JPH0347072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to a secondary resistance control device for a wound induction motor when the operating mode is switched.

[Prior art and its problems]

FIG. 1 is a control circuit diagram showing a conventional example of controlling a wound induction motor. In Fig. 1, AC power from a three-phase AC power supply (R, S, and T phases) is applied to five sets of thyristors 3 as switching means connected in antiparallel through a circuit breaker 1 and a current transformer 2. Three of the five sets of thyristors 3 are operated to apply an alternating current voltage to the primary winding of the wound induction motor 4. That is, if the three sets of thyristors 3 are made conductive so that the R-phase voltage of the power source is applied to the terminal U of this motor 4, the S-phase voltage is applied to the terminal V, and the T-phase voltage is applied to the terminal W, the motor 4 rotates in a fixed direction (hereinafter referred to as normal rotation). Also, the R phase voltage of the power supply is
Then, when three sets of thyristors 3 are made conductive so that the S-phase voltage is applied to terminal V and the T-phase voltage is applied to terminal U as before, the direction of phase rotation of the AC voltage applied to this motor 4 is reversed. Therefore, this electric motor 4 can be rotated in the opposite direction to that described above.

A secondary resistor is connected to the secondary winding of a wound induction motor, but in the conventional example shown in FIG. 1, this secondary resistor is divided into three parts, resistors 6, 7, and 8. A resistive shorting switch is provided for shorting each section. That is, when the resistor shorting switch 23 operates, the resistor 6 is short-circuited, so that only resistors 7 and 8 are connected to the secondary winding of the motor 4. Similarly, if the resistance shorting switch 26 operates, the resistances 6 and 7 will be shorted, and then the resistance shorting switch 29 will be activated.
If it operates, all secondary resistances will be short-circuited. By short-circuiting the resistors 6, 7, and 8 connected to the secondary winding of the wound induction motor 4 in stages in this way, the speed of the motor 4 can be changed in stages.

A speed transmitter 5 is attached to the rotor of the wound induction motor 4.
is coupled to the speed transmitter 5, from which the actual speed signal of the motor 4 is obtained. On the other hand, since a speed target signal is obtained from the speed setter 11 via an acceleration/deceleration adjuster 12, this speed target value signal and the aforementioned actual speed value signal are inputted to the speed adjuster 13 consisting of a PI adjuster. A current target value signal that makes the deviation between both input signals zero is taken out from the speed regulator 13. The actual current value signal output from the current transformer 2 and obtained via the rectifier 14 and the aforementioned current target value signal are input to the current regulator 15, which is also a PI regulator, and the deviation between these two input signals is calculated. A control signal to zero is issued to the firing angle regulators 16 and 17, and both firing angle regulators 16 and 17
is designed so that only one of them works. That is, the firing angle adjuster 16 is for forward rotation of the electric motor 4, and controls the phase of three sets of thyristors 3 for forward rotation, and the firing angle adjuster 17 controls the three sets of thyristors 3 for reverse rotation. Since the phase is controlled,
The magnitude of the voltage applied to the primary winding terminals U, V, and W of the motor 4 and the direction of phase rotation can be freely adjusted.

The speed target value signal from the speed setter 11 obtained via the acceleration/deceleration regulator 12 is sent to a comparator 21,
24, 27, and when this speed target value signal reaches the operating set value of the respective comparator, the short circuit prevention relay 3 as a resistance short circuit prevention means is applied.
Since the resistance short circuit command relays 22, 25, and 28 are excited on the condition that 0 is excited, the resistance short circuit switches 23, 26, and 29 described above operate.
That is, when this electric motor 4 is started, the speed target value signal is at a low level, so the comparator 21,
24 and 27 are all inactive, so all the resistors 6, 7, and 8 are connected to the secondary winding of the motor 4, generating a large starting torque to start and accelerate the motor 4. However, the speed of the electric motor 4 does not exceed the speed determined by the low resistance value of the secondary resistor and the load torque. However, when the speed target value signal reaches a value higher than this speed, the comparator 21 operates and the resistance shorting command relay 22 is energized, and when the resistance shorting switch 23 operates, the resistor 6 is short-circuited. As the value of the resistance connected to the winding decreases, the motor speed increases to a speed determined by this resistance value and the load torque. Similarly, if the comparator 24 operates, only the low resistor 8 will be connected to the secondary winding of the motor 4, and if the comparator 27 also operates, all the resistors 6, 7, and 8 will be short-circuited, so this motor 4 reaches maximum speed close to synchronous speed.

The resistor 6 connected to the secondary winding in this way,
If 7 and 8 are shorted in stages, the speed of the motor 4 will also change in stages, but by combining this secondary resistance change with the phase control of the thyristor mentioned above, the speed of the motor 4 can be changed continuously. It can be changed.

