JPS5914392A - Control system for inverter - Google Patents

Abstract

PURPOSE:To enable to return to the set speed by switching a control mode in response to the lower limit of the operation limit of an inverter and restarting it in a short time after recovery irrespective of the short or long time of a power interruption or the rotating speed of a motor. CONSTITUTION:A frequency command is reduced by a current regulator 24 to constantly control the DC current during the time while the rotating speed of a motor is higher than the lower limit of the operating limit of the inverter at the instantaneously stopping time. When the power interruption time is prolonged or the deceleration of the rotating speed is early so that the frequency of the inverter becomes lower than the operating limit frequency fmin or lower, a logic arithmetic unit 30 is operated to interrupt the flow of a signal from a V/F converter 17 to a ring counter 18, thereby stopping the operation of the ring counter 18. Thus, the inverter is stopped, and the generating operation of the motor 5 is stopped, and the DC current Idc of the inverter becomes zero. This is continued from the time when the frequency of the inverter becomes lower than fmin to the recovery time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for an inverter for driving a motor during a momentary power failure (hereinafter also referred to as momentary power failure).

Generally, inverter-driven electric motors used in textile machinery, water supply and sewage systems, etc. are required to continue operating even if a power outage occurs for less than a few seconds, and to return to the specified operating state immediately after power is restored. It is often done. In this case, it goes without saying that care must be taken to perform such control so that the five-inverter device itself is also safely protected. Conventionally, for example, in the event of a momentary power outage, the output frequency of the inverter is lowered by 1', the rotational energy of the motor is used to generate electricity to keep the inverter in operation, and the inverter is immediately accelerated again after power is restored. A method (hereinafter referred to as the first momentary power outage countermeasure method) has been proposed.

FIG. 1 is a block diagram showing a conventional example of a current source inverter control system that takes the first measure against instantaneous power failure.

In the figure, 1 is an AC power supply, 2 is a forward conversion (rectification) section,
3 is a DC reactor, 4 is an inverse conversion (inverter) section, 5
is an AC motor such as an induction motor, 6 is a current transformer, and 7 is a shunt;
s, c+ij: piezoelectric transformer, 10 frequency command device, I
The IFi adders 12.14 and 23 are respectively 1.
2nd and 3rd comparators, 13 a voltage regulator, 15 a first current regulator (ACJ), 16 a phase shifter, 17 a voltage/voltage regulator;
Frequency (V/F) converter, 18 is a ring counter, 1
9 is a pulse amplifier, 20 is a DC current command generator, 21 is a power failure detector, 22 is a signal converter, 24 is a second current regulator (ACR), and 25 is a switch.

That is, the thickness of the motor current is determined by comparing the current command - obtained as the output of the voltage regulator 13 with the current 1 detected by the current transformer 6 in the second comparator 14. Based on the comparison output, the current regulator 15 performs adjustment calculations, and the phase of the forward conversion (rectification) section 2 is controlled via the phase shifter 16 based on the result. On the other hand, the motor frequency is determined by sending a frequency command f*1 obtained from a frequency command device 10 via a ramp generator 11 to an inverse conversion (inverter) section 4 via a V/F converter 17, a ring counter 18, and a pulse amplifier 19. The ignition control is performed by giving the following information and controlling the ignition.

The above is the normal operation, but next we will explain the operation at the time of power outage and power restoration.

Now, when the AC power supply 1 experiences a power outage, the secondary voltage of the voltage transformer 8 becomes zero voltage, so the power outage detector 21 detects this 7 and provides the detection output to the DC current command generator 20 .

The DC current command generator 20 uses the human power Ii as an initial value and outputs a predetermined value I over time. The magnitude of the output (i) is set to be equal to the excitation current I'M of the motor 5 (g).

Therefore, the DC current command value Idc* having the above characteristics is output from the DC current command generator 20 to the third comparator 2.
is supplied to one terminal of 3. The other terminal of the third comparator 23 is given the inverter DC input current Idc detected by the shunt 7, so the current Idc is compared with the command value 1dc*, and the deviation is determined by the second current regulator. 24
given to. The adjuster 24 performs an adjustment calculation such that the deviation becomes zero, and as a result, a frequency correction signal f. * is output.

