Adaptive Dead-Time Control for LLC Resonant Converters
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Solution Overview
Problem
Half-bridge LLC resonant converters face challenges in achieving zero-voltage switching (ZVS) across all load ranges due to the sensitivity of dead-time periods, which can lead to capacitive mode operation and loss of ZVS if the dead-time is either too long or too short.
Innovation Solution
A control circuit that includes a slope sensing circuit, capacitive mode judge circuit, slope judge circuit, oscillator, and turn-ON control circuit to adjust dead-time periods based on slope signals and current flowing through the resonant tank, ensuring effective ZVS across varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dead-time period is designed too long to achieve ZVS, then zero-voltage switching is improved, but capacitive mode operation occurs which is dangerous
Solution Approach 1:
The patent implements dynamic dead-time adjustment by detecting the voltage slope at the common node and adaptively modifying the dead-time period. The control circuit monitors the voltage variation rate and adjusts dead-time accordingly, transitioning from fixed dead-time to dynamic dead-time control to prevent capacitive mode while maintaining ZVS
Solution Approach 2:
The patent employs feedback control by detecting the voltage slope at the common node during dead-time and using this information to adjust subsequent dead-time periods. The control circuit continuously monitors voltage variation and feeds this information back to the dead-time control mechanism to optimize switching timing and prevent harmful capacitive mode operation
2Object-affected harmful factors
If the dead-time period is designed too short to avoid capacitive mode, then safety is improved, but zero-voltage switching is lost when load current decreases
Solution Approach 1:
The control circuit dynamically adjusts dead-time based on real-time voltage slope detection rather than using a fixed conservative value. This allows the system to extend dead-time when needed for ZVS (at low load currents) while preventing capacitive mode when appropriate, achieving both safety and ZVS reliability through adaptive control
Solution Approach 2:
The patent changes the dead-time parameter dynamically based on detected voltage slope characteristics. By monitoring the rate of voltage change at the common node, the control circuit adjusts the dead-time duration to optimize both ZVS achievement and capacitive mode prevention across varying load conditions
3Device complexity
If fixed dead-time is used for all load ranges, then device complexity is reduced, but ZVS cannot be maintained across all load conditions
Solution Approach 1:
The control circuit performs self-adjustment by automatically detecting voltage slope conditions and modifying its own dead-time control parameters. The system uses built-in voltage sensing and slope detection capabilities to autonomously optimize dead-time without external intervention, maintaining ZVS across all load ranges while adding minimal complexity
Solution Approach 2:
The voltage slope detection mechanism serves multiple functions: it identifies ZVS conditions, detects capacitive mode risks, and provides timing information for optimal switch activation. This single detection mechanism universally addresses multiple control objectives across the entire operating range, reducing the need for separate control circuits for different load conditions
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
The solution allows for adaptive adjustment of dead-time periods, ensuring zero-voltage switching is maintained across all load ranges, preventing capacitive mode dangers and maintaining ZVS efficiency.
Implementation Method 1
a slope sensing circuit, configured to provide a slope signal based on a voltage variation at a common node of the first switch and the second switch
Implementation Method 2
resonant converter, a current flowing through power switches is sinusoidal wave per a resonant tank
Data Source
AI summary
A resonant converter has a switching circuit having a first switch and a second switch, a control circuit and a resonant circuit. The control circuit has a slope sensing circuit providing a slope sense signal based on a voltage variation at the common node of the first switch and the second switch, a slope judge circuit providing a slope judge signal, and a turn-ON control circuit providing a first reset signal to adjust a first dead-time period from turning OFF the first switch to turning ON the second switch based on the slope judge signal, the slope signal, and a current flowing through the resonant tank, and providing a second reset signal to adjust a second dead-time period from turning OFF the second switch to turning ON the first switch based on the slope judge signal, the slope signal, and the current flowing through the resonant tank.