Performance Evaluation of Split NPC 3L Modules for 1500VDC Central Solar Inverter up to 1.5 MW

Abstract:
To pursue a lower system cost and a higher power generation efficiency, solar power industry is heading to the direction of 1500 VDC system. This paper introduces a newly designed split NPC 3L modules together with a built up inverter solution that is designed dedicatedly to meet the new demand of 1500 VDC solar inverters. By splitting the NPC 3L topology into upper and lower sections, a powerful built up 3L leg can be obtained, which has 1200 V blocking voltage and 1200 A current on chip level. The switching characteristics of each IGBT and diode were measured on a built up 3L inverter by double pulse test. Furthermore, the inverter was tested with full power on a back to back inverter test bench. Testing and simulation results show that the split NPC 3L inverter is capable to output 722 Arms current at 5 kHz switching frequency with an efficiency of 98.7 %, namely the inverter can output 750 kW power at 600 VAC without module paralleling and 1.5 MW with 2 pairs of modules in parallel. Compared with 3 half bridge modules build up solution, the introduced split NPC 3L solution has one less module and much easier bus bar design, which can lead to a compact, low stray inductance and cost effective inverter design.