Motor control device, motor control system, and control method

Abstract

A motor control device (100) has an inverter circuit (20) and a control / drive circuit (30) that supplies a drive signal for controlling a motor (10) to each switch element constituting a plurality of switch element pairs of the inverter circuit (20). The control / drive circuit (30) performs control for supplying the drive signal to each switch element so as to alternately repeat, as deceleration control for reducing the rotational speed of the motor (10), an all-off mode in which all the switch elements are turned off and a short brake mode in which one switch element group among all the upper switch elements and all the lower switch elements is turned on and the other switch element group among all the upper switch elements and all the lower switch elements is turned off.

Description

Motor control device, motor control system, and control method

[0001] The present disclosure relates to a motor control device and the like.

[0002] For the deceleration control of a motor by a motor control device, there is, for example, one disclosed in Patent Document 1. When the motor control device of Patent Document 1 decelerates the motor from a high rotation state to a low rotation state, it drives all of a plurality of upper switch elements to be off and all of a plurality of lower switch elements to be on, as shown in (b) of FIG. 2 described later, or drives all of the plurality of upper switch elements to be on and all of the plurality of lower switch elements to be off, and performs short brake control which is a control method.

[0003] Japanese Patent Application Laid-Open No. 2008-228474

[0004] The short brake control described in Patent Document 1 has a problem that the deceleration is too rapid and the load stress on the motor becomes large. Particularly in the case of a fan motor, if the deceleration is too rapid, a high load is applied to the blades.

[0005] Therefore, the present disclosure provides a motor control device and the like that can reduce the load stress on the motor during deceleration.

[0006] The motor control device according to the present disclosure includes a plurality of switch element pairs each including an upper switch element and a lower switch element, an inverter circuit that drives the motor, and a control drive circuit that supplies drive signals for controlling the motor to each of the switch elements constituting the plurality of switch element pairs of the inverter circuit. The control drive circuit performs control to supply the drive signals to the respective switch elements so as to alternately repeat an all-off mode in which all of the switch elements constituting the plurality of switch element pairs are turned off and a short brake mode in which one of the switch element groups of all of the upper switch elements and all of the lower switch elements constituting the plurality of switch element pairs is turned on and the other switch element group of all of the upper switch elements and all of the lower switch elements is turned off, as deceleration control for reducing the rotational speed of the motor.

[0007] The motor control system according to this disclosure comprises the motor control device described above and the motor driven by the motor control device.

[0008] The control method according to this disclosure is a control method for a motor control device having an inverter circuit for driving a motor, which has a plurality of switch element pairs consisting of upper switch elements and lower switch elements, wherein the control method has a total off mode in which all switch elements constituting the plurality of switch element pairs are turned off, and a short brake mode in which one of the switch element groups of all upper switch elements and all lower switch elements constituting the plurality of switch element pairs is turned on, and the other switch element group of all upper switch elements and all lower switch elements is turned off, and in the control method, as a deceleration control to reduce the rotational speed of the motor, a drive signal is supplied to each switch element constituting the plurality of switch element pairs so as to alternately repeat the total off mode and the short brake mode.

[0009] These comprehensive or specific embodiments may be implemented as a system, method, integrated circuit, computer program, or recording medium such as a computer-readable CD-ROM, or as any combination of a system, method, integrated circuit, computer program, and recording medium.

[0010] According to one aspect of this disclosure, a motor control device, etc., can reduce the load stress on the motor during deceleration.

[0011] This is a circuit diagram showing an example of a motor control system according to an embodiment. Figure 2(a) is a circuit diagram showing the state of a three-phase motor in the fully off state, Figure 2(b) is a circuit diagram showing an example of a short-brake state of a three-phase motor, Figure 2(c) is a circuit diagram showing the state of a single-phase motor in the fully off state, and Figure 2(d) is a circuit diagram showing an example of a short-brake state of a single-phase motor. This is a flowchart of a first embodiment of deceleration control of a motor control device according to an embodiment. This is a waveform diagram showing the change in motor rotation speed in the first embodiment of deceleration control of a motor control device according to an embodiment. This is a flowchart of a modified example of the first embodiment of deceleration control of a motor control device according to an embodiment. This is a flowchart of a second embodiment of deceleration control of a motor control device according to an embodiment. This is a waveform diagram showing the change in motor rotation speed in the second embodiment of deceleration control of a motor control device according to an embodiment. This is an operation waveform diagram during short-brake in a third embodiment of deceleration control of a motor control device according to an embodiment. This is another operation waveform diagram during short-brake in a third embodiment of deceleration control of a motor control device according to an embodiment. This is yet another operation waveform diagram during short-brake in a third embodiment of deceleration control of a motor control device according to an embodiment. This is an operation waveform diagram for the transition from short brake mode to full off mode in the third embodiment of the deceleration control of the motor control device according to the embodiment. This is a flowchart for the fourth embodiment of the deceleration control of the motor control device according to the embodiment. This is a waveform diagram showing the change in motor rotation speed in the fourth embodiment of the deceleration control of the motor control device according to the embodiment. This is a flowchart for the fifth embodiment of the deceleration control of the motor control device according to the embodiment. This is a waveform diagram showing the change in motor rotation speed in the fifth embodiment of the deceleration control of the motor control device according to the embodiment.

[0012] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, components, and their arrangement and connection configurations shown in the following embodiments are examples only and are not intended to limit this disclosure.

[0013] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, the scale and other aspects may not necessarily be consistent across all figures. In addition, the same reference numerals are used for substantially identical components in each figure, and redundant explanations are omitted or simplified.

[0014] (Embodiment) The motor control system and motor control device according to the embodiment will be described below.

[0015] Figure 1 is a circuit diagram showing an example of a motor control system 1 according to an embodiment. The motor control system 1 comprises a motor control device 100 and a motor 10 driven by the motor control device 100. The motor 10 is a brushless motor, such as a fan motor. For example, as shown in Figure 1, the motor 10 is a three-phase motor having three-phase windings of U-phase, V-phase, and W-phase connected in a star configuration. Note that the motor 10 may also be a single-phase motor (motor 10A shown in Figure 2, which will be described later).

[0016] The inverter circuit 20 has multiple pairs of switch elements, each consisting of an upper switch element and a lower switch element, to drive the motor 10. For example, as shown in Figure 1, the inverter circuit 20 has three pairs of switch elements, each consisting of an upper switch element and a lower switch element, and the three pairs of switch elements are connected between the power supply and ground, forming a bridge circuit that supplies drive current to each phase of the motor 10 to control the operation of the motor 10. Specifically, a pair of switch elements consisting of an upper switch element 21 and a lower switch element 22 supplies drive current to the U phase of the motor 10. In addition, a pair of switch elements consisting of an upper switch element 23 and a lower switch element 24 supplies drive current to the V phase of the motor 10. Furthermore, a pair of switch elements consisting of an upper switch element 25 and a lower switch element 26 supplies drive current to the W phase of the motor 10. The output voltages of the inverter circuit 20 to each phase of the motor 10 are Vu, Vv, and Vw, and the neutral point voltage of the motor 10 is Vc.

