Motor drive unit

Abstract

To provide a drive device capable of continuously acquiring rotor angle information while preventing an electric motor's rotor angle from being repeatedly updated and stopped updating.SOLUTION: The drive device includes an inverter 10, a current detector 12 for detecting the output current of the inverter 10, and a vector control unit 11 for determining a voltage command value to the inverter 10. The vector control unit 11 includes a unit vector generating unit 35 that generates a unit vector in the same direction as the voltage command vector including the voltage command value to the inverter 10 on its components and a movement control unit 38 that restricts the amount of movement of the unit vector to within a restricted range.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drive device that drives an electric motor such as a synchronous motor or an induction motor, and more particularly to a drive device that performs vector control based on the output current of an inverter. [Background technology]

[0002] Conventional commonly used motor control methods include V / F control, which keeps the motor magnetic flux constant by outputting a voltage corresponding to a command frequency, and vector control, which breaks down the inverter output current into excitation current and torque current, and controls the excitation voltage and torque voltage so that a motor current appropriate for the load flows.

[0003] Patent Document 1 discloses a sensorless vector control that can control a motor without using a rotor position sensor. Fig. 8 is a block diagram showing a conventional sensor vector control. As shown in FIG. 8, vector control unit 511 includes a 3 / 2 phase conversion unit 517 that converts three-phase currents Iu, Iv, Iw detected by current detector 512 into two-phase currents Iα_r, Iβ_r, an output voltage determination unit 518 that determines command voltage vectors Vα_d, Vβ_d based on a deviation between two-phase current command values ​​Iα_d, Iβ_d on a stationary coordinate system and the two-phase currents Iα_r, Iβ_r on a stationary coordinate system converted by the 3 / 2 phase conversion unit 517, an output voltage / angle calculation unit 522 that calculates an output voltage Vt_d of inverter 510 and a phase (angle) θ of a rotor (not shown) of motor M from the command voltage vectors Vα_d, Vβ_d, a speed calculation unit 526 that calculates an angular velocity ωc of the rotor from the rotor phase θ, a target output voltage determination unit 527 that determines a target output voltage value Vdem from the angular velocity ωc, and a phase correction amount Δθ based on the deviation between the target output voltage value Vdem and the output voltage Vt_d. a phase correction unit 533 that corrects the rotor phase θ by adding a phase correction amount Δθ to the rotor phase θ; a voltage fluctuation detection unit 531 that outputs an update stop signal when the fluctuation amount of the output voltage Vt_d is larger than a fluctuation voltage threshold value; a target magnetization current determination unit 539 that determines a magnetization current command value Im_d on a rotating coordinate system; a target torque current determination unit 538 that determines a torque current command value It_d on the rotating coordinate system based on the deviation between the rotor angular velocity ωc and the angular velocity command value ωd; a rotating / stationary coordinate conversion unit 535 that converts the magnetization current command value Im_d and the torque current command value It_d into two-phase current command values ​​Iα_d, Iβ_d on a stationary coordinate system based on the rotor phase θ' corrected by the phase correction unit 533; and a 2 / 3 phase conversion unit 536 that converts the command voltage vectors Vα_d, Vβ_d into three-phase voltage command values ​​Vu*, Vv*, Vw*.

[0004] The basic operation of the vector control unit 511 is as follows. The three-phase currents Iu, Iv, and Iw detected by the current detector 512 are converted into two-phase currents (vectors) Iα_r and Iβ_r. PI control is performed so that there is no deviation between the converted two-phase currents Iα_r and Iβ_r and the corresponding target values ​​(two-phase current command values ​​Iα_d and Iβ_d), and command voltage vectors Vα_d and Vβ_d are obtained. The obtained two-phase command voltage vectors Vα_d and Vβ_d are converted into three-phase voltage command values ​​Vu*, Vv*, and Vw*. Then, a PWM signal corresponding to the voltage command value of each phase is generated, and this PWM signal is sent to the inverter 510.

[0005] An output voltage / angle calculation unit 522 calculates the output voltage Vt_d of the inverter 510 and the rotor phase (angle) θ of the motor M from the command voltage vectors Vα_d, Vβ_d. However, since the command voltage vectors Vα_d, Vβ_d output from the output voltage determination unit 518 are electrical information, their response speed is faster than that of a mechanical time constant, and fluctuations may become large temporarily. When this fluctuation becomes large, if sensorless control is performed based on the voltage (output voltage Vt_d) calculated from the command voltage vectors Vα_d, Vβ_d and the rotor angle (phase) θ of the motor M, the motor M may lose synchronism due to the influence of this fluctuation, and it may not be possible to drive the motor M.

