JPS591076B2 - Induction motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction motor control device that controls the speed of an induction motor using a non-directional detector (for example, a one-phase pulse generator) as a speed detector for the induction motor. It is.

When controlling the speed of an induction motor in both rotational directions using frequency control or vector control, conventionally a two-phase pulse generator that can also detect the rotational direction was used as a speed detector, as shown in Figure 1. .

FIG. 1 shows an example of the above conventional device for driving an induction motor using an inverter, in which an induction motor 3 is driven from a DC power supply 1 via a variable frequency inverter 2.

The rotation speed and rotation direction of the induction motor 3 are detected by a two-phase pulse generator 4, and a speed voltage Vr is obtained via a frequency-voltage converter 5, which is proportional to the speed and whose polarity changes depending on the rotation direction. The speed reference rate SR set by the speed setter 6 and the speed signal Vr are compared and amplified by the amplifier 1, and a torque reference Tr is output.

The torque reference Tr is input to a function generator 8, which outputs a primary current reference IM of the induction motor. On the other hand, a frequency voltage Vs is output from the torque reference Tr via the converter 9, the speed voltage Vr and Vs are added, and the frequency n is n times the frequency f which is supplied to the induction motor 3 by the voltage frequency converter 10.
f is input to the current vector synthesizer 12. On the other hand, the level detector 11 detects the input of the voltage frequency converter 10, and the signal F determines the phase rotation direction of the output current of the inverter.
Outputs X and RX.

The current vector synthesizer 12 receives these primary current references IM n times nf of the inverter frequency and phase rotation direction signals FX and RX, and outputs current references 1u, 1i, and 1w for the inverter 2, and outputs the current references 1u, 1i, and 1w for the inverter 2, 3 to three-phase current iu
, iv, and iw to control the speed of the induction motor. Next, the operation will be explained with reference to FIG.

When the speed reference SR for normal rotation is given by the speed setter 6 at time T, the deviation between the speed reference SR and the speed r is amplified by the amplifier 7, and the torque reference Tr is output. Further, the sum Vr+S of the slip frequency voltage S and the speed voltage Vr becomes the frequency reference of the inverter, and its polarity determines the phase rotation direction of the inverter.

Since S is positive, the phase rotation becomes forward rotation FX, the inverter current becomes a positive phase output, the induction motor rotates forward, the speed accelerates as shown by Vr, and balances with the speed reference SR at time T2, The torque reference Tr is reduced to a value that balances the load and is balanced. Next, at time T3, when the speed reference SR becomes zero, the torque reference Tr and the slip voltage S become negative, and the inverter frequency has a relationship of Vr+Vs<Vr, so that the induction motor regenerates energy to the power supply at a negative frequency. while slowing down. At time T4, the polarity of r+S is reversed, and the phase rotation of the output of the inverter is reversed to become reverse phase RX, further continuing regenerative braking, and the induction motor decelerates to zero speed at time T. If the speed overshoots and reverses at this point, the polarity of r is reversed, the torque reference Tr becomes positive, and the phase rotation becomes positive and the speed becomes zero. Next, a case where the speed reference SR changes from normal rotation to reverse rotation is shown after time T6.

The period between time T6 and T4 is the same as the period between time T and T4. Even after the phase rotation is reversed at time T, the speed reference SR is in the reverse direction, so the torque reference Tr is in the opposite direction and the motor is reversed, and the speed reference SR and speed r are in equilibrium at time TlO. The torque is balanced with the torque reference Tr that balances the load. At time Tl, when the speed reference SR becomes zero and a stop signal is generated, the torque reference Tr becomes positive and the voltage Vs corresponding to the frequency becomes positive, and the frequency reference of the inverter is r+S and the polarity of r is negative. The frequency supplied to the induction motor is below the rotation frequency.

