JPS6225888A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To detect the rotational speed precisely at all times by detecting the primary frequency and the slip frequency from the primary voltage and primary currents of an induction motor and detecting the rotational speed by a deviation between the primary frequency and the slip frequency. CONSTITUTION:A frequency arithmetic circuit 11 arithmetically operates the primary frequency and slip frequency of an induction motor from the primary currents and primary voltage of the induction motor 1 detected by a current detector 2 and a voltage detector 3. A subtracter 12 acquires a difference between primary frequency and slip frequency, and obtains the speed of revolution. A deviation between a speed command and the speed of revolution is inputted to a current vector arithmetic circuit 13, and the arithmetic circuit 13 transmits the amplitude of primary currents and a phase command over a current control circuit 14 for a frequency converter 4. Accordingly, excellent response characteristics are acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an induction motor control device capable of controlling the speed of the induction motor without using a speed detector for detecting the rotational speed of the induction motor.

[Conventional technology]

FIG. 9 is a block diagram showing a conventional control device for an induction motor, which is shown in the literature (Proceedings of the 1984 National Conference of the Institute of Electrical Engineers of Japan, Lecture 7g6602.1984).
In the figure, 1 is an induction motor, 2 is a current detector that detects the primary current of the induction motor 1, 3 is a voltage detector that detects the primary voltage of the induction motor 1, and 4 is a variable voltage detector that detects the primary voltage of the induction motor 1. 5 is a speed command signal generator, 6 is a speed control circuit, and 7 is a current detector 2.
and a slip frequency calculation circuit that calculates the slip frequency of the induction motor 1 based on the output of the voltage detector 3.

8 is a speed calculation circuit that calculates the rotational speed of the induction motor 1 based on the outputs of the speed control circuit 6 and the slip frequency calculation circuit 7; 9 is a current vector calculation circuit; and 10 is a current control circuit.

A vector control method is known as a variable speed control method for the induction motor 1, and first, this vector control method will be explained. As is well known, the voltage equation on the secondary side (rotor side) of the induction motor on the stator coordinate axis (referred to as the d-9 coordinate axis) is given by the following equation.

However, ids l ;q, h The d-axis and q-axis components Φ2d and Φ2q of the primary current are the d-axis of the secondary magnetic flux, and the 9 components P = d
/dt is a differential operator ω, the rotational speed R2, L2 . M is the secondary winding resistance of the induction motor,
The secondary winding inductance and the primary and secondary mutual winding inductance.

Next, the rotating coordinate axis (de
-9@coordinate axis) To convert to the above relational expression, the relational expression of coordinate rotation shown by the following expression is used.

However, oa-4ωodt...
・Time・(41id”龜、iQ'l i 1st S&
I's de axis! q' @e, minute Φ2a@, Φzq@n
2nd order a bundle tD de axis + q' axis component + 2),
By substituting equation (3) into equation (1) and eliminating jds, jqs, and Φ2q, the following equation is obtained.

(R2+PL2)Φ2ae-MR2id"s-Lz(
ωa-G),)Φ2Q' = O・= (5)(R2+
PL2) (1) 24”-MR2iq”s+L2(ωo-
ωr) Φ2de=0 ・−・(6) Here, Φ2q6
Find the conditions for =0. (5) , (Φ2 in formula 61
By setting Q@=O, the following equation is obtained.

From equation (5).

Φ2d0=id6s ・・・・・・・・・・・・
...(7)1+PT2 From equation (6), however, T2 = L2 /R2 At this time, the generated torque TM of the induction motor is expressed by the following equation as is well known.

However, Pm is the number of pole pairs. Therefore, if the angular velocity ω0 of the rotating coordinate axis is determined according to equation (8), Φ2 qa can always be set to zero.

At this time, if id"i is kept constant, Φ
Since 2d' is also constant, 5 generated torque TM tri (
From equation (9), f is proportional to Q”a. Also, from equation (7), i
d'm is a component in phase with Φ2d', and Φ2d'' does not change due to a change in 1q6s, so jq@a is Φ
It can be seen that this is a component orthogonal to 2 de. From this! d'a,! q6- is the exciting current component,
This is called the torque current component.

