Motor control device

Abstract

A motor control device according to one aspect of this disclosure is, in a motor drive system including a drive motor capable of a regenerative operation for driving a drive target and a buffer motor capable of a regenerative operation for driving a flywheel for accumulating energy, a motor control device for controlling the buffer motor, the motor control device including a buffer control unit for causing the buffer motor to perform a power running operation, when power consumption of the drive motor is equal to or smaller than a power threshold value, and a threshold-value change unit for changing a value of the power threshold value on the basis of at least power consumption of the drive motor.

Description

Motor control device

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

[0002] In machine tools and the like where the required load temporarily increases, a known technique is to provide a drive motor that drives the driven object and a buffer motor that drives a flywheel that converts electric power into rotational energy and stores it, and when the load exceeds the output of the drive motor with the electric power that can be supplied from the power source, to operate the buffer motor in a regenerative manner, converting the rotational energy stored in the flywheel into electric power and supplying it to the drive motor.

[0003] For example, in the drive system described in Patent Document 1, the buffer motor is powered and regenerated so that the buffer motor approaches a base speed within a range in which the total power consumption of the drive motor and the buffer motor does not exceed positive and negative thresholds, thereby preventing the total power consumption of the drive motor and the buffer motor from exceeding the power allowed by the power supply.

[0004] Japanese Patent Application Laid-Open No. 2019-7563

[0005] In the drive system of Patent Document 1, when the total power consumption falls below a threshold, the flywheel speed is immediately restored to the base speed using power supplied from the primary power source. Therefore, the flywheel often returns to the base speed before the drive motor begins to generate regenerative power. In other words, in the drive system of Patent Document 1, when the rotational speed of the flywheel decreases, a large amount of power supplied from the primary power source is consumed to increase the rotational speed of the flywheel, and when the rotational speed of the flywheel increases, a large amount of power is discharged to the primary power source to decrease the rotational speed of the flywheel. Power transfer to and from the primary power source requires forward and reverse conversion of power, and this power conversion also results in losses. Therefore, in a system including a drive motor that drives a driven object and a buffer motor that drives a flywheel, power consumption can be effectively reduced if the amount of power discharged to the primary power source can be reduced.

[0006] A motor control device according to one aspect of the present disclosure is a motor control device for controlling a buffer motor in a motor drive system including a drive motor that drives a driven object and a buffer motor that drives a flywheel that stores energy, and includes: a buffer control unit that, when the power consumption of the drive motor is equal to or less than a power threshold, causes the buffer motor to perform powering operation so as to bring the rotational speed closer to a predetermined base speed; and a threshold change unit that changes the value of the power threshold based at least on the power consumption of the drive motor.

[0007] 1 is a block diagram showing the configuration of a motor drive system including a motor control device according to a first embodiment of the present disclosure; FIG. 2 is a flowchart showing a procedure for selecting a power threshold in a threshold changing unit of the motor control device of FIG. 1; FIG. 3 is a graph illustrating the relationship between the power consumption of the drive motor, the total power consumption of the drive motor and the buffer motor, and the rotation speed of the buffer motor in the motor control device of FIG. 2; FIG. 4 is a flowchart showing a procedure for selecting a power threshold different from those in FIGS. 3 and 2 in the threshold changing unit of the motor control device of FIG. 4; and FIG. 5 is a graph illustrating the relationship between the power consumption of the drive motor, the total power consumption of the drive motor and the buffer motor, and the rotation speed of the buffer motor in the motor control device of FIG.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present disclosure will now be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing the configuration of a motor drive system including a motor control device according to an embodiment of the present disclosure.

[0009] 1 is a block diagram showing the configuration of a motor drive system 1 including a motor control device 40 according to a first embodiment of the present disclosure. The motor drive system 1 includes a common power source 10 supplied with power from a primary power source S, a drive motor 22 that drives a driven object (load) 21, a drive servo amplifier 23 that drives the drive motor 22, a flywheel 31 that stores energy, a buffer motor 32 that drives the flywheel 31, a buffer servo amplifier 33 that drives the buffer motor 32, and a motor control device 40 that controls the drive motor 22 and the buffer motor 32 via the drive servo amplifier 23 and the buffer servo amplifier 33.