As a result, the induction motor is decelerated by regenerative braking, and at time T,
At time 2, the polarity of r+Vs is reversed and the phase rotation becomes positive, and the motor further decelerates, and at time T, 3, the motor speed reaches zero and stops. As explained above, ideal control can be achieved by detecting the rotation direction using a two-phase pulse generator, but as the price of the pulse generator increases, a rotation direction detection circuit becomes necessary, and the overall level of improvement becomes higher. becomes higher, so
A more economical control method is desired.

Except for cases where particularly high-speed positioning is required, such as in NC equipment, linearity of braking near zero speed is not particularly required, and four-quadrant operation using an inexpensive method has been desired.

Therefore, let us consider a case where a one-phase pulse generator is applied to the same circuit as shown in FIG. 1, as shown in FIG.

Forward rotation and reverse rotation can be achieved by reversing the phase rotation of the inverter, but in regenerative braking near zero speed, the rotation direction is not detected, so the speed reference SR becomes zero at time T3 in Fig. 4, and the phase rotation at time T4. The rotation becomes reverse phase and decelerates further until time T
, the speed becomes zero. However, if the speed overshoots even slightly, even if the speed reverses, the rotation direction cannot be detected because the pulse generator is in one phase, and the speed detection voltage Vr remains positive and it is determined that deceleration has not been completed. However, in the amplifier 7, the torque reference Tr remains at the maximum negative value, and Vs remains negative, so r+Vs is a lower value than Vr, but always exists, and the inverter maintains an inverter frequency proportional to Vr+Vs. Concerns about supplying to induction motor 1
It rotates in the reverse direction at a constant speed, and continues to rotate without stopping as shown in FIG.

If an inexpensive speed control device is constructed using a single-phase pulse generator as described above, the direction of rotation of the induction motor will be reversed during stoppage or low-speed operation, causing the induction motor to rotate in an undesired direction and becoming uncontrollable.

The present invention has been made in view of the above problems, and is a rational control device for an induction motor that does not cause unnecessary reversal when stopped by externally giving a rotation direction signal even if the pulse generator is set to one phase. It provides: FIG. 5 is a system diagram showing an embodiment of the present invention.

In FIG. 5, the same parts as those in FIGS. 1 and 3 are designated by the same numbers, and their explanations will be omitted. In FIG. 5, a unidirectional polarity voltage r proportional to the speed of the induction motor 3 is obtained by a frequency-voltage converter 5, and a frequency voltage Vs is obtained from a torque reference Tr through a converter 9. Add the two to calculate r+Vs, take out only the polarity output in one direction by the rectifier 13, and supply it to the induction motor 3 by the voltage frequency converter 10. Frequency Ff) n times the frequency N
Output f. On the other hand, from the voltage r proportional to the speed, the low speed detector 14 detects that the induction motor 3 has become low speed.

Output. The logic switch 15 receives the forward rotation command 16 and the reverse rotation command 17, and outputs the phase rotation direction signals FX and RX of the inverter 2 to the current vector synthesizer 12 by logic with the low speed signal SO, and at the same time outputs the speed reference SR. Outputs a drive signal for the electric valve 18 that turns on and off. Next, the operation of the present invention will be explained with reference to FIG.

When the forward rotation command F is input at time t1, the logic switch 15 turns on the electric valve 18 and inputs the speed reference SR set by the speed setting device 6, and simultaneously switches the inverter 2
A command for normal phase rotation FX is output as the phase rotation. Based on the speed reference SR, the amplifier 7 outputs a positive torque reference Tr that accelerates the induction motor 3, and the function generator 8 outputs the primary current reference ! Output IM. On the other hand, the torque reference Tr is determined by the converter 9
A frequency voltage Vs that determines the frequency is outputted, and a frequency Nf proportional to the frequency f of the inverter 2 is outputted by a voltage frequency converter 10 through a rectifier 13. Furthermore, the current vector combiner 12 generates IM,
nf, FX signal to inverter 2's three-phase current reference 1u,
Since it is converted into Iv, Iw and output, the inverter 2 supplies the induction motor 3 with a current 1u proportional to IU, IV, and Iw.
, iv, and iw, the induction motor 3 rotates in the forward direction.
Start rotating. Voltage Vr proportional to the speed of the induction motor
is negatively fed back to the amplifier 7, and at the same time is summed with S, r+Vs
is input to the voltage frequency converter 10, so the inverter 2
The frequency is the rotation frequency of the induction motor 3.3. The induction motor 3 is efficiently accelerated by Veri frequency control, and at time T2, the torque reference Tr balances with the speed reference SR and balances with the load, so the torque decreases between T2 and T3. However, the slip frequency is also reduced and the rapid drinking rate is maintained.

