JPH06284787A - Method for preventing overcurrent stall of inverter device and inverter device - Google Patents

Abstract

PURPOSE:To make it possible to achieve acceleration in the shortest time by decreasing the overcurrent operating level for preventing overcurrent stall based on the maximum- torque current of an induction motor when the overcurrent operating level for preventing the overcurrent stall becomes the same level. CONSTITUTION:An inverter device 1 gradually decreases an operating current value when the inverter output frequency exceeds the rated frequency of a motor and exceeds the frequency, at which the maximum torque becomes the same level for preventing the overcurrent stalling of the inverter. Adjustment is performed in conformity with an induction motor 8 in a control circuit part 5. Then, the overcurrent preventing function is operated, and the increase in output frequency of the inverter is stopped. Therefore, only the revolving speed of the motor is increased, and motor slipping is decreased. The motor current becomes lower than the value of the operating current for preventing overcurrent stalling, and the output frequency is increased again. However, the motor revolving speed cannot follow the output frequency of the inverter, and the motor current exceeds the operating current value again. Thus, the increase in output frequency is stopped. As a result, starting can be completed in the shortest time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing overcurrent stall of an inverter device when the induction motor is operated at a variable speed by the inverter device.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram for explaining the outline of variable speed operation of an induction motor by an inverter device. The inverter device 1 converts an alternating current input from the commercial power supply 7 into an alternating current having a predetermined voltage and frequency and supplies the alternating current to a load, the induction motor 8. Converter unit 2 for converting alternating current input from commercial power supply 7 to direct current 2, this converter unit 2
Smoothing capacitor 3 for smoothing the direct current output by the inverter 3, an inverter unit 4 for inversely converting the direct current smoothed by the smoothing capacitor 3 into an alternating current of a predetermined voltage and frequency, and an inverter unit 4 outputting an alternating current of a predetermined voltage and frequency When the induction motor 8 is accelerated by increasing the output frequency, the overcurrent due to the increase in slip is detected, and the output frequency is increased when the overcurrent exceeds a preset predetermined level. It is composed of a control circuit section 5 having an overcurrent stall prevention function for stopping or lowering, and an overcurrent detector 6 for detecting an overcurrent.

FIG. 3 is a characteristic diagram showing the relationship between the maximum torque Tmax generated by the induction motor 8 driven by the inverter device 1 and the frequency f on the horizontal axis. The inverter device has a capacity suitable for the capacity of the induction motor 8. The maximum torque 5b of the induction motor when combined with 1 is shown. Further, 5a indicates an overcurrent stall prevention level.

A general-purpose induction motor has a frequency of 50 Hz or 60 Hz.
Since the motor is driven at a fixed frequency of Hz, the motor speed is constant, but when the inverter device 1 is driven as a power source, low speed operation of 60 Hz or less and high speed operation of 60 Hz or more are possible. However, when the induction motor 8 is operated in the region of 60 Hz or higher, the magnetic flux in the air gap of the induction motor 8 decreases as the frequency increases, and the generated torque of the induction motor 8 also largely decreases as shown in FIG.

FIGS. 4 and 5 show characteristic patterns at the time of starting the induction motor 8 by the inverter device 1. The horizontal axis shows the elapsed time t after the start signal is given to the inverter device 1, and the vertical axis shows the vertical axis. The inverter output frequency f (Hz) and the motor speed N are converted into the frequency f (Hz), and the inverter output current is shown as a ratio (%) of the rated current reference. In FIG. 4, 1 c is an inverter output frequency f output from the inverter device 1 and applied to the induction motor 8, 2 c is a motor rotation speed (N), 3 c is a motor current, and 4 c is an overcurrent stall prevention operation current of the inverter device 1. Indicates a value (level). The inverter output frequency f is intended to accelerate up to a maximum frequency of 120 Hz in the time of t11.

