US-12618886-B2 - Power conversion apparatus, deterioration determination method for smoothing capacitor

US12618886B2US 12618886 B2US12618886 B2US 12618886B2US-12618886-B2

Abstract

A capacitance acquiring unit acquires a plurality of initial capacitance values indicating capacitance values of a smoothing capacitor in an initial state and acquires a plurality of operation capacitance values indicating capacitance values of the smoothing capacitor in an operation state, and a deterioration determining unit acquires characteristic information indicating a relationship between AC power and the capacitance value of the smoothing capacitor in the initial state on the basis of a statistic amount of the plurality of initial capacitance values acquired by the capacitance acquiring unit and determines a deterioration state of the smoothing capacitor on the basis of a statistic amount of the plurality of operation capacitance values acquired by the capacitance acquiring unit and the characteristic information.

Inventors

Mendez Mauricio TOBON
Masato Ohya
Kazushige Hotta
Yusaku ONUMA

Assignees

HITACHI INDUSTRIAL EQUIPMENT SYSTEMS CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20211005

Claims (10)

1 . A power conversion apparatus, comprising: a power conversion unit that converts DC power to AC power and outputs the AC power; a smoothing capacitor that smoothens the DC power; a capacitance acquiring unit that acquires a capacitance value of the smoothing capacitor; and a deterioration determining unit that determines a deterioration state of the smoothing capacitor, wherein the capacitance acquiring unit acquires a plurality of initial capacitance values indicating capacitance values of the smoothing capacitor in an initial state in accordance with a change in an operation state of the power conversion unit and acquires a plurality of operation capacitance values indicating capacitance values of the smoothing capacitor in the operation state; and the deterioration determining unit: acquires characteristic information indicating a relationship between the AC power and the capacitance value of the smoothing capacitor in the initial state on the basis of a statistic amount of the plurality of initial capacitance values acquired by the capacitance acquiring unit, wherein the smoothing capacitor is in an initial state when a predetermined initial operation period has not elapsed or the acquisition of the characteristic information of the smoothing capacitor has not been finished, and wherein a statistic amount of the initial capacitance values is an average value, a median value, a standard deviation, an upper fence, and a lower fence thereof; and determines a deterioration state of the smoothing capacitor on the basis of a statistic amount of the plurality of operation capacitance values acquired by the capacitance acquiring unit and the characteristic information.
2 . The power conversion apparatus according to claim 1 , wherein the deterioration determining unit calculates a deterioration amount of the smoothing capacitor on the basis of the statistic amount of the operation capacitance value and the characteristic information and determines the deterioration state of the smoothing capacitor on the basis of a comparison result between the calculated deterioration amount and a predetermined threshold value.
3 . The power conversion apparatus according to claim 1 , wherein the deterioration determining unit calculates a statistic amount including at least any one of an average value, a median value, a standard deviation, an upper fence, and a lower fence of the initial capacitance value at each operating point set by separating the values of the AC power by each predetermined range and acquires the characteristic information on the basis of the calculated statistic amount at each of the operating points.
4 . The power conversion apparatus according to claim 1 , comprising: a DC-voltage detector that detects a DC voltage by the DC power; an output-current detector that detects an output current of the power conversion unit; and an output-voltage detector that detects an output voltage of the power conversion unit, wherein the capacitance acquiring unit: calculates the initial capacitance value on the basis of the DC voltage, the output current, and the output voltage detected by the DC-voltage detector, the output-current detector, and the output-voltage detector, respectively, during a predetermined initial operation period; and calculates the operation capacitance value on the basis of the DC voltage, the output current, and the output voltage detected by the DC-voltage detector, the output-current detector, and the output-voltage detector, respectively, after elapse of the initial operation period.
5 . The power conversion apparatus according to claim 1 , comprising: a DC-voltage detector that detects a DC voltage by the DC power; an output-current detector that detects an output current of the power conversion unit; a power-conversion control unit that controls the power conversion unit on the basis of an output instruction input from an outside; and an output-voltage calculating unit that calculates an output voltage of the power conversion unit on the basis of the output instruction, wherein the capacitance acquiring unit: calculates the initial capacitance value on the basis of the DC voltage and the output current detected by the DC-voltage detector and the output-current detector, respectively, during a predetermined initial operation period and the output voltage calculated by the output-voltage calculating unit on the basis of the output instruction input during the initial operation period; and calculates the operation capacitance value on the basis of the DC voltage and the output current detected by the DC-voltage detector and the output-current detector, respectively, after elapse of the initial operation period and the output voltage calculated by the output-voltage calculating unit on the basis of the output instruction input after elapse of the initial operation period.
6 . The power conversion apparatus according to claim 1 , comprising: a DC-voltage detector that detects a DC voltage by the DC power; and a capacitor-current detector that detects a capacitor current flowing through the smoothing capacitor, wherein the capacitance acquiring unit: calculates the initial capacitance value on the basis of the DC voltage and the capacitor current detected by the DC-voltage detector and the capacitor-current detector, respectively, during a predetermined initial operation period; and calculates the operation capacitance value on the basis of the DC voltage and the capacitor current detected by the DC-voltage detector and the capacitor-current detector, respectively, after elapse of the initial operation period.
7 . The power conversion apparatus according to claim 1 , comprising: a DC-voltage detector that detects a DC voltage by the DC power; and an output-current detector that detects an output current of the power conversion unit, wherein the capacitance acquiring unit: calculates the initial capacitance value on the basis of the DC voltage and the output current detected by the DC-voltage detector and the output-current detector, respectively, during a predetermined initial operation period; and calculates the operation capacitance value on the basis of the DC voltage and the output current detected by the DC-voltage detector and the output-current detector, respectively, after elapse of the initial operation period.
8 . The power conversion apparatus according to claim 1 , wherein the capacitance acquiring unit determines whether a predetermined initial operation period has elapsed or not on the basis of at least either one of the number of pieces of data related to the capacitance value acquired for each value of the AC power and an operation time of the power conversion unit and decides which of the initial capacitance value and the operation capacitance value is to be acquired on the basis of a result of the determination.
9 . The power conversion apparatus according to claim 8 , wherein the capacitance acquiring unit decides whether acquisition of the characteristic information is to be continued or to be ended on the basis of the number of operating points of the power conversion unit for which the characteristic information has been acquired, and if it is decided to continue, acquires the initial capacitance value even after elapse of the initial operation period.
10 . A deterioration determination method of a smoothing capacitor for determining a deterioration state of a smoothing capacitor which is coupled to a power conversion unit and smoothens DC power, the power conversion unit converting the DC power to AC power and outputting the AC power, comprising: acquiring a plurality of initial capacitance values indicating capacitance values of the smoothing capacitor in an initial state in accordance with a change in an operation state of the power conversion unit; acquiring characteristic information indicating a relationship between the AC power and a capacitance value of the smoothing capacitor in the initial state on the basis of a statistic amount of the plurality of acquired initial capacitance values, wherein the smoothing capacitor is in an initial state when a predetermined initial operation period has not elapsed or the acquisition of the characteristic information of the smoothing capacitor has not been finished, and wherein a statistic amount of the initial capacitance values is an average value, a median value, a standard deviation, an upper fence, and a lower fence thereof; acquiring a plurality of operation capacitance values indicating capacitance values of the smoothing capacitor in the operation state; and determining a deterioration state of the smoothing capacitor on the basis of a statistic amount of the plurality of acquired operation capacitance values and the characteristic information.

