Analysis of Midpoint Current Characteristics for Novel Six-Phase N+2 Power Converter in Different Working Condition

Abstract

In this paper, a novel N+2 power converter is introduced and be applied to a six-phase switched reluctance motor (SRM) drive system. Compared with six-phase asymmetric half bridge (AHB) converter, the number of power devices required by this N+2 converter is greatly reduced, while the independence and controllability of each phase can be ensured. However, in N+2 converters, the two midpoint switches are also important components and working at much higher switching frequency than phase switches. The value of the midpoint current directly affects the heating problem of these midpoint switches then affects the reliability of the N+2 converter. Hence, different operate modes of multi-phase excitation state of N+2 converter are enumerated to obtain the relation between the midpoint current and phase currents. Then the characteristics of the midpoint current under different control parameters were obtained through MATLAB-Simulink, and the parameter optimization rules for reducing the amplitude of midpoint current are summarized. In addition, the characteristics of midpoint current in several typical fault states are also summarized. Finally, the simulation results are verified by experiments.