JPS63206177A - Speed controller for induction motor - Google Patents

Abstract

PURPOSE:To improve the rise of generating torque and starting characteristic, by increasing the set value of slip frequency when an induction motor is in a starting range. CONSTITUTION:A speed command value omega'm and a speed detection value omegafrom a speed detector 6 are input to a subtracter 17, and the output of its difference omegam is directed to slip frequency setting units 15a, 15b. The setting units 15a, 15b output a first and a second slip frequency omegas1, omegas2 against the difference omegam, respectively. In the meantime, by a speed comparator 14, it is discriminated whether the speed detection value omegam is equal to or less than a reference value omegams, or not, and when a device is in a starting range, then a change-over switch 16 is changed over to the slip frequency setting unit 15b, and when the device is out of the starting range, then the switch 16 is changed over to the slip frequency setting unit 15. Then, from an adder 18, the output of the added value of the slip frequency and the speed detection value omegam, as primary frequency omega' is directed to a PWM circuit 7a.

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) This invention relates to a speed control device for an induction motor, and more specifically, the primary frequency and primary voltage of the induction motor are controlled by an inverter to control the speed of the induction motor. This relates to a speed control device that controls the speed of a motor.

(Prior art) Conventionally, as shown in FIG. 3, for example, power supplied from a DC patch 1 is converted into three-phase AC by a variable voltage/variable frequency inverter 3 via a smoothing capacitor 2 to generate three-phase induction. In a speed control device that drives an electric motor (hereinafter referred to as an electric motor) 4, a speed control circuit 5 receives a speed command value ω*m output from an external device (not shown) to set the rotational speed of the electric motor 4 to a predetermined rotational speed. Then, the speed detection signal from the speed detector 6 that detects the rotational speed of the electric motor 4 at that time is input as the speed detection value ωm, and the slip frequency ωS is determined from both values ω*m and ωm. The inverter 3 is controlled via the drive circuit 7 so that the rotation speed of R4 becomes the speed command value ω*m.

As shown in FIG. 4, the control circuit 5 includes a subtracter 5a, a slip frequency setting device 5b, 1) a zero frequency setting device 5C, and a primary voltage setting device 5.
d, and the primary voltage setting device 5d is configured with a speed detection value ω.
m is input, and as shown in FIG. 5, a primary voltage V*1 uniquely determined with respect to 0 m is output to a pulse width modulation circuit (PWM1 path) as a driving means configured in the drive circuit 7.

On the other hand, the subtractor 5a outputs the speed command value ω*m and the speed detected value ωm.
Find the difference △ωm (-ω*m-ωm) and calculate the difference △ω
m is output to the slip frequency setter 5b.

The slip frequency setting B5b is set by the difference △ωm as shown in FIG.
The slip frequency ωS that is uniquely determined for the sum is output to the next stage adder 5C. Adder 5C uses this slip frequency ωS
and the speed detection value ωm, and the additive value is expressed as the number frequency ω*
(=ωS+ωm) and outputs it to the PWM circuit 7a.

The PWM circuit 7a outputs a PWM pulse train signal to the inverter 3 so as to drive and control the electric motor 4 using the inverter 3's frequency ω* and the primary voltage V*1.

That is, in a speed control device using this slip frequency control method, as the detected speed value ωm approaches the speed command value ω*m (difference Δωm−+O), the slip frequency ωS also approaches zero, and the slip frequency ωS The generated torque T (=k·ωS, where k is a constant), which is approximately proportional to , is made small, so that the rotational speed ωm of the electric motor 4 quickly follows the speed command value ω*m without pulsating.

(Problem to be Solved by the Invention) However, if the slip frequency ωS is set in the same manner as described above in the starting region where the speed command value ω*m is gradually increased from a small value, the speed command value ω *m
Since the detected speed value ωm is small, the difference Δωm (=
ω*m−ωm) is also small, and as shown in FIG. 6, the value of the slip frequency ωS becomes small. Therefore, as shown in FIG. 7, the generated torque T, which is proportional to the slip frequency ωS, becomes smaller in the region.

As a result, in the starting region, although several times the generated torque is required compared to acceleration and deceleration during normal rotation of the electric motor 4 (outside the starting region), the generated torque is small and there is a problem in its responsiveness. there were.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to provide a speed control device for an induction motor that can improve the rise of the generated torque in the starting region and improve the starting characteristics.

Structure of the Invention (Means for Solving Problems) In order to achieve the above object, the present invention provides an induction motor that is driven and controlled by an AC power source from an inverter that can control voltage and frequency, and an inverter that drives the inverter. a driving means, a speed detecting means for detecting the rotational speed of the induction motor, a determining means for determining whether or not the induction motor is in a starting region based on a detected value from the speed detecting means, and a speed detecting means for detecting the rotational speed of the induction motor; a deviation value calculation means for calculating the difference between the speed command value and the detected value from the speed detection means, and a slip for the deviation value calculated by the deviation value calculation means for purposes other than starting the induction motor; A first slip frequency setting means for setting a frequency, and a slip frequency for the deviation value obtained by the deviation value calculating means for starting the induction motor, which is larger than the slip frequency of the first slip frequency setting means. When the second slip frequency setting means determines that the slip frequency is in the starting region and the second slip frequency setting means determines that the slip frequency is outside the starting region. , selects the slip frequency of the first slip frequency setting means, calculates the primary frequency of the motor based on the selected slip frequency, and outputs the primary frequency to the driving means to drive the inverter. The gist of this is a speed control device for an induction motor, which is comprised of a calculation 71 for controlling the IJηD means.

