LLC Converter Hold-Up Time Extension via Synchronous Rectifier Control
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Solution Overview
Problem
Resonant LLC power converters face a trade-off between high efficiency and long hold-up time, where increasing efficiency reduces hold-up time and increasing hold-up time decreases efficiency, and solutions like bulk capacitance result in lower power density and higher costs.
Innovation Solution
A power converter design with a controller that manages switching elements and synchronous rectifier switches to extend hold-up time by controlling their states during pulse cycles, allowing for efficient energy use and maintaining high efficiency while prolonging the converter's output generation after input power interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If magnetizing inductance is increased to reduce switching losses and improve efficiency, then efficiency is improved, but hold-up time decreases significantly
Solution Approach 1:
The patent implements dynamic control of the synchronous rectifier switches during hold-up time, where the conduction period of the rectifier switches is adjusted based on the operating conditions. During normal operation, the rectifier switches conduct for the full resonant half-cycle, but during hold-up time extension, the conduction period is reduced to overlap less than the entire primary switching element conduction period, thereby extending hold-up time while maintaining efficiency.
2Duration of action of moving object
If lower ratio (Lm/Lr) is designed to achieve longer hold-up time, then hold-up time is improved, but efficiency is lowered
Solution Approach 1:
The patent changes the operational parameters of the synchronous rectifier switches during hold-up time extension. Specifically, it adjusts the conduction timing and duration of the rectifier switches to optimize the trade-off between hold-up time and efficiency, allowing the converter to operate in an extended hold-up mode without the need to change the physical inductance ratio.
3Duration of action of moving object
If bulk capacitance is increased to maintain high efficiency while achieving long hold-up time, then hold-up time is improved, but power density decreases and cost increases
Solution Approach 1:
The patent enables the resonant LLC converter to extend its hold-up time by utilizing its own internal energy storage and resonant characteristics, rather than relying on external bulk capacitance. The controller manages the switching elements and synchronous rectifier switches to extract maximum energy from the existing magnetizing inductance and output capacitance, allowing the converter to serve its own hold-up time extension needs without additional passive components.
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 effectively extends the hold-up time of resonant LLC power converters while maintaining high efficiency, avoiding the trade-offs of previous designs and reducing costs associated with increased capacitance, thus achieving a balance between efficiency and power density.
Implementation Method 1
a transformer comprising a first winding coupled with the first and second switching elements... a second winding of the transformer inductively coupleable to the first winding
Implementation Method 2
resonant LLC power converters... resonant circuit coupled to the plurality of primary side switching elements
Data Source
AI summary
A controller of a power converter is coupled to a switch assembly and configured to perform a hold-up time procedure that causes the controller to control first and second switching elements into opposite conducting states during a first period of time of a pulse cycle and into alternate opposite conducting states during a second period of time of the pulse cycle. The hold-up time procedure also causes the controller to control a first pair of synchronous rectifier switching devices into a conducting state during a third period of time overlapping less than all of the first period of time and into the conducting state during a fourth period of time overlapping less than all of the second period of time. A second pair of synchronous rectifier switching devices is controlled into a non-conducting state during the first and second periods of time.