JPS5996885A - Controlling method for starting of induction motor - Google Patents

Abstract

PURPOSE:To start an induction motor with the maximum starting torque without generating a resonance phenomenon of a machine system by starting the motor with a power source of the frequency for maximizing the starting torque and setting the frequency of the power source to the prescribed value or higher when the counterelectromotive force of the motor reaches the prescribed value. CONSTITUTION:When a switch SW2 is opened, a power reactor 15 is fired on the basis of Stheta. Accordingly, an inverter 17 supplies a current of the lowest frequency to an induction motor 19. When the counterelectromotive force Vf of the motor 19 gradually increases so that the output signal Si of a voltage controller 4 becomes -V1 or higher, the output signal Se of a comparator 20 is inverted from positive to negative, and the output signal S7 of a timer circuit 21 becomes the prescribed negative level after the prescribed period of time is elapsed. Thus, the output signal SL of a ramp function generator 3 increases, and the output frequency of the inverter 17 and the output current of the power reactor 15 increase.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction motor starting control method suitable for use in starting a motor.

When operating an induction motor at variable speed, a current source inverter is generally used, and when starting the induction motor, low-frequency starting is performed to obtain a large starting torque even with the same starting current. The output frequency of the inverter at this low frequency origin 'IJJJVc is 2.
~j fiz. Then, the induction motor is continuously rotated at such a low frequency, and then the output frequency of the inverter is increased to rotate the induction motor at the desired rotation speed of PJf.

By the way, when an induction motor is continuously operated at a low frequency of approximately 0 to J Hz, large pulsations occur in the output torque, and this torque pulsation causes negative effects such as resonance on a mechanical system that is linked to the drive motor. Therefore, in order to prevent this inconvenience, the method described below has conventionally been adopted. .

(1) A method of starting at a frequency above which the influence of torque pulsation does not cause much of a problem (for example, j to 6 Hz). However, in this case, the maximum starting torque of the induction motor cannot be extracted, so there is a drawback that the capacity of the inverter must be increased.

(2) A method of reducing jitorque pulsation by multiplexing inverters. Since this method requires the use of multiple inverters, it is often wasteful and expensive when applied to small to medium capacity induction motors that can be driven with only a 6-phase inverter.

(3) Predict the time from the start of startup to the completion of synchronization pull-in when starting with Ko ~ Jflz, and set it in advance.
After the set time elapses after starting at Hz, s~l=
How to accelerate to a suitable frequency of about llz. In this case, it is necessary to allow a relatively long setting time in consideration of load fluctuations, changes in the state of the mechanical system, etc., so the disadvantage of long dead time is increased, and the resonance phenomenon of the VC mechanical system is avoided during the long setting time. There was a problem that occurred.

(4) A method of installing a speed detector on the induction motor and controlling the speed of the time-dependent motor by detecting the completion of synchronous pull-in during low-frequency startup based on the output signal of this speed detector - 1 However, this method has the disadvantage that control becomes complicated and expensive, and there are cases in which a speed detector cannot be installed in an existing induction motor due to structural or installation space constraints.

In view of the above-mentioned circumstances, this invention provides an induction motor system without causing mechanical resonance phenomena. The present invention provides a starting control method for a U-guide motor that can start the U-guide motor with the maximum starting torque and does not require any external mechanism such as a speed detector, thereby maximizing the starting torque of the U-guide motor. The induction motor is started with a power supply having a frequency of This is a method of later increasing the frequency of the power source to a predetermined value or higher.

Embodiments of the present invention will be explained below with reference to the drawings.

FIG. 7 is a block diagram showing the configuration of an induction motor drive circuit according to an embodiment of the present invention, and the circuit except for the portion shown within the dashed line in this figure is the same as the circuit commonly used in the past.

In the figure, 1 is a minimum frequency setting device for setting the minimum output frequency of the inverter 17, and generally the drive motor 19
The starting torque is maximum. Set 2 to 3Hz. 2
is the rotation of the induction motor 19 during normal times (other than when starting) lc!
1. It is a setting device that sets the output frequency of the inverter 17 corresponding to , and when this setting device changes in a stepwise manner, a ramp function generator that converts this step into a 7th order function with time as a variable and outputs it. It is. 4t; is a voltage controller that outputs a current value command signal St such that the deviation is O. based on the deviation obtained from the deviation detection point a2Vc, and 5 is a voltage controller that outputs a current value command signal St that makes this deviation O. :This is a current controller that outputs a phase shift command signal SO that sets the deviation to 0 based on the obtained deviation. The input and output terminals of the current regulator 5 are short-circuited by the switch SW2, and when the current regulator 5 is short-circuited, the Vcll-i forward regulator 15 is not activated. Further, the switch SW2 is controlled to be 0N-OFF by the signal 82 (Fig. It is a phase shifter that outputs the firing angle signal to the gate signal amplifier 7. The gate signal amplifier 7 amplifies the firing angle signal and then supplies it to each thyristor of the hair changer 15.

