Motor control device

Abstract

To suppress influence of ripple current even if an inverter differing in switching frequency exists in a plurality of inverters for supplying power to a plurality of motors.SOLUTION: A motor controller includes: a plurality of inverters for supplying power to a plurality of motors by PWM control: a DC power supply for supplying power to the plurality of inverters; and a capacitor connected to the DC power supply in parallel. The plurality of inverters is classified into any of the plurality of groups based on a switching frequency. In the plurality of groups, a carrier signal corresponding to all inverters belonging to the groups is a triangular wave signal determined on the basis of a reference frequency allocated to the group, and there exist one or more triangular wave signals in which at least one of the frequency and a phase does not overlap with the other triangular wave signal.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, in a servo power supply system, for each of a plurality of motors, power corresponding to the rotational speed of the motor has been supplied from one AC power supply (alternating current power supply). In this way, by supplying power to a plurality of motors, it has been realized that one device operates. However, in such a configuration, there has been a problem that the number of wirings is large and the wiring structure for connecting the motor and the power supply becomes complicated. Furthermore, in such a configuration, many problems such as the wiring becoming thick, noise being easily generated, and heat being easily generated have occurred.

[0003] Therefore, in Patent Document 1, the power of one AC power supply is converted to DC, and this one power is distributed and supplied to a plurality of inverter units that control a plurality of motors. According to this, it is possible to achieve low noise in power supply and make the wiring thinner. Furthermore, in Patent Document 1, when using a plurality of inverters that perform PWM control based on each triangular wave signal (triangular wave) that is a basic waveform of PWM control, the phases of the triangular wave signals of each inverter unit are all made different. According to this, it is possible to suppress the ripple current flowing through the capacitor connected in parallel to the power supply from having an adverse effect on the capacitor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in Patent Document 1, if the switching frequencies of the switching elements are the same in all the inverter sections, the ripple current can be suppressed because the phases of the triangular wave signals of the carrier signals that determine the switching frequency and timing are all different. Therefore, the influence of the ripple current can be effectively suppressed. However, if there is an inverter section with a significantly different switching frequency among the plurality of inverter sections, even if the phases of all the triangular wave signals are made different, the ripple current cannot be sufficiently suppressed, and the influence of the ripple current cannot be effectively suppressed.

[0006] Therefore, an object of the present invention is to provide a technique for suppressing the influence of ripple current even when there is an inverter with a significantly different switching frequency among a plurality of inverters that supply power to a plurality of motors.

Means for Solving the Problem

[0007] To achieve the above object, the present invention adopts the following configuration.

[0008] That is, a motor control device for controlling the operations of a plurality of motors according to one aspect of the present invention includes a plurality of inverters each having a switching element and supplying power to each of the plurality of motors by PWM control based on a carrier signal indicating a basic waveform of the PWM control, a DC power supply for supplying power to the plurality of inverters, and a capacitor connected in parallel with the DC power supply. The plurality of inverters are assigned a reference frequency based on their respective switching frequencies, which is a reference frequency related to the carrier signal for PWM control. The plurality of inverters are classified into any one of a plurality of groups based on the assigned reference frequencies. In each of the plurality of groups, the carrier signals corresponding to all the inverters belonging to the group are triangular wave signals determined based on the reference frequency assigned to the group, and at least one of the carrier signals corresponding to all the inverters does not overlap with other carrier signals in at least one of frequency and phase. It is a motor control device. ​

[0009] According to the above configuration, in the group based on the reference frequency, since the frequencies or phases of the carrier signals (triangular wave signals) do not overlap within each group, the on / off timing of the switching elements can be shifted within each group. Therefore, since the peak of the ripple current generated in the capacitor can be suppressed, the influence of the ripple current in the motor control device can be suppressed.

[0010] In the above motor control device, each of the carrier signals of the plurality of inverters may be a triangular wave signal having a frequency based on the reference frequency of a predetermined group to which the inverter belongs and set so as not to overlap in all the inverters belonging to the predetermined group. Thus, according to the fact that the frequencies do not overlap in one group, different from the case where the phases do not overlap, the synchronization between the carrier signals can be achieved by controlling the frequency change of the carrier signals.

