JPS6350960B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operation control device for an electric motor that drives an electric motor using a frequency conversion device, and in particular to an electric motor operation control device that enables stable acceleration and deceleration of the electric motor.

In general, when starting a motor that is driven by a (voltage-type) frequency converter, such as an induction motor, where a large inrush current flows at the time of starting, it is necessary to suppress the starting current. Therefore, acceleration/deceleration limiting circuits are often used so that even if the frequency setting value changes stepwise, the output frequency changes gradually. Further, in such a device, since the acceleration/deceleration time changes depending on the inertia of the motor and load and the magnitude of the load torque, it is usually considered that the acceleration/deceleration time can be adjusted. However, in most cases, the state of such a load changes in various ways, and it is often practically difficult to adjust the acceleration/deceleration time each time. Therefore, the conventional method was to set the acceleration/deceleration time to match the load condition on average, and then automatically correct the deviation from the average value by separately detecting the motor current. There is.

FIG. 1 shows a schematic configuration of such conventional motor operation control, and in the figure, a frequency converter 1 is composed of a forward converter 2 and an inverse converter 3. As shown in FIG. Further, the acceleration/deceleration limiting circuit 7 includes a frequency setting resistor 8, each resistor 9 to 15, an integrating capacitor 16, operational amplifiers 17 and 18, and a variable resistor 19.
The output frequency and voltage of the frequency conversion device 1 are controlled by the output signal thereof. On the other hand, the current transformer 4 detects the current of the motor 5 connected to the frequency converter 1, and the current limiter 20 detects that the current detected by the current transformer 4 exceeds a preset current limit value. It detects and sends out an output signal. Furthermore, the gate 21 is opened and closed by the output signal of the operational amplifier 17, and applies the output signal from the current limiter 20 to the operational amplifier 18 via the resistor 15. Note that, as mentioned above, as a matter of course, the duration of the starting current flowing through the electric motor 5 changes depending on the state of the electric motor load 6.

FIG. 2 is a diagram for explaining the function of the acceleration/deceleration limiting circuit in FIG. 1. That is, when the signal set by the frequency setting resistor 8 changes stepwise like signal A, signal B changes to positive (+) and negative (-), respectively, as shown in the figure. On the other hand, the signal C becomes a negative (-) output only when the current of the motor 5 exceeds the current limit value of the current limiter 20. Next, the signal B and the signal C are added and integrated by the operational amplifier 18 and the integrating capacitor 16, resulting in a signal waveform like D. Here, signal D
The part indicated by the broken line shows the waveform when the current of the electric motor 5 is small and there is no output from the current limiter 20. Further, the slope of the broken line can be adjusted to any value using the variable resistor 19. Finally, the frequency conversion device 1
It will be controlled according to the signal D which is the output signal of.

Next, the output signal D waveform of the acceleration/deceleration limiting circuit 7 and the driving operation characteristics of the load 6 by the electric motor 5 in this configuration will be described in detail. For example, if the variable resistor 19 is set so that the electric motor 5 is accelerated according to the waveform shown by the broken line in the signal D waveform, if the inertia and torque of the load 6 are very large, this In order for the electric motor 5 to complete starting within the acceleration time corresponding to the broken line, the current of the electric motor 5 becomes extremely large and exceeds the current limit value of the current limiter 20. In this case, the gate 21
is in a closed circuit state, the signal B and the signal C are added in the operational amplifier 18, and the output signal D has a waveform as shown by the solid line as shown in FIG. The degree of change in frequency and output voltage becomes gradual. Therefore, the starting current of the motor 5 is also reduced, and the motor 5 is accelerated with a current within a range that does not exceed the current limit value set by the current limiter 20. On the other hand, since the inertia of the load 6 is large during deceleration, when the waveform of the signal D decreases as shown by the broken line, the motor 5
And the decrease in the rotation speed of load 6 cannot follow this,
The current of the motor 5 will flow back to the frequency conversion device 1. In this case, when the current flowing backward exceeds the current limit value of the current limiter 20, if the gate 21 is in the closed circuit state as in the case of acceleration described above, the signal B and the signal C are added and the output signal is D decreases rapidly as shown by the solid line in FIG. This results in a further increase in the reverse current of the motor 5, contrary to the case during acceleration described above, and there is a possibility that the frequency conversion device 1 may be destroyed. Therefore, in order to prevent such problems, conventionally, as shown in FIG. -) It is considered that the gate 21 is in an open state during the polarity period. In other words, in this case, the output frequency and output voltage of the frequency converter 1 are
The signal D gradually decreases in accordance with the slope indicated by the broken line in FIG.