[0017] The control drive circuit 30 supplies drive signals to control the motor 10 to each switch element constituting a plurality of switch element pairs in the inverter circuit 20. For example, as shown in Figure 1, the control drive circuit 30 generates and outputs drive signals UH for the upper switch element 21 that supplies power to the U phase, VH for the upper switch element 23 that supplies power to the V phase, WH for the upper switch element 25 that supplies power to the W phase, UL for the lower switch element 22 that supplies power to the U phase, VL for the lower switch element 24 that supplies power to the V phase, and WL for the lower switch element 26 that supplies power to the W phase, in order to control the inverter circuit 20. Although not shown in the figures, in this disclosure each switch element has a body diode, such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Alternatively, if there is no body diode, a flywheel diode is assumed to be connected in antiparallel.

[0018] The detection circuit 40 detects the rotational speed of the motor 10. The detection circuit 40 detects the voltage of each phase, compares it with the neutral point voltage Vc to detect and count the zero-crossing point, and transmits a rotational speed signal indicating the rotational speed of the motor 10 to the control drive circuit 30. Although not shown in the figure, the control drive circuit 30 supplies a drive signal to the inverter circuit 20 to control the rotational speed of the motor 10 according to instructions from the higher command unit. Below, the deceleration control that reduces the rotational speed of the motor 10 (i.e., lowers the rotational speed of the motor 10) will be explained using Figure 2.

[0019] Figure 2(a) is a circuit diagram showing the motor 10 in the fully off state, Figure 2(b) is a circuit diagram showing an example of the motor 10 in the short brake state, Figure 2(c) is a circuit diagram showing the motor 10A in the fully off state, and Figure 2(d) is a circuit diagram showing an example of the motor 10A in the short brake state. Motor 10 may be a single-phase motor (motor 10A) as shown in Figures 2(c) and 2(d).

[0020] To decelerate the motor 10, the current supplied to the motor 10 is reduced by decreasing the duty cycle of the drive signal to the inverter circuit 20. Figure 2(a) shows an all-off mode in which the duty cycle of all drive signals is set to zero, i.e., all switch elements are turned off. However, with this deceleration method, even if the supplied current is reduced, the motor 10 continues to rotate due to mechanical inertia, so it takes a considerable amount of time to stop or reach the target rotational speed. The deceleration control disclosed in Patent Document 1 is a method called short brake, in which all upper switch elements are driven to the off position and all lower switch elements are driven to the on position, or all upper switch elements are driven to the on position and all lower switch elements are driven to the off position. Figure 2(b) shows an example of a short brake mode in which all upper switch elements 21, 23 and 25 are driven to the off position and all lower switch elements 22, 24 and 26 are driven to the on position. When such a short brake is used, the voltage across all the windings that make up the motor 10 becomes zero, so a strong brake is applied and the rotational speed is reduced rapidly.

[0021] Although the motor 10 shown in Figure 1 and Figure 2(a) and Figure 2(b) is a three-phase motor, it may also be a single-phase motor. In this case, an inverter circuit 20A is used instead of the inverter circuit 20. For example, the inverter circuit 20A has a pair of switch elements consisting of an upper switch element 21A and a lower switch element 22A, and a pair of switch elements consisting of an upper switch element 23A and a lower switch element 24A. Figure 2(c) shows the all-off mode in which all switch elements in the inverter circuit 20A driving a single-phase motor 10A are turned off. Figure 2(d) shows the short-brake mode in which the upper switch elements 21A and 23A in the inverter circuit 20A driving a single-phase motor 10A are all turned off, and the lower switch elements 22A and 24A are all turned on.

[0022] In the following embodiments, the operation of the motor control device 100 of this disclosure will be explained assuming a three-phase motor 10 and an inverter circuit 20, but the basic operation and effects will not change even if the motor 10 is a single-phase motor. Furthermore, the explanation will be given in a short-circuit brake mode in which all lower switch elements are conductive, but the basic operation and effects will not change even in a short-circuit brake mode in which all upper switch elements are conductive.

[0023] (First Embodiment) Figure 3 is a flowchart showing a first embodiment of the deceleration control of the motor control device 100 according to the embodiment. Figure 4 is a waveform diagram showing the change in the rotational speed of the motor 10 in the first embodiment of the deceleration control of the motor control device 100 according to the embodiment, where the vertical axis is rotational speed and the horizontal axis is time. The first embodiment of the deceleration control of the motor control device 100 will be described below using Figures 3 and 4.

[0024] When deceleration begins at time t0 in Figure 4, the control drive circuit 30 enters a short brake (abbreviated as SB in the figure) mode, which drives all upper switch elements to turn off and all lower switch elements to turn on (step S11). As a result, the rotational speed of the motor 10 decreases rapidly.

[0025] The control drive circuit 30 measures the time in short brake mode and determines whether the time in short brake mode exceeds a first set time (step S12: time determination 1). The first set time is not particularly limited and is set as appropriate. If the time in short brake mode is less than or equal to the first set time, the short brake mode is maintained.

[0026] At time t1, when the short brake mode time reaches the first set time, the control drive circuit 30 resets the timing and enters a fully off mode, turning off all switch elements (step S13). As a result, the braking action is mitigated.

[0027] The control drive circuit 30 measures the time in the all-off mode and determines whether the time in the all-off mode exceeds a second set time (step S14: time determination 2). The second set time is not particularly limited and is set as appropriate. If the time in the all-off mode is less than or equal to the second set time, the all-off mode is maintained.

[0028] At time t2, when the time in the all-off mode reaches the second set time, the control drive circuit 30 resets the timing and returns to the short brake mode. The short brake mode is maintained for only the first set time until time t3, and from time t3 it returns to the all-off mode. In this way, the motor 10 is decelerated by repeatedly alternating between the short brake mode and the all-off mode. The average slope of the rotational speed reduction (hereinafter also referred to as the deceleration speed) can be adjusted by the first set time and the second set time.

[0029] On the other hand, the control drive circuit 30 terminates deceleration control when the rotational speed of the motor 10 reaches a predetermined target value after the start of deceleration control. For example, the detection circuit 40 detects the rotational speed of the motor 10 by detecting the induced voltage generated in the windings of the motor 10 in the all-off mode, and the control drive circuit 30 receives feedback on the rotational speed of the motor 10 from the rotational speed signal from the detection circuit 40 and compares it with a predetermined target value. As shown in the flowchart of Figure 3, the control drive circuit 30 determines the rotational speed at the end of the all-off mode (step S15: rotational speed determination), and terminates deceleration control if the rotational speed is less than or equal to a predetermined target value (step S16). The reason why the rotational speed is determined at the end of the all-off mode is that if all switch elements are in the off state, the induced voltage generated in the windings of the motor 10 through which no current is flowing can be detected, and the rotational speed of the motor 10 can be detected by detecting the zero-crossing point by comparing it with the neutral point voltage Vc. In the short-circuit brake mode, when all lower switch elements are turned on, it is difficult to detect the induced voltage, and therefore it is also difficult to detect the rotational speed of the motor 10. Therefore, in Patent Document 1, which determines the rotational speed of a motor during short braking, the rotational speed is detected by detecting the rotational position using a Hall element (position sensor). In contrast, the motor control device 100, which has a fully off mode during deceleration control, can detect the rotational speed of the motor 10 without a sensor.

