Power Conversion Equipment

Abstract

To provide a power conversion apparatus capable of suppressing heating with occurrence of abnormality relating to a power conversion unit.SOLUTION: A control device performs inverter control processing while defining an inverter as a controlled object. In the inverter control processing, in a case where a motor rotation number Nm achieves a rotation threshold Nb and a motor temperature Tm is higher than a temperature threshold Tb on a situation that inverter abnormality occurs, the control device proceeds to a step S106 and performs target time processing. In the target time processing, a target time TDasc is set in accordance with the motor rotation number Nm and the motor temperature Tm. After delay until a delay time TD achieves the target time TDasc in a step S107, ASC is executed in a step S108. By executing the ASC, in the inverter, one of IGBT of an upper arm and IGBT of a lower arm is switched to an ON state regarding all a plurality of upper / lower arm circuits.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The disclosure herein relates to power conversion devices. [Background technology]

[0002] Patent Document 1 discloses a vehicle equipped with an inverter that converts DC power into AC power and supplies it to a three-phase motor, and a control device that controls the inverter. The inverter has arm circuits provided for each of the three phases. In these arm circuits, the switching elements on the power supply line side and the switching elements on the earth line side are connected in series with each other. The switching elements on the power supply line side in each arm circuit are connected in parallel with each other, and the switching elements on the earth line side in each arm circuit are connected in parallel with each other.

[0003] When a short circuit occurs in a switching element in the inverter, the control device selectively uses one-phase short circuit control or three-phase ON control depending on the rotation speed of the motor. One-phase short circuit control is a process that turns on the switching element connected in series to the switching element where the short circuit occurred. Three-phase ON control is a process that turns on all switching elements connected in parallel to the switching element where the short circuit occurred. For example, the control device performs one-phase short circuit control when the motor rotation speed is in the low rotation speed range, and performs three-phase ON control when the motor rotation speed is in the high rotation speed range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-195026 A Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the control device selectively uses one-phase short-circuit control and three-phase ON control according to the rotation speed of the motor, so that when the rotation speed of the motor is in a high rotation speed range, three-phase ON control is performed immediately after a short circuit occurs in a switching element. In the inverter, the three-phase ON control is performed, so that a current flows through all of the switching elements connected in parallel, including the switching element in which the short circuit occurs. In this state, if the motor's back electromotive force is relatively large due to the motor's rotation speed being in a high rotation speed range, the current flowing through the switching element increases, and there is a concern that the inverter will heat up due to the heat generated by the switching element, etc. For example, when attempting to increase the output of the motor, it is considered that the back electromotive force of the motor increases and the inverter will easily heat up.

[0006] A main object of the present disclosure is to provide a power conversion device capable of suppressing heat generation due to the occurrence of an abnormality in a power conversion unit. [Means for solving the problem]

[0007] The various aspects disclosed in this specification employ different technical means to achieve their respective objectives. The reference symbols in parentheses in the claims and in this section are merely examples showing the corresponding relationship with the specific means described in the embodiments described below as one aspect, and do not limit the technical scope.

[0008] In order to achieve the above object, one disclosed embodiment comprises: A power conversion device (13) that converts electric power supplied from a power source unit (11) to a motor (12) from direct current to alternating current by a power conversion unit (30), a state transition unit (S108) that, when an abnormality occurs in the power conversion unit and the temperature (Tm) of the motor is higher than a temperature threshold (Tb) at which irreversible demagnetization of a permanent magnet provided in the motor occurs, transitions the power conversion unit to a target state in which one of the upper arm switch (32a) on the high potential side and the lower arm switch (32b) on the low potential side for all of a plurality of arm circuits (31) connected in parallel with each other is turned on and the other is turned off; a delay unit (S107) that delays the transition of the power conversion unit to a target state by the state transition unit by at least a target time (TDasc) from the occurrence of the abnormality in the power conversion unit when an abnormality occurs in the power conversion unit and the temperature is higher than a temperature threshold value; A target setting unit (S202, S203, S204) that sets a target time according to at least one of the rotation speed (Nm) and temperature of the motor; The power conversion device is provided with:

[0009] With regard to the power conversion device, it has been found through tests etc. that irreversible demagnetization of the permanent magnet in the motor is likely to occur when the power conversion unit is in the target state and the d-axis current has become large on the negative side. In addition to this finding, it has been found through tests etc. that if a certain amount of time has elapsed between the occurrence of an abnormality in the power conversion unit and the switching of the power conversion unit to the target state, the d-axis current after the switching of the power conversion unit to the target state is likely to become large on the negative side.

[0010] In response to these findings, according to the above aspect, the power conversion unit is transitioned to the target state when a target time has elapsed since an abnormality occurred in the power conversion unit. As a result, the d-axis current after the power conversion unit transitions to the target state is likely to become large on the negative side, which in turn makes it easy for irreversible demagnetization of the permanent magnet to occur. When irreversible demagnetization of the permanent magnet occurs, the back electromotive force of the motor is reduced, so that the current flowing through the power conversion unit in the target state is less likely to be too large and cause the upper arm switch, lower arm switch, etc. to heat up. Therefore, heat generation due to an abnormality occurring in the power conversion unit can be suppressed. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram showing the configuration of a drive system according to the first embodiment. [Diagram 2] FIG. 2 is a block diagram showing the electrical configuration of a control device. [Diagram 3] FIG. 4 is a diagram showing changes over time in the d-axis current and each phase current before and after ASC. [Figure 4] FIG. 13 is a diagram showing the back electromotive force of the motor before and after ASC. [Diagram 5] FIG. 13 is a diagram showing the relationship between the back electromotive force of the motor and the d-axis current and each phase current after ASC is executed. [Figure 6] FIG. 11 is a graph showing the relationship between the motor electromotive force, the d-axis current, and the motor temperature after ASC is executed. [Figure 7] 4 is a flowchart showing a procedure of an inverter control process. [Figure 8] 11 is a flowchart showing a procedure for target time processing. [Figure 9] FIG. 11 is a graph showing the relationship between the deviation time and the d-axis current after ASC is performed in the second embodiment. [Figure 10] 4 is a flowchart showing a procedure of an inverter control process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a number of embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, the same reference numerals may be used to designate parts corresponding to matters described in the preceding embodiment, and duplicated descriptions may be omitted. In each embodiment, when only a part of the configuration is described, other embodiments described previously may be applied to other parts of the configuration. In addition to combinations of parts that are specifically indicated as being possible in each embodiment, it is also possible to partially combine embodiments even if not indicated, as long as there is no particular problem with the combination.

[0013] First Embodiment 1 is mounted on a vehicle such as an electric vehicle (EV), a hybrid vehicle (HV), a fuel cell vehicle, etc. The drive system 10 has a battery 11, a motor 12, and a power conversion device 13. The drive system 10 is a system that drives the motor 12 to drive the drive wheels of the vehicle.

[0014] The battery 11 is a DC voltage source constituted by a chargeable and dischargeable secondary battery, and corresponds to a power supply unit that supplies power to the motor 12 via the power conversion device 13. The secondary battery is, for example, a lithium ion battery or a nickel metal hydride battery. The battery 11 supplies a high voltage (for example, several hundreds of volts) to the inverter 30.

[0015] The motor 12 is a three-phase AC rotating electric machine. The motor 12 has three phases: U-phase, V-phase, and W-phase. The motor 12 functions as an electric motor that is a driving source for running the vehicle. The motor 12 functions as a generator during regeneration. The motor 12 has windings 12a that form an armature and permanent magnets 12b that form a field magnet. In the motor 12, a rotor is formed including the permanent magnets 12b, and a stator is formed including the windings 12a. The motor 12 can also be called a motor generator or an electric motor.

[0016] The power conversion device 13 performs power conversion between the battery 11 and the motor 12. The power conversion device 13 includes a smoothing capacitor 21, an inverter 30, and a control device 40.

