Electrolytic capacitor degradation detection device

Abstract

The present invention provides an electrolytic capacitor degradation detection device that can accurately determine the degradation of electrolytic capacitors. [Solution] An electrolytic capacitor degradation determination device for determining the degradation of an electrolytic capacitor that smooths a DC voltage, comprising an extraction unit that extracts the ripple voltage of the AC component superimposed on the DC voltage applied to the electrolytic capacitor, and determining that the electrolytic capacitor is degraded (step S7) when the ripple voltage continuously exceeds a determination threshold including an upper threshold and a lower threshold (Yes in step S4), the number of times the ripple voltage exceeds the upper threshold and the number of times the ripple voltage exceeds the lower threshold are equal to or greater than a predetermined number (Yes in step S5), and the difference between the number of times the ripple voltage exceeds the upper threshold and the number of times the ripple voltage exceeds the lower threshold is less than a predetermined difference (Yes in step S6).

Description

Technical Field

[0001] This invention relates to a device for determining the deterioration of an electrolytic capacitor for suppressing fluctuations in DC voltage.

Background Art

[0002] Patent Documents 1 and 2 describe devices for determining the life of a smoothing capacitor that rectifies an AC voltage output from an AC power supply by a rectifier and smoothes the rectified voltage to convert it into a DC voltage. Specifically, the life determination device described in Patent Document 1 determines that the life of the smoothing capacitor has arrived when the instantaneous value of the voltage between the terminals of the smoothing capacitor drops below a predetermined voltage. Further, the life determination device described in Patent Document 2 compares the deviation between the voltage of the capacitor and the absolute value of the instantaneous voltage with a specified value, and determines that it is the life of the capacitor if the ripple voltage is below the specified value. Note that the life determination device described in Patent Document 2 does not determine the life of the capacitor or is configured to change the life determination threshold value when the load power connected to the output side of the power supply device fluctuates or when the load is turned on and off.

[0003] Furthermore, Patent Document 3 describes a device for determining the life of a smoothing capacitor that converts an AC voltage output from an AC power supply into a DC voltage by a converter device and smoothes the ripple contained in the DC voltage. This life determination device determines that it is the life of the smoothing capacitor when the value obtained by multiplying the current value or voltage value of the charge and discharge of the smoothing capacitor by the coefficient of the change rate from the initial value exceeds the first threshold value, the number of charge and discharge cycles of the smoothing capacitor exceeds the second threshold value, and further, the ripple voltage of the smoothing capacitor exceeds the threshold value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] The capacitor life determination devices described in Patent Documents 1 to 3 determine the lifespan of a capacitor based on whether or not the voltage across the capacitor terminals exceeds a threshold. On the other hand, the voltage value of a smoothing capacitor installed in a power supply circuit fluctuates in accordance with fluctuations in the power supply voltage. Therefore, for example, if the load on the power supply increases due to the operation of a high-current circuit, the capacitor voltage will decrease as the power supply voltage drops instantaneously. In such cases, since the ripple voltage is included in the fluctuation amount of the capacitor voltage, it is possible that the capacitor may be mistakenly judged to have reached the end of its lifespan due to the drop in the capacitor voltage, even though the capacitor is functioning normally.

[0006] Furthermore, in order to suppress misjudgments of the lifespan due to such a drop in power supply voltage, if the lifespan of the capacitor is not judged when the load power connected to the output side of the power supply is fluctuating or when the load is being switched on and off, as in the lifespan judgment device described in Patent Document 2, the opportunities to judge the lifespan may be limited. Moreover, when the load power connected to the output side of the power supply is fluctuating or when the load is being switched on and off, it is necessary to determine the correction amount of the threshold for judging the lifespan based on the load power, which may make the control and circuit for judging the lifespan complicated.

