Position Control Device

Abstract

To suppress position deviation ripples caused by dead time in a position controller controlling current of a three-phase synchronous motor.SOLUTION: A position controller 1 controlling a rotation speed ωm and a rotation angle θm of a three-phase synchronous motor 20 by calculating a d-axis current command value and a q-axis current command value based on a position command X and by adjusting current values of each phase of the three-phase synchronous motor 20 by a PWM inverter 10 has a d-axis additional current calculation part 15 calculating a d-axis additional current value Idc added to the d-axis current command value to be outputted. The d-axis additional current value Idc oscillates so that a polarity may be changed according to an electric angle θ, and performs zero-cross with inclinations of polarity and reverse polarity of the q-axis current command value in a zero-cross electric angle φ.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a configuration of a position control device that controls the rotation speed and rotation angle of a three-phase synchronous motor. [Background technology]

[0002] Position control devices that control the rotation speed and rotation angle (position) of the feed axis of an NC machine tool often control a three-phase synchronous motor (hereinafter also called a motor) to drive loads such as a table or workpiece connected to the motor. In this configuration, a PWM inverter is usually used as the power converter.

[0003] Conventionally, motor control uses a two-phase rotating coordinate system (generally, the magnetic pole direction is called the d-axis and the electrical orthogonal direction is called the q-axis) to determine the two-phase voltage command value (Vd * , vq * ) is calculated, and this is converted to three phases to obtain the three phase control voltage command value (Vu * , Vv * , Vw * ) is determined. The power is then amplified by a PWM inverter to produce the motor drive voltages (Vu, Vv, Vw).

[0004] Figure 8 is a circuit diagram showing the voltage output section for one phase of the PWM inverter. By controlling the ON / OFF switching of transistors Tr1 and Tr2 at high speed from the DC bus voltage Vdc circuit, the output phase voltage V can be varied between 0 and Vdc on average. The control voltage command value Vo commands the ON / OFF of the two transistors, and during the ON period of Tr1, V=Vdc, and during the ON period of Tr2, V=0. Diodes D1 and D2 are for freewheeling.

[0005] Figure 9 shows the phase voltage V that is output when transistors Tr1 and Tr2 are switched at a certain control voltage command value Vo. The upper part of Figure 9 is an example of the control voltage command value Vo. The dead time Td, during which both transistors Tr1 and Tr2 are turned OFF simultaneously, is a pause time to prevent both transistors Tr1 and Tr2 from being turned ON simultaneously, which could cause a short circuit breakdown.

[0006] The lower part of Fig. 9 shows the phase voltage V output from the PWM inverter at this time. When current flows out (indicated by OUT in Fig. 9), transistor Tr1 is OFF and current flows through diode D2, resulting in an output voltage of 0. When current flows in (indicated by IN in Fig. 9), transistor Tr2 is OFF and current flows through diode D1, resulting in the output phase voltage V being the DC bus voltage Vdc. In other words, even if the same control voltage command value Vo is given to transistors Tr1 and Tr2, a difference occurs in the average output phase voltage V depending on the current direction.

[0007] Fig. 10 is a diagram showing the input / output relationship for one phase of a PWM inverter, with the control voltage command value Vo on the horizontal axis and the phase voltage V output from the PWM inverter on the vertical axis. However, both the control voltage command value Vo and the output phase voltage V are expressed as average voltages according to the ON / OFF duty. The dotted line shows the input / output relationship when current flows out (indicated by OUT in Fig. 10), and the dashed dotted line shows the input / output relationship when current flows in (indicated by IN in Fig. 10). The solid line shows ideal linear characteristics.

[0008] Here, the output phase voltage V transitions as indicated by arrow 300 in FIG. 10 when the current direction changes from current inflow to current outflow, and as indicated by arrow 301 when the current direction changes from current outflow to current inflow, so that the output phase voltage V becomes discontinuous, resulting in a delayed current response and a position deviation DIF occurring in the position control device.

[0009] For this reason, a dead-time compensation process has been proposed in which a dead-time compensation value -Vod is added in advance to a control voltage command value Vo when current flows in, and a dead-time compensation value +Vod is added in advance to a control voltage command value Vo so that the phase voltage V output from the PWM inverter rides on the solid line that indicates the ideal linear characteristic (see, for example, Patent Document 1). This process results in the input voltage of the PWM inverter.

[0010] Here, the configuration of a conventional position control device 30 will be described with reference to Fig. 11. The position control device 30 includes a PWM inverter 10 that converts DC power into three-phase AC power, a position detector 21 that detects a rotation angle θm of a three-phase synchronous motor 20 (hereinafter referred to as motor 20), a differentiator 14 that is a rotation angle conversion unit that converts the rotation angle θm detected by the position detector 21 into a rotation speed ωm of the motor 20 and outputs it, and an electrical angle calculation unit 13 that calculates and outputs a motor electrical angle θ of the motor 20 from the rotation angle θm detected by the position detector 21. The electrical angle calculation unit 13 calculates the motor electrical angle θ of the motor 20 from the rotation angle θm detected by the position detector 21 based on the number of poles of the motor 20 and an electrical angle offset amount.

[0011] The position / speed control unit 2 receives as input a position command value X, a rotation angle θm detected by a position detector 21, and a rotation speed ωm output by a differentiator 14, performs feedback processing by a position control loop and a speed control loop, and various feedforward processing, and outputs a torque command value Tc.

