JPH01318505A - Overcurrent breaking circuit for power controller - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a secondary fault by inputting the second breaking command to break a current to be supplied to a motor when a current value exceeds a set point after outputting the first breaking command. CONSTITUTION:A current signal (i) outputted from a current wave from detection circuit 12 is inputted to an overcurrent detection circuit 91, and when its current value exceeds a specific standard value, the first breaking command (d) is outputted to a power control circuit 3, and power supply to a motor 4 stops. At that time, when a thyristor of the power control circuit 3 is out of order, a current to be supplied to the motor 4 is not cut off even through the first breaking command (d) is received. Therefor, the first breaking command (d) is outputted to the power control circuit 3, and even if a specific time elapss, when a current value obtained from the current waveform detection circuit 12 exceeds a specific value, the second breaking command (f) is outputted from the overcurrent detection circuit 91 to a current cutoff circuit 92, and current supplied to the motor 4 is broke.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an improvement of US Pat. No. 4,052,648, which was invented to optimally control the operation of an induction motor according to load fluctuations. In particular, the present invention relates to a power controller equipped with a protection circuit that reliably protects a motor from overcurrent.

[Conventional technology]

There is a strong demand for the electric motor drive parts in spacecraft to operate for long periods of time without failure and with the minimum amount of power necessary. Therefore, in 1975, Dr. Frank Nola of the National Aeronautics and Space Administration developed the r Power Factor Controller 1. The basic principle is to monitor the load torque of the motor, apply only the minimum amount of power necessary for normal rotation, and cut off excess power. When the load increases, additional power is automatically supplied to compensate for the increased load. Normal equipment uses electric motors with a margin of about 50% to 100% of the average load, so these surplus bones are also cut. In addition, when the motor normally starts up, an inrush current of 700% of the rated current flows, but with the soft start function, this has been improved to 50%. When these are combined, a power saving effect of 10 to 80% can be obtained. This will be explained in more detail based on FIG. The phase difference between the voltage applied to terminals X, The load factor is conversely obtained from the power factor, and when the load factor is low, the effective power given to the electric motor 106 is lowered by Cyrisk-113. As a result, when the load is low, the reactive current, copper loss, and iron loss flowing through the motor windings can be significantly reduced, improving the power factor and saving power. At this time, the terminal voltage of the motor 106 is detected by the transformer 101 and inputted to the comparator 110 via the rectangular wave shaping circuits 102 and 103 and the harmonic shaping circuits 104 and 105. On the other hand, the motor current is taken out as a voltage across the resistor 107, and is input to the phase detection circuit 108 via a transformer, a waveform shaping circuit, a differentiation circuit, and a one-shot. This phase detection circuit 108 also receives the output signal from the rectangular wave shaping circuit 103, and detects the phase difference between the two. The phase difference signal is inputted to an operational amplifier 115 via an integrating circuit 109. At this time, the difference between the value of the negative potential from the control variable resistor 114 and the value of the output of the integrating circuit 109 is output from the operational amplifier 115 and input to the comparator 110. From this comparator 110, the harmonic shaping circuit 1
The difference between the output signals of 04 and 105 and the output signal of the operational amplifier 115 is output, which turns the gate 112 on and off, turns on and off the high frequency signal oscillated by the gate trigger oscillator 111, and outputs the thyristor 113.
The voltage applied to the motor 106 is controlled to have an appropriate effective voltage waveform. The above is the basic operation of the power controller for the induction motor. Although this operation has been explained for a single-phase circuit, it is also similar for a three-phase power circuit. If this power controller is represented in a simplified block diagram, the fifth
The result will be as shown in the figure. Here, the power factor monitor circuit 1 monitors the angle of the Yuki-onna point of intersection of electric potential and current, which vary depending on the load applied to the motor, and outputs it as a monitor power factor a. In the power factor comparison circuit 2, this monitor power factor a is used as a reference angle (reference power factor b).
When the monitor power factor becomes lower than the reference power factor, a signal C is applied to the power control circuit 3 to reduce the voltage supplied to the motor 4. The deviation of the monitor power factor a compared with the reference power factor is integrated, and in the power control circuit 3, the positive and negative halves of the AC power supply voltage are adjusted so that the angle of the voltage and current junction and the delay angle are equal. Performs triggering for the required time in the cycle and controls the thyristor of the voltage controller 3 to set the appropriate voltage to the motor 4.
supply to. Reducing the supply voltage at no load will reduce core losses and reduce stator current. Decreasing the stator current reduces the power consumption (KW) of the motor.
H) will decrease significantly, and at the same time, apparent manpower will also decrease. In this way, it is possible to not only save the power consumption of the electric motor itself, but also to control the power consumption of the entire factory, preventing power loss and generating large profits. 1. Also provided is an overcurrent cutoff circuit that protects the motor 4 by cutting off the thyristor due to overcurrent and cutting off the current supplied to the motor 4.

