JP7568199B2 - Motor Drive Unit - Google Patents

Description

The present invention relates to a motor driving device.

Conventionally, various drive controls have been implemented to rotate a motor at a desired speed. In motor drive control, it is important to prevent abnormal current from flowing through the motor even in the event of an abnormality such as a disturbance, to protect the circuit and the motor, and to perform stable drive.
For example, in a known motor drive control using vector control, when it is detected that the current flowing through the motor exceeds a threshold, the control is stabilized by correcting a d-axis voltage command value or a q-axis voltage command value. For example, this is disclosed in Patent Document 1.

Patent No. 6095561

Conventionally, motors have been driven stably by comparing the current flowing through them with a threshold value, but if the threshold value is not appropriate, the motor cannot be driven efficiently, which could result in inefficient operation.

The object of the present invention is to provide a motor driving device that efficiently drives a motor.

A first exemplary invention of the present application is a motor drive device that drives a motor, comprising: a rotation speed acquisition unit that acquires a rotation speed at which the motor is rotated; a duty ratio setting unit that sets a duty ratio of a PWM signal that drives the motor in accordance with the rotation speed acquired by the rotation speed acquisition unit; a PWM signal output unit that outputs a PWM signal having a duty ratio set by the duty ratio setting unit; a driver that drives the motor based on the PWM signal output by the PWM signal output unit; and a current detection unit that detects a current flowing through the motor, wherein the duty ratio setting unit executes a first control to set the duty ratio to a predetermined value larger than an initial value when driving of the motor is started when the current detected by the current detection unit reaches a first threshold value, and a second control to set the duty ratio to the initial value when the current detected by the current detection unit reaches a second threshold value larger than the first threshold value , and the duty ratio setting unit changes at least one of the first threshold value and the second threshold value in accordance with the rotation speed acquired by the rotation speed acquisition unit.

According to the exemplary first invention of the present application, the motor can be driven efficiently.

1 is a cross-sectional view showing a motor driven by a motor drive device according to a first embodiment of the present invention, taken along a plane perpendicular to the Y axis and passing through a central axis J. FIG. FIG. 2 is a perspective view of the motor 10 of FIG. 1 . 3 is a plan view of the motor 10 in FIG. 2 with a motor housing 23 removed, as viewed from above. 1 is a block diagram showing a configuration of a motor drive device according to an embodiment of the present invention. 4 is a flowchart showing a motor drive process performed by the motor drive device 100. 4 is a flowchart showing a duty ratio setting process performed by the motor drive device 100. 7 is a flowchart showing a first control shown in FIG. 6 . 7 is a flowchart showing a second control shown in FIG. 6 . 7 is a flowchart showing a third control shown in FIG. 6 .

Hereinafter, a motor drive device according to an embodiment of the present invention will be described with reference to the drawings. Note that in the following drawings, the scale and number of each structure may differ from the actual structure in order to make each configuration easier to understand.

In addition, in the drawings, an XYZ coordinate system is appropriately shown as a three-dimensional Cartesian coordinate system. In the XYZ coordinate system, the Z-axis direction is parallel to the axial direction of the central axis J shown in FIG. 1. The X-axis direction is radial to the central axis J. The Y-axis direction is perpendicular to both the X-axis and Z-axis directions. In each of the X-axis, Y-axis, and Z-axis directions, the side indicated by the arrow in the drawing is the + side, and the opposite side is the - side.

In the following description, the positive side (+Z side) in the Z-axis direction is called the "front side" or "one side", and the negative side (-Z side) in the Z-axis direction is called the "rear side" or "other side". The rear side (other side) and the front side (one side) are names used simply for explanation and do not limit the actual positional relationship and direction. Unless otherwise specified, the direction parallel to the central axis J (Z-axis direction) is simply called the "axial direction", the radial direction centered on the central axis J is simply called the "radial direction", and the circumferential direction centered on the central axis J, i.e., around the axis of the central axis J, is simply called the "circumferential direction". The side approaching the central axis J in the radial direction is called the "radial inner side", and the side moving away from the central axis J is called the "radial outer side".

