JPS60113684A - Vector controller of induction motor - Google Patents

Abstract

PURPOSE:To correct the slip frequency even at low speed time including zero speed by correcting the slip by an exciting current component. CONSTITUTION:A current detector 14 obtain a torque current component it' and an exciting current component im' from the primary current i1, and a voltage detector 19 obtains a reactive voltage component eq from a voltage detection value v1. A current vector calculator 8 outputs the primary current command i1* in response to an exciting current command im* and a deviation between a torque current command it* and torque current component it'. A pulse width modulation controller 7 controls an inverter 2 in response to a deviation between the primary current command i1* and the primary current i1. A multiplier 23 multiplies the deviation between the command im* and the component im' by a slip frequency command Ws and outputs a slip frequency correction signal DELTAWs.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to speed control of an induction motor, and in particular, to a vector control device for an induction motor that performs speed control by vector calculation of a torque component and an excitation component. Regarding.

[Background of the invention]

FIG. 1 shows the configuration of a conventional vector control device for an induction motor. The vector control device includes a DC power supply 1 composed of a thyristor, etc., and an inverter 2; (2-1 to 2-6 are GTO mounts that constitute the inverter).

variable frequency with an inverter (which is a semiconductor control element such as
An induction motor 3 driven by alternating current controlled by a variable voltage, a speed detector (PG) 4, a current detector 5, a voltage detector 6, a pulse width modulation (PWM) control circuit 7, and a ball current. The vector control device 8, the reference magnetic flux generation circuit 9, the torque current control circuit 10, the voltage control circuit 11, the torque slip calculator 12, the frequency command generation circuit 13, and detect the torque component and excitation component currents. A current detection circuit 14, a slip correction circuit 15 for orthogonality compensation, an in-bead/strotub compensation circuit 16, a detector 18 for detecting low speed,
It is comprised of a switch 17 and a voltage detection circuit 19 that detects voltages of active components and reactive components. Vector control generally uses an exciting current command 1 ta as shown in FIG.
The primary current command 111 is created by vector calculation from the torque current command 11" and the torque current command 11", and the primary current of the induction motor 3 is controlled by this, as shown in (5), ■, and (C) in the same figure. As the torque current command increases, the angle θ with the magnetic flux axis increases in accordance with the large primary current command 119.

On the other hand, the reference magnetic flux axis (
The actual magnetic flux axis (generated using the reference magnetic flux generation circuit 9) and the actual magnetic flux axis are generally shifted by an angle δ (the frequency given to the machine) as shown in Figure 3.
The speed detection value for calculating the speed differs from the actual speed. That is, due to errors in the speed detector, the detected speed ω,' deviates from the actual speed ω, by Δωa, as shown in FIG. Therefore, the synchronization frequency is ω1′+ω,′
is given, and the engine will be operated on the torque curve shown by the dotted line.

In other words, increase the excitation current (increase the back electromotive force)
, operation with a small torque current component (operation in which δ occurs).The second cause is that the required slip frequency shifts due to changes in the internal impedance of the induction motor.The internal impedance of the induction motor, In particular, the secondary resistance changes due to temperature and deviates from the design value.Since the slip frequency is a function of the secondary resistance, Fig. 4 (2
), the slip is determined by the design value r2'' before changes due to temperature etc., so the operation is not on the torque curve as shown by the dotted line, and as a result, the deviation angle δ occurs.

In this way, if the magnetic flux axis used for the current command (the calculated magnetic flux axis and the actual magnetic flux axis deviate by an angle δ), the induction motor 3
Since only the primary current command is given to the primary current command, the torque current and excitation current jt'', i- of the primary current command are different from the torque component it, excitation component i of the actual primary current, and the torque as per the command is generated. Therefore, in the past, a method has been used in which the reactive component voltage ea is a function of the deviation angle δ, that is, e+=Vtsin δ, to perform absolute compensation and make the deviation angle δ to be zero. was hiring.

