JPH0322867A - Rush current limiting device for dc power source - Google Patents

Abstract

PURPOSE:To reduce rush current and prevent the fusion welding of a relay contact as well as the rupture of a rectifying circuit by a method wherein the opening and closing of the relay contact are controlled by a difference between the voltage of an AC power source and the charging voltage of a smoothing capacitor while differences between respective voltages are kept constant at all times with respect to the fluctuation of the power source voltage. CONSTITUTION:When a power breaker 2 is thrown, a DC voltage from a 3-phase full-wave rectifier is applied to a smoothing capacitor 4 through a diode 21 and a resistor 5 whereby the capacitor is charged. A charging voltage is divided by the resistor R13, R14 of a charging voltage detecting circuit 23 to input them into an A/D converter 24. A microcomputer 26 operates in accordance with the outputs of the A/D converters 24, 25, that is, it operates to energize a relay coil 11 to close a contact 11a when the value of Vac-Vde has become smaller than a predetermined value V1. In this case, the predetermined value V1 is determined so as to be smaller than a value determined by multiplying the maximum opening and closing current of the relay contact 11a by the impedance of a power source whereby a rush current (i) upon closing the contact 11a may be made smaller than the maximum opening and closing current of the relay contact 11a.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for limiting current flowing into a DC power source such as an inverter device.

[Prior art] Figures 6 and 7 are, for example, disclosed in Japanese Patent Application Laid-Open No. 62-1960.
72 is a diagram showing a conventional inrush current limiting device for a DC power supply, FIG. 6 is a circuit diagram, and FIG. 7 is an operation explanatory diagram.

In Figure 6, 5(l) is a three-phase AC power supply, (2) is an AC power supply +
1) is connected to the power supply circuit breaker, (3) is connected to the power supply circuit breaker Ri (
2) is a rectifier circuit connected to the diode bridge, (4) is a smoothing capacitor connected to the DC side of the rectifier circuit (3), and (5) is a rectifier circuit connected to the rectifier circuit (3) and the smoothing capacitor (4). Inrush current suppression resistor inserted between (6
) is an inverter section connected to both ends of a smoothing capacitor (4) and constituted by a transistor bridge, (7) is an induction motor connected to the AC side of the inverter section (6),
(8) is an input voltage detection circuit composed of resistors Rl-R5, capacitor C1, and photocoupler Pl, (9) is a charge 1 voltage detection circuit composed of resistors R6 to nto, capacitor C2, and photocoupler P2, (10) ) is NOR
The gate, TRI, is a transistor whose base is connected to the NOR gate (lO) via a resistor Rll, (1l) is a relay coil connected to the transistor TRl, and f
lla) is a regular contact point of the above-mentioned relay, and is connected in parallel with the resistor (5). (l2) is a flywheel diode connected to both ends of the relay coil (1), and Vcc is a DC positive power supply.

A conventional inrush current limiting device for a DC power supply is configured as described above, and when the power supply circuit breaker (2) is turned on, the rectifier circuit (3)
), the three-phase full-wave rectified DC voltage is applied to the smoothing capacitor (4) through the resistor (5);
) is charged. At this time, the photocoupler pt of the input voltage detection circuit (8) is switched on, and the capacitor CI is discharged, so the NOR gate (101 has rLJ
A signal is input.

On the other hand, the charging voltage of the smoothing capacitor (4), that is, the DC power supply P. Since the potential difference between N and N is still zero, photocoupler P2 of the charging voltage detection circuit (9) remains switched off, and the output of capacitor C2 causes the "H" signal to become NO.
Input to R gate (IO). Therefore, the NOR gate flo) outputs the LJ signal and the transistor TR
Since I is switched off, the relay coil (ill) is deenergized and the contact (llal is in an open state.) Now, the moment the power circuit breaker (2) is turned on, the current flows through the resistor (5). Since the current flows through the rectifier circuit (3), the rectifier circuit (3) will not be destroyed.

When the charging voltage of the smoothing capacitor (4) is charged to a predetermined value V1 set in the charging voltage detection circuit (9), the photocoupler P2 is switched on, and the capacitor C2 is discharged and the "LJ signal is NOR game 1- (
101. therefore. NOR gate (lO
) outputs "]4" signal, the transistor TRI is switched on, the relay coil (1)) is energized, and the contact (llal) is closed.

The smoothing capacitor (4) will now be rapidly charged.

Next, assume that a voltage drop occurs during inverter operation.

