JP2007336634A - Apparatus and method for suppressing leakage current in multi-axis drive system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly practical apparatus and method for suppressing leakage current in a multi-shaft driving system wherein high-frequency leakage current can be suppressed surely without the need for a work, such as measuring the fluctuation pattern in leakage current of a motor of each axis. <P>SOLUTION: The apparatus and method are applied to multi-shaft driving systems so constructed that multiple motors for driving mechanical elements are driven individually by inverter driving means, provided in correspondence with these motors. The inverter driving means (21, 22) are divided into a first group and a second group. The inverter driving means (21) of the first group is supplied with a first PWM carrier signal, and inverter driving means (22) of the second group is supplied with a second PWM carrier signal that is synchronized with the first PWM carrier signal and whose phase is shifted from that of the first PWM carrier signal by 180°. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a leakage current suppressing apparatus and method for a multi-axis drive system in which a plurality of motors for driving mechanism elements are individually driven by inverter-type drive means provided corresponding to the motors.

  When the motor is driven by an inverter-type driving means that performs switching operation based on a carrier signal for PWM (pulse width modulation), high-frequency leakage current is grounded through the stray capacitance of the motor winding due to a sudden voltage change accompanying the switching operation. The phenomenon of flowing to the wire (motor case) occurs. Since this high-frequency leakage current is a source of electromagnetic interference and the like, its limit value is determined by various safety standards.

Even in a multi-axis drive device that drives a plurality of motors that drive mechanism elements and the like by individual inverter-type drive means, the high-frequency leakage current flows, so a measure to reduce it is necessary.
A method of reducing the high-frequency leakage current in this multi-axis drive device is proposed by, for example, Patent Document 1. This conventional leakage current reduction method measures a leakage current fluctuation pattern generated in the motor of each axis in advance, and has a leakage current fluctuation pattern that can be canceled out from a plurality of measured leakage current fluctuation patterns. The combination is selected, and the switching timing of the inverter type driving means for generating these patterns is adjusted so that the leakage current patterns related to this combination are canceled out. (For example, see Patent Document 1)

Japanese Patent No. 398888

However, the conventional leakage current reducing method has the following problems.
(1) It takes time and labor to measure the fluctuation pattern of the leakage current for each axis in advance. Also, determine the combination of fluctuation patterns of leakage current that can be canceled out, and adjust the switching timing of the inverter-type drive means that generates the fluctuation pattern related to the combination so that these fluctuation patterns are canceled out. There is an inconvenience that you have to do.
(2) Since it is based on the principle of reducing the leakage current by using the fluctuation pattern of the leakage current of each motor measured in advance, the switching timing of each inverter type driving means for driving each motor is fixed. Can only be used when This is because when the switching timing changes, the fluctuation pattern of the leakage current also changes.
Therefore, for example, when each inverter type drive means is incorporated in a servo control system having a current control loop, a speed control loop, a position control loop, etc., the switching timing varies based on the deviation of the controlled object. Cannot be applied effectively.

  The present invention has been made paying attention to such a conventional problem, and its purpose is to reduce the high-frequency leakage current without requiring the trouble of measuring the fluctuation pattern of the leakage current of the motor of each axis. It is an object of the present invention to provide a leakage current suppression device and method for a highly practical multi-axis drive multi-axis drive system that can be reliably suppressed.

  The present invention is a leakage current suppression device for a multi-axis drive system in which a plurality of motors for driving mechanism elements are individually driven by inverter type drive means provided corresponding to the motors, and each of the inverter type drives The means is divided into a first set and a second set, a first PWM carrier signal is supplied to the first set of inverter-type drive means, and to the second set of inverter-type drive means, The object is achieved by providing carrier signal generation means for supplying a second PWM carrier signal that is synchronized with the first PWM carrier signal and that is 180 ° out of phase with the first PWM carrier signal.

In order to enhance the effect of suppressing the leakage current of the motor, it is desirable that the number of the first set of inverter-type driving means is the same as the number of the second set of inverter-type driving means. As the motor, for example, a three-phase motor can be applied.
The inverter type drive means may be provided as a drive means of a servo control system.

  The present invention is a leakage current suppression method for a multi-axis drive system in which a plurality of motors for driving mechanism elements are individually driven by inverter type drive means provided corresponding to the motors, and each of the inverter type drives Dividing the means into a first set and a second set, supplying a first PWM carrier signal to the first set of inverter-type drive means, and supplying the second set of inverter-type drive means to the second set of inverter-type drive means On the other hand, the above-mentioned object is achieved by including a step of supplying a second PWM carrier signal that is synchronized with the first PWM carrier signal and that is 180 ° out of phase with the first PWM carrier signal. .