[0011] In the above motor control device, the variation range of the frequency of the carrier signal within each of the plurality of groups is smaller than the difference in the reference frequencies between two groups, i.e., the group and the group closest in reference frequency to the group, and the highest frequency of the carrier signal of the lower group in the two groups may be lower than the lowest frequency of the carrier signal of the higher group. According to this, in two adjacent groups, the frequencies of the carrier signals can be prevented from overlapping. Therefore, between the groups, the on / off frequencies of the switching elements do not overlap. For this reason, since the peak of the ripple current generated in the capacitor can be suppressed, the influence of the ripple current in the motor control device can be suppressed.

[0012] In the above motor control device, the carrier signal of each of the plurality of inverters and the carrier signal of other inverters belonging to the group to which the inverter belongs may have their frequencies switched in different orders from among a predetermined combination consisting of a plurality of frequencies. According to this, synchronization of the carrier signals can be achieved within the group every period of the number of frequencies in the predetermined combination, and it is possible to prevent the peaks of the carrier signals from overlapping except at the synchronization timing. According to this, while realizing synchronization of the carrier signals within the group, it is possible to suppress the peak of the ripple current generated in the capacitor.

[0013] In the above motor control device, all the frequencies included in the predetermined combination may be shifted by a predetermined value obtained by dividing the fluctuation range of the frequency of the carrier signal within the group corresponding to the predetermined combination by the number obtained by subtracting 1 from the number of inverters belonging to the group. According to this, since the frequencies of the carrier signals within the group can be made significantly different, the influence of the ripple current in the motor control device can be further suppressed.

[0014] In the above motor control device, the reference frequency of each of the plurality of inverters may be the same as the reference frequencies of all the other inverters in a predetermined group to which the inverter belongs.

[0015] In the above motor control device, the carrier signal of each of the plurality of inverters is a triangular wave signal having a frequency based on the reference frequency of a predetermined group to which the inverter belongs and is set so that the phases do not overlap in all the inverters belonging to the predetermined group. It may be a signal.

[0016] In the motor control device, the carrier signals of all the inverters belonging to the predetermined group may be shifted in phase by an amount obtained by dividing 180 degrees by the number of inverters belonging to the predetermined group. According to this, since the phases of the carrier signals can be made significantly different within the group, the influence of the ripple current in the motor control device can be further suppressed. More specifically, since the second harmonics in the switching ripple can cancel each other out, the influence of the ripple current in the motor control device can be further suppressed.

[0017] The present invention may be regarded as a device having at least a part of the above means, or may be regarded as a control device, a control system, a motor system, or a motor device. Further, the present invention may be regarded as a control method or a setting method including at least a part of the above processing. Further, the present invention can also be regarded as a program for realizing such a method and a recording medium in which the program is non-temporarily recorded. Note that each of the above means and processing can be combined with each other as much as possible to constitute the present invention.

Effects of the Invention

[0018] According to the present invention, even when there are inverters with significantly different switching frequencies among a plurality of inverters that supply power to a plurality of motors, the influence of the ripple current can be suppressed.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0020] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[0021] <APPLICATION EXAMPLE> Hereinafter, a motor control device 1 that supplies power (AC power) to a plurality of motors 42 as shown in FIGS. 1 and 2 will be described. In the motor control device 1, PWM control (control of the output voltage to the plurality of motors 42) of the inverter 41 is performed by switching the on / off of the switching elements 100 of the plurality of inverters 41. Here, the basic waveform of the PWM control of the inverter 41 is determined by a triangular wave signal (triangular wave) generated by a triangular wave generation circuit 43. Therefore, hereinafter, the motor control device 1 classifies the plurality of inverters 41 into groups based on the switching frequency (reference frequency) of the switching elements 100, and in the inverters 41 of the same group, the phase of the triangular wave signal or the frequency of the triangular wave signal (frequency change) is made different. That is, each of the plurality of inverters 41 performs PWM control based on a triangular wave signal having a phase or frequency different from that of the triangular wave signal used by other inverters 41 in the group to which the inverter 41 belongs. As a result, the on / off timing of the switching elements 100 is shifted between the inverters 41 in the same group, so that the peak of the ripple current in the capacitor 25 connected in parallel with the power supply 20 can be suppressed.