Note that at this time, since the power failure detection signal from the power failure detector 21 is applied to the switch 25, the switch 25 is closed. Therefore, the second current regulator 24 also sends out a frequency correction signal f. * is the frequency command ( setting) value f* to perform frequency correction.

In this case, if the inverter DC input current 1dc supplied to one terminal of the third comparator 23 is also larger (smaller) than the command value Ido supplied to the other terminal, the frequency correction signal f. * becomes a negative (positive) value and decreases (increases) the frequency command value f*. Therefore, the frequency command f*1 sent from the adder 11 is always controlled so that the inverter DC input current Idc is always equal to the excitation current ■o of the induction motor 5.

When the AC power supply 1 is restored in this state, a predetermined voltage is applied to the power outage detector 21 via the voltage transformer 8, and its output signal disappears, so the DC current command generator 20 stops its operation and Switch 25 is opened. At this time, as the power outage detection signal disappears, the output of the signal converter 22 gradually attenuates due to a change corresponding to the inertia of the induction machine 5 and disappears (if configured, the output of the signal converter 22 will be output from the frequency command from the adder 11). With the attenuation of f, the frequency command value f* in the normal state is gradually restored.As a result, -C, the frequency of the inverter section 4 returns to the normal value, and the motor 5 smoothly returns to the state before the power outage. .

That is, in this method, during a power outage, the second current regulator 24
By lowering the frequency of the inverter so that the inverter DC current becomes a preset current (10) equivalent to the no-load current of the motor, the rotational energy of the motor is used to maintain the operating state even during a power outage. After power is restored, acceleration is started immediately to return to the set speed. Therefore, as long as the electric motor has sufficient rotation and energy, this is a very effective method. If the electric machine stops, it is necessary to shut off the inverter and then restart it by charging the commutating capacitor when the power is restored, but this charging generally takes a long time (about a few seconds). ).

In contrast, as soon as a momentary power failure is detected, the inverter operation is stopped, the charge in the commutation capacitor is held, and when the power is restored (in the case There is also a method (hereinafter also referred to as the second instantaneous power outage countermeasure method). All of the above methods were proposed by the present applicant, and the former Fi
Published as No. 7896, the latter was a patent application filed in 1888-1988.
The application is currently being filed as No. 416. In other words, the second instantaneous power outage countermeasure method is suitable when the power outage is relatively long and the residual voltage of the motor disappears before the power is restored and restarted, but when the outage is short and the residual voltage of the motor disappears, the second method is suitable. If the power is restored when the value is large, the system may not be able to restart normally. This is caused because the inverter output current and voltage phase at the time of restart do not match the residual voltage phase of the motor, and this may cause a commutation failure or the like. Therefore, in order to solve this problem, it is necessary to synchronize the inverter and the motor in preparation for restarting when the power is restored, which has the disadvantage that the control circuit becomes complicated. Furthermore, depending on the phase in which the inverter is started, the commutating capacitor must be initially charged, which also has the disadvantage that it takes time to restart the inverter.

This invention has been made in view of this point, and is capable of restarting and returning to the set speed in a short time after power is restored, regardless of the length of the power outage, the rotational speed of the motor, the presence or absence of residual voltage, etc. The purpose is to provide an inverter control method that allows for

The feature is that during a power outage, when the motor has rotational energy, the current regulator lowers the frequency so that the DC input current of the inverse converter reaches a predetermined value. When power is restored within this period, the operation of the current regulator is stopped and the power is gradually restored to normal. However, during the power outage, it was determined that the rotational frequency of the motor had decreased and power generation operation was no longer possible. When the power is restored, the operation of the inverse converter is stopped, and when the power is restored, the motor is restarted from the same thyristor that was used when it was stopped, so that the motor can be restarted stably in a short time under any conditions. That's the point.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of the present invention, and FIG.
Figure 3B and Figure 3B are waveform diagrams for explaining the operation of Figure 2 when the instantaneous power outage time is short and long, respectively.
Figure A is a block diagram showing the details of the logical operation unit in Figure 2, Figure 4B is the 4A motor speed 2 frequency characteristic, (b)
indicates the motor current (IM), and (c) indicates the power failure detection signal, respectively.