The second term on the right side of equation (8) is proportional to l q''* in the case of rotation with the secondary magnetic flux vector.

Vector control is a control method based on the above principle, in which excitation current component id%, ) torque current component i Q6. The respective commands 1ds and IQ- are given from the outside as reference quantities. At this time, the command for the primary current to be supplied to the induction motor becomes the following equation from equation (2).

θo*=Jωo* at ・・・・・・・・・
......αυ(71, from formula (8), therefore, by the current control circuit, 1 given by formula 00
By supplying the induction motor 1 with a primary current according to the next current command, vector control becomes possible.

The current vector arithmetic circuit 9 in FIG. 9 is constructed according to the circuit configuration of the frequency converter 4. When a current type inverter circuit is used as the frequency converter 4 based on the α[~a7J formula,
The amplitude of the primary current is independently controlled by the converter circuit, and the phase of the primary current is independently controlled by the inverter circuit. In this case, the following equation can be obtained by transforming equation 01.

ids” = '17 i d's*2+ i q's
*2aos (θ.′1Δθ)−30,Q3) However, Δ
θ= tan-'(ig@s"/id's")
...... a4 Therefore, the current vector calculation circuit 9 calculates the torque current component command 1q- and the rotational speed ω.
r, the amplitude of the primary current command fT]77]]τζ1
- and phase (θ.′+Δθ). At this time, if the excitation current component command i d's* is constant, 1d8 can be treated as a constant.

The current control circuit 10 inputs these amplitude commands and phase commands and outputs a control signal to the frequency converter 4 (current type inverter circuit here).When performing speed control, it generates a speed command signal. The deviation between the output of the motor 5 and the actual rotational speed is amplified by the speed control circuit 6, and the output thereof is given as a torque current component command 1 q''a.

In this way, in order to control the speed of an induction motor using vector control, it is necessary to detect the actual rotational speed. For this purpose, the slip frequency calculation circuit 7 in FIG.
and a speed calculation circuit 8 were used.

First, the principle of slip frequency calculation will be explained. As mentioned earlier, the slip frequency ωS is the second right-hand side of equation (8).
However, this is only applicable when vector control is applied. Generally, it can be obtained from equations (51 and (61). That is, by multiplying both sides of equations (5) and (6) by Φ2q@ and Φ2d@, respectively, and rearranging, the following equation is obtained.

Here, since the d6-9e coordinate axis is rotating at an angular velocity ω0, on this coordinate axis, (Φ2d@.

Φ2q@) and (p@zd”, PΦ2q”) (
7) The component 'It has 2 and 2 O vectors are orthogonal. α
The numerator of the first term on the right side of Equation 9 represents the inner product of these vectors, so it is zero. Therefore, (1!19. From the equation, the following equation is obtained.

Furthermore, using equations (2) and (3), ld”s, 1
46m, Φ2d@.

By eliminating Φ2q''', the following equation is obtained.

Therefore, Φ2d, Φ2. If we know ωS, we can obtain ωS.

By the way, as is well known, the voltage equation on the primary side (stator side) of the induction motor on the a-q coordinate axis is given by the following equation.

R+ and Ll are the primary winding resistance and primary winding inductance of the induction motor (IFj formula, and Φ2d and Φ2q are given by the following formulas.

Therefore, ida, jqs, Vda, YQm
If detected, Φ2d.

Φ2. can be calculated, ω8 of equation (I7) can be obtained.

The slip frequency calculation circuit 7 in FIG. 9 calculates the α equation based on the output of the current detector 2, the output of the voltage detector 3, and the constant of the induction electric current generator, and outputs the slip frequency ω8. . At this time, the primary current and primary voltage of each winding of the induction motor are usually detected by the current detector 2 and the voltage detector 3, respectively, but these detected amounts are expressed by the following equation as well-known: It is converted into components on the dq coordinate axes.

Next, the principle of speed calculation in the speed calculation circuit 8 will be explained. First, the slip frequency ω8 obtained from the force formula is
It represents the slip frequency of the induction motor regardless of whether vector control is applied. On the other hand, when vector control is applied, the slip frequency becomes the second term on the right side of equation (8). Furthermore, if the excitation vit flow component jd''a is kept constant, the slip frequency command ω shown by the second term on the right side of the equation for α
− is obtained.

