JP4235898B2 - Inverter control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling an inverter device that derives a frequency setting value from a frequency command value and outputs an AC voltage having a frequency based on the frequency setting value.
[0002]
[Prior art]
As this type of inverter device, there is a so-called general-purpose inverter that outputs an AC voltage having a frequency based on a frequency setting value and an amplitude corresponding to the frequency. In an AC electric drive that is driven at a variable speed by the general-purpose inverter, For example, in order to prevent the electric motor from falling into a stalled (undriveable) state in a region where the frequency of the AC voltage output from the general-purpose inverter is low, a lower limit value is provided for the frequency setting value (for example, , See Patent Document 1).
[0003]
FIG. 4 is a circuit configuration diagram of a conventional inverter device including the above-mentioned patent document, in which 1 is an AC power source such as a commercial power source, 2 is an inverter device, 3 is an induction motor that is driven at a variable speed by the inverter device 2, etc. AC motor.
[0004]
This inverter device 2 is referred to as the above-mentioned general-purpose inverter, and includes a diode rectifier circuit 11 that rectifies the voltage of the AC power source 1, a capacitor 12 that smoothes the output of the diode rectifier circuit 11, and a DC voltage across the capacitor 12 to a desired value. In order to convert to AC voltage, an inverter main circuit 13 formed by bridge-connecting a reverse-parallel circuit of a transistor and a diode as a self-extinguishing element as shown in the figure, and a frequency command value and its sign (polarity) are commanded A frequency command device 21, an absolute value computing device 22 for computing the absolute value of the frequency command value output from the frequency command device 21, a lower limit value setting device 23 for setting the lower limit value of the frequency setting value, and the frequency command The absolute value of the value is compared with the lower limit value. When the absolute value ≧ the lower limit value, the contact of the changeover switch 25 is connected to the output of the absolute value calculator 22 as shown in the figure. The comparison circuit 24 for closing the contact of the changeover switch 25 to the output side of the lower limit value setter 23, and the output of the changeover switch 25 and the frequency command device 21 are output. A multiplication calculator 26 that multiplies the sign of the frequency command value and outputs the calculation result as a frequency setting value including the rotation direction of the AC motor 3; and the frequency setting value is set to a predetermined acceleration / deceleration time (per unit time). Acceleration / deceleration calculator 27 for deriving a new frequency setting value via an increase / decrease value of the frequency), and in order to make this new frequency setting value the frequency of the AC voltage output from the inverter main circuit 13 , for example, a pulse And an inverter control circuit 28 that performs control calculation such as width modulation (PWM) control. In addition, each control element which comprises this inverter apparatus 2 is formed by the well-known technique.
[0005]
FIG. 5 is a characteristic diagram showing the relationship between the frequency command value output from the frequency command unit 21 and the frequency setting value output from the multiplication calculator 26 in the inverter device 2 shown in FIG. 4, and the horizontal axis represents the frequency command value. The value and the vertical axis are the frequency setting values.
[0006]
As is apparent from this figure, when the AC motor 3 is rotating forward or reverse, when the frequency command value is greater than or equal to the lower limit value of the output of the lower limit value setter 23, the relationship of the frequency command value = frequency setting value is established. When the frequency command value is less than the lower limit value, the frequency set value is set as the lower limit value, and when the frequency command value is equal to or higher than a predetermined upper limit value, the frequency set value is set as the upper limit value.
[0007]
[Patent Document 1]
JP-A-8-51793 (page 3-4, FIG. 1)
[0008]
[Problems to be solved by the invention]
In the conventional inverter device 2 shown in FIG. 4, when the device connected to the output shaft of the AC motor 3 is a pump of a water supply facility or the like, the frequency set value output by the multiplication calculator 26 is in the state of the lower limit value. When the system is operated, the operation efficiency of the entire facility is reduced, and as a result, it becomes impossible to meet the recent demand for energy saving. In this type of application, the frequency command value output by the frequency command device 21 is less than the lower limit value. In this case, it is desirable to stop the rotation of the AC motor 3.
[0009]
However, in the inverter device 2, in order to stop the rotation of the AC motor 3, the inverter device 2 is stopped. As a result, in order to rotate the AC motor 3 again, the startup operation of the inverter device 2 is performed. There was a problem that it was necessary.
[0010]
An object of the present invention is to provide a method for controlling an inverter device that solves the above problems.
[0011]
[Means for Solving the Problems]
This invention derives a frequency setting value from a frequency command value, and outputs an AC voltage having a frequency based on this frequency setting value.
When the frequency command value is greater than or equal to a predetermined lower limit value, the frequency command value is equal to the frequency setting value. When the frequency command value is less than the lower limit value, the frequency setting value is either zero or the lower limit value. A control method characterized by being selectable is performed.
[0012]
