The single-stage Totem pole dual active bridge (DAB) AC-DC converter has the advantages of low component count, high power density, and low cost, which has a broad application prospect in the field of on-board chargers (OBC). However, in the available research, the traditional single phase shift (SPS) and extended phase shift (EPS) modulation strategies are unable to optimize the quality of grid-connected current and efficiency of the Totem pole DAB AC-DC converter at the same time due to the problem of insufficient modulation degrees of freedom, limiting the further application in on-board chargers.

This paper introduces the asymmetric modulation based on the extended phase shift modulation strategy when the duty cycle of the secondary side switching tubes is no longer 50%. An asymmetric extended phase shift (AEPS) modulation strategy with three degrees of freedom is proposed. Accordingly, a multi-objective optimal modulation strategy is solved by considering the simultaneous optimization of the grid-connected current quality and efficiency of the Totem pole DAB AC-DC converter.

Firstly, the steady-state analytical model of AEPS modulation is established by using the time domain analysis method. The initial value decoupling constraint of the inductor current is considered to optimize the quality of grid-connected current, and the peak-to-peak inductor current is taken as the optimization objective. According to the Lagrange algorithm and Karush Kuhn Tucker conditions, the above multi-objective optimization problem is transformed into mathematical equations to solve the optimization solution of modulation variables. Matlab simulations show that the inductor current’s initial value decoupling and peak-to-peak value optimization are realized under the AEPS optimization modulation strategy. Compared with the SPS and EPS modulation, the proposed AEPS optimization modulation strategy reduces the peak-to-peak and RMS levels of the inductor current in the full power band, which reduces the conduction loss of the converter. Moreover, the optimized solutions in different operating modes under APES modulation are continuous, making seamless switching between different operating modes available.

An experimental prototype of a totem pole DAB AC-DC converter with a rated power of 800 W is constructed. Experimental results show that the converter achieves a peak efficiency of 93.5% under the proposed AEPS optimized modulation strategy, 5% and 14.7% higher than the SPS strategy at full load and light load, respectively; 1.5% and 14.7% higher than the EPS modulation strategy at full load and light load, respectively. The converter's grid-connected current THD is significantly reduced in the full power range, improving its grid-connected current quality. Simulation and experimental results verify the effectiveness of the proposed AEPS-optimized modulation strategy.