LLC Resonant Converter Light-Load Stability Control
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Solution Overview
Problem
Existing LLC resonant converters face instability and increased voltage stress under light-load or no-load conditions, leading to output voltage ripple and switch voltage stress, which are not effectively addressed by current control methods.
Innovation Solution
The LLC resonant converter employs a primary-side circuit with a first and second bridge arm connected in parallel, where the control unit provides control signals with a fixed frequency and variable phase difference, adjusting the switching frequency and phase difference when it reaches a threshold, to maintain stability without increasing frequency or reducing duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the switching frequency is increased to stabilize output voltage under light-load or no-load condition, then output voltage stability is improved, but voltage ripple increases and switch voltage stress increases
Solution Approach 1:
The patent applies periodic action by using burst control mode where the converter operates in intermittent cycles of ON and OFF states. Under light-load or no-load conditions, the converter switches between active conversion cycles and idle periods, maintaining output voltage stability without requiring continuous high-frequency switching. This periodic operation reduces average voltage ripple and switch stress while preserving voltage regulation capability.
Solution Approach 2:
The patent implements dynamics by making the switching frequency variable rather than fixed. The control unit dynamically adjusts the switching frequency based on load conditions: operating at higher frequencies during light-load to maintain voltage stability, and transitioning to fixed frequency at threshold. This dynamic frequency adjustment optimizes the balance between voltage stability and voltage ripple across different operating conditions.
2Stability of the object's composition
If the switching frequency is increased to stabilize output voltage under light-load or no-load condition, then output voltage stability is improved, but switch voltage stress increases
Solution Approach 1:
The burst control mode uses periodic ON-OFF cycling to reduce the duty cycle during which switches are subjected to full voltage stress. By limiting the active conversion window and introducing idle periods, the average voltage stress on switches is reduced while maintaining adequate voltage regulation through the resonant circuit's energy storage capability during active periods.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on load conditions. When load decreases, the frequency increases to maintain voltage stability, but when a threshold is reached, the frequency is capped and other parameters (duty cycle, burst ratio) are adjusted instead. This parameter change strategy prevents excessive switch voltage stress by avoiding unbounded frequency increases.
3Adaptability or versatility
If the duty cycle of primary side switches control signal is reduced to operate under light-load or no-load, then adaptability to light-load condition is improved, but output voltage stability deteriorates
Solution Approach 1:
The burst control mode achieves adaptability to light-load conditions by using periodic bursts of switching activity rather than continuous low-duty-cycle operation. The converter operates in alternating active and idle periods, where the active bursts provide sufficient energy transfer to maintain output voltage, and the idle periods allow the resonant circuit to naturally discharge and reset. This periodic approach maintains voltage stability better than continuous low-duty-cycle operation while adapting to light-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
This approach reduces voltage ripple and switch stress, allowing the LLC resonant converter to operate effectively under light-load or no-load conditions without additional load requirements, maintaining output voltage stability and minimizing switch voltage stress.
Implementation Method 1
LLC resonant converter is a DC-to-DC power converter having features of turning on primary-side switches with zero voltage and turning off secondary-side rectifying switches with zero current
Implementation Method 2
The LLC resonant converter includes a transformer, a primary-side circuit, and a control unit. The primary-side circuit is coupled to a primary-side winding of the transformer
Data Source
AI summary
An LLC resonant converter includes a transformer and a primary-side circuit coupled to the transformer. The primary-side circuit includes a first bridge arm, a second bridge arm, and a control unit. The first bridge arm includes a first switch and a second switch, and the second bridge arm includes a third switch and a fourth switch. The control unit provides a first control signal to control the first switch and provides a fourth control signal to control the fourth switch. The control unit adjusts a switching frequency of the first control signal and the fourth control signal according to an output voltage. When the switching frequency increases to a frequency threshold value, the switching frequency is controlled to be fixed at the frequency threshold, and the first control signal and the fourth control signal are controlled to have a variable phase difference.