JP2002369597A - Method for detecting rotational speed of induction motor in free rotation, and method for restarting induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restart operation with no impact by detecting the rotational speed of an induction motor under free rotation, without coupling a motor with a speed detecting means and supplying the motor with an AC power, having a frequency and a voltage corresponding to a detected rotational speed. SOLUTION: Current and voltage of an induction motor 5 are divided into a d-axis component and a q-axis component which are orthogonal to each other, a q-axis voltage command value to the induction motor 5 in free rotation is brought to zero and a stepwise trigger voltage is applied in the d-axis direction. A q-axis current, having a phase shift of 90 deg. from the trigger voltage, is detected and a control operation for bringing the detection value of q-axis current to zero is conducted, thus obtaining the rotational speed information of the induction motor. Alternatively, the product of a d-axis current command value and the primary resistance of the induction motor is employed as the trigger voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a rotation speed and a method for restarting an induction motor in a free-rotation state in which an AC output of a power converter is interrupted due to a power failure or the like during operation.

[0002]

2. Description of the Related Art Induction motors are widely used because of their simple structure and ruggedness. However, it has been difficult to change the rotation speed. Conventionally, DC motors are used for applications that require variable speed operation, but such DC motors have structural weaknesses such as commutators and are disadvantageous in that they are expensive. However, there were various inconveniences, such as replacement of consumables such as brushes and maintenance and inspection of commutators.

[0003] On the other hand, the performance of semiconductor switch elements and the technology of using them have been further improved, and by appropriately controlling the voltage and frequency of AC power output from an inverter as a power converter, an induction motor can be used. It has become extremely easy to operate at a desired torque and rotational speed. Therefore, in recent years, variable speed operation of an induction motor using an inverter device that outputs AC power of a variable voltage and a variable frequency as a power source has been generally adopted.

[0004]

However, since this inverter device uses commercial power as a power source, the power supply to the inverter device may be temporarily interrupted due to lightning strikes or switching of distribution lines. In the meantime, power supply to the induction motor is interrupted, and power supply to the induction motor is also interrupted when the inverter device breaks down. During this power supply interruption period, the induction motor is in a free rotation state, and its rotation speed gradually decreases. When the power supply recovers soon, the induction motor can be restarted by receiving the supply of the AC power again. However, in practice, it is not possible to restart the operation immediately after the power supply is recovered. If the frequency and voltage of the AC power output from the inverter device are higher than the values corresponding to the rotation speed of the motor at that time, a problem occurs in which a large rush current flows from the inverter device to the motor.
Conversely, if the output voltage and frequency of the inverter device are smaller than the values corresponding to the rotation speed of the motor at that time, a problem occurs in which a large regenerative current flows from the motor to the inverter device. Therefore, when restarting the operation of the induction motor, it is necessary to first detect the current rotational speed of the induction motor.

[0005] Since the voltage remains in the winding of the induction motor even when the power is cut off, the rotational speed can be detected by using the residual voltage. However, since this residual voltage disappears in a very short time, even after the residual voltage disappears, the rotational speed of a speed generator or a pulse generator is detected so that the rotational speed of the induction motor can be detected every moment. The means must be connected to the motor. However, in order to attach such a rotational speed detecting means to an induction motor, there is a problem that the shaft end of the motor must be machined, and it is often difficult to secure a space for attaching these. Therefore, when a speed generator or a pulse generator cannot be provided, the motor that has been in a free-rotation state due to a power failure is temporarily stopped and then restarted. However, even if the power is interrupted for a very short time, waiting until the motor stops every time has a disadvantage that the useless time until the restart of operation is increased and the operating efficiency of the device is reduced. In particular, when a load having a large flywheel effect is connected, such as a centrifuge, it takes a long time to stop, so it is not practical and requires much time and labor.