[0006] Therefore, after calculating the output voltage Vt_d, the voltage fluctuation detection unit 531 detects the change in the output voltage Vt_d over time. When the voltage fluctuation detection unit 531 determines that the change in the output voltage Vt_d is large and that the output voltage is in a transient state, it outputs an update stop signal. Specifically, the voltage fluctuation detection unit 531 compares the amount of fluctuation in the output voltage Vt_d with a fluctuation voltage threshold, and outputs an update stop signal when the amount of fluctuation in the output voltage Vt_d is larger than the fluctuation voltage threshold, and does not output an update stop signal when the amount of fluctuation in the output voltage Vt_d is smaller than the fluctuation voltage threshold. This update stop signal is input to the voltage transmission selector 525a and the phase transmission selector 525b.

[0007] Upon receiving the update stop signal output from the voltage fluctuation detection unit 531, the voltage transmission selector 525a operates to block the transmission of the output voltage Vt_d from the output voltage / angle calculation unit 522 to the phase correction amount determination unit 532. As a result, the update of the output voltage Vt_d in the phase correction amount determination unit 532 is stopped. Similarly, upon receiving the update stop signal output from the voltage fluctuation detection unit 531, the phase transmission selector 525b operates to block the transmission of the rotor angle θ from the output voltage / angle calculation unit 522 to the speed calculation unit 526 and the phase correction unit 533. As a result, the update of the rotor angle θ in the speed calculation unit 526 and the phase correction unit 533 is stopped. In this manner, it is possible to prevent the motor M from losing synchronism due to transient fluctuations in the command voltage vectors Vα_d and Vβ_d. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2020-39227 A [Patent Document 2] JP 2020-162327 A [Non-Patent Document 1] Yuki Nakajima, Junichi Ito: "Maximum Efficiency Control of IPMSM Based on V / f Control", 2013 National Convention of the Institute of Electrical Engineers of Japan, No. 4-115, 2013 Summary of the Invention [Problem to be solved by the invention]

[0009] However, if the update of the rotor angle θ is kept stopped, the rotor continues to rotate during that time, and the difference between the previously updated rotor angle and the actual rotor angle becomes large when the update is resumed. This causes a large voltage to be generated in the self-inductance of each phase of the motor, making it impossible to detect the back electromotive force caused by the rotation, and creating a transient state in which the current command value and the actual current diverge. As a result, the update of the rotor angle θ is stopped again. In this way, once the update of the rotor angle θ is stopped, the update is repeatedly stopped and resumed, and it may become impossible to obtain continuous rotor angle information.

[0010] Therefore, the present invention provides a drive device that can prevent the rotor angle of a motor from being repeatedly updated and stopped from being updated, and can continuously obtain rotor angle information. [Means for solving the problem]

[0011] In one aspect, there is provided a driving device for an electric motor comprising an inverter, a current detector for detecting an output current of the inverter, and a vector control unit for determining a voltage command value to the inverter, wherein the vector control unit comprises a unit vector generating unit for generating a unit vector in the same direction as a voltage command vector whose components include the voltage command value to the inverter, and a transition limiting unit for limiting the amount of movement of the unit vector within a limited range.

[0012] In one aspect, the driving device further includes an update stop unit that stops updating the unit vector when the unit vector generated by the unit vector generation unit is outside an update range, and the transition limiting unit is configured to limit the amount of movement of the unit vector output from the update stop unit to within the limited range. In one embodiment, the update range encompasses a rotation angle from a unit vector generated in a previous control cycle. In one embodiment, the limit range encompasses a rotation angle from a unit vector generated in a previous control cycle. In one embodiment, the limit range is changed in proportion to the rotational speed of the electric motor. In one embodiment, the limit range is a range of linear distance, and the transition limiting unit is configured to calculate a vector of a point that divides the difference between two unit vectors internally as a unit vector with a limited amount of movement. In one aspect, the update range is changed in proportion to the rotational speed of the motor. Effect of the Invention

