Electric motor drive device

Abstract

To provide an electric motor drive device (10) capable of controlling the rotational speed of an electric motor (2) even when the rotational speed of the electric motor is rapidly reduced or stopped.SOLUTION: Driving power is supplied to an electric motor from a switching power supply (20), and operating power is supplied to a control unit (12) to control the rotational speed of the electric motor. When a voltage value of the driving power is detected and fed back to a duty ratio of a switching power supply to adjust the voltage value of driving power to a specified voltage value, the voltage value of operating power is adjusted to a predetermined voltage value. The control unit can detect that the voltage value of the driving voltage exceeds a threshold voltage value, and executes control for maintaining or increasing the rotational speed of the electric motor when the voltage value of the driving power exceeds the threshold voltage value due to execution of deceleration control of reducing or stopping the rotational speed of the electric motor. This makes it possible to maintain the operating power of the control unit at a predetermined voltage value even when the rotational speed of the electric motor is suddenly reduced or stopped.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a motor drive device that drives a motor by supplying drive power of a specified voltage value to the motor and can control the rotational speed of the motor.

Background Art

[0002] In order to drive a motor, it is necessary to supply drive power of a specified voltage value to the motor. Therefore, it is common to drive the motor using a motor drive device that generates drive power of the specified voltage value. Among these motor drive devices, there are also motor drive devices that can control the rotational speed of the motor by mounting a control unit such as a microcomputer. Here, in order to operate a control unit such as a microcomputer, it is necessary to supply operating power of a predetermined voltage value to the control unit, and the voltage value of this operating power is different from the specified voltage value of the drive power supplied to the motor. For this reason, a motor drive device capable of controlling the rotational speed of a motor needs to be equipped with a power supply for generating operating power of a predetermined voltage value in addition to a power supply for generating drive power of a specified voltage value.

[0003] However, since the motor drive device becomes large if two power supplies are mounted, it has been proposed to mount a multi-output switching power supply (Patent Document 1). Here, a multi-output switching power supply is a switching power supply in which a plurality of secondary sides are mounted, with different turns between each system, compared to a general switching power supply in which one primary side and one secondary side are mounted for each system. By using a multi-output switching power supply, it is possible to simultaneously generate drive power of a specified voltage value for the motor and operating power of a predetermined voltage value for the control circuit, so that the motor drive device can be miniaturized.

[0004] In a switching power supply, in order to supply the motor with driving power at an accurate specified voltage value, the voltage value of the driving power supplied to the motor is detected and fed back to the duty ratio of the switching operation on the primary side. By detecting and feeding back the voltage value of the driving power, when the voltage value of the driving power is lower than the specified voltage value, the duty ratio of the switching operation on the primary side is increased, and when the specified voltage value is higher, the duty ratio is decreased, so that the driving power at the accurate specified voltage value can be supplied to the motor. Further, when the voltage value of the driving power abnormally increases due to an abnormality in the motor or the like, the motor can be emergently stopped by setting the duty ratio of the switching operation on the primary side to 0 (that is, stopping the switching operation).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the conventional technology described above, when attempting to rapidly reduce the rotational speed of the motor or when attempting to stop the motor, the voltage value of the operating power supplied to the control unit decreases, making it impossible to operate the control unit normally. As a result, there is a problem that the rotational speed of the motor may become uncontrollable.

[0007] This invention was made to solve the above-described problems of the conventional technology, and an object thereof is to provide a motor drive device capable of controlling the rotational speed of the motor even when attempting to rapidly reduce the rotational speed of the motor or when attempting to stop the motor.

Means for Solving the Problems

[0008] In order to solve the above-described problems, the motor drive device of the present invention employs the following configuration. That is, In a motor drive device that drives the motor by supplying drive power of a specified voltage value to the motor and controls the rotational speed of the motor, a control unit that operates by being supplied with operating power of a predetermined voltage value and controls the rotational speed of the motor; an external power source is connected to the primary side of a transformer via a switching circuit, and a drive power supply circuit that supplies the drive power to the motor and an operating power supply circuit that supplies the operating power to the control unit are connected to the secondary side of the transformer. By adjusting the duty ratio of the switching circuit, when the voltage value of the drive power supplied to the motor is adjusted to the specified voltage value, the voltage value of the operating power supplied to the control unit is adjusted to the predetermined voltage value, a switching power supply; a feedback control unit that detects the voltage value of the drive power supplied to the motor and performs feedback control on the duty ratio of the switching circuit is provided, when the voltage value of the drive power exceeds a predetermined threshold voltage value as the deceleration control for reducing or stopping the rotational speed of the motor is executed, the control unit executes either control for maintaining the rotational speed of the motor or control for increasing the rotational speed characterized in that.