[0017] The smoothing capacitor 21 smoothes the DC voltage supplied from the battery 11. The smoothing capacitor 21 is connected to a P line 25, which is a high-potential power line, and an N line 26, which is a low-potential power line. The P line 25 is connected to the positive electrode of the battery 11, and the N line 26 is connected to the negative electrode of the battery 11. The positive electrode of the smoothing capacitor 21 is connected to the P line 25 between the battery 11 and the inverter 30. The negative electrode of the smoothing capacitor 21 is connected to the N line 26 between the battery 11 and the inverter 30. The smoothing capacitor 21 is connected in parallel to the battery 11. In the power conversion device 13, the P line 25 and the N line 26 are formed by bus bars or the like.

[0018] In the power conversion device 13, a switch 22 is provided between the smoothing capacitor 21 and the battery 11. The switch 22 is formed of a switch, a relay, or the like that can be switched between an open state and a closed state, and is provided on each of the P line 25 and the N line 26. In the P line 25, the switch 22 is provided between the positive electrode of the battery 11 and the positive electrode of the smoothing capacitor 21, and in the N line 26, the switch 22 is provided between the negative electrode of the battery 11 and the negative electrode of the smoothing capacitor 21. When the switch 22 is in a closed state, the battery 11 is electrically connected to the smoothing capacitor 21 and the inverter 30. When the switch 22 is in an open state, the battery 11 is electrically disconnected from the smoothing capacitor 21 and the inverter 30.

[0019] The switch 22 is basically in a closed state when a vehicle switch such as an ignition switch is in an on state, and in an open state when the vehicle switch is in an off state. For example, when the vehicle is in a running state, the switch 22 is basically in a closed state. The switch 22 can be called a system main relay. The closed state of the switch 22 can also be called a conductive state, and the open state of the switch 22 can also be called a cut-off state. Furthermore, when the switch 22 is in a closed state, the battery 11 and the smoothing capacitor 21 are in a conductive state, and when the switch 22 is in an open state, the continuity between the battery 11 and the smoothing capacitor 21 is cut off.

[0020] In this embodiment, the switch 22 is included in the power conversion device 13, but the switch 22 does not have to be included in the power conversion device 13. For example, the switch 22 may be provided between the power conversion device 13 and the battery 11. The switch 22 may be provided only in the P line 25. That is, the switch 22 only needs to be provided in at least the P line 25 of the P line 25 and the N line 26.

[0021] The power conversion device 13 is provided with voltage sensors (not shown). The voltage sensors include, for example, a voltage sensor that detects the voltage of the battery 11 and a voltage sensor that detects the voltage of the smoothing capacitor 21.

[0022] The inverter 30 is a DC-AC conversion circuit. The inverter 30 is configured with upper and lower arm circuits 31 for three phases. The upper and lower arm circuits 31 are sometimes referred to as legs. The upper and lower arm circuits 31 each have an upper arm 31a and a lower arm 31b. The upper arm 31a and the lower arm 31b are connected in series between the P line 25 and the N line 26, with the upper arm 31a on the P line 25 side. A connection point between the upper arm 31a and the lower arm 31b is connected to the winding 12a of the corresponding phase in the motor 12 via an output line 27. The upper and lower arm circuits 31 and the output line 27 are provided for each of the U phase, V phase, and W phase of the motor 12. The inverter 30 has three upper arms 31a and three lower arms 31b. In the power conversion device 13, the output line 27 is formed by a bus bar or the like.

[0023] The arms 31a and 31b each have an n-channel IGBT 32a, 32b as a switching element, and a freewheeling diode 33a, 33b. Hereinafter, the diodes 33a, 33b are referred to as FWD 33a, 33b. The IGBT 32a and FWD 33a are included in the upper arm 31a, and the IGBT 32b and FWD 33b are included in the lower arm 31b. The FWDs 33a, 33b are connected inversely parallel to the IGBTs 32a, 32b. In the upper arm 31a, the collector of the IGBT 32a is connected to the P line 25. In the lower arm 31b, the emitter of the IGBT 32b is connected to the N line 26. The emitter of the IGBT 32a in the upper arm 31a and the collector of the IGBT 32b in the lower arm 31b are connected to each other. The anodes of the FWDs 33a and 33b are connected to the emitters of the corresponding IGBTs 32a and 32b, and the cathodes are connected to the collectors.

[0024] The inverter 30 is composed of a semiconductor device (not shown). The semiconductor device is sometimes called a semiconductor module. The semiconductor device has a plurality of semiconductor elements. In the semiconductor elements, the elements are formed on a semiconductor substrate made of a material such as silicon (Si) or a wide band gap semiconductor having a wider band gap than silicon. The semiconductor element is a semiconductor chip on which the elements are formed. Wide band gap semiconductors are, for example, silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond.

[0025] In this embodiment, an IGBT and an FWD constituting one arm are formed in one semiconductor element. That is, an RC (Reverse Conducting)-IGBT is formed. The semiconductor device has six semiconductor elements constituting each arm. The upper and lower arm circuits 31 correspond to arm circuits, the IGBT 32a of the upper arm 31a corresponds to an upper arm switch, and the IGBT 32b of the lower arm 31b corresponds to a lower arm switch.

[0026] The inverter 30 converts DC voltage into AC voltage in accordance with switching control by the control device 40 and outputs it to the motor 12. This causes the motor 12 to operate to generate a predetermined rotational torque. That is, the inverter 30 converts DC power from the battery 11 into three-phase AC power and corresponds to a power conversion unit. During regenerative braking of the vehicle, the inverter 30 converts the AC voltage generated by the motor 12 upon receiving rotational force from the drive wheels into DC voltage in accordance with switching control by the control device 40 and outputs it to the P line 25. In this way, the inverter 30 performs bidirectional power conversion between the battery 11 and the motor 12.

[0027] The control device 40 is, for example, an ECU, and controls the driving of the inverter 30. ECU is an abbreviation for Electronic Control Unit. The control device 40 is mainly composed of, for example, a microcomputer (hereinafter, referred to as a microcomputer) equipped with a processor, a memory, an I / O, and a bus connecting these. The control device 40 executes various processes related to the driving of the inverter 30 by executing a control program stored in the memory. The memory referred to here is a non-transitory tangible storage medium that non-temporarily stores programs and data that can be read by a computer. The non-transitory tangible storage medium is realized by a semiconductor memory, a magnetic disk, or the like.

[0028] The control device 40 generates a drive command using signals input from a higher-level ECU such as an integrated ECU mounted on the vehicle and signals input from various sensors such as the rotation sensor 29, and causes the IGBTs 32a, 32b to perform on-drive and off-drive in response to the drive command. The control device 40 corresponds to a power conversion control device. The IGBTs 32a, 32b can be switched between an on state and an off state, and transition to the on state in response to on-drive and transition to the off state in response to off-drive.

[0029] A current sensor 28 and a rotation sensor 29 are electrically connected to the control device 40 as various sensors. These sensors 28 and 29 are included in the drive system 10. Of these sensors 28 and 29, the current sensor 28 is included in the power conversion device 13.

[0030] Current sensor 28 is a current detection unit that detects the current flowing through motor 12. Current sensor 28 outputs a detection signal corresponding to the current flowing through each of the three-phase windings 12a to control device 40. Current sensor 28 in this embodiment is provided for output line 27, and therefore for winding 12a, and detects the current flowing through output line 27 to detect the current flowing through winding 12a. Current sensor 28 discretely samples the current flowing through winding 12a at a predetermined sampling period, and outputs a discrete signal as a detection signal. The current flowing through winding 12a can also be referred to as an armature current.

[0031] The rotation sensor 29 is provided in the motor 12 and is a rotation detection unit that detects the rotation speed of the motor 12. The rotation sensor 29 outputs a detection signal corresponding to the rotation speed of the motor 12 to the control device 40. The rotation sensor 29 is configured to include, for example, an encoder, a resolver, etc.

[0032] The control device 40 shown in Fig. 2 performs vector control of the motor 12 via the inverter 30. In vector control, a three-phase AC coordinate represented by the U-phase, V-phase, and W-phase is converted into a dq coordinate represented by the d-axis and q-axis. The dq coordinate is a rotational coordinate defined by the d-axis and the q-axis, for example, where the direction from the south pole to the north pole of the rotor is the d-axis and the direction perpendicular to the d-axis is the q-axis.

