Motor control device

Abstract

[Problem] To safely turn off a brushless motor. [Solution] This motor control device has: (A) a drive unit including three or more sets of half bridges for driving a brushless motor which has two or more phases; (B) a separation switch disposed between the drive unit and a power supply and interrupting at least the current flowing in the regeneration direction by opening thereof; and (C) a control unit performing control so as to execute, when detecting an event indicating that the brushless motor should be turned off, a first step for setting the drive outputs of the half bridges of at least some sets of the three or more sets of half bridges to a ground level or turning off the drive outputs, a second step for opening the separation switch, and a third step for turning off the drive outputs of a set of half bridges, the drive outputs of which are not turned off among the three or more sets of half bridges, during a period in which power flowing to coils included in the brushless motor is positive or zero.

Description

Motor Control Device

[0001] The present invention relates to a motor control technique for safely turning off a brushless motor.

[0002] First, the main terms used in this application will be explained.

[0003] In this application, the on / off state of a brushless motor does not refer to the presence or absence of torque or rotation. The state in which the amplifier output driving the brushless motor (hereinafter sometimes abbreviated as "motor") drives the motor with low impedance is called "motor on," and the state in which the amplifier output driving the motor has high impedance and the drive line is effectively open is called "motor off." Note that "motor on" refers to the state on the motor side, but if the same state is expressed as the state of the amplifier driving the motor, it becomes "drive output on." Similarly, the state of "motor off" refers to the state of the amplifier driving the motor, it becomes "drive output off."

[0004] Motor on includes 1) powering: a state in which the direction of rotation and torque are the same, 2) coasting: a state in which torque is close to zero regardless of the direction of rotation, 3) regenerative braking: a state in which the direction of rotation and torque are opposite and power is returned to the power supply, and 4) loss braking: a state in which the direction of rotation and torque are opposite and power is not returned to the power supply.On the other hand, motor off operates similarly to coasting, but with the amplifier output in a high impedance state, the current consumption and torque generated by the motor are completely zero.

[0005] In this application, "normal speed" refers to a speed at which the peak voltage of the motor's back electromotive force is equal to or less than the power supply voltage, and "overspeed" refers to a speed at which the peak voltage of the back electromotive force exceeds the power supply voltage. In this application, "normal drive" refers to drive when the drive peak voltage command is within the power supply voltage, and "overmodulation drive" refers to drive when the drive peak voltage command exceeds the power supply voltage. Note that even if the drive peak voltage command exceeds the power supply voltage, the actual drive voltage is clipped at the power supply voltage.

[0006] In both normal driving and overmodulation driving, there are various driving states such as power running, coasting, regenerative braking, and loss braking, as well as a motor-off state.

[0007] Coasting may be performed when momentary coasting is required during powering or regeneration, but if cruising at zero torque continues even for a short period of time, transitioning to a motor-off state is advantageous for the following reasons: 1) Since no current flows through the motor coil, the generated torque can be reduced to zero, 2) power loss occurs when powering and regeneration are repeated momentarily because the back electromotive force waveform and the drive waveform do not match perfectly (i.e., match in voltage, phase, and waveform distortion), but this power loss can be prevented, and 3) drive waveform generation can be stopped while the motor is off, so power consumption is also stopped.

[0008] In particular, motor-off may be desirable when the vehicle exceeds the normal speed limit. Specifically, even at overspeed, the driving torque is limited to a small value up to a speed slightly higher than the upper limit of the normal speed limit, but powering is possible through overmodulation. Furthermore, the braking torque is limited to a large value up to a speed slightly higher than the upper limit of the normal speed limit, but regenerative braking is possible through normal driving. However, there are cases where the speed reaches a range that even overmodulation cannot handle. For example, the maximum powering speed of an electrically assisted bicycle is limited by law or for safety reasons. However, on steep downhill slopes, the vehicle may reach a speed far exceeding the speed limit, either naturally or through manual driving alone, even without the assist torque of the motor. In such cases, powering is not possible, and regenerative braking is inappropriate due to overcurrent, excessive torque, overcharging, and other factors. Therefore, motor-off is preferable.

[0009] However, as mentioned above, at excessive speeds the peak voltage of the back electromotive force exceeds the power supply voltage, and if the motor is turned off in this state, current will flow into the power supply through the parasitic diodes of the half-bridge switching elements that drive the motor coils (even if the device does not have a parasitic diode, the same applies if it is a protective reflux diode that is intentionally added to prevent surge voltages during switching), so the peak voltage of the back electromotive force will be clipped by the power supply voltage - or more accurately, the power supply voltage plus the forward voltage of the parasitic diode. This naturally causes regenerative current to flow, which in turn applies unintended regenerative braking, preventing coasting and unintended charging of the power supply.

[0010] If an attempt is made to separate the power supply to cut off this regenerative current, a high surge voltage will be generated the moment the power supply is separated, which could destroy the separation switch, the half-bridge switching elements, and other devices.

[0011] For example, Patent Document 1 discusses the above-mentioned problems, but only shows a means of shorting the midpoint of a Y-connected three-phase motor to a reference potential or ground, and does not realize motor off. Furthermore, compared to general motor drive systems, it assumes additional elements and special structures (for example, elements and circuits for shorting, terminals connected to the motor midpoint, etc.), which leads to system complexity and increased costs.

[0012] Furthermore, for example, Patent Document 2 discloses a configuration for motor control using an H-bridge configuration in which motor terminals are shorted to prevent the back electromotive force from exceeding the power supply voltage. However, this causes the motor to be braked, which results in braking regardless of the driver's intention.

[0013] Furthermore, for example, Patent Documents 3 and 4 disclose overmodulation driving and related control, but do not consider the above-mentioned problems, nor disclose a solution thereto.

[0014] Japanese Patent Application Laid-Open No. 10-323079 Japanese Patent Application Laid-Open No. 2006-262628 Japanese Patent Application Laid-Open No. 2006-320039 Japanese Patent Application Laid-Open No. 2021-106473

[0015] SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a new motor control technique for safely turning off a brushless motor.

[0016] The motor control device of the present invention includes: (A) a drive unit including three or more sets of half bridges for driving a brushless motor with two or more phases; (B) a separation switch for cutting off current flowing at least in the regenerative direction between the drive unit and a power source by opening it; and (C) a control unit that controls the device to execute the following steps when an event that requires the brushless motor to be turned off is detected: a first step of setting the drive output of at least some of the three or more sets of half bridges to ground level or turning them off; a second step of opening the separation switch; and a third step of turning off the drive output of the half bridges of the three or more sets of half bridges whose drive output is not turned off during a period when the power flowing to the coils included in the brushless motor is positive or zero.

[0017] FIG. 1 is a diagram showing the appearance of an electrically assisted bicycle, which is an example of an electrically assisted vehicle. FIG. 2A is a functional block diagram of a motor control device. FIG. 2B is a diagram showing an example of the configuration of a half-bridge group. FIG. 3A is a diagram showing an example of control of powering at normal speed. FIG. 3B is a diagram showing an example of control of coasting at normal speed. FIG. 3C is a diagram showing an example of control of regenerative braking at normal speed. FIG. 3D is a diagram showing an example of control of overmodulation powering (strong powering) at normal speed. FIG. 3E is a diagram showing an example of control of overmodulation powering (weak powering) at excessive speed. FIG. 3F is a diagram showing an example of control of overmodulation coasting at excessive speed. FIG. 3G is a diagram showing an example of control of overmodulation regeneration (weak regeneration) at excessive speed. FIG. 3H is a diagram showing an example of control of normal regeneration (strong regeneration) at excessive speed. FIG. 4A is a diagram showing an example of control of turning off the drive output at normal speed. FIG. 4B is a diagram showing an example of control of turning off the drive output at excessive speed. FIG. 5 is a diagram showing problems that occur when the drive output is turned off at excessive speed. FIG. 6 illustrates a problem that occurs when the separation switch is opened at an excessive speed. FIG. 7 illustrates a control sequence performed in an embodiment of the present invention. FIG. 8 illustrates an example of control performed in the first embodiment. FIG. 9 illustrates an example of a functional configuration according to the first embodiment. FIG. 10 illustrates an example of a configuration of a drive control unit in the first embodiment. FIG. 11 illustrates an example of a configuration of a drive control unit in Modification 1 of the first embodiment. FIG. 12 illustrates an example of control performed in Modification 1 of the first embodiment. FIG. 13 illustrates an example of control performed in the second embodiment. FIG. 14 illustrates an example of control performed in the third embodiment. FIG. 15 illustrates motor variations, with (a) illustrating an example of a star-type coil connection, (b) illustrating an example of a switching-up configuration, and (c) illustrating an example of a delta-type coil connection. FIGS. 16(a) and 16(b) illustrate variations of a seven-phase motor. FIG. 17 illustrates an example of a two-phase motor configuration and drive waveforms. FIG. 18 illustrates an example of a two-phase motor configuration and drive waveforms. FIG. 19 is a diagram for explaining negative ground and positive ground.

[0018] [First Embodiment] [Configuration Example of First Embodiment] Fig. 1 is an external view showing an example of an electrically assisted bicycle, which is an example of an electrically assisted vehicle according to this embodiment. This electrically assisted bicycle 1 is equipped with a motor drive device. The motor drive device has a battery pack 101, a motor control device 102, a torque sensor 103, a crank rotation sensor 104, a motor 105, a display 106, and a brake sensor 107.

[0019] The electrically assisted bicycle 1 also has a front wheel, a rear wheel, a headlight, a freewheel, a transmission, and the like.

[0020] The battery pack 101 is, for example, a lithium ion secondary battery, but may be other types of batteries, such as a lithium ion polymer secondary battery, a nickel-metal hydride battery, etc. The battery pack 101 supplies power to the motor 105 via the motor control device 102, and is also charged by the regenerated power from the motor 105 via the motor control device 102 during regeneration.

