Research on flexible uninterrupted neutral section passing system based on V-clamp multilevel converter

Abstract

This paper proposes a novel flexible uninterrupted neutral section passing system based on four-leg V-clamp multilevel converter (VMC). It can better solve a series of problems such as overvoltage, overcurrent and speed loss caused by the interruptible over-phase scheme used in electrified railway, and compensate the negative sequence and reactive current in traction power supply system at the same time. VMC is a new type of multilevel converter with common DC-link capacitors. VMC has advantages in the number of devices to some extent, and its expansion from odd level to even level is very simple. Compared with schemes based on modular multilevel converter (MMC), this system has the advantages of low converter hardware cost and no energy loss resulting from hot backup. The system configuration, working process and operating principle are analyzed in detail, and a control strategy for the whole process of neutral section passing is designed. Next, the method based on zero-sequence voltage component injection is used to solve the voltage-balancing problem existed in multilevel converter with common DC-link capacitors, which does not need additional switching times and is easy to realize in three-phase three-wire system. Finally, the simulation results are given to verify the feasibility and effectiveness of the system.

Keywords

• Multilevel converter
• Flexible uninterrupted neutral section passing system
• Power quality
• Voltage- balancing