[0022] <EMBODIMENT 1> [Configuration of Motor Control Device] Referring to the configuration diagrams of FIGS. 1 and 2, the configuration of the motor control device 1 that controls a plurality of motors 42 (motors 421 to 427) according to this embodiment will be described. The motor control device 1 includes a power supply 20, a capacitor 25, capacitors 401 to 407, inverters 411 to 417, and a triangular wave generation circuit 43 (see FIG. 2). In FIGS. 1 and 2, seven inverters 41, capacitors 40, and motors 42 are arranged, but any number can be arranged. Also, a device having the motor control device 1 and a plurality of motors 42 may be regarded as a motor system.

[0023] The power supply 20 supplies DC power (DC current) to the inverters 411 to 417. The power supply 20 includes a power grid (AC power supply) and a converter that converts the power from the power grid into DC power (in other words, a DC power supply).

[0024] The capacitor 25 is connected in parallel with the power supply 20. The capacitor 25, in combination with the power supply 20, supplies DC power to a plurality of inverters 411 to 417 connected in parallel to each other. Due to the presence of the capacitor 25, the voltage supplied to the plurality of inverters 411 to 417 is kept substantially constant, so that a sudden (temporary) change (overvoltage / low voltage) in the voltage supplied to the plurality of inverters 411 to 417 can be suppressed. Note that in the capacitor 25, with the change in the operation of the plurality of When the ripple current, which is a current generated with the change in the operation of the inverters 411 to 417, is large, a large heat rise occurs in the capacitor 25, which has an adverse effect on the lifespan of the capacitor 25 and the motor control device 1. Therefore, in this embodiment, it is realized to suppress the peak of this ripple current.

[0025] The capacitors 401 to 407 are smoothing capacitors that suppress the pulsation component of the DC power, and can also accumulate DC power.

[0026] Inverter 41 ,

[0025] , X , , X , X , ,

[0026] , (for each X = 1 to 7) generates AC power at the frequency used by the motor 42 X so as to generate AC power at the frequency used by the motor 42 XControl it. The inverters 411 to 417 are connected in parallel to the power supply 20 and the capacitor 25 with respect to each other. The inverter 41 X As shown in FIG. 2, has six switching elements 100 X and a control circuit 101 X .

[0027] The switching element 100 X changes to an on or off state based on the PWM control signal from the control circuit 101 X . By this, so-called PWM (Pulse Width Modulation) control is performed to control the AC power supplied from the inverter 41 X to the motor 42 X . Here, the frequency (switching frequency) at which the switching element 100 X should be switched on / off is preset (determined) according to the model of the inverter 41 X . More specifically, the larger the capacity of the motor 42 X , the lower the switching frequency.

[0028] The control circuit 101 X compares the triangular wave signal output from the triangular wave generation circuit 43 with the command values of the three-phase voltages of the motor 42 X input from the operation control unit (not shown), and generates a PWM control signal for controlling the on and off of the switching element 100 X . The control circuit 101 X outputs the generated PWM control signal to the six switching elements 100 X .

