JPH0444513B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an induction motor, and particularly to a control device for an induction motor suitable for preventing reverse rotation with respect to a command rotation direction in vector control.

[Background of the invention]

An excitation current that contributes to the generation of magnetic flux in an induction motor,
Vector control of so-called induction motors, which independently controls the torque current that contributes to torque generation, has been in increasing demand in recent years because it can control speed as precisely as a DC motor and is easy to maintain and inspect.

FIG. 6 is a block diagram of conventional vector control. Here, 1 is a three-phase AC power supply, 2 is a three-phase induction motor, 3 and 4 are a three-phase full-wave rectifier circuit connected between the power supply 1 and the three-phase induction motor 2, and a vector control inverter as a frequency conversion means. It is. The inverter 4 as a frequency conversion means includes six transistors 5a to 5f and six feedback diodes 6a to 6.
It consists of f. 7 is the speed setting device, 8 is the electric motor 2
A speed detector 9 generates a number of pulses proportional to the rotational speed of the motor 2, and is a conversion circuit that receives the output of the speed detector 8 and converts it into an analog signal proportional to the rotational speed of the electric motor 2.

10 is a conversion circuit 9 for the output of the speed setting device 7.
The subtracter 11 subtracts the output of the subtracter 10, and the error amplifier circuit 11 performs a proportional integral calculation on the output of the subtracter 10.

This output becomes the torque current component command It, which is used by the vector calculation circuit 12 and the slip angle frequency output circuit 1.
Sent to 3.

14 is an adder which outputs the output signal of the conversion circuit 9, that is, the actual angular velocity ωr and the slip angular frequency output circuit 1.
The outputs ωs of 3 are added and output as ω ₁ =ωr+ωs. ω ₁ is the primary angular frequency given to the motor 2,
This is sent to the voltage controlled oscillation circuit 15. And here a sinusoidal signal sinω ₁ of angular frequency synchronized with ω ₁
is converted into a cosine wave signal cosω ₁ and sent to the vector calculation circuit 12.

Reference numeral 16 denotes excitation current component setting means for providing an excitation current component command Im for the motor 2.

Excitation current component command in vector calculation circuit 12
Im becomes AC two-phase signals im′, it′ with an angular frequency ω ₁ with a phase delay of 90 degrees from the torque current component command It. These AC two-phase signals im' and it' are supplied to the two-phase three-phase conversion circuit 17.
is converted to three-phase.

The current comparison circuit 18 takes in the phase current detected by the current detector 19, and compares this value with the two-phase three-phase conversion circuit 1.
7 and turn it on so that the difference is within a predetermined value. An off signal is generated and this signal is sent to the transistor drive circuit 20. A transistor drive circuit 20 controls transistors 5a to 5f. As a result, the electric motor 2 is responsively controlled to the speed set by the speed setting device.

In addition, the torque current component command means has a total of 40,
The entire excitation current component command means is indicated by 50. C is a smoothing capacitor, and 21 is a regenerative power processing device.

Now, in vector control of such an induction motor, the operation shown in FIG. 7 will be explained. FIG. 7 is a time chart in which the horizontal axis represents time and the vertical axis represents rotational speed. It is now assumed that the speed command of the speed setter 7 is a high speed command H, and the induction motor 2 is rotating at a high speed. Next, at time _t1 , when the speed command is switched from the high speed command H to the low speed command L, the induction motor 2 enters a regeneration mode in which it decelerates as shown by the dashed line. When the low speed command L is a sufficiently low rotation command, the induction motor 2
may result in undershoot and a reversal region where the motor rotates in the direction opposite to the commanded rotation direction.

Such a reverse rotation phenomenon is likely to occur if the gain adjustment of the speed control system is incorrect. In other words, the error amplifying circuit 11 is generally of a proportional-integral type, which has both a proportional element for improving responsiveness and an integral element for suppressing vibrations caused by the response. Therefore, unless the proportional coefficient and the integral coefficient are set appropriately, the electric motor 2 may rotate in the opposite direction to the command rotation direction.

