JPH1052090A - Controller for wound-rotor induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive a quarrying machine without stopping a motor, by constituting a controller for a wound-rotor induction motor of a secondary variable resistor connected in series with a rotor winding and a controller which changes the electric resistance of the resistor in accordance with the current to the rotor winding, and changing the resistance of the resistor in accordance with the load current. SOLUTION: A secondary circuit 6 is connected to a rotor winding 1b through a slip ring 15. A short-circuiting contactor 7 for secondary resistor short-circuits the circuit 6 when a switch 8a is closed, and a contactor 8 for adjusting secondary resistor can variably change a secondary resistor 9 to the corresponding resistance when a switch 8b, 8c, or 8d are closed. The contactors 8 and 9 are controlled by means of a controller 3. Consequently, when the load of a quarrying machine 2 is small, a motor 1 is controlled to a high-energy efficiency condition and, when the load increases, the motor 1 can output a large torque even when the rotating speed of the motor 1 drops. Therefore, the motor 1 can be rotated continuously without stop even when the load of the motor largely fluctuates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a wound-type induction motor for driving a lithotripter used in a cement plant or the like, and more particularly, to a control device without stopping the motor even when a load fluctuating greatly occurs. The present invention relates to a control device for continuing rotation.

[0002]

2. Description of the Related Art FIG. 5 is a speed characteristic curve diagram of a general induction motor. As shown in this figure, when the primary terminal voltage is constant, the torque and the output take a maximum value at a small slip, and a normal operation is performed at a smaller slip speed. When the load fluctuates greatly, such as a wound-type induction motor used for driving a lithotripter for a cement plant, a secondary resistor having a constant resistance value is connected to the rotor winding via a slip ring. It is connected so that rotation can be continued without stopping the motor. That is, when such a secondary resistor is used, the position of the maximum torque shifts to the left in FIG. 5, and a larger torque is generated as the slip increases. The magnitude of the secondary resistance is selected so that the motor output torque increases as the rotation speed of the motor decreases, and the maximum torque is generated when the motor output torque is several tens% lower than the rated speed.

When the above-described wound-type induction motor having a secondary resistor is used for crushing a relatively small stone by a lithotripter, the load torque of the motor is small and the motor is rotating at a rated speed. When a large stone is crushed, the rotation speed is reduced, and a large torque of 200% or more of the rated value is generated to crush the stone. Thus, the wound-type induction motor can drive the crusher without stopping.

[0004]

However, in the above-mentioned conventional wound-type induction motor for driving a lithotripter, since a secondary resistor having a constant resistance is always connected to the rotor winding, the motor is not connected to the motor. However, a part of the input energy is always consumed by the secondary resistor, resulting in low energy efficiency.

On the other hand, in order to improve energy efficiency,
If the secondary resistor is not used, the torque of the motor generates the maximum torque at a rotation speed slightly lower than the rated rotation speed, and when the rotation speed is lower than the rotation speed, the torque tends to rapidly decrease (see FIG. 5). Therefore, when the stone crusher crushes small stones and the load torque is small, the motor rotates at the rated rotation speed, but bites large stones and the torque increases while the rotation speed decreases, but the torque curve near the maximum torque When the rotation speed falls below the maximum torque point, the torque decreases rapidly and the motor stops without grinding the stone. Therefore, the motor torque characteristic is not suitable for a wound-type induction motor for driving a lithotripter, and thus has not been conventionally employed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to drive a lithotripter without stopping a wound-type induction motor, and to achieve a more energy-efficient wound-type induction motor for driving a lithotripter. An object of the present invention is to provide a control device for an electric motor.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, a control device for a wound-type induction motor according to the present invention comprises: a current detection device for detecting a value of a current flowing through a stator winding of the wound-type induction motor; A variable secondary resistor which is connected in series to a rotor winding via a slip ring and whose electric resistance value can be changed, and changes the electric resistance value of the variable secondary resistor in accordance with the current value The resistance control device changes the electric resistance value of the variable secondary resistor according to the load current.

