JPH01291693A - Restarting device for ac motor - Google Patents

Abstract

PURPOSE:To accomplish restarting of an AC motor in case of power recovery by comparing a turning direction command latched in a nonvolatile memory in case of occurrence of an instantaneous power-off with a turning direction command in case of power recovery. CONSTITUTION:In case an instantaneous power-off occurs, a motor 4 runs freely. The occurrence of the instantaneous power-off is detected by a power-off detection circuit 9, and a memory 8 latches the turning direction command by an instruction of a write command 9a. In case of power recovery, the residual voltage at that time is detected by a residual voltage detector 5. The turning direction command in case of power recovery and the latched turning direction command of the memory 8 are loaded into a microcomputer 7 to compare them. In case the directions are coincident, restarting is made by using the residual voltage. In case the directions are not coincident, deceleration is made after doing a speed search, acceleration is applied to a reverse direction at that time when a speed reaches 'zero', and a turning starting is made in accordance with a reverse command.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a restart device for an induction motor, etc., and particularly to a restart device that smoothly restarts an induction motor or the like regardless of rotation commands before and after a momentary power failure. .

[Conventional technology] A conventional example of restarting after an instantaneous power failure is described in the magazine "Mitsubishi Electric Technical Report J.
(1971, Vol. 45. Na11.149
There are papers ranging from pages 6 to 1497).

In this conventional example, in order to restart the motor, the residual voltage of the motor is detected and the detected phase is matched with the phase of the inverter output voltage.

Further, a conventional example of how to give a voltage command and two frequency commands after the end of an instantaneous power failure is disclosed in Japanese Patent Laid-Open No. 148585/1985.

[Problems to be Solved by the Invention] The first conventional example is known as an effective method for setting conditions at the time of restart.

However, although the second conventional example describes how to give voltage commands and frequency commands, it does not consider rotation direction commands before and after a momentary power failure. Therefore, it is considered that the one-rotation direction command is based on the premise that it does not change before and after an instantaneous power failure. An example of this is shown in FIG. According to FIG. 2, the rotation commands are the same in the forward rotation direction before and after the instantaneous power failure. Therefore, the actual rotation direction of the electric motor may continue to rotate in accordance with the normal rotation direction that is this rotation command.

Note that during a momentary power outage, the motor is free-running, and after power is restored, residual voltage is detected and the motor is accelerated (restarted) to approach the frequency command value.

However, the rotation direction command may change before and after the instantaneous power failure. An example of this is shown in FIG. Although a forward rotation command was given before the instantaneous power failure, in FIG. 3, a reverse rotation command was given after the instantaneous power failure. In such a case, if the conventional example is adopted, the speed of the motor when the power is restored is increased, and the reverse phase braking is suddenly performed at the detected frequency. As a result, the inverter trips and cannot be restarted.

SUMMARY OF THE INVENTION An object of the present invention is to provide a restart device for an AC motor that enables smooth restart even if the one-rotation direction command changes before and after an instantaneous power failure.

[Means for Solving the Problems] The present invention provides a non-volatile memory that latches the rotation direction at the time of a momentary power failure, a rotation command direction at the time of power restoration, and a rotation command direction at the time of the instantaneous power failure latched in the memory. If the directions are the same, the vehicle is restarted as is, and if the directions are different, the vehicle is decelerated and then reversed to restart the vehicle.

[Operation] According to the present invention, the rotation direction command at the time of momentary power failure latched in the nonvolatile memory is compared with the rotation direction command at the time of power restoration, and the restart order changes depending on whether the direction is the same or different. Restart is performed according to the rotation direction at the time of power restoration.

[Example] An example of the present invention is shown in FIG. FIG. 4 is the time chart. In FIG. 1, the forward converter 1 is.

Converts three-phase alternating current (R, S, T) to direct current. The parallel capacitor 3 removes ripples from the DC output. The inverter 2 converts the direct current of the forward converter 1 into alternating current, and the voltage and frequency of this alternating current can be freely changed. The circuit means for this purpose is the microcomputer 7.