For this reason, when preventing the electric motor 2 from rotating in a direction opposite to the commanded rotation direction, the following two methods can be considered.

One method is to compare the output signal of the speed detector 8 (or the conversion circuit 9) with the set rotation direction, detect that the motor rotates in the opposite direction, and immediately cut off the power supply to the electric motor 2. The other one is that when the command of the speed setter 7 changes from the high speed command H to the low speed command L, the power supply to the electric motor 2 is immediately cut off and the motor 2 is operated at a slow speed so that the rotation speed of the electric motor 2 is lower than the low speed command L. This method resupplies power after the battery has warmed up.

However, the former has the disadvantage that if digital signals are used in the arithmetic circuit or speed detector of the control device, reverse rotation cannot be completely prevented due to sampling time delay, especially when driving a load with large deceleration. Furthermore, the latter cannot perform regenerative braking. Therefore, particularly when driving a load with a large inertia, the deceleration time from high speed rotation to below the rotation of the low speed command L becomes long, resulting in a disadvantage that work efficiency or responsiveness decreases.

[Purpose of the invention]

The purpose of the present invention is to shorten the deceleration time of the induction motor.
Another object of the present invention is to provide a control device for an induction motor that prevents reverse rotation with respect to a commanded rotation direction.

[Summary of the invention]

A feature of the present invention is that, in vector control of an induction motor, attention is paid to the fact that the primary angular frequency during regenerative operation changes from a positive sign to a negative sign before the actual rotational frequency. I will explain in more detail. During regenerative operation of the induction motor, the primary angular frequency ω ₁ is determined by the following formula.

ω ₁ = ω _r + (−ω _s ) …(1) Therefore, if the actual rotational frequency ω _r becomes smaller than the absolute value of the slip angular frequency ω _s , the primary angular frequency ω ₁
changes to a negative sign.

For this reason, a negative phase detection means is provided which inputs the commanded rotation direction and the primary angular frequency ω ₁ , and this negative phase detection means generates a signal when the primary angular frequency ω ₁ becomes a negative value when the commanded rotation direction is positive rotation. is generated, and the power supply to the induction motor is cut off based on this signal. At the same time, the control signal is reset so that the slip frequency _ωs becomes 0. This causes the primary angular frequency to be ω ₁
= ω _r . Since the actual rotation frequency ω _r at this time is still a positive value, the rotation direction of the primary angular frequency ω ₁ returns to a positive value. Since ω ₁ >0, the signal from the negative phase detection means is no longer output, and the power supply cutoff state to the induction motor is released. Furthermore, the reset of the control signal that had caused the slip frequency ω _s =0 is also released.

If the actual rotational frequency ω _r at this time is higher than the low speed command L, the induction motor is again operated in the regeneration mode and decelerated. In this way, the same operation as above is repeated. When the control signal is reset so that the slip frequency ω _s = 0 by repeating the above operation, if the actual rotational speed ωr of the induction motor is lower than the value of the low speed command L, then the speed command is set to the actual rotational speed. Since it is larger, the induction motor naturally enters a power running mode in which the speed increases as it approaches the low speed command. If there is no change in the speed command value thereafter, the actual rotational speed ω _r asymptotically approaches the value of the low speed command L and enters a steady operating state.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG. Note that the same parts as in FIG. 6 are denoted by the same reference numerals as in FIG. 6, and a description of these parts will be omitted.

In FIG. 1, 37 is a negative phase detector. The output of the adder 14 and the signal of the forward rotation command 35 or reverse rotation command 36 are input to this negative phase detector 37.
The negative phase detector 37 operates as follows. That is, for example, when the forward rotation command 35 is input,
When the output of the adder 14, that is, the primary angular frequency ω ₁ changes from a positive sign to a negative sign, a signal is output.

