Modular Multi-Level Converter Auxiliary Sub-Module
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional modular multilevel converter (MMC) systems require separate auxiliary sub-modules for upper and lower converter arms, increasing complexity and cost, and reducing reliability due to the need for multiple auxiliary units.
Innovation Solution
A single auxiliary sub-module is provided between the upper and lower converter arms, comprising an energy storage unit and three semiconductor switches, with a switching controller that can reconfigure the sub-module to replace failed sub-modules in either arm by controlling the semiconductor switches, allowing the auxiliary sub-module to function as either the lowest or uppermost sub-module in the converter arms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate auxiliary sub-modules are provided for upper and lower converter arms, then each arm can be independently maintained, but the device complexity and cost increase
Solution Approach 1:
The auxiliary sub-module is designed with universal applicability to both upper and lower converter arms. By configuring the auxiliary sub-module with bidirectional connection capabilities through mid-points N1 and N3, a single auxiliary unit can replace failed sub-modules in either arm, eliminating the need for separate auxiliary sub-modules for each arm while maintaining full fault coverage
Solution Approach 2:
The patent merges the previously separate auxiliary sub-modules for upper and lower arms into a single shared auxiliary sub-module. This consolidation reduces the total number of auxiliary units from two to one, simplifying the overall system structure while preserving the ability to maintain both converter arms independently through strategic switching operations
2Device complexity
If a single auxiliary sub-module is shared between upper and lower converter arms, then device complexity is reduced, but the switching control becomes more complex
Solution Approach 1:
The auxiliary sub-module incorporates dynamic reconfigurability through three semiconductor switches that can be selectively activated based on the location of the failed sub-module. The system transitions between different operational states (replacing upper arm sub-modules vs. replacing lower arm sub-modules) by dynamically adjusting which switches are conductive, allowing a single static physical unit to perform multiple functional roles
Solution Approach 2:
The mid-points N1 and N3 serve as intermediary connection points that enable the auxiliary sub-module to interface with both upper and lower converter arms. These intermediary nodes, combined with the semiconductor switches, act as mediators that route current flow appropriately depending on which arm requires maintenance, simplifying the control logic compared to fully independent auxiliary units
3Ease of repair
If separate auxiliary sub-modules are used for each converter arm, then the replacement process is simpler, but the overall system cost increases
Solution Approach 1:
The auxiliary sub-module is designed as a universal replacement unit that can serve both upper and lower converter arms through its bidirectional connection architecture. This universality means that a single auxiliary unit type is sufficient for maintaining the entire system, eliminating the need to stock and install different auxiliary sub-module variants for different arms, thus simplifying maintenance operations while reducing component quantity
Data Source
AI summary
A modular multilevel converter (MMC) converter including an auxiliary sub-module provided between an upper converter arm and a lower converter arm of the MMC converter is provided. An MMC converter includes an auxiliary sub-module including: an energy storage unit storing a DC voltage in the sub-module; a first semiconductor switch connected to the energy storage unit; a second semiconductor switch connected to the first semiconductor switch; a third semiconductor switch connected to the second semiconductor switch; and a switching controller turning ON/OFF the first to third semiconductor switches, wherein a mid-point between the first and second semiconductor switches is connected to the sub-module of the upper converter arm, a mid-point between the second and third semiconductor switches is connected to a load connection terminal, and a mid-point between the third semiconductor switch and the energy storage unit is connected to the sub-module of the lower converter arm.