JPH07274587A - Control method for induction motor operation - Google Patents

Abstract

PURPOSE:To make it possible to swiftly and smoothly restart an induction motor regardless of its state at the restoration of power supply, by judging the presence or absence of residual voltage when power supply is restored, and, if there is no residual voltage, by re-exciting the induction motor to check its state and then restarting it according to the state. CONSTITUTION:If there is no residual voltage when power supply is restored after an instantaneous power interruption, circuits 10, 11 are actuated, and an induction motor 3 is operated in accordance with a specified procedure. The specified procedure is as follows: The interruption of output is canceled, and then the motor is so operated as to obtain a specified voltage and frequency. After a certain time has passed, the output is interrupted again, and further a certain time is allowed. Then residual voltage is detected. If residual voltage is not zero, a soft start is caused by narrowing down output voltage according to set frequencies through circuits 6-9. Since the motor is restarted at a correct number of revolutions, calculated from the residual voltage generated by re-excitation, in this method, it can be automatically and smoothly restarted regardless of the conditions of load.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor operation control method, and more particularly to an induction motor operation control method suitable for restarting the induction motor after power supply is interrupted.

[0002]

2. Description of the Related Art Resumption of operation after a momentary power failure during operation of an induction motor is called restart of the induction motor. Conventional restart methods include those described in JP-A-54-50812 and JP-A-55-8250.

This conventional restart method will be described below. When a power failure occurs, the rotation speed of the induction motor decreases according to inertia. This decrease in rotation speed is reflected as the residual voltage of the induction motor. Therefore, the residual voltage is monitored, and after the power is restored, the power is controlled so that the rotation speed becomes a predetermined value, and the restart is performed.

This conventional restart method is advantageous in that the number of revolutions can be monitored without using a speed generator.

However, the residual voltage may become zero despite the instantaneous blackout and the number of revolutions not having become zero. This is considered to be mainly due to the influence of load. Consider below.

When the primary side of the induction motor is opened (that is, equivalent to the power supply being cut off), the voltage remains at the terminal. This residual voltage v ₁ is

[0007]

[Equation 1]

Here, M: mutual inductance between primary and secondary T ₂ = L ₂ / r ₂ : secondary time constant ω: rotor angular velocity i ₂₀ : second type initial value of secondary current.

In the above condition (1), under the condition that the rotor angular velocity ω does not drop sharply (load: small, GD ² : large),

[0010]

[Equation 2]

[0011] Figure 1 shows the waveform of the residual voltage at this time.
Shown in (a). This diagram is a damped oscillation waveform diagram, the period of which largely depends on the second-order time constant T ₂ and is damped in almost equal periods.

On the other hand, under the condition that the angular velocity of the rotor sharply drops (load: large, GD ² : small), the residual voltage v ₁ is

[0013]

[Equation 3]

[0014] The waveform at this time is shown in FIG. That is, both the cycle and the amplitude change rapidly.

[0015]

The residual voltage greatly depends on the load conditions (the load and the magnitude of GD ² ). Therefore, even if the load is small and GD ² is large, if the secondary time constant is short, it will be impossible to detect the residual voltage depending on the time of the instantaneous blackout. In such a state (rotational angular frequency unknown), if the power converter that constitutes the power supply is turned on, an excessive current flows or a regenerative condition occurs, and the converter shuts off the output due to overcurrent or overvoltage protection, resulting in loss of control. Become. Therefore, the power converter cannot be turned on suddenly when there is no residual voltage.

Further, when the load is large and GD ² is small, the residual voltage cannot be detected depending on the time width of the instantaneous blackout because of the rapid attenuation as shown in FIG. It will be. As a result, the same problem as described above occurs.

An object of the present invention is to provide an operation control method for an induction motor, which can restart the induction motor quickly and smoothly after the power is cut off.

[0018]

Means for Solving the Problems The above object is to provide a method for controlling the operation of an induction motor when the power supply to the induction motor is temporarily cut off and restarted after that: a) When the power is restored after a power failure, A step of determining whether or not there is a residual voltage of the induction motor; b) a step of restarting according to the frequency of the residual voltage when it is determined that there is a residual voltage in the step of a); When it is determined that there is no residual voltage in the step of step a), the step of temporarily supplying electric power to the induction motor, and d) restarting according to the residual voltage generated in the induction motor in the step c). It is achieved by including a process.

[0019]

When the power is restored after the power is cut off, it is necessary to restart the induction motor as quickly as possible. However, the timing of this power restoration is indefinite, and the state of the induction motor at the time of restoration is also indefinite. Therefore, in the present invention, the presence or absence of a residual voltage is determined when the power is restored, and when there is no residual voltage, re-excitation is performed to check the state of the induction motor, and then the restart is performed in accordance with the state. Even if the power is restored, it is possible to restart quickly and smoothly.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 2 is a configuration diagram of an operation control device according to an embodiment of the present invention, FIG. 3 is a flowchart showing the operation processing procedure, and FIG. 4 is an operation time chart.

In FIG. 2, the forward converter 1 takes in an AC three-phase power source and performs rectification. The inverse converter 2 takes in the output of the forward converter 1 (via the smoothing capacitor 4) and performs AC conversion. The main switching element drive circuit 15 controls the firing angle of the inverse converter 2. The forward converter 1 and the inverse converter 2 are power conversion devices that form a part of a power supply. The output of the inverse converter 2 drives and rotates the induction motor 3.

The control circuit 14 is a command circuit for controlling the ignition angle of the main switching element drive circuit 15, and the main switching element drive circuit 15 receives this command and sends out the necessary ignition pulse to the necessary thyristor. And drive the ignition. The above configuration is a general system for controlling an induction motor.

