JPH0797176A - Inverter control device - Google Patents

Abstract

PURPOSE:To instantaneously perform transfer to smooth operation at the time of selecting a mode of operating an induction motor in a condition of inertial rotation by providing a frequency control means for follow-up controlling an output frequency of an inverter to a frequency synchronized with an actual rotational speed of the induction motor. CONSTITUTION:Which of operational modes is selected from power running mode, regenerative braking mode, coasting mode, etc., necessary for running control of a crane, is decided by a mode decision means 12, and when the coasting mode is selected, whether an operating condition of an electric motor 5 is power running or regenetive running is checked by a power/regenerative running deciding means 13. In the case of power running, a prescribed speed adjusting value is calculated, to subtract this speed adjusting value from a speed command value in the preceding time, and this subtracted speed command value is supplied to a driving means 11 as a speed command signal (b). Thus by subtracting the speed adjusting value from the preceding time speed command value, a rotational speed of the electric motor 5 is decreased one after another. On the other hand, at regeneration time, control for successively increasing the rotational speed of the electric motor 5 is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for driving an induction motor, and more particularly to an inverter control device suitable for controlling a traveling motor of a crane having a coasting function.

[0002]

2. Description of the Related Art Conventionally, in a traveling system of a crane, an operating technique of traveling from a predetermined position to a required position by inertial operation after starting traveling by an electric motor may be employed. In some cases, a coasting (inertia running) mode is provided.

In the prior art of the system having the coasting mode, the electric power supply to the electric motor is cut off while the brake is open, so that the electric motor is idled and controlled so that coasting can be obtained. Was.

[0004]

In the prior art described above, it is necessary to take into consideration that a separate means for keeping the brake in the released state after shutting off the power supply to the electric motor is required for the coasting mode. There is a problem that control is complicated because it is not done.

Further, the above-mentioned prior art does not take into consideration the case where the coasting mode is applied to the system using the induction motor controlled by the inverter. At the time point after entering the coasting mode and before stopping. In the case of performing the reacceleration operation by the electric motor, there is also a problem that the control of the inverter at the start of the reacceleration operation becomes complicated.

It is an object of the present invention to allow coasting operation to be continued without interrupting the connection between the inverter and the induction motor even in the coasting mode, and to stop after the coasting mode is entered. In between, restart
An object of the present invention is to provide an inverter control device capable of immediately shifting to sufficiently smooth operation without requiring complicated control even when shifting to (power running, regeneration).

[0007]

The above object is to provide frequency control means for controlling the output frequency of the inverter so as to follow the frequency synchronized with the actual rotation speed of the induction motor. When the coasting mode is selected, the frequency control means is provided. This is achieved by the means being operated.

[0008]

In the coasting mode, the frequency control means works so that no matter how the rotation speed of the induction motor changes, AC power having a frequency synchronized with the actual rotation speed is supplied to the induction motor. As a result, the induction motor is always connected to the output of the inverter and put into the free-run state where the torque is always zero, so that the induction motor can be brought into the coasting state without breaking the circuit.

Further, since the control of the inverter is continued even in this state, when re-accelerating the induction motor,
Since it suffices to simply control so as to increase the output frequency of the inverter, smooth acceleration can be immediately obtained without requiring special control.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An inverter controller according to the present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 shows an embodiment (first embodiment) in which the present invention is applied to a traveling system of a crane. In the drawing, 1 is a commercial three-phase AC power source, 2 is a forward conversion unit (converter module), 3 Is a smoothing capacitor, 4 is an inverse converter (inverter module), 5 is an induction motor for traveling a crane, 6 and 7 are output phase current detection circuits, and 8 is control means. The induction motor 5 will be simply referred to as the electric motor 5 hereinafter.

The forward conversion unit 2 functions to convert the AC power supplied from the AC power supply 1 into DC power, and the smoothing capacitor 3 includes the pulsating component included in the DC voltage output from the forward conversion unit 2. Functions to smooth the. The inverse conversion unit 4 reconverts the DC power smoothed by the smoothing capacitor 3 into AC power, supplies three-phase AC power of variable voltage and variable frequency to the electric motor 5 as a load, and operates to run the crane. . The forward conversion unit 2 and the inverse conversion unit 4 are each composed of a semiconductor element such as a diode, a transistor, or a thyristor.