In this specification, "extending in the axial direction" includes not only extending strictly in the axial direction (Z-axis direction), but also extending in a direction tilted at an angle of less than 45° to the axial direction.
In this specification, "extending in the radial direction" includes not only extending strictly in the radial direction, i.e., in a direction perpendicular to the axial direction (Z-axis direction), but also extending in a direction tilted at an angle of less than 45° to the radial direction. "Parallel" includes not only being strictly parallel, but also being tilted at an angle of less than 45° to each other.

In this specification, when the term "rotation speed" is used simply, it refers to the number of rotations per unit time. For example, a rotation speed of 1300 indicates that the number of rotations per minute is 1300 rotations, or 1300 rpm.

[First embodiment]
<Motor configuration>
FIG. 1 is a cross-sectional view showing a motor driven by a motor drive device according to a first embodiment of the present invention, taken along a plane perpendicular to the Y axis and passing through a central axis J.
FIG. 2 is a perspective view of the motor 10 of FIG.
In this embodiment, the motor 10 is a brushless DC motor. The motor 10 includes motor housings 21 and 23 that accommodate a motor section 30 including a rotor 50 having a motor shaft 41 arranged along a central axis J extending in the axial direction, and a stator 40 that faces the rotor 50 with a gap in the radial direction, and a circuit board 80 on which a drive circuit 81 that drives the motor section 30 is mounted. The motor housings 21 and 23 accommodate the circuit board 80 and the rotor 50 in this order from one axial side to the other axial side.

The motor 10 includes a stator 40, and the stator 40 includes a stator yoke 42. The motor 10 includes a circuit board 80 on one axial side of the stator yoke 42. The circuit board 80 has a through hole 80a that penetrates in the axial direction. The motor shaft 41 passes through the through hole 80a. The motor 10 includes bearings 55a and 55b. The bearing 55a is disposed on the other axial side of the motor housing 23. The bearing 55b is disposed on one axial side of the motor housing 21. The bearing 55a is disposed at one axial end of the motor shaft 41. The bearing 55b is disposed at the other axial end of the motor shaft 41. The bearings 55a and 55b rotatably support the motor shaft 41. The shape, structure, etc. of the bearings 55a and 55b are not particularly limited, and any known bearings can be used.

The rotor 50 includes a rotor magnet 51. The rotor magnet 51 surrounds the motor shaft 41 and is fixed to the motor shaft 41.

The motor 10 has a motor housing 21 that is cylindrical with a bottom. The motor section 30 is accommodated radially inside the motor housing 21. The motor housing 21 may be cylindrical or rectangular. The motor housing 21 is made of, for example, aluminum die-cast. The motor 10 has a motor housing 23 that is cylindrical with a bottom on one axial side of the circuit board 80. The motor housing 23 may be cylindrical or rectangular. The motor housing 23 is made of, for example, aluminum die-cast. The motor housing 21 opens to one axial side, and the motor housing 23 opens to the other axial side. The opening on one axial side of the motor housing 21 is blocked by the motor housing 23, and the opening on the other axial side of the motor housing 23 is blocked by the motor housing 21.

The motor housing 21 has a flange portion 21a extending radially outward at one axial end. The flange portion 21a has a through hole 21aa penetrating in the axial direction. The motor housing 23 has a flange portion 23a extending radially outward at the other axial end. The flange portion 23a has a through hole 23aa penetrating in the axial direction. The through hole 21aa and the through hole 23aa are aligned in the axial and circumferential directions, and the through hole 21aa and the through hole 23aa are continuous through holes. The motor housing 21 and the motor housing 23 can be fixed together by screwing the through hole 21aa and the through hole 23aa so that they penetrate each other.

