Sun Haishun

Multi-index Nonlinear Coordinated Control for TCSC and Hydro-turbine Generator Excitation and Governor

An improved nonlinear control strategy is proposed in this paper. The main improvement made by the authors to the traditional nonlinear control which is based on the differential geometric theory is that an appropriate output function is selected to introduce a nonlinear transformation. Although, such transformation can only partially linearize the nonlinear system, it does provide a way to realize a multi-index control for high order nonlinear systems. Furthermore, with appropriate treatments for the remained part of the nonlinear system after partial linearization, satisfactory performance of the controller can be obtained. The proposed nonlinear control scheme was used to design a coordinated control for a TCSC and a hydro-turbine generator including the excitation and the governor. As the controlled system is a high order nonlinear system characterized with a non-minimum phase problem, design a coordinated control for such system is quite difficult by the conventional nonlinear control theory. Simulation results show very encouraging result. Both dynamic characteristics and the control accuracy of the controlled system are considerably improved.

Investigation on the Arc Ignition Characteristics and Energy Absorption of Liquid Metal Current Limiter Based on Self-Pinch Effect

The GaInSn liquid metal current limiter based on the fluid pinch effect has broad application prospects due to its particular properties. However, the limited rated current and ability of power dissipation are the critical problems for its wide application. Firstly, the temperature distribution of the liquid metal current limiter (LMCL) was obtained by experiments with a rated current of 1 kA and the arc ignition phenomenon was observed with 1.5 kA, which indicates that the rated current is mainly limited by the arc rather than the high temperature compared to the traditional switchgears. Furthermore, an improved method is proposed by adding the paralleled pure resistance, impedance or another LMCL element to protect the setup from the fault energy concentration in the setup. The problem of a slower arc voltage increasing rate can be solved by adding a paralleled impedance with suitable parameters. Finally, the current limiting properties based on the improved method were investigated and the alternating oscillating current was found between two paralleled LMCL elements owing to their deviation of arc ignition in reality.