3-phase AC motor control device

Abstract

To quickly suppress a current detection DC off-set of each phase of a three-phase AC motor.SOLUTION: A position control apparatus 20 detects a current of at least two-phase processing object phases of three-phase current flowing in a three-phase AC motor, executes an off-set compensation processing to a current detection value of the processing object phase on the basis of an off-set compensation, and performs a control of the three-phase AC motor on the basis of the current detection value of the processing object phase after the off-set compensation processing. The processing calculating the off-set compensation amount contains: a processing for a torque command value signal for calculating a Fourier coefficient of a frequency component of a torque ripple; a processing for calculating a torque oscillation range component of the processing object phase; and a processing for calculating the off-set compensation amount of the processing object phase on the basis of the torque oscillation range of the processing object phase. The processing for calculating the torque oscillation range component of the processing object phase contains a processing based on the Fourier coefficient and an electric corner of the three-phase AC motor at the time of reference time of the torque command signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to motor current control when controlling the speed and rotation angle (position of the controlled object) of a feed axis or spindle in axis control of an NC machine tool or the like, or when controlling the speed and transmission torque of a controlled object in general industrial machinery, using a three-phase AC motor such as a synchronous motor or induction motor.

[0002] Below, we will explain in detail an example of how the technology of the present invention is used in axis control of an NC machine tool, but the technology of the present invention can be applied to all applications where torque, speed, and position of a three-phase AC motor are controlled with high precision. [Background technology]

[0003] Generally, three-phase AC motors (hereafter simply referred to as AC motors or motors) are often used to control the axes of NC machine tools. In a three-phase AC motor, the U-phase, V-phase, and W-phase wires are arranged at electrical positions that are 120 degrees apart from each other, and the current of each phase can be controlled with high precision, thereby achieving the high torque controllability of an AC motor.

[0004] To achieve highly accurate current control, it is necessary to detect the current of each phase with high precision over a wide frequency band. However, a (direct current) offset component is superimposed on the current detection circuit due to the influence of high frequency noise conversion, temperature drift, etc., and as a result, current frequency pulsation (torque ripple) occurs in the torque output.

[0005] 6 is a block diagram showing an example of a conventional position control device 200 that uses a three-phase AC motor as a drive motor. The position control device 200 of this example will be described below. A higher-level device (not shown) outputs a position command value X to the position control device 200 of this example. The rotation angle θm of the motor 300 output from a position detector 301 connected to the motor 300 is a position detection value that indicates the position of a load 302 that is connected to and driven by the motor, and is subtracted from the position command value X by a subtractor 50, and the output becomes a position deviation DIF.

[0006] The position error DIF is amplified by the position loop gain Kp in the position error amplifier 51 to generate the speed command value ωm * On the other hand, a differentiator 52 time-differentiates the position detection value θm and outputs a speed detection value ωm. A subtractor 53 calculates the speed command value ωm * The speed detection value ωm is subtracted from the speed deviation output by the subtractor 53, and the speed deviation is amplified by the speed controller 54 using the proportional integral method. The output of the speed controller 54 is converted into the torque command value τc of the motor. * This becomes:

[0007] In the case of a permanent magnet synchronous motor (generally classified into a surface permanent magnet synchronous motor (SPMSM) and an interior permanent magnet synchronous motor (IPMSM)) or a reluctance synchronous motor (SynRM), the current vector control calculation unit 57 calculates the motor torque command value τc * The q-axis current command value iq is calculated from the motor's N-τ (speed-torque) characteristics and the detected speed value ωm. * and the d-axis current command value id * Calculate and output the following.

[0008] On the other hand, in the case of an induction motor (IM), the current vector control calculation unit 57 calculates the d-axis current command value id from the field weakening characteristics of the induction motor and the detected speed value ωm. * is calculated and output, and the torque command value τc * and the d-axis current detection value id is used to calculate the q-axis current command value iq. * Furthermore, the d-axis current detection value id and the q-axis current command value iq are calculated and output. * From this, the slip angular velocity ωs is calculated and added to the electrical angular velocity ωre (described later) (not shown), to calculate and output the current angular velocity ω and its time integral, that is, the current phase angle θ.

