A novel sinusoidal extended phase shift modulation with minimal loss for single-stage onboard chargers for electrical vehicles

Single-stage onboard chargers (SSOBCs) are increasingly gaining attention because of their high power density and reliability. However, achieving high efficiency within a wide operating range while maintaining the unity power factor (PF) remains unsolved due to the single-stage structure. The difficulty is twofold. Firstly, the full-range zero-voltage switching (ZVS) achievement at a wide operating range is challenging, which causes high switching loss. Secondly, sinusoidal input voltage leads to a high inductor current, which increases conduction loss. To address the above issues, this paper presents an adaptive sinusoidal extended phase shift (ASEPS) modulation technique with high PF for SSOBCs to minimize power loss and increase efficiency. Firstly, aiming to minimize the switching loss, the proposed extended phase shift introduces one more degree of freedom in the secondary bridge to extend the ZVS technique range and flexibility, especially at a wide operating range. Then, combined with the ZVS condition, the minimal peak current optimization is presented to minimize the inductor current, which reduces conduction loss. Experimental results in a 6kW silicon carbide (SiC)-based SSOBC prototype verify that the proposed ASEPS technique increases efficiency by 1.7% compared to the existing pulse width modulation (PWM) and by 0.6% compared to the non-extended modulation strategy.