JPH04188084A - Predicting device for lifetime of capacitor - Google Patents

Abstract

PURPOSE:To estimate the lifetime of a capacitor exactly by detecting an output current of an inverter element and an external temperature of the capacitor, by estimating an internal temperature of the capacitor by computation, and by estimating the lifetime of the capacitor on the basis of the above estimation. CONSTITUTION:A value of rise in an internal temperature of a capacitor 4, which corresponds to the value of a ripple current corresponding to an output current detected by a current detector 20, is read out from RAM 30. Meanwhile, an external temperature of the capacitor 4 is detected by a temperature sensor 10 and read in by CPU 27 through an interface 26, and the internal temperature TA being the sum of the external temperature Ta of the capacitor 4 and the rise Ttheta in the internal temperature, i.e. TA = Ta + Ttheta, is computed. Then, a difference TB between a reference temperature Tf of the lifetime of the capacitor 4 and the internal temperature TA of the capacitor 4, i.e. Tf - TA = TB, is computed, and computation is executed in accordance with a '10 deg.C half-life rule' of the lifetime of the capacitor as usual.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitor life prediction device that smooths input voltage.

[Conventional technology]

An inverter device will be described below as an example of a device that converts smoothed DC input into AC.

Generally, the main capacitor used in an inverter device has a shorter lifespan than the inverter device.

For this reason, capacitors that have been used for a certain period of time are replaced during maintenance and inspection of inverter equipment. However, the lifespan of a capacitor is not determined by the period of use, but depends on the temperature, so the temperature of the capacitor is detected to predict when the capacitor should be replaced.

For example, FIG. 6 is a block diagram in which the conventional capacitor life prediction device disclosed in Japanese Patent Application Laid-Open No. 1-260369 is used in an inverter device. FIG. 7 shows a capacitor life curve, and FIG. 8 shows an operating curve of a capacitor life prediction device.

In the figure, [1] is a three-phase AC power supply, (2a), (2
b) and (2c) are the terminals of the three-phase AC power supply, (3) is the converter that converts the three-phase AC to DC, (4) is the capacitor for smoothing the converted DC voltage, and (5) is the DC An inverter (6
) is an inverter device consisting of a converter (3), a capacitor (4), and an inverter (5). (7c), (7b
), (7c) shows a relay terminal, (8) is a three-phase induction motor driven by an inverter (6), (0) is a temperature sensor that measures the external temperature of the capacitor, (11) is a temperature sensor This is an arithmetic circuit that calculates a voltage value as a capacitor life index from a predetermined relationship between temperature and service life based on the detected value of (lO). For every 10°C rise from 10°C, twice the voltage is output, and for every 10°C drop, half the voltage is output. This means that the lifespan of the capacitor decreases by half as shown in Figure 7 (each time the temperature rises by 10°C)
This is due to the fact that it has characteristics that apply to the "half-decreasing law". [
12) is a V/F that inputs the output voltage value of the arithmetic circuit (1o) and outputs a pulse with a frequency proportional to this output voltage value.
The converter (13) is an integration counter that integrates the output pulses of the V/F converter (12). Assuming that the capacitor's reference temperature continues, by setting the count value corresponding to the capacitor's target wild bird in advance,
The life of the capacitor (4) is defined as the time when the count value reaches the above set value. +141 is the integration counter (1
3) is an indicator for displaying the integrated value 6 Next, the operation of the capacitor life prediction device configured as above will be explained.

Now, the temperature detected by the temperature sensor (10) is the reference temperature 2
In the case of 5°C, a voltage value corresponding to the detected temperature is output from the arithmetic circuit 1ll), and by inputting this voltage value, a corresponding output frequency is obtained from the V/F converter (12), and its period is shown in Fig. 8. Let T be as follows.

Furthermore, when the temperature detected by the temperature sensor r10) is 35°C, the output frequency of the V/F converter (12) is twice that of the case of 25°C in the same operation as above, and the period is T/ It becomes 2. Furthermore, when the detected temperature is 15 DEG C., the output frequency becomes 1/2 of that in the case of 25 DEG C., and the period becomes <27 as shown in FIG. 8 in the same operation as described above.

That is, by counting the rising pulses of the output voltage of the V/F converter (12) with the integration counter (13), the life of the capacitor (4) according to the "10°C halving law" is displayed on the display (14). ) can be displayed.

[Problem to be solved by the invention]

In the conventional capacitor life prediction device, the capacitor (4
Since the external temperature of the capacitor (4) was detected regardless of the internal temperature of the capacitor (4), the error in estimating the life of the capacitor (4) was large. In particular, for capacitors (4) where the difference between the internal temperature and the external temperature is large due to the large charging/discharging current of the capacitor (4), the error in life estimation is particularly significant.

The present invention was made to solve these problems, and an object of the present invention is to provide a capacitor life prediction device that more accurately estimates the life of a capacitor.

Means for Solving rIIs] The capacitor life prediction device according to the present invention includes a capacitor that smooths an input voltage, an inverter section that converts the smoothed DC into AC, and an external temperature of the capacitor that is detected. a temperature sensor for detecting the output current of the inverter section; a first storage means for storing the relationship between the output current value and the ripple current value of the capacitor; a second storage means that stores the relationship between the internal temperature rise value of the capacitor; and a second storage means that stores the relationship between the internal temperature rise value of the capacitor, and the first storage means and the second storage means based on the current value detected by the detection M of the temperature sensor and the output current detection means. The device is equipped with a wild bird calculation means for calculating the lifespan of the capacitor based on the stored contents of the capacitor, and a lifespan prediction means for predicting that the lifespan of the capacitor is nearing based on a command from the lifespan calculation means.