Further, the stray voltage value of the induction motor 19 is supplied as a feedback signal vf to the deviation detection point &' 3 via the voltage transformer 13 and the rectifier 14, and the deviation detection point &' 3
For vc, the value of the current flowing through the forward converter 15 via the current transformer 11 and the rectifier 12 is supplied as the feed variable g If. 8 is a V-F converter that converts the output voltage of the ramp function generator 3 into a wave number signal; 9 is the firing angle of each phase thyristor in the inverter 17 based on the output signal of the V-F converter 8; This is a three-phase distributor that derives the firing angle Ig and outputs it to the gate signal amplifier 10 as the firing angle Ig. This firing angle signal is amplified by gate signal amplifier 10 and then supplied to the gate of each thyristor in inverter 17Vc. 20 compares the signal St (negative signal) and the reference voltage -vl, and in the case of S1)V1, the output signal Sc
This is a comparator that sets the output signal Sc to a positive predetermined level, and sets the output signal Sc to a negative predetermined level in the case of Si(-Vl.211/
The reset terminal 2 is a timer circuit that sets the output signal ST to a predetermined negative level after a timer time TB has elapsed since the signal Sc supplied to the i input terminal 21aK became negative.
1bVC voltage V2 is supplied via switch SWa,
A self-holding terminal 21c is connected to the output terminal.

Therefore, once the timer circuit 21 sets its output signal ST to a predetermined negative level, it continues to set the signal ST to a negative level until the switch SW3 is turned on. In addition, switch SW ati milliset number S3 (Figure 1 (c))
ON-OFF control is performed by Tlc. Further, 16 is a smoothing reactor.

Next, the operation of this embodiment having the above-described configuration will be explained with reference to FIG. 1 and FIGS. 2(A) to 2(1).

Note that FIGS. 2(a) to (1) are waveform diagrams of various parts of the circuit shown in FIG. 7, and signal values in negative or positive/negative ranges are shaded.

