JPH055758A - Current detecting apparatus - Google Patents

Abstract

PURPOSE:To obtain a cost-saving current detecting apparatus which detects and transmits an intermediate direct current of an inverter to a control circuit without using an electric insulating circuit, and to obtain an input current detecting apparatus of a capacitor input rectifier circuit not requiring a CT. CONSTITUTION:The temperature and the ambient temperature of a shunt resistance 1 allowing an intermediate direct current to pass through are detected by thermistors 2 and 3. The intermediate direct current value is obtained from a square root of the temperature difference. Since the current value is detected as the temperature amount, the current can be transmitted to a control circuit without being passed through an electric insulating circuit. Moreover, as a resistance is series-connected in the line and the heat generated by the resistance is detected as the change of the resistance of the thermistors, the effective value of the current running in the resistance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for a general-purpose inverter and a current detecting device for detecting an input current of a capacitor input type rectifier circuit.

Assuming that there is a load (for example, a motor) to which a current is supplied by a general-purpose inverter, when the supply current to the motor is a percentage of the inverter rated current, the supply current must be cut off after a few minutes. Since the motor burns out, it is necessary to detect the current of the inverter in the case where the current flowing in the inverter is detected and the control for cutting off the current is performed. However, the present invention can be used in such a case. The present invention relates to a current detection device for an inverter and an input current detection device for a capacitor input type rectifier circuit.

[0003]

2. Description of the Related Art FIG. 7 is a circuit diagram showing a conventional example of a current detecting device for an inverter. In the figure, CON is a converter section, IN is an inverter section, 1 is a shunt resistor, 10
Is a current detection circuit, and 11 is an insulation circuit.

That is, in FIG. 7, a shunt resistor 1 is inserted and connected to an intermediate circuit of an inverter composed of a converter section CON and an inverter section IN. Current detection circuit 1
0 measures the potential difference across the shunt resistor 1 and thereby detects the current value flowing through the shunt resistor 1. Since the potential of the intermediate circuit and the potential of the control circuit (not shown) that uses the current detection value by the current detection circuit 10 must be kept in an insulating relationship, the current detection circuit 10 is connected via the insulation circuit 11 in this sense. The detected current value by is guided to a control circuit (not shown).

FIG. 8 is a circuit diagram showing a conventional example of an input current detecting device of a capacitor input type rectifying circuit. In the figure, 21 is a single phase power source, 22, 23, 24 and 25 are diodes, 28 is a capacitor, 28 is a load, 38 is a CT (current transformer), 39 is a resistor.

In FIG. 8, an input current is detected by a CT (current transformer) 38, converted into a voltage by a resistor 39, and output to terminals E and F.

[0007]

In the conventional current detecting device for the inverter described above, the insulating circuit is indispensable for transmitting the detected current value to the control circuit, and the insulating circuit is indispensable. However, there is a problem in that it becomes complicated and the cost becomes high.

Further, in the above-mentioned conventional input current detection device for the capacitor input type rectifier circuit, the cost is high because the CT 38 is large and expensive, and the current flowing through the CT 38 is a sine wave due to the charging voltage of the capacitor 28. However, there is a problem that it is difficult to detect the input current as an effective value because the waveform of the power source 21 changes significantly due to the impedance of the power supply 21.

The first object of the present invention is to overcome the problems of the prior art and to transmit the detected current value to the control circuit without passing through the insulating circuit, which is low in cost. An object is to provide a current detection device for an inverter.

Further, a second object of the present invention is that the cost is low because it does not require CT, and the input current detection of the capacitor input type rectifier circuit which can easily detect the value corresponding to the effective value of the input current. To provide a device.

[0011]

In order to achieve the above first object, in the present invention, in an inverter including a converter section and an inverter section, a DC intermediate current is inserted between the converter section and the inverter section. A shunt resistor connected to the shunt resistor, first temperature detecting means located near the shunt resistor to detect a temperature due to current heating, and ambient temperature not affected by current heating of the shunt resistor. Second temperature detecting means, an arithmetic circuit for obtaining and outputting a temperature difference between the temperature detected by the first temperature detecting means and the temperature detected by the second temperature detecting means, and a square root of the temperature difference. And a square root circuit that outputs the effective value of the DC intermediate current.