When the forward rotation signal F is turned off at time T3, the logic switch 15 turns off the electric valve 18 and sets the speed reference SR to zero.

Low speed signal S. is "O", that is, while the induction motor is rotating, the phase rotation signal FX is maintained at the previous state. When the speed reference SR becomes zero, the output of the amplifier 7 is reversed and the torque reference Tr becomes negative, attempting to decelerate the motor. As a result, Vs also becomes negative, so Vr+S becomes smaller than Vr as shown. That is, the over frequency becomes negative and negative torque is generated in the induction motor 3, and the energy of the load is regenerated to the DC power supply 1 through the inverter 2, and the induction motor 3 is decelerated. At time T4, Vr+S
becomes zero, so between time points T4 and T6, the rectifier 13 makes Vr+Vs=0, the output frequency of the inverter 2 is fixed at zero, and the induction motor 3 is decelerated by DC braking. At time T, the speed decreases and the low speed detector output S.
detects completion of deceleration. Between T4 and T6, the torque decreases slightly due to DC braking, resulting in a speed that is slightly slower than the ideal speed r output.

Vr matches the velocity waveform, but in FIG. 6, the r waveform is drawn ideally to make the explanation easier to understand. When the above-mentioned stopping operation is performed, direct current braking is automatically applied near low speeds and the phase rotation is not reversed, so the motor does not operate in reverse as in the conventional system.

Next, a case will be described in which an operation is performed to shift from normal rotation to reverse rotation.

When the forward rotation signal F is turned on at time T7 and the forward rotation signal F is turned off at time T9 and the reverse rotation signal R is turned on at the same time, the period from T7 to T is exactly the same as the period from t1 to T3 described above. At time T9, the electric valve 18 is turned off and the speed standard S is set.
Set R to zero and detect low speed S. The phase rotation of the inverter maintains the positive phase FX until it reaches Capi 11. Time T9~T,
. Up to this point, the induction motor is decelerated in exactly the same manner as T3 to T4 described above, decelerated by DC braking between time points TlO and Tll, and low speed detection is performed at time Tl. When outputs 81°, the held phase rotation FX is turned off and the phase rotation is switched to reverse phase RX by the reverse rotation command R. At times T and l, the induction motor rotates slightly and Vr is not zero, so the frequency of the inverter 2 outputs a frequency that is slightly higher than the ideal waveform, as shown by Vr+Vs. At time Tll, the electric valve 18 is simultaneously activated and the speed reference SR is inputted again, so that the output Vr of the amplifier 7 becomes positive, and therefore S also becomes positive.

Between times Tll and Tl2, the phase rotation is in the opposite direction to the rotational direction of the induction motor, so the speed is rapidly decelerated and becomes completely zero at Tl2. After T, 2, only the phase rotation is reversed, and the other operations are the same as those at time t1 to T6, and the reverse rotation is performed, and when the reversal signal R is turned off at time T, 4, it is at time Tl7.
The induction motor decelerates until it stops. In order to make the explanation easier to understand, the slip frequency Vs is shown in a larger scale in Fig. 6, but in an actual induction motor, the slippage is normally around 2 to 3%, so the DC braking period is actually very short.
Induction motors can smoothly accelerate and decelerate down to low speeds and perform four-quadrant operation.