The operation command calculator 18 has a function of receiving signals from the speed setting device 11 and the speed transmitter 5 and instructing the motor 4 to operate/stop and the direction of rotation. That is, the rotational direction signal obtained from the speed setting device 11 passes through the operation command calculator 18, and the signal from the switching command calculator 19 operates one of the firing angle regulators 16 and 17 to control the motor. 4 in the forward or reverse direction. Furthermore, an operation command is sent to the acceleration/deceleration regulator 12 and the speed regulator 13 at the same time as the start of operation, and when the electric motor 4 completely stops, the acceleration/deceleration regulator 12 and the speed regulator 13 are similarly held at zero.

Whether the wound induction motor 4 in operation is in driving operation or braking operation is taken out from the speed regulator 13 as a torque polarity signal. The torque polarity signal is input to the switching command calculator 19 as a driving mode detection means, and this switching command calculator 19 has a function of commanding the switching of the driving mode in addition to the function of commanding the driving direction described above. has. Reverse phase braking is a common method for braking induction motors operated at a constant frequency. Therefore, if the electric motor 4 is driving in the forward rotation direction, the firing angle regulator 16 is in operation and the firing angle regulator 17 is inoperative. When the switching command calculator 19 determines that the torque polarity signal has been switched, the firing angle regulator 16 is stopped and the firing angle regulator 17 is operated even if the motor 4 is running in the forward rotation direction. As a result, the electric motor 4 enters a reverse phase control operating state, and its speed rapidly decreases.

Switching the phase rotation direction of the voltage applied to the motor 4 by switching the operation of the above-mentioned firing angle regulators 16 and 17 will result in a power supply short circuit if the switch is not switched when the current flowing through the thyristor 3 is zero. The switching command calculator 19 also has the function of controlling and monitoring this current. In other words, the torque polarity signal is reversed and the command for switching the operation mode is output to the switching command calculator 1.
9, a pulse shift command is given from this switching command calculator 19 to the current regulator 15,
In response to this pulse shift command, the firing angle regulator 16 in operation shifts the firing angle α of the three sets of thyristors 3 to which voltage is applied in the normal rotation direction to αmax.
As a result, the switching command calculator 19 detects that the current flowing through the electric motor 4 has become zero and operates the firing angle adjuster 17, so that the electric motor 4 enters reverse-phase braking operation without causing a power short circuit. It goes in.

By the way, when the motor 4 enters anti-phase braking operation, if the resistors 6, 7, and 8 connected to the secondary winding are all short-circuited, the impedance of this motor 4 is small, so a very large current flows to this motor. 4, it may damage thyristor 3,
There is a possibility that the overcurrent relay is activated and the operation of the electric motor 4 is interrupted. Therefore, when entering the reverse phase braking operation, the resistors 6, 7, and 8 are all connected to the secondary winding of the motor 4. The short-circuit prevention relay 30 as a resistance short-circuit prevention means is a relay that fulfills this role, and when the electric motor 4 is in driving operation, the short-circuit prevention relay 30 is energized by the output from the switching command calculator 19, so that the resistance is reduced. Short-circuit command relays 22, 25, 28 and resistance short-circuit switches 23, 26, 29 respond to commands from comparators 21, 24, 27, respectively.
7 and 8 can be short-circuited as appropriate. However, when the electric motor 4 enters the braking operation mode, the switching command calculator 1
Since this short-circuit prevention relay 30 is de-energized by the command 9, the resistance short-circuit switches 23, 26, 29 do not operate regardless of the commands of the comparators 21, 24, 27, and therefore the motor 4 All the resistors 6, 7, and 8 are connected to the secondary winding of .

However, while the wound induction motor 4 having such a control device is operating at a maximum speed close to its synchronous speed, an operation mode switching command may be repeatedly input to the switching command calculator 19. For example, when an overhead crane suspends a load and attempts to stop suddenly while the resistors 6, 7, and 8 are short-circuited, i.e., while traveling at full speed or traversing, the operation mode will naturally switch from driving operation to braking operation. , the short-circuit prevention relay 30 is de-energized, all the resistors 6, 7, and 8 are inserted into the secondary winding of the motor 4, and a voltage whose phase rotation is in the opposite direction is applied to the primary winding, causing the reverse rotation. It enters phase control dynamic operation and attempts to rapidly reduce its speed, but when the suspended load vibrates, it is pulled by this suspended load and the speed regulator 13 starts to reduce the speed even though it is in braking operation. The torque polarity signal is reversed, and the switching command calculator 19 again outputs a signal instructing the driving operation. Therefore, the phase rotation direction is switched again to the normal rotation direction and the short-circuit prevention relay 30 is also energized, but if the speed of the motor 4 at that time is higher than the value set by the comparator 27, a resistance short circuit occurs. Since the command relay 28 and the resistance shorting switch 29 operate, the secondary resistors 6, 7,
8 are all short-circuited at once, and motor 4
A large current rushes into the However, if the suspended load vibrates and swings in the opposite direction to the above, the braking operation mode returns.

When driving operation and braking operation are alternately commanded in this way, the resistors 6, 7, and 8 are repeatedly short-circuited and opened at once each time, so the current flowing to the motor 4 fluctuates significantly, causing problems such as overcurrent. This causes various problems.