Therefore, it is only necessary to calculate ωr so that the slip frequency command ωS and the slip frequency ωS output from the collapsing frequency detection circuit 7 always match.

FIG. 10 shows the configuration of a speed calculation circuit 8 based on this principle. In FIG. 1, 81 is a counter, 82 is a subtracter, and 83 is an integrator.

Next, the operation will be explained. When the torque current component command 1q@ output from the speed control circuit 6 is input to the counter 81, the slip frequency command ωS9 shown by the second term on the right side of the equation for α is obtained as an output. The deviation between this slip frequency command ωS1 and the slip frequency ωS output from the slip frequency detection circuit 7 is obtained by a subtracter 82 and inputted to an integrator 83, thereby obtaining an estimated value Qf of the rotational speed. This estimated value rr is then used as the actual rotational speed. As a result, since ωS is controlled to always match ωS, an accurate estimate of the rotational speed ωr can be obtained.

[Problem that the invention seeks to solve]

Since the conventional induction motor control device is configured as described above, it is necessary to detect an accurate slip frequency. However, since the secondary magnetic flux is calculated using the H formula, there is a problem that the secondary magnetic flux cannot be calculated accurately due to the drift of the integrator during low-speed rotation, resulting in an error in the slip frequency calculated using the formula (7). But nine.

In addition, the rotational speed is obtained by integral operation from the command value and the detected value of the slip frequency, but if the time constant of integration is not selected optimally, an error will occur in the estimated value of the rotational speed in a transient state, resulting in a poor transient response. There was a problem that the characteristics could not be obtained.

This invention was made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a control device for an induction motor that can accurately detect rotational speed even at low speeds and that can always provide good transient response characteristics. purpose.

[Means for solving problems]

The control device for an induction motor according to the present invention detects a primary frequency and a slip frequency from a primary voltage and a primary current of an induction motor, and detects a rotational speed as a deviation thereof. It is used.

[For production]

The rotational speed detection means of the present invention does not require secondary magnetic flux as the amount of information, and by detecting the primary frequency and the vector frequency, it is effective as a means for always accurate rotational speed detection in the entire speed range. act.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 9 are designated by the same reference numerals.

In FIG. 1, 11 is a frequency calculation circuit, and 12 is for calculating the difference (ω〇−ωS) between the one-miss frequency ωG of the induction motor 1 outputted from the frequency calculation circuit 11 and the slip frequency ωS to obtain the rotational speed ωrt−. , a subtracter 13f-t, a current vector calculation circuit, which has a configuration similar to the current vector calculation circuit 9 shown in FIG. The current vector calculation circuit 10 has a configuration similar to that of the current vector calculation circuit 10.

Hereinafter, each component will be described in more detail while showing examples of the components. First, the frequency calculation circuit 1 in the embodiment shown in FIG.
Before explaining the configuration of Embodiment 1, the principle of calculating the primary frequency and slip frequency will be explained. By differentiating both sides of the above equation (3), the following equation is obtained.

By transforming the equation (22), the following equation is obtained.

PΦ2, e−ω0Φ2q”=PΦ2d008θo−1
−PΦ2qffilflθ, ・(23)PΦ2qe+
ωoΦ2df''=-pΦ2,1 sinθo+PΦ2q
CO8θo...-(24) So, if de -9
If the angular velocity (first-order frequency) ω0 of the 6-coordinate axis is selected so that Φ2q6 is always zero, the left sides of equations (23) and (24) become PΦ2d" and QIQΦ2d6, respectively. Therefore, if Φ2de is known, % (24 ) the right side of the equation is Φ2
By dividing by de, the angular velocity (primary frequency) ω0 can be estimated.

