JPS60207485A - Detecting speed correcting system - Google Patents

Abstract

PURPOSE:To prevent the accuracy of an output torque with respect to a torque command from decreasing by providing a speed detection correction signal generator to accurately control a torque current and a command current. CONSTITUTION:A value proportional to the difference between a speed at the previous scanning pulse generating time for counting speed pulses at the prescribed time interval and a speed at the scanning pulse generating time this time is obtained by a speed correction signal generator 17, this output signal fc is added to a detecting frequency fn1 by a speed detector 16, the addition output fn2 is added to a slip frequency command fs as the primary current command, thereby minimizing an error.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a detection speed correction method that makes it possible to perform highly accurate vector control.

[Prior art and its problems]

Slip frequency control type vector control is based on the principle that torque is proportional to slip frequency, so the accuracy of motor speed detection directly affects the accuracy.

However, in digital control using sampling processing using a microcomputer, etc., the pulses between the previous scan pulse and the current scan pulse are captured in a counter, and the counter data is read or calculated after the current scan pulse generation time. Therefore, delays due to scanning time and delays due to calculation will occur, and therefore delays due to sampling time and time required for speed detection processing will always occur, so errors in detection delays will increase during acceleration/deceleration etc. Highly accurate vector control could not be performed.

This will be specifically explained based on FIGS. 1 to 3.

FIG. 1 is a control block diagram of a conventional slip frequency type vector control transistor inverter, where tll is a magnetic flux command, (2) is a speed command, (3) is a proportional-integral calculation circuit, (
4) is a primary current calculation circuit, (5) is a phase difference calculation circuit, (
6) is a division circuit, (7) is a vector calculation circuit, (8) is a vector multiplication circuit, (9) is a current control circuit, (10) is a rectifier, (11) is a smoothing capacitor, (12) is a transistor, (13) is a current detector, (14) is an induction motor, (15) is a pulse generator, and (16) is a speed detector. See you again! is the primary current command, Im is the exciting current command,
I2 is the secondary current command, ψ is the phase expressed by tan-ヱ (12/1m), Ts is the torque command, fnl is the output frequency of the speed detector (16), fs is the slip frequency command, fl
represents the primary current command.

+a+ in Fig. 2 is a frequency-torque characteristic diagram during acceleration, (bl is a frequency-torque characteristic diagram during deceleration, fa + fa' in the figure is the motor rotation detection frequency, fb, rb' are the actual motor rotation frequencies, fo, fo' is the output primary frequency, fs, fs
' is the calculated slip frequency.

In Fig. 2 (Ml), during acceleration, in order to obtain the torque at point A with respect to the detection frequency fa, fo, which is the sum of the slip frequency fs, is output as the primary frequency, but the actual speed of the motor is equal to fb. Therefore, if the voltage is constant, the value of ÷the torque at point B will be calculated.

FIG. 3 shows vector decomposition of the primary current 11 into a torque current component I2 and an excitation current component ll11.

In this figure, If,! 2, 1m, 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.

The phase advance angle ψ with respect to the magnetic flux of the primary current is ψ= tan
' (6JS R2/R2>, so the relationship ψ■ωS can be approximated. However, ωS is the very frequency,
R2 is a secondary self-inductance, and R2 is a secondary resistance.

First, when calculating /J based on the detected frequency to give a shift frequency of fs, in fa+ in FIG. 2, it corresponds to an advance of ψ, but in the actual frequency, there is only an advance of ψ''.

Assuming that the amplitude of the primary current does not change, 11=11'+
ψ〉ψ′ (Since it is accelerating, 12
>12', 1m <Im'', and it can be seen that the excitation current increases.

This means that there is no 9Jj as shown by the broken line in Figure 2.
This indicates that the voltage increases as the N flow increases.

Figure 4 (voltage rises in the same way even during deceleration of bl).

As described above, since accurate control of 12.1 m cannot be performed, there is a problem in that the accuracy of the output torque with respect to the torque command is reduced.

[Purpose of the invention]

An object of the present invention is to prevent a decrease in the accuracy of output torque with respect to a torque command by accurately controlling the l·lux current and the command current.

[Structure of the invention]

The detected speed correction method of the present invention uses the difference between the speed at the previous scan pulse generation time and the current scan pulse generation time to count speed pulses at fixed time intervals in the rotational speed detection value of the motor. This method is characterized in that the detected speed is corrected by adding a proportional value.