First, before starting the induction motor 19, the VC information S3 is once set to 'H' level as shown in period T1 in FIG. 2(C), the switch SWa is turned on, and the timer circuit 21 is reset. At this time, the signal 81 is at the 'L' level, so switch SW! is in the OFF state, so that the output signal SL from the ramp function generator corresponds to the lowest frequency set by the lowest frequency setter 1 (see Fig. 2 (G)).
). Therefore, the inverter 17 has the lowest frequency (,2~
JHz), but the signal S
2 is at 'XH' level and switch SW2 is in ON state u
Vch, the input/output terminals of the current controller 5 are short-circuited, the forward converter 15 is not fired, and no current flows through the induction motor 19vc (FIG. 1 (E)). Furthermore, since the induction motor 19 is not rotating and the feedback signal Vf corresponding to the back electromotive force is 0, the output signal Si of the voltage controller 4 saturates to a negative value as shown in Fig. 2). (a negative saturation value determined by the gain of the voltage controller 4). Next, time ti
When the signal s2 becomes 1L level at Vc, the switch S
Since W2 becomes 0FFVC and the IWt converter 15 is fired based on the signal Sθ, the inverter 17 supplies a current of the lowest frequency (2 to 3 Hz) to the induction motor 19. In this case, the starting torque of the induction motor 19 is maximum, but
If the resistance torque of the connected load is large, the induction motor 19 will not rotate quickly and a current as shown in FIG. 2(g) will flow. The saturation value of this current shown in the figure is a limited current value determined by the capacity of the inverter 17. Then, time t
When the induction motor 19 starts to rotate at 2vc, a back electromotive force is generated and the feedback signal Vf! As the voltage gradually increases, the deviation at the deviation detection point a2 becomes smaller and the output signal St of the voltage controller 4 becomes more positive as shown in Fig. 2. Result, time t3
When S i ) -y 1 at VC, the output signal Sc of the comparator 2o is inverted from positive to negative, and the release of the output saturation of the voltage controller 4, that is, the completion of starting of the induction motor 19 is detected. Then, at time t4Vc after the timer time Ts has elapsed from time t3, the output signal ST of the timer circuit 21 becomes a negative predetermined level. This signal ST is the deviation detection point alt/c
As a result, the signal value at the deviation detection point &1 increases from time t4, and as a result, the output signal SL of the ramp function generator 3 increases as shown in FIG. The magnitude of the signal SL after this increase (period T2) in the same figure is the inverter 1.
This is set by adjusting the negative level of the signal ST. In this way, the reason why the output frequency of the inverter 17 during the period T2 is set to j~l, Ilz is because, as already mentioned, when the induction motor 19 is driven at 5~A Ilz, the torque pulsation of the induction motor 19 becomes mechanical. This is because it does not affect the KM system. -1', the timer time T8 is 2' after the output saturation of the voltage controller 4 is released, that is, after the back electromotive voltage value of the induction motor 19 reaches a predetermined level.
~Jllz (lowest frequency) The time required for 1' to completely complete the synchronization pull-in in VC is set. This means that depending on the load condition of the induction motor 19, the back electromotive force value may vary between 7 and 1.
This is because synchronization pull-in at the lowest frequency may not be completely completed even if the fixed level value is exceeded.In this way, providing the timer time T8 ensures completion of synchronization pull-in at the lowest frequency. can be detected. Then, at the poetry collection +1 t 5 Vc, the signal Sl
When SL reaches the 'X1-1' level, the switch SWI turns ON and the setting value of the setting device 2 is supplied to the deviation detection point a1.
increases as shown in FIG. 2()), and correspondingly, the induction motor 19 rotates at high speed as shown in FIG. 2(IJ). 1. At time t7vC, signal S2 becomes 1H"
When the level is reached, the forward converter 15 will not fire, so
The current is no longer supplied to the induction motor 19vc as shown in FIG. Also, for example, the output signal S of the comparator 20 at time t6. Even if the voltage is reversed to a positive level, the timer circuit 2
1 maintains the negative level of the signal ST due to the self-holding function.

Further, the timer time Ts in the above operation is the signal Sc.
Since it is sufficient to take the time from the time when the frequency is reversed until the synchronization pull-in is completed at the lowest frequency, the time can be set to be sufficiently short. Therefore, the driving time at the lowest frequency where torque pulsation becomes a problem can be minimized, so that adverse effects on the mechanical system can be avoided. Also, j
The period T2 for driving the Shihiro motor 19 at ~611z is as follows:
This is a so-called standby state, and from this state the induction motor 19 can be easily driven at high speed at any time.

Therefore, the time t when the signal S1 reaches the level 'Xf("
5 may be arbitrary, and since the output frequency of the inverter 17 during this period T2 is j~AHz, there is no fear of adverse effects on the mechanical system. .

As explained above, according to the present invention, the induction motor is started with a power source having a frequency that maximizes the starting torque of the induction motor, and the back electromotive voltage of the induction motor is compared with a preset reference value. The starting completion state of the induction motor is detected based on the starting completion state, and after the starting completion state is detected, the above ! I made the frequency of the food to be θ [above the fixed value, so
The induction motor can be started with the maximum starting torque, and there is an advantage that no adverse effects are caused to the mechanical VC system.

Furthermore, since the starting current can be made small, the capacity can be reduced instantly, and moreover, it is possible to perform frequent starting without giving extra thermal stress to the induction motor. Furthermore, since it can be implemented by simply adding a comparison means etc. (comparator 20 in FIG. 1) to the conventional drive circuit, it is extremely advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 7 is a block diagram showing the configuration of an induction motor drive circuit that is an embodiment of the present invention, and FIGS. FIG. 2 is a diagram showing the rotational speed of the induction motor 19. 20... Comparator, 21... Timer circuit, -V... Reference 1-channel, Si... Signal,
■f・・・・・・Back electromotive force.

Claims (1)

[Claims] Starting the induction motor with a power source having a frequency that maximizes the starting torque of the induction motor, and detecting a starting completion state of the induction motor based on a comparison between a back electromotive voltage of the induction motor and a preset reference value. A method for controlling starting of an induction motor, characterized in that the frequency of the power source is increased to a predetermined value of nr or more after a starting completion state is detected.