Motor control device

Abstract

In a motor control device (10), in a state in which a motor (40) is rotating by inertia and in which arms corresponding to first phase switching elements (21) and (22), arms corresponding to second phase switching elements (23) and (24), and arms corresponding to third phase switching elements (25) and (26) are all set to an on state, when the current of a first phase winding (41) reaches a first threshold value, a control unit (35) executes a first process for switching the arms corresponding to the phase switching elements (21) and (22) to an off state; when, following the execution of the first process, the current of a second phase winding (42) reaches a second threshold value, the control unit (35) executes a second process for switching the arms corresponding to the second phase switching elements (23) and (24) to an off state, and for switching the arms corresponding to the first phase switching elements (21) and (22) to an on state; and after the execution of the second process, the control unit (35) executes an all-phase off process for setting all the arms corresponding to the first phase switching elements (21) and (22), all the arms corresponding to the second phase switching elements (23) and (24), and all the arms corresponding to the third phase switching elements (25) and (26) to an off state.

Description

Motor control device

[0001] The present invention relates to a motor control device.

[0002] In recent years, vehicles such as automobiles have adopted motors that are three-phase AC motors as drive sources, and accordingly, inverters have been adopted that convert DC current from the vehicle's DC secondary battery into three-phase AC current and supply it to the motor. In such vehicles, when a contactor provided between the motor and the battery is opened, a process may be performed to switch the inverter's switching elements between an ON state and an OFF state.

[0003] Under such circumstances, Patent Document 1 discloses a configuration for an inverter control device that, when a contactor is opened while a motor is rotating, executes partial shutdown control to control a switching element that is controlled to be in the on state in a target arm, which is an arm of one of the phases, to be turned off, and then executes full shutdown control to control the switching elements to be turned off when the currents of the switching elements of the target arms of the other two phases that are controlled to be in the on state both become zero.

[0004] Patent No. 6256597

[0005] However, according to the inventor's investigations, the configuration of Patent Document 1 is intended to suppress the rise in the inverter's DC link voltage and the total amount of return current when the contactor connecting the inverter and battery is opened. However, because the switching element of the target arm, which is an arm of one phase, is controlled to be turned off, and then the switching elements of the target arms of the other two phases are controlled to be turned off, the brake torque of the motor decreases relatively suddenly. As a result, it is thought that drivers of moving vehicles when the motor is rotating by inertia tend to feel a sense of discomfort as if the brakes have been suddenly released. In particular, drivers of lightweight vehicles such as motorcycles tend to feel a greater sense of discomfort due to the sudden release of the brakes, and it is thought that there is room for improvement in this regard.

[0006] The present invention was made based on the above considerations, and aims to provide a motor control device that can prevent the driver from feeling uncomfortable as if the brakes have been suddenly released due to a sudden decrease in the brake torque of the motor while the motor is rotating by inertia.

[0007] In order to achieve the above object, the present invention provides a motor control device having a control unit that controls the energization states of a first phase winding, a second phase winding, and a third phase winding of a motor that is a three-phase AC motor and is a drive source mounted on a vehicle, by controlling the switching of a first phase switching element that connects a DC battery mounted on the vehicle to the first winding, a second phase switching element that connects the DC battery to the second winding, and a switching element that connects the DC battery to the third winding, wherein the control unit controls the energization states of a first phase winding, a second phase switching element that connects the DC battery to the second winding, and a third phase switching element that connects the DC battery to the third winding when the motor is rotating by inertia, In one aspect, when all of the target arms of the first phase switching element are in an on state, when the current in the first phase winding reaches a first threshold, a first process is executed to switch the target arm of the first phase switching element to an off state; subsequent to the execution of the first process, when the current in the second phase winding reaches a second threshold, a second process is executed to switch the target arm of the second phase switching element to an off state and to switch the target arm of the first phase switching element to an on state; and after the execution of the second process, an all-phase off process is executed to turn off all of the target arm of the first phase switching element, the target arm of the second phase switching element, and the target arm of the third phase switching element.

