JPS5970194A - Controlling method for induction motor - Google Patents

Abstract

PURPOSE:To prevent irregular operation without generating reverse torque by exciting by DC a motor by exciting current phase immediately before generating a stop command. CONSTITUTION:The fact that a speed detection value fm becomes 1% of lower of rated value is discriminated by a stop command generator 7 to output a stop command. When a stop command is generated, pulses transmitted to a sinusoidal wave generator 12 and a cosine wave generator 13 are interrupted by an AND circuit 11, the output of a counter 31 is fixed, and the peak values of the sinusoidal wave Y and the cosine wave X are held. The outputs of multipliers 17, 18 are continuously maintained at the value immediately before the stop command is generated. Thus, the primary current value command becomes the magnitude and phase of the exciting current immediately before generating the stop command, and a current value feedback system 110 flows a DC current corresponding to the primary current value command.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a control method for total vector control of an induction motor using a frequency converter.

[Prior art]

Generally, when an induction motor is controlled by vector control, a stopped motor is energized with direct current in advance to increase the torque at startup. This is because the magnetic flux of an electric motor has a certain time constant, so at startup, the magnetic flux is small and the torque is small.

When the induction torque pitcher is frequently started and stopped, it is difficult to generate sufficient torque and operate the motor unless DC excitation is applied immediately after the motor is stopped in preparation for the next start.

Therefore, in the past, in consideration of such a case, a predetermined current (i) was passed through the field immediately after the stoppage of each phase to ensure magnetic flux. This will cause inconvenience.

Figure 1 shows the - next time when the motor receives a stop command (a command that forcibly reduces the motor Ω synchronous frequency from approximately 1% of the rated frequency to 0%) at time t8 and shifts to DC excitation. FIG. 3 is a diagram showing a transient phenomenon of one phase of the current It, the excitation current IN, and the torque current IT.

Note that it is difficult to reduce the synchronous frequency to zero (DC) due to circuit drift, etc., so once the frequency has dropped to an appropriate level, the frequency is forcibly reduced to zero (DC).

At time ts, a predetermined DC current 11 is passed through this phase to start DC excitation, but due to the current value L at that time, the motor moves irregularly, and from the moment the stop command is received, The angle of rotation it takes to actually stop varies.

Figure 2 shows the reason why the above phenomenon occurs. The figure shows the primary turbulent flow 11. Excitation current IM.

It is a diagram showing torque current IT, and magnetic flux φ as vectors. The broken line "t+IM+I'r" in the figure shows the phase relationship immediately after the stop command is received. Immediately after the stop command is issued, the magnetic flux φ maintains its previous direction.

This is because the direction does not change suddenly due to the time constant.

Now, when a stop command is generated and the DC excitation is interrupted, the direction of the DC current is as shown by the broken line 11, so the torque current I'r ((fIl line)) is a component perpendicular to the magnetic flux φ. This torque current I/r (broken line) is generated in the opposite direction to the torque current It (actual) immediately before the stop command, so
Torque is generated in the opposite direction of the motor rotation direction.

FIG. 3 shows the rotational speed of the electric motor from the rated rotational speed (100%) until it stops.

When decelerating the motor speed at time tl., the speed command is decreased. Since the synchronous frequency of the electric motor decreases, it decelerates due to regenerative braking. Assuming that the stop command is designed to be generated when the speed command and the actual rotational speed become 1% of the rated speed, the stop command is generated at time ts.

Immediately after time t9, DC excitation is started for each phase with a predetermined current value, but if DC excitation is performed at this time with the phases shown in Figure 1, reverse torque will occur and the rotation speed will suddenly increase. □
This results in a reversed state during period a.

[Purpose of the invention]

An object of the present invention is to prevent the above-mentioned irregular operation of the motor immediately after a stop command is issued.

[Summary of the invention]

The present invention focuses on the fact that if DC excitation is performed using the excitation current phase immediately before the stop command is generated, the torque component as described above will not be generated.
This is because the motor was excited with direct current.

[Embodiments of the invention]

1. The first embodiment of the present invention will be explained in detail.

FIG. 4 is a configuration diagram of this embodiment.

