Director Power Electronic Systems Laboratory ETH Zurich ETH Zurich
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This intermediate level seminar first introduces participants to state-of-the-art variable speed drive (VSD) systems and gives a short overview of the realization requirements and regulations detailed in corresponding product standards. Next, three-phase PWM inverter topologies with different types of explicit LC output filters, i.e. continuous sinusoidal output voltage, are discussed, which allow the full utilization of ultra-fast switching wide bandgap (WBG) SiC and GaN power semiconductors. The systems do not require shielded motor cables, ensure low motor losses and/or applicability of conventional low-cost motor technology and are preventing dv/dt-related motor insulation stresses, as well as bearing currents and reflections on long motor cables. Different filter structures and the filter design procedure are shown and examples of high switching frequency industrial drive systems with output filters are shown. Furthermore, advanced inverter bridge-leg topologies, including multilevel arrangements with series and/or parallel interleaving are evaluated concerning losses and output filter volume. In this context, a multi-level/cell GaN bridge-leg power module employing 650V GaN power semiconductors, operating at 4.8MHz effective switching frequency and integrating an ultra-compact output filter, is described. Subsequently, new three-phase voltage DC-link or current DC-link inverter concepts featuring buckboost functionality and inherently generating a continuous output voltage waveform are presented. The systems allow operation in a wide DC input voltage and/or AC output voltage/motor speed range and are therefore ideally suited for battery powered or distributed DC link VSD applications. The new converter topologies are derived starting from conventional inverter structures and are grouped into phase-modular and phase-integrated concepts. Continuous and discontinuous modulation schemes are explained and evaluated for both converter groups and a synergetic coupling of the control of the input and output stages of the systems resulting in low overall switching losses is described. Furthermore, measurement results of high power density laboratory demonstrators of the systems employing latest SiC MOSFETs or monolithic bidirectional GaN e-FET technology are presented. Final considerations of the seminar are on the fast and accurate measurement of the switching and conduction losses of WBG power semiconductors, and of the low- and high-frequency losses of ceramic capacitors and magnetic core materials as basis for an inverter and/or output filter design. Furthermore, the advantages and challenges of a future embedding of the inverter into the motor are discussed and topics of latest research on next-generation VSD systems at the Power Electronic Systems Laboratory of ETH Zurich are presented.