[0021] The torque sensor 103 is provided near the crankshaft, detects the pedal force (i.e., input torque) applied by the user, and outputs the detection result to the motor control device 102. Similarly to the torque sensor 103, the crank rotation sensor 104 is provided near the crankshaft, and outputs a signal corresponding to the rotation of the crank to the motor control device 102.

[0022] The motor 105 is, for example, a well-known three-phase DC brushless motor, and is attached to, for example, the front wheel of the electrically assisted bicycle 1. The motor 105 rotates the front wheel, and the rotor is connected to the front wheel so that the rotor rotates in response to the rotation of the front wheel. Furthermore, the motor 105 is equipped with a rotation sensor such as a Hall element, and outputs rotor rotation information (for example, a Hall signal) to the motor control device 102.

[0023] The motor control device 102 performs predetermined calculations based on signals from the rotation sensor of the motor 105 , the torque sensor 103 , the crank rotation sensor 104 , etc., to control the driving of the motor 105 and also controls regeneration by the motor 105 .

[0024] The brake sensor 107 detects a brake operation by the user and outputs a brake signal related to the brake operation (for example, a signal indicating whether or not a brake operation is being performed) to the motor control device 102. Specifically, the brake sensor 107 is a sensor using a magnet and a reed switch.

[0025] The display 106 is also called an operation panel, and typically has a button for turning the light on and off, a button for turning the power on and off, an LCD display, and an LED (Light Emitting Diode) for displaying the assist mode status.

[0026] 2A and 2B show the configuration related to the motor control device 102 according to this embodiment. The motor control device 102 includes a half-bridge group 1030, a control unit 1020, and a separation switch 1040 for separating the battery included in the battery pack 101 from the half-bridge group 1030.

[0027] 2B , the half-bridge group 1030 includes, for example, three half-bridges. Specifically, a high-side switch Suh and a low-side switch Sul are included for the U phase, a high-side switch Svh and a low-side switch Svl are included for the V phase, and a high-side switch Swh and a low-side switch Swl are included for the W phase. Here, each switch is an N-channel field effect transistor (FET), and parasitic diodes Duh, Dul, Dvh, Dvl, Dwh, and Dwl are added to each FET.

[0028] 2A etc., the control unit 1020 outputs a gate signal Guh to the high-side switch Suh, a gate signal Gul to the low-side switch Sul, a gate signal Gvh to the high-side switch Svh, a gate signal Gvl to the low-side switch Svl, a gate signal Gwh to the high-side switch Swh, and a gate signal Gwl to the low-side switch Swl, thereby opening or closing each switch. A voltage Eu at the connection point between the high-side switch Suh and the low-side switch Sul is output to the motor 105 as a U-phase drive output, a voltage Ev at the connection point between the high-side switch Svh and the low-side switch Svl is output to the motor 105 as a V-phase drive output, and a voltage Ew at the connection point between the high-side switch Swh and the low-side switch Swl is output to the motor 105 as a W-phase drive output.

[0029] Returning to the explanation of Fig. 2A, the separation switch 1040 is, for example, an N-ch FET, and has a parasitic diode 1041 added thereto. When opened, this separation switch 1040 is a switch for cutting off the regenerative current flowing from at least the half-bridge group 1030 to the battery of the battery pack 101. Note that a switch that can also cut off the current from the battery of the battery pack 101 to the half-bridge group 1030 may also be used.

[0030] The voltage of the separation switch 1040 on the half-bridge group 1030 side is represented as Eb, and the output voltage of the battery in the battery pack 101 is represented as Ep. The current is flowing through the separation switch 1040 satisfies the equations ib1 = ib2 = ib3, so either may be measured, but it is sufficient to measure the current that is easiest to measure. For example, it is sufficient to measure ib3. In the following explanation, the direction of current is flowing toward the half-bridge group 1030 is considered positive, and the direction of current flowing toward the battery is considered negative.

[0031] Furthermore, the control unit 1020 has a drive control unit 1021, a crank rotation input unit 1022, a motor rotation input unit 1023, a drive waveform data generation unit 1024, a PWM (Pulse Width Modulation) modulation unit 1025 (specifically, 1025u, 1025v, and 1025w), a level shifter 1026 (specifically, 1026u, 1026v, and 1026w), a torque input unit 1027, a brake input unit 1028, and an AD (Analog-Digital) input unit 1029.

[0032] The drive control unit 1021 performs a predetermined calculation using input from the display 106 (e.g., power on / off, etc.), input from the crank rotation input unit 1022, input from the motor rotation input unit 1023, input from the torque input unit 1027, input from the brake input unit 1028, and input from the AD input unit 1029, and outputs the result to the drive waveform data generation unit 1024. The drive control unit 1021 also has a memory 10211, which stores various data used in the calculations and data in the middle of processing. Furthermore, the drive control unit 1021 may be realized by a processor executing a program, in which case the program may be recorded in the memory 10211. The memory 10211 may also be provided separately from the drive control unit 1021.

[0033] The crank rotation input unit 1022 digitizes the crank rotation phase angle (which may include a signal indicating the rotation direction) from the crank rotation sensor 104 and outputs it to the drive control unit 1021. The motor rotation input unit 1023 digitizes a signal (e.g., rotation phase angle, rotation speed, rotation direction, etc.) related to the rotation of the motor 105 (rotation of the front wheel in this embodiment) from the Hall signal output by the motor 105 and outputs it to the drive control unit 1021. The torque input unit 1027 digitizes a signal corresponding to the pedal force from the torque sensor 103 and outputs it to the drive control unit 1021. The brake input unit 1028 digitizes a signal indicating whether or not the brake is being applied from the brake sensor 107 and outputs it to the drive control unit 1021. The AD input unit 1029 digitizes the output voltage from the battery of the battery pack 101 and outputs it to the drive control unit 1021.

[0034] The drive control unit 1021 determines, for example, the envelope voltage of the sinusoidal wave drive voltage according to the various inputs described above and the current speed obtained from rotation information of the motor 105, and also determines the duty ratio and lead angle for PWM modulation, and outputs them to the drive waveform data generation unit 1024. The drive waveform data generation unit 1024 generates reference drive waveform data for each of the UVW phases according to the current phase of the motor 105, and further generates drive voltage waveform data Du, Dv, and Dw by multiplying the reference drive waveform and the envelope voltage, and outputs them to the corresponding PWM modulation units 1025u, 1025v, and 1025w, respectively. The drive control unit 1021 will be described in detail later, but it also controls the opening and closing of the separation switch 1040 at appropriate timing.

[0035] The PWM modulation unit 1025u generates high-frequency switching pulse trains Puh and Pul having a duty ratio corresponding to the drive voltage waveform data Du and outputs them to the level shifter 1026u. The PWM modulation unit 1025v generates high-frequency switching pulse trains Pvh and Pvl having a duty ratio corresponding to the drive voltage waveform data Dv and outputs them to the level shifter 1026v. The PWM modulation unit 1025w generates switching pulse trains Pwh and Pwl having a duty ratio corresponding to the drive voltage waveform data Dw and outputs them to the level shifter 1026w.

[0036] The level shifter 1026u converts, for example, switching pulse trains Puh and Pul, which are at low-voltage logic levels, into gate signals Guh and Gul having appropriate amplitudes based on the source potentials of the high-side switch Suh and the low-side switch Sul in the U-phase half bridge. The level shifter 1026v similarly converts switching pulse trains Pvh and Pvl into gate signals Gvh and Gvl having appropriate amplitudes based on the source potentials of the high-side switch Svh and the low-side switch Svl in the V-phase half bridge. Similarly, the level shifter 1026w converts switching pulse trains Pwh and Pwl into gate signals Gwh and Gwl having appropriate amplitudes based on the source potentials of the high-side switch Swh and the low-side switch Swl in the W-phase half bridge.

[0037] iu represents the current flowing through the U-phase coil of the motor 105, iv represents the current flowing through the V-phase coil of the motor 105, and iw represents the current flowing through the W-phase coil of the motor 105. In the following description, the direction of current flowing from the half bridge to the coil is considered positive.

[0038] In this embodiment, a detailed description will be given of a case in which a three-phase star-connected brushless motor is driven by a two-wire modulated three-phase sine wave drive system using a negative earth circuit, but the present invention is not limited to this, and other application examples will be described later.

[0039] [Example of control of power driving at normal speed] When the vehicle is traveling at a speed at which the peak voltage of the back electromotive force generated in the coil included in the motor 105 is equal to or lower than the battery voltage (also called the power supply voltage) of the battery pack 101, the voltage or current waveforms of each part when power driving is performed will be described using Figure 3A.

[0040] 3A, (1) represents the back electromotive force generated in each coil of the motor 105. Using the terminal voltages Eu, Ev, and Ew, which are the voltages at the output terminals of the half bridge group 1030 described above, and the voltage Ec at the point where all the coils of the motor 105 are connected when the coils are star-connected, the voltage representing the back electromotive force of the U phase is expressed as Eu-Ec, the voltage representing the back electromotive force of the V phase is expressed as Ev-Ec, and the voltage representing the back electromotive force of the W phase is expressed as Ew-Ec. (2) represents the U-phase Hall signal Hu from the motor 105, (3) represents the V-phase Hall signal Hv from the motor 105, and (4) represents the W-phase Hall signal Hw from the motor 105.

[0041] (5) shows, by a solid line and a dashed line, the drive voltage Eu (to ground Gnd) and the back electromotive force (to ground Gnd) of the U phase of the half bridge group 1030. (6) shows, by a solid line and a dashed line, the drive voltage Ev (to ground Gnd) and the back electromotive force (to ground Gnd) of the V phase of the half bridge group 1030. (7) shows, by a solid line and a dashed line, the drive voltage Ew (to ground Gnd) and the back electromotive force (to ground Gnd) of the W phase of the half bridge group 1030.

