Flying Capacitor Voltage Control in Multilevel DC Converters
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Solution Overview
Problem
Existing control methods for flying capacitors in multi-level direct current converters face challenges in stabilizing the voltage at a target value, especially under high-frequency, high-load conditions, requiring precise control that is impractical for real-world applications.
Innovation Solution
A controller adjusts the duty cycle or phase difference between switching transistors based on the inductor current magnitude to stabilize the flying capacitor voltage, using thresholds to determine when to adjust these parameters and maintain operation stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the difference between duty cycles of switching transistors is adjusted to control flying capacitor voltage, then voltage control capability is improved, but control complexity and requirement on control chip increase extremely under high-frequency triangular wave conditions
Solution Approach 1:
The patent changes the control parameter from instantaneous current direction detection to inductor current magnitude comparison. By comparing the absolute value of inductor current with a threshold value, the control method avoids high-frequency switching detection while maintaining voltage control capability, thus reducing control chip complexity
Solution Approach 2:
The patent extracts the essential control function from complex instantaneous current direction control. By focusing only on inductor current magnitude rather than instantaneous direction, the method simplifies the control logic while preserving the ability to regulate flying capacitor voltage effectively
2Reliability
If duty cycle difference is increased to stabilize flying capacitor voltage, then voltage stabilization capability is improved, but control effectiveness deteriorates when inductor current is small and high-frequency
Solution Approach 1:
The patent introduces dynamic control by adjusting duty cycle difference based on inductor current magnitude. When inductor current exceeds a threshold, duty cycle difference is adjusted to stabilize voltage; when below threshold, the adjustment is modified. This dynamic adaptation ensures effective control across varying load conditions without requiring excessively large duty cycle differences
Data Source
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AI summary
Embodiments of this application provide a multi-level direct current converter, a voltage control method for a flying capacitor, and a control apparatus. The multi-level direct current converter includes a controller, a flying capacitor, two switching transistor groups, and an inductor. The method for controlling a flying capacitor includes: in response to that an absolute value of a difference between a sampling voltage and a reference voltage of the flying capacitor is greater than a first threshold, adjusting a duty cycle difference between first switching transistors in two switching transistor groups or a phase difference between carriers of first switching transistors in two switching transistor groups based on a magnitude of an inductor current. According to embodiments of this application, a voltage of the flying capacitor can be controlled, to improve operation stability of the multi-level direct current converter.