[0009] In such a motor drive device of the present invention, a switching power supply that supplies drive power of a specified voltage value to the motor and a control unit that controls the rotational speed of the motor are mounted. The switching power supply incorporates a transformer. An external power supply is connected to the primary side of the transformer via a switching circuit, and a drive power supply circuit that supplies drive power to the motor and an operating power supply circuit that supplies operating power to the control unit are connected to the secondary side of the transformer. Then, by detecting the voltage value of the drive power supplied to the motor and performing feedback control on the duty ratio of the switching circuit, when the voltage value of the drive power supplied to the motor is adjusted to the specified voltage value, the voltage value of the operating power supplied to the control unit is adjusted to a predetermined voltage value. Here, the control unit can detect that the voltage value of the drive voltage has exceeded a predetermined threshold voltage value, and when the voltage value of the drive power exceeds the threshold voltage value following the execution of deceleration control to reduce or stop the rotational speed of the motor, control is executed to maintain the rotational speed of the motor or increase the rotational speed.

[0010] When reducing or stopping the rotational speed of the motor, the control unit decreases the current value flowing through the motor. However, when the current value flowing through the motor is decreased, a counter electromotive force is generated in the coil built into the motor. For this reason, when performing deceleration control to rapidly reduce the rotational speed of the motor or suddenly stop the motor, the voltage value of the drive power supplied to the motor may increase significantly. When the voltage value of the drive power increases significantly, the feedback control unit detects the voltage value and greatly decreases the duty ratio of the switching circuit, so the voltage value of the operating power supplied by the switching power supply to the control unit decreases significantly. As a result, it may become impossible to supply the control unit with operating power of a predetermined voltage value, the control unit may not operate normally, or the control unit may stop operating and it may become impossible to control the rotational speed of the motor. On the other hand, when the voltage value of the drive power exceeds the threshold voltage value, if control is executed to maintain the rotational speed of the motor or increase the rotational speed, no counter electromotive force will be generated, so the voltage value of the drive power exceeding the threshold voltage value can be rapidly decreased. As a result, a situation where the duty ratio of the switching circuit greatly decreases is avoided, so it is possible to supply the control unit with operating power of a predetermined voltage value. For this reason, even when attempting to rapidly reduce the rotational speed of the motor or stop the motor, it becomes possible to control the rotational speed of the motor.

[0011] Also, in the motor drive device of the present invention described above, the control unit may acquire information on the duty ratio that the feedback control unit feeds back to the switching circuit or information on the duty ratio in the switching circuit. Then, based on the information on the duty ratio, it may be determined whether or not the voltage value of the drive power exceeds the threshold voltage value.

[0012] Since the voltage value of the drive power is fed back to the duty ratio of the switching circuit, the duty ratio in the switching circuit reflects the voltage value of the drive power. Therefore, even without detecting the voltage value of the drive power, it is possible to determine whether or not the voltage value of the drive power exceeds the threshold voltage value based on the information on the duty ratio.

[0013] Further, in the motor drive device of the present invention described above, when the voltage value of the drive power exceeds the threshold voltage value as the deceleration control for reducing or stopping the rotational speed of the motor is executed, the control unit may confirm that the state (the state where the voltage value of the drive power exceeds the threshold voltage value) continues for a predetermined time or longer, and execute control to maintain the rotational speed of the motor or increase the rotational speed.

[0014] By doing so, it is possible to prevent a situation in which, due to the influence of noise or the like, it is erroneously determined that the voltage value of the drive power exceeds the threshold voltage value, and as a result, control to maintain the rotational speed of the motor or increase the rotational speed is erroneously executed.

[0015] Further, in the motor drive device of the present invention described above, when the control unit increases the rotational speed of the motor in response to the voltage value of the drive power exceeding the threshold voltage value, the control unit may determine the increase amount for increasing the rotational speed of the motor based on the rotational speed of the motor at the start of the deceleration control or during the deceleration control.

