JPH04312384A - inverter device - Google Patents

Abstract

PURPOSE:To avoid inconvenience such as overcurrent trip or overvoltage trip by a method wherein the rotation direction of a motor is stored when the motor is transferred from an operation state to a free running state and, when the motor is started again, the start control is performed in accordance with the stored rotation direction. CONSTITUTION:When an output signal from an abnormality detecting circuit 8 is transmitted to a control circuit 4, the control circuit 4 cuts off three-phase PWM output signals to put a motor 1 into a free running state. The rotation direction of that state is stored in a non volatile memory 7. When the motor 1 is started again, the rotation direction of the previous operation is read out of the non volatile memory 7 to determine the phase order of the three-phase output signals. Then the frequency of an induced voltage, i. e., the frequency corresponding to the revolution of the motor 1, is detected by a frequency detecting circuit 6 and set as an output frequency for a starting process. By such processes, the motor 1 can be started with the rotation direction before it is put into the free running state. With this constitution, failure trip caused by an overcurrent, an overvoltage, etc., can be avoided.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for variable speed control of an electric motor.

0002

2. Description of the Related Art Generally, inverter devices are widely used because they allow variable speed control of electric motors in a simple manner.

[0003] The output frequency is set to 0Hz, that is, free-run, during operation due to a power outage or an emergency stop by the user, and in the case of a power outage, it is not possible to start up again when the power is restored, or in the case of an emergency stop, by resetting the emergency stop by the user. This is a common occurrence.

[0004] However, since the motor is rotating when restarting operation, if the motor starts at the normal starting frequency,
If the difference between the rotational frequency of the motor and the frequency at startup is large, a large regenerative current will flow, which may cause an overcurrent trip or an overvoltage trip. For this reason, a commonly used method is to detect the rotational frequency of the motor from the induced voltage of the motor and start the motor from the detected frequency rather than from the starting frequency.

[0005]

[Problem to be Solved by the Invention] However, even with the method of starting from the detection frequency described above, if the rotation direction command changes during a power outage or emergency stop, it is difficult to change the rotation direction when the free run occurs. Since the rotation direction cannot be retained, information regarding the rotation direction must depend on the rotation direction command. Therefore, in the conventional inverter, the rotational direction of the electric motor and the rotational direction of the output from the inverter are opposite, and overcurrent trips and overvoltage trips also occur. In addition, if the rotation direction can be detected and the rotation is started in that rotation direction, the rotation will start in a direction different from the rotation direction specified by the user, which may cause problems such as damage to the load machine or motor, depending on the load machine. There are cases.

In view of the above-mentioned problems, the present invention memorizes the rotational direction of the electric motor when it transitions from the operating state to the free-run state, and performs startup control based on this memorized rotational direction when restarting. Accordingly, it is an object of the present invention to provide an inverter device that eliminates problems such as overcurrent trips and overvoltage trips. [Structure of the invention]

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention converts DC power from a DC power source into AC power having an arbitrary frequency, and supplies this AC power to an electric motor as a load. In this way, in the inverter device that controls the electric motor at variable speed, a frequency corresponding to the induced voltage is detected based on a storage means for storing the rotational direction of the electric motor and an induced voltage generated between terminals of the electric motor. a frequency detection means; and a start control means for controlling the electric motor to start based on the rotational direction during the previous operation stored in the storage means and the frequency detected by the frequency detection means when starting the electric motor. An inverter device is provided.

[0008]

[Operation] In the inverter device of the present invention configured as described above, the rotational direction of the motor when the motor goes from the operating state to the coasting state is memorized, and when the motor resumes operation, the memorized rotational direction and the detected rotational direction are stored. Since startup is controlled based on frequency, the rotational direction of the electric motor and the rotational direction of the output of the inverter device can be matched, and smooth startup can be achieved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the inverter device of this embodiment exchanges DC power with AC power having an arbitrary frequency, and supplies the AC power to a three-phase induction motor (hereinafter referred to as motor) 1, which is a load. an inverter section 2 consisting of a three-phase bridge circuit (not shown) formed of power transistors and diodes, and a drive circuit 3 that drives the power transistors that are the main elements of this inverter section 2. A control circuit 4 outputs a three-phase PWM output signal to the drive circuit 3 in accordance with setting signals such as operation commands and rotation direction commands, a residual voltage detection circuit 5 detects induced voltage when the motor 2 is in a free running state, and A frequency detection circuit 6 that detects the frequency based on the induced voltage from the voltage detection circuit 5, a non-volatile memory 7 that stores the rotation direction of the motor 2, and a signal that puts the motor 2 into a free run state in the event of an emergency stop, etc. and an abnormality detection circuit 8 that outputs.

