JP3751919B2 - Electric motor control device - Google Patents

Description

たとえば、ＳＥＧ＝１００、ＣＳＵ＝１６００、ＣＬＫ＝１６００００００とすればＨＬＺ＝１００
ただし、ＳＥＧは交流波形の１サイクルを制御する区画数にあたるので、少なくしすぎると階段状の制御となり、波形に歪みを生じるので、１２を下回らないように決定した方がよい。望ましくは２０以上とする。１セグメントを構成するクロック数は、電力スイッチング素子の通電と遮断を制御し、出力電流の強度に影響するので少なくとも１０区分、望ましくは１００区分程度の分解能を確保した方がよい。
【００３２】
上記の水晶発振器を使用して実現できる最高速度はセグメント数２０、クロック数１００を採用して、８０００ヘルツを実現できるので、実用上十分に必要速度領域をカバーしている。しかし、このような高速領域では、クロック数を仮に１０１とした場合、７９２０．７９２ヘルツとなり、約１％（８０ヘルツ分）の制御不能領域を生む。そのため、４００ヘルツ程度（制御不能領域約０．０２５％）が精度良く制御できる上限となろう。４００ヘルツは６極電動機を採用した場合毎分８０００回転に相当するので、変速が必要な領域は毎分約４０００回転程度以下である実情からすれば（それ以上の速度ではトップかオーバードライブギアーで走行する）十分に変速制御に適用可能である。
【００３３】
ステップ３４では、前記軸角度センサ４により現在の電動機出力軸の軸角度θｒを検出し、この軸角度を出力原点とする。
ステップ３５では、出力セグメントの基準点からの数を計算する。最初はステップ３４で求めた出力原点（０）であり、その後このステップ３５に戻る毎に１ずつカウントアップする。
【００３４】
ステップ３６では、出力セグメントから必要な通電量をＲＯＭに記憶してある予め定めた数表などから検索して決定する。
ステップ３７では、上記通電量から、出力セグメントの通電クロック数と休止クロック数とを算出する。
ステップ３８では、前記通電クロック数に応じた期間、電力スイッチング素子を通電し、休止クロック数に応じた期間電力スイッチング素子を遮断するスイッチング制御を行う。
【００３５】
ステップ３９では、１ヘルツの最終セグメントであるかを判定し、最終セグメントに達するまではステップ３５へ戻り、最終セグメントに達して１ヘルツ分の制御を終了すると、再度ステップ３１で必要回転速度を算出しなおして同様の制御を繰り返していく。
このように、変速時に電動機１を、目標回転速度に応じた交流周波数の電機子電流が流れるようにフィードフォワード制御することにより、電動機側の回転速度を検出するフィードバック制御のように、回転速度センサを用いることなく、速やかに、かつ、極めて滑らかにトルクショックを有することなく変速を行うことができる。
【００３６】
電動機としては上記実施形態に示したように同期電動機を用いるのが、高精度なフィードフォワード制御を確保する上で望ましいが、誘導電動機を用いたフィードフォワード制御を行うことも可能である。既述のように、回転速度制御の必要な変速時は、歯車が中立位置にあり、無負荷運転状態であるため、誘導電動機でもすべり率が比較的小さく、そのすべり率は気温などによって若干変化するものの実験によって得たすべり率が長く保たれる。ベアリングなどの劣化により、スリップ量が変化する事態はモータの使用限度に至った場合でもあり、そのような場合を除外すれば、変速比毎に決まっている目標回転速度について、予めすべり率を算出しておき、目標回転速度にすべり率を加算した駆動電源の周波数に制御すればよい。
【００３７】
なお、誘導電動機を用いたフィードフォワード制御でも回転速度の検出は当然に不要であり、通常運転時にすべり率でトルク制御する場合に電動機の回転速度を知る必要があるが、変速機出力軸の回転速度と変速比とで電動機の回転速度を求められるので、結局電動機の回転速度を検出するセンサは不要である。
【図面の簡単な説明】
【図１】本発明の実施形態に用いる同期電動機の動作原理を示す図。
【図２】本発明の実施形態のシステム構成を示す図。
【図３】同上実施形態で電動機のトルク制御と回転速度制御を切り換えるフローチャート。
【図４】同上の電動機トルク制御のフローチャート。
【図５】１サイクル分の交流波形に相当するセグメント数と、１セグメント当たりのクロック数の関係を示した図。
【図６】同上実施形態における変速時制御の概要を示すフローチャート。
【図７】同上実施形態における歯車の同期制御により変速動作を行う原理を示す図。
【図８】同上実施形態の変速時における電動機回転速度制御のフローチャート。
【符号の説明】
１…電動機 １ａ…電動機の出力軸 ２…変速機 ３…駆動輪
４…軸角度センサ ５…電力制御装置 ６…制御コンピュータ ９…回転速度センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to control of an electric motor, and more particularly to control technology at the time of shifting of an electric motor to which a mechanical transmission is connected.