Further, if the primary angular frequency ω ₁ changes from a positive sign to a negative sign when switching from the forward rotation command 35 to the reverse rotation command 36, no signal is output. The same applies when switching from the reverse rotation command 36 to the forward rotation command 35. The output signal of the negative phase detector 37 is sent to the error amplifier circuit 1.
1 and the transistor drive circuit 20. Then, the error amplification circuit 11 short-circuits the integral element and resets it, and sets the torque current component command _it to zero. At this time, the slip angle frequency output circuit 13 outputs ω _s to 0.
shall be. On the other hand, the transistor drive circuit 20 receives the output signal of the negative phase detector 37, sets the output of the inverter 4 as a frequency conversion means to 0, and cuts off the power supply to the induction motor 2.

The operation of the induction motor control device having such a configuration will be described below. In the time chart of FIG. 2, it is assumed that the electric motor 2 is now rotating at a high speed due to a high speed command H being given. At this time, the primary angular frequency ω ₁ is output as a positive sign from the adder 14 as the sum of the actual rotational frequency ω _r and the slip angular frequency ω _s . Next, at time t ₁ ,
Assume that the command from the speed setter 7 is changed from a high speed command H to a low speed command L. At this time, the primary angular frequency ω ₁ is outputted from the adder 14 as a value smaller than the actual rotational frequency ω _r by the slip angular frequency ω _s from equation (1). The induction motor 2 then enters the regeneration mode and decelerates from time _t1 to time _t2 . As the actual rotational frequency ω _r decreases,
When the slip angular frequency ω 1 becomes smaller than the absolute value of the slip angular frequency ω _s , the primary angular frequency ω ₁ reverses from a positive sign to a negative sign.

Note that the actual rotation frequency ω _r at time t ₂ is a value with a positive sign that is larger than the primary angular frequency ω ₁ by the absolute value of the slip angular frequency ω _s , and the electric motor 2 is rotating in a positive rotation region. When the negative value of the primary angular frequency ω ₁ is input, the negative phase detector 37 outputs a signal depending on whether the rotation direction command is the forward rotation command 35 or the reverse rotation command 36 .
That is, the reverse phase detector 37 is continuously inputted with the forward rotation command 35, and outputs a signal when the primary angular frequency ω ₁ changes from a positive sign to a negative sign, and outputs a signal as a reverse rotation command 35.
6 is input, no signal is output even if the primary angular frequency ω ₁ changes from a positive sign to a negative sign. The signal from the negative phase detector 37 short-circuits the integral element of the error amplifier circuit 11 and resets the torque current component command _it to zero. Further, the transistor drive circuit 20 operates so that the output to the inverter 4 becomes zero. Therefore, the power supply to the induction motor 2 is cut off. When the output ω _s of the slip angular frequency calculation circuit 13 becomes 0, the above equation (1) becomes ω ₁ =ω _r , and the primary angular frequency ω ₁ becomes a positive value. Then, if the actual rotational frequency ω _r is higher than the low speed command L, the induction motor is operated in the regeneration mode again and decelerated. If the actual rotational frequency ω _r is lower than the value of the low speed command L, the induction motor enters the running mode and speeds up toward the low speed command L.

Therefore, in this embodiment, when the commanded rotation direction is the same but the commanded speed changes, the reverse phase detector 37 detects that the sign of the primary angular frequency ω ₁ is reversed, and the error amplifier 11 is reset. At the same time, the power supply to the induction motor is cut off, and when the actual rotation becomes lower than the low speed command, power operation is started, so that regenerative braking can be performed at least until the sign of the primary angular frequency ω ₁ is reversed. Therefore, the responsiveness of the actual rotational speed from the high speed command H to the low speed command L is high. Further, even with sampling control using digital signals, reversal of the command direction can be prevented.

In the above embodiment, the forward rotation command 35 and the reverse rotation command 36 are each inputted to the reverse phase detector 37 separately, but as shown in FIG. The forward rotation command 35 or the reverse rotation command 36 may be determined by the forward/reverse determination circuit 38 from the output signal of the output signal and input to the negative phase detector 37.

Another embodiment of the present invention is shown in FIG.
The output of the negative phase detector 37 is input to the vector calculation circuit 12. The vector calculation circuit 12 is the negative phase detector 3
Two-phase three-phase conversion circuit 1 while signal 7 is input
The AC two-phase signals i _n ′, i _t ′ output to 7 are set to 0.

