Three-Level DC-DC Converter Control for Flying Capacitor Balance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing three-level DC-DC converters face challenges in maintaining stable voltage balance of the flying capacitor due to parasitic parameters and errors, leading to unstable inductor current, particularly when duty ratios approach 0 or 1 in CCM mode and less than 0.5 in DCM mode, compromising circuit reliability.
Innovation Solution
A control method that adjusts both the phase difference and duty ratio of power switches based on the error between the flying capacitor voltage and a predetermined value, ensuring voltage balance across the flying capacitor in all load conditions by using a feedback compensation circuit, capacitor balancing circuit, and driving circuit to stabilize the voltage at a predetermined value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase-shifting control is used to balance flying capacitor voltage, then voltage balance is improved, but voltage-sharing ability becomes insufficient when duty ratio is close to 0 or 1 in CCM mode or less than 0.5 in DCM mode
Solution Approach 1:
The patent dynamically adjusts the phase difference between driving signals of power switches based on the duty ratio. When duty ratio is within a preset range, phase-shifting control is applied; when duty ratio is outside this range, the control strategy is dynamically changed to maintain effective voltage sharing across all operating conditions
Solution Approach 2:
The patent changes the control parameters (phase difference and duty ratio) based on operating conditions. By monitoring the duty ratio and adjusting the phase difference accordingly, the system adapts to different load conditions and maintains voltage balance effectiveness across the entire duty ratio range
2Device complexity
If conventional control methods are used, then circuit structure is simple, but inductor current becomes unstable due to parasitic parameters and errors
Solution Approach 1:
The patent implements a feedback control mechanism where the actual flying capacitor voltage is monitored and compared with the target voltage. The phase difference and duty ratio are continuously adjusted based on the voltage error feedback, compensating for parasitic parameters and errors to maintain stable inductor current
Solution Approach 2:
The patent introduces phase difference adjustment as an intermediary control variable between the voltage error and the power switch operation. This intermediary mechanism allows indirect control of flying capacitor voltage through phase relationship manipulation, improving current stability without requiring complex direct voltage control circuits
Data Source
AI summary
A control circuit of a three-level DC-DC converter, can include where: the three-level DC-DC converter includes first, second, third, and fourth power switches coupled in series between an input voltage and a reference ground, and a flying capacitor coupled between a common node of the first and second power switches and a common node of the third and fourth power switches; and the control circuit is configured to adjust a phase difference between driving signals of the first and second power switches, and duty ratios of the first and second power switches, according to an error between a voltage across the flying capacitor and a predetermined value, such that the voltage across the flying capacitor is stabilized at the predetermined value.