[0002]
[Prior art]
In recent years, development of automobiles that use an electric motor alone or as a hybrid prime mover in combination with an internal combustion engine has been active. During normal operation of an automobile, the torque of the electric motor is controlled in accordance with the traveling load, similar to the control by the internal combustion engine.
On the other hand, when a shift is performed by connecting a mechanical transmission to the electric motor in consideration of travelability, a smooth shift without torque shock can be performed by shifting the motor in synchronization with the rotational speed after the shift.
[0003]
[Problems to be solved by the invention]
Conventionally, some motors perform feedback control while detecting the actual rotational speed during shifting, but there is a delay in convergence to the target rotational speed. That is, even if feedback control is performed according to the deviation between the target rotational speed and the actual rotational speed, the rotational speed of the motor rapidly increases and the deviation from the target rotational speed increases at the moment when the power transmission of the motor is interrupted, Overshoot and undershoot are repeated and convergence is delayed, resulting in prolonged shift completion. Some transmissions have a mechanical synchronization mechanism, but the rotation of the motor is forcibly decelerated by braking, so that torque shocks cannot be absorbed sufficiently and the cost is high.
[0004]
The present invention has been made paying attention to such a conventional problem, and by smoothly converging the electric motor to the target rotational speed without detecting the actual rotational speed at the time of shifting, it is smooth and responsive. The purpose is to enable good gear shifting.
[0005]
[Means for Solving the Problems]
For this reason, the present invention performs torque control for controlling the electric motor connected to the mechanical transmission to the target torque during normal operation with the shift position fixed, whereas during no-load operation during gear shifting, the AC frequency The control signal is formed so that the armature current flows, and the control signal is supplied to switch to rotation speed control for feedforward control of the electric motor to the target rotation speed.
[0006]
As a result, when a control signal formed according to the target rotational speed is supplied to the electric motor at the time of shifting, an armature current having an AC frequency corresponding to the target rotational speed flows, and quickly converges to the target rotational speed. Smooth shifting can be performed with good response as the rotation speed synchronized with each other.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the principle of a synchronous motor used in the embodiment. Although the case of a two-pole machine has been shown as the simplest example, in practice, a multi-pole machine having four or more poles is often used.
The electric motor generates rotational force based on the principle that the same pole generates a reaction force and the different pole generates an attractive force due to the interaction between the magnetic pole generated on the stator side and the magnetic pole generated on the rotor side. . Therefore, when the N pole (S pole) of the stator and the S pole (N pole) of the rotor are constant in phase, the S pole (N pole) of the stator and the N pole (S pole) of the rotor are usually in phase. However, in this case, the torque is stable and torque is not generated. This state is assumed to be “phase difference angle = 0”.
[0008]
FIG. 1A shows a magnetic pole that has a phase difference angle of 60 ° and causes the rotor (rotor) R to rotate forward if the forward rotation of the output shaft of the motor rotates clockwise in the figure. Is generated in the stator (field) S.
In the synchronous motor, the magnetic pole of the rotor is provided at a fixed position with respect to the output shaft. On the other hand, the magnetic pole generated in the stator can be arbitrarily adjusted by the method of energizing the coil. That is, it is possible to generate a magnetic pole different from the previous one even if the direction of the current is changed even in the same coil.
[0009]
Usually, when a magnetic pole is generated in the stator by AC power, the magnetic pole goes around by supplying AC 1 Hz to the coil. In FIG. 1, since a two-pole machine is shown, the output shaft also makes one round during an alternating current of 1 Hz, but in a four-pole machine, one round of the electrical angle corresponds to a mechanical angle of 180 °. Similarly, in a 6-pole machine, an electrical angle of 360 ° corresponds to a mechanical angle of 120 °. The position of the magnetic pole generated in the stator can be controlled by the point of the AC power waveform applied to the stator.