[0009] The detected position value θm is multiplied by the number p of motor pole pairs by a multiplier 55 to obtain an electrical angle θre. A differentiator 56 time-differentiates the electrical angle θre to output an electrical angular velocity ωre. (Normally, in a synchronous motor, the electrical angular velocity ωre = current angular velocity ω.) The motor's U-phase current iu0 and V-phase current iv0 are detected by a U-phase current detection circuit 65 and a V-phase current detection circuit 66. The DC offset described above is superimposed on the detected current value of each phase.

[0010] The current detection offset compensation value adjuster 100 calculates the electrical angular velocity ωre (current angular velocity ω in the case of IM) and the torque command value τc * The adder 67 adds iu0 and duc to output a U-phase current iu. Similarly, the adder 68 adds iv0 and dvc to output a V-phase current iv.

[0011] The W-phase current iw can be calculated as iw = -(iu + iv). As the three-phase current is thus iu + iv + iw = 0, it is common practice to detect two of the three phases and calculate the remaining phase by calculation. The three-phase to dq converter 62 calculates and outputs the d-axis current detection value id and the q-axis current detection value iq by coordinate transformation from the U-phase current iu, V-phase current iv, and electrical angle θre (current phase angle θ in the case of IM).

[0012] The subtractor 58 calculates the d-axis current command value id * The d-axis current controller 59 is configured with an error amplifier that amplifies the d-axis current error Δid by PI (proportional integral) and a non-interference compensation unit (not shown) that compensates for interference components with the q-axis. The d-axis current controller 59 adds the error amplifier output and the non-interference compensation value to calculate the d-axis voltage command value vd * Output.

[0013] The subtractor 60 calculates the q-axis current command value iq *The q-axis current controller 61 is configured with an error amplifier that amplifies the q-axis current error Δiq by PI (proportional integral), a non-interference compensation unit (not shown) that compensates for interference components with the d-axis, and an induced voltage compensation unit (not shown) that compensates for the induced voltage of the motor. The q-axis current controller 61 adds the error amplifier output, the non-interference compensation value, and the induced voltage compensation value to calculate the q-axis voltage command value vq * Output.

[0014] The dq-to-three-phase converter 63 converts the d-axis voltage command value vd * and the q-axis voltage command value vq * and the electrical angle θre (current phase angle θ in the case of IM), the U-phase control voltage command value vu is obtained by coordinate transformation. * , V-phase control voltage command value vv * , W-phase control voltage command value vw * Calculate and output the following.

[0015] The PWM inverter 64 controls the voltage command value (vu * ,vv * ,vw * ) is input, which is power amplified and output as motor drive phase voltages (vu, vv, vw). Each output phase voltage is applied to each phase of the motor, generating each phase current.

[0016] 7 is a block diagram showing an example of the configuration of a conventional current detection offset compensation value adjuster 100. The electrical angular velocity ωre (current angular velocity ω in the case of IM) and the torque command value τc * is input to the FFT transformation unit 101. The DC offset superimposed on the current detection is converted into a torque ripple having an angular frequency of the electrical angular velocity ωre (current angular velocity ω in the case of IM), so the FFT transformation unit 101 outputs the Fourier coefficient absolute value |Ck| which corresponds to the torque ripple amplitude of this angular frequency component.

[0017] Selector 102 is a selector that determines whether to adjust the offset compensation amount for U-phase current detection or the offset compensation amount for V-phase current detection. When the U-phase side is selected first, U-phase offset compensation value adjuster 103 searches for duc that gives the minimum value of torque ripple amplitude |Ck| of angular frequency ωre (ω in the case of IM) while changing U-phase current detection offset compensation amount duc at a specific pitch.

