Hardware-Based Comparative Analysis of Multilevel Inverter Topologies for Integrated Motor Drives Considering Overload Operation

With today's demand for increased industrial process automation a trend towards Integrated Motor Drives (IMDs) has evolved allowing a low complexity and compact installation of the drive system. Especially servo applications with high short-term overload requirements (e.g., three times the nominal current for several seconds) are a thermal challenge for the power electronics. Consequently, high efficiencies and power densities are key requirements of these motor-integrated Variable Speed Drives (VSDs). Multi-Level (ML) inverter topologies allow small $LC$ output filter designs and benefit from utilizing low-voltage semiconductors with superior conduction and switching performance, and thus represent an interesting approach for future IMDs. In this work an experimental comparison between three different $800 \,\mathrm{V}$ DC link supplied drive systems is presented, namely between a 3L Flying Capacitor Converter (3L-FCC) (employing $650 \,\mathrm{V}$ GaN HEMTs), a 7L Flying Capacitor Converter (7L-FCC) (using $200 \,\mathrm{V}$ Si MOSFETs) and its promising alternative, a 7L Hybrid Active Neutral-Point Clamped Converter (7L-HANPC) (using both, $650 \,\mathrm{V}$ GaN HEMTs and $200 \,\mathrm{V}$ Si MOSFETs). All three systems are realized as hardware demonstrators for the same specifications, i.e., for integration into a Permanent Magnet Synchronous Motor (PMSM) with a case temperature of $90 \,\mathrm{^{\circ }C}$, $7.5 \,\mathrm{k}\mathrm{W}$ nominal output power at $>$$99\%$ efficiency and a short-term overload capability of three times the nominal current for $3 \,\mathrm{s}$. Thereby, the efficiencies and the thermally critical overload capability are experimentally verified. Overall, the 3L-FCC shows the best performance trade-off with lowest complexity and/or highest reliability and minimal control effort.