[0033] The control device 40 has, as functional blocks, a command unit 41, a three-phase to two-phase conversion unit 42, a d-axis subtraction unit 43, a q-axis subtraction unit 44, a current control unit 45, and a two-phase to three-phase conversion unit 46. These functional blocks may be configured as hardware using at least one IC or the like, or may be executed by a combination of software execution by a processor and hardware.

[0034] The three-phase to two-phase conversion unit 42 receives the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw detected by the current sensor 28. These phase currents Iu, Iv, and Iw are detection values ​​of currents that actually flow through the windings 12a of each phase in the motor 12. The control device 40 has a current acquisition unit that acquires the phase currents Iu, Iv, and Iw using the detection signal from the current sensor 28. This current acquisition unit may be included in the three-phase to two-phase conversion unit 42.

[0035] The motor rotation speed Nm detected by the rotation sensor 29 is input to the three-phase to two-phase conversion unit 42. This motor rotation speed Nm is a detected value indicating the actual rotation speed of the motor 12. The motor rotation speed Nm is, for example, the number of rotations of the motor 12 per unit time, and is a value indicating the rotation speed.

[0036] The three-phase to two-phase conversion unit 42 converts the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw of the three-phase AC coordinate system into a dq coordinate to calculate a d-axis current Id and a q-axis current Iq of the dq coordinate system. The d-axis current Id is a component in the d-axis direction in the dq coordinate, and the q-axis current Iq is a component in the q-axis direction in the dq coordinate. The three-phase to two-phase conversion unit 42 calculates the d-axis current Id and the q-axis current Iq using the motor rotation speed Nm in addition to the phase currents Iu, Iv, and Iw. For example, the three-phase to two-phase conversion unit 42 converts the phase currents Iu, Iv, and Iw into the dq coordinate based on the motor rotation speed Nm to calculate the d-axis current Id and the q-axis current Iq. The d-axis current Id and the q-axis current Iq are input to a d-axis subtraction unit 43.

[0037] The three-phase to two-phase converter 42 corresponds to a coordinate converter. The d-axis current Id and the q-axis current Iq can also be called the actual d-axis current and the actual q-axis current, since they are actual currents obtained by coordinate-converting the detected values ​​of the phase currents Iu, Iv, and Iw. Furthermore, the d-axis current Id can also be called the field current, and the q-axis current can also be called the drive current.

[0038] The command unit 41 sets target values ​​for the d-axis current Id and the q-axis current Iq as a d-axis current command value Id* and a q-axis current command value Iq*, respectively. The command values ​​Id* and Iq* set by the command unit 41 are input to a d-axis subtraction unit 43 as the d-axis current command value Id* and to a q-axis subtraction unit 44 as the q-axis current command value Iq*. A torque command value is input to the command unit 41 as a signal from a higher-level ECU as the rotational torque to be generated by the motor 12. The command unit 41 sets the command values ​​Id* and Iq* in accordance with the torque command value when, for example, power is supplied from the battery 11 to the motor 12.

[0039] The d-axis subtraction unit 43 calculates the deviation between the d-axis current command value Id* and the d-axis current Id as the d-axis current deviation. The q-axis subtraction unit 44 calculates the deviation between the q-axis current command value Iq* and the q-axis current Iq as the q-axis current deviation. The d-axis current deviation and the q-axis current deviation are input to the current control unit 45.

[0040] The current control unit 45 calculates a d-axis voltage command value Vd* and a q-axis voltage command value Vq* in the dq coordinate system so that the d-axis current deviation and the q-axis current deviation become zero. The current control unit 45 performs feedback control to calculate the d-axis voltage command value Vd* and the q-axis voltage command value Vq* so that the d-axis current Id matches the d-axis current command value Id* and the q-axis current Iq matches the q-axis current command value Iq*. The current control unit 45 performs, for example, PI control as the feedback control. The d-axis voltage command value Vd* and the q-axis voltage command value Vq* are input to a 2-phase to 3-phase conversion unit 46.

[0041] The two-phase to three-phase converter 46 converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* in the dq coordinate system into three-phase AC coordinates to calculate a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw* in the three-phase coordinate system. These voltage command values ​​Vu*, Vv*, and Vw* are voltage values ​​to be output to the three-phase windings 12a, respectively, and are information included in the drive command. The drive command including these voltage command values ​​Vu*, Vv*, and Vw* is input to the inverter 30.

[0042] The control device 40 has a PWM signal generating unit (not shown) as a functional block. The PWM signal generating unit generates PWM signals for driving the IGBTs 32a and 32b using the voltage command values ​​Vu*, Vv*, and Vw*. The control device 40 applies voltages corresponding to the voltage command values ​​Vu*, Vv*, and Vw* to the windings 12a of the U phase, V phase, and W phase, respectively, by turning on and off the IGBTs 32a and 32b in response to the PWM signals.

[0043] In the drive system 10, when the motor 12 is driven and rotated by the power supply from the battery 11 during vehicle running, etc., if an inverter abnormality occurs in the inverter 30, there is a concern that a secondary abnormality will occur along with the inverter abnormality. For example, an inverter abnormality is a short circuit abnormality in which the IGBTs 32a and 32b as switching elements are shorted. Here, a situation in which the IGBTs 32a and 32b unintentionally transition to an on state or a situation in which the IGBTs 32a and 32b are unintentionally held in an on state is referred to as a short circuit abnormality. When a short circuit abnormality occurs in the IGBTs 32a and 32b, there is a concern that a control failure will occur in which the power conversion device 13 does not operate according to the command of the control device 40, such as the IGBTs 32a and 32b not being turned off after being commanded to be turned off by the control device 40. When a control failure occurs, it is considered that secondary abnormalities are likely to occur in the drive system 10, such as an overvoltage occurring in auxiliary devices such as a voltage sensor or the smoothing capacitor 21 due to the back electromotive force of the motor 12, or an overcurrent flowing through the inverter 30.

[0044] In response to this, the control device 40 performs active short circuiting on the inverter 30 when an inverter abnormality occurs. Hereinafter, active short circuiting is referred to as ASC. The control device 40 realizes ASC by turning on one of the IGBT 32a of the upper arm 31a and the IGBT 32b of the lower arm 31b for all three phases and turning off the other for all three phases. If the state of the inverter 30 when the control device 40 performs ASC is referred to as an ASC state, this ASC state corresponds to a target state.

[0045] Regarding ASC, it has been found through tests, simulations, etc. that when the inverter 30 is in the ASC state and the d-axis current Id increases, irreversible demagnetization of the permanent magnet 12b in the motor 12 is likely to occur. In addition, it has been found through tests, simulations, etc. that if a relatively long time has elapsed between the occurrence of an inverter abnormality and the switching of the inverter 30 to the ASC state, the d-axis current Id after the inverter 30 is switched to the ASC state is likely to increase negatively. These findings will be described with reference to Figs. 3 to 6.

[0046] First, irreversible demagnetization will be described. In Fig. 3, the inverter 30 operates normally from timing t1 until just before timing t2. Then, an inverter abnormality occurs at timing t2, and the control device 40 starts ASC in response to the occurrence of the inverter abnormality. If the period from the occurrence of the inverter abnormality to the start of ASC is called a delay time TD, this delay time TD is sufficiently short compared to, for example, the period from timing t1 to t2. For this reason, the delay time TD is not shown in Fig. 3. Note that the d-axis current Id is a negative value both before and after the occurrence of the inverter abnormality.

[0047] At time t2, the inverter 30 switches to the ASC state, and the d-axis current Id momentarily increases to the negative side. The d-axis current Id further rapidly decreases from a negative value smaller than zero, and the absolute value of the d-axis current Id rapidly increases and reaches a maximum value Idmax. The amplitude of the d-axis current Id also rapidly increases with the sudden increase in absolute value, and then the amplitude gradually decreases.

[0048] At time t3, the amplitude of the d-axis current Id decreases and the d-axis current Id almost converges to a steady value. The d-axis current Id at time t3 is larger toward zero than the d-axis current Id at time t1 when no inverter abnormality occurs. In this case, the absolute value of the d-axis current Id decreases by the difference ΔId before and after ASC.