〔Example〕

Hereinafter, the present invention will be specifically explained based on the embodiments shown in FIG. 4 and below.

FIG. 4 shows a control block of a slip frequency type vector control transistor inverter incorporating the detection speed correction method according to the present invention, in which a speed detection correction signal generator (17) is added to the circuit of FIG. The output speed correction frequency fc and the output frequency fn of the speed detector (16)
1 and the summed output fn2 is added as a slip frequency command fs to obtain a primary current command.

The other configurations are the same as those in the block diagram of FIG. 1, so explanations will be omitted.

In the present invention, the output signal fc from the speed correction signal generator (17) which receives the speed command (2) as input is transmitted to the speed detector (16).
) is added to the detection frequency fn1 to minimize the error. fc takes a value of 10 during acceleration to compensate for the error, and takes a value of - during deceleration. FIG. 5 is a block diagram showing details of the speed correction signal generator (17), which is composed of a one-scan delay element (17-1) and a proportional coefficient unit (17-2).

FIG. 6 shows flowchart 1 when this speed correction signal generator (17) is realized by a microcomputer. That is, first, the detected motor frequency fn4 of the speed detector (16) is calculated, and then the command speed Nf at the current scan is calculated.
A value proportional to the difference between n and the commanded speed NfO at the previous scan (K is a proportionality constant) is the correction frequency fc, and the commanded speed at the current scan is replaced with the commanded speed at the previous scan for the next calculation.) , is added to the above-mentioned detected morph frequency fnl to obtain the corrected morph frequency fn2. A slip frequency control type vector control calculation is performed with the morph frequency set to fn2, and a current command is generated.

FIG. 7 is a characteristic diagram of speed, torque, and voltage to which this method is applied, where 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 sudden acceleration and deceleration is suppressed, and the reactive current can be reduced.

In the above embodiment, the input of the speed correction signal generator (17) is the speed command, but as shown in FIG. 8, the speed detection value fn1 can be input to form a speed feedback system.
Alternatively, it is also possible to use both ().

〔Effect of the invention〕

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

■When vector control of the slip frequency control type is realized by sampling control using a microcomputer, etc., calculation errors caused by sampling time delays and speed detection processing delays are greatly reduced, and sudden accelerations or decreases at speed, or rated The effect is significant when controlling motors with small slips.

■Since it is possible to accurately control the torque current and excitation current, it is possible to prevent a decrease in the accuracy of the output torque with respect to the torque command, and at the same time to minimize the increase in reactive current. can be prevented.

[Brief explanation of the drawings] Fig. 1 is a control block diagram of a conventional slip frequency controlled transistor inverter, and Fig. 2 is a characteristic showing the relationship between output 1-lux and frequency during acceleration/deceleration. Figure, 3rd
The figure is a vector diagram showing the relationship between the secondary current component and the excitation current component of the primary current, and FIG. Fig. 5 is a program diagram showing the configuration of the speed detection correction signal generator, Fig. 6 is a flowchart when the correction according to the present invention is processed by a microcomputer, and Fig. 7 is an acceleration/deceleration diagram showing the effects of the present invention. FIG. 8 is a block diagram showing another configuration example of correction. (1): Magnetic flux command (2): Speed command (3): Proportional integral calculation circuit (41: 1 o'clock current calculation circuit (5) - phase difference calculation circuit (6): Division circuit (7)°
Vector calculation circuit (8) Two-vector multiplication circuit (9):
Current control circuit (10) : Rectifier (11) : Smoothing capacitor (12) : ) Ranjisk (13) : Current detector (14) : Induction motor (15) : Pulse generator (16) : Speed detector (17) ): Speed Detection Correction Signal Generator Patent Applicant Yaskawa Electric Co., Ltd. Agent Handmade
(1 person) Figure 5 Figure 7 Figure 8

Claims (1)

[Claims] 1. In a slip frequency control type vector control device,
The detected speed is calculated by adding a value proportional to the difference between the speed at the previous scan pulse generation time and the current scan pulse generation time to count speed pulses at fixed time intervals to the rotational speed detection value of the motor. A detection speed correction method characterized by correction. 2. The detected speed correction method according to claim 1, wherein the speed for obtaining the speed difference is a speed command at the previous scan pulse generation time and a speed command at the current scan pulse generation time. 3. The detected speed correction method according to claim 1, wherein the speed for obtaining the speed difference is a speed detected value at the previous scan pulse generation time and a speed detected value at the current scan pulse generation time.