In FIG. 4, when a start signal is given to the inverter device 1, the output frequency 1c of the inverter device 1 becomes 0.
From 120 Hz to 120 Hz, it gradually rises at the acceleration time t11 set in the inverter device 1. As shown in FIG. 3, the torque generated by the induction motor 8 is small in the low frequency range, the motor rotation speed 2c cannot follow the output frequency 1c of the inverter device 1, and the motor current 3 increases as the slip of the motor increases.
c increases and exceeds the operating current value 4c of the inverter device 1. Then, the inverter overcurrent stall prevention function operates to stop or decrease the increase of the inverter output frequency 1c. When the inverter output frequency 1c is stopped or lowered with an increase, the motor rotation speed 2c increases and the motor slip decreases, and when the motor current 3c falls below the operating current value 4c, the inverter output frequency 1c increases again. Next, when the inverter output frequency 1c reaches around 30 Hz and the electric motor rotation speed 2c also reaches the rotation speed corresponding to the frequency, thereafter, as shown in FIG. 3, the electric motor torque 5a becomes sufficiently large and a predetermined acceleration gradient (motor rotation speed) is reached. The inclination of the speed 2c) can be followed.

However, the inverter output frequency 1c is about 9
From around 0 Hz, as shown in FIG. 3, the electric motor torque 5c gradually decreases, and when the electric motor rotation speed 2c cannot keep up with the inverter output frequency 1c, the electric motor current 3c increases due to an increase in slip of the electric motor. When the operating current value 4c is reached, the inverter output frequency 1c is stopped.

As described above, when the overcurrent stall prevention function operates, the final start completion time becomes t12, which is significantly longer than the set value t11. Therefore, in general, the inverter device 1
As shown in FIG. 5, the overcurrent stall prevention operation current value is reduced at an output frequency higher than the base frequency of the induction motor. However, as shown in FIG. 5, the overcurrent stall prevention operation level 4d is frequently crossed in the region of 60 Hz or higher, and the extension rate of the start completion time is reduced as compared with FIG. become.

[0009]

Since the conventional inverter device does not have an overcurrent stall prevention function that maximizes the characteristics of the induction motor, even if the acceleration time setting is shortened,
Instead, it took a long time to start. Therefore, the acceleration time is
Requires optimal adjustment according to the motor capacity and load characteristics,
Further, when the frequency is higher than the base frequency, there is a problem that the inverter device needs to be externally assisted such as setting the acceleration time longer.

The present invention has been made in order to solve the above problems, and provides an overcurrent stall prevention method for an inverter device which enables acceleration in the shortest time without considering the motor capacity and load characteristics. The purpose is to provide.

[0011]

In order to achieve the above object, in an overcurrent stall prevention method for an inverter device according to the present invention, an induction motor is operated by the inverter device to increase the output frequency and thereby the induction motor. In an overcurrent stall prevention method for an inverter device that detects an overcurrent due to an increase in motor slip when accelerating, the output frequency exceeds the base frequency of the induction motor, and the induction motor When the overcurrent stall prevention overcurrent operation level becomes the same as the maximum torque current of, the overcurrent stall prevention overcurrent operation level is lowered according to the maximum torque current of the induction motor. Is.

Further, in the inverter device according to the present invention, when the induction motor is operated at a variable frequency and the output frequency is increased to accelerate the induction motor, an overcurrent due to an increase in the motor slip is detected to detect the output frequency. In an inverter device having an overcurrent stall prevention control unit that stops or lowers the rise of the current, the output frequency exceeds the base frequency of the induction motor, and the overcurrent operation level of the overcurrent stall prevention against the maximum torque current of the induction motor. If the same is true, an overcurrent stall prevention control unit that lowers the overcurrent operation level of the overcurrent stall prevention according to the maximum torque current of the induction motor is provided.

[0013]

In the inverter device overcurrent stall prevention method and the inverter device according to the present invention, the output frequency of the inverter device exceeds the rated frequency of the induction motor, and the maximum torque of the induction motor becomes the overcurrent stall prevention operation level of the inverter device. If the frequency becomes the same, reduce the stall operation level of the motor current according to the rated current of the induction motor,
To prevent the motor rotation speed from being unable to follow the inverter output frequency due to an increase in motor slip, the over-electric motor stall prevention control unit works at a lower overcurrent level to stop the inverter output frequency from rising. The electric motor is accelerated at a frequency that can generate the maximum electric motor torque at the electric motor rotation speed.

[0014]

Embodiments of the present invention will be described with reference to FIGS. A block diagram showing a schematic configuration of the inverter device is the same as the case of the conventional example shown in FIG. Hereinafter, the same reference numerals denote the same elements as the conventional example.