FIG. 3 is a perspective view showing the motor 10 of FIG. 2 with the motor housing 23 removed.
The circuit board 80 has a shape corresponding to the shape of the cylindrical hole of the motor housing 21. In this embodiment, the circuit board 80 is circular. The drive circuit 81 is composed of a plurality of electronic components. The drive circuit 81 includes, for example, at least one of an IGBT, a bridge diode, a MOSFET, an IPM, and a DC/DC converter. IGBT is an abbreviation for Insulated Gate Bipolar Transistor. MOSFET is an abbreviation for metal-oxide-semiconductor field-effect transistor. IPM is an abbreviation for Intelligent Power Module. The drive circuit 81 is connected to the outside of the motor 10 via wiring connected to a connector 82. The wiring connected to the connector 82 passes through a through hole 83 provided in the motor housings 21 and 23.

<Configuration of the motor driving device>
FIG. 4 is a block diagram showing the configuration of a motor drive device according to an embodiment of the present invention.
The motor drive device 100 is a device that drives the motor 300. The motor 30 in FIG. 1 is an example of the motor 300 in FIG. 4. The motor drive device 100 includes a microcomputer 101, a driver 102, and a current detection unit 103. The microcomputer 101 includes a rotation speed acquisition unit 104 that acquires the rotation speed at which the motor 300 rotates, a duty ratio setting unit 105 that sets the duty ratio of a PWM signal that drives the motor 300 according to the rotation speed acquired by the rotation speed acquisition unit 104, and a PWM signal output unit 106 that outputs a PWM signal with the duty ratio set by the duty ratio setting unit 105. The driver 102 drives the motor 300 based on the PWM signal output by the PWM signal output unit 106. The current detection unit 103 is, for example, a shunt resistor, and detects the current flowing through the motor 300. In this embodiment, the rotation speed acquisition unit 104, the duty ratio setting unit 105, and the PWM signal output unit 106 are realized by executing a program in the microcomputer 101. The motor drive device 100 has a storage unit that stores the program executed by the microcomputer 101. The rotation speed acquisition unit 104, the duty ratio setting unit 105, and the PWM signal output unit 106 may be realized by hardware. The drive circuit 81 in FIG. 1 is an example of the microcomputer 101, the driver 102, and the current detection unit 103 in FIG. 4. A part of the configuration of the motor drive device 100 in FIG. 4 may be provided outside the drive circuit 81 in FIG. 1.

The motor drive device 100 may have a sensor that detects the rotational position of the motor 300 and detect the rotational position of the motor 300 based on the detection result of the sensor. The motor drive device 100 may perform sensorless control without having a sensor that detects the rotational position of the motor 300.

The rotation speed setting unit 200 sets the rotation speed at which the motor 300 is rotated by the motor drive device 100. The rotation speed acquisition unit 104 acquires the rotation speed at which the motor 300 is rotated, which is set by the rotation speed setting unit 200. The motor drive device 100 rotates the motor 300 at the rotation speed set by the rotation speed setting unit 200. The motor drive device 100 may include the rotation speed setting unit 200. The rotation speed setting unit 200 is, for example, a dip switch mounted on the circuit board 80. When the rotation speed setting unit 200 is a dip switch, the operator can set the rotation speed of the motor 300 by the on/off pattern of the dip switch. The rotation speed setting unit 200 may be a dip switch or a rotary switch, or may be a switch configured with a resistor, jumper wire, solder, etc. provided on the circuit board 80, and set the rotation speed at which the motor 300 is rotated. The rotation speed acquisition unit 104 may acquire the rotation speed at which the motor rotates from an external device via communication.

<Operation of the motor driving device>
The duty ratio setting unit 105 executes a first control for setting the duty ratio to a predetermined value larger than the initial value when the motor 300 starts to be driven when the current detected by the current detection unit 103 reaches a first threshold, and a second control for setting the duty ratio to an initial value when the current detected by the current detection unit 103 reaches a second threshold larger than the first threshold . The duty ratio setting unit 105 also changes at least one of the first threshold and the second threshold in accordance with the rotation speed acquired by the rotation speed acquisition unit 104. The duty ratio setting unit 105 also has a third control for setting the duty ratio to 0 percent for a predetermined time when the current detected by the current detection unit 103 reaches a third threshold. The third threshold is larger than the second threshold, and the second threshold is larger than the first threshold.