The components adopted in this embodiment are as follows. The instantaneous blackout detection circuit 13 detects, via the control transformer 12, whether or not the AC three-phase power supply is instantaneously blackened. Transformer 5
Is a transformer for taking in the residual voltage of the primary side of the induction motor 3, and the residual voltage is detected by the residual voltage detection circuit 6.

The frequency detection circuit 7 is a residual voltage detection circuit 6
The detected residual voltage of is taken and the corresponding frequency is calculated.
This calculated frequency is the current frequency of the induction motor 3.

The frequency setting circuit 8 matches the output frequency of the inverse converter 2 with the rotation frequency of the induction motor calculated by the calculation circuit 7 as much as possible.

When the induction motor 3 is restarted, the soft start circuit 9 performs a soft start of the output voltage to gradually increase the output voltage from a predetermined value so that an overcurrent or the like does not occur in the power converter.

The re-excitation command circuit 10 issues a re-excitation command when the residual voltage detected by the residual voltage detection circuit 6 is a predetermined value or less, or when the period detected by the residual voltage is a predetermined value or more.

The residual voltage re-induction command circuit 11 applies a predetermined output voltage and a predetermined frequency to the induction motor for a predetermined time to issue a command to re-induce the residual voltage. The command destination is the control circuit 14.

Next, the flow of operation will be described with reference to FIGS. Under normal operation before the occurrence of a momentary power failure, circuits 6, 7,
8, 9, 10, 11, 13 do not work. Therefore, under the command of the control circuit 14, the main switching element drive circuit 1
Switching control of the inverse converter 2 is performed from 5, and steady operation is performed.

When the instantaneous blackout occurs, the detection circuit 13 detects it and notifies the control circuit 14 of it. The control circuit 14 knows from this notification that the application of the AC three-phase power supply has stopped, and cuts off the output of the drive circuit 15 to the inverse converter 2.

After a slight time delay (τ ₁ ) from the occurrence of the instantaneous power failure, the rotation speed of the induction motor 3 starts to decrease (B). The residual voltage also starts to decrease as the rotation speed decreases (C). This decrease becomes a damping vibration characteristic.

If the residual voltage exists at the momentary power recovery,
Reboot is performed through the circuits 6, 7, 8 and 9. That is, frequency calculation and frequency setting are performed, and a soft start is performed.

The case where the residual voltage exists at the time of recovery from the instantaneous power failure is not disclosed in the time chart of FIG.

Now, when the residual voltage is not present and is zero at the time of recovery from the instantaneous power failure (C), the circuits 10 and 11 are activated and the induction motor 3 is operated under predetermined conditions. The predetermined condition is
First, the output cutoff is released, and the operation is performed so that the voltage becomes a predetermined voltage and a predetermined frequency. This operation is for the purpose of regenerating the residual voltage which has become zero. This operation continuation section is τ ₂ (D). After a certain time τ ₂ ,
The output is shut off again and τ ₃ is allowed to elapse for a certain period of time.
After that, the residual voltage is detected, and if it is not zero, the circuits 6, 7,
A soft start is performed by narrowing the output voltage based on the frequency setting via 8 and 9. In FIG. 2, E is an output frequency command,
F is an output voltage designation.

After the soft start, V / f coincides at an arbitrary time, and thereafter, the control circuit 1 is controlled so as to have a specified rotation speed.
4 controls.

Even if re-excitation is performed, if the residual voltage is zero, it is determined that the induction motor is stopped and zero soft start is performed.

According to this embodiment, the re-excitation operation is performed even if the residual voltage becomes zero at the time of recovery from the instantaneous power failure, so that the rotational speed at that time can be calculated based on the residual voltage generated thereby. Since restart operation is performed based on this calculated rotation speed,
The automatic restart of the induction motor can be smoothly executed regardless of the load condition.

Although the residual voltage is set to zero as a re-excitation condition, it does not have to be zero in view of detection accuracy. The circuits 6, 7, 8, 9, 10, 11, 13, 14 can be replaced by microcomputers.

Furthermore, the present invention can be applied to the case where a state similar to that of an instantaneous blackout occurs. For example, it can be applied when switching from a commercial power source to a power conversion device. Further, the phase can be detected together with the amplitude value of the residual voltage, and the synchronization can be turned on (restart).

[0040]

According to the present invention, the induction motor can always be automatically restarted quickly and smoothly regardless of the timing of power supply restoration.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a residual voltage.

FIG. 2 is a configuration diagram of an operation control device according to an embodiment of the present invention.

3 is a flowchart showing an operation procedure of the operation control device shown in FIG.

FIG. 4 is a time chart showing the operation of the operation control device shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Forward converter, 2 ... Inverse converter, 3 ... Induction motor, 4 ... Smoothing capacitor, 5 ... Voltage detection transformer, 6 ... Residual voltage detection circuit, 7 ... Frequency detection circuit, 8 ... Frequency setting circuit, 9
Output power soft start circuit, 10 ... Re-excitation command circuit, 11 ... Command circuit, 12 ... Control transformer, 13 ... Instantaneous power failure detection circuit, 14 ... Control circuit, 15 ... Main switching element drive circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatomo Wicker 7-1-1 Higashi Narashino, Narashino City, Chiba Prefecture Hitachi Keiyo Engineering Co., Ltd.

Claims (1)

[Claims] 1. A method of controlling the operation of an induction motor when the power supply to the induction motor is temporarily cut off and then restarted, comprising: a) presence or absence of a residual voltage of the induction motor when the power is restored after a power failure. And b) performing a restart according to the frequency of the residual voltage when it is determined that there is a residual voltage in the step a), and c) there is no residual voltage in the step a). If it is determined, the method further comprises a step of temporarily supplying electric power to the induction motor, and d) a step of restarting according to the residual voltage generated in the induction motor in the step c). Induction motor operation control method.