Silicon Carbide Technology for Grid Integrated Photovoltaic Applications: Dynamic Characterization of Silicon Carbide Transistors.

Abstract

For the endorsement of the study of potential utilization of the emerging silicon carbide (SiC) devices, three SiC active switches, namely SJEP120R063 (1200V, 63 mohm) SiC JFET manufactured by Semisouth, BT1206AC-P1 (1200V, 125 mohm) SiC BJT by TranSiC and CMF20120 (1200V, 80 mohm, 33A) SiC MOSFET by Cree have been investigated systematically in this thesis work.The four layer PCB board with the smart layouts like the drain and gate traces are either perpendicular to each other or run into different directions with virtually no overlap or paralleling to each other. The slits between the gate, drain and source and the selection of DC-DC isolated power supply with low isolation capacitance are considered. These all techniques are considered not to have ground bounce and coupling capacitances through the PCB or device. Likewise the use of probe-tip adapter for making test points, using surface mounted components as far as possible, small trace length in high current power loop are some of the techniques implemented to optimize the layout. The correct measurement are recorded using the right probe and oscilloscope which are capable of tracking the fast rising and falling waveforms (about 10 ns rise and fall-time). The test with various combinations of freewheeling diodes, gate voltages, gate- resistors, gate-source capacitances, gate-source resistors, and snubber are carried out. These combination of tests help to realize the cause of voltage and current overshoots, observe the effect of those combinations on voltage and current rise-time and switching energy losses. Moreover, the measurement issues are exemplified. For accurate measurements, it is very important to de-skew the voltage and current probes to insure that all of the delays are the same. De-skewing the voltage probes and current probes is easily done adjusting the channels de-skew on the oscilloscope so that both pulses are time synchronized. It is noticed that faster the device, higher the efficiency, higher the power density, but more the ringings and device stresses. Switching energy losses have minor dependencies on temperature thereby more stable operation in PV inverters.