A Simple and Accurate Circuit Simulation Model for High-Voltage SiC Power MOSFETs

A complete and intuitive methodology to model a SiC Power MOSFET is presented in this paper. A simple and accurate model is defined in SPICE language. The core is a Level 1 MOSFET to determine the voltage dependent character of this type of semiconductor device. It is combined with 2 extra resistors, 2 capacitors and a diode. All the values used to define these components can be easily extracted from the information given in the Datasheet. The model finds the best trade-off between simplicity and accuracy required to perform fast and efficient simulations.

Nowadays, simulation software packages have become an extremely helpful tool for the power electronics industry. The purpose of these software tools is to duplicate the actual behavior as accurately as possible in order to predict the behavior of the final product before a prototype is built. For this reason, designing groups are able to cut down costs and time, increasing the efficiency of the entire design process. Therefore there is a strong need to develop accurate models of semiconductor devices.

Typically, those in need to include these models in their designs do not have enough information of the physical structure and characteristics of the device rather than what is given in the Datasheet of the product. Moreover, these models oftentimes require a deeper knowledge of semiconductor devices that surpasses the converter/control level general knowledge. Among all the semiconductor devices, MOSFETs are the most common. However applications in the range of 1kV and a few kW, IGBTs are the most typical device. However, the development of new materials such as wide bang gap devices and especially SiC have allowed the production of the SiC power MOSFETs that claim improve the performance of Si IGBTs under the same conditions.

For these reason, a simple and structured methodology of creating a SiC power MOSFET model has been developed in SPICE language. For this purpose, only the Datasheet of the device is required.

The core of the model proposed is a Level 1 MOSFET. It is used to define the device as a voltage controlled current source. Completing this Level 1 MOSFET two resistances are placed in series at the Drain and Source. These three components are enough to duplicate the Static Characteristics of the complete model. The required parameters are the Threshold Voltage (V_GS(th)), Transconductance Parameter (K_P) and Drain-Source On-Resistance (R_DS(On)). The three of them can be easily extracted from the Transfer and Output Characteristics of the device. Once these three parameters are extracted the model will be tuned to duplicate the Static Characteristics (Transfer and Output Characteristics). Also, the forward characteristics (Forward Voltage Drop and On-Resistance) will be analyzed and. The paper will provide detailed guidelines to optimize the process.

Next, the dynamic behavior of the device will be analyzed. The dynamic behavior of power MOSFET has been widely defined by the 3 capacitances C_gs, C_gd and C_ds. The information required to define them was found from C_iss, C_oss and C_rss. Once the capacitances are defined, C_dswill be included in the model of Body Diode.

Besides, the paper will discuss different possibilities for the connection of the body diode and its impact in the dynamic behavior. The switching losses under inductive and resistive conditions will be discussed and compared to the experimental results. Finally, the possibility to scale-up the model will be presented as a first approach to evaluate power modules that combine several dies in parallel to increase the power rating.