(Function) When the induction motor is in the starting region, the calculation control means
A slip frequency from the second slip frequency setting means is selected that has a value larger than the slip frequency of the slip frequency setting means. As a result, induced electricity? The induction motor can generate a large amount of torque (',7) at the time of starting because the 1-rook generated in the motor increases in the driving region in conjunction with the l-bevel frequency.

(Example) An example embodying the present invention will be described below with reference to the drawings. In this embodiment, the speed flil+ control device described in the prior art section has a feature in its control circuit 5, and the other parts are substantially the same, so for convenience of explanation, only the control circuit 5 will be described in detail. explain.

As shown in FIG. 1, the control circuit 5 of this embodiment is composed of a primary voltage calculation section 11 and a primary frequency calculation section 12, and the -order voltage calculation section 11 is similar to the conventional one described above. It consists of a primary setting device 13 that is the same as the primary voltage setting device 5d, and the detected speed value ωm is input and the primary voltage ■*1 that is uniquely determined with respect to the detected speed value ωm is set to the PWM circuit as shown in FIG. 7a. In this case, as shown in Fig. 5, the primary voltage v*1 increases in proportion to the detected speed value ωm, and when the detected value ωm exceeds a predetermined value, the primary voltage v*1
is set in advance to be a constant value.

The primary frequency calculation unit 12 includes a speed comparator 14, first and second
It consists of slip frequency setters 15a and 15b, a changeover switch 16, a subtracter 17, and an adder 1B. 11j The speed comparator 14 as another means detects the speed detection value ω.
m is input, and it is determined whether 0 m is less than a predetermined reference value ωms. This determination is to determine whether or not the electric motor 4 is being driven in the starting region, and in this embodiment, the electric motor 4
The electric motor 4 is said to be in the starting region when the rotational speed is 1100 rpm or less. Therefore, the reference value ωms is 110
This value corresponds to a rotational speed of 0 rpm.

When the speed comparator 14 determines that the motor 4 is in the starting region (0 m ωms), the speed comparator 14 selects the slip frequency ωS2 output from the second slip frequency setter 15b, which will be described later, using the changeover switch 16. On the other hand, when it is determined that it is not in the starting region (ωm≧ωms), the switch 16 is switched to select the slip frequency ωS1 output from the first slip frequency setter 15a.

The first slip frequency setter 15a is the same as the conventional slip frequency setter 5b described as
ωm is input, and as shown in FIG. 6, a slip frequency (hereinafter referred to as a first slip frequency) ωS1 that is uniquely determined with respect to the difference Δωm is output. In this case, the difference △ within a predetermined range as shown in Figure 6.
The first slip frequency ωS1 increases in proportion to ωm, and is set in advance so that the first slip frequency ωS1 becomes a constant value when the difference Δωm is outside the above range.

The second slip frequency setter 15b inputs the difference Δωm calculated by the subtracter 17, and as shown in FIG. ) ωS2 is output. In this case, as shown in Fig. 2, when the absolute value of the difference △ωm becomes slightly larger than zero in consideration of calculation errors, the second slip frequency ωS2 increases stepwise to the maximum value, that is, the difference Δωm. Even if the absolute value is small, the first full frequency ωS
It is set in advance to be a value greater than 1.

First and second slip frequency setters 15a.

Each slip frequency ωs1. ωS2 is output to the changeover switch 16, and depending on the switching state of the switch 16, both slip frequencies ωs1. Either one of ωS2 is output to the next stage adder 1B.

The adder 18 adds the detected speed value ωm to either the slip frequency ωS1 or ωS2 of the slip frequencies ωsl and ωS2, and calculates the added value (=ωs1 (or ωS2〉+0m))
is outputted to the PWM circuit 7a as a frequency ω*.

Then, the PWM1 path 7a outputs a PWM pulse train to the inverter 3 so that the AC power having the primary frequency ω* and the primary voltage *1 is applied to the motor 4 via the inverter 3.

Next, the operation of the control circuit configured as described above will be explained.

Now, in order to start the electric machine 4 and rotate it to a predetermined rotational speed, a speed command value ω*m for starting is output from an external device (not shown).
*m and the speed detection value ωm from the speed detector 6 are input, and both values ω1111. The difference Δωm between ωm is determined by the first and second slip frequency dispersion constants 15a.

15b.

Both membrane constants 15a and 15b measure the first and second slip frequencies ωs1. to this difference Δωm, respectively. Set and output ωS2. At this time, the first slip frequency ωS1 becomes a small value as shown in FIG. 5 because ω*m and ωm are small and the difference Δωm is small at the time of starting. Further, as shown in FIG. 2, the second slip frequency ωS2 has a value larger than the first slip frequency ωS1 even if the difference Δωm is smaller.

