JPS6381279A - Preventive maintenance system for smoothing capacitor - Google Patents

Abstract

PURPOSE:To obtain a preventive maintenance system for a smoothing capacitor which enables proper and economical component replacement by monitoring the ripple current or voltage of the smoothing capacitor and detecting its variation, and easily discriminating the deterioration of the capacitor in an operating state. CONSTITUTION:The ripple current DELTAIC of the smoothing capacitor 24 is detected by a current detector 28 and inputs a comparator COMP1 where the ripple current set value DELTAIC* of a normal capacitor 24 based on a load current I0 is determined to compare the set value DELTAIC* with the current DELTAIC, thereby outputting a warning output signal SA when a deviation larger than a specific value is generated. Consequently, the deterioration of the smoothing capacitor 24 is accurately detected while the capacitor is in the operating state without working the capacitor specially, complicate trouble such as predictive component replacement is not necessary, and deterioration discrimination and component replacement are carried out economically and efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a preventive maintenance system for a smoothing capacitor used in a smoothing circuit in a power supply device configured to rectify alternating current voltage to obtain direct current voltage.

[Conventional technology]

Generally, when configuring a power supply circuit that converts an alternating current voltage to a direct current voltage, a choke coil or a capacitor is used to smooth the direct current output voltage. In this case, the capacitor is required to have a large capacity, and an electrolytic capacitor is usually used.

In addition, as a stabilized power supply device, it is possible to downsize the device and reduce loss when controlling the output voltage.
Switching regulators that control output voltage by turning on and off DC voltage have become widespread.

This switching regulator generally includes a DC-DC converter that converts a DC input voltage into an AC voltage, transforms the voltage to an arbitrary voltage, and then rectifies the voltage to obtain a DC output voltage. Even in a switching regulator configured in this manner, an electrolytic capacitor is used, which is inexpensive and has a large capacity, in order to smooth the DC output.

As described above, the reliability of today's stabilized power supplies, as typified by switching regulators, has improved, but on the other hand, electrolytic capacitors still undergo chemical changes and are difficult to avoid deteriorating over time. There is an inconvenience that it cannot be replaced and must be replaced periodically according to its lifespan.

Generally, it is known that the deterioration state of a capacitor appears as an increase in dielectric loss tangent (tan δ), equilateral series resistance (ESR), or leakage current as the capacitance decreases over time. However, in order to detect these deterioration characteristics of a capacitor, it is necessary to remove the capacitor from the circuit and measure each capacitor individually, which not only requires a lot of effort and time, but also requires the circuit operation to be temporarily stopped. There is this inconvenience.

From this point of view, the conventional means of detecting the deterioration state of this type of capacitor is to detect the heat generated by the increase in internal loss of the capacitor and the accompanying mechanical deformation of the internal mechanism or exterior body of the capacitor. Various protection methods have been proposed in which a dangerous condition leading to deterioration and damage of a capacitor is detected in advance and safety operations such as cutting off the circuit are performed (for example, Japanese Patent Laid-Open No. 57-9226, Japanese Patent Laid-Open No. 59-1999) 89521).

[Problem that the invention seeks to solve]

The conventional deterioration detection method for capacitors described above detects overheating of the capacitor and deformation of the capacitor's constituent parts, so the deterioration of the capacitor has progressed considerably, and during this time the electrical characteristics of the capacitor are extremely affected. The situation is getting worse, and the negative impact on highly reliable power supply circuits is extremely large.

Therefore, the present inventors focused on the fact that the capacitor's equilateral array resistance increases as the electrolytic capacitor deteriorates, and as a result of extensive research, the ripples obtained by rectifying the AC voltage or pulse voltage were In a power supply device configured to supply a smoothed DC voltage to a load via a smoothing circuit consisting of a coil and a capacitor,
When we measured the changes in the ripple current in the coil and the ripple current in the capacitor with respect to changes in the load current when normal crystals and degraded capacitors were used as the capacitors in the smoothing circuit, we found that there was almost no difference in the ripple current in the coil. No change was observed, and it was found that when a deteriorated capacitor ripple current was used, the ripple current of the capacitor significantly decreased as the load current increased. In other words, deterioration of a capacitor is detected by detecting a drop in the ripple current of the capacitor using a pickup coil, etc., thereby appropriately determining the state of deterioration of the capacitor's electrical characteristics and easily detecting its lifespan during circuit operation. It turns out that it is possible. Furthermore, this can be interpreted as an increase in ripple voltage due to an increase in the equilateral array resistance of the capacitor.