That is, in FIG. 2, the area surrounded by a dashed line indicates the area where the above-mentioned first momentary power failure countermeasure is taken, and from time t1 to ill or t1 shown in FIG. 3A or 3B (a).
~ t2, that is, while the motor rotational speed is higher than the lower operating limit of the inverter, the second current regulator 24 reduces the frequency command to keep the DC current constant as explained in FIG. (Io) The logical arithmetic unit 30 that performs control and therefore takes the second momentary power failure countermeasure does not perform any function during this period.

If the power outage is short and the inverter frequency is higher than its operating limit (min), the operation is the same as shown in Figure 1.On the other hand, if the power outage is long or the rotation speed is low Because the inverter frequency is fast, the inverter frequency falls below the operating limit frequency fmin during the power outage period (third
See time tll in diagram B. ), the logic operator 30 newly provided in FIG. 2 operates, and the V/F converter 17
In order to interrupt the flow of signals to the ring counter 18, the operation of the ring counter 18 is stopped. For this reason,
Since the inverter stops and the power generation operation by the electric motor 5 stops, the inverter emergency direct current Idc becomes zero. When the DC current Ido becomes zero, the second current regulator 24 has a large deviation from the current command value Idc*, so the switch 2
5 and a large negative frequency correction signal f to one terminal of the adder 11 through the signal converter 22. , the inverter frequency command r** acts in the direction of further lowering it, and finally becomes f″ht−〇.

Note that this state is between time tll and t2 in FIG. 3B.
That is, the inverter frequency continues from the time when it becomes below (min) until the power is restored. Thereafter, when the AC power is restored at time t2, the signal converter 22 is activated by the power outage detector 2.
In order to detect that the power failure detection signal disappears from 1 and gradually decrease its output as described above, the output frequency command f0, on the contrary, starts to gradually increase from zero. Note that at this time, the inverter current is controlled via the voltage regulator 13, the second comparator 14, the first current regulator 15, and the phase shifter 16.

On the other hand, when the power failure detector 21 also learns that the power failure detection signal has disappeared, the logical arithmetic unit 30 supplies the signal from the V/F converter 17 to the ring counter 18. At this point, the ring counter 18 starts operating, and therefore, the inverter current supplied from the power supply 1 through the υ forward converter 2, the DC reactor 3, and the shunt 7 is converted into AC by the inverse converter 4. t'' is applied to the electric motor 5, so that acceleration of the electric motor is started.

Next, the structure and operation of the logical arithmetic unit specifically provided in accordance with the present invention will be explained with reference to FIG. 4A, O6, and FIG. 4B.

As shown in FIG. 4A, the logical operator 3() includes a comparator 31, a Nant gate 32, and an AND gate 33.
It is composed of Toda. The comparator 31 detects that the inverter frequency command f** has become equal to or less than the minimum value fmin (the minimum frequency at which inverter operation can be performed using the rotational energy of the electric motor), and outputs an output signal as shown in FIG. 4A (c). Emit Sb. Nantes Gate 32 is the fourth
In response to the output signal Sa of the power outage detector 21 as shown in FIG. 4A (b) and the output signal Sb of the comparator 31, a signal S as shown in FIG. 4A (b) is generated.

Output. Therefore, during a power outage, the output frequency command f*
By * becoming f**<fmin, the above Shinzuki S
a and Sb are both °1”, resulting in a signal So
is "°O", therefore, the AND gate 33 cuts off the clock pulse 6fl having six times the input frequency as shown at 9 in FIG. 4B, and stops the operation of the ring counter 18. This means that the moment the output signal So becomes zero, that is, the time 111 in FIG. 3B or 4B.
The gate signal for the thyristor that was on at the time is stored as it is in the second/group controller 18, and
This means that an instantaneous commutating capacitor will remain at the polarity it was charged at at time ill. Therefore, after that, the power is restored at time t2 shown in FIG. 3B or 4B, and the output S of the power failure detector 21 is restored.
When a reaches tL O#l, the signal S0 becomes '1', and the AND gate 33 is opened, the ring counter 18 starts operating from the same position where it stopped at the previous time ill. , the same thyristors of the Innomata that were on immediately before time ill will turn on first, and the commutation capacitors will remain charged in the direction of turning on these thyristors, so There is no need for initial charging when restarting after power is restored, so restarting can be performed almost at the same time as power is restored (time t2).In addition, in this invention, the motor speed is sufficiently low during the power outage period. The first measure against instantaneous power failure is to continue operating the inverter until the rotational energy is almost exhausted, and when the inverter frequency falls below f + nin (for example, 5% frequency), the inverter will stop operating. If the power is restored during operation, not only can you immediately start accelerating, but you can also stop the inverter once a day, and the rotational speed of the motor becomes extremely low. Because the voltage is always zero, it is necessary to match the inverter's output level and the residual voltage phase after the power is restored and the inverter restarts f+t+, so the restart 11J is carried out smoothly in a short time. By organically combining two measures against instantaneous power outages, it is possible to restart optimally in a short time regardless of any conditions such as the length of the instantaneous power outage or the degree of decrease in rotational speed. It should be noted that the effectiveness of this invention has been confirmed through various experiments and studies.