[0018] Next, the V-phase side is selected. The V-phase offset compensation value adjuster 104 searches for dvc that minimizes the torque ripple amplitude |Ck| at the angular frequency ωre (ω in the case of IM) while varying the V-phase current detection offset compensation amount dvc at a specific pitch. This paired operation of the U-phase side and the V-phase side is repeated for several cycles while reducing the search pitch, and finally, an offset compensation amount that cancels out or suppresses the superimposed DC offset is calculated and output.

[0019] An example of an operating algorithm for current detection offset compensation in the past has been described above. However, with such a search algorithm involving phase selection, it is not possible to calculate each phase simultaneously, and therefore there are cases where an appropriate offset compensation amount cannot be calculated, such as when the magnitude of the torque ripple fluctuates steadily or when the difference in DC offset superimposed on the current detection of each phase is significantly large.

[0020] It should be noted that Patent Document 1 below describes, as a technique related to the present invention, a technique for reducing torque ripple caused by offset errors in a current sensor of a three-phase AC motor. [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Japanese Patent Application Publication No. 2019-221105 Summary of the Invention [Problem to be solved by the invention]

[0022] An object of the present invention is to quickly suppress the current detection DC offset of each phase of a three-phase AC motor. Also, in an embodiment, a control device for a three-phase AC motor is provided that includes a current detection offset compensation value calculator that can simultaneously calculate and output an optimal offset compensation amount for each phase, thereby minimizing the magnitude of the torque ripple, even when the magnitude of the angular frequency torque ripple of the electrical angular velocity ωre (current angular velocity ω in the case of IM) caused by the DC offset superimposed on the current detection fluctuates steadily or when the difference in the current detection DC offset of each phase is significantly large. [Means for solving the problem]

[0023] The present invention detects currents of at least two phases to be processed among three phases of currents flowing through a three-phase AC motor, and calculates a current based on a predetermined offset compensation amount. each An offset compensation process is performed on the current detection value of the processing target phase, and each The process of controlling the three-phase AC motor based on the current detection value of the phase to be processed and calculating the offset compensation amount includes calculating a Fourier coefficient of a frequency component of a torque ripple for a torque command value signal for the three-phase AC motor. a process of calculating a Fourier coefficient of a fundamental wave component of a discrete Fourier transform of the torque command value signal as a complex number; and the three-phase AC motor each The process of obtaining the torque amplitude component of the target phase is performed by: The real and imaginary parts of and the electrical angle of the three-phase AC motor at the reference time of the torque command value signal, each A process of obtaining the torque amplitude component of the target phase; each Based on the torque amplitude component of the target phase, each and a process of determining the offset compensation amount for the phase to be processed. the reference time is the time when processing in the discrete Fourier transform is started. It is characterized by:

[0024] Preferably, the process of determining the offset compensation amount includes a process of determining an offset compensation change amount, which is an offset compensation change amount relative to the offset compensation amount previously determined for the phase to be processed, based on the torque amplitude component of the phase to be processed, and determining a new offset compensation amount for the phase to be processed based on the offset compensation change amount for the phase to be processed and the offset compensation amount previously determined for the phase to be processed.

[0025] Preferably, the torque command signal indicates a torque command for the three-phase AC motor rotating at a constant speed. Preferably, the process of determining the torque amplitude component of each of the target phases of the three-phase AC motor includes a calculation process based on a relationship established between the torque amplitude component of each of the target phases and the Fourier coefficients for a vector on a complex plane. Preferably, the process of determining the offset compensation amount for each of the target phases based on the torque amplitude component of each of the target phases includes a process of determining the offset compensation amount for each of the target phases by multiplying the torque amplitude component of each of the target phases by a constant.

