JP2000059988A - Rush current preventive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rush current preventive circuit which can securely avoid a rush current exceeding the strength of a rectifying device when a power supply is closed and, further, can turn on a switching means in a shortest time. SOLUTION: A rush current preventive circuit has a parallel circuit which is composed of a rush current preventive resistor 9 and a thyristor 10 and connected between rectifying diodes 2-7 and a smoothing capacitor 8. Further, a sampling circuit 21 which detects the voltages of the smoothing capacitor 8 periodically with a certain time interval and outputs the sampling signals of the detected voltages periodically with a certain time interval, a differential voltage calculation circuit 22 which calculates the differential voltages of the sampling signals which are outputted from the sampling circuit 21 successively, a reference power supply 23 which generates a reference voltage VR2 which defines the reference value of the differential voltage and a comparison circuit 24 which compares the voltage of the output signal of the differential voltage calculation circuit 22 with the reference voltage VR2 of the reference power supply 23 and, if the voltage of the output signal of the differential voltage calculation circuit 22 is lower than the reference voltage VR2 of the reference power supply 23, turns on the thyristor 10 which is in an off-state, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current prevention circuit for preventing an inrush current flowing when a power is turned on, and more particularly to an inrush current exceeding a rectifying element withstand capability when the power is turned on. The present invention relates to an inrush current prevention circuit that can be turned on.

[0002]

2. Description of the Related Art A so-called capacitor input which is composed of a rectifying diode as a rectifying element and a smoothing capacitor and is connected to a DC power supply for generating a bipolar DC voltage used as an AC power supply such as a commercial power supply or a communication power supply. In the type rectifier circuit, when the power is turned on, an inrush current exceeding the rectifier diode's withstand current flows, and the rectifier diode may be damaged. Therefore, in order to prevent an inrush current flowing when the power is turned on, a rush current prevention resistor connected between at least one rectifier diode and a smoothing capacitor constituting a rectifier circuit, and a rush current prevention resistor connected in parallel with the rush current prevention resistor An inrush current prevention circuit is generally provided which includes a switching means such as an electromagnetic relay or a thyristor which is turned on and turned off when the voltage of the smoothing capacitor becomes a steady state. A broken line portion A in FIG. 3 shows a general inrush current prevention circuit incorporated in a capacitor input type rectifier circuit connected to a three-phase AC power supply.
A rush current prevention resistor 9 connected between the rectifier diodes 2 to 7 and the smoothing capacitor 8; a thyristor 10 as a switch connected in parallel with the rush current prevention resistor 9; And a control circuit 11 for outputting an ON signal to the thyristor 10 when the voltage V _C becomes sufficiently high to reach a steady state. The control circuit 11 compares the reference power supply 12 which generates a reference voltage V _R1 for defining the reference value of the voltage V _C of the smoothing capacitor 8, and a reference voltage V _R1 of the voltage V _C and the reference power source 12 of the smoothing capacitor 8 The voltage V _C of the smoothing capacitor 8 is equal to the reference voltage V _{R1 of the} reference power supply 12.
Comparator 1 that outputs _ON signal V _ON when it exceeds
3 and the comparator 13 after a lapse of a preset time.
And a timer circuit 14 for outputting an _ON signal V _ON from the CPU. A load 15 such as an inverter or a DC-DC converter is connected to both ends of the smoothing capacitor 8.

[0003]

By the way, in the conventional inrush current prevention circuit shown in FIG. 3, when the voltage of the three-phase AC power supply 1 is abnormally high, the smoothing capacitor 8 is almost simultaneously supplied with the power supply.
Voltage V _C exceeds the reference voltage V _R1 of the reference power supply 12, and the thyristor 10 is turned on.
There is a possibility that an inrush current exceeding the withstand current will flow in any of 7 to ７7. Also, even if the voltage of the three-phase AC power supply 1 is normal, if the capacity of the smoothing capacitor 8 is sufficiently large,
When the power is turned on, an inrush current exceeding the withstand capability of each of the rectifier diodes 2 to 7 may flow with an increase in the time constant of the inrush current prevention resistor 9 and the smoothing capacitor 8. Therefore, there is a disadvantage that inrush current exceeding the withstand capability of each of the rectifier diodes 2 to 7 cannot be reliably prevented when the power is turned on.
In addition, since the thyristor 10 is turned on after the set time of the timer circuit 14 from the output of the on signal V _ON from the comparator 13, the voltage V _C of the smoothing capacitor 8 becomes sufficiently high before the set time of the timer circuit 14. In other words, the thyristor 10 cannot be turned on even in the steady state. As a result, there is a drawback that an output current flows through the rush current prevention resistor 9 and power loss occurs.

