Synergetic Control of Three-Phase AC-AC Current-Source Converter Employing Monolithic Bidirectional 600 V GaN Transistors

Abstract

AC-AC current-source converters (CSCs) are an interesting alternative to the widely-used voltage-source converters for next-generation motor drive applications, as they inherently feature continuous output voltages and minimum filter effort. This mitigates issues such as reflections on long motor cables, high-frequency motor losses, the need for expensive shielded motor cables, and common-mode currents that damage motor bearings. In this paper, we first propose a new synergetic control for an AC-AC CSC that always operates either the front-end rectifier or the output-side inverter stage with one phase clamped, reducing switching losses compared to conventional modulation that continuously operates all three phases. We then provide calorimetric switching loss measurements of a novel 600 V, 140 mW monolithic bidirectional GaN transistor, and model the impact of the third, passive switch present in CSC commutation cells on switching losses. This facilitates a subsequent quantitative performance evaluation of an exemplary AC-AC CSC motor drive that employs the GaN M-BDS and operates from a 200 V three-phase mains. For a nominal motor power of 1.5 kW and a required AC-AC semiconductor efficiency of 98 %, a conventionally controlled CSC can operate with a switching frequency of 48 kHz, whereas the proposed synergetic control enables twice the switching frequency, i.e., 96 kHz and accordingly facilitates a significant volume reduction of the DC-link inductor and the input and output side filter capacitors.