JPH0726969B2 - Speed detection device in vector control device of induction motor - Google Patents

Description

The present invention relates to a vector control device for an induction motor, and more particularly to a speed detection device for the vector control device.

B. Summary of the Invention The present invention is a vector control device for an induction motor, which adds a filter operation to the speed detection at a very low speed where relatively fast response is not required, and also differentiates the differential value of the speed and the speed setting of the induction motor. By performing the calculation on the condition that the value is equal to or less than the predetermined value, it is possible to obtain a speed detection device having excellent responsiveness in a steady state or an excessive state at an extremely low speed.

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, when 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, causing a torque 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.

Further, (1) the point of zero speed is inevitably passed when the setting is suddenly changed at the time of switching between normal rotation and reverse rotation, so that a speed detection delay occurs near this point and the speed response deteriorates. (2) Even when accelerating more rapidly than stopping, when stopping as in (1),
It causes a delay in the speed response.

The present invention has been made in view of the above problems, and an object thereof is to obtain good characteristics even at an extremely low speed of an induction motor.

E. Means for Solving Problems In order to achieve the above object, the speed detection device of the present invention is
Means for deriving a frequency signal corresponding to the rotation speed of the induction motor, means for calculating the rotation speed based on the count number and cycle of the reference clock corresponding to the frequency signal, and the rotation speed is set arbitrarily. And the differential value of the rotational speed of the induction motor and the differential value of the speed setting are respectively less than or equal to a constant value, and are configured by means for calculating the rotational speed of the filter, At extremely low speeds of the induction motor, the characteristics are good in both the steady state and the transient state.

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 with a 90 ° phase difference. Is applied as the excitation voltage. With respect to this excitation voltage, the output voltage Vr of the resolver 1 is Cos (ωc−ωn) t which is the difference between Sinωct and Cosωct which are the output voltages of the induction motor 2. In this embodiment, a phase comparator 4a and a low-pass filter 4b that receives the phase difference signal of the phase comparator 4a as input and performs predetermined arithmetic processing and a voltage-controlled oscillator (VCO) that receives the output signal of the low-pass filter 4b as input. PLL circuit 5 composed of 4c and
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 which receives the output signals of the multipliers 7a and 7b and an arithmetic processing unit 9, and outputs the output signal Vx = Cos (ωb−ωx) t of the adder 8 from the phase comparator 4a. It is an input. The output signal Vr = Cos (ωc−ωn) t of the resolver 1 is also input to the phase comparator 4a.

In the speed detection device of FIG. 1, the resolver 1 is Sinωct,
Excited by Cosωct, the induction motor 2 rotates the rotational 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 2 at the normal speed.
During extremely low speed operation such as accurate positioning, uneven rotation due to this detection ripple becomes a problem. Therefore, as shown in FIG. 2, as shown in the flow chart of FIG.
A method has been 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.

Further, as a condition for adding the filter calculation at an extremely low speed, speed detection is executed under the condition that the speed is within the range of. +-.. omega.n-min (the angular velocity at which the arbitrary filter calculation is started) and the following two conditions.

(A) The differential value (ωn-def) of the speed is equal to or less than a constant value (an arbitrarily set value).

(B) The differential value (ω'n-def) of the speed setting is less than or equal to a fixed value (value set arbitrarily). As a result, when the induction motor makes a rapid shift from normal rotation to reverse rotation,
Even if it falls within the range of ωn-min, since the differential value (rate of change) of the speed is large, the filter operation is not performed and the over-response caused by the delay element in the speed detection as shown in FIG. Although it deteriorates, it can be improved as shown in FIG. Similarly, when the speed command is suddenly changed while the speed is within the range of ± ωn-min, the speed of the speed command is changed, the filter operation is passed under the condition of the above item (b). Although the responsiveness deteriorates as shown in FIG. 4 (A), the deterioration of response can be prevented as shown in FIG. 4 (B).

To realize the above operation, the operation flow of FIG. 2 is further executed.

That is, FIG. 2 is a flow chart showing the operation of the arithmetic processing unit 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 S2 (Tc is the cycle of the reference clock.) The rotational speed ωn = 2πfx− (ωn−ωb) (5) of the induction motor is calculated in step S3 using fx obtained here. 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 ω'n-def <
Judge A. Here, ω′n-def is the difference between the speed setting value ω ′ and the previous setting value ω ″, and A is the rate of change of the speed command for stopping the filter calculation at an arbitrarily set constant value. If it is not n-def, the process proceeds to step S8 and ω '
If it is n-def, .omega.n-def <B is judged in step S6. Here, ωn-def = ωn-ω'n (6), where ωn is the speed detection value, ω'n is the previous speed detection value, and B is the rate of change in speed at which the filter calculation is stopped. It is a fixed value. At step S6, ωn−
If def <B, the process proceeds to step S8 and ωn-def <B
If so, move to step S7 and use the first-order lag filter calculation means. Is calculated, and then the process is completed as shown in step S8. As described above, when the induction motor is at an extremely low speed (| ωn | <ωn-min) (7), the above (a) and (b) terms are not satisfied, that is, in the steady state, the speed detection value Since a filter calculation is added to eliminate the influence of detection ripple, stable operation without rotation unevenness can be realized and a good response can be obtained even in a transient state such as a change in speed setting.

The filters are not limited to those of the primary delay, and filters of the primary or higher order may be provided, and the speed detection method is not limited to the example of 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 is a problem. As a result, it is possible to significantly improve the rotational unevenness at an extremely low speed, and it is possible to obtain a good response by passing the filter calculation in the transient state of the speed setting command.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a speed detecting device according to an embodiment of the present invention, FIG. 2 is an operation flow chart of the device of FIG.
3 (A) and (B) and FIGS. 4 (A) and (B) are operating characteristic diagrams 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 with respect to the rotation speed of an induction motor, a means for calculating the rotation speed based on a count number and a cycle of a reference clock corresponding to the frequency signal, and the rotation speed is arbitrary. By a means for calculating the rotational speed on the condition that the rotational speed of the induction motor is smaller than the calculated speed, and the differential value of the rotational speed of the induction motor and the differential value of the speed setting are equal to or less than a fixed value, respectively. A speed detecting device in a vector control device of an induction motor, which is characterized by being configured.