JPS62201068A - Controller for inverter - Google Patents

Abstract

PURPOSE:To suppress the hunting of output voltage and current, by averaging voltage command with previous voltage command, and by controlling an inverter with the command. CONSTITUTION:The controller of an inverter 4 is composed of a speed command setting circuit 1, a frequency command production circuit 2, a load current detecting circuit 5, a voltage correction factor setting circuit 6, a voltage correction quantity operation circuit 7, and an ignition signal production circuit 9, and from frequency command and voltage command, ignition signal is produced and is fed to the inverter 4. In this case, a voltage command production circuit 11 is set. One the circuit 11, a speed command is multiplied by a fundamental voltage command conversion constant to find out fundamental voltage command, and a voltage correction quantity is added to the fundamental voltage command to find out voltage command. The voltage command is averaged with voltage command produced previously, to produce the voltage command, and the command is stored as data for the following operational cycle. Then, on the variation of load current, corrected voltage command is averaged with the previous voltage command, and after that, the command is fed to the ignition signal production circuit 9, thereby hunting can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an inverter used for speed control of an electric motor such as an induction motor.

[Conventional technology]

FIG. 6 shows a block diagram of a conventional example of this type of inverter control device. In the figure, 1 is a speed command setting circuit, 2
1 is a frequency command generation circuit that receives a speed command (signal) from the speed command setting circuit 1 and creates a frequency command; 3 is a motor; 4
is an inverter that drives the electric motor 3. This inverter 4 is controlled to have a constant voltage/frequency ratio (V/F). 5
6 is a load current detection circuit that detects the input current of the motor 3;
7 is a voltage correction ratio setting circuit, and 7 is a voltage correction amount calculation circuit. The voltage correction amount calculation circuit 7 calculates the voltage correction amount from the amount detected by the load current detection circuit 5 and the setting ratio of the voltage ratio setting circuit 6. Reference numeral 8 denotes a voltage command creation circuit, which creates a voltage command (signal) from the speed command and the voltage correction amount. 9
is an ignition signal generating circuit which generates an ignition signal from the frequency command and voltage command and supplies it to the inverter 4.

FIG. 3 shows the relationship between the speed command N and the frequency command F, and FIG. 5 shows the relationship between the speed command N and the voltage command (2).

Next, the operation of this device will be explained.

The inverter 4 is controlled so that the V/F is constant, but with only this constant V/F ratio control, the primary resistance of the electric motor 3 and the voltage drop ring due to the power supply cable, especially,
Torque characteristics deteriorate in the low frequency range. Therefore, the voltage correction amount calculation circuit 7 calculates the voltage correction amount ■2 from the current amount detected by the load current detection circuit 5 and the voltage correction ratio set by the voltage correction ratio setting circuit 6, and the voltage correction amount ■2 is calculated based on the voltage correction amount ■2. By correcting the voltage command Vl (shown by the broken line in FIG. 5), the inverter output voltage V under load is corrected, and the motor torque characteristics are improved. In the voltage command generation circuit 8, as shown in the flowchart of FIG. 7, the basic voltage command conversion constant is multiplied by 1 to the speed command N to obtain the basic voltage command ■1, and the voltage correction amount ■2 is added to the basic voltage command ■1. A voltage command V (shown by a solid line in FIG. 5) is created by adding the following.

Note that FIG. 4 shows the relationship between the load current and the voltage correction amount using the voltage correction ratio as a parameter.

[Problem that the invention seeks to solve]

Since the conventional control device is configured as described above,
When the load current increases, the output voltage of the inverter 4 is increased to compensate for the voltage drop due to the motor's primary resistance and the power supply cable, and when the load current decreases, the output voltage of the motor 3 is increased.
In order to reduce the output voltage of the inverter 4 to prevent over-excitation, a transient disturbance current generated by a change in the inverter output voltage flows, and this is detected by the load current detection circuit 5 and fed back, so that the inverter output voltage and There was a problem that the current may hunt and the control may become unstable.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to obtain an inverter control device that can control the inverter output while suppressing hunting of the inverter output voltage and current.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured to control an inverter using an average command value of a voltage command created last time and a voltage command created this time as a voltage command.

[Effect]

In this invention, since the voltage command is averaged with the previous voltage command, the control of the inverter output voltage when the load current fluctuates becomes smoother than before, and hunting of the inverter output voltage and current is suppressed.

[Embodiments of the invention]

FIG. 1 shows a block diagram of an embodiment of the present invention, which differs from the conventional one shown in FIG. 6 in that it includes a voltage command creation circuit 11 in place of the voltage command creation circuit 8. Since the other configurations are the same, the same components are denoted by the same reference numerals.

As shown in the flowchart of FIG. 2, the voltage command generation circuit 11 (1) sets the speed command N to the basic voltage command conversion constant by 1
(2) Add the voltage correction amount ■2 to the basic voltage command ■1 to find the voltage command ■, and (
3) Create voltage command ■ (shown by the solid line in Figure 5) by averaging the voltage command MV created last time with this voltage command V,
(4) Store the voltage command in step (3) and use it as data for the next calculation cycle.

Therefore, in this embodiment, when the load current changes, the voltage command is corrected according to the change, but this corrected voltage command (denoted as Va) remains unchanged at the ignition command generation circuit 9.
Instead, the average value of the command value of this voltage command and the command value of the voltage command MV before the current correction operation is sent to the ignition signal generation circuit 9 as the voltage command V. Therefore, the amount of change in the voltage command (MV-Va/2) is smaller than the amount of change (MV-Va) in the conventional method, and the change in voltage command when the load current fluctuates is smoother than in the past. Therefore, hunting of the inverter output/current is suppressed.

〔Effect of the invention〕

As explained above, in this invention, since the voltage command is the average of the previous voltage command, the change in the voltage command becomes smoother than in the past, and hunting in the inverter output voltage and current is suppressed compared to the past. Therefore, the stability of control can be improved.

[Brief explanation of drawings]

, Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an operation flowchart of the voltage command generation circuit in the above embodiment, Fig. 3 is a speed command-frequency command characteristic diagram, and Fig. 4 is a load current amount. - Voltage correction amount characteristic diagram, Figure 5 is speed command -
FIG. 6 is a block diagram of a conventional inverter control device, and FIG. 7 is an operation flowchart of a voltage command generation circuit in the conventional device. In the figure, ■ - speed command setting circuit, 4 - load current detection circuit, 6 - voltage correction ratio setting circuit, 7 - voltage correction amount calculation circuit, 11 - voltage command generation circuit. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] In an inverter control device that detects the load current, calculates a voltage correction amount based on the detected value, and corrects the reference voltage command value using the voltage correction amount to create a voltage command, the voltage command created previously and the voltage command created this time are An inverter control device that controls an inverter using an average command value of voltage commands as a voltage command.