JPH05184058A - Nonequiblium detecting circuit for 3-phase ac power supply - Google Patents

Abstract

PURPOSE:To provide a nonequliblium detecting circuit for a 3-phase AC power supply, which is capable of detecting that the value of the minimum voltage with respect to the maximum voltage among the voltage of respective phases has exceeded a predetermined value to detect that the voltages of respective phases attains nonequliblium in either high or low directions of the voltage of respective phases. CONSTITUTION:The circuit is constituted of peak value detecting circuits 1-1, 1-2, 1-3 of respective phases, which retain peak values, a selection circuit 2, selecting and taking-out the maximum voltage among the outputs of respective peak value detecting circuits 1-1, 1-2, 1-3, comparing circuits 3-1, 3-2, 3-3, comparing the output voltage of the selection circuit 2 with the output voltage of respective peak value detecting circuits 1-1, 1-2, 1-3, and a logical operation circuit 4, effecting the logical operations of the outputs of the comparing circuits 3-1, 3-2, 3-3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase AC power supply unbalance detection circuit.

[0002]

2. Description of the Related Art Large power devices that directly use three-phase AC have come to be widely used, such as when a communication switching power supply is connected to a three-phase AC power supply terminal. The voltages of the three phases should originally be equal to each other, but sometimes they fluctuated. Therefore, a voltage drop detection circuit has been used, which measures the voltage value for each phase and detects when the voltage value falls below a predetermined value with respect to the rated voltage. Also, since this circuit is connected to each of the three phases, it is possible to detect when any one of the phases has a voltage drop, and when any one of the phases has a voltage drop, it is regarded as unbalanced. , The connection of the relevant phase was cut off.

[0003]

The voltage of each phase of the three-phase alternating current does not always drop in voltage, and one phase may drop in voltage and another phase may rise in voltage. Therefore, when only one phase causes a slight voltage rise and the other two phases have normal voltages, they are actually unbalanced, but the conventional detection circuit cannot detect this. When a three-phase AC is used as a switching power supply for communication and a capacitor input type circuit is used as the rectifier circuit, many ripples are superimposed on the DC supplied to the load when the voltage of only one phase becomes high. Therefore, the ripple amount detection circuit operates, and the connection of the relevant phase may be cut off to perform single-phase operation. Therefore, the power consumption of communication equipment has come to be limited.

The present invention solves the above-mentioned drawbacks in the related art, detects that the value of the minimum voltage with respect to the maximum voltage of each phase voltage exceeds a predetermined value, and detects whether the phase voltage is high or low. An object of the present invention is to provide an unbalance detection circuit that can detect that an unbalance has occurred.

[0005]

The means of the present invention for achieving the above-mentioned object are as follows. That is, each phase voltage of the three-phase AC power supply is rectified, and the peak value detection circuit for each phase that holds the peak value and the maximum voltage of the outputs of each peak value detection circuit are selected and extracted. A selection circuit, a comparison circuit that compares the output voltage of the selection circuit with a voltage obtained by dividing the output voltage of each peak value detection circuit into a predetermined value, and the output of the comparison circuit is logically operated to find a difference between the three phases. And a logical operation circuit that generates an output when there is a balance.

[0006]

[Function] The peak value detection circuit that rectifies each phase voltage and holds the peak value is connected to the selection circuit, and the maximum voltage value out of the output of the peak value detection circuit is extracted to obtain one of the comparison circuits. To enter. The other of the comparison circuits has a value obtained by dividing the output voltage of the peak value detection circuit into a predetermined value. An output is generated in the comparison circuit for the phase in which the minimum value of the maximum voltage value of each phase is abnormally lowered. The output of the comparison circuit is operated in the logic operation circuit, and when the above-mentioned state occurs in any phase and when the output of the logic operation circuit occurs, it is judged that the imbalance is detected.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of an embodiment of an unbalance detection circuit for a three-phase AC power supply according to the present invention. In FIG. 1, U,
V and W are terminals connected to each phase of the three-phase AC power supply, M is a common terminal for each phase, OUT is an output terminal of the logical operation circuit 4, 1-
1, 1-2, 1-3 are peak value detection circuits for each phase, 2 is a maximum voltage selection circuit, 3-1, 3-2, 3-3 are comparison circuits,
Reference numeral 4 represents a logical operation circuit. C1 to C8 are capacitors, R1 to R22 are resistive elements, IC1A to IC9
A is a circuit composed of an integrated circuit, V1 to V8 are DC voltage values at respective points, and D1 to D6 are rectifying diodes.

