JPS60121918A - Protecting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates primarily to a protection device for a circuit that performs variable speed control using a variable frequency device.

<Prior Art> As the above-mentioned type of protection device, there is, for example, one provided in an air conditioner with variable capacity.

In other words, 1 is an AC commercial power supply, 2 is a full-wave rectifier circuit, 3 is a smoothing capacitor, 4 is an inverter that converts a DC power supply into an AC power supply of any frequency, and 5 is an inverter unit that converts the output of the inverter unit 4. 6 is a resistor for detecting the current flowing into the inverter section 4 to detect overcurrent. 7 is an inverter (variable frequency device), 8 is a A detection circuit that detects an overcurrent flowing into the inverter section 4; 9 a photocoupler that electrically separates the inverter 7 and the detection circuit 8; 10 a resistor that limits the forward current of the photocoupler 9; 11 a resistor 6 a variable resistor 12 that indirectly converts the current flowing through the photocoupler 9 into a voltage;
．． 13 is a reference voltage setting resistor that outputs a reference voltage for determining overcurrent; 14 is a comparator that compares the voltage of variable resistor 11 with the reference voltage to determine overcurrent; 15 is an input/output unit When the overcurrent determination signal from the comparator 14 is inputted to the microcomputer 4, the microcomputer outputs an arbitrary frequency command signal to the Isper 2 section 4, and outputs a zero frequency command signal to the Isper 2 section 4 in a timely manner.

The operation of the above-mentioned conventional protection device will be explained.

For example, the electric motor 5 starts, the microcomputer 15
When the rotational speed increases to a frequency corresponding to the specified frequency, if an abnormal current flows into the inverter section 4 due to load fluctuation, a voltage corresponding to this current is generated in the variable resistor 11 via the photocoupler 9. When this generated voltage exceeds the reference voltage, the comparator 14 outputs an overcurrent determination signal to the microcomputer 15, and the microcomputer 15 sets the designated frequency to zero Hz and stops the motor 5.
Mechanical and electrical systems such as the following are protected.

By the way, in the transient region where the inverter section 4 rises to the specified frequency and the steady region where the inverter section 4 reaches the specified frequency, the electric motor 5
In the transient region where the magnitude of the load acting on the refrigerant circuit υ is different, the refrigerant circuit cannot follow the frequency increase of the inverter section 4, resulting in a light load state. Therefore, in the transient region, the level of inrush current that occurs during frequency switching is low, and of course the load fluctuation is also small. Therefore, although the reference voltage for overcurrent determination is set in the transient region where the inrush current and load fluctuation are small, there is a problem that the motor 5 cannot withstand the load in the steady region and stops.

<Summary of the Invention> The present invention has been made in view of the above points, and solves the above conventional disadvantages by changing the reference voltage for overcurrent judgment between the transient output region and the steady output region of the variable frequency device. The purpose is to provide a protective device that

<Embodiment of the Invention> An embodiment of the present invention will be described below based on FIG. 2. Incidentally, the same elements as those in the conventional example are given the same reference numerals and the explanation thereof will be omitted.

21 and 22 are first reference voltage setting resistors that provide a reference voltage for overcurrent determination in the transient region of the inverter section 4;
In addition to the first reference voltage setting resistors 21 and 22, 24 is a second reference voltage setting resistor that provides a reference voltage for determining current flow in the steady state region of the inverter section 4, and 24 is a town reference voltage setting resistor 23. A relay contact 25 connected in series with SS is in the transient output region where the frequency of the output signal of the inverter section 4 rises to a frequency specified by the microcomputer 15.
A base resistor connected to the output terminal of the microcomputer 15, 26 a transistor, 27 a resistor, 28 a transistor, 29 is a relay coil connected to the collector of the transistor 28, and when it is energized, the relay contact 24 is closed, and when it is demagnetized, the relay contact 24 is opened. 30 is a surge absorption diode.

Next, the effect will be explained.

In the transient output region where the frequency of the output signal of the inverter section 4 increases to the frequency specified by the microcomputer 15, the output 0UT2 of the microcomputer 15 becomes "H".
# At the output, the transistor 26 is turned on, the transistor 28 is turned off, and the relay contact 24 is opened, so the reference electrician for overcurrent judgment is determined by the voltage division of the first reference voltage setting resistor 21 and 22. be done.

On the other hand, in the steady output region where the frequency of the output signal of the inverter section 4 reaches the frequency specified by the microcomputer 15, the output 0UT2 of the microcomputer 15 is
When the output is XL/l, the transistor 26 is turned off and the transistor 28 is turned on, and the relay contact 24 is closed, so the first reference voltage setting resistor 21 and the second reference setting resistor are 23 in parallel, the reference voltage for overcurrent determination becomes larger than the value in the above transient output region.

In this way, the reference voltage for determining overcurrent in the transient output region of the inverter section 4 can be made larger than the reference voltage for determining overcurrent in the steady output region, so that each reference voltage can be independently set to the optimal value. Since the frequency can be set to , it is possible to prevent the electric motor 5 from stopping at a load level corresponding to a specified frequency in a steady output region, as in the conventional case.

In the above embodiment, the reference voltage for overcurrent determination is switched using a relay contact, but it may be switched using a transistor contact type switching element, or other contact type switching elements may be used. It may be composed of elements.

<Effects of the Invention> As explained above, according to the present invention, in a circuit for variable speed control of an electric motor using a variable frequency device, there is provided a circuit for controlling a motor at a variable speed by means of a means for detecting a current flowing into the variable frequency device, and a current detected by the means. comparing means for comparing the voltage based on the first set voltage or the second set voltage, means for stopping the electric motor according to the comparison result of the nuclear comparison means, and comparing the voltage based on the first set voltage and the second set voltage. a set voltage for overcurrent determination in the transient output region; and the set voltage for overcurrent judgment in the steady output region can be set independently, so motor stoppages due to motor load fluctuations can be kept to a minimum, ensuring smooth operation. The benefits of being able to do so are demonstrated.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional protection device, and FIG. 2 is a circuit diagram of a protection device according to an embodiment of the present invention. 4...Inverter part 5...Electric motor 6...Resistor 7...Inverter 9...Fuodokagura 11...
- Variable resistor 14... Comparator 15... Microcomputer 21.22... First reference voltage setting resistor 23... Second reference voltage setting resistor 24... Relay 8 points 26 + 28...Trans 2 Star 29...Relay coil agent Masuo Oiwa (and 2 others)

Claims (1)

[Claims] A circuit for variable speed control of an electric motor using a variable frequency device, comprising means for detecting a current flowing into the variable frequency device, a voltage based on the current detected by the means, and a first set voltage or a second set voltage. a comparison means for comparing the first set voltage and the second set voltage according to the comparison result of the comparison means; and means for timely inputting information to the comparison means based on the area.