The output phase current detection circuits 6 and 7 are composed of the inverse conversion section 2
The electric current of each phase of the three-phase alternating current having a variable voltage and a variable frequency flowing between the motor 5 and the electric motor 5 is detected, and the current detection signals f and g are taken out. The control means 8 is composed of a speed setting input means 9, a speed command calculation means 10, a driving means 11, a mode determination means 12, and a power running / regeneration determination means 13. First, the speed command input means 9 is not shown. The speed setting value given from the speed setting device or the speed setting value previously stored in the memory in the control means is taken in, and the speed setting signal a is output to the speed command calculating means 10. Next, the mode determining means 12 determines which of the operation modes such as the power running mode, the regenerative braking mode, and the coasting mode necessary for traveling control of the crane has been selected.
It functions to output the mode determination signal d to the speed calculation means 10. The operation mode is selected by the driver via the crane operating device (not shown).

Further, the power running / regeneration determining means 13 has current detection signals f and g input from the output phase current detection circuits 6 and 7.
The operating state of the electric motor 5 is determined based on the power running / regenerative signal e indicating whether the operating state is in power running or regenerative.
Is output to the speed calculation means 10.

The speed command calculation means 10 inputs a speed setting signal a, a mode determination signal d, and a power running / regeneration signal e, calculates a speed command signal b based on these signals, and outputs it to the driving means 11. It functions to output, and thereby constitutes frequency control means for controlling the output frequency of the inverse converter 4 to follow the frequency synchronized with the actual rotation speed of the induction motor 5.

The driving means 11 serves to output a driving signal c for driving the switching element of the inverse conversion section 4.

FIG. 2 is a flow chart showing the basic operation of the arithmetic processing by the speed command arithmetic means 10, which is executed at a predetermined fixed time of, for example, several ms. The operation of the speed command calculation means 10 will be described with reference to this flowchart. In addition,
Each of S1 to S8 in FIG. 2 represents a processing step. The motor in S6 and S7 in FIG. 2 means an electric motor.

When the processing shown in FIG. 2 is executed, first, in S1, the mode determination signal d is checked to
Determine the currently selected mode. The determination process in S1 turns ON only when the coasting mode is selected, and turns OFF otherwise.

When the result is OFF, that is, when the coasting mode is not selected, the process proceeds to S2, where the speed setting signal a supplied from the speed setting input means 9 is taken in, and then S8. Go to
The process of setting the speed command signal b calculated based on the speed setting signal a is executed.

As a result, the driving means 11 is supplied with the speed command signal b calculated based on the speed setting signal a,
As a result, the inverse converter 4 of the inverter is controlled. At this time, the speed setting input from the speed setting device (not shown) or the speed setting value stored in the inverter becomes the speed command value, Therefore, the electric motor 5 is driven at an arbitrary speed intended by the driver, and the crane travels at a predetermined speed.

Next, when the process of FIG. 2 is entered and the coasting mode is selected, the determination result in S1 is ON. Therefore, at this time, continue with S
Proceeding to the process of No. 3, first, it is checked here whether the operating state of the electric motor 5 is power running or regenerative, and any one of "power running", "regenerative", and "neither" is obtained. Determine if there is. The determination in S3 may be made by examining the powering / regeneration signal e output from the powering / regeneration determining means 13.

The determination operation by the power running / regeneration determining means 13 will be described below. Now, assuming that the electric motor 5 is in the power running state, electric power should be supplied from the inverse conversion unit 4 of the inverter to the electric motor 5. If the electric motor 5 is in the regenerative state, on the contrary, electric power should be supplied from the electric motor 5 to the inverse conversion unit 4. Therefore, by checking the current detection signals f and g fetched from the output phase current detection circuits 6 and 7 and detecting the direction of electric power, it is possible to determine whether the operating state of the electric motor 5 is power running or regenerative. .

Further, at this time, when the magnitudes of the current detection signals f and g become to some extent or less, only the exciting current is flowing to the electric motor 5, so that the operating state of the electric motor 5 is at this time. Is neither powering nor regenerating,
In other words, it can be determined that it is neither. The "neither" state means that electric power having a frequency synchronized with the rotation speed of the electric motor 5 at that time is supplied to the electric motor 5, and the electric motor 5 is rotating in a state where the torque is zero. It means that you are in a free-run state.