By the way, when Φ2Qe=0 always holds true, the relationship of equation (7) holds as explained earlier. and,
If the angular velocity ωO is known from the relationship in equation (2), the id' required for calculating equation (7) is the primary current 1 dl, lqm
Determined from From these relationships, dividing the right side of equation (24) by Φ2d6 calculated from equations (2) and (7), we get
Since the angular velocity ω0 is found and θ0 of equation (4) is also obtained,
The calculation of equation (2) becomes possible. Furthermore, calculation of equation (24) is also possible.

If the estimated value of the trivial angular velocity ωO obtained in this way is wrong, Φ2q11 will not be zero, so
The value of equation (23) is no longer zero. Therefore, by correcting the estimated value of ω0 so that the value of equation (23) becomes zero, an accurate estimated value of ω0 can always be obtained.

(23), PΦz required for calculation of equations (24), 1.
PΦ2q is the primary voltage Vds from the following equation, which is a modification of the aFj equation.

vQCs'' order current 1 dB, lq. It can be calculated from the constant of the induction motor. Moreover, since an integrator is not required, accurate PΦ2d and PΦ2° can always be obtained in the entire speed range.

At this time, since j q''s can also be obtained from the relationship in equation (2), the slip frequency ωS can be obtained by calculating the second term in equation (8).

FIG. 2 shows an example of the frequency calculation circuit 11 based on the above principle. In the figure, 110 is a magnetic flux change calculation circuit;
20.1.40 is a coordinate conversion circuit, 130 is a 3-phase/2-phase conversion circuit, 1501, 1503.1505 is a counter, 15
02.1509 is a subtracter, 1504 is an integrator, 1506
．． 1507 is a divider, 1508 is a differentiator, 1510 is an amplifier, and 1511 is an adder.

The magnetic flux change calculation circuit 110 calculates the primary voltage '1114+v
Input s and primary current 1ux, l□ (20),
(25) is calculated and PΦ26. PΦ2. (The circuit configuration will be described later).

The coordinate conversion circuit 120 calculates PΦ2d, PΦ2qt-manually (23), (24) and performs equation (1) K.
PΦz ao−QIO(2)2 q” +PΦ2q″+
This is a circuit that outputs ω0Φ2de (circuit configuration will be described later)
.

The three-phase/two-phase conversion circuit 130 has a primary current iu.

Input i□ and perform the calculation of formula (21) to calculate % 1ds
This is a circuit that outputs tiQ'' (the circuit configuration will be described later).

The coordinate conversion circuit 140 is a circuit that inputs Ida and lqm and outputs id "l + iQ".

The calculation of equation (7) is performed by the counters 1501, 1503. Subtractor 1
502 and an integrator 1504, Φ2d@
is obtained. PΦ2 output from the coordinate conversion circuit 120
Divider 1507 q6+ω0Φ2d@ by this Φ2d”
By dividing by , the estimated value ω0' of the primary frequency is obtained. Also, PΦ output from the coordinate conversion circuit 120
2d"-ω mouth Φ2q@ and PΦ2d@ obtained as the output of the differentiator 1508 are subtracted by a subtracter 1509 to obtain ω0Φ2q#', which is amplified by an amplifier 1510 and then divided by an adder 1511 into a divider 1507. By adding the output of ω0 to the output of

By inputting j qZ obtained as the output of the coordinate conversion circuit 140 into the counter 1505 and dividing it by Φ2d@ in the divider 1506, the slip frequency ωB given by the second term on the right side of equation (8) is obtained. It will be done.

FIG. 3 is an example of the three-phase/two-phase conversion circuit 130 in FIG. 2. In the figure, 1301.1302°130
3 is a counter, and 1304 is an adder. This circuit performs the calculation of equation (21) and obtains Ids and jqs.

FIG. 4 is an example of the magnetic flux change amount detection circuit 110 in FIG. 2. In the figure, 1101, 1103° 110
6.1107, 1109.1112 are counters, 1102
゜1108 is a differentiator, 1104.1110 is an adder, 1
105°1111 is the subtracter, 1113.1114 is the third
This is a three-phase/two-phase conversion circuit having the configuration shown in the figure.