[0012] The dq-axis current command calculation unit 3 outputs a d-axis current command value Id* and a q-axis current command value Iq* from the torque command value Tc and the rotation speed ωm based on the known dq-axis control theory of a synchronous motor. Note that in the case of a surface permanent magnet synchronous motor (hereinafter referred to as SPMSM) and in the case of a control method that does not use reluctance torque even for an interior permanent magnet synchronous motor (hereinafter referred to as IPMSM), Id*=0 normally except during high speed rotation, and when reluctance torque is used in an IPMSM, Id*≠0.

[0013] The dq-axis voltage command calculation unit 4 receives the d-axis current command value Id*, the q-axis current command value Iq*, the d-axis current detection value Id, and the q-axis current detection value Iq as inputs, performs feedback processing by a current control loop and feedforward processing based on the dq-axis control theory, and outputs the d-axis voltage command value Vd* and the q-axis voltage command value Vq*. The d-axis current detection value Id and the q-axis current detection value Iq are output by a 3-phase / 2-phase conversion unit 19 after performing coordinate conversion on the U-phase current detection value Ium detected by a current detector 11 and the W-phase current detection value Iwm detected by a current detector 12 based on the motor electrical angle θ.

[0014] The 2-phase / 3-phase conversion unit 5 performs coordinate conversion on the d-axis voltage command value Vd* and the q-axis voltage command value Vq* using the motor electrical angle θ, and outputs a U-phase control voltage command value Vu*, a V-phase control voltage command value Vv*, and a W-phase control voltage command value Vw*.

[0015] The dead-time compensation amount calculation unit 6 performs coordinate conversion on the d-axis current command value Id* and the q-axis current command value Iq* using the motor electrical angle θ, calculates current command values ​​for each phase of the U-phase, V-phase, and W-phase, and calculates and outputs the dead-time compensation values ​​(Vud, Vvd, Vwd) described above according to the current command values.

[0016] Adder 7 adds the dead-time compensation value Vud to the U-phase control voltage command value Vu* and outputs a U-phase control voltage command value Vuo after dead-time compensation. Adder 8 and adder 9 similarly add the dead-time compensation values ​​(Vvd, Vwd) to the V-phase and W-phase control voltage command values ​​(Vv*, Vw*), respectively, and output the V-phase control voltage command value Vvo and W-phase control voltage command value Vwo after dead-time compensation.

[0017] As described above, the PWM inverter 10 receives the dead-time compensated phase control voltage command values ​​(Vuo, Vvo, Vwo), amplifies the power of the input, and outputs the motor drive phase voltages (Vu, Vv, Vw). Each output phase voltage is applied to each phase of the motor 20, generating each phase current (Iu, Iv, Iw).

[0018] As described above, since the voltage of each phase during the dead time Td changes depending on the direction of each phase current (Iu, Iv, Iw), it is difficult to accurately perform dead time compensation processing near the zero crossing where the absolute value of each phase current (Iu, Iv, Iw) is small. Therefore, current controllability deteriorates near the zero crossing of each phase current (Iu, Iv, Iw), causing torque disturbance and resulting in position deviation DIF. Since the zero crossing points of each phase current (Iu, Iv, Iw) exist a total of six times per one rotation of the motor electrical angle, in the case of a motor with a pole pair number p, torque disturbance, i.e., position deviation ripple, occurs with a period of motor rotation number x 6 x p.

[0019] In general, the disturbance suppression performance of the position control device 30 improves as the frequency decreases. Also, when the motor rotation speed ωm is high, the minute current section near the zero crossing where torque disturbance occurs in each phase current (Iu, Iv, Iw) becomes shorter, and the effect of torque disturbance becomes smaller. Therefore, in a specific motor rotation speed section, the position deviation ripple due to the torque disturbance caused by the dead time Td becomes larger, leading to a deterioration in the quality of the machined surface. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] JP 2011-188633 A Summary of the Invention [Problem to be solved by the invention]

[0021] The problem of the degradation of the machined surface quality due to position deviation ripple caused by dead time has been reduced by improving the dead time compensation method in the past. However, it is not easy to precisely detect the current direction and accurately switch the dead time compensation value, and there is a limit to the reduction of position deviation ripple by dead time compensation.

[0022] SUMMARY OF THE PRESENT DISCLOSURE In view of the above, an object of the present invention is to suppress position deviation ripples caused by dead time in a position control device that controls the current of a three-phase synchronous motor. [Means for solving the problem]

[0023] The position control device of the present invention includes a PWM inverter that converts DC power into three-phase AC power; a rotation angle converter that converts the rotation angle detected by the position detector into a rotation speed of the three-phase synchronous motor and outputs the converted rotation angle; and an electrical angle calculator that calculates and outputs an electrical angle of the three-phase synchronous motor from the rotation angle detected by the position detector, and calculates a d-axis current command value and a q-axis current command value based on a position command value, calculates a d-axis voltage command value and a q-axis voltage command value from the calculated d-axis current command value and q-axis current command value, and converts the calculated d-axis voltage command value and q-axis voltage command value into a U a d-axis additional current calculation unit that calculates and outputs a d-axis additional current value to be added to the d-axis current command value, and the d-axis additional current value output by the d-axis additional current calculation unit is adjusted in accordance with the electrical angle output by the electrical angle calculation unit. Between positive and negative The q-axis current command value vibrates so as to change polarity, and at the zero-cross electrical angle at which the current values ​​of the U, V, and W phases cross zero, the current crosses zero with a gradient of opposite polarity to the polarity of the q-axis current command value.