[0030] As shown in Figure 4, for example, if the rotational speed of the motor 10 falls below a predetermined target value at time t4 during the short brake mode, the deceleration control ends at time t6 when the all-off mode ends from time t5. In this embodiment, since the ultimate goal of the deceleration control is to stop, the predetermined target value of the rotational speed is set to a value close to zero, and the all-off mode is maintained even after the deceleration control ends until a stop is reached. If the ultimate goal is not to stop, the control drive circuit 30 returns to normal operation, controlling the drive signal with PWM to maintain the target rotational speed.

[0031] As described above, in the motor control device 100 of this embodiment, the control drive circuit 30 supplies a drive signal to each switch element to perform deceleration control to reduce the rotational speed of the motor 10 by alternately repeating between a full-off mode, in which all switch elements constituting the plurality of switch element pairs of the inverter circuit 20 are turned off, and a short-brake mode, in which one group of switch elements from all the upper switch elements and all the lower switch elements constituting the plurality of switch element pairs of the inverter circuit 20 is turned on, and the other group of switch elements from all the upper switch elements and all the lower switch elements is turned off. Since deceleration control is performed by alternately repeating the short-brake mode and the full-off mode, it is possible to decelerate the motor 10 more significantly than deceleration control using only the full-off mode, and more gradually than deceleration control using only the short-brake mode. For this reason, the load stress on the motor 10 during deceleration can be reduced compared to deceleration control using only the short-brake mode. In addition, unnecessary vibrations and noise can be suppressed by the gradual deceleration. The speed of deceleration can be adjusted by the first set time of the short-brake mode and the second set time of the full-off mode.

[0032] Although the flowchart in Figure 3 shows the rotational speed being determined at the end of the fully off mode, this disclosure is not limited to this. As shown in Patent Document 1, the rotational speed can also be detected in the short brake mode by using a sensor such as a Hall element. Figure 5 is a flowchart showing a modified example of the first embodiment of deceleration control of the motor control device 100 according to the embodiment. For example, as shown in the flowchart of Figure 5, the rotational speed determination may be performed both in the short brake mode (step S17 before time determination 1 in the flowchart) and in the fully off mode (step S18 before time determination 2 in the flowchart). This allows the deceleration control to be terminated quickly when the rotational speed of the motor 10 reaches the target value.

[0033] The method for detecting the rotational speed of the motor 10 without a sensor in short-braking mode will be described later in the third embodiment.

[0034] (Second Embodiment) Figure 6 is a flowchart showing a second embodiment of the deceleration control of the motor control device 100 according to the embodiment. Figure 7 is a waveform diagram showing the change in the rotational speed of the motor 10 in the second embodiment of the deceleration control of the motor control device 100 according to the embodiment, where the vertical axis is rotational speed and the horizontal axis is time. The second embodiment differs from the first embodiment in that a first target value is set, which is the target rotational speed in the fully off mode during deceleration control until the rotational speed of the motor 10 reaches a predetermined target value after deceleration (hereinafter referred to as the final target value). The second embodiment of the deceleration control of the motor control device 100 will be described below with reference to Figures 6 and 7.

[0035] When deceleration begins at time t0 in Figure 7, the control drive circuit 30 enters a short brake (abbreviated as SB in the figure) mode, which drives all upper switch elements to turn off and all lower switch elements to turn on (step S21). As a result, the rotational speed of the motor 10 decreases rapidly.

[0036] The control drive circuit 30 measures the time in short brake mode and determines whether the time in short brake mode exceeds a first set time (step S22: time determination). If the time in short brake mode is less than or equal to the first set time, the short brake mode is maintained.

[0037] At time t1, when the short brake mode time reaches the first set time, the control drive circuit 30 switches to a fully off mode, turning off all switch elements (step S23). As a result, the braking action is mitigated.

[0038] The control drive circuit 30 receives feedback on the rotational speed of the motor 10 in the fully off mode from the rotational speed signal from the detection circuit 40, and determines whether the rotational speed of the motor 10 exceeds a first target value (step S24: rotational speed determination 1). The first target value is a value that changes during deceleration control until it reaches the final target value, as shown in Figure 7, and is set separately from the final target value. In the fully off mode, if the rotational speed of the motor 10 reaches (exceeds) the first target value, the control drive circuit 30 switches back to the short brake mode. In the fully off mode, if the rotational speed of the motor 10 does not exceed the first target value, the control drive circuit 30 determines whether the rotational speed of the motor 10 is less than or equal to the final target value (step S25: rotational speed determination 2), and if the rotational speed of the motor 10 is greater than the final target value, the fully off mode is maintained.

[0039] At time t2 in Figure 7, the control drive circuit 30 enters short-brake mode when the rotational speed of the motor 10 exceeds the first target value. This short-brake mode is maintained for a first set time until time t3, at which point it returns to the full-off mode. In this manner, the motor decelerates by alternately switching between short-brake mode and full-off mode so that the rotational speed follows the first target value.

[0040] In Figure 6, if the rotational speed of the motor 10 falls below the final target value in rotational speed determination 2, the deceleration control ends (step S26). In Figure 7, for example, if the rotational speed of the motor 10 falls below the final target value at time t4 during short brake mode, the control drive circuit 30 enters full off mode from time t5. In rotational speed determination 1 in Figure 6, it is determined that the rotational speed of the motor 10 is below the first target value, and subsequently in rotational speed determination 2, it is determined that it is below the final target value, and the deceleration control ends at time t6. In this embodiment, after the deceleration control ends, the control drive circuit 30 returns to normal operation, controlling the drive signal with PWM to maintain the target rotational speed. If stopping is the final goal, as in the first embodiment, the final target value of the rotational speed of the motor 10 is set to a value close to zero, and the full off mode is maintained even after the deceleration control ends until stopping.

[0041] As described above, in addition to the final target value, a first target value is set that changes during deceleration control until it reaches the final target value. The control drive circuit 30 may switch to short brake mode when the rotational speed of the motor 10 reaches the first target value in the fully off mode. If the rotational speed of the motor 10 exceeds the first target value during deceleration control in the fully off mode, the deceleration of the motor 10 at that point is too gradual, so the control drive circuit 30 can switch to short brake mode to increase the deceleration. Therefore, deceleration control can be performed so that the rotational speed of the motor 10 is in line with the first target value.

[0042] (Third Embodiment) In the first and second embodiments, an example was described in which sensorless detection of rotational speed during deceleration control of the motor 10 is performed in the fully off mode. However, this disclosure is not limited to this method and may also be performed in the short brake mode. This is because an induced voltage is generated when the rotor is rotating, even in the short brake mode.