[0026] In one embodiment, a torque / speed / position control device for a three-phase AC motor is provided with a current detection offset compensation value calculator that simultaneously derives the torque ripple amplitude caused by a DC offset error superimposed on the current detection of any one phase and the torque ripple amplitude caused by a DC offset error superimposed on the current detection of one of the other two phases from the Fourier coefficients for the torque ripple of the current frequency component calculated from the torque command value signal sampled and collected while rotating the three-phase AC motor at a constant speed, and the current phase at the start of sampling, and calculates the current detection offset error compensation amount for each phase from the torque ripple amplitude to apply a correction to the current detection.

[0027] In one embodiment, the current detection offset error compensation amount is calculated by a current detection offset compensation value calculator having an algorithm that asymptotically reduces and converges the torque ripple by repeating the calculation over multiple cycles.

[0028] In one embodiment of the present invention, the amplitude and phase of torque ripple at the angular frequency of the electrical angular velocity ωre (current angular velocity ω in the case of IM) due to a DC offset superimposed on the detected current are simultaneously and quickly detected as Fourier coefficients C1. The polarity and relative ratio of the detected current offset for each phase are analytically determined from the Fourier coefficients C1, and the increment of the detected current offset compensation value for each phase is calculated. By repeating this calculation cycle, the offset compensation amount for each phase asymptotically converges to an optimal value. [Effects of the Invention]

[0029] According to the present invention, it is possible to quickly suppress the DC offset in the current detection of each phase. Furthermore, in a position control device for a three-phase AC motor according to one embodiment of the present invention, the DC offset superimposed on the current detection of each phase, which causes torque ripple at the angular frequency of the electrical angular velocity ωre (current angular velocity ω in the case of IM), can be canceled or suppressed by an offset compensation amount calculated quickly and simultaneously for each phase using an analytical algorithm. Therefore, even when the magnitude of the torque ripple fluctuates steadily or when the difference in DC offset between each phase is significantly large, the offset compensation amount for each phase can be optimized to minimize the magnitude of the torque ripple. The technology of the present invention can be applied to all applications requiring high-precision control of the torque, speed, and position of a three-phase AC motor, and similar effects can be achieved. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a block diagram showing an example of the configuration of a position control device using a three-phase AC motor of the present invention as a drive motor. [Figure 2] FIG. 2 is a block diagram showing an example of a current detection offset compensation value calculator according to the present invention; [Figure 3] 10 is a flowchart illustrating an operation sequence of a current detection offset compensation value calculator. [Figure 4] FIG. 1 is a vector diagram of a Fourier coefficient C1 at a torque ripple frequency of a permanent magnet type synchronous motor. [Figure 5]FIG. 1 is a vector diagram of the Fourier coefficient C1 at the torque ripple frequency of an induction motor or a reluctance-type synchronous motor. [Figure 6] FIG. 1 is a block diagram showing an example of the configuration of a conventional position control device that uses a three-phase AC motor as a drive motor. [Figure 7] FIG. 1 is a block diagram showing an example of a conventional current detection offset compensation value adjuster. DETAILED DESCRIPTION OF THE INVENTION

[0031] The best mode for carrying out the present invention will be described below using examples. Fig. 1 is a block diagram showing an example of the general configuration of a position control device 20 for a three-phase AC motor according to the present invention. Components that are the same as those shown in Fig. 6 are given the same reference numerals, and their description will be simplified. The position control device 20 may be composed of a processor that executes a program to realize the functions of each component, a digital electronic circuit, or an analog electronic circuit.

[0032] First, we clarify the relationship between the DC offset superimposed on the detected current of each phase and the resulting torque ripple τrip. In a permanent magnet synchronous motor (SPMSM and IPMSM), the d-axis current command value id * = 0, torque can be generated between the permanent magnet field and the q-axis current iq. Here, the current detection DC offsets of the U phase and V phase are denoted as du and dv, and the three-phase currents iu, iv, and iw when the motor rotates at a constant speed of electrical angular velocity ωre are expressed by equation (1). Note that in this specification, for the sake of simplicity, a sine function is denoted as "S" and a cosine function is denoted as "S".