Accordingly, an object of the present invention is to detect the rotation speed of an induction motor during free rotation without coupling speed detection means to the motor, and to provide the motor with AC power of a frequency and voltage corresponding to the detected rotation speed. The purpose is to allow driving to resume without shock.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, a method for detecting the rotational speed of an induction motor during free rotation and a method for restarting the motor according to the present invention output AC power of a variable voltage and a variable frequency. In the method of detecting the rotation speed of the induction motor during free rotation by interrupting the AC output of the power conversion device for driving the induction motor, a step-like trigger voltage is applied to the induction motor during free rotation, Detects a current having a phase different from the trigger voltage by 90 degrees from
By controlling the detected currents having a phase difference of 90 degrees to zero by the adjustment operation, rotation speed information of the induction motor is obtained.

Alternatively, the current / voltage of the induction motor is separated into a d-axis component and a q-axis component that are orthogonal to each other, and the q-axis voltage command value to the induction motor during free rotation is reduced to zero to reduce the d-axis direction. By applying a step-like trigger voltage, detecting the q-axis current flowing from the induction motor with a phase difference of 90 degrees from the trigger voltage, and performing an adjusting operation of controlling the q-axis current detection value to zero, Obtain rotation speed information of the motor.

Alternatively, a d-axis voltage command value is calculated from a product of a d-axis current command value and a primary resistance of the induction motor, and in a state where the q-axis voltage command value to the induction motor during free rotation is zero, The step-shaped d-axis voltage command value is given as a trigger voltage, rotation speed information is obtained by an adjusting operation for controlling the q-axis current flowing at a phase difference of 90 degrees to zero, and these are obtained when the induction motor is restarted. The d-axis voltage command value and the rotation speed information are used.

Alternatively, the current / voltage of the induction motor is separated into a d-axis component and a q-axis component that are orthogonal to each other, and the d-axis voltage command value is calculated from the product of the d-axis current command value and the primary resistance of the induction motor. In the state where the q-axis voltage command value to the induction motor during free rotation is zero, the q-axis current detected by applying the step-like d-axis voltage command value as a trigger voltage is controlled to zero. By performing the adjustment operation, the rotation speed information of the induction motor is obtained, and the d-axis voltage command value and the rotation speed information are used for restarting the induction motor, and the rotation speed information is used with a predetermined time delay and change speed. Switch to the set rotation speed command value.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of the present invention will be described below. That is, when the induction motor is rotating at an angular frequency of ω ₂ , the current-voltage equation in its steady state can be represented by the following determinant in Equation 1.

[0012]

Where V _d : primary voltage (d-axis) V _q : primary voltage (q-axis) I _d : primary current (d-axis) I _q : primary current (q-axis) φ _2d : secondary magnetic flux (d Axis) φ _2q : Secondary magnetic flux (q axis) R ₁ : Primary resistance R ₂ : Secondary resistance Lσ: Leakage inductance Lm: Exciting inductance ω ₁ : Primary frequency ω ₂ : Rotational speed ω _S : Slip frequency (ω _S = ω ₁ −ω ₂ ) The approximate solution of the characteristic equation represented by Expression 1 is − (R ₂
/ Lm) + jω ₂ to become. Therefore, when a voltage containing ω ₂ as a frequency component is applied, the current waveform oscillates at ω ₂ . Therefore, if the coordinate axis is rotated so that the detected primary current _Id or _Iq becomes zero, the rotation speed information of the induction motor can be obtained from the rotation cycle.

FIG. 1 is a flowchart showing a first embodiment of the present invention. In FIG. 1, a step-like trigger voltage is applied to the motor (process 21), so that a current having a phase different from the trigger voltage by 90 degrees from the motor is detected (judgment 17). Rotational speed information (judgment 18) can be obtained from the result of the adjustment operation (step 23) for setting the currents having 90 ° phase differences to zero.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention. In the circuit of FIG. 2, the three-phase AC power from the three-phase AC power supply 1 is converted into DC power by a forward converter 2, this DC power is smoothed by a smoothing capacitor 3, -It is converted into three-phase AC power of variable frequency, and drives the induction motor 5 at a desired rotation speed. Reference numeral 31 denotes a separately set frequency command value ω
_{This is} a V / F converter that converts ₁ ^* into a voltage command value.
Coordinate converter 32, a voltage command value V _q ^* and V _d ^* mutually orthogonal DC coordinate system, the voltage command value of the AC coordinate system _{V U} ^*, V V ^*, converted to V _W ^*. Reference numeral 33 denotes a PWM (pulse width modulation) controller which converts the three-phase voltage command value into a gate signal of the voltage source inverter 4.
By controlling the voltage source inverter 4 by the controller 33, the induction motor 5 can be driven at a desired torque and rotation speed.