[0024] In this way, by adding an additional d-axis current that crosses zero with a gradient of the opposite polarity to the q-axis current command at the motor electrical angle where each phase current crosses zero, the absolute value of the gradient when each phase current crosses zero is increased. This shortens the minute current section where dead time compensation cannot be performed correctly and reduces the effect of torque disturbance, thereby reducing the position error ripple caused by dead time.

[0025] In the position control device of the present invention, the d-axis additional current calculation unit comprises: an arctangent calculation unit that calculates and outputs a first zero cross electrical angle that is closest to zero among zero cross electrical angles at which the current value of the U phase crosses zero, using the arctangent of the ratio of the d-axis current command value to the q-axis current command value; a subtractor that subtracts the first zero cross electrical angle from the electrical angle output from the electrical angle calculation unit and outputs a corrected electrical angle; and a phase coefficient calculation unit that oscillates so that the corrected electrical angle input from the subtractor crosses zero with a negative gradient when n×60°, and calculates and outputs a phase coefficient with an amplitude of 1. a d-axis amplitude reference value storage unit for storing a preset amplitude reference value of the d-axis additional current value; a speed correction coefficient calculation unit for calculating and outputting a speed correction coefficient according to the rotation speed output from the rotation angle conversion unit; a torque correction coefficient calculation unit for calculating and outputting a torque correction coefficient according to the torque command value calculated by the position / speed control unit; and a multiplier for calculating the product of the amplitude reference value, the speed correction coefficient, the torque correction coefficient, and the phase coefficient to calculate the d-axis additional current value, wherein n is zero or a natural number. It is also possible to use the following.

[0026] Thus, based on the d-axis current command value and the q-axis current command value calculated based on the position command value and the electrical angle output from the electrical angle calculation unit, a phase coefficient is calculated that oscillates so that the polarity changes according to the electrical angle, and that crosses zero with a gradient of polarity opposite to that of the q-axis current command value at the zero-cross electrical angle at which the current values ​​of the U, V, and W phases cross zero. A speed correction coefficient and a torque correction coefficient can be set according to the rotation speed or torque command value of the three-phase synchronous motor, and a d-axis additional current value can be set according to the rotation speed or torque command value.

[0029] In the position control device of the present invention, the speed correction coefficient calculation unit may increase or decrease the speed correction coefficient depending on the rotation speed output from the rotation angle conversion unit.

[0030] This makes it possible to increase or decrease the d-axis additional current value in response to changes in the rotation speed.

[0031] In the position control device of the present invention, the speed correction coefficient calculation unit may make the speed correction coefficient smaller than 1 when the absolute value of the rotation speed is equal to or smaller than a first speed threshold and when the absolute value of the rotation speed is equal to or larger than a second speed threshold that is greater than the first speed threshold, and may increase or decrease the speed correction coefficient between zero and 1 so that the speed correction coefficient is 1 when the rotation speed is between the first speed threshold and the second speed threshold.

[0032] As a result, when the absolute value of the rotation speed at which the disturbance suppression performance of the position control device is high is equal to or less than the first speed threshold, and when the absolute value is equal to or greater than the second speed threshold at which the position deviation ripple caused by the dead time is sufficiently small, the speed correction coefficient can be set to less than 1 to reduce the d-axis additional current value. Furthermore, since the speed correction coefficient can be set to 1 when the absolute value of the rotation speed is between the first speed threshold and the second speed threshold, it is possible to prevent the position deviation ripple caused by the torque disturbance caused by the dead time in this rotation speed range from increasing, and to prevent deterioration of the machined surface quality.

[0033] In the position control device of the present invention, the speed correction coefficient calculation unit may set the speed correction coefficient to zero when the absolute value of the rotational speed is equal to or smaller than a third speed threshold value that is smaller than the first speed threshold value, and when the absolute value of the rotational speed is equal to or larger than a fourth speed threshold value that is larger than the second speed threshold value.

[0034] This makes it possible to set the d-axis additional current value to zero when the absolute value of the rotation speed is smaller and when the absolute value of the rotation speed is larger.

[0035] In the position control device of the present invention, the torque correction coefficient calculation unit may increase or decrease the torque correction coefficient in accordance with the torque command value.

[0036] This makes it possible to increase or decrease the d-axis additional current value in response to changes in the torque command value.

[0037] In the position control device of the present invention, the torque correction coefficient calculation unit may increase or decrease the torque correction coefficient between -1 and 1 such that the polarity of the torque correction coefficient is the same as the polarity of the torque command value, and when the absolute value of the torque command value is equal to or less than a first torque threshold value, the absolute value of the torque correction coefficient increases as the absolute value of the torque command value increases, and when the absolute value of the torque command value is equal to or greater than a second torque threshold value that is greater than the first torque threshold value, the absolute value of the torque correction coefficient decreases as the absolute value of the torque command value increases and becomes 1 between the first torque threshold value and the second torque threshold value, and may set the torque correction coefficient to zero when the absolute value of the torque command value is equal to or greater than a third torque threshold value that is greater than the second torque threshold value.

