Modular Multilevel Converter Reducing Capacitor Volume
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Solution Overview
Problem
Conventional Modular Multilevel Converters (MMC) for DC power transmission face challenges with increased capacitor dimension and power conversion loss due to high DC voltage levels and reactive AC current requirements, leading to larger dimensions and higher power conversion losses.
Innovation Solution
A power converter design with reduced chopper cell count, utilizing series-connected switching elements and chopper cell groups, along with reactor insertion to manage current and voltage, and a control method that includes zero-phase voltage control and capacitor voltage equalization to maintain constant neutral potential, effectively reducing the number of capacitors and switching elements, thereby minimizing power conversion losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of chopper cells is increased to handle high DC voltage levels, then the voltage handling capability is improved, but the capacitor dimension and device size increase proportionally
Solution Approach 1:
The patent divides the chopper cells into two separate groups (first chopper cell group and second chopper cell group) with different capacitor voltage ratings. This segmentation allows each group to be optimized for its specific voltage level, enabling the use of smaller capacitors overall while still handling the required high DC voltage through series connection of the two groups.
2Power
If the number of chopper cells is increased to handle high DC voltage levels, then the voltage handling capability is improved, but the power conversion loss increases
Solution Approach 1:
By segmenting the chopper cells into two groups with different capacitor voltages, the patent reduces the total number of switching elements required compared to using only high-voltage chopper cells. This reduction in component count directly decreases the cumulative power conversion losses from switching operations and conduction through multiple devices.
3Power
If reactive AC current is supplied from DC voltage, then AC power output is achieved, but circulating current increases power conversion loss
Solution Approach 1:
The patent introduces a neutral point potential control mechanism that acts as an intermediary to manage the reactive power flow. By controlling the neutral point potential and using the two chopper cell groups with different voltages, the system can supply reactive AC current while minimizing unnecessary circulating currents that would increase power losses.
Data Source
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AI summary
Provided is a power converter which has a function of outputting AC voltage and current with less harmonic components, and which is capable of reducing a dimension and a power conversion loss. The DC positive terminal of a DC power supply 20 is connected to a switching element 11, the DC negative terminal of the DC power supply 20 is connected to a switching element 14. A capacitor 18 and a capacitor 19 connected in series are connected in parallel with the DC power supply 20, and a DC neutral point divided by the capacitor 18 and the capacitor 18 is connected to a switching element 12 and a switching element 13. The switching element 12 is connected to the positive terminal of a chopper cell group circuit 15, and the switching element 13 is connected to the negative terminal of a chopper cell group circuit 16. The negative terminal of the chopper cell group circuit 15 is connected to the positive terminal of the chopper cell group circuit 16, and the connection node therebetween serves as an output AC terminal.