JPH06262100A - Speed control device of differential centrifugal dehydration machine - Google Patents

Abstract

PURPOSE:To avoid an unusual increase in the regenerative power of a motor on a regenerative operation side when a power supply for a differential centrifugal dehydra tion machine which is powered by motors, one of which is in a power running mode and the other of which is in a regenerative running mode and at the same time, dehy drating, has recovered from a short time power supply failure. CONSTITUTION:If the speed of a motor 22 for a differential governor is accelerated during a power supply failure, a signal switching device 33 activates an instantaneous power supply failure frequency setting device 32 in which a higher value is set during the recovery of power supply. Therefore, the deviation range between the speed of the motor for a differential governor and a command value of frequency for the differential governor is narrow, so that a regenerative power can be restricted. The command value of frequency for the differential governor at a further higher level is gradually restored to an original value by action of a means for calculating a reduced speed. Consequently, the speed of the motor for the differential governor is restored to an original speed in a maintained deviation range, in accordance with a change in the command value of frequency for the differential governor, and thus the regenerative power is well controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power source for a differential type centrifugal dehydrator, in which two electric motors are coupled to each other, one electric motor is in a power running operation, and the other electric motor is in a regenerative operation for dehydration. The present invention relates to a speed control device in the case of doing.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional example of the configuration of a differential centrifugal dehydrator. In water treatment facilities such as waterworks and sewers, dehydration treatment is performed to reduce the weight and volume of sludge generated during water treatment work, and a differential centrifugal dehydrator is often used to dehydrate this sludge. ing. The differential centrifugal dehydrator has a double-rotation cage structure in which the rotation axis of the main machine 10 as the first rotary cage and the rotation axis of the differential speed machine 20 as the second rotary cage coincide with each other. 10 and the differential gear 20 are driven by separate electric motors. That is, the main motor 12 as the first electric motor is connected to the main motor 10 via the main motor drive belt 11.
The differential speed electric motor 22 as the second electric motor drives the differential speed machine 20 through the differential speed drive belt 21. By the way, in this differential centrifugal dehydrator, the motor 22 for the differential speed machine is set to the free state (that is, the power source of the motor 22 for the differential speed machine is turned off) while the main motor 10 is being driven by the main machine motor 12 during sludge dewatering. Then, the differential gear 20 is structured to rotate with the rotation of the main engine 10. Therefore, when the electric motor 12 for the main engine is driven in the power mode to drive the main engine 10 at a predetermined rotation speed,
The differential gear 20 tries to rotate at the same speed as the main engine 10.
Therefore, the electric motor 22 for the differential speed machine is regeneratively operated to lower the rotation speed of the differential speed machine 20 lower than that of the main machine 10 to perform the dehydration operation.

Centrifugal dewatering machines generally possess a very large flywheel effect, so unless the electric motor associated with the centrifugal dewatering machine has a particularly large capacity, it takes a long time to start up the centrifugal dewatering machine. Therefore, the rotation speed must be gradually increased. Therefore, a method is widely used in which an induction motor is used as a motor for driving a centrifugal dehydrator and the output frequency of an inverter that outputs AC power of variable voltage and variable frequency is gradually increased to accelerate the centrifugal dehydrator. Figure 3
In the conventional example shown in FIG. 1 as well, the electric motor 12 for the main engine operates with the AC power of the variable voltage / variable frequency output by the inverter 13 for the main engine. Controlled. The main machine frequency setter 15 sets the target operating frequency of the main machine electric motor 12. Similarly, the differential speed motor 22 is also driven by the variable voltage / variable frequency AC power output from the differential speed inverter 23, and the differential speed inverter 23 is controlled by the differential speed control circuit 24. Further, since the differential speed machine frequency setting device 25 sets a frequency value lower than that of the main machine motor 12 as described above, the differential speed motor 22 is set.
Will be regeneratively driven to operate at this value.

[0004]

FIG. 4 is an operation waveform diagram showing the operation of each part when the power supply is interrupted for a short time in the conventional example shown in FIG. 3, and FIG. Four
Is the change in the rotation speed N1 of the main machine motor 12 and the change in the main machine frequency command value F1 output from the main machine inverter 13, FIG.
Represent changes in the rotation speed N2 of the differential speed motor 22 and changes in the differential speed frequency command value F2 output from the differential speed inverter 23, respectively.

