JPH04105592A - Control system for three-phase induction motor - Google Patents

Abstract

PURPOSE:To achieve a stabilized operation matching to the use mode of user and to achieve free selection of speed-torque characteristics by prescribing the maximum applying voltage of a motor based on the frequency and storing a plurality of modes representing the relation between the voltage and frequency being set according to the application. CONSTITUTION:In order to obtain a speed-torque characteristic required by a user, a frequency is set within the range of frequency F and voltage V and the voltage V is varied thus varying the torque characteristic according to a required speed. It can be applied on a machine requiring a decreasing output characteristics effective for a winder by utilizing the characteristic at part alpha. A constant torque characteristic can be achieved by utilizing the characteristic at part beta. Furthermore, a constant output characteristic can be achieved by varying the frequency under a constant voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control method for an electric motor, and particularly to a control method for a torque motor.

[Conventional technology]

In general induction motors, the rotation speed is almost constant and the torque increases and decreases, so the stability of the rotation system cannot be maintained against changes in torque, so torque control is rarely performed. Further, a torque control method called a vector control method is used, but this method requires complicated control and is very expensive.

By the way, electric motors used in winding and feeding devices for filamentous materials are required to have constant output characteristics (constant rotation speed x torque) or decreasing output characteristics, and are used in roll drive devices, balancers, winches, etc. Constant torque characteristics are often required for motors used in motors.

Note that the above-mentioned constant output characteristic refers to N as shown in FIG.
T=constant [N: rotation speed, T: torque] If you use this characteristic, the rotation speed will be increased when the winding diameter of the filament is small, and the rotation speed will be increased as the winding diameter becomes larger. can be made smaller to keep the winding speed constant.

As shown in FIG. 7(b), the decreasing output characteristic is a characteristic in which the torque is increased in consideration of mechanical loss etc. at high rotations, and is decreased at low rotations, compared to the constant output characteristics.

In other words, this is a characteristic required to maintain the shape of the wound material by reducing the tension as the wound diameter of the filament increases.

When controlling using the above-mentioned constant output characteristic (gradual output characteristic) or constant torque characteristic, torque stability is required rather than rotational stability, and the speed control range is often wide. Torque motors and eddy current motors satisfy these characteristics at low cost. Torque motors use high-resistance materials for the secondary winding of the rotor, and eddy current motors are configured to generate eddy currents in the rotor, and the relationship between torque and rotational speed is shown in Figures 1 and 2, for example. As shown, the motor maintains a characteristic close to linearity with a negative slope, resulting in stable operation.

Conventionally, methods for controlling the speed-torque characteristics of such torque motors and eddy current motors have relied on voltage control and changing the number of poles.

[Problem to be solved by the invention]

Each user who introduces a torque motor uses a variety of machines, such as winders that require "constant output characteristics" or "gradual output characteristics" in which torque decreases in inverse proportion to speed, and also those that require "constant output characteristics" or "decreasing output characteristics" where torque decreases in inverse proportion to speed. There are hoisting machines, hoisting machines, reciprocating compressors, various rolls, etc. that require "constant torque characteristics" that do not change in size.Therefore, when manufacturers install torque motors for users, they have to adjust the characteristics to suit each user. It is set so that

However, as with the conventional method described above, the number of poles can only be changed in stages and even numbers (for example, from 2 poles to 4 poles, from 4 poles to 8 poles), and therefore the speed-torque characteristics also become gradual, so it is difficult for the user to change the number of poles. It is not possible to immediately respond to the characteristics required by machines.

Furthermore, changing the number of poles is limited to a narrow range, such as from 2 poles to 4 poles, and even if the torque and speed can be controlled to the desired values, the slippage will be relatively large, the amount of heat generated will be high, and the loss will increase. It was big.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and provides a control method that enables stable operation and allows free selection of speed-torque characteristics depending on the user's usage pattern. The object of the present invention is to provide a control method that can reduce the slip frequency of the motor, thereby suppressing the amount of heat generated and saving power.

In a method for controlling electric motors using materials, the maximum voltage applied to the motor is specified by the frequency, and the relationship between the voltage and frequency is stored as multiple modes set according to the application, and the maximum voltage applied to the electric motor is determined by the frequency. The mode is changed by a switch depending on the situation.

[For production]

By changing the frequency, and by changing the relationship between the applied voltage V and the frequency F, the above-mentioned constant output (gradual output) characteristics and constant torque characteristics can be easily achieved.

Therefore, the relational expressions corresponding to each of the above modes are stored in the inverter and selected by switches as necessary.

