Research On Control Strategy Of The Cascade STATCOM

With the further development of science and technology,the application of nonlinear,unbalanced or impactive load in distribution network is increasing rapidly.These phenomenon bring a lot of power quality problems.Among them,the prominent one,reactive power problem,attracted main attention of scholars.Static synchronous compensator(STATCOM),as an advanced reactive power compensation device,can compensate the reactive power in the grid system in real time and make outstanding contributions to the safety and stability of the power system.Due to lots of advantages of cascade STATCOM,it has wide application prospect in the power system.In this paper,some key problems of cascade STATCOM are studied.This paper researches and analyzes several key techniques of cascade STATCOM,including reactive power detection,modulation strategy,compensation current control,DC-side capacitor' voltage control and so onIn the begining of this paper,several multi-level inverter topological structure are introduced,and the reason why the H-bridge cascade structure(cascade structure)is selected as the topological structure of main circuit of STATCOM is described.Afterwards,the working principle of cascade STATCOM and H-bridge cascade structure are analyzed.Mathematical modeling of three-phase cascade STATCOM system is made.Then,through analysis of instantaneous reactive power theory,two kinds of real-time reactive current detection methods based on instantaneous reactive power theory are introduced:p-q method and ip-iq method and the ip-iq method is selected and improve its sensitivity and detection accuracy.Following this,the carrier-phase-shifted modulation strategy(CPS-PWM)for cascade STATCOM is studied.Subsequently,the paper constructs a double closed-loop control system to control the STATCOM's compensation current and DC-side voltage.The inner loop controls current and the outer loop controls voltage.The paper compares and analyzes PI control and repetitive control,and applies composite controller based on parallel structure of PI controller and improved repetitive controller to control the compensation current.PI controller is also applied to control DC-side voltage.Finally,the feasibility of the system control strategy is verified by software simulation and experiment on experiment platform.And the experimental results show that the STATCOM device designed in this paper possess a good compensation effect.The rationality and feasibility of the control strategy mentioned in this paper are verified.