The current detecting device is a current transformer provided in a primary circuit for supplying electricity to a rotor winding of the motor, and the variable secondary resistor is provided with a slip ring connected to the rotor winding. And a short-circuit contactor for short-circuiting the secondary resistor by bypassing the variable resistor in the secondary circuit. According to the detection current of the device, either the short-circuiting contactor or the adjusting contactor is connected to change the electric resistance value connected to the secondary circuit side.

According to the configuration of the present invention, when, for example, a lithotripter driven by a winding-type induction motor is crushing relatively small stones, the motor rotates at the rated rotation speed, the load torque of the motor is small, and the current is reduced. The detection current by the detection device is small. In this case, the resistance of the variable secondary resistor is zero or a relatively small value, the input energy consumed by the secondary resistor is small, and the energy efficiency can be kept high.

Next, when crushing a large stone, the load torque increases and the current detected by the current detecting device increases. Therefore, the electric resistance value of the variable secondary resistor is increased by the resistance control device, so that the motor The torque curve switches instantaneously to the conventional one with a secondary resistor. Therefore, the rotation speed decreases, and accordingly, 200% of the rating
The stone is crushed by generating the above large torque. Thus, the wound-type induction motor can drive the crusher without stopping. When the grinding of large stones is completed, the load torque decreases, and the detected current decreases,
The resistance of the variable secondary resistor again becomes zero or a small value,
Increase energy efficiency.

Next, the operation of the present invention will be described in more detail.
In the description, the second current value is larger than the first current value,
The third current value is larger than the second current value, and the Nth current value is larger than the (N-1) th current value. The second set resistance is larger than the first set resistance, the third set resistance is larger than the second set resistance, and the N-th set resistance is N-th.
It is larger than the set resistance value of 1. Here, N is a positive integer.

When crushing a stone having a size equal to or less than the rated capacity of the lithotripter, a current flowing through a circuit (hereinafter referred to as a primary circuit) for supplying electricity to a rotor winding of the electric motor is equal to or smaller than that of the crusher. It is a value equal to or less than the first current value. At this time, the controller is 2
The electric resistance of the next resistor is set to the first set resistance.
The rotational speed and the torque of the motor are rated speed when the rotational speed is reduced by several% from the synchronous rotational speed, and the torque is zero at the synchronous rotational speed, and is maximum when the rotational speed is reduced by 10 to 20% from the synchronous rotational speed. When torque is generated and the rotation speed is further reduced, the torque is rapidly reduced. The motor rotates at a point that is balanced with the load torque at a rotation speed between the rated rotation speed and the rotation speed at which the maximum torque is generated, and is connected to the rotor winding side via a slip ring (hereinafter, a secondary circuit). (Referred to as a circuit) has a small electric resistance, so that heat loss due to the electric resistance is small and energy efficiency is good.

When a stone crusher crushes a larger stone, the rotation speed is lower than that described above, and a larger torque is generated accordingly, and the current value of the primary circuit increases. When the current value of the primary circuit becomes larger than the first set current value, the controller sets 2
The electric resistance of the next resistor is changed to the second set resistance value. The relationship between the rotational speed and the torque of the electric motor is such that the torque is zero at the synchronous rotational speed, and when the resistance of the secondary resistor is the first set resistance value, the torque becomes maximum when the rotational speed further falls below the rotational speed at which the maximum torque was generated. When torque is generated and the rotation speed further decreases, the torque tends to decrease gradually. The motor generates a torque larger than the rated torque by reducing the rotation speed. The secondary resistor generates heat due to electrical resistance,
This does not contribute to the work of the motor and is therefore less energy efficient.

As the load on the lithotripter increases, the torque of the motor increases and the current value of the primary circuit further increases.
When the current value of the primary circuit becomes larger than the Nth set current value, the controller changes the electric resistance of the secondary resistor to the (N + 1) th set resistance value. The relationship between the rotational speed and the torque of the electric motor is that the torque is zero at the synchronous rotational speed, the rated rotational speed is a few percent lower than the synchronous rotational speed, and a large torque is generated as the rotational speed decreases, and the maximum torque is generated. The number of revolutions tends to approach zero. The electric motor further reduces the rotation speed and generates a large torque. The amount of heat generated increases as the electric resistance of the secondary resistor increases,
Energy efficiency is reduced.