[0013] According to the present invention, the transition limiting unit limits excessive movement of the unit vector, and when a fluctuation that exceeds a preset limit range occurs, limits the amount of movement of the unit vector within the limit range. Therefore, the difference between the angle of the unit vector and the actual rotor angle falls within the limit range. As a result, rotor angle information can be continuously acquired, and the electric motor can be stably controlled. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a drive device according to an embodiment of the present invention; [Diagram 2] 2(a) to 2(c) are diagrams showing the state of a unit vector in the same direction as the command value of the motor terminal voltage (inverter output voltage) before and after one control period. [Diagram 3] FIG. 13 is a diagram illustrating an update range used to determine whether or not to update a unit vector. [Figure 4] FIG. 13 is a diagram showing a limit range in which the movement of a unit vector is limited. [Diagram 5] FIG. 13 is a diagram showing a unit vector whose movement is restricted by a transition restriction unit. [Figure 6] Vector with movement restriction FIG. [Figure 7] Vector when Mlimit<1 FIG. [Figure 8] FIG. 1 is a block diagram showing a conventional sensor vector control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing a drive device according to an embodiment of the present invention. This drive device is an inverter device (power conversion device) that drives a motor M as an electric motor, and is composed of a plurality of elements including an inverter 10 and a vector control unit 11 as shown in Fig. 1. That is, the drive device includes the inverter 10 that generates a voltage to be applied to the motor M, the vector control unit 11 that determines a voltage command value to the inverter 10, and a current detector (ammeter) 12 that detects a current flowing from the inverter 10 to the motor M. The motor M is a permanent magnet synchronous motor (PMSM) with a permanent magnet in its rotor. The vector control unit 11 can be composed of a processing unit such as a CPU (central processing unit) and a computer equipped with a memory.

[0016] The current detector 12 measures the three-phase currents Iu, Iv, Iw flowing from the inverter 10 to the motor M. The measured values ​​are input to the vector control unit 11. The three-phase currents Iu, Iv, Iw may be measured by measuring the currents of any two phases and determining the remaining current from the equation Iu+Iv+Iw=0. The vector control unit 11 generates three-phase voltage command values ​​Vu*, Vv*, Vw* based on the three-phase currents Iu, Iv, Iw and a speed command value input from the outside. The vector control unit 11 sends these three-phase voltage command values ​​Vu*, Vv*, Vw* to the inverter 10. The inverter 10 generates voltages based on the three-phase voltage command values ​​Vu*, Vv*, Vw* and applies them to the motor M.

[0017] The vector control unit 11 includes a 3 / 2 phase conversion unit 17 that converts the three-phase currents Iu, Iv, Iw detected by the current detector 12 into two-phase currents Iα, Iβ on a stationary coordinate system, and a stationary / rotating coordinate conversion unit 18 that converts the two-phase currents Iα, Iβ on the stationary coordinate system into two-phase currents Iγ, Iδ on a rotating coordinate system. The δ-axis is the axis of the vector direction of the motor terminal voltage (inverter output voltage), and the γ-axis is the axis perpendicular to the δ-axis.

[0018] The vector control unit 11 further calculates a voltage command value e in the rotating coordinate system for minimizing the deviation between the current Iγ and the γ-axis current command value Iγ* (=0). INV -γ-axis current control unit 21 that generates γ* and a voltage command value e in a rotating coordinate system for minimizing the deviation between the current Iδ and the δ-axis current command value Iδ* INV -δ-axis current control unit 22 that generates -δ* and a voltage command value e INV -γ*,e INV -δ* is the voltage command value e INV -α*,e INV -β*, and a two-phase voltage command value e INV -α*,e INV The controller 20 includes a 2 / 3 phase converter 25 that converts −β* into three-phase voltage command values ​​Vu*, Vv*, and Vw*. The γ-axis current controller 21 and the δ-axis current controller 22 are PI controllers.

[0019] The vector control unit 11 further calculates a voltage command value e INV -α*,e INV Vector e with -β* as its component → INV *Length|e → INV A vector length calculation unit 29 calculates ||*|, a rotation angle estimator 31 calculates an estimated value Δθe* of the rotation angle [rad] per one control period, and a voltage command value e INV -α*,e INV -β* is a unit vector in the same direction as the voltage command vector (u α ,u β ), and a unit vector generating unit 35 for generating a unit vector (u α ,u β ), and a filter 36 (e.g., a low-pass filter) to remove noise from the unit vector (u α ,u β ) is outside the preset update range, the unit vector (u α ,u β ), and an update stop unit 37 that stops updating the unit vector (u α ,u β The output of the transition limiting unit 38 is α >, β > is sent to the stationary / rotating coordinate conversion unit 18 and the rotating / stationary coordinate conversion unit 24.

