Modeling and Loss Analysis of SiC Power Semiconductor Devices for Switching Converter Applications

Since its inception, power electronics has been to a large extent driven by the available power semiconductor devices. Switching power converter topologies, modes of operation, switching frequencies, passive filtering elements are chosen based on the switching and conduction characteristics of power semiconductor devices. In recent times new wide bandgap power semiconductor devices, such as SiC MOSFETs, are emerging with superior performance as compared to conventional silicon devices. In switching power converter design, power losses of the power semiconductor de- vices play a crucial role in determining the physical characteristics of power converter systems in terms of size, weight, efficiency and, ultimately, cost. Switching losses impose an upper limit to the switching frequency, which in turn determines passive filtering element sizes and dimensioning of the cooling system. An accurate power loss model of the power semiconductor devices is needed for switching power con- verter design and optimization and to quantify the system-level advantages of novel SiC devices compared to conventional silicon devices. Since power semiconductor device performance plays a key role in power electron- ics applications, power electronics designers need circuit-oriented device models to simulate the in-circuit performance of power devices in different applications. The basic objective in device modeling is to obtain a predictive description of the current flow through the device as a function of the applied voltages and currents, environ- mental conditions, such as temperature and radiation, and physical characteristics, such as geometry, doping levels, and so on. In general, there is a trade-off between computational speed and model accuracy. The required accuracy and simulation timeare crucial factors considered by device model designers when making this tradeoff. In this dissertation, the analysis and applications of wide bandgap power devices can be divided into two parts: development of analytical loss model for wide bandgap power devices, and development of wide bandgap power semiconductor device models. In the first part, a simple and accurate analytical switching loss model for SiC power devices is developed. This model considers the device capacitances and the parasitic inductances in the circuit, which have a strong impact on switching losses. In addition, the reverse recovery effect of the body diode of SiC MOSFET is considered. The detailed analysis of turn-on and turn-off transitions is presented. The accuracy of the proposed model is validated by experimental results, and the accuracy of the proposed loss model and conventional piecewise linear loss model is compared. The proposed analytical loss model has several advantages: it gives insight into the switching process, showing how different parameters and parasitics affect switching waveforms and determine switching losses; it provides accurate and simple closed-form switching loss calculation; it is useful for optimization given the fast calculation speed and the absence of numerical convergence problems; all power device parameters can be derived from datasheets (but requires parasitics estimation); it includes MOSFET body diode reverse recovery; it provides piecewise linear estimate of actual switching waveforms. In the second part, a simple and accurate circuit-simulator compact model for sili- con carbide (SiC) MOSFET is proposed and validated under both static and switching conditions. A novel feature of the proposed model is that it takes into account the nonlinear parasitic capacitances of the device and parameter extraction requires only data from device manufacturer datasheet. A parameter extraction procedure is pro- posed. A simulation model is built in Pspice software tool. The PSpice simulation results are compared with datasheet results. The comparison shows good agreement between simulation and datasheet results for both static and dynamic characteris-tics