When a strong stone enters the stone crusher, the stone crusher bites the stone, and the electric motor continues to output the maximum torque in a state where the rotation speed is close to zero. After a certain period of time, the stone is crushed and the load torque decreases, so the rotation speed decreases and
The current value of the next circuit becomes smaller. The controller changes the secondary resistor to the second set resistance value when the current value falls below the second current value, and changes the secondary resistor to the first set resistance value when the current value falls below the first current value. Change to a value.

By performing the above control in accordance with the current value of the primary circuit generated by the load of the lithotripter, the motor can always maintain proper torque characteristics. In addition, since large stones are less likely to enter the lithotripter compared to the overall operation time, the overall energy efficiency during the operation time is higher than that of a conventional motor in which the secondary resistor has a constant electric resistance value. .

[0017]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a wiring diagram of the present invention.

In FIG. 1, reference numeral 1 denotes a winding type induction motor, which is shown by an inner circle showing a rotor winding 1b and an outer circle showing a stator winding 1a. 2 is a lithotripter. Reference numeral 3 denotes a controller which receives a signal from the current transformer 4 and outputs a secondary resistance control signal 10. The current transformer 4 detects the current value of the primary circuit,
To communicate. Reference numeral 5 denotes a primary circuit, which is connected to a primary terminal 13 and supplies electricity to the wound induction motor 1. Reference numeral 6 denotes a secondary circuit, which is connected to the secondary terminal 12 and connected to the rotor winding 1b via the slip ring 15. Reference numeral 7 denotes a contactor for short-circuiting a secondary resistor (hereinafter referred to as a contactor for short-circuiting). When the first switch 8a is closed, the secondary circuit can be short-circuited. Reference numeral 8 denotes a contactor for adjusting a secondary resistor (hereinafter referred to as an adjustment contactor), and includes second, third, and fourth switches 8b,
When each of 8c and 8d is closed, the secondary resistor can be adjusted to a corresponding resistance value. Reference numeral 9 denotes a secondary resistor, which is connected to the secondary circuit 6 and loads a resistor in series on the rotor winding 1b of the wound induction motor 1. Reference numeral 10 denotes a secondary resistance control signal, which is indicated by a broken line and transmits a control signal of the controller 3 to the short-circuiting contactor 7 and the secondary resistance adjusting contactor 8. Reference numeral 11 denotes a coupling for connecting the crusher 2 and the power shaft of the wire-wound induction motor 1. A main switch 14 connects the primary circuit to a power supply (not shown).

FIG. 2 is a diagram showing the relationship between the rotation speed of the motor and the torque. This figure is a characteristic graph showing the relationship between the torque and the rotation speed of the wound induction motor 1, in which the horizontal axis represents the rotation speed and the vertical axis represents the torque. The rotation speed is displayed with the synchronous rotation speed of the wound induction motor 1 as 100%. The torque is 100 times the rated torque of the wound induction motor 1.
Displayed as%. Reference numeral 20a denotes a curve showing the relationship between torque and rotational speed when the first switch 8a of the short-circuit contactor 7 is closed and the secondary circuit is short-circuited. 20b is a curve showing the torque-rotational speed relationship when the second switch 8b of the adjustment contactor is closed and the secondary resistor is adjusted to a corresponding specific resistance value. Hereinafter, the curve 20c and the third switch 8c and the curve 20d and the third switch 8d have the same relationship. 22a, 22b and 22c are examples of characteristic curves representing the load torque applied to the wound induction motor 1 and the rotation speed when a specific load is applied to the crusher 2. 2
1a has a characteristic of torque-a rotational speed of 20a and a load torque-
This is a point showing the rotation speed and torque of the wound induction motor 1 when the rotation speed is 22a. 21b, 20b and 22
b, 21c, 20c and 22c have a similar relationship. 23
a is a point where the maximum torque is generated in the characteristic curve 20a. 23b and 20b and 23c and 20c have a similar relationship.

