JPH0667252B2 - Induction motor control system - Google Patents

Description

The present invention relates to a control system for an induction motor, such as a cage induction motor, which controls the primary power supply frequency of an induction motor having a shortened secondary conductor.

Conventionally, there is a device shown in FIG. 1 as this type of device.
(1) is the speed command value And the rotational speed ωr of the induction motor to be controlled to obtain the deviation signal Δωr of both, (2) is the deviation signal Δω
Torque current command that has a predetermined correspondence with r A widening circuit that generates (corresponding component of torque Te in the active current component), (3) relates to the exciting current command in relation to the rotation speed ωr. Circuit that generates (excitation component current, component corresponding to magnetic flux Φ),
(4-1), (4-2), (4-3) are torque current commands And excitation current command Input the absolute current value command Slip angular frequency command (Lr ', rr' are the rotor self-inductance of the induction motor 8 which will be described later, the stator reduced value of the rotor resistance), a circuit for generating a signal, and (5) is a rotation angular frequency ωr and a slip angular frequency command. From the primary frequency command Adder circuit that generates a current absolute value command (6) Phase command And primary frequency command Circuit to generate a three-phase AC signal command (6a)
(7) increases the signal (6a) to increase the current i _M (8) is the current i _M An induction motor driven by, and (9) is a detector that detects the rotation of the induction motor (8) and generates a rotation angular frequency ωr.

Fig. 2 shows the torque current command Excitation current command And absolute value command Phase command It is a vector diagram which shows the relationship of. The motor current i _M is controlled by the following equation so that the vector relationship in the figure is maintained.

When the control is performed as described above, the vector relation of the various quantities inside the motor can be accurately controlled according to the command value even in the transient state when the torque command value changes when the speed command changes, and linear control can be achieved. It has also been proven theoretically. Note that the control corresponding to the field weakening of the DC machine is the excitation current command controlled in relation to the rotation speed ωr. Can be done by.

The problem here is the slip angular frequency command To calculate the secondary self-inductance L which is the motor constant
r ′ and secondary resistance rr ′ are included. When these constants change, an error occurs between the control constant and the actual electric motor constant, and linear control becomes impossible, and changes in the actual magnetic flux and in the actual torque appear. Exciting current command for magnetic inductance considering magnetic saturation However, the secondary resistance fluctuates about 30% depending on the winding temperature.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional ones, and an object thereof is to provide a device that achieves linear control without being affected by a change in secondary resistance.

The main symbols in the following description are as follows.

Subscript (subscript) d or q equivalent biaxial constant (ids) S stator amount (L _S) r rotor weight (Lr) m bond amount (Lm) s1 slip amount (ωs1) T torque amount (i _T) E Excitation current amount (i _E ) e Electric amount (Te) a, b, c Stator phase subscript (superscript) * Command value ′ Stator equivalent rotor amount c Compensation value ・ Vector amount variable and constant v Voltage i current P Differential operator p Number of poles θ Electrical angle T Torque L Inductance n Number of phases φ Linkage magnetic flux Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Third
FIG. 1A shows an embodiment of a control block diagram according to the present invention. The part of the block (100) surrounded by the dotted line in the figure corresponds to the present invention. Motor current sensor (11),
The actual torque component current i _T of the induction motor is calculated by the torque current calculation circuit (13) from the voltage sensor (12), and the adder (14)
The torque current command value And the deviation Δi _T as shown in the figure, and the compensation slip according to the deviation is obtained by the amplifier (15). (However, K's1c compensation gain) is added to the adder (5), Is sent to the three-phase AC signal generation circuit (6).

Fig. 4 shows the vector relationship when there is an error in the actual motor quantities without the * symbol and control commands with the * symbol. Torque current command Is the required torque Is set accurately with a small error. Meanwhile stator current
is is controlled to the required value with very little error. However, a large error occurs in the distribution of the exciting current component i _E and the torque current component i _T. Slip angular frequency command And the actual slip angular frequency ωs1 are given by the following equations.

Compensation slip Can be expected to reduce the accumulated error by correcting the angle error Δθ _T.

To achieve this, the following equation must hold: Here, it should be noted that a proportional relationship is established between the angle error θ _T and the error of the torque component current i _T regardless of the additional condition. Therefore, it is assumed that the compensation slip ωsc ₁ is given by the following equation.

here In other words, from equations (1) to (4) It transforms and the following formula is materialized Thus the time average value _T of the actual torque current i _T is given by the following equation here That is, if the compensation gain Ks ₁ c is sufficiently high, the following equation holds. However, Ks ₁ c +1 ΔR-1 than Ks ₁ c >> ΔR-2 (12) It holds regardless of ΔR. Current amplitude is is the command value Is almost certainly controlled, so the excitation component i _E Is almost equal to. As a result, fluctuations in the rotor magnetic flux and the stator voltage can be greatly reduced.