[0049] At time t2, each of the phase currents Iu, Iv, and Iw momentarily increases to the positive or negative side. Thereafter, like the d-axis current Id, the amplitude of each of the phase currents Iu, Iv, and Iw gradually decreases, and the decrease in amplitude almost converges at time t3. The amplitude of each of the phase currents Iu, Iv, and Iw at time t3 is smaller than the amplitude at time t1 when no inverter abnormality occurs. In this case, the amplitude of each of the phase currents Iu, Iv, and Iw decreases by the difference ΔI before and after ASC. The phase currents Iu, Iv, and Iw can also be referred to as three-phase currents.

[0050] The reason why the absolute value of the d-axis current Id and the amplitude of each phase current Iu, Iv, Iw decrease after ASC starts is because the negative increase in the d-axis current Id accompanying the execution of ASC applies a demagnetizing field to the permanent magnet 12b of the motor 12, causing demagnetization of the permanent magnet 12b. If the maximum value Idmax reached by the absolute value of the d-axis current Id is sufficiently large, the demagnetizing field applied to the permanent magnet 12b becomes sufficiently strong, and it is believed that the demagnetization occurring in the permanent magnet 12b is likely to become irreversible.

[0051] Due to the irreversible demagnetization of the permanent magnet 12b caused by the execution of ASC, the back electromotive force BEMF of the motor 12 has a smaller amplitude at timing t3 after the start of ASC than at timing t1 when no inverter abnormality occurs, as shown in Fig. 4. In Fig. 4, the horizontal axis represents the electrical angle θ, and the vertical axis represents the back electromotive force BEMF of the motor 12.

[0052] Next, the relationship between the delay time TD and the d-axis current Id will be described. In FIG. 5, the absolute value [A] of the maximum value Idmax of the d-axis current Id and the effective value [Arms] of each phase current Iu, Iv, Iw at timing t3 after the start of ASC are plotted on the vertical axis, and the delay time TD is plotted on the horizontal axis. As shown in FIG. 5, the maximum value Idmax of the d-axis current Id increases as the delay time TD increases. On the other hand, each phase current Iu, Iv, Iw has an almost constant value regardless of the delay time TD. This indicates that the longer the delay time TD, the more likely it is that the d-axis current Id will rapidly increase with the execution of ASC, causing irreversible demagnetization of the permanent magnet 12b, while the more unlikely it is that the increase in each phase current Iu, Iv, Iw will occur.

[0053] Next, the relationship between the back electromotive force BEMF of the motor 12 and the motor temperature Tm, which is the temperature of the motor 12, will be described. In the motor 12, the back electromotive force BEMF differs when the motor temperature Tm differs. In this embodiment, the permanent magnet 12b of the motor 12 is formed of a neodymium magnet. A neodymium magnet is a type of rare earth magnet, and has the property that the lower the temperature, the stronger the magnetic force becomes. In the motor 12, the lower the motor temperature Tm, the greater the back electromotive force BEMF tends to be.

[0054] As shown in FIG. 6, in the motor 12, the relationship between the maximum value Idmax of the d-axis current Id and the back electromotive force BEMF of the motor 12 varies depending on the motor temperature Tm. In FIG. 6, the horizontal axis shows the maximum value Idmax of the d-axis current Id as a negative value rather than an absolute value. The vertical axis shows the back electromotive force BEMF of the motor 12 after irreversible demagnetization of the permanent magnet 12b by ASC occurs. That is, the vertical axis shows the back electromotive force BEMF at timing t3. FIG. 6 shows the relationship between the maximum value Idmax and the back electromotive force BEMF for each of the cases in which the motor temperature Tm is a first temperature Tm1, a second temperature Tm2, ​​and a third temperature Tm3. Among these temperatures Tm1, Tm2, ​​and Tm3, the first temperature Tm1 is the highest temperature, and the third temperature Tm3 is the lowest temperature.

[0055] In the motor 12, regardless of whether the motor temperature Tm is at temperature Tm1, Tm2, ​​or Tm3, when the maximum value Idmax of the d-axis current Id increases on the negative side, the back electromotive force BEMF after irreversible demagnetization decreases. On the other hand, because the lower the motor temperature Tm, the less likely demagnetization of the permanent magnet 12b occurs, the lower the motor temperature Tm, the less likely the back electromotive force BEMF after irreversible demagnetization decreases even if the maximum value Idmax of the d-axis current Id increases on the negative side.

[0056] Next, the relationship between the back electromotive force BEMF of the motor 12 and the motor rotation speed Nm will be described. In the motor 12, the back electromotive force BEMF also differs when the motor rotation speed Nm differs. The back electromotive force BEMF increases as the motor rotation speed Nm increases, and the motor rotation speed Nm and the motor rotation speed Nm are in a proportional relationship. In addition, the relationship between the maximum value Idmax of the d-axis current Id and the back electromotive force BEMF differs depending on the motor rotation speed Nm. For example, similar to the motor temperature Tm, regardless of the motor rotation speed Nm, when the maximum value Idmax of the d-axis current Id increases on the negative side, the back electromotive force BEMF after irreversible demagnetization decreases. Furthermore, the back electromotive force BEMF increases as the motor rotation speed Nm increases. Therefore, in order to increase the amount of reduction in the back electromotive force BEMF, it is necessary to increase the maximum value Idmax of the d-axis current Id on the negative side as the motor rotation speed Nm increases.

[0057] When an inverter abnormality occurs, the control device 40 performs ASC so as to reduce the back electromotive force BEMF. The control device 40 performs processing for performing ASC in an inverter control processing for controlling the drive of the inverter 30. This inverter control processing will be described with reference to the flowchart of FIG. 7. The control device 40 repeatedly executes the inverter control processing at a predetermined cycle. The control device 40 has a function of executing each step of the inverter control processing.

[0058] In FIG. 7, in step S101, it is determined whether the motor temperature Tm is equal to or lower than a predetermined temperature threshold Tb. The temperature threshold Tb is information obtained by a test, a simulation, or the like, and is stored in the storage unit of the control device 40. As described in the explanation of FIG. 6, in order to reduce the back electromotive force BEMF by generating irreversible demagnetization of the permanent magnet 12b, it is necessary to increase the maximum value Idmax of the d-axis current Id as the motor temperature Tm decreases. Therefore, if the motor temperature Tm is too low, even if the maximum value Idmax of the d-axis current Id is increased to a value exceeding the upper limit, the permanent magnet 12b may not be irreversibly demagnetized, and the back electromotive force BEMF may not be sufficiently reduced. Note that the upper limit value of the maximum value Idmax of the d-axis current Id is a value that is set according to the rated value of the inverter 30, etc.

[0059] Therefore, in step S101, a value at which irreversible demagnetization of the permanent magnet 12b occurs within a range in which the maximum value Idmax of the d-axis current Id does not exceed an upper limit is set as the temperature threshold value Tb for the motor temperature Tm. If the motor temperature Tm is equal to or lower than the temperature threshold value Tb, the motor speed Nm is limited even in a normal state, and the process proceeds to step S110. In this case, the motor temperature Tm is low enough that the permanent magnet 12b will not be irreversibly demagnetized even if ASC is performed in response to the occurrence of an inverter abnormality.

[0060] In step S110, a motor limiting process is performed. In this motor limiting process, the motor rotation speed Nm is limited so that the back electromotive force BEMF of the motor 12 is equal to or less than a predetermined inverse threshold value BEMFb [V] (not shown). For example, the lower the current motor temperature Tm, the smaller the target value of the motor rotation speed Nm is set. Then, the command unit 41 sets a d-axis current command value Id* and a q-axis current command value Iq* according to the target value of the motor rotation speed Nm in addition to the torque command value. The motor rotation speed Nm is limited by performing vector control of the motor 12 according to these current command values ​​Id* and Iq*.

[0061] The reverse threshold value BEMFb of the back electromotive force BEMF is the upper limit of the voltage applied to the inverter 30. As described above, the upper limit of the voltage applied to the inverter 30 is the withstand voltage value of the inverter 30, and this withstand voltage value is set to the withstand voltage value of the component or device with the lowest withstand voltage value in the inverter 30. The reverse threshold value BEMFb is information obtained by testing, simulation, or the like, and is stored in the memory unit of the control device 40.