[0016] The purpose of increasing the rotational speed of the motor is to rapidly reduce the voltage value of the driving power by generating a counter electromotive force with a polarity different from that of the counter electromotive force caused by reducing or stopping the rotational speed of the motor. Therefore, if the increase amount of the rotational speed of the motor is too large, there is a risk that the voltage value of the driving power will be reduced too much. For example, when the current rotational speed is 300 rpm, if the rotational speed is increased by 100 rpm, the increase amount seems to be too large. However, if the current rotational speed is 3000 rpm, increasing the rotational speed by 100 rpm does not seem to have too large an increase amount. From this, it is considered that the appropriate increase amount of the rotational speed varies according to the rotational speed of the motor. Therefore, if the increase amount of the rotational speed of the motor is determined based on the rotational speed of the motor at the start of the deceleration control or during the deceleration control (for example, when the voltage value of the driving power exceeds the threshold voltage value during the deceleration control), the rotational speed can be increased by an appropriate increase amount, and the voltage value of the driving power can be rapidly reduced. As a result, it is possible to continuously supply the operating power of a predetermined voltage value to the control unit, and it becomes possible to control the rotational speed of the motor.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0018] FIG. 1 is an explanatory diagram showing the circuit configuration of the motor drive device 10 of this embodiment. The motor drive device 10 of this embodiment is connected to an external commercial power supply 1 and a motor 2, generates drive power of a specified voltage value using the power supplied from the commercial power supply 1, and drives the motor 2 by supplying this drive power to the motor 2.

[0019] Inside the motor drive device 10, a transformer 11 for converting voltage and a microcomputer 12 for controlling the rotational speed of the motor 2 are mounted. A smoothing circuit 13 is connected to the primary coil Col0 of the transformer 11 via a switching circuit 14. Here, the smoothing circuit 13 has a function of rectifying and smoothing the AC voltage supplied from the commercial power supply 1 to generate a DC voltage. Further, the switching circuit 14 has a function of converting the DC voltage generated by the smoothing circuit 13 into a pulsed voltage and applying it to the primary coil Col0 of the transformer 11. Note that the microcomputer 12 of this embodiment corresponds to the "control unit" in the present invention.

[0020] On the secondary side of the transformer 11, a first coil Col1 is wound with a number of turns N1, and separately from the first coil Col1, a second coil Col2 is wound with a number of turns N2. Also, a first smoothing circuit 15 including a diode D1 and a capacitor C1 is connected to the first coil Col1 of the transformer 11, and a second smoothing circuit 16 including a diode D2 and a capacitor C2 is connected to the second coil Col2. Therefore, when the commercial power supply 1 is connected to the primary side of the transformer 11 and the switching circuit 14 is operated, a pulsed voltage is generated in the first coil Col1 and the second coil Col2 on the secondary side. Then, by smoothing the voltage generated in the first coil Col1 with the first smoothing circuit 15, a DC voltage V1 can be generated at the output point P1 of the first smoothing circuit 15. Similarly, by smoothing the voltage generated in the second coil Col2 with the second smoothing circuit 16, a DC voltage V2 can be generated at the output point P2 of the second smoothing circuit 16.

[0021] Here, the voltage value of the DC voltage V1 at the output point P1 of the first smoothing circuit 15 is determined by the voltage value of the commercial power supply 1, the turns ratio between the primary coil Col0 and the secondary first coil Col1 of the transformer 11, and the duty ratio of the switching circuit 14 (accurately, the time ratio during which voltage is applied to the primary coil Col0 of the transformer 11). Therefore, the turns ratio between the primary coil Col0 and the secondary first coil Col1 and the duty ratio of the switching circuit 14 are set to appropriate turns ratios and duty ratios such that the DC voltage V1 at the output point P1 of the first smoothing circuit 15 becomes the voltage value of the driving power to be supplied to the motor 2 (i.e., the specified voltage value). For this reason, by connecting the output point P1 of the first smoothing circuit 15 to the motor 2, driving power with the specified voltage value can be supplied to the motor 2.

[0022] Also, downstream of the output point P1 of the first smoothing circuit 15, a feedback circuit 17 is mounted in parallel with the first smoothing circuit 15. The feedback circuit 17 detects the voltage value of the DC voltage V1 output from the first smoothing circuit 15 (therefore, the voltage value of the driving power supplied to the motor 2) and compares the detected voltage value with the specified voltage value of the driving power to be supplied to the motor 2. As a result, when the detected voltage value is higher than the specified voltage value of the driving power, control is performed so that the duty ratio of the switching circuit 14 becomes smaller, and when the detected voltage value is lower than the specified voltage value, control is performed so that the duty ratio of the switching circuit 14 becomes larger. In this way, by detecting the voltage value supplied to the motor 2 and performing feedback control on the duty ratio of the switching circuit 14, it is possible to control the voltage value of the driving power supplied to the motor 2 to become the specified voltage value.