Then, returning to FIG. 2, assuming that the determination result in S3 is "power running", first, in S4, a process for calculating a predetermined speed adjustment value is executed, and then in S6,
A process of subtracting this speed adjustment value from the previous speed command value is executed, then the process of S8 is executed, and the speed command value obtained by subtracting this speed adjustment value is supplied to the driving means 11 as the speed command signal b. Thus, the process of FIG. 2 is exited.

Next, if the determination result in S3 is "regeneration", this time, first, the process proceeds to S5, the process of similarly calculating a predetermined speed adjustment value is executed, and then the process proceeds to S7. , The process of adding this speed adjustment value to the previous speed command value is executed. Then, after that, the process of S8 is executed so that the speed command value obtained by adding the speed adjustment value is supplied to the drive means 11 as the speed command signal b,
The process of FIG. 2 is exited.

On the other hand, when the determination result in S3 is "neither", the process of S8 is executed as it is, and the process is terminated. Therefore, at this time, the same speed command signal b as the previous time is supplied to the driving means 11.

Then, the coasting mode is selected,
When the processing of S3 and thereafter is executed and the operating state of the electric motor 5 is in the power running state, the speed adjustment value is subtracted from the previous speed command, so the rotational speed of the electric motor 5 is gradually decreased. When the control is executed and, conversely, the operating state of the electric motor 5 is in the regenerative state, the speed adjustment value is added to the previous speed command.
Therefore, the speed command follows the actual rotation speed of the electric motor 5 so that the rotation speed is gradually increased and the determination result in S3 converges to the "neither" state. Will be controlled.

As described above, the determination result in S3 is "neither" when the current detection signals f and g reach their minimum values, that is, the actual rotation of the electric motor 5 at that time. A speed command of the same rotation speed as the speed is made,
The rotation speed of the rotating magnetic field is in synchronization with the actual rotation speed, and the electric motor 5 is in the free-run state.

Therefore, according to this embodiment, coasting can be performed and the crane can be coasted while the electric motor 5 is still connected to the inverse conversion unit 4 of the inverter. Further, as a result, even when it is desired to accelerate the crane that is coasting, the speed of the electric motor 5 can be increased as it is by simply changing the speed command, and continuous and smooth acceleration is given. be able to.

Next, the calculation processing of the speed adjustment value in S4 and S5 of FIG. 2 will be explained. This speed adjustment value is gradually decreased (during power running) or increased (in power running) of the rotation speed of the electric motor 5. This is a value that determines the changing speed of the rotation speed during regenerative operation. As this value increases, the rotation speed also changes faster. That is, the magnitude of this speed adjustment value is a value that determines the gain when the speed command is controlled to follow the actual rotation speed of the electric motor 5.

Therefore, if this speed adjustment value is increased,
Although the speed response is increased, hunting may occur in control. Therefore, it suffices to derive an appropriate value according to the inertia (inertia amount) of the load of the electric motor 5 (which is the traveling system of the crane in this embodiment) and the frictional resistance.

Next, another embodiment of the present invention will be described. FIG. 3 shows a second embodiment of the present invention. In the first embodiment shown in FIG. 1, it is used for determining power running / regeneration. Although the output phase current detection signals f and g are used as the signals, in the second embodiment shown in FIG. 3, the DC current detection means 14 is provided in the DC circuit of the inverter, and the DC detected by the detection means 14 is used. The power running / regeneration determination is performed based on the current detection signal h.

In the embodiment of FIG. 3, if the polarity of the DC current detection signal h during power running is positive, the polarity of the DC current detection signal h during regeneration will be negative. Therefore, the power running / regeneration judging means 13 judges this, and the speed command calculating means 10 carries out the power running / regeneration.
It is configured to output the regenerative signal e, and other configurations are the same as those in the first embodiment of FIG.

Therefore, according to the embodiment of FIG. 3 as well, coasting can be performed while the electric motor 5 is still connected to the inverse conversion unit 4 of the inverter, and the crane can be coasted and the coasting can be performed. Even when accelerating the traveling crane, the speed of the electric motor 5 can be increased as it is by simply changing the speed command, and continuous smooth acceleration can be given. Since it is simple, there is an advantage that the cost can be suppressed.