[Effect]

The capacitor life prediction device configured as described above detects the output current of the inverter device and the external temperature of the capacitor, calculates the internal temperature rise of the capacitor from the output current, and estimates the capacitor life.

[Embodiment] FIG. 1 is an overall configuration diagram showing an embodiment in which the present invention is implemented in an inverter device. In the figure, the same symbols as before are the same.
or a corresponding portion. (20) is an inverter device (6)
A current detector is an output current detection means of the device, and its output is an analog voltage. (35) is a capacitor life estimating circuit for estimating the life of the capacitor (4), and (36) is a life end display device which is a life forecast means for predicting that the life of the capacitor is approaching.

FIG. 2 is a configuration diagram showing a specific configuration of the capacitor life estimation circuit (35). In the figure, (25) is an interface for A/D converting the output voltage corresponding to the current value detected by the current detector and inputting it to the CPU, and has an analog/digital conversion function. +261 converts the analog output voltage of the temperature sensor (10) to C
It is an interface for inputting to the PU and is an analog/
Has digital conversion function. (27) is Hun, Densa (
4) CPU, which is a life calculation means for estimating the life of (28
) is a ROM that stores a program that executes the flowchart shown in Figure 4, and (29) is the output current of the inverter (6) and the ripple of the capacitor (4), which were actually measured in advance as shown in Figure 3. The first one stores the current relationship.
RAM (30), which is a storage means, is a second storage means that stores the relationship between the ripple current of the capacitor (4) and the internal temperature rise of the capacitor (4), which was actually measured in advance, as shown in Fig. 4. RAM (31) indicates an interface for outputting the life estimation calculation result of the CPU (27) to the life end display device (36).

The operation of the capacitor life prediction device configured as described above will be explained according to the flowchart shown in FIG.

Now, the inverter device (6) is operating and the three-phase induction motor (
8), the inverter unit W (6) is in a state where current is flowing to the three-phase induction motor (8). The output current is detected by the current detector (20) and read into the CPU [271] through the interface (25).
Step [40A] 3° CPU F271 reads the ripple current value of capacitor (4) corresponding to the above output current from RAM +291 (Step (40B)
), Next, the internal temperature rise value of the capacitor (4) corresponding to the read ripple current value is RAM +30+
(Step [40C)).

On the other hand, the external temperature of the capacitor (4) is detected by the temperature sensor (10), and read into the CPU +271 through the interface (26). Step (step (40E)) of calculating the internal temperature TA of the capacitor, Ta=Ta+To, then the difference between the reference temperature Tf for the life of the capacitor (4) and the internal temperature TA of the capacitor (4), Tf-T= T, is calculated, and the calculation is performed according to rlo "c half-life period" of the capacitor life as in the conventional case (step (40F)).

Furthermore, when the life of the capacitor (4) approaches, the CPU (27
) to the interface (31) to indicate the end of life! (Output to 361 (step f40G+).

End of life indicator bag 51i (361 indicates that the life of the capacitor (4) is approaching. Therefore, the maintenance and inspection worker will replace the capacitor.

Although the inverter device has been described above as an example, the present invention can also be applied to other devices that convert direct current to alternating current, such as a DC-DC converter.

〔Effect of the invention〕

This invention is configured to calculate the internal temperature of the capacitor by detecting the output current of the inverter section and the external temperature of the capacitor, and estimate the life of the capacitor based on the estimation result. This has the effect of being able to be estimated relatively accurately.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing one implementation of the present invention, FIG. 2 is a configuration diagram similarly showing details of a capacitor internal temperature estimation circuit, FIG. 3 is a curve showing the output current versus ripple current of the present invention, and FIG. Figure 4 is a curve showing the ripple current versus capacitor internal temperature rise of this invention, Figure 5 is a flowchart showing the operation of this invention, Figure 6 is a diagram showing the components of a conventional capacitor life prediction device, and Figures 7 and 7 are 8-Figure likewise shows the operating curve. In the figure, (lO) is the temperature sensor (20), which is the current detection means, and (27) is the CP, which is the life calculation means.
U, (29) is the first storage means RAM, (30)
(36) shows a RAM which is a second storage means, and a life end display device which is a life prediction means. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] a capacitor for smoothing input voltage; an inverter section for converting the smoothed direct current into alternating current; a temperature sensor for detecting the external temperature of the capacitor; a current detection means for detecting the output current of the inverter section; The first memory stores the relationship between the current value and the ripple current value of the capacitor.
a storage means for storing the relationship between the ripple current value and the internal temperature rise value of the capacitor; and a second storage means for storing the relationship between the ripple current value and the internal temperature rise value of the capacitor; lifespan calculation means for calculating the lifespan of the capacitor based on the stored contents of the first storage means and the second storage means; and a lifespan prediction for predicting that the lifespan of the capacitor is nearing based on a command from the lifespan calculation means. A capacitor life prediction device comprising means.