[0042] As shown in Figure 3A, both the drive voltage and back electromotive force are not sinusoidal waves, but are alternately divided into a 240° period of two-peak waveforms and a 120° period of ground level. This is called two-wire modulated three-phase sinusoidal wave drive, and is commonly used to improve power supply voltage utilization efficiency and reduce PWM modulation switching power loss by two-thirds compared to direct three-phase drive with sinusoidal waves. The potential difference between each of the three coils has only two degrees of freedom: the relative voltage with respect to one terminal. This takes advantage of the fact that the relative voltage must maintain a three-phase sinusoidal wave regardless of the absolute potential or how it changes. This is achieved by shifting the lowest potential of the three waveforms shown in (1) to ground level.

[0043] Since the drive voltage is fixed to ground level every 120° in three phases in this order, the back electromotive force (dashed line) during drive also repeats a 240° period of a two-peak waveform and a 120° period of ground level.

[0044] It should be noted that the relationship is power supply voltage Ep>peak voltage of drive voltages (Eu, Ev, Ew)>peak voltage of back electromotive force.

[0045] Furthermore, (8) represents the current iu flowing in the U-phase coil, (9) represents the current iv flowing in the V-phase coil, and (10) represents the current iw flowing in the W-phase coil. When the peak voltage of the drive voltage is greater than the peak voltage of the back electromotive force, a current in phase with the back electromotive force flows in each coil of the motor 105, causing the output power of the motor 105 to become positive and enter a powering state.

[0046] And, (11) represents the current isw flowing through the separation switch 1040, that is, the current supplied from the battery of the battery pack 101 to the motor 105. Since it is in the powering state, the current from the battery of the battery pack 101 to the motor 105 is positive, and power is consumed.

[0047] By controlling the circuits shown in FIGS. 2A and 2B to generate waveforms such as those shown in (5) to (7) in FIG. 3A, power driving at normal speed becomes possible.

[0048] [Example of Coasting Control at Normal Speed] When traveling at a speed where the peak voltage of the back electromotive force generated in the coil included in the motor 105 is equal to or less than the battery voltage (also called the power supply voltage) of the battery pack 101, the voltage or current waveforms of each part when coasting will be described using Fig. 3B. Note that the types of waveforms represented by (1) to (11) are the same as those in Fig. 3A.

[0049] Waveforms (5) to (11) differ from those in FIG. 3A. In (5) to (7), the back electromotive force and the drive voltage are the same for each phase. In FIG. 3B, they are the same, so the solid and dashed lines are indistinguishable. In this way, as shown in (8) to (10), the current flowing through the coils of the motor 105 is zero for each phase, and the output power of the motor 105 is also zero, i.e., the average torque is zero, resulting in a coasting state. Furthermore, since the current flowing through the motor 105 is also zero, the current is flowing through the separation switch 1040 is also zero, as shown in (11).

[0050] Coasting at normal speeds is possible by controlling the circuits shown in FIGS. 2A and 2B to generate waveforms such as those shown in (5) to (7) of FIG. 3B.

[0051] [Example of Regenerative Braking Control at Normal Speed] The voltage or current waveforms of each part when regenerative braking is performed while traveling at a speed where the peak voltage of the back electromotive force generated in the coil included in the motor 105 is equal to or less than the battery voltage (also called the power supply voltage) of the battery pack 101 will be described using Figure 3C. Note that the types of waveforms represented by (1) to (11) are the same as those in Figure 3A.

[0052] Waveforms (5) to (11) differ from those in FIG. 3A. In (5) to (7), for each phase, during the period of the two-peak waveform, the drive voltage (solid line) is smaller than the back electromotive force (dashed line), and the peak voltage of the drive voltage < the peak voltage of the back electromotive force < the power supply voltage Ep. When such a drive voltage is output, as shown in (8) to (10), a drive current of opposite phase to the drive voltage flows, and the output power of the motor 105 becomes negative, resulting in a regenerative braking state. Furthermore, as shown in (11), the current is flowing through the separation switch 1040 is negative, i.e., flows from the motor 105 to the battery pack 101, charging the battery pack 101.

[0053] By controlling the circuits shown in FIGS. 2A and 2B to generate waveforms such as those shown in (5) to (7) of FIG. 3C, regenerative braking at normal speeds becomes possible.

[0054] [Example of Control of Overmodulation Powering (Strong Powering) at Normal Speed] When traveling at a speed where the peak voltage of the back electromotive force generated in the coil included in the motor 105 is equal to or lower than the battery voltage (also called the power supply voltage) of the battery pack 101, in order to increase the output power of the motor 105, the peak voltage of the drive voltage command value may be set to be equal to or higher than not only the peak voltage of the back electromotive force but also the power supply voltage Ep. The voltage or current waveforms of each part in this case will be described using Figure 3D. Note that the types of waveforms represented by (1) to (11) are the same as those in Figure 3A.

[0055] Waveforms (5) to (11) differ from those in Fig. 3A. In (5) to (7), the two-peak waveform with the upper portion indicated by the dashed-dotted line is the command value of the drive voltage. Although the portion indicated by the dashed-dotted line exceeds the power supply voltage Ep, it is clipped at the power supply voltage Ep, and the drive voltage indicated by the solid line is output. Note that the peak voltage of the back electromotive force is lower than the peak voltage of the actual drive voltage and its command value.

[0056] The drive voltage represented by the solid line is at least partially higher than the drive voltage for normal power running shown in Fig. 3A, so that although the waveform is distorted as shown in (8) to (10), a large drive current flows that is in phase with the drive voltage, resulting in a power running state with higher output.

[0057] Also, as shown in (11), the current isw flowing through separation switch 1040 contains some AC ripple components, but the DC component is large and positive, resulting in large power consumption.

[0058] By controlling the circuits shown in FIGS. 2A and 2B so as to generate waveforms such as those shown in (5) to (7) in FIG. 3D, strong power driving at normal speeds becomes possible.

[0059] [Example of control of overmodulation powering (weak powering) at excessive speed] When the vehicle is traveling at a speed where the peak voltage of the back electromotive force generated in the coil included in the motor 105 exceeds the battery voltage (also called the power supply voltage) of the battery pack 101, the waveforms of the voltage or current of each part when powering will be described using FIG. 3E.

[0060] Waveforms (5) to (11) differ from those in Fig. 3A. In (5) to (7), the two-peak waveform with the upper portion indicated by the dashed-dotted line is the command value of the drive voltage. The portion indicated by the dashed-dotted line exceeds the power supply voltage Ep, but is clipped at the power supply voltage Ep, and the upper portion is flat at the voltage Ep, resulting in the output drive voltage indicated by the solid line. Note that the peak voltage of the back electromotive force exceeds the power supply voltage Ep, but is lower than the peak voltage of the command value of the drive voltage.

[0061] When driven by such a drive voltage, the current waveform is distorted as shown in (8) to (10), but a current in phase with the drive voltage can flow, resulting in a powering state. Also, as shown in (11), the current is flowing through separation switch 1040 contains an AC ripple component, and the DC component is positive, resulting in a state in which motor 105 consumes power.

[0062] However, if the speed becomes faster than the overspeed and the peak voltage of the back electromotive force is much larger than the power supply voltage Ep, the motor cannot be put into a powering state.

[0063] The circuits shown in FIGS. 2A and 2B enable weak power driving at overspeed by controlling the waveforms as shown in (5) to (7) of FIG. 3E.

[0064] [Example of Control of Overmodulation Coasting at Excessive Speed] The voltage or current waveforms of each part when coasting at a speed where the peak voltage (dotted line) of the back electromotive force generated in the coil included in the motor 105 exceeds the battery voltage (also called the power supply voltage) of the battery pack 101 will be described using Fig. 3F. Waveforms (5) to (11) differ from those in Fig. 3A.

[0065] At excessive speeds, coasting does not occur when the peak voltage of the drive voltage command value is equal to the peak voltage of the back electromotive force (dotted line), as is the case at normal speeds. This is because the drive output voltage is limited by the power supply voltage Ep, and when the peak voltage of the drive output and the peak voltage of the back electromotive force are equal, a distorted, negative-phase current flows, resulting in a weak regenerative braking state.

[0066] Therefore, as shown in (5) to (7), a command value for the drive voltage (the solid line is below the power supply voltage Ep, and the dashed line is above the voltage Ep) that is slightly larger than the peak voltage of the back electromotive force is given, and the drive voltage is actually clipped at the power supply voltage Ep. Then, as shown in (8) to (10), the current waveform is distorted and harmonic current flows, but the time-averaged output power, which is the product of the drive voltage and the drive current, is set to zero. This allows the motor to coast.

[0067] In this way, the current is flowing through separation switch 1040 contains an AC ripple component as shown in (11), and the DC component becomes slightly positive by the amount of heat loss caused by this, so even though it is in a coasting state, a small amount of power is consumed.

[0068] The circuits shown in FIGS. 2A and 2B enable coasting at excessive speeds by controlling the waveforms shown in (5) to (7) of FIG. 3F.

[0069] [Example of Control of Overmodulation Regeneration (Weak Regeneration) at Excessive Speed] The voltage or current waveforms of each part when regenerative braking is performed when traveling at a speed where the peak voltage of the back electromotive force generated in the coil included in the motor 105 exceeds the battery voltage (also called the power supply voltage) of the battery pack 101 will be described using Figure 3G. Waveforms (5) to (11) differ from those in Figure 3A.

[0070] At excessive speeds, as shown in (5) to (7), a lower drive voltage command value is given than in the coasting state shown in FIG. 3F (the solid line is below the power supply voltage Ep, and the portion above the voltage Ep is shown as a dashed line), and the drive voltage is actually clipped at the power supply voltage Ep. As in FIG. 3F, the peak voltage of the drive voltage command value is made higher than the peak voltage of the back electromotive force. This causes a current to flow that is opposite in phase to the drive voltage, although the current waveform is distorted, as shown in (8) to (10), resulting in a weaker regenerative braking state.

