Comparative Evaluation of Three-Phase Three-Level GaN and Seven-Level Si Flying Capacitor Inverters for Integrated Motor Drives Considering Overload Operation

Abstract

Integrated Motor Drives (IMDs) are gaining popularity in industrial Variable Speed Drive (VSD) applications, thanks to their more compact realization and simpler installation. However, mission profiles of, e.g., servo applications, demand overload torques of two to three times the nominal value during several seconds, which is thermally challenging for the power electronics. Accordingly, high efficiency and power density of the inverter are of paramount importance for motor integration. Multi-Level Flying Capacitor inverters (ML-FCis) benefit from a reduced output filter volume and improved switching and on-state performance of low-voltage devices for increasing number of levels $N$ , whereas the PCB overhead and gate drive volume increases. In this paper, the most power dense solution between a seven-level (7L) FCi with Si semiconductors and a three-level (3L) FCi with GaN semiconductors is evaluated. Thereby, a straightforward design procedure allows to dimension both FCis for 99% efficiency at nominal operation, while providing a high short-term overload torque (three times the nominal torque) also for low inverter output frequencies. Due to its slightly higher power density and greatly reduced complexity, a phase module of the 3L GaN FCi is realized as an IMD hardware demonstrator. A transient thermal model is employed to specify the feasible overload operating range, considering the limited heat spreading in the baseplate and parameter variations, e.g., from manufacturing tolerances. The experimental analysis of the demonstrator verifies an efficiency of 98.94% and the practically required overload capability.

Keywords

• Integrated motor drive
• variable speed drive
• multi-level inverter
• flying capacitor
• overload operation
• WBG power semiconductors