MMC Current Detector Failure Detection With Minimal Sensors
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Solution Overview
Problem
Conventional modular multilevel converters (MMCs) require multiple current detectors at the same location to determine failure, leading to increased costs and complexity.
Innovation Solution
A power conversion device with a failure detection unit that allows for the determination of current detector failure with a single or two current detectors at the same location, using a system of determination units to compare detection values and command values across multiple arms and lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple current detectors are installed at the same location to determine failure, then failure detection reliability is improved, but device cost and complexity increase
Solution Approach 1:
The current detectors perform self-diagnosis by comparing their own detection values with each other and with command values. The failure detection unit enables each detector to verify its own functionality through mathematical relationships (Kirchhoff's current law) without requiring external diagnostic equipment, thus improving reliability while maintaining a minimal number of detectors.
Solution Approach 2:
The system implements feedback by continuously comparing detection values from multiple current detectors against each other and against command values from control signals. The failure detection unit uses this feedback to identify inconsistencies that indicate detector failure, enabling reliable failure detection with minimal detectors through continuous verification.
2Reliability
If three or more current detectors are installed at the same location to identify failed detector by majority rule, then failure identification capability is improved, but device cost increases
Solution Approach 1:
Instead of relying solely on the number of detectors (one-dimensional approach), the invention introduces a new dimension of verification by comparing detection values against command values from control signals. This additional verification dimension enables failure identification with fewer detectors, as the system can detect failures through inconsistency between measured and commanded values rather than requiring majority voting among multiple detectors.
Solution Approach 2:
The current detectors serve multiple functions: they measure actual current for control purposes and simultaneously perform self-diagnosis for failure detection. The failure detection unit leverages the same detection values used for normal operation to identify failures, eliminating the need for separate diagnostic detectors and enabling universal use of minimal detectors for both measurement and monitoring.
3Reliability
If at least two current detectors are provided at the same location to compare detection values, then failure determination is possible, but device cost increases
Solution Approach 1:
The invention changes the parameters used for failure determination by introducing command values (control signals) as an additional reference. Instead of relying solely on comparison between two detection values, the system compares detection values against both other detection values and against command values, creating a more robust failure determination mechanism that works with minimal detectors.
Data Source
AI summary
An MMC-type power conversion device includes a failure detection unit that detects presence or absence of failure of each of n upper arm current detectors and n lower arm current detectors. The failure detection unit makes a first determination based on comparison between a sum of detection values of n upper arm current detectors and the sum of detection values of n lower arm current detectors, a second determination based on comparison between a current command value and the sum of detection values of n upper arm current detectors, a third determination based on comparison between a current command value and the sum of detection values of n lower arm current detectors, and a fourth determination of comparing, for each phase, the sum of detection values of the current detectors of an upper arm and a lower arm of the same phase.