Variable frequency triple-phase-shift modulation strategy for minimizing RMS current in dual-active-bridge DC-DC converters

For dual-active-bridge (DAB) DC-DC converters, a variable frequency triple-phase-shift (VF-TPS) modulation strategy based on a particle swarm optimization (PSO) algorithm was proposed to solve the problem of the low efficiency of TPS modulation in larger power conditions. To facilitate the implementation of the PSO algorithm, the mathematical expressions between the transmission power or the RMS square of the inductance current and four control variables including the switching frequency and three phase-shift duty cycles are simplified by the Fourier series decomposition method. An objective function of the particle fitness is presented to find the optimal control variables at any reference transmission power, which achieves the minimum inductance RMS current in the full power range and improves the efficiency under heavy loads. In addition, the PSO algorithm is used to design the appropriate switching frequency range and inductance. Finally, a 1.2 kW DAB converter prototype was established, and experimental results verify the correctness and feasibility of the modulation strategy.