The AC motor 4 is mainly an induction motor, but may also be a synchronous motor. The inverter 2 performs various controls such as speed control and torque control of the AC motor 4.

The microcomma has a program for controlling the AC motor 4, and controls the inverter 2 via the drive circuit 6 according to this program.

The microcomputer 7 receives residual voltage detector 52 oscillator 10° commands a, b. The residual voltage detector 5 is for restarting and detects the residual voltage of the motor itself. Oscillator 10
generates a frequency pulse proportional to the frequency setter 11, which becomes an external frequency command.

The command a is a forward rotation command, and the command A is a reverse rotation command. Normally, the forward rotation command a is given, and as an exception, a reverse rotation command is given.

The nonvolatile memory 8 is composed of a magnetic memory, and its latched contents are retained even when the power is turned off.

The power off detection circuit 9 is a circuit that detects the occurrence of a momentary power outage, and detects the rotation direction command that is present at the time of this detection.

It is latched into memory 8. The rotation direction command that exists at the time of detection is the command a if the forward rotation command is in progress, and the command a if the reverse rotation command is in progress.

The operation will be explained using the time chart shown in FIG.

Before the instantaneous power failure, the inverter 2 is controlled via the microcomputer 7 and the drive circuit 6 according to the rotational direction command a or b and the command from the frequency command unit 11, thereby controlling the electric motor 4.

When a momentary power failure occurs, the electric motor 4 becomes free-running. The point in time when this instantaneous power outage occurs is detected by the power-off detection path 9, and the memory 8 latches the rotation direction command (a or b) at the time of the instantaneous power outage based on the write command 9a.

When the power is restored, the residual voltage at that time is detected by the residual voltage detector 5. Furthermore, the microcomputer 7 takes in the rotation direction command after power restoration and the latch rotation direction command from the memory 8 and compares them. If the directions match, the residual voltage is used to restart. If the directions do not match, as shown in FIG. 4, it means that a new reverse command has been issued, for example, and restarting cannot be performed.

Therefore, in this embodiment, as shown in FIG.

After the speed is searched, it is decelerated, and when the speed reaches zero, it is accelerated in the reverse direction to start rotation in accordance with the reverse direction command.

Incidentally, the nonvolatile memory 8 may be a semiconductor memory having an auxiliary battery.

[Effects of the Invention] According to the present invention, the microcomputer in charge of controlling the inverter can accurately know the status of each forward/reverse command before and after the power is restored, so restarting the AC machine after the power is restored can be smoothly performed. This has the effect of further improving the reliability of the inverter.

[Brief explanation of the drawing]

Figure 1 is an embodiment of the restart device of the present invention, Figure 2, Figure 3.
FIG. 4 is an explanatory diagram of the operation of the conventional example, and FIG. 4 is an explanatory diagram of the operation of the embodiment shown in FIG. DESCRIPTION OF SYMBOLS 1... Forward converter, 2... Inverter, 4... AC motor, 7... Microcomputer, 8... Non-volatile memory, 9
...'Power off detection circuit. Agent Patent Attorney Tadashi Akimoto Sanetomi 1 page'a b 8::ltHashi3dlhMemory Kim Tadashi] L11 Rei
bjjmi詣zen wealth 2 Figure I'l! ↓ It's very easy to get started, Fig. 3.

Claims (1)

[Claims] 1. A power converter that can convert to any voltage and frequency, an AC motor driven by the converter, and a system that detects the residual voltage of the motor when power is restored after a momentary power outage and provides restarting after power is restored. An AC motor restart device comprising a residual voltage detector and a non-volatile memory that latches a rotational direction command value of the AC motor when an instantaneous power failure occurs, and a rotational direction command value of the AC motor when power is restored. It compares the rotation direction command value at the time of momentary power failure, which is latched in the non-volatile memory, and if it is the same direction, restart is executed using the detected residual voltage.
A restart device for an AC motor, comprising means for restarting the AC motor by decelerating the AC motor in the opposite direction and then reversing the rotational direction.