[0043] Figure 8 is an operating waveform diagram during short braking in a third embodiment of the deceleration control of the motor control device 100 according to the embodiment. Figure 8 shows the phase voltages Vu, Vv, and Vw in the short braking mode, and the narrow pulse BEMF generated at the zero-crossing timing when the polarity of each phase voltage changes from negative to positive. In the short braking mode, all lower switch elements are in the ON state, so the generated induced voltage is observed as a voltage with a small amplitude (for example, about ±0.1V) relative to the ground voltage. Therefore, if the comparator that determines the zero-crossing of the induced voltage has the sensitivity to detect this voltage change, it is possible to detect the rotational speed even in the short braking mode. For example, the time from one zero-crossing to the next zero-crossing corresponds to the rotation period (in the case of a three-phase motor, it corresponds to 1 / 3 of the rotation period), so if this time becomes longer than the time corresponding to the target rotational speed (in the case of a three-phase motor, it corresponds to 1 / 3 of the target rotation period), it can be determined that the rotational speed has fallen below the target speed.

[0044] Thus, the detection circuit 40 may detect the rotational speed of the motor 10 by detecting the voltage of one of the conducting switch element groups (for example, all the lower-side switch elements) in the short brake mode. Even in the short brake mode, a minute induced voltage is generated if the rotor is rotating. Therefore, if a comparator that determines the zero crossing of the induced voltage has sensitivity capable of detecting such minute changes in the induced voltage, the rotational speed of the motor 10 can be detected even in the short brake mode.

[0045] Note that, for sensorless detection of the rotational speed of the motor 10 in the short brake mode, it is not necessary to drive all the lower-side switch elements to be on. Even if a lower-side switch element through which current flows from the ground GND to the winding is turned off, current flows through its body diode (or a flywheel diode if the switch element does not have a body diode), so the short brake mode is maintained. A forward voltage drop of the body diode of approximately 1 V occurs as a negative voltage in the turned-off lower-side switch element compared to when it is turned on.

[0046] FIG. 9 is another operation waveform diagram during short braking in the third embodiment of the deceleration control of the motor control device 100 according to the embodiment. FIG. 9 shows each phase voltage Vu, Vv, and Vw and their drive signals UL, VL, and WL when turning off the lower-side switch element that has become a negative voltage in the short brake mode.

[0047] At time t0, the current of the lower-side switch element 26 of the W phase, in which the body diode was conducting in the off state, disappears, and the W-phase voltage Vw of the generated negative voltage suddenly becomes zero voltage, and the detection circuit 40 detects the zero crossing of the W-phase voltage Vw. At the same time, the control drive circuit 30 sets the drive signal UL to the L level and turns off the lower-side switch element 22 of the U phase. Since the current flows through the body diode of the lower-side switch element 22 of the U phase, a forward voltage drop of the body diode of approximately 1 V occurs as a negative voltage in the U-phase voltage Vu.

[0048] At time t1, when the current of the body diode of the lower switch element 22 of the U-phase becomes zero, the U-phase voltage Vu also quickly becomes zero. At this timing, the control drive circuit 30 raises the drive signal UL to the H level to turn on the lower switch element 22 of the U-phase, and at the same time, the detection circuit 40 detects the zero crossing of the U-phase voltage Vu. At the same time, the control drive circuit 30 turns off the lower switch element 24 of the V-phase. At time t2 when the V-phase voltage Vv becomes zero from -1V, the control drive circuit 30 turns on the lower switch element 24 of the V-phase, and the detection circuit 40 detects the zero crossing of the V-phase voltage Vv. At the same time, the control drive circuit 30 turns off the lower switch element 26 of the W-phase. At time t3 when the W-phase voltage Vw becomes zero from -1V, the detection circuit 40 detects the zero crossing of the W-phase voltage Vw.

[0049] As described above, in the short brake mode, the control drive circuit 30 turns off one lower switch element that discharges current to the motor 10 (that is, flows current toward the motor 10) among all the lower switch elements as one switch element group, and the detection circuit 40 may detect, as the zero crossing point, the point at which the voltage of the switch element changes when the body diode of the one lower switch element or the flywheel diode connected in parallel to the one lower switch element becomes non-conductive. Since current flows through the body diode or the flywheel diode even when the above one lower switch element is turned off, the short brake mode is maintained. Since a forward voltage drop occurs in the turned-off lower switch element compared to when it is turned on, the timing at which this voltage suddenly becomes zero voltage can be detected as the zero crossing. Since the forward voltage drop is about 1V in magnitude, the zero crossing of each phase induced voltage in the short brake mode can be detected without requiring a highly sensitive comparator, that is, the rotational speed can be detected.

[0050] Note that in the method of turning off the lower switch element as described above and using the voltage drop of the body diode, since a loss of current × forward voltage drop occurs, it is preferable that the period during which current flows through the body diode is short.

[0051] Figure 10 is yet another waveform diagram of operation during short braking in a third embodiment of the deceleration control of the motor control device 100 according to the embodiment.

[0052] As shown in Figure 10, the control drive circuit 30 stores the zero-cross detection period (t1-t0), and at time t01, after a time elapsed of, for example, 70% (0.7(t1-t0)) of the stored period from the U-phase zero-cross (t1), it turns off the V-phase lower switch element 24 and allows current to flow through the body diode of the lower switch element 24.

[0053] At time t2, the current flowing through the body diode of the lower V-phase switch element 24 ceases, and the detection circuit 40 detects the zero-crossing of the V-phase voltage Vv. Next, the control drive circuit 30 turns off the lower W-phase switch element 26 at time t12, which is, for example, 70% of the period (t2-t1) of this zero-crossing detection, and allows current to flow through the body diode of the lower switch element 26.

[0054] At time t3, the current flowing through the body diode of the lower W-phase switch element 26 ceases, and the detection circuit 40 detects the zero-crossing of the W-phase voltage Vw. By repeating this process sequentially, even if the rotational speed of the motor 10 changes (although not shown in the diagram, the rotational speed decreases moment by moment due to deceleration control), the body diode conduction period can be limited to 30% of the total.

[0055] Thus, in the short-circuit brake mode, the control drive circuit 30 may set the timing for turning off one of the lower switch elements that supplies current to the motor 10 based on the previous zero-crossing point occurrence period. By taking advantage of the fact that the zero-crossing point occurrence period does not change significantly from the previous time, the timing for turning off the lower switch element can be set just before the timing at which the zero-crossing is estimated to occur this time, based on the previous zero-crossing point occurrence period. This shortens the period during which current flows through the body diode or flywheel diode, thereby suppressing the losses incurred.

[0056] As described above, if the rotational speed of the motor 10 can be detected even in short-braking mode, the deceleration control can be quickly terminated when the rotational speed of the motor 10 reaches the target value, as shown in the flowchart of Figure 5.

[0057] Furthermore, when switching from short-circuit brake mode to all-off mode, if the lower switch element 26 is turned off while a suction current is flowing from the W-phase winding to the lower switch element 26, for example, regenerative current will flow to the power supply side via the body diode of the upper switch element 25 of the W-phase, causing the power supply voltage Vdd to rise. To avoid this, instead of turning off all lower switch elements simultaneously when switching from short-circuit brake mode to all-off mode, the lower switch element through which the suction current is flowing should remain in the ON state, and should be turned off only after the suction current has disappeared (or fallen below a predetermined current).

