Analysis and Evaluation of Active/Hybrid/Passive dv/dt-Filter Concepts for Next Generation SiC-Based Variable Speed Drive Inverter Systems

Abstract

State-of-the-art variable speed drive inverter systems are typically employing 1200 V Si IGBTs with antiparallel freewheeling diodes, resulting in a large overall semiconductor chip area, relatively high switching losses and/or low switching frequencies, and causing a substantial on-state voltage drop in both current directions, which inherently limits the peak and part-load efficiency. SiC MOSFETs are seen as natural future replacement of Si IGBTs, since they benefit from high switching speeds and low on-state resistances, which drastically reduces switching and conduction losses. However, the high switching speed of SiC devices results in a dv/dt-stress on the motor windings of up to 60...80 V/ns, which must be limited to 3...6 V/ns in order to prevent partial discharge phenomena and/or progressive insulation aging. Full sinewave filtering could solve this issue, but would also reduce the achievable performance improvement, as a higher switching frequency and/or a bulky filter would be required. Therefore, this paper comparatively evaluates different dv/dt-limitation approaches proposed in literature, i.e. active, hybrid and passive filter concepts, for a next generation 10kW SiC PWM inverter supplied from an 800V DC-bus. First, the different filter concepts are described and analyzed, and in a second step their design procedure is explained based on the design space approach. Afterwards, a Pareto optimization is conducted and Pareto optimal designs are selected, evaluated and compared regarding efficiency and power density. All considered filter designs outperform a state-of-the-art typically 98.3% efficient IGBT inverter drive. The hybrid filter enables a part-load (at 8 kW) efficiency of 99.0% for a dv/dt limited to 6 V/ns. If higher dv/dt -values can be tolerated, e.g. 12 V/ns, 99.3% part-load efficiency with a power density above 80 kW/L can be achieved by the active concept.