JPS63257494A - Speed command circuit for motor driving gear - Google Patents

Abstract

PURPOSE:To shorten an acceleration or deceleration time, by correcting the speed command signal of output generated from an acceleration or deceleration arithmetic means, with a speed command correcting means. CONSTITUTION:The input of speed setting signal and speed command signal to an acceleration or deceleration discriminating circuit 4 is provided, and it is discriminated whether a motor is accelerated or decelerated. The input of acceleration or deceleration discriminating signal, a current detecting value, and the speed command signal to a speed command signal correcting circuit 6 is provided. As a result, under the accelerating operation of the motor, from the speed command signal correcting circuit 6, correction command is applied to an acceleration or deceleration arithmetic circuit 3, and motor current is controlled to be always set between 95 % and 100 %. At the time of decelerating operation, the motor current is controlled to be set between zero and 5 %.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a speed command circuit for an electric motor drive device that can perform acceleration or deceleration optimal to the torque characteristics of a load coupled to an electric motor.

[Conventional technology]

A conventional example of a speed command circuit for a motor drive device will be described below, taking as an example an induction motor and an inverter that supplies alternating current power to the motor.

By using an inverter that outputs alternating current power at a rotating speed voltage and variable frequency through pulse width modulation control, it is extremely easy to operate the induction motor at a desired speed. When changing the operating speed of the induction motor, such as accelerating a stopped motor to a target speed, or decelerating a running motor to a stop or a predetermined speed, a new speed setting value is sent to the inverter. input. However, if the inverter immediately outputs AC power at a voltage and frequency corresponding to this new speed setting, a large inrush current would flow to the induction motor, or regenerative current would flow from the motor to the inverter, causing the inverter to This causes an overcurrent trip or an overvoltage trip on the inverter, resulting in the inconvenience of interrupting the operation of the inverter.

Therefore, instead of directly inputting this speed setting value to the inverter, by inputting it to the inverter while changing it at a constant rate of change over time, the voltage and frequency of the AC power supplied to the induction motor can be gradually changed. An acceleration/deceleration calculation circuit is used that can prevent overcurrent and overvoltage.

The acceleration/deceleration calculation circuit generally uses an integral circuit, and by appropriately selecting the integral constant of this circuit, the speed setting value input to this circuit is converted into a speed command signal that changes at a predetermined rate of change over time. ing.

[Problem that the invention seeks to solve]

When an induction motor is driven by an inverter equipped with a speed command circuit configured as described above, the load coupled to the induction motor may be one with a square-law reduction torque characteristic, such as a pump or fan, or a load. There are loads with various torque characteristics, such as those with constant torque characteristics such as a throwing machine, and the time required for starting and stopping varies depending on the magnitude of the flywheel effect of the load.

Such various load characteristics cannot be handled by the speed command signal outputted from the acceleration/deceleration calculation circuit and whose rate of change is constant over time, which may cause some inconvenience.

For example, if the load is a fan, due to its square-law reduction torque characteristic, even if you try to accelerate or decelerate it according to a speed command signal that changes linearly, there will be a large amount of invalid torque, and the induction motor will This has the drawback that the available acceleration/deceleration torque cannot be used effectively, and therefore the time required for acceleration or deceleration cannot be shortened.

FIG. 4 is a graph showing the characteristics when a square reduction torque load is driven by a conventional speed command circuit using an acceleration/deceleration calculation circuit whose output changes linearly.
Figure (a) shows the characteristics of the acceleration/deceleration calculation circuit, Figure 4 (b) shows the torque characteristics during acceleration, and Figure 4 (c) shows the torque characteristics during deceleration.

, No in this figure 4 is the rated speed of the electric motor,
TL is the load rated torque required by the load at this rated speed No, and T and l are the motor rated torques that the induction motor can output. Therefore, as shown in Figure 4 (a),
When the motor speed is changed linearly by the acceleration/deceleration calculation circuit, if it is during acceleration, the difference between the motor rated torque T and the load rated torque TL, that is, the diagonal line, is calculated as shown in Figure 4 (b). The portion shown is the torque available to accelerate this load. On the other hand, load rated torque T
The part surrounded by L and the load torque curve drawn by the squared curve is invalid torque and cannot be used for acceleration, so as mentioned above, the torque possessed by the electric motor is used effectively. Therefore, a long acceleration time is required. Therefore, we tried to shorten the acceleration time as shown in Figure 4 (
Even if the time rate of change of the speed command signal output by the acceleration/deceleration calculation circuit shown in b) is increased (that is, even if the slope of the straight line shown in the figure is made steeper), the inverter output current increases and an overcurrent trip occurs. Therefore, shortening of acceleration time cannot be expected.