Description

TECHNICAL FIELD The present invention relates to a power conversion apparatus and a deterioration determination method for a smoothing capacitor in the power conversion apparatus. BACKGROUND ART In general, a power conversion apparatus for motor drive has a smoothing capacitor for smoothing DC power. In this smoothing capacitor, with repetition of charging/discharging, deterioration gradually progresses, and when a degree of deterioration becomes large, it leads to defective control of an output voltage in the power conversion apparatus or deterioration of a switching element used for conversion from DC power to AC power. Thus, appropriate evaluation of the degree of deterioration of the smoothing capacitor is in demand. With respect to the evaluation of the degree of deterioration of the smoothing capacitor, an art described in PTL 1, for example, is known. PTL 1 discloses an apparatus for deciding presence/absence of deterioration by calculating a capacitance of a main-circuit capacitor in a certain period during which a voltage change rate of the main-circuit capacitor is negative and a constant value. CITATION LIST Patent Literature [PTL 1] Japanese Patent Application Publication No. 2010-160001 SUMMARY OF INVENTION Technical Problem Since a smoothing capacitor mounted on a power conversion apparatus needs a large capacitance in general, an electrolytic capacitor is employed. However, the electrolytic capacitor has large variation in initial capacitance due to manufacture and thus, the deterioration state cannot be appropriately evaluated in some cases with the art described in PTL 1. On the ground of the aforementioned problem, a major object of the present invention is to appropriately evaluate a deterioration state of a smoothing capacitor in a power conversion apparatus without stopping an operation of the power conversion apparatus. Solution to Problem A power conversion apparatus according to the present invention comprises: a power conversion unit that converts DC power to AC power and outputs the AC power; a smoothing capacitor that smoothens the DC power; a capacitance acquiring unit that acquires a capacitance value of the smoothing capacitor; and a deterioration determining unit that determines a deterioration state of the smoothing capacitor, wherein the capacitance acquiring unit acquires a plurality of initial capacitance values indicating capacitance values of the smoothing capacitor in an initial state in accordance with a change in an operation state of the power conversion unit and acquires a plurality of operation capacitance values indicating capacitance values of the smoothing capacitor in an operation state; and the deterioration determining unit: acquires characteristic information indicating a relationship between the AC power and the capacitance value of the smoothing capacitor in the initial state on the basis of a statistic amount of the plurality of initial capacitance values acquired by the capacitance acquiring unit; and determines a deterioration state of the smoothing capacitor on the basis of a statistic amount of the plurality of operation capacitance values acquired by the capacitance acquiring unit and the characteristic information. A deterioration determination method according to the present invention is a method for determining a deterioration state of a smoothing capacitor which is coupled to a power conversion unit and smoothens DC power, the power conversion unit converting the DC power to AC power and outputting the AC power, comprising: acquiring a plurality of initial capacitance values indicating capacitance values of the smoothing capacitor in an initial state in accordance with a change in an operation state of the power conversion unit; acquiring characteristic information indicating a relationship between the AC power and a capacitance value of the smoothing capacitor in the initial state on the basis of a statistic amount of the plurality of acquired initial capacitance values; acquiring a plurality of operation capacitance values indicating capacitance values of the smoothing capacitor in an operation state; and determining a deterioration state of the smoothing capacitor on the basis of a statistic amount of the plurality of acquired operation capacitance values and the characteristic information. Advantageous Effects of Invention According to the present invention, the deterioration state of the smoothing capacitor in the power conversion apparatus can be appropriately evaluated without stopping the operation of the power conversion apparatus. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a motor-drive system using a power conversion apparatus according to a First Embodiment of the present invention. FIG. 2 is a flowchart of a smoothing-capacitor deterioration-determination processing according to the First Embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a statistic amount of a c