LLC Resonant Converter Control via Zero-Crossing Period Detection
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Solution Overview
Problem
Resonant converters face challenges in maintaining optimal efficiency, especially at light load conditions, where the switching frequency deviates from the resonant frequency due to complex hardware and control logic requirements, making it difficult to operate effectively.
Innovation Solution
A closed-loop control system is implemented for a half-bridge LLC resonant converter, utilizing a resonant period detection circuit to adjust the conduction time of power switches and synchronous rectifier switches, ensuring the switching frequency aligns with the resonant frequency by detecting zero-crossing points of the resonant current and adjusting drive signals accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex hardware and control logic are used to maintain resonant frequency, then measurement precision improves, but device complexity increases
Solution Approach 1:
The resonant converter system uses its own resonant current zero-crossing points to automatically detect and determine the resonant frequency, eliminating the need for external detection circuits or complex control logic. The system self-regulates by utilizing its inherent electrical characteristics to maintain optimal operating frequency.
2Loss of energy
If switching frequency is adjusted to match resonant frequency, then energy efficiency improves, but control complexity increases
Solution Approach 1:
The system implements a feedback mechanism where the detected resonant frequency (based on zero-crossing points) continuously adjusts the switching frequency of the power switches. This closed-loop control ensures the converter operates at optimal efficiency by automatically adapting to load changes and resonant frequency variations.
Solution Approach 2:
The control system uses the resonant current's own characteristics (zero-crossing points) to generate the control signal for adjusting switching frequency, eliminating the need for external frequency detection circuits or complex control logic while maintaining optimal efficiency.
3Measurement precision
If resonant period detection is implemented, then switching frequency accuracy improves, but ease of operation deteriorates
Solution Approach 1:
The system automatically detects resonant frequency and adjusts switching parameters without requiring manual intervention or complex operational procedures. The zero-crossing detection and frequency adjustment happen autonomously, maintaining high accuracy while preserving operational simplicity.
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 allows the resonant converter to maintain optimal operation across varying load conditions by accurately detecting and adjusting the resonant period, ensuring the switching frequency matches the resonant frequency, thereby enhancing efficiency and stability.
Implementation Method 1
resonant converter 1 can include main power topology 11, resonant network 12, and rectifier circuit 13. Resonant network 12 can include resonant inductor Lr and resonant capacitor Cr connected in series between a common node of power switches Q1 and Q2, and one terminal of rectifier circuit 13.
Implementation Method 2
drive circuit 4 can receive resonant period Tr generated by resonant period generation circuit 23, and may control switching period Ts to be equal to resonant period Tr, such that the switching frequency is equal to the resonant frequency.
Data Source
AI summary
A control circuit for a resonant converter, that is configured to: adjust a conduction time of one power switch and a conduction time of one corresponding synchronous rectifier switch in the resonant converter in a resonant period detection mode; control a resonance current to cross zero twice during the conduction time of the synchronous rectifier switch; and obtain a resonant period of the resonant converter.