[0010] The common power supply 10 is a converter that converts AC power supplied from the primary power supply S into DC power consumed by the drive servo amplifier 23 and the buffer servo amplifier 33, and ultimately the drive motor 22 and the buffer motor 32. The drive servo amplifier 23 and the buffer servo amplifier 33 convert the DC power supplied from the common power supply 10 into AC power required to match the rotational position or rotational speed of the drive motor 22 and the buffer motor 32 with command values ​​from the motor control device 40, and supply this AC power to the drive motor 22 and the buffer motor 32. The common power supply 10 can also inversely convert regenerated DC power, which is generated when the drive motor 22 acts as a generator during deceleration and is output through the drive servo amplifier 23 and the buffer servo amplifier 33, back into AC and supply it to the primary power supply S. The regenerated power of the drive motor 22 and the buffer motor 32 is interpreted as negative power consumption.

[0011] As an example, the motor drive system 1 may be a machine tool that performs press working and has a punch as the driven object 21. A large output is temporarily required for the drive motor 22 that drives the punch 21, and the drive motor 22 may be designed so that its power consumption (positive power consumption during power running and negative power consumption during regeneration) temporarily exceeds the power that can be converted by the common power source 10.

[0012] The motor drive system 1 converts electric power into rotational energy of the flywheel 31 by driving the buffer motor 32 to approach a predetermined base speed, thereby storing the energy. When the power consumption of the drive motor 22 during powering exceeds the power conversion capacity of the common power supply 10, the motor drive system 1 converts the rotational energy of the flywheel 31 into electric power by operating the buffer motor 32 in a regenerative manner, and supplies electric power from the buffer motor 32 to the drive motor 22 via the buffer servo amplifier 33 and the drive servo amplifier 23, thereby compensating for the insufficient power supply capacity of the common power supply 10. Furthermore, when the negative power consumption during regeneration of the drive motor 22 exceeds the power conversion capacity of the common power supply 10, the motor drive system 1 operates the buffer motor 32 in a powering manner to convert part of the regenerative power of the drive motor 22 into rotational energy of the flywheel 31, thereby preventing the power supplied in the reverse direction to the common power supply 10 from exceeding the power conversion capacity of the common power supply 10.

[0013] The motor control device 40 may be realized by one or more computers having, for example, a memory, a processor, an input / output interface, etc., and executing an appropriate control unit program. The motor control device 40 may be part of a numerical control device (not shown) that generates command values ​​specifying the position or speed of the drive motor 22 based on a machining program, or may be an independent device disposed between the numerical control device and the drive servo amplifier 23.

[0014] The motor control device 40 includes a buffer control unit 41 and a threshold change unit 42. These components of the motor control device 40 categorize the functions of the motor control device 40, and do not necessarily have to be clearly distinguishable in terms of physical configuration and program configuration.

[0015] When the power consumption of the drive motor 22 is equal to or less than the power threshold set by the threshold change unit 42 described later and the speed of the buffer motor 32 deviates from the base speed, the buffer control unit 41 causes the buffer motor 32 to perform powering operation or regenerative operation within a range in which the sum (absolute value) of the power consumption of the drive motor 22 and the power consumption of the buffer motor 32 is equal to or less than the power threshold, thereby bringing the speed of the buffer motor 32 closer to the base speed.

