Flying Capacitor Power Converter Using Low-Voltage Output Switches
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Solution Overview
Problem
Existing power converters in inverter apparatuses require high-voltage switching elements in the output stage, which are expensive and limit performance, despite using lower-voltage elements elsewhere.
Innovation Solution
A power converter design utilizing three-level flying capacitor circuits with series-connected capacitors and switching elements, allowing the use of low-voltage MOSFETs or IGBTs in the output stage, and controlling the switching elements to maintain voltage differences within manageable limits, reducing recovery current and timing misalignment risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-voltage switching elements are used in the output stage to handle the full DC voltage, then the device can function properly, but the cost increases and performance is limited
Solution Approach 1:
The output stage is divided into multiple parallel branches, each containing switching elements that handle only a portion of the total voltage. This segmentation allows using low-voltage switching elements instead of expensive high-voltage elements, reducing cost while maintaining proper device functionality through the combined parallel structure.
2Ease of manufacture
If low-voltage switching elements are used in the output stage to reduce cost, then manufacturing cost decreases, but voltage handling capability is insufficient
Solution Approach 1:
Multiple parallel branches are merged at the output to collectively handle the full voltage. Each branch uses low-voltage switching elements that are cost-effective, but when combined in parallel, they achieve the required voltage handling capability, thus resolving the contradiction between cost and voltage handling capability.
3Device complexity
If switching elements handle full voltage directly, then circuit structure is simple, but recovery current and timing misalignment cause operational issues
Solution Approach 1:
The voltage handling is segmented across multiple parallel branches with dedicated switching elements. This segmentation distributes the voltage stress and reduces recovery current in each individual switching element, thereby improving operational reliability while maintaining reasonable circuit structure through the modular parallel configuration.
Data Source
Figure 1
Figure 2
Figure 3A~3D
AI summary
A power converter 10 includes: flying capacitor circuits 11 and 12 connected in series so as to be in parallel with a DC power supply; flying capacitor circuits 13 and 14 connected in series so as to be in parallel with the DC power supply and the flying capacitor circuits 11 and 12 connected in series; switching elements S1 and S2 connected in series between output terminals of the flying capacitor circuits 11 and 12; switching elements S3 and S4 connected in series between output terminals of the flying capacitor circuits 13 and 14; a first output end OUT1 provided at a midpoint between the switching elements S1 and S2; and a second output end OUT2 provided at a midpoint between the switching elements S3 and S4, wherein a node between the flying capacitor circuits 11 and 12 and a node between the flying capacitor circuits 13 and 14 are connected to a midpoint of a DC power supply voltage, and an AC power is output from the first output end OUT1 and the second output end OUT2.