[0023] As described above, the motor drive device 10 of this embodiment drives the motor 2 by supplying drive power of a specified voltage value to the motor 2. In addition to this, it is also possible to control the rotational speed of the motor 2. That is, the motor drive device 10 is equipped with a microcomputer 12. The microcomputer 12 detects the rotational speed of the motor 2 and compares the detected rotational speed with a target rotational speed. Then, when the detected rotational speed is greater than the target rotational speed, the current value flowing through the motor 2 is decreased, and when the detected rotational speed is less than the target rotational speed, the current value flowing through the motor 2 is increased to control the rotational speed of the motor 2. In order to operate the microcomputer 12, it is necessary to supply operating power of a specified voltage value to the microcomputer 12, and this operating power is generated as follows.

[0024] First, as described above, when the commercial power supply 1 is connected to the primary side of the transformer 11 and the switching circuit 14 is operated, a DC voltage V1 is generated at the output point P1 of the first smoothing circuit 15 on the secondary side, and a DC voltage V2 is generated at the output point P2 of the second smoothing circuit 16. Here, the number of turns N2 of the second coil Col2 wound around the secondary side of the transformer 11 is a value smaller than the number of turns N1 of the first coil Col1. For this reason, the DC voltage V2 at the output point P2 of the second smoothing circuit 16 is a smaller voltage than the DC voltage V1 at the output point P1 of the first smoothing circuit 15 at a fixed ratio determined according to the turns ratio (=N2 / N1).

[0025] In this embodiment, the turns ratio (= N2 / N1) of the first coil Col1 and the second coil Col2 is set such that when the DC voltage V1 output from the first smoothing circuit 15 becomes the specified voltage value of the driving power, the DC voltage V2 output from the second smoothing circuit 16 becomes a voltage value smaller than the predetermined voltage value of the operating power. Also, a booster circuit 18 is mounted downstream of the second smoothing circuit 16, and after boosting the DC voltage V2 output from the second smoothing circuit 16 to the predetermined voltage value of the operating power to be supplied to the microcomputer 12, it is supplied to the microcomputer 12. By doing so, even if the voltage value of the DC voltage V2 output from the second smoothing circuit 16 fluctuates, the voltage value is boosted to the predetermined voltage value by the booster circuit 18, so that the microcomputer 12 can be stably supplied with the operating power of the predetermined voltage value.

[0026] Note that in this embodiment, the transformer 11, the switching circuit 14 connected to the primary side of the transformer 11, and the first smoothing circuit 15 and the second smoothing circuit 16 connected to the secondary side of the transformer 11 together form one switching power supply 20. Also, the connection line 19a connecting the first smoothing circuit 15 and the motor 2 corresponds to the "driving power supply circuit" in the present invention, and the connection line 19b connecting the second smoothing circuit 16 and the microcomputer 12 corresponds to the "operating power supply circuit" in the present invention. Further, the feedback circuit 17 of this embodiment corresponds to the "feedback control unit" in the present invention.

[0027] Also, the microcomputer 12 of this embodiment monitors the voltage value of the driving power supplied to the motor 2 and reflects the result in the control of the rotational speed of the motor 2. By doing so, even when the rotational speed of the motor 2 is rapidly decreased or the motor 2 is suddenly stopped, it is possible to avoid a situation where the rotational speed cannot be controlled. Hereinafter, the reason why this is possible will be explained.

[0028] In the example shown in FIG. 1, a signal line 17a is connected from the feedback circuit 17 to the microcomputer 12, and the microcomputer 12 monitors the voltage value of the driving power detected by the feedback circuit 17 by acquiring it via the signal line 17a. However, it is sufficient if the microcomputer 12 can monitor the voltage value, and other methods may be used to monitor the voltage value. For example, the microcomputer 12 may directly detect the voltage value of the driving power supplied to the electric motor 2 to monitor the voltage value.

[0029] FIG. 2 is an explanatory diagram showing the circuit configuration of a conventional electric motor driving device 90 in which the microcomputer 12 does not monitor the voltage value of the driving power. When compared with the electric motor driving device 10 of the present embodiment described above with reference to FIG. 1, the conventional electric motor driving device 90 is different in that there is no signal line 17a extending from the feedback circuit 17 to the microcomputer 12. When the rotational speed of the electric motor 2 of this conventional electric motor driving device 90 is rapidly decreased or the electric motor 2 is suddenly stopped, the rotational speed may become uncontrollable. This is due to the following reasons.

[0030] First, when the rotational speed of the electric motor 2 is decreased, the microcomputer 12 decreases the current value flowing through the electric motor 2. Then, the rotational torque generated by the electric motor 2 decreases and the rotational speed decreases. Here, the electric motor 2 has a structure in which a plurality of coils are wound around an iron core called a yoke, and the current supplied to the electric motor 2 flows through the coils. Therefore, when the current value flowing through the electric motor 2 is decreased, a counter electromotive force in the direction of continuing to flow current through the coils is generated due to the self-induction action of the coils.