Next, the operation of the present embodiment will be described. In this description, the second current value is larger than the first current value, and the third current value is larger than the second current value. The second set resistance value is larger than the first set resistance value, and the third set resistance value is larger than the second set resistance value. In the present embodiment, the first set resistance value is zero.

When the lithotripter 2 is crushing ordinary stone, the current flowing through the primary circuit is equal to or less than the first current. The characteristics of the load torque and the rotation speed are shown by a curve 22a. At this time, since the controller 3 selects the first switch 8a of the short-circuiting contactor 7, the secondary circuit is short-circuited.
The rotation speed and torque of the electric motor have characteristics shown by a curve 20a. The winding induction motor 1 rotates at a rotation speed represented by a point 21a which is an intersection of the curve 22a and the curve 23a.

When the crusher 2 crushes a larger stone, the characteristics of the load torque and the rotation speed are represented by a curve 22b. The rotation speed of the winding induction motor 1 decreases, and accordingly a large torque is generated, and the current value of the primary circuit 5 increases. When the current value of the primary circuit 5 becomes larger than the first set current value, the controller 3 selects the second switch 8b of the adjustment contactor 8. The electric resistance of the secondary resistor becomes the second set resistance value. The relationship between motor speed and torque is 2
0b. The winding induction motor 1 has a curve 22
It rotates at a rotation speed represented by a point 21b which is an intersection of the curve 20b and the curve 20b.

When the stone cannot be completely crushed, the torque of the wound induction motor 1 increases and the current value of the primary circuit further increases. When the current value of the primary circuit becomes larger than the second set current value, the controller selects the third switch 8c of the adjusting contactor 8. The electric resistance of the secondary resistor becomes the third set resistance value. The relationship between the motor speed and torque is 20c
It is represented by The winding induction motor 1 rotates at a rotation speed represented by a point 21c which is an intersection of the curve 22c and the curve 20c.

When a solid stone enters the stone crusher, the stone crusher bites the stone, and the electric motor continues to output the maximum torque represented by the point 23c on the curve 20c where the rotation speed is close to zero. After a certain period of time, the stone is crushed and the load torque decreases, so that the rotation speed decreases and the current value of the primary circuit 5 decreases. When the current value falls below the second current value, the controller selects the second switch 8b of the adjustment contactor 8. The electric resistance value of the secondary resistor becomes the second set resistance value. When the current value falls below the first current value, the short-circuit contactor 8
The first switch 8a is selected. The electric resistance of the secondary resistor becomes the first set resistance, that is, zero.

FIG. 3 shows one of the embodiments showing the wiring of the secondary circuit. Referring to FIG.
An embodiment of a method for connecting phase wiring will be described. 5a, 5
b and 5c are three-phase power supply lines of the primary circuit 5. 13a,
13b and 13c are three-phase primary terminals of the wound induction motor 1. 12a, 12b, 12c are winding type induction motors 1
Are the three-phase secondary terminals. Reference numerals 6a, 6b and 6c denote wirings of the secondary circuit three-phase. 30a, 30b and 30c are contacts, which are connected so that the wires 6a, 6b and 6c can be short-circuited with each other, and are opened and closed by a first switch 8a. 32
a, 32b and 32c are variable resistors, one of which is a wiring 6
a, 6b, 6c are connected in series, and the opposite sides are short-circuited to each other. 33a, 33b and 33c are variable resistors 32
a, 32b, and 32c are intermediate terminals of which terminals can be changed in position. 31a, 31
b and 31c are contact points, and the intermediate terminals 33a, 33b, 3
3c are connected so that they can be short-circuited with each other, and are opened and closed by a second switch 8b.

The operation of the embodiment shown in FIG. 3 will be described below.
When the controller 3 gives a command to the first switch 8a, the contacts 30a, 30b, 30c close and the secondary circuits 6a, 6b,
6c is short-circuited. The electric resistance value connected to the secondary terminal becomes zero, and the characteristic of the wound induction motor 1 is
a. The controller 3 is the second switch 8b
, The contacts 31a, 31b, 31c are closed, and the intermediate terminals 33a, 33b, 33c are short-circuited.
The electric resistance value connected to the secondary terminal is the secondary terminal 12a, 1
The electric resistance of the resistor between the terminals 2b and 12c and the intermediate terminals 33a, 33b and 33c is connected to the secondary terminal, and the characteristics of the wound induction motor 1 are as shown by a curve 20b.

