JPS648559B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to motor speed control schemes, and more particularly to motor protection schemes.

A speed control device conventionally used for driving an electric motor has a circuit configuration as shown in FIG. In the figure, a current feedback input is supplied to terminal 11, a speed command input is supplied to terminal 12, a speed feedback input is supplied to terminal 13, and a synchronization input is supplied to terminal 14, and the control consists of an amplifier A, a comparator C, a negative circuit N, etc. Thyristor 2 depending on the circuit
The speed of the electric motor M is controlled by controlling the speeds of the motors 1 to 24. In this device, when an overcurrent flows through the motor, the current limiter operates according to the value specified by the voltage at point a, and controls the motor current to be within the specified value.

However, the overcurrent protection circuit using the above-mentioned current limiter can only perform a limiting operation once an overcurrent flows into the motor, and the field of the motor using permanent magnets caused by an instantaneous overcurrent is There is a problem that demagnetization cannot be prevented.

In view of the problems of the conventional speed control device described above, an object of the present invention is to provide a circuit for limiting the current of the motor, a circuit for turning off all the thyristors that drive the motor, and a circuit for turning on all the thyristors. Based on the idea of selectively operating one or more of the above three types of control circuits at the same time depending on the degree of overcurrent, we prevent demagnetization of the motor field using permanent magnets, thereby reducing the The purpose is to protect the motor from damage and characteristic deterioration due to excessive current.

In the present invention, a motor is energized from an AC power supply via a transformer, a series circuit of the motor and an overcurrent detection resistor is connected to the midpoint of the secondary winding of the transformer, and the other end of the series circuit is connected to the middle point of the secondary winding of the transformer. The thyristor is connected to both ends of the secondary winding of the transformer through a series circuit of a thyristor and an overcurrent cutoff element that are branched into two and each phase controlled, and the thyristor has a speed command input, a speed feedback input, and a motor speed control device controlled by a phase control circuit of the thyristor which receives a current feedback input via a limiter circuit, the speed command input and the speed feedback input are controlled according to the degree of motor overcurrent. A limiter operation that prevents overcurrent by limiting the phase control circuit of the thyristor, which is controlled by the signal controlled by the current feedback input, to a first set value by the limiter circuit; a second set value that detects the armature current of the motor from the voltage and whose value is greater than the first set value;
When the value exceeds a set value, controlling the phase control circuit of the thyristor to turn off all the thyristors;
and detecting the armature current of the motor and turning on all the thyristors when the value is equal to or higher than a third set value that is larger than the second set value. provided.

A block diagram and a circuit diagram of an apparatus using a motor speed control system according to an embodiment of the present invention are shown in FIGS. 2 and 3, respectively. FIG. 2 is a diagram illustrating the outline of this control method. A power source 1 supplies power to an electric motor 4 via a power element 2 such as a thyristor, and the power element 2 is phase-controlled by a control device 3. Power supplied to the electric motor 4 is controlled by phase control of the power element 2. If an overcurrent flows to the motor 4, first the control device 3
The current limiter circuit operates and the power element 2
control. Further, when the degree of overcurrent in the motor is large, in addition to the operation of the current limiter circuit, all control voltages for driving the power element 2 are turned off. Furthermore, when the degree of overcurrent is even greater, in addition to the above two controls, all power elements 2 are forcibly turned on. This three-stage control prevents instantaneous overcurrent from damaging or deteriorating the motor.

FIG. 3 is a circuit diagram showing details of FIG. 2. A current feedback input is applied to current feedback input terminal 31, which is connected via amplifiers 35, 36 and transistor 53 to a non-inverting input of comparator 42, and input terminals 32 and 33 respectively receive a speed command input and a speed feedback input. It is connected via receiver amplifiers 37 and 38 to the non-inverting input of comparator 42. AC power is applied to the input terminal 34 as a synchronous input, compared by comparators 40 and 41, and the transistors 62 and 6 of the sawtooth wave generator after polarity inversion are applied.
Connected to 3. The branched output of amplifier 38 is connected via amplifier 39 to the non-inverting input of comparator 43. The inverting inputs of the comparators 42 and 43 are the transistors 62 and 63 of the sawtooth wave generation circuit.
Supplied from.

Both terminals of a resistor 64 connected in series with the motor are connected to a current detector circuit consisting of a rectifier bridge 48, a photocoupler 50, etc., and the output of the photocoupler 50 passes through an inverting circuit 44 to a thyristor 52.
connected to the gate of The output of thyristor 52 is connected via a diode to the outputs of comparators 42 and 43, respectively. Both ends of the resistor 64 are further connected to a current detector circuit comprising another rectifier bridge 49, a photocoupler 51, etc.
The output of the photocoupler 51 is supplied via the NOT circuit 45 to one input terminal of the diode OR circuit on the input side of the NOT circuit 46 and the diode OR circuit on the input side of the NOT circuit 47, respectively.

The output of the comparator 42 is connected to the other input of the diode OR circuit on the input side of the NOT circuit 46, and the output of the comparator 43 is connected to the other input of the diode OR circuit on the input side of the NOT circuit 47. be done. The outputs of inverters 46 and 47 are each connected to transformer 54.
and 55 to the gate circuit of the motor driving thyristor. AC power is supplied to the primary side of the transformer 56, and the secondary side is connected from the center up to one end of the motor 4, both ends of the secondary winding are connected to the thyristor via a fuse 57, and the other end of the thyristor is connected to the thyristor. are interconnected and connected to one end of a resistor 64, and the other end of the resistor 64 is connected to the other end of the motor 4.