[0071] Then, the current isw flowing through the separation switch 1040 contains an AC ripple component as shown in (11), and the DC component becomes negative, causing the power to be charged into the battery.

[0072] The circuits shown in FIGS. 2A and 2B enable weak regenerative braking at excessive speeds by controlling the waveforms shown in (5) to (7) of FIG. 3G.

[0073] [Example of Control of Normal Regeneration (Strong Regeneration) at Excessive Speed] When traveling at a speed where the peak voltage of the back electromotive force generated in the coil included in the motor 105 exceeds the battery voltage (also called the power supply voltage) of the battery pack 101, the voltage or current waveforms of each part when stronger regenerative braking is performed will be described using Figure 3H. Waveforms (5) to (11) differ from those in Figure 3A.

[0074] As with regenerative braking at normal speeds, by making the peak voltage of the drive voltage lower than the power supply voltage Ep and the peak voltage of the back electromotive force (dotted lines), as shown in (5) to (7), the current waveform can flow a larger current in the opposite phase to the drive voltage, as shown in (8) to (10).

[0075] As a result, as shown in (11), the current isw flowing through the separation switch 1040 contains only negative DC components, allowing a large amount of power to be charged into the power supply, thereby achieving strong regenerative braking.

[0076] By controlling the circuits shown in FIGS. 2A and 2B to generate waveforms such as those shown in (5) to (7) of FIG. 3H, strong regenerative braking at excessive speeds is possible.

[0077] The waveforms of the back electromotive force, the waveform of the drive voltage, and the resulting current waveforms in the coil of the motor 105 and the current waveform flowing through the separation switch 1040 shown in Figures 3A to 3H have somewhat complicated waveform relationships due to the phase difference and frequency characteristics that occur due to the influence of the reactance caused by the L component of the coil, but in this embodiment, the waveforms are shown as those when the reactance component is sufficiently small to make them easier to understand.

[0078] In practice, by giving a lead angle to the drive voltage according to the reactance component, a phase difference is created between the drive voltage waveform and the back electromotive force waveform, and the coil is driven so that the phase difference between the fundamental wave of the current flowing through the coil and the back electromotive force is ensured to be zero. Also, the coil current waveform also has an LPF (Low Pass Filter) effect due to the influence of reactance, which reduces high frequencies, distortion (i.e., harmonics), and loss due to AC current, but the final operation is as explained above.

[0079] [Utilizing the motor-off state] As shown in Figures 3B and 3F, in addition to coasting, which results in zero torque by applying an appropriate drive voltage according to the rotational speed at that time, there is also a method of completely coasting with zero torque and zero output power by, for example, entering a motor-off state in which the drive amplifier (e.g., half bridge, level shifter, PWM modulation unit, etc.) is completely disconnected, so that no current flows through the coil of the motor 105 in the first place.

[0080] 3B and 3F, even if the average torque is zero, AC torque and AC current are generated momentarily due to distortion of the drive voltage waveform and back electromotive force, fluctuations in the phase difference, etc., resulting in some power loss, but the motor-off state method can completely eliminate the loss. Therefore, if coasting continues for even a short period of time, it is preferable to actively utilize the motor-off state.

[0081] The drive amplifier is disconnected by turning off the output of the drive amplifier connected to the coil of the motor 105, that is, by turning off both the low-side switch and the high-side switch to put the output into a high impedance state.

[0082] [Drive output off at normal speed] Figure 4A shows various waveforms when the drive output is off at normal speed. Note that the same row numbers are used for waveforms of the same types as those in Figures 3A to 3H, and (1) back electromotive force and (2) to (4) Hall signals are omitted.

[0083] (5) represents the drive voltage Eu of the U phase of the half bridge group 1030. (6) represents the drive voltage Ev of the V phase of the half bridge group 1030. (7) represents the drive voltage Ew of the W phase of the half bridge group 1030. As shown in (5) to (7), the waveform is a sine wave with the lowest voltage at ground level.

[0084] Also, (8) represents the current iu flowing through the U-phase coil, (9) represents the current iv flowing through the V-phase, and (10) represents the current iw flowing through the W-phase. Note that the direction of current flowing to the motor 105 is positive. Because the drive voltages are as shown in (5) to (7), no current flows in any of the phases, as shown in (8) to (10).

[0085] Furthermore, (11) represents the current is flowing through the separation switch 1040, and (12) represents the state (open (off) or closed (on)) of the separation switch 1040. When the drive output is turned off at normal speed, the separation switch 1040 is closed as shown in (12), but the current through the separation switch 1040 is also zero as shown in (11).

[0086] Note that (13) represents the state (open or closed) of the U-phase high-side switch Suh, (14) represents the state of the U-phase low-side switch Sul, (15) represents the state of the V-phase high-side switch Svh, (16) represents the state of the V-phase low-side switch Svl, (17) represents the state of the W-phase high-side switch Swh, and (18) represents the state of the W-phase low-side switch Swl. As described above, since the drive output is off, all switches are open.

[0087] Note that (19) represents the waveform of the voltage Eb of the separation switch 1040 on the half-bridge group 1030 side, and since the separation switch 1040 is closed, it is the power supply voltage Ep.

[0088] In this way, if the drive output is turned off at normal speed, that is, if all the switches of the half bridge group 1030 are opened, the current flowing through the coils of each phase becomes zero, and a complete coasting state can be achieved.

[0089] [Drive output off at excessive speed] Fig. 4B shows various waveforms when the drive output is turned off at excessive speed. Each row represents the same type of waveform as the same row number in Fig. 4A.

[0090] Here, as shown in (12), when the separation switch 1040 is closed and the speed exceeds the limit, even if all the switches in the half-bridge group 1030 are open, the back electromotive force exceeds the power supply voltage Ep, so that it is clipped by the power supply voltage Ep and a regenerative current naturally flows from the ground via the parasitic diodes of each switch.

[0091] That is, as shown in (5) to (7), the upper limits of the voltages Eu, Ev, and Ew are clipped by the power supply voltage Ep, and they become distorted square waves. Also, as shown in (8) to (10), a current naturally flows from the ground to the coil of the motor 105.

[0092] As shown in (11), a regenerative current containing an AC component flows through the separation switch 1040 in the direction of the battery.

[0093] Note that (13) to (18) indicate that all switches of the half-bridge group 1030 are open, and (19) indicates that the voltage Eb is equal to the power supply voltage Ep, as in FIG. 4A.

[0094] In this way, unintentional regenerative braking occurs naturally, preventing coasting, and the regenerated power is unintentionally charged into the battery.

[0095] [Regarding the Opening of Separation Switch 1040 at Excessive Speed] As shown in Fig. 4B, a regenerative current flows, and it is assumed that this current is cut off by opening separation switch 1040. An example of the waveform that occurs in this case is shown in Fig. 5. Note that each row has the same type of waveform as the same row number in Fig. 4A.

[0096] Here, as shown in (12), it is assumed that the separation switch 1040 is switched from closed to open at time t1. In this case, as shown in (11), a regenerative current is already continuously flowing through the separation switch 1040, so the moment the separation switch 1040 opens at time t1, a high surge voltage is generated in the V phase as shown in (6). This is charged into the stray capacitance or small-capacity capacitor on the line from the half-bridge group 1030 to the separation switch 1040 via the parasitic diode Dvh of the V-phase high-side switch Svh, so that the voltage Eb of the separation switch 1040 on the half-bridge group 1030 side is maintained at a high voltage for a while as shown in (19).

[0097] This will destroy the isolation switch 1040, each switch in the half-bridge group 1030, and other devices around them.

[0098] Also, assume that while driving at an excessive speed, all drive outputs of the half-bridge group 1030 are fixed to the ground level, then the separation switch 1040 is opened, and then all drive outputs of the half-bridge group 1030 are turned off. An example of the waveforms generated in this case is shown in FIG. 6. Note that each row has the same type of waveform as the same row number in FIG. 4A.

[0099] In this case, as shown in (13) to (18), by time t2, the low-side switches Sul, Svl, and Swl are closed and the high-side switches Suh, Svh, and Swh are open in the half-bridge group 1030. Then, as shown in (12), at time t3, the separation switch 1040 is switched from closed to open.

[0100] As shown in (5) to (7), until time t3, all drive outputs of the half bridge group 1030 are fixed at ground level, so the voltages Eu, Ev, and Ew are zero, and as shown in (8) to (10), the current flowing through each coil of the motor 105 is a sine wave, but even if the separation switch 1040 is opened at time t2, these waveforms do not change. In other words, as shown in (11), the current flowing through the separation switch 1040 is zero, so even if the separation switch 1040 is opened at time t2, no surge is generated in any phase.

[0101] However, as shown in (13) to (18), when the remaining low-side switches Sul, Svl, and Swl are opened at time t3, a surge high voltage occurs in the V-phase voltage Ev of the motor 105 at that moment.

[0102] Before the separation switch 1040 is opened, the parasitic diodes act as voltage clips on both the high-side switch and the low-side switch of the half-bridge group 1030. That is, regardless of the timing at which the drive output of each phase is turned off, if the surge voltage from the coil of the motor 105 is positive, a current due to the surge voltage flows through the parasitic diode of the high-side switch, and if the surge voltage is negative, a current due to the surge voltage flows through the parasitic diode of the low-side switch, so the surge voltage remains within the range from the ground level to the power supply voltage Ep, and no high voltage is generated inadvertently.

[0103] However, when separation switch 1040 is open at time t2, current flows toward the battery. When the half bridge (V phase in this case) connected to the coil of motor 105 is opened, a positive high voltage surge is generated from the coil of motor 105 at that moment, as shown in (6). Then, a high voltage is generated on the bridge side of separation switch 1040, as shown in (19), which again destroys separation switch 1040, half bridge group 1030, and other peripheral devices.