[0062] On the other hand, if the motor temperature Tm is greater than the temperature threshold Tb, it is determined that there is a high possibility that the back electromotive force BEMF of the motor 12 can be reduced by performing ASC, and the process proceeds to step S102. In step S102, it is determined whether an inverter abnormality has occurred. Here, it is determined whether the IGBTs 32a, 32b are normally turned on and off in accordance with a drive command from the control device 40 to the inverter 30. For example, the detection signals of various sensors such as the current sensor 28 are compared with the drive command to the inverter 30, and the drive state of the IGBTs 32a, 32b is determined using the comparison result. If it is determined that a short circuit abnormality has occurred in the IGBTs 32a, 32b, it is determined that an inverter abnormality has occurred, and the process proceeds to step S103.

[0063] In step S103, the motor rotation speed Nm is acquired using the detection signal of the rotation sensor 29. In step S104, it is determined whether the motor rotation speed Nm is equal to or greater than a predetermined rotation threshold value Nb. The rotation threshold value Nb is information acquired by a test, a simulation, or the like, and is stored in a storage unit such as a memory in the control device 40. The rotation threshold value Nb is set so that the back electromotive force BEMF of the motor 12 is limited to a value corresponding to, for example, the maximum allowable voltage or the rated voltage of the smoothing capacitor 21, or a value corresponding to the upper limit of the voltage applied to the inverter 30. The upper limit of the voltage applied to the inverter 30 is set according to, for example, the rated value or the maximum allowable voltage of the inverter 30.

[0064] The upper limit of the voltage applied to the inverter 30 may also be referred to as the withstand voltage value of the inverter 30. The withstand voltage value of the inverter 30 is set to the withstand voltage value of the component or device with the lowest withstand voltage value in the inverter 30. For example, if the components with the lowest withstand voltage value in the inverter 30 are IGBTs 32a and 32b, the withstand voltage value is set according to the rated value and maximum allowable voltage of the IGBTs 32a and 32b.

[0065] If the motor speed Nm has not reached the rotation threshold value Nb, the inverter control process is terminated since it is deemed unlikely that an overvoltage of the auxiliary devices or the smoothing capacitor 21 or an overcurrent of the inverter 30 will occur. If the motor speed Nm has reached the rotation threshold value Nb, it is deemed likely that an overvoltage of the auxiliary devices or the smoothing capacitor 21 or an overcurrent of the inverter 30 will occur, and the process proceeds to step S105.

[0066] In step S105, the motor temperature Tm is acquired. In this acquisition process, the motor temperature Tm is acquired as a detection value using signals input from a higher-level ECU and various sensors. In this embodiment, it is assumed that the motor temperature Tm and the permanent magnet 12b are approximately the same.

[0067] In step S106, a target time process is performed to set a target time TDAsc for the delay time TD as a target value when ASC is executed. The target time process in step S106 will be described with reference to the flowchart in FIG.

[0068] In FIG. 8, in step S201, a target value BEMFAsc is obtained for the back electromotive force BEMF of the motor 12 as a target value when ASC is executed. The target value BEMFAsc is information obtained by testing, simulation, or the like, and is stored in the storage unit of the control device 40. For the back electromotive force BEMF, for example, a value corresponding to the maximum allowable voltage or rated voltage of the smoothing capacitor 21, or a value corresponding to the upper limit of the voltage applied to the inverter 30 is set as the target value BEMFAsc. In this step S201, the target value BEMFAsc is read and obtained from the storage unit of the control device 40. The target value BEMFAsc may be variably set to the motor rotation speed Nm or the motor temperature Tm.

[0069] In step S202, a first target time TDAsc1 is calculated for the target time TDAsc of the delay time TD using the motor temperature Tm. The first target time TDAsc1 is a target time calculated using the knowledge that the lower the motor temperature Tm, the longer the target time TDAsc should be to reduce the back electromotive force BEMF. Here, first, a target maximum value Idmax1 of the d-axis current Id is calculated from the target value BEMFasc of the back electromotive force BEMF and the motor temperature Tm using temperature correlation information. The temperature correlation information is correlation information showing the correlation between the motor temperature Tm, the back electromotive force BEMF, and the maximum value Idmax of the d-axis current Id, and is stored in the storage unit of the control device 40 as, for example, a map or a function. For example, when the information shown in FIG. 6 is used as the temperature correlation information, if the motor temperature Tm is the second temperature Tm2, ​​the value that intersects with the target value BEMFasc on the graph of the second temperature Tm2 for the maximum value Idmax of the d-axis current Id is calculated as the target maximum value Idmax1.

[0070] Next, a first target time TDasc1 is calculated from the target maximum value Idmax1 of the d-axis current Id using time correlation information. The time correlation information is correlation information indicating the correlation between the maximum value Idmax of the d-axis current Id and the delay time TD, and is stored in the storage unit of the control device 40 as, for example, a map or a function. For example, when the information shown in Fig. 5 is used as the time correlation information, for the delay time TD, a value at which the flag indicating the maximum value Idmax of the d-axis current Id intersects with the target maximum value Idmax1 is calculated as the first target time TDasc1.

[0071] In step S203, for the target time TDAsc of the delay time TD, a second target time TDAsc2 is calculated using the motor rotation speed Nm. The second target time TDAsc2 is a target time calculated using the knowledge that in order to reduce the back electromotive force BEMF, the target time TDAsc should be made longer as the motor rotation speed Nm increases. Here, first, a target maximum value Idmax2 (not shown) of the d-axis current Id is calculated from the target value BEMFasc of the back electromotive force BEMF and the motor rotation speed Nm using rotation correlation information. The rotation correlation information is correlation information indicating the correlation between the motor rotation speed Nm, the back electromotive force BEMF, and the maximum value Idmax of the d-axis current Id, and is stored in the storage unit of the control device 40 as, for example, a map or a function.

[0072] Next, the second target time TDAsc2 is calculated from the target maximum value Idmax2 of the d-axis current Id using the time correlation information. Here, the second target time TDAsc2 is calculated in the same manner as the first target time TDAsc1, using the time correlation information used in calculating the first target time TDAsc1.

[0073] In step S204, the target time TDAsc is calculated based on the first target time TDAsc1 calculated from the motor temperature Tm and the second target time TDAsc2 calculated from the motor rotation speed Nm. For example, the average value of the first target time TDAsc1 and the second target time TDAsc2 is calculated, and this average value is set as the target time TDAsc. Any method may be used to calculate the target time TDAsc as long as the first target time TDAsc1 and the second target time TDAsc2 are used.

[0074] In addition, the function of the control device 40 that executes the process of step S202 corresponds to a temperature setting unit, and the function that executes the process of step S203 corresponds to a rotation setting unit. Also, the functions that execute the processes of steps S202, S203, and S204 correspond to a target setting unit.

[0075] After step S204 is completed, step S106 shown in FIG. 7 is deemed to be completed, and the process proceeds to step S107. In step S107, it is determined whether the delay time TD has reached the target time TDAsc. Then, the process of step S107 is repeated until the delay time TD reaches the target time TDAsc. If the delay time TD has reached the target time TDAsc, the process proceeds to step S108. Note that in this inverter control process, the delay time TD is measured as the elapsed time from the timing at which the occurrence of an inverter abnormality was determined in step S101.

[0076] In step S108, ASC is executed to transition the inverter 30 to the ASC state. Here, one of the IGBT 32a of the upper arm 31a and the IGBT 32b of the lower arm 31b is driven to be on for all three phases, and the other is driven to be off for all three phases. In this case, the timing at which one of the IGBTs 32a and 32b is switched to the on state is aligned in the upper and lower arm circuits 31 of all three phases. The timing at which the other is switched to the off state is aligned in the upper and lower arm circuits 31 of all three phases. In addition, the timing at which one of the IGBTs 32a and 32b is switched to the on state and the timing at which the other is switched to the off state are also aligned.

[0077] Note that "aligned" includes the cases where the states of the multiple IGBTs 32a, 32b are switched together, the switching timings of the multiple IGBTs 32a, 32b are simultaneous, and the switching timings are slightly shifted.