[0058] Figure 11 is an operation waveform diagram of the motor control device 100 according to the embodiment when transitioning from short brake mode to all-off mode in a third embodiment of deceleration control. Figure 11 shows the currents Iu, Iv, and Iw of each lower switch element, the narrow pulse BEMF generated at the zero-cross timing when the polarity of each phase voltage changes from negative to positive, and the drive signals UL, VL, and WL during the switching operation from short brake mode to all-off mode. During the period on the left side of Figure 11, the control drive circuit 30 is in short brake mode, with all lower switch elements turned on.

[0059] If the switching operation from short brake mode to full off mode is initiated at time t0, the short brake mode is maintained until the zero-crossing point at time t1. In the case of Figure 11, time t1 is the zero-crossing point of the U phase, at which point the current in the U phase becomes zero, the lower switch element 24 of the V phase discharges current, and the lower switch element 26 of the W phase absorbs current.

[0060] At time t1, the control drive circuit 30 turns off the lower switch element 22 of the U phase and the lower switch element 24 of the V phase. No current flows through the lower switch element 22 of the U phase, and the discharge current that was flowing through the lower switch element 24 of the V phase flows through the body diode of the lower switch element 24 of the V phase, the winding of the motor 10, and the lower switch element 26 of the W phase and decays. This current becomes zero at time t2, and although the lower switch element 26 of the W phase is on, the body diode of the lower switch element 24 of the V phase becomes non-conducting, so no more current flows thereafter. The lower switch element 26 of the W phase should be turned off after this time t2. Since the voltage Vu of the lower switch element 22 of the U phase and the voltage Vv of the lower switch element 24 of the V phase are the voltages between the power supply voltage Vdd and ground GND, an induced voltage is generated as the motor 10 rotates, so the zero-crossing of the induced voltage can be detected. In Figure 11, at time t3 when the zero-crossing point of the U phase is detected, the lower switch element 26 of the W phase is turned off, and the system completely transitions to the all-off mode.

[0061] Thus, in deceleration control, when transitioning from short brake mode to all off mode, the control drive circuit 30 may maintain the ON state of one of the lower switch elements that is drawing current from the motor 10, as one of the group of switch elements, until current stops flowing to that switch element, or until the current flowing to that switch element falls below a predetermined value. By turning off the switch element after current stops flowing to the lower switch element through which the drawing current is flowing, or after the current flowing to that switch element falls below a predetermined value, the rise in power supply voltage can be suppressed.

[0062] In this embodiment, we have described an example where one group of switch elements that turns on in short-brake mode consists of all the lower switch elements, and the other group of switch elements that turns off in short-brake mode consists of all the upper switch elements. However, it is also possible for one group of switch elements that turns on in short-brake mode to consist of all the upper switch elements, and the other group of switch elements that turns off in short-brake mode to consist of all the lower switch elements.

[0063] In this case, the control drive circuit 30, in short-circuit brake mode, turns off one of the upper switch elements that is drawing current from the motor 10 (i.e., receiving current from the motor 10) as one of the group of switch elements, and the detection circuit 40 may detect the point at which the voltage of the switch element changes due to the body diode of the upper switch element or the flywheel diode connected in parallel to the upper switch element becoming non-conductive as the zero-crossing point. Even when the upper switch element is turned off, current flows through the body diode or flywheel diode, so the short-circuit brake mode is maintained. Since a forward voltage drop occurs in the turned-off upper switch element compared to when it is turned on, the timing at which this voltage abruptly becomes zero voltage can be detected as the zero-crossing point. Since the forward voltage drop is approximately 1V, the zero-crossing of the phase induction voltage in short-circuit brake mode can be detected without requiring a highly sensitive comparator, and thus the rotational speed can be detected.

[0064] Furthermore, in short-circuit brake mode, the control drive circuit 30 may set the timing for turning off one of the upper switch elements that draws current from the motor 10 based on the previous zero-crossing point occurrence period. By taking advantage of the fact that the zero-crossing point occurrence period does not change significantly from the previous time, the timing for turning off the upper switch element can be set just before the timing at which the zero-crossing is estimated to occur this time, based on the previous zero-crossing point occurrence period. This shortens the period during which current flows through the body diode or flywheel diode, thereby suppressing the losses incurred.

[0065] Furthermore, in deceleration control, when transitioning from short brake mode to all off mode, the control drive circuit 30 may maintain the ON state of one of the upper switch elements that is in the ON state and is discharging current to the motor 10, until current stops flowing to that switch element, or until the current flowing to that switch element falls below a predetermined value. By turning off the upper switch element that is discharging current after current stops flowing to it, or after the current flowing to it falls below a predetermined value, the rise in power supply voltage can be suppressed.

[0066] (Fourth Embodiment) Figure 12 is a flowchart showing a fourth embodiment of the deceleration control of the motor control device 100 according to the embodiment. Figure 13 is a waveform diagram showing the change in the rotational speed of the motor 10 in the fourth embodiment of the deceleration control of the motor control device 100 according to the embodiment. As explained in the third embodiment, if the rotational speed of the motor 10 can be detected even in short brake mode, a first target value and a second target value that is a predetermined value lower than the first target value can be set as target values ​​for the rotational speed of the motor 10 during deceleration control, as shown in the flowchart of Figure 12 and the waveform diagram of Figure 13, and deceleration control can be performed so that the rotational speed of the motor 10 moves between the first target value and the second target value. The fourth embodiment of the deceleration control of the motor control device 100 will be described below with reference to Figures 12 and 13.

[0067] When deceleration begins at time t0 in Figure 13, the control drive circuit 30 enters a short brake (abbreviated as SB in the figure) mode, which drives all upper switch elements to turn off and all lower switch elements to turn on (step S31). This rapidly reduces the rotational speed of the motor 10.

[0068] The control drive circuit 30 receives feedback on the rotational speed of the motor 10 in short-brake mode from the rotational speed signal from the detection circuit 40, and determines whether the rotational speed of the motor 10 has fallen below a second target value (step S32: rotational speed determination 2). The second target value is a value that changes during deceleration control until it reaches the final target value, as shown in Figure 13, and is set separately from the final target value. Also, the second target value is smaller than the first target value. If the rotational speed of the motor 10 is greater than the second target value, the short-brake mode is maintained.

[0069] At time t1, when the rotational speed of the motor 10 reaches the second target value, the control drive circuit 30 enters a fully off mode, turning off all switch elements (step S33). As a result, the braking action is mitigated.

[0070] The control drive circuit 30 receives feedback on the rotational speed of the motor 10 in the fully off mode from the rotational speed signal from the detection circuit 40, and determines whether the rotational speed of the motor 10 exceeds a first target value (step S34: rotational speed determination 1). In the fully off mode, if the rotational speed of the motor 10 is less than or equal to the first target value, the control drive circuit 30 maintains the fully off mode. In the fully off mode, if the rotational speed of the motor 10 exceeds the first target value, the control drive circuit 30 determines whether the rotational speed of the motor 10 is less than or equal to the final target value (step S35: rotational speed determination 3). If the rotational speed of the motor 10 is greater than the final target value, the control drive circuit 30 switches back to the short brake mode.

