JPS58127588A - Drive device for ac motor - Google Patents

Abstract

PURPOSE:To enable to reduce the capacity of an emergency generator by constructing to reduce the input to an AC motor by an emergency generator at the power feeding time to a value less than the rated value. CONSTITUTION:A restarting voltage setter 24 is provided, and the output is used as the input of a voltage controller 23 through a set value switching unit 25. That is, when the reoperation is performed by an emergency power source, the unit 25 is switched from rated voltage value VN to a restarting voltage VR, and is operated. With the above construction, the output voltage of an inverter 13 is reduced until the rated current flow from th generator 15, it becomes safe even at the power interruption time, and it is not necessary to largely increase the capacity of the emergency generator.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a drive device for an AC motor that provides protection against power outages.

(Prior art) In general, the torque-speed characteristics of machines that handle fluid loads exhibit so-called two-bundle load characteristics as shown in Figure 1. In Figure 1, the horizontal axis is the rotational speed N, and the axis is the silk T. The target here is the torque characteristic T shown in the figure. T, is the torque characteristic at full load, and! ,
is that at no load.0 The load targeted by the present invention is:
This is a load that has a critical speed for mechanical plaster at a rotational speed of N, and is a load that causes instability of the mechanical system and excessive vibration near a rotational speed of 1fN. This instability phenomenon is generally more severe as the load torque becomes larger, and as shown in Figure 1, in the shaded area where the load torque exceeds the danger zone torque T1, the vibration of the rotating body exceeds the permissible limit, and in some cases
The rotating body may be damaged. Therefore, the driving force formula for such a special load is the maximum speed N1 with no load.
It is common practice to accelerate to a maximum speed, supply fluid as a load at the maximum speed, and then stop the fluid supply again at the maximum speed to create an unloaded state before stopping. However, if such operation is carried out, if there is a power outage during full load operation, the time constant for reducing the load and the load will re-run at 7 and reach critical speed, causing a competition with the 5 hour rate. What is shown in Figure 2 is the horizontal axis time, which is the time constant for decreasing the load.0 As shown in the figure, the load torque at the speed N? , (N,) decreases with the start of fluid load removal, 1=1. Hazardous load at the time of? , (N, ) or less. Therefore, 1=1. Until [7] If the speed of the rotating body that re-ran is N, then 1
It is safe because it is a rotating body. The condition at this time is expressed as K as follows.

'5.

However, the average load torque GD in N, %N,
Moment of inertia of the rotating body As explained above, in the event of a power outage, the rotating body will come to a safe stop by removing the load, but if the load removing device fails or the removal capacity is If it decreases, (l) t at 2.

may become large and the inequality sign may be reversed.

As a countermeasure for this problem, there is a configuration of a drive device shown in diagram N3. In Fig. 3, 11 is a power receiving switch;
雛 is a transformer 1), Lm is an inverter device, 14 is an AC motor, and the load of the AC motor 14 has the above-mentioned characteristics. The output 11111 wave number of the inverter device 13 is one foot, and its output voltage is signal-compared with the voltage of the output voltage setter B via the output voltage detector 22v, and is subjected to so-called feedbatter control via the voltage control circuit.

The features of the configuration in Figure #I3 are the emergency generator 15 and the emergency switch 4116, and in the case of the above-mentioned malfunction, the emergency generator 1svt is started at the same time as a power outage, the emergency switch 16v is turned on, and the inverter device 13 is restarted. By doing so, a measure is taken to accelerate the AC electric motor lateral 14v again and prevent the speed reduction Y of the AC electric motor @14.

(Problems with the prior art) However, in the case of Fig. 3, since the AC motor 14 is driven by the output of the emergency generator, it is necessary to increase the capacity of the emergency generator by a large amount, which is economically disadvantageous. becomes.

(Object of the Invention) The present invention was made in view of the above-mentioned problems, and its purpose is to significantly increase the capacity of the emergency generator without relying on the load removal capacity during a power outage. 5. To provide a drive device for an AC motor that is not necessary.

(Structure of the Invention) In order to achieve the above object, the present invention provides emergency power generation a! The AC motor drive device is characterized in that the AC motor is configured to limit input to the AC motor to a value below the rated value when power is supplied by the emergency power generation MAK.

(Embodiments of the Invention) First, the characteristics of the AC motor when the load is turned on again using the emergency generator output will be described. Figure 4 shows the output voltage of the AC motor 14 at the input 9-/device port when the power is turned on again.
The output torque Tl1l and the input current of the interface device 13! This is a diagram illustrating the relationship between

The type of AC motor that can be considered is an induction motor or a hysteresis motor, and here the hysteresis motor is considered. As shown in Fig. 4, when the output voltage is turned on again with the rated voltage vM, the output torque TvI
is obtained, and this value is the load torque T, (N,) at full load.
Since the current becomes larger, the AC motor 14, which had been slightly reduced in speed between the power outage and the restart, is accelerated again. However, in this case, the input current of inverter device B is l1lI
Therefore, it is necessary to supply this current from the emergency generator 15.

