JP2531607B2 - Detection speed correction method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a detection speed correction method capable of performing highly accurate vector control.

[Prior art and its problems] In the vector control of the slip frequency control type, since the torque is based on the principle that it is proportional to the slip frequency,
The accuracy of detection of the speed of the electric motor directly affects the accuracy.

However, in digital control by sampling processing using a microcomputer or the like, the pulse between the previous scan pulse and the current scan pulse is fetched into the counter, and the counter data is read or calculated after the current scan pulse generation time. Has become.
For this reason, a delay due to the scan time and a delay due to the calculation occur, and therefore a delay due to the sampling time and the time required for the speed detection processing always occurs. Therefore, during acceleration / deceleration, a delay error due to detection becomes large, and accurate vector control cannot be performed.

This will be specifically described with reference to FIGS. 1 to 3.

FIG. 1 is a control block diagram of a conventional slip frequency vector control transistor inverter. 1 is a magnetic flux command, 2 is a speed command, 3 is a proportional-integral arithmetic circuit, 4 is a primary current arithmetic circuit, and 5 is a phase difference arithmetic circuit. Circuit, 6 division circuit, 7 vector operation circuit, 8 vector multiplication circuit, 9 current control circuit, 10 rectifier, 11 smoothing capacitor, 12 transistor, 13 current detector, 14 induction motor, Reference numeral 15 is a pulse generator, and 16 is a speed detector. I ₁ is the primary current command, I _m is the exciting current command, I ₂ is the secondary current command, and ψ is tan ^−1.
The phase represented by (I ₂ / I _m ), T _s is the torque command, f _n1 is the output frequency of the speed detector 16, f _s is the slip frequency command, and f ₁ is the primary current command.

2 (a) is the frequency during acceleration, and (b) is the frequency during deceleration.
FIG. 4 is a torque characteristic diagram in which f _a and f _a ′ are rotation detection frequencies of the motor, f _b and f _b ′ are actual rotation frequencies of the motor, and f _o and f _o ′.
Is the output primary frequency, and f _s and f _s ′ are calculated slip frequencies.

In the FIG. 2 (a), in order to obtain the torque at the point A with respect to the detection frequency f _a is in addition, it outputs the f _o plus the slip frequency f _s as the primary frequency, the actual motor Since the speed is f _b , if the voltage is constant, torque at point B will be output.

Figure 3 shows the primary current I ₁ as the secondary current component I ₂ and the exciting current component.
It is a vector decomposition into I _m . In this figure,
I ₁ , I ₂ , I _m , and ψ are the predicted primary current, secondary current, exciting current, and primary current phase delay, respectively, and those marked with “′” are their actual values.

Since the phase advance angle ψ with respect to the magnetic flux of the primary current is represented by ψ = tan ⁻¹ (ω _s L ₂ / R ₂ ), the relation ψ ∝ω _s can be approximated. Where ω _s is the slip frequency, L
₂ is the secondary self-inductance and R ₂ is the secondary resistance.

First, when the slip frequency of f ₃ is given by calculation based on the detected frequency, this corresponds to the advance of ψ in FIG. 2 (a), but there is only the advance of ψ ′ at the actual frequency.

Assuming that the amplitude of the primary current does not change, I ₁ = I ₁ ′, ψ
> Ψ ′ is accelerating, so from FIG. 3, I ₂ > I ₂ ′, I _m <
It can be seen that I _m ′ and the exciting current increases.

This means that the voltage rises as the reactive current increases as shown by the broken line b in FIG.

 The voltage similarly rises during deceleration in FIG. 2 (b).

As described above, the conventional slip frequency vector control method cannot accurately control I ₂ and I _m , and thus has a problem that the accuracy of the output torque with respect to the torque command is reduced.

[Object of the Invention]

An object of the present invention is to prevent the accuracy of the output torque from being lowered with respect to the torque command by accurately controlling the secondary current and the exciting current.

[Structure of Invention]

In order to achieve this object, the present invention provides a detection speed correction method for a slip frequency control type vector control device in which rotation speed detection and vector calculation processing of a motor are performed by a digital circuit. Characteristic of correcting the primary frequency command in vector control by adding a value proportional to the difference between the speed command at the previous scan pulse generation time and the current speed command at the current scan pulse generation time for counting at fixed time intervals It is what

[Action]

In the present invention, by correcting the primary frequency command by adding a value proportional to the difference between the speed commands at the previous and present scan pulse generation times to the rotation speed detection value of the electric motor,
Corrects the delay in motor rotation speed detection during sudden acceleration and sudden deceleration. As a result, the voltage during rapid acceleration / deceleration is suppressed and the reactive current is reduced.

