute.

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