[0104] To summarize the explanation so far, even at excessive speeds, the drive voltage waveform is clipped by the power supply voltage Ep until the speed slightly exceeds the upper limit of normal speed, and small torque powering is possible with overmodulation drive, and even beyond that speed, regenerative braking is possible within a certain torque range. However, at even higher speeds, powering is impossible, and regenerative braking also results in excessive torque and excessive current, making it inappropriate to implement.

[0105] Therefore, although it is desirable to completely turn off the motor, it is not possible to safely turn off the drive output at excessive speeds. Specifically, if the drive output is turned off in the same way as at normal speeds, the following problems will arise.

[0106] In other words, since the back electromotive force of the motor 105 becomes higher than the power supply voltage Ep, regenerative current flows to the battery via the parasitic diodes of the switches included in the half-bridge group 1030, which naturally causes unintended regenerative braking.

[0107] Furthermore, if an attempt is made to disconnect the battery using separation switch 1040 in order to prevent this, a high surge voltage will be generated the moment the battery is disconnected while the regenerative current is still flowing, which could destroy separation switch 1040 itself, the switches included in half-bridge group 1030, and other devices. It could also cause insulation breakdown in the coil of motor 105 itself.

[0108] In this way, the motor 105 cannot be turned off once overspeed has occurred.

[0109] Furthermore, if it is not possible to turn off the motor, unintended braking may remain applied, and the battery may be overcharged by unintended regenerative current.

[0110] Therefore, in the past, in order to prevent this, control was performed such that all driving such as power running, coasting, regeneration, loss braking, etc. was stopped and the motor 105 was turned off before the speed exceeded the limit.

[0111] [Specific Contents of Control According to the Present Embodiment] An outline of the control content to be performed in this embodiment will be described using Figure 7. First, the drive control unit 1021 of the control unit 1020 detects an event that requires motor-off (step S1). This event can be defined in various ways, but it may be that the vehicle speed exceeds a predetermined speed at which powering or regenerative braking is not possible, or that the vehicle is in a traveling state where coasting continues for a certain period of time or more. Note that while traveling at an excessive speed will solve the above-mentioned problem, the control shown in Figure 7 may also be performed while traveling at a normal speed.

[0112] Next, the drive control unit 1021 executes control to continuously reduce the output torque of the motor 105 so that the output torque approaches zero (step S3). This control is optional, and is therefore indicated by a dotted line in FIG. 7 . This control is intended to prevent a sudden change from the current output torque of the motor 105 to zero torque, thereby preventing shock, since the drive output will inevitably be turned off in a later control. In this step, it is preferable to smoothly reduce the output torque to zero. Note that the control in step S5 described below corresponds to short-circuit braking, which may generate braking torque and cause a large torque shock. However, since this series of controls can be completed in a short time when the vehicle is traveling at high speed, a momentary clicking sound may occur, but no large torque shock will occur.

[0113] Then, the drive control unit 1021 controls the half-bridge group 1030 to perform a pre-switching operation (step S5). There are several variations on the pre-switching operation, but in this embodiment, the drive outputs of all phases in the half-bridge group 1030 are set to ground level. That is, all high-side switches are opened and all low-side switches are closed. By performing this control, as shown in FIG. 6, the current is flowing through the separation switch 1040 can be stably set to zero, preventing the occurrence of a high surge voltage.

[0114] Thereafter, the drive control unit 1021 opens the separation switch 1040 (step S7), thereby separating the battery of the battery pack 101 from the half bridge group 1030, and preventing the regenerative current from flowing to the battery.

[0115] Finally, the drive control unit 1021 turns off the drive output for the phases in the half-bridge group 1030 whose drive output is not turned off in the order that a predetermined current condition is satisfied (step S9). If the drive output for all phases is set to ground level in step S5, the drive output for all phases is not turned off. Furthermore, in the case of a negative ground assumed in this embodiment, the predetermined current condition is a condition in which the current flowing through each coil included in the motor 105 is positive or zero. The drive output for that phase is turned off while this current condition is satisfied. In this waveform example, the operation is performed the second time the condition is satisfied, but it may be performed the first time or the third time or later as long as the condition is satisfied. Furthermore, the order does not have to be U, V, and W. If the above current condition is satisfied simultaneously, the drive output for those phases may be turned off simultaneously. Furthermore, the timing for opening the separation switch 1040 may also be the same as the timing for turning off the drive output for the phases whose drive output is not turned off. This execution of turning off the drive output is similar in the embodiments described below.

[0116] By turning off the drive output during the period when such a current condition is satisfied, the occurrence of a high surge voltage can be avoided.

[0117] An example of various waveforms when such control is performed will be described with reference to Fig. 8. Note that each row in Fig. 8 represents the same type of waveform as the same row number in Fig. 4A.

[0118] 8, step S1 is executed long before time t10, step S3 is skipped, and the process proceeds to step S5, where the drive outputs of all phases in the half-bridge group 1030 are set to ground level. That is, as shown in (13) to (18), all high-side switches are opened and all low-side switches are closed. Note that, since the drive outputs of all phases are set to ground level, the voltages Eu, Ev, and Ew are at ground level as shown in (5) to (7). Furthermore, the currents iu, iv, and iw flowing through the coils of the motor 105 are sinusoidal as shown in (8) to (10), but the current is flowing through the separation switch 1040 is zero as shown in (11).

[0119] In this embodiment, the current isw flowing through the separation switch 1040 is already 0, so in step S7, the separation switch 1040 is changed from closed to open at an arbitrary time t10.

[0120] Thereafter, at time t11, when current iu becomes positive, the U-phase low-side switch Sul is changed from closed to open. Furthermore, at time t12, when current iv becomes positive, the V-phase low-side switch Svl is changed from closed to open. Then, at time t13, when current iw becomes positive, the W-phase low-side switch Swl is changed from closed to open.

[0121] In this way, the current isw flowing through the separation switch 1040 remains zero, and the voltage Eb of the separation switch 1040 on the half bridge group 1030 side is also maintained at a voltage slightly higher than the power supply voltage Ep.

[0122] As shown in (5) to (7), there are portions where the U-phase voltage Eu and the V-phase voltage Ev momentarily rise, but this is not the moment when the low-side switches of each phase are opened, and is not a surge voltage. Prior to this, the drive outputs of the U and V phases were turned off, and at that moment, the currents iu and iv were positive, so currents flowed through the parasitic diodes on the ground side of those phases and were clamped and fixed at ground potential. However, the current in the coil of the motor 105 gradually changed, and at the moment it went from positive to negative, the clamping by the parasitic diodes ended. Therefore, since a back electromotive force voltage simply appeared suddenly, there is no risk of a voltage higher than the back electromotive force being generated.

[0123] In this way, even when traveling at excessive speed, the current isw flowing through separation switch 1040 does not always flow in the negative direction, i.e., in the regenerative direction, but rather periods of time when it flows in the positive direction or periods when it is zero can be generated, creating a timing when no surge high voltage is generated even when separation switch 1040 is opened. Then, by sequentially turning off the drive output of each phase that satisfies the current condition, no surge is generated at all, and it becomes possible to safely transition to motor off even at excessive speed.

[0124] An example of a functional configuration for executing such control will be described with reference to Fig. 9. Fig. 9 is a more detailed view of the functional block diagram shown in Fig. 2A, showing the portion relating to this embodiment. That is, in this embodiment, logical product units 1051u, 1051v, and 1051w, and drive output control units 1061 to 1066, which are AND gates, have been added.

[0125] The motor rotation input unit 1023 outputs information on the rotation speed and rotation phase of the motor 105 to the drive control unit 1021 and the drive waveform data generation unit 1024 in accordance with the Hall signal.

[0126] As described above, the drive control unit 1021 performs predetermined calculations based on various inputs to determine, for example, the envelope voltage of the sinusoidal wave drive voltage, as well as the duty ratio and lead angle for PWM modulation, and outputs these to the drive waveform data generation unit 1024. The drive waveform data generation unit 1024 generates reference drive waveform data for each of the UVW phases in accordance with the current phase of the motor 105, the duty ratio, and the lead angle, and further generates drive voltage waveform data Du, Dv, and Dw by multiplying the reference drive waveform by the envelope voltage, and outputs these to the corresponding PWM modulation units 1025u, 1025v, and 1025w, respectively.

[0127] Furthermore, when the drive control unit 1021 detects an event that requires the motor to be turned off in step S1 from various inputs and executes step S3, it changes the output to the drive waveform data generation unit 1024 so as to gradually reduce the output torque of the motor 105 to zero. The drive control unit 1021 also generates signals / U-Gnd, / V-Gnd, and / W-Gnd for the pre-switching operation in step S5. When these signals are high (1), the output of the drive waveform data generation unit 1024 is output as is from the logical product units 1051u, 1051v, and 1051w. When these signals are low (0), the logical product units 1051u, 1051v, and 1051w instruct the output of a drive waveform with zero amplitude, and the PWM modulation units 1025u, 1025v, and 1025w turn on the low-side switches, setting each half-bridge to ground level.

[0128] For step S7, drive control unit 1021 also outputs signal SW-Off to open separation switch 1040. For example, if signal SW-Off is high, separation switch 1040 is closed, and if it is low, separation switch 1040 is opened.

[0129] Furthermore, for step S9, the drive control unit 1021 generates signals U-On, V-On, and W-On for turning off the drive output during a period in which the condition that the current flowing through each coil included in the motor 105 is positive or zero is satisfied. These signals are input to the drive output control units 1061 to 1066, respectively, so that when the signals are high, the outputs from the PWM modulation units 1025u, 1025v, and 1025w are output directly by the drive output control units 1061 to 1066 to the level shifters 1026u, 1026v, and 1026w, but when the signals are low, the drive output control units 1061 to 1066 output signals to the level shifters 1026u, 1026v, and 1026w that open the switches included in the half bridges.

[0130] The drive control unit 1021 generates the above-mentioned signals using a configuration as shown in Fig. 10. That is, the drive control unit 1021 has a polarity determination unit 10213 and a timing signal generation unit 10214.