Therefore, it is an object of the present invention to monitor the ripple current or voltage of a smoothing capacitor and detect its changes, thereby easily determining the deterioration of the capacitor while it is in operation, thereby allowing appropriate and economical parts replacement. The purpose of the present invention is to provide a preventive maintenance system for smoothing capacitors that can perform the following steps.

[Means for solving problems]

The preventive maintenance system for smoothing capacitors according to the present invention includes:
In a power supply circuit configured such that a DC voltage including a ripple component obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing capacitor, and the smoothed voltage is supplied to a load, the smoothing capacitor Detect the ripple current or voltage at
The deterioration state of the smoothing capacitor is determined when the deviation obtained by this comparison reaches a predetermined level,
The present invention is characterized in that the smoothing capacitor is configured to be replaceable within an allowable state of deterioration of the smoothing capacitor.

In the above-mentioned preventive maintenance system for smoothing capacitors,
An inductance element is provided in the smoothing circuit, and the ripple current flowing through this element is detected, and the ripple current flowing through the smoothing capacitor is also detected, and the value of the ripple current of the inductance element is used as a reference value, and the ripple current of the smoothing capacitor is calculated using the ripple current value of the inductance element as a reference value. It can also be configured to compare with the current value.

[Effect]

According to the preventive maintenance system for a smoothing capacitor according to the present invention, when a DC voltage including a ripple obtained by rectifying an AC voltage is smoothed and supplied to a load via the smoothing capacitor, the By constantly monitoring the ripple current flowing through the smoothing capacitor or its ripple voltage by detecting it with a current or voltage detector installed so as not to affect the circuit, it can be detected as the smoothing capacitor deteriorates. , compared to a normal smoothing capacitor, the ripple current value gradually decreases or the ripple voltage value gradually increases, so by electrically determining this condition, the smoothing capacitor can be kept in its used state. It is possible to achieve proper life detection and realize proper and economical preventive maintenance of capacitors.

In this case, an inductance element is provided along with the smoothing capacitor, the ripple current flowing through this element is detected, this is used as a reference value, and the deterioration state of the smoothing capacitor can be determined by comparing it with the ripple current of the smoothing capacitor. Electrical discrimination accuracy can be improved.

〔Example〕

Next, embodiments of the preventive maintenance system for smoothing capacitors according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a typical circuit configuration of a switching regulator implementing a preventive maintenance system for smoothing capacitors according to the present invention. That is, in FIG. 1, reference numeral 10 is a DC power supply, 12 is a voltage transformer, 14 is a switching element, 16, 18, and 20 are diodes,
22 is a smoothing coil, 24 is a smoothing capacitor, and 26 is a load, which is configured as a forward type converter. The switching regulator configured in this manner obtains a pulse voltage from the DC voltage Ei supplied by the DC power supply 10 through the switching element 14, converts this pulse voltage into a predetermined voltage value via the transformer 12, and further converts this pulse voltage into a predetermined voltage value through the transformer 12. Pulse voltage to diode 18.2
The signal is rectified by 0, smoothed by the smoothing coil 22 and smoothing capacitor 24, and supplied to the load 26.

Therefore, in the present invention, in the power supply circuit having the above configuration, the smoothing capacitor 24 and the smoothing coil 2
2, a current detector 28 consisting of a pink-up coil or the like for detecting the ripple current flowing individually.
．． 30 will be provided. In this case, in the circuit shown in FIG. 1, equivalent circuits when the switching element 14 is in an on state and an off state are shown in FIGS. 2 and 3. The contents of each element in FIGS. 2 and 3 are as follows.

