Model Predictive Power Control Scheme For Single-phase Cascaded H-bridge Rectifiers

As the heart of high-speed train,electric traction drive system plays an important role in the stable and fast running of the train.To further increase the running speed of trains,it is necessary to improve the power density of traction drive system,and the traction drive system based on power electronic transformer(PET)has gradually become one of the future development directions.The performance of single-phase cascaded H-bridge rectifiers(CHBRs),as the front-end circuit of PET,is particularly important for the stable and reliable operation of the whole system.Therefore,it is of great theoretical value and practical significance to develop the control algorithm based on CHBR.This paper focus on finite-control-set model predictive power control(FCS-MPPC)schemes of single-phase CHBRs,a simplified MPPC algorithm is studied.The main contents are as follows:Firstly,the circuit topology and operating principle of CHBRs are analyzed in detail,and its mathematical model is deduced.In addition,the principle of several common modulation methods and harmonic distribution characteristics are introduced,and the block diagram of the traditional direct power control(DPC)for CHBRs is shown.Secondly,to realize FCS-MPPC scheme,the power prediction model of CHBRs is derived,and two different evaluation functions are introduced in detail according to the realization of voltage balance control method.To solve the shortcomings of the traditional FCS-MPPC method,such as variable switching frequency and large current harmonics,a dualvetor-based model predictive power control(DV-MPPC)algorithm is proposed.Two voltage vectors are simultaneously applied at each switching cycle,which greatly improved the system’s steady-state performance.On this basis,a dual-vetor-based simplified model predictive power control(DV-SMPPC)algorithm is proposed to eliminate the rolling calculation process and reduce the computational cost of the algorithm.Then,the causes and effects of voltage imbalance of CHBRs are analyzed,and a loadcurrent-calculation-based capacitor voltage balance control method is proposed.Combining with the load current,this scheme can adjust the modulation index increment of each module to realize voltage balance control without PI controller in the traditional method,which can further simplify the control system structure.Finally,a single-phase 3-cell CHBR scale-down experimental prototype is built to test and compare the traditional FCS-MPPC,DV-MPPC and DV-SMPPC schemes.Experimental results have verified the correctness and effectiveness of the proposed scheme.