Output Voltage Compensation Using Second Harmonic Ripple in a Two-Stage Converter With Spread Spectrum Modulation

This article proposes a method to compensate for output voltage fluctuations caused by spread spectrum modulation (SSM) using the second harmonic ripple of a boost power factor correction (PFC) rectifier. In the series configuration of a boost PFC and an LLC resonant converter, the LLC resonant converter can conduct the SSM to reduce electromagnetic (EM) noise. However, the operating frequency variation by the SSM induces significant output voltage fluctuations. The proposed method naturally compensates for the output voltage fluctuations induced by the SSM utilizing the second harmonic, filtered by the dc link capacitor with a small capacitance. This enables the compensation without additional components or controllers. Furthermore, the electrolytic capacitor can be replaced with a film capacitor with a longer lifespan due to the small dc link capacitance. Additionally, the output voltage is regulated by the boost PFC. In other words, the LLC resonant converter operates as a dc transformer, performing only the SSM near the resonant frequency. Therefore, the proposed method achieves high cost-effectiveness, longer lifespan, high power conversion efficiency, and EM noise reduction simultaneously. The performance of the proposed method is experimentally validated with an 800-W two-stage converter prototype.