In the same figure, the induction motor 2 is connected to the PWM inverter 1 (
The drawing shows only one phase. ) is driven by. −
Next, the current command circuit 100 receives a speed command f from the speed command circuit 4, a detected speed value f of the induction motor from the speed detector 3,
and excitation current command value ry are input from the excitation current command circuit 19, respectively, and a primary current command is output to the current value feedback system 110. A current feedback system 110 provided for each phase (only one phase is shown in the drawing) detects the output current of the PWM inverter 1 using a current detector 22 (this detector detects both AC and DC currents, e.g. (using a Hall current transformer, etc.), compares it with the negative current value command, and controls the PWM inverter so that the output current of the PWM inverter 1 matches the command.

The primary current command circuit 100 operates as follows.

The speed deviation amplifier 5 that receives the speed command f receives the speed command f.
and the detected speed value f, and outputs the torque current command IT and [2]. The seaside circuit 6 interrupts the torque current command IT in response to a stop command (described later). Slip frequency adjustment circuit 8 converts torque current command IT into slip frequency command f8.

Adder 9 calculates the sum of slip frequency command f8 and speed detection value f, and outputs the sum as synchronous frequency command fo. V-f
The converter 10 receives a synchronous frequency command f.

Converts all frequencies and outputs a pulse train. AND circuit 11
interrupts the pulse train in response to a stop command (described later). Sine wave generation port M12. The cosine wave generating circuit 13 receives the pulses and generates a sine wave Y and a cosine wave. Sine wave generation circuit 12. The cosine wave generating circuit 13 has a groove structure as shown in FIG. The counter 31 counts the pulses output from the AND circuit 11, and starts counting from the beginning when it overflows. 110M32 outputs data for one period of a sine wave or cosine wave from when the counter 31 starts counting until it overflows. The DA converter 32 outputs the sine wave or cosine wave data output from the Oiν 132 as an analog signal.

Returning to FIG. 4, the explanation of the -order d flow command circuit will be continued.

The first multiplier 15 calculates the product of the torque current command IT and the sine wave Y, the second multiplier 16 calculates the product of the torque current command IT and the cosine wave X, and the third multiplier 17 calculates the product of the torque current command IT and the cosine wave X. The fourth multiplier 18 calculates the product of the current command IM and the sine wave Y, and the fourth multiplier 18 calculates the product of the excitation current command IM and the cosine wave X.
The products obtained in steps 5 to 18 are input to the two-phase three-phase conversion circuit 20.

The two-phase three-phase conversion circuit 20 generates each phase-to-order cardiac flow command that creates the field of the motor.

In this embodiment, the stop command is output after the stop command generation circuit 7 determines that the speed index f and the speed detection 1 [f, 7ζ are 1% or less of the rated value.

Next, the operation when the stop command generation circuit outputs a stop command will be explained.

When a stop command is generated, it is transmitted to the sine wave generation circuit 12 and the cosine wave generation circuit 13. The wave heights of the sine wave Y and cosine wave X are held by the count value at that time.

At this time, the output of the seaside circuit 6 (torque current command ■
Since τ) becomes zero, the outputs of multipliers 15 and 16 become zero. On the other hand, since the excitation current command does not change, the multiplier 17
．． The output of 18 continues to hold the image immediately before the stop command was issued. Therefore, the output of the two-phase/three-phase conversion circuit (-order current value command) has the magnitude and phase of the excitation current of the stop command generation circuit.

The current value feedback system 110 causes a direct current corresponding to the secondary current feeding command to flow through the assigned phase according to the primary current value command. Actually, although it is called a direct current, a constant current value is not given, but a pulsating current state centered on the -order current 1 direct current command.

2. A second embodiment of the present invention will be explained in detail.

FIG. 6 is a configuration diagram of this embodiment.

The figure shows the primary turbulent current command circuit 100 when a microcomputer is used as the primary turbulent current command circuit 100 in FIG.
′ is shown. In the figure, multipliers 15 to 1
8 and two-phase to three-phase converter circuit 2° have the same function as that shown in FIG. In this embodiment, C)'LJ20
0.11. AM201.几0M202゜CTC204,
Bus 203. 110205 was installed.

The operation of this embodiment will be explained using the programs stored in the ROM 202 (FIGS. 7 and 8).

FIG. 7 shows the main program flow from when the motor is running to when it is stopped and when DC excitation is performed.

At the start of execution of this program, CTC (Counter/T
Enable interrupts from the imer C7rcLIft) 204.

In step 210, a speed command f is input via l10205.

In step 211, the speed detection value f- of l motor is set to l
Input via 10205.

In step 212, the torque current It is calculated (Ir=+·(f−f, a), where Hkt is a proportionality constant).

In step 213, the torque current ■τ is I/0
205 to multiplier 1'5.16.