Accordingly, an object of the present invention is to provide a rush current prevention circuit which can surely prevent a rush current exceeding the withstand capability of a rectifier element when power is turned on, and can turn on a switch means in a shortest time.

[0005]

According to the present invention, there is provided an inrush current prevention circuit comprising: a rush current prevention resistor connected between at least one rectifier element constituting a rectifier circuit and a smoothing capacitor; A switch connected in parallel with the resistor and turned on from the off state when the voltage of the smoothing capacitor becomes a steady state. In this rush current prevention circuit, a difference voltage detecting means for detecting a difference voltage between a voltage of the smoothing capacitor at a certain time and a voltage of the smoothing capacitor after a lapse of a predetermined time from the time, and a reference value of the difference voltage. A reference voltage generating means for generating a prescribed reference voltage; comparing a reference voltage of the reference voltage generating means with a voltage of a detection signal of the difference voltage detecting means; Comparing means for switching the switch means from the off state to the on state when the voltage becomes equal to or lower than the reference voltage of the voltage generating means.
When the power is turned on, the difference voltage between the voltage of the smoothing capacitor at a certain time detected by the difference voltage detecting means and the voltage of the smoothing capacitor after a certain time has elapsed from the certain time is higher than the reference voltage of the reference voltage generating means. Since it is large, nothing is output from the comparing means, and the switching means keeps the off state. As a result, all the inrush currents that occur when the power is turned on are suppressed by the inrush current prevention resistor.
Inrush current exceeding the withstand capability of the rectifier can be reliably prevented.
Further, after the power is turned on, the difference voltage detected by the difference voltage detecting means decreases with the passage of time, and when the voltage of the smoothing capacitor becomes a steady state, the difference voltage falls below the reference voltage of the reference voltage generating means. Then, the switch means is turned on from the off state by the output signal of the comparison means. Thereby, since the voltage of the smoothing capacitor becomes a steady state and the switch means is turned on from the off state at the same time,
The switching element can be turned on in the shortest time.

In one embodiment of the present invention, the difference voltage detecting means detects a voltage of the smoothing capacitor at regular intervals and outputs a sampling signal of the detected voltage at regular intervals, and the sampling means. And a difference voltage calculating means for calculating a difference voltage of the sampled signal output at regular intervals from the sampling signal. In this case, the voltage of the smoothing capacitor is sampled (sampled) at a fixed time interval by the sampling means, and the difference voltage of these sampled signals is calculated by the difference voltage calculating means. There is an advantage that the difference voltage from the voltage of the smoothing capacitor after a certain time has elapsed from a certain time can be detected more accurately. Further, in the embodiment of the present invention, the comparison means includes a subtraction circuit for calculating a difference between a reference voltage of the reference voltage generation means and a voltage of a detection signal of the difference voltage detection means, and a sign of an output signal of the subtraction circuit. And a positive / negative determination circuit for outputting an ON signal to the switch means when the output signal is a positive value. In this case, the difference between the reference voltage of the reference voltage generation means and the voltage of the detection signal of the difference voltage detection means is calculated by the subtraction circuit, and the sign of the difference signal is discriminated by the sign judgment circuit. Since the on signal is output to the means, even when the difference between the reference voltage of the reference voltage generating means and the voltage of the detection signal of the difference voltage detecting means is extremely small, the switch means can be accurately switched from the off state to the on state. There are advantages.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Inrush current prevention according to the present invention will now be described.
One embodiment of the circuit will be described with reference to FIG. However,
In FIG. 1, the same parts as those shown in FIG.
The reference numerals are used and the description is omitted. Inrush power of this embodiment
The flow prevention circuit is shown in FIG.
Control circuit 11 at a certain time t_n(N = 1, 2, 3,
..))_CnAnd one time
Time t_nAfter a certain time (several hundred μsec to several msec)
The voltage V of the smoothing capacitor 8_{Cn + 1}And the difference voltage V_{Cn + 1}-V_Cn=
ΔV_nVoltage detection circuit as the differential voltage detection means for detecting
Path 20 and differential voltage ΔV₁, ΔV_Two, ΔV_Three,···Standards of
Reference voltage V that defines the value_R2Reference voltage generating means for generating
Power supply 23 as a reference and reference voltage V of reference power supply 23_R2
And the difference voltage ΔV of the difference voltage detection circuit 20₁, ΔV_Two, ΔV_Three,
.. And the difference voltage ΔV of the difference voltage detection circuit 20.
₁, ΔV_Two, ΔV_Three,... Represent the reference voltage V of the reference power supply 23.
_R2Thyristor 10 is turned on from off state when
And a comparison circuit 24 as comparison means for setting a state.
The control circuit 27 has been changed. Difference in this embodiment
The voltage detection circuit 20 detects the voltage V of the smoothing capacitor 8._COne
Detect at regular time intervals (several hundred μsec to several msec) and detect
Voltage V_C1, V_C2, V_C3, V_C4, ... sampling signal
V_S1, V_S2, V_S3, V _S4, ... are output at regular intervals
A sampling circuit 21 as a sampling means,
Sample output from the sampling circuit 21 at regular intervals
Signal V_S1, V _S2, V_S3, V_S4,... Difference voltage ΔV₁
= V_S2-V_S1, ΔV_Two= V_S3-V_S2, ΔV _Three= V_S4−
V_S3,... For calculating the differential voltage
And an arithmetic circuit 22. In addition, the comparison circuit 24
Reference voltage V of source 23_R2And the difference voltage Δ of the difference voltage calculation circuit 22
V₁, ΔV_Two, ΔV_Three, And the difference V_R2-ΔV₁, V_R2−
ΔV_Two, V_R2-ΔV_Three,.
And the output signal V of the subtraction circuit 25_{D F1}, V_DF2, V_DF3,
.. Judgment of positive / negative and output signal V_DFn(N = 1, 2,
3) are positive values, the thyristor 10
ON signal V_ONPositive / negative judgment circuit 26 that outputs
Consisting of Also, the reference voltage V of the reference power supply 23_R2Is the allowable
Source voltage range, minimum source impedance, rectifier diode
2-7, internal resistance of smoothing capacitor 8, sampler
Sampling interval (several hundred μsec to several mse
Determined from c). Other circuit configurations are indicated by broken lines in FIG.
This is the same as the inrush current prevention circuit shown in the section A.