However, as can be seen from the above description, in such a device, even if the output characteristic of the frequency converter 1 is improved to the deceleration characteristic as shown by the broken line indicated by the signal D in FIG. If the inertia is large, the rotational speed of the motor 5 and the load 6 cannot follow this, and the signal B
Even after the negative (-) polarity of the current limiter 20 disappears, the reverse current may still exist. It is not possible to completely eliminate the possibility that the frequency converter 1 may be destroyed due to the continuous decrease due to the output signal of the frequency converter 1, and there is a drawback that stable acceleration/deceleration operation of the electric motor cannot be performed.

The present invention has been made to solve the above-mentioned drawbacks, and its purpose is to prevent damage to the frequency converter due to reverse current that occurs when the motor is decelerated, in a device in which a motor is driven by a frequency converter. An object of the present invention is to provide an operation control device for an electric motor that can reliably prevent acceleration and deceleration of the electric motor in a stable manner.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows an example of the configuration of an electric motor operation control device according to the present invention. The same parts as those in FIG. In the figure, 22 is a current limiter that inputs the motor current detected by the current transformer 4 during acceleration of the motor and the motor reverse current during deceleration. When detected, a negative polarity (-) signal corresponding to the excess current is sent to the gate 21 as the output _Q1 , and the output
As _Q2 , a logic value signal of "0" indicating that current is being detected is sent out (motor current and motor reverse current detection means). Also, 23
is a polarity discrimination circuit which inputs the output signal B of the operational amplifier 17 and discriminates its polarity; when the input signal B has a positive (+) polarity, that is, when the motor is accelerating, the output Q is "0"; when the input signal B has a negative polarity, that is, the motor During deceleration, the output Q is changed to a logic value signal of "0" and sent out (discrimination means). 24 is an output signal Q of the polarity discrimination circuit 23 and a NAND circuit 25 to be described later.
The NAND circuit 26 receives the output signal G of the NAND circuit 24, which is obtained through a delay circuit consisting of a resistor 27, a capacitor 28, and a diode 29 and has a delay time t, and the current. A NAND circuit receives the output signal Q ₂ of the limiter 22 as an input, and 25 is a NAND circuit that receives the output signals H and F of the polarity determining circuit 23 and the NAND circuits 24 and 26, respectively. G opens or closes the gate 21. That is, in this case, when the signal G is "1", the gate 21 is in a closed state, and conversely, when it is "0", it is in an open state. Furthermore, in the above, when the output signal H of the NAND circuit 24 changes from "0" to "1", the output signal E of the delay circuit changes from "0" to "1" with a delay of the time t. be. That is, this delay time t is such that the output signal B of the operational amplifier 17 becomes negative (-) polarity, the output signal D of the operational amplifier 18 begins to decrease, and the output frequency and output voltage of the frequency conversion device 1 decrease. This is selected to correspond to the delay time until signals are generated at the outputs Q ₁ and Q ₂ of the current limiter 22 due to the reverse current generated by the current limiter 22. In addition, in the above, the NAND circuits 24, 25,
26, the polarity discrimination circuit 23 and the delay circuit constitute a gate control circuit 30.

Next, the operation of this configuration will be described with reference to the time chart shown in FIG. In the figure, each symbol corresponds to the symbol of the output signal of each element in FIG. 3 described above. Furthermore, since the operations up to the middle of this embodiment are similar to those of the prior art described above, the gate control circuit 30 will be mainly described here.

(1) When the motor is accelerating In this case, when the signal A set by the frequency setting resistor 8 changes stepwise as shown in Figure 4, the output signal B of the operational amplifier 17 is correct because it is accelerating. It is applied to the polarity determination circuit 23 of the gate control circuit 30 as a (+) polarity signal. As a result, in the polarity discrimination circuit 23, since the input signal B is a positive (+) polarity signal, the NAND circuit 25 determines that the output is "0".
added to. In this case, this signal is applied to the NAND circuit 25 as a "0" signal while the motor 5 is in the acceleration period, so the output signal G of the NAND circuit 25, that is, the gate control signal, is "1" during this period. Since it is applied to the gate 21 as a signal, the gate 21 becomes a closed circuit state,
The output signal D of the operational amplifier 18 in the acceleration/deceleration limiting circuit 7 changes as shown by the solid line in FIG.
In exactly the same way as described above, the electric motor 5 is connected to the current limiter 2.
Acceleration is performed with a current within a range that does not exceed the current limit value set by No. 2.