In step 214, a slip frequency command f is calculated (fs=ka·It: where 2 is a proportionality constant).

In step 215, the synchronous frequency fo is determined by adding the slip frequency command f8 and the detected speed value f1.

n is an appropriate integer) is written to crczo4 as a time constant.

In steps 217 and 218, if the detected speed value f- and the speed command f become 1% or less of the rating, the process branches to step 220; otherwise, the process proceeds to step 219.

At step 219, wait for a time, and at step 21
Return to 0.

When branching from steps 217 and 218 to step 220 (when a stop command occurs), in step 220
Disable T'C2O4 interrupts.

In step 222, the torque current command IT is set to zero, and in step 223, it is output via l10205.

FIG. 8 is a processing program flow when an interrupt occurs from the CTC 204 to the CPU 200.

The timing at which an interrupt occurs from the CTC204 is as follows.
The time constant To specified in step 216 (Figure 7)
/n.

When an interrupt occurs, the main program (FIG. 7) exits the loop and jumps to step 230. At this time,
Interrupts from the CTC 204 are automatically prohibited.

In step 230, the phase θ is calculated 2π.

(θ=-・1: n is n in step 216, i is O
to (n-1)).

In step 231, a sine wave ¥1 cosine wave X is obtained. This calculation is performed by storing the sine wave or cosine wave Y in advance in the memory 202, and calculating the wave Y of the sine wave or cosine wave using θ as an argument.
output to multipliers 15-18 via o.

Steps 233-235 are i? f:o ~(n-1)
This is a step in which the number is increased by one within the range of .

In step 236, interrupts from the CTC 204 are enabled, and in step 237, the main program (7th
Return to figure).

In this example, in step 218 (FIG. 7), ye
If it is determined that s has occurred (this is equivalent to the occurrence of a stop command), interrupts from the CTC 204 are prohibited, so no jump is made to the cutting processing program. Therefore, l
The wave height values of the sine wave Y and cosine wave X are not rewritten in the register 10205, and the wave height values immediately before the stop command is generated are held. Also, at this time, the torque current command IT becomes zero at steps 222 and 233.
Since the register 05 is rewritten, the outputs of multipliers 15 and 16 become zero.

The excitation current command IN is always given to the multipliers 17 and 18, and the output (-molding flow value command) of the two-phase three-phase conversion circuit 2o is the excitation current immediately before the stop command is generated. The magnitude and phase of

〔Effect of the invention〕

According to the present invention, DC excitation is performed so as to maintain the direction of magnetic flux immediately before the stop command is generated, so that there is an effect that irregular movement of the motor does not occur.

Among them, in the embodiment, speed command f and speed detection 1+if.

The stop command is generated when both the rated value and the 1% value are reached, but the 1% value may be arbitrarily changed depending on the device. Also, the speed command f and the speed detection value f
The stop command may be issued when only one of the two has reached 1% of the rating, without checking that both of the two have reached 1% of the rating. In this case, when looking only at the stop command f, the stop command is generated regardless of the actual motor speed, but there is no problem as long as the motor speed closely follows the speed command. Also, when looking at only the speed detection value f7, f is zero while the cardiac iso is stopped, so even if a speed command is output to restart, the stop command continues and is output. Therefore, it is possible that the motor will not restart, but if you want to restart it, if you reset the stop command with a driving pattern/(a pattern that is predetermined for when to start the motor) or a speed command, it will restart without any problem. be able to.

[Brief explanation of drawings]

Figure 1 is a current waveform diagram for one phase before and after the stop command is generated, Figure 2
The figure shows the phase relationship of the field current (-molding flow) and magnetic flux before and after the stop command is issued, Figure 3 shows the change in motor speed during deceleration, and Figure 4 shows the first aspect of the present invention. Example □ Block diagram, Figure 5 shows a sine wave. FIG. 6 is a configuration diagram of a cosine wave generation circuit, FIG. 6 is a configuration diagram of a second embodiment, FIG. 7 is a main program flow, and FIG. 8 is an interrupt processing program flow. 1... PWM inverter, 2... induction motor, 10
0...-Forming flow command circuit, 110...District flow feed back 3 Figure 6 Ryo 7m 500 Mouse 8 Figure

Claims (1)

[Claims] 1. In a method of vector control of an induction motor, when a stop command is generated, the excitation current phase immediately before the stop command is generated is held, and the motor is DC excited at the excitation current phase immediately after the command is generated. A method for controlling an induction motor, characterized in that: