3-Level Buck-Boost Converter With Flying Capacitor Voltage Balancing
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Solution Overview
Problem
In 3-level buck-boost converters, unbalanced flying capacitor voltage leads to increased voltage stress on switches and additional losses, which are not effectively addressed by prior art.
Innovation Solution
A 3-level buck-boost converter with a flying capacitor voltage balancing circuit, which includes an inductor, output capacitor, switches, flying capacitor, balancing switches, and balancing capacitors, allows the flying capacitor to be connected in parallel with either the top or bottom balancing capacitor at different times to maintain balanced voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a 3-level buck-boost converter is used to reduce current ripple and improve efficiency, then inductor current ripple is reduced and efficiency is improved, but flying capacitor voltage becomes unbalanced causing increased voltage stress on switches and additional losses
Solution Approach 1:
The patent introduces balancing capacitors (first and second balancing capacitors) as intermediary elements that work with balancing switches to regulate the flying capacitor voltage. These balancing capacitors serve as mediators to transfer charge and maintain voltage balance across the flying capacitor, preventing voltage stress on switches while preserving the converter's efficiency benefits
Solution Approach 2:
The patent implements a feedback mechanism where the controller monitors the flying capacitor voltage and adjusts the switching states of balancing switches accordingly. When voltage imbalance is detected, the controller activates appropriate balancing switches to charge or discharge the flying capacitor through the balancing capacitors, maintaining voltage balance dynamically
2Adaptability or versatility
If prior art methods are used in 3-level buck-boost converters, then basic conversion function is maintained, but no effective countermeasure exists for flying capacitor voltage unbalance
Solution Approach 1:
The patent segments the voltage balancing function into distinct components: balancing switches (third and fourth switches) that control charge transfer, and balancing capacitors that store and redistribute energy. This segmentation allows the balancing function to be added as a modular extension to the basic converter topology without fundamentally redesigning the entire system
Solution Approach 2:
The balancing switches and capacitors serve multiple functions: they balance the flying capacitor voltage, provide additional energy storage pathways, and work with the main switching sequence to enable both buck and boost operations. This multi-functionality reduces the need for separate dedicated balancing circuitry
Data Source
AI summary
A 3-level buck-boost converter includes: an inductor connected in series between a switching node and a ground terminal; an output capacitor connected between an output terminal from which an output voltage is output and a ground terminal; a first switch connected between an input terminal to which an input voltage is input and a top plate node; a second switch connected between the top plate node and the switching node; a third switch connected between the switching node and a bottom plate node; a fourth switch connected between the bottom plate node and the output terminal; a flying capacitor connected between the top plate node and the bottom plate node; balancing switches connected between the switching node and the balancing node; a top balancing capacitor connected between the input terminal and the balancing node; and a bottom balancing capacitor connected between the balancing node and the output terminal.