[0007] This invention was made in view of the above-mentioned technical problems, and aims to provide an electrolytic capacitor degradation detection device that can accurately determine the degradation of an electrolytic capacitor. [Means for solving the problem]

[0008] To achieve the above objective, this invention provides an electrolytic capacitor degradation determination device for determining the degradation of an electrolytic capacitor that smooths a DC voltage, further comprising: an extraction unit for extracting the ripple voltage of the AC component superimposed on the DC voltage applied to the electrolytic capacitor; and a controller for determining the degradation of the electrolytic capacitor based on the ripple voltage extracted by the extraction unit, wherein the controller determines that the electrolytic capacitor is degraded when at least three conditions are met: a first condition that the ripple voltage has continuously exceeded a determination threshold including a predetermined upper threshold and a predetermined lower threshold; a second condition that the number of times the ripple voltage has exceeded the upper threshold and the number of times the ripple voltage has exceeded the lower threshold is equal to or greater than a predetermined number of times; and a third condition that the difference between the number of times the ripple voltage has exceeded the upper threshold and the number of times the ripple voltage has exceeded the lower threshold is less than a predetermined difference.

[0009] Furthermore, in this invention, the extraction unit may include a capacitor provided between one terminal of the electrolytic capacitor and the controller, which outputs the ripple voltage.

[0010] Furthermore, in this invention, a filter may be provided between the extraction unit and the controller to remove noise contained in the ripple voltage extracted by the extraction unit.

[0011] Furthermore, in this invention, the filter may include an RC parallel circuit comprising a capacitor connected between the extraction unit and the controller, and a resistor connected in parallel with the capacitor. [Effects of the Invention]

[0012] The electrolytic capacitor degradation determination device in this invention extracts the ripple voltage of the AC component superimposed on the DC voltage applied to the electrolytic capacitor using an extraction unit, and determines the degradation of the electrolytic capacitor based on that ripple voltage. Therefore, even if the voltage applied to the electrolytic capacitor fluctuates due to, for example, a decrease in the power supply voltage, it is possible to suppress the influence of that voltage fluctuation on the degradation determination of the electrolytic capacitor. In other words, it is possible to suppress the limitation of opportunities to determine the degradation of the electrolytic capacitor due to factors such as fluctuations in the voltage applied to the electrolytic capacitor.

[0013] Furthermore, when an electrolytic capacitor is degraded, the fluctuation range of the ripple voltage increases. Therefore, by determining that an electrolytic capacitor is degraded when the ripple voltage continuously exceeds a judgment threshold that includes both an upper and lower threshold, the number of times the ripple voltage exceeds the upper threshold and the number of times it exceeds the lower threshold are equal to or greater than a predetermined number, and the difference in the number of times the ripple voltage exceeds each threshold is less than or equal to a predetermined difference, it is possible to suppress the determination that the electrolytic capacitor is degraded even if the ripple voltage extracted by the extraction unit contains noise, because the voltage value containing noise temporarily exceeds the upper or lower threshold. Thus, it is possible to suppress the influence of voltage fluctuations and noise applied to the electrolytic capacitor on the determination of electrolytic capacitor degradation. In other words, it is possible to accurately determine the degradation of the electrolytic capacitor. [Brief explanation of the drawing]

[0014] [Figure 1] This is an electrical circuit diagram illustrating an example of an electrolytic capacitor degradation detection device according to an embodiment of the present invention. [Figure 2] This is a flowchart illustrating an example of control performed by a controller. [Modes for carrying out the invention]

[0015] This invention will be described based on the embodiments shown in the figures. The embodiments described below are merely examples of how this invention can be implemented and do not limit it.

[0016] Figure 1 schematically shows an electrical circuit diagram illustrating an example of an electrolytic capacitor degradation determination device according to an embodiment of this invention. The electrical circuit shown in Figure 1 comprises a battery 1 provided as a power source for a vehicle, a converter 2 that boosts or lowers the output voltage of the battery 1, and an electrolytic capacitor 3 for smoothing the output voltage of the converter 2.

[0017] Battery 1 may be a 12V battery that functions as a power source for the vehicle's auxiliary equipment, or a high-voltage battery that functions as a power source for the motor that serves as the vehicle's driving force source, and may be composed of secondary batteries such as lead-acid batteries, nickel-metal hydride batteries, or lithium-ion batteries. Battery 1 may also be a battery pack in which multiple batteries are connected in series, and may include an electric double-layer capacitor connected in parallel with these batteries.