The AC current detection values I _U and I _W detected by the current detector 6 are converted by the second coordinate converter 34 into current detection values in the DC coordinate system. Reference numeral 35 indicates the q-axis current detection value I.
_q is a current controller that matches q-axis current command value I _q ^* set separately, and frequency switch 36 is a current controller 3
The switching between the rotational speed information ω obtained by the adjustment operation of _No. 5 and the above-described frequency command value ω ₁ ^* is performed. Integrator 3
7 converts the frequency into an angle θ by an integration operation.

In the present invention, the trigger voltage generator 38 is provided, and when the q-axis voltage command value V _q ^* output from the V / F converter 31 is zero, the trigger voltage generator 38 causes the trigger voltage generator 38 to move in the d-axis direction. A step-like trigger voltage V _d ^* is generated. Due to the trigger voltage V _d ^* , a current I _q in the q-axis direction having a phase shifted by 90 degrees from the trigger voltage V _d ^* can be extracted from the second coordinate converter 34, and the q-axis current command value I _q ^* = 0. Thus, the current adjuster 35 sets the q-axis current detection value _Iq to zero by the adjusting operation. The output value ω of the current controller 35 at this time is the rotation speed information of the induction motor 5 at that time.

FIG. 3 is an operation waveform diagram showing a third embodiment of the present invention, and shows a voltage waveform output from the trigger voltage generator 38 described in the circuit of the second embodiment described above with reference to FIG. I have.
That is, as the trigger voltage V _d ^*, adopting the value obtained by multiplying the primary resistance R ₁ of the induction motor 5 to the current command value of the d-axis direction I _d ^*. As a result, the rotation speed detection state of the motor during free rotation and the invalid voltage command value V _d in the normal operation state
^* And can be the same.

FIG. 4 is a block circuit diagram showing a fourth embodiment of the present invention. This fourth embodiment circuit is different from the second embodiment circuit shown in FIG. The difference is that they are added, but the rest is the same as the circuit of the second embodiment, so that the description of the same parts will be omitted. Induction motor 5
Is in free rotation and its rotation speed is calculated, the frequency switch 36 outputs the rotation speed information ω output from the current controller 35, and the second frequency switch 41 is switched from the rotation speed calculation to the normal operation. Switch to the frequency command value ω ₁ ^* to be output, and output this. Here, during the rotation speed calculation, the rotation speed information ω is also supplied to the second frequency switch 41, and the second frequency switch 41 is provided to the second frequency switch 41 in order to reduce a shock at the time of switching from the rotation speed calculation to the normal operation. The rotational speed information ω is set in a built-in filter or an acceleration / deceleration calculator. The V / F converter 31 has a built-in magnetic flux model of the induction motor 5, and converts the conversion coefficient of the induction motor 5.
Is changed by the second order time constant. Therefore, when the operation is switched from the rotation speed calculation to the normal operation, the operation is started based on the rotation speed information ω, and the induction motor 5 during the free rotation can be started without giving a shock.

[0019]

According to the present invention, if the power supply that supplies power to the induction motor during the power running operation fails, the rotation speed of the induction motor decreases during the power failure period. Therefore, if the rotation speed of the induction motor when the power is restored is unknown. In addition, it is impossible to supply an AC power having an appropriate voltage and frequency to the induction motor. Therefore, conventionally, it has been necessary to connect a rotation speed detecting means such as a pulse generator to the induction motor. However, in order to mount the pulse generator, it was necessary to secure the machining and mounting space for the shaft end of the motor. On the other hand, in the present invention, a step-like trigger voltage is applied to the induction motor that is rotating freely, and a current having a phase that differs from the trigger voltage by 90 degrees is detected from the induction motor. By controlling the detection current having a phase difference of 90 degrees to zero by the adjusting operation to zero, the rotation speed information of the induction motor can be obtained.
Even if the residual voltage of the induction motor during free rotation is zero, the effect that the rotation speed can be easily detected without using a pulse generator or the like is obtained, and the rotation speed detection calculation does not give a shock to normal operation. Is also obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a first embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention.

