New Random PWM Technique for a Full-Bridge DC/DC Converter With Harmonics Intensity Reduction and Considering Efficiency

PWM techniques for a full-bridge dc/dc converter are investigated and a new random PWM technique is proposed in this paper. Three PWM techniques with constant switching frequency are discussed and the related random PWM techniques which spread the harmonic clusters and give constant average inductor current to reduce the output voltage ripple are discussed. The pros and cons of three constant switching frequency PWM techniques and the related random counterparts are investigated. Experimental results show that there is a significant efficiency drop of the random PWM technique due to significant increase of switching counts. Therefore, this paper presents a new random PWM technique to significantly reduce the harmonic intensity while not causing relevant impact on the efficiency. An FPGA-based digital-controlled isolated full-bridge dc/dc converter prototype is built to verify the performance of conventional and proposed PWM techniques. The specifications of the converter include the following: input voltage = 400 V, output voltage = 12 V, output power = 528 W, and switching frequency = 100 kHz. Measured efficiency and harmonic spread factor will be used for the evaluation of these PWM techniques.