[0038] As a result, when the absolute value of the torque command value at which the position deviation ripple caused by the dead time is small is equal to or greater than the second torque threshold, the absolute value of the torque correction coefficient is made smaller than 1 to reduce the d-axis additional current value. Furthermore, when the absolute value of the torque command value is equal to or greater than the third torque threshold, the torque correction coefficient is set to zero and the d-axis additional current value is set to zero. Also, since the absolute value of the torque correction coefficient is set to 1 when the absolute value of the torque command value is between the first torque threshold and the second torque threshold, it is possible to suppress an increase in the position deviation ripple due to torque disturbance caused by the dead time within this range of the torque command value, and suppress a deterioration in the machined surface quality.

[0039] The position control device of the present invention may further include a q-axis additional current calculation unit that calculates and outputs a q-axis additional current value to be added to the q-axis current command value, and the q-axis additional current value calculated by the q-axis additional current calculation unit may be set to a magnitude that cancels out a torque generated by the d-axis additional current value.

[0040] This makes it possible to suppress the torque fluctuation that occurs when the d-axis additional current is applied, and to reduce the position deviation ripple caused by the dead time Td.

[0041] In the position control device of the present invention, the q-axis additional current value calculated by the q-axis additional current calculation unit has a magnitude such that a first calculated torque of the three-phase synchronous motor calculated with the d-axis current being the d-axis current command value and the q-axis current being the q-axis current command value is equal to a second calculated torque of the three-phase synchronous motor calculated with the d-axis current being the sum of the d-axis current command value and the d-axis additional current value and the q-axis current being the sum of the q-axis current command value and the q-axis additional current value, The q-axis additional current value is calculated using the following formula: q-axis additional current value Iqc =K2·Idc·Iq1* / (K1+K2·Idc+K2·Id1*) Here, Idc is the d-axis additional current value, Id1* is the d-axis current command value, Iq1* is the q-axis current command value, K1=p Φm, K2=p·(Lq-Ld), p is the number of pole pairs of the three-phase synchronous motor, Φm is the magnetic flux of the permanent magnet, Ld is the d-axis inductance, Lq is the q-axis inductance. It is also possible to use the following. Effect of the Invention

[0042] The present invention can suppress position deviation ripple caused by dead time in a position control device that controls the current of a three-phase synchronous motor. [Brief description of the drawings]

[0043] [Figure 1] FIG. 1 is a block diagram of a position control device according to an embodiment. [Diagram 2] FIG. 4 is a block diagram of a d-axis additional current calculation unit in the position control device according to the embodiment. [Diagram 3] FIG. 4 is a diagram illustrating a phase coefficient in the position control device according to the embodiment. [Figure 4]11A and 11B are diagrams illustrating other examples of phase coefficients in the position control device according to the embodiment. [Diagram 5] 11 is a diagram illustrating a change in a speed correction coefficient with respect to an absolute value of a rotation speed in the position control device according to the embodiment. FIG. [Figure 6] 5 is a diagram illustrating a change in a torque correction coefficient with respect to a torque command value in the position control device according to the embodiment. FIG. [Figure 7] 5 is a diagram showing a change in a U-phase current command value with respect to a motor electrical angle in the position control device according to the embodiment. FIG. [Figure 8] FIG. 2 is a circuit diagram showing a voltage output section for one phase of a PWM inverter. [Figure 9] 4 is a time chart showing a control voltage command value for one phase of a PWM inverter and an output phase voltage. [Figure 10] 4 is a diagram showing the input / output relationship (control voltage command value-output phase voltage) for one phase of a PWM inverter. FIG. [Figure 11] FIG. 1 is a block diagram of a position control device according to the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Hereinafter, a position control device 1 according to an embodiment will be described with reference to Fig. 1. In the following description of Fig. 1, the same parts as those in the position control device 30 of the prior art previously described with reference to Fig. 11 will be given the same reference numerals and will be briefly described.

[0045] 1, the position control device 1 includes a PWM inverter 10 that converts DC power into three-phase AC power, a position detector 21 that detects a rotation angle θm of a three-phase synchronous motor 20 (hereinafter referred to as motor 20), a differentiator 14 that is a rotation angle conversion unit that converts the rotation angle θm detected by the position detector 21 into a rotation speed ωm of the motor 20 and outputs it, and an electrical angle calculation unit 13 that calculates and outputs a motor electrical angle θ of the motor 20 from the rotation angle θm detected by the position detector 21. The electrical angle calculation unit 13 calculates the motor electrical angle θ of the motor 20 from the rotation angle θm detected by the position detector 21 based on the number of poles of the motor 20 and an electrical angle offset amount.

[0046] The position control device 1 also includes a position / speed control unit 2, a dq-axis current command calculation unit 3, a dq-axis voltage command calculation unit 4, a two-phase / three-phase conversion unit 5, a dead-time compensation amount calculation unit 6, adders 7-9, current detectors 11 and 12, and a three-phase / two-phase conversion unit 19, all of which have the same configuration as that described above with reference to Fig. 11. The position / speed control unit 2 calculates and outputs a torque command value Tc based on a position command value X. The motor 20 drives a load 22 such as a table or a workpiece.