In FIG. 4, it is assumed that a power failure occurs at time t1 and this power failure is recovered at time t2, and this power failure time is extremely short. During this short power failure, the motor 12 for the main engine becomes free-running and its rotation speed N1 gradually decreases, but when the power is restored, the rotation speed N1 starts increasing to approach the frequency command value F1 for the main engine. , At time t3, the original rotation speed is restored (see FIG. 4). By the way, at the time point t2 when the power is restored, a large difference is generated between the main engine motor speed N1 and the main engine frequency command value F1. In order to reduce this difference (that is, to increase the main motor speed N1), a large current flows to the main motor 12, but
The current increases more and more as the difference between the two increases, and the motor speed N1 for the main engine is the frequency command value for the main engine.
Since it takes a long time to approach F1, the time during which this large current is flowing also becomes long. Therefore, the main machine inverter 13 may trip due to overcurrent. Therefore, starting from time t2 when the short-time power failure is restored, the frequency command value for the main engine is set.
The main engine speed control circuit 1 is a circuit (so-called synchronous pull-in circuit) for performing an operation of gradually reducing F1 and then gradually returning it to the original value.
It is installed in the inside of 4. In FIG. 4, the frequency command value F1 for the main engine, which is shown by the alternate long and short dash line, temporarily hangs between time t2 and time t3, because the above-mentioned synchronous pull-in circuit operates. Therefore, the difference between the main engine motor speed N1 and the main engine frequency command value F1 becomes small, and the risk of overcurrent trip can be avoided.

On the other hand, the differential gear 20 has the main engine 1 as described above.
It is rotated by 0, and is operating while regenerating energy to the power source side through the differential speed motor 22.
The fact that the regenerative operation is in progress can be seen from the fact that the differential speed motor speed N2 is larger than the differential speed frequency command value F2 (see FIG. 4). When a power failure occurs at time t1, the differential speed motor 22 becomes free, so that the differential speed 20 is rotated along with the main engine 10, so that its rotational speed increases until it matches the rotational speed of the main engine 10. . Therefore, at time t2 when the power is restored, the deviation value δ ₁ between the differential speed motor speed N2 and the differential speed frequency command value F2 has become a large value. Of a large amount of electric power will continue for a long time, which may cause the differential speed inverter 23 to trip due to overvoltage or overload.

If a differential pull-in circuit similar to the main engine inverter 13 is provided in the differential speed inverter 23, the differential speed frequency command value F2 droops between time t2 and time t3 as shown by the broken line. Then, the deviation value Δ ₂ between the differential speed motor speed N2 and the differential speed frequency command value F2 becomes even larger. Therefore, when the regenerative operation is performed, the differential speed control circuit 24 is not provided with the synchronous pull-in circuit, but still the disadvantage due to the large deviation value δ ₁ described above occurs.

As described above, since the centrifugal dehydrator has a great flywheel effect, it takes a long time to start. Therefore, once a trip occurs, it takes a long time to restart, which causes a problem that the operating rate of the device is reduced.
Therefore, an object of the present invention is to connect two electric motors, one electric motor being in a power running operation and the other electric motor being in a regenerative operation to perform dehydration while the power source of a differential centrifugal dehydrator recovers from a short power failure. , To prevent the regenerative electric power of the electric motor on the regenerative operation side from becoming excessive.

[0009]

To achieve the above object, a speed control device for a differential centrifugal dehydrator according to the present invention comprises a first speed control device for controlling the rotation speed of a first electric motor, and A first electric motor driven by being coupled to the first electric motor
Rotation cage, a second rotation cage coaxial with the first rotation cage and rotated by the first rotation cage, and a rotation speed of the second rotation cage connected to the second rotation cage by regenerative operation. In a differential centrifugal dehydrator comprising a second electric motor having a speed lower than that of the first rotary cage and a second speed control device controlling the rotational speed of the second electric motor, The second speed control device is provided with command value changing means for increasing the rotation speed command value of the second electric motor when the power supply recovers from a short-term power failure. First speed setting means for setting a rotation speed command value during operation, second speed setting means for setting a rotation speed command value higher than that during regenerative operation, and when the power supply recovers from a short power failure Select the second speed setting means, and then select the second speed setting means. Shall be composed of a signal switching means switches to speed setting means, a high rotational speed deceleration calculating means for reducing the command value to a lower rotational speed command value at a predetermined time rate of change.

