JPH04304185A - Motor control method - Google Patents

Abstract

PURPOSE:To improve transient speed control response to super low speed operation by detecting a rotational speed and prolonging the zero output duration of an inverter if the difference between thus detected rotational speed and a desired rotational speed is small when a switching pattern written into a ROM is read out and an AC motor is controlled. CONSTITUTION:A switching pattern written into a ROM 5 is read out and six switching elements A1-C2 in an inverter 2 are controlled in response to a control signal fed from a driving circuit 4 thus subjecting a DC power supply 3 to VVVF conversion. An induction motor 1 is rotated with the VVVF power and a rotational speed signal or information relevant thereto is obtained through a speed detector 9. The ROM 5 is then controlled so that the zero vector output duration of the inverter is prolonged as the difference between thus obtained information and a reference signal 11 decreases. According to the invention, speed control response is improved easily at the time of transition to super low speed operation.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method for controlling an inverter by writing a PWM (pulse width modulation) switching pattern (unit vector data) in a memory in advance and reading it out, thereby controlling an AC motor connected to the inverter. The present invention relates to a speed control system, and more particularly, to a method for improving speed control response during transients in a control system that can obtain ultra-low speed operating conditions with a relatively simple configuration.

0002

[Prior Art] In order to control the speed of an AC motor, P
It is known to use WM controlled inverters. It is also known that in order to perform PWM control, a PWM switching pattern is written in advance in a ROM so that an approximate sine wave can be obtained, and the inverter is controlled based on this. Furthermore, a method has already been proposed in which a three-phase inverter is not controlled independently of each phase, but all three phases are collectively controlled, a desired voltage vector is generated, and a desired rotating magnetic field is obtained. Furthermore, the speed of the AC motor connected to the inverter is controlled by reading out the PWM switching pattern from a memory in which the PWM switching pattern for pulse width modulation (PWM) control of the inverter is written and controlling the inverter. In the control method, a detection signal indicating the rotational speed of the motor or information related to the rotational speed is obtained, and this detection signal and a reference signal indicating the desired rotational speed of the motor or desired information related to the rotational speed are combined. Japanese Patent Application Laid-Open No. 62-207196 discloses that the readout of the memory is controlled so that the zero vector output time of the inverter becomes longer as the difference between the two becomes smaller.

0003

However, in the above method, the amplitude of the primary magnetic flux linkage becomes small during the transient period, and a good speed control response during the transient period cannot be obtained. This is because, although primary current is flowing through the motor in order to output torque for a desired speed response, the primary voltage of the motor becomes smaller due to the voltage drop due to the motor's primary winding resistance. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control method capable of achieving a good speed control response during the above-mentioned transition.

0004

[Means for Solving the Problems] To achieve the above object, the present invention reads a PWM switching pattern for pulse width modulation (PWM) control of an inverter from a memory in which the PWM switching pattern is written. In the method of controlling the speed of an AC motor connected to the inverter by controlling the inverter, a detection signal indicating the rotational speed of the motor or information related to the rotational speed is obtained, and this detection signal and the motor In addition to controlling the readout of the memory so that the zero vector output time of the inverter becomes longer as the difference from a reference signal indicating desired information related to the desired rotation angle or rotation speed of the motor becomes smaller; obtaining a detection signal indicative of a primary magnetic flux linkage or information related to the primary magnetic flux linkage, and combining the detection signal with a signal indicative of a desired primary magnetic flux linkage or desired information related to the primary magnetic flux linkage for the motor; This relates to a motor control method using an inverter, characterized in that the primary flux linkage of the motor is controlled to be constant by outputting a vector in the normal direction instead of the zero vector so that the difference is small. be.

[0005]

[Operation] In the above invention, for example, when the speed of the motor is increased, the primary current of the motor to output torque for a desired acceleration increases, and the voltage drop due to the motor's primary winding resistance causes the motor's primary linkage magnetic flux to increase. When becomes small, the normal direction (
This outputs a vector in the radial direction) and attempts to keep the motor's primary flux linkage constant. Thereby, desired acceleration can be easily obtained.

[0006]

Embodiment First, the principle of a method for detecting primary magnetic flux linkage in a motor control method according to an embodiment of the present invention will be explained.

The characteristic equation of the induction motor can be expressed by the following equation (1).

