3-Level Converter Balancing Circuit for Flying Capacitor Voltage
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Solution Overview
Problem
3-level buck and boost converters face challenges in maintaining flying capacitor voltage balancing, leading to increased voltage stress on switches and additional losses, which are not effectively addressed by prior art.
Innovation Solution
A 3-level converter with a flying capacitor voltage balancing circuit that includes an inductor, switches, flying capacitors, and balancing capacitors, where the flying capacitor is connected in parallel with top and bottom balancing capacitors at different times to maintain equal voltages, thereby balancing the flying capacitor voltage at high speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a 3-level converter is used to reduce current ripple and improve efficiency, then inductor current ripple is reduced and efficiency is improved, but flying capacitor voltage balancing becomes difficult to maintain
Solution Approach 1:
The patent introduces balancing capacitors (first balancing capacitor connected to top plate, second balancing capacitor connected to bottom plate) as intermediary elements that mediate the voltage balancing process. These capacitors work together with the flying capacitor to maintain equal voltages across the top and bottom plates, resolving the voltage balancing difficulty while preserving the low current ripple benefit of the 3-level converter.
2Reliability
If prior art methods are used for voltage balancing, then some balancing is achieved, but the balancing speed is insufficient and additional losses occur
Solution Approach 1:
The patent implements periodic switching of the balancing capacitors through controlled switching periods. During specific intervals, the first balancing capacitor is connected to the top plate node while the second is connected to the bottom plate node, and vice versa in alternating periods. This periodic action enables high-speed voltage balancing by actively and repeatedly equalizing the voltages, thereby increasing balancing speed and reducing additional losses compared to passive prior art methods.
3Object-affected harmful factors
If flying capacitor voltage is unbalanced, then voltage stress on switches increases, but maintaining voltage balancing lacks effective countermeasures
Solution Approach 1:
The patent segments the voltage balancing function by separating the balancing capacitors into two distinct components: the first balancing capacitor connected to the top plate node and the second balancing capacitor connected to the bottom plate node. This segmentation allows independent control and optimization of each balancing path, effectively reducing voltage stress on switches while managing the overall circuit complexity through modular design.
Data Source
AI summary
A 3-level converter includes: an inductor connected in series between a switching node and an output terminal from which an output voltage is output, an output capacitor connected between the output terminal 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 a ground terminal, a flying capacitor connected between the top plate node and the bottom plate node, balancing switches connected between the switching node and a 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 a ground terminal.