8 MOS Controlled Thyristors (MCTs) 129 8.6 Simulation Model of an MCT The operation of power converters can be analyzed using PSPICE and other simulation software. As it is a new device, models of MCTs are not provided as part of the simulation libraries. However, an appropriate model for the MCT would be helpful in predicting the performance of novel converter topologies and in designing the control and protection circuits. Such a model must be simple enough to keep the simulation time and effort at a minimum, and must represent most of the device properties that affect the circuit operation. The PSPICE models for Harris PMCTs are provided by the manufacturer and can be downloaded from the internet. However, a sim- ple model presenting most of the characteristics of an MCT is available [9, 10]. It is derived from the transistor-level equiva- lent circuit of the MCT by expanding the SCR model already reported the literature. The improved model [10] is capable of simulating the breakover and breakdown characteristics of an MCT and can be used for the simulation of high-frequency converters. The PMCT can only replace a P-channel IGBT and inher- its all the limitations of a P-channel IGBT. The results of a 2D simulation show that the NMCT can have a higher con- trollable current [13]. It is reported that NMCT versions of almost all Harris PMCTs have been fabricated for analyzing the potential for a commercial product [3]. The NMCTs are also being evaluated for use in zero-current soft-switching appli- cations. However, the initial results are not quite encouraging in that the peak turn-off current of an NMCT is one-half to one-third of the value achievable in a PMCT. It is hoped that the NMCTs will eventually have a lower switching loss and a larger SOA as compared to PMCTs and IGBTs. 8.9 Base Resistance-controlled Thyristor [14] The base resistance-controlled thyristor (BRT) is another gate- controlled device that is similar to the MCT but with a different structure. The Off-FET is not integrated within the p-base region but is formed within the n-base region. The diverter region is a shallow p-type junction formed adjacent to the p-base region of the thyristor. The fabrication process is sim- pler for this type of structure. The transistor level equivalent 8.7 Generation-1 and Generation-2 MCTs