[0047] The position control device 1 of Fig. 1 includes a d-axis additional current calculation unit 15 that calculates and outputs a d-axis additional current value Idc, and a q-axis additional current calculation unit 16 that calculates and outputs a q-axis additional current value Iqc. The d-axis additional current value Idc output by the d-axis additional current calculation unit 15 is added to the d-axis current command value Id1* output by the dq-axis current command calculation unit 3 by an adder 17 to obtain the d-axis current command value Id*. The q-axis additional current value Iqc output by the q-axis additional current calculation unit 16 is added to the q-axis current command value Iq1* output by the dq-axis current command calculation unit 3 by an adder 18 to obtain the q-axis current command value Iq*. The d-axis current command value Id* and the q-axis current command value Iq* are input to the dq-axis voltage command calculation unit 4 and the dead time compensation amount calculation unit 6. The d-axis additional current value Idc is an input for increasing the absolute value of the gradient (dI / dt) of the zero cross point of each phase current (Iu, Iv, Iw), and is the output of a d-axis additional current calculation unit 15, which will be described later. The q-axis additional current value Iqc is an input for compensating for torque changes due to the d-axis additional current value Idc, and is the calculation output of a q-axis additional current calculation unit 16, which will be described later.

[0048] The d-axis additional current calculation unit 15 calculates and outputs the d-axis additional current value Idc that crosses zero with a gradient of opposite polarity to the polarity of the q-axis current command value Iq1* at the motor electrical angle θ0 at which each phase current (Iu, Iv, Iw) crosses zero.

[0049] As shown in FIG. 2, the d-axis additional current calculation unit 15 includes a d-axis amplitude reference value storage unit 151, a speed correction coefficient calculation unit 152, a torque correction coefficient calculation unit 153, a phase coefficient calculation unit 155, an arctangent calculation unit 154, a subtractor 156, and multipliers 157 to 159.

[0050] A preset amplitude reference value Idc' of Idc is stored in d-axis amplitude reference value storage unit 151. d-axis additional current calculation unit 15 sequentially calculates the products of amplitude reference value Idc' stored in d-axis amplitude reference value storage unit 151 by multipliers 157, 158, and 159, speed correction coefficient kω output from speed correction coefficient calculation unit 152, torque correction coefficient kt output from torque correction coefficient calculation unit 153, and phase coefficient kΦ output from phase coefficient calculation unit 155, and outputs the products as d-axis additional current value Idc.

[0051] First, a description will be given of the calculation of the phase coefficient kΦ by the phase coefficient calculation unit 155. As shown in Fig. 2, the phase coefficient calculation unit 155 receives an input of a corrected electrical angle θ'=θ-φ obtained by subtracting the first zero-cross electrical angle φ output by the arctangent calculation unit 154 from the motor electrical angle θ, and outputs the phase coefficient kΦ.

[0052] First, the motor electrical angle θ0 at which each phase current (Iu, Iv, Iw) crosses zero is given by equations (1) and (2), where the angle at which the d-axis and U-phase coincide is θ=0. θ0=(n×60°+φ)mod 360° ···(1) tanφ=Id1* / Iq1* (2) In formula (1), n ​​is a natural number including 0.

[0053] The arctangent calculation unit 154 calculates and outputs a first zero-cross electrical angle φ that is closest to zero among the electrical angles at which the U-phase current Iu crosses zero when n=0 among the zero-cross electrical angles (n×60°+Φ) at which the phase currents (Iu, Iv, Iw) calculated by equation (1) cross zero, using φ=atan(Id1* / Iq1*) from equation (2), where atan is an arctangent function and (Id1* / Iq1*) is the ratio of the d-axis current command value Id1* to the q-axis current command value Iq1*.

[0054] The first zero cross electrical angle φ output from the arctangent calculation unit 154 is subtracted from the motor electrical angle θ by a subtractor 156, and the corrected electrical angle θ'=θ-φ is input to the phase coefficient calculation unit 155. Therefore, when the motor electrical angle θ is the first zero cross electrical angle φ at which the phase currents (Iu, Iv, Iw) cross zero, the corrected electrical angle θ' is θ'=θ-φ=φ-φ=0.

[0055] The phase coefficient calculation unit 155 outputs a phase coefficient kΦ that oscillates with a negative gradient to cross zero when the corrected electrical angle θ' input from the subtractor 156 is n×60°, and has an amplitude of 1. Here, n is a natural number including zero. The phase coefficient kΦ is, for example, a sine wave as shown in the graph of Fig. 3 or a triangular wave as shown in the graph of Fig. 4. Note that the relationship between the corrected electrical angle θ' and the phase coefficient kΦ shown in Figs. 3 and 4 is merely an example, and other waveforms may be used.

[0056] The speed correction coefficient calculation unit 152 outputs a speed correction coefficient kω (0≦kω≦1) according to the rotation speed ωm of the motor 20.

[0057] As described above, when the absolute value of the rotation speed ωm of the motor 20 is small, the disturbance suppression performance of the position / speed control unit 2 is high, and the position error ripple caused by the dead time Td can be suppressed. Also, when the absolute value of the rotation speed ωm of the motor 20 is large, the gradient of the zero crossing point of each phase current (Iu, Iv, Iw) is large and the minute current section near the zero crossing point is short, so that the position error ripple caused by the dead time Td is small. Therefore, the d-axis additional current calculation unit 15 increases or decreases the speed correction coefficient kω between zero and 1 so as to reduce the d-axis additional current value Idc in the motor rotation speed range where the position error ripple caused by the dead time Td is sufficiently small, according to the absolute value of the rotation speed ωm of the motor 20.

[0058] For example, as shown in FIG. 5, the speed correction coefficient kω may be set to be smaller than 1 when the absolute value of the rotational speed ωm of the motor 20 is equal to or smaller than the first speed threshold ωm1 and equal to or larger than the second speed threshold ωm2, and the speed correction coefficient kω may be set to 1 when the absolute value of the rotational speed ωm of the motor 20 is between the first speed threshold ωm1 and the second speed threshold ωm2.

