Short circuit protection of high-voltage high-power three-level inverter system

The penetration level of high-voltage and high-power three-level inverter system in power electronic conversion system has been improved continuously because of its flexibility in power conversion. And it is widely used in renewable energy power supply system, flexible AC transmission system, uninterrupted emergency power supply, AC-DC-VVVF speed control and other fields. However, the short-circuit fault forms of three-level inverter system are various and the traditional protection methods do not have the characteristics of systematization and integrity. Aiming at the above problems, based on the analysis of the main circuit structure and working principle of the three-level inverter system, this paper divides the system into two parts: the front-end rectifier side and the inverter output side, and studies the various types of short-circuit faults existing in these two parts. The mechanism and characteristics of short-circuit current contributed by corresponding phase-shifting transformers, DC busbars and switching devices are analyzed. On the basis of the traditional protection principle, a multi-compound overcurrent protection method for short circuit fault of power switching devices, high-power transformers and AC/DC transmission lines is proposed. A complete short-circuit protection configuration scheme for three-level inverter system is constructed. Finally, a fault simulation model was built by Matlab /Simulink and a dynamic test was conducted to verify the feasibility of the protection principle presented in the paper.