Research On Facts Control Strategy Based On State-space Model

With the rapid development of power electronic devices, Flexible ACTransmission Systems (FACTS) are commonly used. It is AC transmissionequipment based on power electronic technology and other static control devices,which can enhance the control capability of transmission system and increasepower transmission capacity.In this paper, the control strategy of FACTS has been studied, which refers tothe theory, mathematical modeling, parametric design, control target currentdetection algorithm, control algorithm and simulation by MATLAB/SIMULINK and the EMTP. The main work has been done as follows:(1) Built mathematical modeling for single-phase and three-phase convertersbased on state-space averaging method, and fixed various circuit parameters forthe DC capacitor, output reactors, snubber circuit, pre-charge circuit, pre-chargecircuit, filter circuit, etc.(2) Proposed two new current-detection algorithm of the control target currentbased on the traditional reactive current detection algorithm. The first method isto control the output directly to avoid cumbersome process monitoring of active and reactive current components and simplify the process of monitoringharmonics. Deduced the relationship between loss active current and voltage ofDC side based on the principle of power flow between the two sides of theconvertor; proposed the DC side voltage control strategy and a method tocalculate the loss active current and load reactive current. The second method isbased on the attributive character of trigonometric functions and can be realizedeasily. For a harmonic load which contains harmonic in certain characteristicfrequencies, the characteristic harmonic current at the certain frequency can alsobe compensated. It can compensate the reactive current and harmoniccomponent together.(3)Discussed a control algorithm based on the DC voltage control andreactive current feedback control. Modeling and simulation analysis of PIcontrol and hysteresis control was done, and the impact that hysteresis loopwidth would bring was discussed. In addition, three-phase AC/DC converter is asystem with multi-inputs and multi-outputs. Conventional designs based ontransfer functions are usually adopted because of nonlinear characteristics.Using Riccati equation is one of popular methods to the problem, but theparameters of Riccati equation need be fixed artificially. This paper firstlyderived the mathematical model of the system. A new method based on optimalH control was then put forward, which discussed the feasibility problem of linear matrix inequalities and could solve the problem which Riccati equationmethod brings. Moreover, the noise of system was considered, and the controllercan make noise suppression as well. The results of simulation and experimentsproved its good performance.