First, it is obtained as the output of the 3-phase/2-phase conversion circuit 1114! When da t is input to the counter 1101 and the differentiator 1102, R+ +PL1 is output as the output of the adder 1104.
aidm is obtained. Furthermore, this output is subtracted by a subtractor 1105
When subtracted from Vd obtained as the output of the three-phase/two-phase conversion circuit 1113, PΦ2d of equation (25) is obtained as the output of the counter 1106. PΦ2q can also be obtained by a similar operation.

FIG. 5 is an example of the coordinate conversion circuit 120 in FIG. 2. In the figure, 1201 is a V/F converter, 120
2 is a counter, 1203.1204 is a ROM, 1205
, 1206, 1207, 1208 are D with multiplication function.
/A converter, 1209 is an adder, and 1210 is a subtracter.

Next, the operation will be explained. First, the adder 15 in FIG.
The analog signal 1 of ω0 obtained as the output of 11, V/
By inputting it to the F converter 1201, a pulse train with a frequency proportional to the magnitude of ω0 is obtained. Next, by counting this pulse train with the counter 1202, (4)
A digital quantity of the phase θ0 of the rotating coordinate axis is obtained as shown by the equation.

Then, when the output of the counter 1202 is input as the address of the two ROMs 1203 and 1204 that store the values of the sine waves sinθ0 and cogθ0, the two sine waves s
inθ. and cos θ0 digital values are output.

These digital values and the outputs Φ2d and Φ2q of the magnetic flux change detection circuit 110 are converted to a D/A converter 1205.
Multiply by ~1208, adder 1209 and subtracter 121
When inputting 0, (23), (by calculation of the following equation, P
Φ2d@-GJ (1Φ2q' and PΦ2..+ωoΦ2
de is obtained as the respective output.

Since the coordinate conversion circuit 140 in FIG. 2 can be configured in the same manner, explanation of the circuit configuration etc. will be omitted.

FIG. 6 shows the current vector calculation circuit 1 in the embodiment shown in FIG.
This is an example of No. 3. In the figure, 1301 is a divider;
02 is a counter, 1303 is an adder, 131 is a coordinate conversion circuit, and 132 is a 2-phase/3-phase conversion circuit.
When q@ is divided by ia- given as a preset amount in the divider 1301 and inputted to the counter 1302, the second term on the right side of the α2 equation is calculated, and the slip frequency command ω3 becomes can get. This ω3 and the estimated rotational speed ωr (=ω
O−ωS) is added by the adder 1303 to perform the calculation of the α-side formula, and obtain the one-missing frequency command ω0. These ω0 and 1dsylQ8 are the coordinate conversion circuit 1
31, the calculation of the Ql and tiυ expressions is performed, and jds and 44s are obtained. This coordinate conversion circuit 1
The configuration of 31 is similar to the configuration of the coordinate conversion circuit 120 shown in FIG. 5, so a description thereof will be omitted.

Then, by inputting the above 1ds and 1q4 to the two-phase/three-phase conversion circuit 132, the command Su of the primary current to be actually supplied to the induction motor can be obtained from the relationship of equation (21).
m, ImaS are obtained.

FIG. 7 shows an example of the frequency converter 4 in the embodiment shown in FIG. In the figure, 40 is a DC power supply, and 41 is a transistor inverter circuit using a power transistor as a switching element.

FIG. 8 shows an example of the current control circuit 14 in the embodiment shown in FIG. 1, and this circuit controls the primary current supplied to the induction motor 1 by, for example, the frequency converter 4 having the configuration shown in FIG. Used when In the figure, 1400.
1405 and 1410 are subtracters, 1415 is an adder, 1
420.1425 and 1430 are amplifiers, 1435 is a triangular wave generation circuit, 1440.1445 and 1450 are comparators, and 1455.1460 and 1465 are NOT circuits.

Next, the operation of this current control circuit 14 will be explained.

First, when controlling the U-phase primary current 1us of the induction motor 1, the deviation between the U-phase primary current command ius'' and the actual primary current jug obtained from the current detector 2 is calculated using a subtractor. 1400 and amplifying this deviation with an amplifier 1420, the U-phase primary voltage command Vus is obtained.By similar operation, the V-phase primary voltage command vw@, v-phase 1
The next voltage command Vwm is obtained.

