Spread Spectrum Technique for Current-Fed LLC Resonant Converter with Tight Output Voltage Regulation

A spread spectrum technique (SST) reduces an electromagnetic interference (EMI) from a switch mode power supply (SMPS) by spreading the bandwidth of the EM noise. However, it is difficult to apply the SST into a resonant converter because the resonant converter has large voltage gain fluctuation according to the switching frequency variation. Therefore, applying the SST to the resonant converter can increase the output voltage ripple and decrease the output voltage regulation capability of the resonant converter. In this paper, a current-fed LLC resonant converter using a hybrid control algorithm is proposed to implement the SST to reduce the EMI emission and tight output voltage regulation for renewable energy applications. The hybrid control method can effectively compensate the output voltage ripple by the SST. The performances of the proposed converter and control method are verified with a 500-W prototype converter.