[0131] Based on the output from the instantaneous current detection unit 1071 that detects the instantaneous currents iu, iv, iw, and isw, the polarity determination unit 10213 determines whether each instantaneous current is in a state where current is flowing toward the motor 105 side or where the current is zero in the case of a negative earth, i.e., whether the current is zero or greater (positive or zero), and outputs information Piu, Piv, Piw, and Pisw that indicates the polarity (zero or greater or negative) of each instantaneous current to the timing signal generation unit 10214. Note that the instantaneous current detection unit 1071 may already be provided for another purpose, and in that case, it may be utilized.

[0132] The timing signal generation unit 10214 generates and outputs the above-mentioned signals U-On, V-On, W-On, / U-Gnd, / V-Gnd, / W-Gnd and SW-Off based on the output from the polarity determination unit 10213 and various other information.

[0133] If the drive outputs of all phases are set to the ground level in step S5, after step S1 or S3, the timing signal generating unit 10214 outputs the signals / U-Gnd, / V-Gnd and / W-Gnd at low level.

[0134] When the drive outputs of all phases are set to the ground level in step S5, the current isw flowing through separation switch 1040 is always zero after step S5, so information Pisw indicating the polarity is not used, but it may be used in other embodiments described later. In this embodiment, in step S7, timing signal generator 10214 outputs signal Sw-Off at a low level at an arbitrary timing after step S5, thereby opening separation switch 1040.

[0135] Thereafter, the timing signal generating unit 10214 refers to the polarity information Piu, Piv, and Piw, and for the phase for which information indicating positive or zero is obtained, outputs the signal for that phase (either U-On, V-On, or W-On) as low.

[0136] This allows the operations shown in FIG. 7 to be executed at the correct timing.

[0137] In addition, the timing signal generating unit 10214 may also generate a timing signal using other information.

[0138] [First Modification of First Embodiment] In the first embodiment, the instantaneous current is detected and the polarity of the instantaneous current is used, but there are cases where the instantaneous current detection unit 1071 is not provided. In such cases, instead of providing the instantaneous current detection unit 1071, it is also possible to estimate whether each current is equal to or greater than zero based on information about the rotation phase obtained from the Hall signal from the motor 105.

[0139] An example of the configuration in such a case is shown in Fig. 11. That is, the drive control section 1021b includes a phase decoding section 10216 and a timing signal generating section 10214b.

[0140] The phase decoding unit 10216 determines whether or not the timing corresponds to a phase change timing that has been confirmed in advance so that the instantaneous currents iu, iv, iw, and isw become positive or zero in the case of a negative ground, based on the information on the rotation phase of the motor 105 obtained from the motor rotation input unit 1023. When it detects that the timing corresponds to a phase change timing that has been confirmed in advance, it outputs a message to that effect to the timing signal generating unit 10214b.

[0141] The timing signal generating unit 10214b generates and outputs the above-mentioned signals U-On, V-On, W-On, / U-Gnd, / V-Gnd, / W-Gnd and SW-Off based on the output from the phase decoding unit 10216 and various other information.

[0142] If the drive outputs of all phases are set to the ground level in step S5, timing signal generator 10214b outputs signals / U-Gnd, / V-Gnd, and / W-Gnd at low level at any timing after step S1 or S3. In this case, since current is flowing through separation switch 1040 is always zero after step S5, it is not necessary to specify a phase change timing at which instantaneous current is confirmed to be positive or zero.

[0143] If the drive output of all phases is set to ground level in step S5, then in step S7, the timing signal generating unit 10214b outputs the signal Sw-Off low at any timing after step S5, thereby opening the separation switch 1040.

[0144] Thereafter, in response to a notification from the phase decoding unit 10216, the timing signal generating unit 10214b sets the signal (either U-On, V-On, or W-On) for the phase related to the notification to low and outputs it.

[0145] The phase decoder 10216 may shift the timing using not only information about the rotational phase of the motor 105, but also information about the rotational speed and the target output torque, etc. This improves the accuracy of estimating the current direction under any operating conditions, and increases the margin for the timing to open the separation switch 1040 and the timing to turn off the drive output.

[0146] In this modified example, the timing chart shown in Fig. 8 is slightly changed, as shown in Fig. 12.

[0147] 8 up to time t10, but when the phase decode unit 10216 detects that the V-phase Hall signal Hv transitions from high to low at time t21, it notifies the timing signal generator 10214b, which then sets U-On to low in response to the notification, which opens the U-phase low-side switch Sul and turns off the U-phase drive output.

[0148] After that, at time t22, when the phase decode unit 10216 detects that the W-phase Hall signal Hw transitions from high to low, it notifies the timing signal generator 10214b, which then sets V-On to low in response to the notification, thereby opening the V-phase low-side switch Svl and turning off the V-phase drive output.

[0149] Furthermore, when the phase decode unit 10216 detects that the U-phase Hall signal Hu transitions from high to low at time t23, it notifies the timing signal generator 10214b, which then sets W-On to low in response to the notification, thereby opening the W-phase low-side switch Sw1 and turning off the W-phase drive output.

[0150] Other signal waveforms are the same as those in FIG.

[0151] In this way, it is possible to cope with cases where the instantaneous current detection unit 1071 is not provided in advance.

[0152] [Second Modification of First Embodiment] In the first embodiment, an example was shown in which the drive output of the corresponding phase is set to ground level using / U-Gnd, / V-Gnd, and / W-Gnd. However, since the drive control unit 1021 originally outputs the duty ratio in PWM modulation, it becomes possible to set the drive output to ground level by specifying this duty ratio to zero.

[0153] Therefore, such an implementation may be adopted.

[0154] [Embodiment 2] In the first embodiment, the case where the drive outputs of all phases are set to the ground level in step S5 is shown, but the pre-switching operation that is permitted is not limited to setting the drive outputs of all phases to the ground level.

[0155] For example, the drive outputs of only some of the phases may be set to the ground level and the drive outputs of the remaining phases may be turned off. Alternatively, the drive outputs of the remaining phases may be left on. Furthermore, the drive outputs of some of the remaining phases may be turned off and the drive outputs of the remaining phases may be left on.

[0156] For example, Fig. 13 illustrates an example in which two phases (e.g., V phase and W phase) are set to the ground level in step S5, and one phase (e.g., U phase) is turned off in step S5. Note that Fig. 13 illustrates an example in which the phase decoder 10216 shown in Fig. 11 is used, but if an instantaneous current detector 1071 is provided as shown in Fig. 10, operation may be controlled based on the instantaneous current.

[0157] In step S5, the drive output for the U phase is turned off, so the timing signal generator 10214b sets U-On to low and outputs it. Note that the signal / U-Gnd can remain high. On the other hand, for the W phase and V phase, the signals / V-Gnd and / W-Gnd are output low in step S5.

[0158] If two phases (e.g., V and W phases) are set to ground level in step S5 and one phase (e.g., U phase) is turned off in step S5, the voltage Eu will have a peak before and after the timing when the Hall signal Hw of the W phase, which is fixed to ground level, transitions from high to low, as shown in (5), and the U phase current iu shown in (8) will not be a sine wave but will have a waveform that is slightly negative from time t31 to t32. Correspondingly, the current is flowing through the separation switch 1040 will be negative and not zero from time t31 to t32, as shown in (11).

[0159] In the example of FIG. 13, the timing signal generating unit 10214b sets the signal Sw-Off to low to open the separation switch 1040 at time t33 when the W-phase Hall signal Hw transitions from low to high, which is the time margin greatest during the period when the current isw flowing through the separation switch 1040 is positive or zero.

[0160] After this, since the drive output for the U phase has already been turned off, the phase decoding unit 10216 detects the timing at which it is estimated that the condition for turning off the drive output for the V and W phases is satisfied, that is, in the case of a negative earth, the current to the coil of the motor 105 is zero or positive.

[0161] In this example, the phase decoder 10216 detects the timing at which the W-phase Hall signal Hw transitions from high to low and notifies the timing signal generator 10214b, and also detects the timing at which the U-phase Hall signal Hu transitions from high to low and notifies the timing signal generator 10214b.

[0162] When notified by the phase decode unit 10216, the timing signal generation unit 10214b outputs a low signal V-On at time t34, opening the V-phase low-side switch Svl to turn off the drive output. Also, when notified by the phase decode unit 10216, the timing signal generation unit 10214b outputs a low signal W-On at time t35, opening the W-phase low-side switch Swl to turn off the drive output.

[0163] Even in such a case, no surge high voltage is generated when the separation switch 1040 is opened, and no surge high voltage is generated when the drive outputs of the V phase and W phase are turned off.

[0164] If the drive output for the U phase is turned off in step S5, current will flow toward the battery from time t31 to t32. However, since current iu is positive or zero during other periods, current is flowing through separation switch 1040 will also be zero, and there will be many opportunities for separation switch 1040 to be open.

[0165] When the drive output of some phases is set to ground level in this way, the terminals of motor 105 appear to be shorted to ground when viewed from the coil side of motor 105, and although AC current flows in at least the output of that phase, all of this current flows in and out of ground, and neither positive nor negative current passes through separation switch 1040. As a result, the current is flowing through separation switch 1040 via the phase whose drive output is set to ground level becomes zero, and the phases become unbalanced, so there is a period during one cycle of the electrical angle during which the current is flowing through separation switch 1040 is steadily positive or zero rather than negative.

[0166] On the other hand, when the drive output of some phases is turned off, the AC current of the drive output of that phase, particularly the large-amplitude fundamental wave, hardly flows (only the amount by which the instantaneous waveform peak exceeds the power supply voltage Ep flows), causing an imbalance in each phase, and the current is flowing through separation switch 1040 is not steadily negative, but there is a period during one cycle of the electrical angle during which it turns positive or zero.

[0167] From the above, even when the drive outputs for some phases are set to the ground level in step S5 and the remaining drive outputs are turned off, it is possible to turn off the motor without generating a high surge voltage.