These primary voltage commands Vus, Vvs and Vwa
is a triangular wave generation circuit 1435, a comparator 1440.14
45 and 1450, and NOT circuits 1455, 1460 and 1465, the signal is converted into a control signal for the transistor inverter circuit 41. As a result, primary voltages Mum, Vvs, and Vws such that the current deviation becomes zero are applied to the induction motor 1.

In the embodiment shown in FIG. 2, the differentiator 1508 can be omitted if Φ2d'' is controlled to be constant.Also, if the amplifier 1510 is given integral characteristics and the gain is set sufficiently high, , Φ2.@ are always zero, the correction amount Δω0 of ω0 is calculated, so ΔωO can be used as ω0, and the divider 1507 can be omitted.

Since ω0 in this embodiment is the angular velocity of the secondary magnetic flux vector, ω0 obtained in the embodiment of FIG. 2 may be used instead of ωG* in the embodiment of FIG. 6. In the example shown in Figure 2! 46s and Iq- are obtained, so that they match the respective commands, s 1d6s
A current control circuit having 11q''s feedback loops may be configured.

In the embodiment shown in FIG. 1, the case where vector control is used has been described, but in the embodiment shown in FIG. 2, accurate ωa and ω8 can always be obtained regardless of whether vector control is applied.

Therefore, it goes without saying that the present invention can be applied not only to ordinary slip frequency control but also to speed control of an open loop control system of an induction motor using constant V/F control.

〔Effect of the invention〕

As described above, according to the present invention, the primary frequency and slip frequency are detected from the primary voltage and primary current of the induction motor without using an integrator, so it is always accurate in all operating ranges. This has the effect that the primary frequency and slip frequency can be detected.

Furthermore, since the rotational speed can be detected as the difference between the primary frequency and the slip frequency, it is possible to obtain an induction motor control device with excellent transient response characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a control device for an induction motor according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a frequency calculation circuit included in the embodiment of FIG. 1, and FIG. A block diagram of a three-phase/two-phase conversion circuit included in the embodiment of
4 is a block diagram of the magnetic flux variation calculation circuit included in the embodiment of FIG. 2, FIG. 5 is a block diagram of a coordinate conversion circuit included in the embodiment of FIG. 2, and FIG. A block diagram showing an example of the current vector calculation circuit included in the embodiment, FIG. 7 is a block diagram showing an example of the frequency converter included in the embodiment of FIG. 1, and FIG. 8 is a block diagram showing an example of the frequency converter included in the embodiment of FIG. FIG. 9 is a block diagram showing an example of the current control circuit included. FIG. 9 is a block diagram of a conventional induction motor control device. FIG. 10 is a block diagram of a speed calculation circuit included in FIG. DESCRIPTION OF SYMBOLS 1... Induction motor, 2... Current detector, 3... Voltage detector, 4... Frequency converter, 5... Speed command signal generator, 6... Speed control circuit, 11 . . . frequency calculation circuit, 12 . . . subtracter, 13 . . . current vector calculation circuit, 14 . . . current control circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent Applicant Mitsubishi Electric Co., Ltd. Agent Patent Attorney 1) Hiroshi Sawa (2 others) 4rIIJ Figure 6 Procedural Amendment (Voluntary)

Claims (2)

[Claims] (1) A variable voltage, variable frequency frequency converter, an induction motor driven by the frequency converter, and a speed control circuit that receives a speed command signal input from the outside and controls the rotational speed of the induction motor. , a current detector that detects the primary current of the induction motor, a voltage detector that detects the primary voltage of the induction motor, and an output signal of the current detector and an output signal of the voltage detector to detect the induction motor. electric motor 1
a frequency calculation circuit that calculates a secondary frequency signal and a slip frequency signal; and a subtracter that adds a difference signal between the primary frequency signal and the sliding frequency signal to the speed control circuit as a speed feedback signal of the induction motor. A control device for an induction motor. (2) The frequency calculation circuit is characterized by having a magnetic flux change amount calculation circuit that calculates the amount of change in magnetic flux based on the output signal of the voltage detector, the output signal of the current detector, and the constant of the induction machine. A control device for an induction motor according to claim 1.