[0078] In step S108, it is determined in which of the IGBTs 32a and 32b a short circuit has occurred. If the IGBT in which the short circuit has occurred is included in only one of the upper arm 31a and the lower arm 31b among all the IGBTs 32a and 32b, all the remaining IGBTs in the arm 31a or 31b in which the IGBT in question is included are turned on. Then, all the IGBTs in the arm 31a or 31b in which the IGBT in question is not included are turned off. For example, if a short circuit has occurred in the IGBT 32a in the upper arm 31a for the U phase, the IGBT 32a in the upper arm 31a for the V phase and the W phase are switched on. Then, the IGBT 32b in the lower arm 31b for all three phases are switched off.

[0079] In step S109, a termination process is performed. In the termination process, it is determined whether or not the back electromotive force BEMF of the motor 12 has decreased to an allowable range for the target value BEMFasc due to the execution of ASC. For example, it is determined whether or not the magnitude of the amplitude of the d-axis current Id after the execution of ASC is smaller than a predetermined amplitude threshold, and whether or not the difference ΔI before and after the ASC for each phase current Iu, Iv, Iw is smaller than a predetermined difference threshold. Then, when the amplitude of the d-axis current Id is smaller than the amplitude threshold and the difference ΔI is smaller than the difference threshold, it is determined that the back electromotive force BEMF has decreased to an allowable range. Note that at timing t3 shown in FIG. 3, the d-axis current Id is smaller than the amplitude threshold, and the d-axis current Id and each phase current Iu, Iv, Iw are converged to a steady value.

[0080] When the back electromotive force BEMF falls within the allowable range, it is determined that the back electromotive force BEMF has been appropriately reduced by the execution of ASC, and the ASC is terminated. Here, in the inverter 30, all the IGBTs 32a and 32b other than the IGBT in which a short circuit abnormality has occurred are switched to the OFF state, and the inverter 30 is transitioned to a termination state. Note that in the termination process, the switch 22 may be switched to an open state to stop the power supply from the battery 11 to the motor 12.

[0081] In addition, the function of the control device 40 that executes the process of step S107 corresponds to a delay unit, the function that executes the process of step S108 corresponds to a state transition unit, the function that executes the process of step S109 corresponds to a termination unit, and the function that executes the process of step S110 corresponds to a restriction unit.

[0082] Next, a change in the back electromotive force BEMF when the control device 40 performs ASC in response to the occurrence of an inverter abnormality will be described with reference to FIGS.

[0083] In Fig. 3, if an inverter abnormality occurs at timing t2, ASC is started by the control device 40 when the delay time TD reaches the target time TDAsc. With the start of ASC, the amplitude of the d-axis current Id temporarily increases, but at timing t3, the d-axis current Id in the steady state is smaller than the d-axis current Id at timing t1. The amplitudes of the phase currents Iu, Iv, and Iw also temporarily increase, but the amplitudes at timing t3 when the steady state is reached are smaller than the amplitudes at timing t1 when no inverter abnormality occurs. As a result, as shown in Fig. 4, the back electromotive force BEMF at timing t3 when an inverter abnormality occurs is smaller than the back electromotive force BEMF at timing t1 when no inverter abnormality occurs.

[0084] According to the present embodiment described so far, when an inverter abnormality occurs, the inverter 30 is shifted to the ASC state when the delay time TD reaches the target time TDAsc. Therefore, the d-axis current Id after the inverter 30 is shifted to the ASC state is likely to become large on the negative side, and accordingly, irreversible demagnetization of the permanent magnet 12b in the motor 12 is likely to occur. When irreversible demagnetization of the permanent magnet 12b occurs, the back electromotive force BEMF of the motor 12 is reduced, so that the current flowing through the inverter 30 in the ASC state is too large and the IGBTs 32a, 32b, etc. are unlikely to generate heat. Therefore, heat generation due to the occurrence of an abnormality in the inverter 30 can be suppressed.

[0085] According to this embodiment, when executing ASC, the control device 40 aligns the timing of switching one of the IGBTs 32a, 32b to the ON state for all of the upper and lower arm circuits 31. In this configuration, for example, when switching all of the multiple IGBTs 32a to the ON state, it is sufficient to generate the same drive command for all of these IGBTs 32a, so that the processing load of the control device 40 can be reduced. This effect can also be achieved when switching all of the multiple IGBTs 32b to the ON state.

[0086] When performing ASC, the control device 40 aligns the timing of switching one of the IGBTs 32a, 32b to the OFF state for all of the upper and lower arm circuits 31. In this configuration, for example, when switching all of the multiple IGBTs 32a to the OFF state, the same drive command can be generated for all of these IGBTs 32a, thereby reducing the processing load on the control device 40. This effect can also be achieved when switching all of the multiple IGBTs 32b to the OFF state.

[0087] When the motor temperature Tm is equal to or lower than the temperature threshold value Tb, there is a concern that even if the ASC of the inverter 30 is executed, the maximum value Idmax of the d-axis current Id may be insufficient and the permanent magnet 12b may not be irreversibly demagnetized due to the motor temperature Tm being in a too low temperature range. In contrast, according to the present embodiment, when the motor temperature Tm is equal to or lower than the temperature threshold value Tb, the motor speed Nm is limited so that the back electromotive force BEMF is equal to or lower than the reverse threshold value BEMFb. This makes it possible to avoid a situation in which the maximum value Idmax of the d-axis current Id is insufficient and the permanent magnet 12b does not become irreversibly demagnetized despite the execution of the ASC. As a result, it is possible to suppress the inverter 30 from generating heat due to the execution of the ASC.

[0088] According to this embodiment, when the motor temperature Tm is equal to or lower than the temperature threshold value Tb, the motor rotation speed Nm is limited in accordance with the motor temperature Tm. Therefore, in limiting the motor rotation speed Nm so that the back electromotive force BEMF is equal to or lower than the back electromotive force threshold value BEMFb, it is possible to utilize the relationship that the higher the motor rotation speed Nm, the larger the back electromotive force BEMF becomes, and the relationship that the lower the motor temperature Tm, the larger the back electromotive force becomes. Therefore, it is possible to improve the accuracy of limiting the motor rotation speed Nm when the motor temperature Tm is equal to or lower than the temperature threshold value Tb.

[0089] According to this embodiment, the reverse threshold value BEMFb of the back electromotive force BEMF is set to the withstand voltage value of the inverter 30. Therefore, when the motor temperature Tm is equal to or lower than the temperature threshold value Tb, it is possible to more reliably prevent an excessively large voltage from being applied to the inverter 30 by the back electromotive force BEMF of the motor 12.

[0090] According to this embodiment, after the inverter 30 transitions to the ASC state, all IGBTs other than the IGBT in which an abnormality has occurred are switched to the OFF state, and the inverter 30 transitions to the end state. Therefore, when the back electromotive force BEMF of the motor 12 is reduced by the execution of ASC, the inverter 30 transitions to the end state, causing the motor 12 to rotate by inertia. Therefore, even if an inverter abnormality occurs and ASC is executed, the inverter 30 transitions to the end state, allowing the vehicle to safely evacuate.

[0091] According to this embodiment, the target time TDAsc is set according to both the motor rotation speed Nm and the motor temperature Tm. Therefore, the target time TDAsc can be set using both the knowledge that the target time TDAsc should be longer as the motor rotation speed Nm increases and the knowledge that the target time TDAsc should be longer as the motor temperature Tm decreases.

[0092] According to this embodiment, the temperature correlation information is used to set the target time TDAsc, and this temperature correlation information includes the knowledge that the lower the motor temperature Tm, the longer the target time TDAsc should be. Therefore, by utilizing this knowledge, the target time TDAsc can be set with high accuracy from the motor temperature Tm.

[0093] According to this embodiment, the rotation correlation information is used to set the target time TDAsc, and this rotation correlation information includes the knowledge that the target time TDAsc increases as the motor rotation speed Nm increases. Therefore, by utilizing this knowledge, the target time TDAsc can be set with high accuracy from the motor rotation speed Nm.

[0094] <Second embodiment> In the first embodiment, when ASC of the inverter 30 is executed, the timings at which one of the IGBTs 32a and 32b is switched to the ON state are synchronized for the upper and lower arm circuits 31, but in the second embodiment, the timings are not synchronized. The configurations, actions, and effects not specifically described in this embodiment are the same as those in the first embodiment. In this embodiment, the differences from the first embodiment will be mainly described.