First, if the voltage drop is significant, check the input voltage detection circuit (8
) and charging voltage detection circuit (9) output the rJ signal to the NOR gate (flO), the output of the NOR gate (IO) becomes the rLJ signal, and the relay contact fl
la) is open. Then, when the voltage rises to the original state, the smoothing capacitor (4) is connected to the charging voltage detection circuit (9).
), the battery will be charged through the relay contact [1) al.

In this way, the smoothing capacitor (4) is charged through the resistor (5) until the predetermined value V is reached, and the inrush current is at a level that does not destroy the rectifier circuit (3). These states are shown in FIG.

[Problem to be Solved by the Invention 1] In the conventional DC power supply inrush current limiting device as described above,
When the f-slip capacitor (4) is charged until it reaches a predetermined value set in the charging voltage detection circuit (9), the relay contact (llal) is closed, so the rectifier circuit (3) Compared to those using semiconductors, contact parts such as relay contacts (1 1a) are more prone to failures such as welding due to inrush current.This becomes even more noticeable especially when the power supply voltage is high. .For this reason, in order to reduce the inrush current and prevent welding of the relay contact (lla),
It is conceivable to increase the predetermined f/V. However, if the predetermined value ゜V1 is increased, the voltage of the smoothing capacitor (4) will not rise to the predetermined value 57 when used in a place where the power supply voltage is low, so the relay contact fl lal will not close.
, there is a problem that the inverter section (6) cannot be driven.

This invention was made to solve the above problems, and even when there are fluctuations in the power supply voltage, the inrush current is minimized, preventing welding of relay contacts, destruction of the rush current circuit, etc.
An object of the present invention is to provide an inrush current limiting device for a DC power supply that is highly reliable and can operate stably.

[Means for Solving the Problems] The inrush current limiting device for a DC fi source according to the first aspect of the present invention performs smoothing by comparing the difference between the voltage of the AC power supply and the charging TTi voltage of the smoothing capacitor with a predetermined voltage. It is designed to control the opening of a relay contact connected in parallel to the resistor of the capacitor's charging circuit.

Further, in the inrush current limiting device for a DC power supply according to the second aspect of the present invention, in the first aspect, the predetermined value of the voltage difference at which the relay contact opens is set to the predetermined value of the voltage difference at which the relay contact closes. I set it higher than the value.

Further, in the inrush current limiting device for a DC power supply according to the third invention of the present invention, in the first and second inventions, when the relay contact is open, the inrush current limiting device for a DC power supply according to the third invention is This causes the relay contacts to close after a time delay.

[Function 1] In the first aspect of the present invention, since the opening and closing of the relay contact is controlled by the difference between the voltage of the AC power supply and the charging voltage of the smoothing capacitor, even if there is a fluctuation in the 2K voltage, the AC The difference between the power supply voltage and the charging voltage is always constant.

Further, in the second aspect of the present invention, the predetermined value of the voltage difference at which the relay contact opens is set larger than the predetermined value of the voltage difference at which the relay contact closes. , even if there is some fluctuation in the lightning source voltage,
Do not open relay contacts.

In addition, in Komei's third invention, when the relay contact is left open, the relay contact is closed after a predetermined time delay after the voltage difference reaches a predetermined value, so that an inrush current flows through the relay contact. becomes fewer in Akira.

[Embodiment] Figs. 1 to 3 are diagrams showing an embodiment of the first invention of the present invention, in which Fig. 1 is a circuit diagram, Fig. 2 is a flowchart showing a relay control means, and Fig. 3 is a flowchart showing a relay control means. It is an explanatory diagram of the operation, and parts similar to those of the conventional device are designated by the same reference numerals.

In FIG. 1, (2l) is a diode inserted between the rectifier circuit (3) and the resistor (5), and (22) is the resistor R1).
Rl2, an input voltage detection circuit composed of a capacitor C3 and a diode D, (23) is a resistor Rl3, 1{l
(24) is an A/D converter 23 that converts the output of the charging voltage detection circuit (23) into digital data; (25) is also the input voltage detection circuit (22); The A/D converter (26) converts the output, and the microcomputer (26) inputs the output of the A/D converter (24) f25) to control the relay coil (l1).
(hereinafter referred to as a microcomputer).

Next, the program of the microcomputer (26) will be explained with reference to FIG. This program is stored in the memory (not shown) of the microcomputer (26).

In step (3l), it is determined whether the relay coil (1) 1 is energized, and if it is energized, the process proceeds to step (32), and if it is energized, the process proceeds to step (33).