[0010]
In FIG. 1B, since a current corresponding to an electrical angle of 90 ° of AC power is applied to the stator, an N pole is generated at a 90 ° position of the stator. If a current corresponding to 180 ° is applied, an N pole is generated at a position of 180 ° of the stator. Similarly, when a current corresponding to 270 ° of AC power is applied, an N pole is generated at a position of 270 ° of the stator. Then, the S pole of the rotor is positioned at a position delayed by the phase difference angle with respect to the position of the N pole of the stator. These relationships are the same for multipolar machines if the relationship between electrical angle and mechanical angle is applied.
[0011]
In the figure, the switching element is configured in a bridge shape and its control circuit is configured so that the direction of the current is reversed at the midpoint of the AC waveform. Furthermore, this figure is only a schematic display and does not describe the specific coil shape, but the electric power used differs depending on whether it is single-phase AC, three-phase AC, etc., and the number of poles. In the vicinity of the 0 and 180 ° positions, a magnetic pole can be generated by a coil near the position. In phase difference angle control, the current position of the rotor is detected by a detector such as a resolver, and if you want to obtain a driving force for the current position of the rotor, obtain the amount of current from the AC waveform at the advanced position, and use the braking force and power generation action. Is required, the energization amount is obtained from the AC waveform at the delayed position, and the energization amount is converted into an actual current and applied to the stator. Then, the magnetic pole can be generated in the stator at a position advanced or delayed with respect to the rotor phase.
[0012]
From the relationship between the attractive force and the repulsive force of the magnetic pole, the maximum torque is generally generated when a phase difference angle of about half the magnetic pole pitch is given. When a phase difference angle exceeding the magnetic pole pitch is given, a reversing force is suddenly generated, so that a “step-out” phenomenon occurs and the operation becomes impossible. Practically, when the phase difference angle exceeds half of the magnetic pole pitch, the generated torque decreases, so that it is likely to fall out of step and cannot be used.
[0013]
FIG. 2 shows a system schematic diagram of an embodiment of an electric vehicle using the above-described synchronous motor as a prime mover.
A transmission 2 is connected to an output shaft 1a of an electric motor 1 composed of a synchronous motor, and a drive wheel 3 is connected to the output shaft 2a of the transmission 2 via a reduction gear and an axle (not shown). A shaft angle sensor 4 constituted by a resolver or the like that detects the current position (axis angle) of the output shaft 2 a is attached to the output shaft 2 a of the electric motor 2. The transmission 2 is a mechanical transmission that has a plurality of gears and neutral points, and changes the rotational speed of the electric motor 1 by switching the meshing of the plurality of gears.
[0014]
The power control device (inverter) 5 converts DC power from the battery 7 into AC power based on a control signal from the control computer 6 and supplies the AC power to the motor 1 to drive the motor.
The gear ratio selection device 8 controls the transmission 2 to select a gear ratio. The output shaft 2a of the transmission 2 is provided with a rotation speed sensor 9 that detects the rotation speed of the output shaft 2a. The rotational speed detected by the rotational speed sensor 9 is used for controlling the rotational speed of the electric motor 1 at the time of shifting, and can also be used as a vehicle speed signal because it is proportional to the vehicle speed.
[0015]
The control computer 6 includes a CPU, a ROM, a RAM, various interfaces, and the like, and is formed based on a detection signal from an accelerator sensor 10 that detects an accelerator pedal depression amount in addition to the shaft angle sensor 4 and the rotation speed sensor 9. The control signal thus supplied is supplied to the power control device 5, and the electric motor 1 is controlled via the power control device 5. Here, torque control based on the phase difference angle is performed so that the output torque of the electric motor 1 is set as the target torque during normal operation, but the rotational speed control that synchronizes the rotational speed of the electric motor 1 with the rotational speed on the drive wheel side during shifting. A control signal is formed so that Further, the control computer 6 controls the gear ratio of the transmission 2 via the gear ratio selection device 8.
[0016]
FIG. 3 shows a flow for switching between the torque control and the rotational speed control of the electric motor 1.
In step 1, it is determined whether or not a shift request has occurred. During normal operation where no shift has occurred, the motor 1 is torque-controlled in step 2, and when the shift request is generated, the motor 1 is controlled to be controlled in rotational speed.