[0008] According to one aspect of the present invention, the motor control device executes a first process when the current in the first phase winding reaches a first threshold while the target arm of the first phase switching element, the target arm of the second phase switching element, and the target arm of the third phase switching element are all in the on state, to switch the target arm of the first phase switching element to the off state; following the first process, executes a second process when the current in the second phase winding reaches a second threshold to switch the target arm of the second phase switching element to the off state and to switch the target arm of the first phase switching element to the on state; and after executing the second process, executes an all-phase off process to switch the target arm of the first phase switching element, the target arm of the second phase switching element, and the target arm of the third phase switching element all to the off state. Therefore, by appropriately performing each process leading up to the all-phase off process, it is possible to prevent a sudden decrease in brake torque of the motor while the motor is rotating by inertia, from giving the driver an uncomfortable feeling as if the brakes have been suddenly released.

[0009] FIG. 1 is a schematic diagram showing the configuration of a motor control device according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of current flow when the motor is in a driving state under the control of the motor control device according to this embodiment. FIG. 3 is a schematic diagram showing an example of current flow when the motor is in a regenerative state under the control of the motor control device according to this embodiment. FIG. 4 is a flowchart showing an example of motor control processing executed by the motor control device when the contactor is open under the control of the motor control device according to this embodiment. FIG. 5 is a schematic diagram showing an example of current flow when all switching elements are switched off under the control of the motor control device when the contactor is open under the control of the motor control device according to this embodiment. FIG. 6 is a time chart showing an example of three-phase currents that change over time under the control of the motor control device when the contactor is open under the control of the motor control device according to this embodiment. FIG. 7 is a schematic diagram showing an example of current flow when the switching elements of the lower arm are switched on under the control of the motor control device when the contactor is open under the control of the motor control device according to this embodiment. Fig. 8 is a schematic diagram showing an example of a current flow when one of the switching elements of the lower arm is switched to the OFF state under the control of the motor control device while the contactor is open in this embodiment. Fig. 9 is a schematic diagram showing an example of a current flow when one of the switching elements of the lower arm is switched to the OFF state under the control of the motor control device while the contactor is open in this embodiment, and is a diagram that follows Fig. 8 in terms of time series.

[0010] Hereinafter, motor control devices according to embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[0011] FIG. 1 is a schematic diagram showing the configuration of a motor control device according to this embodiment.

[0012] 1 , the motor control device 10 of this embodiment is an electronic control unit (ECU) that is an electronic control device and includes switching elements 21 to 26 that form a three-phase bridge drive circuit and a microcomputer 30. The figure also shows a motor 40 that is a three-phase AC motor, a phase sensor 50 that is typically a magnetic sensor provided for the motor 40, batteries 61 and 62 that are DC secondary batteries that supply power to the motor 40, a contactor 70 that is typically a relay that interrupts the electrical connection between the batteries 61 and 62, a voltage sensor 80 that is provided in parallel with the batteries 61 and 62 to electrically connect the high-potential and low-potential sides of the batteries 61 and 62, and a capacitor 90 that is provided in parallel with the batteries 61 and 62 and the voltage sensor 80 to electrically connect the high-potential and low-potential sides of the batteries 61 and 62. Of these, the voltage sensor 80 and the capacitor 90 are shown as components of the motor control device 10. Alternatively, the batteries 61 and 62 may be a single battery, in which case the contactor 70 may be provided on the high potential side or the low potential side of the battery.

[0013] The switching elements 21 to 26 are connected in a three-phase bridge configuration, and function as an inverter that turns on or off each of the switching elements 21 to 26 in accordance with a control signal from the microcomputer 30 to convert the DC current supplied from the batteries 62 and 64 into three-phase AC current, which is then supplied to the motor 40. Note that the switching elements 21 to 26 are typically transistors, and in the figure, as an example, are each shown as an N-type Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). Typically, the switching elements 21, 23, and 25 are upper arm switching elements, and the switching elements 22, 24, and 26 are lower arm switching elements.

[0014] Specifically, among the switching elements 21 to 26, pairs of switching elements 21, 22, 23, 24, 25, and 26 are provided corresponding to each of the three phases, U, V, and W. That is, the pair of switching elements 21 and 22 for the U phase are electrically connected, and when switching element 21 is in the on state and switching element 22 is in the off state, the drive voltage for the U phase is set to a high level, and when switching element 21 is in the off state and switching element 22 is in the on state, the drive voltage for the U phase is set to a low level. Also, the pair of switching elements 23 and 24 for the V phase are electrically connected, and when switching element 23 is in the on state and switching element 24 is in the off state, the drive voltage for the V phase is set to a high level, and when switching element 23 is in the off state and switching element 24 is in the on state, the drive voltage for the V phase is set to a low level. Furthermore, a pair of switching elements 25 and 26 of the W phase are electrically connected, and when switching element 25 is in the on state and switching element 26 is in the off state, the driving voltage of the W phase is set to a high level, and when switching element 25 is in the off state and switching element 26 is in the on state, the driving voltage of the W phase is set to a low level.