[0095] Regarding the ASC, it has been found that the d-axis current Id tends to become large on the negative side when the timing at which one of the IGBTs 32a, 32b is switched on differs between at least one upper and lower arm circuit 31 and the remaining upper and lower arm circuits 31. This finding has been obtained through tests, simulations, and the like, and will be described with reference to FIG.

[0096] When executing ASC, the control device 40 first switches one of the IGBTs 32a, 32b to the on state for one of the multiple upper and lower arm circuits 31, and then switches one of the IGBTs 32a, 32b to the on state for the remaining upper and lower arm circuits 31. In this embodiment, the difference between the timing at which one upper and lower arm circuit 31 is switched to the on state and the timing at which the remaining upper and lower arm circuits 31 are switched to the on state is referred to as a delay time TS.

[0097] In FIG. 9, the vertical axis is the maximum value Idmax of the d-axis current Id and the phase currents Iu, Iv, and Iw, as in FIG. 5, and the horizontal axis is the delay time TS. As shown in FIG. 9, the longer the delay time TS, the larger the maximum value Idmax of the d-axis current Id. On the other hand, the phase currents Iu, Iv, and Iw are almost constant regardless of the delay time TS. This indicates that the longer the delay time TS, the more likely it is that the d-axis current Id will increase rapidly with the execution of ASC, causing irreversible demagnetization of the permanent magnet 12b, while the phase currents Iu, Iv, and Iw will not increase easily. With regard to the delay time TS, it has been found through testing and the like that if a delay time TS is generated when ASC is executed, an unbalanced current is generated in the inverter 30 and the motor 12, and this unbalanced current causes the d-axis current Id to increase negatively.

[0098] In the inverter control process, the control device 40 sets a delay time TS and executes the ASC in accordance with this delay time. Here, the inverter control process of this embodiment will be described with reference to the flowchart of FIG.

[0099] In FIG. 10, in steps S101 to S107, the same processing as in the first embodiment is performed. In step S107, if the motor temperature Tm is greater than the temperature threshold Tb, the process proceeds to step S301. In step S301, a target delay time TSasc is calculated for the delay time TS as a target value when ASC is executed. Here, first, a target value BEMFAsc for the back electromotive force BEMF is acquired in the same manner as in step S201 in the first embodiment. Next, a target maximum value Idmax1 of the d-axis current Id is calculated from the target value BEMFAsc of the back electromotive force BEMF and the motor temperature Tm using temperature correlation information in the same manner as in step S202 in the first embodiment. In addition, a target maximum value Idmax2 of the d-axis current Id is calculated from the target value BEMFAsc of the back electromotive force BEMF and the motor rotation speed Nm using rotation correlation information. After that, a target maximum value Idmax0 is calculated using the target maximum values ​​Idmax1 and Idmax2. For example, the average of the target maximum values ​​Idmax1 and Idmax2 is calculated, and this average is set as the target maximum value Idmax0.

[0100] Then, using the deviation correlation information, a target deviation time TSasc is calculated from the target maximum value Idmax0 of the d-axis current Id. The deviation correlation information is correlation information that indicates the correlation between the maximum value Idmax of the d-axis current Id and the deviation time TS, and is stored in the storage unit of the control device 40 as, for example, a map or a function. For example, when the information shown in Fig. 9 is used as the deviation correlation information, a value at which the deviation time TS intersects with the target maximum value Idmax0 on a graph showing the maximum value Idmax of the d-axis current Id is calculated as the target deviation time TSasc.

[0101] After step S301, the process proceeds to step S108, and ASC is executed in the same manner as in the first embodiment. Here, first, one of the IGBTs 32a and 32b is switched to the ON state for one of the upper and lower arm circuits 31 among the plurality of upper and lower arm circuits 31. Then, the time elapsed since the switching is measured as the delay time TS, and it is determined whether or not this delay time TS reaches the target delay time TSasc. Then, when the delay time TS reaches the target delay time TSasc, one of the IGBTs 32a and 32b is switched to the ON state for the remaining upper and lower arm circuits 31. The IGBTs 32a and 32b that have not been switched to the ON state are switched to the OFF state with the same timing for all the upper and lower arm circuits 31 of the three phases. For the IGBTs 32a and 32b that are switched to the OFF state, the switching timing is set to the one that is switched to the ON state when the delay time TS reaches the target delay time TSasc.

[0102] After step S108, the processes of steps S108 and S109 are executed in the same manner as in the first embodiment, and the inverter control process ends.

[0103] According to this embodiment, when the control device 40 executes the ASC, the timing at which one of the ASCs 32a, 32b is switched to the ON state is made different between one of the upper and lower arm circuits 31 and the other upper and lower arm circuits 31 among the plurality of upper and lower arm circuits 31. Therefore, by utilizing the knowledge that the d-axis current Id is likely to become large on the negative side when the timing at which one of the ASCs 32a, 32b is switched to the ON state is different between one of the plurality of upper and lower arm circuits 31 and the remaining one, it is possible to cause irreversible demagnetization of the permanent magnet 12b. This makes it possible to reduce the back electromotive force BEMF of the motor 12.

[0104] <Other embodiments> The disclosure of this specification is not limited to the exemplified embodiments. The disclosure includes the exemplified embodiments and modifications by those skilled in the art based thereon. For example, the disclosure is not limited to the combination of parts and elements shown in the embodiments, and can be implemented in various modifications. The disclosure can be implemented by various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure includes those in which parts and elements of the embodiments are omitted. The disclosure includes the replacement or combination of parts and elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiments. The disclosed technical scope is indicated by the description of the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the description of the claims.

[0105] In each of the above embodiments, the permanent magnet 12b of the motor 12 may be formed of a magnet other than a neodymium magnet. For example, the permanent magnet 12b may be formed of a rare earth magnet such as a samarium-cobalt magnet. Since the magnetic force of the permanent magnet 12b formed of a rare earth magnet tends to increase as the temperature decreases, the ASC uses the knowledge that, in order to reduce the back electromotive force BEMF, the lower the motor temperature Tm, the longer the target time Tdasc should be.

[0106] Moreover, it is preferable that different information is used for the temperature correlation information for setting the target time TDAsc of the delay time TD and the target deviation time TSasc depending on the characteristics of the magnet forming the permanent magnet 12b. For example, in a configuration in which the permanent magnet 12b is formed of a ferrite magnet, knowledge is used that differs from the knowledge that the lower the motor temperature Tm, the longer the target time TDAsc should be in order to reduce the back electromotive force BEMF.

[0107] In the first embodiment, the target time TDAsc of the delay time TD for the ASC may be set according to only one of the motor rotation speed Nm and the motor temperature Tm. Also, the target time TDAsc may be set according to the target value BEMFasc of the back electromotive force BEMF, regardless of either the motor rotation speed Nm or the motor temperature Tm. Furthermore, the target time TDAsc may be set to a predetermined specified value. This specified value is, for example, a value stored in the storage unit of the control device 40.

[0108] In the second embodiment, when ASC is performed, two or more of the IGBTs 32a and 32b may be switched on first. For example, one of the IGBTs 32a and 32b is switched on first for two of the upper and lower arm circuits 31, and then the remaining upper and lower arm circuit 31 is switched on.

[0109] In the second embodiment described above, the timing at which one of the IGBTs 32a and 32b is switched to the ON state for the execution of ASC may be different for all of the multiple upper and lower arm circuits 31. For example, one of the IGBTs 32a and 32b is first switched to the ON state for one upper and lower arm circuit 31, and then switched to the ON state for the second upper and lower arm circuit 31 after the target deviation time TSasc has elapsed. Then, after a further target deviation time TSasc has elapsed, switched to the ON state for the third upper and lower arm circuit 31.

[0110] In the second embodiment described above, regarding the execution of ASC, the timing of switching the other of the IGBTs 32a and 32b to the off state does not have to be consistent among the multiple upper and lower arm circuits 31. In other words, the timing may be different between at least one of the multiple upper and lower arm circuits 31 and the rest.

