Analysis of 3-Level NPC Phase-Shifted Full Bridge DC-DC Converter for MV Applications

In this paper, 3-level neutral point clamped based phase-shifted full bridge (3L-NPC PSFB) DC-DC converter is analyzed. The NPC topology has the benefit of reduced blocking voltage of the switches, making it suitable for medium voltage (MV) applications. The 3L-NPC PSFB can operate in three modes-three-level, four-level, and five-level modes. It has been found that the value of inductance required in four-level mode is the lowest for a given inductor ripple current, while it is the highest in three-level mode as well as in a conventional PSFB. Therefore, using four-level mode results in a lower inductor size. Moreover, the input DC-link capacitors are naturally balanced in four and five-level modes, but not in three-level mode. Due to these reasons, operating the 3L-NPC PSFB in four-level mode is advantageous. A 350kW, 1.5kV to 480 V, 3L-NPC PSFB based DC-DC converter is simulated in PLECS using 1200 V SiC MOSFETs. A complete loss analysis is carried out, and the simulation results are presented, which validate the operation and benefits of the converter.