Multilevel Converter Short-Circuit Detection via Current Signal Patterns
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Solution Overview
Problem
Multilevel electrical converters face challenges in detecting short circuit events due to the higher number of commutation and short circuit paths, which complicates current measurement and requires additional information about switching states to identify the short circuit path accurately.
Innovation Solution
A method and electrical converter design that utilize at least two power modules with semiconductor switches connected in series or anti-series, equipped with current sensors to determine collective current signals indicative of the current through both outputs, allowing for the detection of short circuit events by comparing current signal patterns with thresholds and referencing a short circuit event table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multilevel converter topologies are used to reduce voltage rating and increase switching frequency, then converter performance is improved, but the number of commutation and short circuit paths increases significantly
Solution Approach 1:
The converter is divided into multiple power modules (first power module, second power module, etc.), each with its own current sensor. This segmentation allows the system to handle complex multilevel topologies while maintaining manageable current measurement capabilities in each module, addressing the increased complexity from multilevel configurations.
2Measurement precision
If the number of current sensors is increased to detect all short circuit paths in multilevel converters, then detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
Each power module's current sensor serves multiple functions: it detects normal operating currents, identifies short circuit conditions, and helps locate the specific short circuit path when combined with switching state information. This multi-functionality achieves comprehensive monitoring without proportionally increasing the number of sensors.
Solution Approach 2:
The controller acts as an intermediary that combines current sensor signals with switching state information to identify short circuit paths. Instead of requiring direct measurement of all possible short circuit paths, the controller processes the relationship between switching states and current signals to detect and locate faults.
3Device complexity
If a single current measurement signal is used in multilevel converters, then device complexity is reduced, but the ability to detect and identify short circuit paths is insufficient
Solution Approach 1:
The system adds a temporal dimension to current measurement by sampling currents at specific switching instants and combining these measurements with switching state information. This approach extracts sufficient information about short circuit paths without requiring direct spatial measurement of all possible fault currents.
Data Source
Figure 1~2
Figure 3~4A
Figure 4B~4C
AI summary
A multi-level converter (42, 42') is composed of at least two power modules (Ml, M2, M3, M3') electrically interconnected with each other to generate a multilevel output, each power module comprising at least two semiconductor switches (12, 14) electrically connected in series or anti-series between two outputs with each other and each of the power modules comprising a current sensor (30) adapted for determining a current along a flow path through the power module (Ml, M2, M3, M3'), the multi-level converter comprising a controller adapted for performing the method for detecting a short-circuit event. A method for detecting a short circuit event (46) in the multi-level converter (42, 42') comprises: determining at least two current signals (36) with at least two current sensors (30) of the power modules (Ml, M2, M3, M3') wherein for each power module one collective current signal is determined with the current sensor, which collective current signal depends on two currents through the outputs of the power module; determining a current signal pattern from the current signals (36) by comparing each current signal with a threshold; detecting the short circuit event (46) and identifying a short circuit flow path (PI to P4) by searching the current signal pattern in a short circuit event table.