[0071] At time t2 in Figure 13, the control drive circuit 30 enters short-brake mode when the rotational speed of the motor 10 exceeds the first target value. This short-brake mode is maintained until the rotational speed reaches the second target value at time t3, at which point it transitions back to the full-off mode. In this way, the motor 10 is decelerated by repeatedly switching between short-brake mode and full-off mode so that its rotational speed falls between the first target value and the second target value, which is a predetermined value lower than the first target value.

[0072] In the rotation speed determination 3 of Figure 12, if the rotation speed of the motor 10 falls below the final target value, the deceleration control is terminated (step S36). The subsequent steps are the same as in the second embodiment, so the explanation of the termination of deceleration control and the operation after the deceleration control is terminated is omitted.

[0073] As described above, in addition to the final target value, a second target value is set that changes during deceleration control until it reaches the final target value. The control drive circuit 30 may switch to a fully off mode when the rotational speed of the motor 10 reaches the second target value in short brake mode. If the rotational speed of the motor 10 falls below the second target value during deceleration control in short brake mode, the deceleration of the motor 10 at that point is too large, so the control can switch to a fully off mode to slow down the deceleration. Therefore, deceleration control can be performed so that the rotational speed of the motor 10 is in line with the second target value. Furthermore, the speed of deceleration is adjusted to fall between the first target value and the second target value.

[0074] In this embodiment, an example in which both the first and second target values ​​are set has been described, but the first target value does not necessarily have to be set.

[0075] Furthermore, in this embodiment, the control drive circuit 30 may perform the deceleration control of the second or third embodiment.

[0076] (Fifth Embodiment) This disclosure can also be applied to the operation of decelerating the reverse rotation when the motor 10 is rotating in the reverse direction due to a headwind or the like before starting up. Figure 14 is a flowchart of the fifth embodiment of the deceleration control of the motor control device 100 according to the embodiment. Figure 15 is a waveform diagram showing the change in the rotational speed of the motor 10 in the fifth embodiment of the deceleration control of the motor control device 100 according to the embodiment. Figure 14 is a flowchart of the motor control device 100 when it is started up, and Figure 15 is a waveform diagram showing the deceleration control when it is rotating in the reverse direction. The fifth embodiment of the deceleration control during the start-up operation of the motor control device 100 will be described below using Figures 14 and 15.

[0077] First, as shown in Figure 14, when the motor control device 100 is started, the detection circuit 40 determines the rotation status of the motor 10 (step S41: rotation determination).

[0078] If the motor is rotating in the forward direction due to inertia since the last operation stopped, the rotational speed is detected by detecting the zero-crossing of the induced voltage generated in each winding, and the control drive circuit 30 switches to normal control such as PWM control (step S48).

[0079] If no induced voltage is generated in each winding, the motor 10 is stopped and its position cannot be detected, so the control drive circuit 30 forcibly applies an AC voltage to rotate the motor 10 (step S47: forced commutation). Once rotation starts due to forced commutation, induced voltage is generated in each winding, so the rotational position and rotational speed are detected, and the control drive circuit 30 switches to normal control.

[0080] When the motor 10 is rotating in reverse due to external factors such as wind, the control drive circuit 30 detects the reverse rotation by, for example, by observing that the zero-crossing of the induced voltages generated in each winding occurs in the reverse order of U, W, V, which is the reverse of the order of forward rotation, and then switches to deceleration control. The deceleration control during reverse rotation will be explained below. In this specification, the rotational speed and target value are expressed as absolute values, but the rotational speed on the vertical axis of Figure 15 starts from a negative value to indicate reverse rotation, so even though it is deceleration, the rotational speed is increasing.

[0081] At time t0 in Figure 15, the motor starts up, and when it is determined that it is rotating in the opposite direction and deceleration control is started at time t1, the control drive circuit 30 switches to a short brake (abbreviated as SB in the figure) mode, which turns off all upper switch elements and turns on all lower switch elements (step S42). As a result, the rotational speed of the motor 10 decreases sharply (increases towards the positive side in Figure 15).

[0082] The control drive circuit 30 measures the time in short brake mode and determines whether the time in short brake mode exceeds the first set time (step S43: time determination). If the time in short brake mode is less than or equal to the first set time, the short brake mode is maintained.

[0083] At time t2, when the short brake mode time reaches the first set time, the control drive circuit 30 switches to a fully off mode, turning off all switch elements (step S44). As a result, the braking action is reduced, and the rotational speed of the motor 10 increases (decreases to the negative side in Figure 15) due to a reverse rotation bias caused by external factors.

[0084] The control drive circuit 30 receives feedback on the rotational speed of the motor 10 in the fully off mode from the rotational speed signal from the detection circuit 40, and determines whether the rotational speed of the motor 10 exceeds a first target value (step S45: rotational speed determination 1). In the fully off mode, if the rotational speed of the motor 10 is less than or equal to the first target value, the control drive circuit 30 maintains the fully off mode. In the fully off mode, if the rotational speed of the motor 10 exceeds the first target value (falls below it in Figure 15), the control drive circuit 30 determines whether the rotational speed of the motor 10 is less than or equal to the final target value (step S46: rotational speed determination 2). If the rotational speed of the motor 10 is greater than the final target value, the control drive circuit 30 switches back to the short brake mode.

[0085] At time t3 in Figure 15, the control drive circuit 30 enters short brake mode again when the rotational speed of the motor 10 exceeds the first target value, and then alternates between short brake mode and full off mode to decelerate (increase towards the positive side in Figure 15) so that the rotational speed of the motor 10 follows the first target value.

[0086] In Figure 14, the deceleration control ends when the rotational speed of the motor 10 falls below the final target value in rotational speed determination 2. In Figure 15, for example, if the rotational speed of the motor 10 falls below (or exceeds in Figure 15) the final target value at time t4 during short brake mode, the control drive circuit 30 enters full off mode from time t5. In rotational speed determination 1 in Figure 14, it is determined that the rotational speed of the motor 10 is below the first target value, and subsequently, rotational speed determination 2 determines that it is below the final target value, and the deceleration control ends at time t6. At time t6, along with the end of deceleration control, the system transitions to forced commutation mode (step S47). In forced commutation mode, the control drive circuit 30 forcibly applies an AC voltage to make the motor 10 rotate in the forward direction. After detecting that the motor has started rotating in the forward direction at time t7, the control drive circuit 30 transitions to normal control.

[0087] In this embodiment, an example of applying the deceleration control of the second embodiment to deceleration in the reverse direction has been described, but the deceleration control of the first embodiment, the third embodiment, or the fourth embodiment may also be applied to deceleration in the reverse direction.

[0088] As described above, the detection circuit 40 detects whether the motor 10 is rotating in the forward direction, stopped, or in the reverse direction. If the detection circuit 40 detects that the motor 10 is rotating in the reverse direction at startup, the control drive circuit 30 may perform deceleration control that alternates between a fully off mode and a short brake mode. Even if the motor is rotating in the reverse direction due to headwinds or the like before startup, rapidly decelerating the motor 10, which is biased for reverse rotation, puts stress on the motor 10. Therefore, by applying the deceleration control of this disclosure to the operation of decelerating the reverse rotation, the speed of deceleration for reverse rotation can be mitigated, thereby reducing the stress on the motor 10.