FIG. 3 is an operation waveform diagram showing a third embodiment of the present invention.

FIG. 4 is a block circuit diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Three-phase AC power supply 2 Forward converter 3 Smoothing capacitor 4 Voltage source inverter 5 Induction motor 6 Current detector 17, 18 Judgment 21, 23 Processing 31 V / F converter 32 First coordinate converter 33 PWM controller 34 Second Coordinate converter 35 Current controller 36 Frequency switch 37 Integrator 38 Trigger voltage generator 41 Second frequency switch

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuki Suzuki 1-1-1 Tanabe Shinda, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in Fuji Electric Co., Ltd. (Reference) 5H576 AA20 BB09 BB10 CC05 DD02 DD04 EE01 EE11 EE22 FF01 FF02 FF07 GG04 GG07 HA01 HB02 JJ03 JJ06 JJ15 JJ17 KK06 LL14 LL22 LL34 MM02

Claims (4)

[Claims] 1. A method for detecting a rotation speed of an induction motor during free rotation by interrupting an AC output of a power converter for driving an induction motor by outputting AC power of a variable voltage and a variable frequency. Applying a step-like trigger voltage to the induction motor inside, detecting a current having a phase different from the trigger voltage by 90 degrees from the induction motor, and performing an adjusting operation for controlling the detected current having a phase different from the phase by 90 degrees to zero. A method for detecting a rotation speed of an induction motor during free rotation, wherein rotation speed information of the induction motor is obtained from the adjustment operation. 2. A method for detecting a rotation speed of said induction motor during free rotation by interrupting an AC output of a power converter for driving an induction motor by outputting AC power of a variable voltage and a variable frequency. D-axis component and q
When the q-axis voltage command value to the induction motor during free rotation is zero, a step-like trigger voltage is applied in the d-axis direction, and the phase of the trigger voltage and the phase from the induction motor are 90 The rotation of the induction motor during free rotation is characterized by detecting a q-axis current flowing at different degrees and performing an adjusting operation for controlling the detected value of the q-axis current to zero to obtain rotation speed information of the induction motor. Rotation speed detection method. 3. A method for restarting the induction motor during free rotation by interrupting the AC output of a power converter that drives an induction motor by outputting AC power of a variable voltage and a variable frequency, comprising: The d-axis component and q that are orthogonal to each other
The d-axis voltage command value is calculated from the product of the d-axis current command value and the primary resistance of the induction motor, and the q-axis voltage command value to the induction motor during free rotation is zero. Then, the step-shaped d-axis voltage command value is given as a trigger voltage, a q-axis current flowing from the induction motor at a phase different from the trigger voltage by 90 degrees is detected, and the q-axis current detection value is controlled to zero. The rotational speed information of the induction motor is obtained by performing the adjusting operation, and the d-axis voltage command value and the rotation speed information are used for restarting the induction motor. Method. 4. A method of restarting the induction motor during free rotation by interrupting the AC output of a power converter that drives an induction motor by outputting AC power of a variable voltage and a variable frequency, the method comprising: The d-axis component and q that are orthogonal to each other
The d-axis voltage command value is calculated from the product of the d-axis current command value and the primary resistance of the induction motor, and the q-axis voltage command value to the induction motor during free rotation is zero. Then, a trigger voltage is applied to the step-shaped d-axis voltage command value, a q-axis current flowing from the induction motor at a phase different from the trigger voltage by 90 degrees is detected, and the q-axis current detection value is controlled to zero. By performing the adjusting operation, the rotation speed information of the induction motor is obtained, the d-axis voltage command value and the rotation speed information are used for restarting the induction motor, and the rotation speed information is used with a predetermined time delay and change speed. A method of restarting an induction motor during free rotation, wherein the method is switched to a set rotation speed command value.