Research And Simulation Of The Emitter Switched Thyristor(EST)

Rational allocation and utilization of the electric power is more and more important for the construction of environmental protection and energy-saving society. Conversion of the electrical energy cannot be implemented without power electronic technology. The innovation of power device which is the core component of the technology drives the progress of power electronic technology every time.EST(Emitter Switched Thyristor) is a new type of power devices which is put forward on the basis of the IGBT(Insulated Gate Bipolar Transistor). It is well known IGBT is working in the mode of bipolar and MOSFET before parasitic thysistor is latched up. On account of the conductivity modulation effect in the base area, IGBT is able to greatly reduce conduction resistance compared to the VDMOS. But its on-resistance is larger and current density is limited under the condition of high voltage and large current. If using thyristor as the main current path can get better forward turn-on characteristics. EST is working in the mode of thyristor and MOSFET before parasitic thyristor is latched up while the main thyristor have been latched up. Since the current between cathode and anode is controlled through the MOS, the on-resistance of EST is smaller than that of IGBT. At the same time, the forward output current of EST has saturation characteristics, which is distinguished with the MCT(MOS Controlled Thyrsistor) devices. At present, the study of EST is less, this article is started from the discussion of thyristor, gradually to study the features of EST and its optimized devices. The major contents of this paper are:1. In order to determine the relationship of ionization integrals and the reversed voltage applying to PN junction, i.e., Miller formula, curve fitting tool in MATLAB is performed. An empirical Miller formula is obtained, which is more consistent with the simulation results by MEDICI. At the same time, an approximate formula about the relationship of doping concentration and the S parameters in Miller formula is proposed.2. Analysis of the thyristor, the main contents include: the change of internal carrier under blocking state and on state\the change of integral ionization rate along with the applied voltage, etc. In order to get the reason of pressure, theoretical calculation is applied with MATLAB. The study of thyristor is the basis of EST research which is used to control the on and off of thyristor.3. Device structure of EST with the MEDICI is defined. Simulation to the carrier distribution\threshold voltage\ breakdown voltage\dynamic characteristics is done. Under the on state, four regions of the I-V characteristic is put forward.Analytical analysis of different regions and simulation to the characteristics of switching are carried on at the same time.4. The comparative study of the EST and ESTD(Emitter Switched Thyristor with Diverter). Existing problems were discussed and the result of simulation is summarized. Key parameters are defined and the possible optimized and improved structure is given.