[Purpose of the invention]

The present invention provides a secondary resistance control device for a wound induction motor that can suppress fluctuations in the current flowing into the motor even when the wound induction motor is operating at high speed and alternately repeats the driving operation mode and the braking operation mode. The purpose is to

[Key points of the invention]

In order to achieve such an objective, the present invention
In order to suppress fluctuations in the current flowing into the motor even if a wound induction motor operating at high speed is forced to alternate between driving operation and braking operation, resistance short circuit prevention is used when the motor starts driving operation. The invention is characterized in that a release delaying means for delaying the release of the operation of the means is provided.

That is, the present invention provides a method for switching from a braking operation mode to a driving operation mode while a wound induction motor is operating at high speed and releasing the blocking operation of the resistor short-circuit preventing means that prevents short-circuiting of the secondary resistor. A delay time is provided between switching to the operation mode and canceling the above-mentioned blocking operation. As a result, even if the drive operation mode is entered, the motor 2
Since a total resistance is connected to the next winding, this is intended to prevent the current flowing into the motor from becoming excessive.

[Embodiments of the invention]

FIG. 2 is a control circuit showing an embodiment of the present invention, and the content of the present invention will be explained below with reference to FIG.

The difference in FIG. 2 from the conventional example shown in FIG. The circuit is configured such that the circuit is configured such that the circuit breaker 1, current transformer 2, five sets of thyristors 3 connected in anti-parallel, and a wound induction motor 4 are connected to this. a secondary resistor consisting of resistors 6, 7, and 8, a speed setting device 11, an acceleration/deceleration regulator 12, a speed regulator 13, a rectifier 14, a current regulator 15, and a firing angle. Adjusters 16 and 17, operation command calculator 18, switching command calculator 19, comparators 21, 24, and 27,
Resistance short circuit command relays 22, 25 and 28, resistance short circuit switches 23, 26 and 29, short circuit prevention relay 30
Since the symbols, names, and functions given to each are the same as those shown in FIG. 1, their explanations will be omitted.

A timer 38 as release delay means is connected to the output of the switching command calculator 19, and a normally open delay contact of the timer 38 is inserted into a circuit that controls the short-circuit prevention relay 30. If this timer 38 is configured to be de-energized in the braking operation mode and energized in the drive operation mode by the signal output from the switching command calculator 19, when the electric motor 4 is in the braking operation, Since the short-circuit prevention relay 30 immediately becomes non-energized, reverse-phase braking operation is performed with all the resistors 6, 7, and 8 connected to the secondary winding. Even if the operation mode is switched to driving operation in this state, the short-circuit prevention relay remains in the non-excited state for the delay time of this timer 38 due to the action of the timer 38. All the resistors 6, 7, and 8 are maintained connected to the windings to prevent the current flowing into the motor 4 from becoming excessive.

〔Effect of the invention〕

According to this invention, even if the operation mode of the wound induction motor is switched from braking operation to driving operation during high-speed operation, the timer, which is a release delay means, connects the secondary winding of the motor. There 2
The next resistor remains at full resistance for a certain period of time, which prevents the current flowing into the motor from becoming too large, but this effect can be achieved by simply adding one timer, so the required The cost may be small.

[Brief explanation of drawings]

FIG. 1 is a control circuit diagram showing a conventional example of controlling a wound induction motor, and FIG. 2 is a control circuit diagram showing an embodiment of the present invention. 1... Circuit breaker, 2... Current transformer, 3... Thyristor as switching means, 4... Wound induction motor, 5... Speed transmitter, 6, 7, 8... Resistance, 11... Speed Setting device, 12... Acceleration/deceleration regulator, 13... Speed regulator, 14... Rectifier, 15
...Current regulator, 16,17...Ignition angle regulator,
18... Driving follower calculator, 19... Switching command calculator as driving mode detection means, 21, 24, 2
7... Comparator, 22, 25, 28... Resistance short circuit command relay, 23, 26, 29... Resistance short circuit switch, 30... Short circuit prevention relay as resistance short circuit prevention means, 38... Timer as release delay means .

Claims (1)

[Claims] 1. An operation mode in which a switching means for switching the phase rotation direction of the AC voltage is connected to the primary winding, a secondary resistor is connected to the secondary winding, and the driving operation or the braking operation is discriminated. When the wound induction motor equipped with the detection means is in driving operation, the secondary resistor is set to a desired resistance value by the resistance shorting means operated by the command issued by the resistance shorting command means based on the speed signal of the motor, and braking is performed. In a wound type induction machine which is configured to reverse the phase rotation direction of the voltage applied to the primary winding of the motor during operation and to disable the resistance short circuit means by means of a resistance short circuit prevention means, when the motor is operated at high speed, In order to suppress fluctuations in the current flowing into the motor even if the wound induction motor is caused to alternately repeat driving operation and braking operation, when the motor starts driving operation, the resistor short-circuit prevention means operates. A secondary resistance control device for a wound induction motor, comprising: a release delaying means for delaying release.