The input voltage detection circuit (22) input voltage Vac from the A/D converter f25) in the step unit (33),
The difference between the voltage Vdc of the charging voltage detection circuit (23) input from the A/D converter 23f24) is determined by the relay coil [1]
When the voltage difference when energizing relay coil (1) becomes smaller than a predetermined value V1, the process proceeds to step (34), and the relay coil (1
)). In other cases, terminate the program.

At step {32}, the difference between voltage Vac and voltage Vdc is
When the voltage difference when deenergizing the relay coil (I1) is smaller than the predetermined value (2), the program is terminated. In other cases, proceed to step (35) and relay coil (1
)) to deactivate.

Note that the program shown in FIG. 2 is repeatedly executed in a very short time compared to the time constant determined by the resistor (5), power source impedance, and smoothing capacitor (4).

Next, the operation of this "3!" embodiment will be explained.

When the power supply cutoff 23f2) is turned on, a three-phase full-wave DC surge pressure is applied to the smoothing capacitor (4) through the diode (2J) and resistor (5) in the rectifier circuit (3).
The smoothing capacitor (4) is charged. At this time, the capacitor C3 of the input voltage detection circuit (22) is connected to the diode D.
It is quickly charged via the Gito Rl1. A voltage proportional to the input voltage divided by Rl2 is input to the A/D converter (25). Here, since the capacitor C3 may be extremely small in size, the current Iδ is very small and no particular limiting resistor is required. In addition, the output voltage of the input voltage detection circuit {22) is maintained at the voltage before the instantaneous power outage by turning C3 when the power supply voltage temporarily drops due to a power outage, etc. It's like this. On the other hand, the charging voltage of the smoothing capacitor (4), that is, the voltage IQ between the DC power source 1 and N, is determined by the source impedance of Ui and the smoothing capacitor (4). or is upper bounded by the Te constant. The charging voltage of the smoothing capacitor (4) is determined by the resistors R13 and Rl of the charging voltage detection circuit (23).
4 and input to the A/I) converter (24). A/D converter 23f241 (From the output of 251, the microcomputer (26) is programmed (not shown in Figure 2) to disconnect the relay coil (1l) when Vac-Vdc becomes smaller than the predetermined value V+. and the contact (Il
al is closed. Here, set the predetermined value V1 to the relay contact (
By setting the straightness to be smaller than the value determined by the product of the maximum switching current of lla) and the impedance of the power supply,
The inrush current 7J when the relay contact [1) a) is closed can be made smaller than the maximum switching current of the relay contact (l lal). Since flat is operated, Vac-Vdc
is a constant value regardless of the power supply voltage and is not affected by the power supply voltage.

Next, a case will be described in which a voltage drop occurs during inverter operation.

First, if the voltage drop is significant, Vac
becomes larger than the specified {IQ', Vz, and the relay coil (II) is deenergized, so the operation is the same as when the power is turned on for the first time, and the inrush current 1, is smaller than the maximum switching current of the relay. Become.

Next, due to a momentary power outage, etc., the voltage may drop during inverter operation. If it is emitted at a time of 0, the microcomputer (26
) does not reach the predetermined value v2, the relay coil (1.1) maintains the energized state, and if the power returns at this time, i 2 = (Vac-Vdc) An inrush current 12 determined by =('l?fi original in-eventance) flows. Therefore, when Vac-Vdc=V2, the rush current i2 becomes maximum. Here, the predetermined value\
By setting ゛2 to {ρ, which is smaller than {Ii′i} determined by the product of the permissible surge current of the rush current circuit (3) and the impedance of the power supply, the inrush current! Vocal flow circuit (3
) destroys l! I can do it. Also, when the relay contact (llal is closed, the relay contact (l
Since the allowable surge current of la) is larger than the allowable surge current of the cram school circuit (3), there is no risk of failure such as welding occurring at the relay ↑a point (lla). Also,? The allowable surge 'itlt current of the IC current circuit (3) is determined by the relay contact fl
la) maximum opening/closing 71) Since it is larger than the flow, the predetermined value ■
1 can be made smaller than the predetermined value ■2. As a result, once the relay contact (Llal is closed, there will be some voltage fluctuation, and the relay coil (l1
) is maintained at A-1, and the relay contact FLAL never opens, so the operation is stable.

The upward tracing operation is shown in FIG.