Ei: Input voltage Eo: Output voltage C: Capacitance of smoothing capacitor 24: Inductance RL of smoothing coil 22: Load resistance VO2: Forward equivalent voltage source of diode 18 VD3:
Forward equivalent voltage source r1 of diode 20: Input power supply 1
0 internal resistance, the on-state resistance of the switching element 14, and the primary winding resistance of the transformer 12, r2: the internal resistance of the diode 18, the winding resistance of the coil 22, and the secondary winding of the transformer 12. Sum of resistance r: Sum of internal resistance of diode 20 and winding resistance of coil 22 rc: Equivalent series resistance (ESR) of smoothing capacitor 24 ■L: Average value of current flowing through smoothing coil 22 ■. : Load current average value ΔI, : Ripple current of smoothing coil 22 Δ■c:
Ripple current of the smoothing capacitor 24 Therefore, in the circuit configuration described above, the smoothing capacitor 24 has a normal product with a capacitance of 441.2 μF and an ESR of 108, 5 mΩ, and a capacitor with a capacitance of ff 1345.7 /, IF, ESR 996, 3 mΩ.
For a deteriorated product, the ripple current Δ■ of the smoothing coil 22 and the smoothing capacitor 24 with respect to the load current ■o
2. As a result of measuring ΔI(,), the characteristics shown in Fig. 4 (normal product) and Fig. 5 (deteriorated product) were obtained. Almost no change was observed in the ripple current ΔIL of the smoothing capacitor 22, but a remarkable change was observed in the ripple current Δ■c of the smoothing capacitor 24.In addition, in FIGS. 4 and 5, The characteristic curves shown by solid lines are based on calculated values based on the equivalent circuits shown in FIGS. 2 and 3. Furthermore, the characteristic curves shown in FIGS. However, it was confirmed that a similar characteristic curve can be obtained even when feedback is applied.

In addition, in the present invention, the difference between the ripple current ΔI2 of the smoothing coil 22 and the ripple current Δ1 of the smoothing capacitor 24 detected by the circuit shown in FIG.
In other words, take the output ripple current and calculate γ=(Δr1..-
By finding a dimensionless quantity (referred to as an output ripple coefficient) defined by ΔIc)/■o, it is possible to determine the degree of ESR with almost no influence from the load. Therefore, the γ vs. IO characteristic in this case is as shown in FIG. That is, as is clear from Fig. 6, when the load current is 10 = 3A, γ = 0.8% for a normal product, but γ = 6% for a deteriorated product, and the smoothing capacitor The state of deterioration can be sufficiently determined.

Based on the above-mentioned preventive maintenance system of the present invention, the ripple current characteristic (Δ ■c vs. IQ
This can be easily realized by setting the output ripple coefficient characteristic (T vs. IQ characteristic) or the load current characteristic and comparing the set value with the detected value of the actual circuit state.

In this case, the load current can be easily detected using a known instrument current transformer or the like.

FIG. 7 shows the smoothing capacitor 24 by the current detector 28.
The ripple current ΔIc is detected, and this ripple current ΔIc is detected.
■c is the load current! A comparator COMP that determines the ripple current setting value Δ■go8 of a normal smoothing capacitor based on 0.
1, the ripple current set value Δ■c8 and each detected ripple current value Δ■ are compared, and if a deviation of more than a predetermined value occurs, an alarm output signal S^ is output. In this case, smoothing capacitor 2
The ripple voltage ΔE (H) of 4 is detected, and this ripple voltage ΔEC is used to determine the ripple voltage set value ΔEcI7 of a normal smoothing capacitor based on the load current factor, and is input to the ratio layer to set the ripple voltage set value ΔE to 8. The ripple voltage detection value ΔEC may be compared with the ripple voltage detection value ΔEC, and an alarm output signal may be output when a deviation of a predetermined value or more occurs.