Also, the speed comparator 14 receives the speed detection value ω from the speed detector 6.
m is input, and it is determined whether ωm is less than the W-shaped box ωms, that is, whether the electric motor 4 is in the starting region.

At this time, when the electric motor 4 starts rotating, ωm becomes ωm.
Since the speed comparator 14 is in the starting region 1), the selector switch 16 is switched to the second slip frequency setter 15b side, and the second length edge frequency ωS2 (>
ωSl) is output to the adder 18 at the next stage. Adder 18
is the PWM circuit 7a which tightens this slip frequency ωs2 and the speed detection value ωm and sets the added value σ to a number frequency ω*.
Output to.

The PWM circuit 7a has one frequency ω water and the primary voltage setting device 13.
Input the primary voltage v*1 that is uniquely determined for the speed detection value ωm from
The inverter 3 is controlled based on 1 and 1.

Therefore, at the time of starting the electric rBJ 114, the second slip wave number ωS2, which has a large value of C, is selected, so the electric motor 4 can obtain a large generated torque T, and drive control with good responsiveness can be performed. Become. Thereafter, the electric motor 4 is driven and controlled with a large generated torque T until it can handle the starting range, and the starting characteristics are improved.

Then, the rotational speed of the electric motor 4 gradually increases, and the rotation speed of the electric motor 4 increases.
ωm≧ωms), the speed comparator 14 switches the selector switch 16 to select the first slip frequency setter 15a, and sets one frequency ω*(= ωm+ωS1) is calculated, and conventional slip frequency control is performed.

Note that this invention is not limited to the above embodiments,
Slip frequency ωS2 of second slip frequency setter 15b
was changed stepwise as shown in Fig. 2, but the point is that the slip frequency in the starting region only needs to be a large value even if the difference Δωm is small.For example, if the second slip frequency ωS2 for the difference Δωm is It may be implemented by setting as shown by the broken line in FIG.

Furthermore, in the embodiment described above, each circuit of the primary voltage calculation section 11 and the primary frequency calculation section 12 may be configured by a digital circuit, an analog circuit, or a microcomputer, and the point is to perform the calculation and selection control of each value described above. Any circuit (any configuration) is acceptable as long as it can perform this.

Further, although the above embodiment is an example in which the present invention is applied to a slip frequency control method, the present invention is not limited to this, and it is of course possible to apply the present invention to, for example, a solid-wave control method.

Effects of the Invention As detailed above, according to the present invention, it is possible to obtain a large amount of torque generated in the starting range of a %Q motor, and it is possible to improve the starting characteristics of an induction motor.

[Brief explanation of the drawing]

FIG. 1 is an electrical block circuit diagram of the main control section of a speed control device embodying the present invention, and FIG. 2 is a diagram showing the relationship between the second slip frequency and the difference between the speed command value and the detected speed value. Fig. 3 is an electric block circuit diagram for explaining a conventional speed control device, Fig. 4 is an electric block circuit diagram of the main control section in the same speed control device, and Fig. 5 is a diagram showing the primary voltage and the speed detection value. FIG. 6 is a diagram showing the relationship between the first slip frequency and the difference between the speed command value and the detected speed value, and FIG. 7 is a diagram showing the relationship between the heel frequency and the generated torque. In the figure, 1 is a DC battery, 3 is an inverter, 4 is a three-phase induction motor, 5 is a speed control circuit, 11 is a primary voltage calculation unit,
12 is a primary frequency calculation unit, 13 is a primary voltage setting device, 14
is a speed comparator, 15'a is a first slip frequency setter,
15b is a second slip frequency setter, 16 is a changeover switch, 17 is a subtracter, and 18 is an adder. Patent Applicant Toyota Auto Range IM Manufacturing Co., Ltd. Representative Patent Attorney On 1) Hironoden, U ω Machine Figure 2 Figure 8 Drawing No. 2 No drawing afterward Figure 1 Figure 7

Claims (1)

[Scope of Claims] An induction motor whose drive is controlled by AC power from an inverter capable of controlling voltage and frequency; inverter drive means for driving the inverter; speed detection means for detecting the rotational speed of the induction motor; a determining means for determining whether or not the induction motor is in a starting region based on a detected value from the speed detecting means; a speed command value for bringing the induction motor to a predetermined rotational speed; and a detected value from the speed detecting means; a first slip frequency setting means for setting a slip frequency for the deviation value obtained by the deviation value calculation means for purposes other than starting the induction motor; a second slip frequency setting means for setting a slip frequency for the deviation value obtained by the deviation value calculation means to a value larger than the slip frequency of the first slip frequency setting means; and the discriminating means starts. When it is determined that it is in the starting region, the slip frequency of the second slip frequency setting means is selected, and when it is determined that it is outside the starting region, the slip frequency of the first slip frequency setting means is selected, and based on the selected slip frequency. A speed control device for an induction motor, comprising calculation control means for calculating a primary frequency of the induction motor and outputting the same primary frequency to the driving means to control an inverter.