[0010]

[Function] Since the second electric motor, which is in regenerative operation while the differential centrifugal dehydrator is in operation, becomes free during a power outage, it is driven by the first rotary cage and its rotational speed increases. The rotation speed of the second electric motor at the time when the power is restored and the frequency command value of the second electric motor largely deviate from each other. According to the present invention, by increasing the frequency command value of the second electric motor when the power source is restored, the deviation width between the rotation speed of the second electric motor and the frequency command value is reduced, thereby suppressing an increase in regenerative power. It is a thing. Here, the second motor frequency command value is the signal switching means at the same time when the power is restored,
The first speed setting means that sets the speed command value during normal operation is switched to the second speed setting means that sets a higher speed command value to increase the speed, and then the first speed having a lower value again. Although the switching to the setting means, the rotation speed command value is gradually decreased by the operation of the deceleration calculation means in accordance with a predetermined time change rate, so that the second motor can be returned to the original rotation speed without generating a large regenerative electric power. is there.

[0011]

FIG. 1 is a block diagram of a differential centrifugal dehydrator showing an embodiment of the present invention. A main machine 10 as a first rotating cage and a main machine drive shown in the embodiment of FIG. Belt 11,
A main motor 12 as a first motor, a main inverter 13, a main speed control circuit 14, a main frequency setter 1
5, the name of the differential speed machine 20, the differential speed machine drive belt 21, the differential speed machine electric motor 22, the differential speed machine inverter 23, and the differential speed machine speed control circuit 24 as the second electric motor. The purpose and function are the same as those of the conventional example described above with reference to FIG.

In the embodiment of FIG. 1, the differential speed machine frequency setting device 31, the instantaneous power failure frequency setting device 32, and the signal switching device 33.
And a deceleration calculating means (not shown) constitute a command value changing means. However, when controlling the speed of an electric motor, acceleration / deceleration calculation means for converting a rapidly changing speed command value into a slowly changing speed command value at a predetermined rate of change is usually equipped. Means may be used instead of the deceleration calculation means described above.

When the differential centrifugal dehydrator is operating,
Since the contacts of the signal switching device 33 are in the state shown in the figure, the frequency setting device 31 for the differential speed device is operated by the differential speed control circuit 2 for the differential speed device.
4 is connected. Here, when the power supply recovers after a short power failure, the contact point of the signal switch 33 is switched to a state opposite to that shown in the drawing. That is, the instantaneous power failure frequency setting device 32 is connected to the differential speed machine speed control circuit 24. Since the frequency command value set by the frequency setter 32 during the instantaneous power failure is higher than the frequency command value set by the frequency setter 31 for the differential speed device that has been connected until then, the differential speed device during the power failure period The rotational speed of 20 increases due to the above-mentioned reason, and the differential speed electric motor 22 coupled to the differential speed 20 also has a corresponding increase in rotational speed even if the rotational speed increases correspondingly. The deviation value that occurs is slight. Next, this frequency command value is gradually reduced by the action of the deceleration calculation means, so that the rotation speed of the differential speed electric motor 22 also correspondingly decreases, and smoothly returns to the rotation speed before the power failure.

FIG. 2 is an operation waveform diagram showing the operation of each part when the power supply is interrupted for a short time in the embodiment shown in FIG. 1. FIG. 2 shows the presence or absence of the power supply voltage, and FIG. 2 shows the main motor 1
2 changes of the rotation speed N1 and the change of the main machine frequency command value F1 output by the main machine inverter 13, FIG. 2 shows the change of the rotation speed N2 of the differential speed motor 22 and the difference output by the differential speed inverter 23. Each shows the change of the frequency command value F2 for speed machines.

