A development of 6kV three-level NPC inverters with novel DC-link circuit and optimal dead-time configuration

Because of the existence of reverse recovery time of the clamp diode and di/dt-chokes diode of three-level natural point camped (NPC) inverter, the partial over current phenomena will occur at the capacitive load or inductive load condition. This problem limits the energy densities of the system and do harm to the power switch devices. To avoid this over current problem, a novel circuit of three-level NPC inverter is presented. The partial over current problem of traditional three-level NPC inverter can be solved by using this new circuit. At the same time, the optimal dead-time configuration of PWM control technology is presented. In this paper, the system parameter selection and test circuit of the new inverters are analyzed in detail. After using those methods, the security and stability of system operating have been enhanced obviously. At last, some experimental results have been presented and discussed.