NPL.H: Neutral-Point-Less H-Type 3-Level Inverter

This article introduces a neutral-point-less H-type (NPL.H) 3-level dual inverter topology for motor drive applications. This multilevel topology craftily eliminates the neutral clamp and neutral point current altogether, resulting in a drastically lower minimum dc-link capacitance, compared with conventional 3-level inverter topologies, while retaining the multilevel benefits. NPL.H has additional merits, including lower output harmonics, lower current stress, and lower capacitor current ripple. The topology is optimal for balanced 6-phase, dual 3-phase, or 3-phase open-end winding motors. This article proposes a low-order frequency form (LoF) for fast and accurate calculations of the important circuit variables (e.g., rms currents of switching devices, inverter bridge input, and dc-link capacitor, and the voltage ripple of the dc-link capacitor), and demonstrates an example in detail with the sinusoidal pulsewidth modulation. Many practical design parameters (e.g., dead time) are reflected in our method to enhance the accuracy of the analytical model. The theoretical rms current expressions of NPL.H are successfully derived via LoF. Through simulation and experiment, we validate the precision and effectiveness of LoF as well as the strengths of the NPL.H topology. Our NPL.H can eliminate at least 75% of the dc-link capacitance of the conventional T-type 3-level topology while maintaining the same voltage ripple performance under otherwise same operating conditions, and up to 73% compared with the traditional 2-level inverter. Our new NPL.H topology unlocks a significantly higher power density for electric transportation and other high-power applications, where the size of a dc-link capacitor bank has traditionally been a major blockade for a high power density.