(2) When the motor is decelerating In this case, when the signal A set by the frequency setting resistor 8 changes in a stepwise manner as shown in FIG. 4, the output signal B of the operational amplifier 17 is It is applied to the polarity discrimination circuit 23 as a negative (-) polarity signal. As a result, the output signal Q of the polarity determining circuit 23 is applied to the NAND circuit 24 as a "0" signal. As a result, the output signal H of the NAND circuit 24 becomes "0".
to "1", which are applied to the NAND circuit 26 through the NAND circuit 25 and the delay circuit, respectively. On the other hand, due to the deceleration of the electric motor, a reverse current flows as described above, and this flows into the current limiter 22.
If _the current _limit value of
These signals are applied to the NAND circuit 26 after time t. As a result, the output signal F of the NAND circuit 26 is applied as "1" to the NAND circuit 25, and the output signal of the polarity determining circuit 23 is applied as "1" to this NAND circuit 25. As a result, all the input signals of the NAND circuit 25 become "1", so the output signal G
In other words, since the gate control signal is applied to the gate 21 as a "0" signal, the gate 21 is in an open state during the deceleration period, and the output signal _Q1 of the current limiter 22 is blocked by the gate 21.
This signal Q ₁ is not applied to operational amplifier 18 . Moreover, in this case, even if the output signal D of the operational amplifier 18 completes its reduction as shown in FIG. 4, the inertia of the motor load 6 is large as described above, and the motor reverse current remains unreduced. Even if a current exceeding the limit value of the current limiter 22 flows and the output signals Q ₁ and Q ₂ continue as shown by the broken lines in the figure, the NAND circuit 25 does not limit the current. Since the output Q ₂ of the device 22 is continuously applied as a “0” signal,
During this period (while the output _Q2 of the current limiter 22 is present), the output signal G of the NAND circuit 25, that is, the gate control signal, is applied to the gate 21 as a "0" signal, and the gate 21 is in an open state. The output signal Q ₁ of current limiter 22 is not applied to operational amplifier 18 . Therefore,
The output signal D of the operational amplifier 18 during the deceleration period becomes as shown in FIG. 4, and there is no unnecessary decrease in the output signal D due to the reverse current during deceleration as in the conventional case.

In this way, in which the induction motor 5 is driven by the frequency converter 1, the current limiter 22 and the gate 2 are configured to have a predetermined current limit value set.
1. An acceleration/deceleration control circuit 7 that controls the output frequency and output voltage of the frequency conversion device 1 and a gate control circuit 30 that controls the gate 21 are provided, and when the induction motor 5 is accelerated, the current transformer 4 detects the acceleration. On the condition that the motor current exceeds the scheduled current limit value, the increase in the output signal D of the acceleration/deceleration limiting circuit 7 due to this excess current (Q ₁ ) is reduced, while at the time of deceleration. a backflow current of the motor 5 that is greater than the above-mentioned scheduled current limit value caused by deceleration;
In other words, while the output signal _Q2 of the current limiter 22 remains, the gate 21 is opened and the excess current
The control device is configured to prevent _Q1 from being introduced into the acceleration/deceleration limiting circuit 7 and to control the degree of decrease in the output signal D of the acceleration/deceleration limiting circuit 7 to maintain it in a state based on a predetermined set value. This is what I did.

Therefore, as described above, when the induction motor 5 is decelerating, the positive feedback reduction in the output frequency and output voltage of the frequency converter 1 caused by the motor reverse current due to the large inertia of the motor load 6 is prevented. It is possible to reliably prevent damage, and thus to achieve stable acceleration/deceleration operation of the induction motor 5 by the frequency converter 1, which is extremely reliable. Furthermore, as is clear from the figure, it is only necessary to slightly improve the current limiter in the conventional configuration and add a gate control circuit 30 consisting of a logic circuit, which makes the device configuration complicated and large. As mentioned above, a great effect can be obtained without having to do anything, and it is economically advantageous.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be similarly implemented in the following manner.

For example, FIG. 5 shows the configuration of another embodiment. In other words, in addition to _FIG . A gate 32 is provided which receives the output of the polarity inversion circuit 31 and is controlled to open and close by the output signal G of the gate control circuit 30, and the output of the gate 32 is applied to the operational amplifier 18 via the resistor 15. Even if the configuration is configured, it can be implemented in the same way.