〔Example〕

Hereinafter, the present invention will be specifically described based on the embodiments shown in FIG.

FIG. 4 shows a control block of a slip frequency type vector control transistor inverter which adopts the detection speed correction system according to the present invention. A speed detection correction signal generator 17 is added to the circuit of FIG. in it adds the output frequency f _n1 speed correction frequency f _c and the speed detector 16, it adds the added output f _n2 as a slip frequency instruction f _s, is obtained by a primary frequency instruction f _1. The other structure is similar to that of the block diagram of FIG. 1, and therefore the description thereof is omitted.

In the present invention, the error is minimized by adding the output signal f _c from the speed correction signal generator 17 to which the speed command 2 is input to the detection frequency f _n1 by the speed detector 16. f _c
Becomes a positive value during acceleration to give a correction for the error,
A negative value is given during deceleration. Fig. 5 shows speed correction signal generator
17 is a block diagram showing details of 17, which is a one-scan delay element
17-1 and a proportional coefficient unit 17-2.

FIG. 6 shows a flow chart when the speed correction signal generator 17 is realized by a microcomputer.
That is, first, the detection motor frequency f _n1 of the speed detector 16 is calculated, and then a value proportional to the difference between the command speed N _{f n} at this time scan and the command speed N _f0 at this time scan (K is a proportional constant).
Is used as the correction frequency f _c, and the command speed for the current scan is replaced with the command speed for the previous scan for the next calculation. The corrected motor frequency f _n2 is added to the detected motor frequency f _n1 . The motor frequency performs slip frequency control type vector control calculating as f _n2, generates a current command.

FIG. 7 is a characteristic diagram of speed, torque, and voltage to which this method is applied. The solid line shows the case without correction and the broken line shows the case with correction. As can be seen from this figure, the voltage during rapid acceleration and rapid deceleration is suppressed, and the reactive current can be reduced.

〔The invention's effect〕

As described above, the present invention has the following effects.

When the slip frequency control type vector control is realized by sampling control using a microcomputer, etc., the calculation error due to the delay of sampling time and the delay of speed detection processing is greatly reduced. The effect is remarkable in the control of a motor having a small value.

Since the secondary current and the exciting current can be controlled accurately, the accuracy of the output torque with respect to the torque command can be prevented from decreasing, and at the same time, the increase of the reactive current can be suppressed to the minimum and the unnecessary voltage increase can be performed at the same time. Can be prevented.

[Brief description of drawings]

FIG. 1 is a control block diagram of a conventional slip frequency control type vector control transistor inverter, FIG. 2 is a characteristic diagram showing a relationship between output torque and frequency during acceleration / deceleration, and FIG.
A vector diagram showing the relationship between the secondary current component of the secondary current and the exciting current component, FIG. 4 is a control block diagram of a slip frequency control type vector control transistor inverter to which a detection delay correction circuit according to the present invention is added, and FIG. FIG. 6 is a block diagram showing the configuration of a detection / correction signal generator, FIG. 6 is a flow chart in the case where the correction according to the present invention is processed by a microcomputer, and FIG. It is a characteristic diagram. 1: Flux command, 2: Speed command 3: Proportional-integral calculation circuit, 4: Primary current calculation circuit 5: Phase difference calculation circuit, 6: Division circuit 7: Vector calculation circuit, 8: Vector multiplication circuit 9: Current control circuit , 10: rectifier 11: smoothing capacitor, 12: transistor 13: current detector, 14: induction motor 15: pulse generator, 16: speed detector 17: speed detection correction signal generator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Japanese Patent Laid-Open No. 57-74665 (JP, A) Shoukai 58-22099 (JP, U)

Claims (1)

(57) [Claims] 1. In a detection speed correction method of a slip frequency control type vector control device in which a rotation speed detection of an electric motor and a vector calculation process are performed by a digital circuit, a speed pulse is counted at a constant time interval in a rotation speed detection value of the electric motor. For correcting the primary frequency command in vector control by adding a value proportional to the difference between the speed command at the time of the previous scan pulse generation and the speed command at the time of the current scan pulse generation for .