[0029] The triangular wave generation circuit 43 generates a triangular wave signal that is the basic waveform of the PWM control of each inverter 41. Here, the triangular wave signal is a carrier signal (carrier wave) that is a basic wave used for transmitting information. Then, the triangular wave generation circuit 43 outputs the triangular wave signal to the inverters 411 to 417 (control circuits 1011 to 1017). In this embodiment, the inverters 411 to 417 are grouped by reference frequency, and the triangular wave generation circuit 43 groups each By controlling the triangular wave signal, the ripple current generated in the capacitor 25 is suppressed. Specifically, for the inverters 411 to 417, a reference frequency is assigned based on their respective switching frequencies. That is, the same reference frequency is assigned to the inverters 41 with close (the same category of) switching frequencies. Then, the inverters 411 to 417 are grouped for each of the reference frequencies. Here, the triangular wave generation circuit 43 controls the triangular wave signal based on the reference frequency assigned to each group. Note that the reference frequency assigned to a certain group may be the same as the switching frequency of the inverters 41 in that group, or the reference frequency and the switching frequency may be different.

[0030] For example, as shown in FIGS. 3A and 3B, assume that the reference frequencies of inverter models A to C are fa, the reference frequency of model D is fb, and the reference frequency of model E is fc. And assume that the inverter 411 is model A, the inverter 412 is model B, the inverter 413 is model C, the inverters 414 and 415 are model D, and the inverters 416 and 417 are model E. Then, the inverters 411 to 413 with the reference frequency fa are classified into group 1, the inverters 414 and 415 with the reference frequency fb are classified into group 2, and the inverters 416 and 417 with the reference frequency fc are classified into group 3. Note that this classification is assumed to be preset in the triangular wave generation circuit 43.

[0031] (Control of Triangular Wave Signal Using Frequency) First, a method for controlling the ripple current by the triangular wave generation circuit 43 controlling the triangular wave signal according to the frequency will be described. The triangular wave generation circuit 43 varies the frequency change (frequency) of the triangular wave signal among the inverters 41 belonging to each group of reference frequencies. For example, for group 1, the triangular wave generation circuit 43 determines a combination of three frequencies, which is the number of inverters 41 belonging to group 1. In this case, the triangular wave generation circuit 43 determines the combination of frequencies from the frequencies in the frequency range of fa - fr / 2 to fa + fr / 2, which is the range of the variable frequency fr width (fluctuation width) centered on the reference frequency fa corresponding to group 1. Specifically, the triangular wave generation circuit 43 determines a combination having the frequencies of fa, fa - fr / 2, and fa + fr / 2. At these frequencies of the combination, for example, they are shifted by a value obtained by dividing the variable frequency fr by 2, which is the number obtained by subtracting (subtracting) 1 from the number of inverters 3 belonging to the group. However, it is not limited to this, and each frequency of the combination may be any value as long as it is within the frequency range of fa - fr / 2 to fa + fr / 2. Here, for example, the reference frequency fa is 8 kHz and the variable frequency fr is 200 Hz. Then, the triangular wave generation circuit 43 generates a triangular wave signal such that the frequencies included in this combination are switched in a different order in the triangular wave signal for the inverters 411 to 413. Note that the number of frequencies the combination has does not have to be the number of inverters 41 belonging to the group, and may be any number greater than the number of inverters 41 belonging to the group.

[0032] For example, as shown in FIG. 4, the triangular wave generation circuit 43 generates a triangular wave signal that switches in the order of the frequencies fa - fr / 2, fa, and fa + fr / 2 as the triangular wave signal output to the inverter 411. The triangular wave generation circuit 43 generates a triangular wave signal that switches in the order of the frequencies fa, fa + fr / 2, and fa - fr / 2 as the triangular wave signal output to the inverter 412. The triangular wave generation circuit 43 generates a triangular wave signal that switches in the order of the frequencies fa + fr / 2, fa - fr / 2, and fa as the triangular wave signal output to the inverter 413.

[0033] When the triangular wave signal is generated in this way, the triangular wave signals of the same Group 1 can be synchronized with each other every period corresponding to the number of frequencies in the frequency combination (three, which is the number of inverters 41 in Group 1). Also, except at the time of this synchronization, the peak times of the three triangular wave signals do not overlap. Therefore, except at the synchronization time, the switching elements 100 in the inverters 411 to 413 change between on and off at different timings, so that it becomes possible to suppress the peak (maximum value) of the ripple current generated in the capacitor 25.