FIG. 1 shows a characteristic pattern at the time of starting the induction motor 8 by the inverter device 1. The horizontal axis represents the elapsed time (t) starting from the time when the start signal is given to the inverter device 1, and the vertical axis. Inverter output frequency f (H
z), the motor rotation speed (N) in frequency f (Hz) conversion,
The inverter output current I is shown by the rated current reference (%). In the figure, 1a is an inverter output frequency (f) output from the inverter device 1 and applied to the induction motor 8, 2a is a rotation speed (N) of the motor 8, 3a is a motor current, and 4a is a control circuit unit of the inverter device 1. 5 shows the operating current value (I) of the overcurrent stall prevention function of FIG.

Next, the operation will be described. A frequency at which the inverter output frequency 1a exceeds 60 Hz, that is, the rated frequency of the general-purpose electric motor, and the maximum torque of the electric motor becomes the same as the overcurrent stall prevention operation level of the inverter, that is, 5 in FIG.
The operating current value 4a is gradually lowered from the point where the frequency exceeds the point where a and 5b intersect. Although the overcurrent stall prevention operation current value 4a has been set to a value commensurate with the inverter output current until then, it is set to a value commensurate with the rated output current of the electric motor. For this reason, the adjustment is automatically made in the control circuit unit 5 constituting the inverter device 1 so that it can be adjusted according to the induction motor 8 to be used in combination. Then, until then, the motor slip was large and the motor current 3a
Was flowing a current larger than the rated value of the induction motor 8 but exceeded the operating current value, the inverter device 1
The overcurrent protection function operates and the inverter output frequency 1a
Stop increasing. Therefore, only the motor rotation speed 2a increases, the motor slip decreases, the motor current 3a falls below the overcurrent stall prevention operation current value, and the inverter output frequency 1a increases again. However, at this time, since the acceleration time setting of the inverter device 1 is set shorter than the torque capacity of the induction motor 8, the motor rotation speed 2a cannot follow the inverter output frequency 1a, and the motor slip increases again to increase the motor current. 3a exceeds the operating current value 4a, the overcurrent stall prevention function operates, and stops increasing the inverter output frequency 1a. In this way, the inverter output frequency 1a exceeds the base frequency of the induction motor 8,
When the maximum torque of the electric motor exceeds a frequency at which it becomes the same as the overcurrent stall prevention operation level of the inverter device 1, the inverter output frequency 1a is repeatedly increased and stopped by the overcurrent stall prevention function, and the electric motor rotation speed 2a is generated. The start is completed in the shortest time by effectively utilizing the torque.
In the above embodiment, the acceleration range of the induction motor is 0-12.
Although it is set to 0 Hz, the maximum output frequency is not particularly limited. The motor rated frequency may be other than 60 Hz.

[0017]

As described above, according to the present invention, the overcurrent stall prevention current operation level of the inverter device is switched around the rated frequency of the induction motor according to the rated output current of the induction motor. The generated torque of the electric motor can be used most effectively regardless of the combination of the inverter device and the electric capacity or load of the electric motor, and the starting of the electric motor can be completed in the shortest time.

[Brief description of drawings]

FIG. 1 is an acceleration pattern diagram of an inverter drive motor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an inverter device.

FIG. 3 is a maximum torque characteristic diagram of the induction motor.

FIG. 4 is an acceleration pattern diagram of a conventional inverter drive motor.

FIG. 5 is an acceleration pattern diagram of a conventional inverter drive motor.

[Explanation of symbols]

1 ... Inverter device, 5 ... Control part, 7 ... Commercial power supply,
8 ... Induction motor.

Claims (2)

[Claims] 1. When an induction motor is driven by an inverter device and the output frequency is increased to accelerate the induction motor, an overcurrent due to an increase in motor slip is detected to stop or decrease the output frequency. In the inverter overcurrent stall prevention method, if the output frequency exceeds the base frequency of the induction motor and the overcurrent stall prevention overcurrent operation level becomes the same as the maximum torque current of the induction motor, the induction motor An overcurrent stall prevention method for an inverter device, characterized in that an overcurrent operation level for preventing overcurrent stall is lowered according to a maximum torque current. 2. An inverter having an overcurrent stall prevention control section for detecting an overcurrent due to an increase in motor slip when an induction motor is accelerated by increasing the output frequency and stopping or decreasing the increase in the output frequency. In the equipment, if the output frequency exceeds the base frequency of the induction motor and the overcurrent stall prevention overcurrent operation level becomes the same as the maximum torque current of the induction motor, the overcurrent is determined according to the maximum torque current of the induction motor. An inverter device comprising: an overcurrent stall prevention control unit that lowers an overcurrent operation level for stall prevention.