[0033]

number

[0034] The q-axis current iq is expressed by the three-phase → dq converter 62 as in equation (2).

[0035]

number

[0036] In the case of an SPMSM, the generated torque τ is the magnet torque and is proportional to the q-axis current iq (τ ∝ iq). In particular, the torque ripple τrip caused by the current detection DC offsets du and dv can be expressed by equation (3).

[0037]

number

[0038] On the other hand, the d-axis current id is expressed by the three-phase to dq converter 62 as in equation (4).

[0039]

number

[0040] The reluctance torque τr of the IPMSM is proportional to iq·id (τr ∝iq·id). Since the square term of the current detection DC offset is small, it can be ignored as follows:

[0041]

number

[0042] Fig. 2 is a block diagram showing an example of the configuration of the current detection offset compensation value calculator 1 according to the present invention shown in Fig. 1. The following describes the operation of the current detection offset compensation value calculator 1. Fig. 3 is a flowchart illustrating each step in the operation sequence of the current detection offset compensation value calculator 1.

[0043] (Step 1) In the speed range where torque ripple due to the current detection DC offset is large, select the electrical angular velocity ωre and the total number of sampling points N that satisfy equation (6), and * = 0, the motor is operated at a constant speed ωre.

[0044]

number

[0045] (Step 2) Torque command signal τc at point N * [n] is collected at a sampling period Ts. In addition, τc * The electrical angle θre at time [0] is saved as θ0.

[0046] (Step 3) The Fourier coefficient C1 of the fundamental wave component of the known discrete Fourier transform (DFT) is calculated from equation (7).

[0047]

number

[0048] From equation (3), the torque ripple τrip of the electrical angular velocity ωre is a combination of the torque amplitude component τu due to du and the torque amplitude component τv due to dv, and has the relationship with the Fourier coefficient C1 shown in FIG.

[0049] The torque ripple τrip in equation (3) can be expressed by equation (8) using the torque amplitude components τu and τv.

[0050]

Number

[0051] (Step5). For τu and τv in FIG. 4, the relationships of equations (9.1) and (9.2) hold with the Fourier coefficient C1.

[0052]

Number

[0053] Solving this system of simultaneous equations, τu and τv in FIG. 4 can be expressed by equation (10).

[0054]

Number

[0055] (Step6). From the derived τu and τv, the current detection offset compensation increment amounts Δduc and Δdvc are calculated by equation (11).

[0056]

Number

[0057] The current detection offset compensation amounts duc[m] and dvc[m] in the current cycle (the m-th cycle) are represented by the current detection offset compensation amounts duc[m - 1] and dvc[m - 1] in the previous cycle (the m - 1-th cycle) and the current detection offset compensation increment amounts Δduc and Δdvc. That is, the current detection offset compensation amounts duc[m] and dvc[m] in the current cycle (the m-th cycle) operate so as to asymptotically converge the torque ripple to 0 according to equation (12).

[0058]

number

[0059] In this way, the position control device 20 according to an embodiment of the present invention detects two phases (U phase and V phase) of the three phases of current flowing through a three-phase AC motor, performs offset compensation processing on the two-phase current detection values ​​based on a predetermined offset compensation amount, and controls the three-phase AC motor based on the two-phase current detection values ​​after the offset compensation processing.

[0060] The process of calculating the offset compensation amount is performed by calculating the torque command value signal (torque command value signal τc * The torque command value signal may be a signal indicating a torque command value for a three-phase AC motor rotating at a constant speed. The process of determining the offset compensation amounts duc[m] and dvc[m] includes a process of determining two-phase torque amplitude components (τu and τv) of the three-phase AC motor. The process of determining the two-phase torque amplitude components includes a process of determining the Fourier coefficient C1 and the torque command value signal τc * The process includes a process of calculating two-phase torque amplitude components (τu and τv) based on the electrical angle θ0 of the three-phase AC motor at the reference time (n=0) of [n]. Furthermore, the process includes a process of calculating offset compensation amounts duc[m] and dvc[m] for the two phases based on the two-phase torque amplitude components (τu and τv).