With such a configuration, the gate 21 is activated only during the period when the output signal G of the gate control circuit 30 is "0".
At the same time, the gate 32 is closed, and the output signal Q ₁ of the current limiter 22 is applied to the operational amplifier 18 of the acceleration/deceleration limiting circuit 7 through the polarity inverting circuit 31 and the gate 32.
Therefore, the rate at which the output signal D of the operational amplifier 18, that is, the output signal of the acceleration/deceleration limiting circuit 7, decreases during deceleration is more gradual than the waveform shown in FIG. 4 described above, and the duration of the motor reverse current is the shortest. In this way, the output signal D of the acceleration/deceleration limiting circuit 7 during deceleration is controlled, and a similar effect can be obtained.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

As explained above, the present invention provides an electric motor driven by a frequency conversion device controlled based on the integral circuit output of an acceleration/deceleration limiting circuit, in which the electric motor current generated by acceleration of the electric motor is equal to or higher than a predetermined value. A motor current detecting means detects that the motor reverse current generated by deceleration of the motor exceeds a predetermined value and outputs a signal corresponding to this excess current. Reverse current detection means; motor deceleration detection means for outputting a deceleration detection signal upon detecting that a motor reverse current exceeding a predetermined value is being detected by this means; frequency setting for the deceleration detection signal output by this detection means; A delay means for delaying a predetermined time from when the motor deceleration frequency is set by the device until the motor reverse current detection means detects a motor reverse current exceeding a predetermined value, and the output of the operational amplifier in the acceleration/deceleration limiting circuit accelerates and Discrimination means for determining deceleration is provided, and when the discrimination means determines acceleration of the motor, the output signal from the motor current detection means is added to the operational amplifier output in the acceleration/deceleration limiting circuit to control the degree of increase in the integral circuit output to a small value. When deceleration of the motor is determined, the output signal from the motor reverse current detection means is converted to zero or an electrical quantity of opposite polarity to limit acceleration and deceleration during the existence period of the deceleration detection signal delayed by a predetermined time by the delay means. This is added to the output of the operational amplifier in the circuit to control the degree of decrease in the output of the integrating circuit so as to maintain it below a predetermined value.

Therefore, according to the present invention, it is possible to prevent a positive feedback decrease in the output frequency and output voltage of the frequency converter due to a reverse current that occurs when the motor is decelerated, and to reliably prevent the damage thereof, thereby achieving stable acceleration and deceleration of the motor. It is possible to provide an extremely reliable operation control device for an electric motor that can be operated.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a conventional electric motor operation control device, Fig. 2 is a time chart showing the operation in Fig. 1, Fig. 3 is a schematic configuration diagram showing an embodiment according to the present invention, and Fig. 4 3 is a time chart showing the operation in FIG. 3, and FIG. 5 is a schematic configuration diagram showing another embodiment according to the present invention. DESCRIPTION OF SYMBOLS 1... Frequency conversion device, 2, 3... Forward, reverse conversion unit, 5... Induction motor, 7... Acceleration/deceleration limiting circuit,
8... Frequency setting resistor, 9-15, 27... Resistor, 16... Integrating capacitor, 17, 18...
...Operation amplifier, 19...Variable resistor, 22...Current limiter, 21, 32...Gate, 23...Polarity discrimination circuit, 24-26...NAND circuit, 28...
Capacitor, 29...diode, 30...gate control circuit, 31...polarity inversion circuit.

Claims (1)

[Claims] 1. The above-mentioned acceleration/deceleration limiting circuit consisting of a frequency setter that sets the acceleration or deceleration frequency of the motor, an operational amplifier that inputs the setting signal of this setter, an integrating circuit that inputs the output signal of this amplifier and performs integration, etc. The motor is driven by a frequency conversion device controlled based on the output of an integral circuit, and a signal is generated in response to the excess current when it is detected that the motor current generated by acceleration of the motor is equal to or higher than a predetermined value. motor reverse current detection means for detecting that a motor reverse current generated by deceleration of the motor is equal to or greater than a scheduled value and outputting a signal corresponding to this excess current; A motor deceleration detection means detects that a motor reverse current exceeding a value is detected and outputs a deceleration detection signal, and the deceleration detection signal outputted by the detection means is set to the motor deceleration frequency by the frequency setting device. Acceleration and deceleration of the motor are controlled by delay means for delaying by a predetermined time from when the motor reverse current detection means detects a motor reverse current equal to or greater than a predetermined value, and by an output of an operational amplifier in the acceleration/deceleration limiting circuit. a discriminating means for discriminating, and when the discriminating means discriminates acceleration of the electric motor, an output signal from the motor current detecting means is added to an operational amplifier output in the acceleration/deceleration limiting circuit to control a degree of increase in the output of the integrating circuit to a small value; and an acceleration control means for controlling an output signal from the motor reverse current detection means to zero or a reverse polarity during the existence period of the deceleration detection signal delayed by a predetermined time by the delay means when the discrimination means determines that the motor is decelerating. deceleration control means for converting the electric quantity into an electrical quantity and adding it to the output of the operational amplifier in the acceleration/deceleration limiting circuit to control the degree of decrease in the output of the integrating circuit so as to maintain it below a predetermined set value. An operation control device for an electric motor.