A wide zero-voltage-switching range with low reactive power modulation strategy for LCL resonant three-phase dual active bridge DC–DC converter in renewable energy generations

Abstract

LCL resonant three-phase dual active bridge (LCL-TPDAB) dc–dc converter is progressively used in renewable energy systems due to the advantages of low circulating reactive power and wide voltage regulation. Conventional dual-phase-shift (DPS) modulation can effectively reduce the circulating reactive power of the converter, but it cannot achieve zero-voltage-switching (ZVS) of all switches, which increases switching losses and generates electromagnetic interference. To solve the above problems, an optimized modulation strategy based on phase-shift plus duty cycle (PSPDC) control is proposed in this paper. Firstly, the mathematical model of the LCL-TPDAB converter with the PSPDC modulation is established by harmonic analysis. Then, the relationship between the ZVS boundaries and the control variables is determined by analyzing the soft-switching characteristics. In order to accurately describe the ZVS boundaries, the impact of switch junction capacitance is considered in the analysis. Further, an optimized modulation strategy is proposed, which can achieve ZVS for all switches and low reactive power in the whole operating range. Furthermore, the offline particle swarm optimization (PSO) algorithm is introduced to acquire the optimal control variables in the operation of the converter. Finally, a 1.5 kW experimental prototype is applied to verify the effectiveness and excellence of the proposed optimized modulation strategy, where the efficiencies are improved in the whole operating range.