As understood from the above description, if the correction is performed as shown in FIG. 3 according to the equation (4), the linear control can be achieved without being affected by the change in the secondary resistance.

In addition, K's ₁ c in FIG. 3 is Given in.

Further, instead of adding ω s ₁ c to the addition point (5), the amplifier (15) may be set to (15 ') and added to the addition point (5') as shown in FIG. 3 (b).

Now, FIG. 5 shows an example of a detection circuit of the torque component current i _T. This is a circuit that calculates from voltage and current. This principle will be described below.

Set the quantities of the three-phase windings a, b, and c of the stator to the static d
The shaft winding is converted as shown in FIG. The conversion formula is defined as the following formula.

The two-axis equation of the induction motor in this d, q static coordinate system can be expressed by the following equation. here From equations (16) and (17), if idr ′ and iqs ′ are deleted, here If you put Integrating Eq. (21), the stator-converted rotor linkage flux r '
Is calculated by On the other hand, the torque Te is Becomes

Since the torque component current i _T is a component orthogonal to the secondary interlinkage magnetic flux φr ′ as shown in FIG. 7, it is obtained by the following equation.

As shown in FIG. 5, the torque component current i _T can be detected by using the equations (23) and (24).

As described above, according to the present invention, since the change of the secondary resistance due to the temperature is corrected, the fluctuation of the actual magnetic flux
The fluctuation of the actual torque does not occur, the utilization factor of the device is improved, the cost is reduced, and the control with good responsiveness can always be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of the primary frequency control of a conventional cage-type induction motor. Fig. 2 shows the torque current command Excitation current command And absolute value command Phase command FIG. 3 is a block diagram of a motor constant variation compensation method according to the present invention, FIG. 4 is a vector diagram showing a vector relationship when there is an error between a control command and actual motor quantities, and FIG. The figure shows an example of a conventional circuit for detecting the torque current i _T from the amount of the stator, FIG. 6 shows the relationship between the amount of three phases of the stator and the stationary Cartesian coordinates dq axis, and FIG. [phi] r 'and is a vector diagram showing the relationship between the torque current i _T. (1) ... adder, (2) ... widening circuit, (3) ... exciting current command generating means, (4-1) ... stator current absolute value command generating means, (4-2) ... ... Phase command generating means, (4
-3) ... slip angular frequency command generating means, (5) ... adder, (6) ... three-phase AC signal command generating circuit, (7) ...
… Amplifying circuit for 3-phase AC generation, (8) …… Induction motor,
(9) ... Rotational angular frequency detector The same symbols or corresponding parts in the drawings are shown.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuro Ikeda 1-2-2 Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Electric Corporation Control Works (72) Inventor Hideaki Tomei Hyogo-ku, Kobe-shi, Hyogo 1-2, Wadazakicho Mitsubishi Electric Co., Ltd. Control Works (72) Inventor Yasuhiko Hosokawa 1-2-1, Wadasakicho, Hyogo-ku, Kobe Hyogo Prefecture Mitsubishi Electric Co., Ltd. (56) References JP-A-57-25188 (JP, A)

Claims (1)

[Claims] 1. A frequency control means for controlling a power supply frequency and a slip frequency to an induction motor having a primary winding and a short-circuit secondary conductor supplied from a variable frequency power supply device, and a desired torque or a representative value of the torque. Excitation component command And the torque component command In contrast to the above slip frequency command In the induction motor control system provided with the slip frequency command means for commanding (where K ₂ is a constant) to the frequency control means, i _T = (iqsφdr′−idsφqr ′) / | φr ′ | where iqs is the q-axis The stator current ids is the d-axis stator current φdr 'is the stator-equivalent d-axis stator flux φqr' is the stator-equivalent q-axis stator flux φr 'is calculated by the rotor-equivalent rotor flux. Actual torque amount i _T and torque current command according to desired torque Take the deviation Δi _T with, compensation slip ωs ₁ in accordance with the deviation
= Ks ₁ Δi _T (where Ks ₁ is the compensation gain) is the slip frequency command To the frequency control means to compensate for the change in the motor constant.