[0016] The threshold changing unit 42 changes the value of the power threshold based on the power consumption of the drive motor 22. The threshold changing unit 42 may also determine the value of the power threshold taking into consideration the speed of the buffer motor 32. The threshold changing unit 42 may be configured to acquire the power consumption of the drive motor 22 from the drive servo amplifier 23 and the speed of the buffer motor 32 from the buffer servo amplifier 33. By changing the power threshold in accordance with the power consumption of the drive motor 22, it is possible to suppress the power consumption of the buffer motor 32 from the time when the power consumption of the drive motor 22 becomes smaller than the power conversion capacity of the common power supply 10 until the sign of the power consumption of the drive motor 22 is reversed and the power consumption of the drive motor 22 cancels out (becomes opposite to the sign of the power consumption required to return the buffer motor 32 to the base speed). As a result, after the rotational energy of the flywheel 31 is consumed to power the drive motor 22, the buffer motor 32 is driven by the power regenerated by the drive motor 22 to increase the speed of the flywheel 31 to the base speed, and after a portion of the regenerative energy of the drive motor 22 is converted into rotational energy of the flywheel 31, the drive motor 22 is driven by the regenerative power of the buffer motor 32 to decrease the speed of the flywheel 31 to the base speed. This reduces the amount of power conversion by the common power source 10, and suppresses losses associated with power conversion in the common power source 10.

[0017] The threshold change unit 42 may be configured to select the power threshold from among a maximum setting value, which is the maximum power, and one or more limiting setting values ​​that are smaller than the maximum setting value. By selecting the power threshold from a plurality of preset candidates, the calculation for setting the power threshold is simplified and it is easier to achieve stable control compared to when the power threshold is calculated using a function or the like.

[0018] The threshold change unit 42 may be configured to change the power threshold to the limit setting value when the absolute value of the power consumption of the drive motor 22 falls below the limit setting value. In this way, by changing the power threshold to a smaller value as the power consumption of the drive motor 22 decreases, the amount of power converted (powered or regenerated) into rotational energy of the flywheel 31 is suppressed, and the rotational speed of the flywheel 31 can be restored to the base speed using the power consumption after the power value of the drive motor 22 reverses its positive and negative values. Furthermore, since the buffer motor 32 is driven to gradually bring the speed of the flywheel 31 closer to the base speed until the power consumption of the drive motor 22 reverses its positive and negative values, even if the power consumption of the drive motor 22 fluctuates irregularly and exceeds the power conversion capacity of the common power supply 10, the power consumption of the drive motor 22 can be compensated for by the powering or regenerative operation of the buffer motor 32.

[0019] Furthermore, although not shown, the threshold change unit 42 may be configured to change the power threshold to the maximum setting value when the power consumption of the drive motor 22 rises above the maximum setting value. Similarly, when the power consumption of the drive motor 22 increases, the power threshold is changed to a larger value in accordance with the increase in power consumption of the drive motor 22, thereby suppressing excess or deficiency of energy stored in the flywheel due to excessive regeneration or powering. Furthermore, by setting the power threshold to the maximum setting value, it is possible to control the total power consumption so that it does not exceed the power conversion capacity of the common power supply 10 due to the power consumption of the buffer motor 32.

[0020] FIG. 2 shows an example of a procedure for setting the power threshold when the threshold change unit 42 selects the power threshold from two values: a maximum setting value and a single limited setting value. The power threshold selection procedure in this example includes a step S01 of checking whether the power consumption of the drive motor 22 is equal to or greater than the maximum set value; a step S02 of checking whether the current power threshold is equal to the limited set value, which is executed if the power consumption of the drive motor 22 is not equal to or greater than the maximum set value in step S01; a step S03 of checking whether the power consumption of the drive motor 22 is equal to or less than the limited set value, which is executed if the current power threshold is not equal to the limited set value in step S02; a step S04 of setting the power threshold to the limited set value, which is executed if the current power threshold is equal to the limited set value in step S02 and if the power consumption of the drive motor 22 is equal to or less than the limited set value in step S03; and a step S05 of setting the power threshold to the maximum set value, which is executed if the power consumption of the drive motor 22 is equal to or greater than the maximum set value in step S01 and if the power consumption of the drive motor 22 is not equal to or less than the limited set value in step S03.

