Flying-Capacitor Multilevel Converter Control Against Subharmonic Oscillation
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Solution Overview
Problem
Multi-level power converters face stability issues due to flying capacitor voltage imbalances, which can lead to higher voltage stress and subharmonic oscillations, particularly because existing control methods are sensitive to gate drive circuitry mismatches and circuit imperfections.
Innovation Solution
The implementation of a controller system that determines a duty reference, a duty correction factor based on flying capacitor voltage errors, and a sign correction signal based on flying capacitor ripple voltage, to generate a duty command for activating the switches in the switching groups, thereby stabilizing the converter operation and balancing flying capacitor voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing control methods are used for multi-level power converters, then the converter can operate, but flying capacitor voltage imbalances occur leading to higher voltage stress and subharmonic oscillations
Solution Approach 1:
The patent implements feedback control by continuously monitoring flying capacitor voltages and adjusting switching duty cycles accordingly. The controller measures the actual flying capacitor voltages, compares them with reference values, and generates correction signals to eliminate voltage imbalances, thereby preventing voltage stress and subharmonic oscillations while maintaining converter stability.
Solution Approach 2:
The patent dynamically adjusts switching duty cycle parameters based on real-time flying capacitor voltage measurements. By changing the duty cycle parameters in response to voltage imbalances, the system optimizes the operation of each switching group to maintain equal flying capacitor voltages and eliminate harmful voltage stress and oscillations.
2Ease of operation
If gate drive circuitry mismatches and circuit imperfections are present, then the converter can operate, but flying capacitor voltage balancing deteriorates
Solution Approach 1:
The patent applies local quality control by implementing independent duty cycle adjustment for each switching group based on its specific flying capacitor voltage status. Rather than uniform control, each switching group receives customized control signals tailored to its local voltage imbalance conditions, compensating for gate drive mismatches and circuit imperfections individually.
Solution Approach 2:
The system dynamically modifies switching parameters for each group based on measured voltage imbalances, adapting the control strategy to compensate for manufacturing tolerances and circuit imperfections in real-time operation.
3Device complexity
If traditional control methods are used, then the system is simpler, but voltage balancing precision is insufficient
Solution Approach 1:
The patent introduces feedback mechanisms that measure flying capacitor voltages and automatically adjust duty cycles to maintain voltage balance, achieving high precision voltage balancing through closed-loop control while managing system complexity through systematic implementation.
Data Source
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AI summary
According to some embodiments, an apparatus comprises a multi-level power converter configured to convert an input voltage to an output voltage, wherein the multi-level power converter comprises one or more switching groups, wherein a switching group of the one or more switching groups comprises a pair of switches and a flying capacitor, and a controller configured to determine a duty reference for the switching group, determine a duty correction factor for the switching group based upon a flying capacitor voltage error of the flying capacitor, determine a sign correction signal based on a flying capacitor ripple voltage, and determine a duty command for activating the pair of switches based on the duty reference, the duty correction factor, and the sign correction signal.