Performance evaluation of 15 kV SiC IGBT based medium voltage grid connected three-phase three-level NPC converter

Cascaded converters are generally used for Medium Voltage (MV) grid connected applications due to the limitation in the voltage rating of available Silicon (Si) power devices. These converters find application in Active Power Filters, STATCOM or as Active Front End Converters for Solid State Transformers at the distribution voltage levels. The wide bandgap semiconductor devices have enabled the grid connected operation of non-cascaded converters. This results in high power density, less number of switching devices, high efficiency and control simplicity for three-phase MV grid interface. 15 kV SiC IGBT is one such device which can be switched at 5 kHz between MV and zero levels with forced air cooling. However, this device in a grid connected non-cascaded converter introduces few additional challenges which are analyzed in this paper. The paper investigates the performance of the grid connected converter using 15 kV SiC IGBT through simulations and experiments till 4.16 kV, 3-phase operation. The concerned areas of study are Total Harmonic Distortion (THD) at low currents, effect of practical sensor-feedback path errors, effect of switching ripple on the distribution transformer, effect of filter parasitic capacitance and elimination of high common mode current.