Further, in order to achieve the second object, in the present invention,
In a current detection device for detecting an input current of a capacitor input type rectification circuit, between an AC power source and a diode rectification circuit forming the capacitor input type rectification circuit, or a diode rectification circuit and a capacitor forming the capacitor input type rectification circuit. A resistor is connected in series to the electric path through which the input current flows, and a thermistor is placed in a position close to the resistor to transmit heat generated from the resistor, and the resistance value of the thermistor changes. Therefore, the input current is detected.

[0013]

With respect to the achievement of the first object, since the temperature difference is proportional to the square of the effective value of the DC intermediate current, the current value can be measured by measuring the temperature difference and taking the square root. it can. In this way, the current value to be measured is obtained as the amount of temperature, and since the temperature is the amount electrically insulated from the DC intermediate circuit, the measured value can be transmitted to the control circuit without passing through the insulation circuit. It will be possible.

With respect to the achievement of the second object, when the thermistor is sufficiently thermally coupled to the heating resistor, the heat generation of the resistor is proportional to the effective value of the current flowing through the resistor, and thus the resistance of the thermistor is increased. The effective value of the current can be detected as the change. As a result, the effective value of the current can be detected easily without requiring CT.

[0015]

FIG. 1 is a circuit diagram showing an embodiment for achieving the first object of the present invention. In the figure, the same components as those in FIG. 7 are designated by the same reference numerals. In addition, 2 and 3 are thermistors, 4 and 5 are temperature detection circuits, 6 is a subtraction circuit, and 7 is a square root circuit.

In FIG. 1, the thermistor 2 is used to measure the temperature of the shunt resistor 1 (a DC intermediate current flows through the shunt resistor 1 to generate resistance heat and thereby raise the temperature of the shunt resistor 1). It is attached. The thermistor 3 is attached to measure the ambient temperature that is not affected by the heat generated by the shunt resistor 1.

The temperature detection circuit 4 detects the temperature of the shunt resistor 1 from the output of the thermistor 2, and the temperature detection circuit 5
The ambient temperature is detected from the output of the thermistor 3. The temperature difference between the two temperatures is calculated in the subtraction circuit 6, and the square root value is obtained by the square root circuit 7. The square root value is an amount capable of expressing the value of the DC intermediate current flowing through the shunt resistor 1, and is an amount electrically insulated from the DC intermediate circuit, so that it can be directly controlled without an insulation circuit. Can be transmitted to the circuit.

FIG. 2 is a circuit diagram showing an embodiment for achieving the second object of the present invention. In the figure, the same components as those in FIG. 8 are designated by the same reference numerals. Besides, 26 is a resistor and 27 is a thermistor.

In FIG. 2, the current from the single-phase power source 21 flows through the resistor 26. As a result, the resistor 26 generates heat, and the thermistor 27, which is sufficiently thermally coupled to the resistor 26, is heated by the resistor 26, and changes in the resistance value of the thermistor 27 are reflected by the effective current flowing through the resistor 26. The value can be taken out from the terminals A and B. This is because the heat generated by the resistor 26 is proportional to the effective value of the current flowing through the single-phase power supply 21. That is, the current flowing in the single-phase power supply 21 in this way can be detected from the terminals A and B.

FIG. 3 shows another embodiment, in which the resistor 26 is connected between the rectifiers 22 to 25 and the capacitor 28. The same effect as that of the embodiment of FIG. 2 can be obtained.

FIG. 4 shows still another embodiment, which is an embodiment in which the power source is a three-phase power source 30. 31, 3
2 is a diode. This embodiment can also obtain the same effect as the embodiment of FIG.

FIG. 5 shows an embodiment in which the resistor 26 and the thermistor 27 are combined, and the combined structure is entirely cemented with cement 33. In this way, the heat generated by the resistor 26 is sufficiently transmitted to the thermistor 27.

