June/July 2021

PCIM EUROPE 2021 15 www.power-mag.com Issue 3 2021 Power Electronics Europe lower in comparison with existing conventional SiC-modules. The build-up of this interconnection technology concept is shown in Figure 5. The construction of the module consists of three cores, which are mounted with sinter technology together. The outer two cores act as “power supplies” for the centered core with embedded devices. In addition, the thermal management is supported by their cooling capability. This module concept offers single or double side cooling. In case of single sided cooling components can be mounted on topside to shorten the distance to the semiconductor switches. The requirement for lifetime is increasing up to 18.000 hours and maybe more in future. Therefore, the existing solder technology will pass its lifetime already after about 50.000 power cycles. In the project EmPower 300.000 cycles power cycles were achieved with this power module design. Literature Next Generation of Power Electronics Module Packaging, Proceedings PCIM Europe digital days 2021, pages 6-9 Next-Generation SiC/GaN Variable-Speed Drive Inverter Concepts Next-Generation SiC/GaN Variable-Speed Drive Inverter Concepts Industry is at the beginning of a fascinating new chapter of power electronics research, comprising the characterization of novel monolithic bidirectional switches (M-BDSs), the identification and evaluation of optimum three-phase current DC-link converter modulation schemes with respect to switching losses and EMI, and the multi-objective optimization and the realization of industry- like demonstrator systems. Furthermore, a comprehensive comparison with voltage DC-link converter systems is mandatory, which also should consider overload requirements as well as protection aspects. Such analyses will close the gaps in the current knowledge base and prepare the future industrial application of the impressively low-complexity current DC-link converter systems. Johann W. Kolar, Power Electronic Systems Laboratory, ETH Zürich, Switzerland (kolar@lem.ee.ethz.ch) Variable-speed drives (VSDs) are widely used in material processing and for driving pumps, fans and compressors. Typically, a three-phase IGBT-based PWM inverter stage with voltage DC-link is employed for supplying the electrical machine. The switching losses of the IGBTs and anti-parallel freewheeling diodes are limiting the switching frequency around 16 kHz, which is still within the audible range. Furthermore, a relatively large total chip area / power module footprint is required and the constant on-state voltages of the bipolar power semiconductors result in relatively low part-load efficiency. Novel SiC or GaN power MOSFETs feature small chip areas, internal freewheeling diodes and enable synchronous rectification with ohmic conduction characteristics and hence high part-load efficiency. The significantly higher switching speed enable switching frequencies above 100 kHz, facilitating integration of a LC output filter into the inverter system housing leading to continuous (sinusoidal) output voltages. Smooth output voltages prevent harmonic losses in the motor known from IGBT-based drive systems without output filters, and prevent transient over-voltages caused by Figure 1: Four-quadrant switch realized by common-drain connection of power transistors with uni-directional voltage blocking capability. In order to compensate the increase of the on-resistance resulting from the (anti-)series connection, 4 devices are required (a). Accordingly, a monolithic bidirectional switch (M-BDS) facilitates a substantial reduction of the total chip area (b). Simplified internal structure of the novel 600 V GaN M-BDS (c) Figure 2: Power circuit of a three-phase buck-boost current DC-link DC/AC converter (a) and of a buck-boost current DC-link AC/AC converter (b). Both converter circuits employ monolithic bidirectional switches (M-BDSs). The DC-link filter inductors could be replaced by a series connection of a differential-mode and a common-mode filter inductor with potentially lower overall volume. Integrating normally-on devices into the converter structure ensures a freewheeling current path and/or prevents over-voltages in case of gate drive power supply failures