JPS63121488A - Variable speed controller for motor - Google Patents

Abstract

PURPOSE:To generate the fluctuation of a torque having a long repetition period in a motor to reduce the generation of noise due to a gear coupling, by a method wherein a speed command is fluctuated so as to repeat increase and decrease with an arbitrary long period in a low speed area. CONSTITUTION:A low speed detector 11 detects that the output of a speed detector 9 is reduced than a preset reference speed and, then, provides a function generator 10 with an operation command. The output signal of the function generator 10 is outputted to a speed regulator 3 from a speed setter 1 through an unit integrator 2 and is added to a speed commanding signal. A motor 8 repeats accelerations and decelerations within a minute range in accordance with the fluctuation of the speed command. Accordingly, the period in the direction conversion of the generating torque of the motor after passing zero point becomes longer even when there is the pulsation of a torque in a low speed area and the abutting surface of the gears of a gear coupling is changed whereby the cycle of generating noise is decreased and the generation of noise may be reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides variable speed control of an AC motor that drives a load via a gear coupling for the purpose of decelerating or speeding up. The present invention relates to a variable speed control device for an electric motor in which the frequency of the electric motor is controlled by an inverter.

[Conventional technology]

Conventionally, in order to operate an AC motor such as an induction motor at variable speed, an inverter has been used as shown in FIG. 4 to control the frequency of electric power supplied to the motor. In such a device, a commercial
The AC power supplied from 20 is first converted into DC power by a converter 5 made up of a SiRISC rectifier circuit, and this DC power is converted back into AC power by an inverter 7 made of, for example, a SiRISI inverter, and is then inducted. He is trying to supply it to an AC motor 8 such as an electric motor.

At this time, the speed of the electric motor 8 is controlled by controlling the frequency of AC power supplied to the electric motor 8 by the inverter 7. Converter 5 controls the current or voltage of the motor.

In FIG. 4, 1 is a speed setter that sets the command speed for the electric motor 8, 2 is a single integrator for suppressing sudden changes in the speed command value from the speed setter 1, and 3 is this single integrator. The speed command value given from the motor 8 is compared with the actual speed value fed back from the speed detector 9 connected to the motor 8, and depending on the deviation, the current command and frequency are sent to the converter control circuit 4 and the inverter control circuit 6, respectively. Give instructions.

In this device, a speed regulator 3 and a converter control circuit 4. By the action of the inverter control circuit 6, the frequency and current or voltage of AC power supplied to the motor via the converter and inverter are controlled so that the speed of the motor 8 becomes the speed commanded by the speed setting device 1. .

[Problem that the invention seeks to solve]

In this way, when driving an electric motor with an inverter,
Since the output voltage waveform of the inverter is a rectangular wave, it contains many harmonic components, and these harmonic components cause pulsating torque in the electric motor. This pulsating torque is rarely a problem when the motor is operating at high speeds because the output torque is relatively large, but when the motor is operating at low speeds, the output torque of the motor decreases and The pulsating torque becomes relatively large, causing the following problems.

That is, with respect to the torque required by the load shown at A in FIG. 5, the output torque of the motor pulsates as shown at B, and the valley portion exceeds the zero point and becomes a negative torque. Therefore, positive torque (acceleration torque) and negative torque (deceleration torque) act on the load alternately during the torque pulsation period, and the direction of the torque acting on the load is not constant.

Therefore, when a load is coupled to an electric motor via a gear coupling to speed up or decelerate, the contact surface of the gear teeth changes each time the torque is reversed from positive to negative, resulting in loud mechanical noise. , causing noise.

In order to eliminate noise caused by torque pulsations in the gear coupling electric motor, it is necessary to prevent the torque pulsations in the electric motor from occurring. This method has the disadvantage of being expensive because it requires a large capacity filter circuit to convert the waveform into a sine wave.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a variable speed control device for an electric motor that can eliminate such drawbacks and reduce II noise generated by a gear coupling at a low cost.

[Means for solving problems]

The present invention provides a speed regulator that commands an output frequency to the inverter when the motor is at a low speed below a predetermined speed in a motor that is controlled by an inverter and drives a load via a gear coupling. The above object is achieved by providing means for alternating the speed command generated by the electric motor at a cycle larger than the cycle of the pulsating torque generated by the electric motor and at an appropriate width of 5i.

(Operation) According to the present invention, when the speed of the electric motor becomes low, the speed command given to the speed iji!!! device is alternately varied, and the inverter drives the electric motor accordingly. is not constant and repeats acceleration and deceleration within a minute range. Therefore, as shown in Figure 3, the electric motor has
Torque that changes alternately with a cycle greater than the pulsating torque is generated. Since the period in which the generated torque of the electric motor crosses the zero line, that is, the period in which the direction of the generated torque is reversed, becomes longer, the number of times that the contact surface of the teeth in the gear connected to the electric motor changes is reduced, and the generation of noise is reduced.