For inverters without a braking circuit, Figure 4 (c)
As shown in the figure, the deceleration torque that can be used to decelerate the induction motor is only the small shaded area as shown above, so the deceleration time cannot be shortened.
If a deceleration command signal that changes more rapidly is given, the kinetic energy held by the load will be returned to the inverter as electrical energy, which may cause the inverter to overvoltage.

As mentioned above, in a speed command circuit that uses an acceleration/deceleration calculation circuit that outputs a speed command signal that changes linearly, the torque utilization rate of the electric motor that drives a square-law reduction torque load is low, and therefore the acceleration or deceleration time is It has the disadvantage that it cannot be shortened.

SUMMARY OF THE INVENTION An object of the present invention is to shorten the acceleration/deceleration time of an electric motor by providing a speed command signal suitable for the torque characteristics of a load coupled to the electric motor to the electric motor drive device.

[Means for Solving the Problems] In order to achieve the above object, the speed command circuit of the present invention provides a speed command that changes the speed setting signal from the means for setting the motor speed at a predetermined rate of change over time. A speed command circuit for a motor drive device comprising an acceleration/deceleration calculating means for converting into a signal and outputting the signal, an acceleration/deceleration determining means for determining whether the electric motor is accelerating or decelerating from the input signal and output signal of the acceleration/deceleration calculating means. , a means for detecting the motor current, a signal for determining acceleration or deceleration, an electric JAT flow signal, and a speed command signal are input, and during acceleration, the electric a current is set to the rated value and a predetermined value set below it. The output signal of the acceleration/deceleration calculation means is changed so that the output signal of the acceleration/deceleration calculation means is maintained between zero, and the acceleration/deceleration calculation is performed so that the motor current is maintained between zero and a second predetermined value set above the zero during deceleration. and speed command signal correction means for changing the output signal of the means.

[Effect]

The present invention appropriately controls the speed command signal output from the acceleration/deceleration calculation circuit so that the electric motor torque at that time can be effectively utilized depending on whether the electric motor is accelerating or decelerating. Therefore, the acceleration/deceleration calculation means outputs the output by the speed command correction means so that the motor torque (that is, motor current) can be maintained at almost 100% during deceleration, and the motor current commensurate with the loss during deceleration. By correcting the speed command signal to be used, acceleration or deceleration time can be shortened.

〔Example〕

FIG. 1 is a control block diagram showing an embodiment of the present invention.

In FIG. 1, the speed setting device 2 sets the target speed of the electric motor, and the speed setting signal output from this speed setting device 2 is controlled by an adjustment circuit composed of an integral circuit. The signal is input to the speed calculation circuit 3, and the desired speed command signal is output from the acceleration/deceleration calculation circuit 3. According to this speed command signal, a motor drive device, such as an inverter, outputs AC power at an optimal voltage and frequency.

In the present invention, the speed setting signal inputted to the acceleration/deceleration calculation circuit 3 and the speed command/command signal outputted from this are inputted to the acceleration/deceleration discrimination circuit 4, and both human inputs are input to the acceleration/deceleration discrimination circuit 4. Based on the signal, it is determined whether the electric motor is accelerating or decelerating, and this determination signal is provided to the speed command signal correction circuit 6. Furthermore, the electric IT current is input to the current detection circuit 5, and this current detection value is input to the speed command signal correction circuit 6.
Further, a speed command signal from the acceleration/deceleration calculation circuit 3 is also input to the speed command signal correction circuit 6.