[0020] The rotation angle estimator 31 estimates the control period Tc [s] of the vector control unit 11, the back electromotive force constant Ke [Vs / rad] (one-phase electromotive force per electrical angular velocity), and the vector length |e → INV *| is used to calculate an estimated value Δθe* of the rotation angle [rad] per control cycle.

[0021] The unit vector generating unit 35 calculates the voltage command value e INV -α*,e INV -β* is a voltage command vector e → INV * its length |e → INV *| divides the unit vector (u α ,u β ) The unit vector generating unit 35 generates a unit vector for each control period Tc.

[0022] When the unit vector generated by the unit vector generating unit 35 is within the update range, the update stopping unit 37 replaces the previously generated unit vector with a newly generated unit vector (i.e., updates the unit vector), and when the unit vector generated by the unit vector generating unit 35 is outside the update range, the update stopping unit 37 does not update the unit vector and outputs the previously generated unit vector. An example of the unit vector generating unit 35 having such a function is a sample-and-hold circuit.​​

[0023] The vector control unit 11 further calculates each component u of the unit vector. α ,u β a speed converter 41 that calculates a frequency command value f* from a speed command value [rpm] input from the outside to the vector control unit 11, and a speed control unit 42 that calculates a δ-axis current command value Iδ* for minimizing the deviation between the rotation frequency f of the motor M and the frequency command value f*. The speed control unit 42 is a PI controller.

[0024] As described above, the vector control unit 11 incorporates a current control system including αβ-γδ transformation and γδ-αβ transformation, and controls the actual current of the motor M to follow the current command values ​​Iγ* and Iδ*. Note that the δ axis is the axis of the vector direction of the motor terminal voltage (inverter output voltage), and the γ axis is an axis perpendicular to the δ axis. The αβ-γδ transformation and γδ-αβ transformation are not given a coordinate angle, but the voltage command value e to the inverter 10 is INV -α*,e INV -β* is a unit vector in the same direction as the voltage command vector (u α ,u β ) is given by each component of the unit vector u α ,u β are given as cosine and sin values, respectively, and a rotation matrix operation is performed in each block. Since sin and cosine functions are not used, the amount of calculation (calculation load) of the vector control unit 11 can be reduced.

[0025] In this embodiment, the voltage command value e INV -α*,e INV -β* converted to a unit vector, u α ,u β Instead of using it as is, we use u according to given conditions. α ,u β and a transition limiting unit 38 that limits the amount of movement of the unit vector per control period. α >, β ​​In particular, the update stop unit 37 performs coordinate conversion using the unit vector (u α ,u β ) deviates from the direction of the back electromotive force caused by the magnetic flux of the permanent magnet of the rotor of the motor M, this plays an important role in preventing the γδ axes from stepping out.

[0026] This configuration eliminates the need for an integral element used in general sensorless control to obtain a rotation angle signal from an angular velocity signal. This eliminates the need for parameters due to the moment of inertia of the rotating system, and eliminates the need for parameter adjustments, while also significantly improving transient response, such as in the case of sudden acceleration or deceleration.

[0027] In the embodiment of FIG. 1, Iγ*=0 and only Iδ* is manipulated to control the output torque. In this case, the motor M, which is a permanent magnet synchronous motor (PMSM), is driven with a power factor of 1 regardless of the state of the motor M. In an interior permanent magnet (IPM) motor, high efficiency can be obtained by maintaining a power factor close to 1 in most operating ranges, but this is not the case in extremely light loads or operating ranges exceeding the rated torque. To improve this, Iγ* can also be manipulated. When Iγ*≠0, reactive power is supplied to the permanent magnet synchronous motor (PMSM), and adjusting this can be said to be equivalent to the method of maximizing efficiency described in Non-Patent Document 1. However, it is believed that supplying reactive power reduces the conversion efficiency of the inverter. When considering the system efficiency, it is necessary to consider whether or not operation at Iγ*≠0 is effective.

[0028] Next, the update stop unit 37 will be described. FIG. 2 shows a unit vector (u α ,u β ) before and after one control cycle. [n] is a unit vector (u α ,u β ) represents the current sampling point (i.e., the current control cycle), [n-1] represents the previous sampling point (i.e., the previous control cycle). Tc is the control cycle, and ωe is the rotational angular velocity (electrical angle) [rad / s].

