Research On Constant Switching Frequency Model Predictive Control Technology Of Three-level Rectifier

With the development of renewable energy,electric vehicles,and energy storage industries,three-phase PWM rectifier,as a bridge between them and power grid,has the advantages of bidirectional power flow,controllable power factor,and good dc voltage regulation ability.Compared with two-level rectifier,three-level rectifier has the merits of low output harmonics and low voltage stress,and is more suitable for high-voltage and large-capacity applications.This paper combines the third-generation semiconductor silicon carbide(Si C)MOSFET to build a three-level rectifier experiment platform.Compared with the traditional silicon(Si)IGBT,it has higher switching frequency and smaller switching loss.The performance of the three-level rectifier also depends on the selected control strategy.Model Predictive Control(MPC)is a high-performance control algorithm with wide application prospects because of its fast-dynamic response and easy implementation of multi-variable control.These advantages have attracted extensive attention from scholars.However,the traditional finite-control-set model predictive control has the disadvantage that the switching frequency is not constant,which brings great difficulties to design the EMI filter of the rectifiers.In order to solve this problem,this paper proposes a constant switching frequency model predictive control strategy of a three-level rectifier.The feasibility and effectiveness of this control strategy are verified by simulations and experiments.Based on the study of the steady-state performance of the model predictive control and the optimization strategy,a constant switching frequency model predictive control that improves the optimization method is proposed.This control strategy implements the predictive optimal switching sequence control in a three-level rectifier.Moreover,the traversal optimization strategy is optimized,which uses the center vector as the finite control set of model predictive control,and uses the equivalent ideal voltage vector of the optimal switching sequence as the reference value.Finally,the switch sequence output is selected through three cost functions,and the feasibility of the control strategy is verified through simulation analysis.The hardware platform of the T-type three-level rectifier is built and verified by experiments.Among them,the design of the hardware system mainly includes the control circuit,the main circuit,the sampling circuit and the driving circuit.Experimental results show that the proposed control strategy can effectively reduce the amount of calculation compared with traditional model predictive control,and can achieve good static and dynamic performance on the basis of realizing fixed frequency control.