[0015] The switching element 21 has a control terminal electrically connected to the microcomputer 30, one input terminal electrically connected to the high-potential side of the battery 61, and the other input terminal electrically connected to the connection terminal 44 of the switching element 22 and the motor 40. The switching element 21 is turned on / off in accordance with a predetermined control signal applied to the control terminal from the microcomputer 30, and when it is in the on state, a current flows from one input terminal to the other input terminal. The switching element 21 also includes a parasitic diode 21d.

[0016] The switching element 22 has a control terminal electrically connected to the microcomputer 30, one input terminal electrically connected to the connection terminal 44 of the switching element 21 and the motor 40, and the other input terminal electrically connected to the low potential side of the battery 62. The switching element 22 is turned on / off in accordance with a predetermined control signal applied to the control terminal from the microcomputer 30, and when it is in the on state, a current flows from one input terminal to the other input terminal. The switching element 22 also includes a parasitic diode 22d.

[0017] The switching element 23 has a control terminal electrically connected to the microcomputer 30, one input terminal electrically connected to the high-potential side of the battery 61, and the other input terminal electrically connected to the connection terminal 45 of the switching element 24 and the motor 40. The switching element 23 is turned on / off in accordance with a predetermined control signal applied to the control terminal from the microcomputer 30, and when it is in the on state, a current flows from one input terminal to the other input terminal. The switching element 23 also includes a parasitic diode 23d.

[0018] The switching element 24 has a control terminal electrically connected to the microcomputer 30, one input terminal electrically connected to the connection terminal 45 of the switching element 23 and the motor 40, and the other input terminal electrically connected to the low potential side of the battery 62. The switching element 24 is turned on / off in accordance with a predetermined control signal applied to the control terminal from the microcomputer 30, and when it is in the on state, a current flows from one input terminal to the other input terminal. The switching element 24 also includes a parasitic diode 24d.

[0019] The switching element 25 has a control terminal electrically connected to the microcomputer 30, one input terminal electrically connected to the high-potential side of the battery 61, and the other input terminal electrically connected to the connection terminal 46 of the switching element 26 and the motor 40. The switching element 25 is turned on / off in accordance with a predetermined control signal applied to the control terminal from the microcomputer 30, and when it is in the on state, a current flows from one input terminal to the other input terminal. The switching element 25 also includes a parasitic diode 25d.

[0020] The switching element 26 has a control terminal electrically connected to the microcomputer 30, one input terminal electrically connected to the connection terminal 46 of the switching element 25 and the motor 40, and the other input terminal electrically connected to the low potential side of the battery 62. The switching element 26 is turned on / off in accordance with a predetermined control signal applied to the control terminal from the microcomputer 30, and when it is in the on state, a current flows from one input terminal to the other input terminal. The switching element 26 also includes a parasitic diode 26d.

[0021] The microcomputer 30 includes a CPU (Central Processing Unit) and a memory (not shown), and the memory stores necessary control and processing programs and control and processing data. The microcomputer 30 includes, as functional blocks of the CPU, a current detector 31, a phase detector 32, a voltage detector 33, a rotation speed detector 34, and a controller 35. The microcomputer 30 performs switching control to switch the on and off states of each of the switching elements 21 to 26 based on a detection signal from a phase sensor 50 that carries information on the rotation angle (rotational position) of a rotor (not shown), which is provided with a U-phase coil 41, a V-phase coil 42, and a W-phase coil 43 in the motor 40. Programs that cause the current detector 31, the phase detector 32, the voltage detector 33, and the controller 35 to function as functional blocks are pre-stored in a memory (not shown).

[0022] The current detection unit 31 detects the current flowing through the coils 41 to 43 of the motor 40. Specifically, the current detection unit 31 detects the current flowing through the coil 41 from the current flowing between the coil 41 and the other terminal of the switching element 21 and one terminal of the switching element 22, detects the current flowing through the coil 42 from the current flowing between the coil 42 and the other terminal of the switching element 23 and one terminal of the switching element 24, and detects the current flowing through the coil 43 from the current flowing between the coil 43 and the other terminal of the switching element 25 and one terminal of the switching element 26.

