Multi-mode control strategy in three-level DC-DC converter for higher efficiency operation under light-load and standby conditions

A multi-mode control strategy (MMCS) is proposed to improve the efficiency of three-level (3L) DC-DC converter under light-load and standby conditions without auxiliary components. 3L converter is typically controlled in phase-shift control mode (PSCM) in order to achieve zero-voltage-switching (ZVS) to reduce switching loss with rated load. However, since little energy is provided to discharge the parasitic capacitors of the switches, light load leads to hard switching and makes efficiency drop in PSCM. The proposed control strategy aims to overcome this problem. It consists of three modes: PSCM to reduce switching loss with heavy load, pulse-width-modulated control mode (PWMCM) to reduce conduction loss with light load and PWM burst control mode (PWMBCM) to further reduce unnecessary loss under standby condition. A 120V, 1.5kW prototype has been made to validate this control strategy. The efficiency of the 3L converter is increased by up to 24.7 percentage points under standby condition and 3.7 percentage points with light load.