JPH05137364A - Method of switching operational state of inverter - Google Patents

Abstract

PURPOSE:To enable smooth switching of operational states of an inverter while, suppressing generation of overcurrent, by controlling the AC output of the inverter so as to decrease with a first time gradient while keeping its frequency constant, converting the AC output into a DC output at a preset switching level, and then controlling the DC output so as to increase with a second time gradient, thereafter shifting the operational state of the inverter to a DC braking operation after the DC output reaches a predetermined value. CONSTITUTION:To an inverter which continues the ordinary speed control of a load at an AC output voltage Vi1, at a time t0, issued is a command of DC-braking operation of an induction motor of the load. Then, only the voltage of the AC output of the inverter is decreased from the value of Vi1 with a predetermined time gradient, without changing its frequency. When a target decrease value Vi2 is reached at a time t1, the output of the inverter is changed over from AC to DC. Thereafter, the DC output is so controlled as to increase to a predetermined value Vid with a predetermined time gradient. When reaching the predetermined value Vid at a time t2, the output of the inverter subsequently makes a transition to the stationary DC braking operation. In this case, the voltage Vi2 is so selected as to have a adequate value smaller than the voltage Vid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for switching the operating state of an inverter when the operating state of the load induction motor is switched from a normal operation based on an AC output to a braking operation based on a DC output.

[0002]

2. Description of the Related Art As a conventional operation state switching method of this type, a method of controlling the output voltage of an inverter as shown in the operation waveform diagram of FIG. 2 or 3 is known. First, Figure 2
Changes the output of the inverter to a DC output when a DC braking command is issued to the load induction motor at the time t _o to the inverter which is performing normal speed control with the AC output voltage V _i1 . The output value is a predetermined value V
_This is a case where _id is set and the state is changed to the DC braking state. Next, FIG. 3, immediately the inverter in the such time t _o of - direct current to output DC voltage of the predetermined value V _id from data - the inverter at time t ₃ after a predetermined time along with breaking the AC output of the motor It shows a case of shifting to a braking state.

[0003]

However, regarding the conventional operating state switching method as described above, in the case of FIG. 2, if the output frequency of the inverter is high immediately before switching, the counter electromotive force of the load induction motor is instantly changed. There was a risk that an excessive current due to electric power would flow in and the inverter would go into an overcurrent state, resulting in a shutdown. Further, as in the case of FIG. 3, in order to avoid the above-mentioned overcurrent state, a period in which the residual magnetism spontaneously disappears in the load induction motor (in the case of the figure, time t _o ~
Assuming curtailing output data, the output cross period the inverter in immediately before the switching - - In t between ₃₎ the inverter must make long enough to data of the output frequency becomes higher, thus including subsequent DC braking The required stop time from the time t _o becomes longer. That is, the required stop time varies depending on the output frequency immediately before the switching, and if such DC braking control is for positioning control, it is difficult to maintain the accuracy of the stop position. Become.

In view of the above, the present invention reduces the influence of the output frequency immediately before the switching of the operating state as described above to make the switching to DC braking smoother, and shortens the required stop time for the load induction motor. It is an object of the present invention to provide a method of switching the operating state of an inverter that can be achieved.

[0005]

In order to achieve the above object, an inverter operating state switching method according to the present invention changes the operating state of an induction motor whose speed is to be controlled from a normal operation to a DC output by a predetermined AC output. A method of switching the operating state of an inverter when switching to braking operation by means of: applying a switching command, the AC output of the inverter is frequency-invariant, and only the voltage is reduced and controlled at a predetermined time gradient, As soon as the AC voltage reaches the reduction predetermined value, the output of the inverter is immediately changed to the DC output, and the DC output voltage is set to the predetermined value to be applied during the braking operation to shift to the steady DC braking operation. And, the predetermined value for reducing the AC voltage is set as the predetermined value for the DC voltage to be applied during the DC braking operation, or the above-mentioned invertor is used. The operating state switching method according to claim 1, wherein the frequency of the AC output of the inverter remains unchanged with the application of the switching command, and only the voltage is reduced at a predetermined first time gradient, and the AC voltage is the DC braking. When the switching set value set as a value smaller than the steady predetermined value of the DC voltage to be applied in the steady state of operation is reached, the output of the inverter is changed to the DC output and the DC output voltage is changed to the switching set value. From the above to the above-mentioned steady-state predetermined value, the increase control is performed at a predetermined second time gradient, and when the above-mentioned predetermined value is reached, steady DC braking operation is started.