[0023] Based on the electrical signal output from the phase sensor 50, the phase detection unit 32 detects the phase angle of the rotor relative to the stator of the motor 40, which is provided with a group of magnets (all of which are omitted from the drawing), i.e., the phase angle of the motor 40.

[0024] The voltage detection unit 33 detects the voltage between the high potential side and the low potential side of the batteries 61 and 62 , that is, the voltage between both terminals of the capacitor 90 , based on the electrical signal output from the voltage sensor 80 .

[0025] The rotation speed detection unit 34 detects the amount of change in the phase angle of the motor 40 per unit time as the rotation speed of the motor 40 from the phase angle of the rotor of the motor 40 detected by the phase detection unit 32, i.e., the time-series change in the phase angle of the motor 40.

[0026] The control unit 35 determines a conduction pattern for the switching elements 21 to 26 in the next phase angle range of the motor 40 based on the phase angle of the motor 40 detected by the phase detection unit 32, in order to drive the motor 40, and applies high-level and low-level control signals to the control terminals of the switching elements 21 to 26 based on the determination result, thereby causing the switching elements 21 to operate on / off accordingly. Note that the control unit 35 can also determine a conduction pattern for the switching elements 21 to 26 so that a regenerative current flows to the battery 61 when the motor 40 is in a regenerative state to charge it, and apply high-level and low-level control signals to the control terminals of the switching elements 21 to 26 based on the determination result. Furthermore, when a regenerative current flows to the battery 61 when the motor 40 is in a regenerative state to charge it, if the switching elements 21 to 26 have parasitic diodes 21d to 26d, all of the switching elements 21 to 26 may be turned off in consideration of the current flowing through the parasitic diodes 21d to 26d.

[0027] In addition, when the contactor 70 is open and the motor 40 is rotating by inertia, and the control unit 35 turns off all of the switching elements 21 to 26 once, and then turns on all of the target arms of the switching elements 21 and 22, the target arms of the switching elements 23 and 24, and the target arms of the switching elements 25 and 26, when the current of the coil (winding) 41 reaches a first threshold value (a value of zero or a positive value that can be evaluated as substantially zero), the control unit 35 performs a first process of switching the target arms of the switching elements 21 and 22 to the off state. Following the execution of the first process, when the current in coil 42 reaches a second threshold value (zero or a positive value that can be evaluated as substantially zero), a second process is executed in which the target arms of switching elements 23 and 24 are switched to the OFF state and the target arms of switching elements 21 and 22 are switched to the ON state, and after the second process is executed, an all-phase OFF process is executed in which the target arms of switching elements 21 and 22, the target arms of switching elements 23 and 24, and the target arms of switching elements 25 and 26 are all switched to the OFF state. In this way, by appropriately executing each process leading up to the all-phase OFF process, it is possible to prevent the driver from feeling uncomfortable as if the brakes have been suddenly released due to a sudden decrease in the brake torque of the motor while the motor is rotating by inertia. In order to further reduce the discomfort felt by the driver, the control unit 35 may execute a third process, following the execution of the second process, in which the control unit 35 switches the target arm of the switching elements 25 and 26 to the OFF state and switches the target arm of the switching elements 23 and 24 to the ON state when the current in the coil 43 reaches a third threshold value (zero or a positive value that can be evaluated as substantially zero), and then execute the all-phase OFF process after executing the third process. Furthermore, the control unit 35 may execute the all-phase OFF process after repeating the first to third processes in order multiple times, thereby further reducing the discomfort felt by the driver. The target arm may be either the upper arm or the lower arm.

[0028] The motor 40 typically has three-phase coils, namely, a U-phase coil 41, a V-phase coil 42, and a W-phase coil 43, on the rotor side, and has a group of magnets arranged around these on the stator side, and is driven by receiving a supply of three-phase AC current from switching elements 21 to 26 that form a three-phase bridge drive circuit.

[0029] The U-phase coil 41 has a connection terminal 44 electrically connected to the other terminal of the U-phase switching element 21 and one terminal of the U-phase switching element 22. The V-phase coil 42 has a connection terminal 45 electrically connected to the other terminal of the V-phase switching element 23 and one terminal of the V-phase switching element 24. The W-phase coil 43 has a connection terminal 45 electrically connected to the other terminal of the W-phase switching element 25 and one terminal of the W-phase switching element 26.