Next, FIG. 4 shows an embodiment (third embodiment) in which the control processing in the second embodiment shown in FIG. 3 is configured to be performed by software. It is composed of a CPU which is a control arithmetic unit, and I / O which serves as an input / output means for each signal, a RAM which serves as a storage device, and an R.
It is composed of a circuit including an OM and a bus.

The CPU, which is the control calculation unit, performs various control calculations according to the programs stored in advance in the ROM, and the inverse conversion unit 4 of the inverter through the input / output unit I / O.
Outputs a signal for controlling. The flow chart of the basic operation of the speed command calculation means shown in FIG. 2 is programmed and is placed in the ROM as a part of the control program.

Therefore, the CPU executes the program for each sampling and executes the arithmetic processing necessary for controlling the electric motor 5.

That is, when the programmed portion of the flow chart of the basic operation of the speed command calculation means shown in FIG. 2 is executed in the program, first, it is necessary to determine whether or not the coasting mode is selected. A mode command input signal is received through the input / output means I / O, and the mode is judged based on the received signal. Then, when the coasting mode is selected, the DC current detection signal h detected by the DC current detection means 14 is received to determine the power running / regenerative operation state to determine the motor speed or the speed command value one sampling before. The speed control value is added or subtracted to obtain a speed command value, and the drive signal c is output through the input / output means I / O.

Therefore, according to the embodiment of FIG. 4, the electric motor 5 is also provided, as in the above-mentioned first and second embodiments.
Even if the crane can be coasted with the inverter being connected to the inverse conversion unit 4 of the inverter and the crane can be coasted, and the crane is coasting, the speed command is simply changed. As a result, the speed of the electric motor 5 can be increased as it is, and continuous smooth acceleration can be given.

In the above embodiments, the case where the present invention is applied to the inverter control system has been described.
The same can be done when a servo system or the like is used.
Further, in the above-described embodiment, the operating speed command is used as the operation command in order to control the current to the electric motor to zero.

[0040]

As described above, according to the present invention, in the inverter control system, the current flowing through the electric motor can be reduced to zero, which has the effect of minimizing energy consumption. Moreover, there is an effect that a smooth operation can be performed even when the operation is restarted. Further, by applying the present invention to a crane traveling system, there is an effect that the system configuration can be simplified when the coasting function is realized.

Further, even in other systems, even when the electric motor is used in the free run and the energy is especially received from the outside and the electric motor continues to accelerate, according to the present invention, the control of the electric motor is always continued. Therefore, it is possible to control so as to automatically suppress the speed when a certain rotation speed is reached, and it is also possible to issue an alarm to the system, thereby ensuring safety and reliability. Effective for improvement.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an inverter control device according to the present invention.

FIG. 2 is a flowchart showing a basic operation process of speed command calculation means in the embodiment of the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Forward conversion part (converter module) 3 Smoothing capacitor 4 Inverse conversion part (inverter module) 5 Induction motor (motor) 6, 7 Output phase current detection circuit 8 Control means 9 Speed setting input means 10 Speed command calculation means 11 Drive means 12 Mode determination means 13 Power running / regeneration determination means 14 DC current detection means a Speed setting signal b Speed command signal c Drive signal d Mode determination signal e Power running / regeneration signal f, g Output phase current detection signal h DC current detection signal

Claims (3)

[Claims] 1. An inverter for driving an induction motor in a plurality of operation modes, wherein frequency control means is provided for controlling the output frequency of the inverter so as to follow the frequency synchronized with the actual rotation speed of the induction motor, and the induction motor is coasted. An inverter control device characterized in that the frequency control means is operated when a mode for operating in a state is selected. 2. The invention according to claim 1, wherein the frequency tracking control by the frequency control means is executed based on a detection result of an alternating current on the alternating current side of the inverse conversion section of the inverter. An inverter control device characterized in that 3. The invention according to claim 1, wherein the frequency tracking control by the frequency control means is executed based on a detection result of an output current on the DC side of the inverse conversion unit of the inverter. An inverter control device characterized in that