JPS611284A - Controller of induction motor - Google Patents

Abstract

PURPOSE:To effectively operate an induction motor even if a frequency control system is inoperative by providing means for shortening by separating the primary winding from a power source, and means for supplying a DC current to the primary winding. CONSTITUTION:When high speed operation primary power source failure detecting means 8 such as a low voltage detector detects the failure of the primary power source, line switching means 3, 4 is opened, line switching means 5 is closed to abruptly brake by shortcircuiting 3-phases of the primary windings of an induction motor 1, and time limiting means capable of limiting several 10mS is started. The operation of the time limiting means is detected to open the means 5, and to close line switching means 6 to connect a DC power source 7 with the primary winding of the motor 1, thereby shifting to the generating brake. Thus, even if the frequency control system is inoperative, the motor can be braked in a short time, and can be stopped at an accurate position.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a braking device for an induction motor. In particular, the present invention relates to a braking device for an induction motor that is effective when the induction motor is used as a servo motor for an NC machine tool or the like.

Conventional technology Historically, DC motors were used for servo motors in NC machine tools, etc., but synchronous motors have come to be used because they are brushless and robust, and they also have higher torque. Induction motors began to be used due to the possibility of miniaturization. With the development of power semiconductor devices such as power transistors, DC/AC converters,
This is because variable frequency supply means such as frequency converters have become widespread, and frequency control of induction motors (speed control performed by controlling the primary frequency of the induction motor) using them has become easier.

Servo motors used in NC machine tools include so-called spindle motors that rotate a counter, milling cutter, etc., and so-called feed motors that move an L tool or a workpiece. Spindle motors do not necessarily require rapid stopping, but feed motors do require rapid stopping. Otherwise, there is a risk of erroneous addition or damage to the main body of the machine tool.

However, DC generators and synchronous generators can operate without any other power source.

Induction aircraft cannot operate without the presence of another power source. If converted, a DC generator or a synchronous generator will be
Just by rotating the body, it operates as an independent generator, but even if an external force is applied to rotate the dielectric generator, it will not operate as a generator unless a rotating magnetic field is applied. After the induction motor is started as an induction motor by another power source, when it is rotated to some overspeed and the slip is brought to negative 1tli, it closes and operates as an induction generator, and in this case, it also operates as an induction generator. Continuous connection to the power source is a necessary condition for operation with a stable frequency. In short, in order for an induction machine to operate stably, it is essential that the magnetic field for one revolution be stable. Therefore, it cannot be used for dynamic braking systems, which can be used for DC machines and synchronous machines, or for induction machines.

C1] - As noted, when an induction motor is used as a servo motor, there is a frequency control method using variable frequency supply means (an induction motor speed control method that is achieved by controlling the primary frequency of the induction motor). is used, so if this frequency control method is sound, it is possible to perform regenerative braking using this frequency control method.
There's no big problem. However, if the frequency control method becomes inoperable due to burnout of the power transistor, or if there is a power outage, the induction machine will have no effective means of braking other than using a mechanical brake. So the dynamic braking method cannot be used? The inherent limitations of the A-induction machine constitute a major drawback.

To solve the problem, the present invention solves this drawback, and 11. Frequency control is achieved by non-operation of the variable frequency supply T stage or by non-operation of the power supply of the first stage of variable frequency supply. An electric braking device for an induction motor that has the advantage of being able to operate effectively even when the induction motor speed (1^ control force type) or inactive is achieved by controlling the next wave number of the power type (induction type) machine. one stage of which comprises a braking device for an induction motor having means for separating and short-circuiting a primary winding from a power supply and means for supplying direct current to said primary winding.

The present invention utilizes the rotating magnetic field that has been established during the operating period before the start of braking to apply sudden IMI motion for a short period of time (about several tens of seconds), and then converts it into dynamic braking. It is desirable to smoothly switch from sudden braking to dynamic braking without any delay.

Third, is a means added to control the time from the start of sudden braking to the transition to dynamic braking, or
A speed detecting F stage so as to detect each time the speed is decelerated to a certain value as a result of a sudden f1-1 movement and shift to dynamic braking, and a control means that follows this speed detecting means to start dynamic braking. It is realistically advantageous if it is provided.

f'1 River The present invention is based on the following points: (a) When an induction motor is operated and the power is cut off and the primary winding is short-circuited, a large current flows for a period of several OLIIS, and the speed reaches the synchronous speed. Based on the experimental fact that there is a sudden deceleration, (b) First,
This sudden braking is used to rapidly decelerate the motor to a speed just below the synchronous speed (l\), and then DC excitation is applied to the primary winding to perform normal dynamic braking. . At this time, the effect of inserting an external resistor will be obvious, or there is no need to do so unless the brake is repeatedly applied.