[0008]

[Math 1]

[0009] Here, v1 is the primary voltage vector, R1
is the primary winding resistance, i1 is the primary current vector, R2
is the secondary winding resistance, i2 is the secondary current vector, L11
is the primary winding inductance, L22 is the secondary winding inductance, ωω is the rotor rotational angular velocity, M is the primary and secondary winding mutual inductance, d/dt is the differential operator, P
is the polar logarithm.

The induced electromotive force E due to the primary magnetic flux linkage φ1 is given by the following equation (2). E=L11di/dt+Mdi/dt (2) Therefore, the primary flux linkage vector φ1 is expressed by the following equation (3).

[0011]

[Math 2]

If both sides of equation (3) are divided by L11 and this instantaneous vector is designated as i0, the following equation is obtained. i0 =φ1 /L11=i1 +Mi2 /L11
(4) This corresponds to the excitation current for the primary flux linkage, and from this relational expression, an equivalent circuit regarding the vector i0 of the induction motor as shown in FIG. 1 can be obtained.

From equation (1), v1 can be expressed by the following equation (5). v1 = (R1 + dL11/dt) i1 + (dM/
dt) i2 ...(5) When i2 is deleted from equations (3) and (5), the following equation (6) is obtained.
is obtained.

v1 = (R1 +dL11/dt)i1 +d(φ1
−L11i1 )/dt=i1 R1 +(dL11
/dt) i1 +dφ1 /dt-(dL11/dt)
i1 dφ1 /dt=v1 +i1 R1...
(6)

The primary flux linkage vector φ1 is expressed by the following equation (7
) is given by

[0016]

[Math 3]

When expressed in orthogonal coordinates of the d and q axes, the following equation is obtained.

[0018]

[Math 4]

[0019] Therefore, the obtained primary magnetic flux linkage is expressed by the following equation.

[0020]

[Math 5]

Three-phase/two-phase conversion equations for primary voltages V1a, V1b, V1c and primary currents I1a, I1b, I1c are given by the following equations (9) and (10).

[0022]

[Math 6]

Equations (8), (8b), (9), (10) show the process of determining the primary magnetic flux linkage from the primary voltage and primary current.
A block diagram of this is shown in FIG. 2.

Next, a three-phase motor speed control system according to an embodiment of the present invention will be specifically explained. In Figure 3,
A three-phase inverter 2 capable of PWM control is connected to a motor 1 consisting of a three-phase induction motor. The inverter 2 includes a DC power supply 3 and a switching element A1 consisting of a transistor.
, A2, B1, B2, C1, and C2 are bridge-connected. 6 switch elements A1 to C2
is turned on and off in response to a control signal supplied from the drive circuit 4. Note that the upper three switch elements A1, B1, and C1 of the inverter 2 and the lower three switch elements A2, B2, and C2 operate in opposite directions, so if one control is specified, the control of the entire inverter is controlled. Controls are identified. Here, the inverter control state is specified by the first, second, and third signals A, B, and C read from the ROM (read-only memory) 5, and the signals A, B, and C are at high level, that is, logic "1". ”, the switching elements A1, B1, and C1 are turned on, and when the level is low, that is, logic "0", the switching elements A1, B1, and C1 are turned off.

[0025]

[ROM address explanation] ROM5 sets inverter 2 to PW
A PWM switching pattern (unit vector) for M control is written in advance. This ROM5 includes forward rotation PWM pattern memories M1 and M5, forward rotation zero vector memory M2, reverse rotation PWM pattern memories M3 and M7, reverse rotation zero vector memory M4, normal rotation normal vector M6, and reverse rotation normal vector. M
It has 8. Each of the memories M1 to M8 has 512 addresses from 0 to 511, and each memory is addressed by the value of the 9-bit binary output line 6a of the up/down counter 6. However, one of the eight memories M1 to M8 is selected, and only the output of this selected memory is effectively used for controlling the inverter 2. In order to perform this selection, the ROM 5 has a zero vector selection control terminal 7, a forward/reverse rotation selection control signal input terminal 8, and a normal vector selection control terminal 42. First, when the normal vector selection control signal terminal 42 is at logic "0", M1 to M4 including zero vector memories are selected. Also, logic “1”
In this case, M5 to M8 including the normal vector memory are selected. Next, when the zero vector selection control signal input terminal 7 is logic "0", the memories M1 and M3 or M5
When the logic is "1", one of the memories M2 and M4 or M6 and M8 is selected. Furthermore, when the forward/reverse rotation selection control signal input terminal 8 is “0”, the memories M1 and M2
, or M5 and M6, and when it is "1", either one of memories M3 and M4, or M7 and M8 is selected. Now line 6a
If the 9 bits of input terminal 42 are represented by 9 bits B0 to B8, the input bit of input terminal 7 is represented by B9, the input bit of input terminal 8 is represented by B10, and the input bit of input terminal 42 is represented by B11, then B0 The address is specified by 9 bits of ~B8. Also, B9, B10, B1
If 1 is expressed as [B11, B10, B9], then [000
], the first memory M1 (forward PWM switching pattern) is selected, and when [001], the second memory M2 (normal zero vector) is selected, and when [001]
], the second memory (zero vector for normal rotation) is selected, and similarly, at [111], M8 (normal vector for reverse rotation) is selected.