In the above configuration, the smoothing capacitor 8
Voltage V_CIs the sampling circuit 2 in the difference voltage detection circuit 20.
Samples at fixed time intervals (several hundred μsec to several msec) by 1
And the voltage V of the smoothing capacitor 8 at certain time intervals._C
Sampled signal V_S1, V_S2, V_{S Three}, V_S4, ... appear sequentially
Is forced. These sampled signals V_S1, V_S2, V_S3,
V_{S Four},... Are sequentially input to the difference voltage calculation circuit 22,
The sampling signal V previously captured by the voltage calculation circuit 22
_S1, V_S2, V_S3, ... and the sampled signal captured this time
V_S2, V_S3, V_S4, And the difference voltage ΔV₁= V_S2-V
_S1, ΔV_Two= V_S3-V _S2, ΔV_Three= V_S4-V_S3,···But
Is calculated. When the three-phase AC power supply 1 is turned on,
A large inrush current occurs, and both ends of the smoothing capacitor 8
Voltage applied to_CRises rapidly with a pulse width of several tens of milliseconds
Therefore, the difference voltage output first from the difference voltage calculation circuit 22
Pressure ΔV₁Is the reference voltage V of the reference power supply 23_R2Greater than
Becomes Reference voltage V of reference power supply 23_R2And differential voltage calculation times
Differential voltage ΔV first output from the path 22₁Is the comparison circuit
24, each of which is input to a subtraction circuit 25,
5 to reference voltage V_R2And the first difference voltage ΔV₁Difference V_R2−
ΔV₁= V_DF1Is output. At this time, V_R2<ΔV₁so
Therefore, the output signal V of the subtraction circuit 25_DF1Is negative
Nothing is output from the positive / negative discriminating circuit 26. But
Therefore, since the thyristor 10 keeps the off state,
All inrush currents generated when the AC power supply 1 is turned on
Each rectifier diode is suppressed by the input current prevention resistor 9.
No more current than the withstand current flows through 2-7.

