LLC Resonant Converter Control for Secondary-Side Symmetry
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Solution Overview
Problem
Existing LLC circuits face issues with current and voltage asymmetries at the secondary side, leading to high output current peaks and increased filter size requirements, which compromise efficiency and space constraints.
Innovation Solution
The LLC circuit employs dynamic adjustment of switch-on times and duty cycle control based on real-time feedback and lookup tables to maintain symmetry, using a closed-loop DC/DC control circuit and PFC mode to optimize switch-on times and duty cycles for different load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed dead time is used in LLC circuits, then the circuit operation is simplified, but current and voltage asymmetries occur at the secondary side leading to high output current peaks
Solution Approach 1:
The patent applies dynamic adjustment of the dead time parameter based on operating conditions. The control circuit dynamically modifies the dead time between complementary switches depending on the load current magnitude and frequency, transforming a static parameter into a dynamic one that adapts to varying operating conditions, thereby preventing current peaks while maintaining operational simplicity
Solution Approach 2:
The patent changes the dead time parameter according to operating conditions. By adjusting the dead time duration based on load characteristics and frequency, the system optimizes the symmetry of secondary side currents and voltages, eliminating harmful current peaks without complicating the overall circuit operation
2Stability of the object's composition
If duty cycle control is applied to maintain symmetry, then output current symmetry is improved, but the control complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit continuously monitors secondary side currents and voltages, detects asymmetries, and automatically adjusts the duty cycle and dead time parameters. This closed-loop control maintains current symmetry while keeping the control system relatively simple through automated parameter adjustment based on real-time measurements
Solution Approach 2:
The control circuit performs self-adjustment by automatically detecting asymmetries in the secondary side currents and voltages and modifying its own control parameters (duty cycle and dead time) to restore symmetry. This self-service capability maintains stable operation without requiring external intervention or complex manual control
3Object-affected harmful factors
If larger output filter is used to damp high frequency current, then LED module protection is improved, but the filter size and cost increase
Solution Approach 1:
The patent applies preliminary action by preventing the generation of high frequency current peaks through optimized switching control (dead time and duty cycle adjustment) before these peaks can occur. By proactively maintaining symmetry and controlling switching parameters, the system prevents harmful currents from arising, thereby reducing or eliminating the need for large protective filters
Solution Approach 2:
The patent converts the potential harm of current asymmetry into a benefit by using the asymmetry detection mechanism to dynamically adjust control parameters. The control circuit uses information about current imbalances to optimize dead time and duty cycle, transforming what would be a harmful condition into a useful feedback signal that improves overall system performance and reduces filter requirements
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 asymmetry, lowers output current peaks, and minimizes filter size requirements, enhancing efficiency and reducing the need for large capacitors while protecting LED modules.
Implementation Method 1
An LLC is a resonant circuit that may be controlled, by adjusting the frequency and/or duty cycle of switches, to achieve a constant output voltage by controlling a switching mechanism feeding a resonance circuit
Implementation Method 2
When isolated, a LLC comprises a primary side and a secondary side of a transformer
Data Source
Figure 1
Figure 2
Figure 3~3(b)
AI summary
The present invention relates to an LLC circuit (200), method for operating thereof, and LED driver. The LLC circuit (200) having output terminals for supplying an LED load, comprises a half-bridge or full-bridge circuit having two switches (202, 203) in series, wherein the switches (202, 203) are alternatingly switched on with respective switch-on time periods TON1, TON2, a transformer (205), and a control circuit (201). Any asymmetry of two successive voltage cycles at the secondary side of the transformer is at least reduced by the control circuit (201) controlling the switch-on time in each cycle, the switch-on time period TON1 of the first switch differs from the switch-on time period TON2 of the second switch.