When the motor is in acceleration operation, the motor current input to this speed command signal correction circuit 6 is rated current (i.e. 100%
If it is detected that the speed command signal exceeds the current (current), it is determined that this means that the time rate of change of the speed command signal output from the acceleration/deceleration calculation circuit 3 is too large, so that the slope is reduced.
A correction command is given to this acceleration/deceleration calculation circuit 3. Also, if the motor current is a value set below the rated current, for example 95
% current value, it is determined that the time change rate of the speed command signal is too small, and a correction command is given to the acceleration/deceleration calculation circuit 3 to make the slope steeper. Thus, when the motor accelerates, the motor current is always 95%.
Since the torque of the electric motor is controlled to be between 100% and 100%, almost 100% of the torque of the electric motor can be used.

If the acceleration/deceleration determination circuit 4 determines that the motor is in deceleration operation, the motor current is determined to be between zero and a value set above zero, for example, 5% current, as described above.
The speed command signal correction circuit 6 sends a correction signal to the acceleration/deceleration calculation circuit 3, and the electric motor reduces its speed at an appropriate deceleration.

FIG. 2 is a graph showing the operation of the electric motor during acceleration by the embodiment circuit shown in FIG. 1, in which FIG. Each shows the temporal change in motor current. In other words, the straight line A in Figure 2 (a) indicates that the motor is at 95% of the rated torque (
In other words, it is an acceleration straight line when accelerating at 95% of the rated current), and the curve vAB is the actual acceleration curve when the motor current is 95% of the rated value (I□ in Figure 2 (b)). , the actual acceleration curve B coincides with the 95% acceleration straight line A,
However, when the current exceeds 95% of the rated value, the slope of the acceleration curve B actually becomes gentle. In this way, the motor current is always maintained between the rated current A and the 95% current Its, so no matter what the torque characteristics of the load, the torque of the motor can always be used effectively. It is possible to accelerate the vehicle while maintaining the same speed, and there is no risk of overcurrent occurring.

FIG. 3 is a graph showing the operation of the electric motor during deceleration by the embodiment circuit shown in FIG. Each represents the temporal change in current. In other words, Figure 3 (
The straight line aC in a) is a predetermined deceleration straight line, and the curved line represents the actual deceleration curve. The deceleration operation shown in FIG. 3 is also similar to the acceleration operation described above.
1'R.

The deceleration rate is such that the flow is between zero and 5% of the rated value.

〔Effect of the invention〕

According to this invention, when a speed command signal is given to the motor drive device via the acceleration/deceleration calculation means, acceleration is performed at approximately the rated N current of the motor during acceleration, and deceleration is performed at approximately zero current during deceleration. As described above, since a correction signal is given from the speed command signal correction means to the acceleration/deceleration calculation means, the motor performs acceleration or deceleration operation while maintaining the above-mentioned current. Since no voltage is generated and the torque possessed by the electric motor is utilized to the maximum extent possible, acceleration and deceleration times can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram showing an embodiment of the present invention,
FIG. 2 is a graph showing the operation of the electric motor during acceleration by the embodiment circuit shown in FIG. 1, and FIG. 3 is a graph showing the operation of the electric motor during deceleration by the embodiment circuit shown in FIG. Fourth
The figure is a graph showing the characteristics when a square reduction torque load is driven by a conventional speed command circuit using an acceleration/deceleration calculation circuit whose output changes linearly. 2... Speed setter, 3... Acceleration/deceleration calculation circuit, 4.
... Acceleration/deceleration discrimination circuit, 5... Current detection circuit, 6...
Speed command, signal correction circuit. Tomi 1 map

Claims (1)

[Claims] 1) In a speed command circuit of an electric motor drive device, which is equipped with an acceleration/deceleration calculation means that converts a speed setting signal from a means for setting the motor speed into a speed command signal that changes at a predetermined time change rate and outputs the speed command signal. acceleration/deceleration determining means for determining whether the motor is accelerating or decelerating from the input signal and output signal of the speed calculating means; means for detecting motor current; The output signal of the acceleration/deceleration calculation means is changed so that the motor current is maintained between the rated value and a predetermined value set below it during acceleration, and the motor current is maintained between zero and the lower value during deceleration. and speed command signal correction means for changing the output signal of the acceleration/deceleration calculation means so as to maintain a value between the speed command signal and a second predetermined value set on the upper side. circuit.