After the three-phase AC power supply 1 is turned on,
The charging voltage V of the smoothing capacitor 8_CRises and smoothes
When the current flowing into the capacitor 8 gradually decreases,
Voltage V of capacitor 8_CChanges slowly over time
Cana, ΔV₁Thereafter, the output from the difference voltage calculation circuit 22 is output.
Difference voltage ΔV_Two, ΔV_Three, ... are small over time
It will be cheap. Then, the voltage V of the smoothing capacitor 8_CIs steady
State. At this time, the output
Difference voltage ΔV_ThreeIs the reference voltage V of the reference power supply 23_R2Less than
(Ie, V_R2≧ ΔV_Three), The reduction in the comparison circuit 24
Reference voltage V output from arithmetic circuit 25_R2And the difference voltage ΔV_Three
Difference signal V_R2-ΔV_Three= V_DF3Is positive. This and
From the positive / negative determination circuit 26 to the gate terminal of the thyristor 10
ON signal V _ONAnd the thyristor 10 is turned off.
The rectifier diode is turned on from
Smoothing capacitors 8 through 2 through 7 through thyristor 10
And an output current flows through the load 15.

[0010] In the inrush current preventing circuit of this embodiment, it is output since the three-phase AC voltage V _C across the smoothing capacitor 8 during power cycle 1 increases rapidly, from the difference voltage calculation circuit 22 to the first The difference voltage ΔV ₁ is equal to the reference power 23
Becomes a value larger than the reference voltage V _R2, the value of the output signal V _DF1 of the subtraction circuit 25 in the comparison circuit 24 becomes negative. At this time, nothing is output from the positive / negative discriminating circuit 26 in the comparing circuit 24, and the thyristor 10 holds the off state. Therefore, the inrush current generated when the three-phase AC power supply 1 is turned on is all suppressed by the inrush current prevention resistor 9, so that the inrush current exceeding the withstand capability of each of the rectifier diodes 2 to 7 can be surely prevented. Moreover, since the later-on the three-phase AC power supply 1 is the change in voltage V _C of the smoothing capacitor 8 over time is moderate, the difference voltage [Delta] V ₂ sequentially outputted from the difference voltage calculation circuit 22 to [Delta] V ₁ after, [Delta] V ₃ becomes smaller over time. When the voltage V _C of the smoothing capacitor 8 is in a steady state and the difference voltage ΔV ₃ becomes equal to or lower than the reference voltage V _R2 of the reference power supply 23 at the time when the difference voltage ΔV ₃ is output from the difference voltage calculation circuit 22, The value of the output signal _VDF3 of the subtraction circuit 25 is positive. At this time, the ON signal V _ON is sent from the positive / negative determination circuit 26 to the gate terminal of the thyristor 10.
, And the thyristor 10 changes from the off state to the on state. Therefore, the thyristor 10 changes from the off state to the on state at the same time that the voltage V _C of the smoothing capacitor 8 reaches the steady state, so that the thyristor 10 can be turned on in the shortest time. In particular, in the present embodiment, the sampling circuit 21 samples the voltage V _C of the smoothing capacitor 8 at fixed time intervals (several hundred μsec to several msec), and these sampled signals V _S1 , V _S2 , V _S3 , V _S The difference voltages ΔV ₁ , ΔV ₂ , ΔV ₃ ,... Of _S4 ,.
2 so that a certain time t _n (n = 1, 2,
3, the difference voltage [Delta] V _n between the voltage V _{Cn + 1} of the voltage V _Cn and certain time t _n from a certain time (hundreds μsec~ number msec) after the lapse of the smoothing capacitor 8 of the smoothing capacitor 8 in.) There is an advantage that it can be detected accurately. Further, the subtraction circuit 25 in the comparison circuit 24 calculates the difference between the reference voltage V _R2 of the reference power supply 23 and the difference voltages ΔV ₁ , ΔV ₂ , ΔV ₃ ,. 26 determines whether the output signal V _DFn of the subtraction circuit 25 is positive or negative and outputs an _ON signal V _ON to the thyristor 10 when the output signal V _DFn has a positive value.
Differential voltage between the third reference voltage V _R2 and a differential voltage computation circuit 22 delta
There is an advantage that the thyristor 10 can be accurately turned from the off state to the on state even when the difference between V ₁ , ΔV ₂ , ΔV ₃ ,.