FIG. 5 is a flowchart showing the motor drive process performed by motor drive device 100.
In step S501, motor drive device 100 waits for an instruction from an operator to start driving the motor. The instruction to start driving the motor may be, for example, turning on the power or operating a switch. When motor drive device 100 receives an instruction from the operator to start driving the motor (step S501: Yes), motor drive device 100 repeats the rotation speed acquisition process in step S502, the duty ratio setting process in step S503, and the PWM signal output process in step S504 until it receives an instruction from the operator to stop the motor (step S505: Yes).

The rotation speed acquisition process in step S502 is a process in which the rotation speed acquisition unit 104 acquires the rotation speed set by the rotation speed setting unit 200. The rotation speed acquired in the rotation speed acquisition process is handed over to the duty ratio setting process. The duty ratio setting process in step S503 sets a duty ratio by the duty ratio setting unit 105, as described below with reference to Figures 6 to 9. The duty ratio set in the duty ratio setting process is handed over to the PWM signal output process. The PWM signal output process in step S504 generates a PWM signal of the duty ratio set in the duty ratio setting process, and outputs the PWM signal to the driver 102.

FIG. 6 is a flowchart showing the duty ratio setting process performed by motor drive device 100.
First, in step S601, the duty ratio setting unit 105 sets the duty ratio to an initial value. This initial value is a value determined in advance according to the characteristics of the motor 300 to be driven, and is a duty ratio for smoothly and efficiently starting the motor 300 from a stopped state. This initial value is, for example, 1%.

Next, in step S602, the duty ratio setting unit 105 changes the threshold value according to the rotation speed. The threshold values to be changed here are the first threshold value used in the first control and the second threshold value used in the second control. The duty ratio setting unit 105 may change only one of the first threshold value and the second threshold value.

First, the change of the first threshold value will be described. The duty ratio setting unit 105 calculates the first threshold value according to the number of revolutions at which the motor 300 is rotated. For example, the manufacturer or operator of the motor driving device 100 determines one number of revolutions at which the motor 300 is rotated as the number of revolutions at the initial setting, and obtains the first threshold value at the initial setting that allows the motor 300 to be driven with high efficiency when the motor 300 is rotated at the number of revolutions at the initial setting. This first threshold value at the initial setting can be obtained, for example, by measuring the efficiency when the motor 300 is actually driven. For example, the manufacturer or operator of the motor driving device 100 stores the number of revolutions at the initial setting and the corresponding first threshold value at the initial setting in the storage unit of the motor driving device 100. The duty ratio setting unit 105 uses the number of revolutions at the initial setting and the first threshold value at the initial setting stored in the storage unit to calculate the first threshold value when the number of revolutions delivered from the number of revolutions acquisition unit 104 is different from the number of revolutions at the initial setting.

For example, when the rotation speed at the time of initial setting is N1, the first threshold value at the time of initial setting is X1, and the rotation speed delivered from the rotation speed acquisition unit 104 is N2, the first threshold value X2 used when driving the motor 300 at the rotation speed N2 delivered from the rotation speed acquisition unit 104 is calculated by equation (1).
X2=(N1/N2)*X1 (where / is the division operator and * is the multiplication operator) Equation (1)
That is, when changing the rotation speed of the motor 300 from N1 to N2, the duty ratio setting unit 105 changes the first threshold value from X1 to X2 calculated by the formula (1).

