Improved Model Predictive Control for Dual Active Bridge Converters with Variable Frequency Phase-Shift Modulation

The hybrid variable frequency and phase-shift modulation benefits the efficiency of dual active bridge (DAB) converters. However, incorporating it into model predictive control (MPC) algorithms leads to excessive computational complexity due to the high number of control variables. To enable multivariable regulation without overloading the digital processors, we propose an improved MPC strategy for DAB converters for high efficiency. First, the optimal operating point of current stress minimization is analytically derived for control references. The reference for the phase-shift angle is determined by the voltage conversion ratio for output voltage tracking while that for switching frequency is optimized with respect to the output power. Since the switching frequency reference can be expressed as a function of the phase-shift reference, these references are determined in a series sequence and incorporated in the cost function of the MPC. The control variables are adaptively discretized to form the finite control set (FCS) for computation efficiency and trade-off between the dynamic and stead-state performance of the DAB system, and then evaluated by the MPC to approach their references. According to the simulation in PLECS platform, the innovative control framework achieves fast and accurate voltage tracking and high power conversion efficiency for wide output power range in comparison with the single phase-shift modulation and PI control.