[0029] When the rotor rotation and the motor terminal voltage are synchronized, the unit vector (u α ,u β ) will advance the rotation angle by Δθe = Tcωe per control period, as shown in Figure 2(a). When a large load fluctuation occurs, the speed fluctuates and Δθe also changes, but even in the case of a load with small inertia, the control period Tc is sufficiently short compared to the time constant of the mechanical system, so it can be said that the fluctuation in Δθe during one control period is small. When the unit vector follows a transition as shown in Figure 2(a), it can be considered that the phases of the motor terminal voltage and the back electromotive force caused by the rotor rotation are nearly identical, and that the command value of the current control system and the actual current value are nearly identical, so the unit vector (u α ,u β ) can obtain information about the rotation angle of the rotor of motor M.

[0030] On the other hand, Fig. 2(b) shows a case where the unit vector is significantly ahead of the rotation angle Δθe per control cycle, and Fig. 2(c) shows a case where it is significantly behind. In these cases, it is considered that a large voltage is generated in the impedance of each phase of the motor, especially in the self-inductance, and it is not possible to simply find the phase of the back electromotive force caused by the rotation from the phase of the terminal voltage. In other words, u α ,u β I can't get the rotation angle information from

[0031] Therefore, in this embodiment, an update range is set that includes the rotation angle Δθe (Δθrenew>Δθe) as shown by the thick line in FIG. 3. The update range (-Δθrenew to +Δθrenew) is the unit vector (u α [n-1],u β The range includes the rotation angle Δθe from [n-1].

[0032] The unit vector (u α ,u β ) within this update range, each component of the unit vector u α ,u β The rotation angle can be obtained from u α ,u β Sample and output as is. If it is outside the update range, u α ,u β Without sampling, the unit vector (u α ,u β ) is output by the update stop unit 37. α ,u β In the following explanation, the unit vector output from the update stop unit 37 is defined as (u α ',u β ').

[0033] In the embodiment shown in FIG. 3, the update range (−Δθrenew to +Δθrenew) is the unit vector (u α [n-1],u β [n-1]), but in one embodiment, the update range (-Δθrenew to +Δθrenew) is the unit vector (u α [n-1],u β [n-1]) may have an asymmetric angle.

[0034] Next, the transition limiting unit 38 will be described. As described above, if a unit vector in the same direction as the motor terminal voltage is acquired only under conditions where the rotation angle can be acquired, erroneous rotation angle information can be ignored, and operation of the motor M can be maintained by performing γδ-αβ conversion using this information. However, if the unit vector updating stop is maintained, the rotor of the motor M continues to rotate during that time, so the phase of the back electromotive force caused by the rotation continues to advance, and when updating is resumed, the angle difference with the previously sampled unit vector becomes large. In other words, in one control cycle immediately after recovery from the update stop, the unit vector used for control (u α ',u β ') fluctuates significantly, and the angle of the γδ axes fluctuates significantly. This causes a large step to be input into the current control system. This causes a large voltage to be generated in the self-inductance of each phase of the motor, making it impossible to detect the back electromotive force caused by the rotation, and the current control system also enters a transient state in which the current command value and the actual current diverge. At this point, the state shown in Figure 2(b) or Figure 2(c) is reached, and sampling is stopped again. For this reason, stopping the update of the 1-degree unit vector causes sampling to be stopped and restarted repeatedly, which may make it impossible to obtain continuous rotation angle information.

[0035] Therefore, in this embodiment, a limit is placed on the angle of the unit vector that can move in one degree, and the transition control unit (see FIG. 1) operates to limit the amount of movement of the angle of the unit vector to a specified value if a fluctuation exceeding a preset limit range occurs in one control cycle.

[0036] FIG. 4 is a diagram showing a limit range (indicated by a thick line) in which the movement of a unit vector is limited. FIG. 4 is very similar to FIG. 3, but the angle that defines the limit range is given by Δθlimit, and the unit vector is the unit vector (u α ',u β The limit range is given as ±Δθlimit, but just like the update range (-Δθrenew to +Δθrenew), it does not have to be given as an angle symmetrical with respect to the unit vector in the previous control cycle.

[0037] However, for the rotation direction, since it is necessary to catch up with the unit vector that has advanced after the update has stopped, a limit range is basically set that includes the rotation angle Δθe (Δθlimit>Δθe). In other words, the limit range (-Δθlimit to +Δθlimit) is the unit vector (u α '[n-1],u β The range includes the rotation angle Δθe from θ′[n-1].

