Gate driver design for normally-off SiC JFET: Silicon Carbide technology for PV inverters
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In this thesis a research on modern SiC semiconductor devices is made with a bias on the driving methods and requirements. A compact two-stage gate driver circuit for SiC VJFET is developed, the transistor is characterized and its gate requirements are estimated. The performance of developed driver is compared to the commercial SiC VJFET gate driver from SemiSouth. The conclusion is that both drivers behave similarly in switching the device in a half-bridge converter. In addition, the developed gate driver is a rather cheap solution compared to SemiSouth driver which is only available as engineering sample. Though, the optimization and especially shaping of the gate voltage/current waveforms must be done in order to extract the maximum performance of the SiC VJFET and obtain the lowest possible switching and on-state losses.Simulations are also carried out for validating the design of the board. The simulated circuit shows good correspondence with what was expected and described in scientific papers. The SiC BJT base driver circuit, which in addition was used to drive SiC MOSFET and SiC VJFET, is also characterized. The AC-coupled SiC BJT base drive circuit (section 3.6.3), which is also developed during the thesis, displayed a relatively good performance taken into account the simple design and cost effective nature of this driver.A characterization of different SiC transistors, i.e. SiC VJFET, SiC MOSFET and SiC BJT, is made. Two SiC Schottky diodes are also tested as the freewheeling diodes. Extensive experiments are performed on the developed half-bridge converter utilizing various combinations of SiC transistors, SiC diodes and gate/base driver circuits. The obtained results conclude that these new SiC transistors switch extremely fast and with relatively low energy losses, so that they can be used in high-frequency applications. Thus, converters that utilize SiC transistors can be made extremely compact. SiC BJT showed the best result with the highest switching speed and lowest energy losses compared to other two SiC transistors.