In order to control the output voltage of the inverter 2 by controlling the ROM 5 and the counter 6, a speed detector 9 consisting of a speed generator is connected to the motor 1, and this output line 9a is connected to a comparator circuit 10. There is. For this reason, the comparator circuit 10 compares the speed detection signal consisting of a DC level with a reference signal corresponding to a desired rotational speed given from the reference signal line 11, and outputs a difference signal. Comparison circuit 1
The difference signal obtained from 0 is, for example, K(1+1/TiS)
The signal passes through a proportional-integral circuit 12 whose characteristics are expressed as follows. The difference signal VD on the output line 13 of the proportional-integrator circuit 12 is input to the first comparator 14 for determining whether the difference signal VD is positive or negative, and also passes through the absolute value circuit 15 to the second comparator 1.
Enter 6.

The output terminal of the first comparator 14 is connected to the counter 6.
It is connected to the up/down input terminal U/D of the ROM 5, and also to the forward rotation/reverse rotation selection signal input terminal 8 of the ROM 5.

[0028] 17 is an oscillator (OSC), and 20-
Generates a clock pulse of about 50kHz. The output terminal of this oscillator 17 is connected to one input terminal of an AND gate 18, and the output terminal of this AND gate 18 is connected to the clock input terminal CL of the counter 6.
The output of the oscillator 17 is input to the counter 6 as a clock pulse only when the other input terminal of the AND gate 18 is at a high level.

A triangular wave generator 19 is connected to the non-inverting input terminal of the second comparator 16. For example, the triangular wave generator 19 has a frequency of 1.5 kHz, which is lower than the output frequency of the oscillator 17.
A triangular wave voltage Vc (carrier) is generated at z, and this V
c and the absolute value of the difference signal VD are compared by a comparator 16. The output terminal of the second comparator 16 is connected to the input terminal of the AND gate 18 via the NOT circuit 20, and also to the zero vector selection control signal input terminal 7 of the ROM 5.

The magnetic flux detection circuit 100 is configured to detect magnetic flux based on the output voltage and current of the inverter 2. Therefore, the three output lines 31a of the inverter 2
and a current sensor 4 for detecting the input current of the motor 1
Three output lines 34a, 3a, 43b, and 43c, are connected to the magnetic flux detection circuit 100. Magnetic flux detection circuit 100
The output line 101 of is connected to the terminal 42 of the ROM5.

FIG. 4 shows the magnetic flux detection circuit 100 in detail. According to equation (9), the voltage value of the output line 31a of the inverter 2 is converted to a three-phase to two-phase conversion circuit 31 constituted by an operational amplifier.
input and convert it into two phases of Vd1 and Vq1. Also, the expression (
10), the output current of the inverter 2 is detected by the current sensor 43.
Id1
, Iq1. According to equation (8), Id1 is multiplied by the primary winding resistance R1 of the three-phase induction motor 1 in the multiplier 35.
, and the adder 32 adds it to Vd1. Furthermore, the value is integrated by the integrator 33 to obtain the temporary interlinkage magnetic flux φd for the d-axis.
Find 1. Similarly, Iq1 is multiplied by R1 in a multiplier 36, and added to Vq1 in an adder 37. Furthermore, the value is passed to the integrator 38
The temporary interlinkage magnetic flux ψq1 for the q-axis is obtained by integrating. Further, in step 39, the sums of the squares of ψd1 and ψq1 are summed, and the square root is taken to obtain the detected value |ψ1 | of the primary flux linkage. The detected value of the primary magnetic flux linkage |φ1 is detected by the hysteresis comparators 40 and 41 having a hysteresis comparison width of Δ|φ1|
| and the primary flux linkage command value |φ1a| are compared. In other words, when |ψ1 | further increases beyond |ψ1a|+Δ|ψ1 |, the comparator 41 outputs logic “0” and the RO
Blocks M1 to M4 containing zero vectors in M5
Select. Also, |φ1 | is |φ1a|−Δ|φ
If the value exceeds 1 | and further decreases, a logic "1" is output and the block M5 containing the normal vector is stored in ROM5.
Select M8.

