JPS63142269A - Speed detector in vector controller for induction motor - Google Patents

Abstract

PURPOSE:To improve unevenness in extremely low speed rotation by reducing speed detection ripple generated by sampling errors and the like by filter calculation only in the extremely low speed rotation. CONSTITUTION:Frequency signals corresponding to the rotational speed of a motor are led out and the rotational speed is calculated on the basis of the count and the period of reference clocks corresponding to the unit period of the frequency signals. At this time, filter calculation is effected on the rotational speed under the condition that the rotational speed is lower than an arbitrarily set filter calculation speed. Detection ripple is reduced by delaying speed detection at a speed below the arbitrarily set one. Thus, the motor can be operated in stable condition wherein there is no unevenness in rotation even in extremely low speed.

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 particularly to a speed detection device thereof.

B1 Summary of the Invention The present invention is a vector control device for an induction motor that reduces ripple and achieves stable operation by adding filter calculation to speed detection at very low speeds where relatively quick response is not required. It is.

C1 Conventional technology In vector control of an induction motor, the -missing frequency command ω0 is determined by the sum of the detected speed value ωn and the slip frequency ωS determined by calculation.

D0 Problems to be Solved by the Invention In conventional speed detection devices, when there is a ripple in the detected speed value, the -missing frequency command ω0 fluctuates, which is equivalent to a ripple occurring in the slip frequency ωS, causing a torque clip. , this results in uneven rotation of the rotating body. Particularly when operating at very low speeds under light loads, uneven rotation due to this speed detection ripple becomes a problem.

E1 Means for Solving Problems The present invention has been made in view of the above problems, and includes means for deriving a frequency signal corresponding to the rotational speed of an induction motor, and a standard corresponding to the unit period of the frequency signal. The rotation speed is calculated by calculating the rotation speed based on the count number and cycle of the clock, and the rotation speed is calculated by filtering the rotation speed on the condition that the rotation speed is smaller than an arbitrarily set filter calculation speed. , speed detection characteristics are improved.

F. EXAMPLE An example of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, the rotation axis of the resolver 1 is directly determined by the rotation axis of the induction motor 2, and the stator winding of the resolver 1 receives a sine wave signal Sinωbt from an excitation oscillator 3, and a cosine wave having a phase difference of 90 degrees. The signal Co5 (IJbt) is applied as an excitation voltage. With respect to this excitation voltage, the output voltage Vr of the resolver I is equal to Sinωc, which is the output voltage of the induction motor 2.
Cos (ωC-ωn), which is the difference between t and Cosωct
t is obtained. In this embodiment, the phase comparator 4a
A low-pass filter 4c receives the phase difference signal from the phase comparator 4a and performs predetermined arithmetic processing, and a voltage-controlled oscillator (VC) receives the output signal from the low-pass filter 4c.
PLL circuit 4 constituted by
A sine wave oscillator 6 whose input is the output signal of the circuit 4, a multiplication 57a whose inputs are the sine wave output signal Sinωxt of the sine wave oscillator 6 and the sine wave output signal Sinωbt of the excitation oscillator 3, and the cosine of the excitation oscillator 3. Wave output signal Cosωb
t and a cosine wave output signal Cosωxt of the sine wave oscillator 6 as inputs, and an adder 8 that receives each output signal of these multipliers 7a and 7b as inputs.
The output signal Vx=Cos(ωb-ωx)t is used as the input signal of the phase comparator 4a. Further, the phase comparator 4a receives the output signal Vr=Co5(ct+c
-ωn)t is also done manually.

In the speed detection device shown in FIG.
When the induction motor 2 is excited by ωct and Cosωct and rotates at a rotational angular velocity ωn, its output voltage Vr is expressed by equation (1).

V = Co5(, + c −ωn)t−・−(1)
The output signals of the excitation oscillator 3 are Sinωbt and Cosωbt
The output signal of the sine wave oscillator 6 is Sinωxt and Cosωx, which has a phase difference of 90IX from Sinωxt.
It is t.

Therefore, the output signal of the multiplier 7a is SinωX t-5
inωbt.

The output signal of the multiplier 7b is Cosωxt-cosωbt, and the output signal of the adder 8 is Sinωxt-3inωbt+CosωbL=cos
(ωb−ωx)t. Therefore, the phase comparison signal vx
is the formula (2).

V x = Co5 (ωb - ωx) t - (2) Here, due to the action of the PLL circuit 11, equations (1) and (2) are synchronized, and the following equation (3) is obtained.

ωC-ωn=ωb-ωX=・・・・・・(3) This (3
), ωX becomes the following equation (4), and the voltage controlled oscillator 4
The output of b becomes a pulse train of fx.

ωX=ωn+(ωC-ωb) (4) The output signal fx of the voltage controlled oscillator 4b is input to the calculation processing section 9 and the rotation angular velocity ωn of the induction motor 10 is calculated by the equation (5゛).
Detect.

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 obtained by counting how many clocks are included in a period interval using a known reference clock. There is a method.

In this case, a detection ripple occurs due to an error of ±1 of the reference clock. In addition, the output signal Si of the excitation oscillator 3
nωbt, Cosωbt or the amplitude error between the output signals Sinωxt and Cosωxt of the sine wave oscillator 6 (Tc is the period of the reference clock). Detection ripples also occur when there is an error in the phase determined here. Since the absolute value of such ripple is small, the induction motor 1
This is not a problem when operating at normal speeds, but when operating at extremely low speeds for accurate positioning, uneven rotation due to this detection ripple becomes a problem. Therefore, as shown in the flowchart of FIG. 2, a method was adopted in which the detection ripple is reduced by providing a delay in speed detection below an arbitrarily set speed. This realizes stable operation of the induction motor without uneven rotation at extremely low speeds.

That is, FIG. 2 shows an operation flowchart of the arithmetic processing unit 9. In step St, rx is determined according to the speed detection routine by using other methods, not limited to the example of the reference block in interval t. The rotational speed of the induction motor is calculated by using As shown, 1ωnl<ωn−m
If it is not 1n, the process moves to step S8 and the process is completed. If lωnl<ωn-m1n, the process moves to step S5, where ωn-ωn·□ is calculated by the first-order lag filter calculation means, and then the processing section is completed as shown in step 2+5T S6.

Note that the filter is not limited to a first-order filter, but may be one of a first-order filter or higher, and the speed detection method shown in FIG. 1 may also be used.

G9 Effects of the Invention As described above, the present invention minimizes speed detection ripples caused by sampling errors, other circuit errors, etc. by reducing the ripples by filter calculation only at extremely low speeds where this becomes a problem. This has the advantage of significantly improving rotational unevenness at low speeds.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a speed detection device according to an embodiment of the present invention, and FIG. 2 is an operation flowchart of the device shown in FIG. DESCRIPTION OF SYMBOLS 1... Resolver, 2... Induction motor, 3... Excitation oscillator, 4... PLLu path, 9... Arithmetic processing unit. Figure 2

Claims (1)

[Claims] means for deriving a frequency signal corresponding to the rotational speed of the induction motor; means for calculating the rotational speed based on the count number and period of a reference clock corresponding to a unit period of the frequency signal; 1. A speed detection device in a vector control device for an induction motor, characterized in that the speed detection device is configured by means for performing a filter calculation on the rotational speed on the condition that the rotation speed is smaller than a filter calculation speed set in the filter calculation speed.