[0030] An example of the motor control process executed by the motor control device 10 having the above configuration will be described in detail below with reference to FIGS. 2 to 9.

[0031] FIG. 2 is a schematic diagram showing an example of current flow when the motor 40 is in a driving state under the control of the motor control device 10. FIG. 3 is a schematic diagram showing an example of current flow when the motor 40 is in a regenerative state under the control of the motor control device 10. FIG. 4 is a flowchart showing an example of motor control processing executed by the motor control device 10 when the contactor 70 is open. FIG. 5 is a schematic diagram showing an example of current flow when all of the switching elements 21 to 26 are switched to the OFF state under the control of the motor control device 10 when the contactor 70 is open. FIG. 6 is a time chart showing an example of three-phase currents that change over time under the control of the motor control device 10 when the contactor 70 is open. FIG. 7 is a schematic diagram showing an example of current flow when the lower arm switching elements 22, 24, and 26 are switched to the ON state under the control of the motor control device 10 when the contactor 70 is open. Fig. 8 is a schematic diagram showing an example of current flow when one of the switching elements 22, 24, and 26 of the lower arm is switched to the OFF state under the control of the motor control device 10 while the contactor 70 is open. Fig. 9 is a schematic diagram showing an example of current flow when one of the switching elements 22, 24, and 26 of the lower arm is switched to the OFF state under the control of the motor control device 10 while the contactor 70 is open, and is a diagram that follows Fig. 8 in terms of time series.

[0032] 2, when the control unit 35 drives the motor 40, that is, when the control unit 35 determines the conduction pattern of the switching elements 21 to 26 for the next phase angle range of the motor 40 based on the phase angle of the motor 40 detected by the phase detection unit 32, and applies high-level and low-level control signals to the control terminals of the switching elements 21 to 26 based on the determination result, thereby turning on, for example, the switching elements 22, 23, and 25 and turning off the other switching elements 21, 24, and 26 to drive the motor 40, current flows as shown by the dotted arrows in the figure. Note that, for convenience of illustration, the dotted arrows indicating the flow of current in FIGS. 2, 3, and 6 to 9 are shown as dotted lines passing outside the switching elements 21 to 26 and the parasitic diodes 21d to 26d, regardless of whether they are flowing through the switching elements 21 to 26 themselves or through the parasitic diodes 21d to 26d.

[0033] Also, as shown in FIG. 3, when the motor 40 is in a regenerative state, the control unit 35 turns off all of the switching elements 21 to 26, and current flows through the parasitic diodes 21d to 26d (parasitic diodes 22d, 23d, and 25d in the figure) as indicated by the dotted arrows in the figure, charging the battery 61.

[0034] The motor control process shown in the flowchart of FIG. 4 typically begins when the contactor 70 is open, the motor 40 is rotating by inertia, and the control unit 35 temporarily turns off all of the switching elements 21 to 26. The motor control process then proceeds to step S1. As shown in FIG. 5, when the contactor 70 is open, the motor 40 is rotating by inertia, and the control unit 35 temporarily turns off all of the switching elements 21 to 26, current flows through the parasitic diodes 21d to 26d (parasitic diodes 22d, 23d, and 25d in the figure) as indicated by the dotted arrows in the figure, charging the capacitor 90. The voltage across the terminals of the capacitor 90 (corresponding to the voltage between P and N) is measured by the voltage sensor 80. This motor control process is repeatedly executed during operation of the motor control device 10 at the timing when all of the switching elements 21 to 26 are temporarily turned off.

[0035] In the process of step S1, the control unit 35 determines whether the voltage across the both terminals of the capacitor 90 detected by the voltage detection unit 33 is equal to or greater than a first predetermined voltage. The reason for this determination is to limit the voltage of the capacitor 90 as it is being charged so that it does not become excessively high. If the result of the determination is that the voltage across the both terminals of the capacitor 90 is equal to or greater than the first predetermined voltage (step S1: Yes), the control unit 35 proceeds with the motor control process to step S2. On the other hand, if the voltage across the both terminals of the capacitor 90 is less than the first predetermined voltage (step S1: No), the control unit 35 repeats the process of step S1. The first predetermined voltage may be set according to the specifications of the capacitor 90, such as its withstand voltage.