[0032]

[Contents of ROM] Data is written in the ROM 5 as shown in principle in FIG. That is, each memory M of ROM5
1 to M8 have addresses 0 to 511, and normal rotation PWM
For example, data of voltage vectors V6, V2, V6, and V2 are sequentially written to addresses 0 to 3 of pattern memories M1 and M5, and zero vector memory for normal rotation M2.
Addresses 0 to 3 contain zero vectors V7, V0, V7
, V0 are written in order, data of voltage vectors V1, V5, V1, V5 are written in order in addresses 0 to 3 of reverse PWM pattern memories M3 and M7, and zero vector V0 is written in reverse zero vector memory M4. , V7, V0, and V7 are written in order, and the normal vector V4 corresponding to the vector at addresses 0 to 3 of the PWM pattern memory for normal rotation M1 is written to addresses 0 to 3 of the normal vector memory for normal rotation M6. , normal vectors V4 corresponding to the vectors at addresses 0 to 3 of the PWM pattern memory for reversal M3 are written in addresses 0 to 3 of the normal vector memory for reversal M8. Vector data is also written to the remaining addresses 4 to 511 using the same principle as addresses 0 to 3. Since the vector data of each address in FIG. 5 shows the principle, it differs from actual data. Now, the actual voltage vector data of addresses 0 to 84 (corresponding to the 0 degree to 60 degree section) of the normal rotation PWM pattern memory M1 is shown as follows.
V6, V6, V6, V6, V2,
V2, V2, V2, V2, V2,
V6, V6, V6, V6, V2, V2,
V2, V2, V2, V2, V6
, V6 , V6 , V6 , V2 , V2 , V2 ,
V2, V2, V2, V2, V2
, V2 , V2 , V2 , V2 , V2 , V2 ,
V2, V2, V2, V2, V2
, V2 , V2 , V2 , V2 , V2 , V2 ,
V2, V2, V2, V2, V2
, V2 , V2 , V2 , V2 , V2 , V2 ,
V2, V3, V3, V3, V3
, V2 , V2 , V2 , V2 , V2 ,
V2, V3, V3, V3, V3, V2
, V2 , V2 , V2 , V2 , V2
, V3 , V3 , V3 , V3 .

[0033]

[Voltage vector] Figure 6 shows six voltage vectors V1 to V
6 and two zero vectors V0 and V7. The possible switching states of the switching elements A1, B1, and C1 of the inverter 2 are (000), (001),
(010), (011), (100), (101), (
110) and (111), so this is V0
, V1 , V2 , V3, V4 , V5 , V6 , V
Let's express it as 7. In the device of this embodiment, the voltage vectors V0 to V7 are R
Written to OM5, this is control data (A, B, C)
is output as By combining the eight vectors V0 to V7, a sinusoidal output voltage and rotating magnetic field vector can be obtained.

[0034]

[Vector Selection] FIG. 7 shows the selection of a voltage vector to obtain the rotating magnetic field vector φ1. In order to bring the locus of the tip (end point) of the rotating magnetic field vector φ1 closer to a circle, the sixth and second vectors V6 and V2 are set in the 330° to 30° range, and the second and third vectors are set in the 30° to 90° range. Vectors V2, V3, the third in the 90 degree to 150 degree interval
and the first vectors V3, V1, the first and fifth vectors V1, V5, 210 in the 150 degree to 210 degree interval
The fifth and fourth vectors V5 and V in the interval between degrees and 270 degrees
4. Select the fourth and sixth vectors V4 and V6 in the 270 degree to 330 degree range. 33 in Figure 7 showing the principle
In the 0 degree to 30 degree interval, V6 and V2 are significant vectors.
is selected, and zero vector V7 is selected when vector rotation is stopped. In addition, the normal vector is a vector directed in the radial direction from the center of the circular locus of magnetic flux, and in the 330 degrees to 30 degrees section in Fig. 7, V4, 30 degrees to
V6 is selected in the 90 degree section. When the motor 1 rotates forward, the rotating magnetic field vector φ is directed in the direction indicated by UP in Fig. 7.
1 is rotated, and when reversing or braking, it is rotated in the direction indicated by DOWN.