The embodiments of the present invention are not limited to the above embodiments, and various modifications are possible. For example, in the above embodiment, the smoothing capacitor 8 is
Of the voltage V _C is sampled at regular time intervals (hundreds μsec~ number msec), these sampled signals _{V S1, V S2, V S3} ,
The difference voltage ΔV ₁ , ΔV ₂ , ΔV ₃ ,... Of V _S4 ,... Is calculated by the difference voltage calculation circuit 22, but at a certain time t _n (n = 1, 2, 3,. ..) And the voltage V _Cn of the smoothing capacitor 8 after a certain time (several hundred μsec to several msec) from a certain time t _n.
The difference voltage V _{Cn +1} −V _Cn = ΔV _n from _{Cn + 1} may be directly detected. In the above embodiment, the comparison circuit 24 is constituted by the subtraction circuit 25 and the positive / negative discrimination circuit 26. However, as shown in FIG. 2, the reference power supply 23 inputted to the non-inverting input (+) terminal is used. The reference voltage V _R2 and the difference voltages ΔV ₁ , ΔV of the difference voltage calculation circuit 22 input to the inverted input (−) terminal
, V ₂ , ΔV ₃ ,.
, The difference voltages ΔV ₁ , ΔV ₂ , ΔV ₃ ,.
The comparison circuit 24 may be composed of a comparator 28 that outputs a high-level signal V _H (ON signal V _ON ) to the gate terminal of the thyristor 10 when the reference voltage V _R2 becomes equal to or lower than the reference voltage V _R2 . Further, in each of the above embodiments, a mode in which a thyristor is used as the switch means has been described. However, an electromagnetic relay, a power transistor having a high withstand voltage, or the like may be used.
Further, in each of the above embodiments, the form in which the inrush current prevention circuit of the present invention is incorporated in the capacitor input type rectifier circuit connected to the three-phase AC power supply is shown. It is also possible to incorporate the inrush current prevention circuit of the present invention into a capacitor input type rectifier circuit connected to a DC power supply that generates a bipolar DC voltage used as another AC power supply such as a power supply or a communication power supply. Needless to say, there is.

[0012]

According to the present invention, it is possible to reliably prevent an inrush current exceeding the withstand capability of the rectifier element when the power is turned on, so that it is possible to prevent damage to the rectifier element due to the inrush current when the power is turned on. Become. Further, since the switching means can be turned on at the same time when the voltage of the smoothing capacitor becomes steady, the output current does not flow through the inrush current prevention resistor when the voltage of the smoothing capacitor is steady, and the power loss caused by the inrush current is substantially zero. It becomes possible to.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of an inrush current prevention circuit according to the present invention.

FIG. 2 is an electric circuit diagram showing a modified embodiment of FIG. 1;

FIG. 3 is an electric circuit diagram showing a conventional inrush current prevention circuit.

[Explanation of symbols]

1. . . Three-phase AC power supply, 2-7. . . Rectifier diode (rectifier element), 8. . . 8. smoothing capacitor; . . 10. Inrush current prevention resistor; . . 10. thyristor (switch means), . . Control circuit, 12. . . Reference power supply, 1
3. . . Comparator, 14. . . Timer circuit, 1
5. . . Load, 20. . . 21. difference voltage detection circuit (difference voltage detection means); . . 21. sampling circuit (sampling means); . . Difference voltage calculation circuit (difference voltage calculation means),
23. . . 13. reference power supply (reference voltage generating means); . .
25. a comparing circuit (comparing means); . . Subtraction circuit, 2
6. . . Positive / negative determination circuit, 27. . . Control circuit, 2
8. . . comparator

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (3)

[Claims] An inrush current preventing resistor connected between at least one rectifying element forming a rectifying circuit and a smoothing capacitor, and a voltage of the smoothing capacitor connected in parallel with the inrush current preventing resistor. A rush current prevention circuit comprising: a switching unit that changes from an off state to an on state when a steady state is reached, wherein a voltage of the smoothing capacitor at a certain time and a voltage of the smoothing capacitor after a lapse of a predetermined time from the time are determined. Difference voltage detecting means for detecting a difference voltage, reference voltage generating means for generating a reference voltage for defining a reference value of the difference voltage, a reference voltage of the reference voltage generating means, and a voltage of a detection signal of the difference voltage detecting means. And when the voltage of the detection signal of the difference voltage detection means is lower than or equal to the reference voltage of the reference voltage generation means, the switch means is turned on from the off state. Rush current prevention circuit comprising the comparing means for the. 2. The method according to claim 1, wherein the difference voltage detecting means detects a voltage of the smoothing capacitor at regular intervals and outputs a sampling signal of the detected voltage at regular intervals. 2. A rush current prevention circuit according to claim 1, further comprising: a difference voltage calculating means for calculating a difference voltage of the sampled signal output to said sampling signal. 3. The subtraction circuit for calculating a difference between a reference voltage of the reference voltage generation means and a voltage of a detection signal of the difference voltage detection means, and determines whether the output signal of the subtraction circuit is positive or negative. 3. The inrush current prevention circuit according to claim 1, further comprising a positive / negative determination circuit that outputs an ON signal to said switch means when said output signal has a positive value.