[0036] In the process of step S2, the control unit 35 turns on all of the target arms of switching elements 21 and 22, the target arms of switching elements 23 and 24, and the target arms of switching elements 25 and 26 (three-phase short state). In Fig. 6, the waveform diagram before time t1 corresponds to this three-phase short state, and in Fig. 7, with all of the switching elements 21, 23, and 25 of the upper arm maintained in the off state, all of the switching elements 22, 24, and 26 of the lower arm are switched on, and current is circulated without flowing to the capacitor 90. This completes the process of step S2, and the motor control process proceeds to the process of step S3.

[0037] In step S3, the control unit 35 determines whether the rotation speed of the motor 40 detected by the rotation speed detection unit 34 is less than a predetermined rotation speed. The reason for this determination is that one of the conditions for ending the three-phase short circuit state is that the rotation speed of the motor 40 has been appropriately reduced. If the determination results in the rotation speed of the motor 40 being less than the predetermined rotation speed (step S3: Yes), the control unit 35 proceeds with the motor control process to step S5. On the other hand, if the rotation speed of the motor 40 is equal to or greater than the predetermined rotation speed (step S3: No), the control unit 35 proceeds with the motor control process to step S4. The predetermined rotation speed may be set according to specifications such as the amount of charge that the motor 40 charges the capacitor 90.

[0038] In step S4, the control unit 35 determines whether the voltage across the capacitor 90 detected by the voltage detection unit 33 is less than a second predetermined voltage. The reason for this determination is to ensure that the voltage across the capacitor 90, once charged, is appropriately reduced. If the determination results in the voltage across the capacitor 90 being less than the second predetermined voltage (step S4: Yes), the control unit 35 advances the motor control process to step S5. On the other hand, if the voltage across the capacitor 90 is equal to or greater than the second predetermined voltage (step S4: No), the control unit 35 returns the motor control process to step S3. The second predetermined voltage may be set as a predetermined value less than the first predetermined voltage according to the specifications of the capacitor 90, such as its withstand voltage.

[0039] In step S5, the control unit 35 determines whether the current flowing through the U-phase coil 41 detected by the current detection unit 31 is decreasing and becoming equal to or less than the first threshold. This determination is made to ensure that the current flowing through the U-phase coil 41 is decreasing and substantially reaching zero. The "decreasing" condition is used because, if the current flowing through the U-phase coil 41 is increasing, the brake torque of the motor 40 may not be properly eliminated, and it is preferable to address this issue. In FIG. 6 , at time t1, the current IU flowing through the U-phase coil 41 is decreasing and substantially reaching zero. If the determination results in the current flowing through the U-phase coil 41 decreasing and becoming equal to or less than the first threshold (step S5: Yes), the control unit 35 proceeds with the motor control process to step S6. On the other hand, if the current flowing through the U-phase coil 41 is not decreasing and becoming equal to or less than the first threshold (step S5: No), the control unit 35 repeats step S5. The first threshold may be set to zero or a positive value that can be evaluated as substantially zero depending on the specifications of the motor control device 10.

[0040] In step S6, the control unit 35 maintains all of the upper-arm switching elements 21, 23, and 25 in the OFF state, maintains the lower-arm switching elements 24 and 26 in the ON state, and switches the lower-arm switching element 22 to the OFF state (first process). In FIG. 8 , all of the upper-arm switching elements 21, 23, and 25 are maintained in the OFF state, the lower-arm switching elements 24 and 26 are maintained in the ON state, and the lower-arm switching element 22 is switched to the OFF state. At this time, current flows through the parasitic diode 21d of the upper-arm switching element 21 to the capacitor 90, and the induced voltage of the coil 41 is applied to the capacitor 90. However, as shown in FIG. 9 , when the voltage of the capacitor 90 becomes equal to the induced voltage of the coil 41, current stops flowing to the capacitor 90, and only electricity flows back via the lower-arm switching elements 24 and 26. This completes step S6, and the motor control process proceeds to step S7.

