Current Controlled Voltage Source for Balanced Current Sharing in Parallel LLC Converters
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Solution Overview
Problem
Existing LLC resonant converters connected in parallel face challenges in equalizing output currents due to manufacturing tolerances, leading to uneven current sharing and increased stress on higher current modules, which complicates control systems and increases costs.
Innovation Solution
A system utilizing a current controlled voltage source, such as a current balancing transformer, is implemented between parallel resonant converters to induce a voltage proportional to the difference in AC currents, opposing the larger current and supporting the smaller current, thereby reducing current differences and achieving balanced current sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If LLC resonant converters are connected in parallel to handle very high output power applications, then the power handling capability is improved, but the current sharing between converters becomes uneven due to manufacturing tolerances
Solution Approach 1:
A current controlled voltage source is introduced as an intermediary component between parallel resonant converters. This voltage source generates a balancing voltage proportional to the current difference between converters, which is injected into the AC bus to equalize current sharing. The intermediary actively compensates for manufacturing tolerances without requiring precise matching of converter parameters.
2Manufacturing precision
If individual control systems are implemented for each parallel resonant converter to achieve current equalization, then the current sharing precision is improved, but the system complexity and cost increase
Solution Approach 1:
The control functions of multiple parallel converters are merged into a single centralized control system. The controller receives current signals from all converters, processes the combined information to determine current differences, and generates a single balancing voltage that is injected into the common AC bus. This merging approach achieves precise current sharing while reducing overall system complexity compared to individual control systems.
Solution Approach 2:
A feedback mechanism is implemented where the actual current from each resonant converter is measured and fed back to the centralized controller. The controller processes this feedback information to detect current imbalances and automatically adjusts the balancing voltage accordingly. This closed-loop feedback ensures accurate current equalization while maintaining simple control architecture.
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 simplifies the control system, reduces costs, and ensures precise current sharing among parallel LLC resonant converters, with the ability to connect an unlimited number of converters in parallel using a single control circuit, resulting in reduced current differences to about 5% or less.
Implementation Method 1
The current controlled voltage source may be a current balancing transformer that includes a first winding coupled in series to the first resonant converter for carrying the first AC current from the first resonant converter and a second winding coupled in series to the second resonant converter for carrying the second AC current from the second resonant converter. The system may be configured such that a first magnetomotive force generated by the first AC current flowing through the first winding may be oriented opposite to a second magnetomotive force generated by the second AC current flowing through the second winding and the resultant aggregate magnetomotive force may induce a voltage that opposes the greater of the first and second AC currents.
Data Source
AI summary
Methods and systems for balancing output currents of parallel connected resonant converters are disclosed. One such method includes matching switching frequencies for a pair of resonant converters. The method also includes carrying AC output currents of resonant tanks of each of the resonant converters through a current controlled voltage source that is coupled to each of the resonant converters of the pair of resonant converters at an AC side of each of the resonant converters of the pair of resonant converters. The method further includes inducing, for the pair of resonant converters, a voltage that is proportional to a difference in the AC currents carried through the current controlled voltage source by passing the AC currents through the current controlled voltage source. The induced voltage is oriented to oppose the greater of the AC currents and to increase the smaller of the AC currents.