Comparison of a 10 kV SiC Current Switch with two 6.5 kV Series Connected Si SGCTs for Medium Voltage Current Source Converter Applications

Current source converters (CSCs) find extensive applications in medium voltage (MV) motor drive systems, ranging from 100 kWs to 10 s of MWs. In conventional CSC motor drives, Symmetric Gate-Commutated Thyristors (SGCTs) serve as reverse voltage-blocking (RVB) switches, referred to as current switches (CS). However, these SGCT devices operate at relatively low switching frequencies (420-720 Hz), leading to larger passive components and reduced system efficiencies. Furthermore, these devices must be connected in series to achieve the necessary line-line voltage ratings of 4.16 kV for 4.16 kV-rated motors. The emergence of Silicon Carbide (SiC)-based devices has revolutionized CSC technology by enabling high switching frequency, reducing the size of the passives, and the need for a high device count. This paper presents a comparative study between a single 10 kV SiC CS and two series-connected 6.5 kV SGCTs for MV CSC applications with a line-to-line voltage rating of 4.16 kV. The analysis encompasses device sizing, passive component selection and sizing, and the evaluation of system losses, including converter losses and passive component losses. The results highlight the advantages of the SiC-based solution, which offers increased power density, improved waveform quality with reduced total harmonic distortion (THD), enhanced overall system efficiency, and higher thermal limits. Finally, experimental results with the 10 kV XHV-9 module are presented.