[0038] The unit vector (u α '[n],u β When '[n]) is obtained in the next control cycle, the movement (or rotation) of the unit vector is limited to the upper limit value +Δθlimit or the lower limit value -Δθlimit of the limited range. α >, β >) is the output vector of the transition limiter 38. In this case, multiple control periods are used to α '[n],u β The output vector changes to catch up with (u '[n]) in each control period. α ',u β ') is updated, and the output vector ( α >, β That is, since Δθlimit>Δθe as described above, the output vector ( α >, β >) will eventually (u α ',u β ') can catch up. However, trigonometric functions are necessary to limit the transition angle without changing the magnitude of the vector, as shown in Figure 5. A method to avoid this will be described later.

[0039] The transition limiting unit 38 limits excessive movement of the unit vector, and when a fluctuation that exceeds a preset limit range occurs, limits the amount of movement of the unit vector within the limit range. Therefore, the difference between the angle of the unit vector last updated and the actual rotor angle falls within the limit range. As a result, rotor angle information can be obtained continuously. In the embodiment shown in FIG. 1, the unit vector (u α ',u β However, in one embodiment, the transition limiting unit 38 functions effectively even in a configuration without the update stopping unit 37. That is, the transition limiting unit 38 limits excessive movement of the unit vector generated by the unit vector generating unit 35, thereby making it possible for the rotor angle information to be continuously acquired and for the vector control unit 11 to stably control the motor M.

[0040] ​​​​​​Next, the setting of the range related to the update stop and the movement limit adapted to the rotation speed will be explained. If the update range (-Δθrenew to +Δθrenew) shown in FIG. 3 is extremely larger than the rotation angle Δθe=Tcωe per one control cycle, the unit vector will be allowed to be updated even if the motor terminal voltage and the back electromotive force caused by the rotation are not synchronized, and appropriate control cannot be maintained. Similarly, in FIG. 4, if the limit range (-Δθlimit to +Δθlimit) is too large, the fluctuation of the unit vector after the update is resumed will become large, and the update will be stopped again immediately after recovery from the update stop (update restart). Needless to say, Δθe is proportional to the rotation speed, so it is desirable to adjust the update range (-Δθrenew to +Δθrenew) and the limit range (-Δθlimit to +Δθlimit) according to the rotation speed.

[0041] Therefore, in one embodiment, the update range and the limit range are changed in proportion to the rotation speed of the motor M. Mrenew and Mlimit are introduced as coefficients for the rotation angle Δθe per one control cycle, and the update range and the limit range are set as follows: Δθrenew=MrenewΔθe (1) Δθlimit=MlimitΔθe (2) The coefficients Mrenew and Mlimit are parameters given as constants of at least 1. This makes it possible to give update ranges and limit ranges that are adapted to the operating speed.

[0042] However, since Δθe=Tcωe, information on the rotational speed of the motor is required. In the embodiment shown in FIG. 1, there is no angular speed signal in the vector control system. Instead, for speed control, the speed calculator 40 detects zero crossings of each component of a unit vector to obtain speed information f. This causes a time delay for zero crossing detection and a delay in the speed signal obtained due to an integral element for smoothing the speed signal. Therefore, in this embodiment, since the magnitude of the motor terminal voltage is approximately proportional to the rotational speed, the estimated value Δθe* of the rotational angle shown below is used instead of the rotational angle Δθe [rad]. Δθe* = Tc(Φωe / Ke) ≒ Tc(|e → INV *| / Ke) (3) Here, Φωe is the electromotive force due to the magnetic flux of the rotor's permanent magnet, Ke is the back electromotive force constant, |e → INV *| is the voltage command value e on the αβ axis INV -α*,e INV The length of the vector whose components are -β*. Therefore, the update range and the limit range are expressed as follows, respectively: Δθrenew ≒ MrenewTc(|e → INV *| / Ke) (4) Δθlimit ≒ MlimitTc(|e → INV *| / Ke) (5)

[0043] In a permanent magnet synchronous motor (PMSM), there exists speed electromotive forces (ωe Ld Id and ωe Lq Iq) that interfere with each other between the d and q axes, so the approximation error of equation (3) becomes larger as the motor current or speed increases. In the control of Fig. 1, as the load increases, the q-axis current increases and Δθe* shows a value larger than the true value, but since Δθrenew and Δθlimit given in equations (3) and (4) do not need to be strictly proportional to the speed, we will allow the error here.