[0168] When the configuration shown in FIG. 10 using the instantaneous current detection unit 1071 is adopted, the timing or period when the current is flowing through the separation switch 1040 becomes equal to or greater than zero can be detected from the instantaneous current is, and the signal Sw-Off that opens the separation switch 1040 can be output low.

[0169] Furthermore, in step S5, if the drive output for some phases is set to ground level and the drive output for the remaining phases is left on, the signal / W-Gnd for the phases for which the drive output is to be left on is left high, and then in step S9, the signals (U-On, V-On, W-On) are output low so that the drive output is turned off at the timing when the current condition is satisfied.

[0170] Third Embodiment In the present embodiment, the pre-switching operation is performed by turning off the drive outputs of some phases and keeping the drive outputs of the remaining phases on. That is, unlike the first and second embodiments, the pre-switching operation does not set the drive outputs of at least some phases to ground level, but rather just turns off the drive outputs of some phases.

[0171] For example, Fig. 14 shows an example in which the drive output for two phases (e.g., U-phase and V-phase) is set to OFF in step S5, and the drive output for the remaining phase (e.g., W-phase) remains ON without any special control in step S5. Note that before Fig. 14, all three phases are PWM driven (weak regeneration state) at excessive speed.

[0172] Because the PWM is driven at an overspeed, the PWM is significantly overmodulated to reduce the torque generated before turning off the motor 105. However, the torque does not reach zero, and the regeneration state changes to a weak regeneration state as shown in Figures 3G and 3H, and the current is flowing through the isolation switch 1040 remains constantly negative or may be positive for some periods depending on the driving conditions.

[0173] However, if, for example, the drive outputs of the U and V phases are turned off and, for example, the W phase is left PWM driven before the time shown in FIG. 14 , an imbalance between the phases and the complex behavior of the parasitic diodes will cause a period in which the current is of separation switch 1040 is not constantly negative, but is positive or zero, as shown in (11), as before time t41.

[0174] In this embodiment, the separation switch 1040 is opened as shown in (12) at the timing when it is confirmed that the current is of the separation switch 1040 has entered a period in which it is positive or zero, or at the timing when it is known, for example, through a previous experiment, that the combination of Hall signals will result in a period in which the current is of the separation switch 1040 will definitely be positive or zero (in the example of FIG. 14, the timing when the W-phase Hall signal Hw transitions from low to high), that is, at time t41.

[0175] Then, at time t42, when the V-phase current iv and W-phase current iw flowing through the coils of the motor 105 become zero, a change occurs in the voltage waveforms shown in (5) to (7), and the back electromotive forces of all the U, V, and W phases become sinusoidal waveforms clamped to the Gnd potential. Because this is an overspeed state, the peak voltage is higher than the power supply voltage. As a result, as shown in (19), the voltage Eb on the motor 105 side of the separation switch 1040 is also higher than the power supply voltage Ep by that amount. However, because this is not due to a surge in coil current, no abnormally high voltage sufficient to destroy peripheral devices is generated.

[0176] Then, at the timing when the current iw flowing through the motor 105 becomes positive or zero, or the timing when it is known in advance, for example, through an experiment, that the current iw will become positive or zero depending on the combination of Hall signals (in the example of FIG. 14, the timing when the V-phase Hall signal Hv transitions from high to low), that is, at time t43, the high-side switch Swh and the low-side switch Swl are opened, as shown in (17) and (18), to turn off the W-phase drive output.

[0177] This allows the motor to be safely turned off, as in the first and second embodiments.

[0178] It has been stated that the condition for opening the separation switch 1040 is met at time t41, but since the current condition that the W-phase current iw is positive or zero is also met after time t41, the W-phase drive output may be turned off at time t41. In this case, only the high-side switch Swh and the low-side switch Swl are opened, and the other waveforms remain unchanged.

[0179] As described above, if the current condition for each phase in step S9 of FIG. 7 is satisfied, the drive output is simultaneously turned off. However, if the condition that the current is flowing through separation switch 1040 is positive or zero is also satisfied in step S7, steps S7 and S9 may be executed simultaneously.

[0180] [Other Technical Matters] [Regarding Motors to Which the Embodiments Can Be Applied] In the above, it is assumed that coils Lu, Lv, and Lw are star-connected in the motor 105, as shown in FIG. 15(a). As shown in FIG. 15(a), the voltage at the point where coils Lu, Lv, and Lw are connected is designated as Ec. Furthermore, switching amplifiers Ampu, Ampv, and Ampw are connected to the terminals of the motor 105. As shown in FIG. 15(b), the switching amplifier Ampx (x is any one of u, v, and w) includes a set of high-side switch Sxh and low-side switch Sxl of the half-bridge group 1030, a level shifter 1026, and a PWM modulation unit 1025.

[0181] However, the embodiment of the present application is applicable not only to the star-connected motor 105 shown in FIG. 15( a) but also to a motor in which the coils Luv, Lvw, and Lwu are delta-connected (diagonally connected) as shown in FIG. 15( c).

[0182] Star connection and delta connection differ in the way the terminals and coils of the motor 105 are connected, but star connection and delta connection are equivalent exchanges, so if the parameter values ​​of each coil (L, R, etc.) are matched, the voltage, current, and operation seen from the switching amplifier Ampx side of even a delta-connected motor 105 will all be equivalent to those of a star-connected motor 105.

[0183] Furthermore, although the above description has been given of a three-phase motor 105, the present invention is also applicable to a multi-phase motor having two or more phases.

[0184] For example, Figures 16(a) and 16(b) show configuration examples for a seven-phase motor. Figure 16(a) shows an example in which the coils in the motor are star-connected, and Figure 16(b) shows an example in which the coils are delta-connected. The embodiments of the present application can also be applied to such motors.

[0185] Voltages with phases that differ by 360° / 7 are supplied between both ends of each coil in the order of coils L1 to L7. The drive voltage waveform at this time (actually PWM switching drive) outputs voltages with phases that differ by 360° / 7 in the order of switching amplifier outputs E1 to E7.

[0186] 17 and 18 show examples of the configuration of a two-phase motor and examples of drive waveforms for that case. Note that although the motor is two-phase, it is actually four-phase in order to generate a rotating magnetic field, and is driven by a cosine waveform and a sine waveform with a phase difference of 90°.

[0187] 17(a) shows an example of a configuration in which a two-phase motor is connected with three wires and driven by three switching amplifiers Amp (an example of a two-phase, three-wire, three-amplifier connection). In this way, a common wire C is connected to the connection point of two coils L1 and L2, and a cosine waveform is generated by the potential difference between voltage E1 and voltage Ec supplied to the other end of coil L1, and a sine wave is generated by the potential difference between voltage E2 and voltage Ec supplied to the other end of coil L2.

[0188] 17B, ​​(1) represents the waveform of voltage E1, (2) represents the waveform of voltage Ec, and (3) represents the waveform of voltage E2. In this example, voltage Ec is driven at a midpoint potential (fixed duty ratio of 50%), and voltages E1 and E2 are driven by a cosine wave and a sine wave, respectively, centered on voltage Ec.

[0189] Figure 17(c) shows another example of drive waveforms. (1) shows the waveform of voltage E1, (2) shows the waveform of voltage Ec, (3) shows the waveform of voltage E2, and (4) shows the waveforms of voltages E1' and E2' actually applied to each coil. The lowest potential among the potentials of voltages E1, Ec, and E2 in Figure 17(b) is shifted and fixed to Gnd, so that the same potential difference as in Figure 17(b) is applied relatively, i.e., cosine waves and sine waves are applied between both ends of each coil. More specifically, E1' = E1 - Ec, E2' = E2 - Ec, resulting in cosine waves and sine waves as shown in (4).

[0190] FIG. 18 shows an example of a configuration (an example of a two-phase, four-wire, four-amplifier connection) and examples of drive waveforms when a two-phase motor is connected with four wires and driven by four switching amplifiers Amp.

[0191] 18(a), a voltage E1+ is applied to one end of the coil L1, and a voltage E1- is applied to the other end of the coil L1. A voltage E2+ is applied to one end of the coil L2, and a voltage E2- is applied to the other end of the coil L2.

[0192] As a result, a cosine waveform is supplied to the coil L1 by the potential difference between the voltages E1+ and E1-, and a sine waveform is supplied to the coil L2 by the potential difference between the voltages E2+ and E2-.

[0193] In Figure 18(b), (1) represents the waveform of voltage E1+, (2) represents the waveform of voltage E1-, (3) represents the waveform of voltage E2+, and (4) represents the waveform of voltage E2-. In Figure 18(b), the lowest potential of both terminals of each coil is fixed to ground, and the two-wire modulated four-wire drive is used, but the potential difference between the terminals of each coil is (E1+) - (E1-) and (E2+) - (E2-), which are cosine and sine waves, respectively, and are sine waves with a 90° phase difference.

[0194] The embodiments of the present application are also applicable to such two-phase motors.

[0195] [Negative Ground and Positive Ground] In the above-described embodiment, the case of negative ground has been described as an example, but the embodiment of the present application can also be applied to the case of positive ground.

[0196] As shown in FIG. 19(a), the negative ground is a connection configuration in which the negative side of the battery in the battery pack 101 is grounded, and the voltage Eb on the half-bridge group 1030 side of the separation switch 1040 is a positive voltage. Note that the drive waveform data generator 1024 and the switching amplifier Amp are also supplied with power from the battery, and a regulator 1070 is provided for this purpose. In this case, the current condition in step S9 of FIG. 7 is a condition in which the current flowing to each coil included in the motor 105 is positive or zero. The same applies to the current condition for opening the separation switch 1040 in step S7.

[0197] On the other hand, as shown in Fig. 19(b), the positive earth is a connection configuration in which the positive side of the battery of the battery pack 101 is grounded and the voltage Eb on the half bridge group 1030 side of the separation switch 1040 is a negative voltage. In this case, the current condition in step S9 in Fig. 7 is a condition in which the current flowing to each coil included in the motor 105 is negative or zero. The same applies to the current condition for opening the separation switch 1040 in step S7.