[0006]

As described above, the occurrence of the overcurrent state of the inverter at the instant when the operating state of the load induction motor is switched is caused by the large back electromotive force of the motor at the instant when the operating state is switched. It is generated as an obstacle to the change in the amount of magnetic flux in the electric motor due to the change. Therefore, the overcurrent state can be avoided by reducing the temporal change rate of the magnetic flux amount in the electric motor at the switching instant or by reducing the magnetic flux amount itself. According to the above, the present invention, when switching the operating state, reduces only the voltage of the AC output of the inverter with a predetermined time gradient without changing the frequency, and the reduction target value during DC braking. Reduction of the amount of magnetic flux itself in the electric motor at the time of switching the operating state by setting a predetermined value of the DC voltage to be applied to the electric motor or a value close to the predetermined value, and reduction of its temporal change rate that makes the amount of magnetic flux change small. Alternatively, or alternatively, the reduction target value of the AC output voltage is reduced to a value smaller than a predetermined value of the DC voltage as described above, and the reduction is performed. Inver
The output of the magnetic flux is changed to a direct current output and the output voltage is increased to a predetermined value of the direct current voltage with a new predetermined temporal gradient, thereby further reducing the magnetic flux amount itself as in the case described above. It is intended to reduce the temporal change rate.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the operation waveform diagram of the output voltage of the inverter shown in FIG. That is, the present invention controls the output voltage of the inverter as shown in the operation waveform diagram. It is to be noted that FIG. 1 shows a typical example of the present invention and shows an output voltage operation waveform diagram corresponding to the contents of the third aspect. First, FIG. 1, the inverter of the normal speed control in at its AC output voltage V _i1 - a DC braking command for the load induction motor is issued at time to data t _o, the frequency relates to an output of the inverter Once you reach its reduction target value V _i2 at time t ₁ is reduced from the voltage V _i1 that voltage only at a predetermined time gradient without changing the inverter at the time t ₁ - from the AC output of the motor towards its output voltage to a predetermined value V _id of the DC voltage at the DC braking with changing the direct current increases controlled by new predetermined temporal gradient, said it reaches the predetermined value V _id at time t ₂ The figure shows the case where the DC braking is shifted to the steady state after the time t ₂ . In this case, the voltage V _i2 is selected to be an appropriate value smaller than the voltage V _id . Note that FIG. 1 illustrates the reduced state of the AC voltage by an envelope of its amplitude.

[0008]

According to the present invention, in the inverter operating state switching method in the case of switching the operating state of the speed control target induction motor from the normal operation with a predetermined AC output to the braking operation with a DC output, a switching command is issued. When the AC output of the inverter is applied, the frequency of the inverter is constant, but only the voltage is controlled to be reduced at a predetermined time gradient, and the output of the inverter is immediately changed to the DC output when the AC voltage reaches the reduction predetermined value. At the same time, the DC output voltage is set to a predetermined value to be applied during braking operation to shift to steady DC braking operation, and the predetermined AC voltage reduction value is set to the predetermined value of DC voltage to be applied during the DC braking operation. Alternatively, or with the application of the switching command, the AC output of the inverter is unchanged in frequency, but only the voltage is changed to a predetermined first time gradient. When the AC voltage reaches a switching set value that is set as a value smaller than the steady-state predetermined value of the DC voltage to be applied in the steady state of the DC braking operation, the output of the inverter is changed to the DC output. At the same time, the DC output voltage is controlled to increase from the switching set value to the steady predetermined value with a predetermined second time gradient, and when the predetermined value is reached, the AC output is shifted to steady DC braking operation. Therefore, it is possible to smoothly switch to the DC braking operation while suppressing the generation of an excessive current regardless of the frequency during the normal operation, and to shorten the required stop time of the electric motor as compared to when the conventional method is applied. You can
For example, when applied to positioning control, it is possible to improve control position accuracy and control performance by shortening required time.

[Brief description of drawings]

FIG. 1 is an operation waveform diagram of an inverter output voltage showing an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of an inverter output voltage showing a first embodiment of the prior art.

FIG. 3 is an operation waveform diagram of an inverter output voltage showing a second embodiment of the prior art.

[Explanation of symbols]

V _i Inverter AC output voltage V _{i1 Inverter} AC output voltage during normal speed control V _i2 Inverter AC output voltage reduction target voltage _Vid Steady state DC voltage during DC braking t ₀ DC braking command time t ₁ inverter - reduction control ending time t ₂ inverters in motor AC output voltage - motor DC output voltage of increased control completion time t ₃ inverter - re-output time of the data DC output voltage

Claims (3)

[Claims] 1. A method for switching the operating state of an inverter when the operating state of an induction motor, which is the target of speed control, is switched from a normal operation by a predetermined AC output to a braking operation by a DC output, the method including switching command application. The frequency of the AC output of the inverter is constant, but only the voltage is controlled to be reduced with a predetermined time gradient, and when the AC voltage reaches the reduction predetermined value, the output of the inverter is immediately changed to the DC output. A method for switching an operating state of an inverter, characterized in that a direct current output voltage is set to a predetermined value to be applied during braking operation and a steady DC braking operation is performed. 2. The inverter operating state switching method according to claim 1, wherein the predetermined reduction value of the AC voltage is a predetermined value of the DC voltage to be applied during the DC braking operation. State switching method. 3. A method for switching an operating state of an inverter when switching the operating state of an induction motor, which is a speed control target, from a normal operation by a predetermined alternating current output to a braking operation by a direct current output. The AC output of the inverter is controlled so that its frequency is constant, but only its voltage is reduced at a predetermined first time gradient, and the AC voltage is a steady predetermined DC voltage to be applied in the steady state of the DC braking operation. When the switching set value set as a value smaller than the value is reached, the output of the inverter is changed to a direct current output and the direct current output voltage is changed to a predetermined second time gradient from the switching set value to the steady predetermined value. A method of switching the operating state of an inverter, characterized by increasing the control value to reach a predetermined value, and shifting to a steady DC braking operation.