[0044] Next, the range setting taking into consideration the amount of calculation (angle setting based on the cross product value) will be described. If the update range and the limit range are given by the formulas (4) and (5) as described above, they change depending on the driving speed, so that the calculation of the trigonometric function is required for each control cycle. Therefore, in one embodiment, the following method is adopted to reduce the amount of calculation.

[0045] The object of judging whether it is inside or outside the update range and the limit range is the unit vector. Therefore, when the cross product value is calculated from the unit vector of the previous control cycle and the unit vector of the next control cycle, the following relationship is obtained. sinδ = u α [n]u β [n-1] - u α [n-1]u β [n] (6) sinδ' = u α '[n]u β '[n-1]-u α '[n-1]u β '[n] (7) Here, δ and δ' are the angles between the unit vectors before and after one control cycle, respectively. Therefore, the sine value of these angles can be obtained by a simple calculation.

[0046] Considering that the angles given by equations (4) and (5) are small, the sine values ​​of these angles can be obtained as follows: sin(Δθrenew)≒sin[MrenewTc(|e → INV *| / Ke)]≒MrenewTc(|e → INV *| / Ke) (8) sin(Δθlimit)≒sin[MlimitTc(|e → INV *| / Ke)]≒MlimitTc(|e → INV *| / Ke) (9) In other words, if the range is determined by comparing the magnitudes of equations (6) and (8) and (7) and (9), the calculation of trigonometric functions in the control loop can be avoided.

[0047] Next, range setting taking into consideration the amount of calculation (angle setting based on the amount of vector movement) will be described. The range / outside determination method using the above-mentioned formulas (6), (7), (8), and (9) does not hold when sin δ or sin δ' passes the inflection point, i.e., |δ|>π / 2 or |δ'|>π / 2. Therefore, if the unit vector undergoes a large change, appropriate determination may not be possible. As an extreme example, when |δ|=π, sin δ=0, and the update stop unit 37 always returns (u α ',u β ') will be updated.

[0048] In order to avoid such an event, in one embodiment, a method of making a determination based on the amount of movement of a unit vector is adopted instead of the above-mentioned method using the cross product value. The distance traveled by a unit vector is given by the following formula: Δl ≒ √[(u α [n]-u α [n-1]) 2 -(u β [n]-u β [n-1]) 2 ] (10) Δl'=√[(u α '[n]-u α '[n-1]) 2 -(u β '[n]-u β '[n-1]) 2 ] (11)

[0049] If the distances for defining the update range and the limit range are small, these distances can be approximated by Δθrenew and Δθlimit, respectively. Therefore, from equations (8) and (9), Δθrenew ≒ sin(Δθrenew) ≒ MrenewTc(|e → INV *| / Ke) (12) Δθlimit ≒ sin(Δθlimit) ≒ MlimitTc(|e → INV *| / Ke) (13) As a result, the boundary values ​​are the same as those of equations (8) and (9). By comparing the magnitudes of equations (10) and (12) and equations (11) and (13), it is possible to determine whether the value is within the update range or outside the limit range.

[0050] Next, simplification of the transition limiting unit 38 will be described. As described above, in the case of limiting the amount of movement as shown in FIG. 5, trigonometric function calculations are indispensable, which increases the amount of calculations. Therefore, in one embodiment, the rotational movement of the unit vector is approximated by a linear movement. Specifically, the amount of movement between two unit vectors is calculated as the difference between the two unit vectors instead of the angle between the two unit vectors. In the embodiment shown in FIG. 6, the movement distance is given by equation (13) to limit the amount of movement of the unit vector. According to equation (13), the boundary value Δθlimit that defines the movement range is the length |e → INV *| by the back electromotive force constant Ke, and multiplying the resultant value by the control period Tc and the coefficient Mlimit. In this embodiment, the movement range is a linear distance range. As shown in FIG. 6, the transition limiting unit 38 divides the vector of the point that divides the difference between two unit vectors internally into a unit vector with a limited amount of movement. Calculated as [n].

