Study On Control Methods Of Improving System Stability Based On Wams Information

The increasing of the complicity of modern inter-connecting power system often makes solving a actual problem difficult when traditional analysis and control strategy are used. Several large scale blackouts happened both domestic and abroad approve that ensuring securely and the stable operation of power systems are becoming more and more difficult. One of the most important reasons of blackout is the lacking of fast, effective and adaptive control method for improving stability. The widespread application of Wide Area Measurement System (WAMS) provides a new momentum for the research of the analysis and control of power system transient stability.Based on WAMS signal, wide area coordinating control, closed-loop emergency control and islanding control for improving transient stability of power systems are researched in this thesis. The main works of this thesis are:1) A closed-loop emergency control scheme to enhance transient stability of power system using WAMS information is proposed. The proposed method combined the open-loop control and the closed-loop control, resulting in extending the protect area of emergency control. The reasons and the influence of sudden change of the electric power of generators during stability prediction are analyzed. Moreover, corresponding correction method is proposed. The error existed in closed-loop control modal and measuring are analyzed and corrected in order to guarantee the effectiveness of control method. Last, a complete solution of closed-loop emergency control is proposed. Different perturbed trajectory prediction method are applied during the control course. Simulation results approve that the proposed control scheme can improving transient stability of power systems effectively.2) A coordinated control method of Thyristor Controlled Braking Resistor (TCBR) for multi-machine system is proposed. The basic structure and mathematic model of TCBR controller of multi-machine system is researched. Moreover, nonlinear optimizing control is adopted according to three level co-state prediction algorithm. The optimal mathematic modal is proposed, and the nonlinear optimizing feedback control law is acquired. The proposed controller can greatly improve transient stability of the power system. Simulation tests on a 4-machine system show the effectiveness of the proposed method.3) A global control scheme for improving transient stability of power systems by combining exciter and thyristor controlled braking resistor is proposed. The control structure is organized into a two-layer controller by applying hierarchical control strategy of large-scale system principle. The lower layer is composed of decentralized local feedback controllers, each of which takes local feedback signal and controls its connected generator. In the upper layer a global controller is designed to enhance the effectiveness of decentralized local controllers. The global controller coordinates local controllers by generating remote feedback signals which ensuring the global optimal solution of the overall system transient performance. The proposed control scheme can guarantee fast and accurate control actions of local controllers when a power system is subjected to large disturbances. Simulation results show the effectiveness of the proposed control scheme.4) A adaptive islanding method based on WAMS is proposed. First, none synchronizing group of generators is recognized by EEAC method. Moreover, the optimal islanding surface is found by applying minimal power flow surface method. Furthermore, the effect of islanding control as a emergency control method in the second defense line is analyzed.