Modular Converter Submodule Series Switch Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-voltage applications of multi-stage converters require a large number of submodules in series, posing challenges for control and regulation due to limited dielectric strength of commercially available power semiconductor switches, which increases complexity and costs.
Innovation Solution
The submodule design features power semiconductor valves forming a full-bridge or half-bridge circuit with series-connected switches, reducing the number of submodules needed and allowing for higher operating voltage, with each submodule having multiple switches in series to absorb DC voltage and reduce the risk of simultaneous failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If commercially available power semiconductor switches with limited dielectric strength (1.7-6.5 kV) are used, then the converter can be built with standard components, but a large number of submodules (more than 100) must be connected in series to achieve high voltage, increasing control and regulation complexity
Solution Approach 1:
Each power semiconductor valve is segmented into multiple switching units connected in series (e.g., three 3.3 kV units per valve). This segmentation allows each unit to operate within its voltage rating while the series combination achieves the required higher voltage capability, reducing the total number of submodules needed from over 100 to approximately 36 for a 660 kV converter.
Solution Approach 2:
Multiple power semiconductor valves are combined in series within each submodule to create a higher voltage capability valve. This merging of components within the submodule reduces the overall number of submodules required in the converter, thereby simplifying the control and regulation system.
2Power
If more submodules are connected in series to achieve higher voltage, then the operating voltage capability increases, but the control and regulation system complexity increases proportionally
Solution Approach 1:
The power semiconductor valve is segmented into multiple switching units that can be independently controlled. This allows the converter to achieve high operating voltage (e.g., 660 kV) while maintaining manageable control complexity, as each switching unit within a valve can be controlled together as a single functional element rather than requiring separate control of each individual submodule.
Solution Approach 2:
The converter employs dynamic voltage balancing control where the control system actively manages the voltage distribution across the series-connected switching units. This dynamic control approach enables the system to adapt to varying operating conditions while maintaining simplified control architecture compared to static configurations with many independent submodules.
3Device complexity
If power semiconductor valves with series-connected switching units are used, then fewer submodules are needed reducing control complexity, but the reliability depends on the ability of remaining units to absorb DC voltage after a failure
Solution Approach 1:
The converter is designed with beforehand cushioning through the capacitor associated with each submodule, which can absorb voltage transients and provide temporary voltage support. Additionally, the control system is prepared in advance to redistribute voltage across remaining functional switching units when a failure occurs, ensuring continuous operation.
Solution Approach 2:
When a power semiconductor switching unit fails, the system changes operational parameters by redistributing the DC voltage across the remaining (n-1) functional switching units in series. The capacitor voltage of submodules is adjusted to match the reduced voltage capability of the remaining units, allowing the converter to continue operating with modified voltage parameters rather than complete shutdown.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a sub-module (10) for forming a multi-level converter (1) having a power accumulator (11), a power semiconductor circuit (12) which is arranged in parallel to the power accumulator (11) and has controllable power semiconductor valves (14, 15), a first connecting terminal (17) and a second connecting terminal (18), a power accumulator voltage drop at the level of the power accumulator (11) or a zero voltage at the level of the connecting terminals (17, 18) being producible depending on how the power semiconductor valves (14, 15) are controlled. The aim of the invention is to improve said sub-module such that as high a voltage as possible can be generated at its connecting terminals while at the same time increasing its reliability. Every power semiconductor valve (14, 15) comprises a series connection of power semiconductor units (19) that can be switched off and have the same direction of passage, every power semiconductor unit (19) being electrically conducting counter to the direction of passage.