[0089] (Other Embodiments) Embodiments have been described above as examples of the technology relating to this disclosure. However, the technology relating to this disclosure is not limited thereto and can be applied to embodiments that are modified, replaced, added to, or omitted as appropriate. For example, the following modified examples are also included in one embodiment of this disclosure.

[0090] For example, in the above embodiment, an example was described in which the motor control device 100 is equipped with a detection circuit 40, but the motor control device 100 does not necessarily have to be equipped with a detection circuit 40.

[0091] For example, this disclosure can be implemented not only as a motor control device 100, but also as a control method that includes steps (processes) performed by the components constituting the motor control device 100.

[0092] The control method is a control method for a motor control device having an inverter circuit for driving a motor and having a plurality of switch element pairs consisting of upper switch elements and lower switch elements. As shown in Figure 3, the control method has a total off mode (step S13) in which all switch elements constituting the plurality of switch element pairs are turned off, and a short brake mode (step S11) in which one group of switch elements from all upper switch elements and all lower switch elements constituting the plurality of switch element pairs is turned on, and the other group of switch elements from all upper switch elements and all lower switch elements is turned off. In the control method, as a deceleration control to reduce the rotational speed of the motor, a drive signal is supplied to each switch element constituting the plurality of switch element pairs so as to alternately repeat the total off mode and the short brake mode (steps S11 to S15).

[0093] For example, this disclosure can be implemented as a program that causes a computer (processor) to execute the steps included in the control method. Furthermore, this disclosure can be implemented as a non-temporary computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0094] For example, if this disclosure is implemented in a program (software), each step is executed by the program using hardware resources such as the computer's CPU, memory, and input / output circuits. In other words, each step is executed by the CPU obtaining data from memory or input / output circuits, performing calculations, and outputting the calculation results to memory or input / output circuits.

[0095] In the above embodiment, each component included in the motor control device 100 may be implemented by dedicated hardware or by executing a software program suitable for each component. Each component may also be implemented by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0096] Some or all of the functions of the motor control device 100 according to the above embodiment are typically implemented as an integrated circuit (LSI). These may be individually integrated on a single chip, or some or all of them may be integrated on a single chip. Furthermore, the implementation is not limited to an LSI; it may also be implemented using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells inside the LSI, may also be used.

[0097] Furthermore, if advances in semiconductor technology or other derived technologies lead to the emergence of integrated circuit technologies that can replace LSIs, then naturally, those technologies may be used to integrate each component included in the motor control device 100 into an integrated circuit.

[0098] Furthermore, this disclosure also includes forms obtained by applying various modifications to the embodiments that a person skilled in the art could conceive, and forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of this disclosure.

[0099] (Note) The above description of embodiments discloses the following technology.

[0100] (Technology 1) A motor control device having a plurality of switch element pairs consisting of upper switch elements and lower switch elements, an inverter circuit for driving a motor, and a control drive circuit that supplies drive signals for controlling the motor to each switch element constituting the plurality of switch element pairs of the inverter circuit, wherein the control drive circuit supplies drive signals to each switch element in such a manner that it alternately repeats a deceleration control to reduce the rotational speed of the motor, which includes a full off mode in which all switch elements constituting the plurality of switch element pairs are turned off, and a short brake mode in which one group of switch elements from all upper switch elements and all lower switch elements constituting the plurality of switch element pairs is turned on, and the other group of switch elements from all upper switch elements and all lower switch elements is turned off.

[0101] According to this system, deceleration control is performed by alternately switching between short-brake mode and full-off mode. This allows for greater deceleration than using only the full-off mode, and smoother motor deceleration than using only the short-brake mode. Therefore, it reduces the load stress on the motor during deceleration compared to using only the short-brake mode. In addition, the smooth deceleration suppresses unwanted vibrations and noise.

[0102] (Technology 2) A motor control device according to Technology 1, having a detection circuit for detecting the rotational speed of the motor, wherein the control drive circuit terminates the deceleration control when the rotational speed reaches a predetermined target value after the start of the deceleration control.

[0103] According to this, deceleration control can be quickly terminated once the rotational speed reaches a predetermined target value.

[0104] (Technology 3) The motor control device according to Technology 2, wherein the detection circuit detects the rotational speed of the motor by detecting the induced voltage generated in the motor windings in the all-off mode.

[0105] According to this, in fully off mode, the induced voltage generated in the motor's windings where no current is flowing can be detected, and by comparing it with the neutral point voltage, the zero-crossing point can be detected, allowing for sensorless detection of rotational speed.

[0106] (Technical 4) A motor control device according to Technical 3, wherein, in addition to the predetermined target value, a first target value is set that changes during the deceleration control until it reaches the predetermined target value, and the control drive circuit transitions to the short brake mode when the rotational speed reaches the first target value in the all-off mode.

[0107] According to this, if the motor speed exceeds the first target value during deceleration control in full-off mode, the motor deceleration at that point is too gradual, so the system can switch to short-brake mode to increase the deceleration. Therefore, deceleration control can be performed so that the motor speed conforms to the first target value.

[0108] (Technical 5) The motor control device according to any one of Technical 2 to 4, wherein the detection circuit detects the rotational speed of the motor by detecting the voltage of the one switch element group that is conducting in the short brake mode.

[0109] Even in short-brake mode, a small induced voltage is generated when the rotor is rotating. Therefore, if the comparator used to determine the zero-crossing of the induced voltage has the sensitivity to detect such a small change in induced voltage, the motor speed can be detected even in short-brake mode.

[0110] (Technical 6) The motor control device according to Technical 5, wherein in the short brake mode, the control drive circuit turns off one lower switch element from the one group of switch elements that is supplying current to the motor, or turns off one upper switch element from the one group of switch elements that is drawing current from the motor, and the detection circuit detects the point in time when the voltage of the switch element changes due to the body diode of the upper switch element or a flywheel diode connected in parallel to the upper switch element becoming non-conductive, or the body diode of the lower switch element or a flywheel diode connected in parallel to the lower switch element becoming non-conductive, as the zero-crossing point.

[0111] According to this, even when one of the upper or lower switch elements is turned off, current flows to the body diode or flywheel diode, thus maintaining the short-circuit brake mode. When these switch elements are turned off, a forward voltage drop occurs compared to when they are turned on, and the timing at which this voltage abruptly drops to zero can be detected as a zero-cross. Since the forward voltage drop is approximately 1V, the zero-cross of the induced voltage of each phase in short-circuit brake mode can be detected without the need for a highly sensitive comparator, and thus the rotational speed can be detected.

[0112] (Technical 7) The motor control device according to Technical 6, wherein the control drive circuit sets the timing for turning off one of the lower switch elements or the timing for turning off one of the upper switch elements in the short brake mode based on the occurrence period of the previous zero-crossing point.

[0113] In methods that detect zero-crossing using the forward voltage drop of a body diode or flywheel diode, losses equal to current × forward voltage drop occur, so it is preferable to keep the period during which current flows through the body diode or flywheel diode short. Therefore, by taking advantage of the fact that the occurrence period of the zero-crossing point does not change significantly from the previous time, and setting the timing of turning off the switch element based on the occurrence period of the previous zero-crossing point to just before the timing at which the zero-crossing is estimated to occur this time, the period during which current flows through the body diode or flywheel diode can be shortened, and the resulting losses can be suppressed.

