Multiphase VSC for Modular Multilevel Converters
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Solution Overview
Problem
Modular multilevel converter (MMC) topologies face challenges with high semiconductor device counts and increased construction costs due to the need for direct current (DC)-link capacitors, necessitating more variable and efficient solutions.
Innovation Solution
The implementation of multiphase line frequency commutated voltage source converters (VSCs) for MMC and hybrid MMC (HMMC) topologies, which reduce the number of semiconductor devices and capacitor size, enabling smaller volume and lower construction costs through advanced control methods and topology designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If modular multilevel converter topologies are used, then reliability and scalability are improved, but the number of semiconductor devices increases and construction cost increases
Solution Approach 1:
The patent combines the DC-link capacitor function with the submodule capacitor banks by connecting multiple submodule capacitors in series to form an equivalent DC-link capacitor. This merging eliminates the need for separate DC-link capacitors and reduces the total number of semiconductor devices by using a unified capacitor structure that serves dual purposes.
Solution Approach 2:
The submodule capacitors are designed to serve multiple functions: they act as both the DC-link capacitors for the voltage source converter and as the capacitor banks for the modular multilevel converter operation. This multi-functionality reduces the overall component count while maintaining system reliability and scalability.
2Adaptability or versatility
If DC-link capacitors are added to modular multilevel converters, then voltage source converter functionality is achieved, but construction cost and system volume increase
Solution Approach 1:
The patent merges the DC-link capacitor function with the existing submodule capacitor banks by connecting submodules in series. This eliminates the need for separate DC-link capacitors, significantly reducing system volume while maintaining full voltage source converter functionality for AC-to-DC and DC-to-AC conversions.
Solution Approach 2:
The DC-link capacitor is segmented into multiple smaller submodule capacitors connected in series. This segmentation allows the system to achieve the required voltage rating while using smaller, more compact capacitor units, thereby reducing overall system volume compared to using a single large DC-link capacitor.
3Productivity
If high voltage series IGBTs and chain-link structures are combined, then power density is improved, but device complexity and construction cost increase
Solution Approach 1:
The patent employs dynamic control strategies where the voltage source converter can operate in different modes (rectifier or inverter) and the submodule capacitors can be dynamically connected in series or parallel configurations. This dynamic operation achieves high power density while managing device complexity through flexible, adaptive control rather than fixed complex topologies.
Solution Approach 2:
The system changes operational parameters such as the number of submodules connected in series, the switching frequency, and the voltage levels dynamically based on operating conditions. This allows the converter to maintain high power density across different load conditions while avoiding the need for overly complex fixed topologies.
Data Source
AI summary
Aspects are described for line frequency commutated voltage source converters for multiphase modular multilevel converters. A voltage source converter (VSC) capacitor voltage of a multiphase VSC of a multiphase power converter can be identified. The multiphase VSC can include a half-bridge circuit for each phase of the multiphase power converter. A circuit parameter can be identified and utilized to determine an arm voltage of an arm of a branch of the multiphase converter. Switch control signals can be generated to insert or bypass the VSC capacitor for the arm of the branch of the multiphase converter device, based at least in part on a comparison between the arm voltage and the VSC capacitor voltage.