The duty ratio setting unit 105 may calculate the first threshold value using formula (1) each time the rotation speed is delivered from the rotation speed acquisition unit 104. Alternatively, the first threshold value may be calculated in advance using formula (1) for each rotation speed at which the motor 300 can be driven, and stored in association with each other in, for example, a table format, and the first threshold value corresponding to the rotation speed delivered from the rotation speed acquisition unit 104 may be read from the table and used in the first control. For example, the duty ratio setting unit 105 sets the first threshold value to 0.63 A (amperes) when the rotation speed is 1300 [rpm], sets the first threshold value to 0.52 A (amperes) when the rotation speed is 1550 [rpm], and sets the first threshold value to 0.45 A (amperes) when the rotation speed is 1800 [rpm].

The change of the second threshold value will be explained. The duty ratio setting unit 105 calculates the second threshold value according to the number of revolutions at which the motor 300 is rotated. For example, the manufacturer or operator of the motor driving device 100 determines one number of revolutions at which the motor 300 is rotated as the number of revolutions at the initial setting, and obtains the second threshold value at the initial setting that allows the motor 300 to be driven with high efficiency when the motor 300 is rotated at the number of revolutions at the initial setting. This second threshold value at the initial setting can be obtained, for example, by measuring the efficiency when the motor 300 is actually driven. For example, the manufacturer or operator of the motor driving device 100 stores the number of revolutions at the initial setting and the corresponding second threshold value at the initial setting in the storage unit of the motor driving device 100. The duty ratio setting unit 105 uses the number of revolutions at the initial setting and the second threshold value at the initial setting stored in the storage unit to calculate the second threshold value when the number of revolutions delivered from the number of revolutions acquisition unit 104 is different from the number of revolutions at the initial setting.

For example, when the rotation speed at the time of initial setting is N1, the second threshold value at the time of initial setting is Y1, and the rotation speed delivered from the rotation speed acquisition unit 104 is N2, the second threshold value Y2 used when driving the motor 300 at the rotation speed N2 delivered from the rotation speed acquisition unit 104 is calculated by equation (2).
Y2=(N1/N2)*Y1 (where / is a division operator and * is a multiplication operator)...Equation (2)
That is, when changing the rotation speed of the motor 300 from N1 to N2, the duty ratio setting unit 105 changes the second threshold value from Y1 to Y2 calculated by the formula (2).

The duty ratio setting unit 105 may calculate the second threshold value using formula (2) each time the rotation speed is delivered from the rotation speed acquisition unit 104. Alternatively, the second threshold value may be calculated in advance using formula (2) for each rotation speed at which the motor 300 can be driven, and stored in association with each other in, for example, a table format, and the second threshold value corresponding to the rotation speed delivered from the rotation speed acquisition unit 104 may be read from the table and used in the second control. For example, when the rotation speed is 1300 [rpm], the duty ratio setting unit 105 sets the second threshold value to 0.80 A (amperes), when the rotation speed is 1550 [rpm], the second threshold value to 0.67 A (amperes), and when the rotation speed is 1800 [rpm], the second threshold value to 0.58 A (amperes).

The duty ratio setting unit 105 executes the first control in step S603, executes the second control in step S604, and executes the third control in step S605. In the first and second controls, the first and second thresholds changed in step S602 are used. The first, second, and third controls are executed at a predetermined period, for example, by a timer interrupt, while the motor 300 is being driven by the motor driving device 100. Details of the first, second, and third controls will be described later with reference to Figures 7, 8, and 9.

In driving the motor 300, the duty ratio setting unit 105 gradually increases and updates the duty ratio from the initial duty ratio set in step S601 at the start of rotation of the motor 300 until it reaches the duty ratio corresponding to the rotation speed transferred from the rotation speed acquisition unit 104. In steps S606 and S607, the duty ratio setting unit 105 executes a process of updating this duty ratio. In step S606, the duty ratio setting unit 105 determines whether the current duty is a duty ratio corresponding to the rotation speed transferred from the rotation speed acquisition unit 104. If the current duty is a duty ratio corresponding to the rotation speed transferred from the rotation speed acquisition unit 104 (step S606: Yes), the duty ratio setting unit 105 returns to step S602. If the current duty is not a duty ratio corresponding to the rotation speed transferred from the rotation speed acquisition unit 104 (step S606: No), the duty ratio setting unit 105 proceeds to step S607. In step S607, the duty ratio setting unit 105 updates the duty ratio by increasing it by a predetermined amount (for example, 2%). After step S607, the duty ratio setting unit 105 returns to step S602.