[0114] (Technical 8) A motor control device according to any one of Technical 5 to 7, wherein, in addition to the predetermined target value, a second target value is set that changes during the deceleration control until it reaches the predetermined target value, and the control drive circuit transitions to the full off mode when the rotational speed reaches the second target value in the short brake mode.

[0115] According to this, if the motor speed falls below the second target value during deceleration control using the short brake mode, the motor deceleration at that point is too large, so the system can switch to the full off mode to slow down the deceleration. Therefore, deceleration control can be performed to bring the motor speed in line with the second target value.

[0116] (Technical 9) A motor control device according to any one of Technical 2 to 8, wherein the detection circuit detects whether the motor is rotating in the forward direction, stopped, or in the reverse direction, and the control drive circuit performs the deceleration control when the detection circuit detects that the motor is rotating in the reverse direction at startup.

[0117] According to this, even if the motor is rotating in the reverse direction due to headwinds or other reasons before starting up, rapidly decelerating a motor that is biased in the reverse direction puts stress on the motor. Therefore, by applying the deceleration control of this disclosure to the operation of decelerating the reverse rotation, the speed of deceleration in the reverse direction can be mitigated, thereby reducing the stress on the motor.

[0118] (Technical 10) The motor control device according to any one of Technical 1 to 9, wherein the control drive circuit maintains the ON state of the switch element in the deceleration control when transitioning from the short brake mode to the all-off mode, until current stops flowing to the upper switch element in the ON state that is discharging current to the motor or the lower switch element in the ON state that is drawing current from the motor, or until the current flowing to the switch element falls below a predetermined value.

[0119] When switching from short brake mode to fully off mode, for example, if the lower switch element through which the intake current is flowing is turned off, regenerative current flows to the power supply side via the body diode or flywheel diode of the corresponding upper switch element, causing the power supply voltage to rise. Therefore, by turning off the upper switch element that is emitting current or the lower switch element through which the intake current is flowing, either after current stops flowing or after the current flowing has fallen below a predetermined value, the rise in power supply voltage can be suppressed.

[0120] (Technical 11) A motor control system comprising a motor control device described in any of Technical 1 to 10 and a motor driven by the motor control device.

[0121] This allows for the provision of a motor control system that can reduce the load stress on the motor during deceleration.

[0122] (Technical 12) A control method for a motor control device having an inverter circuit for driving a motor, the control method comprising: an all-off mode in which all switch elements constituting the plurality of switch element pairs are turned off; and a short-brake mode in which one group of switch elements from all upper switch elements and all lower switch elements constituting the plurality of switch element pairs is turned on, and the other group of switch elements from all upper switch elements and all lower switch elements is turned off; the control method provides a drive signal to each switch element constituting the plurality of switch element pairs as a deceleration control to reduce the rotational speed of the motor, by alternately repeating the all-off mode and the short-brake mode.

[0123] This provides a control method that can reduce the load stress on the motor during deceleration.

[0124] This disclosure can be applied to systems that control fan motors, etc.

[0125] 1 Motor control system 10, 10A Motor 20, 20A Inverter circuit 21, 21A, 23, 23A, 25 Upper switch element 22, 22A, 24, 24A, 26 Lower switch element 30 Control drive circuit 40 Detection circuit 100 Motor control device

Claims

1. A motor control device comprising: an inverter circuit that drives a motor and has a plurality of switch element pairs consisting of upper and lower switch elements; and a control drive circuit that supplies drive signals to each switch element constituting the plurality of switch element pairs of the inverter circuit for controlling the motor, wherein the control drive circuit supplies drive signals to each switch element in such a manner that it alternately repeats a deceleration control to reduce the rotational speed of the motor, which includes a full off mode in which all switch elements constituting the plurality of switch element pairs are turned off, and a short brake mode in which one group of switch elements from all upper switch elements and all lower switch elements constituting the plurality of switch element pairs is turned on, and the other group of switch elements from all upper switch elements and all lower switch elements is turned off.

2. The motor control device according to claim 1, which has a detection circuit for detecting the rotational speed of the motor, and the control drive circuit terminates the deceleration control when the rotational speed reaches a predetermined target value after the start of the deceleration control.

3. The motor control device according to claim 2, wherein the detection circuit detects the rotational speed of the motor by detecting the induced voltage generated in the motor windings in the all-off mode.

4. A motor control device according to claim 3, wherein, in addition to the predetermined target value, a first target value is set that changes during the deceleration control until it reaches the predetermined target value, and the control drive circuit transitions to the short brake mode when the rotational speed reaches the first target value in the all-off mode.

5. The motor control device according to any one of claims 2 to 4, wherein the detection circuit detects the rotational speed of the motor by detecting the voltage of the one switch element group that is conducting in the short brake mode.

6. The motor control device according to claim 5, wherein the control drive circuit, in the short brake mode, turns off one lower switch element from the one group of switch elements that is discharging current to the motor, or turns off one upper switch element from the one group of switch elements that is drawing current from the motor, and the detection circuit detects the point in time when the voltage of the switch element changes due to the body diode of the upper switch element or a flywheel diode connected in parallel to the upper switch element becoming non-conductive, or the body diode of the lower switch element or a flywheel diode connected in parallel to the lower switch element becoming non-conductive, as the zero-crossing point.

7. The motor control device according to claim 6, wherein the control drive circuit sets the timing for turning off one of the lower switch elements or the timing for turning off one of the upper switch elements in the short brake mode based on the period of the previous zero-crossing point.

8. A motor control device according to any one of claims 5 to 7, wherein, in addition to the predetermined target value, a second target value is set that changes during the deceleration control until it reaches the predetermined target value, and the control drive circuit transitions to the fully off mode when the rotational speed reaches the second target value in the short brake mode.

9. The motor control device according to any one of claims 2 to 8, wherein the detection circuit detects whether the motor is rotating in the forward direction, stopped, or in the reverse direction, and the control drive circuit performs the deceleration control when the detection circuit detects that the motor is rotating in the reverse direction at startup.

10. The motor control device according to any one of claims 1 to 9, wherein the control drive circuit maintains the ON state of the switch element in the deceleration control when transitioning from the short brake mode to the all-off mode, until current stops flowing to the upper switch element in the ON state that is supplying current to the motor or the lower switch element in the ON state that is drawing current from the motor, or until the current flowing to the switch element falls below a predetermined value.

11. A motor control system comprising a motor control device according to any one of claims 1 to 10, and a motor driven by the motor control device.

12. A control method for a motor control device having an inverter circuit for driving a motor, the control method comprising: an all-off mode in which all switch elements constituting the plurality of switch element pairs are turned off; and a short-brake mode in which one group of switch elements from all upper switch elements and all lower switch elements constituting the plurality of switch element pairs is turned on, and the other group of switch elements from all upper switch elements and all lower switch elements is turned off; the control method further comprises a control method that supplies a drive signal to each switch element constituting the plurality of switch element pairs in such a manner that the all-off mode and the short-brake mode are alternately repeated as deceleration control to reduce the rotational speed of the motor.

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