[0198] That is, under the current conditions described above, the current flows in opposite directions between the negative ground and the positive ground, but from the perspective of power, both conditions mean that the power flowing (i.e., supplied) to each coil included in the motor 105 is either positive or zero. In other words, the condition is that the current is either flowing in the direction that consumes power from the power supply or is zero.

[0199] [Other Technical Matters] In the above-described embodiment, N-channel FETs are used as an example for the separation switch 1040 and the switches included in the half-bridge group 1030. However, N-channel and P-channel FETs may be combined for implementation. Furthermore, the switches are not limited to ordinary MOSFETs (Metal-Oxide-Semiconductor FETs), and may be bipolar transistors, IGBTs (Insulated Gate Bipolar Transistors), or the like.

[0200] Furthermore, the half bridge for each phase may be configured by connecting a plurality of half bridges in parallel.

[0201] Furthermore, although the above example shows two-wire modulated three-phase sine wave continuous energization drive, three-wire modulation, intermittent drive, etc. may also be used.

[0202] Furthermore, although PWM modulation has been described as an example, PDM (Pulse Density Modulation), PFM (Pulse Frequency Modulation), PNM (Pulse Number Modulation), etc. may also be used as long as the average duty ratios of high and low are the same.

[0203] Furthermore, the diodes shown above as parasitic diodes may not only be parasitic diodes, but may also be diodes connected in parallel to reinforce them. Even in the case of switching elements that do not have parasitic diodes, they may be bypass diodes intentionally inserted to protect the device from surges generated from the coil of the motor 105 during switching for normal operation.

[0204] The separation switch 1040 was also assumed to cut off at least the current from the motor 105 to the battery of the battery pack 101 when it was opened, but it may also be a type that cuts off the current from the battery to the motor 105 when it is opened.

[0205] While the above example shows an example of an electrically assisted bicycle 1 as an electrically assisted vehicle, the present invention is not limited to electrically assisted vehicles and may be applied to any vehicle requiring a wide rotational speed range of a brushless motor and loss-free coasting without a clutch mechanism. Examples include vehicles such as electric motorcycles, electric kick scooters, electric cars (including hybrids), and trains, as well as transportation devices such as electric propeller airplanes and electric boats (powered by, for example, a screw or Voith Schneider propeller). In some cases, the present invention may also be used to turn off a wind power generator (a motor used in regenerative mode) in strong winds (such as when excessive rotation occurs even when the propeller pitch is set to maximum).

[0206] The above-described embodiment can be summarized as follows.

[0207] The motor control device of this embodiment has (A) a drive unit including three or more sets of half bridges for driving a brushless motor with two or more phases; (B) a separation switch for cutting off current flowing at least in the regenerative direction between the drive unit and a power source by opening it; and (C) a control unit that, when an event that requires the brushless motor to be turned off is detected, performs control to execute a first step of setting the drive output of at least some of the three or more sets of half bridges to ground level or turning them off; a second step of opening the separation switch; and a third step of turning off the drive output of the half bridges of the three or more sets of half bridges whose drive output is not turned off during a period when the power flowing to the coils included in the brushless motor is positive or zero.

[0208] By performing this control, the brushless motor can be safely turned off. Note that the second and third steps may be performed simultaneously if the respective power conditions are met simultaneously. Furthermore, if multiple phases meet the power conditions in the third step, the drive output may be turned off simultaneously. Note that this embodiment is applicable not only to turning off the motor at overspeed, but also to turning off the motor at normal speed.

[0209] The first step may be a step of setting all the drive outputs of the three or more half bridges to the ground level, which allows more time for the second step to be performed and makes implementation easier.

[0210] The control unit may include (c1) a drive waveform data generation unit that generates drive waveforms for each of the three or more half bridges, and (c2) a switching signal generation unit that generates switching signals for each switching element included in the three or more half bridges based on the generated drive waveforms. In this case, the control unit may set the amplitude of the drive waveforms (e.g., drive waveforms for at least some half bridges) to zero in the first step. As a result, the drive output is set to ground level.

[0211] Furthermore, the control unit may include a drive output control unit that controls, for each of the three or more half bridges, a switching signal output to each switching element included in that half bridge so that the switching element to which the switching signal is output is opened. By introducing such a drive output control unit, it becomes possible to turn off the drive output at an appropriate timing in or before the third step by opening the high-side switching element (or, in some cases, a pair of switching elements) and the low-side switching element (or, in some cases, a pair of switching elements) for each half bridge.

[0212] In addition, in the second step, the control unit may open the separation switch while the power flowing from the power supply side to the drive unit side via the separation switch is positive or zero. For example, if not all drive outputs of the three or more half bridges are set to the ground level, the brushless motor can be safely turned off by opening the separation switch when such a power condition is met.

[0213] Furthermore, in the second step, the control unit may detect the current flowing through the separation switch and open the separation switch during a period in which the power flowing from the power supply side to the drive unit side via the separation switch is positive or zero. If the current flowing through the separation switch or a current substantially the same as the current can be detected, such a mechanism can be used to safely turn off the brushless motor.

[0214] On the other hand, in the second step, the control unit may estimate a period during which the power flowing from the power supply side to the drive unit side via the separation switch is positive or zero based on rotational phase information of the brushless motor, and open the separation switch. For example, even if it is not possible to detect the current flowing through the separation switch or a current substantially the same as that, the rotational phase information of the brushless motor (e.g., a Hall signal) may be used to identify the timing and period that satisfy the power conditions.

[0215] Furthermore, in the third step, the control unit may sequentially turn off the drive outputs of the half bridges of the three or more half bridges whose drive outputs are not turned off during a period in which the power flowing to the coils included in the brushless motor is positive or zero. The drive outputs may be turned off sequentially, or may be turned off simultaneously as long as certain conditions are met.

[0216] Furthermore, in the third step, the control unit may detect the current flowing through each drive output of the three or more half bridges, and determine the timing to turn off the drive output of a half bridge among the three or more half bridges whose drive output is not turned off during a period when the power flowing through the coils included in the brushless motor is positive or zero. If the current flowing through the coils included in the brushless motor can be detected, utilizing such a mechanism makes it possible to safely turn off the brushless motor.

[0217] On the other hand, in the third step, the control unit may estimate a period during which the power flowing to the coils included in the brushless motor is positive or zero based on rotational phase information of the brushless motor, and determine the timing to turn off the drive output of the half bridges among the three or more half bridges whose drive output is not turned off. The rotational phase information of the brushless motor (e.g., a Hall signal) may identify the timing and period that satisfy the power conditions, and this information is used.

[0218] The control unit may be configured to gradually bring the output torque of the brushless motor closer to zero by changing at least one of the duty ratio and the lead angle in the switching of the three or more half-bridges before the first step, thereby suppressing shocks that may occur when the brushless motor is turned off.

Claims

1. A motor control device having: a drive unit including three or more sets of half bridges for driving a brushless motor of two or more phases; a separation switch for cutting off current flowing at least in the regenerative direction between the drive unit and a power source by opening it; and a control unit that controls the device to execute the following steps when an event is detected in which the brushless motor should be turned off: a first step of setting the drive output of at least some of the three or more sets of half bridges to ground level or turning them off; a second step of opening the separation switch; and a third step of turning off the drive output of a half bridge of a set of the three or more sets of half bridges whose drive output is not turned off, during a period in which the power flowing to a coil included in the brushless motor is positive or zero.

2. The motor control device according to claim 1, wherein said first step is a step of setting all drive outputs of said three or more half bridges to the ground level.

3. A motor control device as described in claim 2, wherein the control unit includes: a drive waveform data generation unit that generates drive waveforms for each of the three or more sets of half bridges; and a switching signal generation unit that generates switching signals for each switching element included in the three or more sets of half bridges based on the generated drive waveforms, and the control unit sets the amplitude of the drive waveform to zero in the first step.

4. A motor control device as described in claim 1, wherein the control unit includes a drive output control unit that controls, for each of the three or more half bridges, a switching signal output to each switching element included in that half bridge so that the switching element to which the switching signal is output is opened.

5. The motor control device according to claim 1, wherein in the second step, the control unit opens the separation switch during a period in which the power flowing from the power supply side to the drive unit side via the separation switch is positive or zero.

6. A motor control device as described in claim 1, wherein in the second step, the control unit detects the current flowing through the separation switch and opens the separation switch during a period in which the power flowing from the power supply side to the drive unit side via the separation switch is positive or zero.

7. A motor control device as described in claim 1, wherein in the second step, the control unit estimates a period during which the power flowing from the power supply side to the drive unit side via the separation switch is positive or zero based on rotational phase information of the brushless motor, and opens the separation switch.

8. A motor control device as described in claim 1, wherein in the third step, the control unit sequentially turns off the drive outputs of the half-bridges of the three or more pairs of half-bridges whose drive outputs are not turned off during a period in which the power flowing to a coil included in the brushless motor is positive or zero.

9. A motor control device as described in claim 1, wherein in the third step, the control unit detects the current flowing through each drive output of the three or more sets of half bridges, and determines the timing to turn off the drive output of a half bridge of the three or more sets of half bridges whose drive output is not turned off during a period when the power flowing to a coil included in the brushless motor is positive or zero.

10. A motor control device as described in claim 1, wherein in the third step, the control unit estimates a period during which the power flowing to the coils included in the brushless motor is positive or zero based on rotational phase information of the brushless motor, and determines the timing to turn off the drive output of a half-bridge among the three or more sets of half-bridges that has not had its drive output turned off.

11. The motor control device according to claim 1, wherein, before the first step, the control unit controls the output torque of the brushless motor to gradually approach zero by changing at least one of the duty ratio and the advance angle in the switching of the three or more sets of half bridges.

12. A transport device having a motor control device according to claim 1.

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