Fig. 7 is a flowchart showing the first control shown in Fig. 6. In the first control, when the number of times the threshold is exceeded reaches a predetermined number (e.g., 30 times) within a predetermined time (e.g., 0.1 seconds) after the threshold is exceeded, the determination in step S701 is executed. The first control is executed, for example, every approximately 350 microseconds.
First, in step S701, the duty ratio setting unit 105 determines whether the current detected by the current detection unit 103 has reached the first threshold, i.e., whether the current detected by the current detection unit 103 is equal to or greater than the first threshold. If the current detected by the current detection unit 103 is not equal to or greater than the first threshold (step S701: No), the process remains in step S701. If the current detected by the current detection unit 103 is equal to or greater than the first threshold (step S701: Yes), the process proceeds to step S702.

In step S702, the duty ratio setting unit 105 sets the duty ratio to a predetermined value. This predetermined value may be a predetermined constant value, a value predetermined for each current duty ratio, or a value obtained by subtracting a predetermined ratio (e.g., 5%) from the current duty ratio. For example, when the motor 300 is driven with a duty ratio of 50%, if the current detected by the current detection unit 103 becomes equal to or greater than the first threshold, the duty ratio is set to 45%. The predetermined value set in step S702 is a value greater than the initial value of the duty ratio set in step S601. Following step S702, the duty ratio setting unit 105 returns to step S701. Note that the first control proceeds to S604 in FIG. 6 after a series of processes is completed, that is, when step S701 is No and step S702 is completed.

Fig. 8 is a flowchart showing the second control shown in Fig. 6. In the second control, when the threshold value is exceeded, the determination in step S801 is immediately executed. The second control is executed, for example, every PWM period, every few nanoseconds.
First, in step S801, the duty ratio setting unit 105 determines whether the current detected by the current detection unit 103 has reached the second threshold, i.e., whether the current detected by the current detection unit 103 is equal to or greater than the second threshold. If the current detected by the current detection unit 103 is not equal to or greater than the second threshold (step S801: No), the process remains in step S801. If the current detected by the current detection unit 103 is equal to or greater than the second threshold (step S801: Yes), the process proceeds to step S802.

In step S802, the duty ratio setting unit 105 sets the duty ratio to an initial value. This initial value is the initial value of the duty ratio set in step S601. This initial value is, for example, 1%. Following step S802, the duty ratio setting unit 105 returns to step S801. Note that the second control proceeds to S605 in FIG. 6 after the series of processes is completed, that is, if step S801 is No or when step S802 is completed.

Fig. 9 is a flowchart showing the third control shown in Fig. 6. In the third control, when the threshold value is exceeded, the determination in step S901 is immediately executed. The third control is executed, for example, every approximately 350 microseconds.
First, in step S901, the duty ratio setting unit 105 determines whether the current detected by the current detection unit 103 has reached the third threshold, i.e., whether the current detected by the current detection unit 103 is equal to or greater than the third threshold. If the current detected by the current detection unit 103 is not equal to or greater than the third threshold (step S901: No), the process remains in step S901. In addition, in the third control, if the current detected by the current detection unit 103 is less than the third threshold, i.e., if the result of step S901 is No, the process proceeds to S606 in FIG. 6. If the current detected by the current detection unit 103 is equal to or greater than the third threshold (step S901: Yes), the process proceeds to step S902. The third threshold is a threshold for protecting the motor drive device 100 and the motor 300 from burnout due to overcurrent, and is a constant value regardless of the rotation speed delivered from the rotation speed acquisition unit 104, e.g., 1 A (ampere).