[0017]
FIG. 4 shows a flow of torque control of the electric motor 1 in the step 2.
In step 11, the phase difference angle Δθ corresponding to the target torque of the electric motor 1 is calculated based on the detected value from the accelerator sensor 9 representing the driving force required by the driver.
In step 12, the current shaft angle θ0 (of the rotor) of the electric motor 1 detected by the shaft angle sensor 4 is read.
[0018]
In step 13, the magnetic pole angle (electrical angle) θs of the stator is calculated by adding the phase difference angle Δθ to the current shaft angle θ0. This means the phase of the AC armature current.
In step 14, it is determined whether the calculated magnetic pole angle θs of the stator is larger than 360 °. If it is larger than 360 °, the next cycle is electrically entered. Is set as a new magnetic pole angle θs.
[0019]
If the magnetic pole angle θs is 360 ° or less in step 14, it is determined in step 16 whether the magnetic pole angle θs is negative. In a situation where the braking force is generated, the necessary phase difference angle may be negative, and in such a case, the magnetic pole angle may also be negative. Since this is equivalent to the phase obtained by adding 360 °, if it is negative, 360 ° is added to the magnetic pole angle θs in step 17.
[0020]
In step 18, an energization amount corresponding to the magnetic pole angle θs adjusted in the range of 0 to 360 ° as described above is obtained. Specifically, a table (numerical table) in which the energization amount (energization duty) is set for each segment obtained by dividing the sine curve into a predetermined number in the range of 0 to 360 ° is stored in the ROM, and the segment corresponding to the magnetic pole angle θs. What is necessary is just to search and obtain | require energizing amount of. In addition to setting data for 2π (360 °) as described above, it is also possible to set and process data for π (180 °) and π / 2 (90 °) using symmetry. Is possible.
[0021]
In step 19, the number of energized clocks and the number of shut-off clocks are calculated for one segment for controlling energization, corresponding to the energization amount obtained as described above. The clock is generated as a rectangular wave having a frequency defined by the crystal oscillator of the control computer 6.
In step 20, the power switching element of the power control device 5 is controlled based on the number of energized clocks and the number of cut-off clocks. Here, if the switching element is energized over 100% of the segment, a current with full capacity will flow, and if it is cut off, no current will flow.
[0022]
In this way, in the operation region for obtaining the rotational force from the electric motor 1, that is, during normal running, operation is performed by torque control that makes the phase difference angle variable.
Next, the rotational speed control at the time of shifting, which is a feature of the present invention, will be described. When a motor is connected to a mechanical gear transmission for an automobile, precise rotational speed control is required when the gears are engaged. At this time, the initial meshing of the gear is released and the gear is in a neutral state. At this time, the electric motor is released from the load, and in the case of a synchronous motor, it can follow in synchronization with the frequency of the applied power source unless an extreme speed change is instructed. Conventionally, feed-forward control of the rotation speed of an electric motor has not been performed by strictly controlling the frequency of a power supply to be supplied.
[0023]
For this control, precise frequency control of the power source is required. For example, assuming that an alternating current of 100 Hz is generated, the following conditions are assumed. For reference, FIG. 5 shows the relationship between the number of segments corresponding to an AC waveform for one cycle and the number of clocks per segment under the following conditions.
Clock used 16 megahertz Carrier frequency used About 10 kilohertz 100 Hz takes 1/100 second to complete an AC cycle. Since a 16 megahertz clock is used, the number of clocks per 1/100 second is 160 kilos. Here, since the carrier frequency is about 10 kHz, if one cycle of the carrier waveform is defined as one segment, one cycle of the AC waveform can be expressed as 100 segments, and further expressed as the number of clocks, 1600 clocks per segment. .
[0024]
In other words, in reverse, when a segment having a width of 1600/16000000 seconds is executed 100 times, it becomes 1/100 seconds, which is a required time for one cycle. An alternating current with an arbitrary frequency can be generated by changing the time required for one cycle. For example, in order to generate 10 Hz alternating current, one cycle may be composed of 1000 segments under the same conditions as described above. Since the required time per cycle at this time is 1/10 second, an alternating current of 10 hertz can be generated.
