JPH0441756Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a control device that drives an induction motor at a variable speed by primary frequency control, and in particular, the invention relates to a control device that drives an induction motor at variable speed by primary frequency control, and in particular, the invention relates to a control device that drives an induction motor at variable speed by primary frequency control, and in particular, the invention relates to a control device that drives an induction motor at variable speed by primary frequency control. The present invention relates to a stop control device for an induction motor that reduces start-up delay.

[Technical background of the invention and its problems]

In general, in motors that are excited independently, such as separately excited DC motors (hereinafter referred to as "DCM") and permanent magnet motors, if the motor is excited from a stopped state, the armature current flowing through the motor will be reduced. Since it acts as torque immediately, the startup delay is not a big problem.

On the other hand, in an induction motor (hereinafter referred to as "IM"), due to its structure, the excitation current component and the torque current component (corresponding to the armature current of DCM) are connected to the stator windings as a common primary current. We have no choice but to supply it. Therefore, even if the primary current is supplied, there is a time delay before the excitation current component establishes the magnetic flux of the IM, and the generation of torque proportional to the product of the magnetic flux and the torque current is also delayed. This time delay is a value unique to each IM. For the reasons mentioned above, in IM, there is a time delay (i.e., a start-up delay) before the desired torque is generated at the time of start-up. Such start-up delay is particularly problematic during so-called inching operation, in which starting and stopping are frequently repeated within a short period of time, and has caused a significant deterioration in the operability of equipment that requires inching operation.

FIG. 1 shows an operating method during inching operation in a conventional power supply device for driving an induction motor. In the figure, 1 is the operation signal, 2 is the primary current of IM, and 3 is
is the rotation speed of IM. The operation signal 1 is given only during the period indicated by ON, and the operation and stop are repeated in a short period of time. And only during this operation period 1
Since the next current 2 is supplied, there is a delay in the rise of the rotational speed 3 for the reason mentioned above.

As conventional methods for preventing such start-up delays, the following three are typical.

The first method, as shown in FIG. 2, is a method that shortens the time until the magnetic flux of the IM is established by temporarily supplying a large primary current 2 at the time of startup. This method is suitable for use with a fixed frequency, constant voltage power source, such as a commercial power source. However, as a power supply device for primary frequency control of IM, a frequency conversion device with a large current capacity is required to supply a large primary current 2 at startup.
This has the disadvantage that the larger the device, the higher the price.

The second method, as shown in FIG. 3, is a method in which the IM is constantly excited. In other words, Fig. 3 shows only the magnitude of the excitation current 4 supplied to the IM,
Although the frequency supplied to the IM stator is not specifically shown, when the IM is stopped, a DC excitation current is applied corresponding to the secondary frequency, and when the IM is rotating, an AC excitation current with a frequency synchronized with the magnetic flux is applied. give. In this method, the excitation current continues to flow through the IM even when it is stopped, so
Measures to prevent heating may be required. Measures to prevent such heating include using a low-loss IM that does not cause heat generation due to excitation current, or
A possible solution would be to use forced air cooling to allow cooling even when the system is stopped. However, since the excitation current of IM is generally larger than that of DCM, there is a drawback that if such heating prevention means as described above are taken, the structure becomes complicated and the price increases.

The third method, as shown in FIG. 4, uses a preliminary signal 5 for excitation prior to activation. That is, before the operation period is turned on, the preliminary signal 5 is given to the power supply device a time t _p in advance to supply the excitation current 4 . In this method, if the lead time t _p of the preliminary signal 5 can be equal to or longer than the time required to establish the magnetic flux at IM startup, the IM startup delay will be eliminated, and the power supply will also need to supply a large excitation current. This has the advantage that the device itself does not become bulky because there is no need for it. However, the preliminary signal 5 is
It is necessary to apply the signal prior to the driving operation (driving signal 1), and therefore it is often impossible to use in practice.
In particular, operations such as inching operation are often directly performed by humans, and it is often difficult to predict in advance the operations that humans will perform from time to time and create the preliminary signal 5, so this method also has problems.

[Purpose of invention]

The present invention was made to eliminate the above-mentioned drawbacks of the conventional technology, and improves the method of supplying the excitation current component to the induction motor that is operated in increments, thereby reducing the startup delay when restarting the induction motor. It is an object of the present invention to provide a stop control device for an induction motor that can reduce the number of rotations and improve the speed rise characteristics.

[Summary of the idea]

An induction motor stop control device that controls a primary current by separately calculating an excitation current component and a torque current component and vector-synthesizing the same, and stopping an induction motor that is operated in increments according to an operation stop command,
Off-delay means that delays the operation stop command by a predetermined set time; and even if the operation stop command is issued, only the excitation current component is supplied at a primary frequency corresponding to the secondary frequency of the induction motor only for the set time of the off-delay means. It is characterized by having a means for continuing to do so.

[Example of idea]

An embodiment of the present invention will be described below with reference to the accompanying drawings. Note that the same elements as in FIGS. 1 to 4 are given the same reference numerals.

FIG. 5 shows an embodiment of the induction motor stop control device of the present invention. The main circuit of this device includes an AC power source 10, a frequency converter (hereinafter referred to as "FCV") 11 that converts the AC power from the AC power source 10 into AC power of a desired frequency, and this FCV.
Induction motor (IM) driven by 11 outputs
It consists of 12. The FCV 11 may be one with a DC intermediate circuit consisting of a rectifier and an inverter, or may be a cycloconverter without a DC intermediate circuit. The IM 12 is vector-controlled by the control device 20 via the FCV 11. IM1
2 has a speed detector 13 to detect the rotation speed N.
is provided.

