Research On Transmission Congestion Optimization And Stability Control Of Power System

In coupling operation power system of multiple areas, since the power network is open to allow entering, so the traditional transaction method among areas must be changed to adapt the power markets. The electricity transaction within the power market is decided by the price. When the limit cost of each area shows difference significantly, the electricity transaction among areas will happen to reduce the cost and improve the profit. Power systems is a large and complex dynamics system, which is composed of generator set of different types, many substations and electric power loads, different voltage grades of power network and transmission lines in different transmission way. Moreover, the various links and units have complex dynamic characteristics. All those leads to a high dimensional state equation with the complicated nonlinear relation for the power mathematic model of the system. As a result, the organically combination of the new study in nonlinear control theory research and power systems can further improve the quality of the complex dynamic electric power system:1. Based on the three areas power system, analyze the cost of electricity transaction among areas in the power market by considering the wastage of network transmission. The condition of each area of power systems obtaining the biggest profits is given by the modified profit function and the cost minimum model. With the opening of transmission network, the problem of transmission congestion becomes very serious in power market. Therefore to ensure the power network runs safely, how to decrease the congestion cost is a crucial problem. The congestion rate is introduced to the transmission congestion management optimal model, and the new congestion cost optimal models are established for the two cases:open the generate side only, and open the generate side and the load side at the same time. Considering the problem of minimum cost when the transmission congestion is maximum, that is the effective power flow on the line exceeds the safe threshold value, will reduce the complexity and difficulty of the computation.2. The cost control problem of transmission congestion management is invest- tigated in the real-time power markets. The problem of real-time congestion manage-ment is transformed to a nonlinear programming problem to improve the new optimal congestion cost model with the cases:opening the generator side and load side simultaneously, the transmission congestion is maximum while the adjustment cost is minimum by the minimax idea and simulated annealing algorithm. Then the global optimal solution is obtained. The simulation results of loading982.4MW and1052.8MW show that the proposed model can decrease the generation cost dramatically. The load requirement incresing leads to the congestion cost increasing correspondingly. However, adjustment cost decreases dramatically when implements the interruptible load. Especially, the higher load requirement is, the more remarkable result is.3. Optimization and solving are conducted based on the immune and niche genetic algorithm for the new optimization model of transmission congestion, respectively. Although the niche genetic algorithm can guarantee the global optimal solution, immune genetic algorithm has more advantages in saving cost. The simulation results show that both two kinds of genetic algorithm can significantly reduce the generation cost and reduce the adjustment cost in the improved optimization model. Comparing with the simulated annealing algorithm in the previous chapter, niche and immune genetic algorithm are more effective.4. In order to improve the transient stability level of the power system, quick closing turbine control valve can instantaneously reduce the output of the prime mover, and the power system do not break up with fault disturbance. So the design of robust nonlinear valve controller is very important for the reliability. Considering generator rotor and valve by external disturbances for turbine regulating system, the nonlinear large disturbance attenuation controller and parameter updating law of turbine speed governor system are designed by using backstepping method. The simulation results show that the control effect of the large disturbance attenuation controller has more advantages comparing with the control performance of conventional nonlinear robust controller.5. For a class of strongly nonlinear reheat-type turbo generator steam valve control problem, a whole-range nonlinear adaptive large disturbance attenuation control scheme is investigated based on the minimax and backstepping methods. Focus is given on the effect of the generator rotor and steam valve on the output of the system by unknown external disturbances. The minimax method is used to reduce effectively the conserva-tiveness of the disturbance treatment, which is brought by the estimation of the upper bound of the disturbance and the inequality scaling. The purpose is to ensure the good robustness and insensitivity to large disturbances of the valve system. By considering the effect of the short-circuit ground fault and the mechanical power of disturbances, a single-machine infinite-bus system is researched. Simulation results show that the control scheme can effectively improve the dynamic process of the transient stability of the power system. Comparing with the conventional nonlinear controller, the control scheme has more advantages in large disturbances, and the process of controller design is simple and intuitive.6. A nonlinear large disturbance attenuation control scheme based on backstepping method is investigated for the single-machine infinite-bus system with excitation control and STATCOM. Focus is given on the effect of the generator rotor on the output of the system by unknown external disturbances. The design of nonlinear disturbance attenuation controller is to ensure the good robustness and insensitivity to large disturbances for the single-machine infinite-bus system. Considering the effect of the short-circuit ground fault and the mechanical power of disturbances, a useful case of the single-machine infinite-bus system is researched. Simulation results show that the control scheme can effectively improve the dynamic process of the transient stability of the power system.Lastly, the summary of the whole dissertation is given and the research directions in the future are put forward.