Comparative Evaluation of Gate Driver and LC-Filter Based dv/dt-Limitation for SiC-Based Motor-Integrated Variable Speed Drive Inverters

Abstract

Compared to state-of-the-art IGBTs, SiC power semiconductors allow to achieve ever higher system efficiencies and higher power densities in next-generation Variable Speed Drives (VSDs), thanks to their smaller relative chip size, ohmic on-state characteristic and lower specific switching losses resulting in a smaller switching-stage footprint and lower heat sink as well as DC-link capacitor volumes. However, the high slew rate of the switching transitions, an inherent consequence of the low switching losses, represents a major challenge and potentially results in lifetime degrading unequal voltage distribution across the motor windings and bearing currents. This work analytically and experimentally compares different means for dv/dt-limitation, namely, a conventional passive LC-dv/dt-filter and a Gate Driver (GD)-based approach based on increased GD resistances in combination with explicit Miller capacitors, at the example of a 10 kW industrial motor-integrated VSD. For a state-of-the-art dv/dt-limitation of up to 6 V/ns the LC-filter shows lower losses compared to the GD-based limitation. The latter, however, has a higher part-load efficiency and/or lower losses compared to the (roughly) load independent losses in the LC-filter resulting from the dissipation of the energy stored in the filter capacitor within each switching cycle, beneficial for light loads, e.g., < 40 % of rated output power. Next-generation motors with reinforced insulation allow a dv/dt-limitation of up to 15 V/ns. In this case, the GD-based limitation shows lower losses in the whole operating range, since they directly scale with the now smaller overlap of voltage and current resulting from the faster switching transitions. Considering a state-of-the-art motor, finally, a hardware demonstrator of a three-phase VSD employing an LC-filter to limit the dv/dt to 5.6 V/ns is realized, which achieves a full inverter stage power density of 30 kW/dm 3 (497 W/in 3 ) and an inverter efficiency of > 99 %.INDEX TERMS Gate drivers, permanent magnet motors, pulse width modulation converters, silicon carbide, transmission lines, variable speed drives.

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

“…Said dv/dt does not only cause ringing and VOLUME 12, 2024 over-voltages in long motor cables, which advantageously are not present in an IMD, but also result in uneven voltage distribution over the motor windings as well as bearing currents, thus potentially leading to premature insulation aging and/or partial discharge issues [9], [10]. To mitigate these issues, dv/dt-filters can be placed at the inverter's output terminals [11] to lower the switching speed to the ratings accepted by motor manufacturers.…”

“…All in all, especially in industrial applications, it is preferred not to design the system close to the maximum temperature ratings, such that during operation the maximum junction temperatures of, e.g., the semiconductors are well below their temperature limits despite various tolerances, 11 which increases their lifetime considerably [46]. In the case at hand, if a maximum junction temperature of 130 • C is selected, the full overload torque can still be safely provided for output frequencies above 10 Hz (i.e., 150 rpm) with this setup, while for DC operation still about twice the nominal torque is possible.…”

“…Fig. 9 (a.i) and (a.ii) show the top view of a single phase module of the 3L GaN FCi with the most relevant components 11 For example, the motor case temperature could slightly increase above 90 • C and/or the distribution of switching losses between the two parallel devices could be unbalanced due to variations in gate threshold voltage and gate loop inductance, leading to a higher junction temperature than expected from the scenarios considered above. labeled.…”

Autonomous Gate Drivers Tailored for Triangular Current Mode-Based Zero-Voltage Switching Two-Level Three-Phase Inverters for Electric Vehicle Drive Systems

“…At present, silicon carbide (SiC) power electronics have significant advantages to offer for the electric vehicle business [9]. SiC metal-oxide semiconductor field-effect transistors (MOSFETs) enable reduced chip sizes, lower switching losses due to their unipolar carrier characteristic [10], reduced conduction losses with the help of fundamental material improvements [11], and operation at a higher switching frequency up to a hundred kHz or more [12], which reduces the required capacitance/size of the DC-link capacitor and increases power density [13]. By enabling extremely energy efficient and compact power conversion, and better thermal performance than for the silicon counterpart, dramatic volume reductions are possible, which enables considerable freedom to design an overall better vehicle.…”

“…By enabling extremely energy efficient and compact power conversion, and better thermal performance than for the silicon counterpart, dramatic volume reductions are possible, which enables considerable freedom to design an overall better vehicle. However, high-speed switching (which is possible with SiC power electronics) is also associated with EMI issues [13].…”