Six-phase Three-level Neutral Point Clamped Inverter for Capacitor Voltage Balancing and Common-Mode Voltage Cancellation

Abstract

In this paper, a six-phase three-level neutral point clamped (NPC) inverter is proposed to achieve active capacitor voltage balancing as well as common-mode voltage (CMV) cancellation. The conventional three-phase NPC inverter is widely known to have dc-link capacitor voltage balancing issue due to the neutral point current. The proposed six-phase NPC inverter with a balanced six-phase electric machine generates two equal, and opposite neutral currents injected to the same neutral point and canceling out each other. Theoretically, zero neutral current can substantially reduce the size of dc-link capacitor and improve power density and reliability of the system. In addition, the proposed inverter topology naturally cancels out the CMV, leading to noticeably low CM EMI noise generation. Both neutral current and CMV cancellation capabilities are verified with MATLAB and hardware-in-the-loop (HIL) simulations.