According to the experimental results, this sudden braking occurs after a short circuit in the primary winding.
It is only valid for a period of about 0m5, and as a result, the synchronous speed is reduced.
However, after that, no primary current flows, no braking torque is generated, and the rotor coasts as it is. Conversion device, etc., b■Variable frequency supply-1
The system is configured to detect a malfunction, failure, etc. of the induction motor, disconnect the primary winding of the induction motor from the power supply, short-circuit it, activate a time limit device of several IDm5, and shift to dynamic braking when the time limit device operates. Then, the initial period of several tens of m5 is extremely large, and after that the braking rate decreases gradually by 1.
As a result, the vehicle is decelerated by a certain amount of torque. In addition, since a speed detection device is commonly used in ZARPO motors, we decided to use this and first apply sudden braking to reduce the speed to around the synchronous speed, and then decelerate to this speed. Even if this is detected and the shift is made to dynamic braking, the initial GIOmS period of 1'1 is extremely long, and thereafter the vehicle is decelerated with a gradually decreasing braking torque, as described above.

Embodiments 74 of the embodiments of the present invention with reference to the drawings;
? j! The braking device of the FIJ aircraft will be further explained.

"Chopsticks" - Sentence jE example Figure 1! ! 1 is an induction motor, which is supplied with variable three-phase alternating current by an inverter 2 which is supplied with direct current and generates the desired three-phase alternating current quasi-pressure, defined by its frequency and the number of poles of the induction motor. Rotate with the speed as the synchronous speed. 3.
4 is a power line switching means such as an electromagnetic contactor, which is used to connect or disconnect the inverter 2 from the line.

5 is also a power line switching means such as an electromagnetic contactor, and is used to short-circuit the primary winding of the induction motor 1 in three phases. 6 is also a power line switching means such as an electromagnetic contactor, and is used to connect the DC power supply 7 to the primary winding of the induction motor l.

Reference numeral 8 denotes a primary power loss detection means that operates at high speed, such as a low voltage detection circuit.

When the primary power source is healthy, the line switching means 3.4 is closed, the other line switching means 5.6 are opened, and the induction motor l is supplied with the desired three-phase AC from the inverter 2 and rotates. . When the high-speed operation/secondary power loss detection means 8 such as a low voltage detection circuit detects the loss of the primary power source, it opens the line switching means 3 and 4, closes the line switching means 5, and closes the primary winding of the induction motor 1. In addition to short-circuiting three phases of the line to activate sudden braking, there is also a time-limiting means that can limit the distance of several tens of meters.
(not shown). Detecting the operation of the timer, the line opening/closing means 5 is opened, the line opening/closing means 6 is closed, the DC power supply 7 is connected to the primary winding of the induction motor 1, and the system shifts to dynamic braking.

According to the embodiment described below, even though the primary power source is not available, sudden braking is activated and the synchronous speed is reduced to approximately 9 to 100 meters in a very short time (about several tens of meters). When the sudden braking stops working, the system shifts to dynamic braking. Since the torque of dynamic braking varies depending on the applied DC voltage and rotational speed, the braking torque gradually decreases with deceleration, making it possible to stop at a precise point.As a result, variable frequency supply Even if the frequency control method (the speed control method for the induction motor by controlling the primary frequency of the induction motor) is inoperative due to the non-operation of the variable frequency supply means or the absence of the power source for the variable frequency supply means, the short-term It is possible to brake in a timely manner and to stop at a precise position.

The difference from the first embodiment is that a time limit means (not shown) is not included, and instead of this, a tachometer generator constant speed detection means 9 is used.
is provided.

The speed detecting means performs sudden braking in response to the operation of the high-speed primary power loss detection stage 8 of the low voltage detection circuit, etc., and detects that the rotor has decelerated to a set speed (about the same as the synchronous speed). 9 is detected, the system shifts to dynamic braking.

In this embodiment as well, due to the non-operation of the =T variable frequency supply means or the absence of a power source for the variable frequency supply means, a frequency control force type (an induction motor formed by controlling the wave number of the next layer of the induction motor) Even if the speed control system (speed control method) is inactive, the brake is braked with a large braking torque for the initial number of OmS, and the braking torque decreases as it nears a stop, so the brake can be braked in a short time without the need for a primary power source. , it can be stopped at a precise position.

As detailed in the invention, according to the invention, the variable frequency supply 1
Even if the frequency control method (speed control method of the induction motor by controlling the −/next station wave number of the induction motor) is inoperative due to the non-operation of the stage or the absence of a power source for the variable frequency supply stage. , it is possible to provide an electric braking device for an induction motor that has the advantage of being able to operate effectively.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a braking device for an induction motor according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram of a braking device for an induction motor according to a second embodiment of the present invention. 1...Induction motor, 2...Inverter (DC/
AC converter), 3.4.5.6...Power line switching means such as electromagnetic contactor, 7. . . DC power supply,
8... High-speed operation/secondary power loss detection means such as low voltage detection circuit, 9... Speed detection "1st stage.

Claims (3)

[Claims] (1) means for disconnecting and short-circuiting the primary winding from the power supply;
and means for supplying direct current to the primary winding. (2) A claim further comprising means for limiting the time until the means for supplying direct current to the primary winding operates after the means for disconnecting and short-circuiting the primary winding from the power source operates. A braking device for an induction motor according to item 1. (3) means for detecting the speed of the induction motor; and means for operating the means for supplying direct current to the primary winding when the speed detected by the speed detecting means is within a specific value range. A braking device for an induction motor according to claim 1.