Independent Control of Multicolor-Multistring LED Lighting Systems With Fully Switched-Capacitor-Controlled LCC Resonant Network

Current imbalance is a major problem in multistring LED lighting systems. Significant research efforts have been directed to solve the problem by either an active or passive approach. However, in view of some system requirements or other emerging lighting applications, independent control of different LED strings is getting more important to obtain different desirable brightness and/or color spectrums. The existing active and passive approaches have their limitations to perform current balancing and independent control simultaneously, thus posing another great challenge for the design of LED drivers. In this paper, a fully switched-capacitor-controlled LCC resonant converter is designed to address this challenge. With the replacement of all fixed capacitors in the resonant tank of the LCC converter with switch-controlled capacitors (SCCs), the regulation of the common ac bus voltage, current balancing, and individual current control of LED strings can be readily achieved with a single LED driver by varying the effective capacitances of the SCCs under constant switching frequency. In this way, the circuit complexity can be greatly reduced while the circuit performances can be significantly improved. An experimental prototype of driving LED growth light for indoor farming applications is designed and constructed to verify the idea.