Modular Converter Fault Localization Using Capacitor Voltage Variance
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Solution Overview
Problem
Existing power conversion devices struggle to accurately determine the section of failure when a short-circuit failure occurs in a power conversion circuit comprising a large number of unit converters, such as in a modular multilevel converter.
Innovation Solution
The power conversion device employs a failure detection system that includes AC and DC voltage detectors, arm current detectors, and a control device to calculate variance values of capacitor voltages, allowing it to identify the section of failure by analyzing the variance in capacitor voltage during a short-circuit event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage detectors and failure detectors are installed in each unit converter to detect capacitor voltage failures, then unit converter failure detection capability is improved, but the ability to determine failure sections in the entire power conversion circuit remains insufficient
Solution Approach 1:
The patent introduces an arm current detector as an intermediary device that measures arm current flowing through each arm of the modular multilevel converter. This intermediary measurement provides additional information about the overall circuit state, enabling the determination of failure sections by analyzing arm current characteristics in combination with capacitor voltage data, thus resolving the insufficient failure section determination capability
Solution Approach 2:
The patent implements a feedback mechanism where the control device continuously monitors arm current and capacitor voltage, compares measured values with reference values, and uses this feedback information to determine failure sections. The control device adjusts its detection strategy based on the feedback from current and voltage measurements, enabling dynamic failure section identification throughout the power conversion circuit
2Power
If a large number of unit converters are used to construct the power conversion circuit, then power conversion capability is improved, but the complexity of determining failure sections increases
Solution Approach 1:
The patent segments the power conversion circuit into multiple arms (upper arm and lower arm for each phase), with each arm containing multiple sub-modules. By measuring arm current at the arm level rather than at each individual sub-module level, the system reduces the complexity of failure section determination while maintaining the ability to handle large numbers of unit converters. The segmentation allows systematic analysis of failure sections through arm-level current measurements combined with sub-module voltage data
Solution Approach 2:
The arm current detector serves multiple functions: it detects arm current for power control, provides failure detection information, and enables failure section determination. This multi-functionality reduces the need for additional dedicated detection devices, thereby managing system complexity even as the number of unit converters increases to enhance power conversion capability
Data Source
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AI summary
A power conversion device (100) that performs power conversion between a DC circuit (82) and an AC circuit (80) includes a power conversion circuit (2) including a plurality of sub-modules (7) connected in series with each other, a failure detection device (40) that detects an internal failure of the power conversion circuit (2), and a control device (30) that generates an operation command controlling operation of each of the plurality of sub-modules (7). The control device (30) acquires a voltage value of a capacitor (24) included in each sub-module (7), calculates a deviation between a variance value indicating a variation in the voltage value of the capacitor (24) included in the sub-module in a reference period and a reference variance value in the sub-module (7) for each of a plurality of sub-modules (7), determines a failure section of an internal failure based on the deviation in each sub-module (7) when the internal failure is detected, and outputs an operation command based on a determination result to each sub-module (7).