By the way, as shown in FIG. 4, the inverter device 13
By summing the values of the output voltage t/vjK and re-energizing the output voltage, the output torque TM(N, ) is obtained. In this case I
Considering the load characteristics of the rotating body in Figure IE1, it is not possible to re-accelerate the rotating body, but the deceleration torque (TI-T, (
N, )) Deceleration starts at a deceleration rate of K, and deceleration no longer occurs near N0 during N.

Incidentally, if the slip becomes large, the motor output torque will also increase slightly due to the action of current, which is even more convenient. In this way, the input current of the inverter device 13 is! The value of 0 becomes 1, which can be significantly reduced.The present invention is an application of this concept, and one embodiment thereof is shown in FIG.

In FIG. 5, the same elements as those in FIG. 3 are given the same numbers, and their explanations are omitted. The feature in FIG. 5 is that a restart voltage setter 24v is provided and input to the current control circuit B via the set value switch 5. That is, a major feature is that when restarting operation using the emergency power source, the setting value switch 25 is switched from the rated voltage 7M value to the restart voltage vlflK.

By employing such a configuration, as described above, it is possible to provide an AC motor drive device that is safe during a power outage and does not require a significant increase in the capacity of the emergency generator.

(Modified example of invention) Another embodiment of the invention is shown in FIG.

In the egG diagram, the same elements as in FIG. 3 are given the same numbers and their explanations are omitted, 2O is a current transformer connected to the output of the emergency generator, and 2@b is a current converter. 27 is an emergency generator current setter, and the emergency generator controller is a comparator amplifier, which outputs a signal according to the difference between the set value and the actual current. A current control circuit 29 controls the output voltage of the inverter device 13 by its control output.

By adopting such a configuration, the output voltage of the inverter device 13 is reduced from the rated voltage vIf until the rated current of the emergency generator flows, and the following effects are obtained.

(a) Emergency power generation 4I! Since the other loads connected to the generator are usually smaller than the design conditions, the capacity of the emergency generator can be fully utilized.

(b) Therefore, the restart voltage is v! of FIG. 4 while maintaining the emergency start capacity determined by the embodiment of FIG. 5. l, the deceleration rate of the rotating body is further reduced and safety is improved.

In addition, in the explanation of FIGS. 5 and 6, the inverter device 13 is
The concept is the same even if there are multiple units. When applying this idea to Figure 6, for example, N
It is sufficient to set the emergency generator current setting value of each inverter device to the rated current of 17NK.

Furthermore, the same concept applies when one inverter device (multiple AC motors) is connected.

(Effects of the Invention) According to the present invention, the speed of the AC motor can be maintained at a predetermined value or higher even during a power outage, which is not only safe, but also allows the output of the emergency generator to be kept below a predetermined value. It is characterized by the fact that there is no need to significantly increase the capacity of the emergency generator.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of torque speed characteristics of an AC motor, and FIG. 2 is an explanatory diagram of load reduction characteristics of an AC motor. FIG. 3 is a block configuration diagram of a conventional AC motor drive device, FIG. 4 is an explanatory diagram of restart characteristics of an AC motor, and FIG. 5 is a block configuration diagram of an AC motor drive device according to an embodiment of the present invention. Figure 6 is a block diagram of an AC motor drive device according to another embodiment of the present invention. 0 11...Power receiving switch, Ebisu...Transformer, 13...
Inverter device, 14... AC motor, Ru... Emergency generator, 16... Emergency switch, 21... Output voltage setting device, n... Output voltage detector %... Voltage Control circuit, restart voltage footer. δ...Set value switch, 26-tooth alternator, 26b...
Current converter, n...Emergency generator current setting device, 28...
- Comparison amplifier, 29... current control circuit. Applicant's agent Kiyoshi Inomata v11 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. In a drive device I for an AC motor that is supplied with power by switching to an emergency power generator 9 in the event of a power outage in the power receiving system, the input to the alternating current generator is limited to below the rated value when power is supplied by the emergency generator. An AC motor drive device characterized by comprising: 2. The AC motor driving device according to claim 1, wherein the driving voltage of the AC motor is narrowed down to a rated voltage or less. 3. The AC motor according to claim 1, wherein the driving voltage of the AC motor tank is controlled so that the output current of the emergency generator becomes a preset electric fi value. drive unit.