[Issue to be solved]

However, in recent years, cyrisk-utilizing power devices such as inverter motors, welding machines, and laser processing machines have been frequently used in factory equipment. Moreover, filters to prevent noise around the power supply are often inadequate. In particular, the standards for Japanese factory equipment are lax, and the current situation is that the number of cases in which the noise of equipment itself causes adverse effects such as malfunctions on other equipment through power lines is rapidly increasing. The above-mentioned power controller also has the problem of being very strongly influenced by these power supply noises, and as a result, control semiconductor elements such as thyristors in the power control circuit often fail. Moreover, the logic circuit of this power controller may malfunction due to such noise, and the power controller may become uncontrollable. Therefore, with only an overcurrent cutoff circuit configured to protect the motor by cutting off the thyristor due to overcurrent and cutting off the current supplied to the motor, problems such as poor insulation of the motor windings, ground faults in the wiring, etc. If the thyristor is destroyed and remains in a conductive or semi-conductive state due to an overcurrent caused by a motor lock, etc., a large current will continue to flow until the current is cut off by a fuse or thermal. , there is a risk of burnout of the motor windings or other secondary failures.

[Means to solve the problem]

In order to solve the above problems, in the overcurrent cutoff circuit for a power controller according to the present invention, the power factor of the motor is detected by a power factor monitor circuit equipped with a voltage waveform detection means and a current waveform detection means. When the power factor and the reference power factor are compared in a power factor comparison circuit, the electric motor is operated at a predetermined power factor in the power control circuit, and the current value detected by the current waveform detection means exceeds the set value. In a power controller configured to output a first cutoff command from an overcurrent detection circuit and cut off the current supplied to the electric motor in the power control circuit, after outputting the first cutoff command, the current value is an overcurrent detection circuit that outputs a second cutoff command when the set value is exceeded;
A measure was taken to include a current cutoff circuit that cuts off the current supplied to the motor in response to a cutoff command.

[For use]

In the overcurrent cutoff circuit for a power controller according to the present invention, a monitor power factor detected by a power factor monitor circuit including a voltage waveform detecting means and a current waveform detecting means and a reference power factor are used. A power factor comparison circuit compares the power factor, the power control circuit operates the motor at a predetermined power factor, and when the current value detected by the current waveform detection means exceeds a set value, a first cutoff is performed from the overcurrent detection circuit. In a power controller configured to output a command and cut off the current supplied to the electric motor in the power control circuit, after the first cutoff command is output, the current value exceeds the set value due to some accident or the like. At this time, the overcurrent detection circuit outputs a second cutoff command to cut off the current supplied to the electric motor, so even if the power control circuit is out of order, it is reliably cut off.