[0018] Converter 2 can be configured in the same way as a conventional converter, and includes switching elements such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs) (not shown), and is configured to boost or buck the input voltage and output it by switching control of these switching elements.

[0019] The electrolytic capacitor 3 can be configured in the same way as a conventional smoothing capacitor. That is, it is connected between the converter 2 and auxiliary equipment (not shown) or a power control unit including an inverter. Specifically, the electrolytic capacitor 3 is connected between the positive bus 4 connected to the converter 2 and the ground (negative bus) 5, and is configured to suppress fluctuations in the voltage of the positive bus 4 by storing charge when the voltage of the positive bus 4 increases and releasing charge when the voltage of the positive bus 4 decreases.

[0020] This electrolytic capacitor 3 corresponds to the "electrolytic capacitor" in the embodiment of this invention, and a deterioration determination circuit 6 for determining the deterioration of the electrolytic capacitor 3 is coupled by an AC coupling. That is, the positive electrode of the electrolytic capacitor 3 and the deterioration determination circuit 6 are connected via a capacitor 7. Therefore, when the voltage applied to the electrolytic capacitor 3 includes a ripple voltage as an AC component, the ripple voltage is output to the deterioration determination circuit 6. In other words, the ripple voltage of the AC component superimposed on the DC voltage applied to the electrolytic capacitor 3 is extracted by the capacitor 7. This capacitor 7 functions as an "extraction unit" in the embodiment of this invention.

[0021] The deterioration determination circuit 6 is provided with a filter 8 for removing high-frequency noise included in the ripple voltage. Specifically, a capacitor 9 having a predetermined capacitance and a resistor 10 having a predetermined resistance value are connected in parallel. That is, the filter 8 is constituted by an RC parallel circuit.

[0022] A controller 11 that functions as a deterioration determination device in the embodiment of this invention is connected to the output side of the filter 8. This controller 11 is mainly constituted by a microcomputer, and is configured to receive the above-mentioned ripple voltage and determine the deterioration of the electrolytic capacitor 3 based on the input ripple voltage.

[0023] A flowchart illustrating an example of this control is shown in Figure 2. In the control example shown in Figure 2, it is first determined whether the ripple voltage has crossed a judgment threshold that includes an upper threshold and a lower threshold (step S1). The upper and lower thresholds in step S1 are determined based on the magnitude (amplitude) of the ripple voltage that may occur when the electrolytic capacitor 3 deteriorates. This is because when the electrolytic capacitor 3 deteriorates, the internal impedance increases, which increases the amplitude of the ripple voltage and reduces the ripple voltage suppression effect of the electrolytic capacitor 3. Therefore, the above upper and lower thresholds are determined based on the specifications of the electrolytic capacitor 3, or based on experiments using the electrolytic capacitor 3. Note that the magnitude (absolute value) of the upper and lower thresholds may be the same or different.

[0024] If step S1 is negatively determined because the ripple voltage does not cross the judgment threshold, that is, if the ripple voltage is within the range between the upper threshold (positive threshold) and the lower threshold (negative threshold), then electrolytic capacitor 3 is considered to be functioning normally. Therefore, if step S1 is negatively determined, the positive and negative counters described later are cleared (step S2), and this routine is terminated. In other words, it is not determined that electrolytic capacitor 3 is degraded.

[0025] Conversely, if the ripple voltage crosses the judgment threshold and is judged positively in step S1, the counter corresponding to the threshold crossed by the ripple voltage (positive counter or negative counter) is incremented (step S3), and then it is determined whether the ripple voltage has crossed the judgment threshold consecutively (step S4). Specifically, it is determined whether, in step S1 of the previous routine, the ripple voltage crossed either the upper threshold or the lower threshold and was judged positively, and whether, in step S1 of the current routine, the ripple voltage crossed either the upper or lower threshold and was judged positively. In other words, it is determined whether it was judged positively in step S1 of the previous routine. Alternatively, it is determined whether either the positive counter or the negative counter is not "0". Note that if the electrolytic capacitor 3 deteriorates, the ripple voltage is expected to increase continuously, so the determination in step S4 is made to suppress the judgment that the electrolytic capacitor 3 is deteriorated when a positive judgment is made in step S1 due to noise. The condition in step S4 corresponds to the "first condition" in this embodiment of the invention.