[0059] The speed correction coefficient kω may be set to zero when the absolute value of the rotation speed ωm of the motor 20 is equal to or less than a third speed threshold ωm3 which is smaller than the first speed threshold ωm1, and when the absolute value of the rotation speed ωm of the motor 20 is equal to or greater than a fourth speed threshold ωm4 which is larger than the second speed threshold ωm2. Note that the speed correction coefficient kω may vary between 0 and 1 between the first speed threshold ωm1 and the third speed threshold ωm3 and between the second speed threshold ωm2 and the fourth speed threshold ωm4. Here, the third speed threshold ωm3<first speed threshold ωm1<second speed threshold ωm2<fourth speed threshold ωm4.

[0060] As a result, when the absolute value of the rotation speed ωm of the motor 20, at which the disturbance suppression performance of the position / speed control unit 2 is high, is equal to or less than the first speed threshold ωm1, and when the absolute value is equal to or more than the second speed threshold ωm2 at which the position error ripple caused by the dead time Td is sufficiently small, the speed correction coefficient kω can be set to less than 1 to reduce the d-axis additional current value Idc. In addition, when the absolute value of the rotation speed ωm of the motor 20 is between the first speed threshold ωm1 and the second speed threshold ωm2, the speed correction coefficient kω can be set to 1, so that the position error ripple caused by the torque disturbance caused by the dead time Td in this rotation speed range can be prevented from increasing, and the deterioration of the machined surface quality can be prevented. Note that the relationship between the absolute value of the rotation speed ωm and the speed correction coefficient kω shown in FIG. 5 is merely an example, and other functions may be used.

[0061] The torque correction coefficient calculation unit 153 outputs a torque correction coefficient kt (-1≦kt≦1) according to the torque command value Tc. The torque correction coefficient kt is output so that it is in the range of 0≦kt≦1 when Tc>0, in the range of -1≦kt≦0 when Tc<0, and kt=0 when the absolute value of the torque command value Tc is larger than a certain value.

[0062] When the absolute value of the torque command value Tc is large, the amplitude of each phase current (Iu, Iv, Iw) becomes large and the gradient of the zero cross point also increases, so that the position deviation ripple caused by the dead time Td becomes small. Therefore, the d-axis additional current calculation unit 15 may reduce the d-axis additional current value Idc in a torque range where the position deviation ripple caused by the dead time Td is sufficiently small according to the absolute value of the torque command value Tc.

[0063] 6, the torque correction coefficient calculation unit 153 may increase or decrease the torque correction coefficient kt between -1 and 1 so that the polarity of the torque correction coefficient kt is the same as that of the torque command value Tc, and when the absolute value of the torque command value Tc is equal to or less than the first torque threshold value Tc1, the absolute value of the torque correction coefficient kt increases as the absolute value of the torque command value Tc increases, and when the absolute value of the torque command value Tc is equal to or greater than the second torque threshold value Tc2, the absolute value of the torque correction coefficient kt decreases as the absolute value of the torque command value Tc increases, and the torque correction coefficient kt becomes 1 between the first torque threshold value Tc1 and the second torque threshold value Tc2, and may set the torque correction coefficient kt to zero when the absolute value of the torque command value Tc is equal to or greater than the third torque threshold value Tc3. Here, the first torque threshold value Tc1<the second torque threshold value Tc2<the third torque threshold value Tc3.

[0064] As a result, when the absolute value of the torque command value Tc at which the position deviation ripple caused by the dead time Td is small is equal to or larger than the second torque threshold Tc2, the absolute value of the torque correction coefficient kt is made smaller than 1 to reduce the d-axis additional current value Idc. Furthermore, when the absolute value of the torque command value Tc is equal to or larger than the third torque threshold Tc3, the torque correction coefficient kt is set to zero, and the d-axis additional current value Idc can be set to zero. In addition, since the absolute value of the torque command value Tc is set to 1 between the first torque threshold Tc1 and the second torque threshold Tc2, the position deviation ripple caused by the torque disturbance due to the dead time Td can be suppressed from increasing in this range of the torque command value Tc, and the deterioration of the machined surface quality can be suppressed. Note that the relationship between the torque command value Tc and the torque correction coefficient kt shown in FIG. 6 is merely an example, and other functions may be used.