[0041] In step S7, the control unit 35 determines whether the current flowing through the V-phase coil 42 detected by the current detection unit 31 is decreasing and reaching or below the second threshold. This determination is made to ensure that the current flowing through the V-phase coil 42 is decreasing and reaching essentially zero. The "decreasing" condition is used because, if the current flowing through the V-phase coil 42 is increasing, the brake torque of the motor 40 may not be properly eliminated, and it is preferable to address this issue. In FIG. 6 , at time t2, the current IV flowing through the V-phase coil 42 is decreasing and reaching essentially zero. If the determination results in the current flowing through the V-phase coil 42 decreasing and reaching or below the second threshold (step S7: Yes), the control unit 35 proceeds with the motor control process to step S8. On the other hand, if the current flowing through the V-phase coil 42 is decreasing but not reaching or below the second threshold (step S7: No), the control unit 35 repeats step S7. The second threshold value may be set to zero or a positive value that can be evaluated as essentially zero depending on the specifications of the motor control device 10, and although not limited to this, it is convenient to set it to the same value as the first threshold value.

[0042] In the process of step S8, the control unit 35 maintains all of the upper arm switching elements 21, 23, and 25 in the OFF state, maintains the lower arm switching element 26 in the ON state, switches the lower arm switching element 22 to the ON state, and switches the lower arm switching element 24 to the OFF state (second process). Here, the state of the current flowing through the capacitor 90 is the same as that described with reference to Figures 8 and 9, if the lower arm switching element that is turned OFF in the states of Figures 8 and 9 is replaced by switching element 24 instead of switching element 22. This completes the process of step S8, and the motor control process proceeds to step S9.

[0043] In step S9, the control unit 35 determines whether the current flowing through the W-phase coil 43 detected by the current detection unit 31 is decreasing and becoming equal to or less than the third threshold. This determination is made to ensure that the current flowing through the W-phase coil 43 is decreasing and substantially reaching zero. The "decreasing" condition is used because, if the current flowing through the W-phase coil 43 is increasing, the brake torque of the motor 40 may not be properly eliminated, and it is preferable to address this issue. In FIG. 6 , at time t3, the current IW flowing through the W-phase coil 43 is decreasing and substantially reaching zero. If the determination results in the current flowing through the W-phase coil 43 decreasing and becoming equal to or less than the third threshold (step S9: Yes), the control unit 35 proceeds with the motor control process to step S10. On the other hand, if the current flowing through the W-phase coil 43 is decreasing but not becoming equal to or less than the third threshold (step S9: No), the control unit 35 repeats step S9. The third threshold value may be set to zero or a positive value that can be evaluated as essentially zero depending on the specifications of the motor control device 10, and although not limited to this, it is convenient to set it to the same value as the first threshold value and the second threshold value.

[0044] In the process of step S10, the control unit 35 maintains all of the upper-arm switching elements 21, 23, and 25 in the OFF state, maintains the lower-arm switching element 22 in the ON state, switches the lower-arm switching element 24 to the ON state, and switches the lower-arm switching element 26 to the OFF state (third process). Here, the state of the current flowing through the capacitor 90 is the same as that described with reference to Figures 8 and 9, except that the lower-arm switching element that is turned OFF in the states of Figures 8 and 9 is replaced by switching element 26 instead of switching element 22. This completes the process of step S10, and the motor control process proceeds to step S11.

[0045] In the process of step S11, the control unit 35 increments the count value C by 1. This completes the process of step S11, and the motor control process proceeds to the process of step S12.

[0046] In step S12, the control unit 35 determines whether the count value C calculated in step S11 is equal to or greater than a reference value. If the count value C is equal to or greater than the reference value (step S12: Yes), the control unit 35 advances the motor control process to step S13. On the other hand, if the count value C is less than the reference value (step S12: No), the control unit 35 returns the motor control process to step S5. In FIG. 6, the first to third processes are repeated from time t4 to time t6. The reference value may be set to an integer value equal to or greater than 2.

[0047] In the process of step S13, the control unit 35 maintains all of the upper arm switching elements 21, 23, and 25 in the OFF state, and turns all of the lower arm switching elements 22, 24, and 26 in the OFF state (all-phase OFF process). This completes the current series of motor control processes. Note that the processes of steps S9 to S12 may be omitted if necessary.

