A Valley-Fill Driver with Current Balancing for Parallel LED Strings Used for High-Frequency AC Power Distribution of Vehicle

High-frequency ac (HFAC) power distribution system has a broad applications caused by the components saving, weight reduction, and efficiency improvement. Meanwhile, light-emitting diode (LED) lighting becomes popularity for vehicle due to the growing energy conservation and long lifetime. In order to introduce HFAC into vehicle LED lighting system, a valley-fill-based driver method is presented with simple structure and easy modularization. Although no harmonics standard was drafted for HF power distribution, this passive power-factor-correction method can be used to meet Energy Star requirement. Meanwhile, LEDs are often arranged in parallel connection to obtain sufficient luminance and high reliability. Since the current imbalance of parallel LED strings can result in performance degradation and functionality failure of LEDs, a new current balancing scheme is proposed to achieve the desired average current for parallel LED strings. The new method is implemented by pulse-density modulation of rectified voltage, and the modulation frequency is significantly less than the frequency of HF distribution bus. Finally, the simulation model and experimental prototype are implemented for the system with the distribution frequency of 50 kHz and a peak voltage of 30 V. The consistent results of three parallel LED strings confirm the feasibility of the proposed driver and current balancing scheme.