[0031] This back electromotive force acts in a direction to increase the voltage value (V1) at the output point P1 of the first smoothing circuit 15. However, since the capacitor C1 in the first smoothing circuit 15 is charged, the actually increased voltage value is only the voltage value corresponding to the increase in the charge amount charged in the capacitor C1. And if the increase in the voltage value is of this degree, by reducing the duty ratio of the switching circuit 14 in the feedback circuit 17, the voltage value at the output point P1 of the first smoothing circuit 15 can be corrected to the specified voltage value of the driving power. Also, along with the reduction of the duty ratio of the switching circuit 14 by the feedback circuit 17, the voltage value (V2) at the output point P2 of the second smoothing circuit 16 decreases. However, if the amount of decrease is of this degree, it can be boosted to a predetermined voltage value by the boost circuit 18, so that the microcomputer 12 can supply the operating power of the predetermined voltage value.

[0032] However, when the rotational speed of the electric motor 2 is rapidly decreased, the microcomputer 12 needs to rapidly decrease the current value flowing through the electric motor 2. Or, when the electric motor 2 is suddenly stopped, the microcomputer 12 needs to suddenly set the current value flowing through the electric motor 2 to zero. In these cases, a large back electromotive force is generated in the coil in the electric motor 2. Even if a large back electromotive force is generated in the coil in the electric motor 2, while the capacitor C1 in the first smoothing circuit 15 can be charged, the increase in the voltage value (V1) at the output point P1 of the first smoothing circuit 15 is suppressed. However, when the capacitor C1 is full and cannot be charged anymore, the back electromotive force generated in the coil in the electric motor 2 is directly reflected, and the voltage value (V1) at the output point P1 of the first smoothing circuit 15 increases significantly. Then, the feedback circuit 17 detects this increase in the voltage value and as a result, greatly reduces the duty ratio of the switching circuit 14, so that the voltage value (V1) at the output point P1 of the first smoothing circuit 15 is corrected to the specified voltage value of the driving power supplied to the electric motor 2.

[0033] At this time, the voltage value (V2) at the output point P2 of the second smoothing circuit 16 decreases significantly as the duty ratio of the switching circuit 14 decreases significantly. Then, in the boost circuit 18, the voltage value of the operating power supplied to the microcomputer 12 cannot be boosted to a predetermined voltage value, and the voltage value of the operating power supplied to the microcomputer 12 becomes lower than the predetermined voltage value, making it impossible to operate the microcomputer 12 normally. Furthermore, when the voltage value boosted by the boost circuit 18 becomes lower than the reset voltage value of the microcomputer 12, the microcomputer 12 is reset automatically, and the rotational speed of the electric motor 2 cannot be controlled.

[0034] Therefore, in order to avoid such a situation, in the electric motor drive device 10 of this embodiment, the microcomputer 12 monitors the voltage value at the output point P1 of the first smoothing circuit 15 (therefore, the voltage value of the drive power supplied to the electric motor 2), and reflects the result in the control of the rotational speed of the electric motor 2.

[0035] Figure 3 is a flowchart of the rotational speed control process in which the microcomputer 12 mounted on the electric motor drive device 10 of this embodiment controls the rotational speed of the electric motor 2. As shown in the figure, in the rotational speed control process, the target rotational speed of the electric motor 2 is acquired (STEP10). Then, the current rotational speed of the electric motor 2 is detected (STEP11), and it is determined whether the difference between the current rotational speed and the target rotational speed is within a predetermined allowable value (STEP12). As a result, if the difference in rotational speed is within the allowable value (STEP12: yes), it is considered that no change in rotational speed is required, so the process returns to the beginning, and the target rotational speed is acquired again (STEP10).

[0036] On the other hand, when the difference between the current rotational speed and the target rotational speed is greater than the allowable value (STEP12: no), it is considered necessary to bring the current rotational speed closer to the target rotational speed. Therefore, it is determined whether the current rotational speed is greater than the target rotational speed (STEP13). As a result, when the current rotational speed is greater than the target rotational speed (STEP13: yes), it is necessary to decrease the current rotational speed (if the target rotational speed is zero, it is necessary to stop the motor 2). Therefore, according to the difference in rotational speed, the current value flowing through the motor 2 is decreased (STEP14). Conversely, when the current rotational speed is less than the target rotational speed (STEP13: no), it is necessary to increase the current rotational speed. Therefore, according to the difference in rotational speed, the current value flowing through the motor 2 is increased (STEP15).

