Design and analysis of LCC resonant network for quasi-lossless current balancing in multistring AC-LED array

Multistring arrays of LED are increasingly used for high-luminance lighting applications. The parallel connection of multiple LED strings, however, gives rise to the issue of current balancing between the strings, as a common voltage applied to them does not guarantee an equal current sharing due to the manufacturing spread in electrical properties. In relation to the need of current balancing, the emergence of AC-LED has enabled a direct driving of LED with ac voltage/current, and capacitors, whose impedance are designed to dominate over the equivalent resistance of LED string, are employed to achieve quasi-lossless current balancing. Although high-efficiency resonant inverters represent an ideal choice for driving AC-LED, their properties tend to be changed significantly by the addition of current-balancing capacitors, which necessitates a reformulation of the conventional design approach. In this paper, the characteristics of an LCC resonant network, which is based on the conventional parallel resonant network and modified by the addition of current-balancing capacitors, are analyzed in depth, and a systematic design procedure for developing an LCC-based resonant inverter with current balancing is formulated. A 100-W prototype is constructed and its performance is tested to verify the proposed design procedure. It is also shown that, with the proposed LCC resonant network, the inverter is capable of reconfiguring itself and operating stably in the case of LED failures.