In this conventional method, the reactive component voltage e, (l e, 1-■
1) is detected at the output end of inverter 2, but
Since the inverter 2 and the induction motor 3 are often far apart, the impedance drop compensation circuit 16 corrects the detected value V+ for the impedance drop due to the impedance due to wiring and the impedance inside the induction motor 3. . An equivalent circuit of the induction motor 3 is shown in FIG. In the figure, the detected value V1 of the reactive component voltage ed is equal to the wiring impedance (1,.

rQ ) and the primary impedance inside the induction motor (
t+, rl)K, the impedance drop is added to the voltage l' to be actually detected and detected. In other words, the detected value is ly. Therefore, ■1'
To detect V1'=VI +=(bow+”*)×I
: ωx (t: + 17), inverter 2
The wiring from the output end of
, rτ, t7).

However, the set value r: + r7 + t'o Ht: has an error from the actual value ro + "1r to + Al, and in particular, an error always occurs because the resistance changes depending on the temperature and the like.

Generally, the impedance correction amount is 5 to 10% when the induction motor 3 is operated at its rated value, so when the speed is high (voltage is large), even if the impedance error is 2%, it is 0.1%.
A voltage detection error of ~0.2% is enough to cause no problem. However, if the speed is small (voltage is low), for example, 5 inches, the voltage detection error will be 20 times the above value, or 2% to 4%.
%, which poses a problem. Kazuyuki 100 whose speed is further increased by 1%
This will result in a detection error that is twice as large (10% to 20%).
At low speeds, correction cannot be made and a deviation angle δ will occur. When the deviation angle δ occurs, the torque current command and the generated torque are no longer proportional, which poses a problem in the conventional method, especially when applied to tension, control, etc., because the speed is used up to zero.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a vector control device that can correct the frequency even at low speeds including zero speed, and allows the current command value to match the generated torque.

[Summary of the invention]

The present invention focuses on the fact that the excitation current component always exceeds a certain value in the operating state and is a gate of the deviation angle δ of the magnetic flux axis, and performs slip correction using the excitation current component to reduce the deviation angle of the magnetic flux axis. It is designed to eliminate δ.

[Embodiments of the invention]

Embodiments of the present invention will be described with reference to FIGS. 6 to 10.

FIG. 6 to FIG. 8 are diagrams of the principle of the present invention. FIG. 6 shows a vector diagram of the primary current command and a vector diagram of the actual primary current when the actual magnetic flux axis is deviated from the magnetic flux axis of the primary current command by δ2. In this case, the excitation current component decreases and the torque component current increases. In the same figure, the excitation component current 1 m converted to the magnetic flux axis of the -order current command
' and the torque component current jt' are the negative current 11, that is, the three-phase current of Ia+Iw, and the 5? The output signal of the reference magnetic flux generation circuit 9, which determines the magnetic flux axis of the magnetic flux axis, can be detected.

Three-phase current 1++1 +,, 1w0q-axis, d-axis converted current value IQ, and i6 are I q "" I n5In (ωτ t+δ) +i
−tO5(ωτt+δ) −(1)ia −i mc
O3 (GJ: t 1b) 1i t sin (ω:
+a) -(2), so the excitation component current 1 and the torque component current i +' are 'Q+Id and sinωτ and C
05 (from 0:j I rn'"" I q・5111
ω”, j−i 6 CO3ω1t= i, CO5
δ−i i sin δ (3) i <' =
i, −cos OJ: t + i a sinωτ
t=H, cos δ + 1 m 5ill δ ・
(4) Figure 6 shows that the deviation angle δ is positive, and it can be understood that if the deviation angle δ is zero, ii'=it, ti/-iyo. The same applies when the torque current command is small as shown in FIG.