The unbalance detection circuit shown in FIG. 1 has terminals U, V,
When W is connected to the respective predetermined terminals, the diodes D1 to
The positive voltage of each phase rectified by D3 is the capacitor C1.
To C3, and the voltages are set to V1 to V3. The voltages V1 to V3 are peak voltage of each phase. In addition, the resistance elements R1 to R1 whose voltages are selected as will be described later
The voltage divided by R6 is V6 to V8. V1-V
When the voltage of 3 is connected to the capacitor C4 via the diodes D4 to D6, the maximum voltage of the voltages V1 to V3 is stored in the capacitor C4. That is, the maximum voltage is selected and held. The voltage is V4. The voltage V4 is divided by the resistance elements R7 and R8, and the voltage at the connection point is V5. Also, the U-phase voltage V
1 is divided by the resistance elements R1 and R2 to obtain the voltage V6, the V-phase voltage V2 is divided by the resistance elements R3 and R4 to obtain the voltage V7, and the W-phase voltage V3 is divided into the resistance elements R5 and R5.
Divide by 6 to obtain voltage V8. The values of the respective resistance elements R1 to R8 are selected so that V6 = V7 = V8 = V5 when V1 to V3 are 90% of the rated voltage, for example, 90V against 100V.

Further, in order to detect that the voltages of the respective phases have become abnormally low voltages, the comparison circuits 3-1, 3-2, 3-
It is preferable to additionally connect the circuit IC 4A to the circuit 3. The + terminal of the circuit IC4A is connected to a constant reference voltage terminal of 30 V, for example, and the − terminal is connected to the intermediate connection point of the resistance elements R9 and R10. The resistance elements R9 and R10 are selected so that the voltage V5 at the connection point of the resistance elements R9 and R10 is 30 V or less when V1 to V3 are both lower abnormal voltages, for example, 70 V. Comparing circuits 3-1, 3-2, 3-3
The connection circuits of the resistance elements R11 to R22 and the capacitors C5 to C8 between the logic operation circuit 4 and the logical operation circuit 4 and the inverters IC5A to IC8A having the hysteresis characteristic form a malfunction prevention circuit of the detection circuit.

In the above-mentioned circuit of the present invention, U, V, W
When the voltage of each phase is the rated value, the comparison circuits 3-1 and 3-
The outputs of the circuits 2 and 3-3 are "L", and the output of the logical operation circuit 4 is also "L". If the U-phase slightly exceeds the rated value, the maximum voltage among the three phases, the V-phase gradually becomes lower than the rated value, and the W-phase gradually becomes lower than the rated value. It has become.
At this time, when the voltage V7 gradually decreases and becomes V5> V7, the output of the comparison circuit 3-2 (IC2A) changes from "L" to "H". The output change of the comparison circuit 3-2 changes the output of the logical operation circuit 4 from "L" to "H" through the malfunction prevention circuit. Therefore, since an output is generated from the logical operation circuit 4 (IC9A), the imbalance is detected. It should be noted that when the U, V, and W phase voltages become abnormally low voltages, the detection output is similarly obtained. Table 1 below shows a motion truth table for each of the points A to I in FIG.

[0011]

[Table 1]

In Table 1, A corresponds to the display in FIG. 1, the output of the circuit IC1A, the output of the circuit IC2A, the output of the circuit IC3A, the output of the circuit IC3A, and I as shown in the same manner. The output of IC9A is shown. When the output I is "L", it is normal, and when I is "H", it means that the imbalance is detected. For example, column B of the table (that is, IC2A
When the output of the column (representing the output of 1) is “H” and the outputs of the columns A and C are “L”, it corresponds to the unbalanced state of the above operation. Further, if the column A becomes “H”, it means that the U phase has a lower voltage than the other phases, and since B and C are “L”, an imbalance is detected at that time. ..

FIG. 2 is a diagram showing, as an application of the unbalance detection circuit of the present invention, a case where the circuit of the present invention is applied to a switching power supply circuit. That is, in FIG. 2, the unbalance detection circuit may be the circuit shown in FIG. 1, and the switching power supply circuit may be, for example, a capacitor input type. The unbalance detection circuit is connected as shown in FIG. 2 to constantly monitor the input voltage to the switching power supply circuit. If an imbalance is detected, the OUT signal is sent to the switching power supply circuit to stop the operation. Therefore, the power supply circuit does not operate in a single phase, and the input capacitor of the power supply circuit is not affected by a large amount of ripples to affect the life.

[0014]

As described above, according to the present invention, since the voltage values of the minimum voltage phase and the maximum voltage phase are compared,
It became possible to detect the imbalance of the three-phase power supply relatively. That is, even if there is a phase with a voltage slightly higher than the rated voltage, even if it is unbalanced, it cannot be detected by the conventional detection circuit, but according to the present invention, it is detected because the relative comparison detection is performed. Bring the effect that can be.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an application example of a circuit of the present invention.

[Explanation of symbols]

1-1, 1-2, 1-3 Peak value detection circuit
2 Selection circuit 3-1, 3-2, 3-3 Comparison circuit
4 Logical operation circuit

Claims (1)

[Claims] 1. A peak value detection circuit for each phase that rectifies each phase voltage of a three-phase AC power supply and holds a peak value, and selects the maximum voltage of the outputs of each peak value detection circuit. And a comparison circuit for comparing the output voltage of the selection circuit with a voltage obtained by dividing the output voltage of each peak value detection circuit into a predetermined value,
An unbalance detection circuit for a three-phase AC power supply, comprising: a logical operation circuit that logically operates the output of the comparison circuit to generate an output when an imbalance exists between the three phases.