[0026] Therefore, if a negative determination is made in step S4 because the ripple voltage has not continuously crossed the threshold, it is possible that noise caused the ripple voltage to exceed the threshold, and it cannot be said that the electrolytic capacitor 3 is not functioning properly. Therefore, if a negative determination is made in step S4, the positive and negative counters are cleared (step S2), and this routine is terminated. In other words, it is not determined that the electrolytic capacitor 3 is degraded.

[0027] Conversely, if a positive determination is made in step S4 because the ripple voltage has repeatedly crossed the judgment threshold, it is determined in step S5 whether the number of times the ripple voltage has crossed the positive threshold and the number of times it has crossed the negative threshold is equal to or greater than a predetermined number. Specifically, it is determined whether the positive count and negative count counted up in step S3 are equal to or greater than a predetermined count. Note that if the ripple voltage increases due to the deterioration of the electrolytic capacitor 3, it is considered that the ripple voltage will continuously exceed the judgment threshold, so in step S5, the continuity of this is determined. Therefore, the predetermined number is the number of times predetermined in order to determine that the electrolytic capacitor 3 is deteriorating. This condition in step S5 corresponds to the "second condition" in the embodiment of this invention.

[0028] If step S5 is negatively determined because at least one of the number of times the ripple voltage crosses the positive threshold or the number of times it crosses the negative threshold is less than a predetermined number, this routine is terminated. In this case, the values ​​of the positive counter and the negative counter are maintained.

[0029] Conversely, if a positive determination is made in step S5 because the number of times the ripple voltage crosses the positive threshold and the number of times it crosses the negative threshold is greater than or equal to a predetermined number, then it is determined whether the difference between the number of times the ripple voltage crosses the positive threshold and the number of times it crosses the negative threshold is less than a predetermined difference (step S6). This step S6 is a step to suppress the misjudgment that the electrolytic capacitor 3 is degraded when the number of times either threshold is crossed increases due to noise or other factors. In other words, if the electrolytic capacitor 3 is degraded, it is thought that the number of times the ripple voltage crosses the positive threshold and the negative threshold will be equal, and this step is to suppress misjudgment due to external factors such as noise. Therefore, the predetermined difference is predetermined by experimentation or the like. Step S6 can be performed by finding the difference between the positive counter and the negative counter and comparing that difference with the predetermined difference. The condition in this step S6 corresponds to the "third condition" in the embodiment of this invention.

[0030] If step S6 is negatively determined because the difference between the number of times the ripple voltage crosses the positive threshold and the number of times it crosses the negative threshold is greater than or equal to a predetermined difference, it is considered that external factors such as noise are influencing the situation, so the positive and negative counters are cleared (step S2), and this routine is terminated. Conversely, if step S6 is positively determined because the difference between the number of times the ripple voltage crosses the positive threshold and the number of times it crosses the negative threshold is less than a predetermined difference, it is determined that the electrolytic capacitor 3 is degraded (step S7). Then, the fact that the electrolytic capacitor 3 is degraded is notified to the outside (step S8), and this routine is terminated. Note that step S8 may be executed immediately after the determination in step S7, and the determination result of step S7 may be stored so that it can respond to communication from an external tool, and the result may be responded to in response to a read request from an external tool, so it is not necessary to notify the outside immediately after the determination in step S7. Furthermore, the means of notification are not particularly limited.

