LLC Resonant Converter Control Using Selective SR Phase Shifting
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Solution Overview
Problem
Conventional resonant DC-DC converters face challenges in achieving wide gain ranges without sacrificing efficiency, particularly at nominal operating points, due to limitations in frequency modulation and the need for large resonant inductors or wide frequency ranges.
Innovation Solution
The implementation of a selective secondary-side rectifier (SR) phase-shift control method for LLC resonant converters, which involves phase-shifting the switching operations of secondary-side switches with respect to primary-side switching operations, allowing for optimized current flow and reduced frequency range operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If frequency modulation is used to achieve wide gain ranges, then the gain range is expanded, but efficiency is sacrificed especially at nominal operating point
Solution Approach 1:
The patent implements dynamic switching between two operating modes: frequency modulation for wide gain ranges and selective secondary-side rectifier phase-shifting for nominal operating point. This dynamic adaptation allows the system to optimize efficiency at nominal points while maintaining wide overall gain range capability.
Solution Approach 2:
The patent changes the control parameter from frequency modulation alone to a hybrid approach that includes both frequency modulation and phase-shifting control. By introducing phase-shifting as an additional control dimension, the system achieves wide gain range without the efficiency penalties of extreme frequency modulation.
2Adaptability or versatility
If a large resonant inductor is implemented to achieve wide gain ranges, then the gain range is expanded, but the size of magnetic components increases
Solution Approach 1:
The patent uses dynamic phase-shifting control of secondary-side rectifiers to achieve wide gain ranges without requiring oversized magnetic components. The phase-shifting mechanism provides gain adjustment through timing control rather than through large inductance values, thereby maintaining compact magnetic component sizes.
3Productivity
If switching frequency is increased to reduce magnetic component size, then power density is improved, but achieving wide gain ranges becomes more difficult
Solution Approach 1:
The patent adds a temporal dimension to gain control by introducing phase-shifting of secondary-side rectifiers. This phase-angle dimension provides an additional degree of freedom for gain adjustment, enabling wide gain ranges to be achieved at higher switching frequencies without requiring extreme frequency modulation that would compromise power density.
4Device complexity
If conventional frequency modulation is used for gain control, then the control is simple, but SR turn-off losses increase
Solution Approach 1:
The patent implements dynamic phase-shifting control of secondary-side rectifiers that actively manages switching timing to minimize turn-off losses. By controlling the phase relationship between primary switches and secondary rectifiers, the system ensures that rectifier switches turn off when current is minimal, thereby reducing losses while maintaining relatively simple control circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces SR turn-off losses, maintains zero voltage switching (ZVS) for primary devices, and achieves higher power densities and efficiencies across a wide gain range.
Implementation Method 1
resonant converters are desirable due to their ability to achieve soft-switching for the primary and secondary devices. This enables the resonant frequency (fo), and hence the switching frequency (fs) to be increased
Implementation Method 2
phase-shifting the switching operations of secondary-side switches with respect to primary-side switching operations, allowing for optimized current flow and reduced frequency range operation
Data Source
AI summary
An example power converter system includes an input and an output and a power converter between the input and the output. The power converter includes a transformer including N elemental transformers, primary-side switches coupled to a primary side of the transformer and operating based on a primary-side switching operation, and secondary-side switches coupled to each elemental transformer among the N elemental transformers at a secondary side of the transformer. The system further includes a controller configured to generate switching control signals for each secondary-side switches such that a switching operation in at least one elemental transformer among the N elemental transformers is phase-shifted with respect to the primary-side switching operation, while a switching operation in at least one different elemental transformer among the N elemental transformers is in-phase with respect to the primary-side switching operation.