FIG. 5 is a block diagram showing another embodiment of the present invention.

In the figure, 26 is a current transformer, 27 is a magnetic sensing element, 2
8 is a magnetic flux calculator, 29 is a magnetic flux setting device, and 24 is a magnetic flux adjuster. That is, in this embodiment, the motor magnetic flux is detected by calculation by the magnetic flux calculator 28 from the voltage and current values obtained through the voltage transformer 9 and the current transformer 26, or directly by the magnetic sensing element 27, and the detected magnetic flux value is Setter 2
Established at 9! The magnetic flux adjuster 24 adjusts υ to match the set target value.
It is used to control the frequency of the inverter.

Note that the magnetic flux regulator 24 is the second regulator 2 in FIG.
Similar to 4, it operates only during a power outage.

As described above, according to the present invention, the motor can be restarted quickly and smoothly after power is restored under any conditions, regardless of the length of the power outage, the number of revolutions, the presence or absence of residual voltage, etc. speed can be restored.

It should be noted that the present invention is particularly suitable for use in devices that do not have a speed detector among devices that drive a motor using a current source inverter.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example of a current source inverter control system with the first measure against momentary power failure, Fig. 2 is a block diagram showing an embodiment of the present invention, and Figs. 3A and 3B are respectively FIG. 2 is a waveform diagram to explain the operation when the stop time is short and long, FIG. 4A is a configuration diagram showing details of the logical arithmetic unit, and FIG. 4B is a waveform diagram of each part to explain the operation. , FIG. 5 is a block diagram showing another embodiment of the present invention. Code explanation 1... Power supply, 2... Forward conversion unit, 3...
...DC reactor, 4... Inverse conversion section, 5
・・・・・・Electric motor (induction machine), 6.26・・・・・・
Current transformer, 7... Current shunt, 8, 9... Voltage transformer, 10... Frequency command device, 11...
... Adder, 12, 14.23 ... Comparator, 13 ... Voltage regulator (AVR), 15.24
...Current regulator, 16... Phase shifter, 1
7...Voltage/frequency (■/F) converter, 18.
...Ring counter, 19...Pulse amplifier, 20...DC current command generator, 21...
...Power failure detector, 22...Signal converter, 2
4... Magnetic flux regulator, 25... Switch, 27... Magnetic sensing element, 28... Magnetic flux calculator, 29... Magnetic flux Setting device, 30...
...Logic operator, 31...Comparator, 32
...Nant Gate, 33...And Gate agent Patent attorney Akio Namiki Agent Patent attorney Matsuzaki 509 Figure 3A #3B (Masashi) (U)
To connection 4 Figure n Figure 45

Claims (1)

[Claims] The output frequency of an inverter that is equipped with at least an inverse converter and is powered by an AC power source to drive the motor at variable speed should be controlled (a frequency control means for controlling the ignition of the inverse converter, and a frequency control means for controlling the ignition of the inverter, and a frequency control means for detecting momentary interruption of the AC power source) and a frequency correction means for correcting a frequency command value given to the frequency control means in order to keep the DC input current of the inverse converter constant in order to perform power generation operation using the rotational energy of the electric motor. In an inverter control method that allows the inverter to operate continuously even during a momentary power outage, ignition control of the inverse converter is stopped upon detecting that the frequency command value has fallen below a predetermined value during a momentary power outage. At the same time, when the power is restored, by providing a logical means to start the ignition control of the inverse converter under the same conditions as when the power was stopped, the motor can be restarted regardless of the motor frequency during the momentary power interruption. A patented inverter control method that enables smooth startup in a short time.