A new three-level NPC inverter based on phase individual DC-link circuit and high quality digital SPWM control technology

Due to the existence of reverse recovery time of power diodes, the clamp diodes and di/dt-chokes diodes of three-level NPC inverter will enter the reverse recovery region at the same time, and the partial over-circuit phenomena will occur. This problem limits the output power of inverter system and do harm to the devices. To avoid this over-current problem, a new circuit implementation of 6 kV three-level NPC inverter based on three phase individual DC-link is presented. Using this new circuit the partial over-current problem of traditional three-level NPC inverter can be solved. On the other hand, the security, stability and flexibility of three-level NPC inverter control system are much more complicated than traditional two-level system and low-voltage inverter. So the high reliability hardware and software based on layer organization structure has been put forward. This control scheme is realized with only a single FPGA chip and can provide an effective, flexible, and safe solution for high-power three-level NPC inverters. At last, some simulation and experimental results are presented to verify the advantages of the 6 kV three-level NPC inverters.