Study On Reactive Power Series Compensation Technology Of High Voltage Distribution Network

At present, high voltage and extreme high voltage series compensation technology has been widely used in many domestic and overseas system as a relatively mature measure. The stability of electric power system and the capacity of transmission of electric lines can be increased by series compensation fixed in transmission lines. Furthermore, the voltage adjustment and reactive power balance of the system by it. In the 1960s, the development of series compensation device and the application of series compensation technology were applied and once suspended because of many reasons such as control strategy, manufacturing technology and so on. Now. there are many high voltage power distribution lines of long distance in our country. It is equivalent to shortening the electrical distance of line that the line reactance, lower the line voltage loss of the end and line loss can be reduced by using series compensation. At the same time, the transmission capacity can be improved and the safe and stable operation of the power system can be ensured. So the research on series compensation technology of high voltage power distribution network, especially on the control strategy of controlled series compensation is very important.Aiming at the problems of some actual high voltage distribution network, such as low voltage along load and large line loss because of long lines and large reactance, the series compensation technology is employed to make an improvement. By theoretical analysis and software simulation, the feasibility of series compensation technology (including fixed series compensation and controlled series compensation) applied to improve the voltage quality of distribution network is proved, and a new idea put forward for improving power quality, reducing the line loss, ensuring the safe and stable work of power distribution network.In the dissertation, the "strong" and "weak" of node properties in distribution network are evaluated, and the performance of the "weak" nodes is improved by using TCSC. Besides analyzing the two problems, the ratio relation is given between fixed part and controllable part of the capacitive reactance considering reducing engineering cost of TCSC, the compensation effect is verified by simulation.Analyzing the fixed series compensation and controlled series compensation respectively, the overall research work mainly includes the following aspects:First, the study of system application of fixed series compensation.Based on 66kV distribution system of Fuxin power distribution network in Liaoning province, the model employed fixed series compensation is established. Comparative analysis of compensation effects applying scries compensation, parallel compensation and both of them are presented in the paper, and the feasibility of improving the voltage quality of distribution circuit used series compensation technology is proved by the result of theoretical analysis and simulation.Second, working principle, characteristic analysis and simulation of TCSCHaving analyzed merits and demerits of fixed series compensation, an idea of applying to controlled series compensation (TCSC) technology is given. Through the fast and precise control of the thyristor conduction angle, the equivalent reactance can be adjusted flexibly, continuously and smoothly.Analyzing TCSC characteristics of the steady-state and transient, the steady-state impedance model of TCSC is obtained. The resonance problem is analyzed, at the same time, the detailed simulation analysis of the operation features of steady-state in four work modes are made.Third, studv on TCSC mode switchWhen the TCSC mode switches, the transient process of TCSC will be violent due to the leap-change between impedances of different property. After researching on TCSC mode switch speed and stability of dynamic process, several effective switch methods of TCSC work mode are introduced in the dissertation.Fourth, study on impedance control mode of TCSCImpedance control is the connecting link between the preceding and the following of TCSC layered control, is the key to the good work ability of TCSC device. Based on the research of conventional PID and fuzzy PID control of TCSC, fuzzy neural network PID control method of TCSC is put forward. Applying fuzzy neural network to PID control and using the respective characteristics complementarity of fuzzy theory and neural network, the abilities of the neural network learning function and fuzzy system for handling fuzzy or qualitative knowledge can be better, which can help adjust the PID parameters online to solve the difficult question of parameter online setting. Compared to the former two methods, the simulation results in response to various impedance step representation command show that it is a good method with smaller overshoot, faster response and better tracking performance, and can basically realize non-error control.Fifth, comprehensive analysis of applying TCSC to improve the property of distribution networkEmploying voltage fluctuation index put forward based on the feasibility of tidal solution, "strong property" or "weak property" of each node of radial pattern distribution network is estimated. Through comprehensive analysis, when using TCSC to improve the voltage quality of the end of line, the voltage fluctuation index of weak node should be keep in ideal scope, at the same time. Considering reducing the cost of TCSC and synthesizing the previous analysis, the ratio of fixed portion to controlled portion of TCSC is determined finally, which is verified by the simulation.Although the TCSC has less been applied in power distribution network at present and all conditions of actual engineering can't be considered in simulation process, the research of the dissertation is of certain guiding significances to help the design and improvement of the distribution network.