According to the present invention, it is possible to reliably suppress high-frequency leakage current without the need for measuring the fluctuation pattern of the leakage current of the motor of each axis. Moreover, since the switching timing of the inverter type driving means for each axis is not fixed, even if the inverter type driving means is incorporated in a servo control system having a current control loop, a speed control loop or a position control loop. It can be used effectively.
In addition, since the voltage fluctuation and the fluctuation time width in the metal frame that becomes the conduction medium of the motor of each axis are remarkably reduced, a stable leakage current suppressing effect can be obtained and a leakage current suppressing filter is used in combination. Even in this case, there is an advantage that a small and small capacity is sufficient. A technique using a filter is proposed by, for example, Japanese Patent No. 3466118.

  FIG. 1 is a block diagram showing a multi-axis drive system to which a leakage current suppressing apparatus and method according to an embodiment of the present invention is applied. This multi-axis drive system includes two three-phase motors M11 and M12 (in this embodiment, those having a star connection configuration) and an inverter type drive unit that individually drives these motors M11 and M12. 21 and 22 and a triangular wave generator 30. The motors M11 and M12 are provided as actuators such as mechanism elements, for example, a screw moving mechanism of an injection molding machine, a moving mechanism of a mold, and a driving mechanism of a robot.

  The inverter-type drive unit 21 includes comparators 211, 212, and 213 to which a U-phase voltage command, a V-phase voltage command, and a W-phase voltage command are applied to one input, respectively, and outputs of these comparators 211, 212, and 213. The inverter 214 is connected. The other inverter type drive unit 22 includes elements 221 to 224 corresponding to the elements 211 to 214 of the inverter type drive unit 21. Since the configurations of the inverters 214 and 224 are known, the description thereof is omitted.

  The triangular wave generation unit 30 generates a first triangular wave and a second triangular wave, inputs the first triangular wave to the other input of the comparators 211 to 213 of the inverter type driving unit 21 as a PWM carrier signal, and converts the second triangular wave to an inverter type. The other input of the comparators 221 to 223 of the drive unit 22 is input as a PWM carrier signal. The first triangular wave and the second triangular wave are synchronized with each other and their phases are shifted by 180 °.

When the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command are U _com , V _com, and W _com , respectively, there is usually the following relationship between them.
U _com = K · sin θ
_Vcom = K · sin (θ + 1 / 3π) (1)
W _com = K · sin (θ + 2 / 3π)

Next, the operation of the current suppressing device according to this embodiment will be described.
The theoretical analysis on the high-frequency leakage current of the PWM control inverter is described, for example, in the IEEJ paper “Modeling and theoretical analysis of the high-frequency leakage current generated by the voltage-type inverter”, Electrotechnical D, Vol. Yes.
According to this paper, the neutral point voltage V _c of the three-phase motor is expressed by the following equation.
_Vc = ( _VU + _VV + _VW ) / 3 (2)
Here, V _U , V _V and V _W are voltages applied to the U-phase winding, V-phase winding and W-phase winding of the motor, respectively.
When three-phase motors using multiple axes are electrically connected to each other through a metal frame, the voltage _{Vct of the} metal frame can be expressed by the following equation.
V _ct = (V _c1 + V _c2 + V _c3 +... V _cn ) / n (3)
Here, n is the number of axes, and V _{c1 to} V _cn are the neutral point voltages of n three-phase motors.

High-frequency leakage current from each motor is suppressed by suppressing fluctuations in the voltage (common mode voltage) of the metal frame. In other words, the leakage current is suppressed by reducing the sum of neutral point voltages of the motors.
Therefore, in the embodiment of FIG. 1 in which the number of axes n is 2, the voltage V _{ct of the} metal frame is suppressed by reducing the sum of the neutral point voltages V _c1 and V _c2 in the equation (3), that is, High frequency leakage current from each motor M11, M12 can be suppressed.

FIG. 2A illustrates the relationship between the U-phase voltage command _Ucom1 , the V-phase voltage command _{Vcom1, the} W-phase voltage command _Wcom1 and the first triangular wave related to the motor M11 on the first axis. The voltage commands U _com1 , V _com1 and W _com1 are not DC voltage signals as is apparent from the equation (1). However, these voltage commands are linearly approximated as shown in the figure because the frequency is extremely low (for example, about 10 Hz) with respect to the frequency of the first and second triangular waves (for example, 20 KHz).
The comparators 211, 212, and 213 control opening and closing of a switching element (not shown) of the inverter 214 based on the relationship of FIG. As a result, the U-phase winding, V-phase winding and W-phase winding (not shown) of the motor M11 are subjected to PWM-processed voltages V _U1 , V _V and V _W1 as shown in FIG. As a result, the voltage shown in FIG. 2C appears at the neutral point of the motor M11.

