Of Dstatcom Modeling And Nonlinear Control

Currently the electric power quality has been gaining more and more attention due to the rapid consumption increase of industry and domestic power. As an important component in custom power, Distribution Static Compensator (DSTATCOM) is an effective device to improve the power quality of distribution network. Modeling and controlling of a DSTATCOM are the most fundamental work in developing a DSTATCOM. Therefore in this thesis, these two aspects of a DSTATCOM are under carefully studied. Moreover, some improved suggestions based on a 40KVar DSTATCOM prototype are provided.First, asymmetric control is proposed based on the analysis and comparison of several kinds of DSTATCOM main circuit configurations. In order to meet the requirement of asymmetric control, the structure of three single-phase full-bridge inverters combined with isolating transformer is adopted. By sharing one capacitor in the DC side, this circuit configuration can not only implement individual phase control, suppress fluctuation of capacitor voltage, but also implement the modular design.Secondly, this thesis proposed an improved mathematic model of the DSTATCOM by taking more device losses into consideration. The device losses which are in proportion to the square of current can be equivalent to an AC side resistor, and those which are in proportion to the square of voltage can be equivalent to a DC side resistor. The nonlinear relationship between the steady output current and control angle of a DSTATCOM can be explained better by the improved mathematic model.Moreover, the application of the proposed controller based on multivariable nonlinear inverse system for a DSTATCOM is studied. Although inverse system method is nonlinear, it is easy to understand and simple to use. A controller designed by this method can work well at any operation point. If the PI parameters are selected properly, the controller designed by local linearization method combined with inverse state equation can have good performance. Satisfactory performance can also be found in the two-output-variable controller, whose control parameters are easy to determine. By state reconstruction, this controller can have higher performance.Finally, in order to put a DSTATCOM into normal operation under serious asymmetric supply voltages of power system, asymmetric control based on the...