[0021] In this control, when the power consumption of the drive motor 22 increases, the power threshold is set to the maximum set value when the power consumption increases to the maximum set value, and when the power consumption of the drive motor 22 decreases, the power threshold is set to the limit set value when the power consumption decreases to the limit set value. In this way, by setting the power consumption at which the power threshold is switched to the maximum set value to be greater than the power consumption at which the power threshold is switched to the limit set value, the power threshold can be stabilized.

[0022] 3 illustrates the changes in the power consumption of the drive motor 22, the total power consumption of the drive motor 22 and the buffer motor 32, and the speed of the buffer motor 32 under the control of FIG. 2 . As shown in the figure, when the power consumption of the drive motor 22 exceeds the maximum set value, i.e., the power conversion capacity of the common power supply 10, the buffer motor 32 operates in a powering or regenerative mode to convert the rotational energy of the flywheel 31 into electric power, thereby compensating for the lack of power conversion capacity of the common power supply 10. When the power consumption of the drive motor 22 falls below the maximum set value, the operating state of the buffer motor 32 switches, and the recovery of the rotational energy of the flywheel 31 (return to base speed) begins. However, once the power consumption of the drive motor 22 decreases to a certain level, the power threshold set by the threshold change unit 42 is changed to a limited set value, thereby suppressing the rate of change in the rotational energy of the flywheel 31. This delays the rotational speed of the buffer motor 32 from reaching the base speed until the power consumption of the drive motor 22 switches between positive and negative, making it possible to offset the power consumption of the buffer motor 32 with the power consumption of the drive motor 22.

[0023] Furthermore, the threshold value changing unit 42 selects a power threshold value from among a maximum set value and a plurality of limit set values, and the limit set value that can be set when the power consumption of the drive motor 22 increases from the negative maximum set value to the positive maximum set value may be different from the limit set value that can be set when the power consumption of the drive motor 22 decreases from the positive maximum set value to the negative maximum set value. This makes it possible to optimize both the storage of energy during powering operation of the buffer motor 32 and the release of energy during regenerative operation of the buffer motor 32.

[0024] The threshold changing unit 42 is configured to use multiple set values ​​of the power threshold as the judgment threshold used to determine whether to switch the power threshold, thereby reducing the number of set values ​​and preventing setting errors that result in an inappropriate relationship between the power threshold and the judgment threshold. However, the threshold changing unit 42 may set a value different from the value that can be selected as the power threshold as the judgment threshold used to determine whether to switch the power threshold. This allows the timing of switching the power threshold to be further optimized.

[0025] The threshold change unit 42 may monotonically increase the power threshold from the minimum limit value to the maximum limit value, thereby preventing the energy stored in the flywheel 31 from increasing or decreasing due to small fluctuations in the power consumption of the drive motor 22 and reducing energy loss.

[0026] The threshold change unit 42 may set the power threshold to the maximum set value when the rotation speed of the buffer motor 32 reaches a predetermined base speed. This makes it possible to prevent unnecessary release of energy stored in the flywheel 31 as the rotation speed of the buffer motor 32 increases, and to increase the amount of power that can be continuously supplied by regeneration of the buffer motor 32. The base speed is a set speed that is considered to provide an optimal amount of energy stored in the flywheel 31 when it is unknown how the power consumption of the drive motor 22 will fluctuate.

[0027] The buffer control unit 41 may be configured to set the torque command to the buffer motor 32 to zero when the threshold value changing unit 42 determines that the power consumption of the drive motor 22 has decreased from above the maximum set value to a value between the maximum set value and the maximum of the limit set value. If the fluctuations in the power consumption of the drive motor 22 are relatively periodic, the buffer motor 32 is not powered until the power consumption of the drive motor 22 has decreased to a certain extent, thereby making it possible to further increase the power saving effect.