[0034] Regarding the other Groups 2 and 3 as well, as shown in Fig. 3A, the triangular wave generation circuit 43 determines the frequency combination and generates a triangular wave signal such that the frequencies change in different orders within the group. Note that the triangular wave generation circuit 43 may determine the variable frequency fr so that the frequency ranges, which are the ranges for determining the frequency combination, do not overlap with each other between groups having different reference frequencies. That is, the fluctuation range of the frequency of the triangular wave signal within each group may be smaller than the difference in the reference frequencies between the two groups, namely, the group and the group with the closest reference frequency to this group. And in this case, it is preferable that the highest frequency of the triangular wave signal of the lower side group in these two groups is lower than the lowest frequency of the triangular wave signal of the higher side group.

[0035] In the experiment conducted by the inventor, the reference frequency (switching frequency) fa = 8 kHz and the variable frequency fr = 200 Hz. When only the above-described inverters 411 to 413 were operated and the triangular wave signal was controlled as in this embodiment, compared with the case where the frequency change was not controlled in this way, the peak of the amplitude in the frequency band where the switching ripple amplitude was the largest could be reduced by about 15%. Thus, by controlling the triangular wave signal as in this embodiment, the peak of the ripple current in the motor control device 1 can be suppressed.

[0036] (Control of Triangular Wave Signal Using Phase) ​Next, a method for controlling the ripple current by the triangular wave generation circuit 43 controlling the triangular wave signal according to the phase will be described. As shown in FIG. 3B, the triangular wave generation circuit 43 makes the phases of the triangular wave signals different among the inverters 41 belonging to each group of reference frequencies. For example, for Group 1, as shown in FIG. 5, while setting the same frequency (the frequency indicated by the reference frequency), the triangular wave signals of the inverters 411 to 413 are made to differ by 60 degrees between adjacent phases. At this time, the phase to be made different is, for example, obtained by dividing 180 degrees by the number n of inverters 41 in the same group. However, it is not limited to 180 degrees, and may be an arbitrary angle such as 360 degrees.

[0037] Specifically, as shown in FIG. 5, the triangular wave generation circuit 43 uses the triangular wave signal of the inverter 411 as a reference, shifts the phase of the triangular wave signal of the inverter 412 by 60 degrees from the triangular wave signal of the inverter 411, and shifts the phase of the triangular wave signal of the inverter 413 by 120 degrees from the triangular wave signal of the inverter 411.

[0038] Note that, in the present embodiment, since the phase is controlled for each group, unlike the above-described Patent Document 1, the phases of all the triangular wave signals are not different. Specifically, there is always a triangular wave signal with a phase of 0 degrees in each group.

[0039] In the experiment conducted by the inventor, the reference frequency fa = 8 kHz and the variable frequency fr = 200 Hz. When the inverters 411 to 413 were operated and the phase of the triangular wave signal was controlled as in the present embodiment, the peak of the amplitude in the frequency band where the amplitude of the switching ripple is the largest could be reduced by about 95% compared to the case where the phase was not controlled in this way. As a result, the adverse effects of the ripple current in the motor control device 1 can be suppressed.

[0040] In the above description, an example was described in which all the triangular wave signals output to one group of reference frequencies have different frequency changes or phases. However, instead of all the triangular wave signals output to one group of reference frequencies, at least one or more of the triangular wave signals output to one group of reference frequencies may have different frequency changes or phases from other triangular wave signals.

[0041] Also, in all the triangular wave signals output to one group of reference frequencies, both the frequency change and the phase may be made different. For example, in Group 1, triangular wave signals may be generated such that while the phases are different from each other, the frequencies change in different orders from combinations of multiple frequencies.

