HVDC Converter Module Asymmetric Bidirectional Switching
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Solution Overview
Problem
Modular multilevel converters for high-voltage direct current transmission can only block current in one direction, leading to dangerous short circuits when the AC voltage polarity allows diode conduction, posing a risk to the power plant.
Innovation Solution
Incorporating a bidirectional switch in the converter module, allowing control of current flow in both directions, and using a control unit to activate or deactivate switching units individually or in groups, along with overvoltage protection, to prevent short circuits and block current flow effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a half-bridge converter module with diode is used, then the structure is simple and easy to manufacture, but the converter can only block current in one direction, leading to short circuit risks
Solution Approach 1:
The patent applies asymmetry by replacing only one of the two bridge switches with a bidirectional switch, rather than making both switches bidirectional. This asymmetric configuration achieves bidirectional current blocking capability while minimizing device complexity and manufacturing cost, resolving the contradiction between ease of manufacture and short circuit protection reliability.
Solution Approach 2:
The bidirectional switch serves multiple functions: it acts as a switching element for power conversion and simultaneously provides bidirectional current blocking capability for short circuit protection. This multi-functionality eliminates the need for separate protection devices, improving reliability while maintaining manufacturing simplicity.
2Reliability
If both bridge switches are replaced by bidirectional switches, then bidirectional current blocking is achieved, but device complexity and cost increase significantly
Solution Approach 1:
The patent uses asymmetric design by replacing only one bridge switch with a bidirectional switch while keeping the other as a conventional switch. This reduces device complexity compared to replacing both switches, while still achieving the necessary bidirectional current blocking capability for reliable short circuit protection.
Solution Approach 2:
The patent applies partial action by implementing bidirectional switching capability in only one of the two bridge switches, which is sufficient to achieve bidirectional current blocking and short circuit protection. This partial implementation avoids the excessive complexity of making both switches bidirectional.
3Reliability
If a bidirectional switch is incorporated, then short circuit protection in both directions is achieved, but the converter module complexity increases
Solution Approach 1:
The patent resolves this contradiction through asymmetric configuration, replacing only one bridge switch with a bidirectional switch. This provides sufficient bidirectional short circuit protection while minimizing the increase in converter module complexity, achieving an optimal balance between reliability and structural simplicity.
Solution Approach 2:
The bidirectional switch performs dual functions as both a power switching element and a protection device for bidirectional short circuit blocking. This multi-functionality reduces the need for additional protection components, thereby limiting the increase in overall module complexity while enhancing reliability.
Data Source
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AI summary
According to the invention, a switching unit (a bridge switch) of a converter module (301) is replaced by a bidirectional switch, with the result that the converter module can be blocked for currents of different polarities. Thus it is advantageously possible to prevent, for example, a short-circuit in the DC system reacting back on the AC system. One advantage of the asymmetric implementation in this connection is energy efficiency. The invention can be used, for example, in high-voltage DC transmission, in particular in multilevel converters.