FIG. 4 shows another embodiment showing wiring of a secondary circuit. With reference to this drawing, another embodiment of a method for connecting three-phase wiring of the wound induction motor 1 will be described.
The description up to 30a, 30b, and 30c is the same as that described above, and will not be repeated. 32a, 32b, 32c are resistors, one of which is connected to the secondary circuits 6a, 6b, 6c, and the other is further connected to the resistors 35a, 35b, 35c. Further 37
a, 37b, 37c. Resistance 37a, 3
The opposite sides of 7b and 37c are short-circuited to each other. 33
a, 33b and 33c are terminals between the resistors 32a, 32b and 32c and the resistors 35a, 35b and 35c. 36a,
36b, 36c are resistors 35a, 35b, 35c, resistor 3
Terminals between 7a, 37b and 37c. 31a, 31
b and 31c are contact points, and terminals 33a, 33b and 33c
Are connected so that they can be mutually short-circuited, and the second switch 8b
It is opened and closed by. 34a, 34b and 34c are contacts, which are connected so that the terminals 36a, 36b and 36c can be short-circuited with each other, and are opened and closed by a third switch 8c. According to this method, it is possible to set a plurality of resistance values in the secondary resistor 9.

The operation of this embodiment will be described. As described in the embodiment of FIG. 3, when any one of the first, second, and third switches 8a, 8b, and 8c is selected, the corresponding contact is closed and the corresponding terminal is short-circuited. Secondary terminal 12
a, 12b, and 12c are connected to the sum of the resistance values of the resistors between the short-circuited terminals.

The present invention is not limited to the above-described embodiment, and various changes can be made without departing from the gist of the invention. For example, the number of switches of the contactors for adjusting the secondary resistance may be selected according to the requirements of the control, and the resistance of the variable resistor may be set to zero without the contactors for short-circuit.

[0030]

As described above, the control device of the wound induction motor of the present invention controls the motor under conditions of good energy efficiency when the load on the lithotripter is small, and when the load increases, the number of revolutions increases. Even if it drops, it can produce a large torque. In the lithotripter, the time during which the load increases is not a large percentage of the total operation time, so that a motor control device that has high overall energy efficiency and is suitable for driving the lithotripter can be provided.

[Brief description of the drawings]

FIG. 1 is a wiring system diagram of the present invention.

FIG. 2 is a graph showing a relationship between a rotation speed and a torque of an electric motor.

FIG. 3 is a wiring diagram of a secondary circuit.

FIG. 4 is another wiring diagram of the secondary circuit.

FIG. 5 is a speed characteristic curve diagram of a general induction motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Winding induction motor 2 Stone crusher 3 Controller 4 Current transformer 5 Primary circuit 6 Secondary circuit 7 Short contactor (Secondary resistor short contactor) 8 Adjustment contactor (Secondary resistor adjustment 9) Secondary resistor 10 Secondary resistance control signal

Claims (2)

[Claims] 1. A current detecting device for detecting a current value flowing through a stator winding of a wound induction motor, and a current detecting device connected in series to a rotor winding of the motor via a slip ring and capable of changing an electric resistance value. A variable secondary resistor, and a resistance control device that changes an electric resistance value of the variable secondary resistor in accordance with the current value, and adjusts an electric resistance value of the variable secondary resistor according to a load current. A control device for a winding-type induction motor, wherein the control device changes. 2. The current detection device is a current transformer provided in a primary circuit for supplying electricity to a rotor winding of an electric motor, and the variable secondary resistor is provided with a slip ring connected to the rotor winding. And a contactor for adjusting the secondary resistor of the secondary circuit connected through the variable resistor.
And a short-circuit contactor for short-circuiting the secondary resistor. The resistance control device connects either the short-circuit contactor or the adjustment contactor according to the detection current of the current transformer, and connects the secondary contact to the secondary circuit. 2. The control device according to claim 1, wherein the connected electric resistance value is changed.