In FIG. 2, it is assumed that a power failure occurs at time t1 and this power failure is recovered at time t2, and this power failure time is extremely short. Also, at time t3, the main motor 1
2 and the rotation speed of the differential motor 22 is returned to the original value. Here, FIG. 2 is the same as FIG. 4 described above, and FIG. 2 is also the same as FIG. 4 described above, so description thereof will be omitted.

In the present invention, as shown in FIG. 2, the differential speed frequency command value F2 is sharply increased at the time point t2 when the power failure is recovered. Therefore, the deviation value δ from the differential speed motor speed N2 is δ.
Is much smaller than the deviation value δ ₁ or the deviation value δ ₂ shown in FIG. Further, the frequency command value F2 for the differential speed device gradually decreases toward the original value according to the action of the deceleration calculation means, so the motor speed N2 for the differential speed device also decreases corresponding to this decrease. Therefore, the difference value δ between the two in this case is still small.

[0017]

EFFECTS OF THE INVENTION When two electric motors are coupled to each other, one electric motor performs a power running operation, and the other electric motor performs a regenerative operation while performing a regenerative operation. Since the electric motor that was being used becomes free, it will be rotated by the differential centrifugal dehydrator and its rotation speed will increase, so there will be a large gap between the rotation speed of the regeneration side motor and its speed command value. I will end up. At the moment when the power source is restored, the divergence causes the regenerative electric motor to regenerate an extremely large amount of power to the power source side, which may cause overvoltage or overload, which may cause tripping. The speed command value of the regeneration-side electric motor is rapidly increased at the time when is restored to reduce the deviation from the rotation speed of the regeneration-side electric motor. After that, since the increased speed command value is reduced to the original value with a predetermined deceleration, the rotation speed of the regeneration-side motor also correspondingly decreases with a small deviation width maintained. The power that is regenerated is suppressed. Therefore, the trip of the device due to overvoltage or overload can be avoided, and the operation rate of the device can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a differential centrifugal dehydrator showing an embodiment of the present invention.

FIG. 2 is an operation waveform diagram showing the operation of each part when the power supply is interrupted for a short time in the embodiment shown in FIG.

FIG. 3 is a configuration diagram showing a conventional example of the configuration of a differential centrifugal dehydrator.

FIG. 4 is an operation waveform diagram showing the operation of each part when the power supply is interrupted for a short time in the conventional example shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Main machine as a 1st rotary cage 11 Main machine drive belt 12 Main machine electric motor as a 1st electric motor 13 Main machine inverter 14 Main machine speed control circuit 15 Main machine frequency setting device 20 Differential speed machine as a 2nd rotary cage 21 Differential speed machine Drive belt 22 Motor for differential speed machine as second electric motor 23 Inverter for differential speed machine 24 Differential speed machine speed control circuit 25, 31 Differential speed machine frequency setter 32 Instantaneous power failure frequency setter 33 Signal switcher

Claims (2)

[Claims] 1. A first speed control device for controlling a rotation speed of a first electric motor, a first rotary cage which is coupled to the first electric motor and driven by the first electric motor, and a coaxial with the first rotary cage. And the second rotary cage that is rotated by the first rotary cage and the second rotary cage that is connected to the second rotary cage by the regenerative operation.
A differential centrifugal dehydrator comprising a second electric motor having a rotation speed of a rotating cage lower than that of the first rotating cage and a second speed control device for controlling the rotation speed of the second electric motor. , When the power supplies of both electric motors recover from a short power failure,
The speed control device for a differential centrifugal dehydrator, wherein the second speed control device is provided with command value changing means for increasing a rotation speed command value of the second electric motor. 2. The speed control device for a differential centrifugal dehydrator according to claim 2, wherein the command value changing means includes a first speed setting means for setting a rotation speed command value during regenerative operation, and a regenerative operation. A second speed setting means for setting a rotation speed command value higher than the time, and a second speed setting means when the power source recovers from a short power failure, and then selects the first speed setting means. A speed control of a differential centrifugal dehydrator, which comprises signal switching means for switching and deceleration calculating means for reducing a high rotation speed command value to a low rotation speed command value at a predetermined time change rate. apparatus.