Variable-Switching Constant-Sampling Frequency Critical Soft Switching MPC for DC/DC Converters

A variable-switching constant-sampling frequency critical soft switching model predictive control (VSCS-MPC) method is proposed in this paper to improve the dynamic behavior, efficiency and power density of the DC/DC power converter. Firstly, this paper analyzes the boundary constraints of critical soft switching that are derived with the key parameters of the interlock time and threshold current for typical SiC and GaN devices. Then, the VSCS-MPC method is proposed for synchronous DC/DC converter. VSCS-MPC includes two controlling parts. First is the frequency controller to maintain the critical soft switching operation by adjusting the switching frequency based on the pre-defined boundary conditions with a constant sampling frequency. A discretized frequency controller is developed to improve the stability of the system by maintaining a fixed sampling frequency. Second part is the model predictive controller to track the output voltage/current and maintain critical soft switching during dynamic periods. The explicit optimization and oversampling methods are applied in the MPC controller to meet the high frequency demand. A large current ripple is introduced to achieve the critical soft switching and reduce the inductance.