[0065] Below, an example of the waveform of the d-axis additional current value Idc when the phase coefficient kΦ is a sine wave as shown in FIG. 3 is shown. When the phase coefficient kΦ is a sine wave as shown in FIG. kΦ = -sin(6×θ') =-sin(6×(θ-φ)) (6) It becomes. In this case, the d-axis additional current value Idc is expressed by the following equation using the amplitude reference value Idc', the speed correction coefficient kω, and the torque correction coefficient kt described above. Idc=Idc'×kω×kt×kΦ =-Idc'×kω×kt×sin(6×θ') =-Idc'×kω×kt×sin(6×(θ-φ)) ··· (7) At the motor electrical angle θ0 at which the phase currents (Iu, Iv, Iw) cross zero, Idc(θ0) becomes zero as shown in the following equation (8) from equations (7) and (2). Idc(θ0)=-Idc'×kω×kt×sin(6×(θ0-φ)) =-Idc'×kω×kt×sin(6×(n×60°+φ-φ)) =-Idc'×kω×kt×sin(n×360°) =0 (8) Furthermore, the gradient of Idc(θ0) at the motor electrical angle θ0 at which each phase current (Iu, Iv, Iw) crosses zero is given by the following equation (9) by substituting θ0 into the equation obtained by differentiating equation (7) with respect to the corrected electrical angle θ'. dIdc / dθ(θ0)=-6×Idc'×kω×kt×cos(n×360°) =-6×Idc'×kω×kt (9) Here, in the dq-axis control theory of a synchronous motor, the polarity of the torque command value Tc and the q-axis current command value Iq1* match, and the polarity of the torque command value Tc and the torque correction coefficient kt match as shown in FIG. Polarity of torque command value Tc = Polarity of q-axis current command value Iq1* (10) Polarity of torque command value Tc = Polarity of torque correction coefficient kt (11) Therefore, Polarity of q-axis current command value Iq1* = Polarity of torque correction coefficient kt (12) It becomes. Furthermore, the remaining coefficients related to the d-axis additional current value Idc, that is, the amplitude reference value Idc' and the speed correction coefficient kω, are positive coefficients. Therefore, the d-axis additional current value Idc crosses zero with a gradient of opposite polarity to the q-axis current command value Iq1* at the motor electrical angle θ0 at which each phase current (Iu, Iv, Iw) crosses zero.

[0066] 7 is a diagram showing an example of change in U-phase current Iu due to the d-axis additional current value Idc when Id1* = 0 and Iqc = 0 assuming an SPMSM. The U-phase current Iu is expressed by the following equation (13) through three-phase transformation based on the dq-axis control theory. U-phase current=-Iq*×sinθ+Id*×cosθ (13) If we substitute the q-axis current command value Iq1* for Iq* and the d-axis additional current value Idc for Id*, we get U phase phase current=-Iq1*×sinθ+Idc×cosθ =-Iq1*×sinθ-Idc'×kω×kt×sin(6×θ)×cosθ (14) Here, substituting the condition Idc'×kω×kt=0.15×Iq1*, U phase phase current=-Iq1*×sinθ -[0.15×Iq1*×sin(6×θ)]×cosθ (15) It becomes.

[0067] 7, the solid line shows the U-phase current Iu when Idc = 0, and the dashed line shows Idc = -0.15 × Iq1* × sin(6 × θ). The d-axis additional current value Idc increases |dIu / dt| at the zero crossing of the U-phase current Iu, thereby reducing the torque disturbance caused by the compensation mismatch of the dead time Td near the zero crossing of the phase current.

[0068] Next, the q-axis additional current calculation unit 16 will be described. The q-axis additional current calculation unit 16 calculates and outputs the q-axis additional current value Iqc that cancels the torque generated by the d-axis additional current value Idc. The torque T of the synchronous motor is given by the formula (3) using the number p of pole pairs of the motor 20, the magnetic flux Φm of the permanent magnet, the d-axis inductance Ld, the q-axis inductance Lq, the d-axis current Id, and the q-axis current Iq. T=p·Φm·Iq+p·(Lq-Ld)·Id·Iq = K1 Iq + K2 Id Iq (3) Here, K1 = p Φm and K2 = p (Lq-Ld). Regarding the d-axis additional current value Idc and the q-axis additional current value Iqc, the first calculated torque T1 obtained by substituting Iq=Iq1* and Id=Id1* into equation (3) is equal to the second calculated torque T2 obtained by substituting Iq=Iq1*+Iqc and Id1*+Idc, so equation (4) is obtained. K1·(Iq1*+Iqc)+K2·(Id1*+Idc)·(Iq1*+Iqc) =K1·Iq1* +K2·Id1*·Iq1* ···(4) By solving equation (4), the q-axis additional current value Iqc is given by equation (5). Iqc=K2·Idc·Iq1* / (K1+K2·Idc+K2·Id1*)··(5) In the case of an SPMSM in which no torque is generated by the d-axis current, the q-axis additional current calculation unit 16 may be omitted.

[0069] As described above, the position control device 1 according to the embodiment can suppress the position deviation ripple caused by the dead time Td, and can improve the quality of the machined surface. [Explanation of symbols]

[0070] 1,30 position control device, 2 position / speed control section, 3 dq axis current command calculation section, 4 dq axis voltage command calculation section, 5 2-phase / 3-phase conversion section, 6 dead time compensation amount calculation section, 7,8,9,17,18 adder, 10 PWM inverter, 11,12 current detector, 13 electrical angle calculation section, 14 differentiator, 15 d axis additional current calculation section, 16 q axis additional current calculation section, 19 3-phase / 2-phase conversion section, 20 motor, 21 position detector, 22 load, 151 d axis amplitude reference value storage section, 152 speed correction coefficient calculation section, 153 torque correction coefficient calculation section, 154 arctangent calculation section, 155 phase coefficient calculation section, 156 subtractor, 157,158,159 multiplier.