[0061] The process of determining the offset compensation amounts duc[m] and dvc[m] also includes a process of determining offset compensation change amounts (offset compensation increment amounts Δduc and Δdvc) for the offset compensation amounts duc[m-1] and dvc[m-1] previously determined for the two phases based on the torque amplitude components (τu and τv) for the two phases, and determining new offset compensation amounts duc[m] and dvc[m] for the two phases based on the offset compensation change amounts for the two phases and the offset compensation amounts duc[m-1] and dvc[m-1] previously determined for the two phases. Here, an example has been shown in which the U and V phases are directly processed, and processing is performed for the W phase based on the calculation results for the U and V phases, but the U, V, and W phases may also be directly processed (processing target phases).

[0062] 3, after calculating the Fourier coefficient C1 in (Step 3), the magnitude of the Fourier coefficient |C1| is compared with the torque ripple amplitude convergence reference value τref, and the operation sequence from (Step 2) to (Step 6) is executed until |C1|≦τref, and the calculation of the current detection offset compensation amounts duc and dvc is repeated. When |C1|≦τref, the calculation of the current detection offset compensation amounts duc and dvc is completed, and the constant speed operation of the motor is terminated.

[0063] The series of operations explained up to this point has been for permanent magnet synchronous motors (SPMSM and IPMSM). Next, we will explain the difference between the operation of the current detection offset compensation value calculator 1 for induction motors (IM) and reluctance synchronous motors (SynRM) and for permanent magnet synchronous motors (SPMSM and IPMSM). In the case of IM and SynRM, torque is generated between the q-axis current iq and the d-axis current id (τ ∝ iq id), so the d-axis current command value id * ≠0 is a prerequisite.

[0064] Therefore, in the current vector control calculation unit 10 in FIG. 1, the q-axis current command value iq * and the d-axis current command value id* After calculating iq * and id * Calculate the vector resultant current I, and then calculate I and id * The angle ψ between the two is calculated in advance.

[0065] In the case of an IM or SynRM, when the motor rotates at a constant speed of current angular velocity ω (electrical angular velocity ωre in the case of a SynRM), the relationship between the current detection DC offsets du and dv and the three-phase currents iu, iv, and iw is as follows: I and id * Using the angle ψ, it can be expressed by equation (13).

[0066]

number

[0067] The three-phase to dq converter 62 gives the q-axis current iq as given by equation (14) and the d-axis current id as given by equation (15).

[0068]

number

[0069]

number

[0070] Here, if the square term of the minute current detection DC offset is ignored and the generated torque τ is calculated, the equation (16) is obtained.

[0071]

number

[0072] In particular, the torque ripple τrip caused by the current detection DC offsets du,dv can be expressed by equation (17).

[0073]

number

[0074] Next, the operation sequence (Steps) of the current detection offset compensation value calculator 1 in the case of a SynRM will be explained. The steps up to (Step 3) are the same as those in the case of permanent magnet type synchronous motors (SPMSM and IPMSM). In the case of a SynRM, the relationship between the torque amplitude components τu and τv and the Fourier coefficient C1 is as shown in Figure 5.

[0075] Therefore, the torque ripple τrip in equation (17) can be expressed by equation (18) using the torque amplitude components τu and τv.

[0076]

number

[0077] The relationship between τu, τv and the Fourier coefficient C1 is shown in FIG. 5, and therefore the relationships of equations (19.1) and (19.2) hold.

[0078]

number

[0079] By solving this simultaneous equation, τu and τv in FIG. 5 can be expressed by equation (20).

[0080]

number

[0081] Next, we will explain the case of IM. When the motor rotates at a constant speed of current angular velocity ω, the relationship between the current detection DC offsets du and dv and the three-phase currents iu, iv, and iw is as follows: * Using the angle ψ between the phases, the q-axis current iq can be expressed by the above-mentioned equation (13). The 3-phase → dq converter 62 gives the q-axis current iq as given by equation (21).

[0082]

number

[0083] In the case of IM, under constant speed, id * = constant value, and even if there is a current detection DC offset, the d-axis current id * Therefore, the torque ripple τrip is proportional to the ripple component of the q-axis current iq, as in the case of SPMSM, and can be expressed by equation (22).

[0084]

number

[0085] Next, the operation sequence (Steps) of the current detection offset compensation value calculator 1 in the case of an IM will be explained. Up to (Step 3), the operation is the same if the electrical angular velocity ωre is replaced with the current angular velocity ω. However, in the case of an IM, there is a difference in slip angular velocity ωs between the current angular velocity ω and the electrical angular velocity ωre. Therefore, when the load is heavy, it is necessary to operate the motor at a constant speed at the electrical angular velocity ωre that becomes the current angular velocity ω, taking into account the slip angular velocity ωs.

[0086] In the case of an IM, the relationship between the torque amplitude components τu and τv and the Fourier coefficient C1 is the same as that of permanent magnet synchronous motors (SPMSM and IPMSM), as shown in Figure 4. Therefore, the torque ripple τrip in equation (22) can be expressed as equation (23) using the torque amplitude components τu and τv.

[0087]

number

[0088] The relationship between τu, τv and the Fourier coefficient C1 is shown in Figure 4, so the relationships in equations (9.1) and (9.2) hold, and by solving this simultaneous equation, τu and τv can be expressed by equation (10). In other words, in the IM, the sequence of (Step 5), which is the operation of the per-phase torque amplitude component calculation unit 3 in Figure 2, is executed based on equation (10). The subsequent sequences of (Step 6) and (Step 4) are also similar to those in the case of the permanent magnet type synchronous motors (SPMSM and IPMSM) described above.

[0089] Similarly, when the three-phase AC motor is a permanent magnet synchronous motor (SPMSM and IPMSM), the position control device 20 detects two phases (U phase and V phase) of the three phases of current flowing through the three-phase AC motor, performs offset compensation processing on the two-phase current detection values ​​based on the offset compensation amounts duc[m] and dvc[m] obtained in advance, and controls the three-phase AC motor based on the two-phase current detection values ​​after the offset compensation processing.

[0090] The process of calculating the offset compensation amount is performed by calculating the torque command value signal (torque command value signal τc * The torque command value signal may be a signal indicating a torque command value for a three-phase AC motor rotating at a constant speed. The process of determining the offset compensation amounts duc[m] and dvc[m] includes a process of determining two-phase torque amplitude components (τu and τv) of the three-phase AC motor. The process of determining the two-phase torque amplitude components includes a process of determining the Fourier coefficient C1 and the torque command value signal τc * The process includes a process of calculating two-phase torque amplitude components (τu and τv) based on the electrical angle θ0 of the three-phase AC motor at the reference time (n=0) of [n]. Furthermore, the process includes a process of calculating offset compensation amounts duc[m] and dvc[m] for the two phases based on the two-phase torque amplitude components (τu and τv).

[0091] The process of determining the offset compensation amounts duc[m] and dvc[m] also includes a process of determining offset compensation change amounts (offset compensation increment amounts Δduc and Δdvc) for the offset compensation amounts duc[m-1] and dvc[m-1] previously determined for the two phases based on the torque amplitude components (τu and τv) for the two phases, and determining new offset compensation amounts duc[m] and dvc[m] for the two phases based on the offset compensation change amounts for the two phases and the offset compensation amounts duc[m-1] and dvc[m-1] previously determined for the two phases. Here, the U and V phases (V and W phases) are directly processed, and the V phase (U phase) may be processed based on the calculation results for the U and W phases (V and W phases).

[0092] As described above, according to the position control device 20 for a three-phase AC motor of the present invention shown in FIG. 1, even when the drive motor is a permanent magnet type synchronous motor (SPMSM and IPMSM), the d-axis current command value id *Even in the case of an induction motor (IM) or a reluctance-type synchronous motor (SynRM), which is based on the prerequisite that ≠ 0, the magnitude of the torque ripple caused by the current detection DC offset can be minimized by calculating and outputting an appropriate offset compensation amount for each phase. [Explanation of symbols]

[0093] 1 Current detection offset compensation value calculator, 2 Fourier coefficient calculator, 3 Each phase torque amplitude component calculator, 4 Each phase current detection offset compensation value setting unit, 10, 57 Current vector control calculator, 20 Position control device (the present invention), 50 Subtractor, 51 Position error amplifier, 52 Differentiator, 53 Subtractor, 54 Speed ​​controller, 55 Multiplier, 56 Differentiator, 58 Subtractor, 59 d-axis current controller, 60 Subtractor, 61 q-axis current controller, 62 3-phase → dq converter, 63 dq → 3-phase converter, 64 PWM inverter, 65 U-phase current detection circuit, 66 V-phase current detection circuit, 67 Adder, 68 Adder, 100 Current detection offset compensation value adjuster, 101 FFT converter, 102 Selector, 103 U-phase offset compensation value adjuster, 104 V-phase offset compensation value adjuster, 200 Position control device (conventional), 300 motor, 301 position detector, 302 load.

Claims

1. Detecting currents of at least two phases to be processed among three phases of currents flowing through a three-phase AC motor; performing offset compensation processing on the current detection value of each of the processing target phases based on a predetermined offset compensation amount; controlling the three-phase AC motor based on the current detection values ​​of the respective processing target phases after the offset compensation processing; The process of calculating the offset compensation amount includes: a process of calculating a Fourier coefficient of a frequency component of torque ripple for a torque command value signal for the three-phase AC motor, the process calculating a Fourier coefficient of a fundamental wave component of a discrete Fourier transform of the torque command value signal as a complex number; a process of determining a torque amplitude component of each of the target phases of the three-phase AC motor, the process determining the torque amplitude component of each of the target phases based on a real part and an imaginary part of the Fourier coefficients and an electrical angle of the three-phase AC motor at a reference time of the torque command value signal; determining the offset compensation amount for each of the target phases based on the torque amplitude component of each of the target phases; 10. A control device for a three-phase AC motor, wherein the reference time is a time when processing in the discrete Fourier transform is started.

2. 2. The control device according to claim 1, The process of calculating the offset compensation amount includes: an offset compensation change amount relative to the offset compensation amount previously calculated for each of the target phases to be processed is calculated based on the torque amplitude component of each of the target phases to be processed; a process for determining a new offset compensation amount for each of the target phases based on the offset compensation change amount for each of the target phases and the offset compensation amount previously determined for each of the target phases.

3. 3. The control device according to claim 1 or 2, The torque command value signal is A control device for a three-phase AC motor, characterized in that it indicates a torque command value for the three-phase AC motor rotating at a constant speed.

4. A control device according to claim 1 or claim 2, a control device for a three-phase AC motor, wherein the process of determining a torque amplitude component of each of the target phases of the three-phase AC motor includes a calculation process based on a relationship established between the torque amplitude component of each of the target phases of the three-phase AC motor and the Fourier coefficients for a vector on a complex plane.

5. A control device according to claim 1 or claim 2, a process for determining the offset compensation amount for each of the target phases to be processed based on the torque amplitude component of each of the target phases to be processed, the process including multiplying the torque amplitude component of each of the target phases to be processed by a constant to determine the offset compensation amount for each of the target phases to be processed.

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