[0037] Here, as described above with reference to FIG. 2, when the current value flowing through the motor 2 is decreased, the voltage value of the driving power supplied to the motor 2 may increase significantly due to the back electromotive force generated in the coil in the motor 2. When the voltage value of the driving power increases significantly, the duty ratio of the switching circuit 14 decreases due to the operation of the feedback circuit 17. As a result, there is a possibility that the operating power of a predetermined voltage value cannot be supplied to the microcomputer 12. On the other hand, when the current value flowing through the motor 2 is increased, since the back electromotive force generated in the coil acts in the direction of decreasing the voltage value of the driving power supplied to the motor 2, the duty ratio of the switching circuit 14 increases due to the operation of the feedback circuit 17. Therefore, there is no possibility that the voltage value of the operating power supplied to the microcomputer 12 falls below the predetermined voltage value.

[0038] Therefore, when the current value flowing through the electric motor 2 is increased (STEP15), it is considered that the rotation speed control can be continued as it is. So, return to the start of the process, obtain the target rotation speed again (STEP10), and then perform the above-described series of operations. On the other hand, when the current value flowing through the electric motor 2 is decreased (STEP14), in order to avoid a situation where the microcomputer 12 cannot be supplied with the operating power of a predetermined voltage value, the following operations are performed.

[0039] First, obtain the voltage value of the driving power supplied to the electric motor 2 (STEP16). As shown in FIG. 1, in the electric motor drive device 10 of this embodiment, since the microcomputer 12 and the feedback circuit 17 are connected by the signal line 17a, the microcomputer 12 can obtain the voltage value of the driving power detected by the feedback circuit 17. Of course, it is not limited to this, and the microcomputer 12 may directly detect the voltage value of the driving power.

[0040] Then, determine whether the obtained voltage value of the driving power is greater than a predetermined threshold voltage value (STEP17). As a result, if the obtained voltage value is not greater than the threshold voltage value (STEP17: no), it is considered that there is no risk that the microcomputer 12 cannot be supplied with the operating power of a predetermined voltage value. So, return to the start of the process, obtain the target rotation speed again (STEP10), and then perform the above-described series of operations.

[0041] On the other hand, if the acquired voltage value is greater than the threshold voltage value (STEP17: yes), then it is determined whether the state where the acquired voltage value is greater than the threshold voltage value has continued for a predetermined time or more (STEP18). That is, since there is a possibility that a high voltage value has been detected instantaneously due to the influence of noise or the like, it is determined whether the state where the voltage value is greater than the threshold voltage value has continued for a predetermined time or more (STEP18). As a result, if it has not continued for a predetermined time or more (STEP18: no), there is a possibility that an incorrect voltage value has been detected due to the influence of noise or the like. Therefore, once the process returns to the beginning, after acquiring the target rotation speed again (STEP10), the above-described series of operations are continued.

[0042] On the other hand, if the state where the voltage value is greater than the threshold voltage value has continued for a predetermined time or more (STEP18: yes), there is a risk that the operating power of the predetermined voltage value cannot be supplied to the microcomputer 12 as it is. Therefore, in this case, for a certain period of time (for example, about 2 to 5 seconds), the target rotation speed of the electric motor 2 is changed to the current rotation speed (STEP19). By doing so, the current value flowing through the electric motor 2 is maintained at the current current value. According to the so-called law of electromagnetic induction, the magnitude of the back electromotive force generated in the coil is proportional to the change rate of the current value. Therefore, if the current value flowing through the electric motor 2 is maintained, the back electromotive force becomes zero. As a result, the duty ratio of the switching circuit 14 returns to the normal duty ratio, and it becomes possible to supply the operating power of the predetermined voltage value to the microcomputer 12.

[0043] As described above, in the electric motor drive device 10 of this embodiment, even when the rotation speed of the electric motor 2 is rapidly decreased or the electric motor 2 is suddenly stopped, if the voltage value of the drive power supplied to the electric motor 2 exceeds the threshold voltage value, the rotation speed of the electric motor 2 is maintained for a certain period of time, so that the microcomputer 12 can operate normally.

[0044] Furthermore, in the above-described embodiment, it has been described that when the voltage value of the drive power supplied to the motor 2 becomes greater than the threshold voltage value (STEP17: yes) and this state continues for a predetermined time or more (STEP18: yes), the target rotational speed is changed to the current rotational speed for a certain period of time (STEP19). However, in STEP19, instead of changing the target rotational speed to the current rotational speed, the target rotational speed may be changed to a rotational speed that is higher than the current rotational speed by a certain rotational speed (for example, 50 rpm). By doing so, the current value flowing through the motor 2 increases, so a counter electromotive force with a polarity different from that when the current value was decreased is generated. As a result, it becomes possible to quickly eliminate the counter electromotive force generated in the coil within the motor 2.

