Parallel-Series Full-Bridge Submodule for Lower MMC Fault Energy
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Solution Overview
Problem
Modular multilevel power converters face challenges in error behavior and complexity due to the limited bidirectional switching capabilities of semiconductor switches, leading to higher error energy and increased complexity, cost, and reduced availability.
Innovation Solution
A submodule design with eight switchable states using a specific arrangement of semiconductor switches and capacitors, allowing for bidirectional switching and reduced semiconductor count, achieved by connecting capacitors in parallel and using mirror-symmetric submodules with reduced current-carrying capacity for some switches, enabling simpler control and lower error energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional submodule designs with limited bidirectional switching capabilities are used, then the semiconductor switch count and circuit complexity increase, but the error energy and system complexity are reduced
Solution Approach 1:
The submodule is segmented into two independent full-bridge circuits, each capable of bidirectional switching. This segmentation allows each bridge to handle specific voltage levels and current directions independently, improving error behavior by isolating faults to one bridge while the other continues operating, without requiring a complete redesign of the entire submodule architecture.
Solution Approach 2:
Each full-bridge circuit is designed with universal bidirectional switching capability, allowing the same circuit topology to handle both positive and negative voltage levels and both current directions. This multi-functionality reduces the need for additional specialized components and simplifies the overall circuit structure while improving reliability through symmetric fault tolerance.
2Adaptability or versatility
If more semiconductor switches are added to improve switching states, then the number of controllable voltage levels increases, but the number of components and system cost increase
Solution Approach 1:
The invention employs dynamic switching strategies where two full-bridge circuits are coordinated to generate multiple voltage levels. By dynamically controlling the switching states of each bridge and their series/parallel configurations, the system achieves comprehensive voltage level control without requiring a proportional increase in the number of semiconductor switches, as each bridge reuses its switches in multiple configurations.
Data Source
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AI summary
The invention relates to a submodule (1) for a modular multilevel converter (2), having: - nine semiconductor switches (S1, S2, S3, S4, S5, S6, S7, S8, S9) that can be switched off, - four capacitors (C1,1, C1,2, C2,1, C2,2), - six network nodes (N1, N2, N3, N4, N5, N6), - and two terminals (11, 12), the components being mounted such that different voltages are generated between the terminals (11, 12) of the submodule (1) when the semiconductor switches that can be switched off are controlled. According to the invention, the behavior of the converter and of the submodule (1) in the event of a fault is substantially improved.