Motor control device

Abstract

To provide a motor control device capable of suppressing a sense of incongruity caused by a sudden decrease in brake torque of a motor during inertial rotation of the motor.SOLUTION: In the motor control device, the control unit executes a first process of switching a target arm of the first phase switching element to an OFF state when a current of the first phase winding reaches a first threshold while the motor is rotating by inertia and all the target arms of the first to third phase switching elements are in an ON state. Subsequently to the execution of the first process, the controller executes a second process of switching the target arm of the second phase switching element to an off state and switching the target arm of the first phase switching element to an on state when the current of the second phase winding reaches a second threshold, and executes an all-phase off process of turning 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 after the execution of the second process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[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 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6256597 Summary of the Invention [Problem to be solved by the invention]

[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 configuration controls the switching element of a target arm, which is an arm of one phase, to be turned off, and then the switching elements of target arms of the other two phases to be turned off, the brake torque of the motor decreases relatively suddenly. As a result, it is thought that a driver of a moving vehicle when the motor is rotating by inertia tends 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. [Means for solving the problem]

[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 and when 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 an on state. In one aspect, when the inverter is in a non-repeatable state, when a 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 a 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a motor control device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a current flow when the motor is in a driving state under the control of the motor control device in this embodiment. [Figure 3] FIG. 3 is a schematic diagram showing an example of a current flow when the motor is in a regenerative state under the control of the motor control device in this embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of a motor control process executed by the motor control device in the state where the contactor is opened in this embodiment. [Figure 5] FIG. 5 is a schematic diagram showing an example of current flow when all of the switching elements are switched to the OFF state under the control of the motor control device while the contactors are open in this embodiment. [Figure 6]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 in this embodiment. [Figure 7] FIG. 7 is a schematic diagram showing an example of a current flow when the switching element of the lower arm is switched to the on state under the control of the motor control device while the contactor is open in this embodiment. [Figure 8] 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. [Figure 9] FIG. 9 is a schematic diagram showing an example of current flow when one of the switching elements of the lower arm is switched to the off state by the control of the motor control device while the contactor is open in this embodiment, and is a chronological continuation of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[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, motor control device 10 in this embodiment is an ECU (Electronic Control Unit) that is an electronic control device, and includes switching elements 21 to 26 that form a three-phase bridge drive circuit, and a microcomputer (microcomputer) 30. The figure also shows motor 40, which is a three-phase AC motor, phase sensor 50, which is typically a magnetic sensor, provided for motor 40, batteries 61 and 62, which are DC secondary batteries that supply power to motor 40, contactor 70, which is typically a relay that interrupts the electrical connection between batteries 61 and 62, voltage sensor 80 provided in parallel with batteries 61 and 62 to electrically connect the high-potential side and low-potential side of batteries 61 and 62, and capacitor 90 provided in parallel with batteries 61 and 62 and voltage sensor 80 to electrically connect the high-potential side and low-potential side of batteries 61 and 62. Of these, voltage sensor 80 and capacitor 90 are shown as components of 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 drawing, 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 for 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 for 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 for 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 performs on / off operation 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 performs on / off operation 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 performs on / off operation 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 performs on / off operation 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 performs on / off operation 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 memory (not shown), and the memory stores necessary control and processing programs and control and processing data. The microcomputer 30 includes, as CPU functional blocks, a current detector 31, a phase detector 32, a voltage detector 33, a rotation speed detector 34, and a controller 35. The microcomputer 30 controls the switching of the switching elements 21 to 26 between their on and off states 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 includes 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 detector 32 detects the phase angle of the rotor relative to the stator of the motor 40, which is provided with a group of magnets (not shown), i.e., the phase angle of the motor 40.

[0024] Based on the electrical signal output from the voltage sensor 80 , 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 .

[0025] The rotation speed detection unit 34 detects the amount of change in the phase angle of the motor 40 per unit time 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, as the rotation speed 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 correspondingly operating the switching elements 21 to 26 on / off. 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 execution of the second process, 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] Motor 40 typically has three-phase coils, namely U-phase coil 41, V-phase coil 42, and W-phase coil 43, on the rotor side, and 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] U-phase coil 41 has a connection terminal 44 electrically connected to the other terminal of U-phase switching element 21 and one terminal of U-phase switching element 22. V-phase coil 42 has a connection terminal 45 electrically connected to the other terminal of V-phase switching element 23 and one terminal of V-phase switching element 24. W-phase coil 43 has a connection terminal 45 electrically connected to the other terminal of W-phase switching element 25 and one terminal of W-phase switching element 26.