[0045] Alternatively, when changing the target rotational speed to a higher rotational speed than the current rotational speed, as the current rotational speed (the rotational speed at the time when the voltage value of the drive power exceeds the threshold voltage) becomes higher, the increase amount of the rotational speed may be increased. That is, the purpose of increasing the rotational speed of the motor 2 is to quickly reduce the voltage value of the drive power by generating a counter electromotive force with a polarity different from the counter electromotive force generated by reducing the rotational speed or stopping the motor 2. Therefore, if the increase amount of the rotational speed of the motor 2 is too large, there is a risk that the voltage value of the drive power will be reduced too much. For example, when the current rotational speed is 300 rpm, increasing the rotational speed by 100 rpm seems to be too large an increase amount. On the other hand, if the current rotational speed is 3000 rpm, increasing the rotational speed by only 100 rpm does not seem to be too large an increase amount. From this, it is considered that an appropriate increase amount of the rotational speed differs depending on the rotational speed of the motor. Therefore, if the increase amount of increasing the rotational speed is determined according to the rotational speed of the motor 2, the rotational speed can be increased by an appropriate increase amount. As a result, the voltage value of the drive power can be quickly reduced and the operating power of a predetermined voltage value can be continuously supplied to the microcomputer 12, so that the rotational speed of the motor 2 can be controlled.

[0046] So far, in the above description, it has been described that the increase amount of the rotational speed is determined based on the rotational speed of the electric motor 2 when the voltage value of the driving power exceeds the threshold voltage. However, the increase amount of the rotational speed may be determined based on the rotational speed of the electric motor 2 when reducing the current value flowing through the electric motor 2, rather than the rotational speed when the voltage value of the driving power exceeds the threshold voltage. By doing so, it is not necessary to detect the rotational speed of the electric motor 2 when the voltage value of the driving power exceeds the threshold voltage, so the control can be simplified.

[0047] Also, in the above-described embodiment, it has been described that the microcomputer 12 acquires the voltage value of the driving power supplied to the electric motor 2 from the feedback circuit 17 and determines whether the acquired voltage value is greater than the threshold voltage value. However, the feedback circuit 17 determines the duty ratio information to be fed back to the switching circuit 14 by detecting the voltage value of the driving power supplied to the electric motor 2. Therefore, the duty ratio information (or the duty ratio information in the switching circuit 14) fed back by the feedback circuit 17 reflects the voltage value of the driving power supplied to the electric motor 2. Thus, by acquiring this duty ratio information, it may be possible to determine whether the voltage value of the driving power supplied to the electric motor 2 is greater than the threshold voltage value.

[0048] FIG. 4 is a flowchart of the rotational speed control process of a modified example in which it is determined whether the voltage value of the driving power supplied to the electric motor 2 is greater than the threshold voltage value based on the duty ratio. The rotational speed control process of this modified example is different from the rotational speed control process of the present embodiment described above with reference to FIG. 3 only in that the operations of STEP16 to STEP18 in FIG. 3 are changed to the operations of STEP26 to STEP28 in FIG. 4. Hereinafter, focusing on this difference, the rotational speed control process of the modified example will be briefly described.

[0049] Even in the rotational speed control process of the modified example, first, the target rotational speed of the electric motor 2 is obtained (STEP10). Subsequently, the current rotational speed of the electric motor 2 is detected (STEP11), and it is determined whether the difference between the current rotational speed and the target rotational speed is within a predetermined allowable value (STEP12). As a result, if the difference in rotational speed is within the allowable value (STEP12: yes), the process returns to the beginning. However, if the difference between the current rotational speed and the target rotational speed is greater than or equal to the allowable value (STEP12: no), then it is subsequently determined whether the current rotational speed is greater than the target rotational speed (STEP13). As a result, if the current rotational speed is greater than the target rotational speed (STEP13: yes), the current value flowing through the electric motor 2 is decreased according to the difference in rotational speed (STEP14). Conversely, if the current rotational speed is less than the target rotational speed (STEP13: no), the current value flowing through the electric motor 2 is increased according to the difference in rotational speed (STEP15).

[0050] And when the current value flowing through the electric motor 2 is increased (STEP15), the process returns to the beginning to obtain the target rotational speed again (STEP10). In contrast, when the current value flowing through the electric motor 2 is decreased (STEP14), in the rotational speed control process of the modified example, the duty ratio information from the feedback circuit 17 to the switching circuit 14 is obtained (STEP26). Alternatively, the duty ratio information may be obtained directly from the switching circuit 14.

