Study Of Frequency Control Method Used In Interconnected Power Grid With Wind Power Based On CPS Standard

In the modern power grid, the interconnected power systems with complicated structures and large-scale installation capacities have been formed, and the coupling relationship among multiple power systems has become more closely. When a sudden active power disturbance occurs in a power supply area, the frequency fluctuation will be induced in this area, and it may be quickly transmitted to the relevant power systems through the tie-lines. Consequently, the frequency stability and security operating of the power systems may be damaged to a certain extent. In addition, considering that the introduction of large-scale wind power units, the wind power unit’s inherent randomness and fluctuation may easily result in the instantaneous change of active power and frequency, and the study of an effective frequency control method is necessary and meaningful. On the basis of the aforementioned background, in the case that the high-efficiency control method is adopted, the interconnected power systems’whole operation performance and frequency stability can be undoubtedly improved. In this dissertation, aiming at the related technical issues, the primary frequency control characteristic of doubly fed induction generator (DFIG) is firstly investigated; then, the wind power unit’s influence mechanism to CPS evaluation index of Chinese grid is analyzed, and the improvement of the existing CPS evaluation logic is performed. In the end, on the basis of optimal dynamic closed-loop strategy, an automatic generation control (AGC) method suitable for the interconnected grid including wind power units is proposed, and the method’s effectiveness is verified.Chapter2analyzes the primary frequency characteristics of doubly-fed wind power (DFIG), discusses the mathematical model of doubly-fed wind power generation system and summarizes the current active power control methods of DFIG. With regard to different wind speed ranges, different control methods should be applied, and accordingly the DFIG’s operation mode can be divided into low-speed, medium-speed and high-speed mode, so as to determine the reference input and reserve capacity of primary frequency control. For purpose of ensuring that the DFIG can afford reasonable capacity of primary frequency control under different wind speed conditions, this dissertation puts forward a variable droop coefficient method based real-time wind speed. Through the simulation and analysis, the results demonstrate that the proposed control method can obviously enhance the performance of primary frequency control of DFIG, reduce the participation effects of other conventional power units.Chapter3analyzes the wind power’s effects on frequency characteristic coefficient and area control error of interconnected power grid, studies the influence mechanism of wind power on the CPS evaluation indexes, derives the change rule trend of the CPS evaluation indexes of the grid, and the calculation formula of the CPS evaluation indexes for quantitative analysis are given. Using MATLAB/SIMULINK, the simulation analyses are carried out, and the results confirm the correctness of the analytical conclusions. Furthermore, for the sake of reducing the wind power’s negative influence on the CPS evaluation indexes, this chapter suggests a frequency control method that utilizing the DFIG with variable droop coefficient to enhance the CPS evaluation indexes. From the simulation results, the validity and feasibility of the suggested method are proved well.Chapter4firstly analyzes the deficiency of the existing CPS evaluation logic controller of interconnected power grid, proposes the improved CPS modificatory logic controller and gives the specific control strategy and corresponding control process. This strategy can dynamically screening the area control error (ACE), determine the control behavior of AGC units and optimize the frequency control process of the interconnected power system. In the simulation analysis, considering the frequency control characteristics of DFIGs, carry out the simulation analysis on CPS threshold, clear the specific impact of the threshold to CPS evaluation index and conventional units adjusting number, and concluded that:In the case of the same threshold, using the wind turbines to participate frequency control of power system can significantly improve overall operating performance. For a more comprehensive grasp of the overall performance of the proposed strategy, select a group of more ideal CPS threshold, using a proportional integral (PI) control method, comparing the proposed control logic and the traditional CPS control logic, the simulation results show that the mentioned control method can significantly improve the CPS evaluation indexes, reduce the adjusting number of conventional units and improve the overall operation of interconnected power system performance.Chapter5studies the automatic generation control of interconnected power grid with wind power, without considering the secondary frequency control ability of wind generator, aiming at weakness of poor dynamic characteristic and coordination ability among areas with wind power of traditional PI control method, research is mainly focused on the secondary frequency control method of conventional units. Firstly, this paper establishes and standardizes a state space mode of two-area interconnected power grid with hydro and thermal units; second, selecting suitable state variables to establish a new objective function, this paper proposes an optimal dynamic closed-loop automatic generation control strategy of interconnected power grid with wind power; at last, take a two-area interconnected power system with hydro and thermal units as a example, the wind power is connected to the thermal power area as a source of disturbance. Combining with the above proposed improved CPS evaluation control logic, using MATLAB/SIMULINK to establish the simulation model, the author analyzes the optimal dynamic closed-loop control method in detail. Compared with the traditional PI control method, simulation result demonstrates that the proposed control strategy can effectively restrain the fluctuation of the active power and frequency after wind power connected to the grid, significantly improve the overall performance of interconnected power grid.Finally, the paper has carried on the summary to the work, and the development trend of this project is outlooked.