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

Current source inverters (CSIs) are used for various medium voltage (MV) motor drive systems ranging from 100 kWs to MWs. Symmetric gate-commutated thyristors (SGCTs) are used as reverse voltage-blocking (RVB) switches (referred to as a current switch (CS) in this paper) in existing CSI motor drives. However, these devices operate at low switching frequencies (420-720 Hz), leading to bulkier passive components and lower system efficiencies. Moreover, these devices need to be connected in series to obtain the required voltage ratings of 4.16 kV. The SiC-based devices have enabled high switching frequency operation and lower device counts. This paper compares a single 10 kV SiC CS with two series-connected 6.5 kV SGCTs for medium voltage (MV) CSI application rated at a line-to-line voltage of 4.16 kV in terms of device sizing, passive component selection and sizing, and system losses comprising of the inverter losses and passive component losses. It is shown that the SiC-based solution has increased power density, improved waveform quality with reduced total harmonic distortion (THD), increased overall system efficiency, and higher thermal limits.