[0031] As described above, capacitor 7 extracts the ripple voltage of the AC component superimposed on the DC voltage applied to electrolytic capacitor 3, and the degradation of electrolytic capacitor 3 is determined based on this ripple voltage. Therefore, even if the voltage applied to electrolytic capacitor 3 fluctuates, for example, due to a decrease in the power supply voltage, it is possible to suppress the influence of that voltage fluctuation on the degradation determination of electrolytic capacitor 3. In other words, it is possible to suppress the limitation of opportunities to determine the degradation of electrolytic capacitor 3 due to factors such as fluctuations in the voltage applied to electrolytic capacitor 3.

[0032] Furthermore, if the electrolytic capacitor 3 is degraded, the fluctuation range of the ripple voltage will increase. Therefore, if the ripple voltage continuously exceeds a judgment threshold that includes the upper and lower thresholds, and the number of times the ripple voltage exceeds the upper threshold and the number of times it exceeds the lower threshold is greater than or equal to a predetermined number, and the difference in the number of times the ripple voltage exceeds each threshold is less than or equal to a predetermined difference, then it is determined that the electrolytic capacitor is degraded. Therefore, even if the ripple voltage extracted through capacitor 7 contains noise, it is possible to suppress the determination that the electrolytic capacitor 3 is degraded due to the voltage value containing noise temporarily exceeding the upper or lower thresholds. As a result, it is possible to suppress the influence of voltage fluctuations and noise applied to the electrolytic capacitor 3 on the degradation determination of the electrolytic capacitor 3. In other words, the degradation of the electrolytic capacitor 3 can be determined with high accuracy.

[0033] Furthermore, the electrolytic capacitor in this embodiment of the invention is not limited to one that smooths the voltage after it has been regulated by an electrical component using a switching element such as a converter, but may also be one that smooths the voltage after the output voltage of an AC power source has been converted to a DC voltage by a rectifier or the like. Alternatively, it may be used as a capacitor to convert the AC voltage generated by an AC motor into a DC voltage using an inverter, and then smooth the converted DC voltage before outputting it to an energy storage device.

[0034] Furthermore, the capacitors are not limited to those installed in power units mounted on vehicles; they may also be capacitors installed in household electrical appliances or industrial equipment. [Explanation of Symbols]

[0035] 1 Battery 2 Converters 3 Electrolytic Capacitors 4 Positive busbar 5 Grand 6 Deterioration judgment circuit 7,9 Capacitors 8 filters 10 resistor 11 Controllers

Claims

1. An electrolytic capacitor degradation determination device for determining the degradation of an electrolytic capacitor used to smooth a DC voltage, An extraction unit for extracting the AC component ripple voltage superimposed on the DC voltage applied to the electrolytic capacitor, The system further comprises a controller that determines the degradation of the electrolytic capacitor based on the ripple voltage extracted by the extraction unit, The aforementioned controller, The electrolytic capacitor is determined to be degraded if at least three conditions are met: a first condition that the ripple voltage has continuously exceeded a determination threshold that includes a predetermined upper threshold and a predetermined lower threshold; a second condition that the number of times the ripple voltage has exceeded the upper threshold and the number of times the ripple voltage has exceeded the lower threshold is equal to or greater than a predetermined number; and a third condition that the difference between the number of times the ripple voltage has exceeded the upper threshold and the number of times the ripple voltage has exceeded the lower threshold is less than a predetermined difference. A device for determining the deterioration of electrolytic capacitors, characterized by the following features.

2. A device for determining the deterioration of an electrolytic capacitor according to claim 1, The extraction unit includes a capacitor provided between one terminal of the electrolytic capacitor and the controller, which outputs the ripple voltage. A device for determining the deterioration of electrolytic capacitors, characterized by the following features.

3. A device for determining the deterioration of an electrolytic capacitor according to claim 1, Between the extraction unit and the controller, there is a filter to remove noise contained in the ripple voltage extracted by the extraction unit. A device for determining the deterioration of electrolytic capacitors, characterized by the following features.

4. A device for determining the deterioration of an electrolytic capacitor according to claim 3, The filter includes an RC parallel circuit consisting of a capacitor connected between the extraction unit and the controller, and a resistor connected in parallel to the capacitor. A device for determining the deterioration of electrolytic capacitors, characterized by the following features.

Images