[0048] In the first aspect of the motor control device 10 of the present embodiment described above, when the motor 40 is rotating by inertia and the target arms of the first-phase switching elements 21 and 22, the target arms of the second-phase switching elements 23 and 24, and the target arms of the third-phase switching elements 25 and 26 are all in the ON state, the control unit 35 executes a first process to switch the target arms of the first-phase switching elements 21 and 22 to the OFF state when the current in the first-phase winding 41 reaches a first threshold value, and subsequently executes a first process to switch the target arms of the second-phase switching elements 21 and 22 to the OFF state when the current in the second-phase winding 42 reaches a second threshold value. A second process is executed to switch the target arms of 23 and 24 to the OFF state and the target arms of first-phase switching elements 21 and 22 to the ON state, and after executing the second process, an all-phase OFF process is executed to switch all of the target arms of first-phase switching elements 21 and 22, the target arms of second-phase switching elements 23 and 24, and the target arms of third-phase switching elements 25 and 26 to the OFF state.By appropriately executing the all-phase OFF process, it is possible to prevent the driver from feeling uncomfortable as if the brakes have been suddenly released due to a sudden decrease in the brake torque of the motor while the motor is rotating by inertia.

[0049] Furthermore, in the second phase of the motor control device 10 of this embodiment, in addition to the first phase, the control unit 35 executes a third process in which, following the execution of the second process, when the current in the third-phase winding 43 reaches a third threshold, the control unit 35 switches the target arms of the third-phase switching elements 25 and 26 to the OFF state and switches the target arms of the second-phase switching elements 23 and 24 to the ON state, and after executing the third process, executes an all-phase OFF process, thereby reliably preventing the driver from feeling uncomfortable as if the brakes have been suddenly released.

[0050] Furthermore, in the third aspect of the motor control device 10 of this embodiment, in addition to the second aspect, the control unit 35 repeats the first process, the second process, and the third process in sequence multiple times, and then executes the all-phase-off process, thereby more reliably preventing the driver from feeling uncomfortable as if the brakes have been suddenly released.

[0051] The present invention is not limited to the above-described embodiments in terms of the type, shape, arrangement, number, etc. of the components, and it goes without saying that the components can be appropriately modified within the scope of the gist of the invention, such as by appropriately replacing them with components that have equivalent effects.

[0052] As described above, the present invention provides a motor control device that can prevent the driver from feeling as if the brake has been suddenly released due to a sudden decrease in the brake torque of the motor while the motor is inertial rotating, and because of its general-purpose, universal nature, it is expected to be widely applicable to motor control devices for vehicles.

[0053] DESCRIPTION OF SYMBOLS 10... Motor control device 21 to 26... Switching elements 21d to 26d... Parasitic diodes 30... Microcomputer 31... Current detection unit 32... Phase detection unit 32... Command unit 33... Voltage detection unit 34... Rotation speed detection unit 35... Control unit 40... Motor 41 to 43... Coils (windings) 44 to 46... Connection terminals 50... Phase sensor 61, 62... Battery 70... Contactor 80... Voltage sensor 90... Capacitor

Claims

1. A motor control device having a control unit that controls the energization states of a first-phase winding, a second-phase winding, and a third-phase winding of a motor that is a three-phase AC motor and is a drive source mounted on a vehicle, by controlling the switching of a first-phase switching element that connects a DC battery mounted on the vehicle to the first winding, a second-phase switching element that connects the DC battery to the second winding, and a switching element that connects the DC battery to the third winding, wherein the control unit: when the motor is rotating by inertia and a target arm of the first-phase switching element, a target arm of the second-phase switching element, and a target arm of the third-phase switching element are all in an on state, executes a first process to switch the target arm of the first-phase switching element to an off state when the current in the first-phase winding reaches a first threshold; and, following the execution of the first process, executes a second process to switch the target arm of the second-phase switching element to an off state and switch the target arm of the first-phase switching element to an on state when the current in the second-phase winding reaches a second threshold; a motor control device that, after executing the second process, executes an all-phase-off process to turn off all of the target arms of the first-phase switching element, the second-phase switching element, and the third-phase switching element.

2. The motor control device described in claim 1, characterized in that, following execution of the second process, the control unit executes a third process in which, when the current in the third-phase winding reaches a third threshold, the target arm of the third-phase switching element is switched to an OFF state and the target arm of the second-phase switching element is switched to an ON state, and after executing the third process, the control unit executes the all-phase OFF process.

3. The motor control device described in claim 2, characterized in that the control unit repeats the first process, the second process, and the third process in sequence multiple times, and then executes the all-phase-off process.

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