FIG. 6 shows still another embodiment, in which the output of the thermistor 27 is input to the microcomputer. In the figure, 34 and 35 are resistors, 36 is a thermistor for ambient temperature correction, and 37 is a microcomputer.

The output of the thermistor 27 for current detection is connected to the resistor 35 and the A / D (analog / digital conversion) input terminal AD1 of the microcomputer 37 after being divided. The output of the thermistor 36 for ambient temperature correction is connected to the resistor 34 and the A / D (analog / digital conversion) input terminal AD2 of the microcomputer 37 after being divided. Inside the microcomputer 37, the resistance value change of the thermistor 27 and the thermistor 36
From the change in the resistance value of, the input current value flowing through the resistor 26 is calculated. The thermistor 36 can be omitted when the influence of the ambient temperature is small.

[0025]

As described above, according to the present invention,
There is an advantage that it is possible to provide a low-cost inverter current detection device that can transmit the detected current value to the control circuit without passing through the insulating circuit.

Further, according to the present invention, there is an advantage that it is possible to provide an input current detection device of a capacitor input type rectifier circuit which can detect an effective value of an input current at a low cost. The input current detection device can be used for an air conditioner inverter, a vending machine inverter, and the like.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment for achieving the first object of the present invention.

FIG. 2 is a circuit diagram showing an embodiment for achieving the second object of the present invention.

FIG. 3 is a circuit diagram showing another embodiment for achieving the second object of the present invention.

FIG. 4 is a circuit diagram showing another embodiment for achieving the second object of the present invention.

FIG. 5 is a circuit diagram showing still another embodiment for achieving the second object of the present invention.

FIG. 6 is a circuit diagram showing still another embodiment for achieving the second object of the present invention.

FIG. 7 is a circuit diagram showing a conventional example of a current detection device for an inverter.

FIG. 8 is a circuit diagram showing a conventional example of an input current detection device of a capacitor input type rectifier circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Shunt resistance, 2, 3 ... Thermistor, 4, 5 ... Temperature detection circuit, 6 ... Subtraction circuit, 7 ... Square root circuit, 10 ... Current detection circuit, 11 ... Insulation circuit, 21 ... Single-phase power supply, 22-2
5 ... Diode, 26 ... Resistor, 27 ... Thermistor, 2
8 ... Capacitor, 29 ... Load, 30 ... Three-phase power supply, 31,
32 ... Diode, 33 ... Cement, 34, 35 ... Resistor, 36 ... Thermistor, 37 ... Microcomputer

Claims (1)

Claim: What is claimed is: 1. In an inverter comprising a converter section and an inverter section, in a current detecting device for detecting a DC intermediate current flowing between the converter section and the inverter section, a circuit through which the DC intermediate current flows. A shunt resistor inserted in and connected to the shunt resistor; a first temperature detecting means located in the vicinity of the shunt resistor for detecting a temperature due to current heating; and an ambient temperature not affected by current heating of the shunt resistor. Second temperature detecting means for detecting, an arithmetic circuit for obtaining and outputting a temperature difference between the temperature detected by the first temperature detecting means and the temperature detected by the second temperature detecting means, and the temperature difference And a square root circuit for obtaining the effective value of the DC intermediate current by calculating the square root of the current detection device. 2. A current detecting device for detecting an input current of a capacitor input type rectifier circuit, wherein a resistor is connected in series with an electric current path between the alternating current power source and the diode rectifier circuit forming the capacitor input type rectifier circuit. A current detecting device, wherein the thermistor is connected to the resistor, and a thermistor is disposed at a position where heat generated from the resistor is transmitted in proximity to the resistor, and the input current is detected from a change in resistance of the thermistor. 3. A current detecting device for detecting an input current of a capacitor input type rectifying circuit, wherein a resistor is connected in series with an electric current path between the diode rectifying circuit and the capacitor forming the capacitor input type rectifying circuit. connection,
A current detecting device characterized in that a thermistor is arranged in a position where heat generated from the resistor is transmitted in proximity to the resistor, and the input current is detected from a change in resistance value of the thermistor.