In step S902, the duty ratio setting unit 105 sets the duty ratio to 0%. In other words, the motor 300 is stopped. Then, in step S903, the duty ratio setting unit 105 waits for a predetermined time (e.g., 6 seconds) to elapse. If the predetermined time has elapsed (step S903: Yes), the microcomputer 101 resets the process and restarts the process from step S501.

<Functions and Effects of Motor Drive Device 100>
Next, the operation and effects of the motor drive device 100 will be described.

In the invention according to the above-described embodiment, a motor drive device that drives a motor includes a rotation speed acquisition unit that acquires a rotation speed at which the motor is rotated, a duty ratio setting unit that sets a duty ratio of a PWM signal that drives the motor in accordance with the rotation speed acquired by the rotation speed acquisition unit, a PWM signal output unit that outputs a PWM signal having a duty ratio set by the duty ratio setting unit, a driver that drives the motor based on the PWM signal output by the PWM signal output unit, and a current detection unit that detects a current flowing through the motor, wherein the duty ratio setting unit executes a first control to set the duty ratio to a predetermined value larger than an initial value when driving of the motor is started when the current detected by the current detection unit reaches a first threshold, and a second control to set the duty ratio to the initial value when the current detected by the current detection unit reaches a second threshold larger than the first threshold, and the duty ratio setting unit changes at least one of the first threshold and the second threshold in accordance with the rotation speed acquired by the rotation speed acquisition unit.
This allows the motor to be driven efficiently.
Furthermore, torque control becomes possible using a simple method, and the temperature rise of the motor can be suppressed.

In addition, the duty ratio setting unit further has a third control that sets the duty ratio to 0 percent for a predetermined time when the current detected by the current detection unit reaches a third threshold, the third threshold being greater than the second threshold, and the second threshold being greater than the first threshold.
Therefore, even if the current detected by the current detection unit cannot be limited by the first threshold and the current further increases, the current can be limited because it has reached the second threshold, and the motor can be driven stably. Also, before the current detected by the current detection unit reaches the third threshold and the motor is stopped, the current can be limited because it has reached the second threshold, and the motor can be driven stably.

Moreover, the duty ratio setting unit executes the first control in a first period, and executes the second control in a second period that is shorter than the first period.
Therefore, by executing the second control, which compares the current detected by the current detection unit with the second threshold value, more frequently than the first control, which compares the current detected by the current detection unit with the first threshold value, it is possible to more reliably detect when the current has reached the second threshold value, and the motor can be driven stably.

In addition, when changing the motor rotation speed N1 to N2, the duty ratio setting unit changes the first threshold value X1 to X2 expressed as X2 = (N1/N2) * X1 (where / is a division operator and * is a multiplication operator).
Therefore, the changed first threshold value can be calculated using a simple formula.

Moreover, N1 is the motor rotation speed at the time of initial setting, and X1 is the first threshold value at the time of initial setting.
Therefore, since the changed first threshold value is calculated based on the highly reliable initial setting value, a reliable value can be calculated.

Furthermore, when changing the number of rotations N1 of the motor to N2, the duty ratio setting unit sets the second threshold value Y1 as follows: Y2=(N1/N2)*Y1 (where / is a division operator, and *
is a multiplication operator.) to Y2 represented by
Therefore, the changed second threshold value can be calculated using a simple formula.

Moreover, N1 is the motor rotation speed at the time of initial setting, and Y1 is the second threshold value at the time of initial setting.
Therefore, since the changed second threshold value is calculated based on the highly reliable initial setting value, a reliable value can be calculated.

The motor control device further includes a rotation speed setting unit that sets a rotation speed at which the motor rotates, and the rotation speed acquisition unit acquires the rotation speed set by the rotation speed setting unit.
Therefore, the rotation speed of the motor can be set by the rotation speed setting unit.