Moreover, even if the pulse generator has only one phase, it will not run out of control to the reverse direction during deceleration.

Note that in order to improve the accuracy of the calculation of Vr+Vs near zero slip, it is better to perform a digital calculation of the pulse generator output and the slip frequency.

Although FIG. 5 shows the case of slip frequency control, it can be applied in exactly the same way to a vector control method that controls a transient term.

Furthermore, it is also possible to perform these calculation controls using a computer. Although an inverter is used as the alternating current for the induction motor in FIG. 5, the same effect can be obtained by using a cycloconverter or the like, and even if the number of phases is changed.

In addition, as shown in FIG. 7, when using a bipolar speed setter 6, the speed reference is converted into a one-way voltage V2 by an absolute value converter 20, and the speed reference setter output V1 is converted to a polarity discriminator. 30 to determine its polarity, add logic 40, and connect the forward rotation signal F to the circuits SR, F, and R in FIG. It is also possible to operate the induction motor in forward and reverse directions based on speed.

Its operation is shown in FIG. Furthermore, in FIG. 5, the frequency-voltage converter 5 can be omitted if, for example, the output of an AC tacho generator is rectified and used instead of the pulse generator 4.

As explained above, according to the present invention, four-quadrant operation of a high-grade induction motor is realized by using an economical speed detector using a one-phase pulse generator or an AC tacho generator that does not detect directionality. It is possible to obtain a rational induction motor control device that can economically realize stable and safe speed control without any risk of runaway in the opposite direction during deceleration.

[Brief explanation of the drawings] Fig. 1 is a system diagram showing a conventional device, Fig. 2 is a time chart showing its operation, Fig. 3 is a system diagram showing problems with the conventional device, and Fig. 4 is a system diagram showing the conventional device. Its operation time chart, 5th
The figure is a system diagram showing one embodiment of the present invention, FIG. 6 is a time chart showing its operation, FIG. 7 is a circuit diagram showing another embodiment of the present invention, and FIG. 8 is a time chart of its operation. . 1...DC power supply, 2...Inverter,
3...Induction motor, 4...Pulse generator, 5...Frequency voltage converter, 6...
...Speed setting device, 7...Amplifier, 8...
・Function generator, 9...Converter, 10...
・Voltage frequency converter, 11...Level detector,
12...Current vector synthesizer, 13...
- Rectifier, 14...Low speed detector, 15...
...Logic switch, 16...Forward rotation command, 1
7... Reverse command, 18... Electric valve, 2
0... Absolute value converter, 30... Polarity discriminator.

Claims (1)

[Scope of Claims] 1. In an induction motor control device that drives an induction motor in both forward and reverse directions with a variable frequency power source that can perform phase rotation in forward and reverse directions,
A speed detector that detects the speed of the induction motor as a DC voltage of the same polarity regardless of the rotation direction, and a low speed detector that detects that the induction motor is below a predetermined speed are used to set the speed reference voltage of the induction motor. a setting device, a rotation direction setting device that sets the rotation direction, a slip frequency calculation circuit that sets the slip frequency voltage of the induction motor according to the difference between the speed reference voltage and the speed detection voltage, and the speed detection detection voltage and the slip frequency. a frequency setting circuit that sets the frequency of the variable frequency power supply in a range where the algebraic sum with the voltage is positive; and a frequency setting circuit that sets the phase rotation direction of the variable frequency power supply in accordance with a command from the rotation direction setting device; A phase rotation command circuit that holds the set phase rotation until the low speed detector operates; and a current reference circuit that sets the output current of the variable frequency power supply according to the difference between the speed reference voltage and the speed detection voltage. A control device for an induction motor, comprising: 2. Claim 1, wherein the output voltage of the speed setting device is variable in forward and reverse directions, the phase rotation direction is set according to the polarity of the voltage, and the absolute value of the output voltage is used as the speed reference voltage. A control device for the induction motor described above.