Multi-phase LLC Resonant Converter Current Sharing
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Solution Overview
Problem
Existing multi-phase LLC resonant converters face challenges in cost-effective and flexible current sharing due to component tolerances, leading to inefficiencies and high costs in dynamic performance, especially at light loads and in modular designs.
Innovation Solution
A common-inductor, multi-phase LLC resonant converter topology where the resonant inductors in each phase are connected in parallel, allowing for automatic load-current sharing without additional components or complex control methods, enabling expansion to any number of phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple LLC resonant converters are connected in parallel to address current stress in high-power applications, then power handling capability increases, but significant current imbalance occurs due to component tolerances and different resonant frequencies
Solution Approach 1:
A current-sharing capacitor is introduced as an intermediary component connected in parallel with each phase's resonant capacitor. This additional capacitor compensates for the effects of component tolerances and resonant frequency differences between phases, enabling effective current sharing and balancing the output currents across all phases while maintaining high power handling capability
2Object-affected harmful factors
If interleaved parallel power converters are used to provide output with small ripple, then output ripple decreases, but additional MOSFETs and gate-drive circuits are required increasing cost and complexity
Solution Approach 1:
The system utilizes the natural phase-shifted oscillations of the LLC resonant converters and the current-sharing capacitors to automatically achieve current sharing and reduce output ripple. The capacitors self-adjust to balance the currents based on the resonant characteristics, eliminating the need for additional MOSFETs and complex gate-drive circuits while maintaining low output ripple
3Duration of action of stationary object
If interleaved parallel power supplies operate at light loads, then continuous operation is maintained, but efficiency decreases due to switching losses of all MOSFETs
Solution Approach 1:
The system dynamically adjusts the operation of parallel LLC resonant converters based on load conditions. The current-sharing capacitors enable automatic current redistribution among phases, allowing the system to maintain continuous operation at light loads while minimizing switching losses by optimizing the contribution of each phase according to the actual load 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 significantly reduces resonant current errors, achieving efficient load and current sharing with minimal cost and complexity, as demonstrated by simulations and experimental results showing a 63-fold reduction in resonant current error to 0.44% at 600 W total load power.
Implementation Method 1
the resonant inductors in each phase are connected in parallel, allowing for automatic load-current sharing
Implementation Method 2
high efficiency as a result of zero-voltage switching (ZVS) of the primary-side MOSFETs
Implementation Method 3
zero-current switching (ZCS) of the secondary-side diodes in which the secondary-side diodes are switched between current-flowing and current-blocking states so that the diode current decreases to zero before the next half period
Data Source
AI summary
An LLC resonant converter includes a first phase with a first primary circuit and a second phase with a second primary circuit. The first primary circuit includes a first shared inductor, and the second primary circuit includes a second shared inductor. The first and second shared inductors are connected in parallel with each other. The first and second primary circuits do not include a capacitor that is connected in parallel with each other.