[0028] The threshold change unit 42 may set the power threshold to the maximum setting value regardless of the power consumption when the rotation speed of the buffer motor 32 is not within a predetermined standard range. This makes it possible to balance the power running and regeneration of the buffer motor 32 and prevent the rotation energy of the flywheel 31 from being excessive or insufficient. The standard range is preferably set to a range centered around the base speed. In other words, when the rotation speed of the buffer motor 32 deviates greatly from the base speed, the power threshold can be set to the maximum setting value, making it easier to return the rotation speed of the buffer motor 32 to the base speed.

[0029] 4 shows an example of a procedure for selecting a power threshold when the threshold change unit 42 takes into consideration the rotation speed of the buffer motor 32. This control procedure includes a step (step S11) of checking whether the power consumption of the drive motor 22 is equal to or greater than a maximum set value, a step (step S12) that is executed if the power consumption of the drive motor 22 is not equal to or greater than the maximum set value in step S11 and checks whether the speed of the buffer motor 32 is equal to or less than a predetermined speed threshold, a step (step S13) that is executed if the speed of the buffer motor 32 is equal to or less than the predetermined speed threshold in step S12 and checks whether the speed of the buffer motor 32 is equal to or less than a predetermined base speed, a step (step S14) that is executed if the speed of the buffer motor 32 is not equal to the predetermined base speed in step S13 and checks whether the current power threshold is equal to a limited set value, and a step (step S15) that is executed if the current power threshold is not equal to the limited set value in step S14. The process includes a step (step S15) of checking whether the power consumption of the drive motor 22 is equal to or less than the limit setting value, a step (step S16) of setting the power threshold to the limit setting value, which is executed if the current power threshold is equal to or less than the limit setting value in step S14 and if the power consumption of the drive motor 22 is equal to or less than the limit setting value in step S15, and a step (step S17) of setting the power threshold to the maximum setting value, which is executed if the power consumption of the drive motor 22 is equal to or more than the maximum setting value in step S11, if the speed of the buffer motor 32 is not equal to or less than the predetermined speed threshold in step S12, if the speed of the buffer motor 32 is equal to the predetermined base speed in step S13, and if the power consumption of the drive motor 22 is not equal to or less than the limit setting value in step S15.

[0030] 5 illustrates the changes in the power consumption of the drive motor 22, the total power consumption of the drive motor 22 and the buffer motor 32, and the speed of the buffer motor 32 under the control of FIG. 4 . As shown in the figure, when the power consumption of the drive motor 22 exceeds the maximum set value, i.e., the power conversion capacity of the common power supply 10, the buffer motor 32 operates regeneratively to convert the rotational energy of the flywheel 31 into electric power to make up for the power shortfall. When the power consumption of the drive motor 22 falls below the maximum set value, the buffer motor 32 switches to power running and begins to recover the rotational energy of the flywheel 31. However, when the rotational speed of the drive motor 22 decreases to a certain extent, the power threshold set by the threshold change unit 42 is changed to the limited set value, thereby suppressing the rate at which the rotational energy of the flywheel 31 increases. This delays the increase in the rotational speed of the buffer motor 32 until the power consumption of the drive motor 22 reaches a sufficiently negative range, making it possible to operate the drive motor 22 in a regenerative manner and power the buffer motor 32 using the electric power regenerated by the drive motor 22.

[0031] The following supplementary notes are further disclosed regarding the above-described embodiments and modifications. (Supplementary Note 1) A motor control device (40) according to one aspect of the present disclosure is a motor control device (40) for controlling the buffer motor (32) in a motor drive system (1) including a drive motor (22) that drives a driven object (21) and a buffer motor (32) that drives a flywheel (31) that stores energy, the motor control device (40) including: a buffer control unit (41) that causes the buffer motor (32) to perform powering operation or regenerative operation so that its speed approaches a predetermined base speed within a range in which the total power consumption of the drive motor (22) and the buffer motor (32) does not exceed a power threshold; and a threshold change unit (42) that changes the value of the power threshold based on at least the power consumption of the drive motor (22).

