JPH0530746A - Power turn-on circuit for rectifying circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] A charge rush current is reduced by controlling the short-circuit timing of the current limiting resistance inserted in the AC input side of a rectifier circuit composed of a rectifier and a smoothing capacitor. [Composition] A power supply voltage confirmation circuit and a charging voltage confirmation circuit for detecting and confirming that the input AC voltage of the rectifier and the charging voltage of the smoothing capacitor are respectively above a predetermined voltage, and the outputs of both voltage confirmation circuits are both And a relay control circuit that outputs an output after a predetermined time has elapsed from the time when the current limiting resistor is activated to activate the short-circuiting means of the current limiting resistor to short-circuit the current limiting resistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for controlling a charging inrush current when an AC input is applied to a rectifier circuit which is a DC power source for an inverter or the like and which comprises a rectifier and a smoothing capacitor for smoothing the output rectified voltage. Regarding the circuit.

[0002]

2. Description of the Related Art As a conventional power-on circuit of this type,
A current limiting resistor that is inserted in series on the AC input current path of a rectifier circuit that is composed of a rectifier that rectifies an AC input voltage and a smoothing capacitor that smoothes an output rectified voltage of the rectifier, and that suppresses a charging inrush current to the capacitor, A current limiting resistance short-circuiting means such as a contact of an electromagnetic contactor or a semiconductor switching element connected in parallel to the current limiting resistance; and a charging voltage confirmation circuit that outputs an output when the charging voltage of the capacitor is equal to or higher than the predetermined voltage. It is known that the current limiting resistor is short-circuited by exciting the electromagnetic contactor by the output signal of the confirmation circuit to close the contact or to bring the switching element into a conductive state. There is.

[0003]

However, in the conventional power-on circuit as described above, the closed circuit operating condition of the current limiting resistance short circuit means is such that the charging voltage of the smoothing capacitor is set to be lower than the steady value. It is only equal to or more than the value, and the closing operation of the short-circuit means is performed immediately after this condition is satisfied, and the charging voltage of the capacitor is forcibly matched with the output voltage of the rectifier, which is the steady voltage, and increases rapidly. .. Therefore, even during the closing operation of the short-circuiting device during the charging and boosting of the capacitor, or when the charging voltage of the capacitor is equal to or higher than the predetermined value when the AC input is restored after a short power failure, It was unavoidable that an excessively large charging current was transiently generated because the applied voltage suddenly increased under low resistance.

Incidentally, FIGS. 2 and 3 are time charts showing the above variations in the charging voltage Vc and the charging current Ic of the smoothing capacitor. In the figure, Vcf and Vcs are predetermined set voltages that form a steady value of the voltage Vc and a condition voltage for closing the short-circuit means, respectively, and are set as Vcs <Vcf. In FIG. 2, when charging is started at time t ₀ and the current limiting resistance is short-circuited at time t ₁ when Vc reaches Vcs, the voltage Vc is forced to be Vcf.
The Ic becomes a pulse-like transient excessive current as shown in the figure. Further, FIG. 3 shows that, during the steady operation in which the current limiting resistance is short-circuited and Vc is equal to Vcf, the AC input is cut off at time t ₂ and power is restored at time t _{3 and} at time t ₃ 2 shows that when the above-mentioned Vc is larger than Vcs, a pulse-like transient excessive current is generated as in the case of FIG.

In any case, in order to generate the excessive charging current as described above, it is necessary to take measures such as increasing the current capacity of the constituent elements of the rectifier and the contacts as the short-circuit means or the semiconductor element, or inserting the reactor. The rectifier circuit and its power-on circuit have become large and expensive. In view of the above, it is an object of the present invention to provide a power-on circuit for a rectifier circuit that can reduce or prevent the excessive charging current as described above.

[0006]

In order to achieve the above object, a power-on circuit for a rectifier circuit according to the present invention comprises a rectifier for rectifying an AC input voltage and a smoothing capacitor for smoothing an output rectified voltage of the rectifier. A current limiting resistor that is inserted in series on the AC input energizing path of the rectifier circuit to suppress the charging rush current to the capacitor, and is connected in parallel to the current limiting resistor and operates according to the closing command signal to operate the current limiting resistor. In a power-on circuit for a rectifier circuit, which comprises a current limiting resistance short-circuit means for short-circuiting, a power supply voltage confirmation circuit that outputs an output when the AC input voltage is higher than a predetermined voltage, and a charging voltage of the capacitor is higher than the predetermined voltage. If a charging voltage confirmation circuit that outputs an output is present, and a relay control that outputs that output after a predetermined time has elapsed from the time when the state in which both outputs of both voltage confirmation circuits are generated is established. It made and a circuit shall be formed by the circuit closing command signal to the current-limiting resistor short-circuiting means drives out the output signal of the relay control circuit.

[0007]

According to the present invention, the short-circuit point of the current limiting resistor in the capacitor charging circuit via the current limiting resistor for suppressing the charging inrush current is detected by the DC voltage V applied to the charging circuit via the rectifier.
This is defined as the time when a predetermined time ΔT has elapsed from the time when both the AC power supply voltage Va for giving cf and the charging voltage Vc of the capacitor become equal to or higher than the respective predetermined values Vas and Vcs. Note that Vcf is a rectified voltage of the steady value of Va and therefore becomes the steady value of Vc.
Is set appropriately as 0.85 Vcf and ΔT is set appropriately as 0.1 seconds.

