AC Interconnection Converter Chain for Low-Loss Power Flow Control
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Solution Overview
Problem
Existing solutions for flexible interconnection of alternating-current power sources in closed-loop power systems are costly due to the requirement of two sets of back-to-back full-power converters, which is not cost-effective for parallel flexible interconnection.
Innovation Solution
A flexible alternating-current interconnection apparatus comprising interconnection converter chains for three phases, including power balance sub-modules and first-type full-bridge sub-modules, connected with an energy supply unit that can adjust voltage and phase to enable flexible control of transmission power between two alternating-current power sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two sets of back-to-back full-power converters are used for flexible interconnection, then voltage and phase regulation capability is improved, but system cost increases significantly
Solution Approach 1:
The converter chain is divided into multiple sub-modules (first-type full-bridge sub-modules and second-type full-bridge sub-modules) that can be independently controlled. This segmentation allows selective operation of sub-modules based on actual interconnection needs, reducing the number of simultaneously operating converters while maintaining voltage and phase regulation capability.
Solution Approach 2:
The system dynamically adjusts the number of operating sub-modules based on the actual power transmission requirements and voltage/phase differences between the two AC power sources. When voltage and phase are well-matched, fewer sub-modules operate; when mismatches occur, additional sub-modules are activated to provide regulation, optimizing both adaptability and cost-effectiveness.
2Device complexity
If direct interconnection of two power sources is performed, then system simplicity is improved, but over current occurs due to voltage and phase differences
Solution Approach 1:
The converter chain acts as an intermediary device between the two AC power sources. It provides controlled coupling that prevents direct connection issues while maintaining system simplicity. The converter chain regulates current flow and voltage/phase differences, eliminating overcurrent risks without requiring complex protection circuits.
Solution Approach 2:
The system changes the operating parameters (voltage magnitude and phase angle) of the converter chain output to match the receiving power source. This parameter adjustment capability allows safe interconnection even when source parameters differ, preventing overcurrent while maintaining a simple single-device architecture.
Data Source
Figure 1~3B
Figure 4A~4C
Figure 4D~5B
AI summary
The application provides a flexible alternating-current interconnection apparatus and a startup control method. The flexible alternating-current interconnection apparatus comprises: interconnection converter chains for three phases, and an energy supply unit, the interconnection converter chain for each phase comprising N power balance sub-modules, M first-type full-bridge sub-modules and a reactor, wherein each of the power balance sub-module comprises a second full-bridge circuit, a second direct-current capacitor and a first bridge circuit, each of the first-type full-bridge sub-module comprises a first direct-current capacitor and a first full-bridge circuit, and the direct-current ends of the first full-bridge circuit are connected with the first direct-current capacitor in parallel; the alternating-current ends of the first bridge circuits in the interconnection converter chain for each phase are connected with the energy supply unit, such that the energy supply unit performs a power exchange with the power balance sub-modules in the interconnection converter chain for each phase; where M is greater than 0, the alternating-current ends of the second full-bridge circuits in the interconnection converter chain for each phase and the alternating-current ends of the first full-bridge circuits thereof are connected with the reactor in series to form a series branch; an one end of the series branch is connected with a first alternating-current power grid, and another end of the series branch is connected with a second alternating-current power grid.