[0035]

[Operation] Next, the operation of the circuit shown in FIG. 3 will be explained with reference to FIGS. 8 and 9. When a difference signal VD is obtained based on the comparison between the speed detection signal obtained on line 9a and the reference signal (target signal) on line 11, the first comparator 14 determines whether the signal is positive or negative. If it is a signal, the comparison output is at a low level "0" as shown before t4 in FIG. 8(C).
", and this is input to the counter 6. Therefore, the counter 6 operates up during this period. In the second comparator 16, the absolute value of the difference signal VD and the triangular wave voltage V
c is compared as shown in FIG. 8(A), and FIG. 8(B)
) output occurs. That is, the triangular wave voltage Vc is the difference signal V
A high level output "1" is generated when the absolute value of D is higher (t1 to t2), and a low level output "0" is generated at the opposite time (t2 to t3). As from t1 to t2, the output bit B9 of the second comparator 16 is at high level “1”.
”, the output bit B10 of the first comparator 14 is at a low level “0”, and furthermore, as shown in FIG. 8C, the outputs of the hysteresis comparators 40 and 41 in FIG.
L) before t10, in ROM5, [
B11 B10 B9 ]=[001], the normal rotation zero vector memory M2 is selected, and from t2 to
As in t3, [B11 B10 B9 ]=[0
00], the normal rotation PWM pattern M1 is selected. Furthermore, during the period (t1 to t2) in which the output of the second comparator 16 is at a high level (H), the output of the NOT circuit 20 is at a low level, and the clock pulse of the oscillator 17 does not pass through the AND gate 18. Since the counter 6 is not incremented, the same address continues to be specified. On the other hand, the output of the second comparator 16 is at a low level (t
2 to t3), the output of the NOT circuit 20 becomes high level, so the output clock pulse of the oscillator 17 passes through the AND gate 18 and becomes the input pulse of the counter 6. As a result, the values of the 9 bits B0 to B8 of the counter 6 are increased by the up operation, and the addresses of the memory M1 are sequentially designated. However, when the output of the second comparator 16 goes high at time t3, the clock input to the counter 6 is inhibited and the counter 6 retains its current addressing. For example, if memory M2 is selected while vector V6 of memory M1 is being read out at address 2 as shown in FIG.
7 (111) is selected. The zero vector V7 is the second
continues to be generated while the output of the comparator 16 is at a high level, and when the comparison output returns to a low level and a clock pulse is input to the counter 6 again, and the output of the counter 6 is incremented by one stage, the normal PWM pattern memory Voltage vector V2 (010) at address 3 of M1 is selected. There are two types of zero vectors, V0 (000) and V7 (111), and the vector that requires less switching of the switching elements A1 to C2 is selected. counter 6 is 10
When the binary numbers corresponding to the base numbers 0 to 511 are generated, all voltage vector data from 0 to 360 degrees of the normal rotation PWM pattern is read out, three-phase approximate sine wave voltage is generated from the inverter 2, and A rotating magnetic field vector that is close to a circular locus is generated in the motor 1 .

In such control, as the difference between the target rotational speed and the detected speed becomes smaller, the period during which the output of the second comparator 16 is at a high level becomes relatively longer, and the period during which the zero vector is selected becomes longer. becomes longer.

[0037] Also, as shown in t20 to t4, the line 11
If the level of the reference signal is lowered to set a low speed rotation command state, the level of the absolute value of the difference signal VD will also decrease, the output frequency f of the inverter 2 will decrease, and the output voltage V will also decrease, causing the motor 1 to drive at a low speed. become a state.

At t4 in FIG. 8, when the command is switched to reverse rotation and the difference signal VD becomes negative, the output of the first comparator 14 becomes high level, and reverse control is started. In addition, the above PWM
In the control, when the voltage vector is switched, a pair of switch elements A1, A2, or B1,
Since there is a risk that B2 or C1 and C2 may be short-circuited in a storage or the like and may be destroyed, it is desirable to provide an uncontrolled period between the vectors to prevent this.