Further, in FIG. 8, the ripple current ΔI of the smoothing capacitor 24 is detected by the current detector 28, and the ripple current ΔIL of the smoothing coil 22 is detected by the current detector 30.
These ripple currents ΔIc, ΔIl, and load current ro
Output ripple coefficient r=cΔ■, −
ΔId)/IQ is calculated by the calculator OP, and this output ripple coefficient γ is calculated by the comparator C, which determines the set value γ of the output ripple coefficient of a normal smoothing capacitor based on the load current I.
Input into OMP 2 and set value γ of the output ripple coefficient.
* is compared with the detected value γ of the output ripple coefficient, and if a deviation of more than a predetermined value occurs, an alarm output signal SA is output.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention,
To check for deterioration of the smoothing capacitor over time, the ripple current flowing through the smoothing capacitor or its ripple voltage is constantly monitored using a current or voltage detector that does not affect the circuit, and normal smoothing is determined in advance according to the state of the load current. Compare the ripple current or voltage value of the capacitor for
Deterioration of the smoothing capacitor can be easily and easily determined by a significant decrease or increase in the value of the detected ripple current or voltage, the necessary alarm operation is performed, and the smoothing capacitor is replaced based on this. It can be configured as follows.

In this case, an inductance element is provided for the smoothing capacitor, and the ripple current flowing through this element is detected.
By using this as a reference value and determining the output ripple current in relation to the ripple current flowing through the smoothing capacitor, the deterioration state of the smoothing capacitor can be determined more reliably.

In this way, according to the present invention, it is possible to properly detect the deterioration of the smoothing capacitor while it is in its operating state without performing any special processing on the smoothing capacitor. Deterioration determination and parts replacement can be performed economically and efficiently without the need for complicated parts replacement.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. For example, the present invention is not limited to the above-described embodiments. Not only can it be widely applied as a compensation system for determining the deterioration state of a smoothing capacitor in a power supply circuit configured to smooth with a choke input type smoothing circuit, but it can also be used in various designs without departing from the spirit of the present invention. Of course, modifications can be made.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of a switching regulator showing an embodiment of the preventive maintenance system for smoothing capacitors according to the present invention, and FIGS. 2 and 3 are on/off operations of switching elements in the circuit shown in FIG. 1. Fig. 4 is a characteristic curve diagram showing the relationship between ripple current and load current when a normal product is used as the smoothing capacitor in the circuit shown in Fig. 1, and Fig. 5 is a diagram of the smoothing capacitor shown in Fig. Characteristic curve diagram similar to Fig. 4 when using deteriorated products, Fig. 6
The figure is a characteristic curve diagram showing the relationship between the output ripple coefficient and load current when normal and deteriorated smoothing capacitors are used. FIG. 8 is a block circuit diagram for detecting the lifespan. FIG. 8 is a block circuit diagram for detecting the lifespan based on the output ripple coefficient based on the ripple current detection value of the smoothing capacitor and the smoothing coil and the set output ripple coefficient. 10... DC power supply 12... Voltage transformer 14
...Switching element 16,18,20...Diode 22...Smoothing coil 24...Smoothing capacitor 26...Load 28...Current detector 30
...Current detector

Claims (2)

[Claims] (1) In the power supply circuit configured such that a DC voltage including a ripple component obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing capacitor, and the smoothed voltage is supplied to a load. The ripple current or voltage in the smoothing capacitor is detected, and this ripple current or voltage detection value is compared with a reference value set based on the ripple current or voltage value of a normal smoothing capacitor, and the value obtained from this comparison is Prevention of a smoothing capacitor, characterized in that the deterioration state of the smoothing capacitor is determined when the deviation reaches a predetermined level, and the deterioration state of the smoothing capacitor can be replaced within the range of the permissible deterioration state of the smoothing capacitor. Conservation system. (2) In the preventive maintenance system for a smoothing capacitor according to claim 1, an inductance element is provided in the smoothing circuit to detect the ripple current flowing through the element, and the ripple current flowing through the smoothing capacitor is detected. A preventive maintenance system for a smoothing capacitor, which is configured to compare a ripple current value of the inductance element with a ripple current value of the smoothing capacitor using the value of the ripple current of the inductance element as a reference value.