[0011] Then, by sending the output signal from the abnormality detection circuit 8 to the control circuit 4, the control circuit 4
The M output signal is turned off, and the motor 2 is set in a free running state. Normally, the control circuit 4 outputs a three-phase PWM output signal based on a driving command, rotation direction command, etc., and controls the on/off of the power transistor of the inverter section 2 via the drive circuit 3, and has an arbitrary frequency. By generating AC power and supplying the AC power to the motor 2, the motor 2
Performs variable speed control. Next, the free run process performed during a power outage or when an emergency stop command is received from the COSER will be explained using FIG. 2.

First, it is checked whether the inverter is already stopped (2-1), and if it is running, the rotation direction at that time is stored in the non-volatile memory 7 (2-2), and then free run processing is performed. (2-3), if stopped, (2-2
), performs free run processing (2-3), and ends the processing (2-4). By processing in this way, the rotation direction before free run is memorized. Furthermore, the startup process will be explained using FIG. 3.

First, the rotation direction during the previous operation is read from the nonvolatile memory 7 (3-1), and the phase order of the three-phase PWM output is determined. Next, the frequency of the induced voltage, that is, the frequency corresponding to the rotational speed of the motor 2 is detected by the frequency detection circuit 6, and this is set as the output frequency (3-2). Then, startup processing (release of gate block) (3-3) is performed. By processing in this manner, the motor 2 is started in the rotational direction before free running, that is, the rotational direction of the motor 2.

[0014]Furthermore, the starting process when the motor 2, which is a load, must not be operated in a direction different from the rotation command when the rotation direction is different from the rotation command will be explained with reference to FIG.

First, the rotation direction during the previous operation is read from the nonvolatile memory 6 (4-1), and a start timer is started (4-10). If the currently input rotation command matches, set the rotation direction (4-3
), set the frequency corresponding to the induced voltage as the output frequency (
4-4) and startup processing (release of gate block) (4-
Do 5). This is exactly the same as the startup process described above. Conversely, if they do not match, check whether the timer has exceeded (4-9), and if it has, jump to the next process (4-6) and start the start process (4-7). (after). If it is not over, check whether the rotation frequency of motor 2 is below a certain level (4-6)
), and if it is above a certain value, check the timer (4-9)
Return to If it is less than a certain value, start-up processing (4-7 and subsequent steps) is performed. That is, the rotation direction is set (4-7), the starting frequency is set (4-8), and the starting process (gate block release) (4-5) is performed. By doing this, it is possible to avoid a case where the rotation direction specified by the user differs from the actual rotation direction, and it is possible to start the electric motor after it has sufficiently stopped.

Although a non-volatile memory is used as the storage means in this embodiment, it goes without saying that the present invention is also applicable to storage means such as a memory with a backup function.

[0017]

As described above, according to the present invention, when a power outage occurs or the user requests an emergency stop, the rotation direction is switched between forward and reverse rotation, and when the motor is restarted, the motor rotates. This overcomes the conventional problem of tripping due to overcurrent or overvoltage due to the difference in the direction of rotation and the direction of rotation at restart, and enables smooth startup in the direction of rotation before the free run state, that is, the direction of rotation of the motor. Become.

[0018] Also, regarding the problem that may occur between the rotation direction command and the actual rotation direction when the machine is restarted and the rotation direction is opposite to the actual rotation direction, if the rotation direction read from the storage means and the rotation command are different, the electric motor This can be resolved by waiting for the frequency of the induced voltage to become below a certain level or for the motor to stop sufficiently, and then starting it at the starting frequency according to the rotation command.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart of software that performs free run processing in the embodiment shown in FIG. 1;

FIG. 3 is a flowchart of software that performs startup processing of the embodiment shown in FIG. 1;

FIG. 4 is a flowchart of software that performs startup processing of the embodiment shown in FIG. 1;

[Explanation of symbols]

1...Three-phase induction motor (motor) 2...Inverter section 4...Control circuit 5...Residual voltage detection circuit 6...Frequency detection circuit 7...Non-volatile memory

Claims (1)

[Claims] 1. An inverter device that controls the electric motor at variable speed by converting DC power from a DC power supply into AC power having an arbitrary frequency and supplying this AC power to the electric motor as a load. storage means for storing the rotational direction of the motor; frequency detection means for detecting a frequency corresponding to the induced voltage based on the induced voltage generated between the terminals of the motor; An inverter device comprising: start control means for controlling the electric motor to start based on the stored rotational direction during the previous operation and the frequency detected by the frequency detection means.