The rotation speed setting unit is a switch on the circuit board.
This makes it possible to easily set the motor rotation speed using a switch on the circuit board.

The rotation speed acquisition unit acquires the rotation speed at which the motor rotates from an external device via communication.
This makes it possible to easily set the motor rotation speed from outside via communication.

The motor is a motor that rotates an axial flow fan.
Therefore, in the motor for the axial fan, an appropriate threshold value can be set according to the rotation speed, and the temperature rise of the motor can be suppressed.

The use of the motor driven by the motor drive device of the above-mentioned embodiment is not particularly limited. The motor of the above-mentioned embodiment is, for example, a motor that rotates an axial fan. Furthermore, each of the above-mentioned configurations can be appropriately combined within a range that does not contradict each other.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

REFERENCE SIGNS LIST 10 Motor 21 Motor housing 30 Motor section 40 Stator 50 Rotor 80 Circuit board 81 Drive circuit 100 Motor drive device 101 Microcomputer 102 Driver 103 Current detection section 104 Rotation speed acquisition section 105 Duty ratio setting section 106 PWM signal output section 200 Rotation speed setting section 300 Motor

Claims (11)

A motor drive device that drives a motor,
a rotation speed acquisition unit that acquires a rotation speed at which the motor is rotated;
a duty ratio setting unit that sets a duty ratio of a PWM signal that drives the motor in accordance with the rotation speed acquired by the rotation speed acquisition unit;
a PWM signal output unit that outputs a PWM signal having a duty ratio set by the duty ratio setting unit;
a driver that drives the motor based on the PWM signal output from the PWM signal output unit;
a current detection unit that detects a current flowing through the motor;
Equipped with
The duty ratio setting unit is
a first control for setting the duty ratio to a predetermined value greater than an initial value at the time when the current detected by the current detection unit reaches a first threshold value;
a second control for setting the duty ratio to the initial value when the current detected by the current detection unit reaches a second threshold value that is greater than the first threshold value ;
The duty ratio setting unit changes at least one of the first threshold value and the second threshold value in accordance with the rotation speed acquired by the rotation speed acquisition unit.
Motor drive device. the duty ratio setting unit further includes a third control that sets the duty ratio to 0 percent for a predetermined time when the current detected by the current detection unit reaches a third threshold value;
The third threshold is greater than the second threshold,
The second threshold is greater than the first threshold.
The motor drive device according to claim 1 . the duty ratio setting unit executes the first control in a first period and executes the second control in a second period that is shorter than the first period.
3. The motor drive device according to claim 1 or 2. The duty ratio setting unit is
When changing the rotation speed of the motor from N1 to N2,
The first threshold value X1 is
X2=(N1/N2)*X1 (where / is the division operator and * is the multiplication operator.)
Change to X2, which is represented by
The motor drive device according to any one of claims 1 to 3. N1 is the motor rotation speed at the initial setting,
The X1 is the first threshold value at the time of initial setting,
The motor drive device according to claim 4. The duty ratio setting unit is
When changing the rotation speed of the motor from N1 to N2,
The second threshold value Y1 is
Y2=(N1/N2)*Y1 (where / is the division operator and * is the multiplication operator).
Change to Y2 represented by
The motor drive device according to any one of claims 1 to 5. N1 is the motor rotation speed at the initial setting,
The Y1 is the second threshold value at the initial setting.
The motor drive device according to claim 6. A rotation speed setting unit that sets the rotation speed at which the motor is rotated,
The rotation speed acquisition unit acquires the rotation speed set by the rotation speed setting unit.
The motor drive device according to any one of claims 1 to 7. The rotation speed setting unit is a switch on a circuit board.
The motor drive device according to claim 8 . The rotation speed acquisition unit acquires the rotation speed at which the motor rotates from an external device through communication.
The motor drive device according to any one of claims 1 to 7. The motor is a motor that rotates an axial flow fan.
The motor drive device according to any one of claims 1 to 10.

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