[0051] Vector Components of [n] α >[n], β >[n] is given as follows: α >[n] = ku α '[n]+(1-k) α >[n-1] (14) β >[n] = ku β '[n]+(1-k) β >[n-1] (15) where k = Δθlimit / L L = √[(u α '[n]- α >[n-1]) 2 -(u β '[n]- β >[n-1]) 2 ] (16)

[0052] Note that equation (16) requires a square root calculation. The square root calculation can be avoided by using, for example, the following approximation instead of equation (16). L ≒ 0.9834max(|u α '[n]- α >[n-1]|,|u β '[n]- β >[n-1]|) +0.4307min(|u α '[n]- α >[n-1]|,|u β '[n]- β >[n-1]) (17)

[0053] In addition, in equation (10) and Figure 1, |e → INV *|(=√(α 2 +β 2 )) can be substituted by an approximation similar to equation (17). On the other hand, L in equation (17) can also be replaced with S in the following equation: K = Δθlimit / S S = u α '[n] β ​​​​​​​​​​​​​>[n-1] - α >[n-1]u β '[n] (18) In this case, the distance between the two points is approximated by the cross product value S, and if the amount of vector movement is small, the values ​​of equations (17) and (18) will be approximately equal.

[0054] As shown in Figure 6, the amount of movement is limited by equations (14)-(16). follows u' linearly through the inside of the unit circle. Figure 7 shows the vector when Mlimit<1. In the steady state when Mlimit<1, as shown in Fig. 7, u' moves on the unit circle by Δθe per control period, while The movement of is limited to Δθlimit. will move along a circle with a radius of Δθlimit / Δθe = Mlimit. The delay angle of [n] is approximately ε θ ≒ cos -1 (Mlimit)-Δθlimit / 2 ≒ cos -1 (Mlimit) (19) That is, ε θ If a phase delay of M is allowed, it is possible to set Mlimit<1.

[0055] Due to the approximation error of the above formula (5), if you try to set Δθlimit ≒ Δθe near the rated load, you will have to set Mlimit < 1. In this case, ε θ A phase lag occurs, and in the control of Figure 1, the motor is operated with a slight lagging power factor. Since a slight lagging power factor operation is considered desirable in order to prevent loss of synchronism at low speeds, it is possible to actively choose a setting of Mlimit<1. The magnitude of the αβ-γδ conversion and γδ-αβ conversion are affected because the magnitude of the αβ-γδ conversion and γδ-αβ conversion are slightly smaller. To avoid this, it is possible to convert the vectors to unit vectors again, but since these conversions are inside the current control loop, they are corrected by PI control and are not considered to have any effect on steady-state operation.

[0056] Next, the operation of a permanent magnet synchronous motor (PMSM) with a power factor of 1 will be described. The voltage equation in dq coordinates for a permanent magnet synchronous motor (PMSM) is

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[0057] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope according to the technical idea defined by the claims. [Explanation of symbols]

[0058] 10 Inverter 11 Vector control unit 12 Current detector 17 3 / 2 phase converter 18 Static / rotating coordinate conversion section 21 γ-axis current control section 22 δ-axis current control section 24 Rotation / stationary coordinate conversion section 25 2 / 3 phase converter 29 Vector Length Calculation Unit 31 Rotation Angle Estimator 35 Unit Vector Generator 36 Filters 37 Update stop section 38 Transition Restriction Section Medium motor ​

Claims

1. A drive device for an electric motor including an inverter, a current detector that detects an output current of the inverter, and a vector control unit that determines a voltage command value for the inverter, The vector control unit includes: a unit vector generating unit configured to generate a unit vector in the same direction as a voltage command vector, the voltage command value being included in a component of the voltage command value for the inverter, for each control period; an update stop unit that outputs the unit vector as is when a rotation angle per control cycle of the unit vector generated by the unit vector generation unit is within an update range, and stops updating the unit vector and outputs a unit vector of the previous control cycle when the rotation angle per control cycle of the unit vector is outside an update range; The drive device further includes a transition limiting unit that limits an amount of movement of the unit vector output from the update stopping unit within a limited range.

2. 2. The drive device according to claim 1, wherein the update range is a range that includes a rotation angle of the rotor of the electric motor from the unit vector generated in a previous control cycle.

3. 3. The drive device according to claim 1, wherein the limit range is a range that includes a rotation angle of the rotor of the electric motor from the unit vector generated in a previous control cycle.

4. 4. The drive device according to claim 1, wherein the magnitude of the limit range is changed in proportion to the rotational speed of the electric motor.

5. The drive device according to claim 1 , wherein the size of the update range is changed in proportion to a rotational speed of the electric motor.

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