[0030] An example of the motor control process executed by 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 switching elements 22, 24, and 26 of the lower arm 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 the switching elements 22, 23, and 25 and turning off the other switching elements 21, 24, and 26, and driving the motor 40, current flows as shown by the dotted arrows in the figure. For convenience of illustration, the dotted arrows indicating the flow of current in the switching elements 21 to 26 themselves and the parasitic diodes 21d to 26d are similarly shown as dotted lines passing outside the switching elements 21 to 26 and 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 starts when contactor 70 is open, motor 40 is rotating by inertia, and control unit 35 temporarily turns off all of switching elements 21 to 26. The motor control process then proceeds to step S1. As shown in FIG. 5, when contactor 70 is open, motor 40 is rotating by inertia, and control unit 35 temporarily turns off all of switching elements 21 to 26, current flows through parasitic diodes 21d to 26d (parasitic diodes 22d, 23d, and 25d in the figure), as indicated by the dotted arrows in the figure, and charges capacitor 90. At this time, the voltage across both terminals of capacitor 90 (corresponding to the voltage across P and N) is measured by voltage sensor 80. This motor control process is repeatedly executed during operation of motor control device 10, whenever all of 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 advances the motor control process to the process of 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, while all of switching elements 21, 23, and 25 of the upper arm are maintained in the off state, all of switching elements 22, 24, and 26 of the lower arm are switched on, and current is circulated without flowing to capacitor 90. This completes the process of step S2, and the motor control process proceeds to the process of step S3.

[0037] In the process of 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 state is that the rotation speed of the motor 40 has been appropriately reduced. If the result of the determination is that the rotation speed of the motor 40 is less than the predetermined rotation speed (step S3: Yes), the control unit 35 proceeds to the process of step S5 in the motor control process. 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 to the process of step S4 in the motor control process. 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 the process of step S4, the control unit 35 determines whether the voltage across the both terminals of the capacitor 90 detected by the voltage detection unit 33 is less than a second predetermined voltage. The reason for making this determination is to ensure that the voltage of the capacitor 90, which has been charged once, has been appropriately reduced. If the result of the determination is that the voltage across the both terminals of the capacitor 90 is less than the second predetermined voltage (step S4: Yes), the control unit 35 proceeds with the motor control process to the process of step S5. On the other hand, if the voltage across the both terminals of 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 the process of 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 the 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 condition "decreasing" 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 result indicates that the current flowing through the U-phase coil 41 is decreasing and becoming equal to or less than the first threshold (step S5: Yes), the control unit 35 proceeds to step S6 of the motor control process. 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 the process of step S6, the control unit 35 switches the lower-arm switching element 22 to the off state while maintaining all of the upper-arm switching elements 21, 23, and 25 in the off state and the lower-arm switching elements 24 and 26 in the on state (first process). In FIG. 8, all of the upper-arm switching elements 21, 23, and 25 are maintained in the off state, and the lower-arm switching elements 24 and 26 are maintained in the on state, with the lower-arm switching element 22 switched to the off state. At this time, current flows to the capacitor 90 through the parasitic diode 21d of the upper-arm switching element 21, 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 current flows back via the lower-arm switching elements 24 and 26. This completes the process of 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 becoming equal to or less than the second threshold. This determination is made to ensure that the current flowing through the V-phase coil 42 is decreasing and substantially reaching 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 substantially reaching zero. If the determination results in the current flowing through the V-phase coil 42 decreasing and becoming equal to or less than the second threshold (step S7: Yes), the control unit 35 advances 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 becoming equal to or less than 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 substantially zero depending on the specifications of the motor control device 10, and although not limited thereto, 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 the process of 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 substantially 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, if 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 the process of 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 the process of step S12, the control unit 35 determines whether the count value C calculated in the process of step S11 is equal to or greater than a reference value. If the result of the determination is that 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 the process of 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 the process of 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 as 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 the 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 to switch 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 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. [Industrial Applicability]

[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. [Explanation of symbols]

[0053] 10...Motor control device 21 to 26...Switching elements 21d to 26d: Parasitic diodes 30...microcomputer 31...Current detection section 32...Phase detection unit 32…Command department 33...Voltage detection unit 34...Rotation speed detection unit 35...Control unit 40...Motor 41 to 43... Coil (winding) 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 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 switching of a first-phase switching element that connects a DC battery mounted on the vehicle and the first winding, a second-phase switching element that connects the DC battery and the second winding, and a switching element that connects the DC battery and the third winding, The control unit When the motor is rotating by inertia and 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 an ON state, a first process for switching 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; 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 in which the target arm of the second phase switching element is switched to an OFF state and the target arm of the first phase switching element is switched to an ON state; a motor control device characterized in that, after executing the second process, an all-phase OFF process is executed 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 control unit subsequent to the execution of the second process, when the current in the third phase winding reaches a third threshold, a third process is executed in which 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; 2. The motor control device according to claim 1, wherein the all-phase-off process is executed after the third process is executed.

3. 3. The motor control device according to claim 2, wherein the control unit executes the all-phase-off process after sequentially repeating the first process, the second process, and the third process a plurality of times.

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