AC Capacitor Fault Detection During Power Converter Voltage Matching

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Solution Overview

Problem

Conventional power conversion devices fail to detect open faults in alternating-current capacitors during voltage matching operations, leading to potential outflow of higher harmonics and fault spread to normal capacitors.

Innovation Solution

A control device that includes a current sensor to measure current values of each phase through alternating-current capacitors, calculates fundamental wave components, and determines faults by comparing amplitudes with a predetermined value, stopping the power conversion device when a fault is detected.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional voltage matching operation is performed without capacitor fault detection, then the power conversion device can start system interconnection operation, but the fault may not be detected and higher harmonics may flow to system side

Engineering Contradiction:

Improvesystem interconnection operation startVSAvoidhigher harmonics outflow to system

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent performs capacitor fault detection during the voltage matching operation (synchronous control) phase, which occurs before the system interconnection operation starts. By detecting capacitor abnormalities in advance through current amplitude analysis during synchronous control, the system prevents faulty capacitors from causing higher harmonics to flow to the system side when full power operation begins.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If conventional voltage matching operation is performed without capacitor fault detection, then the power conversion device can proceed with operation, but the fault may spread to normal alternating-current capacitors

Engineering Contradiction:

Improvecontinuous operationVSAvoidfault spread to normal capacitors

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent detects capacitor faults during the voltage matching operation phase, which occurs before full system interconnection. By identifying abnormal capacitors through current amplitude analysis during this preliminary phase, the system can take preventive measures (such as alerting operators or isolating faulty capacitors) before they cause cascading failures to other normal capacitors during continuous operation.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If current sensor and amplitude calculation are added to detect capacitor faults, then fault detection capability is improved, but device complexity increases

Engineering Contradiction:

Improvecapacitor fault detectionVSAvoidcontrol device structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent utilizes the existing current sensor that is already present in the power conversion device for the purpose of capacitor fault detection. Instead of adding dedicated detection hardware, the system repurposes the existing current sensing capability by analyzing the amplitude of capacitor currents during voltage matching operation, thereby achieving fault detection without significantly increasing device complexity.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The existing current sensor in the power conversion device serves multiple functions: it monitors capacitor current for fault detection purposes and simultaneously provides data for normal operation control. This multi-functional use of the current sensor eliminates the need for separate dedicated detection hardware, maintaining device simplicity while enabling precise fault detection capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12549084B2Control device and power conversion device for detecting failure of an AC capacitor

Publication Date: 2026.02.10 TMEIC CORP

AI summary

A control device of a power conversion device includes: an amplitude calculating circuit which calculates each of values of amplitudes of fundamental wave components of the alternating currents of the respective phases based on the current values of the alternating currents of the respective phases and a fault determining circuit which performs a magnitude comparison between each of the values of the amplitudes of the fundamental wave components of the alternating currents of the respective phases calculated by the amplitude calculating circuit and a predetermined determination value and which determines a fault of the alternating-current capacitor when the value of the amplitude of at least any phase among the values of the amplitudes of the fundamental wave components of the alternating currents of the respective phases is smaller than the predetermined determination value.