[0111] In the second embodiment, the target deviation time TSasc for the ASC may be set according to only one of the motor rotation speed Nm and the motor temperature Tm. Also, the target deviation time TSasc may be set according to the target value BEMFasc of the back electromotive force BEMF, regardless of either the motor rotation speed Nm or the motor temperature Tm. Furthermore, the target deviation time TSasc may be set to a predetermined specified value. This specified value is, for example, a value stored in the storage unit of the control device 40.

[0112] In the second embodiment, the target shift time TSasc for the ASC may be set to compensate for the insufficient reduction in the back electromotive force BEMF caused by the delay of the ASC. Also, the target time TDAsc for the delay time TD for the ASC may be set to compensate for the insufficient reduction in the back electromotive force BEMF caused by shifting the ON drive in time.

[0113] In the second embodiment, when a target deviation time TSasc is set for the execution of ASC, the switching to the ON state of one of the IGBTs 32a and 32b that is switched to the ON state first may not be delayed. For example, the target time TDAsc of the delay time TD is set to zero in step S106. Also, the processes of steps S106 and S107 in the inverter control process of Fig. 7 may not be performed. In either case, the timing of driving one of the IGBTs 32a and 32b to the ON state differs between one upper and lower arm circuit 31 and the remaining upper and lower arm circuits 31, creating a situation in which the d-axis current Id is likely to rapidly increase on the negative side.

[0114] In each of the above embodiments, regarding the execution of ASC, the other IGBT 32a, 32b does not need to be driven off as long as one of the IGBTs 32a, 32b is turned on in all of the upper and lower arm circuits 31. In this way, if one of the IGBTs 32a, 32b is switched to the on state in all of the upper and lower arm circuits 31, the d-axis current Id becomes large on the negative side, making it easier for irreversible demagnetization of the permanent magnet 12b to occur.

[0115] In each of the above embodiments, a temperature sensor for detecting the motor temperature Tm may be provided around the motor 12 or on the motor itself. For example, a configuration may be adopted in which a temperature sensor is attached to the permanent magnet 12b of the motor 12. In this configuration, it is possible to directly detect the temperature of the permanent magnet 12b as the motor temperature Tm based on a detection signal from the temperature sensor. The control device 40 may also estimate and obtain the motor temperature Tm using the phase currents Iu, Iv, Iw and the phase voltages Vu, Vv, Vw, etc., as detection values. Furthermore, the control device 40 may also estimate and obtain the motor temperature Tm using the d-axis current Id, the q-axis current Iq, the d-axis voltage Vd, the q-axis voltage Vq, etc.

[0116] In each of the above embodiments, current sensor 28 does not have to detect the current flowing through winding 12a for all three phases. For example, current sensor 28 may output detection signals for two of the three phases, a current calculation unit of control device 40 may calculate the phase currents for the two phases corresponding to the detection signals, and the phase current for the remaining phase may be estimated from the phase currents for the two phases.

[0117] In each of the above embodiments, the control device 40 is provided by a control system including at least one computer. The control system includes at least one processor (hardware processor) that is hardware. The hardware processor can be provided by the following (i), (ii), or (iii).

[0118] (i) A hardware processor may be a hardware logic circuit. In this case, the computer is provided by digital circuits including a number of programmed logic units (gate circuits). The digital circuits may include a memory that stores at least one of a program and data. The computer may be provided by analog circuits. The computer may be provided by a combination of digital and analog circuits.

[0119] (ii) The hardware processor may be at least one processor core that executes a program stored in at least one memory. In this case, the computer is provided with at least one memory and at least one processor core. The processor core is referred to as a CPU, for example. The memory is also referred to as a storage medium. The memory is a non-transitive and tangible storage medium that non-transiently stores "at least one of a program and data" that can be read by the processor.

[0120] (iii) A hardware processor may be a combination of (i) above and (ii) above, where (i) and (ii) are located on different chips or on a common chip.

[0121] That is, at least one of the means and functions provided by the control device 40 can be provided by hardware alone, software alone, or a combination thereof.

[0122] In each of the above-described embodiments, the switching elements constituting the inverter 30 are not limited to IGBTs. That is, for example, MOSFETs may be used as the upper arm switches and the lower arm switches.

[0123] In each of the above embodiments, the motor 12 may have a stator including permanent magnets 12b forming a field magnet, and a rotor including windings 12a forming an armature. In addition, the motor 12 does not have to be a three-phase AC motor as long as it is a multi-phase AC motor. For example, the motor 12 may be a two-phase AC motor or a four or more phase AC motor.

[0124] In each of the above embodiments, the vehicle equipped with the power conversion device 13 includes a passenger car, a bus, a construction vehicle, an agricultural machine vehicle, etc. A vehicle is one type of moving body, and the moving body equipped with the power conversion device 13 includes a train, an airplane, etc., in addition to a vehicle. The power conversion device 13 includes an inverter device and a converter device. The converter device includes an AC input / DC output power supply device, a DC input / DC output power supply device, an AC input / AC output power supply device, etc. [Explanation of symbols]

[0125] 11...battery as power supply unit, 12...motor, 13...power conversion device, 30...inverter as power conversion unit, 31...upper and lower arm circuits as arm circuits, 32a...IGBT as upper arm switch, 32b...IGBT as lower arm switch, BEMF...back electromotive force, BEMFb...reverse threshold, TD...delay time, Tdasc...target time, Nm...motor rotation speed as rotation speed, Tb...temperature threshold, Tm...motor temperature as temperature, S107...delay unit, S108...state transition unit, S109...termination unit, S110...limitation unit, S202...target setting unit and temperature setting unit, S203...target setting unit and rotation setting unit, S204...target setting unit.

Claims

1. A power conversion device (13) that converts power supplied from a power source unit (11) to a motor (12) from direct current to alternating current by a power conversion unit (30), a state transition unit (S108) that, when an abnormality occurs in the power conversion unit and the temperature (Tm) of the motor is higher than a temperature threshold (Tb) at which irreversible demagnetization of a permanent magnet provided in the motor occurs, transitions the power conversion unit to a target state in which one of a high-potential side upper arm switch (32 a) and a low-potential side lower arm switch (32 b) for all of a plurality of arm circuits (31) connected in parallel with each other is turned on and the other is turned off; a delay unit (S107) that delays the transition of the power conversion unit to the target state by the state transition unit by at least a target time (TDasc) from the occurrence of the abnormality in the power conversion unit when an abnormality occurs in the power conversion unit and the temperature is higher than a temperature threshold value; a target setting unit (S202, S203, S204) that sets the target time in accordance with at least one of the rotation speed (Nm) of the motor and the temperature; A power conversion device comprising:

2. The goal setting unit, 2. The power conversion device according to claim 1, further comprising a rotation setting unit (S203) that uses rotation correlation information indicating a correlation between the rotation speed (Nm) of the motor and a delay time (TD) delayed from an occurrence of an abnormality in the power conversion unit to set the target time.

3. The goal setting unit, The power conversion device according to claim 1 or 2, further comprising a temperature setting unit (S202) that uses temperature correlation information indicating a correlation between the temperature and a delay time (TD) delayed from an occurrence of an abnormality in the power conversion unit to set the target time.

4. The state transition unit is The power conversion device according to any one of claims 1 to 3, wherein the timing of switching one of the upper arm switch and the lower arm switch to the on state is aligned for a plurality of the arm circuits.

5. The state transition unit is The power conversion device according to any one of claims 1 to 3, wherein the timing of switching one of the upper arm switch and the lower arm switch to the on state is made different between at least one of the arm circuits and the other arm circuits.

6. A power conversion device according to any one of claims 1 to 5, further comprising a limiting unit (S110) that limits the rotation speed (Nm) of the motor so that the back electromotive force (BEMF) of the motor becomes equal to or less than a predetermined reverse threshold (BEMFb) when the temperature (Tm) is equal to or less than the temperature threshold.

7. The power conversion device according to claim 6 , wherein the limiting unit limits a rotation speed (Nm) of the motor in accordance with the temperature.

8. The power conversion device according to claim 6 or 7, wherein the reverse threshold is an upper limit of a voltage applied to the power conversion unit.

9. A power conversion device as described in any one of claims 1 to 8, further comprising a termination unit (S109) that transitions the power conversion device to the target state by the state transition unit, and transitions to a termination state in which all of the multiple arm circuits for both the upper arm switch and the lower arm switch are turned off.

Images