〔Example〕

FIG. 1 shows a block circuit diagram according to an embodiment of the present invention, which will be explained next.

The configuration of the embodiment of the present invention shown in FIG. 1 is basically the same as the conventional one shown in FIG. A generator 10 and a low speed detector 11 are provided. The function generator 10 generates a triangular vibration wave, and is configured so that its amplitude and period can be adjusted. The low speed detector 11 compares the output of the speed detector 9 with an internally preset reference speed, and detects that the output of the speed detector 9 has become lower than the reference speed, and the speed of the motor has decreased. When the function generator 10 is activated, it acts to give an operation command to the function generator 10. The output signal of the function generator 10 is transmitted from the speed setter 1 to the speed! through a single integral n2. F! It is added to the speed command signal given to the moderator 3. electric motor 8
A load is coupled to the motor through a gear coupling (not shown).

In such a device of the present invention, in a normal state where the electric motor 8 is operated at a speed higher than a set reference speed, the low speed detector 11 does not operate, so the function generator 10
Operation commands to are stopped.

Therefore, since the function generator 10 has also stopped operating,
Only the set speed command given from the speed setter 1 via the single integrator 2 is given to the speed regulator 3 as a speed I command, and the electric motor 8 drives the load at a speed according to this speed command.

When the set speed command is lowered and the speed of the electric motor 8 falls below the reference speed, the low speed detector 11 is activated and gives an operation command to the function generator 10, so that the function generator 10 A triangular wave-like vibration signal whose amplitude and period are appropriately selected as shown in Fig. 2) is generated.

This triangular wave signal and the set speed command signal from the speed setter 1 are added to the speed command input terminal of the speed regulator 3, so that the signal given to the speed GI device 3 is shown in FIG. 2(c). It fluctuates as it repeats rises and falls at appropriate intervals.

The period of fluctuation at this time is selected to be considerably larger than the period of torque pulsation that occurs when the electric motor is at a low speed, and the amplitude is selected so that the speed fluctuation of the electric motor is below a permissible value.

When the speed command given to the speed regulator 3 fluctuates in this way, the speed adjuster 3 gives control commands to the converter control circuit 4 and the inverter control circuit 6, respectively, so that the electric motor 8 is accelerated or decelerated accordingly. Therefore, the electric motor 8 repeatedly accelerates and decelerates within a small range according to the fluctuations in the speed command. As a result, the electric motor 8 alternately generates positive torque (acceleration torque) at the fluctuation period of the speed command as shown in FIG. ) and negative torque (deceleration torque) will be generated. Therefore, even if there is torque pulsation caused by harmonic components contained in the voltage supplied from the inverter 7 in the low speed range, the period in which the torque generated by the motor passes through the zero point and reverses direction becomes longer, and the gear camp Noise generation is reduced because the contact surface of the ring teeth changes and the number of times noise is generated is reduced.

〔Effect of the invention〕

As explained above, in the present invention, in the low speed range where the torque pulsation of the electric motor driven by an inverter is relatively large, the speed command is varied so as to repeatedly rise and fall in an arbitrarily long period, and the electric motor Since torque fluctuations with a long repetition period are generated, noise generation can be reduced when a gear coupling is connected.

In this case, since it is only necessary to provide an electronic circuit such as a function generator and a low speed detector on the input side of the speed regulator, the conventional method using a filter circuit to convert the rectangular wave voltage output from the inverter 7 into a sine wave is sufficient. Compared to the method, the structure is only an hour wheel (but it also has the effect of being significantly cheaper).

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams used to explain the operation of the present invention, and FIG.
The figure is a block diagram showing a conventional device, and FIG. 5 is a torque waveform diagram of the conventional device. 1: Speed setting device, 3: Speed! 11 nodes, 4: converter control circuit, 5: converter, 6: inverter control circuit,
7: Inverter, 8: AC motor, 10: Function generator,
11: Low speed detector.・Small −+v・p 1170～・Go・−′1

Claims (1)

[Claims] 1) An AC motor that drives a load via a gear coupling, an inverter that controls the frequency of AC power supplied to the motor, and an output frequency that controls the inverter according to the deviation between the commanded speed and the actual speed for the motor. In a variable speed control device for an electric motor, which is equipped with a speed regulator that commands, when the speed of the electric motor becomes lower than a specified speed, the speed command given to the speed regulator is changed to a pulsation period of the torque generated by the electric motor. 1. A variable speed control device for an electric motor, characterized in that a variable speed control device for an electric motor is provided with means for alternating the speed with a longer cycle and a predetermined amplitude.