t10 to t20 in FIG. 8 is a period in which the outputs of the hysteresis comparators 40 and 41 in FIG. 3 are at a high level. In other words, when the speed reference signal on line 11 in FIG. 3 increases rapidly at t10, the difference signal VD in FIG.
), the period during which the forward rotation vector is output increases rapidly, and the motor operates to rapidly increase the rotational speed. As a result, the motor's primary current increases rapidly to obtain the desired acceleration. However, the voltage drop due to the motor's primary winding resistance also increases, and the motor's primary magnetic flux linkage |φ1 | decreases as shown after t10 in FIG. 8(G). When it falls below |φ1a|−Δ|ψ1|, the hysteresis comparator operates and outputs a high level. At this time, R
In OM5, since the terminal 42 is at a high level, blocks M5 to M8 including the normal vector are selected. Therefore, during the period t10 to t20 and the period t11 to t12 in which the second comparator is at a high level, the normal vector memory for normal rotation M6 is selected instead of the zero vector memory for normal rotation M2. FIG. 9 shows this state in the 30 degree to 90 degree section. Similarly, the second comparator is at a low level during the period t12 to t.
13, M5 is selected. In this way, by outputting the normal vector instead of the zero vector, the magnitude of the motor's primary flux linkage is increased, and the motor's primary flux linkage |φ
1 | can be made larger than |ψ1a|−Δ|ψ1|. As a result, the motor can obtain the desired acceleration, respond well to the increase in the speed reference signal, and reach the desired rotational speed. The level of the speed reference signal on line 11 then decreases, for example, and as the primary current decreases, the voltage drop across the primary winding resistance also decreases and the primary flux linkage increases as a result. At t20, the primary flux linkage is |φ1a
When |+Δ|φ1| is exceeded, the output of the hysteresis comparator becomes low level, so in ROM5,
Block M1 containing zero vector because becomes low level
M4 is selected from , and the primary flux linkage decreases |φ1a
|+Δ|φ1|below. From the above, the primary magnetic flux linkage |φ1 | of the motor is controlled within the range of |φ1a|±Δ|φ1 |. When the direction of rotation is reversed, t4
Similar operations are performed thereafter.

[0040]

[Modifications] The present invention is not limited to the above-described embodiments, but can be modified, for example, as follows. (1) The proportional-integral circuit 12 may be a proportional circuit or an integral circuit. Further, this type of constant circuit may be provided on the line 9a side. (2) Instead of the speed detector 9, a temperature detection signal, a position detection signal, a pressure detection signal, a concentration detection signal, etc. obtained in response to the rotation speed of the motor 1 are used as detection signals, and these are compared with the reference signal. You may. (3) The magnetic flux detection circuit 100 may be configured with a magnetic flux sensor to directly detect the magnetic flux in the motor 1. (4) Instead of using only voltage vector data as the first vector data, a combination of voltage vector data and zero vector data may be used to improve the waveform. That is, a zero vector may be placed in the array of voltage vectors in the memories M1 and M3. (5) The number of addresses in the memories M1 to M8 may be increased, for example to 8193, to improve the waveform.

[0041]

According to the present invention, the speed control response during transient times can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the relationship between primary magnetic flux and primary and secondary currents.

FIG. 2 is a circuit diagram showing the principle of magnetic flux detection.

FIG. 3 is a block diagram showing a motor control circuit according to an embodiment.

FIG. 4 is a circuit diagram showing a magnetic flux detection circuit.

FIG. 5 is a diagram theoretically showing part of the contents of the ROM in FIG. 3;

FIG. 6 is a diagram showing voltage vectors.

FIG. 7 is a diagram showing rotating magnetic field vectors.

FIG. 8 is a diagram showing the state of each part in FIG. 3;

FIG. 9 is a diagram showing the relationship between magnetic flux changes and vectors.

[Explanation of symbols]

1 Motor, 2 Inverter 5 ROM 100 Magnetic flux detection circuit

Claims (1)

[Claims] [Claim 1] The inverter is pulse width modulated (PWM).
In the method of controlling the speed of an AC motor connected to the inverter by reading out the PWM switching pattern from a memory in which the PWM switching pattern for control is written and controlling the inverter, the rotational speed of the motor , or obtain a detection signal indicating information related to the rotation speed, and as the difference between this detection signal and a reference signal indicating the desired rotation angle of the motor or the desired information related to the rotation speed becomes smaller, the zero of the inverter decreases. In addition to controlling the reading of the memory so that the vector output time is longer, a detection signal indicating the primary flux linkage of the motor or information related to the primary flux linkage is obtained, and this detection signal and the motor By outputting a vector in the normal direction instead of the zero vector, the primary magnetic flux of the motor is A method for controlling a motor using an inverter, which is characterized by controlling magnetic flux linkage to a constant value.