FIG. 2D illustrates the relationship between the U-phase voltage command U _com1 , the V-phase voltage command V _com1 and the W-phase voltage command W _com1 related to the second-axis motor M12 and the second triangular wave. In this case, the switching operation of the inverter 224 based on the outputs of the comparators 211, 212 and 213 causes the U phase winding, V phase winding and W phase winding (not shown) of the motor M12 to be shown in FIG. Since the voltages V _U2 , V _V2 and V _{W2 shown} are respectively applied, the voltage shown in FIG. 2F appears at the neutral point of the motor M12.

As is clear from the comparison between FIGS. 2C and 2F, in this embodiment, when the neutral point voltage (maximum value V) of the motor M11 increases or decreases, the neutral point voltage of the motor M12 is reversed. Will be reduced. This contradictory change in the neutral point voltages reduces the sum of the neutral point voltages V _c1 and V _c2 shown on the right side of the equation (3), that is, the voltage V _ct of the metal frame. As a result, the high-frequency leakage current from the motors M11 and M12 is suppressed.

  As described above, in the present embodiment, the first and second triangular waves that are synchronized with each other and whose phases are shifted by 180 ° are used as the PWM carrier signals of the inverter type drive units 21 and 22, respectively. Therefore, from the motors M11 and 12 without performing an operation for measuring a leakage current pattern for each axis in advance, an operation for adjusting the switching timing of the inverter-type drive units 21 and 22 for each axis to cancel the leakage current, and the like. The high-frequency leakage current can be reliably suppressed.

In addition, since the switching timing of the inverter type driving units 21 and 22 is not fixed, the inverter type driving units 21 and 22 are incorporated in a servo control system having a current control loop, a speed control loop, a position control loop, and the like. Even it can be used effectively. Furthermore, even when using a filter for suppressing leakage current, a small and small-capacity filter is sufficient.
When the servo control system has a current control loop, the U-phase voltage command U _com , the V-phase voltage command V _com and the W-phase voltage command W _com are formed based on the current deviation. When the system has a speed control loop, each of the voltage commands is formed based on the speed deviation. Similarly, when the control system has a position control loop, each of the voltage commands is formed based on the position deviation.

  By the way, when a multi-axis drive system is configured, normally, a motor control unit including a PWM carrier signal generator and an inverter type drive unit is provided in a number corresponding to the number of axes. Although the carrier signal generator provided in each control unit is adjusted so as to generate a PWM carrier signal having the same frequency, in reality, the frequency of the carrier signal generated by them is delicately related to accuracy. It is different. In addition, since the carrier signals are not synchronized, the mutual phase relationship changes with the passage of time. As a result, the phase of the carrier signal periodically matches for each axis, and the high-frequency leakage current increases at the time of matching.

That is, in the drive system having the same configuration as the drive system of FIG. 1, when the phases of the first and second triangular waves, which are PWM carrier signals, coincide, the operation waveform of FIG. 2 changes as shown in FIG. become. As is clear from the comparison between FIGS. 3C and 3F, in this case, when the neutral point voltage of the motor M11 increases or decreases, the neutral point voltage of the motor M12 also increases or decreases similarly. The effect of reducing the sum of the neutral point voltages V _c1 and V _c2 shown on the right side of the equation (3) cannot be obtained. Therefore, as shown in FIG. _3G , the voltage V _{ct of the} metal frame greatly fluctuates and the maximum high-frequency leakage current flows.
Since the period in which the phases of the first and second triangular waves coincide with each other increases as the number of axes increases, the generation of high-frequency leakage current may be missed when the number of axes is large. However, according to the above-described embodiment of the present invention, the high-frequency leakage current can be reliably suppressed regardless of the number of axes, and thus the above-described problem does not occur.

The present invention can also be applied to a drive system having a larger number of axes than the drive system having the two-axis configuration according to the embodiment, for example, the drive system having the four-axis configuration shown in FIG.
In the drive system of FIG. 4, in addition to the inverter type drive units 21 and 22 for driving the motors M11 and M12, inverter type drive units 23 and 24 for driving the motors M13 and M14 are provided. The inverter type drive units 23 and 24 have elements 231 to 234 and 241 to 244 corresponding to the elements 211 to 214 of the inverter type drive unit 21, respectively.