[0051] Then, it is determined whether or not the obtained duty ratio is smaller than a predetermined threshold duty ratio (STEP27). As a result, if the duty ratio is larger than the threshold duty ratio (STEP27: no), it is considered that the voltage value of the drive power supplied to the motor 2 does not exceed the threshold voltage value, so the process returns to the beginning and the target rotational speed is obtained again (STEP10). On the other hand, if the duty ratio is smaller than the threshold duty ratio (STEP27: yes), it is considered that the voltage value of the drive power supplied to the motor 2 exceeds the threshold voltage value. Therefore, this time, it is determined whether or not the state where the duty ratio is smaller than the threshold duty ratio has continued for a predetermined time or more (STEP28). As a result, if it has not continued for a predetermined time or more (STEP28: no), there is a possibility that an incorrect duty ratio has been detected due to the influence of noise or the like. Therefore, once, the process returns to the beginning and the target rotational speed is obtained again (STEP10). On the other hand, if the state where the duty ratio is smaller than the threshold duty ratio has continued for a predetermined time or more (STEP28: yes), there is a risk that the operating power of a predetermined voltage value cannot be supplied to the microcomputer 12 as it is. Therefore, in this case, for a certain period of time, the target rotational speed of the motor 2 is changed to the current rotational speed (STEP19).

[0052] Even in the rotational speed control process of such a modification, for the same reasons as in the rotational speed control process of the above-described present embodiment, even when the rotational speed of the motor 2 is rapidly decreased or the motor 2 is suddenly stopped, it is possible to keep the microcomputer 12 operating normally.

[0053] As described above, the motor drive device 10 of the present embodiment and the modification has been described. However, the present invention is not limited to the above-described embodiment and modification, and can be implemented in various modes without departing from the gist thereof.

Explanation of Reference Numerals

[0054] 1... Commercial power supply, 2... Motor, 10... Motor drive device, 11... Transformer 12… Microcomputer, 13… Smoothing circuit, 14… Switching circuit, 15… First smoothing circuit, 16… Second smoothing circuit, 17… Feedback circuit, 17a… Signal line, 18… Boost circuit, 19a… Connection, 19b… Connection, 20… Switching power supply, 90… Motor drive device, Col0… Coil, Col1… First coil, Col2… Second coil, D1… Diode, C1… Capacitor, P1… Output point, D2… Diode, C2… Capacitor, P2… Output point.

Claims

1. In an electric motor drive device that drives the electric motor by supplying driving power of a specified voltage value to the electric motor and controls the rotational speed of the electric motor, a control unit that operates by having operating power of a predetermined voltage value supplied thereto and controls the rotational speed of the electric motor; an external power source is connected to the primary side of a transformer via a switching circuit, a driving power supply circuit that supplies the driving power to the electric motor is connected to a first coil on the secondary side of the transformer, an operating power supply circuit that supplies the operating power to the control unit is connected to a second coil on the secondary side of the transformer, and by adjusting the duty ratio of the switching circuit, the voltage value of the driving power supplied to the electric motor is adjusted to the specified voltage value, and the voltage value of the operating power supplied to the control unit is adjusted to the predetermined voltage value, a switching power supply; a feedback control unit that detects the voltage value of the driving power supplied to the electric motor and performs feedback control on the duty ratio of the switching circuit are provided, the control unit detects the voltage value of the driving power, and when the voltage value of the driving power exceeds a predetermined threshold voltage value with the execution of deceleration control for reducing or stopping the rotational speed of the electric motor, performs either control for maintaining the rotational speed of the electric motor or control for increasing the rotational speed An electric motor drive device characterized by the above.

2. In the electric motor drive device according to Claim 1, the control unit determines whether or not the voltage value of the driving power exceeds the threshold voltage value by obtaining information on the duty ratio that the feedback control unit feeds back to the switching circuit or information on the duty ratio in the switching circuit. An electric motor drive device characterized by the above.

3. In the electric motor drive device according to Claim 1 or Claim 2, when the voltage value of the driving power continuously exceeds the threshold voltage value for a predetermined time or more with the execution of the deceleration control, the control unit performs either control for maintaining the rotational speed of the electric motor or control for increasing the rotational speed. An electric motor drive device characterized by the above.

4. In the electric motor drive device according to any one of Claims 1 to 3, When the control unit increases the rotational speed of the electric motor in response to the voltage value of the drive power exceeding the threshold voltage value, the control unit determines the increase amount for increasing the rotational speed of the electric motor based on the rotational speed of the electric motor at the start of the deceleration control or during the deceleration control. An electric motor drive device characterized by the above.

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