JPH1094279A - Apparatus for compensating starting torque - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a torque in a starting operation and to reduce power consumption in a rated operation by a method wherein a peak current flowing to a capacitor induction motor is detected, whether the peak current is larger than the output of a reference-current-value measuring instrument or not is judged and a capacitor for starting compensation is turned on and off. SOLUTION: At a point of time when the output signal of a peak-hold circuit 6 exceeds the output signal of a reference-current-value measuring instrument 7, a starting compensation signal is output from a comparison circuit 8, a triac 4 is set to a continuity state, and the capacitance of a capacitor becomes the total sum of the capacitance of a capacitor 31 for the rated operation and that of a capacitor 32 for the starting compensation. In addition, when the output signal is lowered, the starting compensation signal is stopped, the triac 4 is returned to a cutoff state, and the capacitance of the capacitor becomes only that of the capacitor 31 for rated operation. Thereby, an induction motor 2 in a starting operation can obtain a sufficient starting torque, and its power consumption can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a starting torque compensating device for starting a capacitor run induction motor.

[0002]

2. Description of the Related Art FIG. 4 shows the relationship between the number of rotations, torque and current of a general capacitor run type induction motor. As shown, when the capacitance of the capacitor is changed, both the torque and the current are changed. If the capacitor capacity is increased and the torque is increased, the current also increases. Therefore, if an attempt is made to secure the starting torque of the induction motor, the power consumption during the rated rotation increases. As a countermeasure, a centrifugal switch or a tachogenerator is combined with a control circuit to detect the number of revolutions of the induction motor, and to switch the capacitor capacity between startup and rated time. Further, an inverter circuit is used without using a startup compensation capacitor.

[0003]

However, in such a conventional technique, a special induction motor equipped with a centrifugal switch or a tachogenerator must be used to detect the rotation speed of the induction motor. However, there are many restrictions such as an increase in the shape of the motor. In particular, the centrifugal switch requires regular maintenance, and it is not easy to change the setting of the number of revolutions at which the condenser capacity is switched. In addition, there is a problem that the price of the whole device in the inverter circuit becomes expensive especially in a small device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a large torque at the time of starting, a small power consumption at the time of rating, and a whole device without attaching a special device to the induction motor. It is an object of the present invention to provide a starting torque compensating device that minimizes a rise in price at a time.

[0005]

According to the present invention, there is provided a peak-hold circuit for detecting a peak current flowing in a capacitor-run type induction motor and holding the peak current, and a reference current value setting device. A comparison circuit for determining the magnitude of the peak current and the output of the reference current value setting device; and switching means for turning on and off the startup compensation capacitor based on the output of the comparison circuit.

[0006]

FIG. 1 is a diagram showing an embodiment of a starting torque compensating device according to the present invention. As shown in the figure,
1 is a power receiving end, 2 is a capacitor run type induction motor, 31 is a rated operation capacitor, 32 is a startup compensation capacitor, 4 is a triac which is a switching means for turning on / off the startup compensation capacitor 32, and 5 is current detection. A resistor 6, a peak hold circuit for detecting and holding a peak current flowing through the induction motor 2, a reference current value setting device 7, a comparison circuit 8 for judging the magnitude of the peak current and the output of the reference current value setting device 7 It is. When a rated voltage is applied to the power receiving end 1, the induction motor 2 is energized through the current detection resistor 5. At this time, the triac 4 is in a cut-off state, and the startup compensating capacitor 32 is not energized. The induction motor 2 is a rated operation capacitor 3
Start up in the rated state using only one. Current detection resistor 5
Is an AC voltage proportional to the motor current of the induction motor 2, but the peak voltage of the AC voltage is applied to the induction motor 2 by the peak hold circuit 6.
The peak current of is detected and held. Peak hold circuit 6
Is given a time constant that is sufficiently longer than the repetition period of the power supply and can be attenuated in a time sufficiently shorter than the decay time of the effective motor current value when the induction motor 2 is started. FIG. 2 shows the relationship between the power input signal and the output signal of the peak hold circuit 6.

When the output signal of the peak hold circuit 6 exceeds the output signal of the reference current value setting unit 7 when the motor is started, a start compensation signal is output from the comparison circuit 8 and the triac 4 is turned on. The capacity of the capacitor connected to the induction motor 2 is the rated operation capacitor 3
1 and the capacity of the start-up compensation capacitor 32, and the output torque of the induction motor 2 increases.

Before the induction motor 2 continues to accelerate further and reaches the rated operation state, if the output signal of the peak hold circuit 6 drops below the output signal of the reference current value setting device 7, the comparison circuit 8 The start compensation signal stops,
The triac 4 returns to the cutoff state. The capacity of the capacitor connected to the induction motor 2 is only the rated operation capacitor 31, and power consumption can be suppressed.

FIG. 3 shows the rotation speed-torque / current characteristics of the induction motor 2 having the starting torque compensator of the present invention. As shown in the figure, when the current crosses the output signal of the reference current value setting device 7, the startup compensation capacitor 32 is turned on and off, and the current and the torque are changed.

As described above, when the rotation speed of the induction motor 2 at the time of startup is less than the set value, a sufficient startup torque can be obtained by increasing the capacitance of the capacitor, and the rotation speed of the induction motor 2 is higher than the set value. If it has increased, the capacity of the capacitor can be reduced and the power consumption of the induction motor 2 can be suppressed.

Further, the use of the current detection resistor 5 for detecting the load state enables high-precision, high-resolution setting at a relatively low cost, and has an effect that the setting can be easily changed. Further, it is possible to improve the characteristics by additionally mounting on an existing device.

[0012]

As described above, in the starting torque compensating device according to the present invention, the starting torque is increased and the power consumption at the rated time is reduced without mounting a special device on the induction motor. be able to. In addition, it is possible to minimize an increase in the price of the entire apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a starting torque compensating device according to the present invention.

FIG. 2 is a diagram illustrating a relationship between a power supply input signal and an output signal of a peak hold circuit.

FIG. 3 is a graph showing the relationship between the rotation speed and the torque / current of an induction motor having a starting torque compensating device according to the present invention.

FIG. 4 is a diagram showing a relationship between the number of revolutions and torque / current according to the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 receiving end 2 induction motor 31 rated operation capacitor 32 start-up compensation capacitor 4 triac 5 current detection resistor 6 peak hold circuit 7 reference current value setting device 8 comparison circuit

Claims (1)

[Claims] 1. A peak hold circuit for detecting a peak current flowing through a capacitor run type induction motor and holding the peak current, a reference current value setter, and an output of the peak current and the output of the reference current value setter. A starting torque compensating device comprising: a comparing circuit for judging the magnitude; and switching means for turning on / off a starting compensating capacitor based on an output of the comparing circuit.