The control device 20 includes an excitation current component calculation circuit (hereinafter referred to as "i ₁ calculation circuit") 22 that calculates an excitation current component i ₁ that is set according to the command speed of the IM 12;
Torque current component calculation circuit that calculates the torque current component i ₂ of the IM12 (hereinafter referred to as "i ₂ calculation circuit")
It is equipped with 23. The calculation results of both calculation circuits 22 and 23 are led to a vector synthesis circuit 24, where vector synthesis is performed to form a control signal. This control signal controls the FCV 11 via the driver 25. The rotational speed N detected by the speed detector 13 is introduced into the i ₁ calculation circuit 22 .

The feature of the control device 20 is that the operating signal 1 is directly input to the i ₂ calculation circuit 23, but the i ₁ calculation circuit 2
2 is that an off-delay circuit 21 is provided in front. Therefore, the control device 20 controls the operation signal 1.
When i 2 is input, both arithmetic circuits 22 and 23 respond without any time delay, but when an operation stop command is issued, that is, when operation signal 1 is suddenly cut off, i ₂
Although the arithmetic circuit 23 is immediately cut off, the _i1 arithmetic circuit 22 is cut off for the set time _tD of the off-delay circuit 21.
However, the same operating state as when operation signal 1 is input continues.

6 and 7 are explanatory views of the operation of the apparatus of FIG. 5 constructed as described above. Now, when the operating signal 1 as shown in FIG.
A conduction angle control signal is given to the FCV 11 to cause the FCV 11 to output a current at a predetermined frequency. Therefore, at the same time as the operation signal 1 rises, a composite current of the excitation current component i ₁ and the torque current component i ₂ is supplied to the IM 12,
The IM 12 is started and its rotational speed 3 increases toward a predetermined rotational speed. Next, when the operation signal 1 turns off (on period ends), the i ₂ calculation circuit 23 is immediately turned off, but the i ₁ calculation circuit 22 continues to operate for a predetermined time t _D. Therefore, when the operation signal 1 is turned off, the control device 20 immediately cuts off the torque current component i ₂ of the IM 12, but continues to flow the exciting current component i ₁ for a time _tD . During the predetermined time _tD
As the excitation current component i ₁ supplied to IM12, IM
When IM 12 continues to rotate due to inertia even after the torque current component i ₂ is interrupted, it is supplied with the same primary frequency as the rotor of IM 12 (slip becomes zero). After the rotor stops, direct current (zero frequency) is supplied.

If the torque current component i ₂ and the excitation current component i ₁ are applied simultaneously as at the time of startup in FIG. 6, the rise of the excitation current component i ₁ will be delayed, resulting in a startup delay. However, by providing the off-delay circuit 21 according to the present invention, during the inching operation in which restart is performed within time _tD , since the excitation current component i ₁ has already been established, the torque current component _{i 2} responding to the operation signal 1 In response to this, IM12 can be activated immediately. Therefore, there is no delay in the second and subsequent IM activations due to the inching operation, and as long as the inching operation is assumed, the same result as when the IM 12 is constantly excited can be obtained. Moreover,
Since the excitation current component _i1 of IM is not so large,
There is no need to make the converter particularly large in capacity for excitation during stoppage, and there is no need to consider the temperature rise of the IM due to continuous excitation during stoppage.

In the above embodiment, the torque current component i ₂ is immediately cut off after the operation signal 1 is turned off, and the excitation current component i ₁ is cut off after a predetermined time t _D has elapsed. Unlike that, the torque current component i ₂ is not cut off immediately after the operation signal 1 is turned off, but the torque current component i ₂ is cut off after the IM decelerates, and then the rotation speed decreases to a predetermined value. By doing so, the torque current component i ₂ may be interrupted, and only the excitation current component i ₁ may be allowed to flow until a predetermined time t _D has elapsed after this interruption. moreover
The excitation current component i ₁ may be made to flow until a predetermined time t _D has elapsed after the IM is completely stopped. In either case, the same effects as in the above-described embodiments can be achieved.

[Effect of idea]

As described above, according to the present invention, only the excitation current component continues for a predetermined period of time in synchronization with the stoppage of the supply of the torque current component. The startup delay can be reduced to a level that does not cause any practical problems, and the device can also be simplified and downsized.

[Brief explanation of the drawing]

1, 2, 3, and 4 are time charts for explaining the operation mode of an induction motor by a conventional control device, and FIG. 5 is a circuit configuration diagram of a control device according to an embodiment of the present invention. , Figures 6 and 7 are
3 is a time chart illustrating the operation mode of the induction motor by the control device shown in the figure. 1... Operating signal, 2... Primary current of induction motor, 3... Rotation speed of induction motor, 4... Exciting current, 10... AC power supply, 11... Frequency converter (FCV), 12... Induction motor (IM), 20...
Control device, 21... Off-delay circuit, 22...
Excitation current component (i ₁ ) arithmetic circuit, 23... Torque current component (i ₂ ) arithmetic circuit, 24... Vector synthesis circuit, 25... Driver.

Claims (1)

[Claims for Utility Model Registration] An induction motor that controls a primary current by calculating excitation current components and torque current components separately and vector-synthesizing them, and that stops an induction motor that is operated in increments in accordance with an operation stop command. The stop control device includes an off-delay means 21 for delaying the operation stop command by a predetermined set time, and a secondary frequency of the induction motor 12 for only the set time of the off-delay means 21 even when the operation stop command is issued. means 13 for continuing to supply only the excitation current component at a primary frequency corresponding to;
22, 24, and 25. A stop control device for an induction motor.