[Means to solve the problem]

In order to achieve the above object, the present invention employs the following means. In other words, high resistance material is used in the secondary winding of the rotor or eddy current is generated in the rotor [Example] (Mode I) As shown in Fig. 4, the magnetic flux of each pole is made to remain unchanged even when the frequency is changed. (See point P in FIG. 4) The relationship between the -order voltage V and the frequency F can be realized by the formula V=aF+α [in this case, a=3.7, α-15].

When this relational expression is expressed as a frequency-voltage relationship, it can be expressed as a limit line of frequency F and voltage V as shown in Fig. 11,
Also, the relationship between torque and rotational speed can be expressed as a graph as shown in Fig. 2.

Here, as shown in Fig. 3, in order to obtain the speed-torque characteristics that the user needs, the frequency F and the voltage ■
The torque characteristics can be changed to the required speed by setting an appropriate frequency within the range of and changing the voltage. Can be used for equipment that requires decreasing output characteristics.

Further, constant torque characteristics can be obtained by utilizing the characteristics of the section β in FIG. Furthermore, by keeping the voltage constant and varying the frequency, constant output characteristics can be obtained as shown in FIG. 7(a).

(Mode ■) Also, as shown in Fig. 5, if the limit line of the frequency F and the pressure V is V = bF + βCb = 2.5, β - 50], the restraining torque is constant as shown in Fig. 6. (45kgcm). The above value is determined by the resistance value of the secondary winding or the ease with which current flows through the eddy current material. By using this mode, a predetermined restraint torque can be maintained even if the frequency is lowered. That is,
kNT=W (k: coefficient, N: rotation speed, T2 torque,
Since the torque T is the same even if the output W is decreased by decreasing the frequency (reducing the rotation speed) from W: output),
When the frequency is decreased, a constant restraint torque can be obtained even though there is less slippage and the amount of heat generated is correspondingly reduced. Therefore, whereas conventional motors of this type were open-type, requiring good ventilation and cooling with an external fan, Kimoto's motors can be closed-type, allowing waste lint from looms to flow into the work site. It is effective for use when it is widespread.

By using this V/F pattern, compatibility can be maintained with a torque motor whose maximum rating is in a restrained state, and even if a control error occurs, damage to the processed material or the device itself can be avoided.

In the above, we have explained the case where the restraining torque is constant, but for example, when trying to obtain a constant torque at a rotation speed of 27 rpm in Fig. 6, it is possible to use 100V and 60Hz, or 75V and 10Hz. However, it is more efficient to use 75V and 10Hz because there is less slippage and the amount of heat generated can be suppressed.

The relational expression between the voltage ■ of each mode and the frequency F as above is written as
As shown in FIG. 8, CPUl0 controls the inverter 1.
Store it in the built-in memory, and press the external switch 11.
to be switched by. This allows use within the rated range in the desired mode.

[Effects of the Invention] As explained above, the present invention has a built-in speed-torque characteristic program in the inverter that matches the user's use mode such as constant gap magnetic flux, constant locking torque, constant rated torque, etc. Since the above program is selected when installing the motor, it has the effect of simplifying the installation work.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between frequency and voltage in this invention when the magnetic flux is constant, Figure 2 is a graph showing the relationship between torque and rotational speed in this mode, and Figure 3 is a graph showing the relationship between torque and rotational speed in this mode. Figure 4 is a graph when the magnetic flux is constant, Figure 5 is a graph showing the relationship between frequency and voltage in this invention when the restraint torque is constant, and Figure 6 is a graph when the restraint torque is constant. , FIG. 7 is a graph showing constant output characteristics and decreasing output characteristics, and FIG. 8 is a conceptual diagram of an embodiment of the present invention. In the figure, ■... Applied voltage, F... Frequency.

Claims (4)

[Claims] (1) In a method of controlling a motor using a high-resistance material in the rotor's secondary winding or a material that generates eddy current in the rotor, the maximum voltage applied to the motor is specified by the frequency, and the voltage (V) and frequency (F) are stored as a plurality of modes set according to the application, and the modes are switched by a switch as necessary. (2) 3 according to claim 1, wherein the relationship between the voltage (V) and the frequency (F) is such that the gap magnetic flux of each pole is kept constant.
Control method of phase induction motor. (3) The control system for a three-phase induction motor according to claim 1, wherein the relationship between the voltage (V) and the frequency (F) is such that the restraint torque is kept constant. (4) The control system for a three-phase induction motor according to claim 1, wherein the voltage (V) is constant, and the output, which is the product of motor speed and torque, is constant.