[0042] Furthermore, instead of the triangular wave generation circuit 43, each of the inverters 411 to 417 may perform a process of making the frequency change or the phase different for the triangular wave signal. In this case, the triangular wave generation circuit 43 may output the same triangular wave signal to a plurality of inverters 41 in the same group. Then, for example, based on the triangular wave signal acquired from the triangular wave generation circuit 43, the control circuit 1011 may generate (convert) the triangular wave signal used for the PWM control of the switching element 1001 so that the frequency change is different from the triangular wave signal used for the PWM control of the switching element 1002 and the switching element 1003 in the same group.

[0043] Also, in the above, the inverters 411 to 417 were grouped by reference frequency. However, after this grouping, a plurality of inverters 41 having the same reference frequency may be further classified into a plurality of groups. By this also, the frequency or phase of the triangular wave signal can be made non - overlapping in each group, so that the peak of the ripple current can be suppressed.

[0044] Note that the interpretation of the claims is not limited only to the matters described in the embodiments. The interpretation of the claims also includes the scope described so that those skilled in the art can recognize that the problems of the invention can be solved, taking into account the common general knowledge in the art at the time of filing.

[0045] (Appendix) A motor control device (1) for controlling the operations of a plurality of motors (42), each having a switching element (100), and a plurality of inverters (41) that supply power to each of the plurality of motors (42) by PWM control based on a carrier signal, a DC power supply (20) that supplies power to the plurality of inverters (41), a capacitor (25) connected in parallel with the DC power supply (20), comprising the plurality of inverters (41) are assigned a reference frequency based on their respective switching frequencies, which is a reference frequency related to the carrier signal, the plurality of inverters (41) are classified into any of a plurality of groups based on the assigned reference frequencies, in each of the plurality of groups, the carrier signals corresponding to all the inverters (41) belonging to the group are triangular wave signals determined based on the reference frequency assigned to the group, and at least one of the carrier signals corresponding to all the inverters (41) does not overlap with other carrier signals in at least one of frequency and phase, Motor control device (1).

Explanation of Reference Numerals

[0046] 1: Motor control device, 20: Power supply, 25: Capacitor, 40: Capacitor, 41: Inverter, 42: Motor, 43: Triangular wave generation circuit, 100: Switching element, 101: Control circuit

Claims

1. A motor control device for controlling the operations of a plurality of motors, each having a switching element and supplying power to each of the plurality of motors by PWM control based on a carrier signal, a plurality of inverters; a DC power supply for supplying power to the plurality of inverters; a capacitor connected in parallel with the DC power supply; comprising: the plurality of inverters are each assigned a reference frequency based on their respective switching frequencies, which is a reference frequency related to the carrier signal for PWM control; the plurality of inverters are classified into any of a plurality of groups based on the assigned reference frequencies; in each of the plurality of groups, the carrier signals corresponding to all the inverters belonging to the group are triangular wave signals determined based on the reference frequency assigned to the group, and at least one of the carrier signals corresponding to all the inverters does not overlap in frequency with other carrier signals; the variation range of the frequencies of the carrier signals within each group among the plurality of groups is smaller than the difference in reference frequencies between the group and the group with the closest reference frequency to the group; the highest frequency of the carrier signals of the lower group among the two groups is lower than the lowest frequency of the carrier signals of the higher group; a motor control device.

2. The carrier signal of each of the plurality of inverters is a triangular wave signal having a frequency based on the reference frequency of a predetermined group to which the inverter belongs and set so as not to overlap in all the inverters belonging to the predetermined group, The motor control device according to claim 1.

3. The carrier signal of each of the plurality of inverters and the carrier signals of other inverters belonging to the group to which the inverter belongs switch in different orders from among a predetermined combination of a plurality of frequencies, The motor control device according to claim 1 or 2.

4. All the frequencies of the predetermined combination are shifted by a predetermined value obtained by dividing the variation range of the frequencies of the carrier signals within the group corresponding to the predetermined combination by the number obtained by subtracting 1 from the number of inverters belonging to the group, The motor control device according to claim 3.

5. The reference frequency of each of the plurality of inverters is the same as the reference frequencies of all the other inverters in a predetermined group to which the inverter belongs. The motor control device according to any one of claims 1 to 4.

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