Analysis Of Nonlinear Stable Operation Mechanism For Semi-controlled Power Devices Parallel Condition

Thyristor devices are favored with advantages such as high voltage resistance and high current resistance. In the cases of SVC, HVDC transmission and high voltage frequency conversion, they are still major power components, and the parallel connection technology is often applied. The current parallel connection technology of thyristors mainly adopts resistance-inductance protection, RC protection and etc, as is far enough for the requirements of parallel connection. However, thyristors are strong nonlinear components, and research result shows that under different driving voltages, working frequencies and suppling voltages, bifurcation and chaos would occur and the current filament of thyristor would be triggered, and the thyristor would break because of partial current. Therefore, how to maintain the great performance of thyristor parallel connection system remains an important subject.This thesis takes thyristor devices as its object of study, builds a non-linear dyna mic model and analyzes nonlinear phenomena, such as periodical bifurcation and cha os. It intends to investigate deeply the non-linear control of parallel connection system of thyristor so as to lay a foundation for the improvement in the security and reliabilit y of the parallel connection system of thyristor. It mainly discuses the following subje cts:(1) Analysis of the internal physical structure and working mechanism of thyristor components, foundation of non-linear dynamic model of thyristor based on physics theory of semi-conductor, research on the dynamic behavior in the drifts, and deduction of the bipolar diffusive dynamic equation of thyristor.(2) Systematic analysis of the mutual between exterior electric characteristics and internal physical changes based on nonlinear dynamic modeling of thyristors, and based on this analysis, further research on the nonlinear phenomenon such as periodical bifurcation and chaos. Furthermore, discussion on these phenomenon’s influence over the parallel connection.As the research result shows, the difference between circuit parasitic parameters and physical parameters of components will lead to bifurcation and chaos and then the thyristors in a parallel circuit will be triggered asynchronously. Thus, dynamic current sharing among the thyristors takes place, which will affect the safe and stable operation of thyristors inevitably.(3) In order to upgrade the stability of the parallel connection system of thyristor, this thesis strives to deal with the synchronous trigger problem from a new perspective with help of the exact linearization method. Firstly, to build the nonlinear simulated modeling of the thyristor parallel connection system, and to examine whether this system has met the premise of exact linearization based on differential geometry theory. Then, to realize the exact linearization of the system based on nonlinear coordinate commutation and to confirm the state feedback control with linear optimal control theory. Finally, to certify the effectiveness of this control plan through digital simulation and to provide a new idea for the synchronous trigger control of the parallel connection system of thyristors.