Designe Of Nonlinear Adaptive DC Complamentary Controller For AC/DC Interconnected Power System

Usually, DC transmission is used for regional interconnection as well as the high power and long-distance transmission. Because the HVDC converter is highly controllable, so when the system suffers from the fault or disturb, it can respond promptly and modulate the capacity of power transmitted by DC line, so as to enhance the system stability. Whereas, the AC/DC system is a nonlinear system, and there are some unknown parameters which vary with the operating point of the system. When the system suffers from small disturbance, the traditional linear DC controller can work steadily; but if it is exposed to severe disturbance, the linear DC controller will be less effective or even fail to work properly. The nonlinear control theory is more widely applied to the design of DC controller so that to improve the stability of the whole system.To enhance the stability of the interconnected AC/DC transmission system, the nonlinear adaptive control law and the back-stepping method is employed in the DC controller design for an interconnected AC/DC power system which contains several generators. The designed controller is used to modulate the DC power of the interconnected system and its characteristic involves a dynamic estimating of unknown system parameter, it can be used to damp the inter-area system oscillation as well. A general expression of nonlinear adaptive control strategy for interconnected AC/DC system is presented.To validate the effect of the controller, the simulation model for a AC/DC parallel transmission system which contains four generators is created using the EMTDC simulation software, and the associated complementary controller is also build based on the general expression of the controller. The modulation signal of the complementary is connected with the current modulation signal of the elementary controller by the master controller. Different faults on the converter bus of the rectifier side are simulated, and for the same fault, the performance of the conventional linear controller is compared with that of the proposed nonlinear adaptive complementary controller. The simulation results of a four generators system show that the proposed controller is obviously superior compared with the conventional controller in damping inter-area oscillation, especially when the power system is subjected to severe disturbance.