According to the present invention, during the operation of the inverter device, for example, the rotation of the AC motor as the load can be made zero (= stop) without performing a stop operation on the inverter device.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit configuration diagram of an inverter device showing a first embodiment of the present invention. In this figure, components having the same functions as those of the conventional circuit shown in FIG. Description is omitted.
[0014]
That is, the inverter device 4 shown in FIG. 1 includes a changeover switch 41 in place of the changeover switch 25 in the inverter device 2, and the comparison circuit 24 compares the absolute value of the frequency command value with the lower limit value. As a result, when the absolute value ≧ the lower limit value, the contact of the changeover switch 41 is closed to the output side of the absolute value calculator 22 as shown, and when the absolute value <the lower limit value, the contact of the changeover switch 41 is “0”. The circuit is closed to the setting side.
[0015]
FIG. 2 is a characteristic diagram showing the relationship between the frequency command value output from the frequency command unit 21 and the frequency set value output from the multiplication calculator 26 in the inverter device 4 shown in FIG. 1, and the horizontal axis represents the frequency command value. The value and the vertical axis are the frequency setting values.
[0016]
As is apparent from this figure, when the AC motor 3 is rotating forward or reverse, when the frequency command value is greater than or equal to the lower limit value of the output of the lower limit value setter 23, the relationship of the frequency command value = frequency setting value is established. When the frequency command value is less than the lower limit value, the frequency setting value is set to “0”, and when the frequency command value is greater than or equal to a predetermined upper limit value, the frequency setting value is set as the upper limit value.
[0017]
Therefore, when the device connected to the output shaft of the AC motor 3 driven by the inverter device 4 is a pump of a water supply facility, the frequency command value output from the frequency setter 21 is output from the lower limit setter 23. When the frequency setting value is less than the lower limit value, the frequency setting value output from the multiplication calculator 26 is set to “0”, and the AC motor 3 is stopped while the rotation is stopped. Thereafter, the frequency command value is equal to or higher than the lower limit value. Then, the AC motor 3 automatically starts to rotate, and eventually, the AC motor 3 rotates at a rotation speed corresponding to the frequency set value at this time.
[0018]
FIG. 3 is a circuit configuration diagram of an inverter device showing a second embodiment of the present invention. In this figure, components having the same functions as those of the conventional circuit shown in FIG. Description is omitted.
[0019]
That is, the inverter device 5 shown in FIG. 3 includes a changeover switch 51 instead of the changeover switch 25 in the inverter device 2, and further includes a changer 52 and a changeover switch 53.
[0020]
In this inverter device 5, the comparison circuit 24 compares the absolute value of the frequency command value with the lower limit value. As a result, when the absolute value <the lower limit value, the contact of the changeover switch 51 is closed to the changeover switch 53 side. In this case, the changeover switch 53 can select the “0” setting side or the lower limit side according to a preset command from the switch 52. That is, with the device connected to the output shaft of the AC motor 3, the frequency setting value is set to “0”, and the AC motor 3 is kept waiting while the rotation of the AC motor 3 is stopped, or simply the AC motor 3 corresponds to the lower limit value. It is possible to select whether to prevent the stalled state of the electric motor by rotating the motor at the rotating speed. Therefore, according to the embodiment of the second invention, it is possible to easily switch the control method corresponding to the application with a common hardware configuration only by the selection operation.
[0021]
【The invention's effect】
According to the present invention, the rotation of the AC motor as the load can be made zero (= stop) without performing a stop operation on the inverter device during the operation of the inverter device. When the device connected to the output shaft is a pump of a water supply facility, energy saving operation can be performed.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of an inverter device showing a first embodiment of the invention. FIG. 2 is a characteristic diagram for explaining the operation of FIG. 1. FIG. 3 is a circuit diagram of an inverter device showing a second embodiment of the invention. Circuit diagram [FIG. 4] Circuit diagram of an inverter device showing a conventional example [FIG. 5] Characteristic diagram for explaining the operation of FIG.
DESCRIPTION OF SYMBOLS 1 ... AC power source, 2, 4, 5 ... Inverter apparatus, 3 ... AC motor, 11 ... Diode rectifier circuit, 12 ... Capacitor, 13 ... Inverter main circuit, 21 ... Frequency command device, 22 ... Absolute value calculator, 23 ... Lower limit value setter, 24... Comparison circuit, 25, 41, 51, 53... Changeover switch, 26... Multiplication operator, 27 ... acceleration / deceleration operator, 28.

Claims (1)

In an inverter device that derives a frequency setting value from a frequency command value and outputs an AC voltage having a frequency based on the frequency setting value.
When the frequency command value is greater than or equal to a predetermined lower limit value, the frequency command value is equal to the frequency setting value. When the frequency command value is less than the lower limit value, the frequency setting value is either zero or the lower limit value. A control method for an inverter device, wherein the control method is selectable.

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