Five-Level Converter Asymmetrical Flying Capacitor Topology
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Solution Overview
Problem
Existing multi-level converting devices face challenges with voltage rating and dv/dt issues in medium-voltage and high-voltage systems, limiting their efficiency and economic viability in high-power applications.
Innovation Solution
A five-level converting device with an asymmetrical circuit structure, utilizing two flying capacitor units connected differently, enhances flexibility and resilience, improving electrical performance compared to three-level conversion technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional three-level conversion technology is used, then the device structure is simpler, but the electrical performance and efficiency are inferior
Solution Approach 1:
The converter is divided into multiple switching units (first switching unit, second switching unit, third switching unit, fourth switching unit) that can be independently controlled. Each switching unit contains specific switching devices and capacitors that operate semi-independently, allowing complex five-level voltage generation through coordinated operation of simpler modular units, thereby improving electrical performance while managing device complexity
Solution Approach 2:
The circuit employs a nested structure where flying capacitors are embedded within the switching units, and switching units are cascaded to form the complete five-level converter. The first and second flying capacitors are nested within respective switching units, which are then integrated into the overall circuit topology, enabling compact implementation of complex functionality
2Loss of energy
If medium-voltage or high-voltage systems are used in high power applications, then efficiency and economy improve, but voltage rating and dv/dt problems arise
Solution Approach 1:
The output voltage is segmented into five distinct levels through the coordinated operation of multiple switching units and flying capacitors. This voltage segmentation reduces the dv/dt stress on individual switching devices compared to a conventional two-level converter, allowing efficient high-power operation while mitigating voltage-related harmful effects
Solution Approach 2:
Flying capacitors serve as intermediary energy storage elements that facilitate smooth voltage transitions between levels. These capacitors act as buffers that reduce the rate of voltage change (dv/dt) during switching operations, thereby improving conversion efficiency and reducing voltage stress on power devices in medium-voltage and high-voltage applications
Data Source
AI summary
A five-level converting device includes a first switch module, a second switch module and a third switch modules each connects to a neutral point, a positive terminal and a negative terminal of a bus capacitor module. A first switch module includes a plurality of bidirectional switching circuits cascaded to each other, and each bidirectional switching circuit includes two first switching units reversely connected in series. Second switch module includes a plurality of second switching units connected in series. Third switch module includes a plurality of third switching units connected in series. A first flying capacitor unit is connected across the first switching module and a second switch module, and a second flying capacitor unit is connected across the first switching module and a third switching module. The first flying capacitor unit and the second flying capacitor unit are connected to different connection points between the first switch units respectively.