[0025]
Similarly, when it is desired to generate 400 Hz alternating current, one cycle may be constituted by 25 segments under the same conditions as described above. However, since the AC waveform that can be generated tends to be distorted as the number of segments constituting one cycle decreases, the number of segments remains 100 and the number of clocks constituting one segment is reduced from 1600 to 400. Good. When a fine output frequency is required, it may be determined so as to constitute a required time for one cycle that requires the product of the number of segments and the number of clocks.
[0026]
First, the outline of the shift control in the present embodiment will be described based on the flowchart of FIG. 6 and FIG. 7 showing the principle of performing a shift operation by gear synchronous control. The rotation speed adjustment device 11 corresponds to the electric motor 1 and the power control device 5, and the gear shift solenoid 12 and the shift fork 13 correspond to the gear ratio selection device 8. Further, this figure is a diagram on the input shaft side to which the driving force is inputted, and the driving force is transmitted to the output shaft side through the gear 15.
[0027]
In FIG. 6, in step 21, the electric motor 1 is operated with no load. For no-load operation, for example, the phase difference angle of the electric motor 1 may be set to substantially zero. When the operation shifts to no-load operation, the process proceeds from step 22 to step 23, and the transmission 2 is shifted to the neutral point. Thereby, the gear 14 becomes free.
In step 24, the rotational speed of the gear 14 is adjusted by the rotational speed sensor 9 via the rotational speed adjusting device 11 based on the detected rotational speed of the gear 15, and the peripheral speed of the gear 14 is changed to the peripheral speed of the gear 15. Synchronize.
[0028]
When the peripheral speed of the gear 14 is substantially synchronized with the peripheral speed of the gear 15, that is, when the difference between the peripheral speeds of the gear 14 and the gear 15 becomes a predetermined value or less, the gear shift solenoid 12 is driven to control the shift fork, The gear 15 is shifted. It should be noted that when performing the power shut-off and transmission switching operation, as a rule, the gear shifting operation should be performed after the peripheral speeds of the gears coincide with each other. When the speed difference is reached, the gear meshing is switched. That way, the switching operation can be performed smoothly.
[0029]
FIG. 8 shows a flow of rotation speed control of the electric motor 1 at the time of shifting in the step 24 of FIG.
In step 31, the rotational speed of the output side (driving wheel side) detected by the rotational speed sensor 9 and the rotational speed of the input side (motor side) are made equal to perform the meshing of the motor 1. The rotational speed (target rotational speed) is calculated.
[0030]
In step 32, the frequency of AC power supplied to the electric motor 1 is calculated according to the target rotation speed. Specifically, the frequency required to obtain the target rotational speed is calculated according to the number of poles of the adopted electric motor. For example, in order to obtain 3000 revolutions per minute in a 6-pole synchronous motor, it is necessary to supply power of 150 hertz. In step 33, the number of segments and the segment width (pulse width) for 1 Hz of AC power are calculated based on the target frequency, and the number of clocks corresponding to the segment width is calculated.
[0031]
For example, in order to generate an alternating current of 150 Hz as described above, it is sufficient to generate one cycle of an alternating waveform in 1/150 seconds. The number of segments constituting the 1/150 second and the number of clocks constituting the segment are determined.
If this calculation is a general formula,

For example, if SEG = 100, CSU = 1600, CLK = 16000000, HLZ = 100
However, since SEG corresponds to the number of sections for controlling one cycle of the AC waveform, if it is too small, it becomes step-like control, and the waveform is distorted. Therefore, it is better to decide not to fall below 12. Desirably 20 or more. Since the number of clocks constituting one segment controls energization and interruption of the power switching element and affects the intensity of the output current, it is better to secure a resolution of at least 10 sections, preferably about 100 sections.
[0032]
The maximum speed that can be realized by using the above-mentioned crystal oscillator employs 20 segments and 100 clocks and can realize 8000 Hz, so that the necessary speed range is sufficiently covered in practice. However, in such a high-speed region, assuming that the number of clocks is 101, it becomes 7920.792 hertz, producing an uncontrollable region of about 1% (80 hertz). Therefore, about 400 hertz (uncontrollable area: about 0.025%) will be the upper limit for accurate control. 400 Hz is equivalent to 8000 revolutions per minute when a 6-pole motor is used, so the area that needs to be changed is about 4000 revolutions per minute (at higher speeds, the top or overdrive gear) It is fully applicable to shift control.
[0033]
In step 34, the current shaft angle θr of the motor output shaft is detected by the shaft angle sensor 4, and this shaft angle is set as the output origin.