On the other hand, as shown in FIG. 8, when the deviation angle δ is shifted by δl in the opposite direction to that in FIG. 17, that is, equation (3), (4
) is a state in which the deviation angle δ of the equation is negative. Therefore, by performing Bessi correction such that the difference between the excitation current command and the detected excitation component current 1□' becomes O, the deviation angle δ of the magnetic flux axis can be set to O.

FIG. 9 is a block diagram of an embodiment of a vector control device according to the present invention. The difference from the conventional example shown in FIG. A deviation calculator 22 for calculating the deviation between the excitation component current 10,1□' and the excitation current command I: and a multiplier 23 for multiplying the calculated output of the deviation calculator 22 by the frequency command ω are provided. , a current detection circuit 14, a deviation calculator 22, and a multiplier 23 constitute a slip correction circuit 21, and the same reference numerals as in FIG. 1 indicate the same components.

Next, a specific configuration of the slip correction circuit 21 is shown in FIG. In the same figure, if lu is set to i, the conversion type flow value id becomes (t n+ -), so from the subtractor 35 (i
u 1w ) is created (-1 subtracter equivalent current value ia can be detected. Therefore, co which is the output signal of the reference magnetic flux generation circuit 9
sωτ and sinωτt and 11+i are multiplier 32.
Multiply by 33 and subtract these calculation outputs with subtractor 31.i q sinω? jiacosω1t), the excitation component current 1 m' is detected, and the subtracter 22 further creates a signal (Im'l:), and the multiplier 23 multiplies it by the slip frequency command ω, thereby obtaining the deviation Δω, [- ω
:(1+a'l2)]. Here (1m' 1
If :) is positive, the correction will increase the slip, and if it is negative, the correction will reduce the slip, and the deviation angle δ of the magnetic flux axis can be made zero.

In other words, when performing vector control on an induction motor, the excitation component current 1+++ flows above a certain value regardless of the speed, and the current is the same both at the inverter output terminal and inside the induction motor, so it is not affected by impedance. .

Therefore, according to this embodiment in which the excitation component current is detected and the deviation angle δ of the magnetic flux axis is corrected, it is possible to correct the slip frequency with good accuracy regardless of the speed and even at low speeds.

〔Effect of the invention〕

According to the present invention, it is possible to correct the slip frequency with good accuracy regardless of the speed of the induction motor, and it is possible to match the current command value and the generated torque.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional vector control device for an induction motor, and Figure 2 shows the relationship between the magnitudes of the excitation current command and torque current command and the magnitude of the primary current command obtained by vector synthesis of these. Figure 3 is a vector diagram showing a state in which the reference magnetic flux axis used for the primary current command and the actual magnetic flux axis are misaligned, Figure 4 is a speed-torque characteristic diagram of an induction motor, and Figure 5 is an induction motor diagram. Equivalent circuit diagram of electric motor,
6 to 8 are vector diagrams for explaining the principle of the vector control device according to the present invention, FIG. 9 is a block diagram showing the configuration of an embodiment of the vector control device according to the present invention, and FIG. FIG. 10 is a block diagram showing a specific configuration of the width correction circuit 21 in the vector control device shown in FIG. 9. 2... Inverter, 3... Induction motor, 8... Current vector calculation circuit, 9... Reference magnetic flux generation circuit, 12
...torque slip calculator, 14...ridge current detection circuit,
19... Voltage detection circuit, 21... Slip correction circuit,
22... Deviation calculator, 23... Multiplier. Agent Patent attorney Tatsuyuki Unuma (8) $y Z. Ku Kaya $7.3

Claims (1)

[Claims] 1. In a vector control device for an induction motor that distinguishes the phase of the primary current of the induction motor into an excitation component current and a torque component current and controls the rotation frequency, detecting the excitation component current of the primary current of the induction motor, An induction motor characterized in that the slip frequency is corrected based on the deviation between the detected value and an excitation current command E of the primary current command, and the reference magnetic flux axis of the -order current command and the actual magnetic flux axis are made to coincide. vector control device.