Study On Physical Mechanism Of Bifurcation And Chaos Behavior In Thyristor

People pay more attention to the external characteristics such as voltage characteristics and driver protection application technology than to the operating characteristics in the study of power electronic devices currently. However, power electronic device is a very complex nonlinear system from the point of the electrical conduction mechanism. The variation of drive signal, power supply and frequency may affect its operating characteristics, which affects the effectiveness and reliability of the power electronic devices directly. Therefore, thyristor, one of the most common of power electronic devices was studied based on semiconductor physics theory and nonlinear dynamics theory in this paper. The instability phenomena and its bifurcation and chaos behavior of thyristor was analyzed systematically in this paper, in order to explore the work characteristics and failure mechanism of thyristor deeply, and thus to improve its reliability, with multidisciplinary research and analysis methods.The main study results are as follows:(1) The conductive mechanism of power electronic devices was studied in this paper, through building their models. It has been found that the dual-transistor model and the macro model were too simple to reflect the working characteristics of thyristor accurately. Physical model based on the devices'physical structure, through which the evolution process of physical variables, for example, the carrier's transient distribution was studied ,can reflect the conductive properties of thyristor better.(2) Based on dual-transistor model of thyristor, nonlinear phenomena of period doubling and chaos in thyristor were obtained with the variation of the frequency and the gate voltage. The results showed that the different bias condition of pn junction between the gate and its cathode of thyristor was the main reason for inducing bifurcation and chaos behavior in thyristor.(3) A spatio-temporal dynamical model for analyzing the bifurcation and chaos behavior in thyristor was proposed. The boundary condition of instability of thyristor dynamical system was discussed based on dynamic stability theory. Then, the intrinsic relationship between chaotic behavior and physical evolution in thyristor was analyzed deeply. The purpose was to point out that the instability of thyristor was not only caused by the characteristics of negative differential conductivity, but also related to the external circuit parameters and physical parameters of the power electronic devices. The spatio-temporal model of thyristor can reflect the internal working characteristics better compared to the dual-transistor model. The proposed method helps us understand the physical mechanism of generating bifurcation and chaos phenomena of thyristor more deeply from a new perspective.(4) Nonlinear dynamic behavior such as its bifurcation and chaos behavior of the parallel thyristor was explored through establishing its spatio-temporal model. It concluded that the instability of thyristor would lead to the current sharing problem in parallel circuit. Thus the study of bifurcation and chaos behavior in thyristor will be expanded from a single device to multiple devices.(5) An improved time-delayed feedback control method was proposed to suppress the bifurcation and chaos behavior in thyristor. The control parameters were optimized based on Floquet theorem. To further inhibit the remaining spiking current, the delayed feedback signal was compressed based on the phase space compression theory, and the spiking current in thyristor was inhibited very well through restricting its periodic motion properly.Summarily, the physical mechanism of bifurcation and chaos phenomena in thyristor was systematically analyzed in this thesis. The dynamical analysis method was proposed for researching the bifurcation and chaos behavior in thyristor, and nonlinear dynamic behavior of the parallel thyristor system has also been explored. In addition, an improved TDFC method was proposed to suppress the bifurcation and chaos behavior in thyristor. It's no doubt that the research will advance the basic theory of nonlinear systems of power electronic devices to some extent.