The protection technology of high voltage variable frequency drive system

The high voltage variable frequency system has complicated structure and high power density. It comprises industrial frequency AC, DC and variable frequency AC. All of these bring new challenges to the system´s protection and stability control. This paper considered the protection strategy in two aspects: device-level protection and system-level protection. Through improving the circuit structure and configuring microcomputer protection system, the paper designed a complete protection strategy for NPC three-level variable frequency drive system. The protection covered the fault of rectifier input, DC link, inverter output and the induction motor. The paper also analyzed the cooperation of protective trip and pulse blocking, which intending to restrain the feedback energy, and validated the feasibility of setting an output breaker to cut the feedback.