The operation of such a control device will be explained with reference to FIG. It is assumed that when the command speed is a high speed command H, it changes to a low speed command L at time _t1 . The induction motor decelerates in regenerative braking mode from time t ₁ to time t ₂ . When the primary angular frequency ω ₁ reverses from positive to negative at time t ₂ , the reverse phase detector 37
outputs a signal. When the signal from the negative phase detector 37 is input to the vector calculation circuit 12, the vector calculation circuit 12 sets this output signal to zero. When the power supply is cut off, the induction motor enters drag operation and decelerates. When the rotation of the induction motor 2 decreases based on the low speed command L, the output of the adder 10 becomes positive and the primary angular frequency ω ₁ becomes positive. Therefore, the negative phase detector 37 sets the output signal to 0 and the vector calculation circuit resumes operation. Then, power supply to the induction motor is resumed, and the induction motor is operated in a forward mode toward the low speed command L.

Therefore, according to this embodiment, the actual rotational frequency ω _r when the sign of the primary angular frequency ω ₁ is reversed is the low speed command L.
Even if the voltage is higher than that, the induction motor 2 will not be operated in instantaneous regeneration mode, so it is possible to prevent failure of the control device due to a voltage increase when power supply is restarted.

[Effects of the Invention] As explained above, the present invention is provided with a negative phase detector that inputs the rotational direction command and the primary angular frequency, and detects a change in the sign of the primary angular frequency to cut off the power supply. , regenerative braking can be performed from a high speed command to near a low speed command, high responsiveness is achieved, and the induction motor can be prevented from reversing in the command direction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a control device for an induction motor according to the present invention, FIG. 2 is a time chart for explaining the operation of the present invention, and FIG. 3 is a block diagram showing another embodiment of FIG. 1. , FIG. 4 is a block diagram showing another embodiment of the induction motor control device of the present invention, FIG. 5 is a time chart for explaining the operation of FIG. 4, and FIG. 6 is a diagram showing a conventional induction motor control device. The block diagram shown in FIG. 7 is a time chart for explaining the operation of FIG. 1 is a power supply, 2 is an induction motor, 4 is an inverter as a frequency conversion means, 12 is a vector calculation circuit, 37 is a negative phase detector, 50 is a control means, ω _s is a slip angular frequency, ω _r is an actual rotation frequency, ω ₁ is the primary angular frequency, H is the high speed command, and L is the low speed command.

Claims (1)

[Claims] 1. A frequency conversion means connected between a power source and an induction motor, and a control means for controlling the frequency conversion means, wherein the control means controls an excitation current that contributes to the generation of magnetic flux of the induction motor. It has a vector calculation unit that calculates an AC two-phase signal from the command, a torque current command that contributes to torque generation, and a primary angular frequency command obtained by adding the feedback actual rotation frequency and slip frequency. In the induction motor control device that controls the speed of the induction motor according to A control device for an induction motor, comprising a reverse phase detector that outputs a signal that cuts off the output of the frequency conversion means and makes the slip frequency command zero when the direction is opposite to the rotation direction command. . 2. The control device for an induction motor according to claim 1, wherein the rotational direction command is output from a forward/reverse determination means that inputs the speed command and determines the rotational direction. 3. The negative phase detector outputs the output signal of the negative phase detector to the switching element drive circuit of the frequency conversion means, and the switching element drive circuit adjusts the frequency according to the output signal of the negative phase detector. The control device for an induction motor according to claim 1, characterized in that the output of the conversion means is cut off. 4. The negative phase detector outputs an output signal of the negative phase detector to the vector calculation circuit, and the vector calculation circuit zeros the output of the vector calculation circuit in accordance with the output signal of the negative phase detector. The control device for an induction motor according to claim 1, characterized in that: 5. The control means for controlling the frequency conversion means further includes an error amplifier that amplifies the difference between the actual rotational frequency and the speed command using at least an integral element and outputs the difference as the torque current command, and the error amplified by the integral element 2. The control device for an induction motor according to claim 1, wherein the error amplifier output for the amplified portion is reset to zero by the output signal of the negative phase detector.