In step 35, the number of output segments from the reference point is calculated. Initially, the output origin (0) obtained in step 34 is counted, and thereafter, every time the process returns to step 35, the count is incremented by one.
[0034]
In step 36, a necessary energization amount is retrieved from the output segment and determined from a predetermined numerical table stored in the ROM.
In step 37, the number of energized clocks and the number of pause clocks of the output segment are calculated from the energization amount.
In step 38, switching control is performed in which the power switching element is energized for a period corresponding to the number of energized clocks and the power switching element is interrupted for a period corresponding to the number of idle clocks.
[0035]
In step 39, it is determined whether it is the last segment of 1 Hertz, and the process returns to Step 35 until the final segment is reached. When the final segment is reached and the control for 1 Hertz is completed, the required rotational speed is calculated again in Step 31. Then, the same control is repeated.
In this way, the rotational speed sensor is controlled by feedback control for detecting the rotational speed on the motor side by performing feedforward control so that the armature current having an AC frequency corresponding to the target rotational speed flows during the speed change. The shift can be performed quickly and extremely smoothly without using a torque shock without using the.
[0036]
As the electric motor, it is desirable to use a synchronous motor as shown in the above embodiment in order to secure highly accurate feedforward control, but it is also possible to perform feedforward control using an induction motor. As described above, the gear is in a neutral position and is in a no-load operation during gear shifting that requires rotational speed control, so the slip rate is relatively small even with induction motors, and the slip rate varies slightly depending on the temperature, etc. However, the slip rate obtained by the experiment is kept long. The slip amount may change due to deterioration of the bearing, etc., even when the motor usage limit is reached. Excluding such a case, the slip rate is calculated in advance for the target rotational speed determined for each gear ratio. In addition, the frequency of the driving power source may be controlled by adding the slip ratio to the target rotation speed.
[0037]
In feed-forward control using an induction motor, detection of the rotational speed is naturally unnecessary, and it is necessary to know the rotational speed of the motor when torque control is performed with the slip ratio during normal operation. Since the rotational speed of the electric motor can be obtained from the speed and the gear ratio, a sensor for detecting the rotational speed of the electric motor is unnecessary after all.
[Brief description of the drawings]
FIG. 1 is a diagram showing an operating principle of a synchronous motor used in an embodiment of the present invention.
FIG. 2 is a diagram showing a system configuration according to the embodiment of the present invention.
FIG. 3 is a flowchart for switching between torque control and rotation speed control of the electric motor in the embodiment.
FIG. 4 is a flowchart of motor torque control same as above.
FIG. 5 is a diagram showing the relationship between the number of segments corresponding to an AC waveform for one cycle and the number of clocks per segment.
FIG. 6 is a flowchart showing an outline of shift control in the embodiment;
FIG. 7 is a diagram showing the principle of performing a shift operation by synchronous control of gears in the embodiment.
FIG. 8 is a flowchart of motor rotation speed control at the time of shifting according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electric motor 1a ... Output shaft of electric motor 2 ... Transmission 3 ... Drive wheel 4 ... Shaft angle sensor 5 ... Electric power control device 6 ... Control computer 9 ... Rotational speed sensor

Claims (5)

A control device for an electric motor to which a mechanical transmission is connected,
During normal operation with the shift position fixed, torque control is performed by setting a control amount according to the target torque. During no-load operation during gear shifting, the control amount is set according to the target rotation speed. Switch to control,
And the said rotational speed control forms a control signal so that the armature current of an alternating current flows, supplies this control signal, and feedforward-controls an electric motor to the target rotational speed, The motor control apparatus characterized by the above-mentioned . The motor control device according to claim 1, wherein the motor is a synchronous motor, and the control signal is formed so that an armature current having an AC frequency synchronized with a target rotation speed flows during no-load operation. 2. The motor control according to claim 1, wherein the motor is an induction motor, and the control signal is formed so that an AC armature current having a slip rate corresponding to a target rotational speed flows during no-load operation. apparatus. The said control signal is an alternating current signal obtained by switching-controlling a direct-current power supply with the pulse width modulation signal which has a pulse width corresponding to the phase of the said alternating current frequency, The Claim 1 or Claim 2 characterized by the above-mentioned. Electric motor control device. The motor control device according to claim 4, wherein when the target rotation speed is high, the switching cycle is adjusted to be short.

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