This paper proposes a new energy management method using the internal capacitor for energy buffer in the boost cascaded buck-boost (BoCBB) power factor correction (PFC) converter. The theory and existing shortcoming of the conventional PFC are first analyzed. A new energy management method realized by model predictive control (MPC) is proposed to maximize the benefit of the internal capacitor with a considerably reduced capacitance. A 500 W PFC is used as a case study. It is found that the energy management method offers more effective control of the output voltage and input current with a much-reduced capacitance. Experimental results validate the proposed concept on a GaN FET based BoCBB PFC prototype.