In the embodiment applied to this four-axis drive system, the first triangular wave output from the triangular wave generator 30 is supplied to the comparators 211 to 213 of the inverter type drive unit 21 and the comparators 221 of the inverter type drive unit 22. To 223 as a PWM carrier signal, and the second triangular wave output from the triangular wave generator 30 is supplied to the comparators 231 to 233 of the inverter type driving unit 23 and the comparators 241 to 243 of the inverter type driving unit 24. Is input as a PWM carrier signal. It should be noted that U-phase voltage command U _com3 , V-phase voltage command V _com3 and W-phase voltage command W _com3 are input to comparators 231, 232 and 233, respectively, and U-phase voltage command W _com3 is input to comparators 241, 242 and 243, respectively. Phase voltage command _Ucom4 , V phase voltage command _Vcom4, and W phase voltage command _Wcom4 are input.

In this embodiment, when the neutral point voltage of the motors M11 and M12 increases or decreases, the neutral point voltage of the motors M13 and M14 decreases. This reduces the sum of neutral voltages V _c1 , V _c2 , V _c3, and V _c4 in equation (3) when the number of axes n is 4, and is a common conductive path for the motors M11 to M14. since the voltage _{V ct} of the metal frame can be suppressed, the high frequency leakage current from the motor M11~M14 is reduced.

  The present invention is also applicable when the number of axes of the multi-axis drive system is an odd number. Now, assuming that the number of axes is five, in this case, five inverter type driving units for individually driving five motors (not shown) are provided. For example, of these inverter type driving units, The first triangular wave is input to the two inverter type driving units, and the second triangular wave is input to the remaining three inverter type driving units.

In short, the present invention divides each inverter type driving unit provided corresponding to a plurality of axes into a first group and a second group, and inputs the first triangular wave to the first group of inverter type driving units. And it can implement by inputting a 2nd triangular wave to a 2nd set of inverter type drive parts.
The first group and the second group include one or more inverter-type drive units. However, when the number of axes is an even number, the above-described high frequency leakage current can be reduced. It is desirable to include the same number of inverter type driving units in the first set and the second set. In addition, when the number of axes is an odd number, for the same reason, each group is set so that the difference between the number of the first group of inverter-type drive units and the number of the second group of inverter-type drive units is 1. It is desirable to adjust the number of inverter type drive units.

  The motors M11 to M14 in the above embodiment are three-phase motors having windings that are star-connected. However, the present invention can also be applied to the case where the number of phases of the motor is two or four or more, and the connection form of the motor windings is not limited to the star connection.

It is a block diagram which shows one Embodiment of the leakage current suppression apparatus which concerns on this invention. It is a wave form diagram which shows operation | movement of the electric current suppression apparatus of FIG. FIG. 3 is an operation waveform diagram corresponding to FIG. 2 when the first and second triangular waves are in phase. It is a block diagram which shows other embodiment of the leakage current suppression apparatus which concerns on this invention.

Explanation of symbols

M11 to M14 Motor 21 to 24 Inverter type drive unit 30 Triangle wave generation unit

Claims (5)

A leakage current suppression device for a multi-axis drive system in which a plurality of motors that drive mechanism elements are individually driven by inverter-type drive means provided corresponding to the motors,
The inverter type driving means is divided into a first group and a second group,
A first PWM carrier signal is supplied to the first set of inverter-type drive means, and the second set of inverter-type drive means is synchronized with the first PWM carrier signal and the first set of inverter-type drive means A leakage current suppressing device for a multi-axis drive system, comprising carrier signal generating means for supplying a second PWM carrier signal whose phase is 180 ° shifted from that of the PWM carrier signal.   2. The leakage current suppressing device for a multi-axis drive system according to claim 1, wherein the number of the first set of inverter-type drive means is the same as the number of the second set of inverter-type drive means. 3. .   The leakage current suppression device for a multi-axis drive system according to claim 1, wherein the motor is a three-phase motor.   2. The leakage current suppression device for a multi-axis drive system according to claim 1, wherein the inverter type drive means is provided as a drive means of a servo control system. A leakage current suppression method for a multi-axis drive system in which a plurality of motors that drive mechanism elements are individually driven by inverter-type drive means provided corresponding to the motors,
Dividing each inverter drive means into a first set and a second set;
A first PWM carrier signal is supplied to the first set of inverter-type drive means, and the second set of inverter-type drive means is synchronized with the first PWM carrier signal and the first set of inverter-type drive means Supplying a second PWM carrier signal that is 180 ° out of phase with the PWM carrier signal;
A leakage current suppression method for a multi-axis drive system.

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