【Example】

EMBODIMENT OF THE INVENTION Below, the overcurrent cutoff circuit for power controllers according to the present invention will be explained in detail based on the drawings. FIG. 1 is a block diagram of an embodiment of a power controller equipped with an overcurrent cutoff circuit for a power controller according to the present invention. In the drawing, ■ is a power factor monitor circuit, 2 is a power factor comparison circuit, 3 is a power control circuit, 4 is a motor, 5 is an automatic stop circuit, 6 is a soft start circuit, 7 is a soft start circuit, and 8 is a reference power factor. 9 is an overcurrent cutoff circuit, IO is a high-speed current detection circuit, 11 is a voltage waveform detection circuit, and 12 is a current waveform detection circuit. In the power factor monitor circuit 1, the voltage waveform detection circuit 11
The voltage waveform signal e detected by the current waveform detection circuit 12
The current waveform signals i detected by the respective voltage waveform shaping circuits 13. The current waveform shaping circuit 14 shapes the waveform, and the power factor detection circuit 15 detects the phase difference between the voltage waveform signal e and the current waveform signal i and outputs it as a monitor power factor a. The power factor comparison circuit 2 compares the power factor set by the reference power factor setting circuit 8 with the monitor power factor a, and the power control circuit 3 is controlled by the signal C obtained by integrating the deviation, thereby controlling the electric motor. 4
The power supplied to the system is controlled to the optimum value. Details of the voltage waveform detection circuit 11 and the current waveform detection circuit 12 are shown in FIG. In addition, in the voltage waveform detection circuit 11, the terminal 11a and the terminal 27a, the terminal 11b and the terminal 27b are connected, and the terminal 2
The signals appearing at terminals 6a and 26b are input to the voltage waveform shaping circuit 13 as voltage waveform signals e, and in the current waveform detection circuit 12, signals appearing at terminals 12a, 27a, and 12
b and the terminal 27b are connected, and the signals appearing at the terminals 26a and 26b are inputted to the current waveform shaping circuit 14 as the current waveform signal i. The overcurrent cutoff circuit 9 includes an overcurrent detection circuit 91 in which a reference value for overcurrent determination is set, and a current cutoff circuit 92 using an electromagnetic circuit breaker. The current signal i output from the current waveform detection circuit 12 is input to the overcurrent detection circuit 91, and when the current value exceeds a predetermined reference value, the first cutoff command d is output to the power control circuit 3, and the electric motor 4 Stop power supply to. At this time, if the thyristor of the power control circuit 3 is out of order, the current supplied to the motor 4 will not be cut off even if the first cutoff command d is received. Therefore, if the current value obtained from the current waveform detection circuit 12 does not fall below a predetermined value even after a predetermined time elapses after outputting the first cutoff command d to the power control circuit 3, the overcurrent detection A second cutoff command r is output from the circuit 91 to the current cutoff circuit 92 to cut off the current supplied to the electric motor 4. In this way, even if the thyristor of the power control circuit 3 is out of order, the current supplied to the motor will be reliably cut off, preventing burnout of the motor windings and other secondary failures. The effect is that it can be prevented. Details of the high-speed current detection circuit 10 are shown in FIG. While the conventional current waveform detection circuit 12 and current waveform shaping circuit 14 include many time constant circuits, this high-speed current detection circuit 10 has a simple circuit configuration, so the signal delay time is different. Therefore, this high-speed current detection circuit 1
The current signal detected at 0 can follow changes in the actual current signal faster than the current signal obtained through the conventional current waveform detection circuit 12 and current waveform shaping circuit 14. Therefore, in the past, if the power was controlled to the lowest level, there was a risk of stalling when the load increased, so power could only be saved to a certain extent. However, due to the operation acceleration effect of the high-speed current detection circuit 10 and correction circuit 16, there is no need to worry about stalling.
Power can be saved by 10% to 20%.

【effect】

In this way, according to the overcurrent cutoff circuit for a power controller according to the present invention, even if the power control circuit using a thyristor or the like is out of order, the current supplied to the motor is reliably cut off by the current cutoff circuit. This has the effect of preventing burnout of the motor windings and the occurrence of other secondary failures. Therefore, it is possible to safely use a power controller that can achieve a large power saving effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power controller using the overcurrent cutoff circuit for a power controller according to the present invention, and FIG. 2 is a circuit diagram of main parts of a current waveform detection circuit and a voltage waveform detection circuit used in the same embodiment. FIG. 3 is a circuit diagram of a high-speed current detection circuit, FIG. 4 is a block diagram of a conventional power controller, and FIG. 5 is a simplified block diagram of the same power controller. ■...Power factor monitor circuit, 2...Power factor comparison circuit, 3
... Power control circuit, 4 ... Electric motor, 8 ... Reference power factor output circuit, 9 ... Overcurrent cutoff circuit, 10 River high-speed current detection circuit, ll- ... Voltage waveform detection circuit, 12-・・Current waveform detection circuit, 91 ・・Overcurrent detection circuit, 92−・
・Current cutoff circuit, a...monitor power factor, b...reference power factor, C...deviation (signal), d...first cutoff command,
f...Second cutoff command.

Claims (1)

[Claims] (1) A power factor comparison circuit compares the monitor power factor detected by a power factor monitor circuit equipped with a voltage waveform detection means and a current waveform detection means with a reference power factor, and controls the power. The circuit operates the motor at a predetermined power factor, and when the current value detected by the current waveform detection means exceeds the set value, the overcurrent detection circuit outputs a first cutoff command, and the power control circuit outputs a first cutoff command. In a power controller configured to cut off current supplied to a motor, an overcurrent detection circuit outputs a second cutoff command when the current value exceeds a set value after outputting a first cutoff command; An overcurrent cutoff circuit for a power controller, comprising a current cutoff circuit that cuts off current supplied to a motor in response to a second cutoff command.