Next, the operation of the above-mentioned circuit will be explained. The difference between the speed command input applied to the terminal 32 and the speed feedback input applied to the terminal 33 is taken, and after being amplified by the amplifier 37, it is compensated by the amplifier 38. This compensation output is controlled by the current feedback input applied from the input terminal 31, and is limited by the transistor 53 to a potential determined by the reference voltage, that is, the voltage at point a, when the motor overcurrent occurs. This allows current limiter control to be performed.

The compensation output is applied to the non-inverting input of comparator 42, and a sawtooth voltage formed by pulses synchronized to the power supply obtained from a synchronous circuit including comparators 40 and 41, etc. is applied to the inverting input of comparator 42, A phase controlled pulse is obtained at the output of comparator 42, the position of the pulse varying according to the level of the compensation input. The compensation output is inverted by the amplifier 39 and sent to the comparator 4 as a speed control signal when the motor is reversed.
3 is applied to the non-inverting input and compared with the sawtooth voltage applied to the inverting input to obtain an output similar to comparator 42.

Rectifier bridge 48 and optocoupler 50 receiving current feedback output or voltage across resistor 64
A thyristor off-level detector including a thyristor off-level detector is set to operate when the current feedback value exceeds a certain value,
When the current is detected, a current flows through the transistor portion of the photocoupler 50, which causes the input of the inverter 44 to go low, and the gate of the thyristor 52 to go high, turning the thyristor 52 on. Thyristor 52
When the thyristor 52 becomes on or conductive, the thyristor 52
The anode side of the signal becomes a low level, and the outputs of the comparators 42 and 43 become a low level through the diodes.
As a result, the phase control pulses output to the comparators 42 and 43 are bypassed and are not sent to the motor side.

Rectifier bridge 49 and optocoupler 51 receiving current feedback output or voltage across resistor 64
The thyristor on-level detector including the thyristor on-level detector is set to a value larger than the detection setting value of the thyristor off-level detector described above. When a current is detected, the current flows through the transistor section of the photocoupler 51 and the negative circuit 4
The input circuit of No. 5 becomes a low level, and the output circuit of the NOT circuit 45 becomes a high level. This causes the high level signal to pass through the diodes to comparators 42 and 4.
The output of No. 3 is set to high level, and all thyristors 58 to 61 are turned on.

As mentioned above, in this device, the current limiter circuit is operated by operating the transistor 53 in response to the first stage overcurrent, and the current limiter circuit and the electric motor are operated in response to the second stage overcurrent. The control operation according to each overcurrent stage is to turn off all the control voltages of the driving thyristors, and for the third stage overcurrent, in addition to the above two control actions, all the motor driving thyristors are turned on. Do the following. According to this, the problem of current limit circuits that do not operate until an overcurrent flows is compensated for, and even if all thyristor control voltages are turned off, once the thyristor is fired, it will not operate until the power supply voltage reaches zero. It can also compensate for the problem of overcurrent within half a cycle of maintaining conduction. Turning on all the motor drive thyristors short-circuits the secondary side of the transformer 56, which prevents the motor from being energized and protects the circuit by blowing out the fuse 57.

According to the present invention, demagnetization of the field of a motor using a permanent magnet can be prevented, thereby protecting the motor from damage and deterioration of characteristics due to excessive current of the motor.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional speed control device, Figure 2 is a circuit diagram of a conventional speed control device.
The figure shows a block diagram of a device using the motor speed control method as an embodiment of the present invention, and FIG. 3 shows a circuit diagram of the device of FIG. 2. 1... Power source, 2... Power element, 3... Control device, 4... Electric motor, 11, 12, 13, 14...
Input terminal, 21, 22, 23, 24... Thyristor, 31, 32, 33, 34... Input terminal, 3
5, 36, 37, 38, 39...amplifier, 40,
41, 42, 43... Comparator, 44, 45, 4
6, 47... Inverting circuit, 48, 49... Rectifier bridge, 50, 51... Photocoupler, 52... Thyristor, 53... Transistor, 54, 55...
...Transformer, 56...Transformer, 58, 59, 60,
61...Thyristor, 62, 63...Transistor, 64...Resistor.

Claims (1)

[Claims] 1. Electricity is supplied to a motor from an AC power supply via a transformer, and a series circuit of the motor and an overcurrent detection resistor is connected to the midpoint of the secondary winding of the transformer, and The other end is connected to both ends of the secondary winding of the transformer through a series circuit of a thyristor and an overcurrent cutoff element, each branched into two and each phase controlled. In a motor speed control device controlled by a phase control circuit of the thyristor which receives an input and a current feedback input via a limiter circuit, the speed command input and the speed are controlled according to the degree of motor overcurrent. a limiter operation that prevents overcurrent by limiting the phase control circuit of the thyristor, which is controlled by the signal controlled by the current feedback input, to a first set value by the limiter circuit; Detecting the armature current of the motor from the voltage at both ends, and when the value is equal to or higher than a second set value larger than the first set value, controlling a phase control circuit of the thyristor to turn off all the thyristors; and Detecting the armature current of the motor, and detecting the value of the armature current of the motor.
An electric motor speed control method characterized by performing the following operation: turning on all the thyristors when the value is equal to or higher than a third set value which is larger than the set value.