Research On Reactive Power Control Method Of Static Synchronous Compensator

With the development of modern industrial technology and continuous improvement of requirements of electric equipment for electric energy quality as well as accompanied by needs of Flexible AC Power Transmission System (FACTS), reactive power compensation for fine power quality has become an important research topic in power system. Static Synchronous Compensator (STATCOM), in short, as a crucial component of FACTS with relatively good regulating performance, is capable of compensating both inductive and capacitive power continuously in the power system rapidly and efficiently. STATCOM has so predominant performance that it has become one of the hot points in power electronics field representing the development direction of dynamic reactive power compensation device. The dissertation describes the control strategies for STATCOM, whose main objects aim at fast reactive power compensation and dynamic characteristics for special loads.Firstly, this dissertation briefly introduces the background, development situation and current development trend of STATCOM at home and abroad, and then describes the working principle, classification, performance characteristics and specific applications in improving electric energy quality of STATCOM in detail. Secondly, it researches briefly the compensation current detecting method which is based on instantaneous reactive power theory, points out its shortage, proposes a reactive detecting method which is based on coordinate conversion of power grid voltage and current under rotational coordinate system in order to detect the system current of reactive accurately under the condition of imbalance and aberration voltage. Meanwhile, the basic principles and theoretical basis of detecting method are analyzed in detail, the low-pass filter used in the detection method is studied, and second-order Butterworth low-pass filter is chosen. Through the experiment comparison of detection method of reactive current ip-iq based on instantaneous reactive power theory with the one based on coordinate conversion of power grid voltage and current under rotational coordinate system in simulation platform, the detection method mentioned in the dissertation is proved to be accurate and efficient. After that, the control strategies for STATCOM are investigated, and current tracking control methods used in reactive power compensation are discussed according to the characteristic of the compensation current signal. In allusion to rapidity of reactive power compensation, two current tracking control methods, called as current-hysteresis comparison control and triangle wave control, are investigated. In view of insufficiency of the two methods, another control method based on forecasting current strategy is proposed. By analyzing the basic principle and characteristic of the third method, its algorithm is studied and the forecasting current controller is designed. It can be concluded that the forecasting current control method has high control precision, small tracking error, constant switch frequency of the main circuit and control system is easy to realize by the comparison of the three different control strategies for STATCOM, therefore forecasting current control method is suitable for reactive current tracking control of STATCOM.At last, by the help of MATLAB/Simulink toolbox, the main circuit's parameters of STATCOM are calculated and selected, then the simulation model is built, hysteresis control module, triangle wave control module and forecasting current control module are applied respectively in the system under using the algorithm of reactive detection method which is based on coordinate conversion of power grid voltage and current on rotational coordinate system, the simulation experiment for STATCOM is completed. The simulation results show that the forecasting current control strategy has a good reactive compensation performance and some engineering application value.