Claims

1. A PWM inverter that converts DC power into three-phase AC power; a position detector for detecting a rotation angle of a three-phase synchronous motor; a rotation angle converter that converts the rotation angle detected by the position detector into a rotation speed of the three-phase synchronous motor and outputs the rotation angle; an electrical angle calculation unit that calculates and outputs an electrical angle of the three-phase synchronous motor from the rotation angle detected by the position detector, a position control device which calculates a d-axis current command value and a q-axis current command value based on a position command value, calculates a d-axis voltage command value and a q-axis voltage command value from the calculated d-axis current command value and the q-axis current command value, converts the calculated d-axis voltage command value and the q-axis voltage command value into control voltage command values ​​for each of U, V and W phases, and inputs the converted control voltage command values ​​for each of U, V and W phases to the PWM inverter to adjust current values ​​of each of U, V and W phases of the three-phase synchronous motor, thereby controlling the rotational speed and the rotational angle of the three-phase synchronous motor, a d-axis additional current calculation unit that calculates and outputs a d-axis additional current value to be added to the d-axis current command value; The d-axis additional current value output by the d-axis additional current calculation unit is the q-axis current command value oscillates so that its polarity changes between positive and negative in accordance with the electrical angle output from the electrical angle calculation unit, and crosses zero at a zero-cross electrical angle at which the current values ​​of the U, V, and W phases cross zero with a gradient of polarity opposite to that of the q-axis current command value; A position control device comprising:

2. 2. The position control device according to claim 1, a position / speed control unit that calculates and outputs a torque command value based on the position command value, The d-axis additional current calculation unit an arctangent calculation unit that calculates a first zero cross electrical angle that is closest to zero among zero cross electrical angles at which the current value of the U phase crosses zero, based on the arctangent of a ratio of the d-axis current command value to the q-axis current command value, and outputs the first zero cross electrical angle; a subtractor that subtracts the first zero-cross electrical angle from the electrical angle output from the electrical angle calculation unit to output a corrected electrical angle; a phase coefficient calculation unit that calculates and outputs a phase coefficient that oscillates so as to cross zero with a negative gradient when the corrected electrical angle input from the subtractor is n×60° and has an amplitude of 1; a d-axis amplitude reference value storage unit for storing a preset amplitude reference value of the d-axis additional current value; a speed correction coefficient calculation unit that calculates and outputs a speed correction coefficient according to the rotation speed output from the rotation angle conversion unit; a torque correction coefficient calculation unit that calculates and outputs a torque correction coefficient corresponding to the torque command value calculated by the position / speed control unit; a multiplier that calculates the product of the amplitude reference value, the speed correction coefficient, the torque correction coefficient, and the phase coefficient to calculate the d-axis additional current value, The n is zero or a natural number; A position control device comprising:

3. 3. The position control device according to claim 2, the speed correction coefficient calculation unit increases or decreases the speed correction coefficient according to the rotation speed output from the rotation angle conversion unit; A position control device comprising:

4. The position control device according to claim 3, the speed correction coefficient calculation unit makes the speed correction coefficient smaller than 1 when the absolute value of the rotation speed is equal to or smaller than a first speed threshold value and equal to or larger than a second speed threshold value that is larger than the first speed threshold value, and increases or decreases the speed correction coefficient between zero and 1 so that the speed correction coefficient becomes 1 when the rotation speed is between the first speed threshold value and the second speed threshold value; A position control device comprising:

5. The position control device according to claim 4, the speed correction coefficient calculation unit sets the speed correction coefficient to zero when the absolute value of the rotation speed is equal to or smaller than a third speed threshold value that is smaller than the first speed threshold value and when the absolute value of the rotation speed is equal to or larger than a fourth speed threshold value that is larger than the second speed threshold value; A position control device comprising:

6. 6. A position control device according to claim 2, further comprising: The torque correction coefficient calculation unit increases or decreases the torque correction coefficient in response to the torque command value; A position control device comprising:

7. 7. The position control device according to claim 6, the torque correction coefficient calculation unit increases or decreases the torque correction coefficient between −1 and 1 such that the polarity of the torque correction coefficient is the same as the polarity of the torque command value, and when the absolute value of the torque command value is equal to or less than a first torque threshold value, the absolute value of the torque correction coefficient increases as the absolute value of the torque command value increases, and when the absolute value of the torque command value is equal to or greater than a second torque threshold value that is greater than the first torque threshold value, the absolute value of the torque correction coefficient decreases as the absolute value of the torque command value increases, and is 1 between the first torque threshold value and the second torque threshold value, and sets the torque correction coefficient to zero when the absolute value of the torque command value is equal to or greater than a third torque threshold value that is greater than the second torque threshold value; A position control device comprising:

8. A position control device according to any one of claims 1 to 7, a q-axis additional current calculation unit that calculates and outputs a q-axis additional current value to be added to the q-axis current command value, The q-axis additional current value calculated by the q-axis additional current calculation unit has a magnitude that cancels out the torque generated by the d-axis additional current value. A position control device comprising:

9. 9. The position control device according to claim 8, The q-axis additional current value calculated by the q-axis additional current calculation unit is a first calculated torque of the three-phase synchronous motor calculated with a d-axis current being the d-axis current command value and a q-axis current being the q-axis current command value; the d-axis current is equal to a sum of the d-axis current command value and the d-axis additional current value, and the q-axis current is equal to a second calculated torque of the three-phase synchronous motor calculated as a sum of the q-axis current command value and the q-axis additional current value, The q-axis additional current value is calculated by the following formula: q-axis additional current value Iqc =K ２ ・Idc・Iq １ * / (K １ +K ２ ・Idc+K ２ ・Id １ *) Here, Idc is the d-axis additional current value, Id １ * is the d-axis current command value, Iq １ * is the q-axis current command value, K １ = p Φm, K ２ = p · (Lq - Ld), p is the number of pole pairs of the three-phase synchronous motor, Φm is the magnetic flux of the permanent magnet, Ld is the d-axis inductance, Lq is the q-axis inductance; A position control device comprising:

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