[0032] (Supplementary Note 2) In the motor control device (40) of Supplementary Note 1, the threshold value changing unit (42) may select the power threshold value from among a maximum set value that is the maximum power and one or more limit set values ​​that are smaller than the maximum set value.

[0033] (Supplementary Note 3) In the motor control device (40) of Supplementary Note 2, the threshold change unit (42) may change the power threshold to the maximum set value when the power consumption of the drive motor (22) increases above the maximum set value.

[0034] (Supplementary Note 4) In the motor control device (40) of Supplementary Note 3, the threshold change unit (42) may change the power threshold to a limit setting value when the power consumption of the drive motor (22) falls below the limit setting value.

[0035] (Supplementary Note 5) In the motor control device (40) of Supplementary Note 3 or 4, the threshold value changing unit (42) may set the power threshold value to a limited set value regardless of the power consumption of the drive motor (22) when the rotation speed of the buffer motor (32) is within a predetermined standard range.

[0036] (Supplementary Note 6) In the motor control device (40) of Supplementary Notes 3 to 5, the buffer control unit (41) may set the power threshold to the limited set value during the period from when the power consumption of the drive motor (22) falls below the limited set value until it reaches or exceeds the maximum set value.

[0037] (Supplementary Note 7) In the motor control device (40) of Supplementary Notes 3 to 6, the buffer control unit (41) may set the torque command to the buffer motor (32) to zero when the power consumption of the drive motor (22) is smaller than the maximum set value and larger than the maximum of the limit set value.

[0038] (Appendix 8) In the motor control device (40) of Appendices 3 to 7, the threshold value changing unit (42) may have different limit setting values ​​that can be set when the power consumption of the drive motor (22) increases and when the power consumption of the drive motor (22) decreases.

[0039] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of each operation and each process in the above-described embodiments is shown as an example and is not limited to these. As a specific example, instead of the common power supply in the above-described embodiments, individual forward converters may be provided for the drive servo amplifier and the buffer servo amplifier.

[0040] REFERENCE SIGNS LIST 1 Motor drive system 10 Common power supply 21 Drive target 22 Drive motor 23 Drive servo amplifier 31 Flywheel 32 Buffer motor 33 Buffer servo amplifier 40 Motor control device 41 Buffer control unit 42 Threshold value changing unit S Primary power supply

Claims

1. A motor control device for controlling a buffer motor in a motor drive system having a drive motor that drives a driven object and a buffer motor that drives a flywheel that stores energy, the motor control device comprising: a buffer control unit that causes the buffer motor to perform powering operation or regenerative operation so that its speed approaches a predetermined base speed within a range in which the total power consumption of the drive motor and the buffer motor does not exceed a power threshold; and a threshold change unit that changes the value of the power threshold based on at least the power consumption of the drive motor.

2. The motor control device according to claim 1, wherein the threshold change unit selects the power threshold from among a maximum set value that is the maximum power and one or more limit set values ​​that are smaller than the maximum set value.

3. The motor control device according to claim 2, wherein the threshold change unit changes the power threshold to the maximum set value when the power consumption of the drive motor rises above the maximum set value.

4. The motor control device according to claim 3, wherein the threshold change unit changes the power threshold to the limit set value when the power consumption of the drive motor falls below the limit set value.

5. The motor control device according to claim 3 or 4, wherein the threshold value changing unit sets the power threshold value to the limited set value when the rotation speed of the buffer motor is within a predetermined standard range.

6. A motor control device as described in any one of claims 3 to 5, wherein the buffer control unit sets the power threshold to the limit setting value during the period from when the power consumption of the drive motor falls below the limit setting value until when it exceeds the maximum setting value.

7. A motor control device according to any one of claims 3 to 6, wherein the buffer control unit sets the torque command to the buffer motor to zero when the power consumption of the drive motor is less than the maximum set value and greater than the maximum of the limit set value.

8. A motor control device as described in any one of claims 3 to 7, wherein the threshold change unit sets different limit setting values ​​for when the power consumption of the drive motor increases and when the power consumption of the drive motor decreases.

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