Therefore, even when both the voltages Vc and Vcs have a relationship of Vc> Vcs at the time of power recovery after the short-term power failure of the AC input, the current limiting resistance is short-circuited from the power recovery time to the time ΔT. However, if the time ΔT is set to a time sufficient for the transient state associated with reapplication of power to be substantially finished, the charging inrush current when the current limiting resistor is short-circuited after the time ΔT elapses from the power recovery time Can be made significantly smaller than when the ΔT is zero. Further, if the current limiting resistor is short-circuited after the time ΔT has elapsed from the time when the voltage Vc becomes Vcs or more during charging of the capacitor,
As the voltage Vc increases within the time ΔT, the voltage difference Vcf
-Vc becomes smaller than that in the case where the ΔT is zero, so that the value of the charging inrush current at the time of short-circuiting of the current limiting resistor can also be made small.

[0009]

Embodiments of the present invention will be described below with reference to the circuit diagram shown in FIG. In FIG. 1, reference numeral 1 denotes a rectifier circuit, which is connected from an AC power source (three phases in the case shown) via a current limiting resistor Rs and an a contact RY-a of a relay (or electromagnetic contactor) RY connected in parallel with the resistor. The AC input is then fed. Then Cf
Is a smoothing capacitor for smoothing the output rectified voltage of the rectifier circuit 1, and Vc and Ic are the charging voltage and charging current of the capacitor, respectively. Reference numeral 2 is an inverter circuit (three phases in the case shown) which uses a power transistor or the like as a switching element and receives the voltage Vc as a DC input.
(Induction motor) is used as the load.

Next, 4 is a power supply voltage confirmation circuit, which divides the rectified voltage of the AC power supply voltage by resistance, and the divided voltage is a constant voltage selected corresponding to a predetermined voltage for judging the presence or absence of the AC power supply voltage. The output signal Ss of the photocoupler PC which is operated by the current of the diode when the voltage is equal to or higher than the Zener voltage of the voltage diode serves as a required AC power supply voltage confirmation signal. Reference numeral 5 denotes a charging voltage confirmation circuit, which has the same circuit configuration as the power supply voltage confirmation circuit, and receives the divided voltage of the charging voltage of the capacitor Cf as an input and confirms that the charging voltage is equal to or higher than the predetermined voltage Vcs. The signal Sc is output, and the Zener voltage of the constant voltage diode is selected corresponding to the voltage Vcs. Further, 6 is a relay control circuit, which detects the simultaneous output state of both signals Ss and Sc by an AND element AND, and outputs the output of the element AND for a predetermined time through a delay circuit composed of a resistor, a capacitor and a diode. It is delayed by ΔT and applied to the base of the transistor to excite the coil of the relay (or electromagnetic contactor) RY by the transistor to close the contact RY-a of the relay. That is, the current limiting resistor Rs is closed after the time ΔT has elapsed after the simultaneous output state of the voltage confirmation signals Ss and Sc is established, and the rectifying circuit shifts to the steady operation state.

[0011]

According to the present invention, a short circuit of the current limiting resistor for suppressing the charging inrush current provided on the AC input side of the rectifier circuit composed of the rectifier and the smoothing capacitor is caused by the AC input voltage. And a charging voltage confirmation circuit as described above, a charging voltage confirmation circuit, and a delay circuit are provided to perform rectification so that a predetermined time elapses after both the charging voltage of the capacitor and the charging voltage of the capacitor are equal to or more than their respective predetermined values. By configuring the circuit power-on circuit, even if the short-circuit point of the current limiting resistor is in the middle of charging or when the AC input is restored after a short power failure, an excessive amount of voltage is applied to the smoothing capacitor. It is possible to prevent the generation of a charging rush current, and to insert a current limiting reactor, or to increase the current capacity of the rectifying element of the rectifier and the contact as the current limiting resistance short-circuiting means or the semiconductor element. Various measures becomes unnecessary etc., it is possible to achieve the miniaturization and cost reduction of its power-on circuit and the rectifier circuit.

[Brief description of drawings]

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

FIG. 2 is an operation time chart in the case of the conventional technique (in the case of closed circuit during charging).

FIG. 3 is an operation time chart in the case of a conventional technique (in the case of closed circuit at power recovery)

[Explanation of symbols]

 1 Rectifier circuit 2 Inverter circuit 3 IM (Induction motor) 4 Power supply voltage confirmation circuit 5 Charging voltage confirmation circuit 6 Relay control circuit AND AND element Cf Smoothing capacitor PC Photo coupler RY Relay (or electromagnetic contactor) RY-a RY excitation Time closed contact

Claims (1)

Claim: What is claimed is: 1. A rectifier circuit comprising a rectifier for rectifying an AC input voltage and a smoothing capacitor for smoothing an output rectified voltage of the rectifier. In a power-on circuit for a rectifying circuit, which comprises a current limiting resistor for suppressing a charging inrush current, and a current limiting resistor short-circuiting means which is connected in parallel to the current limiting resistor and operates according to a closing command signal to short-circuit the current limiting resistor. A power supply voltage confirmation circuit that outputs an output when the AC input voltage is equal to or higher than the predetermined voltage; a charging voltage confirmation circuit that outputs an output when the charging voltage of the capacitor is equal to or higher than the predetermined voltage; A relay control circuit that outputs the output of the circuit after a predetermined time has elapsed from the time when the state in which the outputs of both circuits are established is established. A power-on circuit for a rectifying circuit, which is used as a closing command signal for the current limiting resistance short-circuit means.