4 and 5 do not show other embodiments of this invention.
FIG. 4 shows flowchart 1 showing the relay control means.
FIG. 5 is an explanatory diagram of the operation. Note that FIG. 1 is also used for tlH in this embodiment.

In step (3l), it is determined whether the relay coil Jre (l1) is energized, and if it is energized, the relay coil Jre (l1) is energized.
Proceed to 2), and if it is deactivated, proceed to Sudep (33). In step (33), the difference between voltage Vac and voltage Vdc is 1.
ft constant ftl'l: When it becomes smaller than V + , a timer is started in step (36). In other cases, proceed to step (37). In step (32), if the difference between the voltage Vac and the voltage Vdc is smaller than the predetermined value {1^■2, the process proceeds to step (37); otherwise, the process proceeds to step [35H, where the relay coil (kl) is deenergized. .

In step (37), the count time of the timer and the predetermined time t1 are compared, and if the count time of the timer exceeds the predetermined time, then in step (3ξ) the relay coin (l1
) and stop the timer in step (39).

That is, after the power is turned on and V ac - V dc becomes smaller than the predetermined value, the relay contact (lla) is energized with a delay of time L1.
Inrush current 1) is further reduced, further improving reliability.

The above p operation is shown in FIG.

In each of the above embodiments, a microcomputer (26) is used, but this can also be easily realized using a differential amplifier or the like.

Further, although the rectifier circuit (3) as a DC power source is a three-phase full-wave rectifier circuit, it is also applicable to a single-phase full-wave rectifier circuit or other DC power sources.

[Effects of the Invention] As explained hereafter, in the first aspect of the present invention, the opening and closing of the relay contact is controlled by the difference between the voltage of the AC power supply and the charging voltage of the smoothing capacitor, so that fluctuations in the power supply voltage are avoided. Even if there is, the difference between the voltage of the AC power supply and the charging voltage will always be constant, reducing inrush current, preventing welding of relay contacts and destruction of the rectifier circuit, and improving reliability. .

In addition, in the second aspect of the present invention, the predetermined value at which the relay contact opens is set larger than the predetermined value at which the relay contact closes, so that once the relay contact is closed, the power supply voltage may fluctuate to some extent. Even if there is, the relay contact will not open,
This has the effect of stabilizing the operation of the device.

Further, in the third aspect of the present invention, when the relay contact is open, the relay contact is closed after a predetermined time delay after the voltage difference reaches a predetermined value, so that the current flowing through the relay contact is further reduced, which has the effect of further improving reliability.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing an embodiment of the inrush current limiting device for a DC power supply according to the present invention, in which Figure 1 is a circuit diagram, Figure 2 is a flowchart showing the operation of the relay control means, and Figure 3 is a flow chart showing the operation of the relay control means. 4 and 5 are diagrams showing other embodiments of the present invention, FIG. 4 is a circuit diagram, and FIG. 5 is a flowchart showing the operation of the relay control means. Figure 7 is a diagram showing a conventional inrush current limiting device for a DC power supply.
The figure is a circuit diagram, and FIG. 7 is an operation explanatory diagram. In the figure, (1) is a three-phase AC power supply, (3) is a rectifier circuit, (
4) is a flat Wt capacitor, (5) is an inrush current suppression resistor,
(1)) is a relay, fla) is a relay contact, (22)
is the input voltage detection circuit. (231 is a charging voltage detection circuit, and (26) is a microcomputer. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A smoothing capacitor is connected to the DC side of a rectifier circuit connected to an AC power source, and the circuit is opened and closed between the rectifier circuit and the smoothing capacitor based on the voltage difference between the voltage of the AC power source and the voltage of the smoothing capacitor. An inrush current suppression resistor having relay contacts connected in parallel is inserted, and an input voltage detection circuit for detecting the voltage of the AC power supply and a charging voltage detection circuit for detecting the charging voltage of the smoothing capacitor are provided, A DC power supply characterized by comprising a relay control means for controlling opening/closing of the relay contact by comparing the difference between the voltage detected by the input voltage detection circuit and the voltage detected by the charging voltage detection circuit with a predetermined value. Inrush current limiting device. (2) The inrush current limiting device for a DC power supply according to claim 1, wherein among the predetermined values of the voltage difference, the predetermined value at which the relay contact opens is set to be larger than the predetermined value at which the relay contact closes. (3) Claims 1 or 2 further include a time delay means for closing the relay contact after a predetermined time delay after the voltage difference reaches a predetermined value when the relay contact is open.
Inrush current limiting device for DC power supply as described in .