The nonlinear dynamic characteristics of a simple three-bus power system mathematic model are studied, including phase diagrams and a bifurcation map. To control this undesirable chaos, sliding mode control law without buffeting is presented based on the LaSalle invariance principle, which considers the bounded disturbances. The theoretical analysis is in agreement with numerical simulation in that the designed controller could asymptotically stabilize the unstable power system to a typical steady-state. The research of this paper may help to maintain the power system's security operation.

Running rails used as a return conductor and ungrounded scheme have been widely adopted in DC traction power systems. Due to the longitudinal resistance of running rails and insulation resistance of rail-to-ground, there will be a potential rise between running rails and the ground when return current flows through the running rails, which is known as rail potential. At present, abnormal rise of rail potential exists widely in DC traction power systems. The present rail potential model still cannot simulate and explain the abnormal rail potential in the system. Based on the analysis of power distribution with multiple trains running in multiple sections, a dynamic simulation model of rail potential in the whole line is proposed. The dynamic distribution of rail potential and stray current in DC traction power systems when multiple trains run in multiple sections is analyzed, and the impact of traction current distribution on rail potential is evaluated. Simulation results show that the abnormal rise of rail potential during the dynamic operation of the system can be evaluated effectively.

Abstract:A new design approach is presented in this paper to show that under certain conditions, in a two-coil wireless power transfer system, the double-sided inductor-capacitor-capacitor (LCC) compensated wireless power transfer (LCC-WPT) system can be more energy efficient than the series-series (SS) compensated wireless power transfer (SS-WPT) system for the same load power, with special attention being paid to the effect that the parasitic coil and capacitor resistances have on the system efficiency. To make a fair comparison between the SS and LCC WPT systems, the direct current (DC) link voltage was adjusted to set equal load power for the two systems whilst using identical transmit and receive coils, coil-to-coil distance and load resistance. The system performance in terms of the system efficiency, the voltage stresses on the components, and the losses in the power devices were analysed for a practical system, comparing the LCC-WPT system and the SS-WPT system with respect to the load resistance. The effect of coil misalignment on the transferred power and efficiency for the two systems was compared. The theoretical proof and the conditions for meeting the objective are derived and practically verified in a two-coil WPT practical prototype, showing good agreement between analysis and experiments.

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DC traction power system with running rails as reflux conductor has been adopted in Guangzhou Metro Line 8. During the operation of the Guangzhou Metro Line, a high rail potential has been observed, and the leakage of stray current increases significantly. Because of the electrical connectivity of the catenary, over zone feeding of traction current may exist when multiple trains run in multiple traction substations. Guangzhou Metro Line 8 suspects that over zone feeding of traction current is the major cause of the high rail potential. In this paper, a unified chain model of DC traction power system is proposed to simulate the distribution of rail potential and stray current. Field tests and simulations have been carried out to study whether over zone feeding has an impact on rail potential and stray current. Results show that over zone feeding widely exists in DC traction power system and that the rail potential and stray current can be reduced effectively by preventing the over zone feeding of traction current.