JPH0726968B2 - Speed detection device in vector control device of induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a vector control device for an induction motor, and more particularly to a speed detection device thereof.

B. Summary of the Invention The present invention realizes stable operation in a vector control device for an induction motor by adding filter calculation to speed detection at extremely low speeds where relatively fast response is not required. It is a thing.

C. Conventional Technology In vector control of an induction motor, the primary frequency command ωo is determined by the sum of the speed detection value ωn and the slip frequency ωs determined by calculation.

D. Problems to be Solved by the Invention In the conventional speed detection device, if there is a ripple in the speed detection value, the primary frequency command ωo fluctuates, which is equivalent to a ripple in the slip frequency ωs, which causes a triple ripple. This causes uneven rotation of the rotating body. Especially when operating at an extremely low speed with a light load, uneven rotation due to the speed detection ripple becomes a problem.

E. Means for Solving the Problems The present invention has been made in view of the above problems, and corresponds to a means for deriving a frequency signal corresponding to the rotation speed of the induction motor and a unit period of the frequency signal. A means for calculating the rotation speed based on the count number and the cycle of the reference clock, and a speed detection value obtained by calculating the rotation speed on the condition that the rotation speed is smaller than an arbitrarily set filter calculation speed. And a means for reducing ripples to improve speed detection characteristics.

F. Example An example of the present invention will be described below with reference to FIGS.

In FIG. 1, the rotary shaft of the resolver 1 is directly connected to the rotary shaft of the induction motor 2, and the stator winding of the resolver 1 has a sinusoidal wave signal Sinωct from the induction motor 2 and a cosine wave signal Cosωct of about 90 degrees. Is applied as the excitation voltage. With respect to this excitation voltage, the output voltage V _r of the resolver 1 is the difference between the output voltage of the induction motor 2, Sinωct and Cosωct.
Cos (ωc−ωn) t is obtained. In this embodiment, when the phase comparator 4a and the phase difference signal of the phase comparator 4a are input and the low-pass filter 4b that performs a predetermined arithmetic process and the output signal of the low-pass filter 4b are input, the voltage controlled oscillator (VCO) 4c is input. And a PLL circuit 5 composed of
A sine wave oscillator 6 that receives the output signal of the PLL circuit 5,
A multiplier 7a which receives the sine wave output signal Sinωxt of the sine wave oscillator 6 and the sine wave output signal Sinωbt of the excitation oscillator 3 as inputs.
And a multiplier 7b whose inputs are the cosine wave output signal Cosωbt of the excitation oscillator 3 and the cosine wave output signal Cosωxt of the sine wave oscillator 6.
And an adder 8 that receives the output signals of the multipliers 7a and 7b as input, and the output signal Vx = Cos (ω
b−ωx) t is used as an input of the phase comparator 4a.
Further, the output signal Vr = Cos of the resolver 1 is applied to the phase comparator 4a.
(Ωc−ωn) t is also input.

In the speed detection device of FIG. 1, the resolver 1 is Sinωct,
Excited by Cosωct, the swing motor 2 rotates angular velocity ωn
When rotating at, the output voltage Vr is given by equation (1).

Vr = Cos (ωc−ωn) t (1) The output signals of the excitation oscillator 3 are Sinωbt and Cosωbt, and the output signal of the sine wave oscillator 6 is Sinωxt and Sinωxt
It is Cosωxt with a phase difference of 90 degrees. Therefore, the multiplier 7a
Output signal of Sinωxt ・ Sinωbt, and the output signal of multiplier 7b is C
osωxt · Cosωbt, and the output signal of the adder 8 becomes Sinωxt · Sinωbt + Cosωxt · Cosωbt = Cos (ωb−ωx) t. Therefore, the phase comparison signal Vx is given by equation (2).

Vx = Cos (ωb−ωx) t (2) Here, by the action of the PLL circuit 5, the equations (1) and (2) are synchronized and the following equation (3) is obtained.

[omega] c- [omega] n = [omega] b- [omega] x = ... (3) From this equation (3), [omega] x becomes the following equation (4), and the output of the voltage controlled oscillator 4c becomes a pulse train of fx.

[omega] x = [omega] n + ([omega] c- [omega] b) (4) The output signal fx of the voltage controlled oscillator 4c is taken into the arithmetic processing unit 9 and the rotational angular velocity ωn of the induction motor 2 is detected by the operation of the equation (5) described later.

In order to obtain the value of fx in the arithmetic processing unit 9, for example, the period t of the pulse signal of fx is changed to the period t using a known reference clock.
There is a method such as obtaining by counting how many clocks are included in the section. In this case, detection ripple occurs due to an error of ± 1 reference clock. Also,
The detection ripple occurs even if there is an amplitude error, a phase error, or the like between the output signals Sinωbt, Cosωbt of the excitation oscillator 3 or the output signals Sinωxt, Cosωxt of the sine wave oscillator 6. Since such a ripple has a small absolute value, there is no problem in operating the induction motor 1 at the normal speed.
Even in accurate positioning, the uneven rotation due to the detection ripple becomes a problem during extremely low speed operation. Therefore, as shown in FIG. 2, as shown in the flow chart of FIG.
A method is adopted in which the detection ripple is reduced by delaying the speed detection at a speed equal to or lower than an arbitrarily set speed. As a result, stable operation of the induction motor without uneven rotation is realized even at extremely low speeds.

That is, FIG. 2 shows an operation flow chart of the arithmetic processing section 9. In step S1, the count number n of the reference block in the t section is measured according to the speed detection routine,
Output frequency of speed detector as shown in step S3 (Tc is the cycle of the reference clock). Using the fx obtained here, the rotational speed ωn = 2πfx− (ωc−ωb) (5) of the induction motor is calculated in step S3. The calculated rotational angular velocity ωn is compared with an arbitrarily set angular velocity ωn-min at which the filter calculation is started. If .vertline..omega.n | <.omega.n-min as shown in step S4, the process proceeds to step S8 to complete the processing. ｜ ωn |
If ωn-min, the process proceeds to step S5 and the first-order lag filter computing means is used. Is calculated, and then the process is completed as shown in step S6.

The filters are not limited to primary delays and may be primary or higher, and the speed detection method is not limited to the example shown in FIG. A method may be used.

G. Effects of the Invention The present invention is as described above, and reduces the ripples for speed detection caused by sampling error, other circuit errors, etc. by a filter operation only at extremely low speed where this becomes a problem. As a result, there is an advantage that the rotation unevenness at extremely low speed can be greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block connection diagram of a speed detecting device according to an embodiment of the present invention, and FIG. 2 is an operation flow chart of the device of FIG. 1 ... Resolver, 2 ... Induction motor, 3 ... Excitation oscillator, 5 ... PLL circuit, 9 ... Arithmetic processing unit.

Claims (1)

[Claims] 1. A means for deriving a frequency signal corresponding to the rotation speed of an induction motor, and a means for calculating the rotation speed based on a count number and a cycle of a reference clock corresponding to a unit cycle of the frequency signal. And a means for reducing the ripple of the speed detection value by calculating the rotation speed on the condition that the rotation speed is smaller than the arbitrarily set filter calculation speed. Speed detection device in vector control device.